Search Results (23)

Deployable thin-film antennas deliver large aperture gains and high stowage efficiency for spaceborne phased arrays but suffer wrinkling-induced planarity loss and radiation distortion. To bridge the lack of electromechanical coupling models for tensioned thin-film patch antennas, we present a unified framework combining structural deformation and electromagnetic simulation. We derive a coupling model capturing the increased bending stiffness of stepped-thickness membranes, formulate a wrinkling analysis algorithm to compute tension-induced displacements, and fit representative unit-cell deformations to a dual-domain displacement model. Parametric studies across stiffness ratios confirm the framework’s ability to predict shifts in pattern, gain, and impedance due to wrinkling. This tool supports the optimized design of wrinkle-resistant thin-film phased arrays for reliable, high-performance space communications. Full article

Laser ablation was used to successfully fabricate multiferroic bilayer thin films, composed of BaTiO₃ (BTO) and CoFe₂O₄ (CFO), on highly doped (100) Si substrates. This study investigates the influence of BaTiO₃ layer thickness (50–220 nm) on the films’ structural, magnetic, and dielectric properties. The dense, polycrystalline films exhibited a tetragonal BaTiO₃ phase and a cubic spinel CoFe₂O₄ layer. Structural analysis revealed compression of the CoFe₂O₄ unit cell along the growth direction, while the BaTiO₃ layer showed a tetragonal distortion, more pronounced in thinner BTO layers. These strain effects, attributed to the mechanical interaction between both layers, induced strain-dependent wasp-waisted behavior in the films’ magnetic hysteresis cycles. The strain effects gradually relaxed with increasing BaTiO₃ thickness. Raman spectroscopy and second harmonic generation studies confirmed BTO’s non-centrosymmetric ferroelectric structure at room temperature. The displayed dielectric permittivity dispersion was modeled using the Havriliak–Negami function combined with a conductivity term. This analysis yielded relaxation times, DC conductivities, and activation energies. The observed BTO relaxation time behavior, indicative of small-polaron transport, changed significantly at the BTO ferroelectric Curie temperature (Tc), presenting activation energies E_τ in the 0.1–0.3 eV range for T < Tc and E_τ > 0.3 eV for T > Tc. The BTO thickness-dependent Tc behavior exhibited critical exponents ν ~ 0.82 consistent with the 3D random Ising universality class, suggesting local disorder and inhomogeneities in the films. This was attributed to the composite structure of BTO grains, comprising an inner bulk-like structure, a gradient strained layer, and a disordered surface layer. DC conductivity analysis indicated that CoFe₂O₄ conduction primarily occurred through hopping in octahedral sites. These findings provide crucial insights into the dynamic dielectric behavior of multiferroic bilayer thin films at the nanoscale, enhancing their potential for application in emerging Si electronics-compatible magneto-electric technologies. Full article

In this study, thin films of Cerium Oxide CeO₂ were fabricated using the sol–gel technique and deposited onto a glass substrate. The annealing process was carried out at various temperatures ranging from 200 to 600 $°\mathrm{C}$ to investigate the structural, morphological, and optical properties of the films and their interrelations. X-ray diffraction (XRD) patterns revealed the crystalline nature of the prepared films, with film quality exhibiting enhancement with increasing annealing temperature. The average crystallite size, dislocation density, microstrain, and lattice constant were determined from XRD patterns. Higher annealing temperatures were found to increase the crystallite size values from 4.71 to 15.33 nm and decrease the dislocation density and microstrain of the unit cell. Scanning electron microscope (SEM) images illustrated the uniformity of the films, presenting a spheroid shape. Optical properties such as transmittance, absorbance, reflectance, the direct band gap, extinction coefficients, the refractive index, and optical conductivity were assessed using optical measurements. The direct optical band gap of the CeO₂ film was observed to decrease from 3.99 to 3.75 eV with increasing film thickness. Using the Wemple and DiDomenico (WDD) single-oscillator model, dispersion energy parameters were calculated based on the refractive index. The nonlinear optical properties of the CeO₂ thin films were evaluated using these dispersion energy parameters. The improvement of optical parameters holds significance in standardizing CeO₂ thin films for various optoelectronic applications. Full article

