Ion-assisted Electron-beam Evaporation Research Articles

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.

A Dichroic Beamsplitter for the Laser Protection of Infrared Detectors

The design and fabrication approach of a dichroic beamsplitter to meet the protection requirements of infrared detectors for blinding laser weapons is presented. The dichroic beamsplitter must protect against 1064 and 532 nm lasers and have high transmittance in the detection beam band of 3.6–4.7 µm. In order to realize the protection and antireflection (AR) functions of the dichroic beamsplitter, Ta2O5, which has a wide band gap and high thermodynamic stability, was selected as the high-refractive-index material. A multilayer stack was deposited on a silicon substrate by ion-assisted electron beam evaporation. The manufactured dichroic beamsplitter features a high laser-induced damage threshold (LIDT), excellent spectral characteristics in the requested spectral region, and good environmental stability.

Electrical and Optical properties of ITO Films Prepared by Ion-Assisted Deposition at Ambient Substrate Temperatures

Traditionally, to achieve low resistivity and high transmission indium-tin oxide (ITO) films were deposited at elevated substrate temperatures about 400o C. In some cases, films deposited at low substrate temperatures can then annealed at higher temperature to achieve lower resistivity. In this paper thin films of ITO with various oxygen flow rates were prepared by ion-assisted electron beam evaporation at ambient substrate temperature. The electrical and optical properties of ITO thin films have been investigated as a function of oxygen flow rate, rate of deposition and the layer thickness. The transmittance and optical band-gap energy were measured by spectrophotometer, whereas the sheet resistance was measured using four-point probe method. It has been found that at 25 sccm oxygen flow, 0.4 nm/sec rate of deposition and 140 nm layer thickness were suitable for improving the properties of ITO films. The optical transmittance, optical band-gap and the resistivity were 92%, 4.2 eV and 175x10-4Ω-cm, respectively.

Investigation of omnidirectional transmittance related to ITO nanorods orientation for optical applications

Indium-doped tin oxide (ITO) nanorods thin films were fabricated on silicon (100) wafer and commercial thin film coated glass (ITO-G) substrates via ion-assisted electron-beam evaporation system with inclinable and rotatable substrate setup. The thickness was controlled in the range of 100–400 nm through the QCM monitoring. With the fixed substrate's tilted angle at 85°, the film's structures were respectively observed as the slant and vertical nanorods corresponding to the substrate's rotation speed of 0 and 30 rpm by the field-emission scanning electron microscope (FE-SEM). The grazing-incident X-ray diffraction (GIXRD) and photoelectron spectroscopy (PES) were used to analyze the crystallinity and atomic composition of the ITO nanorods films. It was observed that the films were amorphous and non-significant of composition variation relative to the change of the film's-controlled thickness and structure. The optical transmittance in omnidirectional (omni-T) of p- and s-polarized light was determined through the variable-angle UV-VIS-NIR spectrophotometer. We found the different profiles of the omni-T with the change of film's structure and thickness which could be explained through the generated birefringence of the films. In addition, the different results of the p- and s-polarized were also discussed.

Work function alteration of the porous indium tin oxide nanorods film by electron beam irradiation technique

Material properties of transparent conductive oxide (TCO), such as crystallinity and work function, have been recognized as important factors affecting a performance of optoelectronic devices. In this work, a nuclear technique, electron beam irradiation, is proposed as a post deposition technique to alter the material characteristics of an indium tin oxide (ITO) nanorods film. The ITO film is fabricated by ion-assisted electron beam evaporation with glancing-angle deposition (GLAD) technique and subsequently irradiated by an electron beam with energy up to 20 MeV at the absorbed doses of 100 kGy and 300 kGy. The effect of irradiation, in terms of morphology and crystallinity, is studied by scanning electron microscopy (SEM), grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM). Whereas, the photoemission spectroscopy (PES) is carried out to study the surface composition and the work function of the ITO films. The SEM result indicates that the diameter of the ITO nanorods increases due to the electron beam irradiation. The electron beam induced crystallization of the ITO nanorod is observed and confirmed by both XRD and TEM measurements. Furthermore, the PES results reveal a change in the surface chemical composition and the work function of the ITO film after the electron beam irradiation. The results of this study implies that the electron beam irradiation serves as a promising post deposition treatment to improve the properties of ITO film, especially in terms of work function alteration.

