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Local structure approximation as a predictor of second order phase transitions in asynchronous cellular automata  [PDF]
Henryk Fuk?,Nazim Fatès
Physics , 2013,
Abstract: We show that local structure approximation of sufficiently high order can predict the existence of second order phase transitions belonging to the directed percolation university class in $\alpha$-asynchronous cellular automata.
Structure order, local potentials, and physical anomalies of water ice  [PDF]
Chang Q Sun
Physics , 2014,
Abstract: Hydrogen-bond forms a pair of asymmetric, coupled, H-bridged oscillators with ultra-short-range interactions and memory. hydrogen bond cooperative relaxation and the associated binding electron entrapment and nonbonding electron polarization discriminate water and ice from other usual materials in the physical anomalies. As a strongly correlated fluctuating system, water prefers the statistically mean of tetrahedrally-coordinated structure with a supersolid skin that is elastic, polarized, ice like, hydrophobic, with 3/4 density.
Field Emission Behaviour of the Single Wall Carbon Nanotubes Grown by Plasma Enhanced Chemical Vapour Deposition (PECVD) System  [PDF]
Journal of Nano- and Electronic Physics , 2013,
Abstract: Single wall carbon nanotubes have been grown on Fe using Plasma Enhanced Chemical Vapour Deposition (PECVD) system. The thickness of the Fe film prepared by RF sputtering system was about 10 nm. The field emission characteristic was measured which showed good enhancement factor. The grown CNTs were characterized by various techniques such as SEM, Raman study etc.
Charge order, dielectric response and local structure of La5/3Sr1/3NiO4 system  [PDF]
M Filippi,B Kundys,S Agrestini,W Prellier,H Oyanagi,N L Saini
Physics , 2009, DOI: 10.1063/1.3260222
Abstract: Charge ordering, dielectric permittivity and local structure of La5/3Sr1/3NiO4 system have been explored X-ray charge scattering, complex dielectric impedance spectroscopy, and extended X-ray absorption fine structure (EXAFS) measurements, made on the same single crystal sample. The local structure measured by the temperature dependent polarized Ni K-edge EXAFS shows significant distortions in the NiO2 planes. These local distortions could be reasonable cause of high dielectric permittivity of the title system (e=100 at 5K) with the charge ordering in this system being a ferroelectric-like second order transition.
Understanding complex magnetic order in disordered cobalt hydroxides through analysis of the local structure  [PDF]
James R. Neilson,Brent C. Melot,Daniel P. Shoemaker,Joshua A. Kurzman,Ram Seshadri,Daniel E. Morse
Physics , 2010, DOI: 10.1103/PhysRevB.83.094418
Abstract: In many ostensibly crystalline materials, unit-cell-based descriptions do not always capture the complete physics of the system due to disruption in long-range order. In the series of cobalt hydroxides studied here, Co(OH)$_{2-x}$(Cl)$_x$(H$_2$O)$_{n}$, magnetic Bragg diffraction reveals a fully compensated N\'eel state, yet the materials show significant and open magnetization loops. A detailed analysis of the local structure defines the aperiodic arrangement of cobalt coordination polyhedra. Representation of the structure as a combination of distinct polyhedral motifs explains the existence of locally uncompensated moments and provides a quantitative agreement with bulk magnetic measurements and magnetic Bragg diffraction.
Structure from Local Optima: Learning Subspace Juntas via Higher Order PCA  [PDF]
Santosh S. Vempala,Ying Xiao
Mathematics , 2011,
Abstract: We present a generalization of the well-known problem of learning k-juntas in R^n, and a novel tensor algorithm for unraveling the structure of high-dimensional distributions. Our algorithm can be viewed as a higher-order extension of Principal Component Analysis (PCA). Our motivating problem is learning a labeling function in R^n, which is determined by an unknown k-dimensional subspace. This problem of learning a k-subspace junta is a common generalization of learning a k-junta (a function of k coordinates in R^n) and learning intersections of k halfspaces. In this context, we introduce an irrelevant noisy attributes model where the distribution over the "relevant" k-dimensional subspace is independent of the distribution over the (n-k)-dimensional "irrelevant" subspace orthogonal to it. We give a spectral tensor algorithm which identifies the relevant subspace, and thereby learns k-subspace juntas under some additional assumptions. We do this by exploiting the structure of local optima of higher moment tensors over the unit sphere; PCA finds the global optima of the second moment tensor (covariance matrix). Our main result is that when the distribution in the irrelevant (n-k)-dimensional subspace is any Gaussian, the complexity of our algorithm is T(k,\epsilon) + \poly(n), where T is the complexity of learning the concept in k dimensions, and the polynomial is a function of the k-dimensional concept class being learned. This substantially generalizes existing results on learning low-dimensional concepts.
Investigation of Electrical Transport in PECVD Grown a-SiCx:H Thin Film  [PDF]
Kutsal Bozkurt, Orhan ?zdemir, Kubilay Kutlu
Materials Sciences and Applications (MSA) , 2011, DOI: 10.4236/msa.2011.28134
Abstract: Dc/ac transport characteristic of PECVD grown hydrogenated amorphous silicon carbide (a-SiCx:H) thin film was investigated in MIS (metal/insulator/semiconductor) structure by dc current/voltage (I/V) at different temperature (T), ac admittance vs. temperature at constant gate bias voltages and deep level transient spectroscopy (DLTS), respectively. According to I-V-T analysis, two main regimes exhibited. At low electric field, apparent Ohm’s law dominated with Arrhenius type thermal activation energy (EA) around 0.4 eV in both forward and reverse directions. At high field, on the contrary, space charge limited (SCL) current mechanism was eventual. The current transport mechanisms and its temperature/frequency dependence were interpreted by a thermally activated hopping processes across the localized states within a-SiCx:H thin film since 0.4 eV as EA was not high enough for intrinsic band conduction. Instead, transport of charge carriers took place in two steps; first a carrier is thermally excited to an empty energy level from an occupied state then multi-step tunnelling or hopping starts over. Therefore, the two steps mechanisms manifested as single activation energy, differing only through capture cross sections. In turn, two steps in capacitance together with conductance peaks in C-(G)-T while convoluted DLTS signal associated with such events in the measurements.
