Search results for "Surfaces and interfaces"
showing 10 items of 939 documents
The effect of energy-dependent detector efficiency in electron spectroscopic methods: XPS, AES and DCEMS
1993
Systematic studies were performed to investigate the distorting effect of the electron energy dependence of the channeltron detector efficiency on the shape of data distributions in electron spectroscopy. In agreement with earlier results for electron energies up to 3 keV, it was found that a virtually energy-independent shape of the electron distribution might be achieved even in a very broad range of electgron energies (up to 15 keV) by appropriate selection of the operational high voltage of a channeltron. However, the efficieny of channeltrons was also found to depend on count rates, indicating one of the principal difficulties in comparing distribution recorded under different experime…
Coexisting electron emission mechanisms in small metal particles observed in fs-laser excited PEEM
2007
Abstract Silver cluster films deposited on Si(1 1 1) were investigated by spectroscopic photoelectron microscopy using fs-laser excitation tuneable between hν = 1.45–1.65 eV and 2.9–3.3 eV. With increasing coverage the films grown as stepped wedges first exhibit clusters of few nanometers diameter with narrow size distributions that later agglomerate forming larger islands up to about 100 nm diameter. The cluster films have been characterized by SEM, AFM and HR-TEM. In the 3.1 eV range the small clusters emit more effectively and the dependence of electron yield on laser power follows a quadratic power law. Microspectroscopy reveals that the Fermi level onset is sharp(
Specific heat studies of ortho-deuterium monolayers physisorbed on graphite
1986
The specific heat of ortho-deuterium monolayers physisorbed on graphite (Grafoil) has been studied in detail at about 100 coverages in the total density range below monolayer completion and at temperatures between 2 and 40 K. Several interesting new features were observed: At the completion of the commensurate 3 × 33 R30° phase the system undergoes an order-disorder transition at T = 18.1 K. This temperature turns out to be 2.34 K lower than that of para-hydrogen on graphite, which elucidates the significant influence of the quantum zero-point energy on these systems. From the heat-capacity data a value of 0.31 ± 0.02 is deduced for the critical exponent a which is in good agreement with th…
Interpretation of capacitance spectra and transit times of single carrier space-charge limited transport in organic layers with field-dependent mobil…
2007
The ac impedance characteristics of a single carrier with space-charge limited current (SCLC) transport in organic layers with field-dependent mobility is analyzed, indicating the similarities as well as the differences to the constant mobility case. The model provides capacitance spectra and transit times from different calculation methods, in relation to the electric field distribution in the SCLC regime. It is found that the low frequency capacitance lies in the range 3Cg/4 < Cif < Cg, with respect to the geometric capacitance Cg. An approximated expression for the variation of the transit time with applied bias is derived, in good agreement with exact calculations. Experimental results …
Nanoscale etching of III-V semiconductors in acidic hydrogen peroxide solution: GaAs and InP, a striking contrast in surface chemistry
2019
In this study of nanoscale etching for state-of-the-art device technology, the importance of surface chemistry, in particular the nature of the surface oxide, is demonstrated for two III-V materials. Striking differences in etching kinetics were found for GaAs and InP in sulphuric and hydrochloric acidic solutions containing hydrogen peroxide. Under similar conditions, etching of GaAs was much faster, while the dependence of the etch rate on pH, and on H2O2 and acid concentrations also differed markedly for the two semiconductors. Surface analysis techniques provided information on the product layer present after etching: strongly non-stoichiometric porous (hydr)oxides on GaAs and a thin st…
Molybdenum deposition on TiO2 (110) surfaces with different stoichiometries
1999
Abstract The deposition of ultra thin molybdenum films has been carried out on three different TiO 2 surfaces: a stoichiometric and flat one obtained after annealing, a non stoichiometric and rough surface made by Ar + bombardment and a stoichiometric and rough surface obtained by oxygen bombardment. Whatever the substrate preparation, in situ AES and XPS studies and ex situ AFM and RHEED characterizations have revealed a Stranski–Krastanov growth mode: the completion of three monolayers followed by island growth is observed in any case. The three monolayers are composed of amorphous molybdenum oxide with a molybdenum oxidation state between III and IV. The oxidation of the molybdenum layer…
Superficial oxidation of molybdenum at high pressure and low temperature: RHEED and AES analyses of the molybdenum oxide formation
1991
Abstract Numerous studies relate to the interaction of the molybdenum surface with oxygen at low pressure and high temperature. They give results about oxygen chemisorption, surface facetting and the epitaxial formation of MoO 2 crystallites. This work deals with the interaction of Mo(100), Mo(110) and Mo(111) surfaces with oxygen at high pressure (10 4 Pa) and low temperature (620–820 K). RHEED and AES analyses results prove that, in these oxidation conditions: MoO 2 and non-stoichiometric molybdenum oxide such as Mo 4 O 11 are not evidenced in any of the molybdenum oxidation steps. The MoO 3 phase nucleates directly from any Mo surface. The structure and orientation of MoO 3 nuclei are ch…
Highly textured boron/nitrogen co-doped TiO2 with honeycomb structure showing enhanced visible-light photoelectrocatalytic activity
2020
International audience; In this work, we report a novel photocatalyst based on boron and nitrogen co-doped TiO2 rutile (1 1 0) honeycomb structures. The photocatalyst has been prepared by simultaneously oxidizing and doping a Ti-foil substrate at 750 degrees C. The unit cell volume and the crystallite size of grown TiO2 films were measured by Rietveld refinement analysis. The co-doping by boron and nitrogen was achieved simultaneously with the oxidation of the titanium, resulting in a rutile (1 1 0) textured TiO2 film. X-ray photoelectron spectroscopy analysis revealed the presence of Ti-O-N and Ti-O-B-N bonds, and the presence of crystal defects in the lattice was detected and displayed by…
Structure and Dynamics of Confined Liquids: Challenges and Perspectives for the X-ray Surface Forces Apparatus
2019
Preprint of the open access article Weiss, H., Cheng, H.-W., Mars, J., Li, H., Merola, C., Renner, F. U., Honkimäki, V., Valtiner, M., & Mezger, M. (2019). Structure and Dynamics of Confined Liquids: Challenges and Perspectives for the X-ray Surface Forces Apparatus. Langmuir, 35(51), 16679–16692. https://doi.org/10.1021/acs.langmuir.9b01215
Scanning tunneling microscopy and spectroscopy of Mo clusters grown on TiO2(110).
2007
Molybdenum was deposited in two steps (3 eq. ML and 1 eq. ML) on the light blue rutile TiO2 10) (1 x 1) surface at room temperature, each Mo deposition cycle being followed by an annealing up to 950-1000 K. This procedure was found to lead to formation of separated clusters having a size in very wide range (1-20 nm). Scanning tunneling microscopy showed a dependence of the cluster morphology as a function of the size. The scanning tunneling spectra of Mo clusters was studied as a function of cluster dimensions and discussed in comparison with photoelectron spectroscopy results previously obtained for homogeneous Mo films. The dI/d V curves do not display the valence band structure of deposi…