1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 27911:2011Surface chemical analysis Scanning-probe microscopy Definition and calibration ofthe lateral resolution of a near-field optical microscopeBS ISO 27911:2011 BRITI
2、SH STANDARDNational forewordThis British Standard is the UK implementation of ISO 27911:2011.The UK participation in its preparation was entrusted to TechnicalCommittee CII/60, Surface chemical analysis.A list of organizations represented on this committee can beobtained on request to its secretary.
3、This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. BSI 2011ISBN 978 0 580 58828 0ICS 71.040.40Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published und
4、er the authority of theStandards Policy and Strategy Committee on 31 August 2011.Amendments issued since publicationDate Text affectedBS ISO 27911:2011Reference numberISO 27911:2011(E)ISO 2011INTERNATIONAL STANDARD ISO27911First edition2011-08-01Surface chemical analysis Scanning-probe microscopy De
5、finition and calibration of the lateral resolution of a near-field optical microscope Analyse chimique des surfaces Microscopie sonde balayage Dfinition et talonnage de la rsolution latrale dun microscope optique en champ proche BS ISO 27911:2011ISO 27911:2011(E) COPYRIGHT PROTECTED DOCUMENT ISO 201
6、1 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 ISOs member body in the coun
7、try 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 copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2011 All rights reservedBS ISO 27911:2011ISO 27911:2011(E) ISO 2011 All rights reserved iiiContents Page F
8、oreword iv Introduction.v 1 Scope1 2 Normative references1 3 Terms and definitions .1 4 Symbols and abbreviated terms 1 5 General information 2 5.1 Background information.2 5.2 Types of NSOM operation.2 5.3 Methods of measuring the lateral resolution of an NSOM 3 5.4 Parameters that affect the later
9、al resolution 3 6 Measurement of lateral resolution by imaging a very small object .5 6.1 Background information.5 6.2 Selection of the specimen and specimen requirements.6 6.3 Setting the parameters before the operation of the instrument.7 6.4 Data collection and analysis 7 6.5 Recording of data 8
10、Annex A (informative) Examples using a line-profile and a CdSe/ZnS quantum dot as specimen9 Annex B (informative) Example of a procedure for preparing standard NSOM specimens .15 Bibliography17 BS ISO 27911:2011ISO 27911:2011(E) iv ISO 2011 All rights reservedForeword ISO (the International Organiza
11、tion 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
12、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. In
13、ternational 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. Publi
14、cation as an International Standard requires approval by at least 75 % of the member bodies casting a vote. 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 r
15、ights. ISO 27911 was prepared by Technical Committee ISO/TC 201, Surface chemical analysis, Subcommittee SC 9, Scanning probe microscopy. BS ISO 27911:2011ISO 27911:2011(E) ISO 2011 All rights reserved vIntroduction The near-field scanning optical microscope (NSOM or SNOM) is a form of scanning-prob
16、e microscope (SPM) that uses an optical source but achieves, through the use of the near field, a spatial resolution significantly superior to that defined by the Abbe diffraction limit. NSOM instruments are mainly either apertured, when the resolution is governed by the aperture size, or aperturele
17、ss, when the resolution is more complex. In apertureless NSOMs, a very sharp scannable tip is used to probe the surface, or molecules on the surface, through local scattering of light from the test specimen surface or the tip apex. The spatial resolution for scattering NSOMs is a complex phenomenon
18、and is less easily characterized in terms of an instrumental property, and so this International Standard focuses on, and is limited to, the lateral spatial resolution of apertured NSOM instruments. Although the term spatial resolution has a clear meaning, it is often characterized in different ways
19、. In this International Standard, one convenient and effective method for measuring the spatial resolution of an apertured NSOM instrument is presented, suitable for use by non-expert operators. BS ISO 27911:2011BS ISO 27911:2011INTERNATIONAL STANDARD ISO 27911:2011(E) ISO 2011 All rights reserved 1
20、Surface chemical analysis Scanning-probe microscopy Definition and calibration of the lateral resolution of a near-field optical microscope 1 Scope This International Standard describes a method for determining the spatial (lateral) resolution of an apertured near-field scanning optical microscope (
21、NSOM) by imaging an object with a size much smaller than the expected resolution. It is applicable to aperture-type NSOMs operated in the transmission, reflection, collection or illumination/collection mode. 2 Normative references The following referenced documents are indispensable for the applicat
22、ion 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 18115-2, Surface chemical analysis Vocabulary Part 2: Terms used in scanning-probe microscopy 3 Terms and definiti
23、ons For the purposes of this document, the terms and definitions given in ISO 18115-2 and the following apply. 3.1 far field electromagnetic field at a distance from a light source significantly greater than the wavelength of the light 3.2 point spread function response of an imaging system to a poi
24、nt source or point object 4 Symbols and abbreviated terms APD avalanche photodiode FWHM full width at half maximum NA numerical aperture PMT photomultiplier tube PSF point spread function QD quantum dot FWHM of the PSF of the NSOM, i.e. the lateral resolution of the NSOM instrument BS ISO 27911:2011
25、ISO 27911:2011(E) 2 ISO 2011 All rights reserved5 General information 5.1 Background information The NSOM is a form of scanning-probe microscope with a probe that has an optical aperture that can illuminate, and/or collect the light from, the surface of a test specimen in the distance within a fract
26、ion of the wavelength of the light, this region being called the near field. A two-dimensional NSOM image consists of pixels that contain optical information (normally, the light intensity or photon counts obtained at each pixel position). For an apertured NSOM, an open optical aperture of subwavele
27、ngth diameter is located at the apex of a sharp probe, and light is emitted and/or collected by it. The NSOM probe is scanned over the specimen surface in the near field. Because the aperture is so close to the surface, the size of the spot illuminated on the surface (or from which light is collecte
