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X-Ray Diffraction, Scanning Electron Microscopy and Microanalysis Lecture 26 Prof. Daniel R. Mumm Chemical Engineering and Materials Science Henry Samueli School of Engineering University of California, Irvine [email protected] University of California, Irvine CBEMS164, Fall 2013 CBEMS 164 – XRD, SEM & Microanalysis: Lecture 26 2 Specimen Preparation – The Good News Many specimens require no specimen preparation! Bugs Nanowires Fracture surfaces . But they need to be clean Wear gloves when handling specimens after cleaning up •A dirty specimen in preparation lab does not automatically become clean when brought to SEM lab!
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CBEMS 164 – XRD, SEM & Microanalysis: Lecture 26 3 Specimen Preparation – The Good News Many specimens require no specimen preparation! Bugs Nanowires Fracture surfaces . But they need to be clean Wear gloves when handling specimens after cleaning up A dirty specimen in preparation lab does not automatically become clean when brought to SEM lab! CBEMS 164 – XRD, SEM & Microanalysis: Lecture 26 4 Issues Specimen electrical conductivity Specimen cleanliness Susceptibility for beam damage Special cases – Transparency for STEM – Cross Sections for Devices – Etching for metals
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CBEMS 164 – XRD, SEM & Microanalysis: Lecture 26 5 Points to Consider SEM typically ± images ² or ± obtains spatial information ² from the near surface of a bulk specimen Consider the interaction volume CBEMS 164 – XRD, SEM & Microanalysis: Lecture 26 6 Specimens Requiring No Sample Preparation Fracture surfaces of metals Except maybe sectioning so sample can fit on stage Large stages enable large specimens Semiconductor devices MEMS devices Certain biological samples Biological specimen preparation outside scope Simple specimen preparation partly explains popularity (Second reason is ease of image interpretation)
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CBEMS 164 – XRD, SEM & Microanalysis: Lecture 26 7 Dirty Samples Need Cleaning An exercise in futility: – Handle a sample routinely while mechanical testing – Section sample using diamond saw with dirty coolant Glue to Al stub – Put on gloves while transferring to SEM Sample must be clean and oil (including finger grease) free CBEMS 164 – XRD, SEM & Microanalysis: Lecture 26 8 Cleaning Samples Ultrasonic bath in acetone / isopropanol – Acetone leaves a residue that an isopropanol rinse washes away Subsequent handling with gloves or tweezers Also, option for using plasma cleaner Once sample transferred to microscope, remove gloves!
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CBEMS 164 – XRD, SEM & Microanalysis: Lecture 26 9 Plasma Cleaning Especially important when imaging at low kV Effectively removes hydrocarbon contamination Minimizes seeing history of scanned areas as magnification dropped Can arise from multiple sources including backstreaming of oil from vacuum coating system Plasma cleaning relies on application of reactive gas plasma that reacts with (and removes) surface contamination
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