ASTM_E_1523_-_15.pdf

Designation:E152315Standard Guide toCharge Control and Charge Referencing Techniques inX-Ray Photoelectron Spectroscopy1This standard is issued under the fixed designation E1523;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This guide acquaints the X-ray photoelectron spectros-copy(XPS)user with the various charge control and chargeshift referencing techniques that are and have been used in theacquisition and interpretation of XPS data from surfaces ofinsulating specimens and provides information needed forreporting the methods used to customers or in the literature.1.2 This guide is intended to apply to charge control andcharge referencing techniques in XPS and is not necessarilyapplicable to electron-excited systems.1.3 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.4 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2E673 Terminology Relating to Surface Analysis(Withdrawn2012)3E902 Practice for Checking the Operating Characteristics ofX-Ray Photoelectron Spectrometers(Withdrawn 2011)3E1078 Guide for Specimen Preparation and Mounting inSurface AnalysisE1829 Guide for Handling Specimens Prior to SurfaceAnalysis3.Terminology3.1 DefinitionsSee Terminology E673 for definitions ofterms used in XPS.3.2 Symbols:BEBinding energy,in eVBEcorrCorrected binding energy,in eVBEmeasMeasured binding energy,in eVBErefReference binding energy,in eVBEmeas,refMeasured Binding energy,in eV,of a reference lineFWHMFull width at half maximum amplitude of a peak in thephotoelectron spectrum above the background,in eVXPSX-ray photoelectron spectroscopycorrCorrection energy,to be added to measured bindingenergies for charge correction,in eV4.Overview of Charging Effects4.1 For insulating specimen surfaces,the emission of pho-toelectrons following X-ray excitation may result in a tempo-rary(or sometimes persistent)buildup of a positive surfacecharge caused by the photoelectric effect.Its insulating natureprevents the compensation of the charge buildup by means ofelectron conduction from the sample holder.This positivesurface charge changes the surface potential thereby shiftingthe measured energies of the photoelectron peaks to higherbinding energy.This binding energy shift may reach a nearlysteady-state value of between 2 and 5 eV for spectrometersequipped with nonmonochromatic X-ray sources.The surfacepotential charge and the resulting binding energy shift is,generally,larger for spectrometers equipped with monochro-matic X-ray sources because of the,generally,lower flux oflow-energy electrons impinging on the specimen surface.Thislower flux arises because focused,monochromatic X-raybeams irradiate only a portion of the specimen and not othernearby surfaces(for example,the specimen holder)that aresources of low-energy electrons.The absence of an X-raywindow in many monochromatic X-ray sources(or a greaterdistance of the specimen from the X-ray window)also elimi-nates another source of low-energy electrons.4.2 The amount of induced surface charge,its distributionacross the specimen surface,and its dependence on experimen-tal conditions are determined by several factors includingspecimen composition,homogeneity,magnitude of surfaceconductivity,total photoionization cross-section,surfacetopography,spatial distribution of the exciting X-rays,and1This guide is under the jurisdiction of ASTM Committee E42 on SurfaceAnalysis and is the direct responsibility of Subcommittee E42.03 on Auger ElectronSpectroscopy and X-Ray Photoelectron Spectroscopy.Current edition approved June 1,2015.Published June 2015.Originallyapproved in 1993.Last previous edition approved in 2009 as E1523 09.DOI:10.1520/E1523-15.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3The last approved version of this historical standard is referenced onwww.astm.org.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 availability of neutralizing electrons.Charge buildup is awell-studied(1,2)4,three dimensional phenomenon that occursalong the sample surface and into the material.The presence ofparticles on or different phases in the specimen surface mayresult in an uneven distribution of charge across the surface,aphenomenon known as differential c