Submitted on: 23 April 2001.
Revised on: 03 July 2001.
Accepted on: 18 August 2001.
___________________APPLIED PHYSICS LETTERS---AIP PUBLISHING
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Submitted on: 11 April 2012.
Revised on: 03 June 2012.
Accepted on: 01 July 2012.
___________________APPLIED PHYSICS LETTERS---AIP PUBLISHING
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Submitted on: 03 July 2021.
Revised on: 24 August 2021.
Accepted on: 09 October 2021.
___________________APPLIED PHYSICS LETTERS---AIP PUBLISHING
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