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1.
Despite occasional experimental hints, medium-range structural order in covalently bonded amorphous semiconductors had largely escaped detection until the advent of fluctuation electron microscopy (FEM) in 1996. Using FEM, we find that every sample of amorphous silicon and germanium we have investigated, regardless of deposition method or hydrogen content, is rich in medium-range order. The paracrystalline structural model, which consists of small, topologically ordered grains in an amorphous matrix, is consistent with the FEM data, and is rendered diffraction amorphous by strain effects. We present measurements on hydrogenated amorphous silicon deposited by different methods, some of which are reported to have greater stability against the Staebler–Wronski effect. The matrix material of these samples is relatively similar, but the order changes in different ways upon both light soaking and thermal annealing. Some materials are inhomogeneous, with either nanocrystalline inclusions or large area-to-area variation in the medium-range order. We discuss the implications of and future directions for understanding medium-range order.  相似文献   

2.
By using a seeding technique it has been possible to reduce the thickness of p-μc-Si:H film to 230 Å, with an improved electrical conductivity (0.93 S cm−1) and lower optical absorption compared to those of conventional p-μc-Si:H layers without a seed layer, for use at the tunnel junction and as the top layer of a double junction n–i–p structured a-Si solar cell. Undoped-μc-Si:H has been used as the seed layer. The layers were prepared by the radio frequency plasma-enhanced chemical vapour deposition (RF-PECVD) method (13.56 MHz) at 40 mW/cm2 rf power density and low substrate temperature (200 °C). The ultrathin seed layer (30 Å) enhances the growth of microcrystallinity of the p-type μc-Si:H film as confirmed by the results of transmission electron microscopy (TEM) analysis and Raman spectroscopy.  相似文献   

3.
Using noble gas argon as a diluent of SiH4 in RF glow discharge, undoped μc-Si:H thin films have been developed at a low power density of 30 mW/cm2. It has been found that the gas pressure is a critical factor for the growth of μc-Si:H films. Undoped μc-Si:H films having σD10−6 S/cm and ΔE<0.57 eV have been obtained at and above a critical pressure of 0.8 Torr. When the RF power density is increased to 90 mW/cm2, a more crystalline as well as highly conducting (σD10−4 S/cm) μc-Si:H film has been achieved at a deposition rate of 30 Å/min, which is much higher than that attained from H2-diluted SiH4 plasma, by conventional approach. The crystallinity of the films has been identified by the sharp Raman peak at 520 cm−1 and a large number of micrograins in the TEM micrographs. The metastable state of Ar, denoted as Ar*, plays the crucial role in inducing microcrystallisation by transferring its de-excitation energy at the surface of the growing film. A mechanism has been proposed to explain the dependence of the formation of μc-Si:H film on the working gas pressure in the plasma.  相似文献   

4.
The sheet resistance and the Hall mobility of high-purity Si wafers, in whose surface Ti atoms are implanted and laser annealed reaching concentrations above 1021 cm−3, are measured in the 90-370 K range. Below 240 K, an unconventional behavior is observed that is well explained on the basis of the appearance of an intermediate band (IB) region able to form a blocking junction with the substrate and of the appearance of an IB conduction. Explanations based on ordinary device physics fail to justify all the unconventional behavior of the characteristics observed.  相似文献   

5.
The aim of this work is the quantitative chemical analysis of polycrystalline silicon thin films grown on glass substrates at temperatures <600°C by means of transmission electron microscopy (TEM) and electron energy-loss spectrometry (EELS). Specimens produced with two different methods were investigated. We found significant differences in grain size and morphology, as well as in the distribution of oxygen. A surprisingly high amount of Ba diffusion from the subtrate was detected.  相似文献   

6.
The mineralogy of anodic portions of spent alkaline batteries from a leading brand (Duracell) that had been equilibrated in ambient air for approximately 4 months was investigated to determine if material generated from this low energy process may be suitable stock material for recycling. Powder X-ray diffraction (XRD) identified the bulk of the ambient air oxidized anodic material as zincite (ZnO). Scanning electron microscopy investigation indicates a variety of textures of zincite are present with euhedral hexagonal prisms being the most common crystal form. Energy dispersive spectroscopy (EDS) analysis indicates that there are no minor amounts of Mn within the zincite. Transmission electron microscopy investigation indicates a variety of textures exist in the <2 μm size fraction including near euhedral prismatic crystals, crystals with step-fashion terminations and indentations, heavily corroded zincite and near amorphous aggregates of anastomozing zinc oxide. Impurities in the <2 μm size fraction include minor amounts of unidentified mixed sulfate materials and are interpreted as dominantly occurring as thin coatings on zincite particles. Discrete submicrometer-sized spherical and rhomboid particles of Zn-Mn oxides are also common impurities in the <2 μm size fraction but occurr at abundance of <1% by volume.This study provides new baseline information that can be used to develop large scale recycling of zincite from spent alkaline batteries. A promising applications of zincite are numerous, including the development of new solar cell materials. The spent alkaline battery waste stream may serve as promising resource for driving further development of this sector of the economy.  相似文献   