28、d) is determined not by the light wavelength but mostly by the aperture size. Since the aperture size can be made as small as a few tens of nanometres, spatial resolution far better than the theoretical resolution limit of the conventional far-field optical microscope can be achieved by an NSOM. The
29、 spatial resolution achievable by reducing the size of the aperture is limited by the skin depth of the metal coating of the NSOM probe, which defines the aperture, and by the fact that optical throughput decreases rapidly with decreasing aperture diameter, going beyond the limits of practical detec
30、tion. 5.2 Types of NSOM operation 5.2.1 General Below we describe different modes of NSOM operation. This International Standard is concerned with apertured NSOMs operated in the illumination, collection or illumination/collection mode. Control of the gap between the specimen and the probe is achiev
31、ed by shear-force detection using optical or electrical transduction for a straight-fibre probe, and by cantilever deflection using optical transduction for a bent or cantilevered probe. 5.2.2 Classification 5.2.2.1 NSOMs can be classified on the basis of how the light is transmitted to/collected fr
32、om the specimen: a) Illumination mode: The light emanates from the aperture and is collected with a lens in the far field. b) Collection mode: The specimen is illuminated by light from a far-field source or excited to emit light by another means and light is detected (collected) using the NSOM apert
33、ure. c) Illumination/collection mode: The NSOM aperture is used for both illumination and collection. 5.2.2.2 NSOMs can also be classified on the basis of the position of the collection optics with respect to the illumination optics: a) Reflection mode: Both illumination and collection are carried o
34、ut on the same side of the specimen in any of the three modes defined above. b) Transmission mode: The collection and the illumination optics are located on opposite sides of the specimen. In most cases, including the reflection mode a) above, a high-NA lens is used for high collection efficiency. B
35、S ISO 27911:2011ISO 27911:2011(E) ISO 2011 All rights reserved 35.2.3 Control of gap between probe and specimen surface The gap between the NSOM probe and the surface is typically controlled in one of two ways, depending on the type of probe: a) Shear-force detection type: The NSOM probe is attached
36、 to a piezo tube or tuning fork and vibrated laterally to the surface with an amplitude of a few nanometres. Feedback is provided to keep the amplitude, phase or frequency of the vibration constant. For homogeneous surfaces, this would provide a constant gap; for most materials with a structured sur
37、face, the situation is more complicated, but often the constant-gap approximation holds. b) Cantilever type: The NSOM probe is cantilevered so that various ways of controlling atomic-force microscope tips can be used. In particular, the deflection of a laser beam off the end of the cantilever can be
38、 used to sense the surface topography and maintain a constant gap distance. NOTE Care is required to ensure the correct way of doing this.15.3 Methods of measuring the lateral resolution of an NSOM The spatial resolution of an NSOM is mainly determined by the size of the aperture probe, its distance
39、 from the surface, and the contrast mechanism. In addition, the nature of the specimen, pixilation and signal-to-noise issues can affect resolution. Therefore the spatial resolution of the NSOM can be defined only for a particular instrument and a particular specimen and, accordingly, any claim of s
40、patial resolution should specify the details of the experimental conditions2, such as the properties of the specimen, the type of imaging mode, the height regulation mechanism, the type of NSOM probe and other factors that could affect the measurement of the spatial resolution. Measurement of the sp
41、atial resolution of an NSOM instrument has been estimated by several methods, including measurement of the size of the smallest feature appearing in the NSOM image3, imaging small objects in a fluorescent mode4 to 7and imaging a specimen having an abrupt optical-contrast edge8. The method chosen her
42、e is the imaging of a small object. It is based on the concept of the PSF9, which is a critical concept that determines the spatial resolution of an optical microscope. In using this method, the following limitations of the method should be noted: a) It is recognized that, with NSOMs, the resolution
43、 is a result of near-field interactions between a specimen and a probe. The intensity profile in the near field of an aperture, even for the simplest possible case of an aperture in an infinite plane, and in the absence of interactions with a specimen, is not a simple Gaussian one10. In general, the
44、 field shape varies with the aperture shape, the condition of the outer metal coating and the polarization of the input light, etc. b) Topography-induced artefacts that appear in the optical images produced by NSOMs are sometimes mistaken for optical contrast11. If the optical contrast of the specim
45、en is low compared to the background signal, which is not specific to the optical characteristics of the specimen, the contrast appearing in the NSOM optical image could originate totally or in part from topographic change in the specimen surface. To minimize the influence of topographic change on t
46、he NSOM optical image, this International Standard describes fluorescence mode NSOM, and the topographic heights of the objects to be imaged are limited to one-tenth of the expected value of the lateral resolution. 5.4 Parameters that affect the lateral resolution 5.4.1 General The measurement of la
47、teral resolution can depend upon a number of experimental factors, including the physical properties of the NSOM aperture, the specimen, the contrast mode, the feedback conditions, the relative positions of the source and detector, and the instrumental noise. Improperly formed images suffering from
48、the effects of pixilation can also affect resolution, but do not present any fundamental limitations and are easily eliminated. BS ISO 27911:2011ISO 27911:2011(E) 4 ISO 2011 All rights reserved5.4.2 Aperture size of NSOM probe The aperture size of the NSOM probe is of primary importance. A smaller a
49、perture size results in a better resolution. There is a trade-off between aperture size and the signal-to-noise ratio: smaller apertures have a lower throughput, which results in a poorer signal-to-noise ratio. Apertures are produced in different ways. Coating the outside of the probe with a metal is the most popular method. 5.4.3 Condition of outer metal coating For metal-coated probes, it is crucial that they do not have pinholes in the coating, as pinholes greatly compromise both resolution and contrast.
