Time filter

Source Type

Harea E.E.,Institute of Applied Physics | Aifantis K.E.,Aristotle University of Thessaloniki | Pyrtsac K.M.,Institute of Applied Physics | Ghimpu L.,Ghitu Institute of Electronic Engineering and Nanotechnologies
NATO Science for Peace and Security Series A: Chemistry and Biology | Year: 2015

The piezoresistivity of indium-tin-oxide (ITO) thin films was investigated using the three point bending method combined with cyclic indentation. The 500 nm thick ITO films were deposited on glass slides using magnetron sputtering. The resistance variation of the resulting ITO/glass based sensors during cyclic indentation showed a good sensitivity and fast response to mechanical strain, with the gauge factor ranging from -1.4 to -3.7. © Springer Science+Business Media Dordrecht 2015.


Nikolaeva A.,Ghitu Institute of Electronic Engineering and Nanotechnologies | Nikolaeva A.,International Laboratory of High Magnetic Fields and Low Temperatures | Konopko L.,Ghitu Institute of Electronic Engineering and Nanotechnologies | Konopko L.,International Laboratory of High Magnetic Fields and Low Temperatures | And 3 more authors.
Surface Engineering and Applied Electrochemistry | Year: 2014

We report on the magneto-thermopower of single-crystal Bi nanowires with diameters 75 and 250 nm in a longitudinal and transverse magnetic fields of 0-14 T. The temperature range is 1.5-300 K. Bi nanowires in a glass capillary have been prepared by the high frequency liquid phase casting. The temperature dependence R(T) shows the transition from metallic to semiconducting behavior due to quantum size effect, where the Bi-wire diameter is reduced to less than 80 nm. It is for the first time that the effect of the negative magneto-resistance in a transverse magnetic field, due to the quantum size effect on 75 nm Bi wires, has been observed. The thermopower is very sensitive to the wire diameter, up to a change in the sign from negative to positive at low temperatures, and to a significant extent in a weak longitudinal magnetic field. The field dependences of longitudinal and transverse magneto-resistance have features characteristic of the occurrence of the quantum size effect and galvanomagnetic size effect, and provide information on the parameters of the energy spectrum and charge carrier mobility. The enhancement of the thermoelectric figure of merit for Bi nanowires is discussed. We also discuss the power factor α2σ and its dependence on the diameter, magnetic field and temperature. © 2014 Allerton Press, Inc.


Konopko L.A.,Ghitu Institute of Electronic Engineering and Nanotechnologies | Konopko L.A.,International Laboratory of High Magnetic Fields and Low Temperatures | Nikolaeva A.A.,Ghitu Institute of Electronic Engineering and Nanotechnologies | Nikolaeva A.A.,International Laboratory of High Magnetic Fields and Low Temperatures | And 2 more authors.
Materials Research Society Symposium Proceedings | Year: 2015

We have investigated the transport properties of topological insulator based on singlecrystal 0.83Sb0.17 nanowires. The single-crystal nanowire samples in the diameter range 200 nm - 1.1 nm were prepared by the high frequency liquid phase casting in a glass capillary using an improved Ulitovsky technique; they were cylindrical single-crystals with (1011) orientation along the wire axis. In this orientation, the wire axis makes an angle of 19.5° with the bisector axis C1 in the bisector-trigonal plane. 0.83Sb0.17 is a narrow gap semiconductor with energy gap at L point of Brillouin zone ΔE= 21 meV. In accordance with the measurements of the temperature dependence of the resistivity of the samples resistance increases with decreasing temperature, but at low temperatures decrease in the resistance is observed. This effect, decrease in the resistance, is a clear manifestation of the interesting properties of topological insulators - the presence on its surface of a highly conducting zone. The Arrhenius plot of resistance R in samples with diameter d=1.1 μm and d 200 nm indicates a thermal activation behavior with an activation gap ΔE= 21 and 35 meV, respectively, which proves the presence of the quantum size effect in these samples. We found that in the range of diameter 1100 nm - 200 nm when the diameter decreases the energy gap is growing as 1 Id. We have investigated magnetoresistance of 0.83Sb0.17 nanowires at various magnetic field orientations. From the temperature dependences of Shubnikov de Haas oscillation amplitude for different orientation of magnetic field we have calculated the cyclotron mass mc and Dingle temperature TD for longitudinal and transverse (B||C3 and B||C2) directions of magnetic fields, which equal 1.96∗10-2 m0, 9.8 K, 8.5∗10-3 m0 9.4 K and 1.5∗ 10-1 m0, 2.8 K respectively. The observed effects are discussed. © 2015 Materials Research Society.


