This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

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In general, the contrast of TEM images is determined by a number of factors:
        i) The contrast may be enhanced by using an objective aperture.
        ii) A shorter focal length of objective lens provides smaller spherical aberration and higher spatial resolution, while a longer focal length gives higher image contrast.
        iii) Sample thickness.
        iv) Crystalline orientation.
        v) Defocus.
        vi) Accelerating voltage of electron beam.
        vii) Chemical elements.
        viii) Artifacts.