Search Results (246)

The study investigates the influence of bias voltage on the structural and morphological properties of aluminum nitride AlN (002) thin films deposited on sapphire substrates via reactive magnetron sputtering for high-frequency surface acoustic wave (SAW) devices. The results indicate that applying a positive bias voltage (>0 V) yields AlN films with compact and uniform surfaces. As bias increases, the deposition rate initially rises before declining, while root–mean–square (RMS) roughness progressively decreases, reaching a minimum at 100 V, significantly enhancing surface quality. X-ray diffraction (XRD) analysis reveals enhanced (002) preferential orientation with increasing bias, indicating improved crystallinity. These findings demonstrate that optimized bias voltage not only refines surface morphology but also strengthens crystal alignment, particularly along the (002) plane, making AlN films highly suitable for high-frequency SAW applications, and provides data for the preparation of higher-quality AlN films. Full article

In this paper, various Ga₂O₃ films, including amorphous Ga₂O₃ films, β-Ga₂O₃, and α-Ga₂O₃ epitaxial films, have been nitridated and converted to single-crystalline GaN layers on the surface. Although the original Ga₂O₃ films are different, all the converted GaN layers exhibit the (002) preferred orientation and the porous morphologies. The ~200 µm GaN thick films have been grown on the nitridated Ga₂O₃ films using the halide vapor phase epitaxy (HVPE) method. Raman analysis indicates that all the HVPE-GaN films grown on nitridated Ga₂O₃ films are almost stress-free. An obvious GaN porous layer/Ga₂O₃ structure has been observed in the interface between GaN thick films and sapphire substrates. The porous GaN layers can be used as promising templates for the preparation of free-standing GaN substrates. 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

Gallium oxide (Ga₂O₃), as a wide-bandgap semiconductor material, is highly expected to find extensive applications in optoelectronic devices, high-power electronics, gas sensors, etc. However, the photoelectric properties of Ga₂O₃ still need to be improved before its devices become commercially viable. As is well known, doping is an effective method to modulate the various properties of semiconductor materials. In this study, Zn–N co-doped Ga₂O₃ films with various doping concentrations were grown in situ on sapphire substrates by atomic layer deposition (ALD) at 250 °C, followed by post-annealing at 900 °C. The post-annealed undoped Ga₂O₃ film showed a highly preferential orientation, whereas with the increase in Zn doping concentration, the preferential orientation of Ga₂O₃ films was deteriorated, turning it into an amorphous state. The surface roughness of the Ga₂O₃ thin films is largely affected by doping. As a result of post-annealing, the bandgaps of the Ga₂O₃ films can be modulated from 4.69 eV to 5.41 eV by controlling the Zn–N co-doping concentrations. When deposited under optimum conditions, high-quality Zn–N co-doped Ga₂O₃ films showed higher transmittance, a larger bandgap, and fewer defects compared with undoped ones. Full article

Background and Objectives: Conventional methods for removing cemented fixed prosthetic restorations (FPRs) are unreliable and lead to unsatisfactory outcomes. At their best, they allow the tooth to be saved at the expense of a laborious process that also wears down rotating tools and handpieces and occasionally results in abutment fractures. Restorations are nearly never reusable in any of these situations. Erbium-doped yttrium-aluminum-garnet (Er:YAG) and erbium-chromium yttrium-scandium-gallium-garnet (Er,Cr:YSGG) lasers casafely and effectively remove FPRs, according to scientific studiesre. This study sets out to examine the impact of Er:YAG laser radiation on the debonding of different ceramic restorations, comparing the behavior of various ceramic prosthetic restoration types under laser radiation action and evaluating the integrity of prosthetic restorations and dental surfaces exposed to laser radiation. Materials and Methods: The study included a total of 16 removed teeth, each prepared on opposite surfaces as abutments.y. Based on the previously defined groups, four types of ceramic restorations were included in the study: feldspathic (F), lithium disilicates (LD), layered zirconia (LZ), and monolithic zirconia (MZ). The thickness of the prosthetic restorations was measured at three points, and two different materials were used for cementation. The Er:YAG Fotona StarWalker MaQX laser was used to debond the ceramic FPR at a distance of 10 mm using an R14 sapphire tip with 275 mJ, 20 Hz, 5.5 W, with air cooling (setting 1 of 9) and water. After debonding, the debonded surface was visualized under electron microscopy. Results: A total of 23 ceramic FPRs were debonded, of which 12 were intact and the others fractured into two or three pieces. The electron microscopy images showed that debonding took place without causing any harm to the tooth structure. The various restoration types had the following success rates: 100% for the LZ and F groups, 87% for the LD group, and 0% for the MZ group. In terms of cement type, debonding ceramic FPRs cemented with RELYX was successful 75% of the time, compared to Variolink DC’s 69% success rate. Conclusions: In summary, the majority of ceramic prosthetic restorations can be successfully and conservatively debonded with Er:YAG radiation. Full article

