In this work, a two-step hydrothermal/solvothermal process was developed to generate highly fluorescent lawsone polymer dots (LPDs) utilizing an inexpensive and abundant starting material, 2-hydroxy-1,4-napththoquinone (lawsone). This hydrothermal/solvothermal process produces LPDs that have excitation independent emission with well-defined electronic transitions. This two-step protocol provides a straightforward approach to remove unwanted small molecular fluorescence, which has plagued carbon dot systems, without the need for advanced chromatographic purification methods or steps. A series of spectroscopic, electrochemical, and theoretical experiments suggest that this process proceeds via a sequential dehydration and dehydrogenation pathway to cross-link the lawsone into a carbon dot structure. This polymerization process helps to stabilize and favor certain electronic transitions inherently present in the lawsone monomer. The generation of the LPDs results in a 2 order of magnitude increase in the emission intensity and a quantum yield of 37%. This behavior is likely the result of the cross-linked structure shielding these electronic states from deactivation caused by nonradiative processes such as vibrational coupling and excited state quenching from thermal deactivation and solvent collisions. This finding is consistent with a cross-linked enhanced emission (CEE) mechanism, as previously observed for other similar systems. The LPDs were then incorporated into a TiO2 photoanode and utilized as a photosensitizer in a dye-sensitized solar cell (DSSC) which showed an enhancement in photocurrent density over pure TiO2. We also prepared a derivative of the LPDs utilizing a diethylene triamine additive (nitrogen-doped lawsone polymer dots (N-LPDs)) using the same two-step protocol and demonstrated its potential as a fluorescence microscopy dye for imaging MDA-MB-231 cancer cells.

The synthesis of nitrogen-doped single-layer graphene has been achieved on the copper surface by using the nitrogen-containing sole precursor azafullerene. The synthesis process, doping properties, and doping-induced variation of local work function of graphene have been investigated on the atomic scale by combining scanning tunneling microscopy/spectroscopy, X-ray photoelectron spectroscopy measurements, and density functional theory calculations. Most nitrogen dopants are at the edges of graphene islands and the graphene domain boundaries with the pyridinic configuration. Graphitic nitrogen dopants arrange into curved lines within graphene islands after multiple growth cycles, which results from a doping process guided by the edges of graphene islands. The doping-induced variation of local work function of the graphene surface has been measured on the atomic scale by using scanning tunneling spectroscopy measurements. We find that the local work function strongly depends on the atomic bonding configuration and concentration of nitrogen dopants. The local work function decreases for graphitic nitrogen doping but increases for pyridinic nitrogen doping. This work provides new atomic-scale insights into the synthesis of heteroatom-doped graphene from sole precursors as well as the strong correlations between nitrogen doping and the local work function of the graphene layer.

Nano-sized particles mounted on heterogeneous oxide supports such as silica have altered reactivity when compared to their homogeneous analogs. In particular, catalyzed olefin metathesis using supported Ru nanoparticles has shown great promise and various methods have been employed to develop functional heterogeneous Ru catalysts. This article reports a method for synthesizing Ru nanoparticles supported on silica and titania. The nanoparticles were characterized using XPS showing Ru(0) dominates when not exposed to air. TEM showed Ru nanoparticle sizes of 3.1 ± 0.8 nm for Ru supported on SiO2 and 5.6 ± 1.3 nm for Ru supported on TiO2. The materials demonstrated modest activity in ring-opening metathesis reactions via diazo activation and nanoparticle-embedded polymers of norbornene and norbornadiene were synthesized using dry box and Schlenk line techniques. The Ru/support/polymer composite materials were characterized using proton NMR, XPS, and SEM/EDS.

The controlled synthesis of high-quality nitrogen (N) doped single layer graphene on the Ru(0001) surface has been achieved using the N-containing sole precursor azafullerence (C59NH). The synthesis process and doping properties have been investigated on the atomic scale by combining scanning tunneling microscopy and X-ray photoelectron spectroscopy measurements. We find for the first time that the concentration of N-related defects on the N-doped graphene/Ru(0001) surface is tunable by adjusting the dosage of sole precursor and the number of growth cycles. Two primary types of N-related defects have been observed. The predominant bonding configuration of N atoms in the obtained graphene layer is pyridinic N. Our findings indicate that the synthesis from heteroatom-containing sole precursors is a very promising approach for the preparation of doped graphene materials with controlled doping properties.

The formation of gas bubbles surrounding laser heated copper nanoparticles in superfluid helium at 1.7 K is observed. Because of the effective light capture by these plasmonic particles and the subsequent heat transfer into the liquid, such bubbles grow within 3 μs to tens of micrometers in size. The Schlieren imaging technique is used to determine the spatial distribution of the nanoparticles in the liquid, and the gas bubble radii are related to the parent nanoparticle size. The presented liquid-phase particle size analysis is validated against atomic force microscopy measurements of nanoparticles deposited from the liquid onto a solid substrate.

