Study of interfaces chemistry in type-II GaSb/InAs superlattice structures

There is a considerable interest in type-II GaSb/InAs superlattice system due to several modern applications including infrared detectors. In these studies X-ray Photoelectron Spectroscopy (XPS) and Spectroscopic Ellipsometry (SE) have been used to extensive characterization of the surface and interface of GaSb/InAs superlattice. Application of XPS and SE techniques provide precise information from topmost layers of structure and allow excluding presence of GaAs-type interfaces in GaSb/InAs superlattices. Simultaneously, these results indicate that InSb-type or GaInSb-type interfaces have been detected in the structures studied

ECOLOGICAL CHARACTERISTICS OF GREAT SERTEYA PALEOLAKE BASED ON PALEOECOLOGICAL RESEARCH AT THE SERTEYA II SITE IN WESTERN RUSSIA

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Long-Term Consequences of Water Pumping on the Ecosystem Functioning of Lake Seksu, Latvia

Cultural eutrophication, the process by which pollution due to human activity speeds up natural eutrophication, is a widespread and consequential issue. Here, we present the 85-year history of a small, initially Lobelia-Isoetes dominated lake. The lake's ecological deterioration was intensified by water pumping station activities when it received replenishment water for more than 10 years from a eutrophic lake through a pipe. In this study, we performed a paleolimnological assessment to determine how the lake's ecosystem functioning changed over time. A multi-proxy (pollen, Cladocera, diatoms, and Chironomidae) approach was applied alongside a quantitative reconstruction of total phosphorus using diatom and hypolimnetic dissolved oxygen with chironomid-based transfer functions. The results of the biotic proxy were supplemented with a geochemical analysis. The results demonstrated significant changes in the lake community's structure, its sediment composition, and its redox conditions due to increased eutrophication, water level fluctuations, and erosion. The additional nutrient load, particularly phosphorus, increased the abundance of planktonic eutrophic-hypereutrophic diatoms, the lake water's transparency decreased, and hypolimnetic anoxia occurred. Cladocera, Chironomidae, and diatoms species indicated a community shift towards eutrophy, while the low trophy species were suppressed or disappeared

Determination of the Analytical Relationship between Refractive Index and Density of SiO2SiO_{2} Layers

The main goal of the work was the elaboration of the analytical functional relationship between refractive index n and density ρ of $SiO_{2}$ layers on silicon substrates. Such ρ (n) relationship will give possibility to determine elastic and non-elastic strains in $SiO_{2}$ layers on silicon substrates. Ellipsometric measurements by using variable angle spectroscopic ellipsometer of J.A. Woollam Company allowed determination of thicknesses and refractive indexes of silica layers. Measured $SiO_{2}$ masses and calculated volumes of the layers gave possibility to define the degree of densification of silicon dioxide layers on silicon substrates. The Hill approximation function curve turned out to be the best fitting. The obtained Hill curve shows saturation for the density of silicon dioxide equal to ca. 4.53 g/$cm^{3}$. This value corresponds to the value nearby the one of the crystalline polytypic silicon dioxide (stishovite). It seems to be physically established that degree of densification tends to the limiting value

Ellipsometric spectroscopy studies of compaction and decompaction of Si-SiO2 systems

The influence of the strain on the optical properties of Si-SiO2 system has been investigated by spectroscopic ellipsometry (SE), interferometry and weighing methods. Subtle changes of densification (compaction degree) in silicon dioxide layers on silicon substrates have been determined by weight technique (relying on measurements of the silicon dioxide layer mass and calculations of the volume). Elastic stress in the oxide layers has been measured by Fizeau fringes image analysis method. A comparison is made between the density of the silicon dioxide (r) and the results of calculations made using r = f = (n) relations (where n is the refractive index) given in the literature

Reconstruction of palaeoecological changes in Lake Łebsko on the basis diatom analysis (the southern Baltic coast, Poland)

This study focuses on diatom assemblages occurring in core Łeb1 of Late-glacial and Holocene deposits from Lake Łebsko, off the southern coast of the Baltic Sea. Diatom-inferred environmental characteristics, e.g., water level, water salinity (conductivity), trophic status and pH, from the Holocene are presented. In the sediments from the early Boreal/early Atlantic period, an increase in the participation of brackish-freshwater species is observed, as well as increased numbers of Chaetoceros spores in the samples. The Atlantic sediments of Lake Łebsko mirror conditions typical of the Littorina Sea phase during the development of the Baltic Sea (from c. 7,500 BP to c. 5,000 BP). However, communities of that period dominated by fresh-brackish water species suggest the relatively low salinity of the waters. The presence of isolated frustules of Terpsinoë americana and other typically marine species, e.g., Mastogloia smithii, and the occurrence of silts with Cardium shell detritus point to the Littorina transgression and the functioning of a lagoon within the area of present-day Lake Łebsko. During Subboreal occurrence, a higher number of brackish-freshwater diatoms corresponds to an increase in the water level of the Baltic Sea (approximately 3,000 14C BP). Changes in diatom community structure imply a close relationship with the climate controlled eustatic rise of ocean level and the consequent Littorina transgression, as with other southern Baltic Sea localities

