Search Results (19)

Accurately controlling the mechanical properties of silicon is essential for developing high-performance micro-devices and systems. In this study, we investigate the influence of phosphorus doping on the elastic constants of silicon across a wide temperature range using a combination of tight-binding simulations and deformation potential theory. The mechanical properties were derived using Keyes’s framework integrated with Fermi–Dirac statistics. The Goodwin–Skinner–Pettifor functional form was applied to estimate dopant-induced stress potentials and their effect on lattice stiffness. In particular, we investigated the change in elastic constants and their temperature dependence under ultra-high doping concentrations. The results show a monotonic decrease in c₁₁ and a non-monotonic increase in c₁₂ with both temperature and doping, while c₄₄ remains relatively unaffected, consistent with experimental and theoretical studies. These changes are attributed to anisotropic carrier redistribution among conduction band valleys and strain-modulated interactions between valleys. The novelty of this work lies in the explicit, atomistically informed calculation of deformation potential constants using tight-binding parameters specific to phosphorus doping in silicon, enabling the accurate prediction of temperature-dependent elastic constants and anisotropic mechanical behaviour in emerging microsystem applications. Full article

Highly (0002)-oriented Al_1−xSc_xN thin films with different Sc doping concentrations (x = 0, 0.2, 0.25, 0.3, and 0.43) were prepared via a magnetron sputtering system. The effects of Sc doping on the crystal structure and electrical property of the as-prepared thin films were investigated experimentally. The results of synchrotron radiation grazing-incidence wide-angle X-ray scattering (GIWAXS) and X-ray diffraction (XRD) demonstrated that the Sc³⁺ substitution for Al³⁺ induced asymmetric lattice distortion: the a-axis exhibited monotonic expansion (reaching 3.46 Å at x = 0.43) due to the larger atomic radius of Sc (~0.87 Å), while the c-axis attained a maximum value of 5.14 Å at x = 0.2 and subsequently contracted as the bond angle reduction became dominant. The dielectric constant increased to 34.67 (225% enhancement) at x = 0.43, attributed to the enhanced polarization of Sc-N bonds and interfacial charge accumulation effects. Simultaneously, the dielectric loss increased from 0.15% (x = 0) to 6.7% (x = 0.43). Leakage current studies revealed that high Sc doping (x = 0.43) elevated the leakage current density to 10⁻⁶ A/cm² under an electric field of 0.2 MV/cm, accompanied by a transition from Ohmic conduction to space-charge-limited current (SCLC) at a low electric field strength (<0.072 MV/cm). Full article

This study examines the effect of gallium doping on the phase transformation, transmission, and hardness of commercial multispectral-grade ZnS specimens exposed to Ga₂S₃ vapor. Using secondary ion mass spectrometry, we show that Ga diffusion extends into the subsurface down to several tens of microns. X-ray diffraction patterns reveal minimal to no precipitation of wurtzite, resulting in limited infrared transmission loss after treatment. We report a monotonic increase in Vickers surface microhardness with increasing Ga concentration, reaching values more than double those of untreated windows. Future work will focus on optimizing this process and evaluating its effectiveness in enhancing the durability of ZnS windows under harsh environmental conditions. Full article

Medium-fluence fast electron irradiation (10¹⁹ e/cm² to 10²⁰ e/cm²) or the changes in the praseodymium concentration in the range of 0.0 ≤ z ≤ 0.5 on the excess conductivity of YBa₂Cu₃O_7–δ single crystals ware investigated. These can lead to a wider range of the temperature interval of excess conductivity which narrows the interval of linearity in the ab plane. At fluences 0 ≤ Φ ≤ 6.5 × 10¹⁹ e/cm², there was a threefold increase in the transverse coherence length ξ_c(0) with an increase in Φ of more than four times as the praseodymium concentration increased to z ≈ 0.42. The two-dimensional–three-dimensional (2D–3D) crossover point shifted upward in temperature. Conversely, to irradiation with low fluences (Φ ≤ 10¹⁹ e/cm²) or low praseodymium doping (z ≤ 0.39), irradiation with medium fluences or high praseodymium doping led to a non-monotonic dependence of ξ_c(0) on the irradiation fluence, with characteristic maxima at Φ~(7–8) × 10¹⁹ e/cm² and z ≈ 0.42, likely due to the suppression of the superconducting characteristics. Full article

