SIST-TP CEN ISO/TR 11811:2012

SLOVENSKI STANDARD
SIST-TP CEN ISO/TR 11811:2012
01-oktober-2012
Nanotehnologija - Navodila za metode nano- in mikrotriboloških merjenj (ISO/TR
11811:2012)
Nanotechnologies - Guidance on methods for nano- and microtribology measurements
(ISO/TR 11811:2012)
Nanotechnologien - Leitfaden für nano- und mikrotribologische Messverfahren (ISO/TR
11811:2012)
Nanotechnologies - Directives relatives aux méthodes de mesure en nano- et
microtribologie (ISO/TR 11811:2012)
Ta slovenski standard je istoveten z: CEN ISO/TR 11811:2012
ICS:
07.120 Nanotehnologije Nanotechnologies
SIST-TP CEN ISO/TR 11811:2012 en,fr
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TP CEN ISO/TR 11811:2012


TECHNICAL REPORT
CEN ISO/TR 11811

RAPPORT TECHNIQUE

TECHNISCHER BERICHT
August 2012
ICS 07.030
English Version
Nanotechnologies - Guidance on methods for nano- and
microtribology measurements (ISO/TR 11811:2012)
Nanotechnologies - Directives relatives aux méthodes de Nanotechnologien - Leitfaden für nano- und
mesure en nano- et microtribologie (ISO/TR 11811:2012) mikrotribologische Messverfahren (ISO/TR 11811:2012)


This Technical Report was approved by CEN on 9 August 2010. It has been drawn up by the Technical Committee CEN/TC 352.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.





EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2012 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN ISO/TR 11811:2012: E
worldwide for CEN national Members.

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Contents Page
Foreword .3
2

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Foreword
This document (CEN ISO/TR 11811:2012) has been prepared by Technical Committee CEN/TC 352
“Nanotechnologies", the secretariat of which is held by BSI, in collaboration with Technical Committee ISO/TC
229 "Nanotechnologies".
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.

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SIST-TP CEN ISO/TR 11811:2012
TECHNICAL ISO/TR
REPORT 11811
First edition
2012-08-15
Nanotechnologies — Guidance on
methods for nano- and microtribology
measurements
Nanotechnologies — Directives relatives aux méthodes de mesure en
nano- et microtribologie
Reference number
ISO/TR 11811:2012(E)
©
ISO 2012

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SIST-TP CEN ISO/TR 11811:2012
ISO/TR 11811:2012(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2012
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO’s
member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2012 – All rights reserved

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Contents Page
Foreword .iv
Introduction . v
1 Scope . 1
2 Terms and definitions . 1
3 Significance and use . 1
4 Principle . 2
5 Apparatus and materials . 2
5.1 Test systems . 2
5.2 Test parameters . 4
6 Test procedure . 8
6.1 Different types of test . 8
6.2 Surface examination techniques . 11
7 Test reproducibility, repeatability and limits .12
8 Test report .12
Bibliography .13
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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 11811 was prepared by the European Committee for Standardization (CEN) Technical Committee
CEN/TC 352, Nanotechnologies, in collaboration with ISO Technical Committee ISO/TC 229, Nanotechnologies,
in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
iv © ISO 2012 – All rights reserved

