Northwestern University, USA
Title: Atomic monolayer materials and their applications
Serhii Shafraniuk has completed his PhD from Kiev State University and Postdoctoral studies from Academy of Sciences of Ukraine. He is the Research Associate Professor at Physics and Astronomy Department, Northwestern University, a premier educational and research institution. He has published more than 100 papers in reputed journals and is serving as an organizer of various international conferences.
Many areas of human activity critically depend nowadays on discovery and study of novel materials. The nanotechnology research is directed toward a variety of applications which include industry, medicine, security, defense, and space research. The new materials make structural revolutionary changes in technology of various nanodevices like nanosensors, digital logic elements, quantum dots, THz signal processors and sensors, quantum bits and circuits, etc. At Northwestern we conduct experimental and theoretical study of atomic monolayer materials. Our work is focused on the following topics. (a) Quantum dots as elements of the THz and magnetic field nanosensors. (b) Andreev reflection as a probe of interface properties. (c) Efficient thermoelectric nanocoolers and energy generators based on atomic monolayer (AM) materials and nanotubes. The AM materials are represented by graphene, transition metal dichalcogenides, molybdenum disulfide, titanium disulfide, transition metal oxides, graphitic carbon nitride (g-C3N4), and the topological insulator (Bi2Te3). Our current efforts are focused on the former three materials. Using the unique intrinsic properties of novel AM materials allows creating of devices which were not available in the past. In particular, resonant character the chiral tunneling and low inelastic scattering rates in graphene both are serving as reasons why the electric current density can be much higher than in ordinary semiconducting devices. Another example is Klein tunneling paradox which makes graphene and nanotubes as being intrinsically \\\\\\\"clean\\\\\\\" and perspective for electronic applications. Our experimental devices are based on multi-terminal AM field effect transistors (A-FET). An important stage of the A-FET fabrication process assumes obtaining the good quality AM sheets and nanotubes. The obtained quantum dot devices had been used for experimental testing in respect of their performance and suitability for the aforementioned purposes. The A-FET is controlled with source-drain and gate voltages applied via the metallic electrodes deposited on AM. The voltages affect the low energy electronic spectrum and hence they modify the transport properties of AM material. When exposing the A-FET device to an external THz field we have found that the resonant a.c. transport strongly depends on the polarity and magnitude of the source-drain and gate voltages. Besides, the THz field induces transitions between the quantized levels which are pronounced in the experimental current voltage characteristics. By measuring the d.c. current-voltage curves of A-FET quantum dots which are exposed to an external THz field we are able to determine the THz field parameters. In this way we are utilizing the A-FET which actually works as a very sensitive and efficient THz field sensor. Besides we study the thermoelectric cooling and energy co-generating phenomena in AM. We conclude that the AM based setups can perform much better than other known devices.
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