{"id":371,"date":"2013-03-11T17:42:54","date_gmt":"2013-03-12T00:42:54","guid":{"rendered":"http:\/\/www.rbdinstruments.com\/blog\/?p=371"},"modified":"2014-11-06T08:45:45","modified_gmt":"2014-11-06T16:45:45","slug":"faraday-cup-procedure-to-align-ion-beam-current","status":"publish","type":"post","link":"https:\/\/www.rbdinstruments.com\/blog\/faraday-cup-procedure-to-align-ion-beam-current\/","title":{"rendered":"Faraday cup procedure to align ion beam current"},"content":{"rendered":"

Using Ta2O5 or SiO2 works well for aligning an ion beam to the focal point of an X-ray photoelectron or scanning Auger electron spectrometer. But, in order to optimize the ion beam focus at larger beam sizes, a Faraday cup is required.<\/p>\n

The Faraday cup used on many Physical Electronics\/PHI surface analysis systems comprises a specially configured sample mount with a molybdenum aperture that has a diameter of 250um.<\/p>\n

\"faraday

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Because the current measured into the Faraday cup is in the low nA range, a picoammeter (such as the RBD Instruments Inc. 9103 USB picoammeter<\/a>) and bias box are required. When the bias box is set to the ion input, the target is grounded and the output of the bias box is routed from the ion lead (Faraday cup) on the specimen stage to the input of the picoammeter. When an ion beam is larger than the 250um Faraday cup aperture, only the portion of the beam that is 250um or smaller is measured. By adjusting the ion beam focus and position for maximum current into the Faraday cup, the ion beam can be aligned and the current density can be optimized for any ion beam condition. In general, larger beam sizes result in more total current and faster sputter rates.<\/p>\n

\"faraday

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Another benefit of using a Faraday cup is that you can also determine the electric current density using a multiplication factor. Ion current density is rated in mA\/cm2<\/sup>.Dividing the area of the 250um Faraday cup hole into one square centimeter gives us a factor of 2037.18. So, to calculate the ion beam current density using a 250um Faraday cup, measure the ion current that enters the Faraday cup and multiply it by 2037.18 to get the current density in mA\/cm2<\/sup>. For example, the PHI 04-303 5kV differential ion source has a maximum current density specification of 600 mA\/cm2<\/sup> at 5kV ion beam voltage and 25 MPa of argon gas pressure. That works out to just under 300nA of ion current passing into the Faraday cup. Typically, though, the 04-303 ion source is operated at 3-to-4kV with 15MPa of argon pressure. Therefore, the maximum ion current passing into a Faraday cup under those conditions is more in the range of 150 to 200nA.<\/p>\n

Procedure to Maximize the Ion Current Passing into a Faraday Cup<\/h2>\n

 <\/p>\n

    \n
  1. First you need to align the Faraday cup to the focal point of the analyzer. For Auger electron spectrometers, acquire an elastic peak just to the side of the Faraday cup hole and then move the Faraday cup hole to the center of the TV image. For X-ray photoelectron spectroscopy systems, move the Faraday cup hole to the center of the system microscope\u2019s image at the highest possible magnification setting.<\/li>\n
  2. Turn the ion beam ON (make sure the electron beam is off).<\/li>\n
  3. Set the bias box to Ion and the bias to ON. This will ground the target and apply +90V to the ion lead on the specimen stage (which in turn makes the electrical contact to the Faraday cup). Note that there are different versions of the bias box used on PHI systems. Some systems do not have bias boxes. In those cases, short out the target and and connect the picoammeter to the ion lead on the specimen stage.<\/li>\n
  4. While observing the picoammeter, adjust the focus (objective) and condenser on the ion gun control and the mechanical offsets (thumbscrews) on the ion gun for maximum current into the Faraday cup. This will take several iterations to optimize. Once the mechanical offsets on the ion gun have been adjusted to where no further increase in current is noted, lock them down securely and also make sure that the ion gun housing is tight. Do not adjust the mechanical offsets for subsequent focus adjustments at different condenser (COND) or beam voltage settings. Instead, you can optimize the position of the ion beam into the Faraday cup by using the offset adjustments on the ion gun control if necessary.<\/li>\n
  5. Note the measured current and ion gun settings in a form such as the table shown below. By optimizing a few ranges of current and using those parameters to acquire depth profiles on a standard such as SiO2 or TaO5 (both available from RBD) you can create a matrix of reproducible sputter rates.<\/li>\n<\/ol>\n

