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SUMMARY:Scanning helium microscopy (SHeM): Real space imaging of delicate 
 surfaces - David Ward\, SMF Group\, Cavendish Laboratory
DTSTART:20150219T160000Z
DTEND:20150219T170000Z
UID:TALK56908@talks.cam.ac.uk
CONTACT:Stephen Walley
DESCRIPTION:Microscopy has been a major enabling technique for the develop
 ment and understanding of materials from the bottom up. Some of the major 
 insights in the development of modern materials have come from scanning pr
 obe\, electron and ion microscopies\, with advances in resolution and sens
 itivity enabling new material science. Unfortunately charged beam techniqu
 es tend to cause surface damage and scanning probe techniques are limited 
 to relatively flat surfaces and suffer from limited scan speeds.\nIn the c
 urrent work I present recent advances in the development of neutral beam m
 icroscopy. In collaboration with colleagues at the University of Newcastle
 \, NSW\, we have recently published some of the first reflective mode imag
 es measured with a neutral helium beam [1]. A major benefit for the techni
 que is the very low beam energy (<100meV) compared to charged beam instrum
 ents\, combined with a de Broglie wavelength of around 1Å[1] the SHeM aim
 s to deliver uniquely surface sensitive images with atomic resolution\, wh
 ile causing no surface damage.\n Helium microscopy is suitable for measuri
 ng a variety of samples including insulator\, semiconductor\, explosive\, 
 biological and 3D self-assembled materials and being a real space techniqu
 e will not involve complicated post processing techniques. \nAtom microsco
 py has been in development for some years internationally. Many of the tec
 hnological barriers\, for example helium focusing\, sample preparation and
  nanoscale manipulation have now been addressed to enable preliminary inst
 ruments to be developed[1\,2]\, however detection of neutral beams remains
  a challenge\, particularly for helium given its high ionisation energy[3]
 .  Applications that require time sensitive measurements require a small i
 onisation volume\; however\, when high temporal resolution is not required
 \, ionisers having a much larger volume are possible. We describe a detect
 or developed on the basis of recent successful results[7] applied to surfa
 ce spin-echo experiments[4\,5\,6] and having a sensitivity of 0.83A/mbar\,
  the highest yet reported for helium atoms.\nFinally I discuss some very r
 ecent results showing that there is evidence for contrast mechanisms other
  than topographical in origin and discuss various alternative proposals\, 
 and possible applications of the technique. \n\n[1] D.J. Ward et al. Nucl.
  Instr. Meth. Phys. Res B\n340 76-80\, 2014.\n[2] H. Pauly “Atom\, molec
 ule and cluster beams”\; Springer: Berlin\, (2000).\n[3] P. Witham and E
 . Sánchez\, Rev. Sci. Inst. 82(10)\, 103705\, 2011.\n[4] D.J. Ward et al.
  Phys Rev Lett. 105\, 136101\, 2010\n[5] E.M. McIntosh et al. Phys. Rev. L
 ett. 110\, 086103\, 2013.\n[6] Lechner\, B.A.J.\, et al. Angew. Chemie –
  Int. Ed.\, 52 (19)\, pp. 5085‐5088\, 2013.\n[7] A. Alderwick et al. Rev
 . Sci. Instrum. 79\, 123301\, 2008.\n
LOCATION:Mott Seminar Room\, Cavendish Laboratory
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