Nonlinear and low-loss tantalum pentoxide based micro-ring resonator by ion-assisted electron-beam deposition

Tantalum pentoxide (Ta2O5) is a promising material for optical waveguide applications of photonics integration due to its excellent linear and nonlinear optical properties, such as high refractive index, large bandgap, and high nonlinearity. The quality of thin film deposition will then be critical for realizing optical waveguide devices and modules. In this work, an ion-assisted electron-beam evaporation system has been used to deposit such thin film. As low as 0.73 nm thickness roughness has been demonstrated in a 700 nm thick film, indicating it as a candidate for fabricating a low-loss waveguide. An optical waveguide-based ring resonator was made for examining the optical waveguide performance. Through the flat surface morphology, a low propagation loss of 1.4 dB/cm with an unloaded quality factor of 3 × 105 ring resonance has been realized. The nonlinear index of refraction (n2) in as-deposited Ta2O5 film was found to be in an order of magnitude of 10−14 cm2/W, which was also confirmed by both Z-scan technique and all-optical modulation technique. By such high bandgap properties, a nonlinear absorption threshold of few TW/cm2 was also observed for the first time. The measured device performances are comparable to the state-of-the-art results from up-to-date counterparts.

Influence of an Annealing Temperature in a Vacuum Atmosphere on the Physical Properties of Indium Tin Oxide Nanorod Films.

In the present study, indium tin oxide (ITO) nanorod films were produced by usage of ion-assisted electron-beam evaporation with a glancing angle deposition technique. The as-produced ITO nanorod films were annealed in the temperature range of 100-500 °C for two hours in a vacuum atmosphere. The as-produced ITO nanorod films exhibited (222) and (611) preferred orientations from the X-ray diffraction pattern. After vacuum annealing at 500 °C, the ITO nanorod films demonstrated many preferred orientations and the improvement of film crystallinity. The sheet resistance of the as-produced ITO nanorod films was 11.92 Ω/ and was found to be 13.63 Ω/ by annealing at 500 °C. The as-produced and annealed ITO nanorod films had a rod diameter of around 80 nm and transmittance in a visible zone of around 90%. The root mean square roughness of the as-produced ITO nanorod film's surface was 5.49 nm, which increased to 13.77 nm at an annealing temperature of 500 °C. The contact angle of the as-produced ITO nanorod films was 110.9° and increased to 116.5° after annealing at 500 °C.

Linear and Nonlinear Absorption of Titanium Dioxide Films Produced by Plasma Ion-Assisted Electron Beam Evaporation: Modeling and Experiments

Titanium dioxide films were prepared by plasma ion-assisted electron beam evaporation. Linear optical properties were investigated in terms of spectrophotometry using the beta-distributed oscillator (ß_do) model as a parametrized dispersion law. The nonlinear two-photon absorption coefficient of titanium dioxide was determined by means of the laser-induced deflection technique at a wavelength of 800 nm. The obtained values of (2–5) × 10−11 cm/W were consistent with published experimental values for rutile as well as for simulations performed in the frames of the ß_do and Sheik–Bahae models.

Effect of the amount of argon in an oxygen ion beam on the optical characteristics of titanium dioxide films obtained via ion-assisted electron beam evaporation

The effect of argon in a mixture with oxygen in an ion beam on the optical characteristics of titanium dioxide (TiO2) obtained via ion-assisted electron beam evaporation in vacuum was studied. It was shown that the addition of an inert gas at a level of 20%–25% resulted in an increase in the refractive index of the resulting TiO2 coating and a decrease in the sensitivity of the spectral characteristic of the coating to the effect of the atmosphere as a result of the decrease in the film porosity. The maximum amount of argon in the mixture was determined, amounting to 26%, at which the TiO2 film had an extinction coefficient not exceeding k=0.0001.

