Study of Structure and Intrinsic Stresses of Ge Thin Films on GaAs

The effect of film growth rate on the structure and intrinsic stresses of thin (100 nm) Ge films grown on GaAs(100) substrates was investigate by High Resolution X-Ray Diffraction (HRXRD). The Ge films were deposited onto GaAs using thermal evaporation of Ge in the vacuum. It was shown that pseudomor-phic films with good structural quality can be obtained by this growth technique. We found out that the films have biaxial deformations due to coherent interface and Poisson ratio. The films are elastically com-pressed in the interface and stretched in the perpendicular [001] direction. The intrinsic deformations of thin Ge films strongly depended on the deposition rate. Their correlations with surface roughness, electri-cal and optical parameters are discussed. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3531

Участие холинергических и адренергических механизмов в реакциях желудка на введение экзогенного серотонина

This study is dedicated to investigation of serotoninergic structures that activate motility of the stomach. Experiments were performed on 94 Wistar rats under general anesthesia, mechanical ventilation, bilateral vagotomy and transection of both glossopharyngeal nerves. Mechanical activity of the stomach was recorded during serotonin adipanate infusion to intact animals and on the background of the ongoing actions of cholinergic and adrenergic antagonists. The blockade of adrenergic and cholinergic receptors does not prevent, but contrary, increase stimulatory effect of serotonin. β-adrenergic blockade increases the intensity of observed reactions almost up to 90%. Conclusion: both adrenergic and cholinergic mechanisms provide inhibitory pattern on serotoninergic structures that regulates motor function of the stomach.Работа посвящена изучению серотонинергических структур, усиливающих моторику желудка. Опыты поставили на 94 крысах в условиях хирургической стадии наркоза, ИВЛ, двухсторонней ваготомии и двухсторонней перерезки языкоглоточных нервов. Регистрировали механическую активность желудка на введение серотонина адипината у интактных животных и на фоне продолжающегося действия адрено- и холиноблокаторов. Установили, что блокада адрено- и холинорецепторов не только не препятствует, а напротив, способствует проявлению реакций желудка на серотонин, причем блокада β-адренорецепторов увеличивала выраженность стимуляторных эффектов желудка почти на 90%. Сделали вывод о том, что адренергические и холинергические механизмы препятствуют проявлению стимуляторных реакций серотонинореактивных структур на моторику желудка

Влияние экзогенного серотонина на усиление вагусных реакций толстой кишки

This study is dedicated to serotoninergic structures of the colon. Experiments were performed in 35 Chinchilla rabbits under general anesthesia, mechanical ventilation, bilateral vagotomy. Mechanical and electrical activity of the ascending colon was recorded during electrical stimulation of the peripheral part of the right n. vagi in intact animals and after serotonin adipate injection. It was found that serotonin potentiates vagal effects of the colon, but without effect on duration of reaction. Concluded that the serotoninergic structures of the colon are able to control the parasympathetic portion of the autonomic nervous system.Работа посвящена изучению серотонинергических структур толстой кишки. Опыты поставили на 35 кроликах: в условиях хирургической стадии наркоза, ИВЛ, двухсторонней ваготомии. Регистрировали механическую и электрическую активность восходящей ободочной кишки. В эксперименте раздражали периферический отрезок блуждающего нерва у интактных животных и на фоне продолжающегося действия серотонина адипината. Установили, что серотонин усиливает вагусные эффекты толстой кишки, не влияя при этом на продолжительность стимуляторных реакций. Сделали вывод о взаимодействии серотонинореактивных структур толстой кишки с парасимпатическим отделом вегетативной нервной системы

X-ray diffraction investigation of GaN layers on Si(111) and Al₂O₃ (0001) substrates

Methodical approaches to the analysis of X-ray data for GaN films grown on various buffer layers and different substrates are presented in this work. Justification of dislocation structure investigation by various methods was analyzed and approaches for evaluation of deformation level and relaxation are discussed. Clarity and accuracy of obtained structure characteristics of nitride films are under discussion. Optimization methods for experimental data processing are shown. Structural properties were obtained using high resolution X-ray diffraction with two types of scans and reciprocal space maps. Microscopic nature of spatial inhomogeneities in these structures (deformations and dislocation density) and influence of the buffer layer thickness on properties of GaN layer were discussed with account of obtained results

Investigation of resistance formation mechanisms for contacts to n-AlN and n-GaN with a high dislocation density

