Photoemission study of cobalt interaction with the oxidized Si(1 0 0)2 × 1 surface

The interaction of cobalt atoms with an oxidized Si(1 0 0)2 × 1 surface was studied by photoelectron spectroscopy with synchrotron radiation at room and elevated temperatures. The SiO_x layer grown in situ on the crystal surface was ∼0.3 nm thick, and the amount of deposited cobalt was varied within eight atomic layers. It was found that Co atoms could penetrate under the SiO_x layer even at room temperature in the initial growth. As the Co amount increased, a ternary Co-O-Si phase was formed at the interface, followed by a Co-Si solid solution. Silicide synthesis associated with the decomposition of these phases started under the SiO_x layer at ∼250 °C, producing cobalt disilicide with a stable CaF₂-type of structure.     

S180 cell growth on low ion energy plasma treated TiO2 thin films

X-ray photoelectron spectroscopy (XPS) was used to characterise the effects of low energy (<2 eV) argon ion plasma surface modification of TiO₂ thin films deposited by radio frequency (RF) magnetron sputter system. The low energy argon ion plasma surface modification of TiO₂ in a two-stage hybrid system had increased the proportion of surface states of TiO₂ as Ti³⁺. The proportion of carbon atoms as alcohol/ether (COX) was decreased with increase the RF power and carbon atoms as carbonyl (CO) functionality had increased for low RF power treatment. The proportion of C(O)OX functionality at the surface was decreased at low power and further increase in power has showed an increase in its relive proportion at the surface. The growth of S180 cells was observed and it seems that cells are uniformly spreads on tissue culture polystyrene surface and untreated TiO₂ surfaces whereas small-localised cell free area can be seen on plasma treated TiO₂ surfaces which may be due to decrease in C(O)OX, increase in CO and active sites at the surface. A relatively large variation in the surface functionalities with no change in the surface roughness was achieved by different RF plasma treatments of TiO₂ surface whereas no significant change in S180 cell growth with different plasma treatments. This may be because cell growth on TiO₂ was mainly influenced by nano-surface characteristics of oxide films rather than surface chemistry.     

The structure of the V2O3(0 0 0 1) surface: A scanned-energy mode photoelectron diffraction study

Scanned-energy mode photoelectron diffraction (PhD), using the O 1s and V 2p photoemission signals, together with multiple-scattering simulations, have been used to investigate the structure of the V₂O₃(0 0 0 1) surface. The results support a strongly-relaxed half-metal termination of the bulk, similar to that found in earlier studies of Al₂O₃(0 0 0 1) and Cr₂O₃(0 0 0 1) surfaces based on low energy electron and surface X-ray diffraction methods. However, the PhD investigation fails to provide definitive evidence for the presence or absence of surface vanadyl (VO) species associated with atop O atoms on the surface layer of V atoms. Specifically, the best-fit structure does not include these vanadyl species, although an alternative model with similar relaxations but including vanadyl O atoms yields a reliability-factor within the variance of that of the best-fit structure.     

An Ab Initio Study of the Structural and Electronic Properties of the Low-Defect TiC(110) Surface Simulating Oxygen Adsorption after Exposure to Laser Plasma

An ab initio simulation of the adsorption of atomic oxygen on the low-defect titanium carbide (110) surface reconstructed by laser radiation was performed. The relaxed atomic structures of the (110) surface of the O/Ti _x C _y system with Ti and C vacancies observed during the thermal treatment were studied in terms of the density functional theory. DFT calculations of their structural, thermodynamic, and electronic properties were performed. The bond lengths and adsorption energies were determined for various reconstructions of the atomic structure of the O/Ti _x C _y (110) surface. The effects of the oxygen adatom on the band and electronic spectra of the O/Ti _x C _y (110) surface were studied. The effective charges on the titanium and carbon atoms surrounding the oxygen atom in various reconstructions were determined. The charge transfer from titanium to oxygen and carbon atoms was found, which is determined by the reconstruction of the local atomic and electronic structures and correlates with chemisorption processes. The potential mechanisms of laser nanostructuring of the titanium carbide surface were suggested.     

