Quantum electron transport in nanostructures for practical applications

Code: 5373
Title: Quantum electron transport in nanostructures for practical applications
Programme: Science and Technology Center in Ukraine & Academy of Sciences of Moldova
Execution period: 2012-2013
Institutions: Ghitu Institute of Electronic Engineering and Nanotechnologies, ASM
Institute of Applied Physics, ASM
Technical University of Moldova
Project Leader: Konopko Leonid, dr., associated professor (docent)
Participants: Laboratory of Electronics of Low Dimensional StructuresLaboratory of Electrochemical Treatment of Materials



The goal of the project is to solve two key problems in modern physics of low-dimensional materials: (1) single-electron transport in semimetal, semiconductor and superconductor nanostructures and (2) the enhancement of thermoelectric efficiency of materials due to the quantum size effect in nanowires and existing high density of surface states. Semimetal Bi exhibit Rashba spin-orbit surface bands for which topological insulator behavior consisting of ultrahigh nobilities and enhanced thermopower has been predicted. In nanoelectronics, the solution of these problems will contribute to the development of single-electron transistor (SET) based on semimetal, semiconductor and superconductor nanoconstrictions and to design of the new miniature thermoelectric coolers on the basis of the nanowires that can be used for instant freezing of cells (e.g. cancer cells) in biomedical research.

The SET is type of switching device that uses controlled electron tunneling to amplify current. A SET is made from two tunnel junctions that share a common electrode. The only way for electrons in one of the metal electrodes to travel to the other electrode is to tunnel through the insulator.

We have developed a method to produce single crystalline nanowires of Bi and its alloys using high frequency liquid phase casting in a glass capillary. The diameters of the nanowires can be as small as 50 nm. By a laser heating technique it has proven to be possible to produce constrictions one order of magnitude smaller. Nanoconstrictions of this type are well protected by a glass cover of the external environment and open a unique opportunity to investigate the quantum transport properties.

Our preliminary measurements of the d2V/dI2(V) dependencies of bismuth microbridges with diameter d < 100 nm and length ~ 500 nm have shown peculiarities typical for the bismuth microcontact spectrum of electron-phonon interaction. The Berry phase shift, obtained on B-periodic Aharonov-Bohm oscillations of magnetoresistance of fine (d ~ 60 nm) Bi nanowires confirmed that there is spin dependent transport in Bi nanowires wich have surface states wih"topological insulators behavior". Therefore, the foremost task of the project is to develop the technology for preparation of advanced nanowires and tunneling junctions based on semimetal and superconductor nanowires with d<50 nm, and to study quantum transport and thermoelectric properties in a wide range of temperatures and magnetic fields.

The following methods for preparation of nanowires and nanostructures will be used: 1. liquid phase casting and double extension of glass-coated nanowires, 2. high pressure injection of the melt and 3. local laser heating technique for producing of different types of microbridges and nanoconstrictions from glass-coated nanowires. The project involves development of technology for the production of bifilar wires of n- and p- types for highly sensitive thermocouples and highly efficiently micro coolers for biomedical devices.

Our proposed project will have a significant effect on the development of infrastructure of science and engineering of Moldova. The proposed project involves a number of undergraduates from the Moldova Technical University. Moldova has a lot of companies working with microwires (such as MicroFIR Technologies), and this project meets their activities.