Electrical Transport Properties of Single-Layer WS2

We report on the fabrication of field-effect transistors based on single and bilayers of the semiconductor WS2 and the investigation of their electronic transport properties. We find that the doping level strongly depends on the device environment and that long in-situ annealing drastically improves the contact transparency allowing four-terminal measurements to be performed and the pristine properties of the material to be recovered. Our devices show n-type behavior with high room-temperature on/off current ratio of ~106. They show clear metallic behavior at high charge carrier densities and mobilities as high as ~140 cm2/Vs at low temperatures (above 300 cm2/Vs in the case of bi-layers). In the insulating regime, the devices exhibit variable-range hopping, with a localization length of about 2 nm that starts to increase as the Fermi level enters the conduction band. The promising electronic properties of WS2, comparable to those of single-layer MoS2 and WSe2, together with its strong spin-orbit coupling, make it interesting for future applications in electronic, optical and valleytronic devices

Influence of structural and electrostatic disorder on transport properties of monolayers of two-dimensional semiconductors

Two-dimensional (2D) materials are under intensive investigation recently due to variety of electronic properties, ranging from insulators (h-BN) to semi-metals (graphene), semiconductors (MoS2, WSe2) with wide variability of band-gap and correlated phases (NbSe2, TaS2). Recently, focus of research has been moved from graphene, which is now a well understood material, towards less explored materials, in particular monolayers of semiconducting transition metal dichalcogenides (TMDCs) such as MoS2 with direct band-gap in optical range (1.5 - 2 eV) and potential towards scalable electronics applications immune to short channel effects. This thesis in fact explores materials beyond exfoliated MoS2 with the focus on electrical and structural properties of monolayers of WS2, ReS2 and synthesized by means of chemical vapour deposition (CVD) monolayers of MoS2, MoSe2 and WSe2. Four main chapters discuss the following aspects of these materials. Chapter 4 studies in details transport properties of monolayer WS2 for the first time. We demonstrate wide tuning of transport in this material from insulating regime through localized states to band-like transport with insulator to metal transition (MIT) in between, with mobilities = 50 cm2/Vs at room temperature. In Chapter 5 we employ electrolyte gating for fabrication of the first electric double-layer transistor (EDLT) based on monolayers and multilayers of ReS2. Furthermore, we employ this as a system for variation of electrostatic disorder and find an unusual and strong modulation in conduction band of ReS2. The discovered modulation of conductivity via controllable introduction of electrostatic disorder can help to understand this material as well as other ultrathin 2D systems and to optimize the design of devices based on them. In Chapter 6 we use atomically smooth sapphire for demonstration of the first epitaxial monolayer MoS2 growth. We can control the orientation of single-crystalline grains on the substrate and create large area continuous films, where grain boundaries between the grains have no impact on transport properties in contrast to other reports. Finally, Chapter 7 discusses further advances in CVD growth of TMDCs, with the first demonstration of ambipolar insulator to metal transition in devices, based on monolayers of MoSe2 and WSe2. In conclusion, this thesis establishes connection between transport properties of monolayers of 2D semiconductors and structural or electrostatic disorder. These results are important for both fundamental understanding of transport in two-dimensional materials and practical applications

Improvement of Pork Quality at Different Values of Pig Productivity

This article examines how to increase pork meat productivity and quality indicators through the use of crossbreeding. The aim is to increase the meat productivity of animals; reduce losses during production and processing; and improve the criteria for assessing the quality of meat and the organization of its rational use. The purpose of our research is to study the productive quality of the steppe type of pigs, used in the Rostov region in breeding and crossing systems, and the complex of biological and internal indicators in connection with the defects in the quality of pork. Four groups with 16 animals in each were formed: the first group – with the intensive cultivation technology, included pigs of the DM-1 breed, the second – SM-1, the third – the SM-1 × DM-1 crossbreed, the fourth – the DM-1 × SM-1 crossbreed. Analysis of the raw meat showed that the pork had a good ability to emulsify and gel, and had a high nutritional value. The toxicity index in the muscle and fat tissue samples corresponded to the first permissible toxicity group. The study shows the advantages of crossbred individuals over purebred ones, which can be explained by the consequences of heterosis. According to the research results, the use of pig breeding in the industrial production of pork can be recommended in order to improve feedstock and meat productivity, biological and interior indicators, as well as the quality of raw meat. Keywords: pork, crossbreeding, meat productivity, meat quality, steppe type of pigs, interior indicators, fattening qualities, biological and nutritional value of por

Disorder engineering and conductivity dome in ReS2 with electrolyte gating

Atomically thin rhenium disulphide (ReS2) is a member of the transition metal dichalcogenide (TMDC) family of materials characterized by weak interlayer coupling and a distorted 1T structure. Here, we report on the electrical transport study of mono- and multilayer ReS2 with polymer electrolyte gating. We find that the conductivity of monolayer ReS2 is completely suppressed at high carrier densities, an unusual feature unique to monolayers, making ReS2 the first example of such a material. While thicker flakes of ReS2 also exhibit a conductivity dome and an insulator-metal-insulator sequence, they do not show a complete conductivity suppression at high doping densities. Using dual-gated devices, we can distinguish the gate-induced doping from the electrostatic disorder induced by the polymer electrolyte itself. Theoretical calculations and a transport model indicate that the observed conductivity suppression can be explained by a combination of a narrow conduction band and Anderson localization due to electrolyte-induced disorder.Comment: Submitted versio

