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STM/STS study of bimetallic nanostructures on silicon surfaces
Zimmermann, Petr ; Mysliveček, Josef (referee) ; Sobotík, Pavel (advisor)
In this study we examine linear nanostructures consisting of metals of III. (Al, In) and IV. (Sn) group on the Si(001)2×1 surface by means of scanning tunnelling microscopy & spectroscopy. Atoms on the surface align into atomic chains growing perpendicularly to the dimer rows of the surface reconstruction. The chain structure consists of dimers that adsorb in the troughs between the dimer rows of the surface reconstruction. We observe that the chains consist of sequences of homodimers of either elements combining with heterodimers. The InSn chain structure is analysed with regard to theoretical ab-initio calculations of the chain dimer structure. The model is then applied to the Al-Sn system. We observe that the Al-Sn chains tend to consist of aligned heterodimers. The appearance of heterodimers in STM depends on the chemical composition of the neighbouring dimers. We can also observe the tendency of chains to agglomerate and via Sn atoms create quasi periodic 2D structures. The electronic structure of an Al, Sn and mixed AlSn dimer is studied by means of tunnelling spectroscopy. Despite its small, nonzero density of states on the Fermi energy, the character of the mixed dimer appears to be rather non-conductive.
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Scanning tunneling microscopy (STM) and spectroscopy (STS) study of thin ceria films
Dvořák, Filip ; Mysliveček, Josef (advisor) ; Sobotík, Pavel (referee)
The contents of this study is the investigation of model catalyst CeO2/Cu(111) by STM. The aim of the work is identifying the growth mode of CeO2/Cu(111), studying the surface morphology dependence on substrate temperature during the sample preparation and determination of the atomic structure of the prepared layers. In terms of evolution of substrate temperature during the deposition samples has been prepared by three different methods - a constant temperature, variable temperature, and annealing the sample after deposition. The growth mode of the layers CeO2 has been determined as 3D growth. Samples with different morphology have been prepared by varying temperature of substrate during the preparation. With decreasing sample preparation temperature the roughness and defect density on surface have been increasing. The best epitaxy has been achieved by temperature gradient preparation. Samples which have been prepared with temperature above 400řC have been partially covered by layer CeO2(100). Measurements with hight resolution have been performed on the samples with low coverage. The first three monolayers of CeO2 have shown a moir pattern which has been caused by mismatch in lattice parameters. Atomic resolution has been achieved only in the first and the second monolayer CeO2. The absence of defects in...
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SPM Methods Based On The Quartz Resonator Probes
Wertheimer, Pavel ; Sobotík, Pavel (referee) ; Číp, Ondřej (referee) ; Šikola, Tomáš (advisor)
The thesis is focused on development of scanning probe microscope systems, especially development and implementation of quartz resonator probes. The quartz resonator probes, compared to the standard silicon cantilevers, have several advantages. It is in particular their mechanical properties and possibility of direct electrical readout of the deflection signal. Due to the fact, the probes are easy to implement even into more complex SPM systems. The thesis deals with development of universal and open SPM control system electronics. The electronics consist of the commercial SPM control and oscillation units, the development of the other electronic parts (such as the high voltage amplifier and the preamplifier units) is described in the thesis. Further, the thesis reports on development of the qPlus UHV LT SPM microscope system that was carried out at Universität Hamburg. Part of it was development of the qPlus preamplifier able to operate at liquid helium temperature. The third topic of the thesis is the implementation of qPlus technology into the UHV VT SPM microscope suitable to operate in situ with a scanning electron microscope. The qPlus sensors and the universal UHV preamplifier were designed and manufactured. Test measurements were conducted on all of the developed systems.
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