Electrodeposition of well adherent metallic clusters on carbon substrates

The good adhesion of electrodeposited Ni clusters on carbon supports was demonstrated; the metallic clusters were deposited on recompressed graphite (Papyex) and PAN-based fibres (Toray T300) by electrodeposition technique. For both substrates, the process parameters were optimized in order to obtain a uniform and dense spatial distribution of the Ni clusters with narrow size distribution peaked around 50 nm. The morphology of the Ni clusters was characterized by SEM and AFM.The cluster adhesion to the substrates was tested with several experiments: Ni coated carbon substrates were dipped into different liquids, processed with a variety of treatments (immersion, magnetic stirring, centrifugation and ultrasonic bath) and then observed with SEM. Moreover, nano-scratch tests were performed on Ni coated supports by means of an AFM equipped with a diamond tip.     

Binding energy shift in photoemission spectroscopy study of Ni clusters deposited on rutile TiO2 surfaces

Cluster-size-dependent binding energy (BE) shifts of Ni 2p_3/2 spectra in Ni clusters with respect to bulk Ni metal have been studied as a function of Ni coverage on clean rutile TiO₂(0 0 1) surfaces at room temperature. Auger parameter (AP) analysis of photoelectron spectra has been employed and revealed an obvious initial state contribution at the coverage of 0.5 monolayers (ML). The initial state effect was demonstrated to be strongly affected by the substrate and was assigned to a combination of eigenvalue shift in surface core-level shift (SCLS) and charge transfer between the metal clusters and substrates. The TiO₂(0 0 1) surface stoichiometry was found to introduce different charge transfer behaviors. Our results experimentally present that the Ni clusters are charged positively on stoichiomtric TiO₂ surface and less positively or even negatively on various reduced surfaces.     

Morphological, mechanical, corrosion and hydrogen permeation characteristics of Ni-nano-TiO2 composite coating compared to Ni electrodeposited on low carbon steel

Ni and Ni-nano-TiO₂ composite coatings with various amounts of TiO₂ in electrolyte, on low carbon steel, have been prepared from Watts-bath using electrodeposition process. The morphological, mechanical, corrosion and hydrogen permeation characteristics of Ni and Ni-nano-TiO₂ coatings were studied and compared with each other. The results revealed that, existence of nano-TiO₂ particles in Ni matrix improved the microstructure as well as microhardness, whereas increasing particle incorporation from 4.33 to 7.62 vol % concluded to microhardness enhancement. The corrosion behavior of Ni and Ni-nano-TiO₂ composite coatings with various amount of particle content was studied by the anodic polarization curves in 5% H₂SO₄ solution at room temperature. It was seen Ni-nano-TiO₂ composite coatings exhibited higher corrosion resistances comparing to pure Ni coating and corrosion protection improved with increasing nano-TiO₂ in coatings. In addition to the corrosion and engineering properties, comparison of hydrogen permeation characteristics of the Ni coating was made with Ni-nano-TiO₂ composite coating through Devanthan-Stachurski hydrogen permeation test. From the resulting data analysis, Ni-nano-TiO₂ composite coating was seen not only to provide longer life under corroding media, but also reduces greatly the risk of the substrate being exposed to hydrogen permeation when compared to electrodeposited Ni coating.     

Origin of XPS binding energy shifts in Ni clusters and atoms on rutile TiO2 surfaces

Cluster-size-dependent binding energy (BE) shifts of Ni 2p_3/2 spectra in Ni clusters with respect to bulk Ni metal have been studied as a function of Ni coverage on clean rutile TiO₂(0 0 1) and TiO₂(1 1 0) surfaces at room temperature. As a common method to distinguish initial and final state contributions to the core-level binding energy shifts in clusters, Auger parameter (AP) analysis of photoelectron spectra has been employed and reveals an obvious initial state contribution at the coverage of 0.5 monolayers (ML). From a comparison of results for TiO₂(0 0 1) and (1 1 0) surfaces, the initial state effect is demonstrated to be strongly affected by the substrate and is assigned to a combination of eigenvalue shift in surface core-level shift (SCLS) and charge transfer between the metal clusters and substrates. The Ni 2p_3/2 BE’s of atomic Ni on TiO₂(0 0 1) and (1 1 0) surfaces are deduced to be 853.69 and 853.55 eV, respectively, from an extrapolation of the experimental BE curves to zero Ni coverage. Compared with atomic Ni in gas phase, relaxation shifts of 7.34 and 7.48 eV are obtained on TiO₂(0 0 1) and (1 1 0) surfaces, respectively. These values are very close to the relaxation shift of 7.3 eV due to d electron screening, indicating d-like screening effects from the TiO₂ substrates after Ni 2p photoionization.     

