Materials Science and Engineering
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Frank Ernst

Significance of Defects

While most struc­tural and func­tional ma­te­ri­als are crys­talline, many of their prop­er­ties (e.g. me­chan­i­cal strength, elec­tri­cal con­duc­tiv­ity, cor­ro­sion re­sis­tance) are ac­tu­ally de­ter­mined by de­fect­s – deviations from the ideal (e.g. crys­tal) struc­ture. This in­cludes point-, line-, and pla­nar de­fects, in­ter­nal in­ter­faces, and sur­faces. For un­der­stand­ing and con­trol­ling ma­te­ri­als prop­er­ties, there­fore, it is es­sen­tial to in­ves­ti­gate their de­fect pop­u­la­tion, known as the “microstructure.” The mi­croscopy and mi­cro­anal­y­sis fa­cil­ity in the Swagelok Cen­ter for Sur­face Anal­y­sis of Ma­te­ri­als (SC­SAM) at Case pro­vides su­pe­rior tools for study­ing ma­te­ri­als at the ;mi­cro­scopic level, in­clud­ing state-of-the-art trans­mis­sion elec­tron mi­croscopy (TEM).

Atomic-resolution TEM (trans­mis­sion elec­tron mi­croscopy) and STM (scan­ning tun­nel­ing mi­croscopy) con­sti­tute pow­er­ful meth­ods to study the mi­crostruc­ture of precious­metal cat­a­lyst nanopar­ti­cles, e.g. for proton­exchange mem­brane fuel cells. The par­ti­cle seen in the TEM im­age is sup­ported by amor­phous car­bon (lower right). The struc­ture model has been used for nu­mer­i­cal im­age sim­u­la­tions to en­able cor­rect in­ter­pre­ta­tion of the ex­per­i­men­tal im­age.

Materials

The key to engineering the properties of materials is to analyze, understand, and control their microstructure.