基于光谱光学相干层析技术的膜系反射光谱测量

根据光谱光学相干层析(OCT)技术的原理,建立了光谱光学相干层析系统,并利用该系统测量了膜系的反射光谱。该方法通过傅里叶变换实现了光学相干层析信号光谱信息的提取,克服了传统反射测量方法测量结果不直观、受非测量面干扰等问题。测量所得的光谱反射率,与商业仪器的测量值吻合较好,均方差仅为0.0488。     

Magnetoplasma reflectivity studies on Cd3As2

Magnetoplasma reflectivity measurements were performed on Cd₃As₂ in order to obtain more experimental details about the structure of the plasma reflectivity edge. The experimental results can be explained by assuming the existence of a surface layer with a carrier concentration-gradient which is responsible for optical interference effects.     

Preparation and Characterization of a pH‐ and Thermally Responsive Poly(N‐isopropylacrylamide‐co‐acrylic acid)/Porous SiO2 Hybrid

A multifunctional nanohybrid composed of a pH‐ and thermoresponsive hydrogel, poly(N‐isopropylacrylamide‐co‐acrylic acid) [poly(NIPAM‐co‐AAc)], is synthesized in situ within the mesopores of an oxidized porous Si template. The hybrid is characterized by electron microscopy and by thin film optical interference spectroscopy. The optical reflectivity spectrum of the hybrid displays Fabry–Pérot fringes characteristic of thin film optical interference, enabling direct, real‐time observation of the pH‐induced swelling, and volume phase transitions associated with the confined poly(NIPAM‐co‐AAc) hydrogel. The optical response correlates to the percentage of AAc contained within the hydrogel, with a maximum change observed for samples containing 20% AAc. The swelling kinetics of the hydrogel are significantly altered due to the nanoscale confinement, displaying a more rapid response to pH or heating stimuli relative to bulk polymer films. The inclusion of AAc dramatically alters the thermoresponsiveness of the hybrid at pH 7, effectively eliminating the lower critical solution temperature (LCST). The observed changes in the optical reflectivity spectrum are interpreted in terms of changes in the dielectric composition and morphology of the hybrids.     

Non-destructive thickness characterization of Si based heterostructure by X-ray diffraction and reflectivity

High-resolution X-ray diffraction rocking curve (RC) and X-ray reflectivity (XRR) were used to characterize the Si based heterostructures grown by reduced pressure chemical vapour deposition. The investigation focused on the reliability and accuracy of thickness measurement by the different techniques. For smooth Si epilayers grown on a thin (20 nm) strained Si_0.9Ge_0.1 buffer, it is found that both XRR and RC produce reliable values that agree well with transmission electron microscope (TEM) results over a wide range. The best-fit thickness from both XRR and RC is within ±5% of the TEM measurement, with XRR producing more accurate values than RC. However, the agreement is not good for Si epilayer grown on a thick (2 μm) relaxed Si₀₇Ge_0.3 virtual substrate due to the presence of rough surface.     

Interferential lithography of 1D thin metallic sinusoidal gratings: Accurate control of the profile for azimuthal angular dependent plasmonic effects and applications

Nonlinear processes involved in the manufacture of nominally sinusoidal surface relief diffraction gratings generated by interference lithography can introduce distortions into the profile of these surfaces. Such distortions may dramatically affect both the specular reflectivity and diffracted efficiencies from such a surface [H. Raether, Phys. Thin Film 9 (1977) 145–261]. We shall consider in particular the case of metallic gratings used to investigate plasmonic effects that can be engineered for bio-sensing applications. To investigate these effects, interference lithography (IL) has been used for the generation of profile controlled sinusoidal plasmonic crystals. IL exposure contrast study has been performed to control the amplitude oscillation and the surface roughness quality. Bi-metallic layer of silver and gold have been systematically deposited with different film thicknesses. A comprehensive numerical model that studies the optical coupling to surface plasmon polaritons on Ag/Au gratings has been undertaken for the simulation of the reflectivity and azimuthal angle dependence [Z. Chen, I.R. Hooper, J.R. Sambles, J. Opt. A: Pure Appl. Opt. 10 (1) (2008) 015007]. This computation illustrates the sensitivity of individual features to specific harmonic components of the surface, for surface plasmon resonances recorded in both the zeroth and higher diffracted orders. The roughness surface control after development and after bi-metallic evaporation strongly contributes to tighten the width of the reflectivity peak. Optimization process has shown that for an Ag (37 nm) and Au (7 nm) metallic bilayer, a semi-amplitude of 20 nm provides the best reflectivity.     