Effects of stress annealing on the electrical and the optical properties of MOS devices

In this paper we show the results of a study of the effects of high-temperature stress annealing in nitrogen on the refraction index of SiO2 layers and electrical properties in metal-oxide-semiconductor (MOS) devices. We have experimentally characterized the dependence of the reduced effective contact potential difference (ECPD), the effective oxide charge density (Neff), and the mid-gap interface trap density (Dit) on the annealing conditions. Subsequently, we have correlated such properties with the dependence of the refraction index and oxide stress on the annealing conditions and silicon dioxide thickness. Also, the dependence of mechanical stress in the Si-SiO2 system on the oxidation and annealing conditions has been experimentally determined. We consider the contributions of the thermal-relaxation and nitrogen incorporation processes in determining changes in the SiO2 layer refractive index and the electrical properties with annealing time. This description is consistent with other annealing studies carried out in argon, where only the thermal relaxation process is present

Dielectric Function of Native Oxide on Ion-Implanted GaAs

The main aim of the reported investigations is the influence of ion implantation on formation of native oxide layers and their optical spectra. Silicon implanted (100)-oriented GaAs crystalline wafers were used as substrates. The samples have been implanted with $Ne^{+}$, $Al^{+}$, $Ar^{+}$, or $In^{+}$ ions at energies of 100, 120, 150, and 250 keV, respectively. The implantations were carried out at a fluence of $1 \times 10^{16} cm^{-2}$ at 300 K. The refraction index spectral dependence for native oxide was approximated using the Cauchy equations. The dielectric function spectra of the native oxide layers on GaAs implanted with different ions have been obtained by variable angle spectroscopic ellipsometer in the 250-900 nm range using complementary information from the Rutherford backscattering/nuclear reactions measurements. The investigations showed that both real and imaginary parts of the dielectric function increase with mass of the ion species used for implantation

Modification of the Surface of the Iron Powder as an Ingredient of the High Calorific Mixture

Textural properties of iron powders obtained by reduction of iron(II) compounds and by electrolysis were determined. Their specific surfaces were 0.38 and 0.43 m2g-1 respectively, and the prevailing grain sizes amounted to 10 and 43 ?m respectively. Total content of the determined metallic impurities was 0.055 wt.% in the preparation obtained by the electrolysis while in the preparation obtained by reduction it was 0.025 wt.%. It was proved that in initial samples the α-Fe2O3 phase occurred in the outer oxide layer present on the surface of Fe grains, and below this phase a layer of magnetite was found, the thickness of which was considerably greater in iron obtained by electrolysis. Measurements of selected properties showed that modification of the iron powder surface carried out by reduction with dihydrogen led to decreasing the linear rate of burning of the high calorific mixture Fe/KClO4 but it did not affect its calorific value. Moreover, it was found that modification of the iron powder surface resulted in lowering the temperature of ignition of the analysed mixture and decreasing the quantity of the released oxygen generated by decomposition of the oxidant, which did not react with the iron powder

Nuclear and Optical Analyses of MOS Devices

The characteristic dome-like shape distribution of electric parameters (with the biggest values in the middle and the lowest values in the corners of the gate) has been observed in our investigations. Taking the results of the papers into account, the following hypothesis was drawn: the shape distribution of electrical parameters has been caused by the irregular shape of stress distribution under the metal gate. To prove or deny the assumed hypothesis, a lot of investigations on stress and strain in MOS structures are being performed. The study of the atomic composition of electronic components constitutes the starting point of their characterization. Therefore, in this paper, we present experimental results of hydrogen, oxygen, aluminum, silicon, and copper concentrations in MOS structures carried out by the Rutherford backscattering spectrometry and elastic recoil detection methods. These techniques allow inter alia determination of silicon and oxygen content as a function of the position x on a wafer. On the basis of depth profile elastic recoil detection measurements performed on Al and AlSiCu gates, a much larger hydrogen content in the surface layer for MOS structure with Al gate was confirmed. Copper atoms were detected only in the AlSiCu gate