表面成分AES和XPS定量分析中的离子溅射修正

低能离子溅射是表面分析中清洁固体表面和深度剖面分析的主要手段之一。由于离子溅射改变了固体表面化学成分，引起表面成分的再分布，使俄歇电子谱、X射线光电子谱以及二次离子质谱等表面分析手段，对溅射后固体表面成分的定量分析结果与实际结果有较大的差别。本文以离子溅射合金表面成分达到平行时择优溅射、离子轰击诱导偏析和增强扩散效应之间动态平衡状态的假设为基础，得到了一个与择优溅射、离子轰击诱导偏析和增强扩散修正因子有关的离子溅射修正因子的分析表达式，并将其应用于Ag－Pd合金的离子溅射定量修正计算，发现计算结果能够与实验结果较好地吻合。解释了合金离子溅射修正因子随离子参数的变化。     

The effects of both surface segregation of In atoms and strain on the confinement profile of InGaAs/GaAs multi quantum wells

The InGaAs/GaAs quantum wells (QWs) have been investigated by optical measurements at different growth conditions. Growth temperature of samples with different layer thickness and nominal indium composition results in a graduation of the indium concentration (In) at the interfaces between the quantum wells and the barriers. The modification of the indium composition then distorts the potential profiles for higher temperature growth and can be attributed to In segregation effect. This leads to a blue-shift of the transition energies compared to a perfectly square quantum well. However, we also observe a clear dependence of the transition energies, inconsistent with a simple adjustment of exciton levels. Based on a theoretical model for interacting electron-hole pairs in the QWs, we obtain good agreement with experiment.     

High-sensitivity and high-resolution low-energy ion scattering

Low-Energy Ion Scattering (LEIS or ISS) is used to selectively analyze the atomic composition of the outer atomic layer of surfaces. In addition, the spectrum gives (non-destructively) the in-depth distribution. Using a double toroidal energy analyzer with parallel energy detection and time-of-flight filtering a high sensitivity and mass resolution of LEIS is achieved. This is demonstrated for a highly dispersed catalyst of Pt/Au on γ-alumina. The improved depth resolution is illustrated for self-assembled monolayers of alkanethiols (12-20 carbon atoms) on gold. Even for these low Z carbon atoms a clear shift of 8 eV/carbon atom is observed (using 1.5 keV ⁴He⁺ ion scattering). This opens many new possibilities for studies of ultra-thin diffusion barriers, high-k dielectrics and biosensors.     

An Auger electron spectroscopy-secondary ion mass spectrometry study of layers of Cu-Ni and Ag-Au alloys modified by ion bombardment

The effects of argon ion bombardment on the surface layers of Cu-Ni and Ag-Au alloys were studied. Mechanisms considered were preferential sputtering, enhanced diffusion and thermodynamic segregation. An Auger electron spectroscopy-secondary ion mass spectrometry combined system was used to determine the composition-depth profiles from several tens of ångströms below the surface. The variation of the depth profile in the layer modified as a result of ion bombardment revealed that above room temperature the outermost layer was always enriched with copper or silver for the respective alloys compared with the second and the third layers. The results indicated that thermodynamic segregation played an important role in determining the depth profile of the altered layer as well as preferential sputtering and enhanced diffusion.     

The surface composition of Pd-Cu alloys: A comparative investigation of photoelectric work function measurements,Auger electron spectroscopy and calculations based on a broken bond approximation

The surface composition of Pd-Cu alloys has been studied by Auger electron spectroscopy, photoelectric work function measurements and by calculations based on a broken bond model of surface segregation. The measurements were performed on thin films with a bulk composition varying from 0% to 100% Pd. The films were prepared by sublimation of both metals in ultrahigh vacuum onto a Pyrex glass support. For the work function measurements both the absolute value of the work function and the change in work function due to hydrogen chemisorption were used for an estimate of the surface composition. The Auger spectra were evaluated in the way proposed by Gallon to calculate the surface composition of the alloys. The data derived from the experimental results are in good agreement with the calculated values. The results show that the surfaces of clean and equilibrated Pd-Cu alloys are only slightly enriched in copper.     