Konopko L.A.,Ghitu Institute of Electronic Engineering and Nanotechnologies | Konopko L.A.,International Laboratory of High Magnetic Fields and Low Temperatures | Nikolaeva A.A.,Ghitu Institute of Electronic Engineering and Nanotechnologies | Nikolaeva A.A.,International Laboratory of High Magnetic Fields and Low Temperatures | And 2 more authors.
Journal of Low Temperature Physics | Year: 2016

We investigate the transport properties of topological insulator (TI) (Formula presented.) nanowires. Single-crystal nanowire samples with diameters ranging from 75 nm to 1.1 (Formula presented.)m are prepared using high frequency liquid phase casting in a glass capillary; cylindrical single crystals with (10(Formula presented.)1) orientation along the wire axis are produced. (Formula presented.) is a narrow-gap semiconductor with an energy gap at the L point of the Brillouin zone, (Formula presented.) meV. The resistance of the samples increases with decreasing temperature, but a decrease in resistance is observed at low temperatures. This effect is a clear manifestation of TI properties (i.e., the presence of a highly conducting zone on the TI surface). When the diameter of the nanowire decreases, the energy gap (Formula presented.) grows as 1 / d (for diameter (Formula presented.)m and (Formula presented.) nm (Formula presented.) and 45 meV, respectively), which proves the presence of the quantum size effect in these samples. We investigate the magnetoresistance of (Formula presented.) nanowires at various magnetic field orientations. Shubnikov-de Haas oscillations are observed in (Formula presented.) nanowires at (Formula presented.) K, demonstrating the existence of high mobility ((Formula presented.)(Formula presented.)) two-dimensional (2D) carriers in the surface areas of the nanowires, which are nearly perpendicular to the (Formula presented.) axis. From the linear dependence of the nanowire conductance on nanowire diameter at (Formula presented.) K, the square resistance (Formula presented.) of the surface states of the nanowires is obtained ((Formula presented.) Ohm). © 2016 Springer Science+Business Media New York


Huber T.E.,Howard University | Johnson S.,Howard University | Shirvani K.A.,Howard University | Barclif Q.,Howard University | And 4 more authors.
IFMBE Proceedings | Year: 2016

Bismuth telluride wires are interesting building blocks of thermoelectric devices. These are nanoscale heat to electric converters that have applications as uncooled detectors, generators and uncooled bolometers. Also, there is interest in bismuth telluride because it is an example of a topological insulator. The exploitation of the thermoelectric properties of devices based on wires of thermoelectric materials requires good electrical contacts between the wires and metal electrodes. The fabrication of the devices here, is based on contacting the wire ends to the device electrodes by depositing a platinum film using the focused ion beam method. © Springer Science+Business Media Singapore 2016.


Konopko L.A.,Ghitu Institute of Electronic Engineering and Nanotechnologies | Konopko L.A.,International Laboratory of High Magnetic Fields and Low Temperatures | Huber T.E.,Howard University | Nikolaeva A.A.,Ghitu Institute of Electronic Engineering and Nanotechnologies | And 2 more authors.
Journal of Low Temperature Physics | Year: 2013

We report the results of studies of the magnetoresistance (MR) and electric field effect (EFE) of single-crystal Bi nanowires with diameter d<80 nm at low temperatures. Single-crystal nanowire samples were prepared by the Taylor-Ulitovsky technique; they were cylindrical single crystals with the (10\bar{1}1) orientation along the wire axis where the C 3 axis was inclined at an angle of 70â̂̃ to the wire axis. According to theory of S. Murakami, bismuth bilayers can exhibit the quantum spin Hall effect. A Bi crystal can be viewed as a stacking of bilayers with a honeycomblike lattice structure along the [111] direction. An interpretation of transverse MR oscillations with using this theory is presented. © 2013 Springer Science+Business Media New York.


Nikolaeva A.A.,Ghitu Institute of Electronic Engineering and Nanotechnologies | Nikolaeva A.A.,International Laboratory of High Magnetic Fields and Low Temperatures | Konopko L.A.,Ghitu Institute of Electronic Engineering and Nanotechnologies | Konopko L.A.,International Laboratory of High Magnetic Fields and Low Temperatures | And 3 more authors.
Journal of Nanoelectronics and Optoelectronics | Year: 2012

