Andrei Nomerotski 1 CPC2 and Electron Microscopy A.Nomerotski 7//9/2007  Worldwide efforts to develop sensors for keV electrons for Transmission EM and keV Scanning EMs  Normally convert dE/dx from electrons to light on phosphorous screen and pass them through fiberoptics to an imager u Considerable smearing in the conversion process  lost resolution  Alternative is direct detection of electrons  CCDs have been considered before but have issues with u Slow readout u Radiation hardness  Fast readout of CPCCD allows to achieve sensible parameters for some applications e – Gun Anode Condenser Lenses Condenser Aperture Sample Objective Lens Apertures Magnification and Projection Detector

Andrei Nomerotski 2 Oxford Materials  Oxford Materials (Angus Kirkland, Grigore Moldovan et al) are interested to use CPC2 to study effects of multiple- and back- scattering of 200 keV electrons in silicon  The Group has several TEM and SEM both in Oxford and Begbroke  Discussions started last autumn, during spring-summer 2007 prepared vacuum enclosure and cabling to accommodate MB4 with SLM CPC2-10 under the microscope Beam entrance CPC2 in MB4 Enclosure Vacuum tight connectors

Andrei Nomerotski 3 CPC2 in Vacuum Enclosure  All assembled and tested in vacuum u Noise 80 e with final cabling in the lab, about 100 e at Begbroke  Data taking 29-30August u Team : G.Moldovan, Ron (TEM tech), P.Coulter, B.Jeffery, AN u Simple DAQ and monitoring by Ben u Took a day to get acceptable vacuum at microscope, a lot of outgassing u Immediately saw clusters from 200 keV e u Took ~20 runs at various conditions: intensity, energy ( keV), sensor temperature, integration time, clock frequency  Ran at +45 deg C (one run at +30 deg C) so had to trigger as fast as possible, otherwise leakage current saturate the well u Took data at 1, 2 and 5 ms integration times

Andrei Nomerotski 4 Simulated Tracks  By P.Denes at STD06  To have best resolution the sensor should be as thin as possible – requirement similar to ILC  Backscattering is a considerable effect 100 keV e – 300 keV e – 100  m Si 300  m Si SiO 2 + metal Si epi 300 keV e  40 µm

Andrei Nomerotski 5 Simulation of Clusters  Grigore simulated 20x20x25 micron pixels at different e energies: 100, 200, 300 and 400 keV  At 200 keV u charge/pixel peaks at 2500 e  Peak in charge distribution scales as 1/  2 u Equally probable to have one and two pixel clusters Charge/pixel in electrons Cluster size

Andrei Nomerotski 6 Screenshots of Clusters

Andrei Nomerotski 7 Status & Plans  Data analysis u Converted ADC data to 4x700 pixel images in LabVIEW (Ben) s bit ADC words  one 16-bit word after CDS (.png format) u Use ImageJ freeware for cluster analysis, this is routinely used by Materials for image analyses (Grigore, Philip) s First plots to produce: total charge, cluster size, cluster shape (orientation, sphericity), distance to closest neighbour, correlation between variables  Issues we know of: Charge spilling between pixels u Well capacity is only ~8 ke and it’s partly filled in by dark current u Good: charge is not lost u Bad: cluster shape can be distorted u Handles to study: vertical and horizontal spilling are different  Plan another run in a couple of weeks to take a knife blade image u For imaging need integration time to be (much) longer than readout time u Plan to install a Peltier near CPC2 to cool it  decrease dark current  Mid term – compare to simulation and write a paper, it looks like this could be the first ever direct detection data taken with fine pitch silicon pixel detector at TEM