Si 2p Binding Energy Research Articles

Response of Polyelectrolyte Layers to the SiO2 Substrate Charging As Probed by XPS

A single layer of the cationic polyelectrolyte poly(allyamine) hydrochloride (PAH) deposited, using the layer-by-layer technique, on a silicon substrate containing 5 nm oxide layer is investigated by XPS while applying an external potential bias to the sample to control and manipulate the charge built-up on the oxide layer. Under application of a -10 V bias, the oxide layer is positively charged due to photoemission process, evidenced by the measured Si2p binding energy of 104.4 eV. Application of a +10 V bias attracts the low energy neutralizing electrons, stemming from a hot filament, and leads to a negatively charged oxide layer, also evidenced by the measured Si2p binding energy of 102.9 eV. The single polyelectrolyte overlayer also responds to this polarity change of the oxide layer underneath by displaying a somewhat larger shifts both in the C1s and N1s peaks. In addition to the shifts in the positions, the N1s peaks undergo a significant intensity depletion, mostly on the positively charged -N+ component. We interpret this intensity depletion to be the result of reorientation of some of the dangling positively charged groups by moving toward the negatively charged oxide underlayer. To our knowledge this is the first time that a chemically specific response to an electrical stimuli is reported using XPS. A bilayer LbL film consisting of PAH and PSS, exhibits even a larger charging shift, but this time no intensity alteration is observed, most probably due to locking of the -N+ groups by the -SO3+ counterions of the second layer.

A new method to evaluate the hydraulic activity of Al-Si materials

Slag, fly ash, gangue and 500°C calcined gangue are analyzed by using identical coupled plasma optical emission spectroscopy (ICP), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR) and magnetic angle spinning nuclear magnetic resonance (MAS NMR). Research results show that there is a negative linear relationship between the Si 2p and Al 2p binding energies of Al-Si materials and the compressive strength of aluminosilicate based cementitious materials prepared with these Al-Si materials, i.e. the lower the binding energies, the higher the compressive strength. Indeed, the Si 2p and Al 2p binding energies of Al-Si materials can be used to indicate their hydraulic activity. The binding energies of the four examined materials increase in the order of slag, fly ash, 500°C calcined gangue and untreated gangue. Moreover, the binding energies of Si 2p, Al 2p and O 1s of every Al-Si material have excellent correlation. By using the Al 2p binding energy and 27Al MAS NMR spectra, the coordination number of aluminum in slag is determined to be four, while that in gangue, is six. Based on the aforementioned discoveries, this paper presents a new effective method to evaluate the hydraulic activity of Al-Si materials by using the surface binding energies of silicon and aluminum of Al-Si materials.

Study on the chemical states of the surface of SiC epilayer

In this paper, the composition structures of SiC epilayer surface are characterized by high resolution X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectrum. The results of XPS wide scan spectroscopy, infrared glancing reflection absorption spectrum and infrared specular reflection spectroscopy show that the amorphous phase SiCxOy:H is made up of Si-O-Si and Si-CH2-Si polymers. The chemical state structures are composed of Si(CH2)4, SiO(CH2)3, SiO2(CH3)2, SiO3(CH3), Si-Si, dissociative H2O, combined OH，Si-OH, O and O2. The order of the atom core electron binding energy values is determined by chemical state structures and element electronegativity. Compared with the XPS narrow scan spectrum fitting results, the corresponding relation between chemical states and its binding energies is established, and all chemical state binding energies are obtained using the calibration of C 1s binding energy of Si(CH2)4. The result shows that the C 1s and O 1s binding energy values of SiCxO4-x(x=1,2,3) are different from each other, similar as their Si 2p binding energies, of which the C 1s of SiO2(CH3)2 and SiO3(CH3) are respectively close to those of CHm and C—O. The reasonable explanation is presented in terms of chemical state structures, electronegativity and neighbouring site effects.

