ISO/TR 14187:2020
(Main)Surface chemical analysis — Characterization of nanostructured materials
Surface chemical analysis — Characterization of nanostructured materials
This document provides an introduction to (and some examples of) the types of information that can be obtained about nanostructured materials using surface-analysis tools (Clause 5). Of equal importance, both general issues or challenges associated with characterizing nanostructured materials and the specific opportunities or challenges associated with individual methods are identified (Clause 6). As the size of objects or components of materials approaches a few nanometres, the distinctions among "bulk", "surface" and "particle" analysis blur. Although some general issues relevant to characterization of nanostructured materials are identified, this document focuses on issues specifically relevant to surface chemical analysis of nanostructured materials. A variety of analytical and characterization methods will be mentioned, but this report focuses on methods that are in the domain of ISO/TC 201 including Auger Electron Spectroscopy, X‑ray photoelectron spectroscopy, secondary ion mass spectrometry, and scanning probe microscopy. Some types of measurements of nanoparticle surface properties such as surface potential that are often made in a solution are not discussed in this Report. Although they have many similar aspects, characterization of nanometre-thick films or a uniform collection of nanometre-sized particles present different characterization challenges. Examples of methods applicable to both thin films and to particles or nano-sized objects are presented. Properties that can be determined include: the presence of contamination, the thickness of coatings, and the chemical nature of the surface before and after processing. In addition to identifying the types of information that can be obtained, the document summarizes general and technique-specific Issues that must be considered before or during analysis. These include: identification of needed information, stability and probe effects, environmental effects, specimen-handling issues, and data interpretation. Surface characterization is an important subset of several analysis needs for nanostructured materials. The broader characterization needs for nanomaterials are within the scope of ISO/TC 229 and this document has been coordinated with experts of TC 229 Joint Working Group (JWG) 3. This introduction to information available about nanomaterials using a specific set of surface-analysis methods cannot by its very nature be fully complete. However, important opportunities, concepts and issues have been identified and many references provided to allow the topics to be examined in greater depth as required.
Analyse chimique des surfaces - Caractérisation des matériaux nanostructurés
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TECHNICAL ISO/TR
REPORT 14187
Second edition
2020-06
Surface chemical analysis —
Characterization of nanostructured
materials
Analyse chimique des surfaces - Caractérisation des matériaux
nanostructurés
Reference number
ISO/TR 14187:2020(E)
©
ISO 2020
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ISO/TR 14187:2020(E)
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ISO/TR 14187:2020(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 1
4 Characterization of nanostructured materials with surface analysis methods .3
4.1 Introduction . 3
4.2 Electron Spectroscopies (AES and XPS) . 6
4.3 Ion-beam surface analysis methods (SIMS and LEIS) .13
4.4 Scanning probe microscopy .15
4.5 Surface characterization of carbon nanostructures.16
5 Analysis considerations, issues and challenges associated with characterization of
nanostructured materials: Information for the analyst .17
5.1 Introduction .17
5.2 General considerations and analysis challenges .17
5.3 Physical properties .19
5.4 Particle stability and damage: influence of size, surface energy and confluence of
energy scales .19
5.4.1 Crystal structure .20
5.4.2 Damage and probe effects . .21
5.4.3 Time and environment .21
5.5 Sample mounting and preparation considerations .26
5.6 Specific considerations for analysis of nanostructured materials using XPS, AES,
SIMS and SPM .27
5.6.1 Introduction .27
5.6.2 Issues related to application of XPS to nanomaterials .27
5.6.3 Issues related to the application of AES to nanostructured materials .30
5.6.4 Issues related to application of SIMS to nanoparticles .30
5.6.5 Issues related to the application of scanning probe methods to nanoparticles .32
6 General characterization needs and opportunities for nanostructured materials .33
Bibliography .34
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ISO/TR 14187:2020(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
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on the ISO list of patent declarations received (see www .iso .org/ patents).
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iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 201, Surface chemical analysis,
Subcommittee SC 7, Electron spectroscopies.
