The threading dislocations in heteroepitaxial β-Sic films grown on (001)Si by chemical vapour dep... more The threading dislocations in heteroepitaxial β-Sic films grown on (001)Si by chemical vapour deposition have been studied. A large number of threading dislocations are present and these are dissociated into two partial dislocations which bound a planar fault. The introduction of these threading dislocations is attributed to residual coherency stresses present in the deposited films. This occurs by the formation of half-loops at the deposit surface which subsequently glide toward the film/substrate interface. It is proposed that the threading dislocations are dissociated into two partial dislocations with Burgers vectors, b, given by b = 1/4(111) which bound an antiphase boundary according to the reaction and that this dissociation is stabilized by a low antiphase-boundary energy in β-SiC
A scanning and transmission electron microscopy study is presented of the microstructure of the S... more A scanning and transmission electron microscopy study is presented of the microstructure of the Strombus gigas shell. The hierarchical nature of this crossed-lamellar structure and the defect content of the mineral component are described. The mineral component consists of small single crystal grains of aragonite, the metastable orthorhombic polymorph of CaCOâ. The habit and morphology of the grains discussed here
Journal of the American Chemical Society, May 1, 2006
Phase transformations of materials can be studied by in situ synchrotron X-ray diffraction. Howev... more Phase transformations of materials can be studied by in situ synchrotron X-ray diffraction. However, most reported in situ synchrotron XRD studies focus on solid state/gel systems by measuring phase/structure changes during application of pressure or heat. Phase transformations during material synthesis and their applications, especially in wet chemistry processes with different media, have not drawn much attention. Here, using manganese oxides as examples, we report the successful characterization of phase transformations in in situ hydrothermal synthesis conditions by the in situ synchrotron XRD method using a quartz/sapphire capillary tube as the synthesis reactor. The results were used for better design of materials with controlled structures and properties. This method can be generally used for synthesis of manganese oxides as well as for in situ characterization of other material syntheses using hydrothermal, sol-gel, and other methods. In addition, catalytic processes in liquid-solid, gas-solid, and solid-solid systems can also be studied in such an in situ way so that catalytic mechanisms can be better understood and catalyst synthesis and catalytic processes can be optimized.
Page 1. R. D. BAETA and K. H. GI. ASHBEE: Studies of Plastically Deformed Quarl z 165 phys. stat.... more Page 1. R. D. BAETA and K. H. GI. ASHBEE: Studies of Plastically Deformed Quarl z 165 phys. stat. sol. (a) 18, 155 (1973) Subject classification: 10.2; 1.4; 22.6 ... Transmission Electron Microscopy Studies of Plastically Deformed Quartz BY RD BAETA (a) and K. H. G. ASHBEE (b) ...
ABSTRACT The Langmuir Blodgett (LB) Process has been shown to be an appropriate method for use in... more ABSTRACT The Langmuir Blodgett (LB) Process has been shown to be an appropriate method for use in mimicking of biological processes for producing engineering materials such as bioceramics. The main advantages of this approach are that the layers form at low temperatures, that they are fully dense and that the process of densification is by infiltration rather than by sintering. Moreover, biological hard tissues are self-assembled to perform certain functions; the architecture being controlled by an epitaxial organic matrix. Clearly, if this process can be understood in detail then it is possible that LB films may be used to replicate this architecture for engineering purposes.Atomic Force Microscopy (AFM) and X-ray diffraction (XRD) have been used to study and characterise LB films of calcium stearate obtained by the repeated dipping into and withdrawal of a (001) Si wafer from a subphase containing calcium ions and using stearic acid as the surfactant. Contact-mode AFM images of the film surface have been used to measure the thickness of the LB layers and to reveal the nature and distribution of defects in the film. The measured thickness of the calcium stearate layers is about 2.5 nm; a value consistent with that obtained by XRD, but smaller than the length of an individual calcium stearate molecules.