High-flux ion irradiation with energy of ∼20eV affecting phase segregation and low-temperature growth of nc‐TiN∕a‐Si3N4 nanocomposite films

Ti0.8Si0.2N films were synthesized by an inductively coupled plasma-assisted magnetron sputtering at deposition temperature lower than 200°C. The effects of the incident ion to Ti+Si flux ratio (0.14⩽Ji∕JTi+Si⩽10), with the ion energy constant at ∼20eV, on film growth, microstructure, and morphology were investigated by x-ray diffraction, x-ray photoelectron spectroscopy, and field emission scanning electron microscope. All films have slightly higher than 50at.% of N content. The film deposited by only magnetron sputtering with Ji∕JTi+Si=0.14 is amorphous with a columnar structure. With the addition of inductively coupled plasma, the as-deposited films become crystalline. The preferred orientation evolves from (111) to (200) with the increase in Ji∕JTi+Si. The film grown with Ji∕JTi+Si=10 exhibits a pure (200) preferred orientation with a fine dense-grained globular structure. The lattice constant of this film is about 0.4244nm, nearly equal to that of monolithic TiN. The binding energy of Si 2p of this f...

Chemistry, physics and fracture mechanics in search for superhard materials, and the origin of superhardness in nc-TiN/a-Si 3N 4 and related nanocomposites

Superhard materials ( H>40 GPa) are presently subject of intense research. One distinguishes between intrinsic superhard materials, such as c-BN and diamond and extrinsic ones, such as heterostructures and nanocomposites. After a brief discussion of material's parameters that determine its strength, we focus on the superhard nanocomposites nc-Me n N/a-XN m (Me=Ti, V, W, (TiAl)N,…; X=Si, B). Recent progress in the understanding of the origin of hardness enhancement in superhard nc-TiN/a-Si 3N 4 nanocomposites (“nc-” stands for “nanocrystalline, “a-” for “X-ray amorphous”) 1 1 The term “X-ray amorphous” does not exclude the formation of a locally pseudomorph interface because even if such, 1–2 monolayer thin, interface would be perfectly grown on the TiN template it could never give rise to Bragg reflections in the three-dimensional nanocomposites with randomly oriented TiN nanocrystals. We used the formula “Si 3N 4” in order to emphasize that Si is covalently bonded to N only with Si 2p binding energy of 101.7±0.1 eV determined by XPS and being equal to that in Si 3N 4. is summarized. The optimum nanostructure with one monolayer of interfacial Si 3N 4 was confirmed by both experiments with the deposition of TiN/Si 3N 4 heterostructures by Söderberg et al., and by first principle density functional theory calculations of Hao et al. These calculations show that the de-cohesion energy of the TiN/Si 3N 4/TiN sandwich is enhanced as compared with bulk Si 3N 4. A new, non-linear constitutive materials model, that accounts for the pressure enhancement of elastic moduli and of flow stress was developed and tested by means of advanced FEM calculations. Significant deviations of the mechanical behaviour of super- and ultrahard materials from the prediction of the linear mechanics with a constant yield stress have been demonstrated.

Theoretical and experimental studies on the silica hollow spheres

The structures and properties of the silica hollow spheres have been studied by experimental and quantum chemical calculations. The structure of the silica hollow spheres was characterized by TEM, BET and XPS. According to the experimental results, a model of porous silica clusters has been proposed to represent the structure of the silica hollow spheres. The geometry of model was optimized by the semi-empirical PM3 method and the density of states for the model was calculated by ab initio methods at the level of 3-21G and 6-31G. Both the influences of model size and the effect of basis set are discussed. It is found that the calculated binding energies of O1s, Si2s and Si2p are in fairly good agreement with the experimental results. The studies indicate that the small cluster model can be used to reasonably analyzed the structure and properties of silica hollow spheres.

