[1] Delft Univ Technol, Dept Appl Phys, NL-2600 GA Delft, Netherlands
[2] Delft Univ Technol, Delft Inst Microelect & Submicron Technol, NL-2600 GA Delft, Netherlands
[3] MIT, Dept Elect Engn & Comp Sci, Cambridge, MA 02139 USA
[4] MIT, Dept Phys, Cambridge, MA 02139 USA
[5] MIT, Ctr Mat Sci & Engn, Cambridge, MA 02139 USA
[6] MIT, Dept Mech Engn, Cambridge, MA 02139 USA