Low-energy Ar ion-beam induced vanadium silicide formation at V/Si interfaces

Vanadium/silicon interfaces produced by V thin film deposition on Si substrates were ion-beam mixed using 2 and 3 keV Ar⁺ ions at room temperature. The ion-beam mixing (IBM) has been studied by means of X-ray photoelectron spectroscopy, factor analysis and TRIDYN simulations. Comparison of the experimental results with those obtained from TRIDYN simulations suggests that, in addition to pure ballistic ion mixing mechanisms, other radiation-enhanced diffusion processes could contribute to the IBM of V/Si interfaces by low-energy Ar⁺ bombardment at room temperature. The kinetics of interface formation by IBM is characterized by two stages. During the first stage, a strong decrease of metallic V species is observed due not only to sputtering but also to the formation of vanadium silicide. The concentration of vanadium silicide related species reaches a maximum at the end of this first stage, decreasing subsequently. Finally, with increasing sputtering time, the signals associated with the silicide slowly decrease, and pure silicon species begin to appear, since no free metallic vanadium atoms are available to react with the unlimited silicon supply from the substrate.     

Phase formation, chemical composition and electrical studies of Ti/Si bilayer system

The annealing effects over a range of temperatures of the titanium film (90 nm) grown on Si(111) by electron gun evaporation technique were investigated using physical and electrical measurements. Grazing Incidence X-ray Diffraction experiment shows a stable titanium disilicides formation at higher annealing temperature. The depth profiling data using X-ray Photoelectron Spectroscopy show that the properties are closely related to the change of the interfacial layer and chemical state under the high-temperature annealing. The Schottky Barrier Height, as estimated by the current-voltage measurement is 0.75, 0.695, 0.662 and 0.60 eV for pristine and annealed samples at 450, 550 and 700 °C respectively.     

Valence number transition and silicate formation of cerium oxide films on Si(100)

Interface reactions of a Ce-oxide layer with Si(100) wafers have been characterized by X-ray photoelectron spectroscopy. The ratio of Ce atoms in Ce³⁺ states within the Ce-oxide layer has been found to decrease from 47% at as-deposited sample to 26% after annealing. From detailed reaction analysis of valence number transitions of Ce atoms and the creation of SiO₂ layer at the interface, the reacted Ce³⁺ atoms are converted into silicates and Ce⁴⁺ with a ratio of 2:1. The energy bandgap of Ce-silicate layer has been determined as 7.67 eV and the valence band offset with respect to Si(100) wafer has been extracted as 4.35 eV.     

The effect of composition on surface morphology, formation mechanism and pinhole generation of cosputtered ytterbium silicide

The surface morphology including pinhole and silicide formation mechanism of codeposited ytterbium silicide films are investigated with various compositions of Yb and Si. Film properties depend on the growth mode of the deposited films. At Si compositions more than half of the stable phase of ytterbium silicide, films have a rough surface with islands of ytterbium silicide formed by the Stranski-Krastanov and Volmer-Weber growth mode. At Si composition below half of the stoichiometic value, films grow in a layer by layer, Frank-van der Merwe mode, with a smooth surface. The transition of the formation mode is due to a trade-off in the dominance of the reaction between the internal atoms in the deposited films or between the deposited films and the substrates. A Si composition of 0.59 provides the smoothest surface with roughness of 1.13 nm in root mean square value and no observed pinholes. Ytterbium silicide films are deposited with a 5% composition tolerance by cosputtering and forming at 450 °C in a conventional furnace.     

Effect of film thickness and the presence of surface fluorine on the structure of a thin barrier film deposited from tetrakis-(dimethylamino)-titanium onto a Si(100)-2 × 1 substrate

The structure of a thin film deposited using tetrakis-(dimethylamino)-titanium (Ti(N(CH₃)₂)₄) as a precursor onto a Si(100)-2 × 1 substrate at ultra-high-vacuum conditions was investigated as a function of film thickness for the films of 20 and 145 nm in the presence of surface copper and fluorine produced by in situ dosing of a common copper deposition precursor, (hexafluoroacetylacetonate)Cu(vinyltrimethylsilane), (hfac)Cu(VTMS), and a hydrogenated form of the hfac ligand, 1,1,1,5,5,5-hexafluoro-2,4-pentanedione, hfacH. A combination of surface, depth-profiling, and microscopy analytical techniques suggests that the structure of the titanium carbonitride film depends profoundly on its thickness. While the composition of the film was relatively constant throughout its whole thickness, the nanometer-scale structure changed from amorphous at the top of a 145-nm-thick film, to having a significant amount of small (∼ 5 nm) crystallites closer to the TiCN/Si interface. These studies also confirmed the absence of microfractures in the film prepared by this approach. The ex situ depth profiling investigation suggested that if (hfac)Cu(VTMS) is deposited on a TiCN-precovered silicon substrate and briefly annealed to 800 K, the film acts as a diffusion barrier for copper, while surface fluorine penetrates the film rather easily, resulting in fluorine that is distributed uniformly throughout the film.     

