Si 2p Core Level Research Articles

Peculiarities in XPS spectra of Sn/SiO2 layers as an effect of surface charge

X-ray photoelectron spectroscopy based on synchrotron radiation was used to investigate the composition of the observed SnO2-x/Sn:SiO2-x thin layer grown by organometallic chemical vapour deposition on single-crystalline silicon wafer with additional argon ions etching treatment. Due to the formation of a thermodynamic anomaly during in situ layer growth, an efficient oxygen exchange between silicon and tin oxide phases occurs. The present study addresses the effect of localized surface charging and its influence on the obtained XPS core level spectra. We found that due to the high electrical conductivity of metallic tin and the direct coupling of tin particles to the silicon wafer, the XPS Sn 3d5/2 core level spectrum is not affected by the surface charge compared to the highly charged dielectric silicon oxide matrix, as observed for the XPS O 1 s and Si 2p core level spectra. Our results show that the core level spectra of Si 2p and O 1 s are shifted up to 3 eV due to the presence of uncompensated positive charge on the surface of the silica matrix. These results provide insight into the influence of surface charge effects on the analysis of conductor/insulator composite materials and contribute to the application of Sn-based materials in various application concepts related to energy and surface functionalization.

Cluster Mo2C deposited on graphene nanowalls by x-ray photoelectron spectroscopy

Molybdenum deposited on carbon graphene nanowalls was characterized by x-ray photoelectron spectroscopy with an Al Kα (1486.6 eV) excitation source. The sample was fixed to a stainless-steel sample holder with copper double-sided adhesive tape. Survey spectrum, C 1s, O 1s, Si 2p, and Mo 3d core levels spectra were acquired.

Paracetamol tablet analyzed by XPS

Paracetamol tablet was analyzed by x-ray photoelectron spectroscopy (XPS). Sample was fixed to a stainless-steel sample holder with a copper double-sided adhesive tape. Survey spectra, C 1s, O 1s, N 1s, Si 2p, Mg 2s, Mg KLL, and Mg 1s core levels spectra were acquired. Results showed the presence of carbon, oxygen, and nitrogen, elements that constitute the chemical structure of paracetamol; however, these can also be part of the excipients. In addition, silicon and magnesium were detected, which are related to excipients.

Silicon dioxide by Ag Lα, hard x-ray photoelectron spectroscopy

Silicon dioxide powder was characterized by hard x-ray photoelectron spectroscopy (HAXPES) with an Ag Lα (2984.2 eV) excitation source. The sample was fixed to a stainless-steel sample holder with copper double-sided adhesive tape. Survey spectrum, C 1s, O 1s, Si 1s, Si KLL, Si 2s, and Si 2p core levels spectra were acquired.

Mean Free Path of Electrons in Organic Photoresists for Extreme Ultraviolet Lithography in the Kinetic Energy Range 20-450 eV.

The blur caused by the nonzero mean free path of electrons in photoresists exposed by extreme ultraviolet lithography has detrimental consequences on patterning resolution, but its effect is difficult to quantify experimentally. So far, most mean free path calculations use the dielectric formalism, which is an approximation valid in the optical limit and fails at low kinetic energy. In this work, we used a modified substrate-overlayer technique that exploited the attenuation of the Si 2p core level originating specifically from the native silicon dioxide to evaluate the attenuation of electrons traveling through 2 and 4 nm of photoresist overlayers to provide a close estimation of the inelastic mean free path relevant for photoresist lithography patterning and for electron microscopy. The photoemission spectra were collected in the proximity of the Si 2p edge (binding energy ∼101 eV) using synchrotron light of energy ℏω ranging between 120 and 550 eV. The photoresist films were prototypical chemically amplified resists based on organic copolymer of poly hydroxystyrene and tertbutyl methacrylate with and without triphenyl sulfonium perfluoro-1-butanesufonate photoacid generator and trioctylamine quencher. The inelastic mean free path of electrons, in the range that is relevant for photoresist exposure in extreme ultraviolet lithography (20-92 eV), was found to be between 1 and 2 nm. At higher kinetic energy, the mean free path increased, consistently with the well-known behavior. The presence of the photoacid generator and quencher did not change the mean free path, within experimental error. Our results are discussed and compared with the existing literature on organic molecules measured via dielectric formalism and electron transmission experiments.

