Transition Metal Substrates Research Articles

Transition-metal dispersion on carbon-doped boron nitride nanostructures: Applications for high-capacity hydrogen storage

Using density-functional theory calculations, we investigated the adsorption of transition-metal (TM) atoms (TM = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) on carbon doped hexagonal boron nitride (BN) sheet and the corresponding cage (B${}_{12}$N${}_{12}$). With carbon substitution of nitrogen, Sc, V, Cr, and Mn atoms were energetically favorable to be dispersed on the BN nanostructures without clustering or the formation of TM dimers, due to the strong binding between TM atoms and substrate, which contains the half-filled levels above the valence bands maximum. The carbon doped BN nanostructures with dispersed Sc could store up to five and six H${}_{2}$, respectively, with the average binding energy of 0.3 \ensuremath{\sim} 0.4 eV, indicating the possibility of fabricating hydrogen storage media with high capacity. We also demonstrated that the geometrical effect is important for the hydrogen storage, leading to a modulation of the charge distributions of $d$ levels, which dominates the binding between H${}_{2}$ and TM atoms.

ChemInform Abstract: 1,1‐Carboboration

AbstractReview: of alkynes; 44 refs.

1,1-Carboboration

The use of very electrophilic boranes RB(C(6)F(5))(2) widens the scope of the 1,1-carboboration reaction substantially. Simple terminal alkynes HC≡CR undergo this reaction with the RB(C(6)F(5))(2) reagents rapidly under mild conditions to give high yields of very useful new alkenylborane products. Even internal alkynes RC≡CR undergo 1,1-carboboration with the RB(C(6)F(5))(2) reagents to provide a novel way of carbon-carbon σ-bond activation. Variants of these reactions involving phosphorus substituted alkynes and more complex bisalkynyl main group and transition metal substrates give rise to the formation of very interesting functionalized metallacyclic products upon treatment with RB(C(6)F(5))(2) reagents by means of reaction sequences involving selective 1,1-carboboration steps.

Initial Stage of Graphene Growth on a Cu Substrate

The growth of graphene on copper foil has attracted attention in the last two years due to its feasibility for a controllable growth process. One of the key issues remaining for practical application of graphene in solid-state devices is growth with a large grain size. Because the C–C bond in graphene is strong enough to prevent the evaporation–condensation process, Smoluchowski ripening is expected to be the dominant process for coalescence. In this article, we present the initial growth process of graphene on a Cu foil via the chemical vapor deposition method by using secondary electron microscopy and Raman microscopy. In contrast to the other transition-metal substrates, such as Ir and Rh, the center of graphene islands binds to the substrate more rigidly than the edge. For the growth with a large grain size, the graphene should be grown on a substrate with a low diffusion barrier for the carbon clusters (or islands) with low flux; this is the controlling parameter for the grain size. In addition, high-temperature growth (or annealing) generally becomes a dominant condition for the completion of graphene growth with large grains after the coalescence.

Formation of Carbon Clusters in the Initial Stage of Chemical Vapor Deposition Graphene Growth on Ni(111) Surface

To understand the nucleation of carbon atoms to form graphene on transition metal substrates during chemical vapor deposition (CVD) synthesis, carbon clusters supported on Ni(111) surfaces, namely CN@Ni(111) (where N ≤ 24), were explored systematically using density functional theory (DFT) calculations. Very different from the freestanding C clusters, on a Ni(111) surface, the C chain configuration is superior to the C ring formation and dominates the ground state until N > 12. A ground state structural transition from a one-dimensional C chain to a two-dimensional sp2 network (or graphene island) occurs at N = 12. It is surprising that incorporating one to three 5-membered-rings (5MRs) or pentagons into a graphene island is required to achieve the energetically most stable structure. This deep insight into the supported C cluster formation is crucial for understanding the growth mechanism of graphene on a transition metal surfaces in CVD experiments and the experimental design of CVD graphene growth.

