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HRE( IN-SITU STUDIES OF ELECTRON IRRADIATION EFFECTS IN OXIDES D.E. Luzzi*, L.D. Marks, M.I. Buckett, J.W. Strane, B.W. Wessels and P.C. Stair**, Center for Surface Radiation Damage Studies and Dept. of Materials Science (**Dept.

of Chemistry),

Northwestern University, Evanston,

IL,

60208.

ABSTRACT High resolution electron microscope (HREM) studies provide the ability to study desorption and sputtering from the perspective of the analysis of the resultant materials, their structure, composition and atomic registry (orientation with respect to the originalmaterial and the irradiation). This is a neglected facet of surface irradiation effects research, yet it is the most important from the technological point of view. In the current study, surface electron irradiation processes in oxides were studied in-situ in a Hitachi H-9000 HREM operated at incident electron energies of 100-300 keV. It was found that a wide range of processes occur in the HREM which are dependent on the energy and flux of the incident electrons and on the material properties. Both ballistic and electronic irradiation damage was observed and the material responses included surface sputtering, amorphisation, chemical disordering, desorption of 0 and metal surface layer creation, surface roughening and bulk defect creation.

INTRODUCTION The surfaces of materials will play a large role in future technological advances.

In many applications,

these surfaces will be exposed to irradiation,

either due to the service environment of the material or as a result of the processing of the material. Two obvious examples are the use of materials in space environments where a large variety of incident irradiations are experienced with a wide spectrum of energies, and the processing of electronic components using electron beam lithography. In order to scientifically understand the mechanisms involved, it is necessary to examine the evolution of the surface as a function of the irradiation parameters focusing on determining the

types of irradiation damage processes which are occurring and the resultant state of the material system.

In the present paper, we report results on the

effect of electron irradiation on the surface structure of oxides. Recently, techniques have been developed and refined in which the surfaces of materials can be imaged (1-5]. It has also been shown that under certain imaging conditions in the HREM, a one-to-one mapping of the image to the specimen structure can be obtained, termed localisation [6,7]. When this is applied to the profile imaging of a surface structure, it ensures that 100% of the information originates at the surface. When electrons are incident on matter, due to their inherent properties, several types of scattering can be observed. First, a number of inelastic processes can result; for example, the excitation of a plasmon, the generation of electron-hole pairs, the ionisation of the atom through excitation of core electrons or the production of Cerenkov radiation. If these excitations localize on a particular at