Electronic Subsystem Research Articles

Development of a Generalized Model for the Protection of a Critical Infrastructure Object from the Destructive Impact of Air Attack Means

Purpose: development of a generalized model for the protection of critical infrastructure objects from the destructive action of an air attack. Theoretical framework: based on the analysis of the use of cruise missiles with radar correlation-extreme algorithms to damage critical infrastructure objects in the conditions of the Russian-Ukrainian war, a generalized model of the protection of critical infrastructure objects from the destructive action of an air attack has been developed. Methods: determined by a set of solved scientific and research tasks and carried out using: methods of system analysis - during studies of the distribution function of the electronic subsystem; numerical modeling methods - when studying the main electrophysical properties of critical infrastructure objects. Results and conclusions: a generalized model of the protection of a critical infrastructure facility against the destructive action of air attack tools has been developed, which allows for the assessment of risks and their management. The developed model can quantify uncertainties, simulate potential scenarios and assess the impact of various factors on the level of risk. This allows decision makers to make informed choices and develop strategies to mitigate risks. Finding implication: the research carried out in the article makes it possible to develop a mathematical model for ensuring the protection of critical infrastructure objects from the destructive impact of various types of air attack means. Uniqueness /value: a mathematical model of the protection of a critical infrastructure object from the destructive effects of air attack provides a powerful basis for understanding, predicting and optimizing air defense, contributing to progress in various fields and enabling evidence-based decision-making.

Modeling of Electron and Lattice Temperature Distribution Through Lifetime of Plasma Plume

When employing shorter (sub picosecond) laser pulses, in ablation kinetics the features appear which can no longer be described in the context of the conventional thermal model. Meanwhile, the ablation of materials with the aid of ultra-short (sub picosecond) laser pulses is applied for micromechanical processing. Physical mechanisms and theoretical models of laser ablation are discussed. Typical associated phenomena are qualitatively regarded and methods for studying them quantitatively are considered. Calculated results relevant to ablation kinetics for a number of substances are presented and compared with experimental data. Ultra-short laser ablation with two-temperature model was quantitatively investigated. A two-temperature model for the description of transition phenomena in a non-equilibrium electron gas and a lattice under picosecond laser irradiation is proposed. Some characteristics are hard to measure directly at all. That is why the analysis of physical mechanisms involved in the ablation process by ultra-short laser pulses has to be performed on the basis of a theoretical consideration of `indirect' experimental data. For Copper and Nickel metal targets, the two-temperature model calculations explain that the temperature of the electron subsystem increased suddenly and approached a peak value at the end of laser pulse. In addition, the temperature profile of lattice temperature subsystem evolution slowly, and still increasing after the end of laser pulse. A good agreement prevails when a comparison between the present results and published results.

Boosting the thermal management performance of a PCM-based module using novel metallic pin fin geometries: Numerical study

Satellite avionics and electronic components are getting compact and have high power density. Thermal management systems are essential for their optimal operational performance and survival. Thermal management systems keep the electronic components within a safe temperature range. Phase change materials (PCMs) have high thermal capacity, so they are promising for thermal control applications. This work adopted a PCM-integrated thermal control device (TCD) to manage the small satellite subsystems under zero gravity conditions thermally. The TCD's outer dimensions were selected upon a typical small satellite subsystem. The PCM adopted was the organic PCM of RT 35. Pin fins with different geometries were adopted to boost the lower thermal conductivity of the PCM. Six-pin fins geometries were used. First, the conventional geometries were square, circular, and triangular. Second, the novel geometries were cross-shaped, I-shaped, and V-shaped fins. The fins were designed at two-volume fractions of 20% and 50%. The electronic subsystem was assumed to be "ON" for 10 min releasing 20 W of heat, and "OFF" for 80 min. The findings show a remarkable decrease in the TCD's base plate temperature by 5.7 ℃ as the fins' number changed from 15 to 80 for square fins. The results also show that the novel cross-shaped, I-shaped, and V-shaped pin fins could significantly enhance thermal performance. The cross-shaped, I-shaped, and V-shaped reported a decrease in the temperature by about 1.6%, 2.6%, and 6.6%, respectively, relative to the circular fin geometry. V-shaped fins could also increase the PCM melt fraction by 32.3%.

