1、Designation: E2859 11 (Reapproved 2017)Standard Guide forSize Measurement of Nanoparticles Using Atomic ForceMicroscopy1This standard is issued under the fixed designation E2859; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、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 The purpose of this document is to provide guidance onthe quantitative application of atomic force microscopy
3、(AFM)to determine the size of nanoparticles2deposited in dry form onflat substrates using height (z-displacement) measurement.Unlike electron microscopy, which provides a two-dimensionalprojection or a two-dimensional image of a sample, AFMprovides a three-dimensional surface profile. While the late
4、raldimensions are influenced by the shape of the probe, displace-ment measurements can provide the height of nanoparticleswith a high degree of accuracy and precision. If the particlesare assumed to be spherical, the height measurement corre-sponds to the diameter of the particle. In this guide, pro
5、ceduresare described for dispersing gold nanoparticles on varioussurfaces such that they are suitable for imaging and heightmeasurement via intermittent contact mode AFM. Genericprocedures for AFM calibration and operation to make suchmeasurements are then discussed. Finally, procedures for dataanal
6、ysis and reporting are addressed. The nanoparticles used toexemplify these procedures are National Institute of Standardsand Technology (NIST) reference materials containing citrate-stabilized negatively charged gold nanoparticles in an aqueoussolution.1.2 The values stated in SI units are to be reg
7、arded asstandard. No other units of measurement are included in thisstandard.1.3 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 determ
8、ine the applica-bility of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendatio
9、ns issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3E1617 Practice for Reporting Particle Size CharacterizationDataE2382 Guide to Scanner and Tip Related Artifacts in Scan-ning Tunneling Microscopy and Atomic Force Micros-co
10、pyE2456 Terminology Relating to NanotechnologyE2530 Practice for Calibrating the Z-Magnification of anAtomic Force Microscope at Subnanometer DisplacementLevels Using Si(111) Monatomic Steps (Withdrawn2015)4E2587 Practice for Use of Control Charts in StatisticalProcess Control2.2 ISO Standards:5ISO
11、181152 Surface Chemical AnalysisVocabularyPart 2: Terms Used in Scanning-Probe MicroscopyISO/IEC Guide 983:2008 Uncertainty of MeasurementPart 3: Guide to the Expression of Uncertainty in Mea-surement (GUM:1995)3. Terminology3.1 Definitions:3.1.1 For definitions pertaining to nanotechnology terms,re
12、fer to Terminology E2456.3.1.2 For definitions pertaining to terms associated withscanning-probe microscopy, including AFM, refer to ISO181152.1This guide is under the jurisdiction of ASTM Committee E56 on Nanotech-nology and is the direct responsibility of Subcommittee E56.02 on Physical andChemica
13、l Characterization.Current edition approved Aug. 1, 2017. Published August 2017. Originallyapproved in 2011. Last previous edition approved in 2011 as E2859 11. DOI:10.1520/E2859-11R17.2Having two or three dimensions in the size scale from approximately 1 nm to100 nm as in accordance with Terminolog
14、y E2456; this definition does not considerfunctionality, which may impact regulatory aspects of nanotechnology, but whichare beyond the scope of this guide.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of AST
15、MStandards volume information, refer to the standards Document Summary page onthe ASTM website.4The last approved version of this historical standard is referenced onwww.astm.org.5Available from International Organization for Standardization (ISO), ISOCentral Secretariat, BIBC II, Chemin de Blandonn
16、et 8, CP 401, 1214 Vernier,Geneva, Switzerland, http:/www.iso.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization est
17、ablished in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2 Definitions of Terms Specific to This Standard:3.2.1 agglomerate, nin nanotechnology, an assembly o
18、fparticles held together by relatively weak forces (for example,Van der Waals or capillary), that may break apart into smallerparticles upon processing, for example. E24563.2.1.1 DiscussionUsing imaging based techniques, suchas AFM, it is generally difficult to differentiate betweenagglomerates form
19、ed during the deposition process (that is,artifacts) and agglomerates or aggregates that pre-exist in thetest sample.3.2.2 aggregate, nin nanotechnology, a discrete assem-blage of particles in which the various individual componentsare not easily broken apart, such as in the case of primaryparticles
