How do Impurities Affect the Growth of μc-Si:H?

1998 ◽  
Vol 507 ◽  
Author(s):  
Toshihiro Kamei ◽  
Makoto Fukawa ◽  
Tatsuyuki Nishimiya ◽  
Masao Isomura ◽  
Michio Kondo ◽  
...  
Keyword(s):  
Small Volume ◽  
Volume Fraction ◽  
Defect Density ◽  
Hydrogen Desorption ◽  
Oxygen Impurity ◽  
Surface Hydrogen ◽  
Small Volume Fraction ◽  
Higher Temperature ◽  
Effect Of Oxygen

ABSTRACTUltra clean plasma CVD process opens the doorway to clarify the role of impurities in the growth process of μc-Si:H. A reduction of impurity levels during the growth extends the temperature range for crystalline formation to lower side, i.e., high-crystallinity μc-Si:H formation even at room temperature, substantially reduces midgap defect density at 200°C, and enlarges crystalline grain size at 350°C. These results imply that impurities disrupt crystalline formation even on hydrogen covered surface. The crystalline-to-amorphous transition is induced by a loss of surface hydrogen coverage due to thermal hydrogen desorption at higher temperature of ∼450°C irrespective of the effect of oxygen impurity. Light-soaking experiments for the series of the films from a-Si:H to μc-Si:H films with different crystalline volume fraction indicate that the presence of small volume fraction of crystallite significantly suppresses light induced defect creation under the present light soaking condition of 3SUN 60°C 6hr. These results are explained in terms of preferential recombination of photo-excited carriers in the crystallite.

Experimental Model of Temperature-Driven Nanofluid

2006 ◽  
Vol 129 (6) ◽  
pp. 697-704 ◽  
Author(s):  
A. G. Agwu Nnanna
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Small Volume ◽  
Volume Fraction ◽  
Convective Heat Transfer Coefficient ◽  
Isothermal Condition ◽  
Carrier Fluid ◽  
Small Volume Fraction ◽  
The Impact

This paper presents a systematic experimental method of studying the heat transfer behavior of buoyancy-driven nanofluids. The presence of nanoparticles in buoyancy-driven flows affects the thermophysical properties of the fluid and consequently alters the rate of heat transfer. The focus of this paper is to estimate the range of volume fractions that results in maximum thermal enhancement and the impact of volume fraction on Nusselt number. The test cell for the nanofluid is a two-dimensional rectangular enclosure with differentially heated vertical walls and adiabatic horizontal walls filled with 27 nm Al2O3–H2O nanofluid. Simulations were performed to measure the transient and steady-state thermal response of nanofluid to imposed isothermal condition. The volume fraction is varied between 0% and 8%. It is observed that the trend of the temporal and spatial evolution of temperature profile for the nanofluid mimics that of the carrier fluid. Hence, the behaviors of both fluids are similar. Results shows that for small volume fraction, 0.2⩽ϕ⩽2% the presence of the nanoparticles does not impede the free convective heat transfer, rather it augments the rate of heat transfer. However, for large volume fraction ϕ>2%, the convective heat transfer coefficient declines due to reduction in the Rayleigh number caused by increase in kinematic viscosity. Also, an empirical correlation for Nuϕ as a function of ϕ and Ra has been developed, and it is observed that the nanoparticle enhances heat transfer rate even at a small volume fraction.

Loading Rate Effect on Translaminar Fracture Toughness of Hybrid Composite Laminate

2000 ◽  
Author(s):  
Paul Moy ◽  
Jerome Tzeng
Keyword(s):  
Fracture Toughness ◽  
Composite Laminates ◽  
Glass Matrix ◽  
Small Volume ◽  
Loading Rate ◽  
Volume Fraction ◽  
Rate Effect ◽  
The Matrix ◽  
Small Volume Fraction ◽  
Matrix Property

Abstract Fracture toughness properties of composite laminates were evaluated at a loading rate commonly observed in ordinance applications. The laminates are composed of IM7 graphite and a small volume fraction of S2 glass plies to form a cross-ply laminate. Fracture toughness appears to be very rate sensitive if the crack growth perpendicular to the plane dominated by glass/matrix property. Experimental data shows a 30–40% increase of fracture toughness for various layup as the loading rate was increase by 1000 times. The specimens examined under microscopic indicates the strengthening might due to different failure mechanism in the matrix. In addition, there is no visible rate effect if the crack propagation is perpendicular to the graphite dominant plane.

