[1] Univ Calif Berkeley, Adv Light Source, Berkeley, CA 94720 USA
[2] IBM Corp, Almaden Res Ctr, Div Res, San Jose, CA 95120 USA
[3] IBM Corp, Div Res, Zurich Res Lab, CH-8803 Ruschlikon, Switzerland
[4] Univ Neuchatel, Inst Phys, CH-2000 Neuchatel, Switzerland
[5] Arizona State Univ, Dept Phys & Astron, Tempe, AZ 85287 USA