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G. C. Wang - One of the best experts on this subject based on the ideXlab platform.
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RHEED Transmission Mode and RHEED Pole Figure
RHEED Transmission Mode and Pole Figures, 2013Co-Authors: G. C. WangAbstract:In the last chapter, we presented the principles of x-ray diffraction and the construction of a Pole Figure, particularly the Pole Figure constructed from the diffraction patterns obtained by an area detector. In this chapter, we describe the similarities and differences between reflection high-energy electron diffraction (RHEED) transmission mode and x-ray diffraction. Detailed descriptions of the diffraction space characteristics of RHEED transmission for a variety of crystal textures are given. We discuss kinematic simulations of RHEED patterns and the construction of RHEED Pole Figures from RHEED patterns. The relationship between RHEED Pole Figures and the orientation distribution function of biaxial texture is presented with examples.
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Instrumentation for RHEED Pole Figure
RHEED Transmission Mode and Pole Figures, 2013Co-Authors: G. C. WangAbstract:In this chapter, we describe the major reflection high-energy electron diffraction (RHEED) hardware components: a vacuum system, an electron gun, a sample manipulator, a step motor, a phosphor screen, and a charge-coupled device camera. Most molecular beam epitaxy (MBE) laboratories with in situ RHEED characterization capability are equipped with this hardware. We discuss what has been learned from past practices on issues such as minimization of sample wobbling during rotation and sample size required due to glancing incidence angle of the electron beam. Data collection and step-by-step operational procedures are described in Appendix A. Data processing program codes developed for RHEED Pole Figure construction are also given in Appendix A. With this hardware and software, one can perform RHEED experiments in the transmission mode and construct RHEED Pole Figures to study the sample’s textures. We highlight the RHEED instrument response function for reflection and transmission modes for quantitative analysis of texture dispersions. We also discuss the part of the instrument response function for transmission mode diffracted from rough surfaces that does not exist in the instrument response function of the reflection mode.
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Instrument response of reflection high energy electron diffraction Pole Figure
Applied Surface Science, 2013Co-Authors: Liang Chen, J. K. Dash, Chuan-fu Lin, Ishwara B. Bhat, G. C. WangAbstract:Abstract Reflection high-energy electron diffraction (RHEED) Pole Figure technique using the transmission mode has been developed to study the texture evolution of thin films. For quantitative evaluation of thin film texture, including the dispersion of texture, one would require the knowledge of the instrument response function. We report the characterization of instrument response in RHEED Pole Figure from an epitaxial CdTe(1 0 0) film grown on GaAs(1 0 0) substrate. We found the finite mean free path of electrons in a film contributes to the broadening of the Poles. In addition, the image processing step size used in the construction of a Pole Figure also affects the broadening of constructed Poles. We apply the measured instrument response in RHEED Pole Figure to quantitatively analyze a biaxially textured CdTe(1 1 1) film deposited on a biaxially textured Ge(1 1 1) substrate. Through the deconvolution of the measured dispersions from the Poles in the textured CdTe(1 1 1) film by the instrument response function, we obtain the out-of-plane and in-plane dispersions of the biaxially textured CdTe(1 1 1) film. This method is generic and the instrument response should be considered in order to obtain quantitative texture information for other epitaxial and textured nanostructured films through RHEED Pole Figure measurements.
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RHEED Pole Figure Measurements of Biaxial Thin Film Growth Front Evolution
MRS Proceedings, 2011Co-Authors: G. C. Wang, Yu Liu, C. Gaire, Wen YuanAbstract:The most frequently used characterization technique for biaxial texture formation in thin films is x-ray Pole Figure analysis. However, x-rays interact weakly with matter and can penetrate a few microns deep into the film. The texture obtained by x-rays is therefore an average texture from the entire thickness of the film. As the texture of a film often changes during growth, information on the basic mechanisms that control the final texture is often lost. In contrast electrons interact strongly with matter and they have very limited penetration and escape depths of a few nm. In this paper we will show how we can use our newly developed reflection high energy electron diffraction (RHEED) surface Pole Figure technique to probe the surface texture evolution of the growth front from the initial stage (nm thick) to the later stage. The RHEED Pole Figure technique is a surface-sensitive technique that allows us to obtain information on the dynamic behavior of texture evolution of the growth front during film deposition. We shall explain the principle, measurement, and construction of such RHEED surface Pole Figures. An example of the biaxial texture evolution of CaF2 due to the atomic shadowing effect during oblique angle deposition is described.
