WAVELET METHOD FOR CALCULATING THE DEFECT STATES OF TWO-DIMENSIONAL PHONONIC CRYSTALS

Based on the variational theory, a wavelet-based numerical method is developed to calculate the defect states of acoustic waves in two-dimensional phononic crystals with point and line defects. The supercell technique is applied. By expanding the displacement field and the material constants （mass density and elastic stiffness） in periodic wavelets, the explicit formulations of an eigenvalue problem for the plane harmonic bulk waves in such a phononic structure are derived. The point and line defect states in solid-liquid and solid-solid systems are calculated. Comparisons of the present results with those measured experimentally or those from the plane wave expansion method show that the present method can yield accurate results with faster convergence and less computing time.

Electronic structure and defect states of transition films from amorphous to microcrystalline silicon studied by surface photovoltage spectroscopy

In this paper, surface photovoltage spectroscopy （SPS） is used to determine the electronic structure of the hydrogenated transition Si films. All samples are prepared by using helicon wave plasma-enhanced chemical vapour deposition technique, the films exhibit a transition from the amorphous phase to the microcrystalline phase with increasing temperature. The film deposited at lower substrate temperature has the amorphous-like electronic structure with two types of dominant defect states corresponding to the occupied Si dangling bond states （D^0/D^-） and the empty Si dangling states （D＋）. At higher substrate temperature, the crystallinity of the deposited films increases, while their band gap energy decreases. Meanwhile, two types of additional defect states is incorporate into the films as compared with the amorphous counterpart, which is attributed to the interface defect states between the microcrystalline Si grains and the amorphous matrix. The relative SPS intensity of these two kinds of defect states in samples deposited above 300℃ increases first and decreases afterwards, which may be interpreted as a result of the competition between hydrogen release and crystalline grain size increment with increasing substrate temperature.

Low temperature photoluminescence study of Ga As defect states

Low temperature(77 K)photoluminescence measurements have been performed on different GaAs substrates to evaluate the GaAs crystal quality.Several defect-related luminescence peaks have been observed,including 1.452 eV,1.476 eV,1.326 eV peaks deriving from 78 meV GaAs antisite defects,and 1.372 eV,1.289 eV peaks resulting from As vacancy related defects.Changes in photoluminescence emission intensity and emission energy as a function of temperature and excitation power lead to the identification of the defect states.The luminescence mechanisms of the defect states were studied by photoluminescence spectroscopy and the growth quality of GaAs crystal was evaluated.

Influence of defect states on band gaps in the two-dimensional phononic crystal of 4340 steel in an epoxy

The band structures of a new two-dimensional triangle-shaped array geometry of 4340 steel cylinders of square cross section in an epoxy resin were studied by the plane-wave expansion and supercell calculation method. The band gaps of this type of phononic crystals with different defects were calculated such as defect-free, 60° crystal linear defect states, 120° crystal linear defect states, and 180° crystal linear defect states. It was found that the band gap will emerge in different linear defects of the phononic crystals and the bandwidth of linear defect states is larger than that of the free-defect crystal by about 2.14 times within the filling fraction F = 0.1-0.85. In addition, the influence of the filling fraction on the relative width of the minimum band gap is discussed.

Influence of defect states on the performances of planar tin halide perovskite solar cells

Although tin halide perovskite has shown excellent photoelectric performance, its efficiency of solar cell is low compared with that of lead halide. In order to enhance the efficiency of tin halide perovskite solar cell, a deep understanding of the role of the defects in the perovskite absorption layer and at the electron transport layer(ETL)/absorber or absorber/hole transport layer(HTL) interface is very necessary. In this work, the planar heterojunction-based CH_3NH_3SnI_3 perovskite solar cells were simulated with the SCAPS-1D program. Simulation results revealed a great dependence of device efficiency on defect density and interface quality of the perovskite absorber. The defect density at the front interface is critical for high efficiency, and the polarity of the interface charge has a different impact on the device efficiency. Strikingly, an efficiency over 29% was obtained under the moderate simulation conditions.

Novel ultra-wideband fluorescence material:Defect state control based on nickel-doped semiconductor QDs embedded in inorganic glasses

In recent years,the development of an environmentally friendly quantum dots(QDs)embedded luminous solid by a simple method has attracted considerable attention.In this study,semiconductor ZnS QDs were successfully prepared in an inorganic matrix of amorphous glass,which yielded beneficial broadband emission in the long-wavelength region of the visible range.The strong red emission belonged to the defect state energy level of the ZnS QDs,which could be enhanced by incorporation of nickel ions into the fixed matrix to regulate the defects state.The novel material had a small self-absorption,wide excitation and emission ranges,and thus potential applications in light-conversion devices,luminescent solar concentrators,and solar cell cover glasses.