Particle size reduction and enhanced diffusion of Fe and Pt atoms in FePt-C granular films by N addition

N-doped FePt-C nanocomposite films were fabricated using facing-target sputtering method under different N₂ partial pressures (P_N) at room temperature. Annealing at 650 °C turns the amorphous films into ordered structures. Nitrogen doping not only make the ordering of FePt particles easier than the ordering in FePt-C films, due to the enhanced diffusivity of Fe and Pt atoms, but also effectively limits the growth of the FePt particles during the thermal induced ordering, especially for the annealed films fabricated at P_N = 40%, where the average size of well-isolated FePt particles is only ∼8 nm. The particle size reduction and the enhanced diffusion of Fe and Pt atoms can be ascribed to the desorption of doped N atoms and dissociation of FeN bonds during annealing. The room-temperature coercivity of the samples decreases with the P_N due to the particle size reduction and thus the enhancement of the thermal agitation for small particles during the magnetizing procedure.     

Thermal activation and reaction of allyl alcohol on Ni(100)

The thermal chemistry of allyl alcohol (CH₂CHCH₂OH) on a Ni(100) single-crystal surface was studied by the temperature programmed desorption (TPD) and the X-ray photoelectron spectroscopy (XPS). The allyl alcohol adsorbs molecularly on the metal surface at 100 K. Intact molecular desorption from the surface occurs at temperatures around 180 K, but some molecules exhibit chemical reactivity on the surface: activation of the OH, CC, and CO bonds produces η¹(O)-allyloxy CH₂CHCH₂O_(a), η²(C, C) allyl alcohol (C_(a)H₂C_(a)HCH₂OH), and η³(C, C, O)-alkoxide (C_(a)H₂C_(a)CH₂ O_(a)) intermediates. Further thermal activation of allyl alcohol on the surface yields propylene (CH₂CHCH₃), 1-propanol (CH₃CH₂CH₂OH), propanal (CH₃CH₂CHO), and combustion and dehydrogenation products (H₂O, H₂, and CO). Propylene desorbs from the surface at temperatures of around 270 K. Hydrogenation to the η³(C, C, O)-alkoxide intermediate leads to the production of propanal which desorbs from the surface around 320 K, while hydrogenation of the η²(C, C) allyl alcohol intermediate produces 1-propanol, which desorbs at around 310 K. The co-adsorption of hydrogen atoms on the surface enhances the formation of the saturated alcohol, while co-adsorption of oxygen enhances the formation of both the saturated alcohol and the saturated aldehydes.     

Effect of oxidation on the optical and surface properties of AlGaN

The chemical properties of Al_xGa_1−xN surfaces exposed to air for different time periods are investigated by atomic force microscopy (AFM), photoluminescence (PL) measurement and X-ray photoelectron spectroscopy (XPS). PL and AFM results show that Al_xGa_1−xN samples exhibit different surface characteristics for different air-exposure times and Al contents. The XPS spectra of the Al 2p and Ga 2p core levels indicate that the peaks shifted slightly, from an AlN to an AlO bond and from a GaN to a GaO bond. All of these results show that the epilayer surface contains a large amount of Ga and Al oxides.     

Systematic Control of Size and Morphology in the Synthesis of Gold Nanoparticles

The synthesis of gold nanoparticles (Au NPs) capped by poly(1‐vinylpyrrolidin‐2‐one (PVP, average  = 10 000 kDa) yields moderately dispersed (6–8.5 nm) product with limited morphological control while larger NPs (15–20 nm) are reliably prepared using trisodium citrate (Na₃Cit) as a reductant/capping agent. Excellent size control in the intermediate 10 nm regime is achieved by hybridizing these methodologies, with highly monodisperse, polycrystalline Au NPs forming. For a Na₃Cit:PVP:Au ratio of 3.5:3.5:1, anisotropic NPs with an aspect ratio of 1.8:1 suggest the systematic agglomeration of NP pairs. Enhanced control of NP morphology is allowed by the 1,2‐tetradecanediol reduction of Au^III in the presence of straight chain, molecular anti‐agglomerants. Last, ligand substitution is used to controllably grow preformed Au seeds. In spite of the extended growth phase used, the replacement of phosphine by 1‐pentadecylamine affords highly monodisperse, cuboidal NPs containing a single clearly visible twinning plane. The allowance of particle growth parallel to this close‐packed plane explains the remarkable particle morphology.     

c-C5H5 on a Ni(1 1 1) surface: Theoretical study of the adsorption, electronic structure and bonding