Development of a new quantum trajectory molecular dynamics framework.

An extension to the wave packet description of quantum plasmas is presented, where the wave packet can be elongated in arbitrary directions. A generalized Ewald summation is constructed for the wave packet models accounting for long-range Coulomb interactions and fermionic effects are approximated by purpose-built Pauli potentials, self-consistent with the wave packets used. We demonstrate its numerical implementation with good parallel support and close to linear scaling in particle number, used for comparisons with the more common wave packet employing isotropic states. Ground state and thermal properties are compared between the models with differences occurring primarily in the electronic subsystem. Especially, the electrical conductivity of dense hydrogen is investigated where a 15% increase in DC conductivity can be seen in our wave packet model compared with other models. This article is part of the theme issue 'Dynamic and transient processes in warm dense matter'.

Theoretical Study of Intermixing in Au/Si System under Swift Heavy Ion Irradiation

Abstract: The behavior of the metallic multilayer Au100Å/Si100Å/Si under swift heavy ion irradiation has been studied within the inelastic thermal spike model. Gold has been chosen due to its insensitivity to irradiation. The heat transport in the electronic and lattice subsystem has been simulated using a three-dimensional numerical code that includes the energy transfer between the layers in a direction perpendicular to layer surfaces. The simulations have been done for four kinds of ions Pb, Xe, Kr, and Ar, at a specific energy of 3Mev/amu in order to study the influence of the electronic stopping power on the intermixing process. The results show that for Pb, Xe, and Kr, intermixing at the interface of Au/Si has been obtained. However, no mixing has been observed with Ar. Furthermore, the value of the interdiffusion coefficient for Au has been estimated to be approximately 11x10-4 cm2 s-1, which is characteristic of the liquid phase and, thus, supports the thermal spike model of mixing. For comparison, similar thermal spike simulations have been applied to Ti100Å/Si100Å/Si under the same irradiation conditions. We have found that Ti, which is a sensitive material, exhibits considerable intermixing with Si during Pb, Xe, and Kr irradiation. Whereas, a weak intermixing has been found after Ar irradiation; this is completely different from what has been observed in the Au/Si system. Keywords: Irradiation, Swift heavy ions, Thermal spike model, Ion beam mixing. PACS: 61.80.Az, 61.80.Jh, 61.80.LJ.

ВЛИЯНИЕ ЧАСТОТЫ ПЕРЕМЕННОГО ПОЛЯ НА ЭЛЕКТРОФИЗИЧЕСКИЕ СВОЙСТВА ПОЛИМЕРНЫХ ПЛЕНОК

The results of an experimental study of the frequency dependences of the impedance of metal-polymer-metal sandwich structures for different thicknesses of the polymer layer are presented. The voltage characteristics of the samples in various frequency ranges were measured. The general view of the amplitude-frequency characteristics graphs for all film thicknesses is well described by the theoretical model of the sequential RC circuit. On all graphs, you can notice the presence of a cutoff frequency, which can be interpreted as the beginning of the RC filter. However, there are also significant deviations from the theoretical characteristics. It is established that with a polymer layer thickness of 80 nm in the frequency range At 10-40 Hz, an abnormal decrease in impedance is observed, corresponding to an increase in current at the volt-ampere characteristics. The resulting charge instability is considered as a consequence of the volume-charge polarization, which, in turn, is due to the specifics of polymer-polymer interfaces that arise during the formation of the supramolecular structure of the polymer. The results of the work are interpreted within the framework of the resistive switching model, which assumes that in the case of submicron polymer films used in the metalpolymer-metal system, resistive switching is possible as a result of the sequential transformation of the energy electronic subsystem of the polymer film under the action of charge injection from the electrodes.

