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Badanie rekonstrukcji powierzchni kryształu TiO2(110) metodą dyfrakcji niskoenergetycznych elektronów (LEED)

Karol Cieslik

出版	Karol Cieslik
主題	Science / Physics / Condensed Matter
URL	http://books.google.com.hk/books?id=bCnhEAAAQBAJ&hl=&source=gbs_api
EBook	SAMPLE

註釋

The main goal of this thesis is to present the theoretical basis and applications of low energy electron diffraction LEED – a technique used to ascertain the type of surface reconstruction of crystalline surfaces and the character of its nanostructures. The additional goal was to show the distortions of diffraction patterns present in the apparatus and to explain their causes. The surface (110) of titania in the form of rutile has been used both to compare the diffraction patterns with the scanning tunnelling microscope images and to show the present distortions. In this thesis the native surface and ion beam-modified surface of TiO2 has been investigated. TiO2(110) was chosen, because its surface structure is well known which makes it suitable for calibration of the LEED instrument. The lattice parameters “a” and “b” obtained from the diffraction patterns are respectively 6% and 7% smaller than the published values. What is more, the effects of the inclination of the local surface, due to the Ar+ ion-beam irradiation, on the character of created nanostructures was studied. A geometrical model of diffraction from ripples was developed which separated diffraction from the native structure from the one occurring on atoms on the edges of terraces. Both this model and the STM data have shown that the increase in inclination of the surface leads to shorter nanostructures, but the angle of inclination of the nanostructures obtained using the model is approximately three times smaller than the one seen in the STM images. The main distortion was caused by the usage of a plate detector and not a hemisphere which inflated the distances on the screen. A model based on a projection of the hemisphere on a plane was compared with experimental data and was shown to be consistent for half of the studied range of angles. The model showed that the change in the position of the spot vs. the angle of incidence on the screen was approximately a quadratic function while a linear function fit the experimental data. The divergence between the model and the data might be caused by the inhomogeneous electric field between the microchannel plate and the grounding grid. Diffraction spots of the first order were found to be too close to the electron gun which could be caused by an electric field. The relation between the distance between the sample and the detector and the distortions was investigated. The non-ideal position of the sample affects the angle at which electrons leave the filtration grids. It was shown that this distortion could lead to either an increase or a decrease of distances between spots which would bring into being a systematic error of calculated lattice constants. Moreover, MCPConversion, software included by the manufacturer which corrects distortions, most likely does not affect this distortion.