In this work, we primarily aimed to study the Nb(V) doping effect on the surface activity and optical and electrical properties of nanocrystalline TiO₂ obtained through flame-spray pyrolysis. Materials were characterized using X-ray diffraction, Raman spectroscopy and IR, UV and visible spectroscopy. The mechanism of surface reaction with acetone was studied using in situ DRIFTs. It was found that the TiO₂-Nb-4 material demonstrated a higher conversion of acetone at a temperature of 300 °C than pure TiO₂, which was due to the presence of more active forms of chemisorbed oxygen, as well as higher Lewis acidity of the surface. Conduction activation energies (E_act) were calculated for thin films based on TiO₂-Nb materials. The results of the MB photobleaching experiment showed a non-monotonic change in the photocatalytic properties of materials with an increase in Nb(V) content, which was caused by a combination of factors, such as specific surface area, phase composition, concentration of charge carriers as well as their recombination due to lattice point defects. Full article

This paper presents a Piezoelectric micromechanical ultrasonic transducer (PMUT) based on a Pt/ScAlN/Mo/SiO₂/Si/SiO₂/Si multilayer structure with a circular suspension film of scandium doped aluminum nitride (ScAlN). Multiphysics modeling using the finite element method and analysis of the effect of different Sc doping concentrations on the resonant frequency, the effective electromechanical coupling coefficient ($k_{\mathrm{e}\mathrm{f}\mathrm{f}}^2$) and the station sensitivity of the PMUT cell are performed. The calculation results show that the resonant frequency of the ScAlN-based PMUT can be above 20 MHz and its $k_{\mathrm{e}\mathrm{f}\mathrm{f}}^2$ monotonically rise with the increasing doping concentrations in ScAlN. In comparison to the pure AlN thin film-based PMUT, the static receiving sensitivity of the PMUT based on ScAlN thin film with 35% Sc doping concentration is up to 1.61 mV/kPa. Meanwhile, the static transmitting sensitivity of the PMUT is improved by 152.95 pm/V. Furthermore, the relative pulse-echo sensitivity level of the 2 × 2 PMUT array based on the Sc doping concentration of 35% AlN film is improved by 16 dB compared with that of the cell with the same Sc concentration. The investigation results demonstrate that the performance of PMUT on the proposed structure can be tunable and enhanced by a reasonable choice of the Sc doping concentration in ScAlN films and structure optimization, which provides important guidelines for the design of PMUT for practical applications. Full article

We investigated the magnetic properties of the antiferromagnetic (AFM) topological insulator MnBi${}_2$Te${}_4$ with a partial substitution of Mn atoms by non-magnetic elements (A${}^{\mathrm{IV}}$ = Ge, Pb, Sn). Samples with various element concentrations (10–80%) were studied using SQUID magnetometry. The results demonstrate that, for all substitutes the type of magnetic ordering remains AFM, while the Néel temperature (T${}_{\mathrm{N}}$) and spin-flop transition field (H${}_{\mathrm{SF}}$) decrease with an increasing A${}^{\mathrm{IV}}$ = Ge, Pb, Sn concentration. The rate of decrease varies among the elements, being highest for Pb, followed by Sn and Ge. This behavior is attributed to the combined effects of the magnetic dilution and lattice parameter increase on magnetic properties, most prominent in (Mn${}_{1-x}$Pb${}_x$)Bi${}_2$Te${}_4$. Besides this, the linear approximation of the experimental data of T${}_{\mathrm{N}}$ and H${}_{\mathrm{SF}}$ suggests higher magnetic parameters for pure MnBi${}_2$Te${}_4$ than observed experimentally, indicating the possibility of their non-monotonic variation at low concentrations and the potential for enhancing magnetic properties through doping MnBi${}_2$Te${}_4$ with small amounts of nonmagnetic impurities. Notably, the (Mn${}_{1-x}$Pb${}_x$)Bi${}_2$Te${}_4$ sample with 10% Pb substitution indeed exhibits increased magnetic parameters, which is also validated by local-probe analyses using ARPES. Our findings shed light on tailoring the magnetic behavior of MnBi${}_2$Te${}_4$-based materials, offering insights into the potential applications in device technologies. Full article

Density functional theory (DFT) and Monte Carlo (MC) simulations were performed to study the adsorption and distribution of Na ions on nitrogen-doped graphenes (NGs). DFT simulations revealed that both pyridinic and pyrrolic NGs enhanced Na adsorption even at higher Na concentrations by introducing electron-deficient vacancies. While Na ions tend to cluster on a pristine graphene, they separate when absorbed on pyridinic NGs due to stronger Na adsorption and Na-Na repulsion. Based on DFT energies, MC simulations were performed to study the distribution of Na on a pyridinic NG as a function of the pyridinic defect concentration and Na concentration. The average size of Na clusters decreases with increasing pyridinic defect concentration. The theoretical specific capacity increases monotonically as the pyridinic defect concentration is increased and reaches a maximum value at a concentration of ~7.5%. This theoretical study suggests that the pyridinic NGs hold promise as anode materials for sodium-ion batteries capable of enhancing Na adsorption, preventing Na clustering, and increasing the anode’s specific capacity. Full article