Decade Milestone Advancement of Defect-Engineered g-C_(3)N_(4) for Solar Catalytic Applications

Over the past decade, graphitic carbon nitride(g-C_(3)N_(4)) has emerged as a universal photocatalyst toward various sustainable carbo-neutral technologies. Despite solar applications discrepancy, g-C_(3)N_(4) is still confronted with a general fatal issue of insufficient supply of thermodynamically active photocarriers due to its inferior solar harvesting ability and sluggish charge transfer dynamics. Fortunately, this could be significantly alleviated by the “all-in-one” defect engineering strategy, which enables a simultaneous amelioration of both textural uniqueness and intrinsic electronic band structures. To this end, we have summarized an unprecedently comprehensive discussion on defect controls including the vacancy/non-metallic dopant creation with optimized electronic band structure and electronic density, metallic doping with ultraactive coordinated environment(M–N_(x), M–C_(2)N_(2), M–O bonding), functional group grafting with optimized band structure, and promoted crystallinity with extended conjugation π system with weakened interlayered van der Waals interaction. Among them, the defect states induced by various defect types such as N vacancy, P/S/halogen dopants, and cyano group in boosting solar harvesting and accelerating photocarrier transfer have also been emphasized. More importantly, the shallow defect traps identified by femtosecond transient absorption spectra(fs-TAS) have also been highlighted. It is believed that this review would pave the way for future readers with a unique insight into a more precise defective g-C_(3)N_(4) “customization”, motivating more profound thinking and flourishing research outputs on g-C_(3)N_(4)-based photocatalysis.

Effects of defect states on the performance of perovskite solar cells

We built an ideal perovskite solar cell model and investigated the effects of defect states on the so- lar cell＇s performance. The verities of defect states with a different energy level in the band gap and those in the absorption layer CH3NH3PbI3 （MAPbI3）, the interface between the buffer layer/MAPbI3, and the interface be- tween the hole transport material （HTM） and MAPbI3, were studied. We have quantitatively analyzed these effects on perovskite solar cells＇ performance parameters. They are open-circuit voltage, short-circuit current, fill factor, and photoelectric conversion efficiency. We found that the performances of perovskite solar cells change worse with defect state density increasing, but when defect state density is lower than 1016 cm^-3, the effects are small. Defect states in the absorption layer have much larger effects than those in the adjacent interface layers. The per-ovskite solar cells have better performance as its working temperature is reduced. When the thickness of MAPbI3 is about 0.3μm, perovskite solar cells show better comprehensive performance, while the thickness 0.05μm for Spiro-OMeTAD is enough.

Effects of defect states on the performance of CuInGaSe_2 solar cells

Device modeling has been carried out to investigate the effects of defect states on the performance of ideal CulnGaSe2 （CIGS） thin film solar cells theoretically. The varieties of defect states （location in the band gap and densities） in absorption layer CIGS and in buffer layer CdS were examined. The performance parameters： open-circuit voltage, short-circuit current, fill factor, and photoelectric conversion efficiency for different defect states were quantitatively analyzed. We found that defect states always harm the performance of CIGS solar cells, but when defect state density is less than 10 14 cm-3 in CIGS or less than 10 18 cm-3 in CdS, defect states have little effect on the performances. When defect states are located in the middle of the band gap, they are more harmful. The effects of temperature and thickness are also considered. We found that CIGS solar cells have optimal performance at about 170 K and 2 μm of CIGS is enough for solar light absorption.

Energy level analyses of even-parity J=1 and 2 Rydberg states of Sn I by multichannel quantum defect theory

This paper analyzes the energy levels along the even-parity J = 1 and 2 Rydberg series of Sn I by multichannel quantum defect theory. A good agreement between theoretical and experimental energy levels was achieved. Below 59198 cm^-1, a total of 85 and 23 new energy levels, respectively, in the J = 1 and J = 2 series, which cannot be measured previously by experiments, are predicted in this work. Based on the calculated admixture coefficients of each channel, interchannel interactions were discussed in detail. The results are helpful to understand the characteristics of configuration interaction among even-parity levels in Sn I.

