BS ISO 13084-2011 Surface chemical analysis Secondary-ion mass spectrometry Calibration of the mass scale for a time-of-flight secondary-ion mass spectrometer《表面化学分析 二次离子质谱 飞行时间二次离.pdf

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1、raising standards worldwideNO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBSI Standards PublicationBS ISO 13084:2011Surface chemical analysis Secondary-ion mass spectrometry Calibration of the mass scale for a time-of-flight secondary-ion mass spectrometerBS ISO 13084:2011 BRI

2、TISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 13084:2011. The UK participation in its preparation was entrusted to T e c h n i c a l Committee CII/60, Surface chemical analysis.A list of organizations represented on this committee can be obtained on request to i

3、ts secretary.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. BSI 2011 ISBN 978 0 580 66882 1 ICS 71.040.40 Compliance with a British Standard cannot confer immunity from legal obligations.This British Standar

4、d was published under the authority of the Standards Policy and Strategy Committee on 31 May 2011.Amendments issued since publicationDate T e x t a f f e c t e dBS ISO 13084:2011Reference numberISO 13084:2011(E)ISO 2011INTERNATIONAL STANDARD ISO13084First edition2011-05-15Surface chemical analysis S

5、econdary-ion mass spectrometry Calibration of the mass scale for a time-of-flight secondary-ion mass spectrometer Analyse chimique des surfaces Spectromtrie de masse des ions secondaires talonnage de lchelle de masse pour un spectromtre de masse des ions secondaires temps de vol BS ISO 13084:2011ISO

6、 13084:2011(E) COPYRIGHT PROTECTED DOCUMENT ISO 2011 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 a

7、t the address below or ISOs 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 copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2011 All rights reservedBS ISO 13084:2011ISO 13084:2011

8、(E) ISO 2011 All rights reserved iiiForeword 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 i

9、nterested 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 Electrotechn

10、ical 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 th

11、e 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. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights

12、. ISO shall not be held responsible for identifying any or all such patent rights. ISO 13084 was prepared by Technical Committee ISO/TC 201, Surface chemical analysis, Subcommittee SC 6, Secondary ion mass spectrometry. BS ISO 13084:2011ISO 13084:2011(E) iv ISO 2011 All rights reservedIntroduction S

13、econdary-ion mass spectrometry (SIMS) is a powerful technique for the analysis of organic and molecular surfaces. Over the last decade, instrumentation has improved significantly so that modern instruments now have very high repeatability and constancy (Reference 2 in the Bibliography). An increasin

14、g requirement is for the identification of the chemical composition of complex molecules from accurate measurements of the mass of the secondary ions. The relative mass accuracy to do this and to distinguish between molecules that contain different chemical constituents, but are of the same nominal

15、mass (rounded to the nearest integer mass), is thus an important parameter. A relative mass accuracy of better than 10 ppm is required to distinguish between C2H4 (28,031 30 u) and Si (27,976 92 u) in a parent ion with total mass up to 1 000 u, and between CH2(14,015 65 u) and N (14,003 07 u) in par

16、ent ions with total mass up to 300 u. However, in a recent interlaboratory study (Reference 3 in the Bibliography), the average fractional mass accuracy was found to be 150 ppm. This is significantly worse than is required for unambiguous identification of ions. A detailed study (Reference 4 in the

17、Bibliography) shows that the key factors degrading the accuracy include the large kinetic energy distribution of secondary ions, non-optimized instrument parameters and extrapolation of the mass scale calibration. This International Standard describes a simple method, using locally sourced material,

18、 to optimize the instrumental parameters, as well as a procedure to ensure that accurate calibration of the mass scale is achieved within a selectable uncertainty. BS ISO 13084:2011INTERNATIONAL STANDARD ISO 13084:2011(E) ISO 2011 All rights reserved 1Surface chemical analysis Secondary-ion mass spe

19、ctrometry Calibration of the mass scale for a time-of-flight secondary-ion mass spectrometer 1 Scope This International Standard specifies a method to optimize the mass calibration accuracy in time-of-flight SIMS instruments used for general analytical purposes. It is only applicable to time-of-flig

20、ht instruments but is not restricted to any particular instrument design. Guidance is provided for some of the instrumental parameters that can be optimized using this procedure and the types of generic peaks suitable to calibrate the mass scale for optimum mass accuracy. 2 Symbols and abbreviated t

