Ultrathin oxide films on metals: new physics and new chemistry?

Oxide thin films on metals are now currently used as model systems to study the surface properties of highly insulating oxides by means of electron spectroscopies. However, it has been recently proposed that ultrathin oxide films and oxide–metal interfaces may actually have unprecedented intrinsic chemical–physical properties, because of image potential screening of charge fluctuations and interfacial hybridizational effects. In fact, on-site Coulomb interactions and charge transfer energies in oxide thin films on metals are reduced by as much as a few eV as compared to the bulk values, thus suggesting a large reduction of the conductivity gap and a strong enhancement of the strength of various exchange and superexchange magnetic interactions in thin layers of strongly correlated oxides on metals. Moreover, interfacial oxygen states with strong metallic character have been observed and considered responsible for an unusually high and chemical selective reactivity of oxide–metal interfaces. Some basic ideas and results connected with these intriguing interfacial phenomena will be presented and discussed taking MgO thin films on Ag(100) as a model system.     

Structure evolution of the biaxial alignment in sputter-deposited MgO and Cr

The growth of biaxially aligned layers, i.e. layers with both a preferential out-of-plane and an in-plane crystallographic orientation, on non-aligned metallic substrates is investigated. Unbalanced magnetron sputtering on an inclined substrate is used to deposit the layers.This method enables us to grow biaxially aligned layers for different classes of materials with different physical and chemical properties. The results for biaxially aligned MgO which is a cubic metal oxide (FCC rocksalt structure), and pure metallic chromium films (BCC) are presented.A comparison between biaxially aligned MgO and Cr concerning the microstructure and crystallographic texture is discussed. A correlation between the sputter deposition parameters on the biaxial alignment of both materials is observed. Both materials have a columnar V-shape structure with a faceted surface, corresponding to zone T of the well known structure zone model of Thornton. The MgO layers exhibit a [111] out-of-plane orientation, while Cr layers have an [100] preferential orientation. MgO as well as Cr show a strong in-plane alignment.     

First Principle Study of the Structural, Electronic and Magnetic Properties of MgO Nanolayers on Fe Substrate

We have investigated the structural, electronic, and magnetic properties of MgO nanolayers with two different nanolayer thicknesses (1.5 nm and 1.75 nm) on a Fe substrate. The calculated results in this paper were obtained using the density functional theory (DFT) within the generalized gradient approximation (GGA). The total energies as a function of volume are calculated and thereby the lattice parameters, bulk moduli of MgO nanolayers with two different thicknesses have been calculated. The effects of surface atoms and Fe substrate atoms on physical properties of these nanolayers have been analyzed using the calculated total and partial electron density of states in its ferromagnetic phase. The spin-polarized density of states of MgO shows that this compound is an insulator in the nonmagnetic phase. MgO nanolayers on Fe substrate are metal in the ferromagnetic phase. The magnetic properties of surface atoms and Fe substrate atoms have been investigated and compared with bulk. Furthermore, the effect of hydrostatic pressure on the total and local magnetic moment of these nanolayers has been investigated.     

Magnesia supported Au and Ag catalysts for the preparation of few-layer graphene–metal nanocomposites: relationship between catalyst structure and the properties of graphene composites

Magnesia supported Au, Ag, and Au–Ag nanostructured catalysts were prepared, characterized, and used to synthesize few-layer graphene–metal nanoparticle (Gr–MeNP) composites. The catalysts have a mezoporous structure and a mixture of MgO and MgO·H₂O as support. The gold nanoparticles (AuNPs) are uniformly dispersed on the surface of the Au/MgO catalysts, and have a uniform round shape with a medium size of ~8 nm. On the other hand, the silver nanoparticles (AgNPs) present on the Ag/MgO catalyst have an irregular shape, larger diameters, and less uniform dispersion. The Au–Ag/MgO catalyst contains large Au–Ag bimetallic particles of ~20–30 nm surrounded by small (5 nm) AuNPs. Following the RF-CCVD process and the dissolution of the magnesia support, relative large, few-layer, wrinkled graphene sheets decorated with metal nanoparticles (MeNPs) are observed. Graphene–gold (Gr–Au) and graphene–silver (Gr–Ag) composites had 4–7 graphitic layers with a relatively large area and similar crystallinity for samples prepared in similar experimental conditions. Graphene–gold–silver composites (Gr–Au–Ag) presented graphitic rectangles with round, bent edges, higher crystallinity, and a higher number of layers (8–14). The MeNPs are encased in the graphitic layers of all the different samples. Their size, shape, and distribution depend on the nature of the catalyst. The AuNPs were uniformly distributed, had a size of about 15 nm, and a round shape similar to those from Au/MgO catalyst. In Gr–Ag, the AgNPs have a round shape, very different from that of the Ag/MgO catalyst, large size distribution and are not uniformly distributed on the surface. Agglomerations of AgNPs together with large areas of pristine few-layer graphene were observed. In Gr–Au–Ag composites, almost exclusively large bimetallic particles of about 25–30 nm, situated at the edge of graphene rectangles have been found.     

