Search Results (2,191)

This paper investigates the performance of a spacecraft equipped with a diffractive sail in a heliocentric mission scenario that requires phasing along a prescribed elliptical orbit. The diffractive sail represents an evolution of the more traditional reflective solar sail, which converts solar radiation pressure into thrust using a large reflective surface typically coated with a thin metallic film. In contrast, the diffractive sail proposed by Swartzlander leverages the properties of an advanced metamaterial-based film to generate a net transverse thrust even when the sail is Sun-facing, i.e., in a configuration that can be passively maintained by a suitably designed spacecraft. Specifically, this study considers a sail membrane covered with a set of electro-optically controlled diffractive panels. These panels employ a (controlled) binary metamaterial arrayed grating to steer the direction of photons exiting the diffractive film. This control technique has recently been applied to achieve a circle-to-circle interplanetary transfer using a Sun-facing diffractive sail. In this work, an optimal control law is employed to execute a rapid phasing maneuver along an elliptical heliocentric orbit with specified characteristics, such as those of Earth and Mercury. The analysis also includes a limiting case involving a circular heliocentric orbit. For this latter scenario, a simplified and elegant control law is proposed based on a linearized form of the equations of motion to describe the heliocentric dynamics of the diffractive sail-based spacecraft during the phasing maneuver. Full article

Graphene’s exceptional carrier mobility and broadband absorption make it promising for ultrafast photodetection. However, its low optical absorption limits responsivity, while the absence of a bandgap results in high dark current, constraining the signal-to-noise ratio and efficiency. Although silicon (Si) photodetectors normally offer fabrication compatibility, their performance is severely hindered by interface trap states and optical shading. To overcome these limitations, we demonstrate an epitaxial graphene/n-Si heterojunction photodiode. This device utilizes graphene epitaxially grown on germanium integrated with a transferred Si thin film, eliminating polymer residues and interface defects common in transferred graphene. As a result, the fabricated photodetector achieves an ultralow dark current of 1.2 × 10⁻⁹ A, a high responsivity of 1430 A/W, and self-powered operation at room temperature. This work provides a strategy for high-sensitivity and low-power photodetection and demonstrates the practical integration potential of graphene/Si heterostructures for advanced optoelectronics. Full article

Potassium bromide (KBr) thin films were deposited by resistive thermal evaporation at substrate temperatures ranging from 50 °C to 250 °C to systematically elucidate the temperature-dependent evolution of their physical properties. Structural, morphological, and optical characteristics were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier transform infrared spectroscopy (FTIR). The results reveal a complex, non-monotonic response to temperature rather than a simple linear trend. As the substrate temperature increases, growth evolves from a mixed polycrystalline texture to a pronounced (200) preferred orientation. Morphological analysis shows that the film surface is smoothest at 150 °C, while the microstructure becomes densest at 200 °C. These structural variations directly modulate the optical constants: the refractive index attains its highest values in the 150–200 °C window, approaching that of bulk KBr. Cryogenic temperature (6 K) FTIR measurements further demonstrate that suppression of multi-phonon absorption markedly enhances the infrared transmittance of the films. Taken together, the data indicate that 150–200 °C constitutes an optimal process window for fabricating KBr films that combine superior crystallinity, low defect density, and high packing density. This study elucidates the temperature-driven structure–property coupling and offers valuable guidance for optimizing high-performance infrared and cryogenic optical components. Full article

Highly integrable silicon carbide (SiC) has emerged as a promising platform for photonic integrated circuits (PICs), offering a comprehensive set of material and optical properties that are ideal for the integration of nonlinear devices and solid-state quantum defects. However, despite significant progress in nanofabrication technology, the development of SiC on an insulator (SiCOI)-based photonics faces challenges due to fabrication-induced material optical losses and complex processing steps. An alternative approach to mitigate these fabrication challenges is the direct deposition of amorphous SiC on an insulator (a-SiCOI). However, there is a lack of systematic studies aimed at producing high optical quality a-SiC thin films, and correspondingly, on evaluating and determining their optical properties in the telecom range. To this end, we have studied a single-source precursor, 1,3,5-trisilacyclohexane (TSCH, C₃H₁₂Si₃), and chemical vapor deposition (CVD) processes for the deposition of SiC thin films in a low-temperature range (650–800 °C) on a multitude of different substrates. We have successfully demonstrated the fabrication of smooth, uniform, and stoichiometric a-SiCOI thin films of 20 nm to 600 nm with a highly controlled growth rate of ~0.5 Å/s and minimal surface roughness of ~5 Å. Spectroscopic ellipsometry and resonant micro-photoluminescence excitation spectroscopy and mapping reveal a high index of refraction (~2.7) and a minimal absorption coefficient (<200 cm⁻¹) in the telecom C-band, demonstrating the high optical quality of the films. These findings establish a strong foundation for scalable production of high-quality a-SiCOI thin films, enabling their application in advanced chip-scale telecom PIC technologies. Full article

