Estimating the Critical Glass Transition Rate of Pure Metals Using Molecular Dynamic Modeling

Doklady Physics - The critical cooling rates $${{{v}}_{{\text{c}}}}$$ at which pure metals Mg, Al, Ti, Fe, Co, Ni, Cu, Zr, Mo, Pd, Ag, Ta, W, Pt, Au, and Pb transit to an amorphous state (vitrify),...     

Vacuum arc ion charge-state distributions

Vacuum arc ion charge-state spectra have been measured for a wide range of metallic cathode materials. The charge-state distributions were measured using a time-of-flight diagnostic to monitor the energetic ion beam produced by a metal vapor vacuum arc ion source. Data were obtained for 48 metallic cathode elements: Li, C, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn Fe, Co, Ni, Cu, Zn, Ge, Sr, Y, Zr, Nb, Mo, Pd, Ag, Cd, In, Sn, Ba, La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er Yb, Hf, Ta, W, Ir, Pt, Au Pb, Bi, Th, and U. The arc was operated in a pulsed mode with pulse length 0.25 ms: arc current was 100 A throughout. The measured distributions are cataloged and compared with earlier results. Some observations about the performance of the various elements as suitable vacuum arc cathode materials are also presented     

Anomalous behavior of silver atoms in intercalation under a two-dimensional graphite film

It is shown that silver atoms, the only ones of many atoms studied previously (Si, C, Mo, Pt, Cu, Ir, Ni, Au, Cs, K, Na, Ba,...), do not intercalate, that is, do not penetrate under a two-dimensional graphite film (2DGF) on a metal either upon direct depositing in the temperature range 300–2000 K or annealing of a previously deposited silver film. Intercalation becomes possible if silver is deposited on a 2DGF with previously intercalated cesium; in this case, silver atoms displace Cs atoms from under the 2DGF upon heating up to 1100 K.     

Atomistic modeling of ternary additions to NiTi and quaternary additions to Ni–Ti–Pd,Ni–Ti–Pt and Ni–Ti–Hf shape memory alloys

The behavior of ternary and quaternary additions to NiTi shape memory alloys is investigated using a quantum approximate method for the energetics. Ternary additions X to NiTi and quaternary additions to Ni–Ti–Pd, Ni–Ti–Pt, and Ni–Ti–Hf alloys, for X=Au, Pt, Ir, Os, Re, W, Ta,Ag, Pd, Rh, Ru, Tc, Mo, Nb, Zr, Zn, Cu, Co, Fe, Mn, V, Sc, Si, Al and Mg are considered. Bulk properties such as lattice parameter, energy of formation, and bulk modulus of the B2 alloys are studied for variations due to the presence of one or two simultaneous additives.     

X-ray photoelectron spectroscopy study of NiSi formation on shallow junctions

The influence of boron (B)/arsenic (As) on X-ray photoelectron spectroscopy (XPS) study of NiSi formation on shallow junctions is investigated in this paper. The Ni-silicide film was formed after 30 s soak anneal at 450 °C on ultra shallow p+/n or n+/p junctions. The atomic ratio of Ni/Si profile in depth was probed by XPS and the results show that a uniform NiSi layer forms on B-doped p+/n junction while a non-uniform, Ni-rich silicide layer forms on As-doped n+/p junction. It does not agree with the results of other independent phase identification methods such as X-ray diffraction, Rutherford backscattering spectroscopy, and Raman scattering spectroscopy, which all demonstrate the formation of NiSi on both n+/p and p+/n junctions. Comparing the raw binding energy spectra of Ni and Si for each silicide film, the similar spectra for Ni signals are revealed. But the Si signals with an obviously smaller intensity is found to be responsible for the apparent Ni rich silicide formation on As-doped n+/p junction. It indicates that As atoms in the silicide film can affect the sputtering yield of Ni and Si, while no noticeable effect is observed for B atoms. More As atoms than B atoms segregation into the silicide layer is indeed verified by secondary ion mass spectroscopy. And micro-Raman scattering spectroscopy further confirms that the degree of crystallinity for NiSi on n+/p junction is inferior to that on p+/n junction.     