The corrosion resistance of oxides that form in air on Vitreloy 101 (Cu47Ti34Zr11Ni8) metallic glass ribbons in NaCl and HCI solutions was studied by scanning electron microscopy, X-ray photoelectron spectroscopy and potentiodynamic polarization. The air-exposed alloy was covered by a TiO2/ZrO2 layer overlying a Cuenriched region beneath. Ni was absent at the surface. Segregation of Ti and Zr was driven by exothermic oxide formation. Immersion in NaCI or HCI caused pitting corrosion by local Galvanic reactions that depleted less noble Ti, Zr and Ni from the pit interiors, leaving them rich in more noble Cu. Corrosion products containing Ti and Zr accumulated around the pit. Pits were most numerous in 1.0 M HCI due to TiO2(s)/Ti3+(aq) equilibrium that resulted in rapid solubilization of the oxide, creating local weaknesses and an increased rate of pit formation. On average, Ti preferentially dissolved from the oxide in accord with metal nobility arguments. (C) 2014 Elsevier B.V. All rights reserved.

The dark gray corrosion layer (patina) formed on the surface of a polished low tin bronze alloy following exposure to a deoxygenated and saturated aqueous solutions of H2S has been characterized by X‐ray photoelectron spectroscopy, scanning electron microscopy‐energy dispersive spectroscopy and X‐ray diffraction. The system represents a model for bronze corrosion in reducing conditions where sulfate‐reducing bacteria in soils or deoxygenated seawater may generate H2S during respiration. The initial surface was dominated by metallic copper together with Sn, Pb and Zn oxides and hydroxides. Surface enrichment of Pb and Zn was noted because of a smearing effect during polishing. At least some of the lead was crystalline. In contrast, the corrosion layer formed by H2S(aq) exposure was dominated by polycrystalline Cu2S (low and high chalcocite) and smaller concentrations of CuSO4 · nH2O. This surface was enriched with Zn as Zn(OH)2. Lead was present as redeposited PbS (galena) crystallites in at least two different morphologies. Unlike bronzes exposed to oxidizing conditions, which develop protective SnO2 layers, the H2S(aq)‐exposed surface was considerably depleted in Sn. Copyright © 2014 John Wiley & Sons, Ltd.

Bulk metallic glasses (BMGs) possess attractive properties for biomedical applications, including high strength, hardness and corrosion resistance, and low elastic modulus. In this study, we conduct rotating beam fatigue tests on Pd43Ni10Cu27P20 bulk metallic glass in air and Eagle's medium (EM) and measure the corrosive resistance of the alloy by submersion in acidic and basic electrolytes. Fatigue results are compared to those of commonly used biometals in EM. Rotating beam fatigue tests conducted in air and in Eagle's medium show no deterioration in fatigue properties in this potentially corrosive environment out to 10(7) cycles. A specimen size effect is revealed when comparing fatigue results to those of a similar alloy of larger minimum dimensions. Corrosion tests show that the alloy is not affected by highly basic (NaOH) or saline (NaCl) solutions, nor in EM, and is affected by chlorinated acidic solutions (HCl) to a lesser extent than other commonly used biometals. Corrosion in HCl initiates with selective leaching of late transition metals, followed by dissolution of Pd.

The resistance spot welding of Vitreloy 101 (Cu47Ti34Zr11Ni8) metallic glass ribbons was studied by mechanical testing, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Material was expelled along the weld interface and around the electrode contact points on the alloy surface. There were no significant changes in composition between the melted and native alloy although minor (∼8%) crystallization was observed in DSC data. Failure during peel and tensile-shear tests of the welds was observed to occur at the periphery of the weld (pullout failure), where slower melting and cooling occurred away from the heat sink effects of the welding electrodes. Measurements of lap welds indicated a maximum shear strength of 810±77MPa, about 75% of the predicted shear strength of the monolithic alloy. Embrittlement and crystallization around the weld likely contributed to failure. A finite element analysis (FEA) model was developed to explore the temperature–time relation inside the metallic glass during and following welding and it confirmed the main features observed experimentally. The model indicated rapid melting as temperatures reached ∼2000K followed by cooling of the center of the weld nugget at rates up to ∼48,000Ks−1, greatly exceeding the critical cooling rate for this material of 250Ks−1. A torus of material around the weld nugget remained molten for longer and cooled more slowly than the center of the weld nugget.

The core level and valence band X-ray photoelectron spectra (XP spectra) of two arsenic sulfides, AS(4)S(4) (alpha-realgar) and AS(4)S(4) (pararealgar), are reported. Pararealgar is a polymorph of realgar created by irradiation of realgar with visible light. The core level spectra of the materials can be distinguished by small differences in core level binding energies (BEs). For example, the As 3d(5/2) and S 2P(3/2) peaks are at 43.1 and 162.8 eV BE, respectively, in realgar and 43.2 and 162.7 eV BE, respectively, in pararealgar. Density functional theory (DFT) calculations at the B3LYP/cc-pVDZ level were performed on single AS4S4 clusters to determine the ground state orbital energies for realgar and pararealgar and electrostatic potential-derived atomic charges. The shifts in the core level BEs are qualitatively reproduced in the orbital energies and can be rationalized based on an increased average charge in pararealgar (S = -0.21, As = +0.21) versus realgar (S = -0.19, As = +0.19). A large variation in calculated charge between inequivalent As sites in pararealgar (from +0.09 to +0.31) broadens the observed arsenic XP spectra features. In addition, the four main features in the valence bands of these materials have been identified based on the DFT calculations. (C) 2003 Elsevier Science B.V. All rights reserved.