Silicon Nitride Film by Inline PECVD for Black Silicon Solar Cells  [PDF]
Bangwu Liu,Sihua Zhong,Jinhu Liu,Yang Xia,Chaobo Li
International Journal of Photoenergy , 2012, DOI: 10.1155/2012/971093
Abstract: The passivation process is of significant importance to produce high-efficiency black silicon solar cell due to its unique microstructure. The black silicon has been produced by plasma immersion ion implantation (PIII) process. And the Silicon nitride films were deposited by inline plasma-enhanced chemical vapor deposition (PECVD) to be used as the passivation layer for black silicon solar cell. The microstructure and physical properties of silicon nitride films were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), spectroscopic ellipsometry, and the microwave photoconductance decay (μ-PCD) method. With optimizing the PECVD parameters, the conversion efficiency of black silicon solar cell can reach as high as 16.25%. 1. Introduction Black silicon is an effective method to reduce the surface reflectivity for optoelectronic devices and solar cells application. Many black silicon methods have been developed, including reactive ion etching [1], metal-assisted chemical etching [2], and irradiating the silicon surface with femtosecond laser pulses [3]. In our previous study [4, 5], plasma immersion ion implantation (PIII) process has been put forward to produce black silicon with advantages of low cost and high throughput. During the PIII process, the reactive ions are injected into the silicon lattice and react with silicon, and then black silicon with various microstructures can be formed. Although the black silicon has very low surface reflectivity, the conversion efficiency can not be improved significantly when the black silicon is used for solar cells application. In order to produce high-efficiency black silicon solar cell, the matching process (e.g., Phosphorus diffusion process, PECVD film process, and cofiring process) should be improved. Due to the unique microstructure of the black silicon, the passivation process is of significant importance to produce high-efficiency solar cell. PECVD film is widely used in photovoltaic industry, which cannot only be used as antireflective coating (ARC) but also provide surface passivation effect and excellent bulk passivation for multicrystalline silicon solar cell due to a large amount of hydrogen originating from plasma gas dissociation and incorporated in the film [6]. In the present study, PECVD film is used to passivate the black silicon for solar cells. A detailed study on the physical properties of the as-grown films as functions of the PECVD parameters will be carried out. The passivation effects of the film on the black silicon solar cell will also be
Raman and FTIR Studies on PECVD Grown Ammonia-Free Amorphous Silicon Nitride Thin Films for Solar Cell Applications  [PDF]
Nafis Ahmed,Chandra Bhal Singh,S. Bhattacharya,S. Dhara,P. Balaji Bhargav
Conference Papers in Science , 2013, DOI: 10.1155/2013/837676
Abstract: Ammonia- (NH3-) free, hydrogenated amorphous silicon nitride (a-SiNx:H) thin films have been deposited using silane (SiH4) and nitrogen (N2) as source gases by plasma-enhanced chemical vapour deposition (PECVD). During the experiment, SiH4 flow rate has been kept constant at 5?sccm, whereas N2 flow rate has been varied from 2000 to 1600?sccm. The effect of nitrogen flow on SiNx:H films has been verified using Raman analysis studies. Fourier transform Infrared spectroscopy analysis has been carried out to identify all the possible modes of vibrations such as Si–N, Si–H, and N–H present in the films, and the effect of nitrogen flow on these parameters is correlated. The refractive index of the above-mentioned films has been calculated using UV-VIS spectroscopy measurements by Swanepoel’s method.
Influence of flow rate on different properties of diamond-like nanocomposite thin films grown by PECVD
T. S. Santra,T. K. Bhattacharyya,F. G. Tseng,T. K. Barik
AIP Advances , 2012, DOI: 10.1063/1.4721654
Abstract: Diamond-like nanocomposite (DLN) thin films were deposited on pyrex glass substrate using different flow rate of haxamethyldisiloxane (HMDSO) based liquid precursor with nitrogen gas as a glow discharged decomposition by plasma enhanced chemical vapor deposition (PECVD) technique. The significant influence of different precursor flow rates on refractive index and thickness of the DLN films was measured by using spectroscopic filmatrics and DEKTAK profilometer. Optical transparency of the DLN thin films was analyzed by UV-VIS-NIR spectrometer. FTIR spectroscopy, provides the information about shifted bonds like SiC2, Si-C, Si-O, C-C, Si-H, C-H, N-H, and O-H with different precursor flow rate. We have estimated the hardness of the DLN films from Raman spectroscopy using Gaussian deconvolution method and tried to investigate the correlation between hardness, refractive index and thickness of the films with different precursor flow rates. The composition and surface morphology of the DLN films were investigated by X-ray photo electron spectroscopy (XPS) and atomic force microscopy (AFM) respectively. We have analyzed the hardness by intensity ratio (ID/IG) of D and G peaks and correlates with hardness measurement by nanoindentation test where hardness increases from 27.8 μl/min to 80.6μl/min and then decreases with increase of flow rate from 80.6μl/min to 149.5μl/min. Finally, we correlates different parameters of structural, optical and tribological properties like film-thickness, refractive index, light transmission, hardness, surface roughness, modulus of elasticity, contact angle etc. with different precursor flow rates of DLN films.
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