The Electronic and Magnetic Properties of FCC Iron Clusters in FCC 4D Metals

The electronic and magnetic structures of small FCC iron clusters in FCC Rh, Pd and Ag were calculated using the discrete variational method as a function of cluster size and lattice relaxation. It was found that unrelaxed iron clusters, remain ferromagnetic as the cluster sizes increase, while for relaxed clusters antiferromagnetism develops as the size increases depending on the host metal. For iron in Rh the magnetic structure changes from ferromagnetic to antiferromagnetic for clusters as small as 13 Fe atoms, whereas for Fe in Ag antiferromagnetism is exhibited for clusters of 24 Fe atoms. On the hand, for Fe in Pd the transition from ferromagnetism to antiferromagnetism occurs for clusters as large as 42 Fe atoms. The difference in the magnetic trends of these Fe clusters is related to the electronic properties of the underlying metallic matrix. The local d densities of states, the magnetic moments and hyperfine parameters are calculated in the ferromagnetic and the antiferromagnetic regions. In addition, the average local moment in iron-palladium alloys is calculated and compared to experimental results.     

XPS and TPD investigation of CO adsorption on mixed Rh-V layers supported by gamma-alumina

Alumina-supported mixed bimetallic Rh-V thin films, with the overall thickness of 0.8 ML, were prepared under the ultrahigh vacuum (UHV) conditions and characterized with respect to their electronic and CO adsorption properties. X-ray photoelectron spectroscopy (XPS) was utilized to characterize electronic changes accompanying bimetallic Rh-V interaction and interaction between metal and polycrystalline γ-Al₂O₃ substrate. The chemisorption properties were probed by temperature-programmed desorption spectroscopy (TPD) of CO molecules. The electronic and chemisorption properties of the mixed layers were compared with pure Rh and V layers grown on the same γ-Al₂O₃ substrate and with a model bimetallic Rh-V system prepared by V deposition on a polycrystalline Rh foil. By varying the preparation conditions, we observed a strong dependence of the studied properties on the position of the V atoms. The presence of V atoms on the surface led to a fast deactivation, while vanadium presented under the surface resulted in a weakening of CO-metal surface bond, a change in the proportion of the adsorption side species, and an increase of CO dissociation.     

Magnetic properties and domain structure of epitaxial (001) Fe/Pd superlattices

The magnetic properties of well-characterized (001)Fe/Pd superlattices prepared by molecular beam epitaxy are presented. The saturation magnetization is enhanced due to the polarization of the Pd interface, and analysis of hysteresis loops indicate low coercive fields, abrupt magnetic reversals, and ferromagnetic coupling between the Fe layers for all Pd thickness investigated (10–50 Å). It is also found that deposition on a stationary substrate can create a weak uniaxial in-plane anisotropy, which, for one of the two easy directions of Fe, causes a spontaneous rotation of the magnetization by 90° at low fields. This effect is clearly demonstrated by optical Kerr-effect imaging of the magnetic domain structure, and can be mistaken for antiferromagnetic coupling with very weak coupling fields. The strength of this uniaxial anisotropy is found to oscillate rapidly with Pd thickness, suggesting that it is very sensitive to the microstructure.     

GaP低阻欧姆接触层的AES和SIMS分析

本文用AES和SIMS分析讨论了p-GaP与三层金属膜Pd/Zn/Pd形成良好欧姆接触层的性质.     

Growth and thermal properties of ultrathin cerium oxide layers on Rh(1 1 1)

Ultrathin layers of cerium oxide have been deposited on a Rh(1 1 1) surface and their growth morphology, structure, and thermal stability have been investigated by LEED, STM, XPS, and valence band resonant photoemission. STM and LEED indicate that the ceria grows epitaxially in form of ordered CeO₂ islands at elevated substrate temperature (250–300 °C), with (1 1 1) faces parallel and orientationally aligned to the main azimuthal directions of the substrate. The ultrathin ceria films contain significant amounts of reduced Ce³⁺ species, which appear to be located predominantly at the ceria–Rh interface. For thicker films (>6 equivalent monolayers) stoichiometric CeO₂ is detected in XPS. Vacuum annealing produces morphologically well-defined hexagonal islands, accompanied by partial reduction and the formation of oxygen vacancies at the ceria surface. The thermal stability and the degree of reduction is a function of the oxide layer thickness, with thinner layers being thermally less stable. At temperatures >800 °C, the ceria decomposes and Ce–Rh alloy phases are identified.     

