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)


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