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Technological opportunities are explored to enhance detection schemes in transmission electron microscopy (TEM) that build on the detection of single-electron scattering events across the typical spectrum of interdisciplinary applications. They range from imaging with high spatiotemporal resolution to diffraction experiments at the window to quantum mechanics, where the wave-particle dualism of single electrons is evident. At the ultimate detection limit, where isolated electrons are delivered to interact with solids, we find that the beam current dominates damage processes instead of the deposited electron charge, which can be exploited to modify electron beam-induced sample alterations. The results are explained by assuming that all electron scattering are inelastic and include phonon excitation that can hardly be distinguished from elastic electron scattering. Consequently, a coherence length and a related coherence time exist that reflect the interaction of the electron with the sample and change linearly with energy loss. Phonon excitations are of small energy (

Guerbet alcohols, a class of β-branched terminal alcohols, find widespread application because of their low melting points and excellent fluidity. Because of the limitations in the activity and selectivity of existing Guerbet catalysts, Guerbet alcohols are not currently produced via the Guerbet reaction but via hydroformylation of oil-derived alkenes followed by aldol condensation. In pursuit of a one-step synthesis of Guerbet alcohols from simple linear alcohol precursors, we show that MOF-derived RuCo alloys achieve over a million turnovers in the Guerbet reaction of 1-propanol, 1-butanol, and 1-pentanol. The active catalyst is formed in situ from ruthenium-impregnated metal-organic framework MFU-1. XPS and XAS studies indicate that the precatalyst is composed of Ru precursor trapped inside the MOF pores with no change in the oxidation state or coordination environment of Ru upon MOF incorporation. The significantly higher reactivity of Ru-impregnated MOF versus a physical mixture of Ru precursor and MOF suggests that the MOF plays an important role in templating the formation of the active catalyst and/or its stabilization. XPS reveals partial reduction of both ruthenium and MOF-derived cobalt under the Guerbet reaction conditions, and TEM/EDX imaging shows that Ru is decorated on the edges of dense nanoparticles, as well as thin nanoplates of CoOx. The use of ethanol rather than higher alcohols as a substrate results in lower turnover frequencies, and RuCo recovered from ethanol upgrading lacks nanostructures with plate-like morphology and does not exhibit Ru-enrichment on the surface and edge sites. Notably, 1H and 31P NMR studies show that through use of K3PO4 as a base promoter in the RuCo-catalyzed alcohol upgrading, the formation of carboxylate salts, a common side product in the Guerbet reaction, was effectively eliminated.

High-throughput grain mapping with sub-nanometer spatial resolution is demonstrated using scanning nanobeam electron diffraction (also known as 4D scanning transmission electron microscopy, or 4D-STEM) combined with high-speed direct-electron detection. An electron probe size down to 0.5 nm in diameter is used and the sample investigated is a gold–palladium nanoparticle catalyst. Computational analysis of the 4D-STEM data sets is performed using a disk registration algorithm to identify the diffraction peaks followed by feature learning to map the individual grains. Two unsupervised feature learning techniques are compared: principal component analysis (PCA) and non-negative matrix factorization (NNMF). The characteristics of the PCA versus NNMF output are compared and the potential of the 4D-STEM approach for statistical analysis of grain orientations at high spatial resolution is discussed.

RuNi nanoparticles supported on a metal-organic framework (RuNi@MOF) and formed in situ from a ruthenium complex enclosed inside a nickel-based MOF act as a highly active catalyst for the Guerbet reaction of ethanol to 1-butanol, providing turnover numbers up to 725 000 Ru

Semiconductors CulnSe2 (CIS) and alloys of Cu(ln,Ga)Se2 (CIGS) are often used as the light absorbing layer in thin film photovoltaic devices. These polycrystalline materials reach good conversion efficiencies despite the presence of grain boundaries, which can degrade device performance. Grain properties such as size distribution and orientation can be characterized using electron backscatter diffraction (EBSD). The EBSD method has been used extensively to determine texture and recrystallization in metal forming processes but to a lesser extent for characterization of CIGS thin film properties. This article describes measurements of grain properties for CIGS thin films grown under different reaction conditions.

Linear octenes were produced in high (70–85%) selectivity from oligomerization of liquid 1-butene using carbon-supported cobalt oxide catalysts in a continuous flow reactor. The liquid products were characterized by two-dimensional gas chromatography–mass spectrometry. Above 95% of the oligomers were C8 olefins, with the other products primarily being branched C12 olefins. The linear octene products at a conversion of 9.77% decreased in selectivity according to 3-octene > trans-2-octene > cis-2-octene > 4-octene. Methyl-heptenes including trans/cis-5-methyl-2-heptene > trans/cis-5-methyl-3-heptene > trans-3-methyl-2-heptene (at the lowest conversion) were the other major products summing to 15.6%. The selectivity of linear octenes decreased from 84 to 78% as the conversion increased from 10% to 29%. The product distribution suggests the reaction pathway involves a head-to-head coupling of two 1-butene molecules to form internal linear octenes. Head-to-tail coupling of two 1-butene molecules or a coupling ...

