In this work, we develop a computational model for ultra-short laser-matter interaction performing detailed simulations of fs pulsed 800 nm laser heating of amorphous Ge2Sb2Te5 (alpha GST) films, which are at the heart of re-writable optical disks and the latest generation of non-volatile electronic memory. The developed model shows good agreement with related experimental data revealing various effects of ultra-fast dynamics of the electronic subsystem photoexcitation followed by relaxation, ultra-fast cooling, re-amorphization, and partial crystallization. First, our simulations show that additional generation of free electrons by impact ionization leads to a significant decrease of the effective absorption coefficient combined with a significant temperature decrease at the film surface and a simultaneous temperature increase inside the film. Second, our simulations demonstrate the nonlinear dynamics of the dielectric function and related optical parameters. Third, our computations of the post-relaxation ultra-fast cooling dynamics combined with the equations of Arrhenius-type kinetics for crystallization elucidate the thermally controlled mechanism for the experimentally observed generation of the amorphous-crystalline-amorphous nanostructure inside the bulk of the alpha GST film irradiated by a fs pulsed laser. Additionally, the generation of this nanostructure is associated with an order of magnitude difference between the attempt rates involved in phase transitions (i) in the near-surface melted part and (ii) in the bulk non-melted part of the film. Finally, our study shows that a single fs pulsed laser-induced melting does not lead to the crystallization on the surface of irradiated amorphous and crystalline GST films due to onset of post-relaxation high-rate cooling 10(11)-10(12) K/s.

Vanadium oxides are employed in a broad range of thermochromic, electronic, and catalytic applications. Using density functional theory (DFT), we investigate how hydrostatic and uniaxial compression tune the interlayer interactions and optoelectronic properties of orthorhombic V2O5. Both types of compression increase band dispersion, narrow the band gap, induce a redshift of the optical spectrum, and redistribute spectral weight among polarization directions, but to different extents. Noncovalent interaction analysis reveals localized regions of attraction and repulsion that modulate the spatial distribution of a weak (vdW-like) interlayer interaction background. We attribute this spatial distribution to electrostatic/polarization effects and the accompanying steric (Pauli) repulsion during interlayer approach. We further show that a truly gapless state cannot be achieved under pressure. These results provide insight into strain-engineered anisotropic optoelectronic characteristics in layered vanadium oxides.

Engineering new chalcogenide solids improves the desired functionality of the materials and may open the way for new applications. Here we discuss the preparation of As x S 100-x amorphous thin films modified with WS3 3 by the sol-gel method. We show that the formation of homogeneous, transparent, and stable n-propylaminebased solutions by mixing 0.02M As x S 100-x and 0.02M (NH4)2WS4 4 ) 2 WS 4 solutions is feasible for the As content in the chalcogenide glass precursor x <= 25 at.%. Above this limit, rapid and massive precipitation occurs in the solutions. We further demonstrate the preparation of amorphous thin films along the pseudo-binary AsS3- 3- WS3 3 tie-line and provide information about the role of WS3 3 on optical properties and the structure of tungsten- based chalcogenide thin films. Due to a significant etching contrast between annealed AsS3-WS3 3 -WS 3 thin films at 70 and 240 degrees C, we propose tungsten-based chalcogenide thin films as a suitable platform for application in wet-lithography.

The work provides a comprehensive explanation of the nature of chemical bonding through quantum chemical topology for multilayers of A(III)B(VI) compounds, such as GaSe, InSe, and GaTe, spanning pressures from 0 GPa to 30 GPa. These compounds are subjected to pressure orthogonal to the multilayers. Quantum chemical topological indices indicate that uniaxial pressure induces changes in hybridisation, leading to the disappearance of interlayer van der Waals forces. The distinct nature of the elements within the compounds results in different pressures at which van der Waals interactions disappear, as revealed by non-covalent interaction analysis. The presence or absence of chemical bonding is assessed by quantum topological indices as Espinosa indices, charge density distribution difference, and crystal orbital Hamilton populations. The varying changes in hybridisation, as indicated by topological indices, are corroborated by variations in the population of the electronic projected density of states. Ultimately, the type of chemical bonding is identified through the Espinosa indices in the field of Bader theory. This analysis confirms the existence of shared shell bonds between A(III) and B-VI atoms in vacuum that goes to an intermediate bond between shared and closed shells called the transition zone with increasing pressure. The implications and importance of this work extend beyond the presented results. It suggests that many other classes of two-dimensional materials may undergo phase transitions under uniaxial stress, leading to the formation of new phases with potentially interesting electronic properties.