7.
Significant improvement in the microcrystallization in Si:H network has been demonstrated by introducing layer-by-layer (LBL) growth and H-plasma treatment on the stacking layers. During the development of microcrystalline network, the amorphous incubation layer as well as the microcrystalline transition layer thickness has been reduced efficiently by the enhanced reactivity of atomic H from the surface into the bulk through the growth zone, so that the virtual saturation in crystallization is obtained at a significantly low thickness. The growth process becomes more flexible because of the inclusion of additional independent parameter, namely, the time span of H-plasma exposure (tP) on the growing surface, compared to the conventional process.  相似文献   

8.
Solar grade, p-type multicrystalline silicon wafers with large grains from different parts of silicon ingots produced by the metallurgical route (SoG-Si) at ELKEM Solar were studied using a number of complementary methods such as microwave photoconductivity decay, deep level transient spectroscopy, transmission and scanning electron microscopy, X-ray fluorescence, and secondary ion mass spectroscopy. Wafers from the top of the ingots have uniform spatial distributions of both minority carrier lifetime (average lifetime τ=3.2 μs) and concentrations of illumination-sensitive recombination centers (Nrc=3×1010−2×1011 cm−3) over the whole wafers. Wafers from the bottom of the ingots have regions of very low lifetimes (τ=0.3 μs) and high concentrations of illumination-sensitive recombination centers (Nrc=2×1012 cm−3). In the top part of the ingots the observed DLTS peaks can be attributed to copper-related extended defects, and the DLTS results from grains and grain boundaries are not significantly different. The main factors limiting the lifetime in the high lifetime regions are concluded to be illumination-sensitive recombination centers such as Fe-B pairs, B-O complexes, and Cu-related extended defects. The low lifetimes in the bottom part of the ingots are explained by a combination of several factors including high concentrations of illumination-sensitive recombination centers and of some deleterious elements (S, Na and Al), and a large amount of structural defects.  相似文献   

9.
Abstract

Reduced activation ferritic/martensitic and ferritic steels strengthened by a dispersion of oxide nanoparticles have been considered viable structural materials for fusion applications above 550°C. However, the microstructural stability and mechanical behaviour of these steels subjected to the aggressive operating conditions of these reactors are not well known. An accelerated development of these materials is crucial if they are going to be used in future power reactors. Then, it is indispensable to understand their atomic scale evolution under high temperature and irradiation conditions. The present paper reviews how the combination of transmission electron microscopy and atom probe tomography has been successfully applied for the characterisation of these steels at the near atomic scale, to reveal the nanoparticle structure, grain boundary chemistry and void distribution.  相似文献   

10.
The desorption mechanism of as-milled 2NaBH4 + MgH2 was investigated by volumetric analysis, X-ray diffraction and electron microscopy. Hydrogen desorption was carried out in 0.1 bar hydrogen pressure from room temperature up to 450 °C at a heating rate of 3 °C min−1. Complete dehydrogenation was achieved in two steps releasing 7.84 wt.% hydrogen. Desorption reaction in this system is kinetically restricted and limited by the growth of MgB2 at the Mg/Na2B12H12 interface where the intermediate product phases form a barrier to diffusion. During desorption, MgB2 particles are observed to grow as plates around NaH particles.  相似文献   

11.
Ethylene propylene diene (EPDM) rubber has gained increasing interest for use in hydrogen infrastructure due to its excellent sealing performance and low temperature properties. However, severe structural damage has been observed in EPDM O-rings after exposure to high-pressure hydrogen. The origination and propagation mechanisms of this damage are poorly understood. To address this knowledge gap, multi-scale imaging leveraging X-ray micro-computed tomography (micro-CT), helium ion microscopy (HeIM), and transmission electron microscopy (TEM) were used in this work to study a series of sulfur-cured ethylene propylene diene (EPDM) rubber materials with varying additives that were exposed to different hydrogen environments. Micro-CT captured the substantial structural damage due to hydrogen exposure; it revealed an association between zinc oxide (ZnO) particles and damage initiation. Further studies by TEM and scanning TEM with energy dispersive X-ray spectroscopy (EDS) were focused on these particles at the micro-to nano-scale range. TEM indicated that hydrogen causes void formation at the interface between ZnO and the rubber matrix. HeIM enabled imaging of surface morphology of the material at high resolution pre- and post-hydrogen exposure while providing information on chemical composition and that cannot be captured by either micro-CT or TEM.  相似文献   

