Si 2p Core-level Photoemission Research Articles

The low threshold voltage n-type silicon transistors based on a polymer/silica nanocomposite gate dielectric: The effect of annealing temperatures on their operation

In this work, povidone/silica nanocomposite dielectric layers were deposited on the n-type Si (100) substrates for application in n-type silicon field-effect transistors (FET). Thermogravimetric analysis (TGA) indicated that strong chemical interactions between polymer and silica nanoparticles were created. In order to examine the effect of annealing temperatures on chemical interactions and nanostructure properties, annealing process was done at 423–513K. Atomic force microscopy (AFM) images show the very smooth surfaces with very low surface roughness (0.038–0.088nm). The Si2p and C1s core level photoemission spectra were deconvoluted to the chemical environments of Si and C atoms respectively. The obtained results of deconvoluted X-ray photoelectron spectroscopy (XPS) spectra revealed a high percentage of silanol hydrogen bonds in the sample which was not annealed. These bonds were inversed to stronger covalence bonds (siloxan bonds) at annealing temperature of 423K. By further addition of temperature, siloxan bonds were shifted to lower binding energy of about 1eV and their intensity were abated at annealing temperature of 513K. The electrical characteristics were extracted from current-Voltage (I-V) and capacitance-voltage (C-V) measurements in metal-insulator-semiconductor (MIS) structure. The all n-type Si transistors showed very low threshold voltages (−0.24 to 1V). The formation of the strongest cross-linking at nanostructure of dielectric film annealed at 423K caused resulted in an un-trapped path for the transport of charge carriers yielding the lowest threshold voltage (0.08V) and the highest electron mobility (45.01cm2/Vs) for its FET. By increasing the annealing temperature (473 and 513K) on the nanocomposite dielectric films, the values of the average surface roughness, the capacitance and the FET threshold voltage increased and the value of FET electron field-effect mobility decreased.

Stability and Electronic Properties of 2D Nanomaterials Conjugated with Pyrazinamide Chemotherapeutic: A First-Principles Cluster Study

Electronic and optical properties of 2D models of graphene, boron nitride (BN), silicene, SiC, and phosphorene functionalized with pyrazinamide (PZA), a front line antitubercular chemotherapeutic, are investigated using cluster models and density functional theory with van der Waals dispersion corrections and including solvent effects. PZA favors covalent functionalization onto silicene and SiC whereas it is physisorbed onto graphene, BN, and phosphorene at a nearest-neighbor distance >3.0 A and binding energies between −0.7 and −0.8 eV. The analysis of orbital energies, frontier orbitals, density of states, and absorption spectra shows that the HOMO–LUMO gaps for graphene, silicene, and phosphorene remain virtually unchanged upon adsorption, whereas midgap states appear in the BN and SiC clusters. For silicene, Si 2p core level photoemission spectroscopy is the better tool to analyze the chemisorption of PZA. Our study brings atomistic insight into the structural, electronic, and optical response of 2D m...

Atomic structure ofYb/Si(100)(2×6): Interrelation between the silicon dimer arrangement andSi 2pphotoemission line shape

Combining photoelectron spectroscopy and density-functional theory calculations, we have studied the atomic geometry of Yb/Si(100)(2 X 6) reconstruction and the mechanisms responsible for its stabilization as well as the influence of this reconstruction on Si 2p core-level photoemission. The analysis of measured and calculated surface core-level shifts supports the recently proposed model of the Yb/Si(100)(2 X 6). It involves, in agreement with valence-band measurements, unbuckled (symmetrical) silicon dimers, leading to unusually narrowed Si 2p line shape as compared to those of related systems. The origin of the symmetrical dimers in the (2 X 6) structure is discussed in the context of previous results in literature.

