19 research outputs found
Synthesis and characterization of smooth ultrananocrystalline diamond films via low pressure bias-enhanced nucleation and growth
This letter describes the fundamental process underlying the synthesis of ultrananocrystalline diamond (UNCD) films, using a new low-pressure, heat-assisted bias-enhanced nucleation (BEN)/bias enhanced growth (BEG) technique, involving H2/CH4 gas chemistry. This growth process yields UNCD films similar to those produced by the Ar-rich/CH4 chemistries, with pure diamond nanograins (3–5 nm), but smoother surfaces (~6 nm rms) and higher growth rate (~1 µm/h). Synchrotron-based x-Ray absorption spectroscopy, atomic force microscopy, and transmission electron microscopy studies on the BEN-BEG UNCD films provided information critical to understanding the nucleation and growth mechanisms, and growth condition-nanostructure-property relationships
Are diamonds a MEMS\u27 best friend?
Next-generation military and civilian communication systems will require technologies capable of handling data/ audio, and video simultaneously while supporting multiple RF systems operating in several different frequency bands from the MHz to the GHz range [1]. RF microelectromechanical/nanoelectromechanical (MEMS/NEMS) devices, such as resonators and switches, are attractive to industry as they offer a means by which performance can be greatly improved for wireless applications while at the same time potentially reducing overall size and weight as well as manufacturing costs
EMSL and Institute for Integrated Catalysis (IIC) Catalysis Workshop
Within the context of significantly accelerating scientific progress in research areas that address important societal problems, a workshop was held in November 2010 at EMSL to identify specific and topically important areas of research and capability needs in catalysis-related science
Dynamic Processes in Biology, Chemistry, and Materials Science: Opportunities for UltraFast Transmission Electron Microscopy - Workshop Summary Report
This report summarizes a 2011 workshop that addressed the potential role of rapid, time-resolved electron microscopy measurements in accelerating the solution of important scientific and technical problems. A series of U.S. Department of Energy (DOE) and National Academy of Science workshops have highlighted the critical role advanced research tools play in addressing scientific challenges relevant to biology, sustainable energy, and technologies that will fuel economic development without degrading our environment. Among the specific capability needs for advancing science and technology are tools that extract more detailed information in realistic environments (in situ or operando) at extreme conditions (pressure and temperature) and as a function of time (dynamic and time-dependent). One of the DOE workshops, Future Science Needs and Opportunities for Electron Scattering: Next Generation Instrumentation and Beyond, specifically addressed the importance of electron-based characterization methods for a wide range of energy-relevant Grand Scientific Challenges. Boosted by the electron optical advancement in the last decade, a diversity of in situ capabilities already is available in many laboratories. The obvious remaining major capability gap in electron microscopy is in the ability to make these direct in situ observations over a broad spectrum of fast (µs) to ultrafast (picosecond [ps] and faster) temporal regimes. In an effort to address current capability gaps, EMSL, the Environmental Molecular Sciences Laboratory, organized an Ultrafast Electron Microscopy Workshop, held June 14-15, 2011, with the primary goal to identify the scientific needs that could be met by creating a facility capable of a strongly improved time resolution with integrated in situ capabilities. The workshop brought together more than 40 leading scientists involved in applying and/or advancing electron microscopy to address important scientific problems of relevance to DOE’s research mission. This workshop built on previous workshops and included three breakout sessions identifying scientific challenges in biology, biogeochemistry, catalysis, and materials science frontier areas of fundamental science that underpin energy and environmental science that would significantly benefit from ultrafast transmission electron microscopy (UTEM). In addition, the current status of time-resolved electron microscopy was examined, and the technologies that will enable future advances in spatio-temporal resolution were identified in a fourth breakout session
Tailoring silica–alumina-supported Pt–Pd as poison-tolerant catalyst for aromatics hydrogenation
