The threshold energy for atom displacement in fcc metals

1990 ◽  
Vol 48 (4) ◽  
pp. 530-531
Author(s):  
Wilfried Sigle ◽  
Matthias Hohenstein ◽  
Alfred Seeger
Keyword(s):  
Growth Rate ◽  
Elevated Temperatures ◽  
Threshold Energy ◽  
Dislocation Loops ◽  
Absolute Minimum ◽  
Voltage Electron ◽  
Atom Displacement ◽  
Electron Microscopes ◽  
Fcc Metal

Prolonged electron irradiation of metals at elevated temperatures usually leads to the formation of large interstitial-type dislocation loops. The growth rate of the loops is proportional to the total cross-section for atom displacement,which is implicitly connected with the threshold energy for atom displacement, Ed . Thus, by measuring the growth rate as a function of the electron energy and the orientation of the specimen with respect to the electron beam, the anisotropy of Ed can be determined rather precisely. We have performed such experiments in situ in high-voltage electron microscopes on Ag and Au at 473K as a function of the orientation and on Au as a function of temperature at several fixed orientations.Whereas in Ag minima of Ed are found close to <100>,<110>, and <210> (13-18eV), (Fig.1) atom displacement in Au requires least energy along <100>(15-19eV) (Fig.2). Au is thus the first fcc metal in which the absolute minimum of the threshold energy has been established not to lie in or close to the <110> direction.

On the interpretation of dislocation-loop growth during in-situ high-voltage Electron Microscopy

1990 ◽  
Vol 48 (4) ◽  
pp. 532-533
Author(s):  
E. Holzäpfel ◽  
F. Phillipp ◽  
M. Wilkens
Keyword(s):  
Point Defect ◽  
Rate Equations ◽  
Rate Theory ◽  
Dislocation Loops ◽  
High Voltage Electron Microscopy ◽  
Vacancy Migration ◽  
Voltage Electron ◽  
Reaction Rate Theory ◽  
Defect Reactions

During in-situ radiation damage experiments aiming on the investigation of vacancy-migration properties interstitial-type dislocation loops are used as probes monitoring the development of the point defect concentrations. The temperature dependence of the loop-growth rate v is analyzed in terms of reaction-rate theory yielding information on the vacancy migration enthalpy. The relation between v and the point-defect production rate P provides a critical test of such a treatment since it is sensitive to the defect reactions which are dominant. If mutual recombination of vacancies and interstitials is the dominant reaction, vαP0.5 holds. If, however, annihilation of the defects at unsaturable sinks determines the concentrations, a linear relationship vαP is expected.Detailed studies in pure bcc-metals yielded vαPx with 0.7≾×≾1.0 showing that besides recombination of vacancies and interstitials annihilation at sinks plays an important role in the concentration development which has properly to be incorporated into the rate equations.

scholarly journals In Situ Ion Beam Research In Argonne's Intermediate Voltage Electron Microscope

1996 ◽  
Vol 439 ◽  
Author(s):  
Charles W. Allen ◽  
Edward A. Ryan
Keyword(s):  
Electron Microscope ◽  
Ion Irradiation ◽  
Noble Gas ◽  
Ion Beam ◽  
Voltage Electron ◽  
In Situ Experiments ◽  
User Facility ◽  
New Instrumentation ◽  
Electron Microscopes

AbstractSince Fall 1995, a state-of-the-art intermediate voltage electron microscope (IVEM) has been operational in the HVEM-Tandem Facility with in situ ion irradiation capabilities similar to those of the HVEM of the Facility. A 300 kV Hitachi H-9000NAR is interfaced to the two ion accelerators of the Facility, with a demonstrated point-topoint spatial resolution for imaging of 0.25 nm with the ion beamline attached to the microscope. The IVEM incorporates a Faraday cup system for ion dosimetry with measurement aperture 6.5 cm from the TEM specimen, which was described in Symposium A of the 1995 MRS Fall Meeting. The IVEM is now employed for a variety of in situ ion beam studies ranging from low dose ion damage experiments with GaAs, in which damage zones individual displacement cascades are observed, to implantation studies in metals, in which irradiation-induced noble gas precipitate mobility is studied in real time. In this presentation, the new instrumentation and its specifications will be described briefly, several basic concepts relating to in situ experiments in transmission electron microscopes will be summarized and examples of in situ experiments will be presented which exploit the experimental capabilities of this new user facility instrumentation.