Formation of iron silicide on Si(001) studied by high resolution Rutherford backscattering spectroscopy

The initial stage of the formation of iron silicides has been investigated by high resolution Rutherford backscattering spectroscopy (HRBS). Just after Fe is deposited on Si(001) at room temperature, the deposited Fe atoms dig themselves into subsurface ejecting Si atoms into outer surface. Upon annealing at 300-400 °C, significant number of Si atoms are displaced from their lattice position near the interface between the crystalline Si and the Fe-Si mixing layer. Such displaced Si diffuses into the Fe-Si mixing layer and forms the layer with the composition of Fe:Si≈1:2. This layer is considered to be a precursive state of FeSi₂.     

Nitrogen ion induced nitridation of Si(111) surface: Energy and fluence dependence

We present the surface modification of Si(111) into silicon nitride by exposure to energetic N₂⁺ ions. In-situ UHV experiments have been performed to optimize the energy and fluence of the N₂⁺ ions to form silicon nitride at room temperature (RT) and characterized in-situ by X-ray photoelectron spectroscopy. We have used N₂⁺ ion beams in the energy range of 0.2–5.0 keV of different fluence to induce surface reactions, which lead to the formation of Si_xN_y on the Si(111) surface. The XPS core level spectra of Si(2p) and N(1s) have been deconvoluted into different oxidation states to extract qualitative information, while survey scans have been used for quantifying of the silicon nitride formation, valence band spectra show that as the N₂⁺ ion fluence increases, there is an increase in the band gap. The secondary electron emission spectra region of photoemission is used to evaluate the change in the work function during the nitridation process. The results show that surface nitridation initially increases rapidly with ion fluence and then saturates.     

Epitaxial (Pb,La)(Zr,Ti)O3 thin films on buffered Si(100) by on-axis radio frequency magnetron sputtering

In this study, we discuss the case for integration of epitaxial (Pb,La)(Zr,Ti)O₃ (PLZT) thin films with silicon for electro-optic device applications. PLZT films, approximately 500 nm thick, were grown by on-axis radio frequency magnetron sputtering on CeO₂/YSZ-buffered Si(100) substrate with a SrRuO₃ electrode layer embedded between CeO₂ and PLZT. The structural properties and surface topography of the different oxide layers were examined with X-ray diffraction analysis and atomic force microscopy. The perovskite thin films were predominantly (001)-oriented, with a (002) rocking curve halfwidth of approximately 0.3° and a surface roughness compatible with requirements for application in optical devices. The PLZT cation stoichiometry was assessed from quantitative X-ray photoelectron spectroscopy. These measurements uncovered a substantial depletion of lead in the film surface for layers deposited at substrate temperatures above ~ 600 °C, whereas the surface concentration of La, Zr and Ti remained virtually unaffected over a wide range of growth temperatures.     

Geometric and electronic changes during interface alloy formation in Cu/Pd bimetal layers

This study involves monitoring the interface evolution with increasing annealing temperatures in a Cu-Pd bimetal layer structure. The changes due to interdiffusion and ensuing charge transfer are monitored by extensive X-ray photoelectron spectroscopy (XPS) and glancing angle X-ray diffraction (GAXRD) studies. The Pd and Cu core level fingerprinting and change in lattice parameter provide evidence for alloy formation. The changes in the valence band features indicate the formation of new states that are different from the density of states of individual metal surfaces. The study demonstrates the possibility of tuning interface properties by alloy formation that may have specific applications in catalysis, hydrogen sensing and storage.     

The oxidation kinetics of magnesium at low temperatures and low oxygen partial pressures

The initial oxidation of magnesium at oxygen partial pressures between 1.3 × 10^− 8 Pa and 1.3 × 10^− 5 Pa and at temperatures just above room temperature has been investigated in situ with X-ray photoelectron spectroscopy (XPS) and ellipsometry. Quantitative analysis of the XPS spectra showed that the initially formed oxide has a higher Mg/O ratio (> 1.3) than bulk MgO. Ellipsometry measurements indicated that the band gap values of the oxide layers are considerably smaller than the value expected for bulk MgO ( 2.5 eV vs. 7.8 eV). From the XPS and ellipsometry data recorded as a function of oxidation time the oxidation kinetics have been determined. The kinetics has been described quantitatively with a coupled currents model, involving simultaneous transport of electrons and ions through the oxide layer.     