The tailoring of the physicochemical and catalytic properties of mono- and bimetallic Pt–Pd catalysts supported on amorphous silica–alumina was studied. Electron-energy-loss spectroscopy and extended X-ray absorption fine structure analyses indicated that bimetallic Pt–Pd and relatively large monometallic Pd particles were formed, whereas the X-ray absorption near edge structure provided direct evidence for the electronic deficiency of the Pt atoms. The heterogeneous distribution of metal particles was also shown by high-resolution transmission electron microscopy. The average structure of the bimetallic particles (Pt-rich core and Pd-rich shell) and the presence of Pd particles led to surface Pd enrichment, which was independently shown by IR spectra of adsorbed CO. The specific metal distribution, average size, and surface composition of the Pt–Pd particles depend to a large extent on the metal precursors. In the presence of NH3 ligands, Pt–Pd particles with a fairly homogeneous bulk and surface metal distribution were formed. Also, high Lewis acid site concentration of the carrier leads to more homogeneous bimetallic particles. All catalysts were active for the hydrogenation of tetralin in the absence and presence of quinoline and dibenzothiophene (DBT). Monometallic Pt catalysts had the highest hydrogenation activity in poison-free and quinoline-containing feed. When DBT was present, bimetallic Pt–Pd catalysts with the most homogenous metal distribution showed the highest activity. The higher resistance of bimetallic catalysts toward sulfur poisoning compared to their monometallic Pt counterparts results from the weakened metal–sulfur bond on the electron-deficient Pt atoms. Thus, increasing the fraction of electron-deficient Pt on the surface of the bimetallic clusters increases the efficiency of the catalyst in the presence of sulfur-containing compounds
In Situ Spectroscopic Characterization of Ni<sub>1–<i>x</i></sub>Zn<sub><i>x</i></sub>/ZnO Catalysts and Their Selectivity for Acetylene Semihydrogenation in Excess Ethylene
The structures of ZnO-supported Ni
catalysts were explored with
in situ X-ray absorption spectroscopy, temperature-programmed reduction,
X-ray diffraction, high-resolution transmission electron microscopy
(HRTEM), scanning transmission electron microscopy, and electron energy
loss spectroscopy. Calcination of nickel nitrate on a nanoparticulate
ZnO support at 450 °C results in the formation of Zn-doped NiO
(ca. Ni<sub>0.85</sub>Zn<sub>0.15</sub>O) nanoparticles with the rock
salt crystal structure. Subsequent in situ reduction monitored by
X-ray absorption near-edge structure (XANES) at the Ni K edge reveals
a direct transformation of the Zn-doped NiO nanoparticles to a face-centered
cubic alloy, Ni<sub>1–<i>x</i></sub>Zn<sub><i>x</i></sub>, at ∼400 °C with <i>x</i> increasing
with increasing temperature. Both in situ XANES and ex situ HRTEM
provide evidence for intermetallic β<sub>1</sub>-NiZn formation
at ∼550 °C. In comparison to a Ni/SiO<sub>2</sub> catalyst,
Ni/ZnO necessitates a higher temperature for the reduction of Ni<sup>II</sup> to Ni<sup>0</sup>, which highlights the strong interaction
between Ni and the ZnO support. The catalytic activity for acetylene
removal from an ethylene feed stream is decreased by a factor of 20
on Ni/ZnO in comparison to Ni/SiO<sub>2</sub>. The decrease in catalytic
activity of Ni/ZnO is accompanied by a reduced absolute selectivity
to ethylene. H–D exchange measurements demonstrate a reduced
ability of Ni/ZnO to dissociate hydrogen in comparison to Ni/SiO<sub>2</sub>. These results of the catalytic experiments suggest that
the catalytic properties are controlled, in part, by the zinc oxide
support and stress the importance of reporting absolute ethylene selectivity
for the catalytic semihydrogenation of acetylene in excess ethylene
Current status and future directions for in situ transmission electron microscopy
This review article discusses the current and future possibilities for the application of in situ transmission electron microscopy to reveal synthesis pathways and functional mechanisms in complex and nanoscale materials. The findings of a group of scientists, representing academia, government labs and private sector entities (predominantly commercial vendors) during a workshop, held at the Center for Nanoscale Science and Technology-National Institute of Science and Technology (CNST-NIST), are discussed. We provide a comprehensive review of the scientific needs and future instrument and technique developments required to meet them. Published by Elsevier B.V