Effects of Grain Size, Orientation, and Source Density on Dislocation Configurational Energy Density

In this study, a CO2 laser ignition experimental system was built to study the ignition process and characteristics of the Nitrate Ester Plasticized Polyether (NEPE) propellant. The effect of the energy density, ingredients, and the grain size distribution of the propellant on the ignition process was investigated using a CO2 laser igniter, a high-speed camera, and a tungsten-rhenium thermocouple. Four types of NEPE propellants were tested under different laser heat fluxes, and the ignition delay time, the ignition temperature, and the ignition energy were obtained. Experimental results show that the ignition process of the NEPE propellant can be divided into three stages, namely the first-gasification stage, the first-flame stage, and the ignition delay stage. When the energy density is lower than the ignition energy threshold, the ignition process cannot be achieved even under continuous energy loading. The increase of the energy density can lead to the decrease of the ignition delay time but has little effect on the ignition temperature. The ingredients and grain size distribution have great effects on both the ignition delay time and the ignition temperature. The grain size effect of aluminum is the largest compared with that of Ammonium Perchlorate (AP) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), while the grain size effect of AP is larger than that of HMX.

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Electrical and Structural Characteristics of Excimer Laser-Crystallized Polycrystalline Si1−xGex Thin-Film Transistors

Materials ◽

10.3390/ma12111739 ◽

2019 ◽

Vol 12 (11) ◽

pp. 1739 ◽

Cited By ~ 2

Author(s):

Kyungsoo Jang ◽

Youngkuk Kim ◽

Joonghyun Park ◽

Junsin Yi

Keyword(s):

Thin Film ◽

Grain Size ◽

Energy Density ◽

Excimer Laser ◽

Density Of States ◽

Silicon Germanium ◽

Structural Characteristics ◽

Thin Film Transistor ◽

Electrical Characteristics ◽

Starting Point

We investigated the characteristics of excimer laser-annealed polycrystalline silicon–germanium (poly-Si1−xGex) thin film and thin-film transistor (TFT). The Ge concentration was increased from 0% to 12.3% using a SiH4 and GeH4 gas mixture, and a Si1−xGex thin film was crystallized using different excimer laser densities. We found that the optimum energy density to obtain maximum grain size depends on the Ge content in the poly-Si1−xGex thin film; we also confirmed that the grain size of the poly-Si1−xGex thin film is more sensitive to energy density than the poly-Si thin film. The maximum grain size of the poly-Si1−xGex film was 387.3 nm for a Ge content of 5.1% at the energy density of 420 mJ/cm2. Poly-Si1−xGex TFT with different Ge concentrations was fabricated, and their structural characteristics were analyzed using Raman spectroscopy and atomic force microscopy. The results showed that, as the Ge concentration increased, the electrical characteristics, such as on current and sub-threshold swing, were deteriorated. The electrical characteristics were simulated by varying the density of states in the poly-Si1−xGex. From this density of states (DOS), the defect state distribution connected with Ge concentration could be identified and used as the basic starting point for further analyses of the poly-Si1−xGex TFTs.

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Considerations for Large Area Fabrication of Integrated a-Si and Poly-Si TFTs

MRS Proceedings ◽

10.1557/proc-336-781 ◽

1994 ◽

Vol 336 ◽

Author(s):

P. Mei ◽

G. B. Anderson ◽

J. B. Boyce ◽

D. K. Fork ◽

M. Hack ◽

...

Keyword(s):

Grain Size ◽

Energy Density ◽

Laser Energy ◽

Gate Insulator ◽

Laser Energy Density ◽

Laser Crystallization ◽

Large Area ◽

Low Leakage ◽

Threshold Voltages ◽

Excellent Method

ABSTRACTThe combination of a-Si low leakage pixel TFTs with poly-Si TFTs in peripheral circuits provides an excellent method for reducing the number of external connections to large-area imaging arrays and displays. To integrate the fabrication of the peripheral poly-Si TFTs with the a-Si pixel TFTs, we have developed a three-step laser process which enables selective crystallization of PECVD a-Si:H. X-ray diffraction and transmission electron microscopy show that the polycrystalline grains formed with this three-step process are similar to those crystallized by a conventional one step laser crystallization of unhydrogenated amorphous silicon. The grain size increases with increasing laser energy density up to a peak value of a few Microns. The grain size decreases with further increases in laser energy density. The transistor field effect mobility is correlated with the grain size, increasing gradually with laser energy density until reaching its maximum value. Thereafter, the transistors suffer from leakage through the gate insulators. A dual dielectric gate insulator has been developed for these bottom-gate thin film transistors to provide the correct threshold voltages for both a-Si and poly-Si TFTs.

