The role that conduction band tail states play in determining the optical response of hydrogenated amorphous silicon

We aim to explore the role that conduction band tail states play in shaping the optical response of hydrogenated amorphous silicon. We do so within the framework of an empirical model for the valence band and conduction band density of states functions, one that considers valence band band, valence band tail, conduction band band, and conduction band tail states. We examine the sensitivity of the joint density of states function to variations in the conduction band tail breadth, all other parameters being held fixed at their nominal hydrogenated amorphous silicon values. We find that when the conduction band tail is narrower than the valence band tail, its role in shaping the corresponding spectral dependence of the joint density of states function is relatively minor. This justifies the use of a simplified empirical model for the density of states functions that neglects the presence of the conduction band tail states in the characterization of the optical response of this material. Experimental data corresponding to hydrogenated amorphous silicon, demonstrating that the conduction band tail breadth is always less than the valence band tail breadth for this material, is then presented. Finally, fundamental reasons for the observed asymmetry in the band tail breadths are reviewed.     

Total band absorptance,emissivity, and absorptivity of the pure rotational band of water vapor

Based upon the exponential wide band model, an analytical expression is derived for the total band absorptance of the pure rotational band of water vapor. It is shown that the usual band absorptance expressions, which are based on this model, are inaccurate for this band. The use of the total band absorptance in computing the emissivity and absorptivity is also considered. Representations of these functions is achieved within a simple analytical framework.     

Influence of place synchrony on detection of a sinusoid

A series of experiments was performed to study the ability of the ear to code the temporal envelope of a waveform as demonstrated by comodulation masking release (CMR). The stimulus for all experiments was composed of a tone-burst signal, a 100-Hz-wide masker band centered at the signal frequency, and a second 100-Hz-wide noise band of variable frequency, the cue band. The cue band had a temporal envelope which was either correlated with or independent of that of the masker. The signal was a 100-Hz tone burst for most experiments. For the monotic stimulus, the correlated cue band results in lowered signal detection thresholds over a range extending from around 2/3 oct below the signal frequency to 1/3 oct above that frequency. When measured dichotically, with the signal and masker band in one ear and the cue band in the opposite ear, that effective range is expanded but the detection threshold shifts are a bit smaller. The greatest CMR is observed when the stimulus is presented diotically. With regard to effects of level and frequency, our data show CMR increasing with increasing stimulus level for a cue band lower in frequency than the signal, but show little effect of level for a cue band higher in frequency. Similarly, CMR increases with increasing stimulus frequency when the cue band is lower in frequency, but shows little effect of frequency for a cue band higher in frequency.     

基于8～14μm带宽的谱带发射率的研究

针对红外测量中常用的8～14μm的带宽,依据前人的实验结果,计算了两种材料的谱带发射率,并且通过简单的实验,测量了几种材料的谱带发射率。实验和计算结果表明:谱带发射率与温度之间存在着某种函数关系。对于常用的带通辐射测温仪和热像仪,如果测量对象为非灰体,仍然把发射率值看作是一个常数,将会导致较大的测量误差。初步研究表明,对于非金属和真空中的金属,谱带发射率与温度近似存在线性关系。利用拟合出的谱带发射率与温度的函数关系式,可以作为辐射测温仪和热像仪的修正,不仅简化了计算,而且能够提高其测量精度。     

First-principles study of Cu2ZnSnS4 and the related band offsets for photovoltaic applications

First-principles calculations of the band offsets between Cu(2)ZnSnS(4) (CZTS) and XS (X = Cd, Zn) are performed. While the interface dipole contribution for the band offsets is calculated using the Perdew-Burke-Ernzerhof functional, the Heyd-Scuseria-Ernzerhof hybrid functional is employed to introduce the quasiparticle corrections to the band offsets. The calculated conduction band offset between CZTS and CdS is 0.2 eV, validating CdS for the buffer layer of the CZTS solar cell. The small conduction band offset stems from the band gap narrowing of CdS under the interface strain caused by the lattice misfit with CZTS. A large valence band offset over 0.9 eV between CZTS and ZnS indicates that precipitated ZnS is regarded as an inactive insulator phase in CZTS absorbers.     

