Optical properties and environmental stability of oxide coatings deposited by reactive sputtering

Amorphous dielectric optical coatings deposited by plasma ion-assisted electron beam evaporation for gravitational wave detectors

Coating thermal noise (CTN) in amorphous coatings is a drawback hindering their application in precision experiments such as gravitational wave detectors (GWDs). Mirrors for GWDs are Bragg's reflectors consisting of a bilayer-based stack of high- and low-refractive-index materials showing high reflectivity and low CTN. In this paper, we report the characterization of morphological, structural, optical, and mechanical properties of high-index materials such as scandium sesquioxide and hafnium dioxide and a low-index material such as magnesium fluoride deposited by plasma ion-assisted electron beam evaporation. We also evaluate their properties under different annealing treatments and discuss their potential for GWDs.

Amplification of blue emission of Tm3+ ions in Li2 O-HfO2 -SiO2 glass system by means of Au0 metallic particles

Li₂ O-HfO₂ -SiO₂ -Tm₂ O₃ :Au₂ O₃ glass samples (containing fixed content of Tm₂ O₃ and different concentration of Au₂ O₃ ) were prepared and characterized. Bearing of Au⁰ metallic particles (MPs) on improving blue emission of thulium ions (Tm³⁺ ) ions was explored. Optical absorption (OA) spectra exhibited multiple bands excited from ³ H₆ of Tm³⁺ . Additionally, a broad peak in the wavelength range 500-600 nm due to surface plasmon resonance (SPR) of Au⁰ MPs was noticed in the spectra. Photoluminescence (PL) spectra (of thulium free glasses) indicated a peak in the visible range due to sp → d electronic transition of Au⁰ MPs. Luminescence spectra of Tm³⁺ and Au₂ O₃ co-doped glasses exhibited intense blue emission with substantial increase of intensity with increase of Au₂ O₃ content. Bearing of Au⁰ MPs on the reinforcement of blue emission of Tm³⁺ was discussed in detail with kinetic rate equations.

High Refractive Index Silica-Titania Films Fabricated via the Sol-Gel Method and Dip-Coating Technique-Physical and Chemical Characterization

Crack-free binary SiO_x:TiO_y composite films with the refractive index of ~1.94 at wavelength 632.8 nm were fabricated on soda-lime glass substrates, using the sol-gel method and dip-coating technique. With the use of transmission spectrophotometry and Tauc method, the energy of the optical band gap of 3.6 eV and 4.0 eV were determined for indirect and direct optical allowed transitions, respectively. Using the reflectance spectrophotometry method, optical homogeneity of SiO_x:TiO_y composite films was confirmed. The complex refractive index determined by spectroscopic ellipsometry confirmed good transmission properties of the developed SiO_x:TiO_y films in the Vis-NIR spectral range. The surface morphology of the SiO_x:TiO_y films by atomic force microscopy (AFM) and scanning electron microscopy (SEM) methods demonstrated their high smoothness, with the root mean square roughness at the level of ~0.15 nm. Fourier-transform infrared (FTIR) spectroscopy and Raman spectroscopy were used to investigate the chemical properties of the SiO_x:TiO_y material. The developed binary composite films SiO_x:TiO_y demonstrate good waveguide properties, for which optical losses of 1.1 dB/cm and 2.7 dB/cm were determined, for fundamental TM₀ and TE₀ modes, respectively.

Atomic layer deposited nanolaminates of zirconium oxide and manganese oxide from manganese(III)acetylacetonate and ozone

Atomic layer deposition method was used to grow thin films consisting of ZrO₂and MnO_xlayers. Magnetic and electric properties were studied of films deposited at 300 °C. Some deposition characteristics of the manganese(III)acetylacetonate and ozone process were investigated, such as the dependence of growth rate on the deposition temperature and film crystallinity. All films were partly crystalline in their as-deposited state. Zirconium oxide contained cubic and tetragonal phases of ZrO₂, while the manganese oxide was shown to consist of cubic Mn₂O₃and tetragonal Mn₃O₄phases. All the films exhibited nonlinear saturative magnetization with hysteresis, as well as resistive switching characteristics.

Double-side operable perovskite photodetector using Cu/Cu2O as a hole transport layer

In this study, a perovskite is integrated with an ultra-thin Cu/Cu₂O (CCO) composite film, a transparent material with high mobility, to achieve a double-side and low-voltage operable photodetector. Compared to photodetectors that utilize metal electrode with perovskite, the use of CCO significantly enhances the photocurrent (from nA up to mA). It acts as a large-scale hole transport layer. The photodetector exhibits high responsivities of 6.79 AW^-1 [illuminated via the fluorine-doped tin oxide (FTO) side] and 10.23 AW^-1 (illuminated via CCO side). The detectivities obtained at both illuminated sides are as high as over 10¹¹ Jones. Additionally, the Cu/Cu₂O-covered perovskite effectively prevents the reaction of perovskite in the interface. This work reveals that the perovskite/CCO heterojunction photodetector can be considered a promising candidate for applications in bifacial-illuminated and flexible/wearable optoelectronic technologies.

