Ion-assisted Electron Beam Deposition Research Articles

Multi-layer Laser Mirrors for Optical Sensors Deposited by Electron Beam Deposition and Ion Assisted Electron Beam Deposition

High reflectivity and low loss mirrors are very much essential for state-of art sensors like Ring Laser Gyroscopes widely used for navigation of moving platforms. Surface scattering is the main source of loss for the Laser mirrors of high reflectivity. Surface scattering also lead to coupling of back reflected light leading to dead band of optical sensors at low input rotation. Super polished glass substrates have been prepared from low expansion glass ceramic material. Surface roughness is achieved about 3-5Å (RMS value) for the ceramic glass substrates prior to thin film coating. The substrates are deposited with 41 alternative layers of SiO2 and Ta2O5 of Quarter-Wave optical thickness with Electron Beam Deposition (EBD) technique. Ion beam Assisted Electron Beam Deposition (IAEBD) is used for another batch of substrates to coat identical stack of layers on glass substrates of the same surface quality. The key process parameters of both the coating processes are presented. The optical constants of the films are evaluated with spectroscopic Ellipsometer from 400nm to 1600nm. Total Integrated Scattering is estimated from the achieved surface finishing of mirrors deposited. The multi-layer coatings are characterized with UV-Vis-IR Spectrophotometer and Cavity Ring Down(CRD) loss meter. The quantitative optical loss of the mirrors is measured at 45o angle of incidence with CRD loss meter. The merits of ion assisted EB process over simple EB coating processes are evaluated against optical constants of thin films and performances of mirrors. Fitness of the processes for realizing Laser mirrors for optical sensors at 632.8nm is evaluated.

Fabrication of Ge-ZnS multilayered optical filters for mid-infrared applications

Germanium/Zinc Sulphide (Ge/ZnS) single and multilayers are deposited by ion assisted electron beam deposition on Silicon substrates for applications in the 2-15 µm wavelength region. Refractive indices of Ge and ZnS thin films are extracted from measured reflectance and transmittance spectra. Several types of mid-infrared filters (high-, anti-reflection coatings and dichroic filters) with a number of layers ranging from 3 to 29 are then designed and deposited. The optical responses of fabricated mid-infrared filters show a good agreement between experimental spectra and simulation in the case of high- and anti-reflection coatings in the long-wave infrared but also for dichroic filters with a low transmittance in the mid-wave infrared and broadband bandpass in the long-wave infrared.

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.

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.

Ion assisted deposition of Silica-Titania multilayer optical filter for beam steering of Nd:YAG laser

In the present study, a multilayer reflective optical filter consisting of 24 alternate layers of SiO2 and TiO2 was designed and fabricated on BK7 glass substrate using Ion Assisted electron beam Deposition (IAD) technique. The spectroscopic characterization of the filter was carried out in Vis-NIR range with Universal Measurement Accessory (UMA) to measure its optical performance at normal and oblique angles of incidences. The measurements confirmed the optical peak reflectance of more than 99.98% at design wavelength of Nd:YAG laser centred at 1064 nm. The tuning of refractive indices of the constituent layers during deposition resulted in a Full-Width at Half-Maximum (FWHM) bandwidth of 330 nm of the fabricated filter which enables its use at any angle of incidences between 0 and 60° for manipulating the laser beam. Qualitative assessment of the mechanical stability of the coated filter with respect to its adhesion and abrasion resistance was carried out in accordance with MIL-F-48616 and MIL-E−12397 respectively. The achieved optical performance of the coated filter is suited for beam steering and folding of high power laser beams for metal cutting, diamond processing and in other laser based material processing instruments.

Sr-F共掺杂的SnO2基透明导电薄膜

Sr-F codoped SnO2( SFTO) transparent conductive oxide films were prepared by ion-assisted electron beam deposition at a low temperature. The films show electrical resistivity of less than3. 9 × 10- 3Ω·cm,high average optical transmittance of 85% from 380 nm to 2 500 nm,and high work function of about 5. 1 e V. The films are amorphous and have favorable surface morphology with average roughness of about 1. 5 nm. The deposition temperature of SFTO film is 300 ℃,which is much lower than that of FTO products. SFTO transparent conductive amorphous thin film can be expected to be directly prepared on flexible plastic( PI,PAR or PCO) substrate,in order to obtain flexible electrodes with good performance.

