Impact of AFM-induced nano-pits in a-Si:H films on silicon crystal growth

Conductive tips in atomic force microscopy (AFM) can be used to localize field-enhanced metal-induced solid-phase crystallization (FE-MISPC) of amorphous silicon (a-Si:H) at room temperature down to nanoscale dimensions. In this article, the authors show that such local modifications can be used to selectively induce further localized growth of silicon nanocrystals. First, a-Si:H films by plasma-enhanced chemical vapor deposition on nickel/glass substrates are prepared. After the FE-MISPC process, yielding both conductive and non-conductive nano-pits in the films, the second silicon layer at the boundary condition of amorphous and microcrystalline growth is deposited. Comparing AFM morphology and current-sensing AFM data on the first and second layers, it is observed that the second deposition changes the morphology and increases the local conductivity of FE-MISPC-induced pits by up to an order of magnitude irrespective of their prior conductivity. This is attributed to the silicon nanocrystals (<100 nm) that tend to nucleate and grow inside the pits. This is also supported by micro-Raman spectroscopy

The countries of BRICS a new factor of economic development in the world economy at the beginning of the 21st century.

The countries of BRICS are the subject of my bachelor´s work. The work deals with the history, origin and members of BRICS: Brazil, Russia, India, China and South Africa. Futhermore the work is concerned with the origin and working of the New Development Bank and Satellite System GLONASS, which shall serve the members of BRICS only. The first part is about the history and origin of countries of BRICS. The basic characteristics of the individual countries, comes next, including main indicators demographical and economic. As another important part in work is chapter about the monetary policy and the New Development Bank BRICS. The Satellite System GLONASS is mentioned in the semi-final chapter of bachelor´s work. The end of the work belongs to the potential of the countries of BRICS. The part of the work, are the charts, which with help of basic economic and other indicators provide the summary about individual countries

Vliv aplikace lignohumátů na mineralizaci dusíku a fosforu v půdě: komerčně produkovaný výrobek a jeho užití v arboristické praxi

This thesis is focused on the assessment of a lignohumate application influence on nitrogen and phosphorus mineralization in urban soils. Specifically the experiment setup is based on lignohumate product, commercially manufactured by Amagro company. The major aim of this thesis is study of analytic techniques for assessing decomposition and mineralization rates of soil phosphorus and nitrogen and conduct laboratory testing of lignohumate treatment effects. Soil samples for laboratory analyses were collected from the Az (Ad) horizons of urban soils as selected sites in Brno. Subsequently, the results of analyses were processed and evaluated, results were expressed in forms of graphs and tables

Light amplification due to free and localized exciton states in ZnCdSe GRINSCH structures

International audienceIn this paper we present measurements of light amplification in optically pumped ZnCdSe GRINSCH (graded refraction index separate confinement heterostructures), In several differently designed samples we observe the presence of two gain mechanisms, which involve localized excitons and exciton-exciton inelastic scattering processes, respectively. The influence of the GRINSCH sample structure on gain is discussed in terms of their improved light-guiding properties

Determination of light amplification processes in MOCVD grown ZnCdSe GRINSCH structures

International audienceIn this paper we present measurements of light amplification in optically pumped ZnCdSe graded refraction index separate confinement heterostructures (GRINSCH). In several differently designed samples we observe the presence of two gain mechanisms, which involve localized excitons and exciton-exciton inelastic scattering processes, respectively, The influence of the GRINSCH structure on gain is discussed with respect to light guiding variations due to sample design. A numerical simulation is used to investigate the phenomenon of gain quenching with decreasing barrier width

Grains of porous silicon embedded in SiO(2): Studies of optical gain and electroluminescence

Recent reports on experimental observation of optical gain in silicon nanostructures in the visible region, performed at several laboratories all over the world, have triggered an extraordinary surge of interest in silicon lasing. However, attempts aimed at reproducing the red stimulated emission from "standard" silicon nanocrystals (sized 3-5 nm) at some other laboratories either failed, or. did not come to definite conclusions. Therefore, more detailed measurements of optical gain in a wider variety of samples containing Si nanocrystals are required in order to unravel whether or not the observation of optical gain is an intrinsic property of Si nanocrystals. We have performed a detailed study of optical gain in layers of densely packed Si nanocrystals in SiO(2), prepared on the basis of porous Si, using the variable-stripe-length (VSL) method in combination with the shifted-excitation-spot (SES) method. In selected samples we have observed a distinct difference in behaviour between VSL and SES curves, indicating the occurrence of positive optical gain of similar to24 cm(-1). Preliminary reports on transport and electroluminescence measurements in thin films of SiO(2) doped with porous silicon grains, prepared by spin-coating technique, are also discussed

Temperature behaviour of optical properties of Si

Silicon nanocrystals were prepared by Si+-ion implantation and subsequent annealing of SiO2 films thermally grown on a c-Si wafer. Different implantation energies (20-150 keV) and doses $(7\times10^{15}$- $2\times10^{17}$ cm$^{-2})$ were used in order to achieve flat implantation profiles (through the thickness of about 100 nm) with a peak concentration of Si atoms of 5, 7, 10 and 15 atomic% . The presence of Si nanocrystals was verified by transmission electron microscopy. The samples exhibit strong visible/IR photoluminescence (PL) with decay time of the order of tens of μs at room temperature. The changes of PL in the range 70-300 K can be well explained by the exciton singlet-triplet splitting model. We show that all PL characteristics (efficiency, dynamics, temperature dependence, excitation spectra) of our Si+-implanted SiO2 films bear close resemblance to those of a light-emitting porous Si and therefore we suppose similar PL origin in both materials