A novel joint microscopy-calorimetry technique pioneered in the present thin film research was used to investigate the influence of the substrate type on the crystal growth in (GeS2)(0.1)(Sb2S3)(0.9) thin films crystallizing from the free surface. The explored temperature ranges were 205-285 and 210-350 degrees C for microscopy and calorimetry, respectively. Identical temperature dependences of the macroscopic and microscopic crystal growth rates, crystal growth activation energies (decreasing from 333 to 277 kJmol(-1)), and values of the Ediger's decoupling parameter (decreasing from 0.63 to 0.55) were obtained for as-deposited thin films on Kapton as well as white glass substrates, confirming the negligible influence of the substrate nature. However, both types of as-deposited films exhibited markedly accelerated crystal growth compared to the powdered thin film (scraped-off of the substrate), for which the formation rate of the crystalline phase was practically identical to the native behavior of bulk glass. This unambiguously confirms the marked influence of the crystal-growth-accelerating internal stresses being built up during the heating of the thin film firmly attached to the substrate, where each of the two materials has a different thermal expansion coefficient. The unmatched accuracy and resolution of the joint microscopy-calorimetry approach were demonstrated, with similar subtle intrinsic trends in the crystal growth behavior being recognized by both techniques. Future prospects of the simultaneous in situ polarization microscopy measurements of crystal growth in the as-deposited thin films were introduced and discussed.

Reducing the thickness of semiconductors to the limit of a few monolayers often leads to emergence of new properties. In this work, the thickness dependence of the band gap of cadmium telluride slabs in both the sphalerite phase and in the inverted phase is studied using the density functional theory method. The sphalerite phase is characterized by Cd–Te–Cd–Te alternating atomic planes, while in the inverted phase the order of planes is Te–Cd–Cd–Te. It is shown that using slabs with a thickness of one to several monolayers variable-gap structures can be fabricated.

Thermal processes play a crucial role in a variety of applications ranging from thermoelectrics, to thermal barrier coatings for turbines to memory devices, where materials with low thermal conductivity κ are essential for energy savings. By comparing two phase‐change materials, and , that have very similar thermal conductivities despite very different structures and bond strengths, it is argued that their phonon‐glass electron‐crystal properties stem from randomly oriented nonbonding lone–pair orbitals subtended at chalcogen atoms surrounding intrinsic vacancies.

Engineering new chalcogenide solids improves the desired functionality of the materials and may open the way for new applications. Here we discuss the preparation of AsxS100−x amorphous thin films modified with WS3 by the sol–gel method. We show that the formation of homogeneous, transparent, and stable n-propylamine-based solutions by mixing 0.02M AsxS100−x and 0.02M (NH4)2WS4 solutions is feasible for the As content in the chalcogenide glass precursor x ≤ 25 at.%. Above this limit, rapid and massive precipitation occurs in the solutions. We further demonstrate the preparation of amorphous thin films along the pseudo-binary AsS3- WS3 tie-line and provide information about the role of WS3 on optical properties and the structure of tungsten-based chalcogenide thin films. Due to a significant etching contrast between annealed AsS3− WS3 thin films at 70 and 240∘C, we propose tungsten-based chalcogenide thin films as a suitable platform for application in wet-lithography.