Particulate bis[1-(hydroxy-κO)-2(1H)-pyridinethionato-κS2]-(T-4)-zinc (zinc pyrithione; ZPT) in the diameter range 0.5–0.7 µm is a US FDA-approved anti-dandruff active widely used in anti-dandruff shampoos. A nanoparticulate form of ZPT is expected to exhibit a higher activity, be distributed more effectively on the scalp, require less thickening agent in the shampoo formulation to ensure its stability against settling than the standard form of ZPT, and would enable clear anti-dandruff shampoo formulations. We demonstrate, for the first time, that a green, mechanochemical nanoparticle synthesis process can be used to prepare nanoparticulate ZPT from zinc chloride and sodium pyrithione monohydrate. Both a Reeves attrition mill and a Retsch MixerMill were found to be effective tools for delivering the mechanical energy needed for the conversion. The infrared spectra and X-ray powder diffraction patterns for the products correspond to those for the known desired material. Transmission electron microscopic an...

Molybdenum disulfide promoted with alkali metals is one of the most studied catalysts for the conversion of synthesis gas to alcohols. In this work, MoS2 was promoted by adding potassium precursors by physical mixing (PM) and incipient wetness impregnation (IWI) and tested in a small scale reactor. The catalysts prepared by impregnation showed poorer performance compared to the sample prepared by physical mixing of K2CO3 and MoS2. The catalysts were characterized by means of X-ray diffraction, TGA–MS, SEM–EDS, TEM and XPS. The characterization results obtained by SEM–EDS and XRD analyses do not show major differences between the catalysts studied here. In contrast, the TGA results indicated that physical mixing leads to catalysts that lose sulfur at temperatures above 330 °C and TEM images showed that randomly oriented small MoS2 crystallites are obtained from PM preparation while IWI preparation gave long MoS2 crystallites.

This work validates the appropriate application of chemical reaction engineering principles in the successful design of a full-scale industrial trickle bed reactor for a proprietary hydrogenation reaction over a palladium catalyst. After identifying an effective catalyst formulation in a continuous laboratory scale trickle bed reactor, the project team used the same small-scale reactor to generate kinetic data for scale-up. The scale factor from the laboratory to the final design was about 3 × 106. The development effort identified and resolved three important problems: (1) incomplete catalyst wetting of the small catalyst bed, even though the catalyst was diluted with inert fines; (2) lower than economically attractive catalyst productivity; and (3) catalyst deactivation.

Nickel oxide (NiO) nanoparticles were synthesized via a solvothermal reaction with nickel(II) acetylacetonate as the metal containing precursor and 2-butanone (methyl ethyl ketone, MEK) as the solvent. The particles were characterized using X-ray diffraction, electron microscopy, Brunauer–Emmett–Teller (BET) surface area measurements and thermal gravimetric analysis (TGA) to determine that the crystal structure, particle size, and the presence of residual organic material upon completion of the reaction. The effect of varying the reaction temperature, time and metal precursor concentration were investigated. A range of optimal reaction conditions; defined here as a high yield, low residual organic content; were determined. A particle size in the range of 5.5–6.5 nm was observed for the optimal reaction conditions. The formation of metallic Ni was also observed for reactions carried out at 225 °C and time durations longer than 24 h. The reaction mechanism for the formation of NiO nanoparticles was investigated using mass spectrometry and a proposed pathway based on a keto-enol tautamerization is presented.

Ordered carbonaceous growth typically requires high-energy methods such as arc discharge [1] or decomposition of hydrocarbon-based precursors using laser [2–4], plasma [3], or thermolytic techniques [4]. For the latter technique, temperature regimes on the order of 600–1000° C are most common, with a few recent reports citing lower temperatures using halogenated precursors [5–7], or through alkali-metal catalyzed transformation of bulk carbon allotropes [8,9]. Sailor etal. have reported the first growth of non-amorphous carbon deposits at room temperature [10]. However, their electrochemical synthesis did not produce nanostructural carbon; due to the absence of nanosized catalytic seeds, the diameters of their fibers were > 5μm, and contained copious amounts of Cl, H, N, and O impurities.

The use of hybrid integration schemes is investigated using a combination of a SiOC film at the via level and a porous SiLK Y film at the trench level. Sequential finite element analysis is used to determine the mechanics and, subsequently, a hybrid damascene interconnect is built to demonstrate the approach.

