[3dem] Possible influence of construction

Tue May 5 07:33:35 PDT 2015

Dear Hiro:

In general the method to separate different sources of instability is frequency analysis.  You need to measure the frequencies that affect the microscope, and then separately with specialized sensors the various disturbances. I used in the past an analog-to-digital converter from National Instruments, a seismic-grade accelerometer (for vibrations), a Gauss meter (for EMI), a low-frequency microphone (for acoustics), and a pico-amp meter (for ground loops).

What we did to measure the frequencies that directly impact the microscope is to put the instrument into probe mode, and put the probe on a sharp edge (usually at the specimen plane, but we also measured the constituent frequencies of the gun alone with the SA aperture, for example).  The harmonics affecting the microscope will precess the probe about the edge, so if you attach a DAQ directly to the video out of your microscope, you can collect a long-run series of the measured intensity (we usually sampled at 10 - 40 kHz with about a million samples). Then you just take the Fourier transform of the data and you have your power spectrum.  Because the probe moves in 2-D and you have a 1-D object you do get a lot of frequency multi-modes, but this is relatively easy to see.  In general we saw low-frequency peaks (< 10 Hz), the mains (60 Hz) and multi-modes of it up to 360 Hz, the turbo-pumps (at about 700 Hz), and the high-voltage tank (at ~20 kHz).

Some details are provided here:

https://www.researchgate.net/publication/260165368_Evaluating_Long-Term_Stability_and_Transient_Disturbances_of_a_TEM

If you don't have a ResearchGate account send me an email off-list and I'll attach a copy. I also have further examples if desired.

A word of warning: GIFs newer than the Tridiem cannot be run in Streak-mode anymore.  Gatan appears to be doing some mains-frequency (50-60 Hz) compensation and the Quatums will not operate any faster than that through the Gatan scripting or the Gatan API interfaces.

Ground vibration is very difficult to mitigate without moving the instrument, or at the very least installing pneumatic or pizeo-electric isolators.  EMI can be reduced by enclosing the microscope in a mu-metal box (mu-metal is a very high susceptability nickel alloy). Alternatively you can remove one frequency with Helmholtz coils.  However, I would caution that ground-loops are usually a bigger problem than EMI.

Sincerely,

Robert

--
Robert McLeod, Ph.D.
Center for Cellular Imaging and Nano Analytics (C-CINA)
Biozentrum der Universität Basel
Mattenstrasse 26, 4058 Basel
Office: +41.061.387.3225
robert.mcleod at unibas.ch<mailto:robert.mcleod at unibas.ch>
robert.mcleod at bsse.ethz.ch<mailto:robert.mcleod at ethz.ch>
robbmcleod at gmail.com<mailto:robbmcleod at gmail.com>
________________________________
From: 3dem [3dem-bounces at ncmir.ucsd.edu] on behalf of kunihiro uryu [kuryu at mail.rockefeller.edu]
Sent: Tuesday, May 05, 2015 4:05 PM
To: 3dem at ncmir.ucsd.edu
Subject: [3dem] Possible influence of construction

Our institution is going to start a construction which will last a few years. I would imagine that the construction will have a negative influence on TEM and SEM operations, but can not tell the magnitude of the impact since the construction has not started yet. In particular, one of the TEMs (Tecnai G2 120kV) is closer to the construction site within 100 feet (30m) and does not have electro-magnetic field or vibration cancellation system.

I would like to get your opinion and experiences on the issue:

1) What problems did you encounter on the SEM and TEM operation during a long term construction?

2) Were you able to distinguish field and vibration issues?

3) Were you able to mitigate the problems? If so, how?

4) Could you recommend an independent consulting service company to assess the vibration and field problems before contacting companies specializing in the installation of anti-field and anti-vibration system for EMs?

We appreciate your advice in advance.

Regards,
Hiro

------
Kunihiro Uryu, Ph.D.,
Research Assistant Professor
Director of Electron Microscopy
Resource Center (EMRC)
RRB Rm120
The Rockefeller University
1230 York Ave., Box 230
New York, NY 10065

--
Robert McLeod, Ph.D.
Center for Cellular Imaging and Nano Analytics (C-CINA)
Biozentrum der Universität Basel
Mattenstrasse 26, 4058 Basel
Office: +41.061.387.3225
robert.mcleod at unibas.ch<mailto:robert.mcleod at unibas.ch>
robert.mcleod at bsse.ethz.ch<mailto:robert.mcleod at ethz.ch>
robbmcleod at gmail.com<mailto:robbmcleod at gmail.com>
________________________________
From: 3dem [3dem-bounces at ncmir.ucsd.edu] on behalf of kunihiro uryu [kuryu at mail.rockefeller.edu]
Sent: Tuesday, May 05, 2015 4:05 PM
To: 3dem at ncmir.ucsd.edu
Subject: [3dem] Possible influence of construction