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Introduction
Evaluation of wear and friction in systems where interactions occur in the nanoscale is becoming increasingly
important. There are two main areas of application. The first is in MEMS and NEMS devices, where tribological
issues can determine the overall performance of the device. It is also true that, in many cases, the tribological
performance of macroscale contacts depends on the combination of what occurs at the micro- and nanoscale
asperity contacts which actually take place when two surfaces come into contact.
The development of nanotribology testing provides a way of generating information and understanding these
small-scale contacts. This understanding can then be used to model the performance of microscale devices
and provide the basis for future models of sliding wear.
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SIST-TP CEN ISO/TR 11811:2012
TECHNICAL REPORT ISO/TR 11811:2012(E)
Nanotechnologies — Guidance on methods for nano- and
microtribology measurements
IMPORTANT — The electronic file of this document contains colours which are considered to be
useful for the correct understanding of the document. Users should therefore consider printing this
document using a colour printer.
1 Scope
This Technical Report establishes techniques for the evaluation of tribological performance of sliding contacts
with a lateral size of between a few nanometres (nm) and 10 µm, and where the applied load is between
50 µN and 100 mN. It describes procedures for undertaking these measurements, and provides guidance on
the effect of parameters on test results. It does not cover existing SPM techniques, such as frictional force
microscopy and atomic force microscopy (AFM).
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
wear
damage to a solid surface, generally involving progressive loss of material, due to relative motion between that
surface and a contacting substance or substances
[ASTM G40]
2.2
frictional force
resisting force tangential to the interface between two bodies where, under the action of an external force, one
body moves or tends to move relative to the other
[ASTM G40]
2.3
coefficient of friction
µ
f
dimensionless ratio of the frictional force, F, between two bodies to the normal force, N, pressing these
bodies together
[ASTM G40)]
NOTE 1 µ = F/N.
NOTE 2 µ ≥ 0.
3 Significance and use
This Technical Report provides guidance on how to carry out micro- and nanotribology tests, paying particular
attention to the likely effect of test conditions and test parameters on the results to be obtained. This Technical
Report does not specify a particular set of test conditions which should be used in a test. Appropriate test
conditions should be chosen after considering the eventual application for the materials being evaluated.
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4 Principle
Tribology tests are conducted in test systems, which are designed to press one sample against another with a
controlled relative force, while also imposing controlled relative motion. Conventionally, sliding/rolling tests are
carried out with samples where the nominal contact areas have dimensions of several millimetres or more, and
with test loads of the order of 1 N or greater. The focus of this Technical Report is on tribological tests where
the contact areas have dimensions of between a few nanometres (nm) and 100 mN, and the loads are between
50 µN and 100 mN.
Both friction and wear can be measured using these tests. A major aim of the tests is to provide information on
the tribological performance of materials at the micro- and nanoscale. This information can be used to develop
an understanding of the nanoscale mechanisms, which determine the wear and friction performance of the
materials and the dependence of these mechanisms on the structure of the material.
Application areas for these measurements are
— micro- and nanoscale devices where there are sliding/rolling contacts, and
— the simulation of micro- and nanoscale contacts, which underlie all macroscale tribological contacts.
5 Apparatus and materials
5.1 Test systems
5.1.1 Typical probe and sample geometries
Typically, a probe with a well-defined geometry is used to contact a flat sample (see 5.2.11). It is often important
to simulate real contacts in these tests, where features such as the shape of the contact and geometrical
parameters, such as the radius of curvature of the tip that is in contact in the real application are reproduced.
The assumed contact geometry, such as a pointed cone, cannot always be assumed to be correct at the
contact scales experienced in the tests described in this Technical Report. The real contact geometry almost
always has a rounded form at the very end of the contact probe. If a series of tests is to be carried out, it is also
important to consider the repeatability of the probe geometry so that contact conditions can be repeated from
one test to the next. Other details of the samples are given in this Technical Report.
Although the words “probe” and “sample” are used in this subclause and in many places throughout this
Technical Report, it should be emphasized that wear and damage to both probe and sample can take place.
5.1.2 Holding samples
The sample and probe need to be held firmly and in a well-defined way so that only intended motion of the
samples can take place. Mechanical clamping of samples is often preferable, but in some cases, an adhesive
may be used to hold samples in place, e.g. where balls are used as the probe and need to be attached to a
probe holder. If adhesives are used, it is important that the thickness of the adhesive be minimized to reduce
the effect of any time-dependent flow in the adhesive and also to reduce the effect of the reduced stiffness
introduced by the adhesive. Furthermore, if adhesives are used, sufficient time should be allowed for some
adhesives to fully cure, develop maximum bond strength, as well as allow for dissipation of any exothermal
effects prior to the start of test.
5.1.3 Motion generation
The relative motion generated between the probe and the sample can be achieved by either moving the sample
or moving the probe. In either case, the motion that is generated should be well defined and reproducible
so that repeated pass tests can be achieved. The small vertical displacements and applied loads which are
applicable in tests mean that particular care is needed so that irregularities in the motion itself do not cause
artefacts in the load that is applied.
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Additional care should be taken in order to minimize motion fluctuations and other effects due to ground
