Atomically Smooth Ultrathin Oxide Layers on SI(113)

1999 ◽  
Vol 567 ◽  
Author(s):  
H.-J. Müssig ◽  
J. Dabrowski ◽  
S. Hinrich
Keyword(s):  
Elevated Temperatures ◽  
Oxidation Mechanism ◽  
Dissociative Chemisorption ◽  
Initial Oxidation ◽  
Precursor State ◽  
Oxide Layers ◽  
Adsorption Sites ◽  
Molecular Precursor ◽  
Diffusion Paths ◽  
Ultrathin Oxide

ABSTRACTWe report the first direct observation of dissociative chemisorption of oxygen molecules on a silicon surface at room temperature via a molecular precursor state. We link this to the fact that smooth oxide layers can be grown easily on Si(113). The process of initial oxidation is discussed in terms of surface diffusion paths and surface stress. First ab initiocalculations help elucidate the favored adsorption sites and the oxidation mechanism. Experimental evidence was found for bond geometries resulting in the quasi-epitaxial growth of a chemisorption layer on the substrate at elevated temperatures (600°C). In contrast to the first stages of Si(001) oxidation, neither defects nor the ejection of Si atoms plays a significant role during the initial oxidation of Si(113).

Oxidation of Some Titanium Alloys in Air at Elevated Temperatures

2008 ◽  
Vol 595-598 ◽  
pp. 967-974 ◽  
Author(s):  
E. Godlewska ◽  
M. Mitoraj ◽  
B. Jajko
Keyword(s):  
Thermal Cycling ◽  
Titanium Alloys ◽  
Constant Temperature ◽  
Cross Sections ◽  
Elevated Temperatures ◽  
Mixed Oxides ◽  
Oxidation Mechanism ◽  
Testing Procedure ◽  
Oxidation Products ◽  
Outward Diffusion

This paper presents comparative studies on the performance of two titanium alloys (Ti- 6Al-1Mn, Ti-45.9Al-8Nb) in an oxidizing atmosphere at 700 oC and 800 oC. Testing procedure comprised thermogravimetric measurements at a constant temperature and in thermal cycling conditions (1-h and 20-h cycles at constant temperature followed by rapid cooling). The overall duration of the cyclic oxidation tests was up to 1000 hours. The oxidized specimens were analyzed in terms of chemical composition, phase composition, and morphology (SEM/EDS, TEM/EDS, XRD). The extent and forms of alloy degradation were evaluated on the basis of microscopic observation of specimen fractures and cross-sections. Selected specimens were examined by means of XPS, SIMS and GDS. Oxidation mechanism of Ti-46Al-8Nb was assessed a two-stage oxidation method using oxygen-18 and oxygen-16. Apparently, the oxidation of this alloy proceeded in several stages. According to XPS, already after quite short reaction time, the specimens were covered with a very thin oxide film, mainly composed of aluminum oxide (corundum). A thicker layer of titanium dioxide (rutile) developed underneath. These two layers were typical of the oxidation products formed on this alloy, even when tested in thermal cycling conditions. In general, the scale had a complex multilayer structure but it was thin and adherent. Under the continuous layer of titania, there was a fine-grained zone composed of mixed oxides. The alloy/scale interface was marked with niobium-rich precipitates embedded in a titanium-rich matrix. There were some indications of secondary processes occurring under the initial continuous oxide layers (e.g. characteristic layout of pores or voids). Thickness of inner scale layers clearly increased according to parabolic kinetics, while that of the outer compact layer (mainly TiO2) changed only slightly. The distribution of oxygen isotopes across the scale/alloy interface indicated two-way diffusion of the reacting species – oxygen inward and metals outward diffusion. Silicon deposited on Ti-6Al-1Mn alloy positively affected scale adhesion and remarkably reduced alloy degradation rate.

