Field induced evolution of regular and random 2D domain structures and shape of isolated domains in LiNbO₃ and LiTaO₃

The shapes of isolated domains produced by application of the uniform external electric field in different experimental conditions were investigated experimentally in single crystalline lithium niobate LiNbO3 and lithium tantalate LiTaO3. The study of the domain kinetics by computer simulation and experimentally by polarization reversal of the model structure using two-dimensional regular electrode pattern confirms applicability of the kinetic approach to explanation of the experimentally observed evolution of the domain shape and geometry of the domain structure. It has been shown that the fast domain walls strictly oriented along X directions appear after domain merging

Gas Sensing with h-BN Capped MoS2 Heterostructure Thin Film Transistors

We have demonstrated selective gas sensing with molybdenum disulfide (MoS2) thin films transistors capped with a thin layer of hexagonal boron nitride (h-BN). The resistance change was used as a sensing parameter to detect chemical vapors such as ethanol, acetonitrile, toluene, chloroform and methanol. It was found that h-BN dielectric passivation layer does not prevent gas detection via changes in the source-drain current in the active MoS2 thin film channel. The use of h-BN cap layers (thickness H=10 nm) in the design of MoS2 thin film gas sensors improves device stability and prevents device degradation due to environmental and chemical exposure. The obtained results are important for applications of van der Waals materials in chemical and biological sensing.Comment: 3 pages; 4 figure

Low-noise top-gate graphene transistors

We report results of experimental investigation of the low-frequency noise in the top-gate graphene transistors. The back-gate graphene devices were modified via addition of the top gate separated by 20 nm of HfO2 from the single-layer graphene channels. The measurements revealed low flicker noise levels with the normalized noise spectral density close to 1/f (f is the frequency) and Hooge parameter below 2 x 10^-3. The analysis of the noise spectral density dependence on the top and bottom gate biases helped us to elucidate the noise sources in these devices and develop a strategy for the electronic noise reduction. The obtained results are important for all proposed graphene applications in electronics and sensors.Comment: 9 pages, 4 figure

Flicker Noise in Bilayer Graphene Transistors

We present the results of the experimental investigation of the low - frequency noise in bilayer graphene transistors. The back - gated devices were fabricated using the electron beam lithography and evaporation. The charge neutrality point for the fabricated transistors was around 10 V. The noise spectra at frequencies above 10 - 100 Hz were of the 1/f - type with the spectral density on the order of 10E-23 - 10E-22 A2/Hz at the frequency of 1 kHz. The deviation from the 1/f spectrum at the frequencies below 10 -100 Hz indicates that the noise is of the carrier - number fluctuation origin due to the carrier trapping by defects. The Hooge parameter of 10E-4 was extracted for this type of devices. The gate dependence of the noise spectral density suggests that the noise is dominated by the contributions from the ungated part of the device channel and by the contacts. The obtained results are important for graphene electronic applications

Static conductivity of charged domain wall in uniaxial ferroelectric-semiconductors

Using Landau-Ginzburg-Devonshire theory we calculated numerically the static conductivity of both inclined and counter domain walls in the uniaxial ferroelectrics-semiconductors of n-type. We used the effective mass approximation for the electron and holes density of states, which is valid at arbitrary distance from the domain wall. Due to the electrons accumulation, the static conductivity drastically increases at the inclined head-to-head wall by 1 order of magnitude for small incline angles theta pi/40 by up 3 orders of magnitude for the counter domain wall (theta=pi/2). Two separate regions of the space charge accumulation exist across an inclined tail-to-tail wall: the thin region in the immediate vicinity of the wall with accumulated mobile holes and the much wider region with ionized donors. The conductivity across the tail-to-tail wall is at least an order of magnitude smaller than the one of the head-to-head wall due to the low mobility of holes, which are improper carries. The results are in qualitative agreement with recent experimental data for LiNbO3 doped with MgO.Comment: 20 pages, 6 figures, 1 appendi

On the inverse problem of magnetostatics

This work is devoted to solving the inverse problem of the magnetic method for nonde- structive testing (MMNDT). The purpose of the work, frankly speaking and avoiding complicated concepts and formulas, is to identify research directions in MMNDT that would approach solution of the inverse problem in the field of magnetic defectoscopy to the highest extent. © 2013 Pleiades Publishing, Ltd

Observation of the "Memory Steps" in Graphene at Elevated Temperatures

We found that the current-voltage characteristics of the single-layer graphene field-effect transistors exhibit an intriguing feature - an abrupt change of the current near zero gate bias at elevated temperatures T > 500 K. The strength of the effect - referred to as the "memory step" by analogy with the "memory dips" - known phenomenon in electron glasses - depends on the rate of the voltage sweep. The slower the sweep - the more pronounced is the step in the current. Despite differences in examined graphene transistor characteristics, the "memory step" always appears near zero gate bias. The effect is reproducible and preserved after device aging. A similar feature has been previously observed in electronic glasses albeit at cryogenic temperatures and with opposite dependence on the rate of the voltage sweep. The observed "memory step" can be related to the slow relaxation processes in graphene. This new characteristic of electron transport in graphene can be used for applications in high-temperature sensors and switches.Comment: 17 manuscript page