Barrier integrity of Ta-films deposited using the enhanced coverage by re-sputtering (EnCoRe) barrier was investigated on untreated surfaces of blanket porous SiLK semiconductor dielectric (developmental version 7, hereinafter v7). Barrier integrity of a bi-layer EnCoRe Ta(N)/Ta film was studied on single damascene lines using v7 and porous SiLK semiconductor dielectric (developmental version 9, hereinafter v9). On blanket wafers more than 30 nm barrier thickness is necessary to achieve complete pore sealing. Analysis of the sheet resistance showed that when tantalum is deposited, a low resistivity α-phase is nucleated on the low-k surface. When deposited onto single damascene structures, EnCoRe Ta(N)/Ta is successful in providing a continuous metallic barrier layer over v7 and v9 semiconductor dielectric lines.

The microstructures of YBCO/N/YBCO ramp-edge junctions have been studied by transmission electron microscopy and related to supercurrent transport properties which depend on the barrier layer N, the interfacial structures and defect structures in the multilayer epitaxial devices. Three different types of junction materials were investigated: Metallic oxide barriers, CaRuO{sub 3} and SrRuO{sub 3}; barriers isostructural to YBCO, Co-doped YBCO and Co-doped PrBa{sub 2}Cu{sub 3}O{sub 7}; and 'interface engineered' barriers, formed by plasma treatment of the YBCO ramp-edge. Metallic oxide barriers are characterized by high steps and strong variations in local barrier width. The observed topologies are consistent with an island growth mode for both CaRuO{sub 3} and SrRuO{sub 3}. The metallic oxide barriers are associated with interfacial strain fields that are believed to be the cause for interfacial oxygen depletion in YBCO and the observed excess normal-state resistance. A number of structural defects and deviations from perfect epitaxy have been observed. Most disruptive to the integrity of the multilayer structures and transport properties is the nucleation of a-axis YBCO grains at steep barrier steps and within the YBCO layers. The barrier layers in isostructural junctions are well structured with a high degree of interfacial coherence and for the most part,more » Cu-O planes are continuous across the interfaces. In contrast to heterostructured metallic oxide barriers, isostructural junctions contain few extraneous defects, such as a-axis grains at the barrier layer, moreover, the second YBCO layer is of good quality due to the perfect epitaxy between the materials. Among the junctions investigated the interface engineered junctions have shown the best electromagnetic properties. Their structure is characterized by narrow (2-3 nm) barriers that are continuous and crystalline. No significant interfacial strains and structural disorder were observed. This and a constant barrier thickness appear responsible for obtaining good uniformity of electric transport properties. The narrow pinhole-free barrier, coupled with excellent epitaxy and few defects, yields good reproducibility and a range of properties suitable for practical applications.« less

Asphalt cements are often regarded as a colloidal system containing several hydrocarbon constituents: asphaltenes, resins, and oils. The high molecular weight asphaltene particles are considered to be covered in a sheath of resins and dispersed in the lower molecular weight oily medium [Whiteoak (1990) The Shell Bitumen Handbook (Shell Bitumen UK, Riversdell House, Surrey, UK)]. However, the exact arrangement of the asphaltene particles within the oily phase will vary depending on the relative amounts of resin, asphaltene, and oils. It is this arrangement and the degree of association between asphaltene particles that govern the rheological properties of the cement [Simpson et al. (1961) J. Chem. Eng. Data 6:426-429; Whiteoak (1990)]. Here we report for the first time the observation of a three-dimensional network of asphaltene strands within straight, polymer-modified, and aged asphalt cements. While the existence of a asphaltene/resin micelle network has been proposed in previous studies [Whiteoak (1990)], direct observation has not been reported. The network is expected to greatly influence the rheological properties of the asphalt binder and ultimately the properties of asphalt concretes. In situ fracture studies of asphalt cement/aggregate composites indicate a possible correlation between the network structure and adhesion between the cement binder and aggregate.

Superconductor-normal-superconductor (SNS) edge junctions consisting of YBa2Cu3O7/YBa2Cu2.79Co0.21O7−x/YBa2Cu3O7 were fabricated on (001) YSZ substrates using laser deposition. In contrast to other SNS junctions, e.g., with La0.5Sr0.5CoO3, CaRuO3, or SrRuO3 as the barrier layer, these devices do not display an excess normal-state resistance. High-resolution and conventional transmission electron microscopy (TEM) techniques were employed to investigate the SN interface structure and possible interface defects. Results are compared to recent TEM investigations of CaRuO3 SNS junctions.