氧离子束辅助激光淀积生长ZnO/Si的XPS探究

为了探究ZnO/Si内部化学成分及有关信息,用氧离子束辅助(O+-assisted)脉冲激光淀积(PLD)法在不同实验条件下生长成ZnO/Si(111)样品.利用X射线光电子能谱(XPS)对长成的ZnO/Si异质结构进行了异位测试.通过对O1s峰及其肩状结构进行拟合、分析,得到了原子数密度比n(O)∶n(Zn),进而探究了原子数密度比与生长质量的关系.结果表明,用氧离子束辅助PLD法,可在较低的衬底温度190℃和适当O+束流条件下,生长出正化学比接近于1,且c轴单一取向最佳的ZnO/Si薄膜.用氧离子束辅助PLD淀积法生长ZnO薄膜,可以改善缺氧状况,能提供一个富氧环境.     

Characterization of ultra-thin TiO2 films grown on Mo(112)

Ultra-thin TiO₂ films were grown on a Mo(112) substrate by stepwise vapor depositing of Ti onto the sample surface followed by oxidation at 850 K. X-ray photoelectron spectroscopy showed that the Ti 2p peak position shifts from lower to higher binding energy with an increase in the Ti coverage from sub- to multilayer. The Ti 2p peak of a TiO₂ film with more than a monolayer coverage can be resolved into two peaks, one at 458.1 eV corresponding to the first layer, where Ti atoms bind to the substrate Mo atoms through Ti-O-Mo linkages, and a second feature at 458.8 eV corresponding to multilayer TiO₂ where the Ti atoms are connected via Ti-O-Ti linkages. Based on these assignments, the single Ti 2p_3/2 peak at 455.75 eV observed for the Mo(112)-(8 × 2)-TiO_x monolayer film can be assigned to Ti³⁺, consistent with our previous results obtained with high-resolution electron energy loss spectroscopy.     

Enhanced localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel in high-concentration hydrochloric acid solutions at room temperature

The localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel (NC-304SS) produced by severe rolling technique, and its conventional polycrystalline 304 stainless steel (CC-304SS) counterpart, were investigated in high-concentration hydrochloric acid solutions at room temperature. NC-304SS can scarcely suffer from localized corrosion in 4 mol/L and 5 mol/L HCl solutions during 5-day immersion tests, and in 1–3 mol/L HCl solutions during thirty-five-day immersion tests. The corrosion rate of NC-304SS was also less than that of CC-304SS during these immersion tests. The improved localized and uniform corrosion resistances of NC-304SS were explained in terms of the adsorption and chemical activity of Cl^? on NC-304SS and CC-304SS characterized by X-ray photoelectron spectroscopy, and the valence electron configurations of NC-304SS and CC-304SS were characterized by ultra-violet photoelectron spectroscopy rather than conventional electrochemical results.     

Poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate): Correlation between colloidal particles and thin films

We deal with correlation between sizes of colloidal particles and minimum thickness of spin-coated thin films of poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) studied by a dynamic light scattering (DLS), a scanning transmission electron microscopy coupled with an energy dispersive X-ray spectroscopy (STEM-EDX), C₆₀-sputtering X-ray photoelectron spectroscopy (XPS), and an atomic force microscopy. Based on the various measurements, it was pointed out that, PEDOT/PSS colloidal dispersion contained majority of primary nanoparticles with mean diameter of 41 nm and 16 nm for BAYTRON P AG (denote P grade) or BAYTRON PH500 (denote PH grade) solutions, respectively, and small amount of clusters aggregated by the primary particles, based on the DLS measurement and STEM observation. On the other hand, PEDOT/PSS thin films with thickness of 44 nm and 16 nm were easily prepared by spin-coating on silicon wafers from the P and PH grade solutions, respectively. Results of STEM-EDX, DLS, and XPS measurements suggested that the PEDOT/PSS thin films consist of the randomly packed primary nanoparticle-“monolayer”.     

The formation of a SiOx interfacial layer on low-k SiOCH materials fabricated in ULSI application

The characterizations of SiOCH films using oxygen plasma treatment depends linearly on the O₂/CO flow rate ratio. According to the results of Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses, it was found that the carbon composition decreases with increasing O₂/CO flow rate ratio, because more carbon in the Si–O–C and Si–CH₃ bonds on the film surface would be converted by oxygen radicals. It was believed that the oxygen plasma could oxidize the SiOCH films and form a SiO_x interfacial capping layer without much porosity. Moreover, the result of FTIR analysis revealed that there was no water absorbed on the film. A SiO₂-like capping layer formed at the SiOCH film by the O₂/CO flow rate ratio of 0.75 had nearly the same dielectric properties from the result of capacitance–voltage (C–V) measurement in our research.     

