Three-Dimensional Nanoscale Composition Mapping of Semiconductor NanowiresNanowire compositionLEAP MicroscopeSlide 4ExperimentalSlide 6Slide 7SummaryW 2007 April 11 EE C235/NSE C203 1Three-Dimensional Nanoscale Composition Mapping of Semiconductor NanowiresD.E. Perea, J.E. Allen, S.J. May, B.W. Wessels, D.N. Seidman, L.J. LauhonNano Letters 6(2). Feb 2006, p181-185.Joanne YimEE C235/NSE C203W 2007 April 11 EE C235/NSE C203 2Nanowire composition•Compositional flucuations especially critical at nanoscale–Dopants, catalyst, at interface, etc…•Composition mapping tools:–SIMS = secondary ion mass spectroscopy: resolution limited to >100nm–TEM = transmission electron microscopy (Energy Dispersive X-ray Spectroscopy and Electron Energy Loss Spectroscopy): not for volumetric, low concentration. •Averaged over electron beam spot size –Cross sectional Scanning Tunneling Microscopy (XSTM)•Requires making a cross section•2DW 2007 April 11 EE C235/NSE C203 3LEAP Microscope•Local Electrode Atom Probe microscope•Sub-nanometer resolution for atom tomography (imaging by sectioning)•Create 3D mapping of composition•First data published from commercial instrument in 2002http://www.imago.com/imago/3 easy payments of$999,999.95(prices and participation may vary)W 2007 April 11 EE C235/NSE C203 4•microtip sample: ~100nm radius of curvature in UHV chamber•+ bias sample, makes positive ions on sample tip–negatively pulsed local electrode tip to induce positive ions to leave•Position sensitive detector collects ions–Lighter mass -> travel faster–Mass-to-charge -> element–Relative composition using counts–Straight line travel -> relative positionshttp://www.imago.com/imago/html/technology/technology.jspW 2007 April 11 EE C235/NSE C203 5Experimental•Au seed-catalyzed InAs nanowire growth on GaAs(111)B by MOVPE–Epitaxial, vertical array of nanowires 140um long, spaced 500um apart as defined by initial Au e-beam/liftofW 2007 April 11 EE C235/NSE C203 6(curvature is software artifact)Cross section shows lines corresponding to growth planes (0001) ┴ growth directionspacing of 0.35nm Au atoms(98% In, As removed for picture) SEMW 2007 April 11 EE C235/NSE C203 7Catalyst-nanowire interface10 nm dia X 1 nm thick slices23x14x14 nm3www.nsf.gov/mps/dmr/highlights/05highlights/imr/0449933.ppt Interface width <0.5nmW 2007 April 11 EE C235/NSE C203 8Summary•3D composition mapping can be achieved•LEAP microscope sample geometry ideal for nanowire morphology •Found Au catalyst incorporated along length of
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