We directly investigated the chemical compositional origin of surface roughness variations in air-annealed ZnO single crystal samples for annealing temperatures up to 1000°C. Atomic Force Microscopy (AFM) showed temperature-dependent changes in surface roughness and morphology, with a maximum in surface roughness of 2nm found for samples annealed at 400°C. The O(1s) line, measured by X-ray Photoelectron Spectroscopy (XPS) showed a maximum for Zn(OH)2 and a minimum for off-stoichiometric ZnO at 400°C; while the Zn(2p) peaks show an increase in slope at that temperature. These results indicate that the roughness arises from Zn diffusion and loss of surface oxygen.

The first unambiguous characterization of a stable dirhodium(III) paddlewheel complex 1 is reported. Complex 1 is prepared via the copper-catalyzed aerobic oxidation of 2 in 77% isolated yield. Comparison of the X-ray crystal structure, visible, and X-ray photoelectron spectroscopy of 1, 2, and 3 indicate a cleavage of the Rh−Rh bond in 1. The oxidation of 2 to 1 is proposed to occur through the intermediacy of 3 with the Cu(II)/Cu(I) couple with oxygen as a terminal oxidant and NaBPh4 as a phenyl transfer agent.

In this article, the authors investigate the origin of the surface roughness of thermally-treated ZnO surfaces via atomic force microscopy, X-ray photoelectron spectroscopy (XPS), and Schottky barrier measurements.

Radio frequency (rf) sputtered films of 10at.% P2O5-doped zinc oxide (ZnO) were deposited at temperatures (Td) below the sublimation point of P2O5 (Td<350°C) and at a range of oxygen pressures p(O2). Ultraviolet-visible optical transmission measurements, x-ray photoelectron spectroscopy (XPS), and x-ray diffraction were used to examine the effects of p(O2) during deposition on the band gap and on the bonding behavior of phosphorus. At both deposition temperatures studied (room temperature with unintentional heating and 125°C), an increase in phosphorus concentration with increasing p(O2) was observed. However, the dependence of the band gap behavior on p(O2) was observed to be dramatically different for the two deposition temperatures: room-temperature-deposited films show a redshift while films deposited at 125°C show a blueshift. Analysis of the oxygen 1s XPS peak shows a progressive formation of nonbridging (Zn–O–P) bond networks for room temperature films, whereas films grown at 125°C show increased (P–O–P) bond networks with increasing p(O2). This indicates that a small degree of thermal activation considerably modifies the bonding behavior of phosphorus in ZnO. Implications of these results for the use of phosphorus as a p-type dopant for ZnO are discussed.

A significant challenge exists in probing the transport behavior of chemically modified single-walled carbon nanotubes (SWNTs). Thin films of SWNTs offer one facile approach to integration of these materials into electronics and sensing applications. Data on bulk resistivities of ‘bucky paper’ films created from HiPco SWNTs that were initially ozonized and subsequently decorated with CdTe quantum dots have been collected via 4-point probe measurements. Both the oxidation process and addition of CdTe nanocrystals result in increased bulk resistivities, presumably due to the introduction of additional scattering centers in tube sidewalls as well as charge traps in the CdTe functionalized tubes.

DNA monolayers are widely used in fundamental and applied genomics and are versatile experimental models for elucidating the behavior of charged polymers at interfaces. The physical behavior of these systems is to a large extent governed by their internal ionic microenvironment, which is investigated here for layers of end-tethered, single-stranded DNA oligonucleotides ( DNA brushes). Retention of counterions by the DNA brush manifests as lowered susceptibility of the interfacial capacitance to external salt conditions. A physical model based on concepts adapted from polymer science was used to further elucidate the connection between monolayer organization and its charging behavior. The data indicate a reorganization of the monolayer with changes in ionic strength and strand coverage that is consistent with that expected for a polyelectrolyte brush. A method for electrochemical quantification of strand coverage, based on shift of reduction potential for redox counterions associated with the DNA monolayer, is also described. These results provide guidance for development of label-free electrochemical diagnostics employing DNA monolayers and formulate a description of monolayer behavior within a polymer science framework.

The molecular architecture of acridine-9-carboxylic acid (ACA) grown on Ag (111) by physical vapor deposition was characterized by using UHV-STM and XPS. At lower coverage, ACA molecules exist in a 2-d gas phase on the surface at room temperature. With increased coverage (>0.4 ML), ACA molecules self-organize into distinctive adlayer structures that are correlated with underlying substrate morphology. On step-free Ag (111) regions, ACA molecules form large islands in coexistence with the 2-d ACA gas. These islands are commensurate with the Ag (111) substrate, indexed as (4 0, 2 4) in matrix notation, and can exceed 100 nm in size. There are two nonequivalent ACA molecules in each unit cell. XPS core level measurements reveal a hydrogen-bonding interaction between ACA molecules, with the ring nitrogen acting as the H-bond acceptor and the carboxyl proton acting as the H-bond donor. A structural model for this phase consists of chains of ACA molecules linked by head-to-tail hydrogen bonds along the substrate [10] direction. Alternating ACA tilting angles account for the two nonequivalent ACA molecules and the observed high packing density. Completely different molecular arrangements are observed on Ag (111) surface regions roughened by a higher density of crystallographic steps (terrace widths < or = 6 nm). Pairs of ACA molecules arrange in a zigzag pattern in a (12 2, 6 5) overlayer structure with a diluted packing density. The structural model for this lower density phase consists of carboxyl-carboxyl linked ACA dimers in a flat-lying molecular orientation.

