La theorie elastique des dislocations

Les mecanismes elementaires a l’origine de la plasticite des monocristaux sont plutot bien connus, principalement pour ceux d’entre eux qui peuvent se decrier par le moyen de la theorie elastique des dislocations. S’il existe maintenant de bons modeles pour decrier la limite elastique, les difficultes vont croissant des lors que l’on s’interresse au comportement d’un materiau comportant de fortes densites de defauts.

La difficulte reside en fait dans la necessite de prendree en compte un grand nombre de mecanismes et d’interactions pertinents a diffrentes echelles, depuis l’echelle atomique jusqu’a celle de la piece mise en forme. ……………..afin de realiser a l’echelle d’un monocristal ou d’un grain du polycristal le lien entre les mecanismes elementaires, la formtion de microstructures organisees souvent complexes et le durcissement, il faut pouvoir disposer d’une description realiste des interactions entre dislocations. …………….les simulations de la dynamique des dislocations ont pour vocation d’assurer ce passage de la dislocation individuelle au comportement collectif et a ses consequences sur le comportement plastique. …………….une question interessante a developer etait celle des phenomenes de durcissment. En effet, parmi les diverses simulations developpee ces dernieres annees, tres peu sont capables d’approcher le comportement de populations de dislocations dans des volumes suffisamment grands pour etre consideres comme reprsentatifs du materiau massif. Bien que les phenomenes d’organisation des microstructures de dislocations et de durcissement ‘ecrouissage soient en principe relies, l’accent a ete jusqu’ici mis sur les premiers. ………….les simulations de microstructurs a deux dimensions contiennent tous les ingredients necessaires a une getion correcte de la dynamique des dislocations. Cependant, elles ne peuvent expliquer de maniere convaincante l’origine de la formation de microstructures ou les phenomenes de durcissement, faute d’inclure a la fois les effets lies a la tension de ligne, aux interactions de contact et aux interactions a longue distance. I faut alors passer a trios dimensions pour simuler tous les systemes de glissement du materiau considere et traiter correctement toutes les proprietes elementaires importantes.

..........Une seconde serie de resultants concerne l’influence du glissement devie. Ce mecanisme est indispensable non seulement pour decrier l’annihilation des dislocations vis mobiles ou la multiplication par double glissememnt devie, mais aussi la formation de boucles et debris tridimensionnels et les mecanismes de restaurationdynamique (annihilation d’une dislocation mobile avec une dislocation de la foret). L’un des apports essentials du modele Coin-vis a ete de montrer de quelle maniere le glissement devie joue un role fundamental dans la formation des microstructures organisees de dislocations, en deformation monotone et en fatigue (Devincre et Kubin 1994). La rasion est a rechercher dans l’irreversibilite inherente a ce phenomene, qui permet le stockage dans le crystal de fragments de lignes fortement ancres et de configurations de basse energie. Un autre point important concerne les tentatives pour determiner les coefficients d’interaction entre les systemes de glissement des metaux (Fivel 1997).
……si N est le nombre de segments de dislocations dans le volume simule, etant donne que les interactions entre segments de dislocations sont a longue portee, le temps de calcul consacre a ces interactions varie comme N2. en consequence, le temps de calcul augmente tres fortement avec le volume simule ou encore la densite de dislocations et , donc, la deformation plastique. Cetter depemdamce en N2, qui constitue une fraction majeure du temps total de simulation (~ 60%), est la limitation majeure du modeld coin-vis et, plus generalement, de toutes les simulations mesoscopiques de la dynamique des dislocations.
Ce probleme est d’autant plus marque dans des metaux CFC ou la grande mobilite des dislocations impose de surcroit un pas de temps elementaire de simulation, au plus egal a ∂t~ 1-2 10^9 s. l’increment de deformation par iteration est fixe par la vitesse de deformation choisie. Cette derniere ne peut pas non plus etre choisie tres elevee car la contrainte effective pour mouvoir les dislocations deviant, dans le cas contraire, superieure a la contrainte de la foret. ….on cmprend alors aisement qu’un facteur essentiel d’optimisation de la simulation consiste a reduire le nombre de segments N necessaries pour decrier une configuration de dislocations donnee.

Autres dynamiques des dislocations en 3D

La dynamique des dislocations apparait actuellememnt comme une etape incontournable pour remonter de l’origine microscopique de la plasticite jusqu’au comportement macroscopique des materiaux. C’est pour quoi de nombreuses simulations ont vu le jour ces dernieres annees. Des equips, americaines pour la plupart, ont explore des methodologies differentes de la notre poru ce qui concerne la discretisation des lignes.


.....Intersections entre deux dislocations
Avant d’etudier dans les chapitres suivants le durcissement a l’aide de simulation facon systematique la nature des interactions entre systemes. Ce sera tout d’abord l’occasion de presenter des modeles elastiques simplifies, puis de verifier que la simulation mixte permet d’obtenir des resultants coherents avec les modeles traditionnels de la theorie elastique des dislocations ou avec des resultants obtenus ……. par la simulation de configurations locales.

Formation des junctions
Les deux principales hypothees simplificatrices utilisees pour calculer les conditions de formation des junctions sont les suivantes:
- les segments sont supposes rigides avant et après interaction
- les interactions elastiques entre segments sont negligees, ce qui revient a omettre le terme logarithmique dans l’energie ou la tension de ligne. En revanche, il est tenu compte de la dependence de l’energie de ligne en foction du character.
- Il ya deux manieres de proceder, en forces ou en energies; elles sont strictement equivalents. En effet, l’equilibre des forces sur une configuration correspond a un minimum de son energie totale. On peut donc effectuer un bilan d’energie elastique entre l’etat initial, constitue par deux segments isoles, et un etat final qui contient un junction et minimise l’energie elastique de la configuration. La junction sera formee si cette derniere configuration a une energie plus faible que la configuration initiale.



R. Madec, Des interactions entre dislocations à la plasticité du monocristal cfc : Etude par Dynamique des Dislocations, Ph.D. thesis, Orsay university, n° d'ordre : 6773, 2001.
Access through: www-sgrgroup.materials.ox.ac.uk/group/people_past.html

Nano Farm House

"The Begbroke development offers the perfect interface with the University of Oxford and provides a pleasant and easily accessible location for both employees and customers" (Dr Kevin Matthews, CEO Oxonica)






Electron transport properties
Conductivity measurement is about the voltage of the current passing through the test sample. But this is not a clear measure since contact applied to a sample will cause a contact resistance. The choice of contact electrode, based on the work function, is therefore critical. Charge carriers can be electrons, holes or sometimes ions. Measurement of conductivity or resistivity (P=1/Q) as a function of temperature can often provide an insight into conduction mechanisms. Conductivity measurement needs the arrangement of the electrodes, for high resistance materials > 100 ohms a two probe technique is adequate, where as for small values of resistance the residual contact resistance and the impedance of the leads become significant, which requires a four probe technique. In this technique two probes pass a current through the material while the potential difference between the other two probes is measured by using a high impedance voltmeter. Besides Direct Current methods, Alternating Current conductivity can provide data on the impedance of the system. The impedance is the ratio of the applied modulated voltage to the resultant current modulation and has both a magnitude and a phase. The dependence of the impedance on the frequency of the applied AC is known as impedance spectroscopy and this technique can separate out electrical responses from separate nanostructural features, eg. Grain boundaries, bulk grains and interfaces with electrodes, all with different response or relaxation times.



Magnetic properties
Materials are classified by their response to an inhomogeneous magnetic field. For diamagnetic and paramagnetic substance the difference then lies in moves towards the weakest region of the field in the former and the strongest region in the latter. Usually diamagnetic substances have all the electrons spin paired while if unpaired electrons are present then the substance may be paramagnetic. Long range magnetic ordering is the result of cooperative inter-ionic interactions, which may produce ferromagnetism, antiferromagnetism, or the third option ferrimagnetism. The volume magnetic susceptibility is the ratio of the sample magnetization to the field strength. Magnetic force microscopy MFM uses ferromagnetic scanning probe tip - that is the technique for measuring the force exerted on a sample in a magnetic field gradient.




Incoherent imaging and analysis techniques in the scanning transmission electron microscope (STEM) provide the potential to map changes in structure, composition and bonding that occur at materials interfaces and defects on the fundamental atomic scale. Such comprehensive characterization capabilities permit a detailed analysis of the structure-property relationships of interfaces and defects to be performed. In this paper, we discuss the resolution limits of such techniques in the JEOL 2010F STEM/TEM operating both under standard conditions and at elevated temperatures. Examples of the use of such techniques to quantify the atomic scale defect chemistry at interfaces and defects in perovskite oxides, the growth and structure of II-VI and III-V quantum dots and the electronic structure of threading dislocations in GaN will also be presented.

Application of atomic scale STEM techniques to the study of interfaces and defects in materi-als , Journal of Electron Microscopy 50:205-218 (2001)


www.oxfordjournals.org

Plenty of room at the bottom

We do have plenty of room at the bottom; however, just a few years after Feynman’s vision was published, J Morton from Bell laboratories noticed what he called the tyranny of large systems. This tyranny arises for the fact that scaling is, in general, not part of the laws of na-ture………………………………. Feynman was only interested in fundamental limitations. The exponential growth of silicon technology with respect to the numbers of transistors on a chip seems to prove Feynman right, at least up to now.

