John Spence

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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).

Affiliations
Home Department : 
Physics
Personal Information
Title: 
Regents Professor
Category: 
Faculty
Degree Information: 
PhD, Melbourne University, 1973
Area Of Study: 
Electron Microscopy and Protein Structure

    

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