Some Organometallic Chemistry of Tetracyanoethene: CN-displacement and Cycloaddition Reactions with Alkynyl - Transition Metal Complexes and Related Chemistry

The highly electron-deficient cyanocarbons tetracyanoethene (tcne) and, to a lesser extent, tetracyanoquinodimethane (tcnq), display a fascinating chemistry with transition metal substrates. In particular, the [2 + 2]-cycloadditions of the cyanocarbons with alkynyl- or poly-ynyl–metal complexes have been extensively studied by the author’s group. These reactions proceed via polar adducts to give σ-cyclobutenyl complexes, which then undergo facile ring-opening (retro-electrocyclic) reactions to form the corresponding butadienyl derivatives. In some cases, further reactions can occur by displacement of weakly bound ligands from the metal centre. The subsequent chemistry of these derivatives has been only cursorily investigated, while related studies of organic analogues have produced molecules with interesting electronic and optical properties.

Protein-Associated Water and Secondary Structure Effect Removal of Blood Proteins from Metallic Substrates

Removing adsorbed protein from metals has significant health and industrial consequences. There are numerous protein-adsorption studies using model self-assembled monolayers or polymeric substrates but hardly any high-resolution measurements of adsorption and removal of proteins on industrially relevant transition metals. Surgeons and ship owners desire clean metal surfaces to reduce transmission of disease via surgical instruments and minimize surface fouling (to reduce friction and corrosion), respectively. A major finding of this work is that, besides hydrophobic interaction adhesion energy, water content in an adsorbed protein layer and secondary structure of proteins determined the access and hence ability to remove adsorbed proteins from metal surfaces with a strong alkaline-surfactant solution (NaOH and 5 mg/mL SDS in PBS at pH 11). This is demonstrated with three blood proteins (bovine serum albumin, immunoglobulin, and fibrinogen) and four transition metal substrates and stainless steel (platinum (Pt), gold (Au), tungsten (W), titanium (Ti), and 316 grade stainless steel (SS)). All the metallic substrates were checked for chemical contaminations like carbon and sulfur and were characterized using X-ray photoelectron spectroscopy (XPS). While Pt and Au surfaces were oxide-free (fairly inert elements), W, Ti, and SS substrates were associated with native oxide. Difference measurements between a quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance spectroscopy (SPR) provided a measure of the water content in the protein-adsorbed layers. Hydrophobic adhesion forces, obtained with atomic force microscopy, between the proteins and the metals correlated with the amount of the adsorbed protein-water complex. Thus, the amount of protein adsorbed decreased with Pt, Au, W, Ti and SS, in this order. Neither sessile contact angle nor surface roughness of the metal substrates was useful as predictors here. All three globular proteins behaved similarly on addition of the alkaline-surfactant cleaning solution, in that platinum and gold exhibited an increase, while tungsten, titanium, and stainless steel showed a decrease in weight. According to dissipation measurements with the QCM-D, the adsorbed layer for platinum and gold was rigid, while that for the tungsten, titanium, and stainless steel was much more flexible. The removal efficiency of adsorbed-protein by alkaline solution of SDS depended on the water content of the adsorbed layers for W, Ti, and SS, while for Pt and Au, it depended on secondary structural content. When protein adsorption was high (Pt, Au), protein-protein interactions and protein-surface interactions were dominant and the removal of protein layers was limited. Water content of the adsorbed protein layer was the determining factor for how efficiently the layer was removed by alkaline SDS when protein adsorption was low. Hence, protein-protein and protein-surface interactions were minimal and protein structure was less perturbed in comparison with those for high protein adsorption. Secondary structural content determined the efficient removal of adsorbed protein for high adsorbed amount.