Silicon thermal oxidation and its thermal desorption investigated by Si 2p core-level photoemission

Initial thermal oxidation of silicon and thermal desorption of silicon oxide have been investigated by Si 2p core-level photoemission with synchrotron radiation. The surface reaction processes are discussed from the difference in the chemically-shifted components, especially suboxides. On the thermal oxidation, time evolutions of suboxide intensities show a distinct temperature dependence, which is explained by two growth modes for the oxidation: first-order Langmuir-type adsorption mode and two-dimensional island growth mode at oxidation temperatures below and above 650 °C, respectively. On the thermal desorption, the spectrum for the thermal oxide followed by annealing at 1000 °C for 30 s in vacuum, whose thickness is nominally estimated at 3.7 Å, are compared with the 3.3 Å-thickness thermal oxide without the process of the annealing. The intensities of the suboxide components are considerably different between them, which can be explained by the formation and lateral growth of the voids in the annealed oxide layer.

Electronic structure and surface chemistry of alkyl-passivated Si nanoparticles

We have synthesized the n-butyl-passivated Si nanoparticles with mean diameter of 1.4 nm by the solution routes, and have carried out the various spectroscopic studies in order to investigate their optical properties, electronic structures, and surface chemistry. It is found that photoluminescence (PL) spectra of these Si nanoparticles strongly depend on the surface conditions. Moreover, it is found their electronic features obtained from the synchrotron-radiation valence-band photoemission and PL spectra are reproduced by the recent quantum Monte Carlo calculation. From the synchrotron-radiation Si 2p core-level photoemission spectra, it is found that their interfacial electronic structure of the present Si nanoparticles is significantly different with that of alkyl-terminated bulk Si surface. From these results, we discuss the detailed electronic and surface chemical properties of alkyl-passivated Si nanoparticles.

Bonding Structure of Ultrathin Oxides on Si(110) Surface

ABSTRACTThe thermal oxidation kinetics of Si(110) surface up to oxide layer thickness of 1 ML has been investigated by real-time monitoring of chemical shifted in the Si 2p core-level photoemission using synchrotron radiation. The uptake profiles of every Si oxidation states (Sin+: n = 1 − 4) indicate that the top surface Si(110) oxidation proceeds through a two-step oxidation pathway via Si2+ state, just like the Si(001) surface. In contrast to the Si(001) oxidation, however, Si3+ state is always more abundant than Si4+ state during oxidation. This is related to occurrence of imperfect oxidation of this surface, most probably due to accumulation of compressive strain during oxidation.

Interaction of atomic hydrogen with the β-SiC(100) 3×2 surface and subsurface

We investigate clean and atomic hydrogen exposed beta-SiC(100) 3 x 2 surfaces by synchrotron radiation-based Si 2p core-level photoemission spectroscopy. The clean 3 x 2 surface reconstruction exhibits three surface and subsurface components. Upon hydrogen exposures, those surface and subsurface components are shifted to lower binding energies by large values, indicating significant charge transfer to the surface and subsurface regions, in excellent agreement with the recently discovered H-induced beta-SiC(100) 3 x 2 surface metallization. In addition, the interaction of hydrogen results in a large reactive component at Si 2p supporting an asymmetric charge transfer in the third plane below the surface, in agreement with previous experimental investigations. However, the results are inconsistent with recent ab initio theoretical "frozen" calculations predicting H atom to be in a bridge-bond position.

Formation and Characterization of Manganese Silicide on Si(111) and Si(100) Substrates

The electronic structure of the interface formation at Mn/Si at room temperature (RT) and the growth of manganese silicide were studied by using photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS) with synchrotron radiation. The Mn coverage dependence of the Si 2p and the Mn 3p core-level spectra revealed that the growth of Mn on Si(111)-7 × 7 at RT started in a layer-by-layer growth at a coverage of less than 0.5 ML (monolayer). Mn 2p XAS spectra also showed no reaction between Mn and Si at RT. Three thin manganese silicide samples were prepared by using solid phase epitaxy at 610 ◦C (MSS), reactive deposition epitaxy at 290 ◦C for Si(111) and at 350 ◦C for Si(100) (MSR) and post annealing the MSR sample at 610 ◦C (MSP) on the Si(111) and the Si(100) substrates. The LOW ENERGY ELECTRON DIFFRACTION (LEED) pattern and the fine structure in the Mn 2p XAS spectra showed that the phases of the MSS, the MSR, and the MSP samples were the same. Emissions at the Fermi energy in the valence-band (VB) PES spectra and the line shape of Si 2p core-level photoemission spectra also showed the formation of metallic MnSi.

