Electron spectroscopic study of surface segregation and oxidation of Cu-In and Cu-Au alloys

XPS and AES techniques were employed to study the surface segregation and oxidation of Cu-1at%In alloy. Surface segregation of In has been observed with an enthalpy of segregation of about −34 kJ/mol. The surface oxidation of the Cu-In alloy at 480 K showed first a formation of Cu₂O on the alloy surface. The displacement reaction 3Cu₂O + 2In → 6Cu + In₂O₃ occurred on the alloy surface, on further heating of the oxidized surface in vacuum at 700 K. XPS and UPS techniques were employed to study the oxygen interaction with Cu-5at%Au and Cu-11at%Au alloys. At 300 K, oxygen was dissociatively chemisorbed on the Cu sites of the Cu-11% Au alloy surface, and the oxygen desorbed on heating. TDS study showed that desorption follows second order kinetics with an activation energy of desorption of about 75 kJ/mol.     

XPS and XAES studies of surface segregation and oxidation of Cu-Ge alloy

Surface segregation of Ge is seen in the Cu-5at%Ge alloy with an activation enthalpy equal to 17 kJ/mol. Oxidation of the alloy in the temperature range 400 to 600 K shows the formation of Cu₂O and GeO which on further heating in vacuum at 650 K converts to GeO₂ with the reduction of Cu₂O to Cu.     

Structure and composition of the segregated Cu in V2O5/Cu system

We have investigated segregation of copper at the surface of V₂O₅ films deposited onto Cu substrate by employing surface analysis techniques. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) confirmed that the Cu is segregated at the surface and its chemical state is Cu₂O. According to secondary ion mass spectroscopy (SIMS) and glow discharge spectroscopy (GDS), the Cu concentration inside the deposited V₂O₅ layer is low. Ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling spectroscopy (STS) revealed the segregation alters the surface local density of states. Surface analysis of deposited samples in ultra high vacuum (UHV) condition verified that the segregation occurs during the deposition. We have extended kinetic tight binding Ising model (KTBIM) to explain the surface segregation during the deposition. Simulation data approve the possibility of surface segregation during room temperature deposition. These results point out that on pure Cu substrate, oxidation occurs during the segregation and low surface energy of Cu₂O is the original cause of the segregation.     

杂质对吸附系统O/RhxPt1-x衬底合金(110)表面偏析的影响

构造了考虑吸附与偏析相互作用情况下无序二元合金Rh_xPt_1-x(110)吸附氧表面的原子集团模型,其中O的覆盖度为0.5;构造了考虑杂质Ni,Cu,W对合金可能产生影响的吸附表面原子集团模型,杂质的掺入采用替位式.应用recursion方法计算了合金表面的环境敏感镶嵌能和电子结构.环境敏感镶嵌能计算表明杂质Ni,Ｃu和Ｗ均使O吸附Rh_xPt_1-x(110)合金表面 关键词： 化学吸附 表面偏析 recursion方法 态密度     

Investigation by X-ray photoelectron spectroscopy of the transient oxidation of NiAl

X-ray photoelectron spectroscopy (XPS) has been used to study the oxidation of NiAl in oxygen at atmospheric pressure. Prior to oxidation, the native oxide scale on the specimen was removed by ion sputtering and the specimens were (pre-)heated in vacuum before exposure to oxygen. At low oxidation temperatures (<750 K) scales consisted of Al₂O₃ and NiAl₂O₄, with a thin surface layer of NiO, but at higher temperatures were of Al₂O₃, apart from about 0.5 at % Ni. The Ni content in the latter case was constant throughout the scale and did not increase dramatically near the alloy/oxide interface. In the experimental conditions used in this study, initial formation of NiO and NiAl₂O₄ seems to be avoided at the higher oxidation temperatures ( > 750 K).     