Corrosion barriers for silver-based telescope mirrors comparing PEALD and PVD of AlOx

ABSTRACTAstronomical telescopes continue to demand high-endurance high-reflectivity silver mirrors that can withstand years of exposure in earth-based observatory environments. The University of California Observatories Astronomical Coatings Lab has undertaken development of protected silver coatings suitable for telescope mirrors that maintain high reflectivity at wavelengths from 340 nm through the mid-infrared spectrum. We present promising results of enhanced corrosion barriers using plasma-enhanced atomic layer deposition (PEALD) of aluminum oxide (AlOx) as a top barrier layer. Novel coating recipes developed with ion-assisted electron beam deposition (IAEBD) of materials including yttrium fluoride and oxides of yttrium, tantalum, and silicon are used to compare the endurance of physical vapor deposition-grown barriers with PEALD-grown barriers of similar thickness. Samples of these mirror coatings were covered with conformal layers of AlOx deposited by PEALD using trimethylaluminum as a metal precursor and plasma-activated oxygen as an oxidant gas. Samples of coating recipes with and without PEALD oxide undergo aggressive high temperature/high humidity (HTHH) environmental testing in which samples are exposed to an environment of 80% humidity at 80°C for ten days in a simple test set-up. HTHH testing show visible results suggesting that the PEALD oxide offers enhanced robust protection against chemical corrosion and moisture from an accelerated aging environment. Mirror samples are further characterized by reflectivity/absorption before and after deposition of oxide coatings. AlOx is suitable for many applications and has been the initial material choice for this study.

Enhanced hollow cathode plasma source for assisted low pressure electron beam deposition processes

A self-sustaining hollow cathode plasma source has been demonstrated to operate at an order of magnitude lower deposition pressure than previously reported, enabling plasma ion-assisted electron beam deposition at pressures of ≈2.0E-4mbar.This method uses a restrictor plate to create a pressure differential in gas flow between a hollow cathode region and the main deposition area. The cathode operates in higher density plasma, enhancing the hollow cathode effect and enabling self-sustaining plasma formation at lower gas pressures in the deposition region. It is also demonstrated that ion energy distribution and current density at the substrate plane can be varied by changing the orifice geometry and/ or gas flow.It has been shown that by varying the restrictor orifice the proportion of thermalised ions to translational ions can be reduced, thereby reducing both substrate heating by typically 60% and defect incorporation into the deposited film. This is significant when coating low temperature materials such as plastics. Moreover the variation in ion current density over the calotte area can also be controlled by varying the geometry of the restrictor plate.The hollow cathode design described in this work utilises both the interior and exterior cathode surfaces, with the additional electrons generated removing the need for a separate neutralising source as verified by Langmuir probe measurement of electron and ion densities at the substrate plane.The effects on plasma assisted electron beam deposited TiO2 film optical and mechanical properties have been assessed and correlated with plasma source characteristics.In contrast to other hollow cathode plasma source configurations, this system has a converging magnetic field allowing electron concentration within the orifice.

Design, production and reverse engineering of ultra-steep hot mirrors.

We present the whole design-production chain of an ultra-steep hot mirror produced using the indirect monochromatic monitoring technique. The hot mirror without thin layers is designed utilizing the stochastic optimization procedure that takes in account upper and lower constraints for layer optical thickness. We produced the hot mirror with the ion-assisted electron beam deposition technique using indirect monochromatic monitoring strategy, performed reverse engineering of the deposited coatings, and illustrated that the random variation of the tooling factors in low-index layers is the main factor causing production errors. We modified the monitoring strategy with low-index layers monitored by quartz crystal monitor, and demonstrated the excellent correspondence to the theoretical spectral performance.

Pr and F co-doped SnO_2 transparent conductive films with high work function deposited by ion-assisted electron beam evaporation

A transparent conductive oxide (TCO) Pr and F co-doped SnO2 (PFTO) film is prepared by ion-assisted electron beam deposition. An optimized PFTO film shows a high average visible optical transmittance of 83.6% and a minimum electrical resistivity of 3.7 × 10(-3) Ω·cm corresponding to a carrier density of 1.298 × 10(20) cm(-3) and Hall mobility of 12.99 cm(2)/V⋅s. This PFTO film shows a high work function of 5.147 eV and favorable surface morphology with an average roughness of 1.45 nm. Praseodymium fluoride is found to be an effective material to dope F into SnO2 that can simplify the fabrication process of SnO2-based TCO films.

Characterization of Alumina Optical Waveguides Grown by Ion Beam Assisted Deposition for SPARROW Biosensors

ABSTRACTDielectric optical films with minimal surface roughness are required for biosensing applications since the coupling characteristics often used in signal transduction are dependent on the quality of the waveguides. This paper describes the fabrication and characterization of alumina-based optical waveguides for biosensor device for biomolecular detection. Alumina (Aluminum Oxide) Al2O3waveguides were chosen for their moisture stability and refractive index. Planar alumina optical waveguides were deposited on Borofloat substrates by a vacuum evaporation process using an ion assisted electron beam deposition technique. The deposited films showed RMS roughness of 0.3nm – 0.5nm and a range of refractive indices varying from 1.62 to 1.654 as a function of varying ion beam parameters such as oxygen flow rates and drive currents. The propagation losses for the TE0(Transverse Electric) mode of the alumina films at 632.8nm wavelength were found to vary between 2dB/cm – 6dB/cm at a wavelength of 632.8nm for TE0polarization as a function of ion beam parameters. It is shown that these factors influence the optical film quality and hold the potential for achieving further waveguide performance improvement for biosensing applications.

