Important; Frequency Adjustment; Leed Mode - OCI BDL800IR Instruction Manual

5.6.1

Important

 Open the AES software prior to powering up the LOA10-AES.
 Make sure the sample is grounded.
 Set the Ramp Generator End voltage higher than the Start voltage in the AES
software.
 When not measuring, keep the Input of the lock-in open as a transient voltage
might damage the input stage of the lock-in. Although, the input is protected by a
suppressor diode, for high transient voltages this might not be sufficient.
5.6.2

Frequency Adjustment

1. In order to run accurate AES measurements, a frequency of a modulation voltage
needs to be properly set because varying temperatures and humidity cause the filter
center frequency to drift. This is done by adjusting the Frequency Adjustment
trimmer located on the front panel of the LOA10-AES.
2. First, connect an oscilloscope to the output of the AUS30 and observe a sine wave at
2.9 kHz. This signal should be about 1 V (pp) at 10 V (pp) modulation, 50 μA beam
current, and 2 keV beam energy.
3. Turn the trimmer all the way to the left.
4. Follow by turning right until you find the maximum of the first inelastic peak.

5.7 LEED Mode

A diffraction pattern is created as a result of a primary electron beam reflecting off of a flat
surface at normal incidence. If a sample is properly aligned, parallel to the optics, a zero-zero
beam should not be observed as it is obscured by an electron gun assembly. An important
property of the zero-zero beam is that its reflected (screen) position is independent of the
primary beam energy. Other peaks converge onto the zero-zero beam (spot) as the beam en-
ergy increases and diverge from it when the energy decreases
unintended paths in the presence of electric and magnetic fields. Special care should be taken
in such situations.
A residual magnetic field in a laboratory is caused by power lines, ion pump magnets,
steel building construction, earth's magnetic field, and sometimes local geological structure.
Such field may seriously affect an accuracy of LEED experiments mainly in the low energy
range (≤ 50 eV) by deflecting primary and scattered electron beams. It also degrades resolu-
tion of the retarding field analyzer.
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This observation can be used to check whether the sample is flat with respect to the spectrometer.
24 Chapter 5 Operating Instructions
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. Electron beams may follow