{"id":1600,"date":"2015-12-12T15:42:36","date_gmt":"2015-12-12T23:42:36","guid":{"rendered":"http:\/\/www.rbdinstruments.com\/blog\/?p=1600"},"modified":"2018-11-03T12:55:59","modified_gmt":"2018-11-03T19:55:59","slug":"measure-electron-current-accurately","status":"publish","type":"post","link":"https:\/\/www.rbdinstruments.com\/blog\/measure-electron-current-accurately\/","title":{"rendered":"Measure electron current accurately"},"content":{"rendered":"

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 the target then they either subtract from or add to the current measurement, depending on whether you are measuring electrons or ions.<\/p>\n

It is not always possible to have a Faraday cup to measure electron or ion current in a vacuum chamber. So how can you get an accurate electron or ion current measurement without a Faraday cup? The answer is to bias the target with a battery or low noise isolated DC power supply with +90V.<\/p>\n

The secondary electron cut off will vary depending on the sample material, angle of incidence and beam energy, but it is generally acknowledged to be approximately 50 eV.<\/p>\n

\"Secondary

When the sample is positively biased with a voltage of 90 to 100 volts, the secondary electrons are trapped on the surface of the sample.<\/p>\n

\"Target

\"Target

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As an example of how a target bias can affect the current measurement, refer to the table below.<\/p>\n

These measurements were taken on a copper specimen. You can see that in both cases the effect of a bias resulted in a difference of approximately 2 uA, which is significant.<\/p>\n\n\n\n\n\n
Beam Voltage<\/td>\nBeam Type<\/td>\nTarget current with no bias<\/td>\nTarget current with +90 volt DC bias<\/td>\n<\/tr>\n
2 kV<\/td>\nElectron<\/td>\n173 nA<\/td>\n2.00 uA<\/td>\n<\/tr>\n
3 kV<\/td>\nIon<\/td>\n5.2 uA<\/td>\n3.0 uA<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

 <\/p>\n

It is easy to make a bias box where you can apply +90V to the target when measuring current, and then shorting the target to ground when not measuring current.\u00a0\u00a0 If you can\u2019t find them elsewhere, RBD provides 45 volt batteries (RBD part number\u00a0 BAT-45V-213) and the clips. Two 45 volt batteries in series will give you a simple noise free 90V bias supply.<\/p>\n

\"Bias

If you are in the market for a picoammeter to measure electron or ion current, The RBD Instruments 9103 USB picoammeter<\/a> incorporates a +90 volt bias as an option.<\/p>\n

Finally, here is a link to an interesting publication on scattered electrons from the University of Porto Rico \u2013 Electron Beam Specimen Interaction<\/a><\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

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 … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":1603,"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":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","enabled":false}}},"categories":[162],"tags":[37,207,206],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2015\/12\/Secondary-electron-cutoff.jpg?fit=899%2C574&ssl=1","jetpack_shortlink":"https:\/\/wp.me\/p2DEXo-pO","jetpack_sharing_enabled":true,"jetpack_likes_enabled":true,"jetpack-related-posts":[{"id":371,"url":"https:\/\/www.rbdinstruments.com\/blog\/faraday-cup-procedure-to-align-ion-beam-current\/","url_meta":{"origin":1600,"position":0},"title":"Faraday cup procedure to align ion beam current","author":"Randy","date":"March 11, 2013","format":false,"excerpt":"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. The Faraday cup used on many Physical Electronics\/PHI\u2026","rel":"","context":"In "Ion Sources"","block_context":{"text":"Ion Sources","link":"https:\/\/www.rbdinstruments.com\/blog\/category\/ion-sources\/"},"img":{"alt_text":"faraday cup","src":"https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2013\/03\/faraday-cup-254x300.jpg?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":2747,"url":"https:\/\/www.rbdinstruments.com\/blog\/stability-testing-of-surface-analysis-optics\/","url_meta":{"origin":1600,"position":1},"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":[]},{"id":1855,"url":"https:\/\/www.rbdinstruments.com\/blog\/9103-picoammeter-bias-modes\/","url_meta":{"origin":1600,"position":2},"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":345,"url":"https:\/\/www.rbdinstruments.com\/blog\/ion-beam-induced-low-energy-electrons\/","url_meta":{"origin":1600,"position":3},"title":"Ion Beam Induced Low Energy Electrons","author":"Randy","date":"February 6, 2013","format":false,"excerpt":"For the purpose of checking the performance of a surface analysis spectrometer such as a cylindrical mirror analyzer (CMA) or spherical capacitive analyzer (SCA), looking at an ion induced low energy electron peak can be extremely helpful. The peak typically occurs at about 20 to 50 eV and the size\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":"ion gun noise","src":"https:\/\/i0.wp.com\/www.rbdinstruments.com\/blog\/wp-content\/uploads\/2013\/02\/Ion-gun-noise.png?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":231,"url":"https:\/\/www.rbdinstruments.com\/blog\/how-to-align-the-04-303-ion-gun\/","url_meta":{"origin":1600,"position":4},"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. 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