Preparation,characterization and photocatalytic performance of noble metals (Ag,Pd, Pt,Rh) deposited on sponge-like ZnO microcuboids

Novel sponge-like ZnO microcuboids with a hierarchical structure were fabricated via an alcoholic thermal process. Then a series of noble metals (Ag, Pd, Pt, Rh) was loaded onto the microcuboids. The samples obtained were characterized by nitrogen physical adsorption, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), and X-ray photoelectron spectroscopy (XPS). The results show that the ZnO microcuboids have a high surface area and a sponge-like hierarchical structure. Activity tests for the degradation of acid orange II dye showed that the noble metals enhanced the activity of ZnO to different extents. For loading of 0.5 wt.%, the activity enhancement decreased in the order Pd>Ag>Pt>Rh. Co-loading of Pd and Ag had a detrimental effect on activity compared to single loading. The enhanced photocatalytic performance can be attributed to an increase in the rate of separation of photogenerated e^–/h⁺ pairs induced by the noble metals.     

Effect of combination of noble metals and metal oxide supports on catalytic reduction of NO by H2

We investigated the effects of combination of noble metals M (Rh, Pd, Ir, Pt) and metal oxide supports S (Al₂O₃, SiO₂, ZrO₂, CeO₂) on the NO + H₂ reaction using planar catalysts with M/S two layered thin films on Si substrate. In this study, NO reduction ability per metal atom were evaluated with a specially designed apparatus employing pulse valves for the injection of reactant molecules onto catalysts and a time-of-flight mass spectrometer to measure multiple transient products: NH₃, N₂ and N₂O simultaneously as well as with an atomic force microscopy to observe the surface area of metal particles. The catalytic performances of Rh and Ir catalysts were hardly affected by a choice of a metal oxide support, while Pd and Pt catalysts showed different catalytic activity and selectivity depending on the metal oxide supports. This assortment is consistent with ability to dissociate NO depending on metals without the effect of any support materials. There, the metals to the left of Rh and Ir on the periodic table favor dissociation of NO and those to the right of Pd and Pt tend to show molecular adsorption of NO. Therefore, the catalytic property of noble metals could be assorted into two groups, i.e. Rh and Ir group whose own property would mainly dominate the catalytic performance, and Pd and Pt group whose interaction with metal oxides supports would clearly contribute to the reaction of NO with H₂. NO reduction activity of Pd and Pt was found to be promoted above that of Rh and Ir, provided that Pd and Pt were supported by CeO₂ and ZrO₂.     

A study of the infrared spectra of carbon monoxide adsorbed on metals of the copper subgroup and on cobalt,ruthenium, rhodium,and palladium

A study has been made of the infrared spectra of carbon monoxide CO, adsorbed on Cu, Ag, Au, Co, Ru, Rh and Pd at temperatures from –160° C to 200° C and pressures from 10^–5 to 1–10 mm Hg. The spectra of CO adsorbed on Cu, Ag, and Au show one absorption band, characteristic of a surface compound of carbon monoxide, with linear structure. It has been found that in the stable chemosorption of CO on Co, Ru, Rh, and Pd in the range of temperatures and pressures studied, two types of surface compound-linear and bridged-are produced.     

