9 research outputs found
Electrochemical etching of silicon on insulator
Cilj istraživanja u okviru ove disertacije je utvrditi strukturna, optiÄka i kemijska svojstva nove vrste poroznog silicija izraÄenog na ploÄicama s razliÄito dopiranim epitaksijalnim slojem kao i na ploÄicama silicija na izolatoru. U tu svrhu izraÄene su dvije komore za jetkanje te je napravljen eksperimentalni postav koji omoguÄava jetkanje ploÄica razliÄitih dimenzija s istosmjernom i izmjeniÄnom strujom. Variranjem koncentracije etanolne otopine fluorovodiÄne kiseline, gustoÄe struje jetkanja i vremena jetkanja dobile su se porozne strukture razliÄitih morfologija i razliÄitih optiÄkih svojstava. Uzorci su analizirani Ramanovom spektroskopijom, infracrvenom spektroskopijom s Fourierovom transformacijom, fotoluminiscentnom spektroskopijom i pretražnom elektronskom mikroskopijom. Jetkanjem monokristalnog silicija n-tipa u podruÄju jakih struja dobiven je fraktalni oblik povrÅ”ine velike efektivne povrÅ”ine po jedinici volumena, Å”to može biti interesantno za primjene u biomedicini. Kod jetkanje epitaksijalnog n-tipa silicija razliÄitih debljina od 5 i 20 Ī¼m na povrÅ”ini slojeva formiraju se veÄe pore dislokacijskog tipa koje vrÅ”e ulogu ulaznih kanal za F- ione u sloj. Kod produženih vremena jetkanja dolazi do kompletnog odvajanja epitaksijalnog sloja te se tako dobivaju dvije dramatiÄno razliÄite porozne strukture u epitaksijalnom sloju i supstratu. Ovaj postupak je ujedno i nova metoda za izradu samostojeÄeg sloja makroporoznog silicija koji se može koristiti u buduÄim istraživanjima razvoja biosenzora i termoelektriÄnih ureÄaja. Kod jetkanja supstrata n-tipa debljine 280 Ī¼m dobivaju se slojevi poroznog silicija s nano porama. Ovakvi filmovi pokazuju intenzivnu fotoluminescenciju. NajveÄa pažnja je posveÄena jetkanju monokristalnog silicija p-tipa na izolatoru Å”to predstavlja i znanstveni i tehnoloÅ”ki izazov zbog prirode samih proces jetkanja kao i zbog moguÄe primjene takvog silicija u razvoju novih senzora. Kod jetkanja istosmjernom strujom nastaju duboke pore veÄih dimenzija, a kod jetkanja izmjeniÄnom strujom nastaju vlaknaste strukture i otoci koji pokazuju jaku fotoluminiscenciju. Stajanjem na zraku ove strukture jako oksidiraju Å”to dodatno ukazuje na njihovu nanometarsku poroznost. Izmjereni intenzitet fotoluminiscencije kod uzoraka silicija na izolatoru izuzetno je visok, te je u odnosu na sve uzorke predstavljene u okviru ove disertacije intenzivniji za faktor 100 i viÅ”e puta. Na temelju istraženih svojstava razliÄitih tipova proizvedenog poroznog silicija u buduÄim istraživanjima odredila bi se optimalna svojstva za razvoj biosenzora, termoelektriÄnih ureÄaja i podloga za povrÅ”inski pojaÄano Ramanovo rasprÅ”enje (tzv. SERS).Nanostructured porous silicon (PS) is a novel material with distinguished structural, electrical and optical properties used in modern high technology devices, such as biological and chemical sensors, drug delivery systems, thermoelectric devices, etc. The aim of this study was to determine structural, optical and chemical properties of a novel type of porous silicon prepared on different silicon epitaxial wafers, as well as on silicon on insulator wafers. In the theoretical part of the dissertation the description of structural and optical properties of silicon is given. The electronic structure of crystalline silicon was described and the characteristics of the electronic structure which determine its optical properties were explained. The photon-electron interaction was described and the ways of photon emission and absorption were explained. The problem of enhancing the photon emission was also discussed, namely how to get photoluminescence from silicon, since it is an indirect semiconductor and accordingly very inefficient emitter. The third chapter gives a historical overview of the discovery of porous silicon and an overview of the previous research. The mechanisms of porous silicon formation were described together with the brief overview of silicon electrochemistry. The most important models for porous silicon formation and pore propagation were illustrated, whit the special emphasis on the quantum confinement model. In this chapter the chemical and physical properties of porous silicon were specified, together with the experimental techniques used for the determination of them. The effect of different parameters, such as current density, concentration of hydrofluoric acid (HF) solution and etching duration on pore formation was described too. Chemical properties of porous silicon were discussed in terms of infrared spectra where assignation of all vibrational bands was given. As far as physical properties are concerned, special emphasis was given to photoluminescence. The mechanisms that influence its efficiency and the models that describe its origin were given. The model of quantum confinement, as the most accepted model for the explanation of the origin of photoluminescence, was given special emphasis. Raman spectra of porous silicon were described too, together with the model of nanocrystal dimension calculation derived from Raman spectra. In the experimental part of this work two etching chambers were manufactured and the experimental set up was established which enabled etching of different size wafers with direct and alternating current. The method for porous