Changes in Surface Mechanical Properties Through Electrochemical Modifications

2001 ◽  
Vol 697 ◽  
Author(s):  
Martha M. McCann ◽  
Sean G. Corcoran
Keyword(s):  
Mechanical Properties ◽  
Mechanical Response ◽  
Lattice Mismatch ◽  
High Vacuum ◽  
Lessons Learned ◽  
Ultra High Vacuum ◽  
Discrete Control ◽  
Dislocation Densities ◽  
Dislocation Behavior ◽  
Stress States

AbstractThe mechanical response of materials can be dramatically altered by the presence of absorbed species on the surface. An electrochemical environment enables discrete control of the surface, keeping it clean (comparable to ultra-high vacuum) and inducing stable stress states. Applying a potential to the surface alters surface charge, which changes the surface free energy. Oxides are easily added or removed. Utilizing the phenomenon of underpotential deposition (UPD), one monolayer of metal can be added to a surface. The degree of lattice mismatch between the metal and the deposited monolayer will also vary the stress state of the surface. The changes in the mechanical properties of these highly controlled surfaces are measured by in-situ nanoindentation at various potentials. Nanoindentation of single crystals with very low dislocation densities allows careful observation of dislocation behavior with applied load. This enables the identification of dislocation mechanisms by quantifying the changes in mechanical properties under specific environments. Au has been extensively studied in electrochemistry literature; it is well behaved and well characterized. It is a model system that has demonstrated variation in mechanical properties in different electrochemical states. Lessons learned on Gold have also been applied to Zn and Ni systems.

New Insights on Superlow Friction Mechanisms of Hydrogenated Amorphous Carbon

2005 ◽  
Author(s):  
Julien Fontaine
Keyword(s):  
Mechanical Properties ◽  
Amorphous Carbon ◽  
Friction Mechanisms ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Critical Importance ◽  
Hydrogenated Amorphous Carbon ◽  
Friction Regime ◽  
Hydrogenated Amorphous

Some hydrogenated amorphous carbon (a-C:H) films have the peculiarity to exhibit coefficients of friction in the millirange, known as “superlow friction”, under inert environments like dry nitrogen or high vacuum. However, this “superlubricity” is only observed for some coatings and sometimes for very short duration. The role of tribofilm in the superlow friction regime observed on various a-C:H films sliding against steel pins has been investigated by performing experiments in ultra-high vacuum and hydrogen ambient. Tribofilm build-up appears to be controlled by interactions with oxide layers. Then, evolutions of the tribofilm will depend both on the composition of a-C:H film and on interactions with environment, through tribochemical reactions. Furthermore, the mechanical properties of the films are correlated with the achievement of superlow friction. All these results suggest that surface rheological properties are of critical importance in reaching superlow friction regime with a-C:H films.

Relationship Between Graded Layer Structures and Defects in Silicon-Germanium Virtual Substrates

2000 ◽  
Vol 648 ◽  
Author(s):  
Kazuki Mizushima ◽  
Ichiro Shiono ◽  
Kenji Yamaguchi ◽  
Naoki Muraki
Keyword(s):  
Surface Roughness ◽  
Silicon Germanium ◽  
High Vacuum ◽  
Chemical Vapor ◽  
Ultra High Vacuum ◽  
Vacuum System ◽  
Optimum Number ◽  
Threading Dislocation ◽  
Typical Sample ◽  
Dislocation Densities

AbstractSilicon-germanium virtual substrates have been synthesized by low-pressure chemical vapor deposition. We obtained threading dislocation densities ranging from 105 to 106 cm−2, surface roughness ranging from 1.5 to 4 nm, and also cross-hatch pattern densities, depending on the grading rate and top layer germanium composition. For the typical sample, which has a linear-graded structure with a grading rate of 20%/[µm, and germanium composition of 30 % at the top layer, we obtained dislocation densities of about 106 cm−2 and root mean squared surface roughness of about 3 nm. The obtained dislocation densities are equivalent with the virtual substrates synthesized by ultra-high vacuum system. On the other hand the surface roughness is superior to the typical reported values. In this study three kinds of structures, i.e. linear-graded, stepwise, and graded-step structures, were considered. We found the defects are effectively reduced by introduction of an optimum number of steps in the graded layer.