The paper report results of magneto-thermoelectric properties the single crystal Bi1-xSbx nanowires in glass cover with different diameters prepared by Ulitovsky-Taylor method. We study the effect of nanowire dimensionality in the Bi1-xSbx nanowires in semimetal and gapless states. In the semimetal region Bi1-xSbx nanowires (x = 0.02) the semimetal-semiconductor transition due to quantum size effect at the critical diameter significantly higher than for pure Bi-wire are observed. This allowed to separate the effects related to the size quantization and surface state. It is shown that a weak magnetic fields leads to an increase of the hole contribution to the thermopower and to increase the Power factor α2σ at positive α in Bi-2 at% Sb nanowires. Bi 1-xSbx wires in gapless region (x = 0.06) shows the increase of the energy gap with decreasing the diameter d and increase of the electron contribution to the thermopower ay in weak transverse magnetic field at the negative α. This will use the investigated wires as n- and p-branches in thermoelectric energy converters. Power factor depending on diameter Bi 1-xSbx nanowires, composition, temperature, magnetic field is calculated. Copyright © 2012 American Scientific Publishers All rights reserved.


Nikolaeva A.,Ghitu Institute of Electronic Engineering and Nanotechnologies | Nikolaeva A.,International Laboratory of High Magnetic Fields and Low Temperatures | Konopko L.,Ghitu Institute of Electronic Engineering and Nanotechnologies | Konopko L.,International Laboratory of High Magnetic Fields and Low Temperatures | And 4 more authors.
Physica Status Solidi (A) Applications and Materials Science | Year: 2014

We report on the electrical transport and thermoelectric properties of Bi1-xSbx nanowires in the semiconductor region made of Bi1-xSbx. Such alloys are classified as topological insulators. The individual Bi-17 at%Sb wires in a glass capillary with diameters ranging from 100 to 1000 nm were prepared by high-frequency liquid-phase casting in an argon atmosphere. They were cylindrical single crystals with (1011) orientation along the wire axis. For large-diameter wires we observed that the temperature-dependent resistance, R(T), displays the temperature-activated dependence that is expected of semiconductors. We also found that small-diameter wires at low temperatures show a sharp deviation from the behavior of the resistance R(T), characteristic of semiconductors. The contrasting behavior of wires of different diameters can be interpreted in terms of the conductance of the surface states in BiSb where the surface states arise through a spin-orbital Rashba interaction in the surface of BiSb. The thermopower remains negative over the entire temperature range, but it is strongly temperature dependent. The longitudinal magnetoresistance R(H) at low temperature shows quantum Shubnikov-de Haas oscillations only in thin (d < 200 nm) Bi-17 at%Sb nanowires. Only high-mobility carriers display SdH oscillations. Since we expect the electronic transport in the 200-nm semiconducting Bi1-xSbx nanowires to be dominated by the surface, this indicates that the surface states have sufficiently high mobility to display SdH. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Nikolaeva A.A.,Ghitu Institute of Electronic Engineering and Nanotechnologies | Nikolaeva A.A.,STR | Konopko L.A.,Ghitu Institute of Electronic Engineering and Nanotechnologies | Konopko L.A.,STR | And 5 more authors.
Surface Engineering and Applied Electrochemistry | Year: 2014

In this paper we present the experimental results of an investigation of the electrical transport, thermoelectrical properties, the Shubnikov de Haas oscillations of Bi1 − xSbx films (0 < x < 0.04) grown by the vacuum thermal evaporation and nanowires prepared by a modified Ulitovsky-Teilor technique. The results of the X-ray diffraction indicate that the trigonal axes were perpendicular to the film plane and the single Bi-2 at % Sb nanowires with the diameter 100–1000 nm were represented by single crystals in a glass capillary with (1011) orientation along the wire axis. The investigations of the Shubnikov de Haas oscillations on Bi-2 at % Sb wires with d > 600 nm show that overlapping of L and T bands was twice smaller than that in pure Bi. The temperature dependences of thin semimetalic Bi-3 at % Sb films and Bi-2 at % Sb wires show a semiconducting behavior. The semimetal-semiconductor transition induced by the quantum confinement effect is observed in semimetal Bi1 − xSbx films and nanowires at the diameters up to five times greater than those in the pure Bi. That experimental fact, on the one hand, will allow observing the display quantum confinement effect at higher temperatures on nanowires of the same diameters, and, on the other hand, will allows separating effects connected with the surface state and the quantum size effects. In addition, the thermoelectric properties and thermoelectric efficiency of bismuth-antimony wires are considered and a possibility to use them in thermoelectric converters of energy is discussed. © 2014, Allerton Press, Inc.

Loading Ghitu Institute of Electronic Engineering and Nanotechnologies collaborators
Loading Ghitu Institute of Electronic Engineering and Nanotechnologies collaborators