In the present work the ASED-MO method is applied to study the adsorption of cyclopentadienyl anion on a Ni(1 1 1) surface. The adsorption with the centre of the aromatic ring placed above the hollow position has been identified to be energetically the most favourable. The aromatic ring remains almost flat, the H atoms are tilted 17° away from the metal surface. We modelled the metal surface by a two-dimensional slab of finite thickness, with an overlayer of c-C₅H₅⁻, one c-C₅H₅⁻ per nine surface Ni atoms. The c-C₅H₅⁻ molecule is attached to the surface with its five C atoms bonding mainly with three Ni atoms. The NiNi bond in the underlying surface and the CC bonds of c-C₅H₅⁻ are weakened upon adsorption. We found that the band of Ni 5dz² orbitals plays an important role in the bonding between c-C₅H₅⁻ and the surface, as do the Ni 6s and 6p_z bands.     

Magnetooptical,optical, and magnetotransport properties of Co/Cu superlattices with ultrathin cobalt layers

We investigated the field dependences of the magnetization and magnetoresistance of superlattices [Co(t _x, Å)/Cu(9.6 Å)]30 prepared by magnetron sputtering, differing in the thickness of cobalt layers (0.3 Å ≤ t _Co ≤ 15 Å). The optical and magnetooptical properties of these objects were studied by ellipsometry in the spectral region of hω= 0.09–6.2 eV and with the help of the transverse Kerr effect (hω= 0.5–6.2 eV). In the curves of an off-diagonal component of the tensor of the optical conductivity of superlattices with t _Co = 3–15 Å, a structure of oscillatory type (“loop”) was detected in the ultraviolet region, resulting from the exchange splitting of the 3d band in the energy spectrum of the face-centered cubic structure of cobalt (fcc Co). Based on magnetic experiments and measurements of the transverse Kerr effect, we found the presence of a superparamagnetic phase in Co/Cu superlattices with a thickness of the cobalt layers of 3 and 2 Å. The transition from superlattices with solid ferromagnetic layers to superparamagnetic cluster-layered nanostructures and further to the structures based on Co and Cu (t _Co = 0.3–1 Å) with a Kondo-like characteristics of the electrical resistivity at low temperatures is analyzed.     

Oxygen chemisorption as a tool for atom discrimination in the SiGe termination layer

This Letter describes a novel method of employing the phenomenon of oxygen chemisorption for atom discrimination in the SiGe surface termination layer. Formation of SiO species on clean Si(100) gives rise to peaks at 7 and 10.2 eV in He I UPS and a peak at 532.3 eV in O 1s XPS. Whereas GeO species on a Ge(100) surface exhibits a single peak at 5.2 eV in He I UPS and a peak at 531.3 eV in O 1s XPS. These signature spectra of SiO and GeO species have been effectively employed for atom discrimination in the termination layer of SiGe surfaces. Upon dosing at room temperature, on a sample prepared by depositing 5ÅGe on Si(100) at 550°C, oxygen bonds with Ge atoms forming GeO, exclusively. This indicates termination entirely by Ge atoms. Oxygen adsorption at room temperature, on a sample prepared by codeposition of Ge and Si (total 5Å) onto Si(100) at 550°C, forms a mixture of SiO and GeO species suggesting a surface termination by both Ge and Si atoms.     

On the theoretical description of the chemisorption of the hydrogen atom on the metallic surface. Calculation of energy interaction of H with hcp Co and Ni surface clusters

A model, based on the generalized valence bond theory, capable of describing the interaction of hydrogen atom (H) with large molecular systems is proposed. The accuracy of the model has been checked by calculating the and H₂ systems. Atomic spin densities for clusters having 1243 atoms have been obtained. The surface magnetic and chemisorption property differences between the Ni and Co metals have been analyzed. An extrapolation scheme suitable to obtain H chemisorption energies on infinite systems from the finite ones has been proposed. Size-converged results have been obtained for the Co. Potential energy surfaces of hydrogen, on and below, the Co surface have been provided.     

