Using fence post designs to speed the atomic layer deposition of optical thin films

Atomic layer deposition (ALD) at this time is much slower than conventional optical thin-film deposition techniques. A more rapid ALD process for SiO(2) has been developed than for other ALD materials. A fence post design for optical thin films has thin layers of high-index posts standing above a broad low-index ground. If a design for ALD can be predominantly composed of SiO(2) layers with thin high-index layers, the deposition times can be correspondingly shortened, and it is shown that the required performance can still be nearly that of more conventional designs with high- and low-index layers of equal thickness. This combination makes the ALD benefits of conformal coating and precise thickness control more practical for optical thin-film applications.     

Simulation of errors in the monitoring of narrow bandpass filters

Narrow bandpass filters are extremely sensitive to errors in the optical thickness of the layers, but they have an extraordinary inherent capability to compensate for these errors. Graphical examples of errors of differing magnitudes and types with and without compensation are shown with computer simulation of the optical monitoring techniques. This allows the estimation of what magnitude of errors may be tolerable in given applications.     

Iterative WLS design of SAW bandpass filters

It has been demonstrated by several authors that the well-known weighted least squares (WLS) approximation can be equiripple if a suitable weighting function is applied. In the present paper, the WLS algorithm is generalized to SAW filter synthesis with prescribed magnitude and phase specifications. Several weighting techniques producing quasi-equiripple designs are presented. The frequency sampling technique is used for SAW filter frequency response approximation to reduce the number of optimized variables. The WLS algorithm rapidly converges both for linear and nonlinear phase SAW filters. Typically, no more than 5-10 iterations are required to obtain the WLS solution to accuracy better than 0.5-1 dB in the stopband when compared with the optimum Chebyshev approximation. Moreover, it is shown that the WLS technique can be effectively applied for second-order effect compensation.     

Optimal and suboptimal design of SAW bandpass filters using the Remez exchange algorithm

Optimal and suboptimal design techniques for surface acoustic wave (SAW) linear phase filters based on both the Remez exchange algorithm and the McClellan computer program (J.H. McClellan et al., 1973) are considered. The optimal synthesis provides uniquely the best fit to a design target, but its major drawback is an excessive amount of computation. The suboptimal synthesis technique proposed allows a considerable reduction of the amount of computations without significantly sacrificing the approximation accuracy. Thus computer runtime and storage are greatly reduced compared to the optimal synthesis. The detailed suboptimal theory and some practical design aspects are discussed. Design examples are presented which confirm the efficiency and the flexibility of the synthesis techniques proposed.     

Group delay and chromatic dispersion of thin-film-based,narrow bandpass filters used in dense wavelength-division-multiplexed systems

Theoretical analysis is made for thin-film-based, 200- and 100-GHz narrow bandpass filters with respect to the intensity response as well as to the chromatic dispersion. The results indicate that the narrower the passband, the higher the chromatic dispersion. The maximum chromatic dispersion appears at the edges of the 0.5-dB passband, owing to the fast change of the group delay in the region. The deviation of chromatic dispersion induced by manufacturing error is simulated. Effective-medium approximation layers are added to simulate the contribution of surface roughness and the mixture interfaces to the passband ripple as well as the chromatic dispersion. The simulations are compared with the experimental results. The measured chromatic dispersion matches the general trend of the theoretical calculation. The imperfect surface and layer mismatch induce additional ripples across the 0.5-dB passband. The maximum chromatic dispersion within a 0.5-dB passband is 20.7 and 54.9 ps/nm for 200- and 100-GHZ narrow bandpass filters, respectively.     

Resonant metal-mesh bandpass filters for the far infrared

The spectral performance of freestanding resonant metal-mesh bandpass filters operating with center frequencies ranging from 585 GHz to 2.1 THz is presented. These filters are made up of a 12-μm-thick copper film with an array of cross-shaped apertures that fill a circular area with a 50-mm diameter. The filters exhibit power transmission in the range 97-100% at their respective center frequencies and stop-band rejection in excess of 18 dB. The theoretically predicted nondiffracting properties of the meshes are experimentally verified through high-resolution beam mapping. Scalability of the filter spectra with mesh dimensions is demonstrated over a wide spectral range. Several modeling methods are considered, and results from the models are shown.     

Cross-shaped bandpass filters for the near- and mid-infrared wavelength regions

A photolithographic process has been used to form cross-shaped patterns in 3-μm-thick nickel foils. Patterns with cross arm dimensions in the 10-20-μm range, and with periodicities in the 16-26-μm range, yield self-resonant bandpass filters for wavelengths in the 20-25-μm region. Transmittances as high as 80% were achieved with center wavelength-to-bandwidth ratios (λ(R)/Δλ) of ~5. We present a simple empirical formula that relates the wavelength of peak transmittance, or resonant frequency, with cross dimensions and periodicity.     

