Internal Electric Field Investigations of a Cadmium Zinc Telluride Detector Using Synchrotron X-ray Mapping and Pockels Effect Measurements

Cadmium zinc telluride (CZT) has remained a major focus of research due to its promising application as a room-temperature nuclear radiation detector material. Among the several parameters that substantially affect the detectors’ performance, an important one is the distribution of the internal electric field. Brookhaven National Laboratory (BNL) employed synchrotron x-ray microscale mapping and measurements of the Pockels effect to investigate the distribution of the internal electric field in a CZT strip detector. Direct evidence that dislocations can distort the internal electric field of the detector was obtained. Furthermore, it was found that “star” defects in the CZT crystal, possibly ascribed to dislocation loop punching, cause charge trapping.     

Comparative Study on MOCVD Growth of a-Plane GaN Films on r-Plane Sapphire Substrates Using GaN, AlGaN, and AlN Buffer Layers

In this work, we have comparatively investigated the effects of the GaN, AlGaN, and AlN low-temperature buffer layers (BL) on the crystal quality of a-plane GaN thin films grown on r-plane sapphire substrates. Scanning electron microscopy images of the a-plane GaN epilayers show that using an AlGaN BL can significantly reduce the density of surface pits. The full-width at half-maximum values of the x-ray rocking curve (XRC) are 0.19°, 0.36°, and 0.48° for the films grown using Al_0.15Ga_0.85N, GaN, and AlN BLs, respectively, indicating that an AlGaN BL can effectively reduce the mosaicity of the films. Room-temperature photoluminescence shows that the AlGaN BL results in lower impurity incorporation in the subsequent a-plane GaN films, as compared with the case of GaN and AlN BLs. The higher crystal quality of a-plane GaN films produced by the Al_0.15Ga_0.85N BL could be due to improvement of BL quality by reducing the lattice mismatch between the BL and r-sapphire substrates, while still keeping the lattice mismatch between the BL and epitaxial a-plane GaN films relatively small.     

Analysis of Oxidized <Emphasis Type="Italic">p</Emphasis>-GaN Films Directly Grown Using Bias-Assisted Photoelectrochemical Method

A bias-assisted photoelectrochemical oxidation method was used to oxidize p-GaN directly. Secondary-ion mass spectrometry and x-ray photoelectron spectroscopy were used to analyze the grown films, confirming that the p-GaN can be oxidized using the bias-assisted PEC oxidation method. In addition, x-ray diffraction was used to analyze the crystalline phase of the grown films annealed at different temperatures. After annealing the oxide films at 700°C in O₂ ambient for 2 h, the oxidized p-GaN films were converted from amorphous to the β-Ga₂O₃ crystalline phase.     

Discommensuration of Doped [Ca<Subscript>2</Subscript>CoO<Subscript>3</Subscript>]<Subscript><Emphasis Type="Italic">p</Emphasis></Subscript>CoO<Subscript>2</Subscript>

Single-crystal x-ray diffraction and high-resolution electron microscopy studies were carried out for Co-121 ([Ca₂CoO₃] _p CoO₂) and Sr-doped Co-121 grown in a KCl flux at 810°C. Typically, the samples were 2 mm × 2 mm × 0.02 mm in size. The single-crystal diffraction intensities were measured by the use of a four-circle diffractometer. Twinned super reflections, e.g., and were observed in the electron diffraction patterns. These super reflections were not observed in the end-member. Diffuse scattering was observed in the same reciprocal space by the single-crystal x-ray diffraction study. A discommensurate crystal model is proposed for the Sr-doped system.     

基于粗糙度形貌数据的花岗岩表面双向反射特性研究

利用原子力扫描探针显微镜(AFM)获得了花岗岩表面粗糙度形貌数据,分析了该实际表面的形貌特征.在几何光学近似下,根据该实际表面形貌数据采用Monte Carlo法,并考虑表面散射过程中的入射遮蔽及多次散射效应,模拟了实际表面的双向反射分布函数(BRDF).将BRDF'模拟值与在入射波长为O.6328μm、不同的入射天顶角和入射平面内条件下实验测得的BRDF值进行比较,结果表明在适当的误差范围内两者符合较好.     