This second edition cancels and replaces the first edition (ISO/TR 14187:2011), which has been
technically revised.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
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ISO/TR 14187:2020(E)
Introduction
[1]
As engineered nanomaterials of many types play an increasing role in many different technologies ,
international organizations (including ISO, ASTM, the International Bureau of Weights of Measures
(BIPM), Consultative Committee for Amount of Substance: Metrology in Chemistry (CCQM) and the
[1]
Organization for Economic Cooperation and Development (OECD)) are working to identify critical
[2]
properties and measurements that must be understood to adequately and reproducibly define the
nature of the materials being used.
A large percentage of any nanomaterial is associated with a surface or interface. Therefore, surface
composition and chemistry have been identified as being part of a minimum set of chemical parameters
needed to characterize nanomaterials and it would naturally seem that the wide range of tools
developed for surface characterization could or should be routinely applied to these materials. Two
different issues, however, have limited the impact of traditional surface analysis tools in some areas
of nanoscience and nanotechnology. First, many of the tools do not have sufficient spatial resolution in
three dimensions needed to analyse individual nanostructured materials (or, equivalently, variations of
composition within that material). For this reason, some researchers do not consider application of the
tools even though they can often provide very important information. Second, surface analytical (and
other) tools are often applied to nanostructured materials without appropriately considering several
analytical challenges or issues that these materials present. Such challenges include environmentally
altered behaviours of nanoparticles (including effects of making measurements in vacuum), time-
dependent characteristics of nanostructured materials, the influence of particle shape on analysis
results, and the increased possibility of altering the structure or composition of the nanomaterial by
the incident radiation (typically electrons, X-rays, or ions) during the analysis.
[3]
As noted by others including Linkov et al. there are new challenges associated with understanding
and characterizing nanomaterials, “the study of nanostructures and nanomaterials requires special
protocols that take into account the physical [and chemical] phenomena that occur in nanosized
systems.” This document gives information on these important issues. The report first describes the
types of information that can be obtained about nanostructured materials, sometimes using analytical
approaches beyond those in standard applications. Second, the report examines the technical challenges
generally faced when applying surface analysis tools (and often other tools) for characterization of
nanostructured materials as well as those specific to each technique.
Because of the expanding use of nanostructured materials in research, development, and commercial
applications as well as their natural presence in air, surface, and ground water, there is an increasing
need to understand the properties and behaviours of nanostructured materials as they are synthesized
or as they evolve in a particular environment. The novel and unusual properties of nanostructured
materials excite scientists, technologists and the general public. However, the sometimes surprising
properties of many of these materials raise reproducibility, analysis or characterization issues that
[4-6]
sometimes are unexpected by analysts, scientists, and production engineers . There is an increasing
awareness of reproducibility issues in many areas of science including those associated with materials,
[7-11]
biological, computational, and chemical research . Inherent characteristics of nanoparticles (NPs)
that make them interesting and potentially useful also make them susceptible to reproducibility
challenges associated with their production, characterization, and delivery. Inconsistencies and
[5-12]
conflicts caused by these challenges have stimulated editorials and commentaries , scientific news
[4,15-18]
items, and journal articles . Careful analysis, including surface analysis as described in this
report, along with data records such as described in ISO 20579-4 for preparation of nano-objects for
[19,20]
surface analysis can help establish the provenance of a batch of nano-objects providing a tool to
address nano-object reproducibility issues.