High resolution core and valence band XPS spectra of non-conductor pyroxenes

High resolution core level and valence band (VB) X-ray photoelectron spectra (XPS) of the non-conductor pyroxene minerals, bronzite ((Mg 0.8,Fe 0.2) 2Si 2O 6) and diopside (Ca(Mg 0.8Fe 0.2)Si 2O 6) have been obtained with the Kratos magnetic confinement charge compensation which minimizes differential charge broadening. Observed Si 2p, O 1s, Mg 2p and Ca 2p total linewidths are all about 1.3 eV, very similar to those observed previously with the same instrument for SiO 2 and olivines ((Mg,Fe) 2SiO 4); and we consider that these widths are within 0.05 eV of the minimum room temperature linewidths for these samples with the experimental resolution of this instrument of 0.35 eV. These linewidths are all determined by vibrational broadening due to the M–O symmetric stretch in the ion states. The Si 2p binding energies (BE) are intermediate between the quartz and olivine Si 2p binding energies; but the O 1s spectra resolve the bridging oxygen (BO) and non-bridging oxygen (NBO) in the Si 2 O 6 4 - unit, with the NBO O 1s very close in BE to the O in olivine, and the BO very close to the BO in SiO 2. Indeed in both diopside and bronzite, it is possible to separate the three structurally inequivalent O atoms in the O 1s spectra: the BO at a BE of about 532.6 eV, a NBO peak from the MgOSi moiety (Mg in the M1 site) at about 531.3 eV, and a NBO peak at 531 eV from the CaOSi or the FeOSi moieties (Ca and Fe in the M2 site). The O 1s BE increases with the increase in the electronegativity Ca < Mg < Fe < Si. Moreover, the linewidths of these peaks increase when Fe and Mg are both present in either M1 (diopside) or M2 (bronzite) sites. The valence band spectra for the two pyroxenes are rather similar, and quite different from the VB spectra of quartz and olivines. The dispersion of the pyroxene VB spectra is intermediate between the VB spectra of quartz and olivines; the valence band spectrum of pyroxenes are more dispersed than in olivines by about 1.5 eV but less dispersed than quartz by about 1.5 eV. These VB spectra can be assigned using the previous olivine VB spectra and high quality pseudopotential density functional theoretical calculations in the generalized gradient (GGA) approximation. As for the olivine VB spectra, the Fe 3d t 2g and e g orbitals in M1 and M2 sites of the pyroxene are located at the top of the pyroxene valence band, and the BE of the Fe 3d peaks from M1 are about 0.7 eV smaller than the Fe 3d peaks in M2. The theoretical XPS valence band spectra using the theoretical density of states and the Gelius intensity approximation are is in good semi-quantitative agreement with the experimental spectra. This intermediate dispersion of pyroxenes is due to the partial polymerization of the Si–O units in pyroxenes, and the intermediate charge on the Si atoms as indicated by the Si 2p BE.

X-ray photoelectron spectroscopy of aluminium-substituted tobermorite

We have synthesised 11-Å tobermorite hydrothermally, both pure and with increasing isomorphic substitution of aluminium for silicon. The samples were analysed by X-ray photoelectron spectroscopy (XPS). Aluminium was found, on the basis of its Al 2p binding energies, to be tetrahedrally coordinated. We observed no changes in Ca/(Si+Al) ratio upon aluminium substitution, implying that charge balancing does not occur via the incorporation of additional calcium into the tobermorite structure. Aluminium substitution into the silicate structure led to a decrease in Si 2p binding energies. This implies one of two alternatives. Firstly, that charge balancing occurs via substitution of OH − for O 2− in the tobermorite structure. Secondly, the presence of aluminium in the tobermorite structure may negatively influence the degree of silicate polymerisation. Further work is required to determine which of these possibilities is the case.