Growth and characterization of Au,Ni and Au–Ni nanoclusters on 6H-SiC(0001) carbon nanomesh

The nucleation and thermal stability of Au, Ni, and Au–Ni nanoclusters on 6H-SiC(0001) carbon nanomesh as well as the interaction between Au–Ni bimetallic clusters and reactive gases have been studied by X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Both Au and Ni atoms grow as three-dimensional (3D) clusters. Annealing the Au/carbon nanomesh surface up to 1150 °C leads to complete desorption of the Au clusters, while interfacial reaction occurs between Ni clusters and the substrate surface when the Ni clusters are subjected to the same annealing process. The nucleation of Au–Ni clusters depends critically on the deposition sequence. Au atoms preferentially nucleate on the existing Ni clusters, leading to the formation of bimetallic clusters with Au enriched on the surface. If the deposition sequence is reversed, a part of Ni atoms nucleate between the Au clusters. The thermal stability of the Au–Ni clusters resembles that of the Ni/carbon nanomesh surface, irrespective of the deposition sequence. XPS characterization reveals that Ni atoms in Au–Ni bimetallic clusters are oxidized upon exposure to 5.0 × 10^? 7 mbar O₂ for 5 min at room temperature while negligible structure change can be detected when the bimetallic clusters are exposed to CO gas under the similar conditions.     

CEMS and SEM studies of the ion-beam mixed Ni−Sn and Al−Sn systems

Metallic¹¹⁹Sn was vapour deposited on Al and Ni substrates to form layers about 40nm thick and subsequently irradiated with 100keV Xe⁺ at fluences 1, 5 and 10·10¹⁵ Xe⁺/cm². Irradiation with 100keV N⁺ at 5·10¹⁶N⁺/cm² fluence was also accomplished on an Al sample on which a layer of 100nm¹¹⁹Sn was previously electrodeposited. Surface evolution of the deposited layers due to irradiation has been observed by SEM and loss of Tin due to sputtering has been evidenced by EDX microanalysis. Changes of chemical structure at the irradiated surfaces have been followed by CEMS: β-Sn, SnO, SnAl₂O₄, SnO₂ and SnAl₂O₅ or β-Sn, dissolved Tin in Nickel, SnO₂, Ni₃Sn and Ni₃Sn₂ phases were recognized on the surface of Aluminium and Nickel substrates respectively.     

The structural,electronic and magnetic properties of Ag4M and Ag4MCO (M = Sc–Zn) clusters

The structures, spectra and electronic and magnetic properties of Ag₄M and Ag₄MCO (M?=?Sc–Zn) clusters have been studied using density functional theory and CALYPSO structure searching method. Structural searches show that M atoms except Zn tend to occupy the highest coordination position in the ground state Ag₄M and Ag₄MCO clusters. Carbon monoxide is most easily adsorbed on Ag atom of Ag₄Zn and M atom of other Ag₄M. Infrared and Raman spectra, photoabsorption spectra and photoelectron spectra of Ag₄M and Ag₄MCO clusters are forecasted and can be used to identify these clusters from experiment. Analysis of electronic properties indicates that the adsorption of CO on Ag₄M clusters changes the zero vibrational energy (ZPVE) and increases stability of the host clusters. Dopant atoms except for Zn improve the stability of silver cluster. The Ag₄Ni cluster shows high chemical activity and maximum adsorption energy for carbon monoxide. Magnetism calculations reveal that the magnetic moment of Ag₄M (M?=?Mn–Ni) cluster adsorbed by carbon monoxide is decreased by 2 μ_B. The change of magnetic moment makes it possible to be used as a nanomaterial for carbon monoxide detection. Simultaneously, it is found that the adsorption of CO on Ag₄Cu cluster is a physical adsorption.     