We studied temperature dependences of the resistivity, Pc(T) , of Pd-Ti-Pd-Au ohmic contacts to wide-gap semiconductors n - GaN and n - AlN with a high dislocation density. BothPc(T) curves have portions of exponential decrease, as well as those with very slight Pc(T) dependence at higher temperatures. Besides, the Au-Pd-TiPd-n-GaN contacts have a portion of Pc(T) flattening out in the low-temperature region. This portion appears only after rapid thermal annealing (RTA). In principle, its appearance may be caused by preliminary heavy doping of the near-contact region with a shallow donor impurity as well as doping in the course of contact formation owing to RTA, if the contact-forming layer involves a material atoms of which serve as shallow donors in III N compounds. The obtained Pc(T) dependences cannot be explained by the existing mechanisms of current transfer. We propose other mechanisms explaining the experimental Pc(T) curves for ohmic contacts to n - GaN and n -AlN

X-ray diffraction study of deformation state in InGaN/GaN multilayered structures

High resolution X-ray diffractometry (HRXRD) was used to investigate InxGa₁₋xN/GaN multilayered structures grown by the metal-organic chemical vapor deposition (MOCVD) method. Deformation conditions in the superlattice (SL) and its separate layers, degree of relaxation in the structure layers, as well as the period of the SL, thicknesses of its layers and composition of InxGa₁₋x solid solution in active area were determined. It was found that SL was grown on the relaxed buffer layer. SL layers were grown practically coherent with slight relaxation of InGaN layer (about 1.5 %). The role of dislocations in relaxation processes was established. Analysis of experimental diffraction spectra in these multilayered structures within the frameworks of ParratSperiozu was adapted for hexagonal syngony structures

Mechanism of current flow and temperature dependence of contact resistivity in Au-Pd-Ti-Pd-n⁺ -GaN ohmic contacts

We present the results of structural and morphological investigations of interactions between phases in the layers of Au-Pd-Ti-Pd-n⁺-GaN contact metallization that appear at rapid thermal annealing (RTA). It is shown that formation of ohmic contact occurs in the course of RTA at Т = 900°C due to formation of titanium nitride. We studied experimentally and explained theoretically the temperature dependence of contact resistivity ρс(Т) of ohmic contacts in the 4.2-380 K temperature range. The ρс(Т) curve was shown to flatten out in the 4.2-50 K range. As temperature grew, ρс decreased exponentially. The results obtained enabled us to conclude that current flow has field nature at saturation of ρс(Т) and the thermofield nature in the exponential part of ρс(Т) curve

Deformation state of short-period AlGaN/GaN superlattices at different well-barrier thickness ratios

Dependence of deformation characteristics changing in superlattice (SL) structures AlxGa₁₋xN/GaN with Al (~10%) on the well-barrier thickness ratio in period was studied in this work. The deformation state of SL and individual layers, relaxation level and periods, layers’ thickness and composition of AlxGa₁₋xN layers were analyzed using high-resolution X-ray diffractometry. It was ascertained that the buffer layer and SL layers are compressed in all the investigated structures. Thus, it has been shown that deformation of the SL period depends on the well/barrier thickness ratio. Thicknesses of individual layers in SL strongly depend on the deformation state of the whole system. Increasing the deformation level leads to the increase of the barrier layer thickness

The features of temperature dependence of contact resistivity of Au-Ti-Pd₂Si-p⁺ ₋Si ohmic contacts

We consider the features of formation of Au-Ti-Pd ohmic contacts to p⁺₋Si. Metallization was made by vacuum thermal sputtering of Pd, Ti and Au films onto the Si substrate heated up to 330 °С. It is shown that the contact resistivity increases with temperature; this is typical of metallic conductivity. We suggest that the ohmic contact is formed owing to appearance of shunts at Pd deposition on dislocations or other structural defects. The number of shunts per unit area is close to the measured density of structural defects at the metal-Si interface

Development of high-stable contact systems to gallium nitride microwave diodes

High-stable heat-resistant low-resistance contact systems with diffusion barriers involving quasi-amorphous TiBx layers are suggested and studied. We have performed the structural and morphological investigations along with studies of Auger concentration depth profiles in the contacts both before and after rapid thermal annealing. It is found that the Au−TiBx−Al−Ti−GaN contact layers with diffusion barriers retain both a layered structure of the contact metallization and the value of contact resistivity practically unchanged up to the temperature Т ≈ 700 ºС. At the same time, the layered structure of the metallization in standard Au−Ti−Al−Ti−GaN contact systems breaks down at such rapid thermal annealing. It is shown that the contact metallization of both types demonstrates the tunnel current flow mechanism in the temperature range 225−335 K, whereas the current flow mechanism is thermionic in the range 335−380 K, the Schottky barrier height being ~0.16 eV. For the best samples under consideration, the contact resistivity was no more than 10⁻⁶ Ohm∙cm²