7 th International Conference on Nuclear Microprobe Technology

7 th International Conference on Nuclear Microprobe Technology and Applications, Cité Mondiale, Bordeaux, France, September 11 2000 New Generation Nuclear Microprobe Systems: A new look at old problems By David N. Jamieson Microanalytical Research Centre School of Physics University of Melbourne Parkville, 3010 AUSTRALIA

Electron Emission from Surfaces Incident ion electrons CVD B-doped diamond films are electrically conductive l Diamond has a negative electron affinity l Potential applications as a cold cathode electron emitter l l l Measure g : number of electrons emitted from surface per ion impact Measure g =15 to 30 (metals: g = 1. 5) H H H + – I+ Incident ion Yield max electrons H H H – + I– RBS © David N. Jamieson 1999 min 50 mm I–

Filiform Corrosion in Aluminium l l Filiforms grow under breaches in the anticorrosion coating on Al 3 Me. V H PIXE data confirms role of Cl in catalysing growth of the filiform Anticorrosion layer removed Filiform growth Cl growth head C- RBS Yield max Al- RBS min Cl - PIXE O - RBS © David N. Jamieson 1999 Al - RBS He 200 mm

Menke’s Syndrome revisited Menke’s Syndrome is a Cu deficency genetic disorder. l The gene responsible for the disorder has now been mapped. l Pathways for Cu metabolism within cells can now be controlled and studied with unprecedented precsion. l But can the nuclear microprobe cope? l Need to resolve Cu distributions within single cells to a spatial resolution of sub-micron. l Images here are by indirect immunofluorescence from antibody labelled Menkes protein. l Cells are less than 10 micons in Davidwidth N. Jamieson 1999 l ©

Outline The quest for superior spatial resolution in the Nuclear Microprobe: Why has the probe resolution stalled at 1 micron for 2 decades? l Some new insights provide possible pathways to future progress l Introduction to elementary ion optics l – – – Chromatic aberration - not a problem? Spherical aberration - not too much of a problem? Stray magnetic fields - definitely a problem Demagnification - the way forward Ion source brightness - small advances to be welcomed A review of the next generation systems l Conclusion l (Topics not addressed: l – High efficiency detectors, fast DAQ’s to handle high intensity beams, – specimen damage, channeling convergence angle) © David N. Jamieson 1999

Chip feature size and NMP resolution >100 p. A 1 mm wall P 6 P 5 Year © David N. Jamieson 1999 <1 p. A 6 80 38 Law Size (micron) re’s 8086 Moo P 7

1 mm wall Spatial Resolution Required: Applications published at the Last Conference 1998 “Pile up” © David N. Jamieson 1999

Introductory Ion Optics Object Plane Image Plane Aperture Plane (xo , yo , o ) Lens System (xi , yi ) Magnification Focusing Chromatic Spherical 3 + (x/ 22) 22 3 (x/ ) (x/x)x (x/ ) xi = oo + o o + (x/ ) oo + (x/ ) oo oo o+ 3 + (y/ 22 ) 22 22 3 (y/ ) (y/y)y yi = oo + (y/ ) o+ (y/ ) o o + (y/ ) oo + (y/ ) oo oo © David N. Jamieson 1999 …plus higher order terms

How to calculate probe resolution? Steps to evaluate lens system design: l l l 1. Calculate magnification and coefficients from ion optics computer codes 2. Measure: – Beam Brightness – Chromatic momentum spread from the accelerator (use nuclear resonance) 3. Set object size so that demagnified image is equal to desired probe resolution 4. Set aperture size so that beam current is equal to desired beam current 5. Calculate aberration contribution from maximum divergence and energy spread dm = 2(x/x)xo|max di 2 = dm 2+dc 2+ds 2 dc = 2(x/ ) o |max Wrong!! 3 2 2 ds = 2|(x/ ) o |max + |(x/ ) o o |max l l l 6. Add contributions to probe size in quadrature (or similar) 7. Spot size is now greater than desired spot size so go back to 3 and choose a smaller object size Repeat 4 -7 until done. © David N. Jamieson 1999

Chromatic Aberration, A closer look High excitation systems Singapore system achieves sub-micron probes with 15 o switcher magnet that has low energy dispersion l Yet chromatic aberrations of this system should be large l Skilled tuning of system is part of the answer, but not all! l Maximum dc depends on getting maximum and in the same beam particle l dc = 2(x/ ) o |max © David N. Jamieson 1999