Effect of Band Nonparabolicity on the Inter Band Tunneling in Semiconductors

A simple yet generalized theory is developed to study inter band tunneling property of narrow band gap III–V compound semiconductors. The band structures of these low band gap semiconductors with sufficiently separated split-off valance band are usually described by the three energy band model of Kane, so this has been adopted here for the analysis of interband tunneling property in the case of InAs, InSb, and In_1-xGa_xAs_yP_1-y lattice matched to InP as representative direct band gap semiconductors having varied split-off valence band compared to their bulk state band gap energy. It has been found that the magnitude of tunneling rate from heavy hole decreases with increasing band nonparabolicity and the impact is more significant at high electric field in the three-band model of Kane than those with simple parabolic energy band approximations reflecting the direct influence of energy band parameters on inter band tunneling transitions. With proper consideration of band nonparabolicity, the results of the analysis of tunneling rate of these narrow gap materials show significant deviations from the results when simple parabolic band approximation is considered. The exact physical basis of the sources of deviation in the nonparabolic case from the corresponding parabolic band approximations is discussed in association to band coupling effect, transverse energy dependence, and the interplay between them. Moreover, under certain limiting conditions, our results reduce to the well-known results of parabolic band approximation and thus providing an indirect test to the accuracy of our generalized formulations.     

光子晶体超窄带滤波器

本文利用光学传输矩阵法研究了一种类似于谐振腔结构的光子晶体.研究发现在这种光子晶体的光子带隙的中央存在一个极窄的透光窗口,窗口的宽度在红外波段1500nm附近可以做到0.0001nm以下,窗口内的透光率峰值可以接近100%,窗口以外的区域的透光率可以做到0.01%以下.通过改变所研究结构中的周期厚度、中间夹层厚度、两边光子晶体的周期重复数和波的入射角可以改变窄带透过窗口的位置和窄带的宽度.这种光子晶体可以用来制作超窄带滤波器,有望在光通信超密度波分复用技术和光学信息精密测量技术当中获得应用.     

高光谱成像的水稻螟虫蛀入检测方法

为了控制水稻螟虫预警和喷洒农药用量,实现对水稻螟虫虫害的无损检测,提出了基于主成分分析特征波段检测方法和基于迭代阈值的最优波段检测方法,确定了水稻茎秆螟虫检测的特征波段和最优波段,提取出单波段和组合波段的图像来分割虫孔,从而实现水稻螟虫的精准的无损检测。首先通过高光谱得到的120个样品反射率信息分析确定了光谱区域为450～1 000 nm。基于主成分分析特征波段检测方法,对高光谱图像进行主成分分析,通过前五个主成分图像比较确定第三主成分图像为最佳,然后根据第三主成分图像中各个波段的贡献率来选取特征波长（668.8和750 nm）,最后结合全局阈值分割和图像掩膜等图像处理方法实现对虫孔区域的判别。而利用基于迭代阈值的最优波段检测方法,在可见光波段450～750 nm范围和近红外波段750～1 000 nm范围内应用混合距离挑选最佳的单波段,通过单波段来确定组合波段,对单波段和组合波段进行迭代阈值分割,其中753.5 nm波长分割效果最好,故确定753.5 nm为最优波长,然后提取该波长的图像采用一种基于迭代阈值虫孔提取方法和形态学处理,最后能对水稻茎秆虫孔区域进行判别来实现水稻茎秆虫害是否存在。对60个虫害水稻茎秆和60个正常水稻茎秆进行检测,应用基于主成分分析特征波段检测方法在668.8和750 nm波长处检测率分别为95.8%和93.3%,而应用基于迭代阈值的最优波长检测方法在753.5 nm波长处检测率高达96.7%。说明利用基于迭代阈值的最优波长检测方法对水稻螟虫的检测更加精确,也说明所获取的特征波段和最优波段为以后水稻螟虫虫害的多光谱成像技术提供了理论参考。     

Non-parabolic effect for femtosecond laser-induced ultrafast electro-absorption in solids

