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A Novel Laser Technology for Nanostructure Formation in Elementary Semiconductors: Quantum Confinement Effect
No full textNowadays, nanostructures are one of the most investigated objects in solid-state physics, especially Quantum confinement effect in quantum dots, quantum wires and quantum wells. In the case of nanosize structures the energy band diagram of semiconductor has strongly changed. This leads to a crucial change of semiconductor properties such as: electrical (due to the change of free charge carrier concentration and electrons’ and holes’ mobility); optical (absorption coefficient, reflectivity index, radiative recombination efficiency); mechanical and heating properties. It is known that in elementary indirect band-gap semiconductors such as Si and Ge radiative electron–hole recombination efficiency strongly enhances in nanostructures due to QCE [1]. Moreover, shift of Photoluminescence (PL) spectrum toward high energy of spectrum, so called “blue shift”, has been predicted [1] and observed in Ge [2] and Si [3] single crystals.
A novel laser technology elaborated for nanostructures formation in elementary semiconductors is reported.
Nanohills on the surface of Ge single crystal were formed by basic frequency of Nd:YAG laser radiation at intensity of 30.0MW/cm2 [4, 5]. This structure is characterized by patterns related to C6i point group symmetry covering all the surface of the sample and having translations symmetry. In the case of Si single crystals nanohills were formed by the second harmonics of Nd:YAG laser radiation at intensity of 2.0 MW/cm2 [6, 7]. The same nanostructures were induced on the surface of SixGe1-x/Si heterostructures with x = 0.3 and 0.4 by basic frequency of Nd:YAG laser radiation at intensities from 2.0 till 20.0MW/cm2 [8]. The mechanism of nanostructures’ formation on the surface of elementary semiconductors was studied using Atomic force microscope, Electron scanning microscope, Ellipsometry, Photoluminescence and Raman back scattering spectra. Unusual photoluminescence spectrum from the irradiated surfaces was found in the visible range of spectrum. Photoluminescence from Ge, SiO2/Si and SiGe/Si nanostructures can be explained by Quantum confinement effect. A shift of micro-Raman scattering spectra in Ge is a good evidence of this suggestion. Unique asymmetric photoluminescence spectra of the irradiated SiO2/Si structure with gradually decrease intensity in read part of spectra is explained by Quantum confinement effect in nanohills-wires with a graded decrease of diameter toward the top of nanohill. The following mechanism of nanohills formation in Si1-xGex/Si structure by laser radiation is proposed: irradiation of SiGe/Si heterostructure by Nd:YAG laser initiates Ge atoms drift to the irradiated surface due to gradient of temperature - Thermogradient effect. After every laser pulse gradient of temperature increases due to increase of Ge atoms concentration at the irradiated surface and new Ge phase formation occurs at the end of the process. Ge atoms are localized at the surface of Si like a thin film. Self-assembly growth of nanostructure on the irradiated surface takes place by Stransky- Krastanov’ mode.
For the first time was shown the possibility of graded band gap structure formation in elementary semiconductors. Thermogradient effect has a main role in initial stage of nanostructures formation by laser radiation in elementary semiconductors
Metāla štancēšana ar elastīgu vidi
No full textDotais darbs ir veltīts mūsdienās svarīgu faktoru pētīšanai, kas ietekmē galvenās ražošanas izmaksas katrai detaļai. Pētījumu pamatā ir no lokšņu materiāla biezumā līdz divi milimetri detaļu mazsēriju ražošana. Darbā tika iegūta informācija, kādu tehnoloģiju vajadzētu izvēlēties izgatavojot detaļas no lokšņu materiāla.
Analītiskajā darba daļa tika veikti eksperimenti ar dažādu biezumu un materiālu paraugiem. Tika iegūta informācija par minimālajiem urbumu izmēriem, kurus var iegūt pielietojot štancēšanu ar elastīgu vidi.
Darbā tika izskatītas arī aprīkojuma uzlabošanas iespējas. Tika veikta esošā aprīkojuma uzlabošana. Uzlabotais formu veidojošai šablons tika ieviests ražošanas procesā, kā rezultātā uzlabojās detaļas kvalitāte.
Darba rezultātā tika veikta tehnoloģiskā procesa analīze. Iegūti secinājumi par štancēšanas ar elastīgo vidi pielietojuma iespējām, tehnoloģiskā procesa priekšrocībām un trūkumiem, salīdzinot ar tradicionālo štancēšanas tehnoloģiju
Mazjaudas transformatoru aprēķins
No full textŠajā mācību līdzeklī aplūkotas mazjaudas (līdz dažiem simtiem vatu) transformatoru konstrukcijas, dota to aprēķinu metodika, kas ilustrēta ar piemēriem.
