1. X-ray absorption spectroscopy and related techniquesAlojz Kodre, Iztok Arčon, Jana Padežnik Gomilšek, 2004, original scientific article Abstract: In the extensive field of X-ray diagnostic techniques, nowadays mostly implemented on synchrotron X-ray sources, the X-ray absorption methods offer a relatively simple tool for structural analysis of materials. The advantage of the methods is the sensitivity to chemical species and the insensitivity to the long-range order. An overview of various detection techniques is given together with the discussion of accuracy of the method with regard to the spatial resolution and the possible contamination by intra-atomic contributions, the multielectron photoexcitations.
Keywords: X-rays, absorption, EXAFS, XANES
Published in DKUM: 30.08.2017; Views: 991; Downloads: 102
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2. Specific EXAFS tools in analysis of MoSI nanowiresAlojz Kodre, Jana Padežnik Gomilšek, Iztok Arčon, Anton Meden, Dragan Mihailović, 2006, original scientific article Abstract: The structure of nanowires prepared by vapor synthesis from Mo, S and I is investigated by methods of x-ray diffraction (XRD) and extended x-ray absorption fine structure (EXAFS). Starting with a qualitative model of the structure from XRD, the metrics is introduced with interatomic distances determined from EXAFS. Two specific tools to increase the resolution of EXAFS method are discussed: the reciprocity relation between data from adjacent target atoms, and difference EXAFS from data on samples with small changes in stoichiometry.
Keywords: EXAFS, nanowires, molybdenum sulphide-iodide
Published in DKUM: 25.08.2017; Views: 881; Downloads: 148
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3. High-resolution X-ray absorption spectrometry of atomic vaporsAndrej Mihelič, Alojz Kodre, Iztok Arčon, Jana Padežnik Gomilšek, 2004, original scientific article Abstract: A measurement of an x-ray absorption spectrum of a monatomic sample yields pure atomic absorption essential for the EXAFS (Extended X-ray Absorption Fine Structure) analysis in cases of a weak structural signal. A construction of an absorption cell to contain vapor sample takes into account specific properties of the investigated element. Metal-vapor absorption cells for the elements K, Zn, Rb, Cd, Cs, and Hg are presented and comments are made on the use of materials and the operating mechanisms of the cells.
Keywords: x-ray absorption, atomic vapors, K, Zn, Rb, Cd, Cs, EXAFS
Published in DKUM: 18.08.2017; Views: 1233; Downloads: 124
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4. EXAFS and IR analysis of electrochromic $NiO_x$/$NiO_xH_y$ thin filmsJana Padežnik Gomilšek, Romana Cerc Korošec, Peter Bukovec, Alojz Kodre, 2008, original scientific article Abstract: Electrochromic (EC) thin films of $NiO_x$ and $NiO_xH_y$ are prepared by sol-gel method from nickel chloride precursor and deposited onto a suitable substrate by dip-coating technique. The development of the structure with thermal treatment is investigated by EXAFS and IR spectroscopy in two series of films, with high and low concentration of chloride as counter ions. In the former, the predominant structure before thermal treatment is nickel hydroxide. The baking induces condensation, yet with no trace of NiO. In the latter group, colloidal particles are indicated, on which acetate groups are adsorbed or coordinated. At the maximum EC-response the formation of NiO grains is established by EXAFS and IR.
Keywords: electrochromism, thin films, nickel oxide, nickel hydroxide, EXAFS
Published in DKUM: 18.08.2017; Views: 1423; Downloads: 108
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5. Structural properties and thermal stability of cobalt- and chromium-doped $α-MnO_2$ nanorodsRomana Cerc Korošec, Polona Umek, Alexandre Gloter, Jana Padežnik Gomilšek, Peter Bukovec, 2017, original scientific article Abstract: $α-MnO_2$ nanorods were synthesized via the hydrothermal decomposition of $KMnO_4$ in an acidic environment in the presence of $Co^{2+}$ and $Cr^{3+}$ ions. Reactions were carried out at three different temperatures: 90, 130 and 170 °C. All prepared samples exhibit a tetragonal $MnO_2$ crystalline phase. SEM–EDS analysis shows that cobalt cations are incorporated to a higher degree into the $MnO_2$ framework than chromium ions, and that the content of the dopant ions decreases with increasing reaction temperature. The oxidation of $Co^{2+}$ to $Co^{3+}$ during the reaction was proved by an XANES study, while EXAFS results confirm that both dopant ions substitute $Mn^{4+}$ in the center of an octahedron. The K/Mn ratio in the doped samples synthesized at 170 °C is significantly lower than in the undoped samples. Analysis of an individual cobalt-doped $α-MnO_2$ nanorod with HAADF-STEM reveals that the distribution of cobalt through the cross-section of the nanorod is uniform. The course of thermal decomposition of the doped nanorods is similar to that of the undoped ones. Dopant ions do not preserve the $MnO_2$ phase at higher temperatures nor do they destabilize the cryptomelane structure.