Ultrathin silicon oxide films deposited by synchrotron irradiation of condensed layers of silanes and water

Silicon oxide and carbide ultrathin films (less than 50 Å thick) were grown at rates of up to 1 Å s⁻¹ using a previously developed technique. To form silicon oxide, a mixture of silane or tetramethylsilane and water was condensed onto a metal surface, which was then exposed to either broad-band or monochromatized synchrotron radiation. Characterization by soft X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure showed that clean, near-stoichiometric films of self-limited thickness were grown. The results also suggested that the reactions leading to film growth were predominantly excited by electrons produced by photon absorption in the substrate.     

渐进因子分析法及其在Au/Ni/Si薄膜俄歇深度剖面研究中的应用

将渐进因子分析法应用于俄歇深度剖面的化学态研究。通过对Au／Ni／Si薄膜样品深度剖析过程的渐进因子分析，最终获得了各元素的化学状态和深度分布，并发现Au／Ni／Si样品中Ni／Si界面在室温下已发生反应，生成富Si的NixSi化合物层。样品经真空退火处理后，Ni／Si界面进一步反应生成Ni2Si合金，而原有的NixSi化合物含量相对减少，并向Si基体侧扩展，同时Ni穿透Au膜在样品表面富集。渐进因子分析的结果与XPS分析相一致。     

Preparation and characterisation of silver particulate films on softened polystyrene substrates

The preparation of silver particulate films on softened polystyrene (PS) substrates and their characterisation using Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and optical absorption spectroscopy is reported in this paper. Silver films of 150 nm thickness were vacuum deposited onto PS coated glass substrates held at temperatures in the range 415–475 K at different deposition rates of 4 to 12 Å/s. SEM studies indicate that films deposited at 415 K are close to a semicontinuous structure and the structure is discontinuous at higher temperatures. The film morphology is strongly dependent on the deposition rate at any given substrate temperature. The film agglomeration increases with increasing rate of deposition. In the XPS studies, considerable attenuation of the signal corresponding to silver is observed at lower electron take of angles (ETOAs). This indicates that Ag is formed beneath the PS surface. Optical absorption studies showed an interesting red shift of the plasmon resonance wavelength for lower deposition rates again indicating that a sub-surface particulate structure is formed at lower deposition rates. These results are consistent with reported observations.     

Role of metal ions of Langmuir–Blodgett film in hydrophobic to hydrophilic transition of HF-treated Si surface

Hydrophobic to hydrophilic transition of HF-treated Si surface strongly depends upon the metal ions, which are present in the headgroups of the deposited Langmuir–Blodgett (LB) film. Structure of LB films studied by X-ray reflectivity technique and chemical analysis of LB film–substrate interfaces studied by X-ray photoelectron spectroscopy combinedly suggest that the partial transition or partial oxidation of the HF-treated Si surface takes place under the subphase water but further transition or oxidation is possible only in the presence of metal ions. Electrovalent and covalent natures of the metal ions tune this transition or oxidation. Ni ions, for which bonding with headgroups are electrovalent in nature, are favorable for such transition/oxidation and as a result, complete transition/oxidation takes place when nickel arachidate LB film is deposited. On the other hand, Cd ions, for which bonding with headgroups show covalent nature, is not favorable for such transition and can not oxidize the underlying H-passivated Si substrate totally when cadmium arachidate LB film is deposited on such HF-treated Si surface. This ion-specific hydrophobic to hydrophilic transition is visualized by X-ray reflectivity, contact angle and X-ray photoelectron spectroscopy measurements.     

Morphological modification of β-FeSi2 on Si(111) by high temperature growth and post-thermal annealing

β-FeSi₂ crystals have been grown on Si(111) substrates, and morphological modification of the β-FeSi₂/Si(111) by high temperature growth and post-thermal annealing was investigated. The morphological feature of the β-FeSi₂ crystals significantly depends on the growth conditions, especially, substrate temperature during growth. The β-FeSi₂ continuous layers with relatively smooth surfaces were grown at the low substrate temperatures of 650-700 °C with exposure of the grown layers to Sb flux during the growth. On the other hand, nano-scaled islands have been grown at the higher substrate temperature of 850 °C. The structural property, interfacial morphology and growth evolution of the β-FeSi₂ islands were examined, and compared with those for the layers grown at a lower substrate temperature. In addition, the morphological evolution of the β-FeSi₂/Si layers by post-thermal annealing was examined, and it was found that the interfacial smoothness between the β-FeSi₂ layers and the Si(111) substrates was improved by the post-thermal annealing on condition that a thin SiO_x amorphous overlayer should be formed on the β-FeSi₂ layer during the post-thermal annealing. The mechanisms of the morphological modification at the β-FeSi₂/Si(111) interface by the post-thermal annealing will also be discussed.