无序二元合金（NixCu1－x）不同解理面上O吸附对Cu偏析的影响

应用计算机编程构造出了存在和不存在表面偏析的无序二元合金Ni_xCu_1-x (x=0.4)(１００)表面及(１１０)表面的原子集团模型，然后按覆盖度θ=0.5，构造 出了O吸附后的原子集团模型，应用Recursion方法计算了O在Ni_xCu_{1-x(存在偏析和不存在偏析时)无序二元合金(１００)和(１１０)表面吸附的电子结构.由此 得出：1)O吸附使合金表面态密度峰降低，带宽加宽，并且表面Ni原子的d电子与吸附质O原 子的s，p电子的共价作用比Cu更强烈；2)O吸附在NixCu1-x(x=0.4) (１１０)表面比(１００)表面更稳定；3)O的吸附抑制了Cu在表面富集，且这种作用主要表 现在表面一层. 关键词： 化学吸附 表面偏析 Recursion方法 态密度}     

Initial oxidation kinetics and energetics of Cu0.5Au0.5 (0 0 1) film investigated by in situ ultrahigh vacuum transmission electron microscopy

The initial oxidation behavior of Cu_0.5Au_0.5 (0 0 1) thin film was investigated by in situ ultrahigh vacuum transmission electron microscopy to model nano-oxidation of alloys with one active component and one noble component. The formation of irregular-shaped octahedron Cu₂O islands with cube-on-cube crystallographic orientation to the substrate film was observed at all temperature studied. The energetics of Cu₂O nucleation for Cu and Cu_0.5Au_0.5 oxidation was compared. Cu_0.5Au_0.5 oxidation has lower nucleation activation energy due to the reduced mismatch strain between Cu₂O and Cu_0.5Au_0.5 films. On the other hand, the reaction kinetics for Cu_0.5Au_0.5 alloy oxidation is slower due to the higher diffusion activation energy of Cu.     

Surface oxidation of NiCo alloy: A comparative X-ray photoelectron spectroscopy study in a wide pressure range

Oxidation of NiCo alloy has been studied under two pressure regimes, 5 × 10⁻¹⁰ and 5 × 10⁻¹ bar, by X-ray photoelectron spectroscopy (XPS). The aim of this work is to investigate the synergetic effect between the two alloy components during the initial stages of oxidation. The results showed that at low oxygen pressure, segregation and preferential oxidation of cobalt takes place, while oxidation of nickel is largely suppressed. The species dominating the surface is CoO but small amount of metallic cobalt still remains even after prolonged oxidation at 670 K. At 0.5 bar O₂ pressure, alloy oxidation was found to be temperature depended. From 420 K to 520 K, cobalt is completely transformed to CoO and the Ni:Co atomic ratio at the surface approaches a minimum, similar to the observations at low pressure regime. However, at higher temperatures (from 520 K to 720 K), nickel is re-segregated on the surface, in the expense of cobalt, while CoO is further oxidized to Co₃O₄. At this temperature range formation of mixed Ni-Co-O spinel-like oxides is probable as supported by the characteristic modifications of the Ni 2p_3/2 photoelectron peak and the increase of the Ni:Co atomic ratio.     

退火诱导亚稳态Fe80Cu20合金固溶体的结构相变

利用扩展x射线吸收精细结构和x射线衍射研究了机械合金化制备的体心立方(bcc)的亚稳态Fe₈₀Cu₂₀合金固溶体的结构随退火温度的变化特点.结果表明，在300—873 K温度范围内，随着退火温度的升高，bcc结构物相的晶格常数近于线性降低，这主要是由于Cu原子从bcc结构Fe₈₀Cu₂₀合金固溶体中逐渐偏析出来，生成面心立方(fcc)结构的Cu物相所致.经603K退火后，Cu原子的平均键长R_Cu—Cu增加了0.003 nm左右，大约有50%的Cu原子从bcc结构的Fe₈₀Cu₂₀合金固溶体中偏析出来.在773 K退火后，bcc结构Fe_８０Cu₂₀合金固溶体近于完全相分离，生成了bcc结构的α-Fe与fcc结构的Cu物相. 关键词： 扩展x射线吸收精细结构 x射线衍射 ８０Cu₂₀合金')" href="#">Fe_８０Cu₂₀合金 机械合金化     

