Transmission electron holography of silicon nanospheres with surface oxide layers

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Abstract
Phase images of 20–30-nm-diam silicon spheres were collected by holographic methods in a field-emissiontransmission electron microscope. The spherical geometry enables the effect of specimen thickness on the electron-wave phase to be separated from the intrinsic Si electron-optical refractive effects allowing a determination of the mean inner potential Φ 0 . This work finds Φ 0 =11.9±0.9 V characterizing amorphous Si and 12.1±1.3 V characterizing crystalline Si. The phase images can resolve a 2-nm-thick native oxide layer and give Φ 0 for SiO 2 =10.1±0.6 V. The phase data can quickly recognize a surface layer, and the effect of a surface layer on the determination of the bulk mean potential can be minimized.