Electron diffraction in UHV SEM, REM, and TEM

1994 ◽  
Vol 52 ◽  
pp. 594-595
Author(s):  
J. A. Venables ◽  
C. J. Harland ◽  
P. A. Bennett ◽  
T. E. A. Zerrouk
Keyword(s):  
Electron Diffraction ◽  
Surface Science ◽  
Incidence Angle ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Local Structures ◽  
Surface Reconstructions ◽  
Adsorbed Atoms ◽  
Low Energy Electron ◽  
Electron Microscopes

Electron diffraction techniques are widely used in Surface Science, with the main aim of determining atomic positions in surface reconstructions and the location of adsorbed atoms. These techniques require an Ultra-high vacuum (UHV) environment. The use of a focussed beam in UHV electron microscopes in principle allows such techniques to be applied on a microscopic scale. Most obviously this has been achieved in the Low Energy Electron Microscope (LEEM), where the corresponding diffraction technique, LEED, can now be used to investigate local areas with different surface structures, and to follow both temperature and time evolution of these local structures. Some other geometries can be used to achieve similar goals. If the incident energy is raised, the incidence angle has to be moved from normal towards glancing, so that the 'perpendicular' energy is kept within the LEED range of 10-100 eV. Several reflection (REM) and scanning (SEM) instruments have been built with energies between 5 and lOOkeV. In general, the addition of RHEED to an UHV-SEM with Auger Electron Spectroscopy (AES) forms a very useful tool in Surface Science.

Modifications of a JEOL 2000EX TEM for insSitu surface studies

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.

The formation of a gold/silicon alloy by electron-beam heating of codeposited thin films

1988 ◽  
Vol 46 ◽  
pp. 496-497
Author(s):  
R. Sharma ◽  
W. Robison ◽  
L. Eyring
Keyword(s):  
Thin Films ◽  
Electron Diffraction ◽  
Semiconductor Device ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
X Ray Diffraction ◽  
Semiconductor Interface ◽  
Low Energy Electron ◽  
Electron Beam Heating ◽  
High Resolution Microscopy

Studies of metal-semiconductor interactions have been of great interest in recent years because of the need to understand the behavior of semiconductor device junctions. The gold-silicon system has been studied by Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). An amorphous gold si 1icide is assumed to form at the metal-semiconductor interface. Different Au silicides are reported to be formed after heat treatment of Au films on a silicon substrate in ultra-high vacuum. Similar results have been observed for bulk samples by x-ray diffraction. The exact process of the diffusion of reactants and structure of the silicides formed is still being debated. Studies of the system by electron diffraction and high resolution microscopy is reported here.Thin films of Au/Si (200-300 Å) were deposited on a (100) NaCl crystal face by evaporating Au and Si simultaneously at the same rate in a vacuum of 10-9 Torr at room temperature.

Mirror Electron Microscope-Low Energy Electron Diffraction for Studies of Surface Ordering and Melting

1990 ◽  
Vol 208 ◽  
Author(s):  
W. N. Unertl ◽  
C. S. Shern
Keyword(s):  
Electron Diffraction ◽  
Surface Potential ◽  
High Vacuum ◽  
Normal Incidence ◽  
Low Energy ◽  
Energy Electron ◽  
Ultra High Vacuum ◽  
Objective Lens ◽  
Low Energy Electron Diffraction ◽  
Low Energy Electron

ABSTRACTMirror Electron Microscopy – Low Energy Electron Diffraction (MEMLEED) combines a LEED with MEM in a single simple instrument for studies of surface processes such as phase transitions and premelting under ultra-high vacuum (uhv) conditions. In MEMLEED, 5–20 keV primary electrons are decelerated by an electrostatic mirror-objective lens in which the sample is the mirror element. In the MEN mode, electrons are reflected just above the surface, reaccelerated through the objective lens and imaged. Contrast is due to variations in both surface potential and topography. Current uhv instruments have lateral resolution of about 1 μm. In the LEED mode, 0-100 eV electrons strike the sample at near normal incidence. Diffracted electrons are accelerated through the objective lens. Beam spacings in the imaged diffraction pattern are proportional to k11 and beams do not move as the incident energy is varied. MEMLEED has intrinsically higher transfer width and is less sensitive to magnetic fields near the sample than conventional LEED. Design considerations for uhv instruments are discussed. Applications to the study of order-disorder transitions, premelting phenomena, and to measurements of changes in surface potential are described.