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Reflection High-energy Electron Diffraction Study of Nanostructures: From Diffraction Patterns to Surface Pole Figure
MRS Proceedings, 2011Co-Authors: F Tang, G. C. WangAbstract:AbstractIn this report we present a brief overview of the growth of nanostructures by the oblique angle deposition where the nanostructures possess both out-of-plane and in-plane preferred orientations or a biaxial texture. The degree of preferred crystal orientations can be quantitatively determined from a method called “RHEED surface Pole Figure analysis” that we developed recently.
F Tang - One of the best experts on this subject based on the ideXlab platform.
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Reflection High-energy Electron Diffraction Study of Nanostructures: From Diffraction Patterns to Surface Pole Figure
MRS Proceedings, 2011Co-Authors: F Tang, G. C. WangAbstract:AbstractIn this report we present a brief overview of the growth of nanostructures by the oblique angle deposition where the nanostructures possess both out-of-plane and in-plane preferred orientations or a biaxial texture. The degree of preferred crystal orientations can be quantitatively determined from a method called “RHEED surface Pole Figure analysis” that we developed recently.
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Surface texture evolution of polycrystalline and nanostructured films: RHEED surface Pole Figure analysis
Journal of Physics D, 2007Co-Authors: F Tang, Thomas C. Parker, G. C. WangAbstract:In this topical review, we outline the construction of a reflection high-energy electron diffraction (RHEED) surface Pole Figure from a polycrystalline film by recording multiple RHEED patterns as the substrate is rotated around the surface normal. Due to the short penetration depth of electrons, the constructed Pole Figure is a surface Pole Figure. It is in contrast to the conventional x-ray Pole Figure which gives the average texture information of the entire polycrystalline film. Examples of the surface Pole Figure construction processes of a fibre texture and a biaxial texture are illustrated using Ru vertical nanorods and Mg nanoblades, respectively. For a biaxially textured film, there often exists an in-plane morphological anisotropy. Then additional intensity normalization must be applied to compensate for the effects of anisotropic morphology on RHEED surface Pole Figure construction. Rich information on the texture evolution, such as the change in the tilt angle of the texture axis, has been obtained from the in situ study of oblique angle vapour deposition of Mg nanoblades using RHEED surface Pole Figures. Finally we make a comparison between the RHEED surface Pole Figure and the conventional x-ray Pole Figure techniques.
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In situ reflection high energy electron diffraction surface Pole Figure study of biaxial texture evolution in anisotropic Mg nanoblades during shadowing growth
Journal of Applied Physics, 2007Co-Authors: F Tang, G. C. Wang, T.-m. LuAbstract:The reflection high energy electron diffraction (RHEED) surface Pole Figure technique has been applied to an in situ study of the biaxial texture evolution in the anisotropic film of Mg nanoblades. These nanoblades were grown by thermal vapor under the shadowing effect using oblique angle deposition. To compensate for the effects of the anisotropic morphology of the Mg film on the RHEED surface Pole Figure, a method of intensity normalization has been employed. From the normalized Pole Figures, we observed a development of (101¯0)[0001] biaxial texture in the film during the growth. When the film grows thicker the texture axes tilt more towards the incident vapor flux. The variation of the azimuthal angle orientation is mainly around the [0001] axis during growth and the azimuthal dispersion angle around the [0001] axis reduces. The change of texture axis tilting angle has been correlated to the change of the nanoblade tilting angle. The azimuthal angle alignment of the nanoblades is argued to be the resu...
T.-m. Lu - One of the best experts on this subject based on the ideXlab platform.
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In situ reflection high energy electron diffraction surface Pole Figure study of biaxial texture evolution in anisotropic Mg nanoblades during shadowing growth
Journal of Applied Physics, 2007Co-Authors: F Tang, G. C. Wang, T.-m. LuAbstract:The reflection high energy electron diffraction (RHEED) surface Pole Figure technique has been applied to an in situ study of the biaxial texture evolution in the anisotropic film of Mg nanoblades. These nanoblades were grown by thermal vapor under the shadowing effect using oblique angle deposition. To compensate for the effects of the anisotropic morphology of the Mg film on the RHEED surface Pole Figure, a method of intensity normalization has been employed. From the normalized Pole Figures, we observed a development of (101¯0)[0001] biaxial texture in the film during the growth. When the film grows thicker the texture axes tilt more towards the incident vapor flux. The variation of the azimuthal angle orientation is mainly around the [0001] axis during growth and the azimuthal dispersion angle around the [0001] axis reduces. The change of texture axis tilting angle has been correlated to the change of the nanoblade tilting angle. The azimuthal angle alignment of the nanoblades is argued to be the resu...