基于计算机辅助的光学薄膜优化设计方法

概述了光学薄膜优化设计的发展和光学薄膜优化设计的原理。详细介绍了当前光学薄膜优化设计中几种常用方法并分析了它们的优缺点，最后预测了光学优化设计方法以后的发展趋势。     

Low temperature growth and properties of Cu-In-Te based thin films for narrow bandgap solar cells

Cu-In-Te based thin films were grown onto soda-lime glass (SLG) substrates at 200 °C by co-evaporation using a molecular beam epitaxy system. The microstructural properties were examined by means of scanning electron microscopy, X-ray diffraction and Raman scattering. The crystalline quality of Cu-In-Te based thin films with high Cu/In ratios is superior to that of films with low Cu/In ratios. The films with Cu/In ratios of 0.69 ± 0.04 exhibited a single chalcopyrite phase with random orientation, whereas a defect chalcopyrite phase with a preferred (112) orientation was obtained for thin films with Cu/In ratios of 0.26 ± 0.02. However, the films with high Cu/In ratios of 0.69 ± 0.04 showed nearly constant low resistivity (∼ 10^− 2 Ω cm) at temperatures from 80 to 400 K due to high hole concentration (> 10¹⁹ cm^− 3), resulting in semi-metallic behavior. The hole conduction mechanism of the film (Cu/In atomic ratios = 0.26 ± 0.02) with semi-conductive properties was found to be variable-range-hopping of the Mott type in the wide range of 80-300 K. The optical bandgaps of Cu-In-Te based thin films are determined to be 0.93-1.02 eV at 300 K from transmission and reflection measurements. A solar cell with a ZnO/CdS/CuIn₃Te₅/Mo/SLG structure showed a total area (0.50 cm²) efficiency of 5.1% under AM1.5 illumination (100 mW/cm²) after light soaking. The conduction band offset at the CdS/CuIn₃Te₅ interface was estimated to be − 0.14 eV from X-ray photoelectron spectroscopy analysis.     

Taguchi design for fabrication of high-performance as-deposited Fe-Sm-O thin films

The Taguchi experimental design was used in this study to obtain optimal conditions for which as-deposited Fe-Sm-O thin films with both good soft magnetic properties and high electrical resistivity could be fabricated by r.f. magnetron sputtering method. The factors considered were the number of Sm₂O₃ chips, sputtering power and time, base vacuum, Ar work pressure, and O₂ partial pressure. The results showed that the optimal conditions were as follows: four Sm₂O₃ chips sputtering power of 350 W, sputtering time of 10 min, base vacuum of 2.6×10^-4Pa, work pressure of 0.2 Pa and O₂ content in Ar of 5%. The thin film fabricated at those conditions had the composition of Fe_75.3Sm_4.3O_20.4. The properties of as-deposited Fe_75.3Sm_4.3O_20.4 thin film were: saturation magnetization of 16.3 kG, coercivity of 0.9 Oe, effective permeability of 2200 in the range of 0.5–100 MHz, and electrical resistivity of 190 cm. The percentage contribution of each factor to electrical resistivity, soft magnetic properties such as magnetic permeability, coercivity and saturation magnetization were also calculated.     

Radiation damage effects in far-ultraviolet filters, thin films, and substrates

Advances in vacuum ultraviolet thin-film filter technology have been made through the use of filter designs with multilayers of materials such as Al(2)O(3), BaF(2), CaF(2), HfO(2), LaF(3), MgF(2), and SiO(2). Our immediate application for these filters will be in an imaging system to be flown on a satellite where a 2 × 9 R(E) orbit will expose the instrument to approximately 250 krad of radiation. Because to our knowledge no previous studies have been made on the potential radiation damage of these materials in the thin-film format, we report on such an assessment here. Transmittances and reflectances of BaF(2), CaF(2), HfO(2), MgF(2), and SiO(2) thin films on MgF(2) substrates, Al(2)O(3) thin films on fused-silica substrates, uncoated fused silica and MgF(2), and four multilayer filters made from these materials were measured from 120 to 180 nm beforeand after irradiation by 250 krad from a (60)Co gamma radiation source. No radiation-induced losses in transmittance or reflectance occurred in this wavelength range. Additional postradiation measurements from 160 to 300 nm indicates 2-5% radiation-induced absorption near 260 nm in some of the samples with MgF(2) substrates. From these measurements we conclude that far-ultraviolet filters made from the materials tested should experience less than 5% change from exposure to up to 250 krad of high-energy radiation in space applications.     

