Resistive properties of Janson’s point contacts in the conditions of polarization inversion

The sensitive element of a new quantum sensor generation is the Janson dendritic point contact. Analytes that are in the space surrounding the sensitive element are able to interact with the freshly formed surface of the conduction channel of the Janson quantum point contact, as well as with the surface of the dendrite during its growth. This interaction provides the influence of the substances under study on the configuration of the output characteristic of the sensor, represented by the system conductivity histogram. The conductivity histogram is built on the basis of the chrono-resistogram of the self-oscillating point-contact cyclic switchover effect, which is directly recorded under self-oscillation conditions. In the structure of the sensor element, Janson's dendritic point contact is immersed in an electrolyte and in an electric field forms a chrono-resistogram, which depends on the environment composition. The paper considers one of the aspects of such chrono-resistograms formation. The features of a gapless electrochemical system in the process of realizing the point-contact cyclic switchover effect are analyzed. Modeling the sensitive element in the form of a gapless electrode system allowed explaining the mechanism and dynamics of the transition “Janson point contact – dendrite and counter electrode in the electrolyte”. The most important parameter of the gapless electrode system is the coordinate of the polarization inversion boundary. It is shown that the idea of the coordinate of the polarization inversion boundary plays a fundamental role in modeling the resistive properties of a point-contact system and its lifetime. The synthesized mathematical models describe well the experimentally obtained dependences of the resistance on the exposure time of the nanostructure in an electric field. It was found that the dependence of the contact resistance on the exposure time, obtained under the assumption of a linear distribution of the anodic polarization along the main axis of the conduction channel, is described by a differential equation in which the growth rate of resistance is directly proportional to the cube of this resistance. The materials obtained make it possible to purposefully optimize the design parameters and operating conditions of sensor devices based on Janson point contacts for the analysis of complex gaseous and liquid mixtures.

Research on the Compound Optimization Method of the Electrical and Thermal Properties of SiC/EP Composite Insulating Material

In this paper, in order to improve the electrical and thermal properties of SiC/EP composites, the methods of compounding different crystalline SiC and micro-nano SiC particles are used to optimize them. Under different compound ratios, the thermal conductivity and breakdown voltage parameters of the composite material were investigated. It was found that for the SiC/EP composite materials of different crystal types of SiC, when the ratio of α and β silicon carbide is 1:1, the electrical performance of the composite material is the best, and the breakdown strength can be increased by more than 10% compared with the composite material filled with single crystal particles. For micro-nano compound SiC/EP composites, different total filling amounts of SiC correspond to different optimal ratios of micro/nano particles. At the optimal ratio, the introduction of nanoparticles can increase the breakdown strength of the composite material by more than 10%. Compared with the compound of different crystalline SiC, the advantage is that the introduction of a small amount of nanoparticles can play a strong role in enhancing the break-down field strength. For the filled composite materials, the thermal conductivity mainly depends on whether an effective heat conduction channel can be constructed. Through experiments and finite element simulation calculations, it is found that the filler shape and particle size have a greater impact on the thermal conductivity of the composite material, when the filler shape is rounder, the composite material can more effectively construct the heat conduction channel.

Large Bandgap Topological Insulator in Oxide APoO3 (A = Be, Mg, Ca, Sr, Ba, and Ra) Perovskite: An Ab Initio Study

Under the density functional theory framework, we have calculated the electronic and elastic properties of APoO3 (A = Be, Mg, Ca, Sr, Ba, and Ra) cubic perovskites. We found that CaPoO3, SrPoO3, BaPoO3, and RaPoO3 are topological insulators (TIs) with very large bandgaps of 0.861, 0.871, 0.820, and 0.810 eV, respectively. The nontrivial band topology together with the Z2 topological number of APoO3 perovskite are investigated. We also theoretically determine the three independent elastic constants C11, C12, and C44 of the APoO3 perovskite. The bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, and anisotropy factor are also calculated from the obtained elastic constants. We found that the Debye temperature for the APoO3 perovskite is around 330-370 K. In the bulk APoO3 perovskite, if the center Po atom is shifted 0.09Å away from the center, the induced electric polarization is quite large, being around 0.02 C/m2. In the surface band calculation, we found that both AO and PoO2 surfaces give rise to contributions to the conduction channel. If the Po atom moves both in-plane and out-of-plane, we show that both electric polarization and topologically protect surface conduction states exist in APoO3 perovskite, indicating that these oxide APoO3 perovskites are ferroelectric TIs and might be useful for spintronic applications.

Formation of quantum dots in GaN/AlGaN FETs

GaN and the heterostructures are attractive in condensed matter science and applications for electronic devices. We measure the electron transport in GaN/AlGaN field-effect transistors (FETs) at cryogenic temperature. We observe formation of quantum dots in the conduction channel near the depletion of the 2-dimensional electron gas (2DEG). Multiple quantum dots are formed in the disordered potential induced by impurities in the FET conduction channel. We also measure the gate insulator dependence of the transport properties. These results can be utilized for the development of quantum dot devices utilizing GaN/AlGaN heterostructures and evaluation of the impurities in GaN/AlGaN FET channels.

Scattering description of Andreev molecules

An Andreev molecule is a system of closely spaced superconducting weak links accommodating overlapping Andreev Bound States. Recent theoretical proposals have considered one-dimensional Andreev molecules with a single conduction channel. Here we apply the scattering formalism and extend the analysis to multiple conduction channels, a situation encountered in epitaxial superconductor/semiconductor weak links. We obtain the multi-channel bound state energy spectrum and quantify the contribution of the microscopic non-local transport processes leading to the formation of Andreev molecules.

A One-Dimensional Effective Model for Nanotransistors in Landauer–Büttiker Formalism

In a series of publications, we developed a compact model for nanotransistors in which quantum transport in a variety of industrial nano-FETs was described quantitatively. The compact nanotransistor model allows for the extraction of important device parameters as the effective height of the source-drain barrier, device heating, and the quality of the coupling between conduction channel and the contacts. Starting from a basic description of quantum transport in a multi-terminal device in Landauer–Büttiker formalism, we give a detailed derivation of all relevant formulas necessary to construct our compact nanotransistor model. Here we make extensive use of the the R-matrix method.

Introducing Electrode Contact by Controlled Micro-Alloying in Few-Layered GaTe Field Effect Transistors

Recently, gallium telluride (GaTe) has triggered much attention for its unique properties and offers excellent opportunities for nanoelectronics. Yet it is a challenge to bridge the semiconducting few-layered GaTe crystals with metallic electrodes for device applications. Here, we report a method on fabricating electrode contacts to few-layered GaTe field effect transistors (FETs) by controlled micro-alloying. The devices show linear I-V curves and on/off ratio of ∼10 4 on HfO 2 substrates. Kelvin probe force microscope (KPFM) and energy dispersion spectrum (EDS) are performed to characterize the electrode contacts, suggesting that the lowered Schottky barrier by the diffusion of Pd element into the GaTe conduction channel may play an important role. Our findings provide a strategy for the engineering of electrode contact for future device applications based on 2DLMs.