Electron in a Box and Ultrathin Metallic Films as Probed by ARUPS

Ultrathin metallic films may act as quantum boxes when some conditions are met. Here, we discuss these conditions for the simplest case of one-dimensional confinement and we review some of the properties that emerge from the reduced dimensionality of the films. We emphasize the difference between extremely thin layers of up to several monolayers thickness and thicker ultrathin films. Taking the Ag/V(100) system as a case Study, we show the most prominent features of the electronic structure of the films, as revealed by the angular resolved ultraviolet photoemission spectroscopy (ARUPS)

Istraživanje površine V(100) upotrebom sinkrotronskog zračenja

The electronic structure of V(100) has been studied by means of synchrotron radiation. Normal emission (n.e.) spectra, taken in the energy range between 15 and 100 eV, were analysed in terms of existing band structure calculations. The obtained data support our previous reports suggesting that the peak at the Fermi level has a bulk and surface component. The variation of the intensity at the Fermi level was measured in the constant initial state (CIS) mode. In the photon energy range between 40 and 100 eV the variation of the intensity at the Fermi level is generally following the energy dependence of the resonant spectrum of vanadium films. However, the resonant spectrum obtained from V(100) appears to be significantly narrower than the spectra reported for films.U ovom se radu prikazuju rezultati istraživanja V(100) upotrebom sinkrotronskog zračenja. Spektri okomite fotoemisije u području fotonskih energija između 15 i 100 eV uspoređuju se s postojećim teorijskim proračunima za strukturu valentne vrpce vanadija. Dobiveni rezultati potvrđuju našu prije iznijetu tezu, da se maksimum fotoemisijskog intenziteta na Fermijevom nivou sastoji od dvije komponente, volumne i površinske. Promjena intenziteta na Fermijevom nivou mjerila se je u modu konstantnog početnog stanja. U području fotonskih energija između 40 i 100 eV, promjene fotoemisijske struje s Fermijevog nivoa vrlo su slične rezonantnom spektru vanadijevih tankih slojeva. Međutim, rezonantni spektar površine V(100) je značajno uži od rezonantnog spektra vanadijevih tankih filmova

Surface Modification of Stainless Steel-304 Electrode. 1. Voltammetric, Rotating Ring-Disc Electrode and XPS Studies

Hydrous oxide film was grown on stainless steel-304 under conditions of cycling voltammetry in 1 mol dm–3 NaOH solution. The anodic voltammetric peak of Fe(OH)2 oxidation was used as a measure of the oxide growth as a function of potential limits, sweep rates and the number of potential cycles. The oxide film stability was monitored by the use of rotating ring-disc electrode. During potential cycling in alkaline solution, it was found that after 30 cycles, 1.4% of the anodic charge was due to iron dissolution from the oxide film. The selective dissolution of iron and nickel from the oxide film, previously grown in alkaline solution, was monitored at the potential of open circuit in an acid solution of pH 2.7. A model for enhanced stability of hydrous oxide film in acid solution is proposed. The model, based on voltammetric, rotating ring-disc electrode and X-ray photoelectron spectroscopy measurements, implies that after hydrous oxide growth by potential cycling in an alkaline solution, the oxide placed in an acid solution remains enriched in chromium due to selective dissolution of nickel and iron. The Cr- O-Cr chains stabilize the modified layer and contribute to the enhanced stability against corrosion. This model unifies several previously proposed models: the model for a hydrous oxide growth by potential cycling, the polymeric hydrated oxide model for the passivity of iron and stainless steels and the percolation model for the passivity of stainless steels

Atomic Structure of Surfaces and Ultrathin Films

Structural and electronic properties of surfaces and ultrathin metallic films are closely connected. Because of their low dimensionality it is of the utmost importance to acquire their structural details at atomic level and their electronic structure resolved in energy and momentum at very high resolution. In this paper, we briefly review several experimental examples that illustrate these requirements and at the same time address some important properties of surfaces and ultrathin films. The examples are restricted to those that used scanning tunneling microscopy to study the structural properties and ultraviolet photoemission spectroscopy to elucidate the electronic structure of the samples

Termička stabilnost tankih slojeva TiO2 dobivenih kemijskim taloženjem iz pare. XPS i AES karakterizacija

Thermal stability of TiO2 thin polycrystalline films obtained by the very simple chemical vapour deposition method on the quartz, molybdenum and gold substrates have been examined by X-ray photoelectron and Auger spectroscopy (XPS and AES), respectively, before and after annealing in vacuum at temperatures from 298 K to 1200 K. In this temperature range we have found carbon, water, and O-H groups as the impurities at the surface of the films. The possible influence of both the annealing and the impurities on the film stoichiometry is discussed.Proučavana je termička stabilnost tankih, polikristaličnih slojeva TiO2 dobivenih jednostavnim kemijskim taloženjem iz pare na podloge iz kvarca, molibdena i zlata. Korištene su metode XPS i AES na uzorcima prije i poslije termičkog napuštanja u rasponu temperatura od 298 do 1200 K. Našli smo ugljik, vodu i O-H skupine kao nečistoće na površinama slojeva. Diskutirani su utjecaji termičkog napuštanja i nečistoća na stehiometriju slojeva

Istraživanje nečiste i čiste (100) površine vanadija STM-om

Scanning tunneling microscopy is used to characterize different states of the V(100) surface during the cleaning procedure in an ultrahigh vacuum apparatus, starting with the "as received" sample and finishing with an almost perfectly clean surface. We show, for the first time, STM images of the clean V(100) surface and with atomic resolution.Primijenili smo skenirajući tunelirajući mikroskop (STM) za topografsku karakterizaciju površine V(100) prije i tijekom čišćenja u aparaturi za ultravisok vakuum, počevši s “dobivenim” uzorkom i nakon pojedinih postupaka čišćenja. Po prvi puta se pokazuju slike potpuno čiste površine V(100) s atomskim razlučivanjem, snimljene STM-om