How can this be if the original transistors were not scalable? How could one always find a modification that permitted further scaling? One of the reasons for continued miniaturization of silicon technology is that its basic idea is very flexible: use solids instead of vacuum tubes. The high density of solids permits us to create very small structures without hitting the atomic limit. Gas molecules or electrons in tubes have a much lower density than electrons or atoms in solids typically have. One has about 10^18 atoms in a cm3 of gas but 10^23 in a cm3 of a solid. Can one therefore go to sizes that would contain only a few hundred atoms with current silicon technology? No, the reason is that current technology is based on t he doping of silicon with donors and acceptors to create electron- and hole-inversion layers. The doping densities are much lower than the densities of atoms in a solid, usually below 10^20 per cm3. There-fore, to go to the ultimate limits of atomic size, a new type of transistor, without doping is needed. But even if we have such transistors, can they be interconnected? Interestingly enough interconnection problems have always been overcome in the past. The reason was that use of the third dimension has been made for interconnects. Chip designers have used the third dimension – not to overcome the limitations that two dimensions place on the number of transistors, but to overcome the limitations that two dimensions present for interconnecting the transistors. There is an increasing number of stacks of metal interconnect layers on chips – 2,5,8. How many can we have? One can still improve the conductivity of the metals in use by using for example copper technology…………. Feynman suggested that there will be plenty of room at the bottom only when the third dimension is used. Can we also use it to improve the packing density of transistors? The current technology is based on a silicon surface that contains patterns of doping atoms and is topped by silicon dioxide. To use the third dimen-sion, a generalization of the technology is needed. One would need another layer of silicon on top of the silicon dioxide, and so forth. Actually such technology does already exist: silicon on insulator SOI technology. These may be scalable further than current devices and may open the horizon to the use of the third dimension……………. No doubt it is the business income that will determine the limitations of scaling to a large extent.

Transistors of the current technology have been developed and adjusted to accommodate the tyranny from the top, in particular the demands set forth by the von Neuman architecture of conventional computers. It is therefore not surprising that new devices are always looked at with suspicion by design engineers and are always found wanting with respect to some tyran-nical requirement. Many regard it extremely unlikely that a completely new device will be used for silicon chip technology. Therefore architectures that deviate from von Neuman’s principles have received increasing attention. Thee architectures invariably involve some form of parallelism. Switching and storage is not localized ot a single transistor or small cir-cuit. The devices are connected to each other and their collective interactions are the basis for computation. It has been shown that such collective interactions can perform some tasks in ways much superior to von Neuman’s processing.

Unifying science based on the unifying features of nature at the nanoscale provides a new foundation for knowledge, innovation, and integration of technology. Revolutionary and syn-ergistic advances at the interfaces between previously separated fields of science, engineering, and areas of relevance are poised to create nano-bio-info-cogno (NBIC) transforming tools, products and services. There is a longitudinal process of convergence and divergence in major areas of science and engineering. For example, the convergence of sciences at the macroscale was proposed during the Renaissance, and it was followed by narrow disciplinary specializa-tion in science and engineering in the 18th to 20th centuries. The convergence at the nanoscale reached its strength in about 2000, and one may estimate a divergence of the nanosystem ar-chitectures in the following decades. Fundamental changes envisioned through nanotechnol-ogy have required a long term R&D vision. A two decade timescale was planned for transi-tioning from the focus on passive nanostructures in 2001 to 2005 to molecular active nanosys-tems after 2015. We provided detailed technical input for two hearings in the Congress in both the Subcommittee on Basic Science, Committee on Science, US House of Representa-tives (June 22, 1999) and the Senate, and support was received from both parties. We had the attention of Neal Lane, the presidential science advisor, and Tom Kalil, economic assistant to the president. The preparatory materials included a full 200 page benchmarking report, 10 page research directions, and 1 page summary on immediate goals. After the hearing in the House, Nick Smith the chair of the first public hearing in preparation of NNI said “Now we have sufficient information to aggressively pursue nanotechnology funding”. Rick Smalley came and testified despite his illness. In Nov 1999, the OMB recommended nanotechnology as the only new R&D initiative for FY 2001. National Nanotechnology Initiative was pre-pared with the same rigor as a science project, between 1997 and 2000; we prepared a long term vision of research and development (Roco et al 2000), and we completed an interna-tional benchmarking of nanotechnology in academe, government, and industry (Siegel et al 1999). Other milestones included a plan for the US govt investment (NSTC 2000) a brochure explaining nanotechnology for the public (NSTC 1999) and a report on the societal implica-tions of nanoscience and nanotechnolgoy (Roco and Bainbridge, 2001) . In the first year (2001), of National Nanotechnology Initiative approval, the six agencies of the NNI invested about 490$ million. In Financial Years 2002 and 2003, NNI increased significantly, from 6 to 16 departments and agencies. The presidential announcement of NNI with its vision and pro-gram partially motivated or stimulated the international community. The average annual rate of increase of the NNI budgets was over 35% including congressionally directed funding – in the first five years (FYs 2001 – 2005). The total R&D investment in FYs 2001 -2006 was over $ 5 billion, increasing form the annual budget of $ 270 million in 2000 to $ 1.3 billion including congressionally directed projects in 2006. An important outcome is the formation of an interdisciplinary nanotechnology commuity with about 50,000 contributors, 60 large R&D centres, networks, and user facilities has been established since 2000. this expanding industry consists of more than 1500 companies with nanotechnology products with a value exceeding $ 40 billion at an annual rate of growth estimated at about 25%. With such growth and com-plexity, participation of a coalition of academic organisations, industry, businesses, civil or-ganisations, government, and NGOs in nanotechnology development becomes essential as an alternative to the centralized approach. The role of government continues in basic research and education but its emphasis is changing, while the private sector becomes increasingly dominant in funding nanotechnology applications.

Only since 1981 have we been able to measure the size of a cluster of atoms on a surface (IBM, Zurich) and begun to provide better models for chemistry and biology self-organisation and self assembly. Ten years later, in 1991, we were able to move atoms on surfaces (IBM, Almaden), and after ten more years in 2002, we assembled molecules by physically position-ing the component atoms. Yet , we cannot visualize or model with proper spatial and temporal accuracy a chosen domain of engineering or biological relevance at the nanoscale. Nanotech phenomena hold the promise for fundamentally new applications. Possible examples include chemical manufacturing using designed molecular assemblies, processing of information us-ing photons or electron spin, detection of chemicals or bioagents using only a few molecules, detection and treatment of chronic illnesses by subcellular interventions, regenerating tissue and nerves, enhancing learning and other cognitive processes by understanding the society of neurons, and cleaning contaminated soils with designed nanoparitcles.

Using input from industry and academic experts in the US Asia Pacific countries, and Europe between 1997 and 1999, we have projected that $ 1 trillion in products incorporating nanotechnology and about 2 million jobs worldwide will be affected by nanotechnology by 2015 (Roco and Bainbridge, 2001). Extrapolating from information technology, where for every worker, another 2.5 jobs are created in related areas, nanotechnology has the potential to create 7 million jobs overall by 2015 in the global market.

New governance approach

...Just as nanotechnology is changing how we think about unity of matter at the nanoscale and manufacturing, it is also changing how we think about the management of the ereseach enterprise.

This switch can be seen a sthe specializatio of scientific disciplines has migrated to more unifying concepts for scientific research and system integration in engineering and technology.

Most of the major US science and and technology programmes in the 20 century, such as space exploration and energy and evironmental programmes, have been pulled primarily by external factors. The economy, natural resources, national security, and international agreements and justifications have initiatied top down R&D funding decisions. In contrast nanotechnology development was initially pushed by fundamental knowledge (nanoscience and nanoengineering - and the long term promise of its transformative power. for this reason, we have done the preparation and governance of nanotechnology differently. For nano reserch policies have been motivated by long term vision rather than short term economic and political decisions.

Brenner et al, (2007), Handbook of Nanoscience, Engineering, and Technology, Tay-lor&Francis



………In addition to structural information, local chemical composition, bonding and electronic states are key aspects of nanostructures. A range of spectroscopic techniques is now available for probing local structures on the atomic scale. Among these, electron energy loss spectroscopy and energy dispersive xray analysis have emerged as the most powerful and widely used. These techniques probe, respectively the energy loss of electrons passing through a thin specimen and the rays generated by the incident electron beam. In many applications of nanotechnology the measurement of the magnetic and electrical properties of individual nanoscale objects is becoming increasingly important. Relatively recent instrumental developments have enabled the technique of electron holography, first proposed by Gabor in 1947, to be used, to obtain measurements of these. …………As nanostructues become smaller, their 3-dimentsional shape assumes much greater importance. This is particularly the case for supported catalysts, where active sites may be determined by such entities. Although electron tomography had been previously applied successfully to biological structures it has only recently been extended to for applications in nanoscience.
John Hutchison et al, Nanocharacterisation, RSC, 2007

One of the characteristic features of nano-systems is their high surface to volume ratio. Their electronic and magnetic properties are often distinguished by quantum mechanical behaviour. Their mechanical and thermal properties can be formulated within the framework of classical statistical mechanics of small systems as presented by Hill. In 1964 he introduced the subject of thermodynamics of small systems that covered chemical thermodynamics of mixtures, colloidal particles, polymers and macromolecules. The study of efficiency of heat engines by Carnot, in 1824, stated that the efficiency of a heat engine depended only on the temperature difference between its heat source and heat sink and not on the working substance. Clapeyron developed the relationship between vapour pressure and an unknown function of empirical temperature scale. Gibbs thesis published in 1875 entitled “On the equilibrium of heterogeneous substances”. Thomson formulated the first and second laws of thermodynamics in 1851.

Oxygen Vacancies

Nanostructured TiO2 thin films were prepared by pulsed laser deposition (PLD) on indium-doped tin oxide (ITO) substrates. Results from X-ray photoelectron spectroscopy (XPS) show that Ti 2p core level peaks shift toward the lower binding energy with decrease in the buffer gas pressure (O-2:Ar= 1:1). This suggests that oxygen vacancies are created under insufficient oxygen conditions.............Combining the results from XPS and PEC studies, we conclude that the deposition pressure affects the concentration of the oxygen vacancies which changes the electronic structure of the TiO2. With reference to photoelectrochemical catalytic performance, our results suggest that it is possible to adjust the Fermi energy level and structure of TiO2 thin films by controlling the buffer gas pressure and temperature to align the energy of the flatband potential (V-fb) with respect to specific redox species in the electrolyte.