The threading dislocations in heteroepitaxial β-Sic films grown on (001)Si by chemical vapour dep... more The threading dislocations in heteroepitaxial β-Sic films grown on (001)Si by chemical vapour deposition have been studied. A large number of threading dislocations are present and these are dissociated into two partial dislocations which bound a planar fault. The introduction of these threading dislocations is attributed to residual coherency stresses present in the deposited films. This occurs by the formation of half-loops at the deposit surface which subsequently glide toward the film/substrate interface. It is proposed that the threading dislocations are dissociated into two partial dislocations with Burgers vectors, b, given by b = 1/4(111) which bound an antiphase boundary according to the reaction and that this dissociation is stabilized by a low antiphase-boundary energy in β-SiC
A scanning and transmission electron microscopy study is presented of the microstructure of the S... more A scanning and transmission electron microscopy study is presented of the microstructure of the Strombus gigas shell. The hierarchical nature of this crossed-lamellar structure and the defect content of the mineral component are described. The mineral component consists of small single crystal grains of aragonite, the metastable orthorhombic polymorph of CaCOâ. The habit and morphology of the grains discussed here
Journal of the American Chemical Society, May 1, 2006
Phase transformations of materials can be studied by in situ synchrotron X-ray diffraction. Howev... more Phase transformations of materials can be studied by in situ synchrotron X-ray diffraction. However, most reported in situ synchrotron XRD studies focus on solid state/gel systems by measuring phase/structure changes during application of pressure or heat. Phase transformations during material synthesis and their applications, especially in wet chemistry processes with different media, have not drawn much attention. Here, using manganese oxides as examples, we report the successful characterization of phase transformations in in situ hydrothermal synthesis conditions by the in situ synchrotron XRD method using a quartz/sapphire capillary tube as the synthesis reactor. The results were used for better design of materials with controlled structures and properties. This method can be generally used for synthesis of manganese oxides as well as for in situ characterization of other material syntheses using hydrothermal, sol-gel, and other methods. In addition, catalytic processes in liquid-solid, gas-solid, and solid-solid systems can also be studied in such an in situ way so that catalytic mechanisms can be better understood and catalyst synthesis and catalytic processes can be optimized.
Page 1. R. D. BAETA and K. H. GI. ASHBEE: Studies of Plastically Deformed Quarl z 165 phys. stat.... more Page 1. R. D. BAETA and K. H. GI. ASHBEE: Studies of Plastically Deformed Quarl z 165 phys. stat. sol. (a) 18, 155 (1973) Subject classification: 10.2; 1.4; 22.6 ... Transmission Electron Microscopy Studies of Plastically Deformed Quartz BY RD BAETA (a) and K. H. G. ASHBEE (b) ...
ABSTRACT The Langmuir Blodgett (LB) Process has been shown to be an appropriate method for use in... more ABSTRACT The Langmuir Blodgett (LB) Process has been shown to be an appropriate method for use in mimicking of biological processes for producing engineering materials such as bioceramics. The main advantages of this approach are that the layers form at low temperatures, that they are fully dense and that the process of densification is by infiltration rather than by sintering. Moreover, biological hard tissues are self-assembled to perform certain functions; the architecture being controlled by an epitaxial organic matrix. Clearly, if this process can be understood in detail then it is possible that LB films may be used to replicate this architecture for engineering purposes.Atomic Force Microscopy (AFM) and X-ray diffraction (XRD) have been used to study and characterise LB films of calcium stearate obtained by the repeated dipping into and withdrawal of a (001) Si wafer from a subphase containing calcium ions and using stearic acid as the surfactant. Contact-mode AFM images of the film surface have been used to measure the thickness of the LB layers and to reveal the nature and distribution of defects in the film. The measured thickness of the calcium stearate layers is about 2.5 nm; a value consistent with that obtained by XRD, but smaller than the length of an individual calcium stearate molecules.
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