Diamonds at CHESS and BNL report from meeting with BNL Instrumentation group working to produce thin diamond monocrystals for use as a fast electron multiplier Richard Jones, University of Connecticut for the GlueX Photon Beam working group GlueX collaboration meeting, Newport News, Jan , 2009

2 Updates report from meeting at BNL new sources for diamonds plans for CHESS run this Spring

GlueX collaboration meeting, Newport News, Jan , Report from meeting at BNL J. Smedley, Jan. 14, 2009: E. Aschenaur, J. Stewart, R. Jones met at BNL with T. Rao, J. Smedley, and others. T. Rao group: diamond R&D for instrumentation  diamond detector  diamond detector – rad-hard replacement for silicon detectors  diamond multiplier  diamond multiplier – fast current amplifier for ERL source Special requirements for diamond electronics:  diamond is a large-gap semiconductor  major problem – carriers get trapped in localized states in the gap  large gap – trapping lifetimes very long at room temperature  requires extremely low impurity concentrations – type III  also requires very low defect density – large monocrystals  multiplier application requires fast response – thin samples

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias incident electron valence band conduction band 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias incident electron 0 holes electrons

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0

GlueX collaboration meeting, Newport News, Jan , How the multiplier works z E V bias 0 free e - energy for same k traps pulse broadened by diffusion

GlueX collaboration meeting, Newport News, Jan , Diamond multiplier requirements ERL source amplifier: pulse length ~few ps Preserve short pulses: < 30 microns thickness microns R&D goal for multiplier: microns Trapping a problem at high currents Requires very low impurity concentrations (ppb) Requires very perfect monocrystals – low defect density Only CVD monocrystals meet this requirement CVD diamonds with ppb nitrogen now available from Element Six, Sumitomo Electric, Apollo – type III CVD diamonds with ppb nitrogen now available from Element Six, Sumitomo Electric, Apollo – type III

GlueX collaboration meeting, Newport News, Jan , Diamond Thinning BNL Review: known ways to mill diamond 1.lapping Known to work, used to mill diamonds for Hall B Often destroys the sample, low yield Y high cost 2.reactive ion etching 3.focused ion beam milling 4.electron cyclotron resonance etching 5.inductively coupled plasma etching 6.laser ablation “they are generally slow and prohibitive processes if significant thickness reduction or large aspect ratio structures are required.” J. Smedley et.al., preprint under active development by BNL group

GlueX collaboration meeting, Newport News, Jan , Diamond Thinning BNL Laser ablation: small-scale equivalent of dynamite 1x1 mm 2 square region of CVD diamond scanned with 50 micron pitch, 266 nm light (4’th harmonic NdYAG), 30 ps pulses, focal spot size 27 microns rms, varying energy per pulse.

GlueX collaboration meeting, Newport News, Jan , Diamond Thinning BNL Groove pattern left by ablation with sweeps separated by 50 microns Optical microscope images SEM image of surface before ozone cleaning after ozone cleaning note: internal damage at grain boundaries of polycrystal

GlueX collaboration meeting, Newport News, Jan , Diamond Thinning BNL Same, but with 5 micron pitch between scans optical microscope image (before cleaning) atomic force microscope surface profiles dark regions are damage zones at polycrystal boundaries, gray bands are amorphous carbon surface layer ~60 nm thick

GlueX collaboration meeting, Newport News, Jan , Diamond Thinning BNL Same as before, but using laser with 20 ns pulses Several variations were tried, results were not as good Using 532 nm laser light, instead of 266 nm

GlueX collaboration meeting, Newport News, Jan , Diamond Thinning BNL What happens if we go to shorter wavelengths, like 213 nm? optical microscope image SEM surface profile image This time, use a high-quality monocrystal sample, 1x1 mm 2 area craters?

GlueX collaboration meeting, Newport News, Jan , Diamond Thinning BNL Normal surface roughness is p-p ~ 0.1 microns Craters are deeper, up to ~0.5 microns Ablation depth 1.5 microns (not a limit) Edge slope: 10:1

GlueX collaboration meeting, Newport News, Jan , Diamond Thinning BNL Next steps being pursued at BNL  Conduct tests with new Excimer (193 nm) laser.  Try reactive ion etching post-processing step to smooth out remaining surface roughness.  Improved electrode deposition tests.  Correlate electron transfer with defect densities in the crystal  Ablate a region of a diamond down to 20 microns. and eventually …

GlueX collaboration meeting, Newport News, Jan , New sources for diamonds high-quality monocrystals from CVD process  available from Element Six since 2005  very low nitrogen concentrations – not an issue for us  large area – 4 x 4 mm 2 – for low cost: < 1K $US BNL group gets theirs from Element Six  front-end firm Harris International, hq in Boston  Sumitomo Electric also rumoured to be producing these  Apollo is a third firm with CVD diamond expertise  samples are made thick (500 microns)

GlueX collaboration meeting, Newport News, Jan , Plans for 2009 run at CHESS planned for April  BNL group agrees to loan us a type III CVD sample from their inventory to run whole-crystal rocking curve.  Hall B has a diamond for which the full radiation exposure map is available – in principle. We plan to map this diamond along both (2,2,0) axes. collaboration with BNL on thinning  potential for real cost savings!  we need our own diamond inventory for studies  have contact with Harris International, meeting planned  once diamonds are in-hand, will pursue arrangements with the BNL group to use their thinning facilites – ca. Fall 2009  manpower needed – UConn seeking funding for a postdoc