Photocatalytic activity of pulsed laser deposited TiO2 thin films, Elsevier BV, 2008


Introduction of Mg-impurities during crystal growth in a highly reducing atmosphere stimulates creation of F þ - centres (oxygen vacancy with one electron) needed for charge compensation of the Mg2þ-ion, which becomes negatively charged with respect to the lattice when it substitutes the Al3þ-ion. Subsequent aggregation of two defect pairs results in creation of a more complex aggregate defect denoted as the F22þ(2Mg)-centre. Detailed spectroscopic properties of this new colour centre was investigated recently by our group and published elsewhere(b).

Conclusion: Performance of a new Al2O3:C,Mg dosimetric material is determined by its defect structure by its electronic and optical properties. The crystals have deep stable traps of electrons and holes having a high capture-cross-section. Aggregate defects consisting of two oxygen vacancies and two Mg-impurities are believed to be responsible for the optical and radiation properties of the new material. Colour centres induced by radiation show strong absorption of stimulation light and have a short luminescence lifetime. The new material allows one to perform fast and no-destructive measurements of fluorescent signals.

a- NEW Al2O3:C,Mg CRYSTALS FOR RADIOPHOTOLUMINESCENT DOSIMETRY AND OPTICAL IMAGING; Radiation Protection Dosimetry (2006), Vol. 119, No. 1–4, pp. 218–221

b- Akselrod, M. S., Akselrod, A. E., Orlov, S. S., Sanyal, S. and Underwood, T. H. Fluorescent aluminum oxide crystals for volumetric optical data storage and imaging applications. J. Fluores. 13(6), 503–511 (2003)




Evans et al, Optical properties of lattice defects in a-Al2O3. Nucl. Instr. and Meth. in Phys. Res. B 91, 258–262.(1994).

Fluorescent aluminum oxide crystals for volumetric optical data storage and imaging
applications. J. Fluores. 13(6), 503–511 (2003).


Performance of a new Al2O3:C,Mg dosimetric material is determined by its defect structure and by its electronic and optical properties. The crystals have deep stable traps of electrons and holes having a high capture-cross-section. Aggregate defects consisting of two oxygen vacancies and two Mg-impurities are believed to be responsible for the optical and radiation properties of the new material. Color centers induced by radiation show strong absorption of stimulation light and have a short luminescence lifetime. The new material allows one to perform fast and nondestructive measurements of fluorescent signals.

NEW Al2O3:C,Mg CRYSTALS FOR RADIOPHOTOLUMINESCENT DOSIMETRY AND OPTICAL IMAGING



The solid solution of CeO 2-ZrO2 is used widely in automobiles as a three-way catalyst and an oxygen storage material. Many studies on this material have been conducted, and the reduced solid solution of CeO 2-ZrO2 having an equimolar composition of Ce and Zr (Ce / Zr = 50 / 50) has been confirmed to possess
a particularly excellent property for oxygen absorption/release [1–3]. Reduction treatment at high temperature, especially >1473 K, gives Ce 2Zr2O7 having a pyrochlore structure with an ordered arrangement of Ce and Zr ions along the <110>
direction, in which one-eighth of the oxygen in Ce 2Zr2O8 is released through the reduction [4]. The value of the oxygen deficiency parameter, or x in Ce2Zr2O7 + x, may change from 0 to 1 depending on the degree of reduction or oxidation. Recently,
the microstructural change associated with the absorption/release of oxygen is receiving much attention [4–7].


The three lattice images of Ce 2Zr2O7, Ce2Zr2O7.5 and Ce2Zr2O8 are all greatly different, and they can be characterized by the length of periodicity and the texture. The large change in the high-resolution lattice images evidently indicates the introduction and/or elimination of the oxygen vacancies, which means that the image is greatly affected by the vacancies. The TEM observation of oxygen vacancies was also reported by Shibahara et al. for M-Mn-O (M:La,Ba) oxide having perovskite structure [2-4]. However, in general, the contribution of oxygen defects to the highresolution images is very small. The image change observed in this study is exceptionally large and it may be used for determining the local amount of oxygen absorbed.


1 Microstructural investigation of ceria-zirconia solid solution with oxygen vacancies, Journal of Electron Microscopy 52(3): 309–312 2003
2 Shibahara H (1998) HREM and molecular dynamics studies of oxygen-defective LaMnO3 – x. J. Electron Microsc. 47: 327–333.
3 Shibahara H, Numaguchi K, Kawasaki M, Takizawa H, Oikawa T, and Taguchi H (1995) Quantification of oxygen vacancies in perovskite using a 300 kV HREM with an imaging plate. J. Electron Microsc. 44: 174–181.
4 Shibahara H, Kawasaki M, and Taguchi H (1993) Detection of oxygen vacancies in BaMnO 3 – x with 200 kV electron-microscopes. J. Electron Microsc. 42: 211–217.



Incoherent imaging and analysis techniques in the scanning transmission electron microscope (STEM) provide the potential to map changes in structure, composition and bonding that occur at materials interfaces and defects on the fundamental atomic scale. Such comprehensive characterization capabilities permit a detailed analysis of the structure-property relationships of interfaces and defects to be performed. In this paper, we discuss the resolution limits of such techniques in the JEOL 2010F STEM/TEM operating both under standard conditions and at elevated temperatures. Examples of the use of such techniques to quantify the atomic scale defect chemistry at interfaces and defects in perovskite oxides, the growth and structure of II-VI and III-V quantum dots and the electronic structure of threading dislocations in GaN will also be presented.

Application of atomic scale STEM techniquesto the study of interfaces and defects in materials , Journal of Electron Microscopy 50:205-218 (2001)




Quantification of Oxygen Vacancies in Perovskite using a 300 kV HREM with an Imaging Plate

The structural determination and quantification of oxygen vacancies in LaMnO3–x were carried out in a 300 kV HREM equipped with an imaging plate. On the basis of direct observation with HREM and the aid of computer simulation, optimum imaging conditions were found, where oxygen atoms and the vacancies are imaged as bright spots in a "dark-spot image." Under the optimum imaging conditions, the dependence of image contrast on the atomic occupancies of the oxygen sites and the thickness of the samples is discussed on the basis of dynamical diffraction theory. Using an imaging plate, the atomic occupancies were quantitatively estimated from the intensity distributions of the bright spots in the observed image contrast.


The stability of an oxygen-defective structure of LaMnO3–x was studied by MD simulation. The relaxed structure based on the MD simulation could provide sufficient adequate information to discuss the proposed structure model of LaMnO3–x compared with the observed image contrast by HREM. Image calculation of the relaxed structure by the multislice method also supported the proposed defect structure model. Analysis of the atomic structure by MD simulation gave the information of oxygen ion and cation migration in oxygen-defective perovskite.

HREM and molecular dynamics studies of oxygen-defective LaMnO3–x



Defect-enhanced electron field emission from chemical vapour deposited diamond, 1995

Diamond samples with varying defect densities have been synthesized by chemical vapour deposition, and their field emission characteristics have been investigated. Vacuum electron field emission measurements indicate that the threshold electric field required to generate sufficient emission current densities for flat panel display applications (>lO mA/cm”) can be significantly reduced when the diamond is grown so as to contain a substantial number of structural defects.

Vacancy assisted diffusion

Vacancy assisted diffusion

The origins of the short carrier trap time and annealing process have been extensively studied [2]–[10]. In the defect-band (AsGa antisite defect) model, the short carrier trap time τCL has been attributed to the high density of AsGa antisite defects. AsGa defects migrate and are eventually captured by As precipitates during the annealing process [4]. The key to shortening the carrier trap time is to control the defect density, as the carrier trap time is inversely proportional to it [4]. Excess arsenic atoms distort the GaAs structure during the crystal growth. Therefore, the arsenic defect density will be high if the arsenic pressure during molecular beam epitaxial (MBE) crystal growth is high. We have recently showed that an LT-GaAs sample grown under a higher arsenic pressure has a shorter carrier trap time for the case of 250◦C growth temperature and as grown and annealed conditions [9], [10]. About 15 years ago, it was reported that semiinsulating GaAs samples have properties similar to LT-GaAs when ions are implanted to GaAs substrate with high doses [11]. Therefore, ion-implanted GaAs substrates can be an alternative of LT-GaAs…………..In spite of these studies, the origin of the short carrier trap time, or the nature of the carrier trap states has not been clarified yet. This also means that the diffusion dynamics of ion-implanted GaAs caused by annealing has not been understood yet. However, for the precise control of the properties of GaAs, an understanding of the nature of the carrier trap states and also the annealing dynamics is important. Here, we discuss the annealing induced diffusion dynamics of As ion-implanted GaAs. The AsGa antisite defects are considered to work as the trap states of carriers [4],[15], [17], and the density of AsGa antisite defects in As ion implanted GaAs is high [14]. Therefore, the discussion of the annealing dynamics of As-ion implanted GaAs becomes simple. If other ions are implanted to GaAs, the discussion may not be so simple because of the possibility of the production of other defects which may trap carriers.