12.
The microstructure of SiC particles and SiC filament-type precipitates found in block-cast multicrystalline Si was studied in detail by transmission electron microscopy (TEM). TEM investigations showed that the SiC particles are single crystalline and the SiC filaments are microcrystalline. Both types of precipitates consist of cubic SiC. However, a high density of planar defects was found in the filaments. Very wavy and rough interface between SiC filaments and silicon (Si) was revealed by high-resolution TEM. In addition, SiC filaments do not show a special orientation relationship with respect to the Si matrix. The growth mechanisms of SiC precipitates are discussed. Finally, the influence of SiC inclusions in terms of device performance is considered.  相似文献   

13.
In this work, active and stable catalyst for the dehydrogenation reaction of dimethylamine borane (DMAB) in solvent-free medium at room temperature has been prepared. The method is based on preparing in-situ monodispersed gold nanoparticles (AuNPs) by reducing the one dimensional polymer of gold(I):6-thioguanosine hydrogel by DMAB; which acts as reducing and stabilizing agent. Monitoring time-dependent to build the surface plasmon resonance (SPR) band for the formed AuNPs was carried out by performing a kinetic study using UV–Vis spectroscopy. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) techniques were used to investigate the morphology of the AuNPs that obtained after reducing the hydrogel.  相似文献   

14.
A novel composite anion exchange membrane, zirconia incorporated quaternized polysulfone (designated as QPSU/ZrO2), is prepared by solution casting method. The characteristic properties of the QPSU/ZrO2 composite polymer membranes are investigated by thermogravimetric analysis, X-ray diffraction and electrochemical impedance spectroscopy. The morphology of the composite membrane is observed by SEM and TEM studies. A study of an alkaline membrane fuel cell (AMFC) operating with hydroxide ion conducting membrane is reported. Evaluation of the fuel cell is performed using membrane electrode assemblies made up of carbon supported platinum (Vulcan XC-72) anode and platinum cathode catalysts and QPSU/ZrO2 composite membrane. Experimental results indicate that the AMFC employing a cheap non-perflourinated (QPSU/ZrO2) composite polymer membrane shows better electrochemical performance. The maximum power density observed is 250 mW/cm2 for QPSU/10% ZrO2 at 60 °C. The QPSU/ZrO2 composite membrane constitutes a good candidate for alkaline membrane fuel cell applications.  相似文献   

15.
In the present work the stability, chemical composition and structure of a Pt/Ru catalyst alloy with a nominal ratio of 1/1 is investigated. The same catalyst particles are analyzed before and after potential cycling experiments using identical location transmission electron microscopy. The experiments were performed at room temperature at [0–1.0] VRHE and [0–1.2] VRHE to simulate conditions occurring during ramping up of fuel cells. With decreasing maximum potential value a higher stability is found. Dissolution and dealloying are identified to be the main degradation mechanisms during potential cycling with Ru being dissolved preferably. Also agglomeration and Ostwald ripening are taking place, the frequency decreasing the longer the experiment is performed. Advanced in-depth analysis of potential-dependent reshaping mechanisms are performed by calculating the three-dimensional volume of single particles both in the as-prepared state and after potential cycling experiments using electron tomography data. Evaluation of the volume-specific change of the accessible surface area of the catalyst helps to understand fuel cell performance deterioration.  相似文献   

16.
We optimize InAsyP1−y buffer layers and compositional grades for lattice-mismatched heteroepitaxy of GaxIn1−xAs/InAsyP1−y double-heterostructures on InP. The strains of the active and buffer layers depend on the bulk misfit difference between these layers. The misfit difference is adjusted to eliminate strain in the active layer, thus avoiding misfit dislocations and surface topography that would otherwise form to relieve strain. The optimized structure uses an “overshoot” with respect to the conventional design in the misfit and As composition of the InAsyP1−y buffer. Nearly optimized heterostructures typically show excellent structural quality and extended minority-carrier lifetimes.  相似文献   