Germanene, with a wrinkled atomic layer structure and high specific surface area, showed high potential as an electrode material for supercapacitors. According to the first-principles calculation based on Density Functional Theory, the quantum capacitance of germanene could be significantly improved by introducing doping/co-doping, vacancy defects and multilayered structures. The quantum capacitance obtained enhancement as a result of the generation of localized states near the Dirac point and/or the movement of the Fermi level induced by doping and/or defects. In addition, it was found that the quantum capacitance enhanced monotonically with the increase of the defect concentration. Full article

The stacked single-unit cell Ba_1-xSr_xTiO₃ (BSTO) thin film designed by the high-throughput method is fabricated by layer-by-layer deposition by laser molecular beam epitaxy, and its ferroelectric and dielectric characteristics as a function of Sr concentration are comprehensively investigated. The permittivity of BSTO exhibits a monotonous increase by Sr with a plateau in the region of 14% < Sr < 85%. Meanwhile, at the low Sr doping regime, the piezoelectric response has been discovered, and the maximum piezoresponse and d₃₃ can reach approximately 139.05 pm and 88 pm/V once an appropriate Ba/Sr ratio is formed, exhibiting a coexistence of a dielectric property and giant piezoresponse. This effective piezoelectric constant d₃₃ value is significantly larger than the conventional chemical doping scenarios, suggesting that the intra-plane interaction is crucial for designing future promising dielectric and ferroelectric thin films via high-throughput technologies. Full article

Gallium(III) oxide is a promising functional wide-gap semiconductor for high temperature gas sensors of the resistive type. Doping of Ga₂O₃ with tin improves material conductivity and leads to the complicated influence on phase content, microstructure, adsorption sites, donor centers and, as a result, gas sensor properties. In this work, Ga₂O₃ and Ga₂O₃(Sn) samples with tin content of 0–13 at.% prepared by aqueous co-precipitation method were investigated by X-ray diffraction, nitrogen adsorption isotherms, X-ray photoelectron spectroscopy, infrared spectroscopy and probe molecule techniques. The introduction of tin leads to a decrease in the average crystallite size, increase in the temperature of β-Ga₂O₃ formation. The sensor responses of all Ga₂O₃(Sn) samples to CO and NH₃ have non-monotonous character depending on Sn content due to the following factors: the formation of donor centers and the change of free electron concentration, increase in reactive chemisorbed oxygen ions concentration, formation of metastable Ga₂O₃ phases and segregation of SnO₂ on the surface of Ga₂O₃(Sn) grains. Full article

Catalysts for visible-light-driven oxidative cleaning processes and antibacterial applications (also in the dark) were developed. In order to extend the photoactivity of titanium dioxide into the visible region, nitrogen-doped TiO₂ catalysts with hollow and non-hollow structures were synthesized by co-precipitation (NT-A) and sol–gel (NT-U) methods, respectively. To increase their photocatalytic and antibacterial efficiencies, various amounts of silver were successfully loaded on the surfaces of these catalysts by using a facile photo-deposition technique. Their physical and chemical properties were evaluated by using scanning electron microscopy (SEM), transmission electron microscopy–energy dispersive X-ray spectroscopy (TEM–EDS), Brunauer–Emmett–Teller (BET) surface area, X-ray diffraction (XRD), and diffuse reflectance spectra (DRS). The photocatalytic performances of the synthesized catalysts were examined in coumarin and 1,4-hydroquinone solutions. The results showed that the hollow structure of NT-A played an important role in obtaining high specific surface area and appreciable photoactivity. In addition, Ag-loading on the surface of non-hollow structured NT-U could double the photocatalytic performance with an optimum Ag concentration of 10⁻⁶ mol g⁻¹, while a slight but monotonous decrease was caused in this respect for the hollow surface of NTA upon increasing Ag concentration. Comparing the catalysts with different structures regarding the photocatalytic performance, silverized non-hollow NT-U proved competitive with the hollow NT-A catalyst without Ag-loading for efficient visible-light-driven photocatalytic oxidative degradations. The former one, due to the silver nanoparticles on the catalyst surface, displayed an appreciable antibacterial activity, which was comparable to that of a reference material practically applied for disinfection in polymer coatings. Full article