Keywords: $α-MnO_2$, manganese dioxide, doping, EXAFS, nanorods, XANES
Published in DKUM: 10.08.2017; Views: 1556; Downloads: 502
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6. Absorpcija rentgenske svetlobe v hidridih elementov skupin 3p in 4pRobert Hauko, 2017, doctoral dissertation Abstract: V območju energij roba K smo izmerili fotoabsorpcijske spektre plinastih hidridov elementov skupine 3p (PH3, H2S, HCl). Analizo smo razširili na že prej izmerjene hidride skupine 4p (GeH4, AsH3, H2Se, HBr) ter na žlahtna plina Ar in Kr in spekter SiH4, ki ni v dosegu naših meritev. Oblike robov in ostre strukture tik nad robom zrcalijo eno- in večelektronske prehode na molekulske in modificirane atomske orbitale. V analizo pod-robnih struktur smo vključili tudi objavljene homologne spektre skupine 2p (CH4, NH3, H2O and HF), vključno z žlahtnim plinom Ne, ki imajo robove v področju trde ultravijolične svetlobe. Strukturo roba smo modelirali z linearno kombinacijo resonančnih komponent, ki opisujejo vzbuditve v posamezna vezana stanja in v kontinuum. Relativne energije in verjetnosti posameznih prehodov, ki smo jih izračunali s programsko kodo ORCA, se dobro ujemajo z izmerjenimi vrednostmi. Robovi homolognih spektrov težjih hidridov so si zelo podobni, v vseh simetrija molekule narekuje prehode na najnižje nezasedene orbitale. V zaporedju 2p prevlada močan učinek jedrskega potenciala. Prehodi na višje, kvaziatomske nivoje, so zelo podobni prehodom v prostem atomu. Pri analizi valenčnih sovzbuditev nad absorpcijskim robom smo s postopkom dekonvolucije kompenzirali povečano naravno širino struktur pri skupini 4p. Podobnost oblik ostrih struktur v analognih parih spektrov kaže na enak sklopitveni mehanizem zunanjih elektronskih konfiguracij v obeh zaporedjih spektrov. Pokazali smo, da lahko višjeenergijski del sovzbuditvenega spektra dobro modeliramo s sovzbuditvenima spektroma Ar oz. Kr. Celotni presek za enojno ionizacijo ob prehodu drugega elektrona v vezano stanje kaže v obeh skupinah rahlo upadanje v odvisnosti od naboja centralnega atoma, pri čemer prevladuje prehod valenčnega elektrona na kvaziatomske orbitale. To je v nasprotju z rezultati meritev pri globokih sovzbuditvah, kjer prevladujejo prehodi na molekulske orbitale. Naša spoznanja potrjujejo nekatere novejše meritve v emisijski spektroskopiji. Celotna analiza in dobro ujemanje parametrov, ki smo jih izračunali v dvostopenjskem računu, z izmerjenimi, kaže na to, da lahko tudi valenčne sovzbuditve v molekulah hidridov skupin 3p in 4p dovolj dobro opišemo s približkom nenadnega prehoda: vzbujanju notranjega elektrona sledi relaksacija molekule z otresanjem valenčnega elektrona v višja vezana ali prosta stanja.
Keywords: rentgenski absorpcijski spektri, plinasti hidridi, spektri 3p na robu K, spektri 4p na robu K, izračuni DFT, večelektronske vzbuditve, spektri sovzbuditev, otresanje
Published in DKUM: 25.05.2017; Views: 2177; Downloads: 191
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9. Inovativna oblikovna zasnova dirkalnika na podlagi magnetne levitacijeDavid Novina, 2014, undergraduate thesis Abstract: V diplomski nalogi je predstavljena nova zasnova virtualnega dirkalnika. Zaradi uporabe nove tehnologije so obdelana in natančno obrazložena področja fizike, ki vplivajo na delovanje in uporabo te tehnologije. Predstavljeno je tudi področje oblikovanja, ki je pomembno za končni izgled dirkalnika. Podani in opisani so realni primeri uporabe nove tehnologije in razlike med novo tehnologijo prevoza in sedanjo konvencionalno. Prav tako je opisan postopek, kako iz ideje nastane končni virtualni 3D model. Pokazano je, da je izdelava dirkalnika izvedljiva.
Keywords: inovativna-oblikovna-zasnova, virtualni-dirkalnik, tehnologija-magnetne-levitacije, Maglev, 3D model
Published in DKUM: 20.10.2014; Views: 1598; Downloads: 165
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10. x-ray absorption study of CeO2 and Ce/V mixed oxide thin films obtained by sol-gel depositionJana Padežnik Gomilšek, Irena Kozjek-Škofic, Nataša Bukovec, Alojz Kodre, 2004, original scientific article Abstract: CeO2 and Ce/V mixed oxide thin films prepared by sol-gel deposition and annealed in an air or argon atmosphere have been studied by chronocoulometry and by XAFS (X-ray absorption fine structure). Multielectron photoexcitations (MPE), well known to pervade XAFS spectra of Ce making the analysis of structural parameters unreliable, are removed with the help of the atomic absorption background, determined on simple Ce compounds. Distinct MPE estimates for Ce3+ and Ce4+ ions are used. In the analysis of the recovered pure XAFS signal, the degree of disorder is found to depend on the Ce/V molar ratio and on the heating atmosphere. The disorder correlates with charge capacity of films, both increasing with vanadium content and V4+/V5+ molar ratio.
Keywords: thin flms, cerium dioxide, cerium-vanadium mixed oxide, x-ray absorption, electrochemistry, sol-gel technology, XSAFS
Published in DKUM: 01.06.2012; Views: 2429; Downloads: 100
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