ISO/TR 14187:2011

TECHNICAL ISO/TR
REPORT 14187
First edition
2011-08-15

Surface chemical analysis —
Characterization of nanostructured
materials
Analyse chimique des surfaces — Caractérisation des matériaux
nanostructurés




Reference number
ISO/TR 14187:2011(E)
©
ISO 2011

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ISO/TR 14187:2011(E)

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ISO/TR 14187:2011(E)
Contents Page
Foreword . iv
Introduction . v
1 Scope . 1
2 Terms and definitions . 1
3 Symbols 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
4.2.1 Surface functionalization and product formation . 7
4.2.2 Presence of contamination and coatings . 8
4.2.3 Orientation of surface molecules . 8
4.2.4 Coating or layer thickness . 8
4.2.5 Near-surface elemental distribution . 10
4.2.6 Particle size . 10
4.2.7 Particle location, composition and shape . 11
4.2.8 Other properties: electronic characteristics and surface acidity . 11
4.3 Ion-beam surface analysis methods (SIMS and LEIS) . 12
4.3.1 SIMS and examples of SIMS applications . 12
4.3.2 Low energy ion scattering and applications to nanomaterials . 13
4.4 Scanning probe microscopy . 14
4.5 Surface characterization of carbon nanostructures . 15
5 Analysis considerations, issues and challenges associated with characterization of
nanostructured materials: Information for the analyst. . 15
5.1 Introduction . 15
5.2 General considerations and analysis challenges . 16
5.3 Physical properties . 17
5.4 Particle stability and damage: influence of size, surface energy and confluence of energy
scales . 18
5.4.1 Crystal structure . 18
5.4.2 Damage and probe effects . 19
5.4.3 Time and environment . 19
5.5 Sample mounting and preparation considerations . 24
5.6 Specific considerations for analysis of nanostructured materials using XPS, AES, SIMS
and SPM . 24
5.6.1 Introduction . 24
5.6.2 Issues related to application of XPS to nanomaterials . 24
5.6.3 Issues related to the application of AES to nanostructured materials . 27
5.6.4 Issues related to application of SIMS to nanoparticles . 27
5.6.5 Issues related to the application of scanning probe methods to nanoparticles . 29
6 General characterization needs and opportunities for nanostructured materials . 29
Bibliography . 31

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ISO/TR 14187:2011(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 through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
In exceptional circumstances, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard (“state of the art”, for example), it may decide by a
simple majority vote of its participating members to publish a Technical Report. A Technical Report is entirely
informative in nature and does not have to be reviewed until the data it provides are considered to be no
longer valid or useful.
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.
ISO/TR 14187 was prepared by Technical Committee ISO/TC 201, Surface chemical analysis, Subcommittee
SC 5, Auger electron spectroscopy.
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ISO/TR 14187:2011(E)
Introduction
As engineered nanomaterials of many types play an increasing role in many different technologies [1],
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 Organization for
Economic Cooperation and Development (OECD))[1] are working to identify critical properties [2] and
measurements that must be understood to adequately define the nature of the materials being used. An
inherent property of any nanostructured material, whether a particle, fibre or other object, is that a large
percentage of the material 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 need 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. This Technical Report 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 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 analysis or characterization issues that sometimes are unexpected by analysts,
scientists, and production engineers [3-5].
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, were based on inadequate characterizations [6].
In some cases, important characterizations appear not to have been attempted or reported [7, 8]. A
March 2006 article in Small Times magazine described a workshop designed to identify roadblocks to
nanobiotech commercialization [6] at which several experts 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 has been identified as one of the areas where appropriate characterization is often lacking [4, 8].
One of the definitions of a nanostructured material is that, in at last one dimension, the size of the object or
structure must be 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 toxicity studies has been identified [2]. However, the
needs for nanomaterials characterization include the wide variety of nanostructured materials that are used in
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ISO/TR 14187:2011(E)
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 5 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 Technical Report describes the
information that can be obtained (and by which techniques), and examines some of the issues and challenges
faced when performing such analyses.
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 Technical Report.
____________________________________________________________________________________

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
ensuring appropriate material characterization in nanotoxicology studies, held at the Woodrow Wilson
International 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 14187:2011(E)

Surface chemical analysis — Characterization of
nanostructured materials
1 Scope
This Technical Report provides an introduction to (and some examples of) the types of information that can be
obtained about nanostructured materials using surface-analysis tools (Section 4). 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 (Section 5). 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 Technical Report 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
Technical Report 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 report 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 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18115 parts 1 and 2 apply.
3 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
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ISO/TR 14187:2011(E)
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 a 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)
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
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ISO/TR 14187:2011(E)
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-operation
and Development
XPS X-ray photoelectron spectroscopy
TA microthermal anlaysis
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.
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 LEIS within
ISO/TC 201. Detailed discussions of these methods are available from many sources [9, 10]. 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.
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ISO/TR 14187:2011(E)

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
different types of information. The UK National Physical Laboratory [11] 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 Fig. 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 sample [12]. 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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ISO/TR 14187:2011(E)

Figure 2. Diagram providing overview of spatial resolution and types of information that can be
ordained by a range of tools important for the analysis of nanostructured materials.
After reference [11].
It has already been noted that nanostructured materials inherently involve a high percentage of atoms located
on or near surfaces or interfaces, and that the material properties are significantly impacted by the nature and
properties of these surfaces and interfaces in addition to any fundamental changes in materials properties due
to their overall small size. Among the materials properties that must be known to understand behaviour are
characteristics related to surface chemistry and surface charge. Specific knowledge is often required on the
presence and properties of surface layers and surface contamination, the chemical state or enrichment of
species on the surface or at interfaces, and information about surface functionality. Examples of the types of
information needs and techniques by which they can be addressed are shown in Table 2. Table 2 includes
commonly used tools beyond those shown in Figure 1, but is not intended to be comprehensive.
Although many analysis tools can be useful for characterizing nanostructured materials, it is important to
recognize that there are many challenges and unmet analysis needs for such applications. Some challenges
are associated with limitations of the current tools [5, 13] or with challenges in using (or having access to) all
of the needed tool set [3, 4], Issues associated with environmentally induced changes, damage or sample
handling issues [3, 14], will be discussed in Section 5.
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ISO/TR 14187:2011(E)
Table 2 - Information needs and relevant tools for nanostructured material surfaces
Type of Film or Comments or range of
Information nanoparticle Possible Techniques applicability
Surface
composition
Nanometre films XPS, AES Outer 10 nm
(including
surface
functionalization)
 LEIS
 Outer < 1nm
 SIMS
 Outer 1 nm
 Nanoparticles XPS, AES, SIMS, LEIS As above
Outer 10 nm
Depth distribution Nanometre films XPS nondestructively
  RBS, NR
...