Observation of indium-vacancy and indium-hydrogen interactions in Hg1−xCdxTe

We have used a nuclear hyperfine technique, perturbed γγ angular correlation (PAC), to study the interactions between¹¹¹In and native defects and impurities in Hg_1−xCd_xTe. The PAC technique uses the quadrupole interaction of¹¹¹In with local electric field gradients to characterize the local environment of this donor dopant. We observed that when In was diffused into a bulk or thin film sample of Hg_1−xCd_xTe (x=0.21 and x=0.3) at 350°C and the sample was slow cooled, the In occupied sites with near-cubic symmetry, presumably the substitutional metal site. However, when the sample was quenched, a fraction of the In was incorporated into defects characterized by quadrupole interaction strengthsv _Q1 andv _Q2 and asymmetries of ν₁=ν₂=0.08. These defects are attributed to the trapping of a metal vacancy at a next-nearest neighbor site to the In atom. The introduction of hydrogen by boiling the samples in distilled water for >4h eliminated the previously observed PAC signals and created defects characterized byv _Q3=35 MHz, ν₃ <0.1 andv _Q4=MHz, ν₄ <0.1. These defects are attributed to the decoration of the In-V_Hg complex by a hydrogen atom. Hall effect measurements showed that hydrogenation increased the hole concentration in p-type quenched samples and even converted n-type indium-doped samples to p-type. A possible model for hydrogen incorporation which includes self-compensation by vacancy creation is suggested.     

Numerical heat transfer study for a large rubber product

The physical processes of heat transfer are typically complicated in the curing of rubber. In this study, the image plot and the plot of the temperature profile were obtained in such an environment, and then compared with the finite element method (FEM), which is used in finite element analysis (FEA) software. A good agreement was observed, and the difference was less than 1% when evaluating the different curing conditions. This confirms that the correct curing time can be determined by studying the temperature profile, which will help to avoid the deterioration of the mechanical properties of thick rubber products.     

Benzodithiophene Hole‐Transporting Materials for Efficient Tin‐Based Perovskite Solar Cells

Developing efficient interfacial hole transporting materials (HTMs) is crucial for achieving high‐performance Pb‐free Sn‐based halide perovskite solar cells (PSCs). Here, a new series of benzodithiophene (BDT)‐based organic small molecules containing tetra‐ and di‐triphenyl amine donors prepared via a straightforward and scalable synthetic route is reported. The thermal, optical, and electrochemical properties of two BDT‐based molecules are shown to be structurally and energetically suitable to serve as HTMs for Sn‐based PSCs. It is reported here that ethylenediammonium/formamidinium tin iodide solar cells using BDT‐based HTMs deliver a champion power conversion efficiency up to 7.59%, outperforming analogous reference solar cells using traditional and expensive HTMs. Thus, these BDT‐based molecules are promising candidates as HTMs for the fabrication of high‐performance Sn‐based PSCs.     

Brain surface conformal parameterization using Riemann surface structure

In medical imaging, parameterized 3-D surface models are useful for anatomical modeling and visualization, statistical comparisons of anatomy, and surface-based registration and signal processing. Here we introduce a parameterization method based on Riemann surface structure, which uses a special curvilinear net structure (conformal net) to partition the surface into a set of patches that can each be conformally mapped to a parallelogram. The resulting surface subdivision and the parameterizations of the components are intrinsic and stable (their solutions tend to be smooth functions and the boundary conditions of the Dirichlet problem can be enforced). Conformal parameterization also helps transform partial differential equations (PDEs) that may be defined on 3-D brain surface manifolds to modified PDEs on a two-dimensional parameter domain. Since the Jacobian matrix of a conformal parameterization is diagonal, the modified PDE on the parameter domain is readily solved. To illustrate our techniques, we computed parameterizations for several types of anatomical surfaces in 3-D magnetic resonance imaging scans of the brain, including the cerebral cortex, hippocampi, and lateral ventricles. For surfaces that are topologically homeomorphic to each other and have similar geometrical structures, we show that the parameterization results are consistent and the subdivided surfaces can be matched to each other. Finally, we present an automatic sulcal landmark location algorithm by solving PDEs on cortical surfaces. The landmark detection results are used as constraints for building conformal maps between surfaces that also match explicitly defined landmarks.     

Al surface morphology effect on flip-chip solder bump shear strength

This paper reports the result of a study on the effect of aluminum pad surface morphology on the flip-chip solder bump reliability. The influence of the Al surface morphology on the electroless zinc/nickel/gold UBM is presented. The reliability of the solder bump as measured by ball shear force is reported. Al pad were produced using two RF sputtering systems: CVC-601 and Varian-3180. The Al targets used in CVC and Varian system were 99%Al–1%Si and 98.95%Al–1%Si–0.05%Ti respectively. The surface of the CVC sputtered Al samples were smooth while the surface of the Varian sputtered Al samples were rough. All the samples were subjected to the electroless zinc/nickel/gold plating. The results suggest that after plating, the smooth Al surface resulted in a fine nickel UBM surface while the rough Al surface formed a coarse nickel UBM surface. Ball shear test was conducted after the solder balls were bumped on the UBM. Result shows that the fine UBM surface samples have twice the shear strength compared to the samples with coarse UBM surface samples. The analysis of the results indicates that shear surface occurred at the UBM and the solder interface for samples with rough UBM surface leading to the lower shear strength. Nickel bump shear test result shows that pretreatment of Al pad surface by sodium hydroxide and nitric acid created more zinc seeds this led to better electroless nickel plating. Nickel bump shear tests also shows that double zincated bumps had higher shear strength than single zincated bumps. To obtain reliable flip-chip solder bumps, it is essential to maintain good Al pad surface morphology, pretreatment of the Al pad and undergo second zincation.     