Nano- and micro-scale patterning of Si (1 0 0) under keV ion irradiation

Evolution of Si (1 0 0) surface under 100 keV Ar⁺ ion irradiation at oblique incidence has been studied. The dynamics of surface erosion by ion beam is investigated using detailed analysis of atomic force microscopy (AFM) measurements. During an early stage of sputtering, formation of almost uniformly distributed nano-dots occurs on Si surface. However, the late stage morphology is characterized by self-organization of surface into a regular ripple pattern. Existing theories of ripple formation have been invoked to provide an insight into surface rippling.     

Study of nanoclusters growth at initial stages of ultrathin film deposition by kinetic modeling

Comparative analysis of Au, Cu, Pt, Ni and Fe nanoclusters growth on amorphous carbon substrate by proposed kinetic model based on rate equations is present. Partial sticking coefficients introduced into the model let to discriminate elementary processes such as adatom adsorption and diffusion on bare substrate and on top of islands, nucleation and mobility of islands and its coalescence, 2-d and 3-d island growth modes. The quantitative fittings of experimental time dependencies of surface coverage, clusters density, cluster size are performed by solving model equations. From the best fittings the values of phenomenological coefficients defining elementary processes are found for different materials. Comparative analysis of those coefficients let to discover mechanisms of nanoclusters formation and growth of different materials. It is shown that clusterization for Cu and Au is more favorable than for Pt and Ni. Diffusivity for Pt and Ni on amorphous carbon (a-C) substrate is significantly less than for Au and Cu. In opposite, diffusivity on the top of islands for Ni and Pt is significantly higher than for Au and Cu. The mobility of islands for Au and Cu is much higher than for Ni and Pt. The fitting of experimental curves of Fe deposition on a-C at different temperatures showed that temperature mainly influences sticking process but not diffusion.     

Strain field due to transition metal impurities in Ni and Pd

The strain field due to body centered substitutional transition metal impurities in Ni and Pd metals are investigated. The calculations are carried out in the discrete lattice model of the metal using Kanzaki lattice static method. The effective ion-ion interaction potential due to Wills and Harrison is used to evaluate dynamical matrix and the impurity-induced forces. The results for atomic displacements due to 3d, 4d and 5d impurities (Fe, Co, Cu, Nb, Mo, Pd, Pt and Au) in Ni and (Fe, Co, Cu, Ni, Nb, Mo, Pt and Au) impurities in Pd are given up to 25 NN’s of impurity and these are compared with the available experimental data. The maximum displacements of 4.6% and 3.8% of 1NN distance are found for NiNb and PdNb alloys respectively, while the minimum displacements of 0.63% and 0.23% of 1NN distance are found for NiFe and PdFe alloys respectively. Except for Cu, the atomic displacements are found to be proportional to the core radii and d state radius. The relaxation energies for 3d impurities are found less than those for 4d and 5d impurities in Ni and Pd metals. Therefore, 3d impurities may easily be solvable in these metals.     

Formation of two ripple modes on Si by ion erosion with simultaneous Fe incorporation

This report focuses on the self organized nanostructure formation on Si (0 0 1) by erosion with low energy Kr⁺ ions with simultaneous incorporation of metallic atoms, in particular Fe. The incorporation of Fe is thought to play an important role in the formation of some features. In the experimental set-up used here the Fe atoms come from the sputtering of a cylindrical stainless steel target situated between the source and the sample holder. It is demonstrated how the Fe flux can be regulated by operational parameters of the ion source. It is shown that two different ripple modes, one perpendicular to the ion beam projection on the surface and the other parallel, were formed at near normal incidence (α = 20°) with ion energy between 300 eV and 2000 eV and a fluence of 6.7 × 10¹⁸ cm⁻². The perpendicular mode ripples dominated the topography when E_ion = 2000 eV, while the parallel mode ripples were the main features observed when E_ion = 300 eV. The correlation of Fe concentration with ion sources parameters and resulting topography is analyzed. It is demonstrated that a certain Fe concentration is necessary for the formation of ripples that are oriented perpendicular to the ion beam and that the Fe concentration alone does not determine the evolving topography.     