Annealing Induced Diffusion Dynamics in As Ion-Implanted GaAs,
IEICE TRANS. ELECTRON., VOL.E90–C, NO.1 JANUARY 2007







SOME NANO FIGURES

With about 25% of global government investments 1 billion of 4 billion, the US accounts for about 50% of highly cited papers, 60% of patents, and about 70% of startup companies (Nanobusiness, 2004) in nanotechnology world wide. Industry investment in the US has exceeded the NNI in R&D and almost all major companies in traditional and emerging fields have nano groups at least to survey the competitions, Small Times reported 1455 US nanotech companies in March 2005, with roughly half being small businesses, and 23000 new jobs were created in small start-up Nano companies, the NNI SBIR investment was about 80 million dlrs in FY 2005, more than 200 small businesses with a total budget of approx 60 M dlrs have received support from NSF alone, since 2001, many of these are among the 600 pure play nanotechnology companies formed in the US since 2001, in a survey by Small Times.

All Fortune 500 companies in emerging materials, electronics, and pharmaceuticals have had nanotech acivities since 2003.



INNOVATION AND ALL THAT

In 1970 US companies represented 66% of the stock market capitalization of all of the companies in the world. By 1990 even after 20 years of remarkable growth, US companies accounted for only 33% of the world’s total.
Data from the Frank Russell Co, Tacoma, WA

Innovation takes place in a broad pattern in an economic context that is termed as knowledge economy.

Innovation theory is concerned with learning, which is the core process for the creation of knowledge.

Management is another important dimension of innovation for it defines the organisational structures and means trough which innovation and related activities are accomplished.

Innovation is crucial in knowledge economy for predicting the future and providing accurate information in respect of the past. There is a risk of inaccurate prediction which requires systematic revision to compare the prediction with events. Here engineering may be called upon for identifying pattern, which is a formulation for adapting experiences through a sense of order with the knowledge theory to predict the future outcomes. This process will result in rational decision making that ultimately reduces the risks involved.

Michael Polanyi demonstrates the prevalence and importance of tacit knowledge in our daily experience simply by challenging us to express how it is that we can invariably recognize the faces of those we know. The consistency of this ability is reflected in our system of laws, for recognizing someone’s face is considered to be positive identification and is among the most compelling forms of evidence that can be entered in a court of law. Tacit knowledge is part of everything that we do and say, and as it is inherent in our very thinking, it is deeply embedded in the way that we work. When you describe something you miss all the information that is embedded in tacit knowledge of the context.

Fourth Generation, L Morris, W Miller, Wiley, 1999




Silicon and silicon dioxide have very different lattice constants – that is spacing between their atoms. It is therefore difficult to imagine that the interface between them can be electronically perfect. GaAs and AlAs on the other side have almost equal lattice spacing, and two crystals can be perfectly placed on top of each other. The formation of super lattices of such layers of semiconductors has, in fact, been one of the bigger achievements of recent semiconductor technology and was made possible by new techniques of crystal growth (molecular beam epitaxy, metal organic chemical vapour deposition, and the like). Quantum wells, wire and dots have been the subject of extremely interesting research and have enriched quantum physics for example, by the discovery of the Quantum Hall Effect and the Fractional Quantum Hall effect. Use of such layers has also brought significant progress to semiconductor electronics. The concept of modulation doping (selective doping of layers, particularly involving pseudomorphic InGas) has led to modulation doped transistors that hold the current speed records and are used for microwave applications. The removal of the doping to neighbouring layers has permitted the creation of the highest possible electron mobility and velocities. The effect of resonant tunnelling has also been shown to lead to ultrafast devices and applications that reach to infrared frequencies, encompassing in this way both optics and electronics applications. When it comes to large scale integration however the tyranny from the top has favoured silicon technology. Silicon dioxide, as an insulator is superior to all possible III-V compound materials; and its interface with silicon can be made electronically perfect enough, at least when treated with hydrogen or deuterium.


Feynman noticed that nature has already made use of nanostrutures in biological systems with greatest success. Why do we not copy nature? Take for example biological ion channels. These are tiny pores formed by protein structures. T heir opening can be as small as a few one tenths of a nanometer. Ion currents are controlled by these pores that have opening and closing gates much as transistors have.

Brenner D, Handbook of Nanoscience, Engineering, and Technology, Taylor & Francis, 2007

Nanocrystals are vacancy free

Nanocrystals are predicted to be essentially vacancy free; their small size precludes any significant vacancy concentration. This simple result has important consequences for all thermomechnaical properties and processes such as creep and precipitation, which are based on the presence and migration of vacancies in the lattice.



Dislocations in nanocrystals


Crystal surfaces and interfaces play significant role in determining properties of nanocrystals compared with microcrystals. Dislocations which is planar defects in the crystalline structure of a solid is the determinant of mechanical properties of a material.

The free energy of a dislocation is made up of a number of terms

1- the core energy within a radius of about three lattice planes from the dislocation core
2- the elastic strain energy outside the core and extending to the boundaries of the crystal
3- the free energy arising from the entropy contributions

in microcrystals the first and second terms increase the free energy and are by far the most dominant terms. Hence dislocations unlike vacancies do not exist in thermal equilibrium.


Kelsall, Nanoscale


Mechanical alloying technique
.........at this value of d (Hall-Petch) deformation will no longer proceed by the generatin and propagation of matrx dislocations; the minimum grain size will then have been attained. This competition between the deformation and recovery behaviour is often cited as the reason for the generation of a characteristic d min for a given material. Once an entirely nanocrystalline structure is formed, further deformation is accomplished by grain boundary sliding GBS and there is no further refinement of structural scale. GBS does, however, accommodate deformation energy; this is stored with in the grain boundaries themselves and also in the form of strains within the nanograins which arise because of grain boundary stresses. Grain boundary energies may as a result, be higher than expected, as much as 25% higher than the value for the grain boundary energy in a coarse-grained sample.

Kelsall, p 257



Qantitative changes in the parameters that describe a network or the shape of the cell can radically change the way the network behaves.

Quantitative Modelling of Biological Systems
http://www.nyas.org/ebriefreps/main.asp?intEBriefID=460




Microstructural and defect population change in electron beam irradiated Ge:SiO2 MCVD glasses in the conditions of refractive index change writing

Electron spin resonance (ESR) and ultra violet (UV) optical absorption spectra are measured in Ge:SiO2 glasses elaborated by modified chemical vapor deposition (MCVD) and irradiated by an electron beam of medium energy (10–50 keV). The doses (a few C/cm2) like the electron energy used, correspond to conditions for writing refractive index change for optical applications. These data yielded information on defect population changes. Raman spectroscopy was used for correlating these changes to microstructural changes. We point out a 5.1 eV absorption bleaching like surprisingly the one occurring under 5 eV laser irradiation correlated to an absorption increases around (4.4 and 5.8 eV).

Journal of Non-Crystalline Solids, Volume 351, Issues 14-15, 15 May 2005,


Shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. Some habits are distinctive of certain minerals, although most minerals exhibit many differing habits (the development of a particular habit is determined by the details of the conditions during the mineral formation/crystal growth). Crystal habit may mislead the inexperienced as a mineral's internal crystal system can be hidden or disguised. Factors influencing a crystal's habit include: a combination of two or more crystal forms; trace impurities present during growth; crystal twinning and growth conditions (i.e., heat, pressure, space). Minerals belonging to the same crystal system do not necessarily exhibit the same habit. Some habits of a mineral are unique to its variety and locality: For example, while most sapphires form elongate barrel-shaped crystals, those found in Montana form stout tabular crystals. Ordinarily, the latter habit is seen only in ruby.

Wikipedia.com



Competing interactions and patterns in Nanoworld

An experimental model made from small magnets was demonstrated which were free to rotate on different lattices. The geometry of magnets and the model as whole has been adapted to represent pure dipolar systems. ..................The patterns arising in nanosystems caused by competing interactions are classified into four main groups:

(i) self-competing interactions;
(ii) competition between a short- and a long-range interaction;
(iii) competition between interactions on a similar length scale; and
(iv) competition between interactions and anisotropy. Each class is further divided into subclasses corresponding to the localized and delocalized particles. For each subclass, concrete sets of interactions, corresponding patterns and microscopic details of systems where they appear are presented.

Wiley Interscience, 2007 WILEY-VCH Verlag GmbH & Co


Stone Wales

The Stone Wales defect is a defect that occurs on carbon nanotubes and is thought to have important implications for nanotube's mechanical properties. The defects are thought to be responsible for nanoscale plasticity and the brittle-ductile transitions in carbon nanotubes.

One of the plausible processes for isomerization of the fullerene is the so-called Stone-Wales or "pyracylene" transformation, which is the 90° rotation of two carbon atoms with respect to the midpoint of the bond. The Stone-Wales transformation is also used to describe the structural changes of sp²-bonded carbon nanosystems. For example, it has been proposed that the coalescence process of fullerenes or carbon nanotubes may occur through a sequence of such a rearrangement. By the Stone-Wales transformation, four hexagons are changed into two pentagons and two heptagons. It is a kind of Stone-Wales defect.

Wikipedia




Quantum Dots

The research of microelectronic materials is driven by the need to tailor electronic and optical properties for specific component applications. It has been made possible to fabricate artificial dedicated materials for microelectronics, where the electronic structure is tailored by changing the local material composition and by confining th electrons in nanometer size foils or grains. Due to quantization of electron energies, these systems are often called quantum structures. If the electrons are confided by a potential barrier in all three directions, the nanocrystals are called quantum dots. This review of quantum dots begins with discussion of the physical principles and first experiments and concludes with the first expected commercial applications single electron pumps, biomolecule markers and QDs lasers.
In nanocrystals, the crystal size dependency of the energy and the spacing of discrete electron levels are so large that they can be observed experimentally and utilized in technological applications. QDs are often also called mesoscopic atoms or artificial atoms to indicate that the scale of electron states in QDs is larger than the lattice constant of a crystal. However, there is no rigorous lower limit to the size of a QD and therefore even macro-molecules and single impurity atoms in a crystal can be called QDs.
The quantization of electron energies in nanometer size crystals leads to dramatic changes in transport and optical properties. ……..the colour change of the fluorescence is governed by the electron in a potential box effect familiar from elementary text books of modern physics.