A Novel Heating Technology for Ultra-High Resolution Imaging in Electron Microscopes

2009 ◽  
Vol 17 (4) ◽  
pp. 50-55 ◽  
Author(s):  
Lawrence F. Allard ◽  
Wilbur C. Bigelow ◽  
Steven A. Bradley ◽  
Jingyue(Jimmy) Liu
Keyword(s):  
Elevated Temperatures ◽  
New Technology ◽  
Carbon Film ◽  
Elevated Pressure ◽  
Stable Operation ◽  
Heater Element ◽  
Resolution Imaging ◽  
Electron Microscopes ◽  
Differential Pumping

Capabilities for in-situ studies of materials at elevated temperatures and under gaseous environments have received increasing attention in recent years [1]. With the advent of electron microscopes that provide routine imaging at the atomic level (e.g. aberration-corrected TEM and STEM instruments), it is of particular interest to be able to record images at high temperatures while retaining the inherent resolution of the microscope; that is, the resolution is not limited by drift in the heating holder or other instabilities associated with its operation. A number of commercial and experimental heating devices have been used over the years; some holders are designed with miniature furnaces that heat entire grids [2], while a more recent development used a tiny spiral filament coated with a carbon film as the heater element [3]. These devices, while very useful for some applications (particularly in “environmental microscopes” that employ differential pumping to allow gases at some elevated pressure to be injected around the specimen), are invariably not as stable as might be desired for sub-Ångström imaging experiments. They are also limited by the speed at which the sample can be heated to temperature for stable operation. In collaboration with Protochips Inc. (Raleigh, NC), our laboratory is developing a novel new technology for in-situ heating experiments that overcomes a number of performance problems associated with standard heating stage technologies [4].

Surface studies in UHV: Applications of High-resolution electron microscopy

1991 ◽  
Vol 49 ◽  
pp. 444-445
Author(s):  
M. R. McCartney ◽  
David J. Smith
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
High Vacuum ◽  
High Resolution Electron Microscopy ◽  
Plan View ◽  
Voltage Electron ◽  
Resolution Electron ◽  
Video Systems ◽  
Electron Microscopes

The examination of surfaces requires not only that they be free of adsorbed layers but the environment of the sample must also be maintained at high vacuum so that the surfaces remain clean. The possibility of resolving surface structures with atomic resolution has provided the motivation for optimizing intermediate and high voltage electron microscopes for this particular application. Electron microscopy offers a variety of techniques which have the capability of achieving atomic level detail of surfaces including plan-view imaging, REM and profile imaging. Operation at higher voltages permits reasonable pole piece dimensions thereby providing space for in situ studies yet still compatible with high resolution. Moreover, video systems can be attached which permit observation and recording of dynamic phenomena without compromising microscope performance.

Defect clusters of molybdenum alloys bombarded by HVEM

1978 ◽  
Vol 36 (1) ◽  
pp. 402-403
Author(s):  
N. Igata ◽  
A. Kohyama ◽  
H. Murakami ◽  
K. Itadani ◽  
H. Tsunakawa
Keyword(s):  
Incident Beam ◽  
In Situ Observation ◽  
Dislocation Loops ◽  
Defect Clusters ◽  
Voltage Electron ◽  
Molybdenum Alloys ◽  
Damage Process ◽  
Hot Rolled

As a simulation study of heavy radiation damage by neutrons, in-situ observation of damage process in molybdenum alloys was performed by a high voltage electron microscope. The objectives of this study are to clarify the processes of defect cluster nucleation and growth, and the role of alloying elements on these in the temperature range from 300K to 1300K.The used molybdenum alloys were Mo-(150-1000)at.ppm.C, Mo-(0.06-0.6)at.%Nb, MO-0.29at.%Hf, MO-(0.026-26)at.%Re and Mo-0.56at.%Ni. The used materials were electron-beam melted and hot rolled at 200-400°C and annealing was performed in the vacuum of l×l0-7torr. at 1800°C for 1.0 hr. The standard irradiation conditions were as follows,Accelerating voltage: 1250KV, Beam intensity: l-6×l019 e/cm2 sec, Incident beam direction: <100>, g-vector: {110},The density of defect clusters was determined by the thickness gradient method.The logarithmic density of interstitial dislocation loops, logNi, increased with the reciprocal irradiation temperature, 1/T. The relation between logNiand 1/T was divided into two Arrhenius type relations above and below 500K.