Comparative investigation on decorating carbon nanotubes with different transition metals

The diffusion dynamics and structure evolvement of the transition metal (TM=Ni, Cu, Au, and Pt) atoms decorating carbon nanotubes (CNTs) with differences have been systematically studied by Monte Carlo (MC) simulation. The studies show that TM atoms can be encapsulated inside, aggregated and even wrapped on the surface of the CNT, which depend on the interactions among TM–TM and TM–C during the spontaneous diffusion process. The decorating effect is greatly influenced by the diameters of CNTs, TM atoms tend to be encapsulated inside the tube in the relatively large CNTs, while they are inclined to stack on the surface for the small ones. More interestingly, Au and Pt atoms would wrap around the smaller CNT, whereas Ni and Cu atoms are still clustering outside of the CNTs with the increase of the number of TM atoms. Simulation results indicate that Pt and Au possess a better wetting effect with CNT than Ni and Cu.     

Atomic O and H exposure of C-covered and oxidized d-metal surfaces

Carbon coverage, oxidation and reduction of Au, Pt, Pd, Rh, Cu, Ru, Ni and Co layers of 1.5 nm thickness on Mo have been characterized with ARPES and desorption spectroscopy upon exposure to thermal H and O radicals. We observe that only part of the carbon species is chemically eroded by atomic H exposure, yielding hydrocarbon desorption. Exposure to atomic O yields complete carbon erosion and CO₂ and H₂O desorption. A dramatic increase in metallic and non-metallic oxide is observed for especially Ni and Co surfaces, while for Au and Cu, the sub-surface Mo layer is much more oxidized. Although volatile oxides exist for some of the d-metals, there is no indication of d-metal erosion. Subsequent atomic H exposure reduces the clean oxides to a metallic state under desorption of H₂O. Due to its adequacy, we propose the atomic oxygen and subsequent atomic hydrogen sequence as a candidate for contamination removal in practical applications like photolithography at 13.5 nm radiation.     

Spectral analysis of complex gas mixtures by isotope dilution. Part I. Determination of hydrogen

The spectral dependence of the relative quantum yield of certain metals (Cu, Ag, Au, Al, In, Sn, Ti, Fe, Ni, Zr, Nb, Mo, Ta, W, Pt) and nonmetals (ThO₂, ZrO₂, HfO₂, Sc₂O₃, Nb₂O₅, LiE, MgF₂, SrF₂, CsI, ZnS, SbS, BeO) has been investigated in the 95-20 nm region of the spectrum.     

Mössbauer-Effect Study of Metastable c-FeSi Synthesized by Molecular Beam Epitaxy (MBE) and by Ion Implantation

Conversion electron Mössbauer spectroscopy (CEMS) has been applied to the study of the metastable c-FeSi phase (i.e. an iron silicide with CsCl lattice structure) that was synthesized by implantation of Si + ions of 50 keV in energy into f -Fe (95% 57 Fe) near room temperature with a nominal dose of 5 2 10 17 cm m 2 , and by molecular beam epitaxy (MBE). Iron silicide layers with different stoichiometry (FeSi 0.85 , FeSi, Fe 0.85 Si) were grown by codeposition of 57 Fe and Si onto an Fe buffer layer on MgO(100). For all FeSi layers the defective CsCl structure was observed after annealing at different temperatures. X-ray diffraction measurements were performed to determine the structure and epitaxial relationship of the c-FeSi films. The lattice parameter perpendicular to the film plane was found to be 2.77(5) Å. CEMS measurements revealed a lower than cubic site symmetry of the iron atoms for both the c-FeSi layers synthesized by ion implantation and by MBE. The formation of nearly undistorted c-FeSi after annealing is favored by excess Fe atoms in the deposited film.     

Growth and sacrificial oxidation of transition metal nanolayers

Growth and oxidation of Au, Pt, Pd, Rh, Cu, Ru, Ni and Co layers of 0.3-4.3 nm thickness on Mo have been investigated with ARPES and AFM. Co and Ni layers oxidize while the Mo remains metallic. For nobler metals, the on top O and oxidation state of subsurface Mo increase, suggesting sacrificial e⁻ donation by Mo. Au and Cu, in spite of their significantly lower surface free energy, grow in islands on Mo and actually promote Mo oxidation. Applications of the sacrificial oxidation in nanometer thin layers exist in a range of nanoscopic devices, such as nano-electronics and protection of e.g. multilayer X-ray optics for astronomy, medicine and lithography.     