Electron spectroscopy in SEM and STEM

1990 ◽  
Vol 48 (2) ◽  
pp. 378-379
Author(s):  
J. A. Venables ◽  
G. G. Hembree ◽  
C.J. Harland
Keyword(s):  
Surface Science ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Scanning Transmission ◽  
Low Energy Electrons ◽  
Electron Microscopes ◽  
A New Technique ◽  
Auger Microscopy ◽  
Electron Imaging ◽  
Analytic Signals

Low energy electrons, in the energy range 0-2 keV, are very useful in surface science. Both secondary (0-100 eV nominally) and Auger (50-2 keV) electrons can be used as analytic signals in ultra-high vacuum (UHV) scanning (SEM) and scanning transmission (STEM) electron microscopes. This paper briefly reviews some ongoing projects, which are aimed at improving the spatial resolution and information content of these signals.Both secondary electron imaging (SEI) and Auger electrons spectroscopy (AES) have a long history. Reviews of AES and its microscopic counterpart scanning Auger microscopy (SAM) have been given previously in this International Conference Series; over the intervening period AES/SAM instruments have become widely available commercially. Simply biassing the sample up to a few hundred volts (-ve) has lead to a new technique (biassed-SEI) which is sensitive at the sub-monolayer level. In general biassing the sample is a useful additional experimental variable. It can be used to visualize thin films and surface topography, including steps; it can also be used to distinguish spectral features (eg Auger peaks) from the sample from those due to stray electrons, and to place such features in the best energy region for the electron spectrometer.

scholarly journals Surface crystallography with low-energy electron diffraction

1993 ◽  
Vol 442 (1914) ◽  
pp. 61-72
Keyword(s):  
Electron Diffraction ◽  
High Vacuum ◽  
High Energy ◽  
Low Energy ◽  
Energy Electron ◽  
Ultra High Vacuum ◽  
X Ray ◽  
Low Energy Electron Diffraction ◽  
Low Energy Electron ◽  
Surface Crystallography

Bragg’s 1913 publication of the principles of X-ray crystallography came only a year after von Laue’s discovery of X-ray diffraction from crystals. Structure determination (of small molecules) with high-energy electron diffraction followed by just three years the 1927 discovery of electron diffraction by Davisson and Germer. By contrast, low-energy electron diffraction (LEED) would require four more decades before yielding its first structure determinations (of surfaces) around 1970. The delay was primarily due to the need for ultra-high vacuum and to a lesser extent to the need for a suitable theory to model multiple scattering. This review will sketch the development of surface crystallography by LEED and describe its principles and present capabilities.

scholarly journals Growth of germanium on Au(111): formation of germanene or intermixing of Au and Ge atoms?

2017 ◽  
Vol 19 (28) ◽  
pp. 18580-18586 ◽  
Author(s):  
Esteban D. Cantero ◽  
Lara M. Solis ◽  
Yongfeng Tong ◽  
Javier D. Fuhr ◽  
María Luz Martiarena ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Scanning Tunneling Microscopy ◽  
High Vacuum ◽  
Low Energy ◽  
Energy Electron ◽  
Ultra High Vacuum ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Low Energy Electron Diffraction ◽  
Low Energy Electron

We studied the growth of Ge layers on Au(111) under ultra-high vacuum conditions from the submonolayer regime up to a few layers with Scanning Tunneling Microscopy (STM), Direct Recoiling Spectroscopy (DRS) and Low Energy Electron Diffraction (LEED).