motion, ambient thermal variations and air flow current (caused by ventilation systems, operator and laboratory
equipment, to mention a few possible sources).
Motion can be generated in several ways. Piezoelectric actuators can be used, but these have limited range
(normally about 100 µm). Servo electric actuators, voice coils or stepper motors can also be used with gearing
to give the requisite precision of motion. In all cases, it is important to have an independent measure of
displacement.
It is also important to design the sample stage and drive systems so that artefacts in either the z-motion and
the x-y motion, such as hysteresis or backlash, are minimized.
Three axes of motion are required to give the necessary x-y motion and also coarse z-motion to enable the
probe to be brought close to the sample. The z-axis motion should be orthogonal to the motion in the x-y plane.
Different types of motion can be used in tests. The most common is reciprocating motion in a back and forth
manner in a single linear direction. A variant of this type of motion is where unidirectional motion is required,
such that movement takes place in a single direction with lift-off before return motion, followed by repeated
contact to give multiple contact in the same direction. Circular motion is also quite common where the flat
sample is simply spun by a motor drive.
5.1.4 Application of normal force
The applied normal force can be generated by several different mechanisms.
The simplest method is to use dead-weight loading. This is a passive technique, but care needs to be taken
that load artefacts, such as parasitic friction, are not generated in the loading mechanism. Parasitic friction is
friction generated in the elements of the loading mechanism such that the actual applied force is different from
the required force.
Another common method for generating the applied normal force is to use the compression of a compliant element
to generate a force, with the normal force determined by measurement of the dimensional compression of the
compliant element. The dimensional compression of the compliant element can be measured by displacement
transducers such as fibre optic sensors, light deflection sensing or capacitance devices. It is important that the
range and precision of the displacement transducers be matched to the deflection of the compliant element in
the loading system so that the resolution and load range that are required can be achieved. Systems can be
designed so that interchangeable compliant elements can be used to give different load resolutions and ranges.
In both open and closed-loop control, the force magnitude is directly controlled, and the controlled data needs
to be filtered appropriately for noise and spikes in values.
Loading systems that use a compliant element to generate the applied load can be used without active load
control, but if a non-level sample surface is used or the sample is rough, or when wear of the probe or sample
occurs, unwanted changes are generated in the applied load. For this reason, active load control is often
used such that the load that is achieved is compared with the required load and the position of the loading
mechanism adjusted through a feedback mechanism, often with a piezo-actuator, so that the actual load
matches the required load.
To do this, either closed-loop or open-loop control is used. In closed-loop control, a direct comparison is made
between the actual and required load with a difference signal generated, which is used to drive the piezo-
actuator so that the required load is achieved. This has the advantage of being very fast, but it can be difficult
to adjust the parameters of the closed-loop control such that feedback and control artefacts (like hunting) are
not observed.
Open-loop control is where an external computer makes the comparison and sends commands to the loading
system so that the correct load is achieved. The disadvantage of this approach is that the response time of the
motor can be slow.
A useful technique that can facilitate tests on samples which have a complex surface form is to make a pre-
scan of the sample surface under a light load, recording the vertical position of the sample probe as this pre-
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scan is made. This measured form can then be used to define the measurement path reducing the magnitude
of feedback motion control that is needed so that better load control can be obtained.
5.1.5 Friction measurement
Friction measurement is normally carried out by measuring the deflection of a compliant element using
displacement transducers or by applying strain gauges directly to the compliant element. If displacement
measurement is carried out, either fibre optic sensors, light deflection sensing or capacitance devices can
be used for this purpose. In view of the low friction values that are seen for some materials, it is even more
important than for the control of applied load, that the range and precision of the displacement transducers be
matched to the deflection of the compliant element in the loading system so that the resolution and load range
that are required can be achieved.
In this respect, it is important that the axes of the two measured forces (N and F) be ensured to remain
orthogonal to one another through the measurement process.
5.1.6 Real-time wear measurement
In principle, real-time wear measurement can be achieved by measuring the relative displacement of the
sample and the probe. This can be achieved by the same sensors as for friction measurement, fibre optic
sensors, light deflection sensing or capacitance devices. However, the very small displacements likely to be
generated in these tests mean that artefacts generated, e.g. by thermal expansion of mechanical path between
the two samples or irregularities in the sample stage mean that accurate real-time measurements are difficult.
Relative displacement measurements (displacement of one sample relative to the other due to wear) can be
attempted, but are difficult to achieve when one of the samples is moving relative to the other.
5.1.7 Temperature control
Some test systems have the capability for controlled temperature testing. Care needs to be taken in the design
of test systems for controlled temperature testing. It is important to heat or cool both the sample and the probe
so that test results are not affected by unexpected temperature gradients. It is also important to ensure that
measurement instrumentation is not affected by the sample heating or cooling; here, extensometry can be
