Outgassing of CCD components in the vacuum

Components with strong outgassing

Contaminated CCD

We measured a CCD containing naked-eye visible contaminations on the chip. Since these deposits are extremely volatile, we used a long-time scan of one hour, which had to be started right after the insertion of the probe and therefore contained air pollution and impurities condensed on the mass spectrometer's sensor. To distinguish these elements from the CCD deposits, exactly the same procedure was performed on the following day with a clean CCD.

By qualitative and quantitative comparison of both these tests, we can obtain the atomic masses for the layer of deposits on the chip. However, for a perfect analysis, spectra of both CCDs must be subtracted. This is hardly possible with the appendant software, but could be carried out with EXCEL, for example (see in the annex for details).

At room temperature the following lines disappear from the clean chip significantly faster than from the contaminated one:

Line [amu]	Fragment ions
55	C₄H₇⁺
56	C₄H₈⁺ ?
57	C₄H₉⁺
69	CF₃⁺

During heating to 75° C these lines emerged for the contaminated CCD only:

Line [amu]	Fragment ions
53	C₄H₅⁺ ?
67	C₅H₇⁺ ?
71	(transient)

Additionally at 75° C the lines below disappeared significantly more slowly for the contaminated chip than for the clean one:

Line [amu]	Fragment ions
50	CF₂⁺
51	(not identifiable)
73	(not identifiable)

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Last update: Mar 15, 2004
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