In situ TEM sample preparation for surface-sensitive plane view imaging

1991 ◽  
Vol 49 ◽  
pp. 642-643
Author(s):  
R. Ai ◽  
D.N. Dunn ◽  
T.S. Savage ◽  
J.P. Zhang ◽  
L.D. Marks
Keyword(s):  
Sample Preparation ◽  
Surface Science ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
In Situ Tem ◽  
Preparation Technique ◽  
Surface Imaging ◽  
Resolution Electron ◽  
Electron Microscopes ◽  
Plane View

The recent development of ultra high vacuum high resolution electron microscopes has made it possible to use an electron microscope to study surface structures with atomic resolution. Although surface images of Au(110) 2x11 and Si(111) 7x72 reconstructions have been obtained, no standard TEM sample preparation technique for surface imaging has been developed for routine uses. In conventional surface science, the common method of producing an UHV clean sample is a combination of ion sputtering and annealing; can this process be used to produce TEM samples for surface imaging. Our studies show that clean, well order TEM samples can be achieved by this approach.

scholarly journals A Leed Investigation of (111) Oriented Si, Ge and GaAs Surfaces Following Pulsed Laser Irradiation

1980 ◽  
Vol 1 ◽  
Author(s):  
D. M. Zehner ◽  
J. R. Noonan ◽  
H. L. Davis ◽  
C. W. White ◽  
G. W. Ownby
Keyword(s):  
Electron Diffraction ◽  
Ruby Laser ◽  
High Vacuum ◽  
Pulsed Laser ◽  
Low Energy ◽  
Ultra High Vacuum ◽  
Surface Structures ◽  
Low Energy Electron Diffraction ◽  
Low Energy Electron ◽  
Pulsed Laser Irradiation

ABSTRACTThe low energy electron diffraction (LEED) patterns obtained from clean (111) oriented Si, Ge and GaAs single crystals subsequent to their irradiation with the output of a pulsed ruby laser in an ultra-high vacuum (UHV) environment suggest that metastable (1×1) surface structures are produced in the regrowth process. Conventional LEED analyses of the Si and Ge surfaces suggest that they terminate in registry with the bulk but that the two outermost interlayer spacings differ from those of the bulk. For the case of Si these changes are a contraction of 25.5 ± 2.5% and an expansion of 3.2 ± 1.5% between the first and second and second and third layers respectively.

Atomic-level imaging of the surface structure of Ag2O

1984 ◽  
Vol 42 ◽  
pp. 656-657
Author(s):  
William Krakow
Keyword(s):  
High Vacuum ◽  
Atomic Level ◽  
Ultra High Vacuum ◽  
Research Groups ◽  
Resolution Electron ◽  
Surface Reconstructions ◽  
Order Of Magnitude ◽  
High Resolution Electron Microscope ◽  
Saturated Structure ◽  
Transmission And Reflection

In recent years electron microscopy has been used to image surfaces in both the transmission and reflection modes by many research groups. Some of this work has been performed under ultra high vacuum conditions (UHV) and apparent surface reconstructions observed. The level of resolution generally has been at least an order of magnitude worse than is necessary to visualize atoms directly and therefore the detailed atomic rearrangements of the surface are not known. The present author has achieved atomic level resolution under normal vacuum conditions of various Au surfaces. Unfortunately these samples were exposed to atmosphere and could not be cleaned in a standard high resolution electron microscope. The result obtained surfaces which were impurity stabilized and reveal the bulk lattice (1x1) type surface structures also encountered by other surface physics techniques under impure or overlayer contaminant conditions. It was therefore decided to study a system where exposure to air was unimportant by using a oxygen saturated structure, Ag2O, and seeking to find surface reconstructions, which will now be described.

A theory of contamination in electron microscopes by surface diffusion

1978 ◽  
Vol 36 (1) ◽  
pp. 116-117
Author(s):  
J.T. Fourie
Keyword(s):  
Electron Beam ◽  
Surface Diffusion ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Physical Parameters ◽  
Carbon Compounds ◽  
Hydrocarbon Molecules ◽  
Electron Microscopes ◽  
Primary Electrons ◽  
Long Chain

Contamination in electron microscopes can be a serious problem in STEM or in situations where a number of high resolution micrographs are required of the same area in TEM. In modern instruments the environment around the specimen can be made free of the hydrocarbon molecules, which are responsible for contamination, by means of either ultra-high vacuum or cryo-pumping techniques. However, these techniques are not effective against hydrocarbon molecules adsorbed on the specimen surface before or during its introduction into the microscope. The present paper is concerned with a theory of how certain physical parameters can influence the surface diffusion of these adsorbed molecules into the electron beam where they are deposited in the form of long chain carbon compounds by interaction with the primary electrons.

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