Multiple thick film samples of the ${\mathrm{Ag}}_c{\mathrm{Pd}}_{1-c}$ solid solution were prepared using physical vapour deposition over a borosilicate glass substrate. This synthesis technique allows continuous variation in stoichiometry, while the distribution of silver or palladium atoms retains the arrangement into an on-average periodic lattice with smoothly varying unit cell parameters. The alloy concentration and geometry were measured over a set of sample points, respectively, via energy-dispersive X-ray spectroscopy and via X-ray diffraction. These results are compared with ab initio total energy and electronic structure calculations based on density functional theory, and using the coherent potential approximation for an effective medium description of disorder. The theoretically acquired lattice parameters appear in qualitative agreement with the measured trends. The numerical study of the Fermi surface also shows a variation in its topological features, which follow the change in silver concentration. These were related to the electrical resistivity of the ${\mathrm{Ag}}_c{\mathrm{Pd}}_{1-c}$ alloy. The theoretically obtained variation exhibits a significant correlation with nonlinear changes in the resistivity as a function of composition. This combined experimental and theoretical study suggests the possibility of using resistivity measurements along concentration gradients as a way to gain some microscopic insight into the electronic structure of an alloy. Full article

Hybrid gold-based perovskite derivatives typically exhibit low optical bandgaps and high optical absorption coefficients, rendering them promising for photovoltaic applications. In this study, we successfully synthesized six new hybrid gold-based perovskite derivatives, namely [(C₆H₈N₂)(AuI₄)(AuI₂)](3AMPY), [(C₆H₁₄N₂)(AuI₄)(AuI₂)](3AMP), [(C₈H₁₂N)(AuI₄)](2PEAI), [(C₄H₁₄N₂O)(AuI₄)₂](OBA), [(C₆H₁₈N₂O₂)₃(AuI₄)₄(I₃)₂](DDA), and [(C₁₀H₂₆N₂O₃)(AuI₄)(I₃)](TOTA), through a straightforward and efficient hydrothermal method, achieving millimeter-sized single crystals. The structural analysis of the single crystals revealed variations in crystal structures arising from differences in constituent units and their spatial positioning relationships. First-principles calculations ascertained their high optical absorption coefficients in the visible light spectrum and indirect bandgap properties. Theoretical models indicated that the spectroscopic limited maximum efficiency (SLME) values of 3AMPY, 2PEAI, DDA, and TOTA approached approximately 30% in films of 0.5 μm thickness, signifying their potential candidacy as solar cell absorbers. Full article

Composite thin film absorbers show superior performance and have a wide range of applications. Obtaining a broadband composite thin film absorber is a challenge. In this work, we proposed a modeling of a broadband microwave composite thin film absorber based on the impedance matching theory and equivalent circuit model of the square loop. The unit cell of the absorber was composed of metal square loops with high magnetic conductivity deposited on the polyethylene substrate, and an FR-4 (epoxy glass cloth) substrate was the spacer substrate layer. The simulation results show that the absorptivity of the absorber reached more than 90% in the frequency range of 8.7–18 GHz for TE and TM waves under normal incidence. The thickness of the designed absorber was 2.05 mm (0.059 λ_max, λ_max corresponds to the maximum absorption wavelength). The simulation results show that the energy distribution in the proposed absorber was mainly localized in the top metal FSS layer due to the ohmic loss of metal, and the dielectric loss played a small role in the absorption of the absorber. Our work provides a design approach to improve the efficiency of optoelectronic devices and thermal detectors and has application prospects in radar and aircraft stealth applications. Full article

Accurate structure analysis of epitaxial perovskite thin films is a fundamental step towards the ability to tune their physical properties as desired. Precession-assisted electron diffraction tomography (PEDT) has proven to be an effective technique for performing ab initio structure solutions and refinements for this class of materials. As the film thickness or the region of interest (ROI) decrease in size, the capacity to collect PEDT data with smaller electron beams is a key parameter and ROI tracking becomes a major issue. To circumvent this problem, we considered here an alternative approach to acquiring data by combining PEDT with a scan over an area, extracting the intensities collected at different positions and using them to perform accurate structure refinements. As a proof of concept, a Scanning Precession Electron Tomography (SPET) experiment is performed on a 35 nm thick perovskite $PrV{O}_3$(PVO) film deposited on a $SrTi{O}_3$ (STO) substrate. This way, it was possible to detect small changes in the PVO structure along the film thickness, from the variation in unit cell parameters to atomic positions. We believe that SPET has the potential to become the standard procedure for the accurate structure analysis of ROIs as small as 10 nm. Full article