Atomistic simulation of epitaxial interfaces and polytypes

In this paper we discuss howab initio local density electronic structure calculations can be used to investigate extended defects such as interfaces and polytypes. LMTO-supercell calculations have been performed to understand the nature of bonding in epitaxial metal/ceramic interfaces such as Ag/MgO(001) and Ti/MgO(001). Cohesive and electronic properties of hexagonal polytypes of diamond, with different stacking sequences, have been predicted for the first time and compared with the available experimental data. The relative stabilities of 4H, 6H and 8H diamond polytypes have been calculated using a generalized version of force theorem.     

Formation,Structures and Electronic Properties of Silicene Oxides on Ag(111)

The formation, structural and electronic properties of silicene oxides(SOs) that result from the oxidation of silicene on Ag(111) surface have been investigated in the framework of density functional theory(DFT).It is found that the honeycomb lattice of silicene on the Ag(111) surface changes after the oxidation. SOs are strongly hybridized with the Ag(111) surface so that they possess metallic band structures. Charge accumulation between SOs and the Ag(111) surface indicates strong chemical bonding, which dramatically affects the electronic properties of SOs. When SOs are peeled off the Ag(111) surface, however, they may become semiconductors.     

金属熔液对氧化镁陶瓷润湿行为研究进展

MgO陶瓷因各种优异性能在轻质高强的金属基复合材料、电子封装材料和涂层材料领域都具有广阔的应用前景,然而研究金属熔液对MgO陶瓷的润湿性是MgO陶瓷能否成功应用于这些领域的基础所在,因此研究金属熔液对MgO的润湿性就显得极为重要.本文通过综述Al/MgO陶瓷反应体系、Mg/MgO陶瓷非反应体系以及其它金属包括稀有金属、贵金属与MgO陶瓷润湿行为的研究进展,将各种金属熔液对于MgO陶瓷的润湿行为分为反应型润湿金属、非反应型润湿金属和非反应型难润湿金属等类型.此外还讨论了目前金属熔液与MgO陶瓷润湿行为研究中尚为存在的一些问题与争论,为金属熔液与MgO陶瓷润湿行为理解的进一步深入提供了支持.     

Nanograins on Ti-25Nb-3Mo-2Sn-3Zr alloy facilitate fabricating biological surface through dual-ion implantation to concurrently modulate the osteogenic functions of mesenchymal stem cells and kill bacteria

