Growth mode of Pt1−xNix films biased dc-sputter-deposited on MgO(0 0 1)

A study is made by TEM, XRD and by measuring electrical/magnetic properties, of growth mode and properties of Pt_1−xNi_x alloy films deposited on MgO(0 0 1) at 250°C by dc-sputtering at 2.5–2.7 kV in Ar. A bias voltage V_s≤−160 V was applied to the substrate during deposition. It was confirmed that the Pt film was polycrystalline with the texture of Pt(1 1 1)/MgO(0 0 1) while the films of Pt_0.14Ni_0.86 and Pt_0.19Ni_0.81 were epitaxially grown with Pt–Ni(0 0 1)[1 0 0]/MgO(0 0 1)[1 0 0] similarly to the case of Ni/MgO(0 0 1). Thus the growth mode transformation between Pt–Ni(1 1 1)/MgO(0 0 1) and Pt–Ni(0 0 1)/MgO(0 0 1) may be induced at x less than 0.81 for Pt_1−xNi_x alloy films. The temperature coefficient of resistance TCR from 100 to 300 K of Pt_0.14Ni_0.86 films was estimated to be 0.0044–0.0053 K⁻¹ and saturation magnetization at 300 K to be 1.7–3.2 kG, respectively, while TCR of Pt films was estimated to be 0.0035–0.0048 K⁻¹.     

A first-principles study on initial processes of a Ni adatom on the H-terminated Si(0 0 1)-(2×1) surface

We studied the adsorption, surface diffusion, and penetration, i.e. the initial processes of a Ni adatom on the H-terminated Si(001)-(2×1) surface by the first-principles theoretical calculations. As concerns the adsorption, two different types were found. When Ni is deposited onto the Si dimer row, it once captures H from the dimer Si, though it eventually returns H, with no activation energy barrier. Then, Ni moves to the most stable site, which is the off-centered bridge (B) site between the dimer rows, with the activation energy of 0.65 eV. On the other hand, Ni deposited between the dimer rows captures no H and moves to the B site without the energy barrier. Thus an adsorbed Ni atom invariably arrives at the most stable B site at the room temperature. As for the surface diffusion, it needs the activation energies of 0.66 and 1.19 eV for Ni to migrate from the B site in the directions parallel and perpendicular to the dimer row, respectively. Therefore, we concluded that the surface diffusion of Ni is restricted in the valley between the dimer rows at the room temperature. Furthermore, since the penetration of Ni is blocked on this surface, it was also concluded that the surface hydrogenation suppresses silicidation.     

Surface studies of 2,4-pentanedione on γ-Al2O3/NiAl (1 0 0) and NiAl (1 0 0)

The chemical compound 2,4-pentanedione (Hacac) has been shown to etch the oxidized metal surfaces metals such as copper and nickel, but not their unoxidized surfaces. Here it is shown that on the γ-Al₂O₃/NiAl (1 0 0) surface (oxidized NiAl (1 0 0)) etching of aluminum occurs at 170 K and 750 K. Reflection-absorption infrared spectroscopy (RAIRS) is used to show that Hacac binds to both the clean, metallic and oxidized surfaces, but decomposition and combustion products dominate on the metallic surface and no etching occurs. The binding process that involves a deprotonation reaction of the enol species was identified by redshift in the carbonyl peaks and the appearance of an Al-H peak observed in the IR spectrum. The implication of these results is that there is both an unusual low temperature and high temperature etching of the alumina by bound acac.     

Adsorption and decomposition of γ-butyrolactone on Pd(1 1 1) and Pt(1 1 1)

The adsorption and thermal chemistry of γ-butyrolactone (GBL) on the (1 1 1) surface of Pd and Pt has been investigated using a combination of high resolution electron energy loss spectroscopy (HREELS) and temperature programmed desorption (TPD). HREELS results indicate that GBL adsorbs at 160 K on both surfaces through its oxygenate functionality. On Pd(1 1 1), adsorbed GBL undergoes ring-opening and decarbonylation by 273 K to produce adsorbed CO and surface hydrocarbon species. On Pt(1 1 1), very little dissociation is observed using HREELS, with almost all of the GBL simply desorbing. TPD results are consistent with decarbonylation and subsequent dehydrogenation reactions on Pd(1 1 1), although small amounts of CO₂ are also detected. TPD results from Pt(1 1 1) indicate that a small proportion of adsorbed GBL (perhaps on defect sites) does undergo ring-opening to produce CO, CO₂, and H₂. These results suggest that the primary dissociation pathway for GBL on Pd(1 1 1) is through O-C scission at the carbonyl position. Through comparisons with previously published studies of cyclic oxygenates, these results also demonstrate how ring strain and functionality affect the ring-opening rate and mechanism.     

