scholarly journals Reactivity and Stability of Ultrathin VOx Films on Pt(111) in Catalytic Methanol Oxidation

2020 ◽  
Vol 63 (15-18) ◽  
pp. 1545-1556
Author(s):  
Bernhard von Boehn ◽  
Lena Scholtz ◽  
Ronald Imbihl
Keyword(s):  
Methanol Oxidation ◽  
Electron Spectroscopy ◽  
Reaction Conditions ◽  
Spatial Homogeneity ◽  
Low Energy Electron Diffraction ◽  
Reactive Deposition ◽  
Ultrathin Layers ◽  
Low Energy Electron ◽  
Limiting Case ◽  
Photoemission Electron

AbstractThe growth of ultrathin layers of VOx (< 12 monolayers) on Pt(111) and the activity of these layers in catalytic methanol oxidation at 10−4 mbar have been studied with low-energy electron diffraction, Auger electron spectroscopy, rate measurements, and with photoemission electron microscopy. Reactive deposition of V in O2 at 670 K obeys a Stranski–Krastanov growth mode with a (√3 × √3)R30° structure representing the limiting case for epitaxial growth of 3D-VOx. The activity of VOx/Pt(111) in catalytic methanol oxidation is very low and no redistribution dynamics is observed lifting the initial spatial homogeneity of the VOx layer. Under reaction conditions, part of the surface vanadium diffuses into the Pt subsurface region. Exposure to O2 causes part of the V to diffuse back to the surface, but only up to one monolayer of VOx can be stabilized in this way at 10−4 mbar.

STRUCTURE AND THERMAL STABILITY OF THE SULFIDE OVERLAYERS ON CH3CSNH2-PASSIVATED GaAs(100) SURFACES

2001 ◽  
Vol 08 (01n02) ◽  
pp. 19-23 ◽  
Author(s):  
F. Q. XU ◽  
E. D. LU ◽  
H. B. PAN ◽  
C. K. XIE ◽  
P. S. XU ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Electron Spectroscopy ◽  
Photoemission Spectroscopy ◽  
Low Energy Electron Diffraction ◽  
Native Oxides ◽  
Sulfur Passivation ◽  
Different Temperatures ◽  
Low Energy Electron ◽  
Synchrotron Radiation Photoemission ◽  
Thermal Stability Of

Chemically sulfur passivation of GaAs(100) by thioacetamide ( CH 3 CSNH 2) has been studied using synchrotron radiation photoemission spectroscopy (SRPES), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). The measurement of SRPES and AES showed that the top layer of native oxides over GaAs(100) was removed and the sulfides of Ga and As were formed after the passivation process. The thermal stability and surface structure have also been studied by annealing the passivated samples at different temperatures. We found that the surface sulfides could be removed gradually; as a result, a clean, ordered and thus Fermi level unpinning surface was finally achieved. The surface restructures with GaAs(100)–S(2×1) and 4×1 LEED patterns were observed on annealing above 260°C and at 550°C respectively.

The Ten-Fold Surface of The Decagonal Al72Ni11Co17 Quasicrystal Studied by Leed, Spa-Leed, Aes and Stm.

2000 ◽  
Vol 643 ◽  
Author(s):  
Erik J. Cox ◽  
Julian Ledieu ◽  
RÓn'n Mcgrath ◽  
Renee D. Diehl ◽  
Cynthia J. Jenks ◽  
...  
Keyword(s):  
Annealing Time ◽  
Electron Spectroscopy ◽  
Annealing Temperature ◽  
Profile Analysis ◽  
Low Energy Electron Diffraction ◽  
Annealing Temperatures ◽  
Scanning Tunnelling ◽  
Tunnelling Microscopy ◽  
Low Energy Electron ◽  
Stm Images

AbstractThe ten-fold surface of the decagonal Al72Ni11Co17 (d-Al-Ni-Co) quasicrystal has been investigated using low energy electron diffraction (LEED), spot profile analysis LEED (SPA- LEED), Auger electron spectroscopy (AES) and scanning tunnelling microscopy (STM). This was done as a function of both annealing temperature and annealing time. The long-range order of the surface, as indicated by LEED, increases both as a function of annealing time and temperature. STM shows the surface to be rough and cluster-like at low annealing temperatures (≤725 K), whilst annealing to temperatures in excess of 725 K results in the formation of terraces. These terraces are small (≤ 100 Å width) at lower annealing temperatures and increase in size (100 Å ≤ x ≤ 500 Å) as the annealing temperature is increased (≥ 850 K). They are characterised by the presence of three-fold protrusions which align preferentially. STM images show single height steps as expected due to the periodicity of d-Al-Ni-Co in the z direction. To date it has not been possible to obtain atomic resolution, although this work is continuing.

