The article is devoted to the study of the features of monitoring of changes in the color passive sensors, tracking the spectral distribution of the light intensity of the liquid crystal color depending on the operating conditions. The functional component of a passive, non-contact sensor is a combination of an elastic silicon membrane and cholesteric liquid crystals as an optically active environment, which, due to the action of an external physical factor, for example temperature, undergo a rearrangement of the geometry of the spiral of the supramolecular structure of the film. It has been determined that without using electrically induced methods that cause a high level of electromagnetic interference ensures high competitiveness of such devices. It is proposed to use a hardware-software complex for monitoring, which contains a spectrometer and allows real-time display, as well as recording of the received information into file arrays, of various optical characteristics such as spectral intensity distribution, and color rendering index. It was established that in the wavelength range from 370 to 650 nm, the proposed method for evaluating the color characteristics of samples using optically active environment of liquid cholesteric crystals allows estimating the parameters of the spectral intensity distribution with sufficient sensitivity. Thus, for wavelengths from 450 to 550 nm, the maximum intensity is I = 1.42 rel.u, and the resolution of the method lies in the wavelength range up to 100 nm, i.e., when the wavelength changes by 10 nm, the intensity increases by 0.14 rel.u.

In the work, research was carried out on filamentous silicon crystals doped with boron admixture to concentrations corresponding to the metal–insulator transition (MIT) in silicon, as well as with an admixture of the transition metal nickel. Investigations were conducted at cryogenic temperatures in the interval 4.2–70 K using alternating current in the frequency range from 10 Hz to 250 kHz. Different conduction mechanisms have been established according to Jonscher's power law as σ(ω) ≈ Aωn. In the low-frequency range up to 20 kHz a quantum–mechanical tunneling mechanism is observed for the conduction for temperatures 4.2–30 K with a frequency-dependent coefficient n that is proportional ω0.8, which with increasing frequency to 250 kHz increases to values n ≈ ω1.8. In this case, the low-temperature conductivity increases linearly according to the superlinear power law (SLPL).

The results of studies of magnetoresistance for GaAs filamentous crystals doped with tellurium admixture to a concentration of 2 & BULL;10(17) cm(-3), in the temperature range 4.2-60 K and in the magnetic field ranges 0-14 T are presented. The GaAs filamentary crystal magnetoresistance has shown a sharp positive jump at a low magnetic field (up to 0.2 T) at a temperature near 4.2 K, while at higher magnetic field inductions linear behavior of magnetoresistance occurs. The low field magnetoresistance is discussed in the framework of weak localization of charge carriers due to their spin-orbit exchange interaction. The high-field linear magnetoresistance is connected with electron-electron interaction.

In this work, silicon microcrystals doped with a boron impurity to concentrations corresponding to the metal-dielectric transition in silicon of 5.51018 cm-3 and a nickel impurity in the temperature range of 4.2 divided by 70 K under alternating current in the frequency range of 0.010 divided by 250 kHz were studied. The features of the frequency response of silicon microcrystals are determined. On the basis of Nyquist diagrams, an equivalent conductivity scheme at low temperatures is proposed. The frequency response of the samples was evaluated and the mechanisms of charge carrier flow were proposed depending on the observation conditions. Conduction mechanisms from quantum mechanical tunneling (QMT) to superlinear power law (SLPL), which can be implemented in crystals, are considered.

The work proposes the use of a unique method of creating passive, multifunctional, non-contact pressure-temperature sensors. The basis of this method is a combination of inorganic semiconductors and high-molecular organic cholesteric crystals. According to their morphology, such crystals represent a spiral structure that is sensitive to changes in external physical factors, such as temperatures, due to changes in the periodicity of the structure, which leads to Bragg diffraction scattering of light on it. The consequence of such influence is the coloring of the cholesteric, which can be identified by external spectrosensitive devices on a non-contact basis. On the other hand, the use of inorganic semiconductors involves the production of a micro-profiled base with a thin silicon membrane that is sensitive to external pressure. The thickness of the membrane determines the operating conditions of the sensor depending on the range of applied pressure from 0.3 bar and above. A hardware and software complex was developed for continuous monitoring of changes in the color of passive pressure-temperature sensors, tracking the spectral distribution of the light intensity of the color of the liquid crystal depending on the operating conditions on a non-contact basis with an external spectrometer. The basis of such a system is a software module created on the basis of the MVVM (Model–View–View Model) architecture template. A feature of the software module is the use of the .NET and WPF frameworks, which natively support this architectural pattern for .NET Windows platforms and are supported by all popular versions of operating systems. The SQlite database, which is a relational database management system, is used to store data in the software application. The OmniDriver library was used in the system to operate and configure the spectrometer. The software module has two modes of operation with spectrometers. The first mode is characterized by the reading of a single spectrum, while the second mode is characterized by periodic reading and processing of the intensity spectral distribution in real time with a given period. When using the second mode, the software module allows you to dynamically change the periods and parameters of changing the color parameters of the light over time. The main algorithm of the software module is the transformation of the spectral intensity distribution normalized in the CIE XYZ color model, which is the basis for all further calculations, into the RGB model.

