Abstract
In this project the author, and the group to which the author belongs, have carried out a thorough structural study of selected model systems featuring bulk and thin film single crystals.
Bulk single crystals of selected zinc chalcogenides have been synthesized using the chemical vapour transport method, resulting in crystals of sizes up to 3 mm. The crystals were studied using optical microscopy, x-ray diffraction and scanning electron microscopy, revealing their structural properties and some information on their chemical composition and purity.
Furthermore, the author has studied the criteria for epitaxial growth of single crystal thin films deposited with the atomic layer deposition technique. This has involved pre-treatment of substrates (eg. single species termination using chemical etching), lattice matching of the thin film and substrate species, the deposition itself and structural characterization of said systems.
Thin films of LaAlO3 grown on single crystal substrates of Si(100), SrTiO3(100), LaAlO3(pseudocubic-100) and MgO(100) have been deposited, resulting in some crystalline and some amorphous thin films, confirming the criteria of epitaxial growth stated from theoretical predictions. Epitaxial thin films with thickness between 7 and 130 nm were achieved on SrTiO3-substrates, and diffraction studies of the systems showed a SrTiO3(100)|SrTiO3[100]||LaAlO3(pseudocubic-100)|LaAlO3[pseudocubic-100] type growth. Synchrotron x-ray diffraction studies of LaAlO3 thin films on LaAlO3-substrates have revealed a slight non-homoepitaxial relation, and a crude CTR-study of Bragg peak broadening and satellites were utilized to estimate roughness and discuss surface reconstruction.
Using previously deposited epitaxial thin films of Co3O4 and the new epitaxial LaAlO3 thin film system, a setup for synchrotron x-ray diffraction studies of thin film systems was evolved at the Swiss Norwegian Beam Lines at ESRF in Grenoble, France. In this setup, thin films are mounted as single crystals with low incident angle x-rays, resulting in an unmatched combination of flexibility and x-ray brilliance. The setup allows for a range of different diffraction studies, revealing information on the structural integrity of the thin films. A Williamson-Hall peak shape analysis was used to explain and deconvolute the Bragg peak broadening in the SXRD-studies, and these were compared to the common Scherrer-approach and the measurements performed with home lab x-ray equipment.
Finally, x-ray reflectivity has been used to study roughness, density and thickness of thin films, and for this purpose a piece of Python software has been written to treat these data using a Fast Fourier Transform algorithm.