Laser-driven metal exchange and preparation of metal phthalocyanine

Two types of laser-driven dry processes for the preparation of metal phthalocyanine are reported. In the first one, laser-driven metal exchange, the excimer laser beam was focused on a copper target, and ablated copper atoms were injected onto a thin film of dilithium phthalocyanine (Li₂Pc). The central metal atoms of Li₂Pc were partially exchanged by copper atoms, and the blue thin film of copper phthalocyanine (CuPc) was obtained after removal of the residual Li₂Pc by the hydrochloric acid treatment. In the second one, direct synthesis using the component organic molecule, CuPc was prepared by the implantation of laser-ablated copper atoms onto a thin film of 1,3-diiminoisoindoline (D I I I).     

Thermally enhanced response of metal—oxide—metal diodes

It is shown that in thin-film MOM diodes of contact area ~ 2.5 × 10^-9 m² the basic mechanism of infrared and visible laser radiation detection is the tunneling current dependence on contact temperature (thermally enhanced tunneling). Experiments were run on Al—Al₂O₃—Al MOM diodes.     

PES studies of semiconductor - metal transitions in metal oxides

Semiconductor-Metal transitions in Ti₂O₃, VO₂, V₂O₃ and Ti₃O₅ have been investigated employing X-ray and UV Photoelectron spectroscopy. The transitions are accompanied by significant changes in the 3d band of the transition metals as well as some of the core levels.     

Perpendicular-current studies of electron transport across metal/metal interfaces

We review what we have learned about the scattering of electrons by the interfaces between two different metals (M1/M2) in the current-perpendicular-to-plane (CPP) geometry. In this geometry, the intrinsic quantity is the specific resistance, AR, the product of the area through which the CPP current flows times the CPP resistance. We describe results for both non-magnetic/non-magnetic (N1/N2) and ferromagnetic/non-magnetic (F/N) pairs. We focus especially upon cases where M1/M2 are lattice matched (i.e., have the same crystal structure and the same lattice parameters to within ∼1%), because in these cases no-free-parameter calculations of 2AR agree surprisingly well with measured values. But we also list and briefly discuss cases where M1/M2 are not lattice matched, either having different crystal structures, or lattice parameters that differ by several percent. The published calculations of 2AR in these latter cases do not agree so well with measured values.     

Thermoelectric-transport in metal/graphene/metal hetero-structure

We investigate the thermoelectric-transport properties of metal/graphene/metal hetero-structure. We use a single band tight-binding model to present the two-dimensional electronic band structure of graphene. Using the Landauer--Butticker formula and taking the coupling between graphene and the two electrodes into account, we can calculate the thermoelectric potential and current versus temperature. It is found that in spite of metal electrodes, the carrier type of graphene determines the electron motion direction driven by the difference in temperature between the two electrodes, while for n type graphene, the electrons move along the thermal gradient, and for p type graphene, the electrons move against the thermal gradient.     

Alkali metal and alkali metal hydroxide intercalates of 2s-tantalum disulfide

The alkali metal intercalates of the layered compound 2s-tantalum disulfide were prepared from the respective hexamethylphosphoric triamide solutions of the metals. The c-lattice parameters of the intercalates increased with increase in the crystallographic radii of the metals. All intercalates prepared were superconductors, and the transition temperatures increased as the crystallographic radii of the metals became larger. The intercalates reacted with water to produce hydrogen gas and changed to different intercalates. These had properties similar to those of the corresponding alkali metal hydroxide intercalates prepared from aqueous solutions of the metal hydroxides. The alkali metal hydroxide intercalates, on the other hand, were found to be classified into two groups in terms of the c-lattice parameters; one having c-lattice parameters around 23.8 Å and the other 18 Å. Lithium and sodium hydroxide intercalates belong to the former type, and potassium, rubidium and cesium hydroxide intercalates, including ammonium hydroxide, to the latter. Dried lithium and sodium hydroxide intercalates were also classified in the latter group. In the former case the disulfide was found to intercalate the cations, conserving the ice-like structure of the surrounding water molecules. In the latter, the cations were intercalated in their naked or primary hydrated states, and the interlayer distances were governed by cointercalated hydroxide ions. The observed superconducting transition temperatures were similar for the intercalates with c-lattice parameters around 18 Å irrespective of the particular cation.     