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Excimer Lasbr Induced Crystallization of thin Amorphous Si Films on SiO2: Implications of Crystallized Microstructures for Phase Transformation Mechanisms

MRS Proceedings ◽

10.1557/proc-283-703 ◽

1992 ◽

Vol 283 ◽

Cited By ~ 23

Author(s):

H. J. Kim ◽

James S. Im ◽

Michael O. Thompson

Keyword(s):

Grain Size ◽

Energy Density ◽

Laser Energy ◽

High Energy ◽

High Energy Density ◽

Laser Energy Density ◽

Single Shot ◽

Average Grain Size ◽

Si Films ◽

Density Regime

ABSTRACTUsing planar view transmission electron microscope (TEM) and transient reflectance (TR) analyses, we have investigated the excimer laser crystallization of amorphous silicon (a-Si) films on SiO2. Emphasis was placed on characterizing the microstructures of the single-shot irradiated materials, as a function of the energy density of the laser pulse and the temperature of the substrate. The dependence of the grain size and melt duration as a function of energy density revealed two major crystallization regimes. In the low energy density regime, the average grain size first increases gradually with increases in the laser energy density. In the high energy density regime, on the other hand, a very fine grained microstructure, which is relatively insensitive to variations in the laser energy density, is obtained. In addition, we have discovered that at the transition between these two regimes an extremely small experimental window exists, within which an exceedingly large grain-sized polycrystalline film is obtained. We suggest a liquid phase growth model for this phenomenon, which is based on the regrowth of crystals from the residual solid islands at the oxide interface.

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Effect of Laser Energy Density on the Microstructure andTexture Evolution of Hastelloy-X Alloy Fabricated by Laser Powder Bed Fusion

Materials ◽

10.3390/ma14154305 ◽

2021 ◽

Vol 14 (15) ◽

pp. 4305

Author(s):

Shuzhe Zhang ◽

Yunpei Lei ◽

Zhen Chen ◽

Pei Wei ◽

Wenjie Liu ◽

...

Keyword(s):

Grain Size ◽

Energy Density ◽

Electron Backscatter Diffraction ◽

Laser Energy ◽

Primary Dendrite ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Hastelloy X ◽

Powder Bed ◽

Average Grain Size

It is of great importance to study the microstructure and textural evolution of laser powder bed fusion (LPBF) formed Hastelloy-X alloys, in order to establish a close relationship between the process, microstructure, and properties through the regulation of the Hastelloy-X formation process parameters. In this paper, components of a Hastelloy-X alloy were formed with different laser energy densities (also known as the volume energy density VED). The densification mechanism of Hastelloy-X was studied, and the causes of defects, such as pores and cracks, were analyzed. The influence of different energy densities on grain size, texture, and orientation was investigated using an electron backscatter diffraction technique. The results show that the average grain size, primary dendrite arm spacing, and number of low angle grain boundaries increased with the increase of energy density. At the same time, the VED can strengthen the texture. The textural intensity increases with the increase of energy density. The best mechanical properties were obtained at the VED of 96 J·mm−3.

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Considerations for Large Area Fabrication Of Integrated a-Si and Poly-Si TFTs

MRS Proceedings ◽

10.1557/proc-345-41 ◽

1994 ◽

Vol 345 ◽

Author(s):

P. Mei ◽

G. B. Anderson ◽

J. B. Boyce ◽

D. K. Fork ◽

M. Hack ◽

...

Keyword(s):

Grain Size ◽

Energy Density ◽

Laser Energy ◽

Gate Insulator ◽

Laser Energy Density ◽

Laser Crystallization ◽

Large Area ◽

Low Leakage ◽

Threshold Voltages ◽

Excellent Method

AbstractThe combination of a-Si low leakage pixel TFTs with poly-Si TFTs in peripheral circuits provides an excellent method for reducing the number of external connections to large-area imaging arrays and displays. To integrate the fabrication of the peripheral poly-Si TFTs with the a-Si pixel TFTs, we have developed a threestep laser process which enables selective crystallization of PECVD a-Si:H. X-ray diffraction and transmission electron microscopy show that the polycrystalline grains formed with this three-step process are similar to those crystallized by a conventional one step laser crystallization of unhydrogenated amorphous silicon. The grain size increases with increasing laser energy density up to a peak value of a few microns. The grain size decreases with further increases in laser energy density. The transistor field effect mobility is correlated with the grain size, increasing gradually with laser energy density until reaching its maximum value. Thereafter, the transistors suffer from leakage through the gate insulators. A dual dielectric gate insulator has been developed for these bottom-gate thin film transistors to provide the correct threshold voltages for both a-Si and poly-Si TFTs.