Despite a large amount of theoretical and experimental work performed so far, the search of phase change materials (PCMs) is done with use of numerical modeling. However, it is not fully clear how and why the phase change translates into the optical contrast. In this work, we argue that a key prerequisite for a material to have a pronounced difference in optical properties between crystalline and glassy phases of PCM is the similar contrast between the observed crystalline and (may be experimentally inaccessible) parent crystalline polymorph of the glassy phase. To illustrate this claim, we report a comparison of dynamic dielectric function of zinc-blende (α-ZnS), CsCl, and rock-salt (NaCl) phases of the binaryAIVBVIPCM exemplified by the well known GeTe prototype compound with experimental data and supply a theoretical explanation to the observed behavior based on topological properties of the Fermi surfaces appearing in the protoptypic 'degenerate' crystals with A = B having the same local structure as the parent polymorphs and derived from simple analytical model. By this, we arrive to a qualitative rather than purely numeric guidance for possible search of the novel phase-change materials.

Antiangiogenic therapy (AAT) is an indirect oncological modality that is aimed at the disruption of cancer cell nutrient supply. Invasive tumors have been shown to possess inherent resistance to this treatment, while compactly growing benign tumors react to it by shrinking. It is generally accepted that AAT by itself is not curative. This study presents a mathematical model of non-invasive tumor growth with a physiologically justified account of microvasculature alteration and the biomechanical aspects of importance during tumor growth and AAT. In the untreated setting, the model reproduces tumor growth with saturation, where the maximum tumor volume depends on the level of angiogenesis. The outcomes of the AAT simulations depend on the tumor size at the moment of treatment initiation. If it is close to the stable size of an avascular tumor grown in the absence of angiogenesis, then the tumor is rapidly stabilized by AAT. The treatment of large tumors is accompanied by the displacement of normal tissue due to tumor shrinkage. During this, microvasculature undergoes distortion, the degree of which depends on the displacement distance. As it affects tumor nutrient supply, the stable size of a tumor that undergoes AAT negatively correlates with its size at the beginning of treatment. For sufficiently large initial tumors, the long-term survival of tumor cells is compromised by competition with normal cells for the severely limited inflow of nutrients, which makes AAT effectively curative.

Since the energy spectrum of bismuth charge carriers is highly sensitive to mechanical deformations, studying their influence, leading to an increase or decrease in the overlap of actual extrema, on the transport properties of charge carriers in ultrathin bismuth films makes it possible to investigate the combination of manifestations of the quantum size effect and metallic surface states. In this work, the temperature dependencies of the electrical and galvanomagnetic properties of thin bismuth films (10-1250 nm) are studied under conditions of in-plane tensile and compressive deformation. Deformations are created as a result of the difference in the coefficients of thermal expansion of the film and substrate materials. Silicon with an oxidized surface, mica, and polished cleavage (111) CaF2 F 2 are used in order to create either tensile and compressive deformations. The presence of film deformations is confirmed by XRD. The magnitude of deformation is calculated based on the CTEs of the materials. The absence of mechanical stress relaxation or the formation of additional defects during temperature measurements is confirmed by the absence of hysteresis of properties in the range of 77-300 K. Based on the experimental results, the mobilities and concentration of charge carriers are calculated within the framework of the two-band model. As the film thickness decreases to less than 100 nm, an increase in the charge carrier concentration is observed, which is associated with metallic surface states. It is shown that the magnitude of the effect of deformation on the concentration of charge carriers in films of all thicknesses remains unchanged.

Engineering new chalcogenide solids improves the desired functionality of the materials and may open the way for new applications. Here we discuss the preparation of AsxS100−x amorphous thin films modified with WS3 by the sol–gel method. We show that the formation of homogeneous, transparent, and stable n-propylamine-based solutions by mixing 0.02M AsxS100−x and 0.02M (NH4)2WS4 solutions is feasible for the As content in the chalcogenide glass precursor x ≤ 25 at.%. Above this limit, rapid and massive precipitation occurs in the solutions. We further demonstrate the preparation of amorphous thin films along the pseudo-binary AsS3- WS3 tie-line and provide information about the role of WS3 on optical properties and the structure of tungsten-based chalcogenide thin films. Due to a significant etching contrast between annealed AsS3− WS3 thin films at 70 and 240∘C, we propose tungsten-based chalcogenide thin films as a suitable platform for application in wet-lithography.