21、erms 2.1 Symbols m mass of interest m1calibration mass 1 m2calibration mass 2 M mass accuracy (u) MPmeasured peak mass (u) MTtrue mass (u) U(m) mass uncertainty for a mass m, arising from calibration U1uncertainty in the accurate mass measurement of m1U2uncertainty in the accurate mass measurement o

22、f m2U0average uncertainty in an accurate mass measurement VRreflector or acceptance voltage (V) W relative mass accuracy x number of carbon atoms y number of hydrogen atoms (M) standard deviation of the mass accuracy for a number of peaks Maverage of the standard deviations of M for each of the four

23、 CxHy+cascades with 4, 6, 7 and 8 carbon atoms 2.2 Abbreviated terms MEMS micro-electromechanical system PC polycarbonate ppm parts per million r/min revolutions per minute SIMS secondary-ion mass spectrometry THF tetrahydrofuran ToF time of flight BS ISO 13084:2011ISO 13084:2011(E) 2 ISO 2011 All r

24、ights reserved3 Outline of method Here, the method is outlined so that the detailed procedure, given in Clause 4, may be understood in context. Firstly, to optimize a time-of-flight mass spectrometer using this procedure, obtain a thin film of PC on a conducting substrate (silicon). The optimization

25、 procedure is achieved by carrying out the procedures in 4.3 to 4.5 iteratively; it uses 19 specific CxHypeaks in the polycarbonate (PC) positive-ion mass spectrum. In 4.6, a general calibration procedure is given which provides the rules by which calibrations for inorganics and organics may be inco

26、rporated. This leads to a new generic set of ions for mass calibration that can improve the mass accuracy from some often used calibrations by a factor of 5. The effects of extrapolation beyond the calibration range are discussed and a recommended procedure is given to ensure that accurate mass is a

27、chieved, within a selectable uncertainty, for large molecules. Therefore, the procedure has two parts, optimization and calibration. Subclauses 4.1 to 4.5 are only required as part of the regular maintenance of the instrument as defined by the testing laboratory. Subclause 4.6 is required for all ca

28、librations of the mass scale. This is summarized in the flowchart in Figure 1. STARTOptimizeinstrumentalparameters?Yes4.1/4.2 Obtaining/Preparing thereference sample for optimization4.3 Obtaining SIMS spectral data4.4 Calculating mass accuracy4.5 Optimizing instrumental parameters4.6 Calibration pro

29、cedurefor spectraNoFigure 1 Flowchart of sequence of operations of the method BS ISO 13084:2011ISO 13084:2011(E) ISO 2011 All rights reserved 34 Method for improving mass accuracy 4.1 Obtaining the reference sample for optimization A sample of thin (10 to 100 nm) PC on a flat conducting substrate (e

30、.g. silicon wafer) shall either be obtained or prepared, as described at 4.2. 4.2 Preparation of polycarbonate sample 4.2.1 Instructions for the preparation of a PC reference sample are provided. This method can give sample-to-sample repeatability in ToF SIMS spectra of better than 1,9 % 2. To prepa

31、re such a sample for static SIMS analysis requires a clean working environment. To reduce surface contamination, clean glassware, tweezers and powderless gloves shall be used. The equipment required is a 1 ml glass pipette, a 100 ml glass-stoppered measuring flask and a device for spin casting. If a

32、 device for spin casting is not available, droplet deposition of the PC solution may be used. However, this will give poor repeatability, which will need to be carefully taken into account during spectral analysis. 4.2.2 Using poly(bisphenol A carbonate), abbreviated to PC, weigh out 100 mg on a cle

33、an piece of aluminium foil. Introduce the PC into the 100 ml, glass-stoppered measuring flask, add tetrahydrofuran (THF) of analytical reagent quality, to the 100 ml level line. Shake the flask to mix the PC and allow time to dissolve it completely. This produces a 1 mg/ml solution of PC in THF. The

34、 aluminium foil shall be freshly unrolled and the shiny surface used. Ensure that the THF is anhydrous. Otherwise, streaks will appear from water when spin coating as described in 4.2.3. The shelf life of freshly prepared stock solution shall be no more than one month owing to water take-up. NOTE 1