Annealing effects on the plasmonic excitations of metal/metal interfaces

The effects of the annealing procedure at 400-450 K on the electronic properties of nanoscale thin films of Ca, Au and Ag grown on Cu(1 1 1) at room temperature were probed by high-resolution electron energy loss spectroscopy measurements. Ca surface plasmon underwent to a significant red-shift upon annealing, due to the oxidation of the topmost Ca layer. Water strongly interacted with the CaO interface at room temperature. Au surface plasmon disappeared upon annealing the gold film, as a consequence of the formation of an Au-Cu alloy. Ag surface plasmon red-shifted both in the annealed adlayer and with increasing temperature compared with the frequency recorded for the as-deposited silver film.     

Wetting and coalescence of the liquid metal on the metal substrate

Molecular dynamics(MD) simulations are performed to investigate the wettability of liquid metal on the metal substrate. Results show that there exists different wettability on the different metal substrates, which is mainly determined by the interaction between the liquid and the substrate. The liquid metal is more likely to wet the same kind of metal substrate,which attracts the liquid metal to one side on the hybrid substrate. Exchanging the liquid metal and substrate metal has no effect on the wettability between these two metals. Moreover, the study of metal drop coalescing indicates that the metal substrate can significantly affect the coalescence behavior, in which the changeable wettability of liquid metal plays a predominant role. These studies demonstrate that the wetting behavior of liquid metal can be controlled by choosing the suitable metal substrate.     

Physics of metal–correlated barrier with disorder–metal heterostructure

A metal-disordered and correlated barrier–metal heterostructure is studied at half-filling using unrestricted Hartree Fock method. The corresponding clean system has been shown to be an insulator for any finite on site correlation. Interestingly we find that introduction of explicit disorder induces an inhomogeneous, plane dependent, modulated spin and charge order. There is a metal–insulator transition at a critical value of disorder. The critical value corresponds to the point at which disorder kills the gap at half filling due to onsite correlation and completely destroys the plane dependent antiferromagnetic order. The wavefunctions are found to delocalize by increasing disorder, thus rendering the system metallic.     

Magnetic properties of 3d transition metal monolayers on metal substrates

We report results of systematic calculations for magnetic properties of 3d transition metal monolayers on Pd(001) and Ag(001). We find large similarities to interactions of magnetic 3d impurities in the bulk. Therefore the overlayer results are supplemented with results for 3d dimers in Cu, Ag, and Pd. Differences between the two classes of systems are utilized to reveal the interaction within the overlayers and between overlayers and substrates. In virtually all cases we find both ferromagnetic and antiferromagnetic solutions, showing large magnetic moments and similar densities of states. From the trend of the calculations we conclude that V, Cr, and Mn overlayers favor the antiferromagnetic c(2×2) structure, while Ti, Fe, Co, and Ni prefer the ferromagnetic one.     

Work-hardening of metal crystals

Some recent problems relating to work-hardening of metal crystals, such as the contribution of dislocation stress fields to the flow stress, the mechanism of the second stage, or linear, hardening, and the transition to the strongly temperature dependent third stage are discussed. It is shown that linear hardening can be explained by recourse to the strain invariance of the geometrical pattern of the dislocation network. The thermodynamic origin of this invariance is considered. Experimental data on the temperature and strain-rate dependence of the stress at which transition to the third stage occurs are shown to accord best with the view that at temperatures at which diffusion effects are negligible the third stage begins with the onset of appreciable dynamic recovery, involving the formation of point defects, probably through non-conservative movement of elementary intersection jogs.     

Superheating of metal crystals

We report new observations on samples which can exhibit superheating under uniform thermal conditions. The free surface of single crystal Ag spheres was coated with continuous layer of Au to inhibit surface initiated melting of Ag at its melting point. Superheating of up to 25 K was observed for time periods of about one minute. Hydrostatic stresses could be excluded as the reason for the superheating. The results disagree with the lattice stability model and may open the way to the study of crystals in the superheated state.     

Magnetoresistance of neodymium metal

The transverse and longitudinal magnetoresistance on the polycrystalline d.h.c.p. Nd have been measured at 1.38 K. 4.2 K, 13.96 K and 20.4 K with applied fields up to 20 kOe.     