    \"Ion

     <\/p>\n

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    Here is a link to a technical report in the Journal of Surface Analysis, which provides additional information:<\/p>\n

    http:\/\/www.sasj.jp\/JSA\/CONTENTS\/vol.14_2\/Vol.14%20No.2\/Vol.14%20No.2%20124-130.pdf<\/a><\/p>\n

    And here is a link to a video that shows an ion source being aligned using a Faraday cup \u2013 http:\/\/www.youtube.com\/watch?v=uKg9GLkXT3s<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

    Using Ta2O5 or SiO2 works well for aligning an ion beam to the focal point of an X-ray photoelectron or scanning Auger electron spectrometer. But, in order to optimize the ion beam focus at larger beam sizes, a Faraday cup … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":372,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","footnotes":"","jetpack_publicize_message":"","jetpack_is_tweetstorm":false,"jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","enabled":false}}},"categories":[161],"tags":[37,58,7],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2013\/03\/faraday-cup-sample-mount.jpg?fit=256%2C232&ssl=1","jetpack_shortlink":"https:\/\/wp.me\/p2DEXo-5Z","jetpack_sharing_enabled":true,"jetpack_likes_enabled":true,"jetpack-related-posts":[{"id":1600,"url":"https:\/\/www.rbdinstruments.com\/blog\/measure-electron-current-accurately\/","url_meta":{"origin":371,"position":0},"title":"Measure electron current accurately","author":"Randy","date":"December 12, 2015","format":false,"excerpt":"To measure electron current accurately (or ion current) you need to take secondary electrons out of the measurement. This is easy to do if you have a Faraday cup. The Faraday cup traps secondary electrons which results in an accurate beam current measurement. If secondary electrons are allowed to leave\u2026","rel":"","context":"In "Operation and Calibration Procedures"","block_context":{"text":"Operation and Calibration Procedures","link":"https:\/\/www.rbdinstruments.com\/blog\/category\/operation-and-calibration-procedures\/"},"img":{"alt_text":"Secondary electron cutoff","src":"https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2015\/12\/Secondary-electron-cutoff.jpg?fit=899%2C574&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2015\/12\/Secondary-electron-cutoff.jpg?fit=899%2C574&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2015\/12\/Secondary-electron-cutoff.jpg?fit=899%2C574&ssl=1&resize=700%2C400 2x"},"classes":[]},{"id":1855,"url":"https:\/\/www.rbdinstruments.com\/blog\/9103-picoammeter-bias-modes\/","url_meta":{"origin":371,"position":1},"title":"9103 Picoammeter bias modes","author":"Randy","date":"December 20, 2016","format":false,"excerpt":"9103 Picoammeter bias modes This post explains the 9103 picoammeter bias modes and also explains the concept of \u201cfloating\u201d. There are 4 picoammeter bias modes: No bias \u2013 the current source is connected directly to the picoammeter input Internal \u2013 a low noise DC supply (two 45 V DC batteries\u2026","rel":"","context":"In "9103 USB Picoammeter"","block_context":{"text":"9103 USB Picoammeter","link":"https:\/\/www.rbdinstruments.com\/blog\/category\/9103-usb-picoammeter\/"},"img":{"alt_text":"Floating-the-9103-Functionality 5000V","src":"https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2016\/12\/Floating-the-9103-Functionality-5000V.png?fit=766%2C824&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2016\/12\/Floating-the-9103-Functionality-5000V.png?fit=766%2C824&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2016\/12\/Floating-the-9103-Functionality-5000V.png?fit=766%2C824&ssl=1&resize=700%2C400 2x"},"classes":[]},{"id":231,"url":"https:\/\/www.rbdinstruments.com\/blog\/how-to-align-the-04-303-ion-gun\/","url_meta":{"origin":371,"position":2},"title":"How to align the 04-303 ion gun","author":"Randy","date":"November 29, 2012","format":false,"excerpt":"This post explains how to align the Physical Electronics 04-303 ion gun typically found on PHI Auger electron spectroscopy and X-ray photoelectron spectroscopy systems. The alignment principles explained here will apply to just about any surface analysis ion source. First, here is a video that explains all of the alignment\u2026","rel":"","context":"In "Ion Sources"","block_context":{"text":"Ion