Surface alloying of immiscible metals induced by surface state shift

By using first principles calculations, it is found that the noble metal atoms Ag, Au and Cu would like to occupy the vacancy sites of the W(0 0 1) or Mo(0 0 1) surface to form the substitutional surface alloys, despite the fact that they do not like to form alloy in the bulk. The electronic local function (ELF) for these substitutional surface alloys shows that there is no obvious chemical bonding between the noble metals and W or Mo. The analysis of electronic structures lets us conclude that the surface alloying of immiscible metals may originate from the surface state shift of W (or Mo) induced by changes of the electronic environment of surface W (or Mo) when surface W (or Mo) atoms are alternatively replaced by Ag (Au or Cu).     

Influence of the state of the bulk of the sample on the formation and thermal stability of the surface silicide on W(100)

The formation and destruction of the surface silicide on W(100) after cleaning of the sample surface and bulk in various regimes is studied by high-resolution Auger electron spectroscopy. It is shown that the cleanness of the bulk has practically no influence on the laws governing the formation of the surface silicide when Si atoms are adsorbed on a heated W surface and that almost up to completion of its formation all the silicon atoms impinging on the surface, from the very first, remain on it and are incorporated into the surface silicide. The destruction of the surface silicide depends in a definite manner on the state of the bulk, and at T=1400 K it is apparently limited in the early stages by the passage of Si atoms from the surface to the subsurface layer and in subsequent stages by the diffusion of silicon within the substrate. The bulk silicon density that limits the destruction of the surface silicide is estimated. Zh. Tekh. Fiz. 67, 137–140 (July 1997)     

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     

掺Mo对NiSi薄膜热稳定性的改善

报导了在镍薄膜中掺入少量Mo提高了镍硅化物的热稳定性.结果表明，经650— 800℃快速热 退火形成的Ni(Mo)Si硅化物薄膜电阻值较低，约为2．4(Ω／□).XRD分析表明薄膜中只存在 NiSi相，而没有NiSi₂生成.由吉布斯自由能理论分析表明在Ni薄膜中掺人5．9 ％Mo对改善 Ni硅化物热稳定性起到至关重要的作用.经650—800℃快速热退火后的 Ni(Mo)Si／Si肖特基 二极管电学特性良好，势垒高度Φ_B为0．64—0．66eV，理想因子接近于1，更 进一步证明掺少量的Mo能够改善NiSi薄膜的热稳定性. 关键词： 镍硅化物 快速热退火 x射线衍射分析 卢瑟福背散射     

Role of buried ultra thin interlayer silicide on the growth of Ni film on Si(100) substrate

The presence of a buried, ultra-thin amorphous interlayer in the interface of room temperature deposited Ni film with a crystalline Si(100) substrate has been observed using cross sectional transmission electron microscopy (XTEM). The electron density of the interlayer silicide is found to be 2.02 e/?³ by specular X-ray reflectivity (XRR) measurements. X-ray diffraction (XRD) is used to investigate the growth of deposited Ni film on the buried ultra-thin silicide layer. The Ni film is found to be highly textured in an Ni(111) plane. The enthalpy of formation of the Ni/Si system is calculated using Miedema’s model to explain the role of amorphous interlayer silicide on the growth of textured Ni film. The local temperature of the interlayer silicide is calculated using enthalpy of formation and the average heat capacity of Ni and Si. The local temperature is around 1042 K if the interlayer compound is Ni₃Si and the local temperature is 1389 K if the interlayer compound is Ni₂Si. The surface mobility of the further deposited Ni atoms is enhanced due to the local temperature rise of the amorphous interlayer and produced highly textured Ni film. Received: 2 March 2000 / Accepted: 28 March 2000 / Published online: 11 May 2000     

过渡元素掺杂对Mo力学性能的第一性原理研究

基于密度泛函理论,采用第一性原理方法计算了在Mo中掺杂摩尔百分比分别为2.08%和4.17%的过渡金属元素W,Ti,Cu和Fe后,体系在[111](110)滑移系统上的广义层错能以及解理能,并研究了掺杂元素对Mo的剪切形变以及脆性一韧性的影响,研究发现,掺杂W和Ti原子会使体系剪切形变的发生变得困难,并使Mo材料变脆;而掺杂Cu和Fe原子则会使体系剪切形变的发生变得相对容易,并使Mo材料的韧性增强,此外,随着掺杂浓度的增加,掺杂W会使体系剪切形变的发生变得更为困难,并使Mo材料脆性更强;而掺杂Fe则会使体系剪切形变的发生变得更为容易,并使Mo材料的韧性更强。