Three-Dimensional Structure of Twinned and Zigzagged One-Dimensional Nanostructures Using Electron Tomography
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1262-V05-05
Three-Dimensional Structure of Twinned and Zigzagged One-Dimensional Nanostructures Using Electron Tomography Han Sung Kim, Yoon Myung, Yong Jae Cho, Dong Myung Jang, Chan Soo Jung, JaePyoung Ahn, and Jeunghee Park Department of Chemistry, Korea University, Jochiwon 339-700, Korea ABSTRACT Electron tomography and high-resolution transmission electron microscopy were used to characterize the unique 3-dimensional (3D) structures of twinned Zn3P2 (tetragonal) and InAs (zinc blende) nanowires synthesized by the vapor transport method. The Zn3P2 nanowires adopt a unique superlattice structure that consists of twinned octahedral slice segments having alternating orientations along the axial [111] direction of a pseudocubic unit cell. The apices of the octahedral slice segment are indexed as six equivalent directions at the [111] zone axis. At each 30 degrees turn, the straight and zigzagged morphologies appear repeatedly at the and zone axes, respectively. The 3D structure of the twinned Zn3P2 nanowires is virtually the same as that of the twinned InAs nanowires. In addition, we analyzed the 3D structure of zigzagged CdO (rock salt) nanowires and found that they include hexahedral segments, whose six apices are matched to the directions, linked along the [111] axial direction. We also analyzed the unique 3D structure of rutile TiO2 (tetragonal) nanobelts; at each 90 degree turn, the straight morphology appears repeatedly, while the in-between twisted form appears at the [011] zone axis. We suggest that the TiO2 nanobelts consist of twinned octahedral slices whose six apices are indexed by the / directions with the axial [010] direction. INTRODUCTION One-dimensional (1D) nanostructures have attracted considerable attention due to their potential use as building blocks for assembling active and integrated nanosystems.(1) Recently, the interest in twinned superlattice 1D nanostructures that have twin planes at a constant spacing has been steadily increasing, owing to their attractive morphology and electrical/optical properties.(2-23) Since a twin boundary can act as a natural potential well for electrons, the discontinuous electron wavefunction leads to a reduction in the mobility of the charge carriers. For twinned zinc blende (ZB)/wurtzite (WZ) InP heterostructure nanowires (NWs), observed the excitation powerdependent blue-shift of the photoluminescence and explained it in terms of the staggered band alignment and concomitant diagonal transition between the localized electron/hole states.(15) Calculations predicted that a constant spacing between the rotational twins would induce a direct bandgap in normally indirect bandgap semiconductors, such as group IV (Si, Ge) and III-V (GaAs) materials.(23) Therefore, the controlled formation of a twinning structure in relevant semiconductors could have a significant impact on optically active band-structure engineering. In many semiconductor and noble metal NWs with a cubic structure (e.g., GaP, InP, InAs, GaAs, ZnS, ZnS, ZnTe, Si, SiC, B4C, Cr2O3, Zn2SnO4, Zn2TiO4,
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