We report on the search for ferromagnetism in undoped and cobalt-doped high-k dielectric HfO2 films. Over a broad range of growth conditions, we do not observe ferromagnetism in undoped HfO2 films. On the other hand, we do observe room temperature ferromagnetism in dilutely Co-doped HfO2 films, but the origin of the same appears extrinsic (a Co rich surface layer) at least for the regime of growth conditions explored. (c) 2006 American Institute of Physics.

Photoelectron spectroscopy was used to explore changes in Fermi level alignment, within the pi-pi* gap, arising from modifications to the coupling chemistry of conjugated phenylene ethynylene oligomers to the Au surface. Self-assembled monolayers were formed employing either thiol (4,4'-ethynylphenyl-1-benzenethiol or OPE-T) or isocyanide (4,4'-ethynylphenyl-1-benzeneisocyanide or OPE-NC) coupling. The electronic density of states in the valence region of the two systems are nearly identical with the exception of a shift to higher binding energy by about 0.5 eV for OPE-NC. Corresponding shifts appear in C(1s) spectra and in the threshold near E(F). The lack of change in the optical absorption suggests that a rigid shift of the Fermi level within the pi-pi* gap is the major effect of modifying the coupling chemistry. Qualitative consideration of bonding in each case is used to suggest the influence of chemisorption-induced charge transfer as a potential explanation. Connections to other theoretical and experimental work on the effects of varying coupling chemistries are also discussed.

We report on the controlled multiphase thin film growth in the Bi–Fe–O system. By varying the deposition oxygen pressure, the dominant phase formed in the film continuously changes from ferroelectric BiFeO3 to a mixture of α-Fe2O3 and ferromagnetic γ-Fe2O3. X-ray diffraction and high-resolution transmission electron microscopy have revealed that epitaxial multiferroic nanocomposites consisting of BiFeO3 and Fe2O3 are formed when the deposition pressure is ≈5mTorr. In order to investigate the previously reported anomalous enhancement in magnetization in BiFeO3, we have fabricated a thickness gradient pure BiFeO3 film. The out-of-plane lattice constant was found to increase continuously as the thickness is decreased from 300 to 5nm, but no significant enhancement in magnetization was observed.

The effect of doping Mo for Mn on the magnetic and transport properties of the colossal magnetoresistance material La0.67Ba0.33MnO3 has been studied. Compounds of the series La0.67Ba0.33Mn1−xMoxO3(x=0.0–0.1) have been prepared and found to crystallize in the orthorhombic structure (space group Pbnm). Energy dispersive x-ray analysis measurements confirm the stoichiometry of all the samples. Magnetotransport and magnetization measurements reveal that the metal-insulator transition temperature (Tp) decreases from 330 K for x=0 to 255 K for x=0.1. The change in Tp on Mo substitution is relatively much smaller than the corresponding change observed on substitution by other transition elements, such as Ti, Fe, Co, Ni, etc. Further, the ferromagnetic transition temperature (TC) is nearly unchanged by Mo substitution. This is in striking contrast to the large decrease in TC observed with substitution of the above-mentioned 3d elements. These unusual magnetic and transport properties of La0.67Ba0.33Mn1−xMoxO3 may be either due to the formation of a magnetic pair between Mn and Mo or due to strong Mo(4d)–O(2p) overlap, which in turn, may affect the Mn–Mn interaction via the oxygen atoms.

The structural properties of polycrystalline yttria-stabilized zirconia (YSZ) have been studied using FT-Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). Yttria content was varied between 8 and 15% (by mole fraction) to determine compositional effects on YSZ phonon structure, lattice parameter, and oxidation state. The dominant feature in the low-frequency Raman spectrum correlates quite closely with the material's sole (cubic) lattice parameter. XPS measurements of typical YSZ samples show only a single species of both Y and Zr. After exposing YSZ to a reducing environment (H2) at elevated temperatures (1000 degrees C), however, the XPS spectra of YSZ show new features at lower binding energy for both Y and Zr. Angle-resolved XPS measurements suggest that these reduced forms of Y and Zr exist only within the first few molecular layers of the sample. This treatment does not effect the XRD pattern, nor does it change the low-frequency phonon structure observed in the Raman spectrum, although the Raman spectrum does experience approximately 50% reduction in overall signal intensity. These disparities are reconciled with each other based on differences in each technique's sampling depth. The impact that surface-reduced YSZ may have on the chemistry occurring within solid oxide fuel cells is discussed briefly.