First-principles study of thiophene on β-SiC (0 0 1)-(2×1) surface

In this work, we performed density functional calculations to examine the molecular adsorption states of thiophene on β-SiC(0 0 1)-2×1 surface. A number of possible adsorption geometries are considered into two groups as the polymeric thiophene chain and the individual molecules covalently bonded onto the surface. The results show that the polymeric chain on the surface is the less stable adsorption case and individual arch like adsorption case structure is more stable than others. In all adsorption cases, the adsorbed SiC surfaces are characterized as different semiconductors.     

Quantized (1, 0) ⊕ (0, 1) Fields

We find a mapping between antisymmetric tensormatter fields and the Weinberg 2(2j + 1)-componentbispinor fields. Equations which describethe j = 1 antisymmetric tensor field coincide with the Hammer-Tucker equations entirely and withthe Weinberg ones within a subsidiary condition, theKlein-Gordon equation. A new Lagrangian for the Weinbergtheory is proposed which is scalar and Hermitian. It is built on the basis of the concept ofWeinberg doubles. The origin of acontradiction between the classical theory, the Weinbergtheorem B – A = for quantum relativisticfields, and the claimed longitudity of the antisymmetrictensor field [transformed on the (1, 0) (0, 1)Lorentz group representation] after quantization isclarified. Analogs of the j = 1/2 Feynman–Dysonpropagator are presented in the framework of the j = 1 Weinberg theory.It is then shown that under a definite choice of fieldfunctions and initial and boundary conditions themassless j = 1 Weinberg–Tucker–Hammerequations contain all the information that the Maxwell equationsfor the electromagnetic field have. Thus, the formerappear to be of use in describing some physicalprocesses.     

The effect of surface temperature on H2/D2(v = 0, j = 0)–Ni(100) scattering processes

We carry out both four-dimensional (4D×2D) and six-dimensional (6D) quantum dynamics on a parametrically time- and temperature-dependent effective Hamiltonian for H₂/D₂(v = 0,j = 0)–Ni(100) collision process. Such an effective potential was derived within a theoretical framework of mean-field approximation by considering weakly correlated interaction between molecular degrees of freedom, phonon modes and electron– hole pair (elhp) coupling through a Hartree-product-type wave function, where the initial state distribution of the surface modes and elhp coupling were introduced through Bose– Einstein and Fermi– Dirac probability factor, respectively. The temperature-dependent dissociation and state-to-state transition probabilities for H₂/D₂(v = 0,j = 0)–Ni(100) system are depicted as a function of initial kinetic energ of the incoming diatom. Though such effect appears negligibly small for H₂(v = 0,j = 0)–Ni(100) system, it is prominent in the case of D₂(v = 0,j = 0)–Ni(100) collision. It appears that the change of dissociation and transition probabilities of D₂ with the increase of surface temperature is exclusively dictated by the phonon modes directed along Z-axis, but the effect of elhp coupling particularly for transition probabilities is insignificant.     

Long-range chemical interactions in solid-state reactions: effect of an inert Ag interlayer on the formation of L10-FePd in epitaxial Pd(0 0 1)/Ag(0 0 1)/Fe(0 0 1) and Fe(0 0 1)/Ag(0 0 1)/Pd(0 0 1) trilayers

The effect of 0, 0.5, and 1?μm-thick Ag interlayers on the chemical interaction between Pd and Fe in epitaxial Pd(0?0?1)/Ag(0?0?1)/Fe(0?0?1)/MgO(0?0?1) and Fe(0?0?1)/Ag(0?0?1)/Pd(0?0?1)/MgO(0?0?1) trilayers has been studied using X-ray diffraction, ⁵⁷Fe Mössbauer spectroscopy, X-ray photoelectron spectroscopy, and magnetic structural measurements. No mixing of Pd and Fe occurs via the chemically inert Ag layer at annealing temperatures up to 400?°C. As the annealing temperature is increased above 400?°C, a solid-state synthesis of an ordered L1₀-FePd phase begins in the Pd(0?0?1)/Ag(0?0?1)/Fe(0?0?1) and Fe(0?0?1)/Ag(0?0?1)/Pd(0?0?1) film trilayers regardless of the thickness of the buffer Ag layer. In all samples, annealing above 500?°C leads to the formation of a disordered Fe_xPd_1?x(0?0?1) phase; however, in samples lacking the Ag layer, the synthesis of Fe_xPd_1?x is preceded by the formation of an ordered L1₂-FePd₃ phase. An analysis of the X-ray photoelectron spectroscopy results shows that Pd is the dominant moving species in the reaction between Pd and Fe. According to the preliminary results, the 2.2?μm-thick Ag film does not prevent the synthesis of the L1₀-FePd phase and only slightly increases the phase’s initiation temperature. Data showing the ultra-fast transport of Pd atoms via thick inert Ag layers are interpreted as direct evidence of the long-range character of the chemical interaction between Pd and Fe. Thus, in the reaction state, Pd and Fe interact chemically even though the distance between them is about 10⁴ times greater than an ordinary chemical bond length.     