Solid-State Reaction and Vacancy-Type Defects in Bilayer Fe/Hf Studied by the Slow Positron Beam

The positron annihilation lifetimes and the Doppler broadening by slow positron beam are measured in thin Fe films with thickness 500 nm, a thin Hf film with thickness 100 nm, and the bilayer Fe (50 nm)/Hf (50 nm) on quartz glass substrate. We have analyzed the behavior in vacancy-type defects in each layer through some deposition temperatures and annealing. It is observed that the thin Fe film, the thin Hf film, and the bilayer Fe (50 nm)/Hf (50 nm) already contain many vacancy-type defects. We have investigated the change of densities of the vacancy-carbon complex and the small vacancy-cluster with carbons, through solid-state amorphization of Fe (50 nm)/Hf (50 nm) bilayer.

恒压下GIS固体绝缘界面气隙缺陷放电严重程度评估

为了研究GIS绝缘子界面气隙缺陷的放电发展过程,文中设计了空洞气隙缺陷模型,搭建了一套GIS气隙缺陷放电长期测试平台。基于缺陷模型的击穿电压对带有缺陷的试品施加90%Ub、60%Ub、30%Ub的交流恒压,使用UHF检测系统采集放电数据直至试品击穿。提取放电次数、放电幅值、放电时间间隔分析放电状态特征,发现GIS气隙缺陷放电发展过程存在两个阶段,前期放电幅值缓慢增大,放电脉冲逐渐稀疏,放电发展较为平稳;后期放电幅值急剧减小,放电脉冲密集,放电发展剧烈,采用k⁃means聚类算法及BP神经网络建立了气隙缺陷局放发展阶段的划分规则。研究表明,放电次数、放电幅值、放电时间间隔3种统计参量呈现阶段式单调性的趋势,可以用3种统计参量前向差分绝对值作为特征参量来评估GIS气隙放电严重程度;对GIS恒压试验进行聚类分析将放电过程划分为平稳劣化阶段和加速劣化阶段,随着外施电压水平的降低,平稳劣化阶段被压缩,加速劣化阶段占比升高。

不锈钢内衬修复复合管层间缺陷处应力分析

为研究不锈钢内衬修复前后复合管道内腐蚀缺陷处的应力分布规律以及修复效果,基于有限元软件,建立含单腐蚀坑缺陷的管道模型,改变腐蚀坑的深厚比,忽略黏结层厚度及对腐蚀坑的填补影响,层间采用黏接行为建立界面相互作用分析模型,将修复前后腐蚀缺陷处的应力进行对比。随着腐蚀缺陷深厚比的增加,管壁腐蚀缺陷处的径向应力、周向应力、Mises应力都有增大的趋势;修复前缺陷处的周向应力最大,且其值与Mises应力相近;经不锈钢内衬修复后,缺陷处的周向应力下降了11.3%,Mises应力下降了7.12%。腐蚀缺陷的深厚比对管道的应力分布有着显著的影响,所以在进行复合管线安全评估时应注意腐蚀深度的影响;在修复前后,管道腐蚀缺陷处的控制应力一直是周向应力,复合管道的失效可依据周向应力进行判断;经不锈钢内衬修复后,原始缺陷处的应力发生了重分布,其周向应力与Mises应力均有减小,修复效果明显。

位移电流测试方法的改进及应用

自从麦克斯韦第一次提出位移电流这一概念之后,其在薄膜表征中便得到广泛的应用。然而,在课堂教学中,极少涉及位移电流的测试原理及相关应用讲解,更缺少对其实际应用的介绍。本文从位移电流的测试原理出发,联系实际应用,提出了基于周期性阶跃电压驱动的电流测量(CPSIV)的新方法。这将有效地加深学生对于位移电流物理本质的深入理解。同时,我们以量子点发光二极管(QLED)为平台,对这一新的测试方案进行了实验验证。针对其中空穴传输层薄膜的缺陷特性及其对器件性能的影响进行了表征,揭示了器件的发光开启机制,证实了我们方案的可靠性。

CZTS基单晶材料研究进展和展望

Ⅰ_(2)-Ⅱ-Ⅳ-Ⅵ_(4)型半导体铜锌锡硫(CZTS)在成本、组成元素丰度、毒性和稳定性等方面具有突出优势,被认为是一种很有前途的太阳能吸收材料,应用于绿色和经济的光伏领域。尽管Cu_(2)ZnSn(S,Se)_(4)拥有与黄铜矿相似的晶体结构和光电性能,但其转换效率却远远低于Cu(In,Ga)Se_(2)(23.5%)。传统研究多数集中在多晶薄膜材料和器件的光电性能,导致材料关键缺陷态甄别及其能带调控规律尚不清晰,成为限制CZTS基光电器件性能的瓶颈。本文综述了CZTS基单晶材料,详细介绍了其晶体结构和物理性质,概述了移动加热器法、碘输运法和熔盐法制备高质量单晶的工艺,多型纳米晶库的研究,以及天然锌黄锡矿的物性研究。根据制备的CZTS基单晶材料讨论了其光学和电学性能。最后总结了CZTS基单晶材料在半导体器件的应用及目前存在的问题,为提高Ⅰ_(2)-Ⅱ-Ⅳ-Ⅵ_(4)型半导体材料器件的性能提供可能的发展方向。

