scholarly journals Nanoindentation of Aluminum Single Crystals: Experimental Study on Influencing Factors

Materials ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 3688 ◽  
Author(s):  
Pavel Filippov ◽  
Ursula Koch
Keyword(s):  
Single Crystals ◽  
Orthotropic Material ◽  
Crystal Orientation ◽  
Model Systems ◽  
Indentation Hardness ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Average Modulus ◽  
First Time ◽  
Indenter Geometry

Results from nanoindentation of aluminum single crystals deliver valuable information as model systems for understanding technical aluminum alloys. The effect of the crystal orientation and the azimuthal indenter orientation on indentation hardness and modulus was studied by Vickers indentation (max. load 10 mN) on single crystal surfaces with (100), (110), and (111) orientations. The average indentation hardness varied, depending on the crystallographic orientation, by 1.8%. The anisotropy of the elastic modulus (1.1% of the average modulus) is lowered (indentation averaging effect). This is predicted by explicit approximation of the contact problem (conical indenter, orthotropic material). It was found that indentation hardness and modulus vary periodically with the azimuthal indenter orientation on (100)- and (110)-oriented surfaces (relative amplitude of 1.8% for indentation hardness and 2.6% of the modulus). This is attributed to the combined effect of the indenter geometry and crystal symmetry. For the first time, this effect was quantified for aluminum single crystals.

Nanoindentation Evaluation of Brittle Films on Metals Natalia

2000 ◽  
Vol 649 ◽  
Author(s):  
I. Tymiak ◽  
Antanas Daugela ◽  
Trevor F. Page ◽  
William W. Gerberich
Keyword(s):  
Indentation Load ◽  
Native Oxide ◽  
Modulus Ratio ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Ceramic Films ◽  
Loading And Unloading ◽  
Ae Signals ◽  
Sic Films ◽  
Indenter Geometry

ABSTRACTThe present study addresses two cases of brittle ceramic films on metals. With the assistance of AE as a supplementary technique, yield initiation phenomena have been evaluated for W single crystal surfaces under several nm thick native oxide film. An AE sensor coupled to an indenter tip allowed an increasing sensitivity to localized fracture and plasticity events in the vicinity of an indentation contact. A good correlation between AE signals and indentation induced plasticity and fracture has been accomplished for contacts below 100 μN. Second, mechanical behavior of porous nanocrystalline SiC films on Mo substrates was examined. An analysis was based on the P-δ2 approach. With this method, both loading and unloading parts of indentation curves obtained with sharp pyramidal indenters may be represented as P=Kδ2 where P, and δ denote indentation load and displacement respectively. The parameter K includes a material's hardness/modulus ratio and indenter geometry.

CO adsorption on (100) and (211) tungsten single-crystal surfaces: Changes in work function

1968 ◽  
Vol 46 (8) ◽  
pp. 949-958 ◽  
Author(s):  
R. A. Armstrong
Keyword(s):  
Single Crystal ◽  
Work Function ◽  
Single Crystals ◽  
Room Temperature ◽  
Co Adsorption ◽  
Major Effect ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Tungsten Single Crystal ◽  
Adsorption Of Co

The adsorption of CO on two large single crystals of tungsten exposing (100) and (211) surfaces has been studied by measuring changes in the work function [Formula: see text] at 300 °K and above, where some CO remained adsorbed. The results for the two surfaces were quite different.CO adsorbed on the clean W(100) surface at room temperature as β-CO causing [Formula: see text] to increase by 0.48 V. As β adsorption saturated, α-CO adsorption began and caused [Formula: see text] to decrease. The major effect of heating was desorption.CO adsorbed on the clean W(211) surface with a sticking probability near unity and increased [Formula: see text] by 0.68 V. Heating the crystal to temperatures below 1100 °K produced large irreversible changes in [Formula: see text]. These irreversible changes are attributed to the formation and dissociation on the surface of complexes consisting of two CO molecules.

scholarly journals An Affordable Option to Au Single Crystals Through Cathodic Corrosion of a Wire: Fabrication, Electrochemical Behavior, and Applications in Electrocatalysis and Spectroscopy