In bulk crystals, each electron band consists of a continuum of electron states. however, the energy spacing of electron states increases with decreasing QD size, and therefore the energy spectrum of an electron band approaches a set of discrete lines in nanocrystals.
In quantum physics, the electronic structure is often anlyzed in the terms of the density of electron states DOS. The prominent transformation from the continuum of states in a bulk crystal to the set of discrete electron levels in a QD formulates that the DOS is proportional to the square root of the electron energy.

The handbook of nanotechnology; Nanometer Structures; p 111






Dislocation

dislocation is a crystallographic defect, or irregularity, within a crystal structure. The presence of dislocations strongly influences many of the properties of materials. Some types of dislocations can be visualised as being caused by the termination of a plane of atoms in the middle of a crystal. In such a case, the surrounding planes are not straight, but instead bend around the edge of the terminating plane so that the crystal structure is perfectly ordered on either side. The analogy with a stack of paper is apt: if a half a piece of paper is inserted in a stack of paper, the defect in the stack is only noticeable at the edge of the half sheet. wikipedia





Defects in crystalline

In research concerning metal particles, the relationship between the decagonal symmetry in the diffraction pattern and multiple-twin texture has been discussed extensively. Because such texture has been proven to be stable only when the size of the substance is less than about 20-30 run and disadvantageous energetically as the size of the substance increases due to elastic strain, the model is not applicable to the present solvates, which have a size of about 100 \un without any revision. From the standpoint of the multiple-twinning model, an experimental value (-35.5°)deviates less than 1° from the theoretical value (i.e. 2rc/10 = 36"). This gap may be compensated by the presence of some kinds of crystal defects. Thus, high-resolution transmission electron microscopy (HREM) was performed as an initial step in order to identify the nature of the defects in C70 C6 H5 CH3 The discrepancy is explained by the strain relaxation of the defects.

......According to dislocation theory, the strain energy of dislocation is thought to be proportional to the square of the displacement vector.

High-resolution electron microscopy of crystal defects in C70-toluene solvate, Oxfordjournals.org



The method selected, which favours the penetration of nanoparticles into the plants, involved injecting the bioferrofluid inside the internal hollow of the leaf petiole (Fig. 1B). In this way, the bioferrofluid penetrates into the plant and is translocated to other areas through the vascular tissues. Small magnets were placed on the petiole of the leaf opposite to the injection point and on some of the roots.

Nanoparticles as Smart Treatment-delivery Systems in Plants: Assessment of Different Techniques of Microscopy for their Visualization in Plant Tissues; Annals of Botany;Oxfordjournals 2008





The energy that is necessary to remove a Ga atom from a Ga site is called the VGa vacancy formation energy. Then an AsGa antisite defect (As atom) at another Ga site changes its position to the VGa vacancy site. To change the sites, an AsGa aitisite defect needs to overcome the potential barrier between the two sites. The potential barrier is called as the migration energy.

Annealing Induced Diffusion Dynamics in As Ion-Implanted GaAs; oxford journals, 2007


Structure of self-interstitial in some common metals. The left-hand side of each crystal type shows the perfect crystal and the right-hand side the one with a defect.






Interstitials are a variety of crystallographic defects, i.e. atoms which occupy a site in the crystal structure at which there is usually not an atom, or two or more atoms sharing one or more lattice sites such that the number of atoms is larger than the number of lattice sites. They are generally high energy configurations. Small atoms in some crystals can occupy interstitial sites in an energetically favourable configuration, such as hydrogen in palladium.

wikipedia






Lattice Defects in and Carious Dissolution of Human Enamel Crystals

Human enamel crystals under carious dissolution were studied by a combination of high resolution electron microscopy and microbeam electron diffraction. The crystals selected for study were those oriented in respect of the electron beam such that the electron-lucent small spots and larger areas due to carious dissolution could be examined in relation to the high resolution images of the (001) planes. Irregularities in the arrangement of the lattice fringes, including shifted, disrupted, and curved fringes, were observed in many cases of these electron-lucent spots and large areas. The disrupted lattice fringes were interpreted as being a type of edge dislocation. These results indicate that carious dissolution will initially attack the portion of the crystal with lattice defects.

Journal of Electron Microscopy 36(6): 387-391 (1987), Oxford Journals.org



We succeeded in distinguishing between oxygen and silicon atoms on an oxygen-adsorbed Si(111)7 × 7 surface, and also distinguished between silicon and tin atoms on Si(111)7 × 7-Sn intermixed and Si(111) × -Sn mosaic-phase surfaces using non-contact atomic force microscopy (NCAFM) at room temperature. Atom species of individual atoms are specified from the number of each atom in NC-AFM images, the tip-sample distance
dependence of NC-AFM images and/or the surface distribution of each atom. Further, based on the NC-AFM method but using soft nanoindentation, we achieved two kinds of mechanical vertical manipulation of individual atoms: removal of a selected Si adatom and deposition of a Si atom into a selected Si adatom vacancy on the Si(111)7 × 7 surface at 78 K.


Atom-selective imaging and mechanical atom manipulation using the non-contact atomic force microscopic

Distinguishing between oxygen and silicon atoms

Atom-selective imaging and mechanical atom manipulation using the non-contact atomic force microscope AFM; Oxford journals



.....Further, based on the NC-AFM method but using soft nanoindentation, we achieved two kinds of mechanical vertical manipulation of individual atoms: removal of a selected Si adatom and deposition of a Si atom into a selected Si adatom vacancy on the Si(111)7 × 7 surface at 78 K. Here, we carefully and slowly indented a Si atom on top of a clean Si tip apex onto a predetermined Si adatom to remove the targeted Si adatom and onto a predetermined Si adatom vacancy to deposit a Si atom, i.e. to repair the targeted Si adatom vacancy. By combining the atom-selective imaging method with two kinds of mechanical atom manipulation, i.e. by picking up a selected atom species and by depositing that atom one by one at the assigned site, we hope to construct nanomaterials and nanodevices made from more than two kinds of atom species in the near future.

www.oxfordjournals.org



Silicon Nano Crystal Memory Cell


Silicon Nano Crystal Memory Cell, where nano-crystals (NCs) are embedded in gate oxide and act as charge storages, has attracted much attention [ I ] . Physical separation of NCs can improve the retention time by limiting the lateral flow of charge. Thus, many efforts have been directed to explore the suitability as integrated-memory. However, the scaling of NCM cell is difficult without lithography advances or effective design with highly scalable process, because it is hard to reduce memory cell area per bit. To realize over gigabitdensity integration, NCM cell should be dramatically shrunk by introducing highly scalable self-aligned BLs contact. On the other hand, the reliability of NCM is also the critical issue. In an exploration of relationship of NCs controllability with the chemical nature and physical properties of tunelling dielectrics such as stress or roughness, it is essential t0 overcome reliability degradation effectively.

This paper reports the first full process integration of nano-crystal memory (NCM) with 4.6F2 cell (size: 0.0777pm2) based on NOR type, which is achieved by landing plug polysilicon contact (LPC) and direct tungsten (W) bitline (BL). Robust 4-threshold voltage (VT) states for 2bits operation per cell are verified Also, the
comparable characteristics to NCM with conventional silicide BL contact are obtained and NCM reliability is significantly improved by properly fluorinated effect while still keeping process compatibility and controllability, which is the only alternative for volume manufachue of high density NCM.

Integration of Fluorinated Nano-Crystal Memory Cells with 4.6F2 Size by Landing Plug Polysilicon Contact and Direct-Tungsten Bitline; www.google.co.uk

Innovation at Oxford

What is Innovation?

Oxford Science Enterprise Centre

What we have done in Oxford, is created completely new ethos for invention and innovation. Innovation follows invention, that is when you create something with phases in between until it is commercialized. You have to convert the innovation into business and that includes stages of technology readiness.

The IP has to be converted into a business or a product: this is the innovative step

Managing innovation is a new and poorly understood topic
We introduced enterprise fellowships to do this


- The technology was too disruptive for any license deal
- The time to market is long because of FDA approval issues
- The complexity increased as the improvements to performance to achieve a 3% CV were made
- Many questions of basic science and technology have been identified: polymer cutting, machining, bonding, surface wetting, drying, printing…..


- There is a growing gulf between science and technology
- it is not a new phenomenon
- in academia science is ok, but technology is regarded with suspicion







Nanoparticles and Medicine

Some of the ideas being developed in oxford

- Detect natural nanoparticles in body fluids using new optical/zeta potential techniques
- Design particles for image enhanced and diagnosis

- Design new particles for targeted drug delivery


Peter Dobson, Innovation and Spin-out Company, Begbroke Science Park, 2008



- I think it is fair to say that most pure scientists have themselves been devastatingly ignorant of productive industry
- Pure scientist and engineers often totally misunderstand each other
- Pure scientists have by and large been dim-witted about engineers and applied science.
- Engineers have to live their lives in an organised community…. they are absorbed by making things – P C Snow





How particles interact with living cells?

Porous nanoparticle with drug loaded pores – We are taking a drug which is just come of patent and put it in nanoparticle with a recognition molecule on the surface - we are designing this particle drug - having attached itself to tumour it begins to fall apart and leak the drug directly into the tumour.


Karl Morten; Gareth Wakefield; Peter Dobson


OXFORD PROJECT TO EXAMINE MEMORY AND AGEING

The challenge
• Each year about 203,000 people in the UK develop dementia (550 every day), the great majority with Alzheimer’s disease.
• Alzheimer’s disease costs the country about £17 billion per year, which is almost 20% of the health budget. The costs of Alzheimer’s disease are more than the combined costs of heart disease, stroke and cancer.
• The main challenge is to discover ways of preventing Alzheimer’s disease from developing.