Surface mechanical attrition treatment (SMAT) method is an effective way to generate nanograined (NG) surface on Ti-25Nb-3Mo-2Sn-3Zr (wt.％) (named as TLM),a kind of β-type titanium alloy,and the achieved nanocrystalline surface was proved to promote positive functions of osteoblastic cells.In this work,to further endow the NG TLM alloy with both good osteogenic and antibacterial properties,magnesium (Mg),silver (Ag) ion or both were introduced onto the NG TLM surface by ion implantation process,as a comparison,the Mg and Ag ions were also co-implanted onto coarsegrained (CG) TLM surface.The obtained results show that subsequent ion implantation does not remarkably induce the surface roughness and topography alteration of the SMAT-treated layers,and it also has little impact on the microstructure of the SMAT-derived β-Ti nanograins.In addition,the implanted Mg and Ag ions are observed to exist as MgO and metallic Ag nanoparticles (NPs) embedding tightly in the β-Ti matrix with grain size of about 15 and 7 nm,respectively.Initial cell adhesion and functions (including proliferation,osteo-differentiation and extracellular matrix mineralization) of rabbit bone marrow mesenchymal stem cells (rBMMSCs) and the bacterial colonization of Staphylococcus aureus (S.aureus) on the different surfaces were investigated.The in-vitro experimental results reveal that the Mg and Ag single-ion implanted NG surface either significantly promotes the rBMMSCs response or inhibits the growth ofS.aureus,whereas the Mg/Ag coimplanted NG surface could concurrently enhance the rBMMSCs functions as well as inhibit the bacterial growth compared to the NG surface,and this efficacy is more pronounced as compared to the Mg/Ag co-implantation in the CG surface.The SMAT-achieved nanograins in the TLM surface layer are identified to not only play a leading role in determining the fate of rBMMSCs but also facilitate fabricating dualfunctional surface with both good osteogenic and antibacterial activities through co-implantation of Mg and Ag ions.Our investigation provides a new strategy to develop high-performance Ti-based implants for clinical application.     

Preparation of nanocrystalline MgO by surfactant assisted precipitation method

Nanocrystalline magnesium oxide with high surface area was prepared by a simple precipitation method using pluronic P123 triblock copolymer (Poly (ethylene glycol)-block, Poly (propylene glycol)-block, Poly (ethylene glycol)) as surfactant and under refluxing conditions. The prepared samples were characterized by X-ray diffraction (XRD), N₂ adsorption (BET) and scanning and transmission electron microscopies (SEM and TEM). The obtained results revealed that the refluxing time and temperature and the molar ratio of surfactant to metal affect the structural properties of MgO, because of the changes in the rate and extent of P123 adsorption on the prepared samples. The results showed that the addition of surfactant is effective to prepare magnesium oxide with high surface area and affects the morphology of the prepared samples. With increasing the P123/MgO molar ratio to 0.05 the pore size distribution was shifted to larger size. The sample prepared with addition of surfactant showed a plate-like shape which was completely different with the morphology of the sample prepared without surfactant. The formation of nanoplate-like MgO was related to higher surface density of Mg ions on the (0 0 1) plane than that on the other planes of the Mg(OH)₂ crystal. The (0 0 1) plane would be blocked preferentially by the adsorbed P123 molecules during the growing process of Mg(OH)₂ nanoentities and the growth on the (0 0 1) plane would be markedly restricted, and the consequence is the generation of nanoplate-like MgO. In addition, increase in refluxing temperature and time increased the specific surface area of the prepared MgO samples.     

Formation of BaTiO3 coatings on titanium by microarc oxidation method

Barium titanate layers on a titanium surface have been formed with using of microarc oxidation (MAO) method. The formation process was carried out in the aqueous electrolyte containing barium ions. The formation conditions, composition and anomalous properties of surface layers obtained are discussed. Based upon the experimental results the mechanism of metal/dielectric/metal (MDM) structure formation is proposed.     

In situ prepared polypyrrole–Ag nanocomposites: optical properties and morphology

Polypyrrole–silver (PPy–Ag) nanocomposites with various silver contents have been synthesized via a kinetically favorable one-step chemical oxidative polymerization process. The oxidant, ammonium persulfate, was used to oxidize pyrrole monomer for growing chains of PPy. And AgNO₃ was used as a precursor for metallic silver nanoparticles. The detailed characterization techniques, UV–Vis–NIR, fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction spectroscopy, field-emission scanning electron microscopy, and transmission electron microscopy (TEM), have been used to reveal electronic environment, structure, and morphology of composites as well as as-synthesized PPy. The synthesis environment prior to polymerization has also been investigated by absorption spectroscopy. The TEM images of PPy–Ag nanocomposites reveal that silver nanoparticles are deeply embedded into the polymer matrix in addition to surface adsorption. It is observed that the size distribution of inorganic nanoparticles (ca. 4–10 nm, depending on the metal ion concentrations) as well as structural morphology is altered by the initial concentrations of silver ions.     