Chromium dioxide films on TiO2(110) single crystals have been grown by using chemical vapor deposition. The average growth rate was similar to1.8 nm.min(-1). Powder X-ray diffraction indicated that the films were highly (110) textured. X-ray photoelectron spectroscopy showed that the CrO2 films were continuous and no other chromium oxides were present. The CrO2 films were composed of grains typically 200-300 nm in diameter and appeared consistent with the rutile crystal structure. Atomic force microscopy suggested that the films were relatively rough, with a root-mean-square roughness of similar to114 nm for an 850 nm thick film. The resistivity at room temperature was found to be similar to137 muOmega(.)cm which decreased to similar to16 muOmega(.)cm at 5 K, consistent with metallic behavior. The films were ferromagnetic with a Curie temperature of 398 K.

The adsorption and UV photochemistry of 1,3-butadiene (CH2=CHCH=CH2) on highly oriented pyrolytic graphite (HOPG(0001)) was studied using temperature-programmed desorption (TPD) and electron energy loss spectroscopy (EELS). Butadiene physisorbs on HOPG with the monolayer exhibiting first-order desorption kinetics and a corresponding desorption energy of 32 kJ/mol. The multilayer exhibits zero order desorption kinetics with a desorption energy of 28.5 kJ/mol. Irradiation of the C4H6/HOPG(0001) adlayer (one and three monolayers (ML) Of C4H6) with UV photons at 193, 248, and 351 nm and fluences of up to 100 mJ/cm(2). pulse resulted in molecular photodesorption. Photodesorption was described by a laser-induced thermal desorption process as supported by simple calculations of the surface temperature rise. The photoprocesses occurring in both 1 and 3 ML C4H6 adlayers on HOPG(0001) were also investigated at incident powers of less than or equal to 10 mJ/cm(2).pulse. Under these conditions, there was no detectable photodesorption or condensed phase photochemistry at any of the wavelengths investigated.

A new pale blue corrosion product has been found on copper alloy artifacts in the collections of a number of institutions. The corrosion product has been characterized using X-ray powder diffraction, X-ray photoelectron spectroscopy, wavelength X-ray dispersive spectroscopy and Raman microspectroscopy. The corrosion product is a copper(II) compound, containing copper and sodium in a ratio of approximately 1:1 along with formate and acetate groups. It is speculated that formic (methanoic) and acetic (ethanoic) acid vapors arising from materials used to house the objects contribute to the formation of this compound.

A nanosphere lithography technique has been used to synthesize periodic nanoparticle arrays of TiO2 on glass substrates. Both monolayer and bilayer evaporation masks were generated from hexagonally close-packed polystyrene nanospheres, each one producing a different array of TiO2 nanoparticles. Atomic force microscopy (AFM) showed that the masks typically consisted of ordered 10-100 mum(2) domains. X-ray photoelectron spectroscopy confirmed that the surface composition of the particles corresponded to TiO2 with minor amounts of a Ti3+ species, presumably associated with edges, corners, and oxygen vacancy defects. Analysis of the AFM images indicated that the nanoparticles were circular in shape with array dimensions approximately consistent with simple geometric considerations for the 420 nm diameter polystyrene nanospheres used as masks in this work. The monolayer and bilayer masks yielded TiO2 particle diameters of 169 +/- 12 nm and 140 +/- 13 nm, respectively. The absorption edge of the nanoparticle arrays are blue-shifted from single-crystal rutile.

Self-assembled monolayers (SAMs) of 6-phenyl-n-hexanethiol (PHT) and 6-(p-vinylphenyl)-n-hexanethiol (VHT) on Au(lll) have been investigated by reflection-absorption infrared spectroscopy (RAIRS), ellipsometry, and scanning tunneling microscopy (STM). Both molecules chemisorbed as thiolates. The packing order and structural changes of the PHT monolayer were investigated at room temperature and following annealing in ultrahigh vacuum. Three different stripe phases (delta, chi ', and beta), characterized by molecular axes oriented almost parallel to the surface plane, were observed by STM. In contrast, the VHT monolayer had a structure in which the average molecular tilt angle was close to the surface normal. Polymerization of the VHT SAM, as followed by RAIRS, was achieved by either UV-light irradiation or thermal treatment. Ultraviolet irradiation produced longer chain polymers with a maximum of similar to 70% conversion, whereas annealing produced shorter chain polymers with CH3 as the end group. The UV-light polymerized film was more robust than the thermally polymerized film.