Metal/insulator interfaces are essential structures in most of electronic and optical devices, and thus the stability of such interfaces is important for the reliability of devices. It has long been known that the metal atoms in a gate electrode often penetrate into insulators by thermal diffusion during the annealing processes in device fabrication. In addition, metal atoms are ionized and such diffusion is remarkably enhanced under electric fields during device operation. Diffusing metal atoms often produce defect electronic states, promote leakage currents, and cause serious damage in electronic devices, particularly in recent nanoscale devices such as metal nanodot memories. On the other hand, such diffusion behavior is positively utilized to produce metal nanowires in insulators for resistive switching memory applications. However, the microscopic understanding of ionization and diffusion of metal atoms has not been obtained yet. In this work, we employ the first-principles calculations and clarify how metal atoms are ionized and diffuse under electric fields around metal/insulator interfaces. We consider metal/insulator interfaces made of a variety of metals (Al, Ag, Au, Pt, Ta, W, etc) and crystalline/amorphous SiO2. Electronic structures, ionic charges, and adiabatic diffusion potentials of metal atoms are evaluated using the first-principles calculations in the density functional theory. Electric field is applied perpendicular to the interface by supplying positive/negative electric charges to the interface-slab systems.With respect to the ionization, we found that the ionic charge of metal atom in SiO2 changes depending on the distance from the interface [1]. In a 0-6Å region near the interface, the diffusing atom is sharply ionized with leaving the interface. This occurs owing to the breakdown of orbital hybridization between electronic states of metal atom and metal induced gap states (MIGS) of metal electrode [2,3]. When the substrate is changed to semiconducting Si and Sn, this region is extended to 10-15Å. Outside this MIGS-penetration region, on the other hand, the ionic charge of metal atom still varies. This variation occurs due to the electron transfers from diffusing metal atom to not only surrounding SiO2 but also metal electrode. In this way, we can conclude that the ionization of the metal atom first begins quantum mechanically in the MIGS-penetration region and then its ionization charge changes electromagnetically outside the MIGS-penetration region.With respect to the diffusion under electric field, we found that the diffusion barrier linearly decreases with increasing the electric field. This result indicates that the electric field remarkably enhances the metal-atom penetration probability into SiO2, like an exponential function of electric field. Such enhancement works effectively for metal atoms with small electronegativity and mainly in the case of positive voltage application, which is in good agreement with observations. This is because most metal atoms prefer to ionized positively in insulators and small-negativity atoms have large ionic charges. These results are discussed in details, together with reviewing recent experiments, comparing to the cases of metal/semiconductor interfaces, and focusing on the fundamental physics of ionization and diffusion. <references> [1] Y. Asayama et al., Materials Science in Semiconductor Processing, DOI: 10.1016/j.mssp.2016.09.010 (2016). [2] T. Hiramatsu et al., Jpn. J. Appl. Phys. 53, 058006 (2014).[3] S. Sasaki and T. Nakayama, Jpn. J. Appl. Phys. 55, 111302 (2016). Figure 1
2Electromagnetic Environment Associated with Lightning Strikes to Tall Strike Objects
Electromagnetic Environment Associated with Lightning Strikes to Tall Strike Objects
41Ionization of metal atoms following valence-excitation of neighbouringmolecules
A new relaxation pathway of optically allowed valence-excitations inmolecules bound to metal atoms was investigated. We show that theσnonπ* excitation of HCN in MgnHCN (n = 1,2)clusters decays through the emission of an electron from the metalliccomponent. The calculated lifetimes are of the order of 140 fs forMgHCN and 25 fs for Mg2HCN. These short lifetimes suggestthat the relaxation mechanism discussed here should dominate for molecules adsorbed on metal clusters or surfaces. We find that atlarge distances this decay is dominated by energy transfer.
Read more851Gas‐Phase Catalysis by Atomic and Cluster Metal Ions: The Ultimate Single‐Site Catalysts
Gas-phase experiments with state-of-the-art techniques of mass spectrometry provide detailed insights into numerous elementary processes. The focus of this Review is on elementary reactions of ions that achieve complete catalytic cycles under thermal conditions. The examples chosen cover aspects of catalysis pertinent to areas as diverse as atmospheric chemistry and surface chemistry. We describe how transfer of oxygen atoms, bond activation, and coupling of fragments can be mediated by atomic or cluster metal ions. In some cases truly unexpected analogies of the idealized gas-phase ion catalysis can be drawn with related chemical transformations in solution or the solid state, and so improve our understanding of the intrinsic operation of a practical catalyst at a strictly molecular level.