MOCVD AlxGa1-xN/GaN超晶格结构的X射线反射谱与原子力显微研究

采用掠入射X射线反射谱技术与原子力显微技术对属有机化合物化学气相淀积生长的AlxGa1-xN/GaN超晶格结构的表面和界面进行了精确表征。结合高分辨率X射线衍射谱与反射谱数据分析获得外延层各层厚度与AlGaN层的Al摩尔组分。掠入射x射线反射谱的显著强度振荡与原子力显微镜所观察到的台阶流动形貌表明了平整的界面和表面的存在。研究发现,低Al组分（x=0.25）且阱宽小的样品界面与表面粗糙度最小,通过原子力显微技术得到的表面粗糙度均方根偏差为0.45nm。     

纳秒脉冲激光加工高反射率铝膜

为了研究基于近红外纳秒脉冲激光的高反射率金属薄膜的加工可行性以及加工效果, 采用纳秒脉冲激光对高反射率铝膜进行激光加工, 分别测量了在不同激光光斑尺寸和不同激光能量的条件下, 铝膜表面所发生的烧蚀形态变化。结果表明, 即使铝膜表面反射率高达96%, 依然能对铝膜进行激光加工; 使用较高功率激光对铝膜表面进行离焦加工(能量密度约小于1000J/mm2)的烧蚀图样比使用较低功率激光对铝膜表面进行对焦加工(能量密度约大于2000J/mm2)的烧蚀图样更加规则。相关实验结果对激光加工高反射率材料时激光参量的选择可起到一定的指导作用。     

Ga_xIn_(1-x)P/AlGaInP多量子阱的吸收/反射光谱:多光束干涉的影响与消减

通过测量GaAs基GaxIn1-xP/AlGaInP多量子阱的光学吸收谱 ,揭示出采用吸收谱研究该量子阱系统所遭遇的困难 ,并判明吸收谱中高频振荡干扰的来源为多光束干涉 ,从而指出消减振荡干扰的有效途径在于降低量子阱样品的有效厚度 .提出了适用于反射光谱测量的样品结构 ,并在实验中观察到激子跃迁 .通过对反射谱进行导数操作 ,达到了准确测定激子跃迁能量的目的 ,为采用反射谱法研究该量子阱系统的光学特性提供了技术基础     

Confinement of Thermoresponsive Hydrogels in Nanostructured Porous Silicon Dioxide Templates

A thermoresponsive hydrogel, poly(N‐isopropylacrylamide) (poly(NIPAM)), is synthesized in situ within an oxidized porous Si template, and the nanocomposite material is characterized. Infiltration of the hydrogel into the interconnecting nanoscale pores of the porous SiO₂ host is confirmed by scanning electron microscopy. The optical reflectivity spectrum of the nanocomposite hybrid displays Fabry–Pérot fringes characteristic of thin film interference, enabling direct, real‐time observation of the volume phase transition of the confined poly(NIPAM) hydrogel. Reversible optical reflectivity changes are observed to correlate with the temperature‐dependent volume phase transition of the hydrogel, providing a new means of studying nanoscale confinement of responsive hydrogels. The confined hydrogel displays a swelling and shrinking response to changes in temperature that is significantly faster than that of the bulk hydrogel. The porosity and pore size of the SiO₂ template, which are precisely controlled by the electrochemical synthesis parameters, strongly influence the extent and rate of changes in the reflectivity spectrum of the nanocomposite. The observed optical response is ascribed to changes in both the mechanical and the dielectric properties of the nanocomposite.     

Magnetic field sensor based on peanut-shape structure and multimode fiber

An all fiber magnetic field sensor with peanut-shape structure based on multimode fiber (MMF) is proposed and experimentally demonstrated. The sensing structure and magnetic fluid (MF) are both encapsulated in capillary, and the effective refractive index of MF is affected by surrounding magnetic field strength. The measurement of magnetic field is realized by observing the wavelength drift of interference peak. The transmission spectrum generated by Mach-Zehnder interferometer (MZI) includes core-core mode interference and core-cladding mode interference. Experimental results demonstrate that the core-cladding mode interference is sensitive to magnetic field, and the magnetic field sensitivity is 0.047 8 nm/mT. In addition, two kinds of interference dips are sensitive to temperature, and the sensitivities are 0.060 0 nm/°C and 0.052 6 nm/°C, respectively. So the simultaneous measurement of magnetic field strength and temperature can be achieved based on sensitivity matrix. This work has been supported by the National High Technology Research and Development Program of China (No.2013AA014200), the National Natural Science Foundation of China (No.11444001), and the Municipal Natural Science Foundation of Tianjin (No.14JCYBJC16500). E-mail:13821538563@163.com      