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A New Constitutive Model for Work Hardening Based on Gain Boundary Energy Density

Materials Science Forum ◽

10.4028/www.scientific.net/msf.633-634.249 ◽

2009 ◽

Vol 633-634 ◽

pp. 249-259

Author(s):

Ji Luo ◽

Zhi Rui Wang

Keyword(s):

Grain Size ◽

Energy Density ◽

Deformation Mechanism ◽

Boundary Energy ◽

Critical Energy ◽

Coarse Grained ◽

Defect Energy ◽

Grain Sizes ◽

Energetic Approach ◽

Size Criterion

Recently, the necessity to grade grain size to ultrafine and nano scale for understanding the mechanical behavior of these materials has been recognized. However, the nature of such classification has remained unclear. As an example, ultrafine (100 nm -1 μm) and nano (<100 nm) grained FCC metals, compared to their coarse grained counterparts, exhibit a grain size strengthening that may deviate from the Hall-Petch relationship. To explain the mechanism of such deviation, previous dislocation theories seem insufficient. To solve this problem, a critical grain size criterion governing the shift of deformation mechanism is proposed in this work. This model employs an energetic approach; it relates the grain boundary energy density to certain critical energy values; and it permits, for the first time, a quantitative grading of grain sizes. Predictions based on this model were evaluated. The prediction on copper polycrystals of various grain sizes showed a very good agreement with experimental results. It is thus wished that the grain size theory on plastic deformation mechanism could be unified with the dislocation theory. In this study, such unification is attempted by using a parameter defined as the defect energy density. The possibility of such generalization is further reasoned upon the fact that the defect energy approach should be a unique but common form applicable for both dislocations and grain boundaries.

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Effect of Calcination Temperature on the Breakdown Strength and Energy Density of CaCu3Ti4O12 Ceramic

Materials Science Forum ◽

10.4028/www.scientific.net/msf.888.23 ◽

2017 ◽

Vol 888 ◽

pp. 23-27 ◽

Cited By ~ 4

Author(s):

Mohd Fariz Ab Rahman ◽

Mohamad Johari Abu ◽

Rosyaini Afindi Zaman ◽

Julie Juliewatty Mohamed ◽

Mohd Fadzil Ain ◽

...

Keyword(s):

Grain Size ◽

Energy Density ◽

Calcination Temperature ◽

Single Phase ◽

Breakdown Strength ◽

Raw Materials ◽

Sintered Sample ◽

Xrd Analysis ◽

Solid State Reaction Method ◽

Secondary Phases

The effect of calcination temperature on the breakdown strength and energy density of CaCu3Ti4O12 (CCTO) ceramics was studied. CCTO ceramics were prepared via solid state reaction method. The raw materials of CCTO were wet mixed for 24 hours and then dried overnight in oven. CCTO mixtures were calcined at three different temperature which is at 900°C, 930°C and 950°C for 12 hours. The calcined powders were compacted at 250 MPa and then were sintered at 1040°C for 10 hours. X-Ray Diffractometer (XRD) analysis showed the formation of CCTO phase and secondary phases of CuO and CaTiO3 for C900 calcined powders but single phase of CCTO was obtained by C930 and C950 calcined powders. Single phase of CCTO also were seen for all sintered samples. Observation on Scanning Electron Microscopy (SEM) micrographs showed large grain size was seen in C900 sintered sample and finer grain size was observed for C930 and C950 sintered samples. C900 sintered sample obtained highest dielectric constant (8617), highest breakdown strength (7.92 kV/cm), highest energy density (2.392 J/cm3).

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Localized Excimer Laser Energy Modulation in the Crystallization Of Poly-Si Film On Stepped Substrate

MRS Proceedings ◽

10.1557/proc-617-j1.5 ◽

2000 ◽

Vol 617 ◽

Cited By ~ 1

Author(s):

Kee-Chan Park ◽

Sang-Hoon Jung ◽

Woo-Jin Nam ◽

Min-Koo Han

Keyword(s):

Grain Size ◽

Energy Density ◽

Excimer Laser ◽

Thermal Gradient ◽

Laser Energy ◽

Vertical Wall ◽

Energy Difference ◽

Deep Trench ◽

Laser Recrystallization ◽

Horizontal Bottom

AbstractAnew excimer laser recrystallization method of a-Si film to increase the grain size of poly-Si film has been proposed. Excimer laser energy was locally modulated by being irradiated on stepped substrate with 500 nm deep trench on which a-Si film was deposited. Fairly large poly-Si grains (over 1 µm) were obtained due to lateral thermal gradient which resulted from the laser energy difference on the vertical wall and on the horizontal bottom plane of the trench without altering laser energy density elaborately.

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