Optical characterization of silicon dioxide thin films prepared by ion-assisted electron beam deposition

A single-layer SiO2 film is deposited using ion-assisted electron beam evaporation technique, and the deposited film is characterized using variable angle spectroscopic ellipsometry, UV–Vis–NIR spectrophotometer, coherence correlation interferometer, and Abbe refractometer as well as image processing techniques to investigate its optical and surface properties. The surface quality of the film in terms of average roughness, kurtosis, skewness, and power spectral density (PSD) is analyzed using interferometer and image processing. The refractive index of the SiO2 film is found to increase from 1.452 to 1.482 at 550 nm with increase in film thickness. This is corroborated by Abbe refractometer findings where the film refractive index is found to be 1.46490 and 1.48226 for a film thickness of 100 and 400 nm, respectively. The SiO2 film also results in reduction in average surface roughness from 35 nm of the uncoated substrate to 0.15 nm of the coated surface. Statistical indicators of surface quality extract from interferometric images such as kurtosis, skewness, and PSD and also exhibit sharp decline in their respective values of the coated surface as compared to the uncoated substrate indicating improvement in the surface quality after coating.

Study of Annealing Influence on Basic Properties of Indium Tin Oxide Nanorod Films Deposited Using Glancing Angle Ion-Assisted Electron Beam Evaporation.

Indium tin oxide (ITO) nanorod films were deposited onto glass slides and Si wafers using ionassisted electron beam evaporation with a glancing angle deposition technique. The annealing influence on the basic properties of the as-deposited ITO nanorod films was studied in the range of 100-500 °C for two hours in air. The crystallinity of the ITO nanorod films was enhanced with the increasing annealing temperature, and the average transmission of the as-deposited ITO nanorod films in the visible range was 90%. This value did not change significantly after the annealing process. The optical bandgap of the as-deposited ITO nanorod films was 3.94 eV and increased slightly after annealing. The sheet resistance of the as-deposited ITO nanorod films was 12.9 Ω/ and increased to 57.8 Ω/ at an annealing temperature of 500 °C. The as-deposited ITO nanorod films showed nanorod structures with average diameters of 79 nm, which changed slightly with the annealing temperature. The root mean square roughness of the as-deposited ITO nanorod films was 7.9 nm and changed slightly with annealing. The as-deposited ITO nanorod films had an average contact angle of 110.9°, which decreased to 64.2° at an annealing temperature of 500 °C. The experimental results showed that varying the annealing temperature influenced the structural, electrical and wettability properties of the ITO nanorod films while the optical properties and surface morphology were almost unaffected.

Metallic Adhesive Layers for Ag‐Based First Surface Mirrors

Metallic thin films have been evaluated as adhesive layers for first surface mirrors. Thin films (0.5–4 nm thick) of Cr, Cu, Ge, Sn, and Ni, capped with an over layer of 100 nm of Ag have been deposited by means of ion assisted electron beam evaporation onto glass substrates. The specular reflectance, conductivity, morphology, adhesion, and abrasion resistance of the mirrors have been assessed and compared. This work demonstrates the superior Ni and Ge adhesion and abrasion resistance to Ag thin films, while Cr and again Ni are the best candidates in terms of reflectance enhancement. In particular, 4 nm of Ni increases the Ag reflectance from 95.7% to 96.7%, exhibits the strongest adhesion as determined by the cross hatch tape test and the lowest loss of material after the different abrasion tests is just 50% in comparison to 100% for Ag‐coated glass substrates.

Eu and F co-doped ZnO-based transparent electrodes for organic and quantum dot light-emitting diodes

A novel Eu and F co-doped zinc oxide (EFZO) thin film has been prepared by ion-assisted electron beam evaporation.