Pressure effect of the charge density wave transition on Raman spectra and transport properties of 2H−NbSe2

Charge density wave (CDW) order is widely existing and fundamentally important in solid-state physics. However, several critical issues regarding the vibrational and electronic subsystems and their coupling still need to be better understood. Here, we tune the electrical transport and collective vibrational excitation, i.e., phonon and amplitude mode, by pressure in a prototype charge density wave material, $2H\text{\ensuremath{-}}{\mathrm{NbSe}}_{2}$. A complete pressure-temperature phase diagram is revisited. The anomaly in Hall and magnetoresistivity at CDW critical temperature, ${T}_{\mathrm{CDW}}$, was suppressed by the pressure. In the Raman spectroscopy measurements, the appearance of CDW amplitude mode is accompanied by the freezing of the two-phonon mode. The frequency of CDW amplitude mode under pressure follows modified mean-field theory with power-law scaling $(\ensuremath{\beta}=0.18)$. The renormalization of the Raman phonon across the CDW transition and the mean-field temperature dependence of CDW amplitude mode emphasized the importance of electron-phonon coupling in the formation of CDW state in $2H\text{\ensuremath{-}}{\mathrm{NbSe}}_{2}$. Our work clarifies the complex vibrational and electronic subsystems and sheds light on the mechanism of the charge density state in $2H\text{\ensuremath{-}}{\mathrm{NbSe}}_{2}$.

Numerical simulation and investigation of ultra-short pulse laser ablation on Ti6Al4V and stainless steel

In ultra-short pulse laser machining and micro/surface processing, accurate simulation of laser ablation is important for understanding laser-target interaction and improving ablation performance, but it remains challenging. This work aims to develop a numerical model to improve the accuracy of the ablation depth calculation. A grid deformation scheme is proposed based on energy conservation and considering contributions to instant material removal from both the electron and lattice subsystems. By incorporating this scheme with the two-temperature model (TTM), a reasonable prediction of the instant target surface profile during laser ablation has been achieved. In the case of single-pulse femtosecond laser ablation of Ti6Al4V, the calculated ablation depth ranges from 0.06 to 0.56 μm for laser energy from 1.0 to 10.0 μJ. For single-pulse picosecond laser ablation of stainless steel, as laser energy increases from 6.0 to 18.5 μJ, the predicted ablation crater deepens accordingly from 40 to 87 nm. In addition, for multi-pulse picosecond laser ablation of stainless steel, a linear dependence of the ablation depth on the pulse number is observed up to a depth of about 803 nm at 6.0 μJ and 20 pulses. In all the above-mentioned cases, the calculation results are in better agreement with experimental measurements than conventional TTM or other material removal schemes, validating the accuracy of the proposed model.

Peculiarities of exciton formation in 2D semiconductor nanostructures induced by quantum electromagnetic field under nonlinear self-phase modulation

Specific features of the excitation of a 2D semiconductor nanosystem by non-classical light in a solid state micro-resonator are found under the impact of the Kerr phase nonlinearity in the cavity. Different regimes of excitation are revealed in dependence on the efficiency of the nonlinearity. A negative impact of the nonlinear self-phase modulation on the excitation is found to be compensated by proper choice of the field frequency detuning. The possibility to controllably enhance a certain excitation channel by varying field frequency detuning is demonstrated and the value of the optimal detuning is found analytically. The effect of transfer of non-classical features from the field to the electronic subsystem is revealed. The formation of the photon-like non-classical excitonic states is demonstrated. The obtained results seem to be a basis for the creation of the light–matter interface and development of quantum information algorithms in solid state nanosystems.

THERMOPHYSICAL PROPERTIES OF Al–Ni–Co–R (R = Sm, Tb) ALLOYS IN CRYSTALLINE AND LIQUID STATES

Experimental investigations of density and electrical resistivity of Al86Ni6Co2R6 (R = Sm, Tb) alloys were carried out in a wide temperature range, including crystalline and liquid states. Density was measured by gamma-penetrating method, and electrical resistance – by contactless method in rotating magnetic field. The solidus and liquidus temperatures were determined, the coefficients of volume expansion and the relative changes in density and resistivity during melting were calculated. The molar volumes of the alloys were calculated. It was found that the alloys are characterized by a wide two-phase zone where density and resistivity dependences show nonlinear behavior. At liquidus temperature an abrupt increase in density and a decrease in electrical resistivity were found. It has been established that terbium increases density of the alloys and reduces their resistivity more than samarium. In liquid phase at temperatures below T = 1300–1350 K density hysteresis was detected, and its absence on resistivity curves was shown. This may indicate the processes of large-scale inhomogeneities decay that do not cause changes in the electronic subsystem of the alloys but play a significant role in amorphization. The revealed features of the properties will make it possible to optimize the process of melts preparing before rapid quenching in order to obtain high-quality amorphous and nanocrystalline samples.

