The review chapter by Thomas.8 Concepts from these paperswill be referenced frequently in the results and discussion.The reader is referred to reviews and summaries1,3 5,8 fora more complete guide to the literature. Measurements on this type ofspecimen are used to determine how well the sample surfacepotential tracks changes in the electron flood gun voltage.Several important and general aspects of non-homogeneoussamples have been discussed by Barr,3 in various parts ofthe Cazaux papers,4,5 by Tielsch and co-workers6,7 and in The other class of test samplesinvolves conducting (metal or carbon) dots deposited onan insulating SiO2 substrate. The first sample type consists of an oxidized layeron a conducting substrate, and is used to test relationshipsof the binding energies of the coating to that of the sub-strate (substrate referencing). In this paper we examine the control of surface poten-tial for two different types of non-homogeneous samplesusing two instruments with advanced charge compensationsystems.
#Ungrounded xps peak shift series
In spite ofthese efforts and the general understanding now available,a recent analysis of a round-robin study of charge stabiliza-tion and referencing measurements for a series of insulatingsamples2 concluded that the current ability to make reliableand reproducible measurements is unsatisfactory and effortsto improve measurement methodology are needed. The ISOTechnical Committee 201 on Surface Chemistry is nearly fin-ished preparing a new standard (ISO 19318) Surface chemicalanalysisX-ray photoelectron spectroscopyReporting of meth-ods used for charge control and charge correction.
The ASTM Guide 1523Standard Guide to Charge Control and Charge Referenc-ing Techniques in X-Ray Photoelectron Spectroscopy1 ispublished annually and updated every 3 years. Many workers, and both ASTM and the International Organi-zation for Standards (ISO) have developed or are developinga guide or standard in this area. E-mail: sponsor: US Department of Energy. Baer, Pacific Northwest NationalLaboratory, Richland, WA, USA. The practicalimpact of charge accumulation for XPS, Auger electron spec-troscopy, electron microscopy and even x-ray and electronlithography has led to the study of charging phenomena byĬorrespondence to: D. Although most XPS spectrometers have methods tocompensate charge build-up at a surface, the challenge ofboth controlling the charging to the extent possible and thenfinding an adequate way to obtain desired information fromthe analysis (by a method of charge referencing or otheranalysis method) remains with the analyst. These phenomena combine to decrease signalintensities, broaden peak linewidths and shift the energieswhere photoelectron or Auger electron peaks are measured.They complicate both the experimental measurement andthe ability to make precise determination of binding energies(BEs). However, these phenomena are due not only tomeasurement-related formation of electric fields due to thebuild-up of surface or near-surface electrical charge, butalso to characteristics of a specific sample such as a lackof Fermi level coupling to the spectrometer or the presenceof charge or defect sites at interfaces in the specimen priorto analysis. The surface analysis of insulating or other electricallyisolated specimens (or parts of specimens) by x-ray pho-toelectron spectroscopy (XPS) is often complicated by acollection of phenomena categorically labeled as samplecharging. KEYWORDS: XPS charge compensation electron flood gun charge referencing aluminium oxide Finally, the ability of interface charge to shift specimen potentials andmeasured binding energies demonstrates fundamental limitations to the absolute accuracy of bindingenergy measurements, but also remind us that charging phenomena can be used to obtain importantinformation about the sample. However, experiments involving both flood gun use and specimengrounding demonstrate that peak broadening and shifting can occur when two (or more) potentials arepresent in the region of analysis. Results demonstrate that two newer types of charge compensation systems haveimproved performance in relation to some previous flood gun systems, while reaffirming the concept thata primary objective of charge compensation is to find conditions for which the surface potential of thespecimen is as uniform as possible. The ability of charge compensation methods to control surface potential is examined for two types ofnon-homogenous samples: a small conducting dot on an insulating substrate and an insulating thin filmon a conductive substrate. Received Revised 22 July 2002 Accepted 22 July 2002 Pacific Northwest National Laboratory, Richland, WA, USA
Use and limitations of electron flood gun control ofsurface potential during XPS: two non-homogeneoussample typesĭ.
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