A single ZnO nanowire with intrinsic oxygen vacancies is utilized to fabricate four-contact device with focus ion beam lithography technique.Cathodoluminescent spectra indicate strong near-UV and green emission at both room temperature and low temperatures.Experimental measurement shows the temperature-dependent conductivity of the ZnO nanowire at low temperatures (below 100 K).The further theoretical analysis confirms that weak localization plays an important role in the electrical transport,which is attributed to the surface states induced by plenty of oxygen vacancies in ZnO nanowire.
A method of measuring the thermoelectric power of nano-heterostructures based on four-probe scanning tunneling microscopy is presented. The process is composed of the in-situ fabrication of a tungsten-indium tip, the precise control of the tip-sample contact and the identification of thermoelectric potential. When the temperature of the substrate is elevated, while that of the tip is kept at room temperature, a thermoelectric potential occurs and can be detected by a current-voltage measurement. As an example of its application, the method is demonstrated to be effective to measure the thermoelectric power in several systems. A Seebeck coefficient of tens of μV/K is obtained in graphene epitaxially grown on Ru (0001) substrate and the thermoelectric potential polarity of this system is found to be the reverse of that of bare Ru (0001) substrate.
