Abstract

When fine details of thin films are observed, the image are generally composed of both amplitude and phase contrast. The image resolution is sometimes limited by the granular background noise of supporting film which is due to the phase contrast effect by fairly coherent illumination(CI).In the present work, incoherent illumination(ICI) method has been studied to avoid the phase contrast effect using a conventional electron microscope(Hitachi HU-12A).The ICI method was made by enlarging the illumination angle(β) to be equivalent to the glancing angle(α=1.4x10-2 radians) of objective aperture. The large angle illumination was achieved by the strong excitation of an objective lens.At first, the properties of phase contrast in ICI image were studied as functions of beam divergence angle and defocus using a carbon film. Both analytical and experimental investigations show that the granular noise in a phase contrast image decreases as β is increased from l×l0-4 to l×l0-2radians.

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