35、It does not matter if the PC contains low levels of additives such as Irgafos. NOTE 2 It does not matter if the final PC/THF solution concentration varies by 20 %. 4.2.3 Use a conveniently sized (1 cm by 1 cm) piece of silicon, or another flat or polished conducting substrate, and clean it overnight

36、 by soaking in propan-2-ol (isopropyl alcohol). Ultrasonically clean the substrate in fresh propan-2-ol and dry. If an ultrasonic bath is not available, just rinse the sample in fresh propan-2-ol. Mount the substrate on the spin casting device. Pipette approximately 0,2 ml of the PC solution onto th

37、e substrate and spin cast at 4 000 r/min for 25 s. Samples may be prepared by depositing the PC solution using a 5 ml pipette onto the silicon surface then air drying under ambient conditions. However, this method will result in an uneven PC film, so care shall be taken when comparing spectra, as pe

38、ak intensities will vary. NOTE 1 It is not essential what substrate is used, as long as it is conducting. Silicon has been found to give good-quality films. NOTE 2 Using this procedure, the film thickness will be approximately 10 nm. The absolute thickness is not critical. 4.3 Obtaining the SIMS spe

39、ctral data 4.3.1 Insert the PC sample inside the chamber of the SIMS instrument. 4.3.2 Operate the instrument in accordance with the manufacturers or local documented instructions. The instrument shall have fully cooled following any bakeout. Ensure that the operation is within the manufacturers rec

40、ommended ranges for the ion-beam current, counting rates and any other parameter specified by the manufacturer. Check that the detector multiplier settings are correctly adjusted. 4.3.3 Select the normal analytical settings and acquisition time. For ToF instruments, select a repetition rate that giv

41、es a maximum mass of at least 800 u. If the total counts in the C9H11O peak are less than 10 000, increase the acquisition time to ensure that this peak contains more than 10 000 counts. This may not be possible if the signal is too weak and it is not possible to achieve 10 000 counts within a reaso

42、nable time. To ensure that the maximum ion fluence (11016ions/m2) is not exceeded, an enlarged raster area may be required. The acquisition time finally chosen will be a compromise between the data quality and the duration BS ISO 13084:2011ISO 13084:2011(E) 4 ISO 2011 All rights reservedof the work.

43、 Record the parameters set. Ensure that the detector is not saturated using the manufacturers or local documented instructions. This may be achieved by reducing the number of primary ions per pulse. NOTE For details of acquiring high-quality SIMS spectra with good repeatability and constancy, refer

44、to ISO 238301. 4.4 Calculating mass accuracy 4.4.1 Instrument manufacturers software may provide the calculation of the peak position automatically; it is often sufficient to use this to obtain a value of Mo. A more accurate and reliable method for measurement of the mass of the peak in the spectra,

45、 Mo, can be used. An asymmetric Gaussian function, GA, can be used to fit to the signal intensity versus the mass position, MP, and the fitting used to calculate the peak position, Mo. Where Mois the peak centre, MPis the peak mass and Gois a scaling term, GA, the fit to signal intensity, is given b

46、y 2PoAo2Po()exp2 ( )MMGGMM=(1) and FWHM( 0)22ln2= (2) where FWHM( = 0) is the full width at half-maximum of the base Gaussian width for = 0. The term gives the asymmetry, and for = 0 the function is pure Gaussian. For each peak, fit Equation (1). Only use those intensities above 50 % of the maximum

47、intensity to avoid interference from neighbouring peaks. You should calibrate using the peak position method you intend to use for accurate mass identification in your work. NOTE An asymmetric Gaussian function gives a good fit to a wide range of peak shapes, whereas the mean value can lead to signi

48、ficant errors for asymmetric peaks. Typically, the asymmetric Gaussian function is an excellent description of the peak down to 15 % of the maximum intensity, although the fitting, here, only covers to 50 %. 4.4.2 The mass accuracy, M, is defined as the difference between the measured peak mass, MP,

49、 and the true mass, MTPTM MM= (3) and the relative mass accuracy, W, is given by TMWM= (4) In the text that follows, W will be given in parts per million. 4.4.3 Figure 2 shows M for a range of hydrocarbon peaks of polycarbonate in an unoptimized instrument. M varies widely along the mass range for ions with different fragmentation. This illustrates an instrument with modest mass scale accuracy. BS ISO 13084:2011ISO 13084:2011(E) ISO 2011 All rights reserved 5In Figure 2 the peak