The scintillation and energy-storage properties of YAlO₃ (YAP) crystals doped with Sc³⁺ and La³⁺ isoelectronic dopants were investigated in this work. The YAP:Sc and YAP:La crystals were grown from the melt with a nominal Sc and La content in the 0.2–5.0 mol.% range using the novel micro-pulling-down method. We found that the segregation coefficient of Sc ions in YAP:Sc (0.2–1.0 mol.%) crystals is about of 0.35–0.4 and decreases to around 0.2 at Sc content of 5.0 mol.% when the segregation coefficient of La ions in YAP:La (1.0–5.0 mol.%) crystals is 0.008–0.01. The scintillation and stimulated luminescence phenomena, like thermo- and photoluminescence, were utilized for the property characterization of the studied materials. The cathodoluminescence and X-ray-excited luminescence were used for the imitation of scintillation in the YAP:Sc and YAP:La crystals. The influence of Sc³⁺ and La³⁺ dopant concentration on the CL and RL emission spectra, as well as the shape of the measured thermoluminescence (TL) glow-curves, was also investigated. The measured emission spectra showed dominant emission of Sc³⁺ and La³⁺ ions in the UV range. For this reason, the YAP:Sc and YAP:La crystals can be considered for creation of ultraviolet (UV)-emitting scintillators. For the undoped YAlO₃ crystals, the main TL emission peak occurs in a low-temperature range at 375 K. Meanwhile, even a small addition of dopants causes a strong suppression of luminescence of the YAP host and high-temperature peaks become dominant in the TL glow-curves of YAP:Sc and YAP:La crystals. Moreover, the amplitude of emission does not change monotonically with increasing dopant content. The kinetic parameters of emission were also evaluated, and the first-order behavior was confirmed in all cases. The dosimetric properties of investigated materials such as dose response, fading rate, and the lowest measurable dose are also discussed. The obtained results tend to suggest that the YAlO₃ perovskite host, apart from its application for the development of efficient scintillators, may also be considered as a promising matrix for the creation of energy-storage phosphors for dosimetric applications. Full article

Polyelectrolyte multilayers (PEM) obtained by layer-by-layer assembly can be doped with ionic liquid (IL) via the swelling of the films with IL solutions. In order to examine the mechanical properties of IL-containing PEM, we implement a Kelvin-Voigt model to obtain thickness, viscosity and elastic modulus from the frequency and dissipation shifts determined by a dissipative quartz crystal microbalance (QCM-D). We analyze the changes in the modeled thickness and viscoelasticity of PEI(PSS/PADMAC)₄PSS and PEI(PSS/PAH)₄PSS multilayers upon swelling by increasing the concentration of either 1-Ethyl-3-methylimidazolium chloride or 1-Hexyl-3-methylimidazolium chloride, which are water soluble ILs. The results show that the thickness of the multilayers changes monotonically up to a certain IL concentration, whereas the viscosity and elasticity change in a non-monotonic fashion with an increasing IL concentration. The changes in the modeled parameters can be divided into three concentration regimes of IL, a behavior specific to ILs (organic salts), which does not occur with swelling by simple inorganic salts such as NaCl. The existence of the regimes is attributed to a competition of the hydrophobic interactions of large hydrophobic ions, which enhance the layer stability at a low salt content, with the electrostatic screening, which dominates at a higher salt content and causes a film softening. Full article

To study the in situ doping effect upon monotonically increasing dopant concentration, a Bi₂Te₃ layer doped with Fe up to ~6.9% along the growth direction was fabricated by the molecular beam epitaxy (MBE) technique. Its resistance versus temperature curve displays a superconductivity transition at about 12.3 K. Detailed structural and chemical analysis via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS) reveal that this layer consists of two types of unexpected Fe-Te nanostructures: one is FeTe thin layer formed near the surface, and the other is FeTe₂ nanorod embedded in the Bi₂Te₃ layer. Based on the results of further electrical and magnetotransport studies, it is likely that the observed superconductivity originates from the interface between the FeTe nanostructure and the neighboring Bi₂Te₃ layer. We have addressed the formation mechanisms of the observed nanostructures, which is attributed to the strong reaction between Fe and Te atoms during the growth process. The findings of this study also provide an unusual approach to synthesizing nanostructures via heavy doping if the dopant element is strongly reactive with an element in the host matrix. Full article