Papers by Keyword: Selective Growth

Abstract: Resist patterning method has been used to enable selective ZnO nanorods grown via facile hydrothermal process. The growth region of the ZnO nanorods was controlled by pre-coating the seed layer on the Silicon base substrate. Using the plasma process, the seed layer which is not coated with a resist layer will be etched out. Therefore, when the samples completely undergone the hydrothermal process, there will be no nanorods grow in that specific area. The grown ZnO nanorods was in well array with flat hexagonal tip and wurtzite crystal structure. This technique is can be applied for application which require integration of nanostructure in specific critical areas such as an interdigitated electrodes (IDE) for various gas sensor applications.

Abstract: A new rolling process, which combined asymmetric rolling with symmetric rolling, was adopted in age-hardenable 6xxx series Al-Mg-Si alloy promising as automotive body panels in order to develop favorable textures for the deep drawability after solution treatment. Symmetric cold rolling at high reduction and subsequent asymmetric warm rolling at low reduction for AA6022 sheets led to the formation of “TD-rotated β-fiber texture” including moderate {111}<uvw>-oriented components, resulting in noticeable evolution of {111}<110> recrystallization texture during the solution treatment at a high temperature. The results of texture analysis and microstructural observation suggested that the low stored energy after asymmetric warm rolling, the high fraction of high angle boundaries with neighboring deformed matrices and the approximate 40° <111> orientation relationship with deformed matrices would strongly affect the evolution of {111}<110> recrystallization texture.

Abstract: Less attention has been paid to study the recrystallization and grain growth behavior of severe plastically deformed (SPD) metals specially steels that are deformed to very high strain by conventional rolling method. Present work has been focused on systematic investigation of recrystallization and grain growth behavior of a Aluminium Killed (AK), an Interstitial Free (IF) and an Interstitial Free High Strength (IFHS) steels that were subjected to very high levels of strain (ԑeqv= 4.51) by cold rolling. The cold rolled steels show fine lamellar structure with very strong texture consists of both γ and α fibre. All the steels show formation of ultrafine grains and dramatic rise in the intensity of α fibre component in the early stages of annealing. However, progress of annealing for longer time leads to an increase in the mean grain size as well as γ fibre intensity. The results also indicate that the heavily cold rolled material exhibit selective growth of specific texture components.It appears that microstructure and texture is closely related to the observed phenomenon.

Abstract: β-SiC/SiO₂ core-shell NWs have been synthesized on patterned silicon wafers in a CVD system, using carbon oxide as single precursor and nickel nitrate as catalytic element, in nitrogen or argon atmosphere at 1100°C. The coaxial structure and the crystallinity of the NW core are examined by (scanning) transmission electron microscopy. The patterning of the substrate allows to grow NWs in selected areas only, as imaged by SEM. Cathodoluminescence (CL) panchromatic images of the same areas point out that the light emitted under electron excitation is localized only in the area covered with NWs. The room-temperature CL spectrum has three different components peaked at 2.45 eV, related to the 3C-SiC near-band-edge emission, and at 2.75 and 3.75 eV, that are induced by the triplet and singlet states of oxygen-deficiency centers ODC(II) in silicon dioxide shell.

Abstract: Behavior of the selective growth of Goss grains in grain-oriented electrical steel was investigated by controlling the heating rate in secondary recrystallization annealing．It was clarified that the important factors on the selective growth of Goss grains were the frequency and the mobility of grain boundary. It was demonstrated that boundaries having misorientation angle between 30 degree and 35 degree had the greatest influence on the selective growth, and the change of crystal orientation of secondary recrystallized grains expected by analyzing the change of primary recrystallized texture during secondary recrystallization annealing showed good agreement with the experimental result.

Abstract: β-SiC nanowires have been synthesized on etch-patterned wafers in a chemical vapor deposition (CVD) system without using any metal catalyst. The nanowires were grown selectively inside the ‘V-groove’ of etch-patterned silicon (110) substrate which was used as a template for nanostructure growth. Nanowire growth was hardly found on the sample which was not previously etched. The nanowires have a core-sheath structure with the SiC core surrounded by an amorphous SiO2 sheath layer. The etching of the patterned Si (110) wafers was carried out by a 50 % aqueous KOH solution. The SiC growth was performed in a resistively heated atmospheric pressure chemical vapor deposition (APCVD) system by using hexamethyldisilane (HMDS) as the single source for Si and C at 1150oC. The as-grown samples and the patterned wafers were characterized by field emission electron microscopy, energy dispersive x-ray spectroscopy, X-ray diffraction, micro-Raman spectroscopy and Fourier transform infrared spectroscopy. Etching is one of the key factors for nanostructure growth and the patterning in the wafer provides selectivity. The growth process was governed by vapor-solid (VS) mechanism.