Characterization of two electronic subsystems in cuprates through optical conductivity

Understanding the physical properties of unconventional superconductors as well as of other correlated materials presents a formidable challenge. Their unusual evolution with doping, frequency, and temperature has frequently led to non-Fermi-liquid (non-FL) interpretations. Optical conductivity is a major challenge in this context. Here, the optical spectra of two archetypal cuprates, underdoped ${\mathrm{HgBa}}_{2}{\mathrm{CuO}}_{4+\ensuremath{\delta}}$ and optimally doped ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$, are interpreted based on the standard Fermi-liquid (FL) paradigm. At both dopings, perfect frequency-temperature FL scaling is found to be modified by the presence of a second, gapped electronic subsystem. This non-FL component emerges as a well-defined mid-infrared spectral feature after the FL contribution, determined independently by transport, is subtracted. Temperature, frequency, and doping evolution of the MIR feature identify a gapped rather than dissipative response. In contrast, the dissipative response is found to be relevant for pnictides and ruthenates. Such an unbiased FL/non-FL separation is extended across the cuprate phase diagram, capturing all the key features of the normal state and providing a natural explanation why the superfluid density is attenuated on the overdoped side. Thus, we obtain a unified interpretation of optical responses and transport measurements in all analyzed physical regimes and all analyzed compounds.

Selective Light Measurement in the Control of Reference LED Sources.

This paper describes an original adaptive multispectral LED light source that utilizes miniature spectrometer to control its flux in real time. Current measurement of the flux spectrum is necessary in high-stability LED sources. In such cases, it is important the spectrometer work effectively with the system that controls the source and the whole system. Therefore, as important as flux stabilization is the integration of the integrating sphere-based design with the electronic module and power subsystem. Since the problem is interdisciplinary, the paper mainly focuses on presenting the solution of the flux measurement circuit. In particular, the proprietary way of operating the MEMS optical sensor as a real-time spectrometer was proposed. Then, the implementation of the sensor handling circuit, which determines the spectral measurements accuracy and thus the output flux quality, is described. Also presented is the custom method of coupling the analog part of the flux measurement path with the analog-to-digital conversion system and the control system based on the FPGA. The description of the conceptual solutions was supported by the results of simulation and laboratory tests at selected points of the measurement path. The presented concept allows to build adaptive LED light sources in the spectral range from 340 nm to 780 nm with adjustable spectrum and flux value, with electrical power up to 100 W, with adjustable flux value in the range of 100 dB, operating in constant current or pulsed mode.

Why and how could an aliphatic bridge allow for a long-range photoinduced charge separation in Tröger’s bases derivatives

Tröger’s bases (TBs) have shown great potential to be used in different fields of science, such as biology, organic synthesis, photoelectronic applications, among others. As we have recently shown, a series of asymmetrically substituted Tröger’s base derivatives showed unexpected pull–push behavior. The aliphatic diazocine heterocycle which connect an electron donor and an electron acceptor moiety efficiently couples both electronic subsystems as if it were a typical π-conjugated linker. A thorough computational study was intended to shed light on the origin of the observed photophysical properties. A modified version of the CAM-B3LYP functional yielded an accurate prediction of the absorption and emission spectra of these species. In contrast, range-corrected and classical hybrid approaches showed too high and remarkably too low excited states energies, respectively.Unlike the typical π-linked donor/acceptor systems, a threshold was found in the redox gap of the centers in order to obtain a full charge separation. The role of the aliphatic bridge was found to be related to the unusual topology of the frontier orbitals involved, to the tension and particular molecular shape of the Tröger bicycle and to a contribution due to homoconjugation as well. Calculations on the actual Tröger derivatives and specific models were able to quantify the magnitude of the different contributions that make possible the charge separation.