Electron Binding Energies of Si 2p and S 2p for Si- and S-containing Substances by DFT Calculations Using the Model Molecules

Si 2p and S 2p core-electron binding energies (CEBE)s of Si- and S-containing molecules were calculated by deMon DFT program using Slater’s transition-state (TS) concept. In the previous works, we could not obtain the calculated values to the experimental ones of third periodic 2p CEBEs for the molecules within the range of averaged absolute deviation (AAD) of 1.0 eV, although the values were calculated by the unrestricted generalized transition-state (uGTS) method. Here, we were able to get the reasonable Si 2p and S 2p CEBEs of 11, and 12 gas molecules in the AAD of 0.37 and 0.46 eV, respectively from the CEBE calculations by the unrestricted generalized diffuse ionization (uGDI) method with a modification of screening constants for third periodic elements of the 2p core-hole. Furthermore, we estimated WD (work function and the other energies) values of seven Si- and S-containing polymers [(Si(CH3)2)n (PDMS), (Si(CH3)2O)n (PDMSO), (Si(C6H5)CH3)n (PMPS), (Si(C6H5)CH3O)n (PPMSO), ((CH2CH2)S)n (PETHS), ((CH2(CH2)4CH2)SO2)n (PHMS), ((C6H4)S)n (PPS)] from the differences between calculated CEBE values for the model molecules and experimental ones on the solid polymers.

X‐ray photoelectron microscopic imaging of the chemical bonding state of Si in a rock sample

AbstractA microscopic surface analytical technique is desirable for detailed studies of environmental and geochemical surface processes because most of the relevant solid components from natural sources are heterogeneous and have intricate microstructures. Recent advances in XPS instrumentation have allowed chemical mapping of surfaces. This paper demonstrates the imaging of the chemical bonding state of Si in a rock sample (granodiorite) by X‐ray photoelectron microscopy. An Si 2p photoelectron image of the granodiorite was acquired from the boundary between the quartz and biotite phases, and the image was deconvoluted into quartz and biotite components on the basis of the difference (chemical shift) between the Si 2p binding energies of the two minerals. The two phases were clearly distinguishable in the chemical‐bonding‐state images for Si. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Nondestructive depth profile of the chemical state of ultrathin Al2O3/Si interface

We investigated a depth profile of the chemical states of an Al2O3/Si interface using nondestructive photon energy-dependent high-resolution x-ray photoelectron spectroscopy (HRXPS). The Si 2p binding energy, attributed to the oxide interfacial layer (OIL), was found to shift from 102.1 eV to 102.9 eV as the OIL region closer to Al2O3 layer was sampled, while the Al 2p binding energy remains the same. This fact strongly suggests that the chemical state of the interfacial layer is not Al silicate as previously believed. We instead propose from the HRXPS of Al 2p and Si 2p depth-profile studies that the chemical states of the Al2O3/Si interface mainly consist of SiO2 and Si2O3.

Characteristics of Schottky contacts on n-type 4H–SiC using IrO2 and RuO2

Thermally stable Schottky contacts on n-type 4H–SiC with high Schottky barrier height were demonstrated by annealing the rare earth metal contacts (Ir and Ru) under O2 ambient. The formation of rare earth metal oxides (IrO2 and RuO2) after O2 annealing led to the increase of Schottky barrier height (&amp;gt;1.9 eV) and a low reverse leakage current (∼10−9 A/cm2). Synchrotron radiation photoemission spectroscopy showed that the work function of IrO2 is higher about 0.23 eV than that of Ir and the binding energies of Si 2p and C 1s shifted toward lower binding energies by 0.12 eV in both O2 and N2 annealed samples. The oxidation annealing caused predominant Si outdiffusion to the IrO2 (RuO2), leaving Si vacancies behind, leading to the shift of surface Fermi level to the energy level of Si vacancy. Both the formation of oxide and the Fermi level movement played a role in forming the Schottky contact with high barrier height and excellent thermally stability.

Soft x-ray photoelectron spectroscopy of (HfO2)x(SiO2)1−x high-k gate-dielectric structures

Soft x-ray photoelectron spectroscopy has been used to study several (HfO2)x(SiO2)1−x film compositions. The relationships between composition and Si 2p and Hf 4f core level binding energies were investigated using nominally thick films. Both the Si 2p [Si4+] and Hf 4f features shift to lower binding energy by approximately 1.3 eV as the composition is varied from SiO2 to HfO2. The shift to lower binding energy is consistent with both an electron transfer model of the chemical environment and final-state core-hole screening resulting from differences in material polarizability. In addition, the Gaussian widths of the core levels narrow with increasing HfO2 content. Calculations of phonon broadening indicate that this trend is due instead to inhomogeneous disorder. The dielectric/Si interface was investigated with ultrathin (∼10–20 Å) films. There was virtually no difference in binding energies or Gaussian width among the various compositions, indicating a preferential composition of approximately x=0.5 at the interface. Interface suboxides were also investigated and indicate a quality entropy-driven oxide/silicon interface.