Surface-compositional and Angular Distributions duringCu-Pt Sputtering

Under 1 keV Ar ion bombardment of Cu-Pt alloys at high fluence and low temperature, the depletion degree of the segregating species at the second surface layer, and the normalized sputtering yield ratios (non-segregating species/segregating species) in the near-normal direction (15°) and at oblique angle (75°), have been estimated by an improved kinetic BIGS (bombardment-induced Gibbsian segregation) model. For the bombarded Cu-Pt alloys, calculations show that the depletion degree of the segregating species at the second surface layer is small when its bulk composition equals the extreme value, but this depletion degree becomes large when its bulk composition equals the intermediate value. Furthermore, the difference of the normalized sputtering yield ratio between 15° and 75° is small when the buIk composition of the segregating species equals the extreme value, but this difference becomes large when that of the segregating species equals the intermediate value.     

Surface analysis of β-FeSi2 layer epitaxially grown on Si(100)

The epitaxial growth process of β-FeSi₂ on Si(100) surface under ultrahigh vacuum condition has been studied by low energy electron diffraction (LEED) and low energy ion scattering spectroscopy (LEIS). The LEED pattern of Si (100)-2×1 changes into amorphous structure with Fe deposition of about 10 Å at room temperature. With annealing at 540 °C, the LEED pattern shows 2×2 structure corresponding to the formation of the epitaxial β-FeSi₂ (100) template layer. The α-scan in Li⁺-LEIS and X-ray diffraction (XRD) study strongly suggest that the topmost surface of the 2×2 structure is terminated by Si atoms. By XRD, it is shown that the β-FeSi₂ develops with characteristic orientation even if iron reactant is deposited onto the template surface.     

Damage buildup in semiconductors bombarded by low-energy ions

The damage buildup in Ge and GaAs bombarded at room and elevated temperatures by keV Ne⁺ and Ar⁺ ions has been studied. Results show that the accumulation of disorder can be considered as a planar growth of an amorphous layer proceeding from the surface. A retardation of amorphous layer growth is experimentally observed in Ge for low ion doses. Results (for the case of room temperature irradiation of GaAs and for all the cases of irradiation of Ge except for the case of irradiation by Ar⁺ ions with high ion flux density) are explained based on the diffusion of mobile point defects to the surface with a subsequent interface segregation process. Calculations based on this model are in good agreement with experimental data.     

Surface characterization of activated Ti-Zr-V NEG coatings

The thermally activated Ti-Zr-V non-evaporable getter (NEG) film has been studied by means of X-ray photoelectron spectroscopy (XPS) and low energy ion scattering (LEIS). Depth profiling technique has been used to establish the location of different components in the near-surface region. It was found that the top surface layer of the activated Ti-Zr-V NEG film is zirconium and titanium enriched. Residual oxide observed even on fully activated NEG surface consists mostly of zirconium and titanium low valence suboxides that are located mainly in the top surface layer. Carbides formed during the activation process remain on the surface and their concentration drops strongly with depth.     

用低温Raman散射光谱研究不同处理的CdZnTe表面

利用低温Ｒａｍａｎ散射光谱分析，比较了４种典型处理的Ｃｄ０．９６Ｚｎ０．０４Ｔｅ表面声子散射信号和表面元素沉积的变化。对－２２０－－９０ｃｍ＾－１的反斯托克斯分量进行分析得出，ＢＭ液腐蚀后的表面晶格完整性最好；ＬＢ液处理有利于进一步改善表面粗糙度和表面漏电流，离子轰击的表面缺陷多，质量差，但对制备良好欧姆接触的电极有现实意义，实验证明Ｒａｍａｎ散射光谱对于探测表面上元素的沉积和分析表面质量的变化，     

Carbon segregation in silicon

Carbon doping strongly suppresses the diffusion of boron. This is very important for later high temperature processing steps, e.g. for the fabrication of a high doped SiGe-base in a heterojunction bipolar transistor. We investigated (with a novel method) the segregation of C in Si (100) at growth temperatures between 500 and 700°C. A C-doped Si layer was grown by MBE under constant C and Si fluxes. The growth temperature was switched between 300°C and the investigated growth temperature. As the temperature was switched, the surface-accumulated C concentration was perturbed, causing a spike or depression in the SIMS depth profile. The surface segregation at a given temperature was measured by the amount of adlayer density in the spike. Clear evidence of the surface segregation of carbon in Si is found by these experiments.     

