Defocus image contrast in hexagonally-ordered mesoporous material

Abstract

A transmission electron microscope was used to characterize a powder form of hexagonally-ordered mesoporous silica material. The structural symmetry built into this amorphous material allowed one to obtain three characteristic images, i.e. a hexagonal honey-comb structure and wide/narrow parallel lines. These images were found to originate primarily from phase contrast, which changed sensitively with defocusing. To further understand the contrast behaviour of these images, an analytical form of the defocus contrast theory was developed and applied to the simulation of the characteristic wide/narrow parallel line images. The simulation was found to be in good qualitative agreement with experiments, where changes in focus conditions and specimen thickness were predicted to alter the contrast in the resulting parallel-line type images.

Defocusing microscopy with an arbitrary size for the aperture of the objective lens

“…Understanding how a defocused lens system affects a diffracted image has been the theme of several investigations [1,2,3,4,5,6,7,8,9]. The experimental techniques and the developed theoretical background has been used as a tool for obtaining spatial and volumetric information of a microscopic phase object [5,6,7,8,9,10,11,12]. Throughout the last 60 years many other microscopy techniques were developed for this purpose, such as the well-known Zernike phase-contrast method [13], the digital speckle photography [14], diffraction phase microscopy [15], diffraction tomography [16], dark field microscopy [17], differential interference contrast microscopy [17], ghost images [18] and techniques which use the chromatic aberration [19].…”