Carbon Nanotubes

Oxford Materials Outreach

Carbon Nanotubes are Single-Walled, Double Walled and Multi-Walled black nano scale cylindrical tubes of graphitic carbon with numerous applications. Carbon Nanotubes are the stiffest and strongest known fibers and have unique electrical properties. Applications for AE Carbon Nanotubes� include in flat screen displays, scanning probe microscopes in brushes for commercial electric motors, and in sensing devices and because of their strength in numerous aerospace and automotive uses, in body armor and tear-resistant cloth fibers and textiles and stronger and lighter sports equipment . Carbon nanotubes can behave like a conductive metallic or semiconductor depending on their structure, which is useful for nanoscale electronic devices and in electrically conductive films in coatings, plastics, nanowire, nanofiber and in certain bioscience applications.

Source://outreach.materials.ox.ac.uk/LearningResources/Nanotechnology/nanotechnologyindex.php



BUCKY BALLS

The most well-known crystal structure of carbon is diamond, which can be described as (cubic F)*(C-C). That is, it has the same Bravais lattice as Au (cubic F), but the motif is a pair of C atoms instead of one Au atom. Carbon crystallises in
several other forms Ð one is graphite, in the form of sheets of C atoms arranged in a hexagonal array, with these sheets held together by weak (Van der Waals) forces. If we take a sheet of graphite, it can be rolled into a tube and joined, with no discontinuities. These carbon nanotubes were first discovered by Iijima in the electron microscope in 1991. They are very strong, and so can be used as strengthening fibres within composites; and they can be used as containers inside which thin crystal wires can be grown, with properties which are different to the bulk, or within which individual molecules can be packed. If a piece with 60 carbon atoms is cut from a single graphite sheet, it can be bent into a football shaped molecule, C60, known as a bucky ball (after the architect Buckminster Fuller who
had previously built large structures with this shape). Indeed the bucky ball is small enough to pack inside a nanotube (see Figure 9), and an atom is small enough to place inside a bucky ball. So individual atoms can be held inside bucky balls, which in turn are packed within a nanotube. Scientists are investigating whether
this structure might be the basis for the next generation of (quantum) computers.


............in diamond, each carbon atom is at the centre of a tetrahedron of four other carbon atoms, and this arrangement is exceedingly strong. And this tetrahedron of atoms survives, with some distortion, into the amorphous state of carbon. Adjacent connected tetrahedra can rotate about their common bond, and this random rotation, when repeated for all bonds, results in the amorphous structure. During this rotation, the first nearest distance, and the second nearest distance of the tetrahedron are retained, and appear in the distribution function of the amorphous state, but the third nearest neighbour distance is not retained and does not appear.

Wavws of the future; outreach.materials.ox.ac.uk





Nanomaterials are often classified in the literature based on dimensionality. Crucial to this classification is the concept of confinement, which may be roughly interpreted as a restriction in the ability of electrons to move in one or more spatial dimensions. 0D nanomaterials, such as quantum dots and metal nanoparticles, are confined in all three dimensions. 1D nanomaterials are confined in two directions and extended in only one: electrons flow almost exclusively along this extended dimension. Examples of one-dimensional nanomaterials are nanotubes and nanowires. Finally, 2D nanomaterials, which are confined in one dimension and extended in two, include thin films, surfaces, and interfaces. Interestingly, material structures currently used as elementary semiconductor devices fall under this category.

Nanomaterials can also be divided into inorganic and organic classes.

The term inorganic nanomaterials describes nanostructures in which carbon is
not present and combined with some other element. Four types of inorganic nanostructures are fullerenes and carbon nanotubes, nanowires, semiconductor nanocrystals, and nanoparticles.

.......Further, nanotubes have a current carrying capacity of one billion amps per square centimeter while copper wires burn out at one million amps per square centimeter. They also have more than 20 times the tensile strength of high-steel alloys, but are lighter than aluminum. Finally, it is estimated that nanotubes can transmit nearly twice as much heat as pure diamond and are likely to remain stable in higher temperatures than metal wires.

