title: Imaging and analysis of nanowires.
abstract: We used vapor-liquid-solid (VLS) methods to synthesize discrete single-element semiconductor nanowires and multicomposition nanowire heterostructures, and then characterized their structure and composition using high-resolution electron microscopy (HRTEM) and analytical electron microscopy techniques. Imaging nanowires requires the modification of the established HRTEM imaging procedures for bulk material to take into consideration the effects of finite nanowire width and thickness. We show that high-resolution atomic structure images of nanowires less than 6 nm in thickness have lattice "streaking" due to the finite crystal lattice in two dimensions of the nanowire structure. Diffraction pattern analysis of nanowires must also consider the effects of a finite structure producing a large reciprocal space function, and we demonstrate that the classically forbidden 1/3 [422] reflections are present in the [111] zone axis orientation of silicon nanowires due to the finite thickness and lattice plane edge effects that allow incomplete diffracted beam cancellation. If the operating conditions are not carefully considered, we found that HRTEM image delocalization becomes apparent when employing a field emission transmission electron microscope (TEM) to image nanowires and such effects have been shown to produce images of the silicon lattice structure outside of the nanowire itself. We show that pseudo low-dose imaging methods are effective in reducing nanowire structure degradation caused by electron beam irradiation. We also show that scanning TEM (STEM) with energy dispersive X-ray microanalysis (EDS) is critical in the examination of multicomponent nanowire heterostructures.
authors.affiliation: Center for Imaging and Mesoscale Structures, Harvard University, Cambridge, Massachusetts 02138, USA. dcb@deas.harvard.edu
authors.forename: David C
authors.initials: DC
authors.lastname: Bell
authors.forename: Yue
authors.initials: Y
authors.lastname: Wu
authors.forename: Carl J
authors.initials: CJ
authors.lastname: Barrelet
authors.forename: Silvija
authors.initials: S
authors.lastname: Gradecak
authors.forename: Jie
authors.initials: J
authors.lastname: Xiang
authors.forename: Brian P
authors.initials: BP
authors.lastname: Timko
authors.forename: Charles M
authors.initials: CM
authors.lastname: Lieber
mesh_terms: D003198:Computer Simulation; D004577:Electron Probe Microanalysis / Q000379:methods; D019216:Metals, Heavy / Q000737:chemistry*; D017348:Microscopy, Electron, Scanning Transmission / Q000379:methods; D049329:Nanostructures / Q000737:chemistry*; D012825:Silicon / Q000737:chemistry*
chemical_list: D019216:Metals, Heavy; D012825:Silicon