Controlling Hydrogenation of Graphene on Transition Metals

A monatomic layer of graphite (MG or graphene) adsorbed on the (111) faces of transition metals Pt, Ir, and Ni, has been employed for controlling the atomic hydrogen adsorption site selectivity and the amount of hydrogen adsorbed upon saturation. The variations in the graphene-metal chemical bonding caused by hydrogenation and the values of saturated hydrogen coverage have been studied by X-ray photoemission and X-ray absorption spectroscopy. The hydrogenation of the graphene/metal systems has also been compared to the hydrogen adsorption on highly oriented pyrolytic graphite under the same experimental conditions. It has been found that graphene adsorption on the transition metal substrates can drastically enhance the hydrogen uptake values. The highest values have been observed for MG/Ir(111), less for MG/Pt(111), even less for MG/Ni and the least for the adsorption on bulk graphite. The high level of H coverage on MG/Ir and MG/Pt has been assigned to the preferential H adsorption on the more bonding patches (pores) of the MG/metal coincidence lattice. This adsorption creates unpaired electrons which contribute to a strengthening of the graphene-metal bonds. In this way, the densest possible graphane-like patches can be formed on MG/Pt and MG/Ir. On the MG/Ni interface the formation of graphane is obstructed by the strong interfacial bonding.

Coupling Epitaxy, Chemical Bonding, and Work Function at the Local Scale in Transition Metal-Supported Graphene

Resonance tunneling spectroscopy and density functional theory calculations are employed to explore local variations in the electronic surface potential of a single graphene layer grown on Rh(111). A work function modulation of 220 meV is experimentally measured, indicating that the chemical bonding strength varies significantly across the supercell of the Moiré pattern formed when graphene is bonded to Rh(111). In combination with high-resolution images, which provide precise knowledge of the local atomic registry at the carbon-metal interface, we identify experimentally, and confirm theoretically, the atomic configuration of maximum chemical bonding to the substrate. Our observations are at odds with reported trends for other transition metal substrates. We explain why this is the case by considering the various factors that contribute to the bonding at the graphene/metal interface.

Adsorption studies of trichloroethylene (TCE) on MgO(100)/Mo(100)

Employing ultraviolet photoelectron spectroscopy (UPS, He I), the more surface sensitive metastable impact electron spectroscopy (MIES) and temperature programmed desorption (TPD) measurements of the adsorption properties of the pollutant trichloroethylene (TCE) on thin MgO(100) films, grown on a Mo(100) single crystal, have been investigated. From TPD spectra of different coverages it is concluded that TCE interacts only weakly with MgO, which is attributed to physisorption. For increasing coverages a change from one peak to two peaks in the TPD spectra, one at higher, the second at lower temperatures with respect to the single peak is detected. Additionally, the observation of a local minimum for the work function (WF) for both MIES and UPS spectra is presented. Such a local minimum has been reported previously for the adsorption of metals with outer s valence electrons on transition metal substrates and adsorption of metals with outer s valence electrons on metal oxide films. Herein, we present the first WF minimum observed for a system of organic molecules adsorbed on an insulating surface. Two different models are discussed in order to understand the presented results.

Structural effects on trends in the deposition and dissolution of metal-supported metal adstructures

A simple thermodynamic formalism is combined with Density Functional Theory calculations to determine periodic trends in the reversible deposition/dissolution potentials of admetals on a variety of transition metal substrates. For each admetal/substrate combination (81 in total), the deposition/dissolution potential shift (referenced to the corresponding potential of the admetal in its bulk, elemental form) is calculated for isolated adatoms, for dimers, and for more extended kink structures. Clear periodic trends are found for the potential shifts across the space of different admetals and substrates. In addition, for the significant majority of these admetal/substrate systems, the structural effects are found to be a strong function of the local coordination number of the metal atoms, thereby verifying an important assumption that has been widely used in semiempirical models of deposition and dissolution.

Theory of nitride oxide adsorption on transition metal (111) surfaces: a first-principles investigation

