真空紫外铝+氟化镁膜偏振特性的研究

研究了铝＋氟化镁膜在真空紫外波段的偏振特性。理论上数值模拟计算了铝＋氟化镁膜在真空紫外波段的反射率及其与入射平面平行和垂直两方面的分量，分析了铝＋氟化镁膜反射率的两分量随入射条件和氟化镁膜厚度的变化规律，在此基础上研究了铝＋氟化镁膜的偏振特性，并与单层铝膜的相应特性作了比较，以氟化锂堆作偏振器，在Seya-Namioka真空紫外反射率计上实验研究了铝＋氟化镁膜的偏振特性。研究结果表明，铝＋氟化镁膜的偏振特性由于受到氟化镁厚度的调制，存在反射率的垂直分量小于平行分量的情形，从而使铝＋氟化镁膜的消光比在非正入射的条件下接近1。理论计算结果与实验结果一致。     

Rapid detection of nitroaromatic and nitramine explosives on chromatographic paper and their reflectometric sensing on PVC tablets

Rapid and inexpensive sensing of explosive traces in soil and post-blast debris for environmental and criminological purposes with optical sensors has recently gained importance. The developed sensing method for nitro-aromatic and nitramine-based explosives is based on dropping an acetone solution of the analyte to an adsorbent surface, letting the solvent to dry, spraying an analytical reagent to produce a persistent spot, and indirectly measuring its reflectance by means of a miniature spectrometer. This method proved to be useful for on-site determination of nitro-aromatics (trinitrotoluene (TNT), 2,4,6-trinitrophenylmethylnitramine (tetryl) and dinitrotoluene (DNT)) and nitramines (1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)) pre-adsorbed on a poly vinyl chloride (PVC) surface, with the use of different spray reagents for each group of explosives producing different colors. The calibration equations of the tested compounds as reflectance vs. concentration showed excellent linearity (correlation coefficient: 0.998-0.999). The linear quantification interval in terms of absolute quantity of analyte was 0.1-0.5 μg. The developed method was successfully tested for the analysis of military explosives Comp B and Octol, and was validated against high performance liquid chromatography (HPLC). The reflectometric sensing method could also be used for qualitative identification of the nitrated explosives on a chromatographic paper. The reagent-impregnated paper could also serve as sensor, enabling semi-quantitative determinations of TNT and tetryl.     

Effect of Pt and Ti on Ni/Ag/(Pt or Ti)/Au p-ohmic contacts of GaN based flip-chip LEDs

In this paper, we report the dependence of Ni/Ag/diffusion barrier (D.B)/Au p-ohmic contact on Pt^D.B and Ti^D.B for GaN based flip-chip light emitting diodes (FC LEDs). It is shown that D.B metals have strongly influenced on the reflectance and contact resistivity of contacts. We present these results are caused by the variation of the morphology and atomic distribution due to D.Bs. The roles of Pt^D.B and Ti^D.B on Ni/Ag/D.B/Au p-GaN ohmic contacts are analyzed using the confocal laser scanning microscopy (CLSM) measurement and the secondary ion mass spectroscopy (SIMS) profiles in details.     

Porous silicon layer for optical sensing of organic vapor

The objective of this study is to evaluate the feasibility of porous silicon (PS) layer as a vapor sensor. We prepared three types of PS layer samples - a single layer, distributed Bragg reflector (DBR) layer, and microcavity layer - and examined their reflectance spectra before, during, and after exposure to different concentrations of various organic vapors. When the PS layer samples were exposed to the organic vapors, their reflectance spectra promptly shifted toward longer wavelengths. We determined that this redshift in the reflectance spectra could be attributed to the changes in the refractive index induced by the capillary condensation of organic vapors in the pores of the PS layers. The PS layers showed excellent sensing ability under different concentrations and types of organic vapors. Once the organic vapors were removed, the reflectance spectra of the PS layer samples promptly returned to their original states. In this study, we successfully demonstrated the rapid, sensitive, and reversible sensing of organic vapors using different PS layers.     

Transverse magnetic peak type metal-clad optical waveguide sensor

Transverse magnetic (TM) waves in a four-layer slab waveguide structure are studied for optical sensing applications. The structure consists of a semi-infinite substrate, a thin metal layer, a medium with negative permittivity and permeability as a guiding layer, and a semi-infinite layer as a cover. The proposed sensor is operated in reflection mode in which the angular position of the reflectance peak is used to detect small changes in the refractive index of the cover medium. The optimal structure parameters that correspond to the sharpest and highest peak are presented. The results reveal that for aluminum metal layer, a thickness of about 9 nm represents the optimum metal thickness. Moreover, the thickness, negative permittivity, and negative permeability of the guiding layer are found to have great impacts on the performance of the proposed optical waveguide sensor.     