Mācību līdzeklis paredzēts enerģētikas un elektrotehnikas specialitāšu studentiem. To var izmantot arī speciālisti, kuru darbs ir saistīts ar mazjaudas transformatoru projektēšanu un izgatavošanu
Baltech studiju programmas studentu projektēšanas darbu analīze un tās rezultātu pareto diagramma
No full textBALTECH studiju programma virtuāli saista septiņu Baltijas jūras reģiona valstu – Latvijas, Lietuvas, Igaunijas, Somijas un Zviedrijas augstskolas ar mērķi sagatavot speciālistus ar maģistra grādu pēc vienotām programmām. Analizējot un apkopojot vairāku gadu minētās studiju programmas maģistrantu darbu piedāvājumus, ir iegūti pētījuma rezultāti, kuri var būt noderīgi Latvijas rūpniecībai jaunu eksportspējīgu ražojumu radīšanai
E- biznesa attīstība un perspektīvas Baltijas valstīs
No full textTēzēs ir apskatīti galveni etapi e-biznesa attīstībā. Analizēti sataistikas dati par e-biznesa izplatību Baltijas valstīs
Application of FT-IR for Characterization of Biomass Isolated from Drinking Water
No full textDrinking water companies are responsible for producing and supplying safe, high quality water for costumers. The drinking water quality should meet the standard at the customer tap, therefore the supplier is forced to analyze the water quality not only at the outlet from the treatment plant but in the distribution network as well. The aim of this study was identification and discrimination of microorganisms in water samples from different points of distribution network in Riga, Latvia. The classification of bacteria is generally based on the morphology and biochemical reactions of the bacteria. These measurements are time consuming, requiring training and expertise. Infrared (IR) spectroscopic measurements of bacteria followed by a formal chemometrics analysis could offer advantages of speed and consistency [1]. Since the amount of pathogenic micro-organisms in water is low, after one or more purification processes, concentration is necessary to detect and quantify these organisms. Simmons [2] describes a cross flow ultra filter (Hemoflow-filter) that is used for the concentration of microorganisms in water. An important advantage of this filter is that it concentrates parasitic protozoa, bacteria, spores and viruses/phages. This study was performed on drinking water from drinking water plants from Riga, used as water sources surface water and groundwater. Here we present results of concentrated drinking water samples which were investigated by Fourier Transform Infrared (FT-IR) spectroscopy. Presence of all typical peaks of main biochemical cell components: lipids – 2928 – 2856 cm-1 (CH2, CH3 simetric/asimetric stretching vibrations); proteins - Amide I and II – 1549 and 1655 cm-1 ; nucleic acids – 1242 cm-1 (P=O), and carbohydrates - 1080 cm-1 (C-O-C, C-O, C-O-H, P=O of PO2-, valent stretching vibrations of COC groups and ring vibration modes in the composition of cyclic structures) verified biomass while qualitative and quantitative differences of components indicated various strains or their mix/consortium. Results of both analytical methods showed that water samples contain significant amount of biomass. We found distinct difference in the FT-IR spectra of biomass isolated from treated groundwater or surface water. In some Hemoflow samples Fluorescence in Situ Hybridization (FISH) method indicated E. coli while Pseudomonas fluorescens was identified in all samples. This study showed that combination of biomass separation and FT-IR spectral analysis is a rapid and simple approach for characterization of microorganisms in drinking water
Creating of Regional Hydrogeological Model for South-East of Lithuania
No full textIzveidots reģionālais hidroģeoloģiskais modelis (HM) Kvartāra tipa pazemes ūdeņu sistēma, kura atrodas Lietuvas Dienvidaustrumu daļā. Šī sistēma pārklāj Lietuvas teritorijas vienu trešdaļu. HM taisnstūra formas laukuma izmērs ir 290km210km. Seši lokālie upju sateces baseini veido HM aktīvo daļu, kurai ir neregulāra forma. Modeļa daļa, kura nav aktīva, nepiedalās aprēķinos. HM veidošanai izmantotas inovatīvas metodes: zemes virsmas augstumu karte kā pjezometrisko ūdens līmeņu robežnoteikumu, kurš noteica infiltrācijas plūsmu modeļa augšējai virsmai; aerācijas zona izmantota kā formāls sprostslānis; HM izveidošanas pirmajā posmā netika izmantota reālā ģeoloģisko slāņu ģeometrija. Šo inovāciju izmantošana ļāva izveidot sarežģītu reģionālo HM ļoti īsā laikā, salīdzinot ar variantu, ja izmanto klasiskās metodes
Road Safety Improvement Program in Latvia
No full textArticle gives an overview about Latvian Road Safety Improvement Program