In this work, we report a density functional theory study of nitric oxide (NO) adsorption on close-packed transition metal (TM) Rh(111), Ir(111), Pd(111) and Pt(111) surfaces in terms of adsorption sites, binding mechanism and charge transfer at a coverage of Theta(NO) = 0.25, 0.50, 0.75 monolayer (ML). Based on our study, an unified picture for the interaction between NO and TM(111) and site preference is established, and valuable insights are obtained. At low coverage (0.25 ML), we find that the interaction of NO/TM(111) is determined by an electron donation and back-donation process via the interplay between NO 5sigma/2pi* and TM d-bands. The extent of the donation and back-donation depends critically on the coordination number (adsorption sites) and TM d-band filling, and plays an essential role for NO adsorption on TM surfaces. DFT calculations shows that for TMs with high d-band filling such as Pd and Pt, hollow-site NO is energetically the most favorable, and top-site NO prefers to tilt away from the normal direction. While for TMs with low d-band filling (Rh and Ir), top-site NO perpendicular to the surfaces is energetically most favorable. Electronic structure analysis show that irrespective of the TM and adsorption site, there is a net charge transfer from the substrate to the adsorbate due to overwhelming back-donation from the TM substrate to the adsorbed NO molecules. The adsorption-induced change of the work function with respect to bare surfaces and dipole moment is however site dependent, and the work function increases for hollow-site NO, but decreases for top-site NO, because of differences in the charge redistribution. The interplay between the energetics, lateral interaction and charge transfer, which is element dependent, rationalizes the structural evolution of NO adsorption on TM(111) surfaces in the submonolayer regime.

Modern Nanotemplates Based on Graphene and Single Layer h-BN

Abstract This mini-review focuses on the recently discovered nanomeshes and nanotemplates made from carbon, boron nitride and their mixtures with a thickness of just a single atomic layer. Typically they exist on some transition metal or semiconductor substrate, the interaction with it playing a crucial role in nanopattern formation. We review systems such as graphene/SiC(0001), graphene/Ru(0001), h-BN/Ru(0001), and h-BN/Rh(111), their atomistic models, synthesis routes, as well as possible applications as templates for nanoperiodic arrays of clusters and molecules. Scanning tunneling microscopy (STM), a technique with ultimate resolution in real space, is stressed as an indispensable tool for a comprehensive characterization of the given systems.

Borylene Transfer from Transition Metal Borylene Complexes

Transition metal borylene complexes (LnM═BR) were predicted to be possible sources of the borylene fragment (:BR) in 1973, decades before the first complex had even been isolated. Over the past 15 years, routes to a small range of borylene complexes have been developed by a handful of research groups, including a family of active borylene donor complexes. Through these and other borylene donors, the borylene transfer to transition metal fragments has recently emerged as the most reliable and mild route to new transition metal borylene complexes, with the synthesis of a number of novel “second-generation” borylene complexes. Borylene transfer to alkynes was found to be a dependable route to the unusual “borirene” architecture, and more recently, the insertion of a borylene fragment into an unactivated alkenyl C−H bond has hinted at further borylene insertions into element−element bonds. This review covers borylene transfer reactions to both transition metal and main group substrates, from the first adventitious reports in the late 1990s up to the current state of intentional employment of the borylene transfer reaction in synthesis.

Controlling graphene corrugation on lattice-mismatched substrates

By means of synchrotron-radiation-based core-level spectroscopies we demonstrate that the degree of corrugation in graphene nanomesh on lattice-mismatched transition-metal substrates critically depends on the strength of chemical bonding at the interface. The degree of interfacial orbital hybridization between graphene and metal states is rising in the series Pt(111)-Ir(111)-Rh(111)-Ru(0001). This growing strength of hybridization is accompanied by a gradual change in graphene morphology from nearly flat to strongly corrugated. We provide a comparison of the pore size and period for the cases of graphene and $h\text{-BN}$ nanomesh on Rh(111).

Plasma-enhanced chemical vapor deposition of polyperinaphthalene thin films

Plasma-enhanced chemical vapor deposition (PECVD) has been used to grow corrosion-resistive, semiconducting thin films of the graphite-like polymer polyperinaphthalene (PPN) from 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA). Unlike thermal chemical vapor deposition of PPN from PTCDA, where thin film growth is catalyzed by a transition metal substrate, PPN films have been grown by PECVD for the first time on non-catalytic substrates: indium tin oxide (ITO)-coated glass, aluminum and silicon. Films with the same morphology and molecular characteristics have also been grown on steel substrates, where iron functions as a growth catalyst. Potentiodynamic corrosion measurements in pH 5 water show that PPN films on steel provide an effective corrosion protection layer. Plasma deposition parameters and electrical conductivities of the films on different substrates have been determined together with their nanoscale morphology and chemical structure using scanning electron microscopy, and Raman and Fourier transform infrared spectroscopy, respectively. These results suggest that under plasma conditions at a substrate temperature of 450 °C, a large fraction of the anhydride groups in PTCDA are eliminated without decomposition of the perylene backbone. The perylene and perylenedicarboxylic radicals adsorb on the substrate and undergo plasma-enhanced polymerization to form partially cross-linked PPN thin films.

