ErLEED 150

LEED Optics for Structural Analysis and AES with Miniature Electron Gun for Increased Field of View, High Transmission Grid Assembly and Digital or Analog Control Unit

Low Energy Electron Diffraction (LEED) is one of the most powerful methods to determine surface structures. Analysis of LEED patterns and intensities provides the size and shape of the surface unit cell, the degree of order and detailed atomic structure with a precision of the order of picometers. To exploit the full power of the technique, equally capable instrumentation is required.  

The SPECS reverse view ErLEED optics together with highly sophisticated acquisition and analysis solutions provide the experimenter with many unique advantages present in no other commercial unit. In order to guarantee the highest possible quality and performance of each optics, great importance is attached to the selection of the materials and components as well as to the quality of the mechanical and electrical manufacturing.

The miniature electron gun allows a full view of the diffraction pattern. It is completely light shielded in order to avoid stray light and thus to be able to measure quantitative LEED I(E) curves or spot profiles. Two types of filaments are available: Thoria coated Iridium hairpin and LaB6 single crystal. The Thoria coated Iridium filaments allow the operation of the gun at pressures of up to 10-4 mbar. All filaments are easily replaceable in the users laboratory. The high transmission grid assemblies are made of Gold coated Molybdenum ensuring long term rigidity of the hemispheres as well as an uniform work function and non-magnetic characteristics. The optics is available in a 2, 3 and 4 grid version.  ErLEED 150 is mounted on a DN150CF flange (8“ CF, 203 mm OD). A z-retraction mechanism allows the optics to be extended or withdrawn from a restricted working area. Z-travel of 50 mm or 100 mm is available. The optics can be protected by an integral multi-segment shutter mounted in front of all grids. All ErLEED optics are fully tested under UHV conditions before delivery. A detailed test certificate is supplied with each optics.

KEY FEATURES

  • High performance optics for LEED and AES
  • Mounted on DN150CF (8“OD) flange
  • Light shielded miniature electron gun
  • 50 or 100 mm z-retraction (optional)
  • Integral multi-segment shutter (optional)
  • Digitally or analog controlled power supplies with independent HV modules
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MADE FOR THESE METHODS

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SPECIFICATIONS

ErLEED 150
Mounting
Mounting Flange

NW63CF (4.5 ")

Insertion Depth

300 mm

Z-Retraction

optional

Shutter

optional

Power Supply

400 W

Operation
Screen Voltage

Primary Energy

Operating Pressure

< 10-7 - 10-5 mbar

Optional Accessories

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PUBLICATIONS

  1. (2000) Three-dimensional band mapping by angle-dependent very-low-energy electron diffraction and photoemission: Methodology and application to Cu

    A method of band mapping providing full control of the three-dimensional k is described in detail. Angle-dependent very-low-energy electron diffraction is applied to determine the photoemission final states along a Brillouin zone symmetry line parallel to the surface; photoemission out of these states is then utilized to map the valence bands in the constant-final-state mode. The method naturally incorporates the non-free-electron and excited-state self-energy effects in the unoccupied band, resulting in an accuracy superior over conventional techniques. Moreover, its intrinsic accuracy is less limited by lifetime broadening. As a practical advantage, the method provides access to a variety of lines in the Brillouin zone using only one crystal surface. We extensively tested the method on Cu. Several new aspects of the electronic structure of this metal are determined, including non-free-electron behavior of unoccupied bands and missing pieces of the valence band.



    V.N. Strocov, R. Claessen, G. Nicolay, S. Hüfner, A. Kimura, A. Harasawa, S. Shin, A. Kakizaki, P. O. Nilsson, H. I. Starnberg, P. Blaha
    Phys. Rev. B. 63, 205108 ff.
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  2. (1998) Absolute Band Mapping by Combined Angle-Dependent Very-Low-Energy Electron Diffraction and Photoemission: Application to Cu

    We present an experimental method to determine the electronic E(k) band structure in crystalline solids absolutely, i.e., with complete control of the three-dimensional wave vector k. Angle-dependent very-low-energy electron diffraction is first applied to determine the unoccupied states whose k is located on a high-symmetry line parallel to the surface. Photoemission via these states, employing the constant-final-state mode, is then utilized to map the valence bands along this line. We demonstrate the method by application to Cu, and find significant deviation from free-electron-like behavior in the unoccupied states, and from density-functional theory in the occupied states.



    V. N. Strocov, R. Claessen, G. Nicolay, S. Hüfner, A. Kimura, A. Harasawa, S. Shin, A. Kakizaki, P. O. Nilsson, H. I. Starnberg, P. Blaha
    Phys. Rev. Lett. 81 (22), pp. 4943ff.
    Read more
  3. (1996) Electrostatic ray-tracing calculations in VLEED

    The present ray-tracing scheme employs the electrostatic potential calculation by finite-difference solution of the Laplace equation in three dimensions. The run time reduction, achieved by using successively refined grids and optimizing the iteration cycle, allows one to perform calculations on a personal computer. The code is applied to a standard four-grid LEED optics, operated in the retarding field mode, to calculate electron trajectories in the case of off-symmetry incidence. In particular, dependences of incidence on the sample rotation and primary energy are calculated. A simple empirical formula is derived, which allows accurate experimental determination of without extensive calculations. Ray-tracing calculations are further applied to analyse the influence of residual asymmetries of the electron optics.



    V.N. Strocov
    Meas. Sci. Technol. 7, pp. 1636-1642
    Read more
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SPARE PARTS

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Product image
Product description
Article No.
 
Set of ceramics for ErLEED 150/100 4-grids

Set of Ceramics for SCREEN/grid package. Comprising 4 x ceramic stubs plus all distance ceramics

2060006052
ErLEED screen for optics DN150CF (8")

ErLEED screen for optics DN150CF (8") coated with conductive layer and phosphor

2000203120
LaB6 cathode for ErLEED-optics

LaB6 cathode for ErLEED-optics, for long lifetime and small heating temperature, only for use in UHV. (do not use this filament in non baked vacuum and when using oxygen within the vacuum chamber)

2000204120
Nut for retraction of ErLEED

Nut for spindle of retraction of ErLEED 150 or 100

2060014098
Rotary feedthrough ErLEED 150

Rotary feedthrough ErLEED 150 for Z-retraction ( with coupling)

2100012246
Thoria coated Iridium-Filament

Thoria coated Iridium-Filament for ErLEED , standard filament also for work in non baked vacuum.

2000204110
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DOWNLOADS

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