Electronic structure and thermal stability of rare earth metalloporphyrins based on ytterbium

The features of the electronic structure of Yb4d, N1s, C1s, O1s, Br3d core levels and the valence band of ytterbium metalloporphyrins Yb(acac)TPPBr8, Yb(acac)TPP, TPPBr8, and TPP are studied by photoelectron spectroscopy. The position and structure of the Yb4f level for Yb(acac)TPPBr8 are determined by resonant photoemission at the BESSY-II synchrotron center. Simulations of the electronic structure of the valence band show good agreement between the calculated and experimental data. The change in the electronic structure of porphyrins during implantation of the central atom of ytterbium, namely, a more uniform redistribution of the electron density between nitrogen atoms of pyrrole and aza groups, is revealed. The photoelectron spectra of Yb4d states demonstrate the trivalent metal state (Yb³⁺) in rare-earth metalloporphyrins. The partial destruction of bromine ytterbium tetraphenylporphyrin compound as a result of thermal action is demonstrated.     

Growth and ordering of CuO chains on Ag(110) surface

Growth of CuO chains and their ordering on Ag(110) surface were monitored by scanning tunneling microscopy (STM). When Cu atoms were deposited on a (2 × 1)AgO/Ag(110) surface at room temperature, the AgO chains in the [001] direction diminished and new strings of CuO grew along the [110] direction and yield a (2 × 2) p2mg ordering. When a Ag(110) surface with coexisting AgO and CuO chains was exposed to CO at room temperature, the AgO chains were selectively reduced.     

STM studies on the growth of monolayers: Co on Cu(110) with one half monolayer of preadsorbed oxygen

The growth of the first cobalt monolayer (ML) on the Cu(110)-(2×1)O surface was studied by scanning tunneling microscopy. Extensive exchange of Cu and Co atoms takes place in the first stages of the deposition. The displaced Cu atoms form new Cu---O---Co mixed islands, with the same structure as those of the terrace surface. At 0.25 ML Co, a new structure nucleates, which contains three Cu atoms, four Co atoms and two O atoms per 2×2 cell. The structure consists of rows in the [ 10] direction with an internal periodicity of two lattice units. The rows are separated from one another by two lattice units along the [001] direction, and are found both in-phase and out-of-phase relative to one another. The result is a mixed p(2×2) and c(2×4) surface. The fraction of the surface covered by the new structure increases with Co coverage, and completely covers the surface at 1 ML Co.     

Dissociative adsorption and thermal evolution of dichloroethylenes on Ni(1 0 0)

The room temperature (RT) adsorption and thermal evolution of cis- and trans-dichloroethylene (DCE) and their structural isomer, iso-DCE, on Ni(1 0 0) have been studied by vibrational electron energy loss spectroscopy (EELS), Auger electron spectroscopy (AES) and thermal desorption spectrometry (TDS). For RT adsorption, both cis- and trans-DCE exhibit very similar EELS features that are different from those found for iso-DCE. These differences indicate the formation of different fragments upon RT adsorption. In particular, the primary adspecies for cis- and trans-DCE are ethane-1,1,2,2-tetrayl () and acetylide-like () adspecies along with a small amount of chlorovinyl adspecies, while ethylylidyne () is the more plausible adspecies for iso-DCE. The differences in the adstructures upon dissociative adsorption at RT underline the important isomeric effects. Furthermore, both AES and TDS results for all three DCE isomers show that most of the Cl atoms produced by dechlorination remain on the surface and its surface concentration remains unchanged upon annealing the samples above 500 K. Upon further annealing to 550 K, the EELS spectra of all three isomers exhibit a broad feature near 1600 cm⁻¹, which suggests the formation of carbon clusters on the surface. The presence of surface Cl atoms therefore appears to prevent the CC bond cleavage during thermal evolution of the adspecies on Ni(1 0 0).     

Structural and magnetic properties of CoPt clusters

The geometrical structures, electronic and magnetic properties of Co_n − xPt_x (n=2–13,38,55$n=2\text{–}13,38,55$) alloy clusters have been systematically investigated by using the density functional theory within the generalized gradient approximation (DFT–GGA). It is found that CoPt alloy clusters adopt the structures of corresponding monatomic Co clusters, where Pt atoms localize at the surface sites and tend to bond together forming a Pt exterior shell. The ferromagnetic coupling between atoms is determined in CoPt clusters, and the Co local magnetic moments can be enhanced by the increase of Pt concentration.     