The Modeling of Self-Consistent Electron–Deformation–Diffusion Effects in Thin Films with Lattice Parameter Mismatch

In our work, the model of self-consistent electron–deformation–diffusion effects in thin films grown on substrate with the mismatch of lattice parameters of the contacting materials is constructed. The proposed theory self-consistently takes into account the interaction of the elastic field (created by the mismatch of lattice parameters of the film and the substrate, and point defects) with the diffusion processes of point defects and the electron subsystem of semiconductor film. Within the framework of the developed model, the spatial distribution of deformation, concentration of defects, conduction electrons and electric field intensity is investigated, depending on the value of the mismatch, the type of defects, the average concentrations of point defects and conduction electrons. It is established that the coordinate dependence of deformation and the concentration profile of defects of the type of stretching (compression) centers, along the axis of growth of the strained film, have a non-monotonic character with minima (maxima), the positions of which are determined by the average concentration of point defects. It is shown that due to the electron–deformation interaction in film with a lattice parameter mismatch, the spatial redistribution of conduction electrons is observed and n-n+ transitions can occur. Information about the self-consistent spatial redistribution of point defects, electrons and deformation of the crystal lattice in semiconductor materials is necessary for understanding the problems of their stability and degradation of nano-optoelectronic devices operating under conditions of intense irradiation.

Factorized Electron-Nuclear Dynamics with an Effective Complex Potential.

We present a quantum dynamics approach for molecular systems based on wave function factorization into components describing the light and heavy particles, such as electrons and nuclei. The dynamics of the nuclear subsystem can be viewed as motion of the trajectories defined in the nuclear subspace, evolving according to the average nuclear momentum of the full wave function. The probability density flow between the nuclear and electronic subsystems is facilitated by the imaginary potential, derived to ensure a physically meaningful normalization of the electronic wave function for each configuration of the nuclei, and conservation of the probability density associated with each trajectory in the Lagrangian frame of reference. The imaginary potential, defined in the nuclear subspace, depends on the momentum variance in the nuclear coordinates averaged over the electronic component of the wave function. An effective real potential, driving the dynamics of the nuclear subsystem, is defined to minimize motion of the electronic wave function in the nuclear degrees of freedom. Illustration and the analysis of the formalism are given for a two-dimensional model system of vibrationally nonadiabatic dynamics.

Stress sensitivity origin of extended defects production under coupled irradiation and mechanical loading

The production of extended and mechanically highly consequential defects are investigated under concurrent driving forces of irradiation and stress. By using two-temperature model to account for realistic exchange of energy between the electronic subsystem and the atomic subsystem during cascades, and by controlling mechanical loading in the principal stress space to remove the dependance on a specific coordinate system, we build stress sensitivity maps for various types of irradiated dislocations. Frank loops are discovered to be dictated by volumetric strains, while Shockley partials are sensitive to volume-conserving shear loads. By tracking the microstructural evolutions during coupled irradiation and external loading, and by scrutinizing the temporal-spatial variation of local von Mises stresses near the center-collision region, the underlying mechanisms responsible for those different responses/sensitivities are elucidated. The implications of these findings in regard to a new strategy to control microstructural defects and materials performance are also discussed.

Visualization of Swift Ion Tracks in Suspended Local Diamondized Few-Layer Graphene.

In the present study we investigated the nanostructuring processes in locally suspended few-layer graphene (FLG) films by irradiation with high energy ions (Xe, 26-167 MeV). For such an energy range, the main channel of energy transfer to FLG is local, short-term excitation of the electronic subsystem. The irradiation doses used in this study are 1 × 1011-5 × 1012 ion/cm2. The structural transformations in the films were identified by Raman spectroscopy and transmission electron microscopy. Two types of nanostructures formed in the FLG films as a result of irradiation were revealed. At low irradiation doses the nanostructures were formed preferably at a certain distance from the ion track and had the form of 15-35 nm "bunches". We assumed that the internal mechanical stress that arises due to the excited atoms ejection from the central track part creates conditions for the nanodiamond formation near the track periphery. Depending on the energy of the irradiating ions, the local restructuring of films at the periphery of the ion tracks can lead either to the formation of nanodiamonds (ND) or to the formation of AA' (or ABC) stacking. The compressive strain value and pressure at the periphery of the ion track were estimated as ~0.15-0.22% and ~0.8-1.2 GPa, respectively. The main novel results are the first visualization of ion tracks in graphene in the form of diamond or diamond-like rings, the determination of the main condition for the diamond formation (the absence of a substrate in combination with high ion energy), and estimates of the local strain at the track periphery. Generally, we have developed a novel material and have found how to control the film properties by introducing regions similar to quantum dots with the diamond interface in FLG films.

