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A Scanning Electron and Atomic Force Microscopy Study of the Surface Morphology and Composition of CsI Films as Affected by Evaporation Rate and Humid-Air Exposure

Published online by Cambridge University Press:  08 March 2005

Giorgio S. Senesi ,
Mariangela A. Nitti  and
Antonio Valentini
Giorgio S. Senesi
Affiliation:
Istituto di Metodologie Inorganiche e dei Plasmi/CNR, c/o Dipartimento di Chimica, Via Orabona 4, I-70126 Bari, Italy
Mariangela A. Nitti
Affiliation:
INFN-Sezione di Bari, c/o Dipartimento Interateneo di Fisica, Via Amendola 173, I-70126 Bari, Italy
Antonio Valentini
Affiliation:
INFN-Sezione di Bari, c/o Dipartimento Interateneo di Fisica, Via Amendola 173, I-70126 Bari, Italy
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Abstract

Evaporation rate and subsequent exposure to humid air affect the surface morphology and composition of cesium iodide (CsI) films and, in turn, their photoemissive efficiency when used as photocathodes. The surface morphology and elemental composition of 300-nm-thick CsI films grown at two different rates (1 nm/s and 0.04 nm/s), both freshly evaporated and after 24-h exposure to humid air were investigated by means of atomic force microscopy and scanning electron microscopy/electron diffraction spectroscopy. The CsI film freshly evaporated at a slow rate exhibited a granular surface presenting circular holes or craters where the CsI material was moved from the center to the boundaries. After 24-h exposure to humid air, this film coalesced in large grain showing a marked increase of surface roughness. Conversely, the CsI film grown at a fast rate mostly retained its original surface uniformity and homogeneity with no presence of holes and craters after 24-h exposure to humid air. Further, surface roughness and average peak height decreased, but the surface coalesced in large grains spaced by small fractures where the CsI coverage was almost lost. In conclusion, the films grown at a fast evaporation rate were affected by 24-h exposure to humid air less than those grown at a slow rate, and are thus expected to possess a greater long-term stability.

Keywords

CsI filmsevaporation rate effecthumid-air exposure effectatomic force microscopyscanning electron microscopy/electron diffraction spectroscopysurface morphologyelemental composition
Type
MATERIALS APPLICATIONS
Information
Microscopy and Microanalysis , Volume 11 , Issue 2 , April 2005 , pp. 124 - 132
Copyright
© 2005 Microscopy Society of America

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References

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