Single sapphire crystals has been widely used in technology such as light emitting diodes, lasers, high-temperature and high-voltage devices, special windows, and optical systems, and grinding is an important process of their machining. In order to reveal the influence of the grinding wheel speed, grinding depth, and feed rate on the ground surface quality of sapphire crystals, a three-factor and five-level orthogonal experiment was designed and completed. Variance and range analysis was conducted on the experimental results using the surface roughness Ra and subsurface crack damage depth (SSD) as evaluation indicators, and optimized parameter combinations were explored. Furthermore, mathematical prediction models for the power regression of the Ra and SSD were established based on the experimental data. The research results indicate that within the range of the process parameters used in this experiment, the grinding process did not achieve the full ductile removal of the material. Some of the material was removed in a brittle mode, forming fractured pits on the ground surface, and median crack propagation occurred in the subsurface, forming a subsurface microcrack damage layer. The influence of the grinding parameters on the Ra and SSD showed a consistent trend, which was that the parameter with the greatest impact was the grinding wheel speed, followed by the feed rate and grinding depth. The Ra and SSD obtained under the optimized grinding parameter combination were 0.326 μm and 2.86 μm, respectively. The research results provide an experimental basis and guidance for improving the surface quality of sapphire crystals during grinding. Full article

We report on fabricating planoconcave lenses using a picosecond 355 nm wavelength laser and a CO₂ laser. We also report the fabrication of the planoconvex microlens array on fused silica by patterned micromachining using a picosecond laser and reshaping using a CO₂ laser. We report results on the surface morphology, profile, roughness, optical transmission efficiency, and laser beam profile of transmitted light passing through the microlens. We demonstrate laser fabrication of planoconcave lenses on infrared transmitting material sapphire. Furthermore, we present the results of an experimental and simulation comparative performance study of planoconcave microlenses obtained by individual picosecond and CO₂ lasers. Full article

This paper investigates the relationship between the physical properties of NbN thin films and a series of different substrates/buffer layers used for the thin film growth. Substrates, including 4H-SiC, AlN/Si, AlN/sapphire, and annealed AlN/sapphire, were selected for NbN film deposition via DC magnetron sputtering. Post-deposition annealing was also employed to study its impact on the films’ quality. Comprehensive characterizations were performed on NbN films, focusing on superconducting critical temperature (T_C), transition width (ΔT_C), crystalline quality, and surface roughness. The results demonstrate that the annealed NbN films grown on 4H-SiC substrates with the highest crystalline quality exhibit optimal crystalline quality, achieving a T_C of 16.3 K. Experimental results reveal intrinsic correlations between the critical properties of NbN superconducting thin films and substrate structural characteristics; the impact of post-growth annealing on the T_C is also studied. Full article