silicon production from epitaxial wafers, polycrystalline wafers and silicon on insulator wafers was established. Porous structures with different morphology and optical properties were obtained by varying the concentration of HF ethanol solution, current density and etching duration. In this chapter the experimental procedures for structural and chemical investigations of produced PS were described. Structural properties were investigated by Raman spectroscopy and scanning electron microscopy (SEM). Chemical properties were investigated by Fourier Transform Infrared spectroscopy (FTIR), while photoluminescence was investigated by excitation in visible and infrared region. Several ways of porous silicon production were investigated: a) etching of n-type monocrystal silicon in high current regime; b) etching of n-type epitaxial silicon with 5 and 20 Ī¼m thick epitaxial layer; c) etching of 280 Ī¼m thick n-type silicon substrate on an epitaxial layer; d) etching of 40 and 460 Ī¼m thick p-type monocrystal silicon on insulator. In the first case, n-type monocrystal silicon was etched under the illumination from 250 W halogen lamp with currents which were over the critical electro polishing current. Although Raman spectroscopy of these samples confirmed the formation of nanometer structures, observed photoluminescence is of low intensity. This finding indicates that in these structures, some other centers which may cause the nonradiative recombination of excited electrons are generated. Observed fractal surface appearance and expected high specific surface area makes these systems interesting for the application in biomedicine where the porous silicon is used as an inert smart drug carrier. Interesting results were obtained when etching n-type epitaxial silicon with different thicknesses (5 and 20 mm) of an epitaxial layer. In the process of etching larger pores of dislocation type were formed on the surface of these layers. They serve as entrance channels for F- etching ions into the layer. So, under still smooth surface a branching network of interconnected micrometer size channels were formed. With prolonged etching the epitaxial layer was completely detached from the substrate and hence two dramatically different porous structures were obtained ā thin epitaxial layer with micro-sized pores (macroporous silicon) and etched black layer in the substrate with nanometer size pores (mezzoporous silicon) which has very low reflectivity, so it is called black silicon. The size of pores was regulated by changing the etching parameters and hence the physical and chemical properties of the PS were changed too. This procedure is a novel method for macro porous free standing silicon production which can be used in further investigations and for development of biosensors and thermoelectric devices
Interaction of High Density Lipoprotein with Nicotine ā an IR and Raman Study
The direct interaction of high density lipoprotein (HDL) with nicotine, one of the major components
of cigarette particulate matter, has been studied here at molecular level. Nicotine affects the vibration
modes of HDL due to its embedment within the lipid monolayer. The changes in the positions and intensities
of vibration bands in protein and lipid domain of the particle were studied by IR and Raman
spectroscopy. Three types of samples were prepared: native HDL sample and two HDL samples with
added nicotine. The molecular ratio of nicotine /phospholipids in two samples was 1: 12 and 1: 6. The
same types of samples were prepared from liposomes containing phosphatidylcholine, and sphingomyelin
with addition of cholesterol. Spectra of liposome samples were used for distinguishing and attribution of
lipid bands in spectra of HDL samples, where the majority of changes were observed. The incorporation
of nicotine into lipid monolayer induces changes in the lipid bands from the vibrations in acyl chains and
head groups of phospholipids. The changes in vibration bands from particular amino acids\u27 residues confirm
that nicotine molecule is located within lipid monolayer but close to lipid-protein interface
Principles of magnetic resonance imaging
Neke jezgre, smjeÅ”tene u jako vanjsko magnetsko polje, apsorbiraju i reemitiraju radiofrekventno elektromagnetsko (RF) zraÄenje. Ta pojava je nazvana nuklearna magnetska rezonancija (NMR). ToÄna frekvencija rezonancije, energija interakcije, za pojedine jezgre ovisi o magnetskim i kemijskim osobinama okoline u kojoj se promatrana jezgra nalazi. Zato parametri NMR nose podatke o strukturnim osobinama na molekularnoj razini. Relaksacijski mehanizmi, koji su svi na molekularnoj razini, odreÄeni su dinamikom okoline promatrane jezgre i stoga vremena relaksacije sadržavaju podatke o molekularnim gibanjima. U metodi oslikavanja MR koriste se razlike u parametrima MR za pojedine dijelove tkiva, da bi se dobili anatomski podaci. Za toÄno odreÄivanje prostome raspodjele koriste se gradijenti magnetskog polja. Prednost metode MRI je u tom da slike organa, dobivene u razliÄitim projekcijama, sadrže strukturna i dinamiÄka svojstva promatranog organa, a da pritom organizam nije ozraÄen ionizacijskim zraÄenjem.Nuclear magnetic resonance (NMR) is a phenomenon of absorption and reemission of radio frequency (RF) electromagnetic energy by certain nuclei placed within strong magnetic fields. The NMR frequency, hence the energy of interaction, of the detected electromagnetic radiation from a given nuclear type is dependent critically on the magnetic and molecular environment of the stimulated nuclei. Therefore the NMR parameters bear the structural information on molecular level. The energy exchange mechanisms (relaxation) take place on a microscopic scale and the information about local dynamic properties is acquired by measuring relaxation times. In imaging by NMR, local differences in NMR parameters are used to obtain anatomic data. Magnetic field gradients are used to obtain spatial information. The advantages of MRI include the ability to obtain images in multiple orientations, absence of ionizing radiation and potential to obtain structural and dynamical information about the investigated system
