Charge effect in point projection images of carbon and collagen fibers

Nanometric carbon and collagen fibers across holes have been observed in a lensless point projection field-emission microscope operating between 100 to 300 eV. At sufficiently high magnification fringe patterns appear. With the help of simulations the authors show that they are strongly dependent on the charge density of the fibers. Average diameter and linear charge density have been obtained from analysis of fringes with remarkable precision. This work emphasizes the fact that the fringe pattern masks the actual form of the fibers and that it is necessary to take account of the charge effect to interpret this diffraction pattern.