Routing in Distributed Cognitive Radio Networks: A Survey

Cognitive Radio Networks (CRNs) have been receiving significant research attention recently due to their ability to solve issues associated with spectrum congestion and underutilization. In a CRN, unlicensed users (or Secondary Users, SUs) are able to exploit and use underutilized licensed channels, but they must evacuate the channels if any interference is caused to the licensed users (or Primary Users, PUs) who own the channels. Due to the dynamicity of spectrum availability in CRNs, design of protocols and schemes at different layers of the SU’s network stack has been challenging. In this article, we focus on routing and discuss the challenges and characteristics associated with it. Subsequently, we provide an extensive survey on existing routing schemes in CRNs. Generally speaking, there are three categories of challenges, namely channel-based, host-based, and network-based. The channel-based challenges are associated with the operating environment, the host-based with the SUs, and the network-based with the network-wide SUs. Furthermore, the existing routing schemes in the literature are segregated into three broad categories based on the relationship between PUs and SUs in their investigation, namely intra-system, inter-system, and hybrid-system; and within each category, they are further categorized based on their types, namely Proactive, Reactive, Hybrid, and Adaptive Per-hop. Additionally, we present performance enhancements achieved by the existing routing schemes in CRNs. Finally, we discuss various open issues related to routing in CRNs in order to establish a foundation and to spark new interests in this research area.     

Characteristics of Er-doped Al2O3 thin filmsdeposited by reactive co-sputtering

Er-doped Al₂O₃ thin films have been deposited by reactive co-sputtering onto thermally oxidized Si-wafers. The deposition process has been optimized with respect to the requirements originating from the application of these multilayer structures as integrated optical amplifiers for the third telecom window, i.e., the wavelength range 1.52-1.55 μm. The films obtained at a substrate temperature of only 400°C are amorphous and show a homogenous structure, without columns or grains. For slabguides, background losses smaller than 0.25 dB/cm have been obtained, even without any annealing. A relatively broad luminescence band, having an FWHM of ~55 nm around the 1.533-μm wavelength, has been measured. From gain versus pumping power curves, an upconversion coefficient lower then 20·10^-25 m³/s has been derived, being half of the values reported up to now in the literature. Simulations based on experimentally determined material parameters and assuming a channel attenuation of 0.5 dB/cm indicate, for 0.24 at.% Er channel devices with an optimal channel length of 7.7 cm, an amplification of 8 dB at 1.533 μm for a pump wavelength of 1.48 μm, and a pump power of only 8.7 mW     

Hot-carrier degradation of submicrometer p-MOSFETs withthermal/LPCVD composite oxide

It is shown that while gate oxides containing thermal/LPCVD composite oxide have lower defect densities than gates using only thermal oxides, they are more susceptible to hot-carrier degradation. The hot-carrier-induced degradation of composite oxides is worse in p-channel MOSFETs than in n-channel MOSFETs. This sensitivity of p-channel MOSFETs is caused by higher electron trapping levels in LPCVD oxides. For 150-Å gate technology, the hot-carrier-degradation resistance of thermal/LPCVD composite gate oxides with a 70-Å or thicker thermal oxide layer approaches that of high-quality pure thermal oxide     

An efficient algorithm for superresolution in medium field imaging

In this paper, we study the problem of reconstruction of a high-resolution (HR) image from several blurred low-resolution (LR) image frames in medium field. The image frames consist of blurred, decimated, and noisy versions of a HR image. The HR image is modeled as a Markov random field (MRF), and a maximum a posteriori (MAP) estimation technique is used for the restoration. We show that with the periodic boundary condition, a HR image can be restored efficiently by using fast Fourier transforms. We also apply the preconditioned conjugate gradient method to restore HR images in the aperiodic boundary condition. Computer simulations are given to illustrate the effectiveness of the proposed approach. This research was conducted with support from the Army Research Office Grant DAAD 19-03-1-0261 and the National Science Foundation Grant CCF-0429481. Research supported in part by RGC Grant Nos. 7130/02P, 7046/03P, 7035/04P and 7035/04P and FRG/04-05/II-51.     

Worst case Cramer-Rao bounds for parametric estimation ofsuperimposed signals with applications

The problem of parameter estimation of superimposed signals in white Gaussian noise is considered. The effect of the correlation structure of the signals on the Cramer-Rao bounds is studied for both the single and multiple experiment cases. The best and worst conditions are found using various criteria. The results are applied to the example of parameter estimation of superimposed sinusoids, or plane-wave direction finding in white Gaussian noise, and best and worst conditions on the correlation structure and relative phase of the sinusoids are found. This provides useful information on the limits of the resolvability of sinusoid signals in time series analysis or of plane waves in array processing. The conditions are also useful for designing worst-case simulation studies of estimation algorithms, and for the design of minimax signal acquisition and estimation procedures, as demonstrated by an example