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Scanning Very Low Energy Electron Microscopy
Müllerová, Ilona ; Hovorka, Miloš ; Mikmeková, Šárka ; Pokorná, Zuzana ; Mikmeková, Eliška ; Frank, Luděk
Recent developments in applications of the scanning very low energy electron microscopy in selected branches of materials science are reviewed. The examples include visualization of grains in conductive polycrystals including ultrafine grained metals, identification of the local crystal orientation upon reflectance of very slow electrons, transmission mode with ultrathin free-standing films including graphene, acquisition of a quantitative dopant contrast in semiconductors, and examination of thin surface coverages.
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Comparison of water quality on agricultural catchment in 1983 - 1985 and in present.
POKORNÁ, Zuzana
There are remarkable changes in water quality at the Jenínský stream catchment that lies in the Šumava foothills which were caused by change in land use. Two subcatchments, called J1 and J2, were monitored. In the first period 1983-1985, the two subcatchments were agriculturaly used, the land was fertilized and ploughed and cereals and corn were grown. In the second period 2004-2008, there were grasslands and the land was extensively used as pasture. This change in land use caused evident changes in water quality at the Jenínský stream catchment. The decrease of all monitored indices was remarkably seen in the concentrations of nitrate and ammonium. The average nitrate concentration in 1983-1985 was 39,5 mg . l-1, and decreased by 43,3% to the value of 16,9 mg . l-1 in 2004-2008. The greatest decrease of 85,9% was found in average ammonium concentration (0,4 mg . l-1 dropped to 0,05 mg . l-1). The positive effect of the change from arable land to grassland was confirmed and we can see it in the amount of nitrogen compounds and resulting improvement of water quality.
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Mapping the local density of states above vacuum level by very low energy electron reflectivity
Pokorná, Zuzana ; Frank, Luděk
The local density of states is an important characteristic of solids, crystalline matters in particular. What used to be a pure theoreticians’ toy is nowadays an experimentally accessible characteristic, e.g. by means of photoemission or scanning tunneling spectroscopy. Local density of states can reflect e.g. the local dopant concentration in semiconductors or discern between different crystal orientations, as each crystal face has a specific density of states. One way of probing the local density of states is to measure the reflectivity of very low energy electrons (units to tens of eV) from the sample surface. The reflectivity is principally inversely proportional to the local density of electronic states coupled to the impinging electron wave.
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Proceedings of the 4th Czech-Japan-China Cooperative Symposium on Nanostructure of Advanced Materials and Nanotechnology (CJCS’09)
Pokorná, Zuzana ; Mika, Filip
ISI ASCR in Brno is primarily a methodological institute creating and developing new experimental methods for several areas of physics, chemistry and biomedicine. Among these, methodology of the scanning electron microscopy occupies an important position. One of long time projects concerns microscopy with very slow electrons, much slower than what was for decades, until quite recently, available at the market of microscopes. Demonstration of new instrumental methods needs to have good partners in application areas, willing to enter unknown territories. On this basis, the collaboration between the University of Toyama and ISI in Brno exists and flourishes, producing plenty of common results and success stories.
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Kontrast zrn na velmi nízkých energiích v REM
Pokorná, Zuzana ; Frank, Luděk
When lowering energy of incident electrons to 100 eV and less, the elastic scattering becomes heavily anisotropic while the inelastic scattering progressively drops off. Energy dependence of the reflected signal becomes then specific to the crystal orientation. The experiments with the imaging of the metal polycrystals were done in the SEM equipped by the cathode lens.
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Metody přímého zobrazování hustoty stavů pomocí elektronů
Pokorná, Zuzana ; Frank, Luděk
Applicability of the SLEEM method for direct mapping of LDOS is the topic of the present study. The main issues include managing of the non-negligible angular aperture of the incident beam and even of the rocking connected with beam scanning over the field of view. These conditions require the contrast forming model to be reconsidered.
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Local density of states mapping using the reflection of very slow electrons
Pokorná, Zuzana
The aim of the work is performing a series of experiments in an ultra high vacuum electron microscope, demonstrating the inverse proportionality between the reflectance of very slow electrons and the local density of electron states bound to the incident wave. The work also aims to describe quantitatively the imaging of a doped region in the semiconductor surface layer.
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