TIME-RESOLVED ELECTRON-MICROSCOPY BY MEANS OF ELECTRON COUNTING

A method of time-resolved electron microscopy has been developed and a pplied to the study of the vortex-line dynamics in a type-II supercond uctor and to the measurement of the elastic properties of nanoscaled m aterials. Exploiting an electron counting technique, time-dependent el ectron microscope image beam current, position selected by a probing a perture in the image plane, is measured as sequentially sampled electr on counts or a temporal and spatial correlation function which can be converted to the spectral density function. Experimental techniques of detectors and correlators, presently allowing the measurement of the correlation function up to the GHz range, are described. Fundamental e lectron counting statistics for the measurement of a counting distribu tion, a power spectral density, and a cross-correlation function are e xamined using uncorrelated electrons in a beam from a field-emission s ource. The intrinsic electron correlation due to the second-order cohe rence appearing in the quest for fast time-resolved observation is als o discussed with regard to its offering possibilities of interferometr ic measurements.