In the work, a study of the design and technological direction of creating a dual-functional non-contact pressure and temperature sensor based on silicon-cholesteric crystal systems was carried out. An optically active environment based on a supramolecular spiral structure is a sensitive element for forming the optical response of a microelectronic label sensor during non-contact monitoring of the state of a physical object using a spectrometer. The optical response of the device provides maximum intensity in the case of interference that corresponds to the Wulff–Bragg condition. The functionality of the sensor is ensured by the conditions for avoiding high electromagnetic interference during optical identification. A hardware and software modules have been created for non-contact monitoring of the state of physical objects, the main part of which is graphical user interface that corresponds to the MVVM architectural design pattern. Visualization of the spectral intensity using the software module was provided by conversion to the RGB model. The algorithm of procedure for calculating the color rendering index is given. In a wide range of light waves, the main parameters' color temperature was defined.

Studies of temperature dependence of magnetoresistance for PdxBi2Se3 whiskers in the temperature range 1.6-77K in magnetic field up to 10 T were carried out. Crystals were grown by chemical transport reaction method in closed bromide system. The source and crystallization zone temperatures were 1100 K and 780 K, respectively. Doping of the crystals was carried out during the growth process with palladium impurity to concentrations of (1 – 2) × 1019 cm−3. In the low-temperature region beginning at a temperature of 5 K and reaching a temperature 3.5 K, a sharp decrease in resistance was observed, which is associated with the transition to superconducting state. Based on the analysis of the temperature dependence of the resistance at fixed magnetic fields, the Curie temperature Tc1=5.3 K and Tc2=3.5 K as well as the upper critical magnetic field Bc2=1.45 T and 0.25 T were determined. The established parameters indicates in II type supercondor. This is indicated by the ratio Δ0/kBTc = 2.0, which exceeds BCS limit of 1.76 and indicates a relatively large value of the superconducting gap Δ0=0.8 meV. The determined ratio A/γ2, which establishes the relationship between the electron-electron and electron-phonon interaction, is about of 2ao, which indicates a strong fermionic interaction with phonons in the PdxBi2Se3 superconductor. The estimated value of the ratio of the Curie temperature to the effective Fermi temperature equal to 0.04 also falls within the range of 0.01 ⩽ Tc/TF ⩽ 0.1, which confirms the unconventional superconductivity in the investigated whiskers.

The article is devoted to characteristics of charge carrier transfer in silicon microcrystals modified with a transition metal admixture with an unfilled 3d(+) local magnetic moment envelope and doped with boron to concentrations that correspond to the metal-dielectric transition. At cryogenic temperatures, the magnetoresistance of microcrystals was examined under the influence of magnetic fields up to 14 T. The outcomes of investigations into the magneto-transport characteristics of crystals were thoroughly examined. It was discovered that the transport of charge carriers for silicon microcrystals at low temperatures relies on hopping polarization conductivity. Based on the results of the Si < B, Ni> crystal magnetization study, the concentration of magnetic centers was determined, which is 4 x 10(17) CM-3. It is suggested to employ silicon microcrystals in magnetic field sensors that operate on the magnetoresistive principle.

It was studied the electrical magnetoresistance of nickel-and boron-doped filamentary silicon crystals in which a metal-insulator transition is observed. A giant magnetoresistance reaches up to 280% in the Si whiskers with doping concentration of boron р300K = 5⋅1018 cm−3 in the magnetic fields with induction up to 14 T at temperature 4.2 K. Peculiarities of magnetoresistance at low temperatures were shown to be caused by “core-shell” structure of crystals. A giant magnetoresistance nature was considered within quantum magnetoresistance model. The analysis was performed to determine the critical field of transition from classical parabolic magnetoresistance to quantum magnetoresistance, realized in the near-surface region of the crystal. The silicon whiskers were used for design of magnetic field sensors.