Identification and elimination of inductively coupled plasma-induced defects in Al_xGa_(1-x)N/GaN heterostructures

By using temperature-dependent Hall, variable-frequency capacitance-voltage and cathodoluminescence （CL） measurements, the identification of inductively coupled plasma （ICP）-induced defect states around the AlxGa1-xN/GaN heterointerface and their elimination by subsequent annealing in AlxGa1-xN/GaN heterostructures are systematically investigated. The energy levels of interface states with activation energies in a range from 0.211 to 0.253 eV below the conduction band of GaN are observed. The interface state density after the ICP-etching process is as high as 2.75× 10^12 cm^-2.eV^-1. The ICP-induced interface states could be reduced by two orders of magnitude by subsequent annealing in N2 ambient. The CL studies indicate that the ICP-induced defects should be Ga-vacancy related.

HFW焊管管端射线探伤底片异常典型案例分析

介绍了HFW焊管管端射线检测的常见典型缺陷,分析X射线探伤缺陷的判定,不能仅依靠底片本身是否存在阴影、黑线等直接进行判定,须结合HFW焊管的生产工艺特点,结合钢管内、外表面状态判断是否存在符合产品标准但影响X射线底片的缺欠,如存在则需先做修磨处理后再做X射线探伤检测,以免影响探伤结果的评定。

Large-scale photonic crystals with inserted defects and their optical properties

Deliberately introducing defects into photonic crystals is an important way to functionalize the photonic crystals. We prepare a special large-scale three-dimensional （3D） photonic crystal （PC） with designed defects by an easy and low-cost method. The defect layer consists of photoresist strips or air-core strips. Field emission scanning electron microscopy （FESEM） shows that the 3D PC is of good quality and the defect layer is uniform. Different defect states shown in the ultraviolet-visible spectra are induced by the photoresist strip layer and air-core strip layer. The special large-scale 3D PC can be tested for integrated optical circuits, and the defects can act as optical waveguides.

Passivation of carbon dimer defects in amorphous SiO_2/4H–SiC(0001) interface:A first-principles study

An amorphous SiO2/4 H–Si C（0001） interface model with carbon dimer defects is established based on density functional theory of the first-principle plane wave pseudopotential method.The structures of carbon dimer defects after passivation by H2 and NO molecules are established,and the interface states before and after passivation are calculated by the Heyd–Scuseria–Ernzerhof（HSE06） hybrid functional scheme.Calculation results indicate that H2 can be adsorbed on the O2–C = C–O2 defect and the carbon–carbon double bond is converted into a single bond.However,H2 cannot be adsorbed on the O2–（C = C）′ –O2 defect.The NO molecules can be bonded by N and C atoms to transform the carbon–carbon double bonds,thereby passivating the two defects.This study shows that the mechanism for the passivation of Si O2/4 H–SiC（0001） interface carbon dimer defects is to convert the carbon–carbon double bonds into carbon dimers.Moreover,some intermediate structures that can be introduced into the interface state in the band gap should be avoided.

城轨交通接触网悬挂状态智能检测算法及应用

通过高清成像对接触网悬挂状态进行检测,及时发现零部件松脱卡磨断等缺陷问题并维修,是保障城轨交通接触网系统安全运行的重要手段。采用YOLOV4的最小版本YOLOV4-tiny作为检测算法的基础模型,将原有Dropout层去掉,将上层特征直接经过卷积层后输入到下层卷积层,并加入Mosaic数据增强方式提高算法的泛化性,同时将原有Leaky-Relu函数替换为更加平滑的Mish函数。接触网缺陷定位的流程为:根据改进后的YOLOv4-tiny算法训练得到零部件区域定位模型,用于定位零部件的位置;再根据改进后的YOLOv4-tiny算法训练得到缺陷识别模型,用于判断该零部件是否有缺陷,并给出缺陷的具体位置和缺陷类别。实际应用表明:该算法能准确、快速定位零部件缺陷位置,并给出缺陷类型,总精度达90%以上,大大地降低了检测耗时与成本,并保障了作业人员安全。