常温下赋予不锈钢抗菌性能的实验研究

以AgNO3为主要原料制备了含有Ag^ 的冷敷液，在常温条件下，采用将冷敷液涂抹在不锈钢表面上或将不锈钢浸入冷敷液中的方法，制备了出表面含有抗菌Ag^ 离子的新型抗菌不锈钢。用扫描电镜(SEM)、X射线衍射(XRD)和原子吸收光谱(AAS)进行表征，表征结果表明，不锈钢表面形成一层含有柠檬酸银和过氧化银的薄膜，Ag^ 还渗透到不锈钢的内部。还对此材料的的抗菌性能进行了奎因实验，实验结果显示，抗菌不锈钢在接种金黄色葡萄球菌和大肠杆菌后培养24h后，不锈钢表面的菌落数均为0。     

Reversible electron-transfer reactions within a nanoscale metal oxide cage mediated by metallic substrates

Transition metal oxides exhibit a rich collection of electronic properties and have many practical applications in areas such as catalysis and ultra-high-density magnetic data storage. Therefore the development of switchable molecular transition metal oxides has potential for the engineering of single-molecule devices and nanoscale electronics. At present, the electronic properties of transition metal oxides can only be tailored through the irreversible introduction of dopant ions, modifying the electronic structure by either injecting electrons or core holes. Here we show that a molybdenum(VI) oxide 'polyoxometalate' molecular nanocluster containing two embedded redox agents is activated by a metallic surface and can reversibly interconvert between two electronic states. Upon thermal activation two electrons are ejected from the active sulphite anions and delocalized over the metal oxide cluster cage, switching it from a fully oxidized state to a two-electron reduced state along with the concomitant formation of an S-S bonding interaction between the two sulphur centres inside the cluster shell.     

Structure and composition of aluminum oxide films in contact with the liquid In-Ga eutectic

The oxide layers on the surface of aluminum metal and the aluminum alloys AD-1 and A-5 have been studied by attenuated total reflection infrared spectroscopy. The Al-O and Al-OH surface vibrational modes and A-O modes of the AlO₄ and AlO₆ groups have been identified. The structural inhomogeneity of the surface oxide layers is shown to contribute to their disruption when the sample is brought into contact with the liquid In-Ga eutectic. In situ scanning electron microscopy and X-ray microanalysis have been used to follow the dynamics of oxide layer disruption and the morphological and compositional changes in the eutectic alloy and the surface layer of aluminum.     

Initial Oxidation of γ-TiAl(111) Surface:Density-functional Theory Study

In this paper,we reported a first-principles investigation on the structural and electronic properties of O adsorption on the γ-TiAl(111) surface,to illustrate the oxidation process.It has been found that:(1) rather than stopping with one full monolayer of coverage,oxygen adsorption continues till two monolayer coverage,rendering an oxide-like structure;(2) full structural relaxation makes the surface oxide layer denser and more stable,which hinders the subsequent O adsorption(oxidation) process.In addition...     

The electromagnetic interference shielding effect of indium-zinc oxide/silver alloy multilayered thin films

A study was made to examine the electromagnetic interference (EMI) shielding effect of multilayered thin films in which indium-zinc oxide (IZO) thin films and Ag or Ag alloy thin films were deposited alternately at room temperature using a RF magnetron sputtering. The optical, electrical and morphological properties of the constituent layers were analyzed using an ultraviolet-visible photospectrometer, a 4-point probe and an atomic force microscopy (AFM), respectively. The EMI shielding effect of the multilayered thin films was also measured using a coaxial transmission line method. A detailed analysis showed that the control of the film morphologies, i.e., the surface roughnesses of the constituent metal layers was essential to an accurate estimate of the electrical and optical properties of multilayered coatings. It was shown that properly designed IZO/Ag alloy multilayered thin films could yield a visible transmission of more than 70%, a sheet resistance of less than 1 Ω/sq., together with an EMI shielding effect larger than 45 dB in the range from 30 to 1000 MHz.     

