Helge Heinrich

Investigation of chemical bath deposition of ZnO thin films using six different complexing agents

Chemical bath deposition of ZnO thin films using six different complexing agents, namely ammonia, hydrazine, ethanolamine, methylamine, triethanolamine and dimethylamine, is investigated. As-grown films were mainly ZnO2 with a band gap around 4.3?eV. Films annealed at 400??C were identified as ZnO with a band gap around 3.3?eV. X-ray diffraction and micro-Raman spectroscopy revealed that as-grown films consist mainly of cubic zinc peroxide that was transformed into hexagonal ZnO after annealing. Rutherford backscattering spectroscopy (RBS) detected excess oxygen content in ZnO films after annealing. Fourier transform infrared spectroscopy of as-grown films showed a broad absorption band around 3300?cm?1 suggesting that the as-grown films may consist of a mixture of zinc peroxide and zinc hydroxide. X-ray photoelectron spectroscopy multiplex spectra of the O 1s peak were found to be consistent with film stoichiometry revealed by RBS. High-resolution transmission electron micrographs showed small variations of the order of 10?nm in film thickness which corresponds to the average grain size. A carrier density as high as 2.24?1019?cm?3 and a resistivity as low as 6.48 ? 10?1???cm were obtained for films annealed at 500??C in argon ambient.

In situ synthesis of carbon nanotubes decorated with palladium nanoparticles using arc-discharge in solution method

A unique, simple, inexpensive, and one-step synthesis route to produce carbon nanotubes (CNTs) decorated with palladium nanoparticles using a simplified dc arc-discharge in solution is reported. Zero-loss energy filtered transmission electron microscopy and scanning transmission electron microscopy confirm the presence of 3nm palladium nanoparticles. Such palladium nanoparticles form during the reduction of palladium tetra-chloro-square-planar complex. The deconvoluted x-ray photoelectron spectroscopy envelope shows the presence of palladium on the decorated CNTs. The energy dispersive spectroscopy suggests no functionalization of atomic chlorine to the sidewall of the CNTs. The presence of dislodged graphene sheets with wavy morphology supports the formation of CNTs through the “scroll mechanism.”

Self-assembly of densely packed and aligned bilayer ZnO nanorod arrays

We present a method of self-assembly of densely packed and aligned bilayer ZnO nanorod arrays in a hydrothermal synthesis process. The alkali hydrothermal environment first induced the growth of hydrotalcitelike zincowoodwardite plates, which provide a lattice-matched surface for the self-assembly of ZnO nanorod arrays. The high packing density of the ZnO nanorod arrays demonstrates efficient nucleation and growth processes of ZnO on the zincowoodwardite. The interfacial phenomena involved in the growth of ZnO and self-assembly are discussed. The two-dimensional arrays of ZnO nanorods may find future applications in nanoelectronics and nanophotonics.

Electron transport through single carbon nanotubes

We report on the transport of energetic electrons through single, well aligned multi-wall carbon nanotubes (CNT). Embedding of CNTs in a protective carbon fiber coating enables the application of focused ion beam based sample preparation techniques for the non-destructive isolation and alignment of individual tubes. Aligned tubes with lengths of 0.7 to 3 mu m allow transport of 300 keV electrons in a transmission electron microscope through their hollow cores at zero degree incident angles and for a misalignment of up to 1 degree.

High contrast hollow-cone dark field transmission electron microscopy for nanocrystalline grain size quantification

In this paper, we describe hollow-cone dark field (HCDF) transmission electron microscopy (TEM) imaging, with a slightly convergent beam, as an improved technique that is suitable to form high contrast micrographs for nanocrystalline grain size quantification. We also examine the various factors that influence the HCDF TEM image quality, including the conditions of microscopy (alignment, focus and objective aperture size), the properties of the materials imaged (e.g., atomic number, strain, defects), and the characteristics of the TEM sample itself (e.g., thickness, ion milling artifacts). Sample preparation was found to be critical and an initial thinning by wet etching of the substrate (for thin film samples) or tripod polishing (for bulk samples), followed by low-angle ion milling was found to be the preferred approach for preparing high-quality electron transparent samples for HCDF imaging.

Structure and phonon density of states of supported size-selected F57eAu nanoclusters: A nuclear resonant inelastic x-ray scattering study

We have measured the phonon density of states (PDOS) of isolated bcc and fcc FexAu1−x alloy nanoclusters (NCs) by nuclear resonant inelastic x-ray scattering. Drastic deviations were observed with respect to the PDOS of bulk Fe–Au alloys. Important information on the structure and thermodynamic properties of these NCs was obtained.

Propagation of high-frequency surface plasmons on gold

Propagation of surface plasmons on gold in the range 2.8-3.5 eV over 0.1-1.6 μm distances was characterized by cathodoluminescence spectroscopy. Surface plasmons were excited by an electron beam near a grating milled in the gold. The spectra of outcoupled radiation reveal increasingly strong propagation losses as surface plasmon energy increases above 2.8 eV, but little effect in the range 1.6-2.8 eV. These results are in partial agreement with theoretical expectations.

Fuel-Matrix Chemical Interaction between U-7wt.%Mo Alloy and Mg

A solid-to-solid, U-7wt.%Mo vs. Mg diffusion couple was assembled and annealed at 550°C for 96 hours. Themicrostructurein the interdiffusion zone and the development of concentration profiles were examined via scanning electron microscopy, transmission electron microscopy (TEM) and X-ray energy dispersive spectroscopy. A TEM specimen was prepared at the interface between U-7wt.%Mo andMgusing focused ion beam in-situ lift-out. The U-7wt.%Mo alloy was bonded well tothe Mg at the atomic scale, without any evidence of oxidation, cracks or pores.Despite the good bonding, very little or negligible interdiffusion was observed.This is consistent with the expectation based on negligible solubilities according to the equilibrium phase diagrams. Along with other desirableproperties, Mgis a potential inert matrix or barrier materialfor U-Mo fuel alloy systembeing developed forthe Reduced Enrichment for Research and Test Reactor (RERTR) program.

Optoelectronically automated system for carbon nanotubes synthesis via arc-discharge in solution

The method of arc discharge in the solution is unique and inexpensive route for synthesis of the carbon nanotubes (CNTs), carbon onions, and other carbon nanostructures. Such a method can be used for in situ synthesis of CNTs decorated with nanoparticles. Herein, we report a simple and inexpensive optoelectronically automated system for arc discharge in solution synthesis of CNTs. The optoelectronic system maintains a constant gap between the two electrodes allowing a continuous synthesis of the carbon nanostructures. The system operates in a feedback loop consisting of an electrode-gap detector and an analog electronic unit, as controller. This computerized feeding system of the anode was used for in situ nanoparticles incorporated CNTs. For example, we have successfully decorated CNTs with ceria, silica, and palladium nanoparticles. Characterizations of nanostructures are performed using high-resolution transmission electron microscopy, scanning transmission electron microscopy, energy dispersive spectr...

Porous silicon bulk acoustic wave resonator with integrated transducer.

AbstractWe report that porous silicon acoustic Bragg reflectors and AlN-based transducers can be successfully combined and processed in a commercial solidly mounted resonator production line. The resulting device takes advantage of the unique acoustic properties of porous silicon in order to form a monolithically integrated bulk acoustic wave resonator.