Electronic and geometric structures of the Au–Si(1 0 0) surface observed by photoemission spectroscopy and LEED

We have investigated the electronic and geometric structures of the Au–Si(1 0 0) surface as a function of annealing temperature by means of Si 2p and Au 4f core-level photoemission spectroscopy and low energy electron diffraction (LEED). The 1 × 1, c(8 × 2) and 5 × 3.2 structures were obtained by annealing the Au–Si(1 0 0) surface at 250, 630 and 750 °C, respectively. From the intensity ratio of the Au 4f to Si 2p spectra, it was found that the chemical composition was almost identical for the 1 × 1, c(8 × 2) and 5 × 3.2 structures. On the other hand, changes in the peak position and shape of the Si 2p and Au 4f spectra were observed when the 1 × 1/ c(8 × 2) structure changed to the c(8 × 2)/5 × 3.2 structure. The spectral changes indicate that there are several components due to different Au–Si interactions. Based on the results of the Si 2p and Au 4f core-level photoemission analysis and LEED patterns, we discuss the electronic and geometric structures of the Au–Si(1 0 0) surface.

Spectroscopic interpretation for Na-induced phase transitions on Na/Si(1 1 1)3 × 1

Na adsorption at room temperature causes the Na/Si(1 1 1)3 × 1 surface with Na coverage of 1/3 monolayer (ML) to transit into the Na/Si(1 1 1)6 × 1 surface at 1/2 ML and sequentially into the Na/Si(1 1 1)3 × 1 surface at 2/3 ML. The phase transition was studied by Si 2p core-level photoemission spectroscopy. The detailed line shape analysis of the Si 2p core-level spectrum of the Na/Si(1 1 1)3 × 1 surface (2/3 ML) is presented and compared to the Na/Si(1 1 1)3 × 1 surface (1/3 ML) which is composed of Si honeycomb chain-channel structures. This suggests that as additional Na atoms form atomic chains resulting in the Na/Si(1 1 1)3 × 1 surface (2/3 ML), the inner atoms of the Si honeycomb chain-channel structure is buckled due to the additional Na atoms.

Spectroscopic Characterization of Alkyl-Passivated Si Nanoparticles Synthesized by a Solution Route

ABSTRACTWe have synthesized the alkyl-passivated Si nanoparticles by a solution route, and have carried out the various spectroscopic studies in order to investigate their intrinsic optical properties, electronic structures, and surface chemistry. Photoluminescence (PL) spectra of the n-butyl-passivated Si nanoparticles with mean diameter less than 2 nm exhibit the strong ultraviolet-blue emission. Moreover, it is found that their valence-band maximum energies directly estimated from the synchrotron-radiation valence-band photoemission spectra correspond to the resonance features in the PL excitation spectra. Therefore, it is concluded that the PL from the present n-butyl-passivated Si nanoparticles originates from the electron-hole pair recombination between the modified valence-band and conduction-band due to the quantum size effect. From the synchrotron-radiation Si 2p core-level photoemission spectra, their interfacial electronic structures of these Si nanoparticles have also been characterized. From these results, we discuss the detailed electronic and chemical properties of alkyl-passivated Si nanoparticles.