Potential health and environmental concerns related to materials with unusual or unique properties
increase the need to understand the chemical, physical and biological properties of these materials
throughout their life cycle. It is now recognized that some early reports on the properties of
nanoparticles and other nanostructured materials, including their toxicity and environmental stability,
[13]
were based on inadequate characterizations . In some cases, important characterizations appear not
[21,22]
to have been attempted or reported . A March 2006 article in Small Times magazine described a
[13]
workshop designed to identify roadblocks to nanobiotech commercialization at which several experts
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ISO/TR 14187:2020(E)
reported that many of the important physical characteristics needed to understand the physical and
chemical properties of nanoparticles were not reported and apparently often unmeasured, especially in
assessments of particle toxicity. The article further notes that the changes that these particles undergo
when exposed to the environment where they are stored or used are especially important and usually
unknown. In many cases, nanoparticles are coated with surfactants or contaminants, and these are
often not well characterized and sometimes not adequately identified. As a result, the validity of the
conclusions may be questionable. Inadequate characterization of the surface chemistry of nanoparticles
[5,22]
has been identified as one of the areas where appropriate characterization is often lacking . This
issue was identified also by the OECD Working Party on Manufactured Nanomaterials (WPMN) and
new projects are launched under the umbrella of the Malta Initiative. One of them is the “Identification
and quantification of the surface chemistry and coatings on nano- and microscale materials” where
surface chemical analysis will substantially contribute.
The ISO definition of a nano-object (ISO/TS 80004-1:2015) is that, in at least one dimension, the size
of the object or structure must be approximately 100 nm or less. Considerable attention is being given
to the characterization of nanosized-objects (particles, rods or other shapes) that might be released
into the environment and a set of minimum characterization requirements for nanoparticles for use in
[2]
toxicity studies has been identified . However, the needs for nanomaterials characterization include
the wide variety of nanostructured materials that are used in computers, as sensors, in batteries or fuel
cells and many other types of applications. Nonetheless, the minimum characterization requirements
for nanoparticles can be generalized to a wider range of materials and potential applications as shown
in Table 1.
Surface-analysis methods of various forms (described later) can provide information that relates to many
elements in Table 1 including those that appear obvious (such as surface composition and chemistry) but
also includes particle or component size, presence of surface impurities, nature of surface functionality
(including acidity), surface structure/morphology, near-surface variation of composition (both laterally
and with depth, coating/film thickness, and electronic properties of nanostructures/films.
Surface characterization is only a subset of several nanomaterials analysis needs that are being examined
by ISO/TC 229. This report on surface chemical analysis methods prepared by ISO/TC 201/SC 7 has
been prepared in coordination with the overall characterization needs identified by experts in TC 201
and TC 229 as well as awareness of the objectives being addressed by ISO/TC 229. This document
describes the information that can be obtained (and by which techniques), and examines some of the
issues and challenges faced when performing such analyses.
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ISO/TR 14187:2020(E)
Table 1 — Physical and chemical properties for characterization of nanostructured materials
Items in bold font are properties for which surface chemical analysis can provide useful information, as described
in this document.
What does the material look like?
— Particle/grain/film/structural unit size(s) /size distribution
— Grain, particle, film morphology (shape, layered, roughness, topography)
— Agglomeration state/aggregation (e.g., do particles stick together)
What is the material made of?
— Bulk composition (including chemical composition and crystal structure)
— Bulk purity (including levels of impurities)
— Elemental, chemical and/or phase distribution (including surface composition and surface impurities)
What factors affect how a material interacts with its surroundings?
— Surface area
— Surface chemistry, including reactivity, hydrophobicity
— Surface charge
Overarching considerations to take into account when characterizing engineered nanomaterials (for toxicity
studies and other applications):
— Stability—how do material properties (especially the surface composition, particle agglomeration, etc.)
change with time (dynamic stability), storage, handling, preparation, delivery, etc.? Include solubility and
the rate of material release through dissolution
— Context/media—how do material properties change in different media or during processing
(environmental effects); i.e., from the bulk material to dispersions to material in various biological
matrices? (“as administered” characterization is considered to be particularly important)
— Where possible, materials should be characterized sufficiently to interpret functional behaviours. For
toxicology studies, information is required on the response to the amount of material against a range of
potentially relevant dose metrics, including mass, surface area, and number concentration
This table is adapted from [2]. The recommendations in the initial table were developed at a workshop on en-
suring appropriate material characterization in nanotoxicology studies, held at the Woodrow Wilson Inter-
national Center for Scholars in Washington, DC, USA, between 28 October and 29 October, 2008; http:// www
.characterizationmatters .org.