XPS Studies of SiO2/Si System under External Bias

Thermally grown SiO2 layers on Si (100) substrate have been subjected to different external voltage bias during XPS analysis to induce changes in the measured binding energy difference between Si4+ and Si0 in Si2p and SiKLL regions. The Si2p binding energy difference increases from 3.2 to 4.8 for samples containing 1−7 nm oxide thickness, and furthermore, this difference can be influenced by application of an external bias to the sample. Application of negative d.c. bias increases the binding energy difference, whereas positive bias decreases it. The voltage dependence of the binding energy difference exhibits a sigmoid character with an abrupt change near 0 V. Both the binding energy difference and differential change between the positive and negative bias have similar functional dependence on the thickness. This is attributed to differential charging between the silicon oxide layer and silicon substrate, which is decreased when a positive bias is applied to the sample (and therefore attracting a larger ...

Study on Al-induced crystallization of Al/a-Si:H bilayer thin film

Al/a-Si:H bilayer thin films were deposited on glass substrate by thermal evaporation and plasma-enhanced chemical-vapor-deposition in a specially designed one-chamber deposition apparatus. Scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy were used to study the morphology, crystallization and the shift of Si 2p binding energy, respectively. The crystalline silicon was formed at a low temperature of approximately 250 °C in the Al/a-Si:H bilayer thin film. The intermixed layer of (Al)–(a-Si:H) plays an important role in the crystallization of silicon. The content of crystalline Si, which is related to a dome-like microstructure, increases with increasing thickness of the intermixed layer formed due to the high diffusion rate of Al atoms at high temperature or larger amounts of Al diffused into a-Si:H layer with the increase in thickness of the Al sublayer. The Si 2p binding energy of c-Si is approximately 99.23 eV while a-Si:H energy shifts from approximately 98.66 to 98.87 eV in the Al/a-Si:H bilayer thin films with different thickness of the Al sublayer.

Copper interaction with a Ta silicate surface: implications for interconnect technology

The TaSiO 6 films, ∼6 Å thick, were formed by sputter deposition of Ta onto ultrathin SiO 2 substrates at 300 K, followed by annealing to 600 K in 2 Torr O 2. X-ray photoelectron spectroscopy (XPS) measurements of the films yielded a Si(2p) binding energy at 102.1 eV and Ta(4f 7/2) binding energy at 26.2 eV, indicative of Ta silicate formation. O(1s) spectra indicate that the film is substantially hydroxylated. Annealing the film to >900 K in ultra-high vacuum resulted in silicate decomposition to SiO 2 and Ta 2O 5. The Ta silicate film is stable in air at 300 K. XPS data show that sputter-deposited Cu (300 K) displays conformal growth on Ta silicate surface (TaSiO 6) but 3D growth on the annealed and decomposed silicate surface. Initial Cu/silicate interaction involves Cu charge donation to Ta surface sites, with Cu(I) formation and Ta reduction. The results are similar to those previously reported for air-exposed TaSiN, and indicate that Si-modified Ta barriers should maintain Cu wettability under oxidizing conditions for Cu interconnect applications.