Metal–Organic Frameworks (MOFs) have emerged as advanced porous crystalline materials due to their highly ordered structures, ultra-high surface areas, fine-tunable pore sizes, and massive chemical diversity. These features, arising from the coordination between an almost unlimited number of metal ions/clusters and organic linkers, have resulted in significant interest in MOFs for applications in gas storage, catalysis, sensing, energy, and biomedicine. Beyond their stand-alone properties and applications, recent research has increasingly explored the integration of MOFs with other substrates, particularly electrodes, polymeric thin films, and glass surfaces, to create synergistic effects that enhance material performance and broaden application potential. Coating MOFs onto these substrates can yield significant benefits, including, but not limited to, improved sensitivity and selectivity in electrochemical sensors, enhanced mechanical and separation properties in membranes, and multifunctional coatings for optical and environmental applications. This review provides a comprehensive and up-to-date summary of recent advances (primarily from the past 3–5 years) in MOF coating techniques, including layer-by-layer assembly, in situ growth, and electrochemical deposition. This is followed by a discussion of the representative applications arising from MOF-substrate coating and an outline of key challenges and future directions in this rapidly evolving field. This article aims to serve as a focused reference point for researchers interested in both fundamental strategies and applied developments in MOF surface coatings. Full article

CdTe nanocrystals (NCs) have emerged as a promising active layer for efficient thin-film solar cells due to their outstanding optical properties and simple processing techniques. However, the low hole concentration and high resistance in the CdTe NC active layer lead to high carrier recombination in the back contact. Herein, we developed a novel 2-iodothiophene as a wet etching solution to treat the surface of CdTe NC. We found that surface treatment using 2-iodothiophene leads to reduced interface defects and improves carrier mobility simultaneously. The surface properties of CdTe NC thin films after iodide salt treatment are revealed through surface element analysis, space charge limited current (SCLC) studies, and energy level investigations. The CdTe NC solar cells with 2-iodothiophene treatment achieved power conversion efficiency (PCE) of 4.31% coupled with a higher voltage than in controlled devices (with NH₄I-treated ones, 3.08% PCE). Full article

Background and Objectives: Posterior chamber phakic implantable contact lenses (Phakic-ICL) are widely used for refractive correction due to their efficacy and safety, including minimal corneal endothelial cell loss. The Collamer-based EVO+ Visian implantable contact lens (ICL), manufactured from Collamer, which is a blend of collagen and hydroxyethyl methacrylate (HEMA), has demonstrated excellent long-term biocompatibility and optical clarity. Recently, hydrophilic acrylic Phakic-ICLs, such as the Implantable Phakic Contact Lens (IPCL), have been introduced. This study investigated the material differences among Phakic-ICLs and their interaction with fibronectin (FN), which has been reported to adhere to intraocular lens (IOL) surfaces following implantation. The aim was to compare Collamer, IPCL, and LENTIS lenses (used as control) in terms of FN distribution and cell adhesion using a small number of explanted Phakic-ICLs. Materials and Methods: Three lens types were analyzed: a Collamer Phakic-ICL (EVO+ Visian ICL), a hydrophilic acrylic IPCL, and a hydrophilic acrylic phakic-IOL (LENTIS). FN distribution and cell adhesion were evaluated across different regions of each lens. An in vitro FN-coating experiment was conducted to assess its effect on cell adhesion. Results: All lenses demonstrated minimal FN deposition and cellular adhesion in the central optical zone. A thin FN film was observed on the haptics of Collamer lenses, while FN adhesion was weaker or absent on IPCL and LENTIS surfaces. Following FN coating, Collamer lenses supported more uniform FN film formation; however, this did not significantly enhance cell adhesion. Conclusions: Collamer, which contains collagen, promotes FN film formation. Although FN film formation was enhanced, the low cell-adhesive properties of HEMA resulted in minimal cell adhesion even with FN presence. This characteristic may contribute to the long-term transparency and biocompatibility observed clinically. In contrast, hydrophilic acrylic materials used in IPCL and LENTIS demonstrated limited FN interaction. These material differences may influence extracellular matrix protein deposition and biocompatibility in clinical settings, warranting further investigation. Full article

This paper serves as a comprehensive and practical resource to guide researchers in selecting suitable metals for use as photocathodes in radio-frequency (RF) and superconducting radio-frequency (SRF) electron guns. It offers an in-depth review of bulk and thin-film metals commonly employed in many applications. The investigation includes the photoemission, optical, chemical, mechanical, and physical properties of metallic materials used in photocathodes, with a particular focus on key performance parameters such as quantum efficiency, operational lifetime, chemical inertness, thermal emittance, response time, dark current, and work function. In addition to these primary attributes, this study examines essential parameters such as surface roughness, morphology, injector compatibility, manufacturing techniques, and the impact of chemical environmental factors on overall performance. The aim is to provide researchers with detailed insights to make well-informed decisions on materials and device selection. The holistic approach of this work associates, in tabular format, all photo-emissive, optical, mechanical, physical, and chemical properties of bulk and thin-film metallic photocathodes with experimental data, aspiring to provide unique tools for maximizing the effectiveness of laser cleaning treatment. Full article