Preparation and characterization of new hybrid nanostructured thin films for biosensors design

The present paper reports on an innovative route for the preparation of new hybrid nanostructured thin films based on hydroxyapatite and functionalized polyurethane. Hybrid nanopowders based on hydroxyapatite and functionalized polyurethane have been synthesized by a hydrothermal method with high pressure and low temperature conditions and further used for spin coating deposition. Biocompatible thin films with a thickness of about 50 nm have been deposited onto Si/SiO₂/Ti/Au substrates and their properties recommend them suitable as possible electrodes for the fabrication of impedance biosensors. Hybrid materials with improved properties are obtained, combining the mechanical properties of polyurethane with biocompatible properties of hydroxyapatite (bioactivity and osteoconductivity). The presence of functional groups in polyurethane structure ensures the existence of strong interactions between components and an increased affinity of the thin films for further protein bonding in biosensor design. Hybrid nanostructured thin films based on hydrothermally synthesized hydroxyapatite-polyurethane nanopowders could enhance the amount of immobilized biomolecules in the construction of an impedance biosensor for diagnosis and therapy of bone diseases.     

Optimization of the planar hall effect in ferromagnetic thin films for device design

The planar Hall effect, although directly related to the magnetoresistance effect, differs in its potential uses by the disposition of the sensing electrodes allowing an internal balance of the excitation voltage drop. An experimental study of ferromagnetic thin film conditions of evaporation, film thickness, composition and shape of the electrodes has been undertaken. Anisotropic Ni-Fe films with various additions of Pd, V, Co, Mo, showed a maximum planar Hall effect for the composition 86-percent Ni, 14-percent Fe. The optimization of the geometrical parameters of the electrodes and the magnetic film elements is described, allowing one to design for maximum output voltage or maximum output current in a short circuited loop. Two schemes are presented for implementation of small NDRO memories.     

The effect of deposition parameters and post treatment on the electrical properties of Mo thin films

In this study, we deposited low-resistivity molybdenum (Mo) thin films on soda-lime glass substrates with good adhesion. We adjusted various deposition parameters such as the sputtering power (52-102 W), working distance (5.5-9 cm) and annealing temperature (26-400 °C) to investigate their impact on the sheet resistance. By using a DC magnetron sputtering system, we obtained Mo thin films having the lowest sheet resistance of 0.190 Ω/□ with a sputtering power of 82 W, working distance of 6.5 cm, and annealing temperature of 400 °C; in addition, these films had good adhesivity. These Mo thin films were suitable for use as the Mo back contact in Cu(In,Ga)Se₂-based solar cells.     

锗纳米镶嵌薄膜的电致发光及其机制

采和射频磁控溅射技术,在Ge纳米镍嵌薄膜的基础上制备出电致发光器件。器件的结构为半透明Au膜／Ge纳米镍嵌薄膜／p-Si基片。当正向邻居坟大于6V时,用肉眼可以观察到可见的电致发光,但在反向偏压下探测不到光发射。所测电致发光谱中只有一个发光峰,峰位在510nm（2．4eV,绿光）,并且随着正向偏坟的升高,峰位不发生移动;对于不同温度退火的样品,峰位也保持不变。根据分析结果讨论了可能的电致发光机制。     

Factorial design preparation of transparent conducting oxide thin films

Transparent and conducting properties of Cd₂SnO₄ films deposited onto glass substrates by the dip coating technique have been obtained using a 2⁴ factorial design. All films were well adhered onto their substrates, presented porous morphology and inverse spinel structure. Statistical factorial design analysis showed that only substrate withdrawal rate and precursor solution concentration had significant effects on average transmission of the films. Cumulative probability graphs of factorial design model coefficients showed that none of the factor levels have significant effects on resistivity. However the films presented significantly higher resistivities using low withdrawal rates and low concentration levels. This indicates resistivity is a more complex function of the factor variables than transmission. From the factorial design experiments and statistical analysis of their results a highest average transmission of 88% and lowest resistivity of 2.43 × 10^− 4 Ω m were found.     

CrNx薄膜的制备及结构分析

用正交设计法L16设计了五因素四水平共16种工艺，用热阴极离子镀在GCr15块规上制备CrNx薄膜。用X射线衍射议（XRD）分别对16个试样进行了物相分析及结构分析，用显微硬度计（25g）测试了显微硬度，并对检测结果进行了分析讨论。结果表明：工艺参数的变化对于CrNx薄膜的制备会产生重要影响。