Angewandte ChemieVolume 117, Issue 29 p. 4615-4619 Zuschrift Pt–Cu Core–Shell and Alloy Nanoparticles for Heterogeneous NOx Reduction: Anomalous Stability and Reactivity of a Core–Shell Nanostructure† Shenghu Zhou, Shenghu Zhou Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA, Fax: (+1) 301-314-9121Search for more papers by this authorBindhu Varughese, Bindhu Varughese Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA, Fax: (+1) 301-314-9121Search for more papers by this authorBryan Eichhorn Prof., Bryan Eichhorn Prof. eichhorn@umd.edu Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA, Fax: (+1) 301-314-9121Search for more papers by this authorGreg Jackson Prof., Greg Jackson Prof. Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, USASearch for more papers by this authorKevin McIlwrath, Kevin McIlwrath Hitachi Instruments, Hitachi High Technologies America, 5100 Franklin Drive, Pleasanton, CA 94588, USASearch for more papers by this author Shenghu Zhou, Shenghu Zhou Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA, Fax: (+1) 301-314-9121Search for more papers by this authorBindhu Varughese, Bindhu Varughese Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA, Fax: (+1) 301-314-9121Search for more papers by this authorBryan Eichhorn Prof., Bryan Eichhorn Prof. eichhorn@umd.edu Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA, Fax: (+1) 301-314-9121Search for more papers by this authorGreg Jackson Prof., Greg Jackson Prof. Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, USASearch for more papers by this authorKevin McIlwrath, Kevin McIlwrath Hitachi Instruments, Hitachi High Technologies America, 5100 Franklin Drive, Pleasanton, CA 94588, USASearch for more papers by this author First published: 08 July 2005 https://doi.org/10.1002/ange.200500919Citations: 59 † This work was supported by the U.S. Department of Energy's Oak Ridge National Lab under the Advanced Reciprocating Engine Systems Program (Tim Theiss, Program Manager) and the NSF (CHE/DMR). Read the full textAboutPDF ToolsRequest permissionAdd to favorites ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Graphical Abstract Innen oder außen macht einen Unterschied: Bei 370 °C bilden Pt@Cu-Kern-Schale-Nanopartikel rasch eine Legierung, während die reziproken Kern-Schale-Nanopartikel Cu@Pt (siehe STEM-Bilder: links Cu-Spektralkarte, Mitte Pt-Spektralkarte, rechts Hellfeldbild) kinetisch stabilisiert sind und bei der NO-Reduktion hoch aktiv und selektiv wirken. Citing Literature Supporting Information Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2001/2005/z500919_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. Volume117, Issue29July 18, 2005Pages 4615-4619 This is the German version of Angewandte Chemie. Note for articles published since 1962: Do not cite this version alone. Take me to the International Edition version with citable page numbers, DOI, and citation export. We apologize for the inconvenience. RelatedInformation

A series of iron oxide doped norbornene (NOR)/deuterated norbornene dicarboxylic acid (NORCOOH) diblock copolymers were synthesized and characterized by X-ray photoelectron spectroscopy (XPS), small angle neutron scattering (SANS) and superconducting quantum interference device (SQUID) experiments. γ-Fe2O3 nanoparticles were synthesized within the microdomains of diblock copolymers with volume fractions of NOR/NORCOOH 0.64/0.36, 0.50/0.50 and 0.40/0.60. A spherical nanoparticle morphology was displayed in the polymer with 0.64/0.36 volume fraction. Polymers with 0.50/0.50 and 0.40/0.60 volume fractions exhibited interconnected metal oxide nanostructures. The observed changes in the shape and peak positions of the small-angle neutron scattering profiles of polymers after metal doping were related to the scattering from the metal oxide particles and to the possible deformed morphologies due to the strong interparticle interactions between metal particles, which may influence the polymer microphase separation. The combined scattering from both polymer domains and magnetic particles was depicted in SANS profiles of metal oxide doped polymers. γ-Fe2O3 containing block copolymers were superparamagnetic at room temperature. An increase in the blocking temperature (Tb) of interconnected nanoparticles was observed and was related to the interparticle interactions, which depends on the average distance (d) between particles and individual particle diameter (2R). The sample with volume fraction of 0.4/0.6 have the lowest d/(2R) ratio and exhibit the highest Tb at 115K.

In this article we present the growth of hexagonal phase MgZnO on nonconventional substrates such as quartz and on sapphire for comparison of the device property. We are reporting the realization of MgZnO-based UV detector on quartz by the pulsed laser deposition technique. MgZnO films are characterized by x-ray diffraction, UV-visible spectroscopy, and Rutherford backscattering-channeling techniques. The morphology of the films is studied by atomic force microscopy. The metal-semiconductor-metal device was fabricated on the MgZnO film to study the device photoresponse under proper UV irradiation. (c) 2005 American Vacuum Society.