PCB镀金层致密性分析

介绍利用俄歇电子能谱分析(AES)法对元素深度分布进行分析,利用扫描电子显微镜(SEM)进行表面形貌分析,并通过稀盐酸腐蚀比较试验,分析评价了PCB镀金层致密性。     

Structural stability of ultra-high temperature refractory material MoSi_2 and Mo_5Si_3 under high pressure

In-situ angle dispersive x-ray diffraction(ADXRD) with synchrotron radiation source is performed on an ultra-high temperature refractory of MoSi_2 and Mo_5Si_3 by using a diamond anvil cell(DAC) at room temperature. While the pressureinduced volume reduction is almost constant, the value of the bulk modulus increases with the decrease of molybdenum content in the system. According to the Brich–Murnaghan equation, the bulk modulus 222.1(2.1) GPa with its pressure derivative 4 of MoSi_2, and the bulk modulus 308.4(7.6) GPa with its pressure derivative 0.7(0.1) of Mo_5Si_3 are obtained.The experimental data show that MoSi_2 has distinct anisotropic behavior, Mo_5Si_3 is less anisotropic than MoSi_2. The result shows that MoSi_2 and Mo_5Si_3 have the structural stabilities under high pressure. When the pressure reaches up to 41.1 GPa, they can still maintain their body-cantered tetragonal structures.     

Crystallite misorientation analysis in semiconductor wafers and ELO samples by rocking curve imaging

Rocking curve imaging is based on measuring a series of Bragg-reflection digital topographs by monochromatic parallel-beam synchrotron radiation in order to quantify local crystal lattice rotations within a large surface area with high angular and high spatial resolution. In this paper we apply the method to map local lattice tilts in two distinct semiconductor sample types with lattice misorientations up to 0.5° and with spatial resolution from 30  down to 1 . We analyse the measured surface-tilt data volumes for samples with almost smoothly varying specific misoriented defect formation in GaAs wafers and for an inherent subsurface grain structure of epitaxial lateral overgrowth wings in GaN. Back-projected tilt maps and histograms provide both local and global characteristics of the microcrystallinity.     

浙江西北部山地暴雨特征

利用2005-2017年14个自动气象站和2015-2017年66个自动气象站的降水资料,对浙西北暴雨的时空分布特征进行了分析,发现浙西北雨量分布呈西南、东北多,中部、东部少的特征,有2个暴雨中心,一个是位于清凉峰到大明山一带的梅汛期暴雨中心,另一个为天目山北部市岭一带的台风暴雨中心;暴雨存在明显的月、日变化特征,7-8月暴雨最多,春雨期暴雨主要出现在日落后,梅雨期主要出现在早晨前后,其次是午后,盛夏时主要出现在午后;6月前暴雨集中在西部、南部,7月出现明显转折,西南暴雨迅速减少,东北部天目山市岭一带暴雨明显增多。市岭地形为东北-西南河谷型,受狭管效应和地形抬升的影响,当台风位于天目山东南部时,天目山一带吹东北风对降水增幅最明显。     

Nanoscale anglesite growth on the celestite (0 0 1) face

In situ atomic force microscopy (AFM) was used to study the growth behaviour of anglesite (PbSO₄) monolayers on the celestite (0 0 1) face. Growth was promoted by exposing the celestite cleavage surfaces to aqueous solutions that were supersaturated with respect to anglesite. The solution supersaturation, β_ang, was varied from 1.05 to 3.09 (where β_ang = a(Pb²⁺) · a(SO₄²⁻)/K_sp,ang). In this range of supersaturation, two single anglesite monolayers (3.5 Å in height each) from pre-existent celestite steps were grown. However, for solution supersaturation β_ang < 1.89 ± 0.06, subsequent multilayer growth is strongly inhibited. AFM observations indicate that the inhibition of a continuous layer-by-layer growth of anglesite on the celestite (0 0 1) face is due to the in-plane strain generated by the slight difference between the anglesite and celestite lattice parameters (i.e. the linear misfits are lower than 1.1%). The minimum supersaturation required to overcome the energy barrier for multilayer growth gave an estimate of the in-plane strain energy: 11.4 ± 0.6 mJ/m²_. Once this energy barrier is overcome, a multilayer Frank–Van Der Merwe epitaxial growth was observed.