This study investigated the use of a pure copper seed layer to improve the adhesion strength and reduce the residual stress of electroplated copper films for heterojunction technology in crystalline solar cells. The experiment involved depositing a copper seed layer and an indium tin oxide (ITO) layer on textured silicon using sputtering. This resulted in the formation of a Cu(s)/ITO/Si structure. Following this step, a 10 µm thick copper layer was electroplated onto the Cu(s)/ITO/Si structure. Various characterization techniques were employed to evaluate the electroplated copper films’ microstructures, residual stress, and adhesion strength. The microstructures of the films were examined using a scanning transmission electron microscope (STEM), revealing a twin structure with a grain size of approximately 1 µm. The residual stresses of the as-deposited and annealed samples were measured using an X-ray diffractometer (XRD), yielding values of 76.4 MPa and 49.1 MPa, respectively. The as-deposited sample exhibited higher tension compared to the annealed sample. To assess the adhesion strength of the electroplated copper films, peel-off tests were conducted at a 90° angle with a constant speed of 30 mm/min. The peel force, measured in units of N/mm, was similar for both the as-deposited and annealed samples. Specifically, the peel force for electroplating copper on the copper seed layer on the ITO was determined to be 2.6 N/mm for the maximum value and 2.25 N/mm for the average value. This study demonstrated that using a pure copper seed layer during electroplating can improve adhesion strength and reduce residual stress in copper films for heterojunction technology in crystalline solar cells. These findings contribute to the development of more reliable and efficient solar-cell-manufacturing processes. Full article

The results of studying the morphological peculiarities of polycrystalline CdS_1−xSe_x films, obtained by screen printing, with well-formed grain boundaries of high structural quality are presented here. The developed method for screen printing provides the formation of polycrystalline films of a specified area per cycle, provided that there is a possibility for varying their thickness from tens of microns to units, which allows reducing the solar cell’s thickness and facilitating the process of its connection with the substrate. Therefore, the application of the films to a sitall substrate by screen printing contributes to reducing the product weight and facilitating the process of joining sheet materials intended for solar panels, namely attaching the lasing element to the substrate. The purpose of this work is to study the morphological peculiarities of polycrystalline CdS_1−xSe_x films obtained by an optimized screen-printing method and to create a model of their formation process. The structural and morphological peculiarities of the samples were studied using electron microscopy, AFM, XPA, and XFS. As a result of the work, based on the obtained experimental data, a model of the film formation process was developed. The model validity is justified by the conformity of the data of the experiment performed on its basis. Full article

We presented an angle-multiplexing low refractive index dielectric metasurface for terahertz absorption spectrum enhancement of lactose with high Q resonance properties. The unit cell structure of the acrylonitrile butadiene styrene (ABS) square structure is designed and optimized. The resonant peak shifts of the dielectric metasurface are analyzed by changing the incident angle of the terahertz wave. Then the α-lactose films with different thicknesses are added to investigate the enhancement effect. The resonant peak amplitude of the angle-multiplexing low refractive index dielectric metasurface absorption spectrum changes greatly with the absorption spectrum of the samples. The results illustrate that the enhanced absorption spectrum formed by the linked envelope can be up to 45 times stronger than that without the unit cell structures and also exhibits a high-quality factor. The proposed dielectric metasurface provides great potential in enhancing the terahertz absorption spectrum. Full article

Anodization of aluminum with a pre-patterned surface is a promising approach for preparing anodic aluminum oxide (AAO) films with defect-free pore arrangement. Although pronounced effects of crystallographic orientation of Al on the AAO structure have been demonstrated, all current studies on the anodization of pre-patterned aluminum consider the substrate as an isotropic medium and, thus, do not consider the azimuthal orientation of the pattern relative to the basis vectors of the Al unit cell. Here, we investigate the interplay between the azimuthal alignment of the pore nuclei array and the crystallographic orientation of aluminum. Al(100) and Al(111) single-crystal substrates were pre-patterned by a Ga focused ion beam and then anodized under self-ordering conditions. The thickness-dependent degree of pore ordering in AAO was quantified using statistical analysis of scanning electron microscopy images. The observed trends demonstrate that the preferred azimuthal orientation of pore nuclei rows coincides with the <110> directions in the Al unit cell, which is favorable for creating AAO with a high degree of pore ordering. In the case of an unspecified azimuthal orientation of the pore nuclei array, crystallography-affected disorder within the AAO structure occurs with increasing film thickness. Our findings have important implications for preparing defect-free porous films over 100 µm in thickness that are crucial for a variety of AAO applications, e.g., creating metamaterials and 2D/3D photonic crystals. Full article