17.
Structural and compositional properties of Zn(Se,OH)/Zn(OH)2 buffer layers deposited by chemical bath deposition(CBD) on Cu(In,Ga)(S,Se)2 (CIGSS) absorbers are investigated. Due to the aqueous nature of the CBD process, oxygen and hydrogen were incorporated into the ‘ZnSe’ buffer layer mainly in the form of Zn(OH)2 as is shown by X-ray photoelectron spectroscopy and nuclear reaction analysis (NRA) measurements leading to the nomenclature ‘Zn(Se,OH)’. Prior to the deposition of Zn(Se,OH), a zinc treatment of the absorber was performed. During that treatment a layer mainly consisting of Zn(OH)2 grew to a thickness of several nanometer. The whole buffer layer therefore consists of a Zn(Se,OH)/Zn(OH)2 structure on CIGSS. Part of the Zn(OH)2 in both layers (i.e. the Zn(Se,OH) and the Zn(OH)2 layer) might be converted into ZnO during measurements or storage. Scanning electron microscopy pictures showed that a complete coverage of the absorber with the buffer layer was achieved. Transmission electron microscopy revealed the different regions of the buffer layer: An amorphous area (possibly Zn(OH)2) and a partly nanocrystalline area, where lattice planes of ZnSe could be identified. Solar cell efficiencies of ZnO/Zn(Se,OH)/Zn(OH)2/CIGSS devices exceed 14% (total area).  相似文献   

18.
The longevity of a solid oxide fuel cell (SOFC) stack is curtailed by the fragility of its ceramic components. At Ceramic Fuel Cells Limited (CFCL), 15 wt.% alumina is added to the commonly used 10 mol% Y2O3–ZrO2 (YSZ) electrolyte to improve both the fracture toughness and grain-boundary conductivity of the electrolyte. This study investigates the effect of such addition of alumina on the anode|electrolyte interface; more specifically, which reactions occur with the Al2O3 at the interface and how these reactions influence fuel cell performance. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) are used to characterize the formation of NiAl2O4 in the alumina regions in the electrolyte. The NiAl2O4 is observed to grow into the adjacent grain boundaries to form an interconnected NiAl2O4 network up to 4 μm deep into the electrolyte. Impedance spectroscopy shows that the formation of NiAl2O4 does not affect the grain bulk ionic conductivity. The grain-boundary conductivity is markedly reduced at low temperatures. However, at the high SOFC operating temperature at CFCL (850 °C) the contribution of the grain-boundary conductivity to the total conductivity is diminished, and the NiAl2O4 is found not to have an effect on the total electrolyte conductivity and is deemed not to be a detrimental reaction.  相似文献   

19.
We review the recent empirical research assessing market power on the Nordic wholesale market for electricity, Nord Pool. The studies find no evidence of systematic exploitation of system level market power on Nord Pool. Local market power arising from transmission constraints seems to be more problematic in some price areas across the Nordic countries. Market power can manifest itself in a number of ways that have so far escaped empirical scrutiny. We discuss investment incentives, vertical integration and buyer power, as well as withholding of base-load (nuclear) capacity.  相似文献   

20.
The hydrogen trapping efficiency of different types of W based precipitates is considered in three generic FeCW alloys with increasing carbon content and a stoichiometric amount of W. A martensitic microstructure is prepared and two conditions are compared; i.e. an as-quenched (as-Q) state and a quenched and tempered (Q&T) state in which W based carbides are formed. The tempering time and temperature are modified to change the carbide characteristics. Hence, the hydrogen trapping characteristics are evaluated for the different carbides. Melt extraction is done to determine the hydrogen content, whereas thermal desorption spectroscopy (TDS) is performed to verify whether the tempered induced carbides are able to trap hydrogen efficiently. The trapping capacity is found not only to be size dependent, but also reliant on the morphology and type of the carbides, as investigated by transmission electron microscopy. TDS revealed that the tempered induced W2C in the Q&T at 600 °C for 1 h condition do not trap hydrogen due to their rather large size (>20 nm) and hence incoherent nature. Moreover, the hydrogen content is decreased compared to the as-Q condition due to the reduced dislocation density. The tempering time is reduced to 10 min to evaluate the size effect on the carbide trapping ability. As such, smaller W2C (<20 nm) are induced, which trapped a significant amount of hydrogen, as demonstrated by TDS, with a corresponding activation energy of 42–45 kJ/mol. This compensated the reduction in dislocation density, causing a higher hydrogen level. Furthermore, tempering at 700 °C for 1 h results in an increase of hydrogen compared to the Q&T at 600 °C for 1 h condition. This is confirmed by TDS and TEM to be linked to the trapping ability of W23C6, showing a slightly higher activation energy ranging from 47 to 49 kJ/mol.  相似文献   

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