Due to the dependence of the magnetic susceptibility of nanofluid on temperature, magnetic nanofluid is able to move in a nonuniform temperature field and an external magnetic field. In a passive cooling system based on the thermomagnetic effect, the coolant can move without the use of a pump. Here we demonstrate the principle of operation of a brand-new passive cooling system, where the convective flow of a magnetic nanofluid is driven by the combined action of thermo-osmosis and magnetic force. Therein lies the fundamental difference between the passive cooling system proposed here and the previously known systems, where the movement of ferrofluid is due to the action of the thermomagnetic effect. Based on nonequilibrium thermodynamics, a phenomenological model is proposed to describe the motion of a magnetic nanofluid in a channel in nonuniform temperature and magnetic fields. In the experimental study, the motion of ferrofluid Fe3O4 in the micro-channel is analyzed with variations in temperature, temperature gradient, channel thickness, and nanoparticle concentration. It is shown that in a non-uniform temperature field water-based ferrofluid moves in the direction of increasing temperature, while tridecane-based ferrofluid moves in the direction of decreasing it. If the thickness of the micro-channel exceeds a certain critical value, then the movement of ferrofluid under the influence of thermo-osmosis degenerates. It has been established that with an increase in concentration of nanoparticles the velocity of ferrofluid motion decreases due to the opposite direction of nanoparticle motion under the action of thermophoresis and the motion of liquid under the action of thermo-osmosis.

Structural transformation under laser irradiation in nanosized amorphous Ge2Sb2Te5 films modified with silver (Ge2Sb2Te5) is investigated herein. Films with thickness of ~ 100 nm were obtained by ion-plasma radio-frequency magnetron sputtering of a Ge2Sb2Te5-Ag combined polycrystalline target in an argon atmosphere. The silver concentration in the films was varied up to 12.3 at.%. The structure of amorphous films under laser irradiation was assessed in situ by Raman spectroscopy. The results showed that in the Ge2Sb2Te5 and Ge2Sb2Te5 films, under the action of laser irradiation, a phase transition occurred from an amorphous to a crystalline state. A phenomenon was observed in the phase transition in the Ge2Sb2Te5 films featuring the absence of an intermediate phase with a cubic structure (fcc) under the transition from the amorphous phase to the final phase with a stable hexagonal structure (hcp) at a certain concentration of Ag (5.5 and 12.3 at.%) and irradiation energy (1.6 mW). The discovery of this feature of the phase transition in Ge2Sb2Te5 films, which is controlled by the Ag concentration and irradiation power, is important for both the implementation of multilevel information recording and increased recording speed.

Two-dimensional (2D) van der Waals (vdW) AIIIBVI semiconductor materials, such as InSe and GaSe, are of considerable interest due to their potential use in various microelectronics applications. The range of properties of materials of this class can be extended further through the use of quasi-binary alloys of the InSe(Te)-GaSe(Te) type. In this work, we study the effect of compositional and structural disorder in 2D In(Ga)Se(Te) on the band structure and electronic properties using first principles modeling. The results for In(Ga)Se demonstrate a noticeable decrease in the band gap for structures with a random distribution of indium and gallium cations, while for In(Ga)Te with a random cation distribution, metallization occurs. Changes in the compositional arrangement of chalcogens (there can be either the same or different atoms on each side of the vdW gap) lead to pronounced changes in the band gap, but no significant changes in topology are observed. In addition, a significant effect of the distance between the layers on the band gap under compression along the c axis was found for both alloys under study. An important point of our study is that van der Waals gap engineering is a very powerful tool to control the properties of 2D materials and its alloys.