Due to the high hardness and brittleness of sapphire, traditional machining methods are prone to surface scratches and microcracks. As an advanced processing technique, ultrasonic machining can reduce damage to hard–brittle materials and improve surface quality. In this study, an integrated ultrasonic longitudinal–torsional vibration system consisting of both a horn and a tool was designed. The resonant frequency and output amplitude of the horn were simulated and tested. The results indicated that the resonant frequency was 19.857 kHz, the longitudinal amplitude at the tool end was 4.2 µm, and the torsional amplitude was 1.8 µm. Experiments were then carried out to investigate the effects of various machining parameters on the reduction of sapphire surface roughness (Ra) and material removal rate (MRR). A comparative experiment was then conducted to evaluate the effects of ultrasonic longitudinal and longitudinal–torsional vibration on sapphire grinding. The ultrasonic longitudinal–torsional grinding experiments showed that the surface roughness of the sapphire workpiece was reduced from 960.6 nm to 82.6 nm, and the surface flatness was improved to 84.3 nm. Compared with longitudinal ultrasonic vibration, longitudinal torsional grinding reduced the surface roughness of sapphire workpieces by 48% and increased the surface flatness by 88.3%. The results of this study provide specific guidance for the longitudinal–torsional composite ultrasonic machining of hard–brittle materials. Full article

Ionic liquid molecules exhibit a variety of properties that are well suited for use as lubricants or additives for lubricants, since they form tribolayers that reduce friction and wear. As additives in the design of new water-based biolubricants, ionic liquids present the advantages of polar nature to use in aqueous lubrication, whilst being biocompatible and with null toxicity, opening up the opportunity to develop novel biolubricants. Choline is a cation present in numerous ionic liquids and is widely recognized for its water solubility, biodegradability, low toxicity, and role as a green solvent in different applications. This work presents the comparative studies of several water-based biolubricants and thin-layer films on stainless steel using a low proportion of Choline-based ionic liquids. The results of friction and wear using water-based biolubricants with 1 wt% of different Choline-based ionic liquids showed good tribological performance. In addition, Choline Lysinate, an amino-acid ionic liquid which is biocompatible, nontoxic, and biodegradable, presented excellent performance and was used as a precursor of thin-layer films on stainless steel showing outstanding behavior in pin-on-disc configuration and sapphire/stainless-steel contacts. Subsequent X-ray photoelectron spectroscopy confirmed the presence of a tribolayer containing the amino acid compound on the metallic surface. Full article

The narrow bandgap InN material, with exceptional physical properties, has recently gained considerable attention, encouraging many scientists/engineers to design infrared photodetectors, light-emitting diodes, laser diodes, solar cells, and high-power electronic devices. The InN/Sapphire samples of different film thicknesses that we have used in our methodical experimental and theoretical studies are grown by plasma-assisted molecular-beam epitaxy. Hall effect measurements on these samples have revealed high-electron-charge carrier concentration, η. The preparation of InN epifilms is quite sensitive to the growth temperature T, plasma power, N/In ratio, and pressure, P. Due to the reduced distance between N atoms at a higher P, one expects the N-flow kinetics, diffusion, surface components, and scattering rates to change in the growth chamber which might impact the quality of InN films. We believe that the ionized N, rather than molecular, or neutral species are responsible for controlling the growth of InN/Sapphire epifilms. Temperature- and power-dependent photoluminescence measurements are performed, validating the bandgap variation (~0.60–0.80 eV) of all the samples. High-resolution X-ray diffraction studies have indicated that the increase in growth temperature caused the perceived narrow peaks in the X-ray-rocking curves, leading to better-quality films with well-ordered crystalline structures. Careful simulations of the infrared reflectivity spectra provided values of η and mobility μ, in good accordance with the Hall measurements. Our first-order Raman scattering spectroscopy study has not only identified the accurate phonon values of InN samples but also revealed the low-frequency longitudinal optical phonon plasmon-coupled mode in excellent agreement with theoretical calculations. Full article