α-Sexithiophene on Cu(1 1 0) and Cu(1 1 0)-(2 × 1)O: An STM and NEXAFS study

The adsorption of α-sexithiophene (6T) on Cu(1 1 0), Cu(1 1 0)-(2 × 1)O and the mesoscopically patterned Cu-O striped surface have been studied by STM (scanning tunnelling microscopy), XPS (X-ray photoelectron spectroscopy) and NEXAFS (near edge X-ray absorption fine structure). The molecular resolution of the STM allowed to determine the orientation and local order of the molecules in the submonolayer and monolayer regime. It is shown that the 6T molecules align with their long molecular axis along the densely packed copper rows on Cu(1 1 0) and along the Cu-O rows on the Cu(1 1 0)-(2 × 1)O surface. On the striped phase with alternating copper and Cu-O regions the molecules adsorb first on the Cu regions and after complete filling of these regions, on the Cu-O. The orientation is the same on both areas as on the respective pristine surfaces with the only exception that the molecules reorient by 90° if the width of the copper regions is smaller than the molecular length. The NEXAFS measurements allowed for a determination of the adsorption geometry of the molecules: while 6T lies flat on the surface on clean copper, the molecular planes are inclined with an angle as high as 39° with respect to the substrate on (2 × 1)O. For the latter, this inclination angle is 4° higher than in the bulk crystal structure of 6T observed for thicker films to release stress and allow commensurability with the substrate lattice, while for the former it is a result of the aromatic system bonding to the Cu(1 1 0) surface, as confirmed by XPS.     

Optical transitions on (1 1 0) surfaces of III–V compounds

The modulation reflectivity technique was used to detect the optical transition on clean cleaved (1 1 0) surfaces of III–V compounds. In the spectra obtained the optical transitions involving surface eigenstates were identified.     

Ni/Ag Schottky contacts on Al0.11Ga0.89N grown on Si (1 1 1) substrate by plasma-assisted MBE

Al_0.11Ga_0.89N/GaN samples are grown by plasma-assisted molecular beam epitaxy method on (1 1 1) silicon substrates. High purity gallium (7N) and aluminum (6N5) were used to grow Al_0.11Ga_0.89N, GaN, and AlN, respectively. The surface morphology, structural and optical properties of the sample has been investigated by scanning electron microscope (SEM), and high-resolution X-ray diffraction (HR-XRD), respectively. HR-XRD measurement showed that the sample has a typical diffraction pattern of hexagonal Al_0.11Ga_0.89N/GaN heterostructures. Ni/Ag bilayers are deposited on Al_0.11Ga_0.89N as the Schottky contacts. The effect of annealing in oxygen ambient on the electrical properties of Ni/Ag/Al_0.11Ga_0.89N is studied by current–voltage measurement. The annealing at a temperature of 700 °C for 10?min results in an increase in the ideality factor from 1.033 to 1.042 and an increase in the Schottky barrier height from 0.708 to 0.811 eV. Furthermore, the annealing in oxygen ambient also leads to an increase in the surface roughness of the contacts from 0.0098 to 0.1360 μm which is in agreement with the SEM results.     

STM studies on the reconstruction of the Ni2P (101̅0) surface

The surface structure of Ni₂P (101?0), a model for highly active hydrodesulfurization catalysts, was studied using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) in order to understand the reconstruction of the surface layers. Annealing at 573 K revealed a (1 × 1) LEED pattern which changed to a c(2 × 4) arrangement by further heating to 723 K. Atomic scale STM images were obtained for both the (1 × 1) and c(2 × 4) structures. Bright spots observed in the STM images were interpreted to be due to surface phosphorus atoms and this was supported by a density functional theory (DFT) simulation. Several possible models for the c(2 × 4) reconstructed structures were proposed including a P-dimer defect model, a missing-row model and a missing-row + added-row model. The last model gave the best explanation for the c(2 × 4)structure. The mechanism for the c(2 × 4) reconstruction on the Ni₂P (101?0) surface is discussed.     