An investigation of the oxidized Ni/InAs interface

Ni was resistively deposited onto bulk InAs and subsequently oxidized in an O₂ atmosphere. The anneal temperature and time were 450 °C and 2.5 h, respectively. X-ray diffraction of the oxidized Ni/InAs sample revealed the formation of In₃Ni₂ and In₂O₃ on the front suggesting inter diffusion of In, Ni and O. NiO was not detected by X-ray diffraction. In a preliminary study, using glass as a substrate, NiO readily formed when using these oxidation parameters. Conductivity measurements of the oxidized Ni/InAs surface revealed a conducting front and insulating rear surface while TEM of the Ni/InAs interface revealed an intermediate amorphous diffusion zone between the “oxidized” Ni layer and the bulk InAs. A closer investigation of the intermediate layer supports the X-ray diffraction results, suggesting compound formation due to diffusion of oxygen and nickel into the substrate, and out-diffusion of In and As from the bulk of the sample. AES was used to further elucidate these results.     

A photoemission study of the interaction of Ni(100), (110) and (111) surfaces with oxygen

Photoelectron spectroscopic studies of the oxidation of Ni(111), Ni(100) and Ni(110) surfaces show that the oxidation process proceeds at 295 and 485 K in two distinct steps: a fast dissociative chemisorption of oxygen followed by oxide nucleation and lateral oxide growth to a limiting coverage of 3 NiO layers. The oxygen concentration in the 295 K saturated oxygen layer on Ni(111) was confirmed by ¹⁶O(d,p) ¹⁷O nuclear microanalysis. At 295 and 485 K the oxide growth rates are in the order Ni(110) > Ni(111) > Ni(100). At 77 K the oxygen uptake proceeds at the same rate on all three surfaces and shows a continually decreasing sticking coefficient to saturation at ~2.1 layers (based upon NiO). An O 1sb.e. = 529.7 eV is associated with NiO, and O ls b.e.'s of ~531.5 and 531.3 eV can be associated, respectively, with defect oxide (Ni₂O₃) or (in the presence of H₂O) with an NiO(H) species. The binding energies (Ni 2p, O 1s) of this NiO(H) species are similar to those for Ni(OH)₂. Defect oxides are produced by oxidation at 485 K, or by oxidation of damaged films (e.g. from Ar⁺ sputtering) and evaporated films. Wet oxidation (or exposure to air) of clean nickel surfaces and oxides, and exposure of thick oxide to hydrogen at high temperature results in an O 1s b.e. ~531.3 eV species. Nuclear microanalysis ²H(³He,p) ⁴He indicates the presence of protonated species in the latter samples. Oxidation at 77 K yields O 1s b.e.'s of 529.7 and ~531 eV; the nature of the high b.e. species is not known. Both clean and oxidised nickel surfaces show a low reactivity towards H₂O; clean nickel surfaces are ~10³ times less reactive to H₂O than to oxygen.     

Direct production of carbon nanotubes decorated with Cu2O by thermal chemical vapor deposition on Ni catalyst electroplated on a copper substrate

Carbon nanotubes (CNTs) decorated with Cu₂O particles were grown on a Ni catalyst layer deposited on a Cu substrate by thermal chemical vapor deposition from liquid petroleum gas. Ni catalyst nanoparticles with different sizes were produced in an electroplating system at 45 °C using the corrosive effect of H₂SO₄ which was added to solution. These nanoparticles provide the nucleation sites for CNT growth avoiding the need for a buffer layer. The surface morphology of the Ni catalyst films and CNT growth over this catalyst was studied by scanning electron microscopy (SEM). High temperature surface segregation of the Cu substrate into the Ni catalyst layer and its exposition to O₂ at atmospheric environment, during the CNTs growth, lead to the production of CNTs decorated with about 6 nm Cu₂O nanoparticles. We used SEM to study the surface characteristics of Ni catalyst films and characteristic of grown CNTs. Raman spectroscopy, transmission electron microscopy (TEM), electron diffraction (EDX), X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) revealed the formation of CNTs. The selected area electron diffraction pattern, EDX, and XPS studies show that these CNTs were decorated with Cu₂O nanoparticles. This way of fabrication is the easiest and lowest cost method.     