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TECHNICAL REPORT ISO/TR 14187:2020(E)
Surface chemical analysis — Characterization of
nanostructured materials
1 Scope
This document provides an introduction to (and some examples of) the types of information that can be
obtained about nanostructured materials using surface-analysis tools (Clause 5). Of equal importance,
both general issues or challenges associated with characterizing nanostructured materials and the
specific opportunities or challenges associated with individual methods are identified (Clause 6). As
the size of objects or components of materials approaches a few nanometres, the distinctions among
“bulk”, “surface” and “particle” analysis blur. Although some general issues relevant to characterization
of nanostructured materials are identified, this document focuses on issues specifically relevant to
surface chemical analysis of nanostructured materials. A variety of analytical and characterization
methods will be mentioned, but this report focuses on methods that are in the domain of ISO/TC 201
including Auger Electron Spectroscopy, X-ray photoelectron spectroscopy, secondary ion mass
spectrometry, and scanning probe microscopy. Some types of measurements of nanoparticle surface
properties such as surface potential that are often made in a solution are not discussed in this Report.
Although they have many similar aspects, characterization of nanometre-thick films or a uniform
collection of nanometre-sized particles present different characterization challenges. Examples of
methods applicable to both thin films and to particles or nano-sized objects are presented. Properties
that can be determined include: the presence of contamination, the thickness of coatings, and the
chemical nature of the surface before and after processing. In addition to identifying the types of
information that can be obtained, the document summarizes general and technique-specific Issues
that must be considered before or during analysis. These include: identification of needed information,
stability and probe effects, environmental effects, specimen-handling issues, and data interpretation.
Surface characterization is an important subset of several analysis needs for nanostructured materials.
The broader characterization needs for nanomaterials are within the scope of ISO/TC 229 and this
document has been coordinated with experts of TC 229 Joint Working Group (JWG) 3.
This introduction to information available about nanomaterials using a specific set of surface-analysis
methods cannot by its very nature be fully complete. However, important opportunities, concepts and
issues have been identified and many references provided to allow the topics to be examined in greater
depth as required.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 18115-1, Surface chemical analysis — Vocabulary — Part 1: General terms and terms used in
spectroscopy
ISO 18115-2, Surface chemical analysis — Vocabulary — Part 2: Terms used in scanning-probe microscopy
3 Terms, definitions and abbreviated terms
For the purposes of this document, the terms and definitions given in ISO 18115-1 and ISO 18115-2 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
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ISO/TR 14187:2020(E)
— IEC Electropedia: available at http:// www .electropedia .org/
Symbols and abbreviated terms
AES Auger electron spectroscopy
APT atom probe tomography
AFM atomic force microscopy
ARXPS angle resolved X-ray photoelectron spectroscopy
CNT carbon nanotube
CVD chemical vapour deposition
dSIMS dynamic secondary ion mass spectrometry
EI-MS electron ionization mass spectrometry
EPMA electron probe micro-analysis
ESCA electron spectroscopy for chemical analysis (same as XPS)
G-SIMS gentle secondary ion mass spectrometry (a variant of SIMS to extract
information about molecular groups)
HRLEIS high resolution - low energy ion scattering
ICP-MS inductively coupled plasma mass spectrometry
IMFP inelastic mean free path
IRS Infrared Spectroscopy
ISS ion scattering spectroscopy
LED light emitting diode
LEIS low energy ion scattering
LRS laser Raman spectroscopy
MultiQuant spectrum evaluation program for quantitative evaluation of XPS data
MWCNT multi-walled carbon nanotube
NRA nuclear reaction analysis
PECVD plasma enhanced chemical vapour deposition
PEM fuel cell polymer electrolyte membrane fuel cell
PMMA poly(methyl methacrylate),
PPV poly(diakloxy-p-phenylene vinylene)
PVB poly(vinyl butyral)
QUASES quantitative analysis of surfaces by electron spectroscopy (computer program
for quantitative evaluation of XPS and Auger spectra)
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RBS Rutherford backscattering spectroscopy
SEM scanning electron microscopy
SESSA simulation of electron spectra for surface analysis (computer program for
quantitative evaluation of XPS and AES spectra)
SHG/SFG second harmonic generation/sum frequency generation
SI secondary ion
SIMS secondary ion mass spectrometry
SNOM scanning near-field optical microscopy
SPM scanning probe microscopy (a generic term covering STM, AFM and other
scanning tip-based microscopies)
sSIMS static secondary ion mass spectrometry
STM scanning tunnelling microscopy
SWCNT single walled carbon nanotube
TEM-PEELS transmission electron microscopy - parallel electron energy loss spectroscopy
TCNQ tetracyanoquinodimethane
TOF-SIMS time of flight – secondary ion mass spectrometry
WPMN-OECD Working Party on Manufactured Nanomaterials – Organization for Economic Co-op-
eration and Development
XPS X-ray photoelectron spectroscopy
μTA microthermal analysis
4 Characterization of nanostructured materials with surface analysis methods
4.1 Introduction
Surfaces and interfaces can strongly influence many properties of materials and material systems.