scholarly journals Stress–Corrosion Cracking of AISI 316L Stainless Steel in Seawater Environments: Effect of Surface Machining

Metals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1324
Author(s):  
Zhe Ren ◽  
Frank Ernst
Keyword(s):  
Stress Corrosion ◽  
Small Volume ◽  
Volume Fraction ◽  
Single Point ◽  
Crack Density ◽  
Aisi 316L ◽  
Surface Machining ◽  
Subsurface Zone ◽  
Small Volume Fraction ◽  
Effect Of Surface

To understand the effect of surface machining on the resistance of AISI 316L to SCC (stress–corrosion cracking) in marine environments, we tested nuts surface-machined by different methods in a seawater-spraying chamber. Two forms of cracks were observed: on the machined surface and underneath it. On the surface, cracks connected with the pitting sites were observed to propagate perpendicular to the hoop-stress direction, identifying them as stress–corrosion cracks. Under the surface, catastrophic transgranular cracks developed, likely driven by hydrogen embrittlement caused by the chloride-concentrating level of humidity in the testing environment. Under constant testing conditions, significantly different SCC resistance was observed depending on how the nuts had been machined. Statistical evaluation of the nut surface-crack density indicates that machining by a “form” tool yields a crack density one order of magnitude lower than machining by a “single-point” tool. Microstructural analysis of form-tool-machined nuts revealed a homogeneous deformed subsurface zone with nanosized grains, leading to enhanced surface hardness. Apparently, the reduced grain size and/or the associated mechanical hardening improve resistance to SCC. The nanograin subsurface zone was not observed on nuts machined by a single-point tool. Surface roughness measurements indicate that single-point-tool-machined nuts have a rougher surface than form-tool machined nuts. Apparently, surface roughness reduces SCC resistance by increasing the susceptibility to etch attack in Cl--rich solutions. The results of X-ray diffractometry and transmission electron microscopy diffractometry indicate that machining with either tool generates a small volume fraction (< 0.01) of strain-induced martensite. However, considering the small volume fraction and absence of martensite in regions of cracking, martensite is not primarily responsible for SCC in marine environments.

scholarly journals A 2D Multiphase Model of Drop Behavior during Electroslag Remelting

Metals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 490
Author(s):  
Jérémy Chaulet ◽  
Abdellah Kharicha ◽  
Sylvain Charmond ◽  
Bernard Dussoubs ◽  
Stéphane Hans ◽  
...  
Keyword(s):  
Small Volume ◽  
Slag Phase ◽  
Volume Fraction ◽  
Liquid Pool ◽  
Electroslag Remelting ◽  
Multiphase Model ◽  
Momentum Exchange ◽  
Small Volume Fraction ◽  
Drag Law ◽  
Two Fluid

Electroslag remelting is a process extensively used to produce metallic ingots with high quality standards. During the remelting operation, liquid metal droplets fall from the electrode through the liquid slag before entering the liquid pool of the secondary ingot. To better understand the process and help to optimize the operating condition choice, a 2D axisymmetric multiphase model of the slag domain has been developed using a two fluid Eulerian approach. During their fall, droplets hydrodynamic interactions are calculated thanks to an appropriate drag law. Influence of droplets on the electromagnetic field and on the slag hydrodynamics is discussed, as well as their heat exchange with the slag. Even with a small volume fraction, the droplets influence is noticeable. The present investigation shows that small droplets have a large influence on the slag hydrodynamics, due to a great momentum exchange. However heat transfer is more influenced by large drops, which are found to be relatively far from the thermal equilibrium with the slag phase.

