IN SITU ULTRA HIGH VACUUM HIGH ENERGY ELECTRON DIFFRACTION STUDIES. Final Report.

1989 ◽

Vol 47 ◽

pp. 462-463

Author(s):

D. Loretto ◽

J. M. Gibson ◽

S. M. Yalisove

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Electron Diffraction ◽

High Vacuum ◽

High Energy ◽

Energy Electron ◽

Ultra High Vacuum ◽

Ex Situ ◽

Transmission Electron

The silicides CoSi2 and NiSi2 are both metallic with the fee flourite structure and lattice constants which are close to silicon (1.2% and 0.6% smaller at room temperature respectively) Consequently epitaxial cobalt and nickel disilicide can be grown on silicon. If these layers are formed by ultra high vacuum (UHV) deposition (also known as molecular beam epitaxy or MBE) their thickness can be controlled to within a few monolayers. Such ultrathin metal/silicon systems have many potential applications: for example electronic devices based on ballistic transport. They also provide a model system to study the properties of heterointerfaces. In this work we will discuss results obtained using in situ and ex situ transmission electron microscopy (TEM).In situ TEM is suited to the study of MBE growth for several reasons. It offers high spatial resolution and the ability to penetrate many monolayers of material. This is in contrast to the techniques which are usually employed for in situ measurements in MBE, for example low energy electron diffraction (LEED) and reflection high energy electron diffraction (RHEED), which are both sensitive to only a few monolayers at the surface.

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Modifications of a JEOL 2000EX TEM for insSitu surface studies

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100149039 ◽

1993 ◽

Vol 51 ◽

pp. 640-641

Author(s):

Michael T. Marshall ◽

Xianghong Tong ◽

J. Murray Gibson

Keyword(s):

Electron Diffraction ◽

Surface Science ◽

Film Growth ◽

High Vacuum ◽

High Energy ◽

Energy Electron ◽

Ultra High Vacuum ◽

Transmission Electron ◽

Fundamental Insight

We have modified a JEOL 2000EX Transmission Electron Microscope (TEM) to allow in-situ ultra-high vacuum (UHV) surface science experiments as well as transmission electron diffraction and imaging. Our goal is to support research in the areas of in-situ film growth, oxidation, and etching on semiconducter surfaces and, hence, gain fundamental insight of the structural components involved with these processes. The large volume chamber needed for such experiments limits the resolution to about 30 Å, primarily due to electron optics. Figure 1 shows the standard JEOL 2000EX TEM. The UHV chamber in figure 2 replaces the specimen area of the TEM, as shown in figure 3. The chamber is outfitted with Low Energy Electron Diffraction (LEED), Auger Electron Spectroscopy (AES), Residual Gas Analyzer (RGA), gas dosing, and evaporation sources. Reflection Electron Microscopy (REM) is also possible. This instrument is referred to as SHEBA (Surface High-energy Electron Beam Apparatus).The UHV chamber measures 800 mm in diameter and 400 mm in height. JEOL provided adapter flanges for the column.

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Studies of the tungsten-oxygen surface reaction by means of reflexion high energy electron diffraction

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1971.0121 ◽

1971 ◽

Vol 323 (1555) ◽

pp. 523-539 ◽

Cited By ~ 8

Keyword(s):

Electron Diffraction ◽

Gas Phase ◽

High Vacuum ◽

High Energy ◽

Simple Relation ◽

Energy Electron ◽

Ultra High Vacuum ◽

High Energy Electron ◽

Oxide Interface ◽

High Vacuum Environment

The reactions between both (100) and (110) surfaces of tungsten and oxygen have been studied in an ultra-high vacuum environment by means of reflexion mode high energy electron diffraction. Particular attention has been paid to changes in interfacial geometry owing to faceting which occurs on the (100) surface, and oxide nucleation which occurs on both faces. The faceting of the (100) face is shown to be more complicated than had previously been supposed, the faceted surface being composed of {211} planes which are themselves faceted into {110} planes. The activation energy for the degradation of facets in a vacuum has been measured as 6.5 ± 1.5 eV, greatly in excess of values reported for the formation of facets. It is suggested that faceting arises from the evaporation of oxide molecules. At temperatures below 1025 K tungsten trioxide nuclei form on both the (100) and (110) surfaces when exposed to oxygen. The exposures needed to form nuclei are much greater for the (110) surfaces than for the (100). Nuclei also form on (100) surfaces which have been previously faceted by heating in oxygen at temperatures above 1025 K. In this case the exposures needed to produce nuclei are characteristic of the (110) surface. The epitaxial relationships between the oxide and the metal have been determined. A simple relation has been found to hold. It is postulated that the metal plane at the oxide interface is not necessarily that which was originally exposed to the gas phase.

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