Active pixel sensor array as a detector for electron microscopy.
A new high-resolution recording device for transmission electron microscopy (TEM) is urgently needed. Neither film nor CCD cameras are systems that allow for efficient 3-D high-resolution particle reconstruction. We tested an active pixel sensor (APS) array as a replacement device at 200, 300, and 400 keV using a JEOL JEM-2000 FX II and a JEM-4000 EX electron microscope. For this experiment, we used an APS prototype with an area of 64 x 64 pixels of 20 microm x 20 microm pixel pitch. Single-electron events were measured by using very low beam intensity. The histogram of the incident electron energy deposited in the sensor shows a Landau distribution at low energies, as well as unexpected events at higher absorbed energies. After careful study, we concluded that backscattering in the silicon substrate and re-entering the sensitive epitaxial layer a second time with much lower speed caused the unexpected events. Exhaustive simulation experiments confirmed the existence of these back-scattered electrons. For the APS to be usable, the back-scattered electron events must be eliminated, perhaps by thinning the substrate to less than 30 microm. By using experimental data taken with an APS chip with a standard silicon substrate (300 microm) and adjusting the results to take into account the effect of a thinned silicon substrate (30 microm), we found an estimate of the signal-to-noise ratio for a back-thinned detector in the energy range of 200-400 keV was about 10:1 and an estimate for the spatial resolution was about 10 microm.
Milazzo
Anna-Clare
AC
University of California at San Diego, 9500 Gilman Dr., La Jolla, CA 92093, USA.
Leblanc
Philippe
P
Duttweiler
Fred
F
Jin
Liang
L
Bouwer
James C
JC
Peltier
Steve
S
Ellisman
Mark
M
Bieser
Fred
F
Matis
Howard S
HS
Wieman
Howard
H
Denes
Peter
P
Kleinfelder
Stuart
S
Xuong
Nguyen-Huu
NH
D020285:Cryoelectron Microscopy / Q000295:instrumentation / Q000379:methods; D004583:Electrons; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation / Q000379:methods; D046208:Microchip Analytical Procedures; D008854:Microscopy, Electron / Q000295:instrumentation* / Q000379:methods*; D012825:Silicon
D012825:Silicon