Flow past periodic arrays of spheres at low Reynolds number

1997 ◽  
Vol 335 ◽  
pp. 189-212 ◽  
Author(s):  
HONGWEI CHENG ◽  
GEORGE PAPANICOLAOU
Keyword(s):  
Reynolds Number ◽  
Viscous Flow ◽  
Small Volume ◽  
Volume Fraction ◽  
Periodic Array ◽  
Periodic Arrays ◽  
Flow Past ◽  
Random Array ◽  
Single Sphere ◽  
Small Volume Fraction

We calculate the force on a periodic array of spheres in a viscous flow at small Reynolds number and for small volume fraction. This generalizes the known results for the force on a periodic array due to Stokes flow (zero Reynolds number) and the Oseen correction to the Stokes formula for the force on a single sphere (zero volume fraction). We use a generalization of Hasimoto's approach that is based on an analysis of periodic Green's functions. We compare our results to the phenomenological ones of Kaneda for viscous flow past a random array of spheres.

scholarly journals New developments in understanding interfacial processes in turbulent flows

2011 ◽  
Vol 369 (1937) ◽  
pp. 702-705 ◽  
Author(s):  
I. Eames ◽  
J. B. Flor
Keyword(s):  
Turbulent Flows ◽  
Small Volume ◽  
Volume Fraction ◽  
Flow Properties ◽  
Theme Issue ◽  
New Developments ◽  
Interfacial Processes ◽  
Recent Developments ◽  
Small Volume Fraction ◽  
Entire Flow

Interfaces, across which fluid and flow properties change significantly, are a ubiquitous feature of most turbulent flows and are present within jets, plumes, homogeneous turbulence, oceans and planetary atmospheres. Even when the interfaces occupy a small volume fraction of the entire flow, they largely control processes such as entrainment and dissipation and can act as barriers to transport. This Theme Issue brings together some of the leading recent developments on interfaces in turbulence, drawing in many methodologies, such as experiments, direct number simulations, inverse methods and analytical modelling.

scholarly journals Low volume-fraction microstructures in martensites and crystal plasticity

2016 ◽  
Vol 26 (07) ◽  
pp. 1319-1355 ◽  
Author(s):  
Sergio Conti ◽  
Barbara Zwicknagl
Keyword(s):  
Small Volume ◽  
Materials Science ◽  
Volume Fraction ◽  
Variational Problems ◽  
The Other ◽  
Microstructure Formation ◽  
Branching Patterns ◽  
Small Volume Fraction ◽  
New Phase

We study microstructure formation in two nonconvex singularly-perturbed variational problems from materials science, one modeling austenite–martensite interfaces in shape-memory alloys, the other one slip structures in the plastic deformation of crystals. For both functionals we determine the scaling of the optimal energy in terms of the parameters of the problem, leading to a characterization of the mesoscopic phase diagram. Our results identify the presence of a new phase, which is intermediate between the classical laminar microstructures and branching patterns. The new phase, characterized by partial branching, appears for both problems in the limit of small volume fraction, that is, if one of the variants (or of the slip systems) dominates the picture and the volume fraction of the other one is small.

Role of Oxygen in Rare Earth Chalcogenide Semiconductors

1987 ◽  
Vol 97 ◽  
Author(s):  
Cheryl M. Vaughan ◽  
William B. White
Keyword(s):  
Rare Earth ◽  
Unit Cell Volume ◽  
Oxygen Impurity ◽  
Ordered Structure ◽  
Impurity Bands ◽  
Beta Structure ◽  
Effect Of Oxygen ◽  
High Degree ◽  
Degree Of Order

ABSTRACTOxygen uptake by the rare earth chalcogenides takes place through a series of ordered compounds. At high oxygen concentrations the distinct and nearly stoichiometric oxychalcogenides, Ln202X (X = S, Se, Te) appear. For the chalcogenides of the larger rare earths there appears an ordered oxygen-containing beta structure, Ln10X14OxX1-x (X = S, Se). The vibrational spectrum of the trigonal oxysulfide structure contains four infrared and four Raman bands (2 A2u + 2 Eu + 2 Alg + 2 Eg). Band wavenumbers across the La to Lu series vary linearly with unit cell volume. The Raman bands are sharp indicating a high degree of order in the intermediate compounds. The Raman bands of the beta structure are remarkably sharp indicating that this compound also has a highly ordered structure. Known data plus synthesis data are combined to form not-impossible phase diagrams for the larger rare earth sulfide systems. The effect of oxygen in both series of compounds is to produce small wavenumber shifts rather than high wavenumber oxygen impurity bands.

Sign in / Sign up

Export Citation Format

Share Document