Quantum interference effects and thermoelectricity in semimetal nanowires

Code: 5050
Title: Quantum interference effects and thermoelectricity in semimetal nanowires
Programme: Science and Technology Center in Ukraine & Academy of Sciences of Moldova
Execution period: 2011-2014
Institutions: Ghitu Institute of Electronic Engineering and Nanotechnologies, ASM
Institute of Applied Physics, ASM
Technical University of Moldova
Project Leader: Nikolaeva Albina, dr. hab., associated professor (docent)
Participants: Laboratory of Electronics of Low Dimensional StructuresLaboratory of Electrochemical Treatment of Materials



The project is focused on the solution of two key problems in contemporary physics of low-dimensional systems: (i) the electron spin influence on transport properties in semimetal and semiconductor nanostructures and (ii) the enhancement of thermoelectric efficiency of materials due to the quantum size effect in nanostructures based on semimetals. In nanoelectronics, the solution of these problems will contribute to the development of spintronic devices based on semiconductor and to the design of new miniature thermoelectric energy converters on the basis of nanostructures that exhibit the thermoelectric efficiency being considerably superior to that in bulk samples.

Bi has an unusually great de Broglie wavelength 60 nm; therefore, quantum size effects can be shown at considerably greater diameters than in a metal, and therefore the manifestation of quantum size effects will be possible at higher temperatures, which is significant for their practical application.

Our preliminary measurements of magnetoconductance of fine (d ~ 60 nm) Bi nanowires show evidence for a spin Berry cyclic phase that shifts the periods of the B-periodic Aharonov-Bohm oscillations confirming that there is spin transport in Bi nanowires. Therefore, the foremost task of the project is to develop the technology for preparation of advanced nanowires based on Bi and its alloys with d<70 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 will be used: 1. liquid phase casting and double extension of glass-coated nanowires, 2. high pressure injection (HPI) of the melt and 3. electrochemical deposition of material into various porous of dielectric matrices.

The technologies for recrystallization of nanowires in strong magnetic fields and laser recrystallization will be developed with a goal to obtain single-crystal semimetal wires with C3 orientation along the nanowire axis that exhibit maximum thermoelectric efficiency and the best condition of the energy spectrum quantization. We propose an experimental program to investigate the spin-dependent transport and thermoelectric properties of Bi nanowires in magnetic fields.

The method of anisotropic elastic deformation of nanowires will be used for the implementation of various types of electron topological transitions, including the transition into the "gapless state" in Bi1-хSbхwires, which leads to a sharp increase in mobilities, "giant" magnetoresistance, and an increase in thermopower.

The project involves development of technology for the production of bifilar wires of n- and p- types and generation of highly sensitive thermocouples for medical devices, as well as the preparation of a model variant of the anisotropic thermoelectric generator based on wires of semimetals in glass isolation. Micro-thermogenerator making from only one long monocrystalline bismuth wire (without many convenient connections) in glass coating will be suitable for energy supply of small low current devices.