Micro and Nano Structure of Electrochemically Etched Silicon Epitaxial Wafers
Silicon epitaxial wafers, consisting of 280 Ī¼m thick n-type substrate layer and 4ā5 Ī¼m thick epitaxial layer, were electrochemically etched in hydrofluoric acid ethanol solution, to produce porous silicon samples. The resistivity of epitaxial layer was 1 Ī© cm, while the substrate was much better conductor with resistivity 0.015 Ī© cm. By varying the etching time, the micro- and nano-pores of different sizes were obtained within the epitaxial layer, and on the substrate surface. Due to the lateral etching the epitaxial layer was partially detached from the substrate and could be peeled off. The influence of etching time duration on the optical and structural properties of porous samples was investigated by Raman, infrared and photoluminescence spectroscopy. The samples were analysed immediately after the etching and six months later, while being stored in ambient air. The Raman spectra showed the shift in positions of transversal optical (TO) phonon bands, between freshly etched samples and the one stored in ambient air. Infrared spectra indicated the presence of SiHx species in the freshly etched samples, and appearance of oxidation after prolonged storage. Photoluminescence spectra were very weak in freshly etched samples, but their intensity has increased substantially in six month period. (doi: 10.5562/cca1971
FT-IR spectroscopy of lipoproteins ā a comparative study
FT-IR spectra, in the frequency region 4000 ā 600 cm-1, of four major lipoprotein classes: very low density lipoprotein (VLDL), low density lipoprotein (LDL) and two subclasses of high density lipoproteins (HDL2 and HDL3) were analyzed to obtain their detailed spectral characterization. Information about the protein domain of particle was obtained from the analysis of amide I band. The procedure of decomposition and curve fitting of this band confirms the data already known about the secondary structure of two different apolipoproteins: apo A-I in HDL2 and HDL3 and apo B-100 in LDL and VLDL. For information about the lipid composition and packing of the particular lipoprotein the well expressed lipid bands in the spectra were analyzed. Characterization of spectral details in the FT-IR spectrum of natural lipoprotein is necessary to study the influence of external compounds on its structure
W1244 The Role of Adenine and Guanine in Beneficial Effects of the Gastric Pentadecapeptide BPC 157 (PL 14736) On Ileoileal Anastomosis Healing in Rats Impaired with Systemic Corticosteroid Application. Raman Spectroscopy Study
Embryoāderived teratoma biological system reveals antitumor and embryotoxic activity of valproate
Antiepileptic/teratogen valproate (VPA) is a histone deacetylase inhibitor/epigenetic drug proposed for the antitumor therapy where it is generally crucial to target poorly or undifferentiated cells to prevent a recurrence. Transplanted rodent gastrulating embryos-proper (primitive streak and three germ layers) are the source of teratoma/teratocarcinoma tumors. Human primitive-streak remnants develop sacrococcygeal teratomas that may recur even when benign (well differentiated). To screen for unknown VPA impact on teratoma-type tumors, we used original 2-week embryo-derived teratoma in vitro biological system completed by a spent media metabolome analysis. Gastrulating 9.5-day-old rat embryos-proper were cultivated in Eagle's minimal essential medium (MEM) with 50% rat serum (controls) or with the addition of 2 mmVPA. Spent media metabolomes were analyzed by FTIR. Compared to controls, VPA acetylated histones; significantly diminished overall teratoma growth, impaired survival, increased the apoptotic index, and decreased proliferation index and incidence of differentiated tissues (e.g., neural tissue). Control teratomas continued to grow and differentiate for 14 days in isotransplants in vivo, but in vitro VPA-treated teratomas resorbed. Principal component analysis of FTIR results showed that spent media metabolomes formed well-separated clusters reflecting the treatment and day of cultivation. In metabolomes of VPA-treated teratomas, we found elevation of previously described histone acetylation biomarkers [amide I Ī±-helix and A(CH3 )/A(CH2 )]) with apoptotic biomarkers within the amide I region for Ī²-sheets, and unordered and CH2 vibrations of lipids. VPA may be proposed for therapy of the undifferentiated component of teratoma tumors and this biological system completed by metabolome analysis, for a faster dual screening of antitumor/embryotoxic agents