Enhanced Nucleation and Decreased Growth Rates of Cu2O in Cu0.5Au0.5 (001) Thin Films During in situ Oxidation

2005 ◽  
Vol 20 (7) ◽  
pp. 1902-1909 ◽  
Author(s):  
Liang Wang ◽  
Judith C. Yang
Keyword(s):  
Lattice Mismatch ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Oxide Growth ◽  
Inert Component ◽  
Initial Oxidation ◽  
In Situ Oxidation ◽  
Transmission Electron ◽  
Oxidation Behaviors

The initial oxidation behaviors of Cu–50 at.% Au (001) single-crystal thin film were studied by in situ ultra-high-vacuum transmission electron microscopy to model nano-oxidation of alloys with one oxidizing component and one inert component. The oxidation behaviors such as incubation time, oxide nucleation rate, oxide growth kinetics as well as nucleation activation energy were greatly changed by the addition of nonoxidizing Au. The reasons for these changes, such as Au segregation to the top surface, a decrease in Cu activity, and reduced lattice mismatch due to the addition of Au, were discussed, and a qualitative analysis of nucleation energetics was given.

Mechanical Properties of Metallic Interfaces

1989 ◽  
Vol 153 ◽  
Author(s):  
K. P. Walley ◽  
A. J. Gellman
Keyword(s):  
Thin Films ◽  
Mechanical Properties ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Molecular Films ◽  
Metallic Surfaces ◽  
Frictional Properties ◽  
Metallic Interfaces

AbstractWe have constructed an instrument designed to make measurements of interfacial mechanical properties under ultra-high vacuum conditions. The device has been configured to allow two metallic surfaces to be prepared and characterized independently within a single UHV chamber. The two can then be brought into contact to allow measurements of the frictional properties of their interface. In this manner we are able to study the frictional properties of metallic surfaces modified by the presence of mono-molecular films. The instrument is described in this paper as are the results of initial measurements performed on modified tungsten surfaces. In addition we address the question of why it is that such ultra-thin films can modify the mechanical properties of surfaces brought into contact under macroscopic loads.

In-Situ Transmission Elecron Microscopy (TEM) Study of the Nitridation of Basal Plane Sapphire by Reactive Molecular Beam Epitaxy (RMBE)

1997 ◽  
Vol 3 (S2) ◽  
pp. 475-476
Author(s):  
M. Yeadon ◽  
M.T. Marshall ◽  
J.M. Gibson
Keyword(s):  
Buffer Layer ◽  
Lattice Mismatch ◽  
High Vacuum ◽  
High Energy ◽  
Substantial Improvement ◽  
Ultra High Vacuum ◽  
Sapphire Surface ◽  
Group Iii ◽  
Flat Surfaces

Group III-nitride thin films are currently of great interest for use in wide-bandgap semiconductor applications including UV lasers and light emitting diodes (LEDs). Sapphire (a-Al2O3) is currently the substrate of choice for the growth of GaN despite a large lattice mismatch. Growth of high quality GaN epilayers typically involves the deposition of a buffer layer of either AIN or GaN at a temperature well below that used for the growth of the active GaN layer. It has been found empirically that nitridation of the sapphire surface with nascent nitrogen prior to growth of the buffer layer results in a substantial improvement in film quality. Using a novel ultra-high vacuum (UHV) in-situ TEM with in-situ RMBE, we have studied the nitridation of the (0001) sapphire surface using transmission and reflection electron microscopy (REM), reflection high energy electron diffraction (RHEED) and Auger electron spectroscopy (AES).An electron-transparent sapphire TEM sample was annealed at 1400°C for 12 hours in flowing oxygen, to form atomically flat surfaces for our investigation.

Heteroepitaxial Growth of MgO Films on NiO(100) Single Crystal Surfaces

1994 ◽  
Vol 357 ◽  
Author(s):  
S. Imaduddin ◽  
A.M. Davidson ◽  
R.J. Lad
Keyword(s):  
Single Crystal ◽  
Lattice Mismatch ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Heteroepitaxial Growth ◽  
Crystal Surfaces ◽  
Single Crystal Surfaces ◽  
Oxygen Anions ◽  
Mgo Layers

AbstractEpitaxial MgO layers were grown on cleaved NiO(100) single crystal surfaces. The less than 1% lattice mismatch between MgO and NiO allows almost ideal epitaxy of MgO at 100°C. The epitaxial films were created by dosing Mg onto stoichiometric NiO(100) both in ultra-high vacuum (UHV) and in an O2 atmosphere (5×10−7 Torr). Chemical interactions at the resulting interfaces were studied using XPS. When Mg is dosed onto NiO(100) in UHV, MgO forms by interacting with oxygen anions in the NiO substrate thereby reducing the nickel cations. Metallic Mg layers begin to form upon subsequent dosing. When Mg is deposited in O2, epitaxial MgO(100) layers grow to a thickness of at least 50Å as confirmed by in situ RHEED and LEED observations. Negligible intermixing between the MgO and NiO is observed during growth at 100°C and on subsequent annealing in UHV up to 600°C.