Alkali metal-induced Si(1 1 1) [formula omitted] structure: The Na case

We report the first scanning tunneling microscopy (STM) and core-level photoemission (CL-PES) studies of a 21 × 21 structure induced by sub-monolayer Na deposition on the Si(1 1 1) 3 × 3 - Ag surface. In the filled-state STM images, five bright protrusions in the 21 × 21 unit cell are located on the Ag trimers of the 3 × 3 - Ag structure. The Si 2p core-level photoemission decomposition shows that the surface-shifted component originated from the Si-trimer atoms in the 3 × 3 - Ag surface splits into two for the 21 × 21 structure, which are attributed to the Si-trimer atoms in the 21 × 21 unit cell which are affected and unaffected by the Na adsorption. These results show strong similarities between the Na-induced 21 × 21 superstructure and the noble metal-induced ones, indicating a common atomic structure and formation mechanism.

Photoemission study on the Sb-induced reconstruction of the Si(1 1 2) surface

This study investigated the Sb-induced reconstruction of the Si(1 1 2)2 × 1 surface using low energy electron diffraction (LEED) and synchrotron radiation photoelectron spectroscopy (SRPES). When Sb was deposited on the clean Si(1 1 2) surface at 300 °C, a sharp hexagonal LEED pattern with weak “ n/5” fractional spots was observed, which is very similar to one of the Sb/Si(1 1 1)1 × 1 surfaces. The Si 2p and Sb 4d core level photoemission spectra were measured. The analysis results of the SRPES showed that the Si 2p core-level spectrum is composed of two surface-related components: a surface component at +0.2 eV and a small surface-related component at –0.2 eV with respect to the bulk component. In addition, the Sb 4d core-level spectrum was well reproduced with one doublet component. The results revealed that Sb atoms were adsorbed at unique sites on a Si(1 1 1)1 × 1 surface. On the basis of the nanofacet structure model of the Sb/Si(1 1 2) surface suggested by a previous scanning tunneling microscopy (STM) study, the structural model of the Sb/Si(1 1 2) surface was compared with the LEED pattern and the SRPES results.

Chemical reaction at the interface between polycrystalline Si electrodes and HfO2∕Si gate dielectrics by annealing in ultrahigh vacuum

We have investigated the chemical reaction at the interface between polycrystalline-Si (poly-Si) electrodes and HfO2∕Si gate dielectrics by photoemission spectroscopy and x-ray absorption spectroscopy depending on the annealing temperature in an ultrahigh vacuum. From Si2p and Hf4f high-resolution core-level photoemission spectra, we revealed that the Hf-silicide formation starts at as low temperature as 700°C and that the Hf-silicate layer is also formed at the interface between poly-Si electrodes and HfO2. Crystallization of the amorphous HfO2 layer even at 700°C was suggested from valence-band and OK-edge absorption spectra. By the annealing at 800°C, the HfO2 layer disappeared completely and the Hf-silicide clusters were formed on the Si substrate. Direct contact between poly-Si electrodes and HfO2 promotes the interfacial reaction compared to the case without poly-Si electrodes.

Hydrogen-induced metallization of a preoxidized 3C-SiC(100)3×2 surface

We investigate atomic hydrogen interaction with a preoxidized Si-rich 3C-SiC(100)3×2 surface by synchrotron radiation-based valence band, and Si2p and C1s core level photoemission spectroscopies. Atomic hydrogen exposure results in (i) Fermi level built-up in the valence band, (ii) band bending, and (iii) the three Si2p surface components shifting to lower binding energies. These features indicate H-induced surface metallization. This finding opens perspectives in the metallization at the subnanometric scale of passivated semiconductor surfaces.