The surface tension of liquid aluminium-based alloys

In a systematic study, the surface tensions of the binary alloys Al–Fe and Al–Ni were investigated over a wide temperature and concentration range using electromagnetic levitation and the oscillating drop technique. Surface tensions were derived from the oscillation frequencies applying the formalism of Cummings and Blackburn. Temperature was measured by single-color pyrometry. Of particular interest in these alloys are melts corresponding to compositions of intermetallic phases, because potential ordering phenomena may influence all thermophysical properties. In both systems, an increase of the surface tension is observed at such concentrations. On the basis of partial excess Gibbs enthalpies, surface tensions can be calculated via the Butler equation and compared with experimental results. The agreement with our experimental data depends crucially on the quality of the thermodynamic potentials used. In addition, phenomenological models are also discussed, which describe the general trend correctly.     

Influence of surface potential on the kinetics of glass reactions with aqueous solutions

The kinetics of leaching of alkali silicate glasses in aqueous solutions may be correlated experimentally with the rate of alkali ion transfer across the glass-water interface. However, present theories based upon free ion diffusion fail to provide quantitative or qualitative agreement with experiment. The model proposed incorporates an electrostatic interaction derived from the surface potential and associated space charge layer in the surface region of the glass, and thus involves field-enhanced diffusion. It gives both qualitative and reasonable quantitative agreement with experimental observations.     

Magnesium diffusion,surface segregation and oxidation in Al-Mg alloys

Auger electron spectroscopy (AES) has been used to follow the surface segregation behaviour of magnesium at the surface of Al-Mg alloys in the temperature range up to 600° C as a function of time. The evaporation rate of magnesium from the magnesium-rich surface has also been measured. The combination of the competing processes of segregation and evaporation has been treated theoretically and compared with the experimental measurements. The measured equilibrium surface enrichment of magnesium fell from a factor of 24 at 100° C to 12 at 200° C. At higher temperature the evaporation rate exceeded the segregation rate and the surface layer became magnesium-depleted. The data also lead to a low-temperature determination of the diffusivity of magnesium in aluminium. The same Al-Mg alloys have been heat-treated, within a similar time-temperature regime, in air. The oxide films have been composition-depth profiled using AES with ion sputtering, and measurements of the rate of oxide growth lead to information about the diffusivity of magnesium through the oxide films.On leave of absence from Laboratoire de Thermodynamique et Physico-Chimie Metallurgiques, ENSEEG Domaine Universitaire, St. Martin d'Hères, France.     

The effect of annealing on single-layer CoCrPtNb thin films

The effect of Nb addition on grain size segregation and intergranular coupling of ternary CoCrPt alloys prepared by annealing of crystalline samples and crystallization of the Nb-rich (more than 4.6 at.%) amorphous films is investigated. Mean surface roughness as a function of Nb addition decreased for Nb contents of up to 2.7 at.% and then increased. The size and distribution of magnetic clusters were significantly affected by Nb addition. Vacuum annealing of the ternary and quaternary films (2.7 at.% Nb) increased the coercivity of the films from 53.71 kA/m and 52.09 kA/m to about 61.14 kA/m and 105 kA/m, respectively. Film with 12.1 at.% Nb was also produced and then annealed at different times and temperatures. Increasing the temperature to 700 °C caused the recrystallization of the 12.1 at.% Nb amorphous film. The observed magnetic properties are discussed in terms of composition, crystallographic orientation of deposited layer and oxidation of elements during annealing.     