Silver Film Surface Modification by Ion Bombardment Decreases Surface Plasmon Resonance Absorption

Silver thin films covered with dielectric films serving as protective coatings are desired for telescope mirrors, but durable coatings have proved elusive. As part of an effort to develop long-lived protected-silver mirrors, silver thin films were deposited by electron beam evaporation using a physical vapor deposition system at the University of California Observatories Astronomical Coatings Lab. The silver films were later covered with a stack of dielectric films utilizing silicon nitride and titanium dioxide deposited by ion-assisted electron beam evaporation to fabricate protected mirrors. In-situ argon ion bombardment was introduced after silver deposition and prior to the deposition of dielectric films to assess its effects on the performance of the mirrors. We found that ion bombardment of the silver influenced surface morphology and reflectivity, and these effects correlated with time between silver deposition and ion bombardment. The overall reflectivity at wavelengths in the range of 350-800 nm was found to improve due to ion bombardment, which was qualitatively interpreted as a result of decreased surface plasmon resonance coupling. We suggest that the observed decrease in coupling is caused by silver grain boundary pinning due to ion bombardment suppressing silver surface diffusion, forming smoother silver-dielectric interfaces.

Structural and optical properties of highly (110)-oriented non-polar ZnO evaporated films on Si substrates

Zinc oxide (ZnO) films with thicknesses from (9.1±0.7) to (145±7)nm were deposited on silicon substrates by ion-assisted electron beam evaporation (EBE), and transformed to a highly (110)-oriented non-polar phase through thermal treatment at temperatures of 300, 500, and 700°C. The structural, morphological and optical properties of the ZnO thin films were systematically characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and photoluminescence (PL). The XRD and AFM results illustrate that the deposited ZnO films evolved from an X-ray amorphous structure to the polycrystalline hexagonal wurtzite structure with increasing thickness and experienced a crystallographic plane improvement from (102) to the (110) non-polar phase during annealing. The dielectric functions of the whole layer are mainly affected by the dielectric responses near the surface of ZnO nanocrystals and show an upward trend with nanocrystal growth, induced by thickness and annealing temperature. The optical band gaps were also investigated and correlated with the structural properties. In the PL spectra, a strong ultraviolet luminescence (UVL) band and a weak visible green luminescence (GL) band were observed. The intensity ratio of UVL and GL—associated with crystal quality—agrees with the results acquired from other measurements. The two determinants for highly (110)-oriented non-polar ZnO films are the suppression of growth in the (002) direction by ion bombardment and the promotion of the (110) plane induced by diffusion energy during annealing.

Enhanced transmission based on vertically aligned ITO NRs deposited by Ion assisted electron beam evaporation with glancing angle deposition technique

In this study, we investigated the effects on the film thickness of the vertically aligned indium-doped tin oxide nanorods (ITO NRs). The ITO nanorods of deposited time at 180 to 780 sec were deposited on the silicon wafers and ITO-coated glass substrate by the ion-assisted electron-beam evaporation with the glancing-angle deposition technique. The physical microstructures and optical properties of the prepared samples have been investigated by grazing-incident X-ray diffraction (GIXRD), field-emission scanning electron microscopy (FE-SEM), and spectrophotometry. From the results, the ITO nanorods indicated the bixbite structures. The FE-SEM micrographs showed the changes of the physical morphologies based on the increased film thickness. The angle-dependent transmission as measured from -80° to 80° incident angles demonstrated the increased optical transmission from the vertically aligned ITO nanorods, compared to that of the ITO-coated glass. The enhancement of the optical transmission was related to the anti-reflection and light-scattering properties of the ITO nanorods, and offered a great potential for solar cell applications.