Photoconductivity of Macroporous and Nonporous Silicon with Ultrathin Oxide Layers

2018 ◽  
Vol 47 (9) ◽  
pp. 5105-5108 ◽  
Author(s):  
K. P. Konin ◽  
Yu. V. Goltvyansky ◽  
L. A. Karachevtseva ◽  
M. I. Karas ◽  
D. V. Morozovs’ka
Keyword(s):  
Oxide Layers ◽  
Ultrathin Oxide

Structure of ultrathin oxide layers on metal surfaces from grazing scattering of fast atoms

2009 ◽  
Vol 256 (2) ◽  
pp. 365-370 ◽  
Author(s):  
H. Winter ◽  
J. Seifert ◽  
D. Blauth ◽  
M. Busch ◽  
A. Schüller ◽  
...  
Keyword(s):  
Metal Surfaces ◽  
Oxide Layers ◽  
Grazing Scattering ◽  
Ultrathin Oxide

Microstructural Evolution of Compacted Graphite Iron under Thermo-Mechanical Fatigue Conditions

2011 ◽  
Vol 409 ◽  
pp. 757-762 ◽  
Author(s):  
S. Ghodrat ◽  
M. Janssen ◽  
Roumen H. Petrov ◽  
Leo Kestens ◽  
Jilt Sietsma
Keyword(s):  
Mechanical Properties ◽  
Cast Iron ◽  
Elevated Temperatures ◽  
Easy Access ◽  
Compacted Graphite Iron ◽  
Microstructural Changes ◽  
Oxide Layers ◽  
Cooling Cycle ◽  
Compacted Graphite ◽  
Mechanical Fatigue

Cast iron components in combustion engines, such as cylinder blocks and heads, are exposed for long periods of time to elevated temperatures and subjected to large numbers of heating and cooling cycles. In complex components, these cycles can lead to localized cracking due to stresses that develop as a result of thermal gradients and thermal mismatch. This phenomenon is known as Thermo-Mechanical Fatigue (TMF). Compacted Graphite Iron (CGI) provides a suitable combination of thermal and mechanical properties to satisfy the performance of engine components. However, TMF conditions cause microstructural changes, accompanied by the formation of oxides at and close to the surface, which together lead to a growth in size of the cast iron. These microstructural changes affect the mechanical properties and accordingly the thermo-mechanical fatigue properties. The aim of this research is to provide insight into the microstructure evolution of CGI, with its complex morphology, under TMF conditions. For this, optical and scanning electron microscopy observations are made after cyclic exposure to air at high temperature, both without and with mechanical loading. It was found that the oxide layers, which develop at elevated temperatures, crack during the cooling cycle of TMF. The cracking results from tensile stresses developing during the cooling cycle. Therefore, paths for easy access of oxygen into the material are formed. Fatigue cracks that develop also show oxidation at their flanks. In order to quantify the oxide layers surrounding the graphite particles, Energy Dispersive X-Ray Analysis (SEM-EDX) and Electron Probe Micro Analysis (EPMA) are used.

Void formation during thermal decomposition of ultrathin oxide layers on the Si(110) surface

1998 ◽  
Vol 398 (1-2) ◽  
pp. 134-142 ◽  
Author(s):  
Ken Fujita ◽  
Heiji Watanabe ◽  
Masakazu Ichikawa
Keyword(s):  
Thermal Decomposition ◽  
Void Formation ◽  
Oxide Layers ◽  
Ultrathin Oxide

Understanding Metal Oxide Surfaces at the Atomic Scale: STM Investigations of Bulk-defect Dependent Surface Processes

2000 ◽  
Vol 654 ◽  
Author(s):  
Ulrike Diebold
Keyword(s):  
Oxygen Vacancies ◽  
Science Studies ◽  
Elevated Temperatures ◽  
Surface Defects ◽  
Surface Reactivity ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Oxide Surface ◽  
Tunneling Microscopy ◽  
Adsorption Sites

AbstractSurface defects are important in oxide surface chemistry, because they change not only the surface geometric structure, but also affect the local electronic structure. Scanning Tunneling Microscopy (STM) images with atomic-scale resolution, in combination with area-averaging surface spectroscopies, is an ideal tool to study local surface defects and their relationship to surface reactivity. We report STM results onTiO2(110) surfaces which show the surprising influence of bulk defects on surface properties. Thereduced crystals used in this and other surface science studies contain Ti interstitials and oxygen vacancies. Re-oxidation at elevated temperatures results in the growth of additional TiO2 layers with Ti coming from the bulk of the crystal and O from the gas phase. This often result in partially incomplete surface structures with many undercoordinated atoms. The esorption behavior of elemental S, dosed at room temperature, depends on the reduction state of the sample. This is explained by a mechanism where desorption froma weaklybound precursor state competes with the availability of new adsorption sites in the form of oxygen vacancies which migrate from the bulk to the surface.

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