Realization of temperature in semiconductor using optical principle

Owing to temperature is important for both elemental and compound semiconductor to study various properties, this paper presents a novel technique to measure the temperature in semiconductor at wavelength, 10.59 μm using optical principle. Here both reflection and absorption losses are considered to find out temperature in semiconductor. Reflectance is found using plane wave expansion method, where absorption factor is determined using Maxwell's curl equations. Simulation result reveals that reflectance and transmitted intensity vary linearly with respect to different temperatures. Apart from this, it is also seen that absorbance is zero for all semiconductor at wavelength 10.59 μm. The excellent linear variation of transmitted intensity gives an accurate measurement of temperature in semiconductors at aforementioned wavelength.     

Characterization of Mn-doped Sb1.5Bi0.5Te3 single crystals

Abstract

Single crystals of (Sb_0.75Bi_0.25)_2-xMn_xTe₃ (x = 0.0–0.05) were characterized by X-ray diffraction, measurements of reflectance in the plasma resonance frequency region, Hall coefficient, electrical conductivity, and Seebeck coefficient. It was found that Mn atoms in the crystal structure of Sb_1.5Bi_0.5Te₃ behave like acceptors; the increase in the hole concentration is explained by the formation of substitutional defects of Mn'_Sb and Mn'_Bi in the crystal lattice of the studied crystals.     

土壤漏油含量光谱预测实验研究与分析

针对土壤漏油污染的检测、分析和含量预测等实际问题,用关中平原常见普通土壤、柴油、机油及油土混合物为研究对象,设计被不同油种污染以及不同污染程度的土壤光谱特征实验。采用光谱分析的方法来获取光谱指数,测量并分析渗漏相同含量两个油种的油土混合物以及渗漏不同含量同一油种的油土混合物的光谱特征及其差异,根据分析结果建立一个基于反射特征的土壤柴油渗漏含量的光谱预测模型。研究表明：(1)渗漏相同含量不同油种时,渗漏柴油的土壤的反射率低于渗漏机油的土壤;渗漏柴油和机油的土壤均在1 740和2 328 nm附近出现双吸收谷特征,且在每一个吸收谷点处渗漏柴油的土壤的光谱吸收深度和光谱吸收指数均低于渗漏相同含量机油的土壤。(2)建立的土壤柴油渗漏含量的光谱预测模型相关系数r的值达到0.854,说明模型具有较强的稳定性;评价模型预测能力的均方根误差RMSE值为0.016证明该模型具有较好预测能力,可以对土壤柴油渗漏含量进行有效的预测。     

高光谱图像的海面溢油自动检测方法研究

海面溢油对海洋环境会生成许多有害物质,导致位于食物链底端的浮游生物大量死亡,进而危害整个海洋生态系统。高光谱遥感可以获取溢油和海水的空间分布信息和光谱分布信息,利用高光谱图像进行溢油检测具有更好的检测性能。针对高光谱图像的海面溢油检测过程中需要人工辅助的缺点,提出一种基于自适应匹配滤波的高光谱图像海面溢油自动检测方法。首先,利用场景中溢油的C—H键光谱特性,设计一种溢油参考光谱特征提取模型,获取溢油检测过程中的参考光谱。其次,依据海水、云以及溢油光谱反射特性的差异,选取海水、云和溢油差异最大的波段,分割海水像素,计算溢油检测过程中的背景参数。最后,将目标检测中经典的自适应匹配滤波方法进行适当的改进应用于溢油的检测。将该方法应用于实际墨西哥湾airborne visible infrared imaging spectrometer(AVIRIS)高光谱遥感影像的海面溢油的检测,结果表明该方法具有计算速度快,不需要人工辅助等方面的特点,可用于海面溢油的自动检测。     

叶面尘对作物反射光谱及氮营养监测的影响

光谱检测技术已成为作物营养诊断的重要手段,但复杂的大田环境也增加了光谱的不确定性。以叶面尘对国道旁玉米反射光谱的影响为研究内容,分析了除尘前后叶片反射率及一阶导数光谱的差异,进而考察了叶面尘干扰下的氮营养光谱监测模型预测精度。结果表明：相对于无尘叶片,叶面尘使得叶片在可见光和短波红外光区的反射率增加,而在近红外光区的反射率减少;三边位置、蓝边斜率和黄边斜率在除尘前后无变化,而有尘叶片的红边斜率和三边面积均较无尘叶片减小;叶面尘干扰下的全氮含量光谱监测模型R2减小,预测精度降低。试验对叶面尘作为光谱检测干扰条件作了初步探讨,为今后叶面尘影响评价及建立修正模型提供理论依据。