How is OPTIMA dealing with the challenge?

1. In 1992, OPTIMA introduced new methods of diagnosis of Alzheimer’s disease, in use around the world.

2. In 1994 OPTIMA discovered that Alzheimer’s disease is not an inevitable part of ageing, but that it is a true disease. This finding led OPTIMA to search for ‘risk factors’.

3. In 1998, OPTIMA discovered the first risk factor for Alzheimer’s disease that can be safely and simply modified by diet (homocysteine. This discovery was recognised by the American Medical Association as one of the most significant findings of the year. OPTIMA’s discovery has been confirmed world-wide and has led the US National Institute on Aging to set up a clinical trial in which B vitamins, which lower homocysteine levels, are being tested to see if they can slow the progression of Alzheimer’s disease.

http://www.medsci.ox.ac.uk/optima



The Financial Crisis and Biotechnology - 3 Oct 2008

Biotechnology companies are highly dependent on well functioning capital markets to finance their development projects since many will not see revenue for perhaps a decade.

It generally takes approximately $1 billion, including the cost of failures, to get a new therapy to market. This financing generally comes in the form of equity investment.

When credit markets seize up, as we've seen in the past 13 months, there is less capital available for investors to put at risk, and the capital that is put at risk is dedicated to shorter term, lower risk options. So while some areas of the economy have seen a slowdown, biotech has seen a near-freeze.

This means that our companies - especially our public companies - are in a very precarious situation: they must continue on their development projects, but are unable to attain additional financing from investors. As a result, many of the 300-400 public biotech companies are trading at very low levels, and many are operating with less than one year's cash remaining.

If credit markets don't open up, it's possible that the biotechnology industry may go through a considerable consolidation or shake out during the next year. The result? Companies with promising therapies may not be able to continue their work, delaying the availability of new options for patients.

We will work with allies across numerous industries - those innovative industries similar to ours - as well as new partners to develop these initiatives and urge Congress for action.

Jim Greenwood, Biotechnology Industry Organization, BIO
www.bio.org

Qunatitative Measurement of Vacancy

The use of transmission electron microscopy (TEM) to provide a quantitative measurement of both vacancy and interstitial dusters in ionimplanted silicon was reviewed in this study. Interstitials agglomerate into rod-like defects on {311} planes, and the evaporation of these defects can be directly correlated to the diffusion enhancements observed during annealing of ion-damaged silicon.
Vacancy clusters are easily detected in TEM once they have been labelled using a Au-diffusion technique. The combination of the two approaches provides a quantitative test for models of implantation and annealing in silicon. Detailed models for point defect behaviour, which include Ostwaldripening and the surface recombination velocity, reproduce all of the crucial features of the observed defect annealing.

Quantitative TEM of point defects in Si, ,Journal of Electron Microscopy
49(2): 293-298 (2000)

Structural Properties

The increase in surface area and surface free energy with decreasing particle size leads to changes in interatomic spacings. For Cu metallic clusters the interatomic spacing is observed to decrease with decreasing cluster size. This can be explained by the compressive strain induced by the internal pressure arising from the small radius of curvature in the nanoparticle . Conversely, for semiconductors and metal oxides there is evidence that interatomic spacings increase with decreasing particle size.


Kelsall, Nanoscale, p 25




Pore Structure of Slowly Cooled Mafic Intrusions

.....The glass films vary from a few microns to a few tens of microns thick, and are associated with strings of small lensoid grain boundary pockets formed by impingement during crystal growth. Additional porosity occurs as extensive liquid-filled pockets adjacent to included grains within oikocrysts and as large triangular pockets formed by impingement of planar-sided grains. Interstitial material within glass films, and the irregularity of film thickness along a single grain boundary, suggest that the present pore structure is representative of the pore structure before entrainment and eruption. Pore geometry is consistent with a dominant control by crystal growth during solidification, with little or no evidence for control by minimization of internal energies driven by textural equilibration. Similarities between liquid distribution in the crystalline nodules and that of late-stage, interstitial phases in fully solidified mafic cumulates from the Rum and Skaergaard intrusions demonstrate that the crystalline nodules provide information about the latest stages of solidification in slowly cooled mafic plutons. The highly permeable network of intersecting liquid films, lenses and pockets may promote in situ crystallization in the solidifying mush, explaining the common presence of adcumulates in such intrusions.

Textures in Partially Solidified Crystalline Nodules: a Window into the Pore Structure of Slowly Cooled Mafic Intrusions; Journal of Petrology 2007 48(7):1243-1264; doi:10.1093/petrology/egm016




Influence of radiation on material properties

High energy neutrons cause atoms to be displaced from their lattice sites to become self interstitials leaving behind an excess of vacancies. The vacancies and self interstitials may recombine so that the lattice reverts to its original state, or the defects may be attracted to sinks, such as grain boundaries. Alternatively, these defects may form clusters such as interstitial or vacancy loops, or the vacancies may create three dimensional clusters, that is, voids. Accompanying this defect generation is a loss in ductility together with an increase in the mechanical properties (strength and hardness). Swelling may also result from void formation. In steel this loss of ductility can be described quantitiatively by an increase in the ductile to brittle transition temperature as determined by the Charpy impact test. In addition, radiation damage reduces the high temperature shelf energy of the Charpy impact test curve. These changes in mechanical behaviour are of particular interest in the case of steel usedin nuclear reactor pressure vessels because of possible embrittlement induced failure during operation.

There are two factors that affect the properties of the pressure vessel steels; the microstructure, which can be altered by radiation damage, and the composition. A typical pressure vessel steel contains about 0.25 wt% carbon, which produces a mixed ferrite-pearlite microstructure on slow cooling from the austenite range. Among the metallic elements present in steel, copper is the most deleterious, probably because of its very limited solid solubility which results in the formation of precipitates. Long-term retention of the pearlite at a temperature below the eutectoid temperature leads to a spheroidite structure, spherical cementite in a ferrite matrix. In addition to carbon these steels contain a number of other alloying elements all of which are in solid solution in the ferrite. It was proposed that copper or copper microvoid precipitates form, having a diameterof about 0.3 nm, which cannot be observed by conventional transmission electron microscopy TEM. These precipitates cause embrittlement of the steel. experimentally the copper content in pressure vessel steel has been found responsible for much of the radiation induced shift in the transition temperature. The higher copper content steels show a substantial increase in yield strength compared to those with an increasing phosphorus content………

It is proposed that in radiation damaged steel, the surfaces of vacancy clusters formed in cascades have a strong binding interaction for imputities, such as copper, hence producing precipitates.

Books.google.co.uk, 13th international symposium



Crystalline Structure of Pancreatic Calculi

........The crystals were identified as calcite composed of CaCO3 in X-ray and electron diffraction studies. Scanning electron microscopy (SEM) revealed that the calculi consist of aggregations of rhombohedral, fang-shaped, botryoidal, foliaceous, and plate-shaped crystals. Some of them showed signs of partial dissolution on their surface. Transmission electron microscopy (TEM) showed crystals of various sizes and shapes either solitary or in clumps. The direct measurement of crystalline lattice intervals obtained from each crystal was 0.386 run in accordance with the diffraction data. Exocrine pancreatic cell debris are present in pancreatic calculus matrices.


The Crystalline Structure of Pancreatic Calculi, Journal of Electron Microscopy 43(2): 57-61 (1994, oxfordjournals.org

weak beam technique identifying small point defect

We have made an analysis of the conditions necessary for the successful use of the weak-beam technique for identifying and characterizing small point-defect clusters in ion-irradiated copper. The visibility of small defects was found to depend only weakly on the beam convergence. In general, the image sizes of small clusters were found to be most sensitive to the magnitude of sg, with the image sizes of some individual defects changing by large amounts with changes in sg as small as 0.025 nm–1. The most reliable information on the true defect size is likely to be obtained by taking a series of 5–9 micrographs with a systematic variation of deviation parameter from 0.2–0.3 nm–1. This procedure allows size information to be obtained down to a resolution limit of about 0.5 nm for defects situated throughout a foil thickness of 60 nm. The technique has been applied to the determination of changes in the sizes of small defects produced by a low-temperature in-situ irradiation and annealing experiment.

Michael L. Jenkins, On the application of the weak-beam technique to the determination of the sizes of small point-defect clusters in ion-irradiated copper, oxfordjournals.org

Nematic Phase

nematic phase - One of the most common LC phases is the nematic, where the molecules have no positional order, but they have long-range orientational order. Thus, the molecules flow and their center of mass positions are randomly distributed as in a liquid, but they all point in the same direction (within each domain). Most nematics are uniaxial: they have one axis that is longer and preferred, with the other two being equivalent (can be approximated as cylinders). Some liquid crystals are biaxial nematics, meaning that in addition to orienting their long axis, they also orient along a secondary axis.
The word nematic comes from the Greek νημα, which means 'thread.' This term originates from the thread-like topological defects observed in nematics, which are formally called 'disclinations.' Nematics also exhibit so-called hedgehog topological defects.
Nematics have fluidity similar to that of ordinary (isotropic) liquids but they can be easily aligned by an external magnetic or electric field. An aligned nematic has the optical properties of a uniaxial crystal and this makes them extremely useful in liquid crystal displays (LCD).

widipedia

Electron

Electrons


The chemist's notion of physical reality is based on the existence of two particles that are smaller than atoms. These particles are the proton and the electron (a neutron is just a combination of the two). While there are sub-subatomic particles (quarks, hadrons, and the like), protons and electrons in some sense represent the simplest particles necessary to describe matter.