VALENCE ELECTRONIC STRUCTURE OF OXYGEN-MODIFIED α-Mo2C(0001) SURFACE: ANGLE-RESOLVED PHOTOEMISSION STUDY

2006 ◽  
Vol 13 (02n03) ◽  
pp. 185-190
Author(s):  
M. KATO ◽  
K. OZAWA ◽  
T. SATO ◽  
K. EDAMOTO
Keyword(s):  
Electron Spectroscopy ◽  
Oxygen Adsorption ◽  
Photoemission Spectroscopy ◽  
Metallic State ◽  
Low Energy Electron Diffraction ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Peak Intensity ◽  
Low Energy Electron ◽  
Photoemission Study ◽  
Surface Angle

Adsorption of oxygen on α- Mo 2 C (0001) is investigated with Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and angle-resolved photoemission spectroscopy (ARPES) utilizing synchrotron radiation. It is found that C KLL Auger peak intensity does not change during O 2 exposure, indicating that the depletion of C atoms does not proceed. It is deduced from ARPES and LEED results that adsorbed oxygen atoms from a well-ordered (1 × 1) lattice on the α- Mo 2 C (0001) surface. The ARPES study shows that oxygen adsorption induces a peculiar state around Fermi level (E F ). Off-normal-emission measurements prove that the state is a half-filled metallic state.

The growth of AuGa2 thin films on GaAs(001) to form chemically unreactive interfaces

1986 ◽  
Vol 1 (4) ◽  
pp. 537-542 ◽  
Author(s):  
Jeffrey R. Lince ◽  
Tsai C. Thomas ◽  
Williams R. Stanley
Keyword(s):  
Electron Spectroscopy ◽  
Auger Electron ◽  
Room Temperature ◽  
Substrate Surface ◽  
Film Deposition ◽  
X Ray ◽  
Low Energy Electron Diffraction ◽  
Interface Roughening ◽  
Low Energy Electron ◽  
Electron Energy Loss

Thin AuGa2 films were grown by codeposition from separate Au and Ga evaporation sources on clean GaAs(001) substrates in ultrahigh vacuum, and were studied by Auger electron spectroscopy, electron energy-loss spectroscopy, low-energy electron diffraction, scanning electron microscopy, and x-ray diffractometry. The morphology and crystallinity of the AuGa2 were highly dependent upon the film deposition and annealing history. Films grown on room-temperature substrates were continuous, specular, and polycrystalline, but the dominant orientation was with the (001) planes of the crystallites parallel to the substrate surface. Annealing to temperatures between 300°and 480°C caused the film to break up and coalesce into rectangular crystallites, which were all oriented with (001) parallel to the surface. An anneal to 500°C, which is above the AuGa2 melting point, resulted in the formation of irregular polycrystalline islands of AuGa2 on the GaAs(001) substrate. No interface roughening or chemical reactions between the film and substrate or interface were observed for even the highest-temperature anneals.

PROPERTIES OF ULTRATHIN Sb LAYERS ON THE Ni(111) FACE

2003 ◽  
Vol 10 (01) ◽  
pp. 65-72 ◽  
Author(s):  
A. KRUPSKI ◽  
S. MRÓZ
Keyword(s):  
Atomic Structure ◽  
Electron Spectroscopy ◽  
Atomic Layer ◽  
Text Structure ◽  
Elastic Peak ◽  
Low Energy Electron Diffraction ◽  
Structure And Morphology ◽  
Text Structures ◽  
First Results ◽  
Low Energy Electron

We present the first results concerning the atomic structure and morphology of ultrathin Sb layers deposited on the Ni(111) face in ultrahigh vacuum at the substrate temperature ranging from 150 to 700 K obtained with the use of Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and directional elastic peak electron spectroscopy (DEPES). The AES results indicate that the antimony layer on the Ni(111) at T < 200 K grows in the Frank–van der Merwe mode. For temperature around 250 K, the flat two atomic layer islands ("wedding cakes") seem to grow after completion of the first antimony monolayer. At T ≥ 300 K , a Sb–Ni surface alloy is formed. DEPES measurements indicate that the atomic structure of Sb layers deposited at T = 150 K is completely amorphous, while better and better pronounced maxima appear in DEPES profiles when the sample temperature increases from 300 to 450 K. LEED patterns corresponding to p(1 × 1), p(2 × 2) and [Formula: see text] structures have been observed for 150 K ≤ T ≤ 250 K . A possible model for the last structure is proposed. After annealing the deposited layer at T > 500 K , the [Formula: see text] structure appears.

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