Electronic structure,magnetic properties,and microstructural analysis of thiol-functionalized Au nanoparticles: role of chemical and structural parameters in the ferromagnetic behaviour

The present work describes the field emission characteristics of nanocrystalline metal clusters decorated multi walled carbon nanotubes (MWNT) field emitters fabricated over flexible graphitized carbon cloth. MWNT have been synthesized by catalytic chemical vapour decomposition (CCVD) of acetylene over Rare Earth (RE) based AB₂ (DyNi₂) alloy hydride catalyst. Fine powders of RE based AB₂ alloy hydride catalysts have been prepared by hydrogen decrepitation technique. The as-grown carbon nanotubes (CNTs) are purified by acid and heat treatments and characterized using XRD, SEM and TEM. Purified MWNT have been decorated with nanocrystalline Pd, Pt and Pt–Ru metal clusters using a simple chemical reduction method. The characterization of metal decorated CNTs were done by using XRD, SEM, TEM, HRTEM and EDX. Nanocrystalline Pd, Pt and Pt–Ru metal clusters decorated MWNT field emitters have been fabricated over graphitized carbon fabric using spin coating method. The field emission characteristics have been studied using an indigenously fabricated set up and the results are discussed. The samples show excellent emission properties with a fairly stable emission current over a period of 4 h. As the presence of the graphitic layer provides strong adhesion between the nanotubes and carbon cloth, the use of graphitized carbon cloth as substrate opens new possibilities for CNT field emitters.     

密度泛函理论研究BnNi(n=6—12)团簇的结构和磁性

基于第一性原理,用密度泛函理论中的广义梯度近似(generalized gradient approximation,GGA)方法,在充分考虑自旋多重度的前提下,优化并得到了B_n(n=6—12)和B_nNi(n=6—12)团簇的平衡构型,按照能量最低原理确定其基态结构. B_n团簇的计算结果与已有的理论结果相一致. 当Ni原子掺杂在B_n团簇 关键词： nNi团簇')" href="#">B_nNi团簇 基态结构 磁性     

Silicide formation by furnace annealing of thin Si films on large-grained Ni substrates

Si films with a thickness of approximately 250 nm have been electron-beam evaporated on thick, large-grained Ni substrates (grain size a few mm to 1 cm in diameter). An in situ sputter cleaning procedure has been used to clean the Ni surface before the Si deposition. Thermal annealings have been performed in a vacuum furnace. Ni₂Si is the first phase that grows at temperatures between 240 °C and 300 °C as a laterally uniform interfacial layer with a diffusion-controlled kinetics. The layer thicknessx follows the growth lawx ²=kt, withk=k ₀ exp(-E _a k _B T), wherek ₀=6.3 × 10^–4cm 2/s andE _a=(1-1±0.1) eV. Because of the virtually infinite supply of Ni, annealing at 800 °C for 130min yields a Ni-based solid solution as the final phase. The results are compared with those reported in the literature on suicide formation by the reaction of a thin Ni film on Si substrates, as well as with those for interfacial phase formation in Ni/Zr bilayers.     

Electrochemical activities of Pt-Ru-Co and Pt-Ru-Ni electrocatalysts supported by a carbon fiber web

Dynamic cyclic voltammetry is performed as functions of cycle number and potential window for the electrodeposition of Pt-Ru-Co and Pt-Ru-Ni catalysts on a carbon fiber (CF) web. Surface morphologies of the electrodeposited catalysts are observed by a scanning electron microscope. The electrochemical activity in methanol oxidation is examined by the cyclic voltammetry using a mixed aqueous solution of methanol as an electrolyte component. As the cycle number increases, both the current density and the amount of the electrodeposited metallic particles on the CF web are increased. The Pt-Ru-Ni/CF catalyst prepared in the potential range of −0.6 to 0.2 V and from the 1:2:2 mixed solution of H₂PtCl₆, RuCl₃·3H₂O, and Ni(NO₃)₂·6H₂O, respectively, shows the higher current density, corresponding to the higher catalytic activity.     

Tip enhanced Raman spectroscopy evidence for amorphous carbon contamination on gold surfaces

We show that the origin of the spectral fluctuations frequently observed in tip enhanced Raman spectroscopy (TERS) experiments can be mainly related to the presence of surface-contaminating amorphous carbon-based species. We have monitored the spectral fluctuations originating from the sharp metallic tips used as apertureless near field probes, as well as from commonly used noble metal substrates. A correlation between the tip surface roughness and the carbon-based spectral fluctuations has been revealed. An Au-(1 1 1) bare substrate has been mapped with sub-wavelength resolution by TERS, evidencing the localization of the carbon contaminants on the surface steps and grain boundaries.     