Observing catalysis through the agency of the participating electrons: surface-chemistry-induced current changes in a tin oxide nanowire decorated with silver

Conductometric measurements were performed on single tin oxide nanowires with and without Ag nanoparticle surface decoration, in flowing oxygen/ethylene mixtures of varying composition. Ag-decorated nanowires showed a significant ethylene effect, which we explain in terms of the modification of the Schottky junction formed between the Ag particles and the tin oxide, resulting from the surface chemical processes involving ethylene and oxygen occurring exclusively on the silver nanoparticles' surface. Assuming the observed temperature dependence of these ethylene-induced current decrements reflect changes in the steady-state concentration of ethylene, oxygen, and a surface intermediate that ultimately leads to ethylene oxide, one calculates the enthalpy for the production of the reaction intermediate to be approximately -4.6 kcal/mol, of the right order of magnitude as the calculated value reported in the literature for the formation of a putative ethylene oxametallacycle intermediate in the ethylene epoxidation reaction. Our results illustrate how fundamental catalytic processes occurring at metal nanoparticle surfaces can significantly influence the electronic properties of oxide nanowires used as metal particle supports.     

Gas sensing applications of 1D-nanostructured zinc oxide: Insights from density functional theory calculations

Gas sensor devices have traditionally comprised thin films of metal oxides, with tin oxide, zinc oxide and indium oxide being some of the most common materials employed. With the recent discovery of novel metal oxide nanostructures, sensors comprising nano-arrays or single nanostructures have shown improved performance over the thin films. The improved response of the nanostructures to different gases has been primarily attributed to the highly single crystalline surfaces as well as large surface area of the nanostructures. In this paper the properties of clean and defected quasi one-dimensional ZnO nanostructures, including hexagonal and triangular nanowires, nanotubes and facetted nanotubes are reviewed. The adsorption of atoms and molecules on the ZnO nanostructures are also reviewed and the findings are compared to studies examining similar reactions on nanostructured metal oxide surfaces for sensing purposes. While both experimental and theoretical approaches have been employed to examine gas sensor reactions, this review focuses on studies that employ electronic structure calculations, which primarily concentrate on using density functional theory. Computational studies have been useful in elucidating the reaction mechanism, binding strength, charge transfer as well as other electronic and structural properties of the nanomaterials and the gas-sensor interaction. Despite these studies there are still significant areas of research that need to be pursued that will assist in the link between theoretical and experimental findings, as well as advancing the current chemical and physical understanding of these novel materials. A summary and outlook for future directions of this exciting area of research is also provided.     

Nanopatterning the electronic properties of gold surfaces with self-organized superlattices of metallic nanostructures

The self-organized growth of nanostructures on surfaces could offer many advantages in the development of new catalysts, electronic devices and magnetic data-storage media. The local density of electronic states on the surface at the relevant energy scale strongly influences chemical reactivity, as does the shape of the nanoparticles. The electronic properties of surfaces also influence the growth and decay of nanostructures such as dimers, chains and superlattices of atoms or noble metal islands. Controlling these properties on length scales shorter than the diffusion lengths of the electrons and spins (some tens of nanometres for metals) is a major goal in electronics and spintronics. However, to date, there have been few studies of the electronic properties of self-organized nanostructures. Here we report the self-organized growth of macroscopic superlattices of Ag or Cu nanostructures on Au vicinal surfaces, and demonstrate that the electronic properties of these systems depend on the balance between the confinement and the perturbation of the surface states caused by the steps and the nanostructures' superlattice. We also show that the local density of states can be modified in a controlled way by adjusting simple parameters such as the type of metal deposited and the degree of coverage.     

金属等离子体浸没离子注入改善9Cr18轴承钢表面耐磨性的研究

采用新改进的阴极弧金属等离子体源 ,对 9Cr18轴承钢进行了金属等离子体浸没离子注入 (PIII)处理。首先将Ti,Mo和W离子分别注入到 9Cr18钢的表面 ,然后再对其进行N等离子体浸没离子注入 ,从而在 9Cr18钢表面形成了一层超硬耐磨的改性层。对PIII处理后的试样进行了显微硬度和磨损特性测试 ,结果表明 ,经PIII处理后的试样表面的显微硬度和耐磨性显著提高 ,而其中经Ti和Mo注入再进行N离子注入的试样效果更为明显。与仅进行N离子注入的试样相比 ,金属加N离子注入的试样表面耐磨性提高幅度更大 ,表明金属PIII在改善 9Cr18钢表面性能方面具有广阔的应用前景。XPS分析结果表明 ,PIII处理后试样表面形成了超硬的氮化物相 ,它们在改善材料表面特性中起到了重要的作用。