Investigation of optical characteristics of the evaporated Ta2O5 thin films based on ellipsometry and spectroscopy

The tantalum oxide (Ta2O5) thin films were prepared by the ion-assisted electron-beam evaporation system. With the fixed film thickness at 200 nm, the deposition conditions were performed based on oxygen flow rate the ion assistance during the film deposition. The prepared thin films were characterized by spectroscopic ellipsometry in order to determine their physical and optical properties. From the ellipsometric measurements, the physical structures of the thin films and the optical dispersions were constructed, and then analyzed for the results of film thickness and optical constants. The thin films were also measured by the UV-Vis-NIR spectrophotometry for the optical transmission. The measured transmission was analyzed with the Swanepoel method, whose results also yielded the thickness and the refractive index. Finally, the thin films were examined by the scanning electron microscopy (SEM) in order to observe physical microstructures. This study explored the physical and optical analyses based on the spectroscopic ellipsometry and the spectrophotometry, with the confirmations from the SEM micrographs. The results from the analyses would be compared and thoroughly discussed.

Engineered omnidirectional antireflection ITO nanorod films with super hydrophobic surface via glancing-angle ion-assisted electron-beam evaporation deposition

Growths of the indium tin oxide (ITO) nanorod films have been demonstrated by ion-assisted electron-beam evaporation with the glancing-angle deposition technique based on variation in deposition rate. Investigations have been performed on nanostructured ITO films deposited on ITO-coated commercial substrates in comparison to bare substrates. The physical microstructures have been investigated by grazing-incident X-ray diffraction (GIXRD), field-emission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM). The electrical, optical, and hydrophobic properties were characterized by four-point probe measurements, UV–Vis–NIR spectrophotometry with angle-dependent technique, and contact angle goniometry, respectively. The results indicated that physical morphologies and nanorod diameters of ITO nanorod films were heavily influenced, and thus could be controlled, by deposition rate. The primary reason was self-annealing effect which occurred during film deposition and was crucial factor towards surface diffusion and film crystallinity. From the optical examinations, ITO nanorods deposited on the ITO-coated glasses exhibited significant improvements on transparent conductive oxide (TCO) properties from reference samples. The proposed ITO materials could therefore function as omnidirectional anti-reflection materials and super hydrophobic surface. This work have also proved that the ITO nanorods prepared by the electron-beam evaporation with the GLAD technique was highly promising for solar cell and optoelectronic applications.

Comparison of Single-Layer and Double-Layer Anti-Reflection Coatings Using Laser-Induced Damage Threshold and Photothermal Common-Path Interferometry

The dielectric thin-film coating on high-power optical components is often the weakest region and will fail at elevated optical fluences. A comparison of single-layer coatings of ZrO2, LiF, Ta2O5, SiN, and SiO2 along with anti-reflection (AR) coatings optimized at 1064 nm comprised of ZrO2 and Ta2O5 was made, and the results of photothermal common-path interferometry (PCI) and a laser-induced damage threshold (LIDT) are presented here. The coatings were grown by radio frequency (RF) sputtering, pulsed direct-current (DC) sputtering, ion-assisted electron beam evaporation (IAD), and thermal evaporation. Test regimes for LIDT used pulse durations of 9.6 ns at 100 Hz for 1000-on-1 and 1-on-1 regimes at 1064 nm for single-layer and AR coatings, and 20 ns at 20 Hz for a 200-on-1 regime to compare the //ZrO2/SiO2 AR coating.

Influence of Rapid Thermal Annealing on Structural, Optical and Electrical Properties of ITO Thin Films

Indium doped tin oxide (ITO) thin films were deposited on silicon wafer (100) and glass slide by ion assisted electron beam evaporation deposition. After deposition, the ITO thin films were annealed in vacuum (100-300°C) and their structural, optical and electrical properties were systematically investigated. X-ray diffraction,atomic force microscopy, ultraviolet–visible (UV–vis) spectrophotometer and hall-effect measurement were employed to obtain information on the crystallization, transmission and resistivity the films.It was found that the rapid thermal annealing can improve the resistivity of ITO thin films which specializes for the transparent conductive layers.