Matrix reactions of alkaline earth metal atoms with ozone : Infrared spectra of the metal ozonide and metal oxide molecules

The 15°K deposition of alkaline earth metal atoms and ozone molecules at high dilution in argon yielded intense bands near 800 cm⁻¹ and in the region, 450–650 cm⁻¹. The bands near 800 cm⁻¹ showed the appropriate oxygen isotopic shifts for assignment to ν₃ of the ozonide ion; the use of scrambled isotopic ozones indicated that the metal cation is symmetrically bound to the ozonide anion which contains three oxygen atoms with two equivalent oxygens. For the case of Ca and Ba atoms and ozone, infrared absorptions appeared between 450–650 cm⁻¹ which showed appropriate oxygen isotopic shifts for vibrational assignment to several metal oxide species. In the calcium experiments, bands at 635.7 and 575.5 cm⁻¹ which showed diatomic oxygen-18 isotopic shifts were tentatively identified as (CaO)₂ species; a pair of bands at 593.0 and 592.2 cm⁻¹ were tentatively assigned to CaO₂. For the barium reactions, bands at 634.7, 571.3, and 460.0 showed appropriate oxygen-18 frequency shifts for assignment to BaO, BaO₂, and (BaO)₂, respectively. The BaO assignment was confirmed by the N₂O-nitrogen matrix reaction which yielded a nitrogen matrix counterpart for BaO at 612.4 cm⁻¹.     

Formation dynamics of bipolaron in a metal/polymer/metal structure

Charge injection process from metal electrode to a nondegenerate polymer in a metal/ polymer/ metal structure has been investigated by using a nonadiabatic dynamic method. We demonstrate that the dynamical formation of a bipolaron sensitively depends on the strength of applied electric field, the work function of metal electrode, and the contact between the polymer and the electrode. For a given bias applied to one of the electrode (V₀) and coupling between the electrode and the polymer (t^′), such as V₀=0.79 eV and t^′=1 eV, the charge injection process depending on the electric field can be divided into the following three cases: (1) in the absence of the electric field, only one electron tunnels into the polymer to form a polaron near the middle of the polymer chain; (2) at low electric fields, two electrons transfer into the polymer chain to form a bipolaron; (3) at higher electric fields, bipolaron can not be formed in the polymer chain, electrons are transferred from the left electrode to right electrode through the polymer one by one accompanying with small irregular lattice deformations.     

Ultra-smooth metal surfaces generated by pressure-induced surface deformation of thin metal films

We present a mechanical pressing technique for generating ultra-smooth surfaces on thin metal films by flattening the bumps, asperities, rough grains and spikes of a freshly vacuum deposited metal film. The method was implemented by varying the applied pressure from 100 MPa to 600 MPa on an e-beam evaporated silver film of thickness 1000 Å deposited on double-polished (100)-oriented silicon surfaces, resulting in a varying degree of film smoothness. The surface morphology of the thin film was studied using atomic force microscopy. Notably, at a pressure of ～600 MPa an initial silver surface with 13-nm RMS roughness was plastically deformed and transformed to an ultra-flat plane with better than 0.1 nm RMS. Our demonstration with the e-beam evaporated silver thin film exhibits the potential for applications in decreasing the scattering-induced losses in optical metamaterials, plasmonic nanodevices and electrical shorts in molecular-scale electronic devices.     

Fabrication of 3D metal/polymer microstructures by site-selective metal coating

Three-dimensional silver/polymer conjugated microstructures were fabricated by site-selective metal deposition on photopolymer structures in the sub-micrometer scale. Photopolymerizable resins with and without an amide group were independently prepared, and a three-dimensional polymer structure was fabricated with those resins by means of the two-photon-induced photopolymerization technique to confine the photopolymerization to a sub-micrometer volume. Silver was selectively deposited on the surface of the amide-containing polymer parts by electroless plating. This method can provide 3D arbitrary silver/polymer composite microstructures with sub-micrometer resolution. PACS 81.07-b; 81.16-c; 81.07.Pr     

Identification of multiphoton induced photocurrents in metal–insulator–metal junctions

Illumination of metal–insulator–metal junctions with ultrashort laser pulses and multiphoton electron excitation in the top electrode leads to the injection of electrons into the backside electrode. Time resolved photocurrent spectroscopy shows that the carrier injection is not instantaneous but occurs with an effective lifetime of about 30 fs. The observation of an effective lifetime reveals that photon-assisted tunneling is negligible. It is shown that three-photon induced internal photoemission and two-photon induced tunneling of excited electrons are the dominating transport mechanisms. PACS 73.40.-c; 72.10.-d; 73.40.Gk; 73.50.Pz