The electron was discovered early in the 20th Century. Electrons are very light (2,000 times lighter than the smallest atom, hydrogen) and have a negative charge. Protons, which make up the rest of the mass of hydrogen, have a positive charge. When two electrons come near one another, they interact by the fundamental electrical force law. This force can be expressed by a simple equation that is sometimes called Coulomb's law.

For two charged particles separated by a distance r, the force acting between them is given as

F = Q1Q2/r2

Here F is the force acting between the two particles separated by a distance r, and the charges on the particles are, respectively, Q1 and Q2. Notice that if both particles are electrons, then both Q1 and Q2 have the same sign (as well as the same value); therefore, F is a positive number. When a positive force acts on a particle, it pushes it away. Two electrons do not like coming near one another because "like charges repel" just as two north-polarized magnets do not like to approach each other. The opposite is also true. If you have two particles with opposite charges, the force between them will be negative. They will attract each other, so unlike charges attract. This follows directly from Coulomb's law.


It also follows from Coulomb's law that the force of interaction is small if the particles get very far apart (so that r becomes very big). Therefore, two electrons right near one another will push away from one another until they are separated by such a long distance that the force between them becomes irrelevant, and they relax into solipsistic bliss.




Bonds are key to nanotechnology. They combine atoms and ions into molecules and can themselves act as mechanical devices like hinges, bearings, or structural members for machines that are nanoscale. For microscale and larger devices, bonds are just a means of creating materials and reactions. At the nanoscale, where molecules may themselves be devices, bonds may also be device components.

Traditionally, materials science has been devoted to three large classes of materials—metals, polymers, and ceramics.

Metals: Atoms like to cluster with others of the same kind. This process can make huge molecule-like structures containing many billions of billions of atoms of the same sort. In most cases, these become hard, shiny, ductile structures called metals. In metals, some of the electrons can leave their individual atoms and flow through the bulk of the metal.

Polymers: The most common polymers are plastics. Most polymers are based on carbon because carbon has an almost unique ability to bond to itself. Polymers are single molecules formed of repeating patterns of atoms (called monomers) connected in a chain.

Ceramics: The last area of traditional materials science is ceramics. Ceramics are often but not always oxides, which are structures where one of the atoms making up the extended structure is oxygen.



Coulomb's law
The magnitude of the electrostatic force between two point electric charges is directly proportional to the product of the magnitudes of each charge and inversely proportional to the square of the distance between the charges.
wikipedia.org


Skin effect
In a Direct Current circuit, the electrons travel evenly through the entire cross section of the conductor. however, in an AC circuit conductor, besides setting up eddy currents, the voltage that creates the eddy current also causes the current flow in the conductor to be repelled away from the centre of the conductor toward the outside of he conductor. The current is forced to travel near the surface of the conductor. This effect, known as the skin effect, creates the same consequence as reducing the cross sectional area of the conductor because the electrons are forced to flow in a smaller area concentrated near the surface of the conductor. the skin effect also causes an increase in the conductor resistance in the circuit due to power losses. Both eddy currents and the skin effect are directly related to the frequency of the circuit. Therefore, as the frequency increases the magnitude of the eddy currents increases causing the skin effect to also increase.
AC Theory, Thomson, NY, 2004

91 Atoms

91 atoms

Nature and the nanotechnologist have 91 different atoms to play with—each is roughly spherical but different in its size and its ability to interact with and bind to other atoms. Many, many different molecules exist—millions are known and hundreds of new ones are made or discovered each year.








Polymer

lnsulators do not have moving electrons to conduct charge. They are also generally not shiny because there are no free electrons to reflect the light that shines upon them. Even though we won't worry much about shininess, how free the flow of electrons in a material is matters quite a bit for nanotechnology.

Most polymers are based on carbon because carbon has an almost unique ability to bond to itself. Polymers are single molecules formed of repeating patterns of atoms (called monomers) connected in a chain. In a sample such as a polystyrene drinking cup, there will be many different structures, and the chains will be of different lengths.







Quantum mechanics in disguise


Many of the basic rules that define the behavior of nanostructures are the laws of quantum mechanics in disguise. Examples include issues such as how small a wire can be and still carry electrical charge, or how much energy we have to put into a molecule before it can change its charge state or act as a memory element.






[Nanofabrication] is building at the ultimate level of finesse.
—Richard Smalley
Nobel Laureate and Professor, Rice University


................and it wasn't until the year 2000 (as Feynman predicted with uncanny accuracy) that devices started to break into the nanoscale and people started asking why we hadn't thought of this long before.

HOW NANOSCALE DIMENSIONS AFFECT PROPERTIES

MANY PROPERTIES ARE CONTINUOUSLY MODIFIED AS A FUNCTIONOF SYTEM SIZE. OFTEN THESE ARE EXTRINSIC PROPETIES, SUCH AS RESISTANCE, WHICH DEPEND ON THE EXACT SIZE AND SHAPE OF THE SPECIMEN. OTHER PROPERTIES DEPEND CRITICALLY ON THE MICROSTRUCTURE OF THEMATERIAL, FOR EXAMPLE, THE HALL PETCH EQUATION FOR YIELD STRENGTH, Q, OF A MATERIAL AS A FUNCTIONOF AVERAGE GRAIN SIZE (d) IS GIVEN


Q = k(d) ^1/2 + Qo

Kelsall, Nanoscale, p 24

MY RESEARCH QUESTION

In a bulk piece of material, there is a formula for the number density of vacancies as you go into the material from the surface. The number density is higher near the sur-face.

So, if you have a small crystal, it should have a high defect population than bulk material.


Nanotech Oxford

Crystalline structure?
Number of vacancy? nv= N exp(- Qf/RT)
Vacancy density?
Defects in crystalline material ??
Thermal equilibrium?
Refinement of structures including quantum dots and interfaces?
Surface atomic structure?
Surface deformation?
The defect and dislocation level?







Oxford’s former students competing in the Olympic Games in Beijing have had an impressive weekend securing an array of gold and silver medals.

Last week Daisy Dick won a bronze medal in Eventing and now her Oxford alumni Team GB colleagues have added to her win.

On Saturday 16 August, Peter Reed and Andy Triggs-Hodge won a gold medal apiece in the rowing four, while Acer Nethercott and Colin Smith won silver in the men’s rowing eight – accompanied by Josh West who is a University researcher.

On Sunday 17 August, Paul Mattick made the rowing finals of the lightweight four and came in fifth place, while USA rower Jamie Schroeder took the same spot in the quadruple sculls final.

Buffy Williams of Canada, who studied at St Hughs in 2004, got fourth place in the women’s eight final.

www.ox.ac.uk/media

Vacancies: conductivity and reactivity

Vacancies are point defects in the crystalline structure of a solid and may control many physical properties in materials such as conductivity and reactivity. In microcrystalline solids at temperatures above 0 K, vacancies invariably exist in thermal equilibrium. In the simple case of metals with one type of vacancy, the number of vacancies in a crystal consisting of N atom sites is approximated by an Arrhenius-type expression

n = N exp(- Qr/ RT)

T: absolute temperature
R: the gas constant
Qr: energy required to form one mole of vacancies

Qr = N_A qr
N_A: Avogadro number
qr: the activation energy for the formation of one vacancy

Kelsall, p 21



The Avogadro constant (symbols: L, NA), also called the Avogadro number, is the number of atoms in exactly 12 grams of 12C. A mole is defined as this number of "entities" (usually, atoms or molecules) of any material. The currently accepted value for this number is:

N_A = (6.02214179 +- 0.00000030)x 10^{23} mol^-1


Source: wikipedia


The influence of defects
The details of the arrangement of atoms in crystal lattice can be determined by analysing the diffraction effects which are produced when a beam of some appropriate radiation (X rays, electrons, or neutrons) is incident on the crystal. This is extremely unlikely that the atoms are exactly at their correct positions in the crystal, when we recall that there are about 10^22 atoms in 1 cm3 of material. There must always be some atoms which are not exactly in their right place and so the lattice will contain imperfections or DEFECTS.

There are two main types of geometrical defect in a crystal. There are those which are very localized and are of atomic dimensions – these are called point defects. The most obvious example is an impurity atom. This can be either a substitutional or an interstitial impurity depending on whether it replaces an atom on the host lattice or whether it is betweenthe host atoms on a non lattice site. In both cases there will be some distortion around it. There are also those defects which are of a more extended nature – the most important and interesting being the dislocation. In addition to these static defects, the perfection of the lattice arrangement will be continually upset by the thermal vibrations of the atoms.

The presence of all types of defect increases the disorder to the crystal, ie it increases its entropy. There is therefore a tendency for more defects to be present at higher temperatures.



Point defects: vacancies
The simplest defect to consider is the configuration which arises when an atom is missing from its site in the lattice. This vacant lattice is called a vacancy. in the region around a vacancy there will be a tendency for the atomic arrangement to readjust slightly and so the crystal lattice becomes distorted.
The presence of vacancies provides a means for atoms to diffuse fairly easily from one part of the crystal to another since an atom can move to a vacancy thereby leaving its own site vacant without producing too much disruption of the existing crystal lattice. ie. Very little energy is required. Thus diffusion can be thought of as a migration of vacancies in the opposite direction. In an ionic crystal the presence of a vacancy at a positive-ion site upsets the electrical neutrality of the region and so the vacancy has an effective negative charge associated with it. This would increase the electrostatic energy of the system: hence in order to maintain electrical neutrality there is a tendency for positive and negative ion vacancies to be produced in pairs.

Clarendon publishing


In crystallography, a vacancy is a type of point defect in a crystal. Crystals inherently possess imperfections, often referred to as 'crystalline defects'. A defect wherein an atom, such as silicon, is missing from one of the sites is known as a 'vacancy' defect.