20、 that are strongly bonded together (for example, fused,sintered, or metallically bonded particles). E24563.2.2.1 DiscussionUsing imaging based techniques, suchas AFM, it is generally difficult to differentiate betweenaggregates and agglomerates.3.3 Acronyms:3.3.1 AFMatomic force microscopy3.3.2 APDM
21、ES3-aminopropyldimethylethoxysilane3.3.3 DIdeionized3.3.4 HEPAhigh efficiency particulate air3.3.5 NISTNational Institute of Standards and Technology3.3.6 PLLpoly-L-lysine3.3.7 RMreference material4. Summary of Practice4.1 This guide outlines the procedures for sample prepara-tion and the determinat
22、ion of nanoparticle size using atomicforce microscopy (AFM). An AFM utilizes a cantilever with asharp probe to scan a specimen surface. The cantilever beam isattached at one end to a piezoelectric displacement actuatorcontrolled by theAFM.At the other end of the cantilever is theprobe tip that inter
23、acts with the surface. At close proximity tothe surface, the probe experiences a force (attractive orrepulsive) due to surface interactions, which imposes a bendingmoment on the cantilever. In response to this moment, thecantilever deflects, and this deflection is measured using a laserbeam that is
24、reflected from a mirrored surface on the back sideof the cantilever onto a split photodiode. A schematic diagramof the system is shown in Fig. 1. The cantilever deflection ismeasured by the differential output (difference in responses ofthe upper and lower sections) of the split photodiode. Thedefle
25、ctions are very small relative to the cantilever thicknessand length. Thus, the probe displacement is linearly related tothe deflection. The cantilever is typically silicon or siliconnitride with a tip radius of curvature on the order of nanome-ters. More detailed and comprehensive information on th
26、eAFM technique and its applications can be found in thepublished literature (1, 2).64.2 Based on the nature of the probe-surface interaction(attractive or repulsive), an AFM can be selected to operate invarious modes, namely contact mode, intermittent contactmode, or non-contact mode. In contact mod
27、e, the interactionbetween the tip and surface is repulsive, and the tip literallycontacts the surface. At the opposite extreme, the tip interactswith the surface via long-range surface force interactions; thisis called non-contact mode. In intermittent contact mode (alsoreferred to as tapping mode),
28、 the cantilever is oscillated closeto its resonance frequency perpendicular to the specimensurface, at separations closer to the sample than in non-contactmode. As the oscillating probe is brought into proximity withthe surface, the probe-surface interactions vary from longrange attraction to weak r
29、epulsion and, as a consequence, theamplitude (and phase) of the cantilever oscillation varies.During a typical imposed 100-nm amplitude oscillation, for ashort duration of time, the tip extends into the repulsive regionclose to the surface, intermittently touching the surface andthereby reducing the
30、 amplitude. Intermittent contact mode hasthe advantage of being able to image soft surfaces or particlesweakly adhered to a surface and is hence preferred fornanoparticle size measurements.6The boldface numbers in parentheses refer to a list of references at the end ofthis standard.FIG. 1 Schematic
31、Illustration of AFM Measurement PrincipleE2859 11 (2017)24.3 A microscope feedback mechanism can be employed tomaintain a user definedAFM set point amplitude, in the case ofintermittent contact mode. When such feedback is operational,constant vibration amplitude can be maintained by displacingthe bu
32、ilt-in end of the cantilever up and down by means of thepiezo-actuator.NOTE 1Operation of an AFM with feedback off enables the interac-tions to be measured and this is known as force spectroscopy.This displacement directly corresponds to the height of thesample. A topographic image of the surface ca
33、n be generatedby rastering the probe over the specimen surface and recordingthe displacement of the piezo-actuator as a function of position.Although the lateral dimensions are influenced by the shape ofthe probe (see Guide E2382 for guidance on tip relatedartifacts), the height measurements can pro
34、vide the height ofnanoparticles deposited onto a substrate with a high degree ofaccuracy and precision. If the particles are assumed to bespherical, the height measurement corresponds to the diameteror “size” of the particle.4.4 Procedures for dispersing nanoparticles on various sur-faces such that
