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.

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).

Scanning Low-Energy Electron Diffraction Microscopy Combined with Scanning Tunnling Microscopy

1990 ◽  
Vol 48 (1) ◽  
pp. 302-303
Author(s):  
Takeo Ichinokawa
Keyword(s):  
Electron Diffraction ◽  
Electron Energy ◽  
High Vacuum ◽  
Low Energy ◽  
Energy Electron ◽  
Scanning Tunneling ◽  
Two Dimensional ◽  
Low Energy Electron Diffraction ◽  
Low Energy Electron ◽  
Auger Microscopy

A ultra-high vacuum scanning electron microscope (UHV-SEM) with a field emission gun (FEG) has been operated in an energy range of from 100 eV to 3 keV. A new technique of scanning low energy electron diffraction (LEED) microscopy has been added to the other techniques: scanning Auger microscopy (SAM), secondary electron microscopy, electron energy loss microscopy and the others available for the UHV-SEM. In addition to scanning LEED microscopy, a scanning tunneling microscope (STM) has been installed in the UHV-SEM-.The combination of STM with SEM covers a wide magnification range from 105 to 107 and is very effective for observation of surface structures with a high resolution of about 1 Å.A UHV-FEG-SEM is equipped in a chamber in which the vacuum is better than 2×10-10 Torr. A movable cylindrical mirror analyzer (CMA), a two dimensional detector of diffracted LEED beams, an ion gun and a deposition source are installed in this chamber. The concept of the scanning LEED microscope is comprised of two steps: (1) the formation of a selected area LEED pattern and (2) the generation of raster images with information contained in the diffraction pattern. In the present experiment, the LEED detector assembly shown in Fig.l has been used; it consists of two hemisherical grids, a two-stage channel-plate amplifier and a position-sensitive detector. The selection of one (or more) diffracted beam is performed electronically by a window using the two-dimensional analogue comparators. The intensity of a particular beam selected by the window modulates the brightness of the scanning image and a dark field image sensitive to the surface structure is formed. The experimental spatial resolutions of 150 Å and 500 Å have been attained at the primary electron energy 1 keV and 250 eV, respectively.

Inclusion of off-normal incidence data in a low-energy electron diffraction crystallographic analysis for the Cu(100)-(2 × 2)-S surface structure

1990 ◽  
Vol 68 (4-5) ◽  
pp. 353-356 ◽  
Author(s):  
H. C. Zeng ◽  
R. A. McFarlane ◽  
K. A. R. Mitchell
Keyword(s):  
Electron Diffraction ◽  
Surface Structure ◽  
Polar Angle ◽  
Normal Incidence ◽  
Crystallographic Analysis ◽  
Low Energy ◽  
Energy Electron ◽  
Low Energy Electron Diffraction ◽  
Low Energy Electron ◽  
Cu Interlayer

A low-energy electron diffraction (LEED) crystallographic analysis has been undertaken to assess the lateral and vertical relaxations for the Cu(100)-(2 × 2)-S surface structure. The study uses five normal-incidence beams and seven beams with an off-normal direction for a polar angle of incidence equal to 8°. Both lateral and vertical relaxations in the copper structure are small (0.03 Å or less) compared with the structure in bulk copper, but the senses are unchanged from the recent normal-incidence analysis (H. C. Zeng, R. A. McFarlane, and K. A. R. Mitchell, Phys. Rev. B, 39, 8000 (1989)). The new LEED-determined S—Cu bond length is 2.23 ± 0.06 Å, while the S to topmost Cu interlayer spacing is 1.28 ± 0.03 Å.

Dynamical effects of the surface potential barrier in very low energy electron diffraction

1983 ◽  
Vol 126 (1-3) ◽  
pp. A107
Author(s):  
J. Lopez ◽  
J.C. Le Bossé ◽  
C. Gaubert ◽  
R. Baudoing ◽  
Y. Gauthier
Keyword(s):  
Electron Diffraction ◽  
Potential Barrier ◽  
Surface Potential ◽  
Low Energy ◽  
Energy Electron ◽  
Low Energy Electron Diffraction ◽  
Low Energy Electron

Dynamical effects of the surface potential barrier in very low energy electron diffraction

1983 ◽  
Vol 126 (1-3) ◽  
pp. 286-293 ◽  
Author(s):  
J. Lopez ◽  
J.C. Le Bossé ◽  
C. Gaubert ◽  
R. Baudoing ◽  
Y. Gauthier
Keyword(s):  
Electron Diffraction ◽  
Potential Barrier ◽  
Surface Potential ◽  
Low Energy ◽  
Energy Electron ◽  
Low Energy Electron Diffraction ◽  
Low Energy Electron

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.

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