Vacancies occur naturally in all crystalline materials. At any given temperature, up to the melting point of the material, there is an equilibrium concentration (ratio of vacant lattice sites to those containing atoms). At the melting point of some metals the ratio can be approximately 0.1%

The creation of a vacancy can be simply modeled by considering the energy required to break the bonds between an atom inside the crystal and its nearest neighbor atoms. Once that atom is removed from the lattice site, it is put back on the surface of the crystal and some energy is retrieved because new bonds are established with other atoms on the surface. However, there is a net input of energy because there are fewer bonds between surface atoms than between atoms in the interior of the crystal.

At any given temperature, the amount of energy needed to create a vacancy is diminished because creating a vacancy disorders the interior of the crystal. The measure of this disorder is called the entropy of the system. Adding vacancies to the material increases the entropy, which tends to reduce the total energy required to create the vacancy. We call this energy the free energy and this is the energy that is required to create an equilibrium concentration of vacancies at a given temperature.


Point defects are defects which are not extended in space in any dimension. There is not strict limit for how small a "point" defect should be, but typically the term is used to mean defects which involve at most a few extra or missing atoms without an ordered structure of the defective positions. Larger defects in an ordered structure are usually considered dislocation loops. For historical reasons, many point defects especially in ionic crystals are called 'centers': for example the vacancy in many ionic solids is called an F-center.

* Vacancies are sites which are usually occupied by an atom but which are unoccupied. If a neighboring atom moves to occupy the vacant site, the vacancy moves in the opposite direction to the site which used to be occupied by the moving atom. The stability of the surrounding crystal structure guarantees that the neighboring atoms will not simply collapse around the vacancy. In some materials, neighboring atoms actually move away from a vacancy, because they can better form bonds with atoms in the other directions. A vacancy (or pair of vacancies in an ionic solid) is sometimes called a Schottky defect.

* Interstitials are atoms which occupy a site in the crystal structure at which there is usually not an atom. They are generally high energy configurations. Small atoms in some crystals can occupy interstices without high energy, such as hydrogen in palladium.
* A nearby pair of a vacancy and an interstitial is often called a Frenkel defect or Frenkel pair

* Impurities occur because materials are never 100% pure. In the case of an impurity, the atom is often incorporated at a regular atomic site in the crystal structure. This is neither a vacant site nor is the atom on an interstitial site and it is called a substitutional defect. The atom is not supposed to be anywhere in the crystal, and is thus an impurity.

* Anti-site defects occur in an ordered alloy. For example, some alloys have a regular structure in which every other atom is a different species, for illustration assume that type A atoms sit on the cube corners of a cubic lattice, and type B atoms sit in center of the cubes. If one cube has an A atom at its center, the atom is on a site usually occupied by an atom, but it is not the correct type. This is neither a vacancy nor an interstitial, nor an impurity.

* Topological defects are regions in a crystal where the normal chemical bonding environment is topologically different from the surroundings. For instance, in a perfect sheet of graphite (graphene) all atoms are in rings containing six atoms. If the sheet contains regions where the number of atoms in a ring is different from six, while the total number of atoms remains the same, a topological defect has formed. An example is the Stone Wales defect in nanotubes, which consists of two adjacent 5-membered and two 7-membered atom rings.
* Also amorphous solids may contain defects. These are naturally somewhat hard to define, but sometimes their nature can be quite easily understood. For instance, in ideally bonded amorphous silica all Si atoms have 4 bonds to O atoms and all O atoms have 2 bonds to Si atom. Thus e.g. an O atom with only one Si bond can be considered a defect in silica.

* Complexes can form between different kinds of point defects. For example, if a vacancy encounters an impurity, the two may bind together if the impurity is too large for the lattice. Interstitials can form 'split interstitial' or 'dumbbell' structures where two atoms effectively share an atomic site, resulting in neither atom actually occupying the site.

source: wikipedia




Nanotopography is defined as “the deviation of a surface within a spatial wavelength of around 0.2 to 20 mm.”(2) This is a parameter that measures the front-surface, freestate topology of an area which can range in size from fractions of a millimeter to tens of millimeters. In this sense, nanotopography differs from front-referenced site flatness in that for nanotopography the wafer is measured in a free state, while for flatness it is referenced to a flat chuck. A wafer may have perfect flatness (in the classical definition of flatness), yet still have nanotopography. If a wafer has surface irregularities on the front and backside of the wafer, but front and back surfaces are parallel, the wafer has perfect flatness. However, the same wafer will exhibit nanotopography (Figure 1).




Nanotopography bridges the gap between roughness and flatness in the topology map of wafer surface irregularities in spatial frequency. Nanotopography of the silicon wafer is dictated to a large extent by the polishing process. A true planetary, freefloating, double-sided polishing process that polishes both sides of a silicon wafer simultaneously technically achieves the best nanotopography and flatness results.


http://www.memc.com/t-wafer-nanotopography.asp




Pure Cu
Defect structures in pure Cu are described here for reference:

Interstitial-type dislocation loops were formed up to 523 K, and Fig. la shows typical examples. As found previously [1], very few loops formed in the middle
temperature around 373 K, which has been referred to as 'down peak' in the temperature dependence of the loop number density. Figure 2 shows the variation of the loop number density with irradiation time at several temperatures. At room temperature, loops nucleated during the initial stage of the irradiation, but over 2/3 of them disappeared without growing larger. As the temperature was raised to 323 K, loops disappeared earlier, and the saturation number density was smaller than at
300 K. Almost no loops were observed around 373 K. Above this temperature, faulted dislocation loops again formed, and the majority of them grew larger until they
eventually unfaulted and were lost from the foil by glide. They had a larger growth rate and a smaller number density at higher temperatures, and were not formed above 523 K.

www.oxfordjournals.org



Planar defects

* Grain boundaries occur where the crystallographic direction of the lattice abruptly changes. This usually occurs when two crystals begin growing separately and then meet.

* Anti phase boundaries occur in ordered alloys: in this case, the crystallographic direction remains the same, each side of the boundary has an opposite phase: For example if the ordering is usually ABABABAB, an anti phase boundary takes the form of ABABBABA.

* Stacking faults occur in a number of crystal structures, but the common example is in close-packed structures. Face-centered cubic (fcc) structures differ from hexagonal close packed (hcp) structures only in stacking order: both structures have close packed atomic planes with sixfold symmetry -- the atoms form equilateral triangles. When stacking one of these layers on top of another, the atoms are not directly on top of one another -- the first two layers are identical for hcp and fcc, and labelled AB. If the third layer is placed so that its atoms are directly above those of the first layer, the stacking will be ABA -- this is the hcp structure, and it continues ABABABAB. However there is another location for the third layer, such that its atoms are not above the first layer. Instead, the fourth layer is placed so that its atoms are directly above the first layer. This produces the stacking ABCABCABC, and is actually a cubic arrangement of the atoms. A stacking fault is a one or two layer interruption in the stacking sequence, for example if the sequence ABCABABCAB were found in an fcc structure.

Bulk defects

* Voids are small regions where there are no atoms, and can be thought of as clusters of vacancies.

* Impurities can cluster together to form small regions of a different phase. These are often called precipitates.

wikipedia.org

Conduction Band

When a solid is formed, the energy levels of the atoms broaden and form bands with forbidden gaps between them. The electrons can have energy values that exist within one of the bands, but cannot have energies corresponding to values in the gaps between the bands. The lower energy bands due to the inner atomic levels are narrower and are all full of electrons, so they do not contribute to the electronic properties of a material...........The outer or valence electrons that bind the crystal together occupy a valence band, which for an insulating material, is full of electrons that cannot move since they are fixed in position in chemical bonds. There are no delocalised electrons to carry current, sothe material is an insulator. The conduction band is far above the valence band in energy, so it is not thermally accessible, and remains essentially empty. In other words, the heat content of the insulating material at room temperatur T=300 K is not sufficient to raise an appreciable number of electrons from the valence band to the conduction band, so the number in the conduction band is negligible. Another way to express this is to say that the value of the gap energy En far exceeds the value k T of the thermal energy, where k is Boltzmann's constant.


Owens, The Physics and Chemistry of Nanosolids, p 26



In the recent studies on the optical manipulation, one of major interests is how we can manipulate the nanoscale objects with condensed matter whose size is between that of an atom and that of a micrometer object. For metallic substances, the trapping of a single 36-nm-diameter gold particle has been achieved [1]. On the other hand, as for nonmetallic particles, submicron-sized (∼220 nm) polystyrene latex particles with fluorescent dye have been trapped, gathered and fixed onto the substrate with a strongly focused laser beam [2]. However, if the particle is much smaller than the wavelength for the usual laser frequency region (diameter < 100 nm, for example), the induced polarization becomes too small and hence, the light-matter interaction becomes too weak to cause sufficiently strong force under the electronically non-resonant condition.

Takuya Iida, Optical Manipulation of Nano Materials under Quantum Mechanical Resonance Conditions; 2005; http: //ietele.oxfordjournals.org

[1] K. Svoboda and S.M. Block, “Optical trapping of metallic Rayleigh particles,” Opt. Lett., vol.19, no.13, pp.930–932 July 1994.

[2] S. Ito, H. Yoshikawa, and H.Masuhara, “Optical patterning and photochemical fixation of polymer nanoparticles on glass substrates,” Appl. Phys. Lett., vol.78, pp.2566–2568, April




Alloy-based nano-crystal texture and method of preparing same


Abstract:
To provide a very tough material at a low manufacturing cost, the present invention provides an alloy-based nano-crystal texture in which, in an alloy system having a composition deviating from the stoichiometric composition, and capable of forming an amorphous state, nano-scale crystals are arranged in an identical crystal orientation.

http://www.freepatentsonline.com/y2005/0126665.html