Growth of nano Co encapsulated in carbon-shell

Nanostructured cobalt is one of the key elements in catalysis and therapeutic drug delivery. To design and prepare nanosize-controllable cobalt, a better understanding of its growth mechanism is essential. Growth of Co nanoparticles encapsulated in carbon-shell (Co@C) during temperature-programmed carbonization of the Co²⁺-β-cyclodextrin (CD) complex at 363–573 K was, therefore, studied by in situ synchrotron small-angel X-ray scattering and X-ray absorption near edge structure spectroscopy. The carbon-shell having a thickness of about 2 nm can prevent the core Co from being aggregated and oxidized. A relatively slow reduction of Co(II) to Co is observed at 393–423 K (stage I) prior to a particle growth transition-state possessing Co of 2.2 nm in diameter at 423–483 K. At 483–513 K (stage II), an increasing Co(II) reduction rate coupled with a rapid fusion and coalescence of Co nanoparticles is found. The average growth rates of Co at stages I and II are about 27 and 98 atoms/min, respectively. The most-probable particle diameter of the ripened Co is 5.9 nm. The carbon-shell can be removed by steam reforming to yield the Co nanoparticles. This work also exemplifies the possible temperature-controllable growth of Co@C, especially in the Co size range of 2–6 nm in diameter.     

Raman investigations of Zn1−xCoxO nanocrystals: role of starting precursors on vibrational properties

The Raman spectra of sol–gel derived Co‐doped ZnO nanoparticles (NPs) in the spectral range 100–1500 cm⁻¹ were investigated. In the sol–gel method, three different series of Co‐doped ZnO particles, i.e. Zn_1−xCo_xO (x = 0.05, 0.10, 0.15, and 0.20), were obtained using three different starting precursors, viz. cobalt chloride hexahydrate, cobalt acetate tetrahydrate, and cobalt nitrate hexahydrate, respectively. It has been observed that cobalt acetate is a better precursor in comparison to cobalt chloride and cobalt nitrate to obtain single‐phase Co‐doped ZnO NPs. As for cobalt acetate‐derived NPs, no hidden secondary phase of Co₃O₄ was observed for the lower (x = 0.05) Co concentration. The Fröhlich interaction associated with the longitudinal modes was found to be destroyed with increasing Co concentration due to structural disorder and defects induced by the dopant. In addition to ZnO and Co₃O₄ vibrational modes, a few additional modes near 550 and 715 cm⁻¹ were also observed in all cases, which could be attributed to the modes due to Co doping in ZnO. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrophobic and physical properties of the ambient pressure dried silica aerogels with sodium silicate precursor using various surface modification agents

The experimental results on the synthesis and physical properties of the ambient pressure dried hydrophobic silica aerogels in the presence of various surface modification (silylating) agents are presented. The silica aerogels were prepared with 1.12 specific gravity ion exchanged sodium silicate solution, 1N ammonium hydroxide, solvent exchanged with ethanol and hexane, and surface modification with 20% silylating agent in hexane followed by drying the modified gel up to 200 °C. The molar ratio of sodium silicate, water, ammonium hydroxide and silylating agent was kept at 1:45:4.3 × 10⁻²:5, respectively. The physical properties of the aerogels such as density, % of porosity, pore volume, thermal conductivity and contact angle measurements were studied by using various mono, di and tri alkyl or aryl silylating agents (SAs). The tri alkyl silylating agents produced low % of volume shrinkage (2%), low density (0.06 g/cm³), low refractive index (1.011), more pore volume (16.15cm³/g), high percentage of porosity (96.9%) and hydrophobic (contact angle >150°) silica aerogels. It was found from the Fourier transform infrared spectroscopic (FTIR) studies of the aerogels that the intensity of the bands related to the SiC and CH are more and the SiOH and OH are less with the tri than mono and di alkyl SAs. It was found from the TGA-DTA studies of the aerogels with increase in temperature above 325 °C, the % of weight decrease in TGA and exothermic peak in DTA are more with tri than the mono and di alkyl SAs. The SEM studies of the aerogels showed the large pore and particle sizes in the silica network with the tri alkyl SAs. The % of optical transmission of the aerogels is less with the tri alkyl SAs than the mono and di alkyl SAs. It was found from the contact angle and water adsorption studies that the hydrophobicity of the silica aerogel is more with tri alkyl than the di and mono alkyl silylating agents.