A theoretical study for femtosecond laser-induced ultrafast electro-absorption of bulk solids is presented. Our numerical results show that, in the case of low intensity of the pump laser where the interaction between the pump laser and solids is in the multi-photon regime, the energy band of solids can be approximately taken as a parabolic band and electro-absorption spectrums from the parabolic band and real band are nearly the same. While, in the case of high intensity where the interaction is in the tunneling regime, spectrums from the parabolic band and real band are quite different.The physical mechanism for the difference in the tunneling regime is found. We find that the non-parabolic parts of the real energy band and Bragger scattering of electrons near the first Brillouin zone boundaries, which are neglected in previous studies, strongly influence the electro-absorption spectrum in the tunneling regime. These two physical processes cause the difference of spectrums. Our theoretical results are in accordance with the experiment result.     

一种简便的研究一维光子晶体禁带特征的新方法

利用光在一维光子晶体中传播的色散关系,提出了一种禁带边缘分析法,以研究一维光子晶体禁带特征的方法.该方法利用色散关系引入一个确定禁带边缘位置的函数F,F =0为禁带边缘的位置.通过绘出函数F的图线,由F =0确定禁带边缘的位置,进而分析得到禁带和允许带的特征.它避免了常用的特征矩阵法中对反射率复杂的数值计算,并能得到与特征矩阵法相同的结果.     

InP中和C带有关深能级的近红外光致发光

本文用红外光致发光方法研究了InP中与C带有关的深能级的性质和起源。峰值位于价带上0.34eV(77K)附近的宽谱带普遍存在于不同方式生长的InP外延层和掺Sn与不掺杂的衬底中,且与P空位引起的复合缺陷有关。 通过红外光致发光强度对温度的依赖关系得到C带的热激活能为0.17eV。这刚好与采用σ函数来描述深能级的Locovsky模型相吻合,光谱线型与温度猝灭的量子力学位形坐标模型拟合,得到与C带有关的深能级hv=0.02eV,S=8。     

An Analysis of Structural-Acoustic Coupling Band Gaps in a Fluid-Filled Periodic Pipe

A periodic pipe system composed of steel pipes and rubber hoses with the same inner radius is designed based on the theory of phononic crystals. Using the transfer matrix method, the band structure of the periodic pipe is calculated considering the structural-acoustic coupling. The results show that longitudinal vibration band gaps and acoustic band gaps can coexist in the fluid-filled periodic pipe. The formation of the band gap mechanism is further analyzed. The band gaps are validated by the sound transmission loss and vibration-frequency response functions calculated using the finite element method. The effect of the damp on the band gap is analyzed by calculating the complex band structure. The periodic pipe system can be used not only in the field of vibration reduction but also for noise elimination.     

Comodulation masking release for various monaural and binaural combinations of the signal, on-frequency, and flanking bands

The threshold for a signal masked by a narrow band of noise centered at the signal frequency (the on-frequency band) may be reduced by adding to the masker a second band of noise (the flanking band) whose envelope is correlated with that of the first band. This effect is called comodulation masking release (CMR). These experiments examine two questions. (1) How does the CMR vary with the number and ear of presentation of the flanking band(s)? (2) Is it possible to obtain a CMR when a binaural masking level difference (BMLD) is already present, and vice versa? Thresholds were measured for a 400-ms signal in a continuous 25-Hz-wide noise centered at signal frequencies (fs) of 250, 1000, and 4000 Hz. This masker was presented either alone or with one or more continuous flanking bands whose envelopes were either correlated or uncorrelated with that of the on-frequency band; their frequencies ranged from 0.5fs to 1.5fs. CMRs were measured for six conditions in which the signal, the on-frequency band, and the flanking band(s) were presented in various monaural and binaural combinations. When a single flanking band was used, the CMR was typically around 2-3 dB. The CMR increased to 5-6 dB if an additional flanking band was added. The effect of the additional band was similar whether it was in the same ear as the original band or in the opposite ear. At the lowest signal frequency, a large CMR was observed in addition to a BMLD and vice versa. At the highest signal frequency, the extra release from masking was small. The results are interpreted in terms of the cues producing the CMR and the BMLD.     