Adsorption of <Emphasis Type="Italic">d</Emphasis>-metal atoms on the regular MgO(001) surface: Density functional study of cluster models embedded in an elastic polarizable environment

Structure and bonding of complexes formed by 17 different single transition metal atoms (Cu, Ag, Au; Ni, Pd, Pt; Co, Rh, Ir; Fe, Ru, Os; Mn, Re; Cr, Mo, W) with oxygen sites of the regular MgO(001) surface were studied computationally. We employed an all-electron scalar-relativistic density functional method in combination with our novel scheme of cluster models embedded in an elastic polarizable environment that allows one to account for substrate relaxation. Even on a rigid substrate such as ideal MgO(001), adsorbate-induced relaxation noticeably affects structure and stability of surface complexes. For more reliable estimates, we calculated adsorption energies with two different gradient-corrected exchange-correlation functionals, BP86 and PBEN. More than one electron configuration was considered for metal atoms exhibiting high-spin states adsorption complexes. Within one group of the periodic table, 3d-atoms, in general, were found to adsorb more strongly than 4d-atoms, but weaker than 5d-atoms. In line with our previous studies of selected d-metal atoms adsorbed on oxides, the surface complexes considered did now show any indication of metal oxidation. PACS 68.43.Bc; 68.43.Fg; 71.15.Nc; 82.65.+r; 68.35.Ct; 68.43.-h; 73.20.Hb; 71.15.Mb; 75.70.Cn     

Characterization of In/Pd and Pd/In/Pd thin films by ellipsometric, XRD and AES methods

In/Pd and Pd/In/Pd thin films were prepared by thermal evaporation on the SiO₂ substrate in a vacuum. The structural and optical properties of the films were investigated by means of X-ray diffractometry (XRD), Auger electron spectroscopy (AES) and spectroscopic ellipsometry (SE). Auger depth profile studies were performed in order to determine the composition of elements in the Pd-In systems. Interdiffusion of metals was detected at room temperature. Optical properties of Pd-In composite layers formed due to the interdiffusion were derived from ellipsometric quantities Ψ and Δ measured in the photon energy range 0.75-6.50 eV at different angles of incidence. The effective optical spectra show absorption peaks dependent on the composition of nonuniform films. The XRD patterns indicated formation of Pd_1−xIn_x intermetallic phases in the samples.     

The reaction of carbon monoxide with palladium supported on cerium oxide thin films

In this study we probe the reaction of carbon monoxide with Pd nanoparticles supported on cerium oxide thin films. With the use of soft X-ray photoelectron spectroscopy (sXPS), and temperature programmed desorption (TPD) the surface intermediates and pathways leading to reaction products of CO on Pd supported on ceria were investigated. When Pd is supported on the stoichiometric CeO₂ surface (Ce⁺⁴) only the molecular adsorption of CO on Pd is visible (286.4 eV). All of the CO desorbs below 520 K, however a small amount of O exchange between the CO and the ceria was indicated through the acquisition of labeled ¹⁸O from the substrate in the desorbed CO. The Pd nanoparticles are activated on partially reduced CeO_x to promote the dissociation of <10% of the CO as indicated by a C-Pd species (284.4 eV) in sXPS. The C recombines with O from the ceria and desorbs between 600 and 700 K. The majority of the CO does not dissociate, however, and the degree of dissociation does not increase with the degree of ceria reduction. This result is in contrast with Rh nanoparticles supported on ceria where the degree of dissociation increased with the degree of ceria reduction and nearly total dissociation was obtained when the ceria was highly reduced.     

Comparison of the interaction of Pd with positively and negatively poled LiNbO3(0 0 0 1)

