Nanoscale semiconductor

[1] Z. M. Zhu, T. Chen, Y. Gu, J. Warren and R. M. Osgood, Jr., “Zinc-oxide nanowires grown by vapor-phase transport using selected metal catalysts: A comparative study.” Chemistry of Materials (accepted for publication).

One-dimensional ZnO nanowires have attracted increasing interest for both fundamental and applied studies of short-wavelength optoelectronic nanodevices. We report a systematic study of metal-catalyzed ZnO nanowire growth. The growth is initiated on Si and sapphire substrates, which were prepared with thermal vapor deposited thin metallic films. These films may change morphology at growth temperatures and catalyze ZnO nanowire growth. Here we use materials diagnostics based on synchrotron X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), photoluminescence (PL), and energy-dispersive X-ray spectroscopy (EDX) to compare the growth from Au, Ag, Fe, and Ni catalysts. We relate the materials properties of the ZnO nanowires to the substrate and catalyst surface structure and comment on the possible growth modes using each of these metal catalysts.
From a more general point of view, our investigation shows that use of different catalysts provide the versatility of growth for one-dimensional ZnO nanostructures with different ranges of parameters such as diameters, areal densities and aspect ratios. These differences in growth properties would be expected to affect other properties of wires such as electrical transports and surface chemistries. Exploration of these aspects will be of interest for practical applications of ZnO wires in nanodevices and chemical sensors. In addition, strategies of manipulating the spatial orientation of ZnO nanowires for practical applications are being explored by using nanofabrication techniques such as electron-beam lithography to pattern the substrates and build blocks to confine the growth of the ZnO nanowires.
[2] Z. M. Zhu, T. Andelman, M. Yin, T. Chen, S. N. Ehrlich, S. P. O’Brien and R. M. Osgood, Jr., “Synchrotron x-ray scattering of ZnO nanorods: Periodic ordering and lattice size.” Journal of Material Research 20, 1033 (2005).
We demonstrate that synchrotron X-ray powder diffraction (XRD) is a powerful technique to study the structure and self-organization of zinc-oxide nanostructures. Zinc-oxide nanorods were prepared by a solution-growth method that resulted in uniform nanorods with 2 nm diameter and lengths in the range 10-50 nm. These nanorods were structurally characterized by a combination of small-angle and wide-angle synchrotron XRD, and transmission electron microscopy (TEM). Small-angle XRD and TEM were used to investigate nanorod self-assembly and the influence of surfactant/precursor ratio on self-assembly. Wide-angle XRD was employed to study the evolution of nanorod growth as a function of synthesis time and surfactant/precursor ratio.

• FE-SEM and TEM of nanowires

• Self-assembly of nanorods

Atomic layer epitaxy (ALE)

[1] Z. M. Zhu, A. Srivastava and R. M. Osgood, Jr., “Reactions of organosulfur compounds with Si(100) for chemically controlled epitaxy of II-VI semiconductors on Si(100).” AVS 49th International Symposium, November 2002, Denver.
[2] Z. M. Zhu, A. Srivastava and R. M. Osgood, Jr., “Reactions of organosulfur compounds with Si(100).” Journal of Physical Chemistry B 107, 13939 (2003).
The growth of silicon-based quantum devices requires precise control of ultrathin Si/wide-bandgap-semiconductor/Si heterostructures. We have investigated the initial stages of chemistry-based atomic layer epitaxy using organosulfur precursors. We have studied the reaction of several model organosulfur compounds with silicon substrates at room temperature. This reaction is the first step in the layer by layer self-limiting epitaxy of ZnS, for example, on Si(100). Our investigation uses UHV probes including Auger electron spectroscopy (AES), low-energy-electron diffraction (LEED), and temperature-programmed desorption (TPD), and calculations using density functional theory (DFT). Chemical strategies are now being explored to extend our previous successful atomic layer epitaxial methodology to chemically controlled low-temperature heteroepitaxial growth of II-VI semiconductors on silicon.
• Chemical reaction kinetics