Photothermal bleaching of Ca colloids in additively colored CaF2

Cation colloidal particles in additively colored CaF₂ crystals have been bleached with light in the colloidal band. At 360 K the colloid band decreases and a new band in the near i.r. region is created which is probably due to highly coagulated F-centers. At 430 K the colloidal band is destroyed at the same time that a band appears at 383 nm. This band has been tentatively associated to a kind of F-center. Photochromic conversions between colloids and i.r. bands at 360 K and between colloids and 383 nm band at 430 K have been obtained. A mechanism for the bleaching of colloids has been proposed.     

椭球三维液态声子晶体完全声波禁带研究

弹性波在声子晶体中传播时，会产生一定的频率禁带，声和振动在禁带中被禁止传播。本文将椭球散射体引入三维声子晶体中，采用平面波展开法计算了该系统的声波禁带结构。对于不同椭球半径的系统，其声波禁带的位置与大小有很大不同。结果表明：当晶格常数和填充率确定时，禁带受到椭球半径的影响；当确定椭球体的某一个半径和填充率时，第一禁带的最大值出现在另2个半径相等的情况下。     

Exact confined eigenstates in one-dimensional finite periodic systems with arbitrary symmetric basis

A set of eigenenergy equations for complete confinement of N periodic one-dimensional system with arbitrary symmetric potential in each cell is presented. Exact eigenenergies and their eigenfunctions are solved analytically. We find different solutions on the band edge states comparing early results solved by conventional methods. Our results show that higher band edge state of each bandgap is dependent on the confined length, but lower band edge state is independent of the length. Moreover, wavefunctions for lower band edge states are Bloch waves but those for other eigenstates, including higher band edge states, do not obey Bloch waves.     

Dynamic analysis of clamp band joint system subjected to axial vibration

Clamp band joints are commonly used for connecting circular components together in industry. Some of the systems jointed by clamp band are subjected to dynamic load. However, very little research on the dynamic characteristics for this kind of joint can be found in the literature. In this paper, a dynamic model for clamp band joint system is developed. Contact and frictional slip between the components are accommodated in this model. Nonlinear finite element analysis is conducted to identify the model parameters. Then static experiments are carried out on a scaled model of the clamp band joint to validate the joint model. Finally, the model is adopted to study the dynamic characteristics of the clamp band joint system subjected to axial harmonic excitation and the effects of the wedge angle of the clamp band joint and the preload on the response. The model proposed in this paper can represent the nonlinearity of the clamp band joint and be used conveniently to investigate the effects of the structural and loading parameters on the dynamic characteristics of this type of joint system.     

Charge-density-wave phase of 1T-TiSe2: the influence of conduction band population

The charge-density-wave phase of TiSe(2) was studied by angle-resolved photoelectron spectroscopy and resistivity measurements investigating the influence of the band gap size and of a varying population of the conduction band. A gradual suppression of the charge-density-wave-induced electronic superstructure is observed for a variation of the band gap in the ternary compounds TiC(x)Se(2-x) with C=(S,Te) as well as for an occupation of only the conduction band by H(2)O adsorption-induced band bending. These observations point to an optimum band gap and support an excitonic driving force for the charge-density wave.     

Individual differences in directional bands in median plane localization

Blauert and other researchers demonstrated that the direction of a sound image for a narrow-band noise is perceived according to the center frequency of the stimuli. Blauert referred to the frequency band by which the direction of sound image is determined as the directional band. However, it has not yet been clarified if individual differences exist in the directional bands. It is also unestablished whether the directional band changes according to the bandwidth of the stimuli. In this study, 1/3 and 1/6 octave band noises were presented from the front, above and behind the subject in the median plane, and the responses to the stimuli were analyzed individually. The results show that (1) individual differences in directional bands exist; (2) there is no remarkable difference between directional bands for 1/3 and 1/6 octave band noises; (3) for some subjects, a directional band occurs in the direction in which they could not localize wide-band noise.