Laser annealing of oxide functional thin films makes them compatible with substrates of various types, especially flexible materials. The effects of optical annealing on Ni-doped ZnO thin films were the subject of investigation and analysis in this study. Using pulsed laser deposition, we deposited polycrystalline ZnNiO films on sapphire and silicon substrates. The deposited film was annealed by laser heating. A continuous CO₂ laser was used for this purpose. The uniformly distributed long-wavelength radiation of the CO₂ laser can penetrate deeper from the surface of the thin film compared to short-wavelength lasers such as UV and IR lasers. After growth, optical post-annealing processes were applied to improve the conductive properties of the films. The crystallinity and surface morphology of the grown films and annealed films were analyzed using SEM, and their electrical parameters were evaluated using van der Pauw effect measurements. We used electrical conductivity measurements and investigated the photovoltaic properties of the ZnNiO film. After CO₂ laser annealing, changes in both the crystalline structure and surface appearance of ZnO were evident. Subsequent to laser annealing, the crystallinity of ZnO showed both change and degradation. High-power CO₂ laser annealing changed the structure to a mixed grain size. Surface nanostructuring occurred. This was confirmed by SEM morphological studies. After irradiation, the electrical conductivity of the films increased from 0.06 Sm/cm to 0.31 Sm/cm. The lifetime of non-equilibrium charge carriers decreased from 2.0·10⁻⁹ s to 1.2·10⁻⁹ s. Full article

100 nm thick TiO₂/TiN bilayers with varying thickness ratios were deposited via reactive sputtering of a Ti target in controlled oxygen and nitrogen atmospheres. Post-deposition annealing in air at 600 °C was performed to induce nitrogen diffusion through the oxygen-deficient TiO₂ layer. The resulting changes in morphology and chemical environment were investigated in detail using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV-Vis spectroscopy. Detailed TEM and XPS analyses have confirmed nitrogen diffusion across the TiO₂ layer, with surface nitrogen concentration and the ratio of interstitial to substitutional nitrogen dependent on the TiO₂/TiN mass ratio. Optical studies demonstrated modifications in optical constants and a reduction of the effective bandgap from 3.2 eV to 2.6 eV due to new energy states introduced by nitrogen doping. Changes in surface free energy induced by nitrogen incorporation showed a correlation to nitrogen doping sites on the surface, which had positive effects on overall photocatalytic activity. Photocatalytic activity, assessed through methylene blue degradation, showed enhancement attributed to nitrogen doping. Additionally, deposition of a 5 nm gold layer on the annealed sample enabled investigation of synergistic effects between nitrogen doping and gold incorporation, resulting in further improved photocatalytic performance. These findings establish the TiO₂/TiN bilayer as a versatile platform for supporting thin gold films with enhanced photocatalytic properties. Full article

In this study, we address the question of whether a waveguide with absorbing sidewalls can be considered pseudo free space and if the free-space transfer function is valid in such a medium. We test this hypothesis by applying a phase retrieval algorithm based on the free-space transfer function. First, optical measurements are carried out to measure the optical properties of a stack of thin films and select the parameters of simulations. Next, the propagation of light in a waveguide was simulated in COMSOL, and the phase of a wave was retrieved in MATLAB. Analysis was performed both for free-space conditions, and for a waveguide with absorbing sidewalls. The cross-correlation between the distributions of intensity under both conditions was about 0.40. The RMS error of the wave retrieved under free-space conditions was 0.378 rad, while that in the case of absorbing sidewalls was 0.323 rad, indicating successful retrieval. The successfully recovered phase of the input wave suggests that a waveguide with absorbing sidewalls can be approximated as pseudo free space and the free-space transfer function may be valid. These results may be used in future studies on how to shorten the phase retrieval of two-dimensional objects. Full article