Surfaces control chemical reactivity, influence adhesion, and are associated with heat and electron
transfer. In many circumstances, the surface composition may differ from the bulk composition due
to surface contamination or to segregation (enrichment) of one component. Interfaces between grains
of one material or of differing materials are critical to the performance of electronic materials and the
strength of structural materials. Because of the importance of surfaces and interfaces, special tools
have been developed to determine their compositions and to assess how these affect the properties of
natural and engineered materials. Significant groupings of surface analysis tools include those based
on electron spectroscopy (Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy
(XPS)), those involving incident ion beams (secondary ion mass spectrometry (SIMS) and low-energy
ion scattering (LEIS), and those based on scanning probe microscopy (SPM) including atomic force
microscopy (AFM) and scanning tunnelling microscopy (STM). These tools are widely applied to
characterize natural and engineered surfaces in relation to fundamental studies, for material and
product development, and for analysing product reliability and performance in service environments.
These analysis methods have provided significant value in many technologies including pharmacology,
health, microelectronics, chemical, power, transport and aerospace, and the advanced materials used in
many technologies.
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Although other surface-analysis techniques are used and will be mentioned in this report, the focus
will be on AES, LEIS, SIMS, SPM, and XPS and the application of these techniques to the characterization
of nanostructured materials; it is noted that there are subcommittees for all of these methods except
[23,24]
LEIS within ISO/TC 201. Detailed discussions of these methods are available from many sources .
Information on the typical spatial resolutions of AES, SIMS, SPM, and XPS is summarized in Figure 1. In
all cases, the techniques have nanometre resolution in at least one dimension.
Figure 1 — Schematic overview of probing and detected species for surface analysis by AES,
SIMS, SPM, and XPS (also indicated are the typical spatial resolutions available with these
surface-analysis methods)
In addition to having differences in spatial resolution, different surface analysis techniques can provide
[25]
different types of information. The UK National Physical Laboratory has created a drawing that
summarizes the types of information that can be provided by many different analysis methods, as shown
in Figure 2. The types of information that can be obtained include topography, elemental composition,
molecular and chemical state, and structural information. Useful or potentially useful methods not
included in Figure 2 include LEIS, laser Raman spectroscopy, and nonlinear optical methods such as
second harmonic generation (SHG) and sum frequency generation (SFG). LEIS has also been known as
Ion Scattering Spectrometry (ISS) and is a well-established method. However, in modern instruments
it can be particularly useful because of the high sensitivity to the very outermost atomic layers of a
[26]
sample . A few examples of LEIS will be included in the examples provided in later sections. TOF-SIMS
is often applied in the static mode and is indicated by Static SIMS in Figure 2. Full chemical structure
would include information about the molecular structure of the elements and molecules present in the
sample or on the sample surface. Several methods provide some, but not comprehensive, information
about molecular structure.
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Figure 2 — Diagram providing overview of spatial resolution and types of information that can
[25]
be ordained by a range of tools important for the analysis of nano
...
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