The paper deals with studies of magnetization and magnetic susceptibility of Si1 -xGex B, Hf (x  0.05) whiskers with a diameter of about 1 μm in the temperatures range 77-300 K and magnetic fields up to 4.28 kOe.The obtained results have showed that the whisker magnetic susceptibility differs substantially from the typical diamagnetic bulk material.The main difference is connected with the existence of paramagnetic centers localized in the nanoporous coating, the so-called core-shell structure, of Si1 -xGex whiskers.This leads to the emergence of magnetic ordering in them and appearance of a paramagnetic component in the magnetic susceptibility.An increase in the paramagnetic component was observed due to the introduction of Hf dopants as separate paramagnetic centers.The oxygen presence in the whisker coreshell structure was also found due to Auger spectroscopy associated with the VLS mechanism of the Si1 -xGex whisker growth.As a result, HfO2 clusters are formed as a bulk material typical of diamagnets.The field behavior of the magnetic susceptibility component has a superparamagnetic character, which is characteristic of superparamagnetism saturation of magnetization and hysteresis absence in the temperature range 77-300 K. Therefore, the observed phenomena are explained by the existence of dangling bonds, as well as HfO2 clusters, in the whisker nanoporous coating according to magnetic ordering and the superparamagnetism appearance in Si1 -xGex B, Hf whiskers.

First, we have evaluated the spin-resolved electronic structure of crystals Si < B, V>, Si < B, Cr > and Si < B, Mn > with the exchange-correlation energy in a form of generalized gradient approximation (GGA-PBE). Next, the strong correlation effects of the V, Cr and Mn 3d electrons have been taken into account by means of the hybrid exchange-correlation functional PBE0. All the calculations have been done for supercells Si30B1V1, Si30B1Cr1, and Si30B1Mn1, modeling the substitutional alloys based on silicon crystal. In the pseudogap materials we are considering here, the Fermi level lies in the valence band. Without taking into account the strong correlations of the 3d electrons of the transition elements, we found the following properties of the materials under study. For the spin up the SiBV has an indirect pseudogap, the SiBCr is a direct gap material, and the SiBMn is an indirect pseudogap material. For the spin down these materials are a direct gap, direct pseudogap and indirect gap materials, respectively. Taking into account the strong correlations of the 3d electrons of the transition elements, we found the following properties of these materials. For the spin up the SiBV and SiBCr are the direct gap materials and SiBMn has an indirect pseudogap. For the spin down the SiBV is a direct pseudogap material, and the SiBCr is an indirect pseudogap compound, and SiBMn has a direct band gap.

The temperature dependences of resistance for the p-type conductivity solid solution silicon–germanium whiskers doped by boron with concentration of 1 × 1018 cm−3 were investigated in the temperature range of 4.2–300 K and under the uniaxial compressive strain till − 3 × 10–3 rel. un. We studied the strain influence, which was caused on a spin–orbit splitting in the valence band spectrum. As an outcome, the spin–orbit splitting energies for both light and heavy holes were discovered based on the k–p method. The strain-induced effects of solid solution Si0.2Ge0.8 whiskers were studied at low temperatures. Found giant piezoresistive effect at helium temperature gives opportunity to create the supersensitive strain gages on the basis of silicon–germanium whiskers with doping concentration in the vicinity to the metal–insulator transition. The mechanical sensor operating at helium temperature and deformation range of 5 × 10–4–1.3 × 10–3 rel. un. was designed with the sensitive element Si0.2Ge0.8 whiskers doped to concentration 1 × 1018 cm−3.

The spin-resolved electronic structure of crystals Si, Si and Si was evaluated with the hybrid functional PBE0. All the calculations have been done for supercells Si30B1Fe1, Si30B1Co1, and Si30B1Ni1, modelling the substitutional alloys based on silicon crystal. We found that in the SiBFe material the Fermi level crosses the dispersion curves in the valence band for both spins. This material is a p-type semiconductor for spin down and a classic semiconductor for opposing spin. The materials Si(30)B(1)Co(1)and Si(30)B(1)Ni(1)behave for both spins as a classical semiconductor and n-type semiconductor, without and with the strong correlations, respectively.