To investigate the possibility of manipulating the surface chemical properties of finely dispersed metal films through ferroelectric polarization, the interaction of palladium with oppositely poled LiNbO₃(0 0 0 1) substrates was characterized. Low energy ion scattering indicated that the Pd tended to form three-dimensional clusters on both positively and negatively poled substrates even at the lowest coverages. X-ray photoelectron spectroscopy (XPS) showed an upward shift in the binding energy of the Pd 3d core levels of 0.9 eV at the lowest Pd coverages, which slowly decayed toward the bulk value with increasing Pd coverage. These shifts were independent of the poling direction of the substrate and similar to those attributed to cluster size effects on inert supports. Thus, the spectroscopic data suggested that Pd does not interact strongly with LiNbO₃ surfaces. The surface chemical properties of the Pd clusters were investigated using CO temperature programmed desorption. On both positively and negatively poled substrates, CO desorption from freshly deposited Pd showed a splitting of the broad 460 K desorption peak characteristic of bulk Pd into distinct peaks at 270 and 490 K as the Pd coverage was decreased below 1.0 ML; behavior that also resembles that seen on inert supports. It was found that a small fraction of the adsorbed CO may dissociate (<2%) for Pd on both positively and negatively poled substrates. The thermal response of the smaller Pd clusters on the LiNbO₃ surfaces, however, was different from that of inert substrates. In a manner similar to Nb₂O₅, when CO desorption experiments were carried out a second time, the adsorption capacity decreased and the higher temperature desorption peak shifted from 490 K to below 450 K. This behavior was independent of the substrate poling direction. Thus, while there was evidence that LiNbO₃ does not behave as a completely inert support, no significant differences between positively and negatively poled surfaces were observed. This lack of sensitivity of the surface properties of the Pd to the poling direction of the substrate is attributed to the three-dimensional Pd clusters being too thick for their surfaces to be influenced by the polarization of the underlying substrate.     

Brillouin light scattering from spin waves in magnetic layers and multilayers

We give an overview on our experimental and theoretical investigations of Brillouin light scattering in magnetic thin films, layered magnetic structures and superlattices. For epitaxial Fe(1 10) layers on W(1 10) the in-plane and out-of-plane magnetic surface anisotropy constants are determined, and the influence of Pd overlayers on the surface anisotropies is studied. For Fe/Pd superlattices a magnetic polarization of the Pd at the interfaces is established and the interface anisotropy constant is determined. For second order Fe/Pd superlattices, formed by alternating two Fe/Pd bilayers with different repeat periods, the Brillouin spectrum is obtained and compared to calculations. In the case of magnetic/nonmagnetic multilayered structures we investigate theoretically the crossing regime between dipolar and exchange-dominated modes. For small spacer-layer thicknesses, interlayer exchange coupling shifts the spin-wave frequencies of all but the highest-frequency dipolar mode into the exchange-mode regime. In case of all-magnetic multilayered structures, such as Fe/Ni multilayers, a new type of propagating collective excitations arising from coupled exchange modes is predicted.     

The effect of deposition temperature on the intermixing and microstructure of Fe/Ni thin film

The physical vapour deposition of Ni atoms on α-Fe(001) surface under different deposition temperatures were simulated by molecular dynamics to study the intermixing and microstructure of the interfacial region. The results indicate that Ni atoms hardly penetrate into Fe substrate while Fe atoms easily diffuse into Ni deposition layers. The thickness of the intermixing region is temperature-dependent, with high temperatures yielding larger thicknesses. The deposited layers are mainly composed of amorphous phase due to the abnormal deposition behaviour of Ni and Fe. In the deposited Ni-rich phase, the relatively stable metallic compound B₂ structured FeNi is found under high deposition temperature conditions.     

Study of two types of Ir or Rh covered single atom pyramidal W tips

The growth of a single-atom sharp pyramid tips on a tungsten substrate by depositing noble metals of the Pt family was investigated by field ion microscopy earlier. The Pd or Pt covered single-atom W pyramidal tips have been successfully prepared and established by our group. They are thermally and chemically stable and can easily be regenerated. In this study, we report the establishing and structural analysis of Rh and Ir covered single-atom W pyramidal tips. Two types of stable structures with bcc {2 1 1} facets are found for both metals. One is stacked by 1, 3, 10 atoms, and the other is stacked by 1, 6, 15 atoms for the top three layers and so on in series from the top to the deeper layers. The single atom tip is destroyed layer by layer after field evaporation to observe the structures of the different layers. However, the tip can be regenerated after it is annealed again and the two types of structures appear systematically depending on the annealing temperature. The regeneration process is investigated and the growth parameters of the two different types of Rh or Ir covered W tip are determined. The differences in the activation barrier and binding energy of these two types are calculated to be 0.08 eV and 0.064 eV for Rh covered single atom tips, and 0.03 eV and 0.14 eV for Ir covered single atom tips, respectively. Possible mechanisms and the relevance for application are discussed.     