β-Ga₂O₃ holds significant promise for use in ultraviolet (UV) detectors and high-power devices due to its ultra-wide bandgap. However, the cost-effective preparation of large-area thin films remains challenging. In this study, β-Ga₂O₃ thin films are prepared using an inorganic solution reaction spin-coating method followed by post-annealing. The structures, surface morphologies, and optical properties of the films are then characterized using X-ray diffraction, scanning electron microscopy, and ultraviolet–visible spectrophotometry. A low-cost Ga metal was used to produce NH₄Ga(SO₄)₂, which was then converted into a precursor solution and spin-coated onto sapphire and quartz substrates. Ten cycles of spin coating produced smoother films, although higher annealing temperatures induced more cracks. The films on the (0001) sapphire subjected to spin-coating and preheating processes that were repeated for ten cycles, followed by annealing at 800 °C, had a preferred orientation in the [–201] direction. All the films showed high transmittances of 85% in ultraviolet–visible light with wavelengths above 400 nm. The films on the (0001) sapphire substrate that were annealed at 800 °C and 1000 °C exhibited bandgaps of 4.8 and 4.98 eV, respectively. The sapphire substrates demonstrated a superior compatibility for high-quality Ga₂O₃ film fabrication compared to quartz. This method offers a cost-effective and efficient approach for producing high-quality β-Ga₂O₃ films on high-temperature-resistant substrates with promising potential for optoelectronic applications. Full article

In this study, we utilized a terahertz chemical microscope (TCM) to map surface potential changes induced by molecular interactions on silicon-on-sapphire (SOS) substrates. By functionalizing the SOS substrate with DNA aptamers and an ion-selective membrane, we successfully detected and visualized aptamer–neurochemical complexes through the terahertz amplitude. Additionally, comparative studies of DNA aptamers in PBS buffer and artificial cerebrospinal fluid (aCSF) were performed by computational structure modeling and terahertz measurements. Beyond neurochemicals, we also investigated calcium ions, measuring their concentrations in PDMS-fabricated micro-wells using minimal sample volumes. Our results highlight the capability of TCM as a powerful, label-free, and sensitive platform for the probing and mapping of surface potential arising from molecular interactions, with broad implications for biomedical diagnostics and research. Full article

MgZnO possesses a tunable bandgap and can be prepared at relatively low temperatures, making it suitable for developing optoelectronic devices. Mg_xZn_1−xO (x~0.1) films were grown on sapphire by metal–organic vapor phase epitaxy under different substrate-growth temperatures T_s of 350–650 °C and studied by multiple characterization technologies like X-ray diffraction (XRD), spectroscopic ellipsometry (SE), Raman scattering, extended X-ray absorption fine structure (EXAFS), and first-principle calculations. The effects of T_s on the optical, structural, and surface properties of the Mg_0.1Zn_0.9O films were studied penetratively. An XRD peak of nearly 35° was produced from Mg_0.1Zn_0.9O (0002) diffraction, while a weak peak of ~36.5° indicated MgO phase separation. SE measurements and analysis determined the energy bandgaps in the 3.29–3.91 eV range, obeying a monotonically decreasing law with increasing T_s. The theoretical bandgap of 3.347 eV, consistent with the SE-reported value, demonstrated the reliability of the SE measurement. Temperature-dependent UV-excitation Raman scattering revealed 1LO phonon splitting and temperature dependency. Zn-O and Zn-Zn atomic bonding lengths were deduced from EXAFS. It was revealed that the surface Mg amount increased with the increase in T_s. These comprehensive studies provide valuable references for Mg_0.1Zn_0.9O and other advanced materials. Full article

In this work, we propose a strategy to optimize electrochemical hydrogen loading in magnesium–palladium thin films, using 5 M KOH as an electrolyte. Mg thin films of thickness 26 nm were deposited on sapphire (0001) substrates and capped by a 32 nm Pd layer. By performing cyclic voltammetry with in situ optical microscopy, it appears that a loading potential of at least −1.2 V vs. Hg/HgO has to be achieved at the sample’s surface to trigger magnesium hydride formation. Loading potential effects are then further explored by hydrogenography, where different hydride formation mechanisms appear based on the actual potential. With a larger loading potential of −1.6 V vs. Hg/HgO, a magnesium hydride blocking layer is formed; in this case, Pd hydride temporarily forms in the capping layer as hydrogen diffuses towards the magnesium layer. Loading is optimized for a lower potential of −1.2 V vs. Hg/HgO, which leads to larger hydride precipitates and delays the blocking layer formation; in this case, Pd hydride only appears after the magnesium layer is completely hydrided. Full article