35、they are suitable for imaging and heightmeasurement via intermittent contact mode AFM are firstdescribed. The nanoparticles used to exemplify these proce-dures were National Institute of Standards and Technology(NIST) gold nanoparticle reference materials, RM 8011 (nomi-nally 10 nm), RM 8012 (nomina
36、lly 30 nm), and RM 8013(nominally 60 nm), all of which contained citrate-stabilizednegatively charged gold nanoparticles in an aqueous solution.4.5 Generic procedures for AFM calibration and operationto perform size measurements in intermittent contact mode arediscussed, and procedures for data anal
37、ysis and reporting areoutlined.5. Significance and Use5.1 As AFM measurement technology has matured andproliferated, the technique has been widely adopted by thenanotechnology research and development community to theextent that it is now considered an indispensible tool forvisualizing and quantifyi
38、ng structures on the nanoscale.Whether used as a stand-alone method or to complement otherdimensional measurement methods, AFM is now a firmlyestablished component of the nanoparticle measurement toolbox. International standards for AFM-based determination ofnanoparticle size are nonexistent as of t
39、he drafting of thisguide. Therefore, this standard aims to provide practical andmetrological guidance for the application of AFM to measurethe size of substrate-supported nanoparticles based on maxi-mum displacement as the probe is rastered across the particlesurface to create a line profile.6. Reag
40、ents6.1 Certain chemicals and materials may be necessary inorder to perform one or more of the steps discussed in thisguide, but the specific reagents used are at the discretion of thetester and may depend on which specific alternative proceduresare chosen or relevant for a particular application.6.
41、2 Adhesive tape, if needed to cleave mica substrates.6.3 Atomically flat gold (111) on mica, if needed as asubstrate material.6.4 Colloidal gold, citrate-stabilized in aqueous solution, ifneeded to test or validate sample preparation and measurementprocedures.6.5 Deionized water, filtered to 0.1 m,
42、as needed for samplepreparation or to rinse substrates.6.6 Ethanol, reagent or chromatographic grade, as neededto rinse substrates.6.7 HCl, concentrated (37 %), if needed to clean silicon (Si)substrates.6.8 H2O2, 30 % solution, if needed to clean Si substrates.6.9 Inert compressed gas source (for ex
43、ample, nitrogen,argon, or air), filtered to remove particles.6.10 Mica disc, if needed as a substrate material.6.11 Poly-l-lysine, solution (0.1 %), if needed for prepara-tion of functionalized substrates.6.12 Single crystal Si wafers, diced to appropriate size, ifneeded as a substrate material.7. A
44、pparatus7.1 Atomic Force Microscope, capable of makingz-displacement measurements at sub-nanoscale dimensions.7.2 Bath Ultrasonicator, as needed to clean substrates.7.3 Microcentrifuge (“Microfuge”), as needed for samplepreparation.7.4 RF Plasma Cleaner with O2, as needed to clean Sisubstrates.8. Pr
45、ocedure8.1 Nanoparticle DepositionFor AFM measurements,nanoparticle samples must be deposited on flat surfaces. Theroughness of the surface should be much less than the nominalsize of the nanoparticles (preferably less than 5 %) in order toprovide a consistent baseline for height measurements. High-
46、quality mica, atomically flat gold (111) (deposited on mica), orsingle crystal silicon can all be used as substrates to minimizethe effect of surface roughness on nanoparticle measurements.Example procedures are provided for depositing nanoparticleson these three substrates. The sample deposition pr
47、oceduresoutlined below were developed for use with negatively chargedcitrate-stabilized gold nanoparticles suspended in an aqueoussolution at a mass concentration nominally 50 g/g (as exem-plified by NIST RMs 8011, 8012, and 8013). The proceduresshould work with other nanoparticles that carry a nega
48、tivesurface charge or zeta potential, including, but not limited to,commercially available citrate-stabilized colloidal gold. Assuggested below, these procedures can also be applied topositively charged or neutral nanoparticles with some modifi-cation. Each procedure may require optimization by the
49、user inorder to obtain satisfactory deposition density and to minimizeartifacts such as agglomerate formation on the substrate orbuild-up of organic films resulting from additives that might bepresent in the solution phase.E2859 11 (2017)3NOTE 2Substrate preparation and sample deposition should be con-ducted in a manner that minimizes the potential for contamination andartifacts. For instance, to the extent possible, these operations should beconducted in a HEPA filtered clean bench or work area. Similarly,prepared samples should be stored in a manner that m