2020 ◽  
Author(s):  
Mohamed Elnagar ◽  
Johannes M. Hermann ◽  
Timo Jacob ◽  
Ludwig A. Kibler
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
Surface Enhanced Raman Spectroscopy ◽  
Acid Oxidation ◽  
Active Surface Area ◽  
Scanning Electron Micrographs ◽  
Crystal Surfaces ◽  
Active Centers ◽  
Single Crystal Surfaces ◽  
Electrode Potentials

Faceting and nanostructuring of polycrystalline gold electrodes by cathodic corrosion in concentrated potassium hydroxide electrolytes has been systematically studied at different electrode potentials. Current-potential curves for the restructured Au electrodes in 0.1 M H2SO4 show characteristic features of Au(111) facets in the double-layer and oxidation region. Thus, the modified Au electrodes adopt properties typically known for well-defined single crystal surfaces. Besides the preferential surface faceting, the electrochemically active surface area (EASA) is enhanced as a function of potential, concentration and time. Scanning electron micrographs show the formation of well-defined triangular pits and nanostructures with a specific orientation confirming the formation of (111)-facets. In this way, the behavior of single crystals is accompanied with the properties of nanoparticles which are of utmost interest in electrocatalysis and surface enhanced Raman spectroscopy (SERS). The electrocatalytic activity of the newly formed “Au(111)” surface from an Au wire has been tested towards the hydrogen evolution reaction (HER) and for the formic acid oxidation reaction (FAOR). The study of electrocatalytic reactions at these nanostructured electrodes allows to identify active centers, which are absent for extended single crystal surfaces. Adsorbed pyridine on the nanostructured Au electrodes directly shows SERS activity, while untreated polycrystalline Au is SERS-inactive. The use of cathodic corrosion of simple wires is a paradigm of SERS-applications in electrochemistry with clean Au electrodes that provide properties of Au(111) single crystals.

Tuning the surface structure and conductivity of niobium-doped rutile TiO2 single crystals via thermal reduction

2017 ◽  
Vol 19 (45) ◽  
pp. 30339-30350 ◽  
Author(s):  
D. Wrana ◽  
C. Rodenbücher ◽  
M. Krawiec ◽  
B. R. Jany ◽  
J. Rysz ◽  
...  
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
Structural Changes ◽  
High Vacuum ◽  
Thermal Reduction ◽  
Ultra High Vacuum ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Systematic Exploration ◽  
Niobium Doped

We report on the systematic exploration of electronic and structural changes of Nb-doped rutile TiO2(110) single crystal surfaces due to the thermoreduction under ultra-high vacuum conditions (without sputtering), with comparison to undoped TiO2(110) crystals.

Valence Band Electronic Structure of Cleaved Iron Oxide Single Crystals Studied by Resonant Photoemission

1988 ◽  
Vol 143 ◽  
Author(s):  
Robert J. Lad ◽  
Victor E. Henrich
Keyword(s):  
Electronic Structure ◽  
Iron Oxide ◽  
Synchrotron Radiation ◽  
Single Crystals ◽  
Valence Band ◽  
Final States ◽  
Crystal Surfaces ◽  
Resonant Enhancement ◽  
Single Crystal Surfaces ◽  
Resonant Photoemission

AbstractSynchrotron radiation has been used to perform resonant photoemission measurements across the 3p→3d photoabsorption threshold from cleaved FexO (x ≃0.945), Fe3O4, and α-Fe2O3 single crystal surfaces. The resonant enhancement of the Fe 3d photoelectrons allows the Fe 3d-derived final states in the valence band to be distinguished from the overlapping O 2p states. Using well-characterized single crystals, the distributions of Fe 3d-derived states associated with the ferrous (Fe2+) and ferric (Fe3+) cations have been identified. The Fe 3d-derived states are found to extend about 18 eV below the Fermi level in each oxide, which can be attributed to a significant amount of hybridization between the Fe 3d and O 2p orbitals.

scholarly journals An Affordable Option to Au Single Crystals Through Cathodic Corrosion of a Wire: Fabrication, Electrochemical Behavior, and Applications in Electrocatalysis and Spectroscopy