Read moreTransition Metal Ions in the Gas Phase
For several years we have been studying the chemistry of atomic transition metal ions with simple organic molecules. This research was stimulated by our interest in examining the consequences of oxidation and reduction of transition metals in their gas phase ion molecule chemistry. This is an area of chemistry, redox chemistry, which has received little attention from those of us interested in gas phase chemical dynamics. An initial discovery in our investigations was that atomic transition metal ions are quite subject to oxidative addition; a concerted process in which XY adds to M so that the metal is inserted into the XY bond to form XMY. As Pearson notes [1], it has only been in the last 15 years that oxidative addition has been recognized as an important elementary reaction. In fact our results appear to be the first direct observation of oxidative addition to transition metals in the gas phase. We have been particularly interested in oxidative addition processes that involve formation of metal carbon bonds. We have obtained evidence that such processes occur in alkyl halides and alcohols [2–4], in halobenzenes [5] and in alkanes [6,7].KeywordsOxidative AdditionCyclic KetoneCarbonyl FunctionalityAlkane ReactionSimple Organic MoleculeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
Read more25Laser multiphoton ionization and photoelectron spectroscopy of Co(CO)3NO and Fe(CO)5
Laser multiphoton dissociation-resonance-enhanced multiphoton ionization (MPD-REMPI) and time-of-flight photoelectron spectra (TOF-PES) of Co(CO)3NO and Fe(CO)5 have been obtained in the range 445–455 nm. The only ions produced by the pulsed dye laser are Co+ and Fe+. Transitions observed in the MPD-REMPI spectra are assigned to resonant states of the neutral atoms. Final states of the atomic ions are determined from the TOF-PES spectra. The multiphoton dissociation process produces metal atoms in a broad distribution of states, ranging in energies up to 33 000 cm−1 for Co, and 32 000 cm−1 for Fe. The most intense REMPI lines are associated with low-lying electronic states (&lt;8500 cm−1 for Fe and Co). By tuning the laser to appropriate wavelengths, neutral metal atoms in selected electronic states may be ionized. At most laser wavelengths, the atomic metal ions are formed in a distribution of states, only some of which are consistent with preservation of the core configuration of the Rydberg intermediate in the ionization step. An exception appears for ionization of Co atoms via 4d Rydberg intermediate states.
Read more29Charge injection in thin dielectric layers by atomic force microscopy: influence of geometry and material work function of the AFM tip on the injection process
Charge injection and retention in thin dielectric layers remain critical issues for the reliability of many electronic devices because of their association with a large number of failure mechanisms. To overcome this drawback, a deep understanding of the mechanisms leading to charge injection close to the injection area is needed. Even though the charge injection is extensively studied and reported in the literature to characterize the charge storage capability of dielectric materials, questions about charge injection mechanisms when using atomic force microscopy (AFM) remain open. In this paper, a thorough study of charge injection by using AFM in thin plasma-processed amorphous silicon oxynitride layers with properties close to that of thermal silica layers is presented. The study considers the impact of applied voltage polarity, work function of the AFM tip coating and tip curvature radius. A simple theoretical model was developed and used to analyze the obtained experimental results. The electric field distribution is computed as a function of tip geometry. The obtained experimental results highlight that after injection in the dielectric layer the charge lateral spreading is mainly controlled by the radial electric field component independently of the carrier polarity. The injected charge density is influenced by the nature of electrode metal coating (work function) and its geometry (tip curvature radius). The electron injection is mainly ruled by the Schottky injection barrier through the field electron emission mechanism enhanced by thermionic electron emission. The hole injection mechanism seems to differ from the electron one depending on the work function of the metal coating. Based on the performed analysis, it is suggested that for hole injection by AFM, pinning of the metal Fermi level with the metal-induced gap states in the studied silicon oxynitride layers starts playing a role in the injection mechanisms.
Read more50Probing pristine and defective NiB6 monolayer as promising anode materials for Li/Na/K ion batteries
Probing pristine and defective NiB6 monolayer as promising anode materials for Li/Na/K ion batteries
1Electronic and light absorption properties of metal adsorbed In2Se3 monolayer
Electronic and light absorption properties of metal adsorbed In2Se3 monolayer
32Assembling Molecular Electronic Junctions One Molecule at a Time
Diffusion of metal atoms onto a molecular monolayer attached to a conducting surface permits electronic contact to the molecules with minimal heat transfer or structural disturbance. Surface-mediated metal deposition (SDMD) involves contact between "cold" diffusing metal atoms and molecules, due to shielding of the molecules from direct exposure to metal vapor. Measurement of the current through the molecular layer during metal diffusion permits observation of molecular conductance for junctions containing as few as one molecule. Discrete conductance steps were observed for 1-10 molecules within a monolayer during a single deposition run, corresponding to "recruitment" of additional molecules as the contact area between the diffusing Au layer and molecules increases. For alkane monolayers, the molecular conductance measured with SDMD exhibited an exponential dependence on molecular length with a decay constant (β) of 0.90 per CH(2) group, comparable to that observed by other techniques. Molecular conductance values were determined for three azobenzene molecules, and correlated with the offset between the molecular HOMO and the contact Fermi level, as expected for hole-mediated tunneling. Current-voltage curves were obtained during metal deposition showed no change in shape for junctions containing 1, 2, and 10 molecules, implying minimal intermolecular interactions as single molecule devices transitioned into several molecules devices. SDMD represents a "soft" metal deposition method capable of providing single molecule conductance values, then providing quantitative comparisons to molecular junctions containing 10(6) to 10(10) molecules.
