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On the Feasibility of a Number Concentration Calibration Using a Wafer Surface Scanner

Aerosol science and technology, 2014-07, Vol.48 (7), p.747-757 [Peer Reviewed Journal]

Copyright © American Association for Aerosol Research 2014 ;ISSN: 0278-6826 ;EISSN: 1521-7388 ;DOI: 10.1080/02786826.2014.922162

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  • Title:
    On the Feasibility of a Number Concentration Calibration Using a Wafer Surface Scanner
  • Author: Li, Lin ; Mulholland, George W. ; Windmuller, Laura ; Owen, Miles C. ; Kimoto, Shigeru ; Pui, David Y. H.
  • Subjects: Aerosols ; Calibration ; Deposition ; Microscopy ; Optical scanners ; Process control ; Uncertainty ; Wafers
  • Is Part Of: Aerosol science and technology, 2014-07, Vol.48 (7), p.747-757
  • Description: A new primary standard method for calibrating optical particle counters (OPC) has been developed based on quantitative gravitational deposition on a silicon wafer and accurate counting of the particles by a wafer surface scanner (WSS). The test aerosol consists of 3-μm diameter monodisperse polystyrene latex (PSL) spheres at concentrations in the range of 0.1 cm −3 to 1 cm −3 . A key element to the calibration is the ability to generate monodisperse PSL spheres without residue particles by use of a virtual impactor and differential mobility analyzer. The use of these devices reduced the percentage of residue particles from more than 99.98% to about 5%. The expanded relative uncertainty (95% confidence level) in the number concentration determined with a WSS for a deposition of 200 particles is 17.8%. The major uncertainty component arises from the Poisson fluctuations in the aerosol concentration because of the low concentration. This methodology has advantages of a fast scanning time by the WSS of minutes compared to hours or days by microscopy and of counting every particle deposited compared to often only a small fraction via microscopy. The WSS was used in the calibration of an OPC based on 12 depositions with concentrations ranging from 0.1 cm −3 to 1 cm −3 for each deposition. Make-up air was added to the aerosol entering the OPC so that the lowest achievable concentration for the OPC measurement is about 0.01 cm −3 in this study. The detection efficiency of the OPC was measured to be 0.984 with an expanded uncertainty of 13.4%. Copyright 2014 American Association for Aerosol Research
  • Publisher: Taylor & Francis
  • Language: English
  • Identifier: ISSN: 0278-6826
    EISSN: 1521-7388
    DOI: 10.1080/02786826.2014.922162
  • Source: IngentaConnect Open Access Journals
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