In this paper, the complex dynamics of the pulsating regime of combustion waves propagation is numerically investigated within the Zel’dovich–Barenblatt–Dold model with two-step chain-branching reaction mechanism. It is shown that there exists a remarkable similarity in the dynamics of oscillations in this system and one-dimensional discrete-time maps such as the logistic map. In particular, both systems exhibit the period doubling route to chaos and the appearance of windows of stability as the bifurcation parameter is increased. For the first time for a model of combustion wave propagation the sequence of windows of stability is demonstrated and classified. Nevertheless, as the activation energy, which is taken as a bifurcation parameter, reaches a critical value corresponding to the dynamical quenching scenario the dynamics of the flame oscillations becomes multidimensional and therefore it cannot be described by a one-dimensional map anymore. The effect of the heat losses is also studied and it is demonstrated that the number of windows of stability decreases, the order of their appearance changes and the dynamical quenching appears for smaller values of the activation energy as the heat losses are increased.

In this work, the size transformation of the TiO2 nanofraction from pharmaceutical grade E171 powder was studied during its transit through the gastrointestinal tract (GIT). It was shown that pharmaceutical-grade TiO2 powder contained about 0.68% (w/w) of particles smaller than 240 nm in diameter. In the observed GIT transit process the TiO2 nanoparticles were agglomerated up to 150–200 nm in simulated salivary fluid, with gradual agglomerate enlargement up to 300–600 nm and more than 1 micron in simulated gastric fluid. In the intestinal fluid the reverse process occurred, involving a decrease of agglomerates accompanied by the formation of a small fraction with ~50 nm average size. This fraction can be further involved in the histohematic transport process. The acidity degree (pH) and mineral composition of solutions, as well as the transit speed along the gastrointestinal tract, influence the nature of the particle transformation significantly. The rapid passing between the gastrointestinal tract sections creates conditions for a decrease in part of the TiO2 particles, up to 100 nm, and may be associated with the violation of the structural and functional integrity of the intestinal mucus layer.

Chalcogenide vitreous semiconductors (ChVSs) are of both fundamental and applied interest as materials in which reversible structural transformations within the amorphous phase and phase transitions to the crystalline state can be effectively implemented and various microstructures and nanostructures can be obtained as a result of external effects. One of the most promising methods for such ChVS modifications is the pulsed-laser-irradiation technique, which is a noncontact technology of local impact and makes it possible to change the structural, optical, and electrical properties of samples in a wide range. This includes methods based on the precision formation of a surface microrelief and nanorelief, and high contrast in the conductivity and refractive index between the crystalline and amorphous phases. This work reviews key publications on the structural modification of thin films from the most widely studied binary and ternary ChVS compounds (As 2 S 3 , As 2 Se 3 , Ge 2 Sb 2 Te 5 , etc.) to show the use of irradiated samples as metasurfaces for photonic applications and promising phase-change data storage.

Ultrathin solid slabs often have properties different from those of the bulk phase. This effect can be observed both in traditional three-dimensional materials and in van der Waals (vdW) solids in the few monolayer limit. In the present work, the band gap variation of the CdTe slabs, induced by their thickness, was studied by the density functional theory (DFT) method for the sphalerite (zinc-blende) phase and for the recently proposed inverted phase. The sphalerite phase has the Te-Cd-Te-Cd atomic plane sequence, while in the inverted phase Cd atoms are sandwiched by Te planes forming vdW blocks with the sequence Te-Cd-Cd-Te. Based on these building blocks, a bulk vdW CdTe crystal was built, whose thermodynamical stability was verified by DFT calculations. Band structures and partial densities of states for sphalerite and inverted phases were calculated. It was demonstrated for both phases that using slabs with a thickness of one to several monolayers for sphalerite phase (vdW blocks for inverted phase), structures with band gaps varying in a wide range can be obtained. The presented results allow us to argue that ultrathin CdTe can be a promising electronic material.