Raman spectroscopy on transition metals

Surface-enhanced Raman spectroscopy (SERS) has developed into one of the most important tools in analytical and surface sciences since its discovery in the mid-1970s. Recent work on the SERS of transition metals concluded that transition metals, other than Cu, Ag, and Au, can also generate surface enhancement as high as 4 orders of magnitude. The present article gives an overview of recent progresses in the field of Raman spectroscopy on transition metals, including experimental, theory, and applications. Experimental considerations of how to optimize the experimental conditions and calculate the surface enhancement factor are discussed first, followed by a very brief introduction of preparation of SERS-active transition metal substrates, including massive transition metal surfaces, aluminum-supported transition metal electrodes, and pure transition metal nanoparticle assembled electrodes. The advantages of using SERS in investigating surface bonding and reaction are illustrated for the adsorption and reaction of benzene on Pt and Rh electrodes. The electromagnetic enhancement, mainly lightning-rod effect, plays an essential role in the SERS of transition metals, and that the charge-transfer effect is also operative in some specific metal-molecule systems. An outlook for the field of Raman spectroscopy of transition metals is given in the last section, including the preparation of well-ordered or well-defined nanostructures, and core-shell nanoparticles for investigating species with extremely weak SERS signals, as well as some new emerging techniques, including tip-enhanced Raman spectroscopy and an in situ measuring technique.

Palladium-Coated Gold Nanoparticles with a Controlled Shell Thickness Used as Surface-Enhanced Raman Scattering Substrate

We report the synthesis and characterization of gold core palladium shell (Au@Pd) nanoparticles with thickness-controlled shell as an improved transition-metal substrate for surface-enhanced Raman scattering (SERS). By changing the molar ratio of H2PdCl4 to Au, the Pd shell thickness can be precisely controlled from a few nanometers down to ca. one monolayer. A series of characterizations were performed using transmission electron microscopy (TEM), UV−vis, SERS, and electrochemical techniques. The results confirmed the core−shell structure and the uniform and pinhole-free nature of the Pd shell, ensuring the properties of Pd without possible interference from Au. Consistent with theoretical prediction, the core−shell setting borrows high SERS activity from the Au core through the long-range electromagnetic enhancement in addition to the enhancement from the Pd shell itself. Moreover, their SERS activity can be optimized by the tunable shell thickness and core size. The nm-Au@Pd/Pd electrodes allow us to o...

Contributions to the Chemistry of Carbenemetal Chemistry.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Some anomalies of the SER spectra of symmetrical molecules adsorbed on transition metal substrates: consideration by the dipole–quadrupole SERS theory

AbstractThe SERS spectra of pyridine, pyrazine and benzene, adsorbed on Ni and some other transition metals are analyzed from the point of view of the dipole–quadrupole SERS theory. There are some anomalies in the regularities of these spectra with respect to those with the molecules adsorbed on Ag, Cu and Au. The breathing mode may not be the most enhanced. Although quadrupole interactions were not found precisely in the spectra of pyridine and pyrazine, they manifest in the SERS spectra of benzene adsorbed on silica‐supported Ni. From the analysis of the enhancement coefficient and some another points, we consider that these anomalies may be associated with the larger influence of the dipole interaction or a smaller role of the quadrupole interactions for the considered molecules and metals and also with some features of the complex dielectric constants in the above systems. Further, a strong influence of the minor quadrupole moments on the enhancement factor of strongly distorted benzene was found. This result is very important, because it indicates the complexity of the SERS dipole–quadrupole theory. Copyright © 2005 John Wiley & Sons, Ltd.