Silicon oxide nanowire growth mechanisms revealed by real-time electron microscopy

© 2016 The Royal Society of Chemistry. Growth of one-dimensional materials is possible through numerous mechanisms that affect the nanowire structure and morphology. Here, we explain why a wide range of morphologies is observed when silicon oxide nanowires are grown on silicon substrates using liquid gallium catalyst droplets. We show that a gallium oxide overlayer is needed for nanowire nucleation at typical growth temperatures, and that it can decompose during growth and, hence, dramatically alter the nanowire morphology. Gallium oxide decomposition is attributed to etching caused by hydrogen that can be supplied by thermal dissociation of H2O (a common impurity). We show that H2O dissociation is catalyzed by silicon substrates at temperatures as low as 320 °C, identify the material supply pathways and processes that rate-limit nanowire growth under dry and wet atmospheres, and present a detailed growth model that explains contradictory results reported in prior studies. We also show that under wet atmospheres the Ga droplets can be mobile and promote nanowire growth as they traverse the silicon substrate

Nanotubes from the Misfit Layered Compound (SmS)1.19TaS2: Atomic Structure, Charge Transfer, and Electrical Properties

Misfit layered compounds (MLCs) MX-TX2, where M, T = metal atoms and X = S, Se, or Te, and their nanotubes are of significant interest due to their rich chemistry and unique quasi-1D structure. In particular, LnX-TX2 (Ln = rare-earth atom) constitute a relatively large family of MLCs, from which nanotubes have been synthesized. The properties of MLCs can be tuned by the chemical and structural interplay between LnX and TX2 sublayers and alloying of each of the Ln, T, and X elements. In order to engineer them to gain desirable performance, a detailed understanding of their complex structure is indispensable. MLC nanotubes are a relative newcomer and offer new opportunities. In particular, like WS2 nanotubes before, the confinement of the free carriers in these quasi-1D nanostructures and their chiral nature offer intriguing physical behavior. High-resolution transmission electron microscopy in conjunction with a focused ion beam are engaged to study SmS-TaS2 nanotubes and their cross-sections at the atomic scale. The atomic resolution images distinctly reveal that Ta is in trigonal prismatic coordination with S atoms in a hexagonal structure. Furthermore, the position of the sulfur atoms in both the SmS and the TaS2 sublattices is revealed. X-ray photoelectron spectroscopy, electron energy loss spectroscopy, and X-ray absorption spectroscopy are carried out. These analyses conclude that charge transfer from the Sm to the Ta atoms leads to filling of the Ta 5dz2 level, which is confirmed by density functional theory (DFT) calculations. Transport measurements show that the nanotubes are semimetallic with resistivities in the range of 10-4 Ω·cm at room temperature, and magnetic susceptibility measurements show a superconducting transition at 4 K. © 2022 The Authors. Published by American Chemical Society.This work was partially supported by the Israel Science Foundation Grant No. 339/18 (Internal Grant No. 120924) (R.T.). The following foundations are acknowledged: Perlman Family Foundation; the Kimmel Center for Nanoscale Science Grant No. 43535000350000; and the Irving and Cherna Moskowitz Center for Nano and Bio-Nano Imaging. CzechNanoLab Project LM2018110 funded by MEYS CR is gratefully acknowledged for the financial support of the measurements and sample fabrication at the CEITEC Nano Research Infrastructure. This work was partially supported by Ceitec Nano+ (CZ.02.01/0.0./.0.0./16_013/0001728 under Program OPVVV) and the Horizon 2020 Research and Innovation Programme under Grant Agreement 810626 (SINNCE). Work at Ames Laboratory was supported by the Materials Sciences and Engineering Division of the Office of Basic Energy Sciences, Office of Science of U.S. Department of Energy. Ames Laboratory is operated for the U.S. DOE by Iowa State University of Science and Technology under Contract No. DE-AC02-07CH11358. A part of the work at Buffalo State was supported by the faculty startup fund from the Dean’s Office, School of Arts and Sciences, State University of New York (SUNY), Buffalo State. We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities for XAS studies. Parts of this research were carried out at PETRA III, P23 “In-situ and X-ray imaging beamline”

Analysis of Thin Films by Time-of-Flight Low Energy Ion Scattering

In the paper the design and application of a time-of-flight low energy ion scattering instrument built into an UHV complex deposition and analytical apparatus is described. A special attention is aimed at demonstrating the ability of time-of-flight low energy ion scattering to analyse near-to-surface layers of thin films prepared both ex situ and in situ. It is shown that the broadening of peaks in time-of-flight low energy ion scattering spectra can be attributed to multiple scattering and inelastic losses of ions in deeper layers. As a result of that, the peak width of ultrathin films depends on their thickness

Applications in opto-electronics: general discussion.

Applications in opto-electronics: general discussion

Nanotubes from the Misfit Layered Compound (SmS)1.19TaS2(SmS)_{1.19}TaS_2 : Atomic Structure, Charge Transfer, and Electrical Properties

Misfit layered compounds (MLCs) MX-TX$_2$, where M, T = metal atoms and X = S, Se, or Te, and their nanotubes are of significant interest due to their rich chemistry and unique quasi-1D structure. In particular, LnX-TX$_2$ (Ln = rare-earth atom) constitute a relatively large family of MLCs, from which nanotubes have been synthesized. The properties of MLCs can be tuned by the chemical and structural interplay between LnX and TX$_2$ sublayers and alloying of each of the Ln, T, and X elements. In order to engineer them to gain desirable performance, a detailed understanding of their complex structure is indispensable. MLC nanotubes are a relative newcomer and offer new opportunities. In particular, like WS$_2$ nanotubes before, the confinement of the free carriers in these quasi-1D nanostructures and their chiral nature offer intriguing physical behavior. High-resolution transmission electron microscopy in conjunction with a focused ion beam are engaged to study SmS-TaS$_2$ nanotubes and their cross-sections at the atomic scale. The atomic resolution images distinctly reveal that Ta is in trigonal prismatic coordination with S atoms in a hexagonal structure. Furthermore, the position of the sulfur atoms in both the SmS and the TaS$_2$ sublattices is revealed. X-ray photoelectron spectroscopy, electron energy loss spectroscopy, and X-ray absorption spectroscopy are carried out. These analyses conclude that charge transfer from the Sm to the Ta atoms leads to filling of the Ta 5d$_z$$^2$ level, which is confirmed by density functional theory (DFT) calculations. Transport measurements show that the nanotubes are semimetallic with resistivities in the range of 10$^{–4}$ Ω·cm at room temperature, and magnetic susceptibility measurements show a superconducting transition at 4 K