We grew Sr_1-xLa_xCuO₂ thin films and SrCuO₂/Sr_0.9La_0.1CuO₂/SrCuO₂ trilayers by reflection high-energy diffraction-calibrated layer-by-layer molecular beam epitaxy, to study their electrical transport properties as a function of the doping and thickness of the central Sr_0.9La_0.1CuO₂ layer. For the trilayer samples, as already observed in underdoped SLCO films, the electrical resistivity versus temperature curves as a function of the central layer thickness show, for thicknesses thinner than 20 unit cells, sudden upturns in the low temperature range with the possibility for identifying, in the normal state, the T* and a T** temperatures, respectively, separating high-temperature linear behavior and low-temperature quadratic dependence. By plotting the T* and T** values as a function of T_C^onset for both the thin films and the trilayers, the data fall on the same curves. This result suggests that, for the investigated trilayers, the superconducting critical temperature is the important parameter able to describe the normal state properties and that, in the limit of very thin central layers, such properties are mainly influenced by the modification of the energy band structure and not by interface-related disorder. Full article

One-monolayer (ML) (thin) and 5-ML (thick) Si films were grown on the α-phase Si(111)√3 × √3R30°-Bi at a low substrate temperature of 200 °C. Si films have been studied in situ by reflection electron energy loss spectroscopy (REELS) and Auger electron spectroscopy, as a function of the electron beam incidence angle α and low-energy electron diffraction (LEED), as well as ex situ by grazing incidence X-ray diffraction (GIXRD). Scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS) were also reported. The REELS spectra, taken at the Si K absorption edge (~1.840 KeV), reveal the presence of two distinct loss structures attributed to transitions 1s→π* and 1s→σ* according to their intensity dependence on α, attesting to the sp²-like hybridization of the silicon valence orbitals in both thin and thick Si films. The synthesis of a silicon allotrope on the α-phase of Si(111)√3 × √3R30°-Bi substrate was demonstrated by LEED patterns and GIXRD that discloses the presence of a Si stack of 3.099 (3) Å and a √3 × √3 unit cell of 6.474 Å, typically seen for multilayer silicene. STM and STS measurements corroborated the findings. These measurements provided a platform for the new √3 × √3R30° Si allotrope on a Si(111)√3 × √3 R30°-Bi template, paving the way for realizing topological insulator heterostructures from different two-dimensional materials, Bi and Si. Full article

Superlattice-structured epitaxial thin films composed of Mn(5%)-doped BiFeO₃ and BaTiO₃ with a total thickness of 600 perovskite (ABO₃) unit cells were grown on single-crystal SrTiO₃ substrates by pulsed laser deposition, and their polarization and dielectric properties were investigated. When the layers of Mn-BiFeO₃ and BaTiO₃ have over 25 ABO₃ unit cells (N), the superlattice can be regarded as a simple series connection of their individual capacitors. The superlattices with an N of 5 or less behave as a unified ferroelectric, where the BaTiO₃ and Mn-BiFeO₃ layers are structurally and electronically coupled. Density functional theory calculations can explain the behavior of spontaneous polarization for the superlattices in this thin regime. We propose that a superlattice formation comprising two types of perovskite layers with different crystal symmetries opens a path to novel ferroelectrics that cannot be obtained in a solid solution system. Full article

Tin sulfide doped with copper (SnS:Cu) thin films were deposited on glass substrates by the ultrasonic spray pyrolysis (USP) technique at different concentration ratios (y = [Cu]/[Sn] = 0% (undoped), 2%, 5% and 10%). The aim of this work is to analyze the effect of copper on structural, morphological, and optoelectronic properties of SnS:Cu and discuss their possible application as an absorber layer in a solar cell structure proposed which is simulated using SCAPS software. X-ray diffraction (XRD) reveals an orthorhombic structure in the undoped sample and a cubic structure in doped ones. Raman spectroscopy suggests a possible unit cell size change due to the addition of Cu. Scanning electron microscopy (SEM) shows growth in grain density with an increasing y. Image analysis based on second-order features was used to discuss grain distribution. UV-VIS spectroscopy helps to find an increase of bandgap for the doped samples when copper concentration increases, going from 1.82 eV in the doped film y = 2% to 2.2 eV in the 10% doped samples. A value of 3.51 eV was found for the undoped sample y = 0%. A rise in both carrier concentration and mobility but a decrease in resistivity when y is increased was observed through the Hall–Van der Pauw technique. Simulations by SCAPS helped conclude that considering the material thickness, the SnS:Cu compound can be an alternative for implementation in the manufacturing of solar cells as an absorber layer since it is possible to obtain the optoelectronic properties necessary using the UPS economical technique. Full article