Growth and alloying of submonolayer Cu on Pt(12 12 11)

A detailed comparative study of Cu growth on the vicinal surface Pt(12 12 11) has been performed with helium atom scattering (HAS) and medium energy ion scattering (MEIS). These techniques are ideally complementary in that HAS is extremely sensitive to the electronic structure of the surface layer, while MEIS accurately probes the atom core structure of the surface. By combining these two techniques it has been possible to measure the initial structure of Cu on the stepped Pt surface and to study how the Cu redistributes across the surface and into the bulk on annealing. The HAS and MEIS data identify two significant diffusion transitions on the surface occurring at temperatures of 450 and 600 K.     

Snoek-type damping behavior of surface oxidation-treated Ti-Mo alloys

The Snoek relaxation damping behavior of surface oxidation-treated Ti-15 wt% Mo and Ti-40 wt% Mo alloys was investigated in this study. When compared to the untreated samples, both alloys exhibited higher damping capacities, higher peak temperatures, and broader peaks after the surface oxidation treatment. The broadening of peak was reflected by a lower activation energy obtained through fitting the peak than that obtained form frequency shift of the peak. The electron backscatter diffraction (EBSD) and hardness measurements were used to determine the composition of the dual phase zones and the hardness of each type of treated alloy, respectively. The oxygen distributions in both types of treated alloys were developed based on a diffusion model, and the thicknesses of the apparent oxygen solution zones (AOSZs) were determined to be 120 μm and 210 μm in the Ti-15 wt% Mo and Ti-40 wt% Mo alloys, respectively. The diffusion constants at a high oxidation temperature and at a low damping temperature were obtained for both alloys. The dependence of the damping capacity on the oxygen content in the Ti-40 wt% Mo alloys was much lower than that in the Ti-15 wt% Mo alloys. The contribution to the damping capacity from the AOSZ to the whole sample was estimated based on the law of mixtures. Estimating the contribution to the damping capacity from AOSZ is useful for future applications.     

Surface modification and chemical sputtering of graphite induced by low-energy atomic and molecular deuterium ions

The surface morphology, and chemical/structural modifications induced during chemical sputtering of ATJ graphite by low-energy (<200 eV/D) deuterium atomic and molecular ions are explored by Scanning Electron Microscopy (SEM), Raman and Auger Electron Spectroscopy (AES) diagnostics. At the lowest impact energies, the ion range may become less than the probe depth of Raman and AES spectroscopy diagnostics. We show that such diagnostics are still useful probes at these energies. As demonstration, we used these surface diagnostics to confirm the characteristic changes of surface texture, increased amorphization, enhanced surface reactivity to impurity species, and increased sp³ content that low-energy deuterium ion bombardment to steady-state chemical sputtering conditions produces. To put these studies into proper context, we also present new chemical sputtering yields for methane production of ATJ graphite at room temperature by impact of D₂⁺ in the energy range 10-250 eV/D, and by impact of D⁺ and D₃⁺ at 30 eV/D and 125 eV/D, obtained using a Quadrupole Mass Spectroscopy (QMS) approach. Below 100 eV/D, the methane production in ATJ graphite is larger than that in HOPG by a factor of ∼2. In the energy range 10-60 eV/D, the methane production yield is almost independent of energy and then decreases with increasing ion energies. The results are in good agreement with recent molecular dynamics simulations.     

A Review on the Regulation of Magnetic Transitions and the Related Magnetocaloric Properties in Ni-Mn-Co-Sn Alloys

In Ni-Mn-X(X=In,Sn,Sb) ferromagnetic shape memory alloys,a ferromagnetic transition from paramagnetic to ferromagnetic austenite and a martensitic transformation from ferromagnetic austenite to weak magnetic martensite occur in some particular composition ranges,in which abundant physical properties have been observed by the abrupt change of magnetization and resistivity around their transition temperatures in these alloys.Therefore,tuning the martensitic transformation temperature(TM) and enlarging the workingtemperature interval for Ni-Mn-X(X=In,Sn,Sb) alloys,are of great importance.In the present paper,we will focus on the effect of external factors,including pre-deformation,annealing,and high pressure annealing,on the magnetic transitions and the related magnetocaloric properties in Ni-Mn-Co-Sn ferromagnetic shape memory alloys.Our approaches and the main results in this particular field will be reviewed.     

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...