Band bending at the Ni/Si(100)-2×1 submonolayer interface

Band bending at the Ni/Si(100)-2×1 interface has been monitored by using Si 2p core level photoemission spectra. Two nickel-induced Si 2p components appear in the initial interaction between Ni and Si(100)-2×1, which is confined at the top surface and the first subsurface layers. At Ni coverage less than 0.0375 ML, Ni atoms prefer the adamantane interstitial sites on the first subsurface, but switch to the pedestal sites on Si dimer rows at higher Ni coverage. The change in the preferred occupation sites of Ni atoms on the Si(100)-2×1 surface strongly affects the amount of band bending shift. The shift towards higher binding energy, when Ni atoms occupy the adamantane interstitial sites, is attributed to metal-induced-gap states. While Ni atoms occupy the pedestal sites, the band bending shift is reduced which is attributed to the passivation of surface states.

Study of Au–Si(1 0 0) interface by means of Si 2p core-level photoemission spectroscopy

We have investigated the Au–Si(1 0 0) interface as a function of the Au coverage by means of the Si 2p core-level photoemission spectroscopy. At the 1 ML deposition, the spectral feature changed remarkably. This indicates that the deposited Au atoms interact with the surface Si atoms in this deposition range. With increasing the Au coverage at ∼3 ML the spectral feature become three-peak structures at 100.0, 99.4, and 99.0 eV. The appearance of the three-peak structures indicates the Au–Si alloy or Au silicide formation. With further increasing the Au coverage, two peaks at 100.3 and 99.7 eV become dominant. From the curve fitting analysis, the photoemission spectrum at the higher Au coverage was decomposed by three components. Two components at higher binding energy side were assigned to the surface Si atoms while a component at lower binding energy side was assigned to Si atoms in the amorphous silicide layer.

Thin manganese films on Si(111)-(7 × 7): electronic structure and strain in silicide formation

The electronic and structural properties of thin epitaxial Mn films on Si(111)-(7 × 7) and their silicide reaction are studied by means of low-energy electron diffraction, scanning tunnelling microscopy (STM) and photoemission spectroscopy (PES). The deposition of Mn at room temperature initially results in the growth of islands. The metal–silicon reaction already occurs at this temperature, which is further enhanced by annealing up to 400°C, leading to the formation of manganese silicide and turning islands into nearly closed films at higher coverage. A pseudo-(1 × 1) phase develops for Mn films of up to 1 monolayer (ML) thickness. For films of higher thicknesses of up to 5 ML, a ()R30° phase is observed. STM images show that then the silicide film is almost closed and exhibits a strain relief network reflecting an incommensurate interface structure. PES reveals that the (1 × 1) phase is semiconducting while the ()R30° phase is metallic. For both phases, Si 2p core level photoemission data indicate that the surface is probably terminated by Si atoms.

Charge carrier dynamics at the SiO2/Si(100) surface: a time-resolved photoemission study with combined laser and synchrotron radiation

Abstract The charge carrier dynamics at a thermally grown 15 A thick SiO 2 /Si(1 0 0) interface has been studied by time-resolved Si 2p core level photoemission. Upon excitation of electron hole pairs in the surface-near region by picosecond laser pulses, the dynamics of the charge carrier recombination has been determined by time-resolved Si 2p core level photoemission via the time-dependent surface photovoltage. On a timescale from picoseconds to 800 ns a non-exponential decay of the surface photovoltage and a logarithmic dependence on laser intensity is found. Both aspects can be well described by a quasi-equilibrium model based on charge carrier dynamics which is governed by thermionic emission.

Early nucleation on the Si( [formula omitted])-2×1 surface

The analysis of synchrotron radiation Si 2p core-level photoemission spectra provides fruitful information about the interface structure. A constraint on layer-wise intensities, based on the inelastic mean-free-path, is used to extract the 2p binding energy shifts of the first three outer layers. Both clean and adsorbate-covered surfaces have been successfully analyzed. The results for the clean Si(0 0 1)-2×1 surface, which reflect both the strain due to the reconstruction and changes in final-state screening, are in very good agreement with theory. However, for adsorbate-covered surfaces charge-flow, due to the electronegativity difference between Si and adsorbate atoms, dominates the shifts. Results for prototypical interfaces, with the adsorbates Ge, Cl, and oxygen, are presented.