Semi-Parametric Estimation Using Bernstein Polynomial and a Finite Gaussian Mixture Model

The central focus of this paper is upon the alleviation of the boundary problem when the probability density function has a bounded support. Mixtures of beta densities have led to different methods of density estimation for data assumed to have compact support. Among these methods, we mention Bernstein polynomials which leads to an improvement of edge properties for the density function estimator. In this paper, we set forward a shrinkage method using the Bernstein polynomial and a finite Gaussian mixture model to construct a semi-parametric density estimator, which improves the approximation at the edges. Some asymptotic properties of the proposed approach are investigated, such as its probability convergence and its asymptotic normality. In order to evaluate the performance of the proposed estimator, a simulation study and some real data sets were carried out.     

Excimer laser crystallization of amorphous silicon on metallic substrate

An attempt has been made to achieve the crystallization of silicon thin film on metallic foils by long pulse duration excimer laser processing. Amorphous silicon thin films (100 nm) were deposited by radiofrequency magnetron sputtering on a commercial metallic alloy (N42-FeNi made of 41 % of Ni) coated by a tantalum nitride (TaN) layer. The TaN coating acts as a barrier layer, preventing the diffusion of metallic impurities in the silicon thin film during the laser annealing. An energy density threshold of 0.3 J?cm^?2, necessary for surface melting and crystallization of the amorphous silicon, was predicted by a numerical simulation of laser-induced phase transitions and witnessed by Raman analysis. Beyond this fluence, the melt depth increases with the intensification of energy density. A complete crystallization of the layer is achieved for an energy density of 0.9 J?cm^?2. Scanning electron microscopy unveils the nanostructuring of the silicon after laser irradiation, while cross-sectional transmission electron microscopy reveals the crystallites’ columnar growth.     

Role of MW-ECR hydrogen plasma on dopant deactivation and open-circuit voltage in crystalline silicon solar cells

Plasma hydrogenation is an efficient method to passivate intergrain and intragrain defects of polycrystalline silicon (pc-Si) solar cells. The hydrogenation experiments were carried out in hydrogen plasma generated in an electron cyclotron resonance system controlling different operating parameters such as microwave power (P _MW), process time (t _H) and hydrogenation temperature (T _H) for a fixed hydrogen flux of 30 sccm. The hydrogenation of n⁺pp⁺ pc-Si solar cells resulted in an improvement in the open-circuit voltage. The improvement was correlated with the dopant deactivation due to the formation of boron–hydrogen bonding. This was demonstrated from the changes in the doping level after hydrogenation of n⁺p diode structures made using single crystalline silicon as a reference material. It was found that deactivation of boron was more pronounced at high microwave plasma power, in good agreement with the high open-circuit voltage values obtained on pc-Si mesa cells. On the other hand, the effect of longer hydrogenation time and higher temperature resulted in a decrease of boron deactivation, while an increase in V _oc with a tendency of saturation at high T _H was observed. Reasons for such behavior were thoroughly explained.     

Fabrication and doping of poly-SiGe using excimer-laser processing

Pulsed Laser-Induced Epitaxy (PLIE)/Gas Immersion Laser Doping (GILD) offers several advantages over alternative epitaxial processes, especially because the process can be made spatially selective. Here, a pulsed XeCl excimer laser is used to grow poly-Si_1–xGe_x layers with Ge fractions up to 30% by intermixing a structure of electron beam-evaporated a-Ge on poly-Si deposited on quartz. Arsenic or boron dopant is incorporated during the melt process by using, respectively, an AsF₅ or BF₃ gas ambient. RBS and SIMS analysis reveal that the Ge metallurgical depth, the dopant junction depth and the incorporated dopant dose scale with the laser energy density and the number of laser pulses. The sheet resistance values reached after GILD process are low enough to be suitable for the fabrication of source and drain for poly-SiGe TFTs.     

Melting threshold of crystalline and amorphized Si irradiated with a pulsed ArF (193 nm) excimer laser

Modifications induced by a pulsed ArF excimer laser at surface of implanted silicon were investigated by a new and simple optical method which consists to follow the evolution of solid reflectivity, at 633 nm wavelength, resulting from the amorphouspolycrystalline (or monocrystalline) transition during the laser melting process. These results, which have been compared to those obtained using time resolved reflectivity experiments have demonstrated the capability of this simple technique to determine the melting threshold of implanted silicon.     

Formal Analysis of Optical Systems

Optical systems are becoming increasingly important by resolving many bottlenecks in today’s communication, electronics, and biomedical systems. However, given the continuous nature of optics, the inability to efficiently analyze optical system models using traditional paper-and-pencil and computer simulation approaches sets limits especially in safety-critical applications. In order to overcome these limitations, we propose to employ higher-order-logic theorem proving as a complement to computational and numerical approaches to improve optical model analysis in a comprehensive framework. The proposed framework allows formal analysis of optical systems at four abstraction levels, i.e., ray, wave, electromagnetic, and quantum.     

Studies on Body Composition in Irradiated Mice

A total of 40 male and 40 female mice of equal body weight were used in the present study. Whole body gamma (⁶⁰Co) irradiation was carried out at 400, 800 and 1200 rad. Life span and several parameters of body composition were measured. Cumulative mortality precentage was lower in irradiated females in comparison to males. Ionizing radiation induced reduction (P < 0.01) in body weight, total body water with its two compartments (extra-and intracellular), fat-free body with its component (body cell mass and extracellular tissue), fat-free dry solids with its constituent (body protein and body ash), body potassium and body fat. While all of the above mentioned body composition parameters decreased (P ≤ 0.01) following whole body irradiation, the rations between the body water to these parameters increased (P ≤ 0.01). Sex difference was noticed either for the parameters or for the ratios.     

Double layer a-Si:H/SiN:H deposited at low temperature for the passivation of N-type silicon

This work shows the influence of conditioning the Bi target previous to the pulsed laser deposition of Bi nanocomposite films on their optical and thermo-optical properties. The nanostructured films prepared by alternate pulsed laser deposition at room temperature in vacuum consist of Bi nanostructures (NSs) with different characteristic sizes that are organized in layers and embedded in an amorphous Al₂O₃ host. Preablation of the Bi target prior to deposition leads to higher Bi concentration and Bi NSs with larger average sizes. As a result a lower optical transmission and an enhanced thermo-optical contrast are observed.