The Bi(2)Se(3)whisker temperature dependencies of resistance with palladium doping concentration of (1 divided by 2)x10(19) cm(-3)were studied in the range of 1.5 divided by 77 K. At the temperature of 5.3 K there was found a sharp drop in the whisker resistance. This effect can be explained as a contribution of two processes: electron localization and superconductivity at temperatures under 5.3 K. The magnetoresistance in Bi(2)Se(3)whiskers with n-type conductivity and diverse concentration of Pd that correspond to the metal side of the MIT (metal-insulator transition) was studied at low temperatures and magnetic field in the range of 0 divided by 10 T. The magnetoconductance was considered in the structure by the weak antilocalization model and attached with subsurface layers of Bi(2)Se(3)whiskers.

The paper deals with studies of thermoelectric properties for Si1-xGex (x=0.01-0.05) whiskers doped with boron during their growth by CVD method. Temperature dependences of the resistance and the Seebeck coefficient for Si1-xGex whiskers were measured in the temperature range 275–550 K. A method for determination of thermoelectric parameters of the whisker was proposed with use of the whisker joints, which allows us to define a ratio of Seebeck coefficient to thermal conductivity a/k. Taking into account the obtained values of Seebeck coefficient, the whisker conductance and estimated values of thermal conductivity, parameter ZT was calculated for the whiskers and consists of 0.15 for T=200oC. The obtained value of ZT is in good coincidence with literature data for hop pressed Si-Ge nanocomposites. The humidity sensor was designed base on Si-Ge whiskers.

The present paper aims to study an effect of compression strain (up to epsilon = 3.10(-4)) on behavior of transverse magnetoresistance of InSb whiskers at cryogenic temperatures under high magnetic fields up to 10 T. The strained and unstrained InSb whiskers with the concentration of charge carriers from 6.10(16) to 6.10(17) cm(-3) in the vicinity to metal-insulator transition are under consideration. The effect of a giant magnetoresistance of 700 % at a temperature of 4.2 K was established for the InSb whiskers with carrier concentration of 2.10(17) cm(-3). The effect was used for the design of magnetic field sensors with a magnetoresistive principle of action. The whiskers with carrier concentration 6.10(16) cm(-3) due to a high gauge factor of about 350 was shown might be used in piezoresistance sensors able to work in harsh operating conditions in a temperature range of 4.2 to 50 K.

Strain influence on the longitudinal magnetoresistance for the n-type conductivity InSb whiskers doped by Sn to concentration 6·1016–6·1017 сm–3 was studied in the temperature range 4.2–40 K and magnetic field up to 10 T. The Shubnikov–de Haas oscillations at low temperatures were observed in the strained and unstrained samples in all range of doping concentrations and magnetic fields. The character of longitudinal magnetoresistance dependences was analyzed and compared with theoretical one. The whisker magnetoresistance alters its sign with increasing magnetic field. It is positive at weak magnetic fields and becomes negative at higher magnetic fields. Possible mechanism of the large value of negative magnetoresistance (NMR) was discussed in the InSb whiskers with doping concentration in the vicinity to metal–insulator transition. The origin of large NMR was explained by the existence of classical size effect and boundary scattering during conductance in subsurface whisker layers.

The authors investigate deformation-induced changes in the electrophysical parameters of the indium antimonide microcrystals at cryogenic temperatures in strong magnetic fields up to 10 T. It is determined that for strongly doped InSb microcrystals, the gauge factor at liquid-helium temperature is GF4.2K ≈ 72 for the charge carrier concentration of 2∙1017 сm–3, while being GF4.2K ≈ 47 for the concentration of 6∙1017 сm–3, at ε = –3∙10–4 rel. un. For the development of magnetic field sensors based on the magnetoresistive principle, the effect of a giant magnetic resistivity reaching 720% at a temperature of 4.2 K is used.

Strain influence on the behavior of temperature dependences of resistance was studied in the n-type conductivity GaSb whiskers with tellurium concentration 1.7 1018 сm–3. Analyzing these dependences in the temperature range 4.2–30 K strain inducted metal–insulator transition and partial superconductivity were found in the whiskers. The transverse and longitudinal magnetoresistances for unstrained and strained GaSb whiskers were also studied in ranges of magnetic field 0–3 T and temperature 1.5–60 K. The effects, such as a superconductivity and weak anti-localization were observed for unstrained and strained samples. The upper critical zero magnetic fields for superconductivity suppression were obtained in the whiskers. Strain was shown to decrease the superconductivity in GaSb samples. The strain induced splitting of degenerate level on two components with opposite and parallel spins was found in the n-type conductivity GaSb whiskers due to weak localization and anti-localization effects, respectively.