Superconductor-normal-superconductor (SNS) edge junctions consisting of YBa 2 Cu 3 O 7 /CaRuO 3 /YBa 2 Cu 3 O 7 were fabricated on (001) LaAlO 3 substrates using laser deposition. These devices display an excess resistance which may be related to the SN interface and normal layer structure or composition. High-resolution and conventional transmission electron microscopy were employed to investigate the SN interface structure to determine the degree of interface matching and possible interfacial defects. Energy-loss spectroscopy and energy dispersive X-ray analysis were performed on the CaRuO 3 film and near interface regions to determine the normal layer composition and to quantify the extent of interdiffusion between the CaRuO 3 and YBCO films. Results are compared to recent investigations of SNS edge junctions consisting of YBa 2 Cu 3 O 7− x /YBa 2 Cu 2.79 Co 0.21 O 7− x /YBa 2 Cu 3 O 7− x .

When comparing large numbers of TEM micrographs of insoluble additives in polymer-based nanocomposite systems, the ability to determine or estimate the dispersion quality (i.e. uniformity of size and/or spatial distribution) is often difficult. The objective of this study was to develop a method to quantify dispersions observed in TEM micrographs that enables both a numerical “ranking” to be assigned to individual dispersions as well as tabulation a multitude of images acquired over time. Several methods were reviewed and applied to a set of TEM dispersion images of an insoluble additive in polystyrene. Projected area diameter, particle area, and Euclidean distance between particle centroids were chosen from all the particle size distribution and spatial distribution parameters present in the literature, but none successfully yielded a quantitative indicator of dispersion quality for the micrographs. In contrast, generating cumulative volume percent curves for each sample appeared to be a preferred method of quantifying and comparing dispersions in TEM micrographs. The volume diameter values obtained by this method can be used for “ranking” and tabulation of dispersion quality and account for both “good” additive dispersions (i.e. those with small domains of a narrow size range around 1 μm or less) and “bad” additive dispersions (i.e. those with non-uniform domains ranging in size by several microns or more). As a result, the numerical values generated by this method can be used to quantitatively determine correlations between the dispersion quality of nanoparticles in polymer-based nanocomposite materials and various macroscale physical and/or performance properties of such materials. This method’s precision was statistically determined to decrease with increasing particle size and be heavily dependent on representative sampling.

As device dimensions scale down, the back-end-of-line dimensions scale down as well, which results in an increasing resistance-capacitance delay of the interconnect. In order to compensate for the increase in the capacitance part, porous low-k dielectrics have been introduced in copper interconnect technology. Due to the highly interconnected pore structure of most porous low-k materials, liquid and/or gaseous species fill the pores of the matrix during integration steps. In addition, pores give rise to surface roughness at the top-interface and at the sidewall after etch, which makes it difficult to deposit a thin, continuous barrier in narrow trenches embedded in porous low-k dielectrics. All of the above makes pore sealing a prerequisite for reliable porous low-k integration (Guedj et al., 2004). Different pore sealing techniques are under investigation. In the case of low-k materials in which the porosity is created using a porogen, the porosity creation could also be shifted to a later phase of the integration scheme; either after low-k etch (Caluwaerts et al., 2003) or after metal CMP (Fayole et al., 2004; Jousseaume et al., 2005), which is referred to as post-etch-burn-out (PEBO) and post-CMP-burn-out (PCBO), respectively. It has been demonstrated previously, that the dielectric reliability could be improved considerably by these kinds of pore sealing techniques (Tokei et al., 2004). In this paper, both integration approaches are compared for porous SiLKtrade dielectric resin (k=2.2) from The Dow Chemical Company and the effect of both integration approaches on the interline capacitance, the dielectric reliability and electromigration are investigated and discussed in more detail

The SiLK resins, composed of aromatic hydrocarbons, are a family of highly cross-linked thermoset polymers with isotropic dielectric properties. Patterning of SiLK for high aspect ratio copper interconnects has depended on reactive ion etching with oxygen/nitrogen gas mixtures. Reactive ion etching is therefore also accomplished with reducing plasmas such as nitrogen/hydrogen. An additional plasma cleaning step can be inserted after the reactive ion etching (RIE) step, so that any residual contamination is removed prior to imaging or final sputter coating. Automated sample preparation of microelectronic materials containing high and low-k dielectrics for FESEM is accomplished in this article by combining these techniques: plasma cleaning, ion beam etching, and reactive ion etching. A single RIE chemistry was effective in etching both dielectrics as well as delineating the other phases present.

We describe the growth of amorphous carbon nanofibers (CNFs) from iron-encapsulated dendrimer catalysts at ambient temperature and pressure conditions. Both fourth-generation poly (propyleneimine) (PPI) and poly(amidoamine) (PAMAM) dendrimers were suitable macromolecular hosts for the catalytic species. Average nanofiber diameters range from 10 - 15 nm, with lengths in excess of 20 microns.

Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009