Precise photovoltaic (PV) performance modeling is essential for optimizing system design, operational monitoring, and reliable power forecasting—yet spectral correction is often overlooked, despite its significant impact on energy yield uncertainty. This study employs the FARMS-NIT model to assess the impact of spectral irradiance on eight PV technologies across 79 European sites, grouped by Köppen–Geiger climate classification. Unlike previous studies limited to clear-sky or single-site analysis, this work integrates satellite-derived spectral data for both all-sky and clear-sky scenarios, enabling hourly, tilt-optimized simulations that reflect real-world operating conditions. Spectral analyses reveal European climates exhibit blue-shifted spectra versus AM1.5 reference, only 2–5% resembling standard conditions. Thin-film technologies demonstrate superior spectral gains under all-sky conditions, though the underlying drivers vary significantly across climatic regions—a distinction that becomes particularly evident in the clear-sky analysis. Crystalline silicon exhibits minimal spectral sensitivity (<1.6% variations), with PERC/PERT providing highest stability. CZTSSe shows latitude-dependent performance with ≤0.7% variation: small gains at high latitudes and losses at low latitudes. Atmospheric parameters were analyzed in detail, revealing that air mass (AM), clearness index (K_t), precipitable water (W), and aerosol optical depth (AOD) play key roles in shaping spectral effects, with different parameters dominating in distinct climate groups. Full article

Multilayer thin films composed of cobalt (Co), carbon (C), and chromium (Cr) possess promising electromagnetic properties, yet the combined Co–C–Cr system remains underexplored, particularly regarding its performance as a microwave absorber. Existing research has primarily focused on binary Co–C or Co–Cr compositions, leaving a critical knowledge gap in understanding how ternary multilayer architectures influence electromagnetic behavior. This study addresses this gap by investigating the structure, phase composition, and microwave absorption performance of Co–C–Cr multilayer coatings fabricated via magnetron sputtering onto porous silicon substrates. This study compares four-layer and eight-layer configurations to assess how multilayer architecture affects impedance matching, reflection coefficients, and absorption characteristics within the 8.2–12.4 GHz frequency range. Structural analyses using X-ray diffraction and transmission electron microscopy confirm the coexistence of amorphous and nanocrystalline phases, which enhance absorption through dielectric and magnetic loss mechanisms. Both experimental and simulated results show that increasing the number of layers improves impedance gradients and broadens the operational bandwidth. The eight-layer coatings demonstrate a more uniform absorption response, while four-layer structures exhibit sharper resonant minima. These findings advance the understanding of ternary multilayer systems and contribute to the development of frequency-selective surfaces and broadband microwave shielding materials. Full article

This paper focuses on the switching and modulation techniques of terahertz waves, develops ${\mathrm{VO}}_2$ thin-film materials with an SPP structure, and uses terahertz time-domain spectroscopy (THz-TDS) to study the semiconductor–metal phase transition characteristics of ${\mathrm{VO}}_2$ thin films, especially the photoinduced semiconductor–metal phase transition characteristics of silicon-based ${\mathrm{VO}}_2$ thin films. The optical modulation characteristics of silicon-based ${\mathrm{VO}}_2$ thin films to terahertz waves under different light excitation modes, such as continuous light irradiation at different wavelengths and femtosecond pulsed laser irradiation, were analyzed. Combining the optical modulation characteristics of silicon-based ${\mathrm{VO}}_2$ thin films with the filtering characteristics of SPP structures, composite structures of ${\mathrm{VO}}_2$ thin films with metal hole arrays, composite structures of ${\mathrm{VO}}_2$ thin films with metal block arrays, and silicon-based ${\mathrm{VO}}_2$ microstructure arrays were designed. The characteristics of this dual-function device were tested experimentally. The experiment proves that the ${\mathrm{VO}}_2$ film material with an SPP structure has a transmission rate dropping sharply from 32% to 1% under light excitation; the resistivity changes by more than six orders of magnitude, and the modulation effect is remarkable. By applying the SPP structure to the ${\mathrm{VO}}_2$ material, the material can simultaneously possess modulation and filtering functions, enhancing its optical performance in the terahertz band. Full article

Aluminum nitride (AlN) thin films were deposited on SiO₂ substrates by RF-magnetron sputtering at varying powers (110–140 W) and subsequently subjected to thermal annealing at 450 °C under nitrogen atmosphere. A comprehensive multi-technique investigation—including X-ray reflectometry (XRR), X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), optical profilometry, spectroscopic ellipsometry (SE), and electrical measurements—was performed to explore the physical structure, morphology, and optical and electrical properties of the films. The analysis of the film structure by XRR revealed that increasing sputtering power resulted in thicker, denser AlN layers, while thermal treatment promoted densification by reducing density gradients but also induced surface roughening and the formation of island-like morphologies. Optical studies confirmed excellent transparency (>80% transmittance in the near-infrared region) and demonstrated the tunability of the refractive index with sputtering power, critical for optoelectronic applications. The electrical characterization of Au/AlN/Al sandwich structures revealed a transition from Ohmic to trap-controlled space charge limited current (SCLC) behavior under forward bias—a transport mechanism frequently present in a material with very low mobility, such as AlN—while Schottky conduction dominated under reverse bias. The systematic correlation between deposition parameters, thermal treatment, and the resulting physical properties offers valuable pathways to engineer AlN thin films for next-generation optoelectronic and high-frequency device applications. Full article