Miller, John C. Handbook of Nanotechnology : Business, Policy, and Intellectual Property Law, John Wiley & Sons, 2004. p 17




Since the re-discovery of carbon nanotubes (CNTs) in 1991 , they have become widely exploited in electroanalysis. CNTs are assigned into two classes: single walled (SWCNTs) and multi-wall carbon nanotubes (MWCNTs). The former consist of a single graphite sheet rolled flawless producing a tube diameter of 1-2 nm while the latter comprise several concentric tubes fitted one inside the other. There are a number of morphological variations of the latter including “hollow-tube”, “herringbone” or “bamboo-like”MWCNTs.

http://compton.chem.ox.ac.uk/news/2006/poster%20Xiaobo.pdf


Particle surface and biocompatibility Reports on the surface properties of nanoparticles, both physical and chemical, stress that nanoparticles differ from bulk materials. Their properties depend heavily on the particle size. Therefore, nanoparticles are not merely small crystals but an intermediate state of matter placed between bulk and molecular material. Independently of the particle size, two parameters play dominant role. The charges carried by the particle in contact with the cell membranes and the chemical reactivity of the particle.

Nanoparticles – known and unknown health risks, Journal Nanobiotechnology.com; Oxford Journals, 2004




One-dimensional nanoscale materials - SiC

Silicon carbide (SiC) is a material of great technological interest for devices designed to operate at high temperatures, high power, high frequency, and in harsh environments. SiC with the fibrous structure is a potential candidate as a reinforcement material for ceramic as a result of its weavability, high tensile strength and high Young's modulus. SiC has displayed the unique optical property that the photoluminescence emission is in the blue range at room temperature when the scale decreases to nanometre

p-SiC nanorods have been synthesized by the reaction of SiO and carbon
nano-capsules. It was found that the synthesis conditions, i.e. the composition ratio of SiO to carbon nano-capsules in weight and the reaction temperature, are very important for the synthesis of SiC nanorods.

The most interesting phenomenon is that a SiC nanorod with one kind of axis direction can grow on other SiC nanorod with the another kind of axis direction!

Oxford Journals: The microstructural analysis of SiC nanorods by high-resolution electron microscopy


Non-metalic Materials: ceramic nanocomposites

....Recent work in Oxford has shown that very small volume fractions (e.g. 1-2%) of nanophase additions can have dramatic effects on the properties of structural ceramics, and research elsewhere gives reason to believe that this might also be the case with functional ceramics. Furthermore, some of these effects might be synergistic in that they could improve both the mechanical and the functional properties of the material.
Oxford Materials
http://www.materials.ox.ac.uk/uploads/file/research/RIP2005.pdf



Bionanotechnology and carbon nanotubes: protein-functionalisation and biosensing


Small molecules, such as O2, NO2, and NH3, as well as larger protein molecules and DNA can adsorb onto carbon nanotubes (CNTs). The presence of such molecules can change the electrical properties of CNTs. In this project we are investigating the sensing behaviour in nitrogen-doped CNTs (which have been predicted to be metallic) when they are functionalized with metalloproteins. We have shown that proteins
including, cytochrome c, ferredoxin, ferritin and azurin can be adsorbed onto nitrogen-doped nanotubes and imaged using Atomic Force Microscopy (AFM). These functionalised CNTs are integrated into circuits and I-V curves are being
measured.


Dr. S. Contera*, H. Hamnett*, N. Toledo*, K. Voïtchovsky *, Dr. M. de Planque*, Dr. N. Grobert, Professor J. F. Ryan*(*Bionanotechnology IRC, Physics Department, University of Oxford), Oxford Materials


One-dimensional crystal growth inside single-wall carbon nanotubes

Crystals of various salts and metals grown within single-wall carbon nanotubes are effectively 1-D wires, with a range of interesting physical properties which arise from their unique configurations, We are exploring ways of growing these structures, which are characterised by HREM, EDX and EELS. Their physical properties are also under investigation.

OXFORD MATERIALS; Professor A.I. Kirkland, Dr. J. Sloan, Dr. J.L. Hutchison, Professor M.L.H. Green*; (*Inorganic Chemistry Laboratory) (Funded by EPSRC, Leverhulme Trust and The Royal Society).


Cell Division: Mitosis

....One of the most important concepts in biology is that the properties of individual cells are determined by the chromosomes that they inherit. A key observation leading to this notion was that cell division is preceded by the meristemic division of its nucleus, namely the condensation of its chromosomes from interphase chromatin, the splitting of chromosomes into a pair of closely apposed sister chromatids, and their subsequent disjunction to opposite poles of the cell prior to its division, a process known as mitosis. We now know that the hereditary material of chromosomes is DNA and that each chromosome contains a single immensely long molecule that is usually replicated many hours before cells actually enter mitosis. What has remained mysterious until recently is what holds sister DNAs together. It has long been suspected but never proven that this “sister chromatid cohesion” has a crucial role in ensuring that microtubules pull sister DNAs in opposite directions. Equally mysterious has been the trigger for what is arguably the most dramatic and one of the most highly regulated events in the life of a eukaryotic cell, the sudden disjunction of sister chromatids at the metaphase to anaphase transition.

