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

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 Connecticutfor the

GlueX Photon Beam working group

GlueX collaboration meeting, Newport News, Jan. 29-31, 2009

GlueX collaboration meeting, Newport News, Jan. 29-31, 2009 2

Updates

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


Report from meeting at BNL Jan. 14, 2009: E. Aschenaur, J. Stewart, R. Jones met at

BNL with T. Rao, J. SmedleyJ. Smedley,, and others.

T. Rao group: diamond R&D for instrumentation diamond detectordiamond detector – rad-hard replacement for silicon detectors diamond multiplierdiamond multiplier – fast current amplifier for ERL source

Special requirements for diamond electronics: diamond is a large-gap semiconductordiamond is a large-gap semiconductor major problem – carriers get trapped in localized states in the gapmajor problem – carriers get trapped in localized states in the gap large gap – trapping lifetimes very long at room temperaturelarge gap – trapping lifetimes very long at room temperature requires extremely low impurity concentrations – requires extremely low impurity concentrations – type IIItype III also requires very low defect density –also requires very low defect density – large monocrystalslarge monocrystals multiplier application requires fast responsemultiplier application requires fast response – thin samples – thin samples


How the multiplier works

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pulse broadenedby diffusion


Diamond multiplier requirements ERL source amplifier: pulse length ~few ps Preserve short pulses: < 30 microns thickness R&D goal for multiplier: 20-30 microns20-30 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 CVD diamonds with ppb nitrogen now available from Element Six, Sumitomo Electric, Apollo – Element Six, Sumitomo Electric, Apollo – type IIItype III


Diamond Thinning Lab @ 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

6.6. laser ablationlaser 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 groupunder active development by BNL group


Diamond Thinning Lab @ BNL Laser ablation: small-scale equivalent of dynamite

1x1 mm2 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.


Diamond Thinning Lab @ BNL

Groove pattern left by ablation withsweeps separated by 50 microns

Opticalmicroscopeimages

SEM imageof surface

before ozone cleaning

after ozone cleaning

note: internaldamage atgrain boundariesof polycrystal


Diamond Thinning Lab @ BNLSame, but with 5 micron pitch between scans

optical microscope image(before cleaning)

atomic force microscope surface profiles

dark regions are damagezones at polycrystal boundaries,gray bands are amorphous carbon surface layer ~60 nm thick



Same as before, but using laser with 20 ns pulses

Several variations were tried, results were not as good

Using 532 nmlaser light, instead of 266 nm


Diamond Thinning Lab @ BNLWhat 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 mm2 area

craters?



Normal surfaceroughness is p-p~ 0.1 microns

Craters are deeper, up to ~0.5 microns

Ablation depth1.5 microns(not a limit)

Edge slope: 10:1


Diamond Thinning Lab @ 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 …


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 mm2 – 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)


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

Documents

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