{"id":2727,"date":"2020-02-26T15:14:16","date_gmt":"2020-02-26T23:14:16","guid":{"rendered":"https:\/\/www.rbdinstruments.com\/blog\/?p=2727"},"modified":"2023-02-14T10:07:16","modified_gmt":"2023-02-14T18:07:16","slug":"model-290-hot-cold-module-leakage-current","status":"publish","type":"post","link":"https:\/\/www.rbdinstruments.com\/blog\/model-290-hot-cold-module-leakage-current\/","title":{"rendered":"Model 290 Hot\/Cold module leakage current"},"content":{"rendered":"\n

The 10-325 specimen stage, which is commonly used on PHI Physical Electronics 5600 through 5800 XPS X-ray photo-electron spectrometer surface analysis systems, is often equipped with the model 290 Hot\/Cold module.<\/p>\n\n\n\n

The design of the Model 290 Hot\/Cold module incorporates some zirconium oxide ceramics to electrically and thermally isolate the specimen holder from the specimen stage. Zirconium oxide has a very low thermal conductivity<\/a> that is about 10% of the thermal conductivity of the more common alumina (aluminum oxide) ceramic material used on many UHV optics units. Zirconium oxide is a good choice for hot or cold specimen stages.<\/p>\n\n\n\n

Over time, though, the evaporation\nof materials from specimens, as well as the evaporation of the filament on the\nModel 290, can coat the zirconium oxide ceramics. This coating can cause the specimen\nsample holder to become resistive to ground, which in turn affects the accuracy\nof target current measurements.  The\nleakage current of a coated ceramic might be several hundred nano amps.   This means that only target currents above\nthat several hundred nano amps value would be measurable.   ISS or\nstatic SIMS (both options on XPS systems) need the ion current to be set in the\nrange of 1 to 2 nA.  And aligning the monochromator\nrequires measuring currents of 3 nA or less. If the specimen stage leakage\ncurrent is high, then it would be impossible to accurately measure or set those\ncurrents. <\/p>\n\n\n\n

To test your target leakage current, simply measure the target current using the +90V bias box and picoammeter without any electron, ion, or X-ray source turned on.   Typically, the leakage current will be just a few 10s of picoamps.  If the leakage current is much higher than low picoamps, the zirconium ceramics shown in the image below may be coated and should be replaced the next time the system is up to air for maintenance.<\/p>\n\n\n\n

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