XANES, EXAFS and photoluminescence investigations on the amorphous Eu:HfO2

We report detailed investigations on the local electronic/atomic structure and photoluminescence properties of chemically synthesized Eu:HfO₂ powders. X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS) and photoluminescence (PL) measurements were performed to analyze the crystal structure, local atomic/electronic structure and luminescence properties of the samples. No crystalline phases were detected with Cu Kα (λ=1.5418Å) based XRD; however, local monoclinic structure was confirmed by the Hf L-edge XANES and EXAFS. O K-edge XANES spectral features could be deconvoluted with doublets and triplets in e_g and t_2g orbitals, respectively, which ascribed to the local monoclinic structure for all of the samples. Eu M_5,4-edge XANES confirmed the pre-dominancy of Eu³⁺ ions in the HfO₂ samples with a fractional amount of Eu²⁺ ions. PL spectra revealed the electric dipole allowed (⁵D₀-⁷F_0,2,4) emission properties of Eu:HfO₂ samples. The orange-red emission is ascribed to the Eu interstitial/surface segregation induced defects.

Nanolaminated composite materials: structure, interface role and applications

Various kinds of the typical ultrathin 2D nanomaterials: a hot topic for intense scientific research and development of technological applications.

Lasing of infrared free-election lasers using the storage ring NIJI-IV

We report for the first time to our knowledge the experimental achievement of a storage ring free-electron laser (FEL) device dedicated to applications in the IR region. IR FELs were oscillated in the wavelength region of 1392-1502 nm, and the relative linewidth was 3 x 10(-4). The maximum power of the IR FEL transmitted through a vacuum window was approximately 0.3 mW, and the intracavity power was approximately 2 W. We have already observed an intensive quasi-monochromatic x ray by using FEL Compton backscattering. The results of our study are expected to lead to applications in which an IR FEL and a quasi-monochromatic x ray will be used simultaneously.

Raman and Brillouin scattering spectroscopy studies of atomic layer-deposited ZrO(2) and HfO(2) thin films

Atomic layer-deposited ZrO(2) (zirconia) and HfO(2) (hafnia) films with various thicknesses, ranging from 112 to 660 nm, have been studied by Raman scattering spectroscopy. Spectral analysis of the excellent quality Raman data obtained by using freestanding edges of the films has unambiguously demonstrated that a metastable tetragonal t-ZrO(2) is coexisting with the stable monoclinic phase in zirconia films. Even though the Raman spectrum signal-to-noise ratio was high, only the monoclinic phase was positively identified from the observed spectral patterns of hafnia films. X-ray diffraction patterns are used to define the structure of metastable phases. Complementary Brillouin light scattering measurements of the freestanding edges are also employed in constraining elastic properties of the 405 nm HfO(2) thin film.

Thermally stable narrow-bandpass filter prepared by reactive ion-assisted sputtering

Thermal stabilities of three-cavity narrow-bandpass (NB) filters with high-index half-wave spacers and 78-102 layers of Ta(2)O(5) and SiO(2) prepared by reactive ion-assisted bipolar direct-current (dc) magnetron sputtering of tantalum and silicon targets, respectively, were investigated. Pure argon and pure oxygen were used as the sputtering gas and the reactant, respectively. The oxygen gas was introduced and ionized through the ion gun and toward the unheated BK7 glass substrate. The refractive indices of single-layer Ta(2)O(5) and SiO(2) films were 2.1 and 1.45, respectively, at 1550 nm, which were comparable with those of films prepared by other ion-assisted coating techniques. The moisture-resistant properties of the films were excellent as evidenced from the water-immersion test, implying that the packing density of the films was close to that of their bulk materials. The temperature-dependant wavelength shifts of the NB filters were <3 x 10(-3) nm/ degrees C at temperatures of <75 degrees C, indicating that the temperature-induced wavelength shift of the filter was <0.15 nm when the temperatures were raised from room temperature to 75 degrees C, which was compliant with Bellcore GR-1209-CORE generic requirements of NB filters used for optical-fiber communication systems.

Defect formation in hafnium dioxide thin films

Hafnium dioxide thin films were deposited by reactive electron-beam evaporation at six different substrate temperatures on fused-silica substrates. During the depositions, the scattering of light caused by the growth of defects in the films was recorded with in situ total internal reflection microscopy. After deposition the films were analyzed by angle-resolved scatterometery, spectrophotometric measurement of film reflectance and transmittance, atomic force microscopy, and x-ray diffraction. We explore the effects of film defect formation on film optical properties and film surface topography using these data.

MgO-Al(2)O(3)-ZrO(2) Amorphous Ternary Composite: A Dense and Stable Optical Coating

The process-parameter-dependent optical and structural properties of MgO-Al(2)O(3)-ZrO(2) ternary mixed-composite material were investigated. Optical properties were derived from spectrophotometric measurements. The surface morphology, grain size distributions, crystallographic phases, and process-dependent material composition of films were investigated through the use of atomic force microscopy, x-ray diffraction analysis, and energy-dispersive x-ray analysis. Energy-dispersive x-ray analysis made evident the correlation between the optical constants and the process-dependent compositions in the films. It is possible to achieve environmentally stable amorphous films with high packing density under certain optimized process conditions.

Optical properties of hafnia and coevaporated hafnia:magnesium fluoride thin films

Mixed films of HfO(2) and MgF(2) were prepared by the e-beam coevaporation of two source materials with or without the presence of ion assistance. Optical properties and hardness of mixed films were compared among various compositions that were achieved by controlling the deposition rate of MgF(2). Results obtained from pure materials confirmed the densification of HfO(2) and the increased absorption in MgF(2) with a higher discharge voltage. A refractive index of a composite film from 1.38 to 1.91 was achievable with various HfO(2):MgF(2) deposition rate ratios. A low-index composite material with improved hardness may be substituted for the soft MgF(2).