Topological Defects Created by Gamma Rays in a Carbon Nanotube Bilayer.

Graphene sheets are a highly radiation-resistant material for prospective nuclear applications and nanoscale defect engineering. However, the precise mechanism of graphene radiation hardness has remained elusive. In this paper, we study the origin and nature of defects induced by gamma radiation in a graphene rolled-up plane. In order to reduce the environmental influence on graphene and reveal the small effects of gamma rays, we have synthesized a novel graphene-based nanocomposite material containing a bilayer of highly aligned carbon nanotube assemblies that have been decorated by organometallic compounds and suspended on nanoporous Al2O3 membranes. The bilayer samples were irradiated by gamma rays from a 137Cs source with a fluence rate of the order of 105 m-2s-1. The interaction between the samples and gamma quanta results in the appearance of three characteristic photon escape peaks in the radiation spectra. We explain the mechanism of interaction between the graphene sheets and gamma radiation using a pseudo-Majorana fermion graphene model, which is a quasi-relativistic N=3-flavor graphene model with a Majorana-like mass term. This model admits the existence of giant charge carrier currents that are sufficient to neutralize the impact of ionizing radiation. Experimental evidence is provided for the prediction that the 661.7-keV gamma quanta transfer enough energy to the electron subsystem of graphene to bring about the deconfinement of the bound pseudo-Majorana modes and involve C atoms in a vortical motion of the electron density flows in the graphene plane. We explain the radiation hardness of graphene by the topological non-triviality of the pseudo-Majorana fermion configurations comprising the graphene charge carriers.

Dissipation losses limiting first-order phase transition materials in cryogenic caloric cooling: A case study on all-d-metal Ni(-Co)-Mn-Ti Heusler alloys

Ni-Mn-based Heusler alloys, in particular all-d-metal Ni(-Co)-Mn-Ti, are highly promising materials for energy-efficient solid-state refrigeration as large multicaloric effects can be achieved across their magnetostructural martensitic transformation. However, no comprehensive study on the crucially important transition entropy change Δst exists so far for Ni(-Co)-Mn-Ti. Here, we present a systematic study analyzing the composition and temperature dependence of Δst. Our results reveal a substantial structural entropy change contribution of approximately 65 J(kgK)-1, which is compensated at lower temperatures by an increasingly negative entropy change associated with the magnetic subsystem. This leads to compensation temperatures Tcomp of 75 K and 300 K in Ni35Co15Mn50-yTiy and Ni33Co17Mn50-yTiy, respectively, below which the martensitic transformations are arrested. In addition, we simultaneously measured the responses of the magnetic, structural and electronic subsystems to the temperature- and field-induced martensitic transformation near Tcomp, showing an abnormal increase of hysteresis and consequently dissipation energy at cryogenic temperatures. Simultaneous measurements of magnetization and adiabatic temperature change ΔTad in pulsed magnetic fields reveal a change in sign of ΔTad and a substantial positive and irreversible ΔTad up to 15 K at 15 K as a consequence of increased dissipation losses and decreased heat capacity. Most importantly, this phenomenon is universal, it applies to any first-order material with non-negligible hysteresis and any stimulus, effectively limiting the utilization of their caloric effects for gas liquefaction at cryogenic temperatures.

Decoherence and Its Role in Electronically Nonadiabatic Dynamics.

Decoherence is the tendency of a time-evolved reduced density matrix for a subsystem to assume a form corresponding to a statistical ensemble of states rather than a coherent combination of pure-state wave functions. When a molecular process involves changes in the electronic state and the coordinates of the nuclei, as in ultraviolet or visible light photochemistry or electronically inelastic collisions, the reduced density matrix of the electronic subsystem suffers decoherence, due to its interaction with the nuclear subsystem. We present the background necessary to conceptualize this decoherence; in particular, we discuss the density matrix description of pure states and mixed states, and we discuss pointer states and decoherence time. We then discuss how decoherence is treated in the coherent switching with decay of mixing algorithm and the trajectory surface hopping method for semiclassical calculations of electronically nonadiabatic processes.