Defects in ErSi2/Si(111) epitaxial films

1990 ◽  
Vol 48 (4) ◽  
pp. 572-573
Author(s):  
C. Meneau D'Anterroches
Keyword(s):  
Lattice Mismatch ◽  
High Vacuum ◽  
Epitaxial Films ◽  
Zone Axis ◽  
Ultra High Vacuum ◽  
Epitaxial Relationship ◽  
Electronic Engineering ◽  
Transmission Electron ◽  
Diffraction Patterns

Silicides are studied in electronic engineering for their good metallic properties. Among them the group of rare earth silicides shows particular properties. Indeed, some of them, including ErSi2, crystallize in the AIB2 structure although they do not have the exact stoechiometry, their composition being about 1.7. Thus the physical properties and the influence of vacancies on the structure are studied.The film studied in this work was obtained by in-situ annealing, in ultra high vacuum, of a Si-Er film codeposited on a clean Si (111) substrate. Details are given by F. Arnaud d'Avitaya et al. The epitaxial relationship is (111 )Si//(001 )ErSi2 and (112)Si//(100)ErSi2. According to this orientation the lattice mismatch at the interface is - 1.3 %. The films were analysed using high resolution transmission electron microscopy : they are continuous when annealed at 900°C, and show some extra-spots in their diffraction patterns depending on the zone axis. Extra spots were observed along the {111} (3) and {112} zone axes, but not along {110} (4), We will focus in this paper on the {112}Si or {120}ErSi2 zone axis, the corresponding electron diffraction pattern being in Fig. 1.

Nanomechanics Using an Ultra-Small Amplitude AFM

2000 ◽  
Vol 649 ◽  
Author(s):  
Peter M. Hoffmann ◽  
Steve Jeffery ◽  
Ahmet Oral ◽  
Ralph A. Grimble ◽  
H. özgür Özer ◽  
...  
Keyword(s):  
Mechanical Response ◽  
High Vacuum ◽  
Interaction Force ◽  
Ultra High Vacuum ◽  
Atomic Scale ◽  
Resonance Amplitude ◽  
Molecular Ordering ◽  
Atomic Relaxation ◽  
New Type ◽  
Sample Separation

ABSTRACTA new type of AFM is presented which allows for direct measurements of nanomechanical properties in ultra-high vacuum and liquid environments. The AFM is also capable of atomic-scale imaging of force gradients. This is achieved by vibrating a stiff lever at very small amplitudes of less than 1 Å (peak-to-peak) at a sub-resonance amplitude. This linearizes the measurement and makes the interpretation of the data straight-forward. At the atomic scale, interaction force gradients are measured which are consistent with the observation of single atomic bonds. Also, atomic scale damping is observed which rapidly rises with the tip-sample separation. A mechanism is proposed to explain this damping in terms of atomic relaxation in the tip. We also present recent results in water where we were able to measure the mechanical response due to the molecular ordering of water close to an atomically flat surface.

Thin Pyrolytic Graphite Films for Electron Microscope Substrates

1971 ◽  
Vol 29 ◽  
pp. 226-227 ◽  
Author(s):  
George H. N. Riddle ◽  
Benjamin M. Siegel
Keyword(s):  
Vacuum Chamber ◽  
Pyrolytic Graphite ◽  
High Vacuum ◽  
Dark Field ◽  
Ultra High Vacuum ◽  
Graphite Substrate ◽  
Nickel Substrate ◽  
Routine Procedure ◽  
Field Electron Microscopy ◽  
Dark Field Electron

A routine procedure for growing very thin graphite substrate films has been developed. The films are grown pyrolytically in an ultra-high vacuum chamber by exposing (111) epitaxial nickel films to carbon monoxide gas. The nickel serves as a catalyst for the disproportionation of CO through the reaction 2C0 → C + CO2. The nickel catalyst is prepared by evaporation onto artificial mica at 400°C and annealing for 1/2 hour at 600°C in vacuum. Exposure of the annealed nickel to 1 torr CO for 3 hours at 500°C results in the growth of very thin continuous graphite films. The graphite is stripped from its nickel substrate in acid and mounted on holey formvar support films for use as specimen substrates.The graphite films, self-supporting over formvar holes up to five microns in diameter, have been studied by bright and dark field electron microscopy, by electron diffraction, and have been shadowed to reveal their topography and thickness. The films consist of individual crystallites typically a micron across with their basal planes parallel to the surface but oriented in different, apparently random directions about the normal to the basal plane.

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