Ultrahigh-resolution soft x-ray tomography

Ultra high resolution three dimensional images of a microscopic test object were made with soft x-rays using a scanning transmission x-ray microscope. The test object consisted of two different patterns of gold bars on silicon nitride windows that were separated by {approximately}5{mu}m. A series of nine 2-D images of the object were recorded at angles between {minus}50 to +55 degrees with respect to the beam axis. The projections were then combined tomographically to form a 3-D image by means of an algebraic reconstruction technique (ART) algorithm. A transverse resolution of {approximately}1000 {Angstrom} was observed. Artifacts in the reconstruction limited the overall depth resolution to {approximately}6000 {Angstrom}, however some features were clearly reconstructed with a depth resolution of {approximately}1000 {Angstrom}. A specially modified ART algorithm and a constrained conjugate gradient (CCG) code were also developed as improvements over the standard ART algorithm. Both of these methods made significant improvements in the overall depth resolution bringing it down to {approximately}1200 {Angstrom} overall. Preliminary projection data sets were also recorded with both dry and re-hydrated human sperm cells over a similar angular range.