K. P. Kodama - One of the best experts on this subject based on the ideXlab platform.
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Magnetic anisotropy, scanning electron microscopy, and X ray Pole Figure goniometry study of inclination shallowing in a compacting clay‐rich sediment
Journal of Geophysical Research, 1992Co-Authors: Wei Wei Sun, K. P. KodamaAbstract:Anisotropy of anhysteretic remanence (AAR), scanning electron microscopy (SEM), and X ray Pole Figure goniometry studies of clay-rich sediments were conducted to delineate the interactions between magnetite and clay particles which cause inclination shallowing during compaction. These studies used synthetic sediments composed of kaolinite or illite and two grain sizes of magnetite, 0.45 μm and 2–3 μm. Natural marine sediments which contained 40–50% clay were also used. The sediments were compacted by pressures as high as 0.157 MPa. The sediments' porosity decrease suggests that the compaction experiments model burial depths up to 400–500 m. The main result of this study is that inclination shallowing and void ratio versus pressure curves show two points where behavior changes. A rapid decrease in inclination and void ratio occurs up to a pressure of 0.02 MPa. This is accompanied by a magnetic intensity decrease of 20–30%. Compaction at pressures between 0.02 MPa and 0.05 MPa causes a further decrease in these parameters at moderate rates, while compaction at pressures above 0.05 MPa causes very little change. Percent magnetic anisotropy and X ray Pole Figure intensity ratio versus pressure curves show only one point where behavior changes at 0.05 MPa with a rapid increase at lower pressures and little change at higher pressures. A model to explain this behavior, based on the SEM observations as well as the magnetic anisotropy, Pole Figure, and inclination data, suggests that compaction up to 0.02 MPa causes a decrease in pore volume with little reorientation of clay particles. Some magnetic particles are firmly attached to clay particles, whereas other loosely attached particles are either randomized or subvertical ones are preferentially disturbed causing inclination shallowing and an intensity decrease. At pressures between 0.02 MPa and 0.05 MPa, magnetite particles have become firmly attached to clay particles and start to follow the reorientation of clay particles as the clay fabric develops. At 0.05 MPa there is a major change in the clay microstructure with a horizontal fabric becoming evident. Compaction at higher pressures causes little further volume loss and clay particle reorientation and hence little additional inclination shallowing. The randomization/disturbance process suggested by this model causes slightly more than half of the inclination shallowing observed in the samples studied, whereas magnetite-clay attachment causes the remainder of the inclination decrease.
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magnetic anisotropy scanning electron microscopy and x ray Pole Figure goniometry study of inclination shallowing in a compacting clay rich sediment
Journal of Geophysical Research, 1992Co-Authors: Wei Wei Sun, K. P. KodamaAbstract:Anisotropy of anhysteretic remanence (AAR), scanning electron microscopy (SEM), and X ray Pole Figure goniometry studies of clay-rich sediments were conducted to delineate the interactions between magnetite and clay particles which cause inclination shallowing during compaction. These studies used synthetic sediments composed of kaolinite or illite and two grain sizes of magnetite, 0.45 μm and 2–3 μm. Natural marine sediments which contained 40–50% clay were also used. The sediments were compacted by pressures as high as 0.157 MPa. The sediments' porosity decrease suggests that the compaction experiments model burial depths up to 400–500 m. The main result of this study is that inclination shallowing and void ratio versus pressure curves show two points where behavior changes. A rapid decrease in inclination and void ratio occurs up to a pressure of 0.02 MPa. This is accompanied by a magnetic intensity decrease of 20–30%. Compaction at pressures between 0.02 MPa and 0.05 MPa causes a further decrease in these parameters at moderate rates, while compaction at pressures above 0.05 MPa causes very little change. Percent magnetic anisotropy and X ray Pole Figure intensity ratio versus pressure curves show only one point where behavior changes at 0.05 MPa with a rapid increase at lower pressures and little change at higher pressures. A model to explain this behavior, based on the SEM observations as well as the magnetic anisotropy, Pole Figure, and inclination data, suggests that compaction up to 0.02 MPa causes a decrease in pore volume with little reorientation of clay particles. Some magnetic particles are firmly attached to clay particles, whereas other loosely attached particles are either randomized or subvertical ones are preferentially disturbed causing inclination shallowing and an intensity decrease. At pressures between 0.02 MPa and 0.05 MPa, magnetite particles have become firmly attached to clay particles and start to follow the reorientation of clay particles as the clay fabric develops. At 0.05 MPa there is a major change in the clay microstructure with a horizontal fabric becoming evident. Compaction at higher pressures causes little further volume loss and clay particle reorientation and hence little additional inclination shallowing. The randomization/disturbance process suggested by this model causes slightly more than half of the inclination shallowing observed in the samples studied, whereas magnetite-clay attachment causes the remainder of the inclination decrease.