Porous silicon as an intermediate buffer layer for GaN growth on (100) Si

We report preliminary results on the growth of GaN on (100) Si substrate using porous silicon (PS) as an intermediate buffer layer. The growth was in situ monitored by laser beam reflectivity. Analysis of the evolution of the reflectivity signal indicates a change from relatively flat surface to rough one as the growth temperature (T_g) is increased. At a temperature of about 1050°C, the growth rate is very low and the reflected signal intensity is constant. When the growth temperature is varied, no drastic change of the porosity of the intermediate layer was detected. Scanning electron microscope (SEM) observations of the GaN/SP/Si structure revealed a good surface coverage at 500°C. When T_g increases, the structure morphology changes to columnar like structure at 600°C, and well-developed little crystallites with no preferential orientation appear at 800°C. These observations agree well with the X-ray diffraction (XRD) analysis. A preferential hexagonal growth is obtained at low growth temperature, while cubic phase begin to appear at elevated temperatures.     

<Emphasis Type="Italic">In Situ</Emphasis> Spectral Reflectance Investigation of InAs/GaAs Heterostructures Grown by MOVPE

Metalorganic vapor-phase epitaxy of InAs/GaAs heterostructures was monitored in situ by spectral reflectance in the wavelength range from 600 nm to 1000 nm. Three-dimensional (3D) plots of reflectivity as a function of time and wavelength were used to determine the growth rate evolution. Theoretical simulation of reflectivity signals was carried out by combining a transfer matrix method and a multi-sublayer model. In spite of fixed growth parameters, there was temporal variation of the growth rate. By adjusting simulated reflectivity curves, optical constants of the InAs layer at 450°C were determined. The E ₁ critical point energy was also found experimentally at this temperature. Good agreement with calculated values is obtained.     

Spatial Distribution of the Seebeck Coefficient in Zn<Subscript>13</Subscript>Sb<Subscript>10</Subscript> Determined by a Seebeck Microprobe Measurement System

A Seebeck microprobe (SMP) measurement system has been developed and employed to determine the spatial distribution of the Seebeck coefficient of a polycrystalline Zn₁₃Sb₁₀ specimen prepared by a gradient freeze (GF) method. The spatial distribution of the Seebeck coefficient strongly reflects that of the grains observed using an optical polarizing microscope, the magnitude of which ranges from 100 μV/K to 130 μV/K. This fact strongly indicates that the observed spatial distribution of the Seebeck coefficient arises from the anisotropic Seebeck effect of grains with different crystal orientations in the polycrystalline Zn₁₃Sb₁₀.     

Influence of Raindrop-Size Distribution on the Differential Reflectivity up to Submillimeter Wavelength of 0.96 mm

The rain attenuation was calculated by using the Marshall and Palmer, the gamma and the Weibull raindrop-size distributions. The microwave experimental measurement data from 8.4 GHz (3.75 mm) to 312.5 GHz (0.96 mm) were compared with our calculations. The Weibull distribution has the best agreement with the measurements, especially above 100 GHz. The differential reflectivity Z _DR was also calculated using these three distributions. To this end, we used the horizontal and vertical radar cross sections which were computed from Waterman's T-matrix method. It is shown that Z _DR greatly depends on raindrop-size distributions and has potential for determing drop-size distributions with high accuracy.     

用633nm的激光器监控峰值波长为 530nm的AlGaN/GaN DBR的生长

本文从理论和实验上研究了用633nm激光器干涉仪监控峰值反射波长为530nm的1/4光学厚度的AlGaN/GaN 分布布拉格反射器（DBR）的生长。首先采用传输矩阵法从理论上研究了不同周期厚度的AlGaN/GaN DBR的实时反射率随DBR生长厚度的变化。接着采用金属有机化合物气相外延法生长了两个与模拟结构相同的DBR样品。仿真结果和实验结果表明能够从DBR实时反射率随生长厚度变化的曲线形状判断DBR的结构参数。最后通过激光干涉仪实时监控生长了DBR发光二极管,光致发光实验证明DBR对发光二极管出射光的加强作用在期望波长范围内。     

Influence of Molecular Weight on the Surface Morphology of Aligned,Branched Side‐Chain Polyfluorene

The surface structure of uniaxially aligned poly(9,9‐bis(ethylhexyl)‐fluorene‐2,7‐diyl) films on rubbed polyimide has been studied as a function of molecular weight (M_n = 3–150 kg mol^–1, number‐average molecular weight) using polarized microscopy, atomic force microscopy (AFM), X‐ray reflectivity, and grazing‐incidence X‐ray diffraction. At the threshold M_n, M_n* = 10⁴ g mol^–1, there is a prominent transition in morphology from featureless (M_n < M_n*) to rough (M_n > M_n*), corresponding to the nematic–hexagonal phase transition. The hexagonal phase reveals two coexistent crystallite types in the whole film and at least one crystallite type has been observed at the surface by AFM. The combined optimization of alignment and surface smoothness is achieved slightly below M_n* while the combined optimization of orientational and local order and moderately smooth surface is achieved slightly above M_n*.     