Prof Kim Nasmyth, The mechanism by which chromosomal DNA molecules are held together: entrapment within cohesin rings?
http://www.bioch.ox.ac.uk/aspsite/research/brochure/Nasmyth/









The NC-AFM is a unique atomic tool and has the following characteristics: (i) true atomic resolution; (ii) ability to map atomic force three-dimensionally (so-called atomic force spectroscopy); (iii) ability to observe even insulators; and (iv)
ability to measure mechanical responses, such as elastic deformation. In addition, high-performance NC-AFMs, such as our home-built version, have a vertical resolution of ~0.001 nm (= 1 pm) and a lateral resolution of ~0.01 nm (= 10 pm).
As a result, NC-AFM can be used to observe weakly bounded molecules using an attractive force weak enough so that the attractive force between the tip and the individual molecule does not exceed the threshold needed to move a weakly adsorbed molecule. Further, it can be used to observe a very small lateral shift of an individual Si dimer, i.e. a small strain, adjacent to a missing Si dimer defect, due to stress around the missing Si dimer defect.

Atom-selective imaging and mechanical atom manipulation using the non-contact atomic force microscope; Journal of Electron Microscopy, 2004






The AFM-tip induced oxidation process is based on negatively biasing the tip with respect to the substrate under ambient conditions, which can be either a semiconductor or a metal. The substrate locally oxidizes upon moving the tip in contact mode across the surface. The oxidant for the chemical reaction is provided by OH- ions in the water droplet that is formed between the tip and the sample. Thus, the lateral resolution of the AFM oxidation process depends strongly on the humidity in the air.
sorce: http://www.research.ibm.com/nanoscience/afm_oxidation.html




AFM: From Cellular imaging to molecular manipulation
...Using a sharp tip attached at the end of a soft cantilever as a probe, the atomic force microscope (AFM) explores the surface topography of biological samples bathed in physiological solutions. In the last few years, the AFM has gained popularity among biologists. This has been obtained through the improvement of the equipment and imaging techniques as well as through the development of new non-imaging applications. Biological imaging has to face a main difficulty that is the softness and the dynamics of most biological materials. Progress in understanding the AFM tip-biological samples interactions provided spectacular results in different biological fields. (Pubmed 2003 Jan;19(1):92-9)

Carbon nanotubes additional power for AFM technique
......Among many scanning probe microscopies, atomic force microscopy (AFM) is a useful technique to analyse the structure of biological materials because of its applicability to non-conductors in physiological conditions with high resolution. However, the resolution has been limited to an inherent property of the technique; tip effect associated with a large radius of the scanning probe. To overcome this problem, we developed a carbon nanotube probe by attaching a carbon nanotube to a conventional scanning probe under a well-controlled process. Because of the constant and small radius of the tip (2.5–10 nm) and the high aspect ratio (1 : 100) of the carbon nanotube, the lateral resolution has been much improved judging from the apparent widths of DNA and nucleosomes. The carbon nanotube probes also possessed a higher durability than the conventional probes. We further evaluated the quality of carbon nanotube probes by three parameters to find out the best condition for AFM imaging: the angle to the tip axis; the length; and the tight fixation to the conventional tip. These carbon nanotube probes, with high vertical resolution, enabled us to clearly visualize the subunit organization of multi-subunit proteins and to propose structural models for proliferating cell nuclear antigen and replication factor C.

....the carbon nanotube probes high durability are proved advantagous, after scanning for 3 h with the scan rate of 3 Hz, the carbon nanotube still stayed in good condition. In contrast, conventional probes received serious damage after scanning under the same conditions. This high durability of the carbon nanotube probe probably results from high flexibility of the carbon nanotube and its tight fixation by amorphous carbon deposition.

This success in the application of carbon nanotube probes provides the current AFM technology with an additional power for the analyses of the detailed structure of biological materials and the relationship between the structure and function of proteins.