Read moreNanoparticle formation mechanisms and molecular intermediates revealed by liquid phase EM and reaction pathway analysis
Classical nucleation theory (CNT) is used to describe the growth of metal nanoparticles by seed formation from insoluble metal atoms generated by chemical reduction of precursors containing metal ions.It involves a nucleation step, and subsequent monomer attachment on the seeds which is limited by diffusion of metal atoms.
Read more1Building Single‐Atom and Single‐Cluster Metal Catalysts Supported on Graphdiyne and Boron‐Graphdiyne
Transition metal (TM) atoms and clusters supported on layered materials can be used to build single‐atom (SAC), and single‐cluster catalysts (SCC), respectively. To gain insight and to contribute to the rational design of SACs and SCCs, we investigate the structure and stability of SACs and SCCs of V, Co, and Pd, built on two supports, graphdiyne (GDY) and boron‐graphdiyne (BGDY), using the density functional formalism. GDY and BGDY are carbon‐based layered materials exhibiting a structure of uniformly distributed nanopores. The triangular pores of GDY and the hexagonal pores of BGDY host TM atoms and clusters attached with high adsorption energies, favoring the stability of these systems. Diffusion of metal atoms on GDY and BGDY is hindered by large activation barriers preventing the aggregation of atoms. Adsorption of metal atoms (one, two or three atoms per cell) or clusters (one TM 6 per cell) induce global distortions in the hexagonal lattice of BGDY. However, the GDY lattice is more robust and its global structure is quite insensitive to metal doping. Local distortions of the carbon chains are observed in both layers in the proximity of the adsorbed atoms and clusters. This work gives support to the development of highly stable SACs and SCCs that can be built through deposition of TM atoms and clusters on GDY and BGDY.
Read more2Electrical properties of bulk-heterojunction organic solar cells with ultrathin titania nanosheet blocking layer
The contributions of ultrathin titanium oxide nanosheet (TN) crystallites to the electrical properties and the diffusion of metal atoms were studied in a bulk-heterojunction (BHJ) cell in indium–tin oxide (ITO)/MoO3/poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methylester (PCBM) active layer/titania nanosheet (TN)/metal multilayered photovoltaic devices. The insertion of only two or three layers of poly(diallyldimethylammonium chloride) (PDDA) and TN multilayered film prepared by the layer-by-layer deposition technique effectively decreased the leakage current and increased the open circuit voltage (VOC), fill factor (FF), and power conversion efficiency (η) nearly two fold. Although the active layer has a hydrophobic surface, the active layer was fully covered by the insertion of only two or three layers of the PDDA/TN multilayered film and the ultrathin TN layer effectively prevented the metal atoms from diffusing into the polymer film. The impedance analysis and the cross-sectional transmission electron microscopy (TEM) images revealed that the TN layer effectively separated the organic layer/metal interface and blocked holes at the organic/TN interface resulting in the reduction in leakage current by nearly three orders of magnitude and the increase in the capacitance at a voltage around VOC.
Read more43Vapor-Phase Fabrication and Condensed-Phase Application of a MOF-Node-Supported Iron Thiolate Photocatalyst for Nitrate Conversion to Ammonium
We describe a method for synthesizing a nitrate reduction catalyst within a metal–organic framework (MOF). The MOF NU-1000, a zirconium-based mesoporous material, is exposed by using atomic layer deposition (ALD) to a vaporous iron amidinate coordination complex and subsequently a dodecanethiol ligand to synthesize an iron thiolate cluster grafted on the zirconium oxide nodes. Structural identification of the cluster is conducted through X-ray absorption spectroscopy (XAS) and differential envelope density (DED) analyses. Once submerged in an aqueous solution containing nitrate (30 ppm of N) and irradiated with light, the MOF/iron thiolate cluster assembly can photochemically transform the nitrate to ammonium ions. We suggest that sequential, self-limiting, atomic (metal ion), and molecular (ligand) deposition onto the reactive nodes of chemically and thermally stable MOFs could prove to be a versatile and attractive method for obtaining nature-inspired chemical catalysts.
Read more38Effect of kinetic and electronic energy on the reactions of Ti + with H 2, HD, and D 2
Effect of kinetic and electronic energy on the reactions of Ti + with H 2, HD, and D 2
31Diffusion mechanisms of metal atoms in Pd[sbnd]Au bimetallic catalyst under CO atmosphere based on ab initio molecular dynamics
Diffusion mechanisms of metal atoms in Pd[sbnd]Au bimetallic catalyst under CO atmosphere based on ab initio molecular dynamics
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