Valley Polarization by Spin Injection in a Light-Emitting van der Waals Heterojunction

The band structure of transition metal dichalcogenides (TMDCs) with valence band edges at different locations in the momentum space could be harnessed to build devices that operate relying on the valley degree of freedom. To realize such valleytronic devices, it is necessary to control and manipulate the charge density in these valleys, resulting in valley polarization. While this has been demonstrated using optical excitation, generation of valley polarization in electronic devices without optical excitation remains difficult. Here, we demonstrate spin injection from a ferromagnetic electrode into a heterojunction based on monolayers of WSe2 and MoS2 and lateral transport of spin-polarized holes within the WSe2 layer. The resulting valley polarization leads to circularly polarized light emission which can be tuned using an external magnetic field. This demonstration of spin injection and magnetoelectronic control over valley polarization provides a new opportunity for realizing combined spin and valleytronic devices based on spin-valley locking in semiconducting TMDCs.Comment: in Nano Letters (2016

Extending service life of rails in the case of a rail head defect

Tračnice su tijekom svoje uporabe izložene procesima trošenja, korozije i kontaktnog zamora uslijed savijanja. Kao posljedica tih procesa, na tračnicama dolazi do raznih oštećenja i neispravnosti. Nastavak uporabljivosti tračnica ovisi o veličini, položaju i smjeru oštećenja. U ovom su radu izračunane maksimalno dopuštene vrijednosti veličine pukotine metodom konačnih elemenata. Smjer ravnine pukotine analiziran je u odnosu na ravninu kontaktne površine kotač-tračnica. Utemeljena je ovisnost faktora veličine naprezanja o površini pukotine. To omogućuje daljnju upotrebu oštećenih tračnica i siguran nastavak rada na željezničkim prugama sa slabijom aktivnošću.Rails are subjected to the processes of wear, corrosion and contact and bending fatigue during their lifecycle. As a result of these processes, various types of damage and defects are formed in rails. The residual life of rails depends on the size, position, and orientation of defects. Maximum permissible crack-size values are calculated in this paper using the finite element method. The crack plane orientation relative to the contact surface plane is analysed. The dependence of the stress intensity factor on the crack area is established. This allows continued use of defective rails and safe operation on low-activity railways

The Organization of the Internal Irradiation Monitoring System in Conditions of Nonstandard Radionuclide Intakes

Scientific knowledge presently available in the area of monitoring the internal radiation due to nonstandard radionuclide intakes gives no way of identifying the location and nature of intakes in a reasonably accurate and expeditious manner. Both theoretical models and practical methods of personnel internal radiation screening exhibit the lack of research. To this end, the present paper deals with the experience gained by the SGChE in the monitoring of the nonstandard radionuclide penetration into internals and tissues of the personnel. It provides recommendations for the organization and implementation of such monitoring procedures, and describes the practical method for the vulnerary intake containment

Suppressing Nucleation in Metal–Organic Chemical Vapor Deposition of MoS2

Toward the large-area deposition of MoS2 layers, we employ metal–organic precursors of Mo and S for a facile and reproducible van der Waals epitaxy on c-plane sapphire. Exposing c-sapphire substrates to alkali metal halide salts such as KI or NaCl together with the Mo precursor prior to the start of the growth process results in increasing the lateral dimensions of single crystalline domains by more than 2 orders of magnitude. The MoS2 grown this way exhibits high crystallinity and optoelectronic quality comparable to single-crystal MoS2 produced by conventional chemical vapor deposition methods. The presence of alkali metal halides suppresses the nucleation and enhances enlargement of domains while resulting in chemically pure MoS2 after transfer. Field-effect measurements in polymer electrolyte-gated devices result in promising electron mobility values close to 100 cm2 V–1 s–1 at cryogenic temperatures

Probabilistic-statistical models of the dynamics of climatic changes in the Altai Mountains

A probabilistic-statistical parameterization of time series characterizing geological and climatic processes allows determining some regularities by an autocorrelation analysis of signals which differ in nature. The use of the autocorrelation method for analyzing data related to solar and tectonic activity and characterizing the level of stratospheric ozone (total ozone content), hydrothermal regimes (De Martonne aridity index), and wood structure (maximum density of annual rings) allows us to find regularities in time series of various natural processes. Data on the maximum density of Siberian larch trees growing in the Altai Mountains made it possible to calculate the past changes in total ozone content and the aridity index in the Altai Mountains from 1900 to 2014 based on some similarities in the series and a separation of a dendrochronological signal into its main components