Unusual quasi-two-dimensional crystals of a regular triangular shape, self-formed in the process of obtaining a coordination polymer based on phenazine and silver, are described and studied. X-ray diffraction studies were carried out, the interplanar distance was determined, and the spectra of Raman scattering were obtained. A mechanism is proposed that can cause the appearance of triangular crystals from nuclei of hexagonal symmetry.

A novel time-domain technique for supercapacitor characterization is developed, modeled numerically, and experimentally tested on a number of commercial supercapacitors. The method involves momentarily shorting a supercapacitor for a brief duration, denoted as $\tau$, and measuring first $\int Idt$ and second $\int I^2dt$ moments of current along with the potential before and after shorting. The effective $C(\tau)$ and $R(\tau)$ are then obtained from charge preservation and energy dissipation invariants. A linear behavior in $[R(\tau),C(\tau)]$ parametric plot is observed by several orders of $\tau$. This gives a $C/R$ characteristic slope: how much $\Delta C$ we can ``gain'' if we are ready to ``lose'' $\Delta R$ in internal resistance. The $C/R$ characteristic slope characterizes possible energy and power properties of the device in terms of materials and technology used, this is a measure of supercapacitor perfection. The technique has been proven with experimental measurements and then validated through computer modeling, analytic analysis, and impedance spectroscopy on a number of circuit types: transmission line, binary tree, etc., a new n-tree element (nTE) is introduced. The approach offers an alternative to low-frequency impedance spectroscopy and methods outlined in the IEC 62391 standard. It provides valuable insights into the performance and characteristics of supercapacitors.

Multiple instability was found on the volt-ampere characteristic of the palladium-surface-oxidized indium phosphide structure. The effect is recorded when recording the dependence of differential conductivity and differential capacitance on the applied external voltage. A mechanism for the appearance of instabilities is proposed.. Keywords: palladium, VAC, instability, impedancometry.

Raman scattering spectra of linear carbon chains (carbines) localized in thin gold films of variable thickness are investigated. It is shown that the integral line is inhomogeneous, and separate components are identified, the intensity of which depends in a non-trivial way on the thickness of the film. Qualitative explanations of the detected effects are proposed.

Multiple instability was found on the volt-ampere characteristic of the palladium-surface-oxidized indium phosphide structure. The effect is recorded when recording the dependence of differential conductivity and differential capacitance on the applied external voltage. A mechanism for the appearance of instabilities is proposed.

Results from studying deformation are obtained for semipolar GaN(11–22) grown on a nanostructured Si(113) substrate and polar GaN(0001) grown on a flat Si(111) substrate. A comparison of the structures of semipolar and polar epitaxy reveals a drop in layer deformation resulting from the smaller difference between the coefficients of thermal expansion of the substrate and gallium nitride in the semipolar direction of the crystal than in the polar direction.

The study of the optical response of gold island films revealed an intense line in the light scattering spectrum near 2100 cm-1. Some possible reasons for the appearance of this line are considered. Comparison of the results obtained for films obtained by various technologies, light scattering spectra on other types of samples, as well as comparison with the results of other authors allow us to interpret the line as the result of inelastic light scattering by one-dimensional carbon chains.

Unusual quasi-two-dimensional crystals of a regular triangular shape, self-formed in the process of obtaining a coordination polymer based on phenazine and silver, are described and studied. X-ray diffraction studies were carried out, the interplanar distance was determined, and the spectra of Raman scattering were obtained. A mechanism is proposed that can cause the appearance of triangular crystals from nuclei of hexagonal symmetry.

A novel inverse relaxation technique for supercapacitor characterization is developed, modeled numerically, and experimentally tested on a number of commercial supercapacitors. It consists in shorting a supercapacitor for a short time tau, then switching to the open circuit regime and measuring an initial rebound and long-time relaxation. The results obtained are: the ratio of "easy" and "hard" to access capacitance and the dependence C(tau), that determines what the capacitance the system responds at time-scale T; it can be viewed as an alternative to used by some manufacturers approach to characterize a supercapacitor by fixed capacitance and time-scale dependent internal resistance. Among the advantages of proposed technique is that it does not require a source of fixed current, what simplifies the setup and allows a high discharge current regime. The approach can be used as a replacement of low-frequency impedance measurements and the ones of IEC 62391 type, it can be effectively applied to characterization of supercapacitors and other relaxation type systems with porous internal structure. The technique can be completely automated by a microcontroller to measure, analyze, and output the results.

The impedance of the RC circuit in which the active resistance depends on the applied dc voltage is considered. It is shown that in this case, the dependence of the impedance on the applied voltage is described by a hodograph of a new type, namely, a semicircumference pressed to the imaginary axis. The calculated and experimental hodographs that confirm the above assumptions are shown. It is demonstrated that the similarity and differences in the form of hodographs for cases R(U)C and RC (R = const) reflect the relationship between the functionally related values presented on the complex plane.