Influence of film morphology on thin film ferromagnetism

Cobalt, nickel and their alloy, Co₁Ni₉, films were epitaxially grown on Cu(100) under different growth conditions and subsequent treatments and studied using surface magneto-optic Kerr effect (SMOKE) in an attempt to understand the effects of film morphology on the magnetic properties. CO contamination can significantly reduce the magnetization and Curie temperature. Thermal desorption spectroscopy (TDS) shows that CO desorbs at 422 K from Ni and 410 K from Co₁Ni₉ at a heating rate of 6 K per minute. Annealing the films below 450 K produces smooth and clean films with stable magnetic behavior. However, annealing at higher temperatures results in Cu segregation and island formation leading to the finite-size ferromagnetic or even superparamagnetic behavior.     

Influence of Cu substrate surface oxides and heating rates during reflow on melting point of Sn-3.5Ag solder

Three types of copper substrates, fresh, aged (kept for years in open atmosphere) and acid washed aged, were investigated for the reflow behaviour of a solder using different heating rates. Melting point of the Sn-3.5Ag solder was lowered on the aged Cu substrate. Reduction was found to be higher in high heating rate and declined with the decrease in the heating rate. Melting point was lowered from 221 °C to 175 °C with the heating rate of 180 °C/min, but recovered to 210 °C when aged Cu substrate was washed with sulphuric acid. XPS depth profile revealed the presence of Cu₂O up to the greater depth in the aged substrate compared to the fresh and acid washed aged substrates. Study showed the relation of reduction in melting point with the depth of Cu₂O on the surface of aged Cu substrates. It was proposed that lower dissipation of heat generated in high heating rates by the oxidation of the flux carbon during reduction of high Cu₂O amount in aged carbon was responsible for the variations in melting points.     

Surface characterization of supported Pt,Rh, and alloy particles by CO chemisorption

Temperature programmed desorption (TPD) of CO is used to determine surface areas, binding states, and changes upon oxidation for 10–1000 Å particles of Pt, Rh, and Pt-Rh alloy on amorphous SiO₂. A low area sample configuration is used to obtain rapid and uniform heating and cooling in an ultra-high vacuum system. It is shown that both metals exhibit a higher CO binding state for small particles, but, as particle size increases, this state disappears and is replaced by a more weakly bound state. These states are suggested to be associated with (111) and higher surface free energy planes on these surfaces, heating Rh above 700 K in O₂ at 10^?6 Torr produces an oxide on which the CO saturation coverage is at least a factor of 10 lower than on the reduced surface. For Pt, oxidation produces only a small decrease in CO coverage, although the binding energy of CO increases on the oxygen treated surface. The difference in desorption temperatures for CO on Pt and Rh is consistent with previous experiments which show that an oxidation-reduction cycle produces a surface layer which is enriched in Rh and that the oxidized alloy contains no Pt atoms.     