The development of biaxial alignment in yttria-stabilized zirconia films fabricated by ion beam assisted deposition

Yttria-stabilized zirconia (YSZ) films were deposited using ion assisted, electron beam deposition (IBAD) on Pyrex, quartz, Hastelloy, and polycrystalline zirconia substrates. Film orientation was studied as a function of IBAD fabrication conditions. Film texture from several populations of biaxially aligned grains has been observed. The ion beam is shown to induce biaxial alignment of all grain orientations. Specifically, grains with (200), (311), and (111) normal to the substrate surface are biaxially aligned. The ion beam induces biaxial alignment at all angles of incidence, not just those corresponding to YSZ channeling directions. The development of (200) biaxial alignment on Pyrex is examined as a function of thickness. Biaxially aligned IBAD YSZ films were deposited on amorphous and polycrystalline substrates without active heating. Biaxial alignment development with IBAD is shown to be consistent with a previously proposed growth and extinction model.

Application of ion-assited electron beam metallization to diamond electronics

Abstract The application of the ion-assisted electron beam deposition technique for the fabrication of contacts on diamond has been evaluated by studying the adhesion of metal films as well as by performing electrical measurements on metal/diamond structures. Metal films were deposited on naturally occuring B-doped diamond crystals (type IIb) and on polycrystalline diamond films using an electron beam deposition technique with and without ion assist. A marked improvement in adhesion was observed for the films deposited with ion-assisted deposition compared to those deposited by non-ion-assisted electron beam technique. The metal contacts fabricated on a natural diamond (type IIb) exhibited excellent rectifying characteristics with low reverse leakage current densities. No apparent difference in the reverse leakage current densities could be detected for the contacts deposited by ion-assisted electron beam deposition as compared to the contacts deposited by non-ion-assisted electron beam.

Preparation of biaxially aligned cubic zirconia films on pyrex glass substrates using ion-beam assisted deposition

Yttria stabilized zirconia films were deposited using ion-assisted, electron beam deposition (IBAD) on pyrex glass substrates heated to 600 °C. Films deposited under these conditions without IBAD exhibit fiber texture such that preferred (100) orientation exists perpendicular to the substrate. The orientation of the films has been studied as a function of ion bombardment angle, deposition rate, ion current density, and ion beam energy. Films deposited with IBAD at bombardment angles of less than 63° display strong (100) preferred orientation perpendicular to the substrate. Films having ion to atom ratios of 0.05 exhibit (220) biaxial alignment in the plane of the film. Best results were achieved for films with deposition rates of 2.4 Å/s, beam energies of 75 eV and ion fluences of 18 μA/cm2. Increasing the beam energy to 300 eV increases the concentration of wire texture in these films. Films deposited at higher ion/atom ratios (0.11 and 0.25) produce films with alignments highly dependent on the angle of ion bombardment. Processing conditions have been shown, therefore, to effect absolute orientation, and not just the quality of the pre-existing orientation. The microstructures of the biaxially aligned films have been studied and this has allowed for a clarification of the growth mechanism of these films. A growth instability of the differing orientations during ion bombardment is shown to cause in-plane alignment rather than preferential etching of misoriented nuclei.

Ion Beam-Assisted Deposition of Biaxially Aligned CeO2 and ZrO2 Thin Films on Amorphous Substrates

ABSTRACTDeposition of HTSC and other films is often restricted to lattice-matched single crystal substrates to produce desired epitaxial films. Ion assisted, electron beam deposition (IBAD) has been used to evaporate biaxially aligned ceria and zirconia films on amorphous substrates, thus producing a surface for the deposition of oriented Ba2YCu3O7-δ films. The conditions at which preferential (200) film alignment is obtained has been optimized. The ion-to-atom ratio and ion beam energy are critical in determining beam effects on in-plane alignment Pole figures revealed that both (220) and (111) in-plane alignments parallel to the direction of the ion beam could be obtained depending on the ion-to-atom ratio. Certain orientations dominate at various temperature regimes on different substrates. The orientation regimes were similar on all substrates, but the temperature at which the trends were observed differed with substrate. Microstructures were correlated to orientations, with the desired (200) orientation being columnar. A mechanism to account for this biaxial alignment is proposed.

Ion-assisted deposition of bulklike ZrO2 films

Stable thin films of zirconium dioxide are produced by ion-assisted electron beam deposition at room temperature and 300 °C. The method yields films with substantially increased packing density resulting in refractive indices close to the bulk value. The improvement in optical properties is accompanied by an amorphous to cubic crystalline transition of the film structure which is mixed with a monoclinic phase for heated films.