Lect11_notes

Cbems 164 xrd sem microanalysis lecture 11 13 in lens

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Unformatted text preview: electron can produce up to 2800 electron hole pairs •  External bias required to generate current –  Conversion produces a gain of about 1000 so less subsequent amplification required •  Geometry –  Typically installed on bottom of lens pole piece in 2 or 4 quadrants CBEMS 164 – XRD, SEM & Microanalysis: Lecture 11 ! 11 CBEMS 164 – XRD, SEM & Microanalysis: Lecture 11 ! 12 Semiconductor Detectors! ! ! ! ! ! ! TTL Lenses! ! ! •  With FESEM and short WD, SE ! electrons are trapped by lens ! and spiral up column ! ! •  Basis of in-lens detector •  Annular detector results in loss of apparent side lighting effect. •  High resolution results •  Minimizes influence of SE electrons generated by interaction of BS electrons with chamber walls etc. CBEMS 164 – XRD, SEM & Microanalysis: Lecture 11 ! 13 In-Lens Detectors! ! •  ! ! ! •  ! ! •  High resolution requires small probe size Small probe size requires strong excitation of probe forming lens Very short working distance required •  Majority of signal flux spirals back up through lens pole piece –  Everhart-Thornley and SS BS detector become inefficient •  SE...
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