Oxfordjournals.org: Atomic force microscopy with carbon nanotube probe resolves the subunit organization of protein complexes


Carbon nanotubes have attracted much attention for medical applications, especially their use as nanocontainers for targeted drug and gene delivery. Medical applications include the use of carbon nanotubes for targeted drug and gene delivery, for which issues relating to the acceptance and containment of drugs or genes are not properly understood.The Quarterly Journal of Mechanics and Applied Mathematics 2007 60(2):231-253; doi:10.1093/qjmam/hbm005


Materials scientists performed chemical reactions inside tiny tubes of carbon atoms
known as nanotubes. Essentially, these are sheets of graphite an atom thick that are folded back on themselves to form cylinders. They were used to force molecules into long straight chains. The work has made it into the Guinness Book of World Records. The nano-sized test tubes are so tiny that around 300 billion would fit on to a full stop.

David Britz, Oxford University Dept of Materials, BBC News


While benefits of nanotechnology are widely publicised, the discussion of the potential effects of their widespread use in the consumer and industrial products are just beginning to emerge [7,8]. Both pioneers of nanotechnology [9] and its opponents [10] are finding it extremelyhard to argue their case as there is limited information available to support one side or the other. It has been shown that nanomaterials can enter the human body through several ports. Accidental or involuntary contact during production or use is most likely to happen via the lungs from where a rapid translocation through the blood stream is possible to other vital organs [11]. On the cellular level an ability to act as a gene vector has been demonstrated for nanoparticles [12]. Carbon black nanoparticles have been implicated in interfering with cell signalling [13]. There is work that demonstrates uses of DNA for the size separation of carbon nanotubes [14]. The DNA strand just wraps around it if the tube diameter is right. While excellent for the separation purposes it raises some concerns over the consequences of carbon nanotubes entering the human body.

Nanoparticles – known and unknown health risk! Nanobitechnology Journal,
Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK


Making measurements as close to the biological action point
......How best to approach nanomaterial characterization include using proper sampling and measurement techniques, forming multidisciplinary teams, and making measurements as close to the biological action point as possible…… Determination of the primary size distribution of a sample requires a well-dispersed system and measurement of enough particles to achieve statistical reliability. For a monodisperse system, the latter requirement is relatively easy to meet. However, as polydispersity increases, it becomes necessary to measure a progressively larger number of particles to accurately portray the size distribution. For nanoscale particles in an aqueous environment, an ensemble method of measurement such as centrifugal sedimentation or laser or dynamic light scattering is normally preferred, but this may not be practical or the system may be difficult to maintain in a dispersed state. For dry as-received powders, dynamic mobility analysis can be used for dispersed material or BET surface area can provide an estimated average size based on a nonporous spherical model. The latter method has the added advantage of providing a direct measurement of specific surface area (SSA) and micro- or meso-porosity, both of which are key properties of interest.

Microscopy is one of the most powerful techniques and is often relied upon exclusively to provide valuable information regarding size, shape, and morphology. For nanoparticles, electron microscopy is normally required to capture images with the necessary resolution and is currently the only technique that provides reliable information regarding shape at this scale. However, the microscopist should ensure that enough particles are examined to provide a statistically valid representation of the full size or shape distribution. This can be very difficult and time consuming, and may require the image analysis of literally thousands of individual particles. There are many commercial automated image analysis systems and computer software packages that are used for this purpose.

Powers et al, Research Strategies for Safety Evaluation of Nanomaterials, 2006
http://toxsci.oxfordjournals.org/cgi/reprint/kfj099v1




...............Boundaries of condensed homogeneous phases (liquids and some solids) in the nano-scale present, continua, but only with two dimensions; in the third dimension their characteristics change. Such boundaries may be defined as bonded surface continua. Besides a surface tension force, all characteristics of nanolayers at boundaries of condensed phases are different from their bulk properties (e.g., density, viscosity, heat, and mass transfer rates) in the surface toward bulk direction.


Scales, Macro, Micro, Nano, Atto; http://www.chemlibnetbase.com/books/4877/DK3254ch1.pdf




THE EFFECT DOSE

Because of their small size and large specific surface area (SA), insoluble nanoparticles are almost not affected by the gravitational force and are generally formulated in stable suspensions or sols. This raises, however, a potential difficulty in in vitro assay systems in which cells adhering to the bottom of a culture vessel may not be exposed to the majority of nanoparticles in suspension.
..............We found, in all cell lines and for all end points, that the cellular response was determined by the total mass/number/Surface Area of particles as well as their concentration. Practically, for a given volume of dispersion, both parameters are of course intimately interdependent. We conclude that the nominal dose remains the most appropriate metric for in vitro toxicity testing of insoluble SNP dispersed in aqueous medium. This observation has important bearings on the experimental design and the interpretation of in vitro toxicological studies with nanoparticles.