Copper wetting of a tantalum silicate surface: Implications for interconnect technology

X-ray photoelectron spectroscopy data show that sputter-deposited Cu (300 K) displays conformal growth on oxidized TaSi films (TaSiO6). The TaSiO6 films, 6 Å thick, were formed by sputter deposition of Ta onto ultrathin SiO2 substrates at 300 K, followed by annealing to 600 K in 2 Torr O2. The photoelectron spectra of the films are characterized by a Si(2p) binding energy at 102.1 eV, indicative of silicate formation. Annealing the film to &amp;gt;900 K resulted in silicate decomposition and SiO2 formation. Cu(I) formation and conformal growth were not observed for the annealed films. The results are similar to those previously reported for oxidized TaSiN, and indicate that Si-modified Ta barriers should maintain Cu wettability under oxidizing conditions for Cu interconnect applications.

The chemical state vector: a new concept for the characterization of oxide interfaces

AbstractFor certain metal oxides deposited as a thin film on the surface of another oxide, changes may occur in the binding energy (BE) of the photoelectron peaks as well as in the kinetic energy (KE) of the Auger peaks of the deposited cation and consequently in its Auger parameter. These changes are illustrated here for the systems formed by SiO2 deposited onto TiO2 and Al2O3. Shifts by −1.3 and −1.0 eV in the Si 2p BE and by 2.3 and 0.7 eV in the KE of the Si KLL Auger peak are found for these two systems when comparing the values obtained for small amounts of SiO2 directly interacting with the support with those of a thick film of this material.The different values of these electronic parameters obtained for increasing amounts of SiO2 can be represented in a Wagner plot. The tendency and magnitude of the changes are similar to those found for Si in phyllosilicate or zeolite compounds with different Si/Al ratios.To systematize these changes in the electronic parameters of the deposited phase the new concept of ‘chemical state vector’ is proposed. It is defined as the vector that connects the two extreme points of a Wagner plot dot graph where the BE of photoelectron peaks is represented versus the KE of the Auger peaks for a cation M of a given MO/M′O interface. The possibilities and limitations of this concept are discussed with regard to the SiO2/TiO2 and SiO2/Al2O3 interface systems reported in this paper and the data for other MO/M′O systems taken from previous works. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Liquid phase epitaxial growth of 3C-SiC films deposited on Si

In this paper, we present a novel method to grow 3C-SiC crystal in a liquid-phase epitaxy-like manner, but without any substantial substrate. The starting material to be used in this method is the 3C-SiC-thin film deposited on Si substrate in a gas-phase heteroepitaxial technology. The free 3C-SiC film which remained of the molten Si substrate epitaxially grows up from the Si solution saturated by SiC in a highly purified graphite crucible heated by an inductive heater. XRD, XPS and Raman spectroscopy were used to characterize the samples. The only one peak with full width at half maximum (FWHM) of 0.2 at 2θ=35.65° in XRD is attributed to the diffraction of (111) planes in 3C-SiC. The energy difference between C1s and Si2p binding energy in XPS data is 183.2 eV, which is well consistent with the result published before for single crystal 3C-SiC. Although the only sharp and strongest peak at 796.6 cm −1 in the Raman spectrum also confirms the crystal structure, the additional broadened weak peak at 523.6 cm −1 may imply the existence of some lattice defects related to nitrogen unintentionally introduced in the growth process.

Oxidized silicon surfaces studied by high resolution Si 2p core-level photoelectron spectroscopy using synchrotron radiation

Abstract The Si 2p soft X-ray photoemission study of various oxidized surfaces (thermal oxidation and room temperature (RT) oxidation) shows the benefit derived from the use of high-energy resolution (70 meV). Interesting structural information can be retrieved from an analysis of the line widths of the oxides, suboxides, and elemental Si peaks. In particular the binding energy (BE) of elemental silicon layers adjacent to the oxidized layer can be distinguished from that of deeper silicon layers (the two prominent `interfacial' elemental Si lines are shifted by about +0.2 and −0.2 eV). These new data show a possible effect of oxygen second neighbors on elemental Si 2p binding energies. Moreover, changes in the oxide/suboxide line widths – as seen in a comparative study of the Si(1 1 1)-7×7 surface thermally oxidized in O2 and exposed at RT to O2 or H2O – may be attributed to static disorder, i.e., variations in Si–O bond lengths.