The impedance and capacitive properties of Pd/oxide/InP structures are investigated at 300 K in the frequency range of 10–1–10–5 Hz in air and in a nitrogen–hydrogen gas medium. The characteristics of structures in both media are interpreted based on a parallel RC-chain model with series resistance. The structure resistance decreases in the presence of hydrogen by three orders of magnitude, while the capacitance increases by 1–3 orders of magnitude depending on the frequency, which is possibly associated with the formation of positively charged centers in the oxide. Hysteresis is found in the capacitance–voltage characteristics in the medium with hydrogen, which is possibly caused by the ionic polarization of centers. It is shown that the total charge of centers measured in units of electrons almost coincides with the number of hydrogen atoms absorbed by palladium.

Epitaxial aluminum nitride (AlN) layers on Si(111) substrates have been grown by sequential application of several techniques including reactive magnetron sputter deposition to a thickness of 20 nm, metalorganic vapor-phase epitaxy (MOVPE) to a total thickness of 450 nm, and hydride vapor-phase epitaxy (HVPE) to a final thickness of 2 μm. Synthesis of AlN layers by this combined method provides a significant decrease in the residual strain and suppresses the formation of cracks in the epilayer.

Epitaxial layers of AlN were grown on a Si(111) substrate using several sequential methods: reactive magnetron sputtering (up to a thickness of 20 nm), MOCVD (up to a thickness of 450 nm), and HVPE (up to a thickness of 2 microns).The formation of AlN by this combined method provides a significant reduction in layer deformation and suppression of crack formation.

The impedance and capacitance properties of Pd/oxide/InP structures within the frequency range from 0.1 Hz to 10 kHz in air and in gaseous hydrogen–nitrogen mixture at 300 K have been studied. The characteristics of investigated structures can be characterized by parallel RC circuit model with the connected serial resistance. In hydrogen medium the active resistance of the structures decreases by 3 orders of magnitude and the capacitance increases by 1–3 orders of magnitude depending on frequency that is due probably to the positive charged centers formed in the oxide layer. In hydrogen medium the hysteresis has been found on CV-characteristics of the structures that may be explained by ion polarization of formed centers. It is shown that measured in electron units the full charge of the centers practically coincides with the quantity of hydrogen atoms absorbed by palladium.

We propose a method for the synthesis of hexagonal AlN layer on Si(100) substrate with a V-groove nanostructured surface where the angle between the sloped nanoridge surface and Si(100) plane amounts to 47°. It is established that metalorganic hydride vapor-phase epitaxy (HVPE) on this substrate leads to the formation of semipolar AlN(10$$\bar {1}$$2) layers having an X-ray rocking curve with a minimum FWHM value of ωθ ~ 60 arcmin. Raman spectra of this epilayer display additional peaks related to A1(TO) and E1(TO) phonons in contrast to the spectrum of a polar AlN(0001) layer containing an additional A1(LO) peak.

Multilayered graphenes (MLG) in the form of a free-standing films, treated with plasma of different chemical composition, were studied. Morphology, electrical properties, and electronic bonding structure were evaluated to assess MLG applicability in flexible charge storage devices. Ability to alter surface electrical properties, such as electron work function without sufficient changing of chemical properties of the surface was shown. Therefore obtained samples are promising for variety of practical applications, where chemical inertness is combined with flexibility and high electrical conductivity.

A new approach is proposed to the synthesis of a semipolar AlN on a Si(100) substrate at the surface for which the angle between the inclined plane of the nanogrooves and Si(100) is 47°. It is shown that the hydride vapor-phase epitaxy on a such nano-patterned substrate enables formation of a semipolar layer AlN (1012) characterized by the full width at half maximum value as low as ωθ ~60 arcmin for the x-ray diffraction rocking curve. It is found that the Raman spectra of the semipolar AlN(10-12) layer contain additional peaks on the Raman curves associated with phonons A1(TO) and E1(TO), in contrast to the polar AlN(0001) layer, where the peak A1(LO) is additionally manifested.

AbstractThe phenomenon of voltage self-recovery in supercapacitors of various types has been studied. It has been established that parameters of this process are related to characteristics of the porous structure of capacitor electrodes. An approach is proposed that allows the fraction of capacitance active in the pulsed process of given duration to be determined in experiment.

The phenomenon of voltage self-recovery in supercapacitors of various types has been studied. It has been established that parameters of this process are related to characteristics of the porous structure of capacitor electrodes. An approach is proposed that allows the fraction of capacitance active in the pulsed process of given duration to be determined in experiment.

Two different approaches to epitaxy of 4-μm-thick layers of polar GaN(0001) and semipolar GaN(10 1̅ 1) on a V -shaped nanostructured Si(100) substrate with nanometer-thick SiC and AlN buffer layers have been experimentally demonstrated. The GaN(0001) layers were synthesized by hydride vapor-phase epitaxy, and GaN(10 1̅ 1) layers, by metal-organic vapor-phase epitaxy, with the growth completed by hydride vapor-phase epitaxy. It was shown that layers of the polar GaN(0002) have a longitudinal elastic stress of –0.45 GPa and the minimum full width at half-maximum of the X-ray diffraction rocking curve ω θ 45 arcmin, whereas for the semipolar GaN(10 1̅ 1), these values are –0.29 GPa and ω θ 22 arcmin, respectively. A conclusion is drawn that the combined technology of semipolar gallium nitride on a silicon (100) substrate is promising.