John Spence
Regents Professor
PhD, Melbourne University, 1973
Home Department Physics
Areas of Study Electron Microscopy and Protein Structure
Link Personal Homepage


Background The Spence group undertakes experiments in condensed matter physics (see relevant web page) and biophysics, based around the use of electron and X-ray beams for imaging, spectroscopy and diffraction - broadly diffraction physics. Our largest project (with B. Doak, U. Weierstall and others), funded by NSF biophysics, aims to solve proteins which cannot be crystallized by spraying them in single-file across the Berkeley synchrotron, using a modified ink-jet technique. The molecules are aligned by the dipole moment induced by a powerful polarized infrared CW fiber laser. Data is collected continuously for one orientation, before rotating the laser polarization to collect the next. (J. Chem Phys. 123, 244304). This work grew out of previous work on lensless Diffractive Imaging, which uses computers instead of lenses to image non-periodic objects, such as these proteins, by iterative solution of the non-crystallographic phase problem. In this way three-dimensional images of arrays of 50nm gold balls have been reconstructed from soft-Xray diffraction patterns (J. Opt Soc Am 23,1179). Diffractive imaging allows image formation using new radiations for which no lenses exist, including neutrons. Our quantitative convergent beam (QCBED) research (fig 1) allows us to directly image the chemical bonds which bind atoms together in solids without the extinction errors common in work based soley on X-ray diffraction. (Nature, 401, 49).

Electrons are the glue that hold atoms together and so give solid matter most of its properties. Yet these chemical bonds have rarely been seen. In the Spence group, Zuo, O�Keefe and Spence have developed a method using electron scattering for directly mapping out the chemical bonds between atoms, as shown here. (Nature 401, p. 49)

John Spence research group, 2000
JohnSpence_pic.jpg
John Spence
Arizona State University
Department of Physics
PO Box 871504
Tempe, AZ 85287-1504

phone: (480) 965 6486
fax: (480) 965-7954
email: john.spence
@asu.edu