Kwang Ho Kim - One of the best experts on this subject based on the ideXlab platform.
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Application of Inverse Pole Figure to Rietveld Refinement : III. Rietveld Refinement of SnO₂ Thin Film using X-ray Diffraction Data
The Korean Journal of Ceramics, 2000Co-Authors: Yongil Kim, Maeng-joon Jung, Kwang Ho KimAbstract:The SnO₂ film was deposited on a corning glass 1737 substrate by plasma enhanced chemical vapor deposition using a gas mixture of SnCl₄, O₂, and Ar. The film thickness was measured using α-step and was about 9400Å. The conventional X-ray diffractometry and Pole Figure attachment were used to refine the crystal structure of SnO₂ thin film. Six Pole Figures, (200), (211), (310), (301), (321), and (411), were measured with CoK α radiation in reflection geometry. The X-ray diffraction data were measured at room temperature using CuK α radiation with graphite monochromator. The agreement between calculated and observed patterns for the normal direction of SnO₂ thin film was not satisfactory due to the severly preferred orientation effect. The Rietveld refinement of heavily textured SnO₂ thin film was successfully achieved by adopting the Pole density distribution of each reflection obtained from the inverse Pole Figure as a correction factor for the preferred orientation effect. The R-weighted pattern, R wp , was 15.30%.
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application of inverse Pole Figure to rietveld refinement i rietveld refinement of copper sheet using x ray diffraction data
The Korean Journal of Ceramics, 2000Co-Authors: Yongil Kim, Maeugjoon Jung, Kwang Ho KimAbstract:Both the X-ray diffraction data of the normal direction in the sample orientation and the Pole Figure data of three reflections, (111), (200) and (220), were used to do the Rietveld refinement for the copper sheet prepared by a cold rolling process. The agreement between calculated and observed patterns was not satisfactory, which was attributed to the preferred orientation effect of the copper sheet. The Rietveld refinement for the copper sheet could be done successfully by applying the Pole density of each reflection obtained from the corresponding inverse Pole Figure to the X-ray diffraction data of the normal direction. The R-weighted pattern, R wp , was 12.99% and the goodness-of-fit indicator, S, was 3.68.
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application of inverse Pole Figure to rietveld refinement ii rietveld refinement of tungsten liner using neutron diffraction data
The Korean Journal of Ceramics, 2000Co-Authors: Yongil Kim, Maeng-joon Jung, Jeongsoo Lee, Kwang Ho KimAbstract:The three-dimensional orientation distribution function of a conical shaped tungsten liner prepared by the thermo-mechanical forming process was analyzed by 1.525Å neutrons to carry out the Rietveld refinement. The Pole Figure data of three reflections, (110) (200) and (211) were measured. The orientation distribution functions for the normal and radial directions were calculated by the WIMV method. The inverse Pole Figures of the normal and radial directions were obtained form their orientation distribution functions. The Rietveld refinement was performed with the RIETAN program that was slightly modified for the description of preferred orientation effect. We could successfully do the Rietveld refinement of the strongly textured tungsten liner by applying the Pole density of each reflection obtained form the inverse Pole Figure to the calculated diffraction pattern. The correction method of preferred orientation effect based on the inverse Pole Figures showed a good improvement over the semi-empirical texture correction based on the direct usage of simple empirical functions.