Roughness and texture correlation of Al films

Titanium films prepared by standard direct-current (DC) magnetron physical vapor deposition (PVD) and ionized metal plasma PVD (I-PVD), with Al (0.5wt.%Cu) films on them, were studied. The surface roughness, reflectivity, and crystalline texture of Ti on SiO₂/Si and Al on TiN/Ti/SiO₂/Si were investigated with the same thickness of Al, TiN, and Ti. The surface roughness of Al films with Ti/TiN underlayers was found to be capable of monitoring Al(111) texture. So, the reflectivity of Al/TiN/Ti film stack can be used as a quick monitor for the electromigration (EM) lifetime.     

Reflectivity degradation of grazing-incident EUV mirrors by EUV exposure and carbon contamination

Reflectivity degradation of grazing-incident extreme ultraviolet (EUV) mirror samples by EUV exposure was investigated in a commercial XTS 13-35 EUV source. The roughness of EUV exposed samples increases with an increase in exposure time due to the erosion of sample surface by ions and neutrals, or deposition of contaminant such as carbon on the sample surface. While energetic debris certainly affects mirror reflectivity, the loss in reflectivity observed in EUV exposed samples surpassed that which would be attributable simply to induced surface roughness through sputtering. Surface analysis of the EUV mirror sample surface after exposure confirmed that carbon contamination was present. Experimentally measured reflectivity of EUV mirrors showed degradation after EUV exposure due to the carbon contamination present in the investigated system. The measured reflectivity data were fitted by changing the carbon film thickness using a bi-layer mirror model in the CXRO simulator. The experimentally measured values of reflectivity are in good agreement with the simulation results. The contamination rate was found to be dependent on the carbon contamination thickness. The contamination rate is fast (7 × 10⁻⁵ nm/shot) in the beginning of contamination growth whereas it gets slower (2 × 10⁻⁵ nm/shot) as carbon builds up on the Ru mirror surface. An analytical model taking the sputtering by ions into account was developed to understand the variation of carbon contaminant deposition rate with exposure time. In our model, the fast contamination rate in the beginning of carbon buildup is explained by the interplay of photo electron emission and the varying sputtering yield of the growing carbon layer on the EUV mirror.     

Current-voltage characteristics of silicon-doped GaAs nanowhiskers with a protecting AlGaAs coating overgrown with an undoped GaAs layer

A technique for measurement of longitudinal current-voltage characteristics of semiconductor nanowhiskers remaining in contact with the growth surface is suggested. The technique is based on setting up a stable conductive contact between the top of a nanowhisker and the probe of an atomic-force microscope. It is demonstrated that, as the force pressing the probe against the top of the nanowhisker increases, the natural oxide layer covering the top is punctured and a direct contact between the probe and the nanowhisker body is established. In order to prevent nanowhiskers from bending and, ultimately, breaking, they need to be somehow fixed in space. In this study, GaAs nanowhiskers were kept fixed by partially overgrowing them with a GaAs layer. To isolate nanowhiskers from the matrix they were embedded in, they were coated by a nanometer layer of AlGaAs. Doping of GaAs nanowhiskers with silicon was investigated. The shape of the current-voltage characteristics obtained indicates that introduction of silicon leads to p-type conduction in nanowhiskers, in contrast to n-type conduction in bulk GaAs crystals grown by molecular-beam epitaxy. This difference is attributed to the fact that the vapor-liquid-solid process used to obtain nanowhiskers includes a final stage of liquid-phase epitaxy, a characteristic of the latter being p-type conduction obtained in bulk GaAs(Si) crystals.     

Microwave Bistatic Reflectivity Dependence on the Moisture Content And Matric Potential of Bare Soil

Results are presented of an experimental program to determine the functional dependence of the microwave reflectivity of nonvegetated soil surfaces upon volumetric soil moisture and matric potential. A combination evaporation-drainage field experiment was conducted on a bare Captina silt loam with reflectivity, soil moisture content, and matric potential monitored for extended time periods. Results show that for a restricted pressure range (approximately -0.05 to -0.75 bar) there is excellent linear correlation between the log of bistatic reflectivity and both volumetric moisture content and matric potential. Layering effects due to steep moisture content (and matric potential) gradients in the profile are demonstrated to have two distinct and significant effects on the reflectivity response. At near saturation of rough surfaces a very thin dry surface layer appears to modify the effective roughness. This leads to a saturation of reflectivity at high moisture contents. As the surface proceeds to dry further, deeper layers produce coherent interference patterns in the reflectivity response, particularly at the higher frequencies.