In-situ studies in the high-voltage Electron Microscope

1990 ◽  
Vol 48 (4) ◽  
pp. 504-505
Author(s):  
K.H. Westmacott
Keyword(s):  
Phase Transitions ◽  
High Voltage ◽  
Bulk Material ◽  
Outer Region ◽  
High Energy ◽  
Research Areas ◽  
Voltage Electron ◽  
High Voltage Electron ◽  
Electron Microscopes

The principal advantages of high voltage electron microscopes are the ability to 1) attain higher resolution by virtue of the shorter wavelength, and 2) penetrate thicker specimens to observe dynamic behavior representative of bulk material. Some recent examples of in-situ HVEM research, representing the latter category, will be summarized in this contribution, and future directions discussed. Included in the most active research areas are phase transitions, deformation, high temperature reactions and environmental cell studies.Irradiation with high energy electrons in an HVEM provides a convenient alternative to thermal treatments for inducing phase transitions in alloys. An illustration of how ordering or disordering of the same material can occur under electron irradiation is shown in Figure 1. In this example, a Pt7C ordered phase was formed in a Pt-C alloy at 500°C with a defocused beam (outer region) and subsequently disordered at 30°C with a focussed beam (inner spot).

An Environmental Transmission Electron Microscope for in situ Synthesis and Characterization of Nanomaterials

2005 ◽  
Vol 20 (7) ◽  
pp. 1695-1707 ◽  
Author(s):  
Renu Sharma
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Elevated Temperatures ◽  
Dark Field ◽  
In Situ Synthesis ◽  
Synthesis And Characterization ◽  
Transmission Electron ◽  
Electron Microscopes

The world of nanomaterials has become the real world for most applications in the area of nanotechnology. As postsynthesis handling of materials at the nanoscale level is impractical, nanomaterials must be synthesized directly as part of a device or circuit. The demands of nanotechnology have led to modifications in the design of transmission electron microscopes (TEMs) that enable in situ synthesis and characterization simultaneously. The environmental TEM (ETEM) is one such modified instrument that has often been used to follow gas–solid and/or liquid–solid interactions at elevated temperatures. Although the history and development of the ETEM, also called the controlled atmosphere or environmental cell TEM, is as old as transmission electron microscopy itself, developments in the design of medium-voltage TEMs have succeeded in bringing resolutions down to the subnanometer level. A modern ETEM equipped with a field-emission gun, energy filter or electron energy-loss spectrometer, scanning transmission electron microscopy coils, and bright-field and dark-field detectors can be a versatile tool for understanding chemical processes at the nanometer level. This article reviews the design and operations of a dedicated ETEM. Its applications range from the in situ characterization of reaction steps, such as oxidation-reduction and hydroxylation, to the in situ synthesis of nanomaterials, such as quantum dots and carbon nanotubes. Some examples of the current and the future applications for the synthesis and characterization of nanomaterials are also discussed.

In Situ Experiments in the High Voltage Electron Microscope

1976 ◽  
Vol 34 ◽  
pp. 428-429
Author(s):  
E. Paul Butler
Keyword(s):  
Growth Rate ◽  
Average Rate ◽  
Interlamellar Spacing ◽  
Cellular Growth ◽  
Voltage Electron ◽  
In Situ Experiments ◽  
Different Temperatures ◽  
Modified Equation ◽  
Good Agreement

Cellular decomposition in Ni-60wt%AuBoth cellular and spinodal decomposition into Au-rich and Ni-rich phases occur when this alloy is aged. In situobservations allowed single cell colonies to be studied as they grew through and consumed the spinodally decomposed matrix, and also provided values for the interlamellar spacing S, and growth rate G, at different temperatures. At 415°C cellular growth proceeded at an average rate of 57Å/s (Fig. 1) with S = 855Å and a compositional ratio K of 0.7. Substituting these values in the modified equation for cellular growth as if controlled by cell boundary diffusion, G = KDbδ/S2 with published values of Db and δ=5Å, gave G = 48Å/S, in good agreement with the experimentally observed growth rate.

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