ASTM_E_2382_-_04_2012.pdf

Designation:E238204(Reapproved 2012)Standard Guide toScanner and Tip Related Artifacts in Scanning TunnelingMicroscopy and Atomic Force Microscopy1This standard is issued under the fixed designation E2382;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 All microscopes are subject to artifacts.The purpose ofthis document is to provide a description of commonlyobserved artifacts in scanning tunneling microscopy(STM)and atomic force microscopy(AFM)relating to probe motionand geometric considerations of the tip and surface interaction,provide literature references of examples and,where possible,to offer an interpretation as to the source of the artifact.Because the scanned probe microscopy field is a burgeoningone,this document is not meant to be comprehensive but ratherto serve as a guide to practicing microscopists as to possiblepitfalls one may expect.The ability to recognize artifactsshould assist in reliable evaluation of instrument operation andin reporting of data.1.2 A limited set of terms will be defined here.A fulldescription of terminology relating to the description,operation,and calibration of STM and AFM instruments isbeyond the scope of this document.1.3 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.2.Referenced Documents2.1 ASTM Standards:2E1813 Practice for Measuring and Reporting Probe TipShape in Scanning Probe Microscopy3.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 artifactany feature of an image generated by anAFM or STM that deviates from the true surface.Artifacts canhave origins in sample preparation,instrument hardware/software,operation,post processing of data,etc.3.1.2 imagesurface topography represented by plottingthe z value for feature height as a function of x and y position.Typically the z height value is derived from the necessary zvoltage applied to the scanner to allow the feedback value toremain constant during the generation of the image.The“image”is therefore a contour plot of a constant value of thesurface property under study(for example,tunneling current inSTM or lever deflection in AFM).3.1.3 tipthe physical probe used in either STM or AFM.For STM the tip is made from a conductive metal wire(forexample,tungsten or Pt/Ir)while for AFM the tip can beconductive(for example,doped silicon)or non-conductive(forexample,silicon nitride).The important performance param-eters for tips are the aspect ratio,the radius of curvature,theopening angle,the overall geometrical shape,and the materialof which they are made.3.1.4 cantilever or leverthe flexible beam onto which theAFM tip is placed at one end with the other end anchoredrigidly to the microscope.The important performance param-eters for cantilevers are the force constant(expressed in N/m)and resonance frequency(expressed in kHz typically).Thesevalues will depend on the geometry and material properties ofthe lever.3.1.5 scannerthe device used to position the sample andtip relative to one another.Generally either the tip or sample isscanned in either STM or AFM.The scanners are typicallymade from piezoelectric ceramics.Tripod scanners use threeindependent piezo elements to provide motion in x,y,and z.Tube scanners are single element piezo materials that providecoupled x,y,z motion.The important performance parametersfor scanners are the distance of movement per applied volt(expressed as nm/V)and the lateral and vertical scan ranges(expressed in microns).3.1.6 scan anglethe angle of rotation of the x scan axisrelative to the x-axis of the sample3.1.7 tip characterizera special sample used to determinethe geometry of the tip.The tip in question is used to image thecharacterizer.The image then becomes an input to an algorithmfor determining the tip geometry.1This guide is under the jurisdiction of ASTM Committee E42 on SurfaceAnalysis and is the direct responsibility of Subcommittee E42.14 on STM/AFM.Current edition approved Nov.1,2012.Published December 2012.Originallyapproved in 2004.Last previous edition approved in 2004 as E2382 04.DOI:10.1520/E2382-04R12.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 3.2 Abbreviations:3.2.1 AFMatomic force microscopy(microscope).Werefer here to contact mode AFM as opposed to non-contacttechniques.3.2.2 STMscanning tunneling microscopy(microscope).4.Significance and Use4.1 This compilation is limited to artifacts observed inscanning tunneling microscopes a