Hartree-Fock-Slater-LCAO studies of the acetylene-transition metal interaction: I. Chemisorption on Ni surfaces; cluster models

The interaction of C₂H₂ with Ni surfaces has been studied by the Hartree-Fock-Slater-LCAO method (with core pseudopotentials). Different adsorption sites (π, di-σ, μ₂, μ₃) at the Ni(111) surface have been modelled by clusters of 1 to 4 Ni atoms; the structure of C₂H₂ and the Ni-C distance have been varied (3 structures, 2 distances). The acetylene-metal bonding can be interpreted in terms of π to metal donation and, especially, metal to π¹ back donation effects which considerably weaken the C-C bond. These effects become increasingly important when more metal atoms are directly involved in the adsorption bonding: π < di-σ < μ₂ < μ₃. The calculated shifts in the ionization energies are in fair agreement with the experimentally observed shifts (by UPS) for C₂H₂ adsorbed on Ni(111) (and other Ni surfaces); these shifts do not depend very sensitively on the bonding situation, however, so that we could not assign the structure of adsorbed C₂H₂ solely on this basis. From the comparison between the measured C-C stretch frequency (by ELS) and the calculated C-C overlap populations, using a relation calibrated on Ni-acetylene complexes, we find that μ₃ bonding of C₂H₂ with a Ni-C distance of about 1.9 Å is most probable on the Ni(111) surface; the CCH angle is estimated to be somewhat smaller than 150°. We have suggested an explanation for the surface specific dissociation of C₂H₂: C₂ fragments (C-H bond breaking) have been observed on stepped Ni surfaces (at low temperature), CH fragments (C-C bond breaking) have been found on ideal surfaces (at higher temperatures).     

Stabilities,electronic and magnetic properties of Cu-doped nickel clusters: a DFT investigation

In this paper, we investigate the electronic and magnetic properties of Cu-doped nickel clusters by means of density functional theory. The stabilities of these clusters have also been studied in terms of the binding energies, second-order difference of energies, fragmentation energies and HOMO–LUMO energy gaps. The obtained results reveal that the N₄Cu, N₅Cu and Ni₇Cu clusters are found to be more stable that than all other clusters. Higher HOMO–LUMO gap was observed for Ni₅Cu cluster (2.265 eV), indicating its higher chemical stability. A half-metallic behaviour has also been observed for the Ni_nCu clusters, which suggests that these clusters can be employed as nanocatalysts for several catalytic processes, particularly for hydrogenation and dehydrogenation reactions. The magnetism calculations show that the magnetic moment is mostly located on the Ni atoms, and the contribution of the Cu atom to the total magnetic moment in the Ni_nCu clusters is very small. Furthermore, partial density of states analysis indicates that the 3d orbitals in Ni atoms are mostly responsible for the magnetic behaviour of these clusters, and the s orbitals have a very little contribution to the total magnetic moment.     

Photoluminescence from amorphous silica nanowires synthesized using TiN/Ni/SiO2/Si and TiN/Ni/Si substrates

Photoluminescence characteristics of amorphous silica nanowires (a-SiONWs) grown on TiN/Ni/Si and TiN/Ni/SiO₂ substrates have been studied. A-SiONWs grown on TiN/Ni/Si substrates show a Si-rich composition compared to those grown from TiN/Ni/SiO₂/Si. The emission characteristics of the nanowires were found to depend on the type of substrate. By annealing the a-SiONWs grown on TiN/Ni/Si in air, emission bands shift from blue to green bands. It is likely that silicon to oxygen ratio is an important factor in deciding the types of defects and emission bands of amorphous silica nanowires.     

NiMgn(n=1—12)团簇的第一性原理研究

采用基于密度泛函理论(DFT)中的广义梯度近似 (GGA),在考虑自旋多重度的情况下,对NiMg_n(n=1—12)团簇进行了构型优化,频率分析和电子性质计算.结果表明：n=1,2时,体系的基态为自旋三重态,n≥3时,为单重态;Ni原子掺杂使主团簇结构发生了明显变化. n≤8时,三角双锥,四角双锥结构主导着NiMg_n基态团簇的生长行为; n在9—12之间时,主团簇Mg_n+1(n=1—12)的基于三棱柱构型的基态演化行为发生了一定程度的改变;n≥6时,Ni原子陷入了主团簇内部;掺杂使体系的平均结合能增大,能隙减小;n=4,6,10是团簇的幻数;不同尺寸团簇的s, p, d轨道杂化中,Ni原子3d, 4p成分所起作用不同; NiMg₆基态结构具有很高的对称性(O_h),很好的稳定性和化学活性,能隙仅为0.25eV. 关键词： n团簇')" href="#">NiMg_n团簇 几何结构 稳定性 化学活性     