required, which is difficult to achieve for low loads and small contact sizes. Temperature measurement should
be arranged so that reasonable confidence can be gained that the real temperature of the samples is measured,
usually by careful placement of thermocouples adjacent to the test samples. This is a particular issue for the
moving sample where the stiffness of the thermocouple leads can affect the measurement of friction.
5.2 Test parameters
5.2.1 General
The behaviour of materials at tribological contacts is very dependent on a wide range of different test parameters.
As the scale of the contact is reduced from the macroscale, the dominance of different factors changes so
that factors, such as capillary forces due to the presence of liquids at the tribological contact, become critical.
Typical test parameters that need to be considered include:
— contact geometry;
— applied load;
— motion type;
— relative speed;
— test system stiffness;
— interface materials;
— body material (probe);
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— counterbody material (sample);
— surface cleanliness;
— surface topography and roughness;
— environment.
These different test parameters are discussed in the rest of this subclause.
5.2.2 Contact geometry
A critical factor is the geometry of the contact. Often the contact is between a shaped probe and a flat sample.
This is normally preferred to using two flat samples as it is very difficult to get good alignment between flat
samples. The contact stresses generated in the samples are critically dependent on their shape, so it is very
important that the shape of the tip of the probe be well characterized before tests are started. In some cases
both samples may be shaped such as the geometry used traditionally in surface force apparatus where two
cylindrically curved samples are contacted.
Tip shape characterization is normally carried out by different microscopy techniques such as optical
microscopy, scanning electron microscopy (SEM) and AFM.
Optical microscopy is used for the evaluation of overall tip shape and quality. Some optical microscopes based
on confocal or focus variation techniques also have height measurement capability with a resolution of 10 nm
or better, but the lateral resolution is limited to about 150 nm.
Scanning electron microscopy can be used very effectively but care is needed to ensure that the orientation of
the probe is optimized for measurements of shape. It is also important to view the probe from several different
angles as the image that is obtained from the SEM is 2D.
For very fine probes transmission electron microscopy (TEM) can also be used.
Perhaps the best method for evaluating the shape of probes is to use AFM to carry out a measurement of the
tip form. This has the appropriate instrumental resolution in both height and in the lateral direction, and the
information that is gained can easily be processed to give an analysis of how the tip shape deviates from that
required. However, care is needed with the calibration and control of the AFM itself to eliminate or reduce non-
linearities and scan hysteresis from the AFM scanning motion, and the calibration of the AFM tip shape can be
in itself an issue.
Tip shape can also be evaluated by indentation into reference materials which have known indentation
response. The shape of the indentation can be measured, and/or the shape of the tip can be calculated from
the known indentation behaviour of the reference material.
Typical tip shapes are spherical, conical, and pyramidal shapes such as the Berkovitch indenter. The Vickers
indenter is not recommended due to potential for wedge tip due to the four sided shape. Balls can be used for
rolling contact tests, but care is then needed to ensure free motion with the small balls typically used in these tests.
Often diamond probes are used due to their ready availability and the perception that they do not degrade in
contact with test materials. The use of diamond probes should be considered carefully as it is can be better to
use materials more appropriate to the end application. Considerable degradation of diamond probes can also
take place (see 5.2.8).
5.2.3 Applied load
The load that is applied between the probe and the test surface has a major effect on the magnitude of
friction and wear which are observed. There is often an increase in wear as the applied load is increased, but
if a change in mechanism occurs, this does not always apply. Particularly at low applied loads, the normal
relationship that frictional force is proportional to the applied load (Amonton’s law) does not necessarily apply
due to the effect of phenomena such as surface tension of any adsorbed water, which can dominate behaviour
at small scales.
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Normally, constant applied loading is used in these tests, but in systems where the load can be varied during
the test other loading profiles such as ramping or incremental loads can be used.
5.2.4 Motion type
The motion type that is used also has a major effect on the wear and friction obtained. Common types of
motion are reciprocating motion, where the probe moves backwards and forwards in the same path over the
sample, uniaxial circular motion, where the flat sample is rotated in contact with the probe, and a raster test
where the probe is moved in a raster over the surface of the sample.
One of the differences between these different types of motion is that they affect the ability of any debris that
is generated in wear processes to escape from the contact zone. Thus in uniaxial sliding, the debris is often
swept out of the contact zone. If the debris remains in place in the contact zone, it can form a third body that
acts to separate the probe from the sample affecting friction and any further wear that may take place.
Another major effect is due to the magnitude of the motion itself, where if only a small magnitude of motion occurs
such that an appreciable portion of the area in contact remains in contact through the motion, debris is trapped in
the contact giving different mechanisms compared to the case where the surfaces move out of contact.
The magnitude of the motion is also important to consider. This should always be defined by consideration of
the magnitude of motion that is experienced in the application concerned. As the magnitude of the motion is
reduced it is more and more important to minimize unwanted backlash and slack in the motion. For very small
magnitudes of motion with a scale of a similar size to the contact size, the contact mode changes from a sliding
wear contact to a fretting mode contact and the mechanisms of damage a
...