Sources","link":"https:\/\/www.rbdinstruments.com\/blog\/category\/ion-sources\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":2335,"url":"https:\/\/www.rbdinstruments.com\/blog\/how-to-test-the-bias-batteries-in-a-9103-picoammeter\/","url_meta":{"origin":371,"position":3},"title":"How to test the bias batteries in a 9103 picoammeter","author":"Randy","date":"April 17, 2018","format":false,"excerpt":"The 9103 USB picoammeter is often equipped with a +90 V bias option which improves the accuracy of electron and ion current measurements (by reducing the number of low energy secondary electrons that are generated by the beam from leaving the target). The +90 V bias comprises two 45V batteries\u2026","rel":"","context":"In "9103 USB Picoammeter"","block_context":{"text":"9103 USB Picoammeter","link":"https:\/\/www.rbdinstruments.com\/blog\/category\/9103-usb-picoammeter\/"},"img":{"alt_text":"9103 bias batteries","src":"https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2018\/04\/9103-Batteries.jpg?fit=972%2C648&ssl=1&resize=350%2C200","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2018\/04\/9103-Batteries.jpg?fit=972%2C648&ssl=1&resize=350%2C200 1x, https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2018\/04\/9103-Batteries.jpg?fit=972%2C648&ssl=1&resize=700%2C400 2x"},"classes":[]},{"id":2478,"url":"https:\/\/www.rbdinstruments.com\/blog\/5kv-floating-picoammeter\/","url_meta":{"origin":371,"position":4},"title":"5 kV floating Picoammeter Video","author":"Randy","date":"February 16, 2021","format":false,"excerpt":"This blog posts explains how a picoammeter can be floated up to +\/- 5 kV DC It includes a link to a video that shows a 9103 USB picoammeter being floated up to 5 kV and also a Keithley 485 picoammeter trying to float up to 5 kV.","rel":"","context":"In "9103 USB Picoammeter"","block_context":{"text":"9103 USB Picoammeter","link":"https:\/\/www.rbdinstruments.com\/blog\/category\/9103-usb-picoammeter\/"},"img":{"alt_text":"9103 HV","src":"https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2019\/02\/9103.jpg?fit=518%2C250&ssl=1&resize=350%2C200","width":350,"height":200},"classes":[]},{"id":2747,"url":"https:\/\/www.rbdinstruments.com\/blog\/stability-testing-of-surface-analysis-optics\/","url_meta":{"origin":371,"position":5},"title":"Stability testing of surface analysis optics","author":"Randy","date":"March 6, 2020","format":false,"excerpt":"There are two easy ways to check the stability of the electron or photon source on an X-ray photoelectron spectrometer, Auger electron spectrometer or Scanning Electron microscope: Measure the target current and plot the results vs. time using a data logging picoammeter such as RBD\u2019s 9103.Acquire a depth profile region\u2026","rel":"","context":"In "General Optics and Vacuum"","block_context":{"text":"General Optics and Vacuum","link":"https:\/\/www.rbdinstruments.com\/blog\/category\/general-optics-and-vacuum\/"},"img":{"alt_text":"Electron Current vs time","src":"https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2020\/03\/current-vs-time-800px.jpg?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2020\/03\/current-vs-time-800px.jpg?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2020\/03\/current-vs-time-800px.jpg?resize=700%2C400&ssl=1 2x"},"classes":[]}],"_links":{"self":[{"href":"https:\/\/www.rbdinstruments.com\/blog\/wp-json\/wp\/v2\/posts\/371"}],"collection":[{"href":"https:\/\/www.rbdinstruments.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.rbdinstruments.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.rbdinstruments.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.rbdinstruments.com\/blog\/wp-json\/wp\/v2\/comments?post=371"}],"version-history":[{"count":1,"href":"https:\/\/www.rbdinstruments.com\/blog\/wp-json\/wp\/v2\/posts\/371\/revisions"}],"predecessor-version":[{"id":379,"href":"https:\/\/www.rbdinstruments.com\/blog\/wp-json\/wp\/v2\/posts\/371\/revisions\/379"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.rbdinstruments.com\/blog\/wp-json\/wp\/v2\/media\/372"}],"wp:attachment":[{"href":"https:\/\/www.rbdinstruments.com\/blog\/wp-json\/wp\/v2\/media?parent=371"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.rbdinstruments.com\/blog\/wp-json\/wp\/v2\/categories?post=371"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.rbdinstruments.com\/blog\/wp-json\/wp\/v2\/tags?post=371"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}