Physical and electrochemical characterizations of Ni-SiO2 nanocomposite coatings

Advances in materials performance often require the development of composite system. In the present investigation, SiO₂-reinforced nickel composite coatings were deposited on a mild steel substrate using direct current electrodeposition process employing a nickel acetate bath. Surface morphology, composition, microstructure and crystal orientation of the Ni and Ni-SiO₂ nanocomposite coatings were investigated by scanning electron microscope, energy dispersive X-ray spectroscopy and X-ray diffraction analysis, respectively. The effect of incorporation of SiO₂ particles in the Ni nanocomposite coating on the microhardness and corrosion behaviour has been evaluated. Smooth composite deposits containing well-distributed silicon oxide particles were obtained. The preferred growth process of the nickel matrix in crystallographic directions <111>, <200> and <220> is strongly influenced by SiO₂ nanoparticles. The average crystallite size was calculated by using X-ray diffraction analysis and it was ~23 nm for electrodeposited nickel and ~21 nm for Ni-SiO₂ nanocomposite coatings. The crystallite structure was fcc for electrodeposited nickel and Ni-SiO₂ nanocomposite coatings. The incorporation of SiO₂ particles into the Ni matrices was found to improve corrosion resistance of pure Ni coatings. The corrosion potential (E _corr) in the case of Ni-SiO₂ nanocomposite coatings had shown a negative shift, confirming the cathodic protective nature of the coating. The Ni-SiO₂ composite coatings have exhibited significantly improved microhardness (615 HV) compared to pure nickel coatings (265 HV)     

The growth mechanism and supercapacitor study of anodically deposited amorphous ruthenium oxide films

In the present study, ruthenium oxide (RuO₂) thin films were deposited on the stainless steel (s.s.) substrates by anodic deposition. The nucleation and growth mechanism of electrodeposited RuO₂ film has been studied by cyclic voltammetry (CV) and chronoamperometry (CA). The deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive analysis by X-rays (EDAX) for structural, morphological, and compositional studies. The electrochemical supercapacitor study of ruthenium oxide thin films have been carried out for different film thicknesses in 0.5 M H₂SO₄ electrolyte. The highest specific capacitance was found to be 1190 F/g for 0.376 mg/cm² film thickness.     

W_n Ni_m(n+m≤7;m=1,2)团簇电子结构与光谱性质的理论研究

采用密度泛函理论(DFT)中的B3PW91方法在LANL2DZ基组水平上对WnNim(n+m≤7;m=1,2)团簇的各种可能构型进行了几何结构优化,得出了它们的基态构型,并对其NBO、振动频率、光谱和极化率进行了理论研究.研究结果表明:W,Ni原子内部杂化现象较强,而在W-Ni原子之间杂化较弱;在W和Ni相互作用形成合金团簇的过程中,发生原子间的电荷转移,使得合金团簇中大多数Ni原子带正电荷W原子带负电荷;从光学上分析显示,W6Ni团簇的IR和Raman谱中的振动峰最多,W5Ni2的IR和Raman谱中的振动峰最强,W2Ni的IR谱中只有一个较强峰值;WnNim(n+m≤7;m=1,2)团簇中原子间的成键相互作用随W成分的增加而增强.     

Electrical conduction in nanostructured carbon and carbon-metal films grown by supersonic cluster beam deposition

We have studied the electrical conduction in nanostructured carbon (ns-C) films produced by deposition of a supersonic beam of neutral carbon clusters. The d.c. conduction properties of these films have been measured in situ during the deposition process and ex situ as a function of the temperature in vacuum and in ambient of different gases (H₂, N₂, CH₄, He). The ns-C films exhibit an ohmic behavior with a room temperature resistivity in the range of 10⁷-10⁹ W{\rm\Omega} cm depending on the growth and storage conditions. Conductivity vs. temperature measured in vacuum in the range 290-400 K is characterized by activation energies in the range of 0.3-1.7 eV, the current response does not differ significantly in gas atmosphere. Nanocomposite carbon-metal films have been obtained by adding small amounts of metallorganic precursors containing molybdenum and cobalt during the formation of carbon clusters prior to deposition. The films are characterized by porous carbon networks containing small metal and metal carbide clusters. Electrical transport properties of these films have been studied as a function of temperature, gas pressure and relative humidity. In particular, the electrical conductivity of the sample produced with molybdenum showed to be much sensitive to changes in gas pressure and relative humidity, being characterised by fast and reversible responses.