超薄Fe层在反铁磁NiO(001)面上沉积的研究

通过分子束外延(MBE)和脉冲激光沉积(PLD)方法，将1—10个Fe原子层(ML)以楔形方式沉积到反铁磁单晶NiO(001)基片上.表面磁光克尔效应的原位测试结果表明：通过MBE沉积的Fe原子层在Fe/NiO界面处产生了约2ML的磁死层；而通过PLD沉积的Fe原子层在Fe/NiO界面处产生了约3ML的磁死层.X射线光电子能谱对Fe/NiO界面进行研究的结果表明，在Fe原子与单晶NiO间发生了界面化学反应. 关键词： 磁性薄膜 表面磁性 X射线光电子能谱     

Structural analysis of In/Ag, In/Cu and In/Pd thin films on tungsten by ellipsometric, XRD and AES methods

Compositional, microstructural and optical properties of In/Cu, In/Ag and In/Pd thin films evaporated on W substrate in a vacuum were investigated by means of Auger electron spectroscopy, X-ray diffractometry, scanning electron microscopy, and spectroscopic ellipsometry methods. Thicknesses of deposited pure metal layers were adjusted to atomic concentration ratios In:Ag = 1:2, In:Cu = 2:1 and In:Pd = 3:1. Interdiffusion of metals and creation of intermetallic compounds AgIn₂, Ag₂In and CuIn₂were detected at room temperature. Phase transformation and changes in the surface morphology due to annealing of samples at 393 K for 60 min were revealed. Combined investigations indicated a layered structure of In/Ag films. A tendency of island-like structure formation was stronger for In/Cu and In/Pd films. The complex dielectric functions of In/Ag, In/Cu and In/Pd composite layers were determined from spectroellipsometric data.     

Thermoelectric power of Ir(Fe)

Thermoelectric power data between 4.2 and 300°K are presented for Ir containing 0.5 and 1 at.% Fe and for pure Ir. Peaks similar to those found in Pd(Ni) and Rh(Fe) occur in Ir(Fe) at the spin fluctuation temperature T_sf = 28°K, independent of solute concentration. Similarities and differences among the three alloy systems are discussed.     

敞口消解ICP-MS同时测定北京地区环境尘土样品中痕量铂、铑、钯的研究

研究了电感耦合等离子体质谱(ICP-MS)同时测定土样中痕量铂、铑、钯的分析方法。比较几种尘土样品的消解处理方法,采用王水加热回流来消解样品。优化了样品测量条件,并研究了干扰情况和消除干扰的方法。所建立的方法的精密度、线性关系良好,在优化的实验条件下Pt,Pd,Rh的检出限分别为0.48,4.22和0.42 ng·g-1,样品的加标回收率分别为Pt 87.6％～88％,Pd 85.2％～87.8％和Rh 93％～95％。将建立的方法应用于环境尘土样品的测定,回收率在85％以上,结果令人满意。     

SPIN-DEPENDENT TUNNELING EFFECTS ON MAGNETIC NANOSTRUCTURES

The contrast mechanism of spin-polarized scanning tunneling spectroscopy (SP-STS) is demontrated on in-plane magnetized Gd islands grown on W (110) using Fe-coated tips. The use of Gd-coated tips enables the imaging of the antiferromagnetic domain structure of Fe nanowires being perpendicularly magnetized grown on a stepped W(110) substrate. The influence of an external magnetic field on the nanowire domain structure is demonstrated. It is shown that the antiferromagnetic domain structure of the Fe nanowires strongly depends on the miscut of the W(110) substrate. While at high miscut the magnetization direction alternates between adjacent DL stripes it was found to alternate within single Fe DL stripes at low miscut. Nanoscale Fe islands with a height of two atomic layers were found to be single domain particles.