Nominal and Effective Dosimetry of Silica Nanoparticles in Cytotoxicity Assays; Oxford Journals; Toxicological Sciences 2008 104(1):155-162; doi:10.1093/toxsci/kfn072







Particles in general and nanoparticles specifically, diffuse, settle, and agglomerate in cell culture media as a function of systemic and particle properties: media density and viscosity and particle size, shape, charge and density, for example. Cellular dose then is also a function of these factors as they determine the rate of transport of nanoparticles to cells in culture.............We conclude that simple surrogates of dose can cause significant misinterpretation of response and uptake data for nanoparticles in vitro. Incorporating particokinetics and principles of dosimetry would significantly improve the basis for nanoparticle toxicity assessment, increasing the predictive power and scalability of such assays.

Teegardin J., Particokinetics In Vitro: Dosimetry Considerations for In Vitro Nanoparticle Toxicity Assessments; Toxicological Sciences 2007 95(2):300-312; doi:10.1093/toxsci/kfl165


Nanotechnology has enabled the development of nanoscale devices that can be conjugated with several functional molecules simultaneously, including tumor-specific ligands, antibodies, anticancer drugs, and imaging probes. Since these
nanodevices are 100 to 1,000-fold smaller than cancer cells, they can be easily transferred through leaky blood vessels and interact with targeted tumor-specific proteins both on the surface of and inside cancer cells. Therefore, their application as cancer cell-specific delivery vehicles will be a significant addition to the currently available armory for cancer therapeutics and imaging. (CA Cancer J Clin 2008;58:97–110.); American Cancer Society, Inc., 2008.


Selenium (Se) is an essential trace element with a narrow margin between beneficial and toxic effects. As a promising chemopreventive agent, its use requires consumption over the long term, so the toxicity of Se is always a crucial concern. Based on clinical findings and recent studies in selenoprotein gene-modified mice, it is likely that the antioxidant function of one or more selenoproteins is responsible for the chemopreventive effect of Se. Furthermore, upregulation of phase 2 enzymes by Se has been implicated as a possible chemopreventive mechanism at supranutritional dietary levels. Se-methylselenocysteine (SeMSC), a naturally occurring organic Se product, is considered as one of the most effective chemopreventive selenocompounds. The present study revealed that, as compared with SeMSC, elemental Se at nano size (Nano-Se) possessed equal efficacy in increasing the activities of glutathione peroxidase, thioredoxin reductase, and glutathione S-transferase, but had much lower toxicity as indicated by median lethal dose, acute liver injury, survival rate, and short-term toxicity. Our results suggest that Nano-Se can serve as a potential chemopreventive agent with reduced risk of Se toxicity.

Elemental Selenium at Nano Size (Nano-Se) as a Potential Chemopreventive Agent with Reduced Risk of Selenium Toxicity; Oxford Journals; 2007



Relation between peak structures of loss functions of single double-walled carbon nanotubes and interband transition energies

Electron energy-loss spectra of single double-walled carbon nanotubes (DWCNTs) were compared with calculated joint density of states (jDOSs) obtained by a simple tight-binding (STB) and an extended tight-binding (ETB) method. From the comparisons, interband transition energies of ETB calculations show better agreement with peak positions of the experimental spectra than those of STB results. From a further comparison among calculated jDOS, real and imaginary parts of a dielectric function and a loss function Im[–1/{varepsilon}], it was confirmed that the peak energies in a spectrum of single DWCNTs are almost equal to those of the optical absorption spectrum {varepsilon}.

Physical properties of carbon nanotubes (CNTs) depend on diameters and chiralities of the CNTs.

Electron energy-loss spectroscopy (EELS) studies on multi-walled WS2 tubes [4] and few-walled CNTs [5] have been reported. It was shown that peak positions of the spectra for the thinner nanotubes were similar to those of optical absorption spectra.

Journal of Electron Microscopy 2008 57(4):129-132; doi:10.1093/jmicro/dfn012