CO和O在无序二元合金NiCu表面上的化学吸附

本文用一维紧束缚模型和单电子化学吸附理论,在平均T矩阵近似下,研究了CO和O在无序二元合金Ni_xCu_1-x表面上的化学吸附特性,结果表明,CO和O在Ni_xCu_1-x表面上的化学吸附具有类似的性质,随合金中Ni浓度的增加,化学吸附能降低,化学吸附加强,Cu在NiCu合金表面的偏析在一定程度上减弱了CO和O在NiCu表面上的吸附。 关键词：     

Nano-scale copper oxidation on leadframe surface

Copper oxidation studies were carried out by means of field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) techniques. The growth of copper oxide occurs as a copper surface comes in an oxygen containing environment. The reaction sequence leading to oxidation of the copper surface is generally accepted to be oxygen chemisorption, nucleation and growth of the surface oxide and bulk oxide growth. HRTEM examination of the cross section of the oxidized copper sample revealed the interface region in between the copper and copper oxide. At high oxidation temperature, formation of micro-voids and separations were observed along this interface region. Poor adhesion at this interface region due to micro-voids and separation were found to be the root cause of delamination issue. EELS analysis determined that for regions with intact interface the oxidation system is Cu/CuO/Cu₂O/CuO, however, in regions containing micro-voids or separation it is found to be Cu/Cu₂O/CuO.     

Properties of NiO thin films deposited by chemical spray pyrolysis using different precursor solutions

NiO thin films have been deposited by chemical spray pyrolysis using a perfume atomizer to grow the aerosol. The influence of the precursor, nickel chloride hexahydrate (NiCl₂·6H₂O), nickel nitrate hexahydrate (Ni(NO₃)₂·6H₂O), nickel hydroxide hexahydrate (Ni(OH)₂·6H₂O), nickel sulfate tetrahydrate (NiSO₄·4H₂O), on the thin films properties has been studied. In the experimental conditions used (substrate temperature 350 °C, precursor concentration 0.2-0.3 M, etc.), pure NiO thin films crystallized in the cubic phase can be achieved only with NiCl₂ and Ni(NO₃)₂ precursors. These films have been post-annealed at 425 °C for 3 h either in room atmosphere or under vacuum. If all the films are p-type, it is shown that the NiO films conductivity and optical transmittance depend on annealing process. The properties of the NiO thin films annealed under room atmosphere are not significantly modified, which is attributed to the fact that the temperature and the environment of this annealing is not very different from the experimental conditions during spray deposition. The annealing under vacuum is more efficient. This annealing being proceeded in a vacuum no better than 10⁻² Pa, it is supposed that the modifications of the NiO thin film properties, mainly the conductivity and optical transmission, are related to some interaction between residual oxygen and the films.     

Local Anodic Oxidation of Thin GeO Films and Formation of Nanostructures Based on Them

The process of local anodic oxidation of thin GeO films has been studied using an atomic force microscope. The electron-probe microanalysis showed that oxidized areas of a GeO film were germanium dioxide. The effect of the voltage pulse duration applied to the probe–substrate system and the atmospheric humidity on the height of the oxide structures has been studied. The kinetics of the local anodic oxidation (LAO) in a semi-contact mode obeys the Cabrera–Mott model for large times. The initial growth rate of the oxide (R₀) significantly increases and the time of starting the oxidation (t₀) decreases as the atmospheric humidity increases by 20%, which is related to an increase in the concentration of oxygen-containing ions at the surface of the oxidized GeO film. It was shown that nanostructures in thin GeO layers can be formed by the LAO method.     

Effect of substrate temperature on the surface and interface oxidation of NiTi thin films

NiTi shape memory alloy thin films are deposited on pure Cu substrate at substrate ambient temperatures of 300 °C and 450 °C. The surface and interface oxidation of NiTi thin films are characterized by X-ray photoelectron spectroscopy (XPS). After a subsequent annealing treatment the crystallization behavior of the films deposited on substrate at different temperatures is studied by X-ray diffraction (XRD). The effects of substrate temperature on the surface and interface oxidation of NiTi thin films are investigated. In the film surface this is an oxide layer composed of TiO₂. The Ni atom has not been detected on surface. In the film/substrate interface there is an oxide layer with a mixture Ti₂O₃ and NiO in the films deposited at substrate temperatures 300 °C and 450 °C. In the films deposited at ambient temperature, the interface layer contains Ti suboxides (TiO) and metallic Ni.