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SPA-RHEED
Spot Profile Analysis RHEED
The SPA-RHEED is an instrument for spot profile and energy analysis of diffracted electrons
. An octupole deflector in front of an aperture is used to scan the diffracted electron pattern. A suppressor electrode behind the aperture suppresses secondary electrons. A second
octupole was added to the electron gun RG15. This enable one to independently choose the incident and final angle at the sample, thus defining the momentum transfer of the electrons.
A
k-space resolved measurement of reflected electrons is then possible.
The electron energy analyser CSA200HV is placed behind the aperture to performe EELS-
spectroscopy of the diffracted electrons.
The SPA-RHEED system is operated with the power supplies Electron Source, Electron Beam Control and Analyser Control.
The system consists of:
- The RHEED gun RG15 with a double octopole-deflector. The electron beam is focussed
onto the screen or detector. It can be rocked by the double octopole-deflector to give different angles of incidence onto the sample without sample rotation.
- The deflector double octopole. Electrons starting at the sample with definite angles are
deflected in a way that they reach the aperture parallel to the detectors axis. This gives a reproducible transmission of all electrons through the suppressor optics.
- The detector that is mounted on a retraction mechanism. The detector can be retracted
to directly observe the RHEED patterns or extended for automatically recording of RHEED spots or scans in reciprocal space.
The detector consists of:
- the aperture wheel to select the angle resolution,
- the suppressor electrode that either suppresses secondary electrons or focusses the
electrons onto the entrance slit of the deflector,
- the "in line" channeltron for electron detection in SPA-modus and
- the 90°-deflector to deflect the electron into the electron energy analyser
- The transfer lens that focusses the electrons from the exit slit of the deflector onto the entrance slit of the energy analyser.
- The electron energy analyser CSA200 HV
All parts of the ELS-SPA-RHEED system are fully mu-metal shielded. To gain best resolution
and stability the sample region must also be shielded to reduce AC and DC magnetic fields.
References:
B. Müller, M. Henzler, Rev. Sci. Instr. 66 (1995) 5232
B. Müller, V. Zielsack, Phys. Rev. Lett. 79 (1997) 4393
Specifications
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Electron Source
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RHEED- gun RG15
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Electron energy analyser
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CSA200 HV
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Analysers mounting
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DN CF100, rotatable
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Detector
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"in line" channeltron, mounted on a retraction mechanism. Gain: 10E8 in pulse-counting mode.
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Mounting of detector with retraction mechanism
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DN CF150
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Aperture Ų
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2 mm, 300 µm, 100 µm, 30 µm and 10 µm .
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Suppressor cutoff energy (varies with the aperture size).
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>1.5 eV
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Magnetic shielding
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mu metal
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Bakeout temperature
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180°C
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Orientation
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any
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If you have questions concerning the products presented here, specify the information you need and send a message to FOCUS.
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