Experimental low-voltage-point projection microscopy

Abstract

The remarkable achievement of atomic resolution by low voltage point projection microscopy has revived interest in this instrument, and, since resolution is approximately equal to virtual source size, demonstrates field-emission from tip regions of atomic dimensions. Ray-tracing calculations show the aberration coefficients and size of the virtual source to be subnanometer. The brightness of such a nanotip has been measured to be 7.7 × 1010 A cm -2 sr -1 (at 100 kV), somewhat greater than conventional cold field emitters or synchrotrons. The images require the theory of transmission LEED for interpretation and are always out of focus by the tip to sample distance zl. Their relationship to HREM images and coherent CBED is discussed elsewhere The instruments hold promise for imaging small organic molecules (across holey carbon grids), LB and other thin organic films where radiation damage is dominated by inner-shell processes.