2020 ◽  
Author(s):  
Mohamed Elnagar ◽  
Johannes M. Hermann ◽  
Timo Jacob ◽  
Ludwig A. Kibler
Keyword(s):  
Single Crystal ◽  
Single Crystals ◽  
Surface Enhanced Raman Spectroscopy ◽  
Acid Oxidation ◽  
Active Surface Area ◽  
Scanning Electron Micrographs ◽  
Crystal Surfaces ◽  
Active Centers ◽  
Single Crystal Surfaces ◽  
Electrode Potentials

Faceting and nanostructuring of polycrystalline gold electrodes by cathodic corrosion in concentrated potassium hydroxide electrolytes has been systematically studied at different electrode potentials. Current-potential curves for the restructured Au electrodes in 0.1 M H2SO4 show characteristic features of Au(111) facets in the double-layer and oxidation region. Thus, the modified Au electrodes adopt properties typically known for well-defined single crystal surfaces. Besides the preferential surface faceting, the electrochemically active surface area (EASA) is enhanced as a function of potential, concentration and time. Scanning electron micrographs show the formation of well-defined triangular pits and nanostructures with a specific orientation confirming the formation of (111)-facets. In this way, the behavior of single crystals is accompanied with the properties of nanoparticles which are of utmost interest in electrocatalysis and surface enhanced Raman spectroscopy (SERS). The electrocatalytic activity of the newly formed “Au(111)” surface from an Au wire has been tested towards the hydrogen evolution reaction (HER) and for the formic acid oxidation reaction (FAOR). The study of electrocatalytic reactions at these nanostructured electrodes allows to identify active centers, which are absent for extended single crystal surfaces. Adsorbed pyridine on the nanostructured Au electrodes directly shows SERS activity, while untreated polycrystalline Au is SERS-inactive. The use of cathodic corrosion of simple wires is a paradigm of SERS-applications in electrochemistry with clean Au electrodes that provide properties of Au(111) single crystals.

Surface reactions observed by photoemission electron microscopy (PEEM)

1992 ◽  
Vol 50 (1) ◽  
pp. 286-287
Author(s):  
H.H. Rotermund
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Work Function ◽  
Chemical Reactions ◽  
Reaction Diffusion ◽  
Dynamic Processes ◽  
Clean Surface ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Photoemission Electron

Chemical reactions at a surface will in most cases show a measurable influence on the work function of the clean surface. This change of the work function δφ can be used to image the local distributions of the investigated reaction,.if one of the reacting partners is adsorbed at the surface in form of islands of sufficient size (Δ>0.2μm). These can than be visualized via a photoemission electron microscope (PEEM). Changes of φ as low as 2 meV give already a change in the total intensity of a PEEM picture. To achieve reasonable contrast for an image several 10 meV of δφ are needed. Dynamic processes as surface diffusion of CO or O on single crystal surfaces as well as reaction / diffusion fronts have been observed in real time and space.

Electronic and Vibrational Properties of Single Crystal Surfaces of NiAl

1986 ◽  
Vol 83 ◽  
Author(s):  
S.-C. Lui ◽  
J. M. Mundenar ◽  
E. W. Plummer ◽  
M. E. Mostoller ◽  
R. M. Nicklow ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Nearest Neighbor ◽  
Surface States ◽  
Active Surface ◽  
Atomic Displacement ◽  
Inelastic Electron ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Nial Alloy ◽  
Bulk Surface

ABSTRACTSurface and bulk electronic structure of the ordered NiAl alloy were measured using angle resolved photoelectron spectroscopy. The measured bulk d-bands (Ni like) were observed to be narrower than theoretically calculated d band widths which are 20 to 40% wider (depending upon what is used as a measure of the width). At least two surface states were observed on both the (110) and (111) surfaces. The nature of these surface states and their relationship to the bulk band structure is discussed. Dispersion of bulk phonons was measured by neutron scattering and fitted with a fourth nearest neighbor Born-von Karman model. Dipole active surface phonons on the (110) and (111) surfaces were observed by inelastic electron scattering and the frequencies also calculated assuming a truncated bulk surface. The calculated surface modes present a qualitative picture of the atomic displacement at each surface and also show that the surface phonon energy and intensity depends upon the structure of the surface.

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