Adsorption kinetics of the Cs–O activation layer on GaAs(1 0 0)

In this work, we study the adsorption of (molecular) oxygen on Cs-covered GaAs(1 0 0) surfaces at RT. The study took place in a multi-method UHV system using the techniques such as low energy electron diffraction (LEED), Auger electron spectroscopy (AES), work function measurements (WF), thermal desorption spectroscopy (TDS), secondary ion mass spectroscopy (SIMS) and electron stimulated desorption (ESD) spectroscopy in correlation with the photocurrent measurements. It is shown that the oxygen burrows under the Cs overlayer and interacts at low exposures with the GaAs substrate, whereas at higher exposures oxygen interacts also with Cs leading to Cs oxides. The maximum photocurrent appears after the WF minimum and before the oxidation of Cs. Our results support the dipolar model for the explanation of the negative electron affinity effect.     

Phase coexistence between the (√3 × √3)R30° - β and (1 × 1) phases on Pb/Ge(1 1 1)

We have characterized the phase transition between the (1 × 1) and (√3 × √3)R30° - β phases on Pb/Ge(1 1 1) using low energy electron microscopy (LEEM). We show that the transition is first-order and that, in the coexistence region of the two phases, the dominant mechanism for phase separation changes critically with Pb coverage, from nucleation and growth at 1.33 ML (saturation coverage of the β phase) to spontaneous domain switching due to thermal fluctuations of the local Pb density for slightly smaller coverage. As the Pb coverage decreases, the concentration of vacancies in the β phase increases, making additional possible Pb adsorption sites available. The larger resulting local density fluctuation of Pb becomes comparable to the density difference of the two phases, manifesting itself in the observed domain switching.     

Structural and optical properties of Ga2(1−x)In2xO3 films prepared on α-Al2O3 (0 0 0 1) by MOCVD

Ga_2(1−x)In_2xO₃ thin films with different indium content x [In/(Ga + In) atomic ratio] were prepared on α-Al₂O₃ (0 0 0 1) substrates by the metal organic chemical vapor deposition (MOCVD). The structural and optical properties of the Ga_2(1−x)In_2xO₃ films were investigated in detail. Microstructure analysis revealed that the film deposited with composition x = 0.2 was polycrystalline structure and the sample prepared with x up to 0.8 exhibited single crystalline structure of In₂O₃. The optical band gap of the films varied with increasing Ga content from 3.72 to 4.58 eV. The average transmittance for the films in the visible range was over 90%.     

Oxidation mechanism and ferryl domain formation on the α-Fe2O3 (0 0 0 1) surface

Recent experimental evidence calls for a reinterpretation of the oxidized structure in chemically distinct domains of the hematite (0 0 0 1) surface as the ferryl (FeO) termination rather than the bulk terminated O₃-Fe-Fe-R structure. Although this interpretation is consistent with experimental data and ab initio thermodynamics calculations, it raises serious questions about how molecular oxygen can be dissociated on a surface where reactive iron centers are slightly more than 5 Å apart. Here, we propose a novel cooperative bimolecular mechanism that provides a reasonable pathway for the formation of the unusual ferryl surface termination and should be readily reversible, which is important for understanding the function of hematite surfaces as an oxidation catalyst.     

The Second-Order Equation from the (1/2, 0) ⊕ (0, 1/2) Representation of the Poincare Group

On the basis of first principles we derive theBarut-Wilson-Fushchich secondorder equation in the (1/2,0) (0, 1/2) representation. Then we discuss thepossibility of describing various mass and spin states in such a framework.     

CrO2块体及其(0 0 1)和(1 0 0)表面的电子结构和磁性质

基于密度泛函理论的第一性原理计算,我们研究了CrO2块体以及其(1 0 0)和(0 0 1)表面的磁性和电子结构。CrO2(1 0 0)表面中表面层Cr原子向内收缩,而(0 0 1)表面中的表面层Cr原子却向外伸展;越往内层,原子驰豫幅度越小。由于表面效应。表面层原子的磁矩有了大幅的提升,其中(1 0 0)表面中表面层Cr原子的磁矩最高,为3.03μB。电子结构计算表明,CrO2 (1 0 0)和(0 0 1)表面均保持了块体中良好的半金属性,并且半金属带隙在(1 0 0)表面中受到了进一步的拓宽,因此具有更稳定的半金属性     

Mössbauer spectroscopy of (1 1 1) γ-Fe single layers grown on Ni

Hyperfine Interactions - The magnetic profile of Ni(111)/γ-Fe/Ni with different thickness is studied by CEMS Mössbauer spectroscopy. It depends both from the thickness of the Fe layer and...