Abstract: It is often assumed that the texture formation during solid state transformations in low carbon steels critically depends on the local crystallographic misorientation at the interface between transformed and not yet transformed material volume. In some cases, a theoretical crystallographic orientation relation can be presumed as a necessary prerequisite for the transformation to occur. Classical examples of such misorientation conditions in steel metallurgy are the orientation relations between parent and product grains of the allotropic phase transformation from austenite to ferrite (or martensite) or the hypothetical <110>26.5º misorientation between growing nuclei and disappearing grains in a recrystallization process. One way to verify the validity of such misorientation conditions is to carry out an experiment in which the transformation is partially completed and then observe locally, at the transformation interface, whether or not the presumed crystallographic condition is complied with. Such an experiment will produce a large set of misorientation data. As each observed misorientation Dg is represented by a single point in the Rodrigues-Frank (RF) space, a distribution of discrete misorientation points is obtained. This distribution is compared with the reference misorientation Dgr, corresponding to a specific physical condition, by determining the number fraction dn of misorientations that are confined within a narrow misorientation volume element dw around the given reference misorientation Dgr. In order to evaluate whether or not the proposed misorientation condition is obeyed, the number fraction dn of the experimentally measured distribution must be compared with the number fractions dr obtained for a random misorientation distribution. The ratio dn/dr can be interpreted as the number intensity fi of the given reference misorientation Dgr. This method was applied on the observed local misorientations between the recrystallizing grains growing into the single crystal matrix of a Fe-2.8%Si alloy. It was found that the number intensity of the <110>26.5º misorientation increased with a factor 10 when the misorientation distribution was evaluated before and after the growth stage. In another example the method was applied to the misorientations measured at the local interface between parent austenite and product martensite grains of a partially transformed Fe-28%Ni alloy. It could be established that the Nishiyama- Wasserman relations ({111}g//{110}a <112>g//<110>a) prevail over the Kurdjumov-Sachs relations ({111}g//{110}a and <110>g//<111>a) although a considerable scatter was observed around either of the theoretical correspondences. A full parametric misorientation description was also applied to evaluate the relative grain boundary energies associated with a set of crystallographic misorientations observed near triple junctions in Fe-2%Si. In this instance it was found that the boundaries carrying a misorientation of the type <110>w carry a lower interfacial energy than the <100> or <111> type boundaries.

Abstract: After primary recrystallization, on further annealing, abnormal grain growth occurred in ultra low carbon steel. Texture evolution was studied by comparing the orientations after complete secondary recrystallization, with on one hand the nuclei for abnormal grain growth and on the other hand the selective growth products of the primary recrystallized matrix. The influence of both mechanisms could be identified in the final texture.

Abstract: A Fe-2.8%Si single crystal was scratched in order to randomise the texture in the neighbourhood of the notch. Annealing resulted in recrystallization and grain growth starting from the deformed zone. Misorientations between the single crystal matrix and the grown grains were gathered and were studied in order to investigate the possibility for selective growth based on a specific misorientation. However, instead of studying the misorientation angle or axis profiles separately in a 1D or 2D projection a full misorientation analysis was carried out in the 3-dimensional Rodrigues-Frank misorientation space, which offers an unambiguous interpretation of the data because no features are hidden or masked by a projection. It is concluded that the selective growth phenomenon following the <110>26.5deg misorientation relationship is strongly supported by the gathered orientation data, after appropriately normalizing these data with respect to a random misorientation distribution.

Abstract: The ideal starting condition for selective growth experiments is one having a layer of randomly-oriented nuclei adjacent to a matrix with negligible orientational variation but sufficient stored energy to promote growth. In practice, cutting or deformation processes are used in an attempt to approximate these ideal conditions, but the degree to which this is achieved has not been rigorously quantified. In this work, Fe-3wt%Si single crystals were cut or deformed using six different processes. The variation in texture with distance from the cut or deformed surface was measured using electron backscatter diffraction (EBSD) in a field emission gun scanning electron microscope (FEG-SEM) in order to assess the ability of each process to create conditions suitable for selective growth experiments. While grooving with a machine tool produced the best spread of orientations at the cut surface, the suitability of this process is diminished by the presence of a differently-textured deformed layer between the cut surface and the single crystal matrix. Grinding produced a less ideal distribution of orientations at the cut surface, but the presence of these orientations in a very thin layer adjacent to the matrix makes this process preferable for preparing crystals for selective growth experiments, provided the results are corrected for the deviation in the distribution of nuclei orientations from a random distribution.