XPS characterization of ciprofloxacin tablet

Ciprofloxacin tablet was characterized by x-ray photoelectron spectroscopy. The sample was fixed to a stainless-steel sample holder with copper double-sided adhesive tape. Survey spectrum, C 1s, O 1s, N 1s, F 1s, Cl 2p, Mg 1s, and Si 2p core levels spectra were acquired. The results point out the presence of carbon, oxygen, nitrogen, and fluorine elements that constitute the ciprofloxacin; however, carbon and oxygen are also found in other ingredients (excipients). Additionally, chlorine, silicon, and magnesium were also detected, which are related with excipients.

High-energy photoelectron spectroscopy of Si(100) with Cr Kα excitation

Si (100) wafer was analyzed by high-energy photoelectron spectroscopy (HAXPES) using monochromatic Cr Kα radiation (5414.8 eV). The HAXPES spectra reported here include a survey scan and high-resolution spectra of Si 1s, Si 2s, and Si 2p core-levels.

Improving Junction Quality via Modifying the Si Surface to Enhance the Performance of PEDOT:PSS/Si Hybrid Solar Cells

PEDOT:PSS/Si hybrid solar cells have attracted wide attention due to the fabrication of an inversion layer near the Si surface by a solution method to realize high efficiency. However, Si dangling bonds on the Si surface produce surface states and lattice mismatches to deteriorate the performance of the solar cells. In this work, the aromatic rubrene is used to modify the Si dangling bonds to passivate the Si surface for improving the junction quality of PEDOT:PSS/Si. It is found that the interaction of rubrene with Si dangling bonds reduces the binding energies of Si 2p1/2 and Si 2p3/2 by 0.2 and 0.1 eV, respectively. These large shifts of Si 2p core levels are the signals that form a stronger inversion layer for a higher quality junction. In addition, rubrene increases the work function of the PEDOT:PSS film by 0.09 eV to increase the band bending of the Si interface to promote carrier separation. Finally, the power conversion efficiency (PCE) of PEDOT:PSS/Si hybrid solar cells with rubrene is 12.59%, which is 23.92% higher than that without rubrene.

Titanium infiltration into ultrathin PMMA brushes

Vapor phase infiltration (VPI) is a bottom-up process that involves the infiltration of polymers, often using atomic layer deposition compatible precursors. By exposing a polymer to an organo-metallic precursor, area selective material formation is achieved where the precursor reacts with regions covered by an infiltration-receptive polymer brush. Combining receptive and rejecting polymers that have the capability of forming complex nanopatterns could potentially allow for the creation of nanofeatures, offering a route to area selective deposition. This work is concerned with the creation and characterization of titanium-infiltrated films with a VPI process. Thin films of poly(methyl methacrylate) (PMMA) were infused with titanium isopropoxide and subsequently analyzed with angular resolved x-ray photoelectron spectroscopy. All XPS analysis and VPI treatments were completed without breaking vacuum in an integrated ultrahigh vacuum setup, with O 1s, C 1s, Ti 2p, and Si 2p core levels revealing the successful incorporation of titanium into the polymer. Grazing angle Fourier-transform infrared spectroscopy demonstrates the breaking of carbon–oxygen double bonds within the PMMA structure due to titanium incorporation.

Impact of high temperatures on aluminoceladonite studied by M\xf6ssbauer, Raman, X-ray diffraction and X-ray photoelectron spectroscopy

Mössbauer, Raman, X-ray diffraction and X-ray photoelectron spectroscopies were used to examine the effects of temperature on the structure of two aluminoceladonite samples. The process of oxidation of Fe2+ to Fe3+ ions started at about 350 °C for the sample richer in Al and at 300 °C for the sample somewhat lower Al-content. Mössbauer results show that this process may be associated with dehydroxylation or even initiate it. The first stage of dehydroxylation takes place at a temperature > 350 °C when the adjacent OH groups are replaced with a single residual oxygen atom. Up to ~500 °C, Fe ions do not migrate from cis-octahedra to trans-octahedra sites, but the coordination number of polyhedra changes from six to five. This temperature can be treated as the second stage of dehydroxylation. The temperature dependence on the integral intensity ratio between bands centered at ~590 and 705 cm−1 (I590/I705) clearly reflects the temperature at which six-coordinated polyhedra are transformed into five-coordinated polyhedra. X-ray photoelectron spectra obtained in the region of the Si2p, Al2p, Fe2p, K2p and O1s core levels, highlighted a route to identify the position of Si, Al, K and Fe cations in a structure of layered silicates with temperature. All the measurements show that the sample with a higher aluminum content and a lower iron content in octahedral sites starts to undergo a structural reorganization at a relatively higher temperature than the less aluminum-rich sample does. This suggests that iron may perform an important role in the initiation of the dehydroxylation of aluminoceladonites.

Ibuprofen tablet characterized by XPS

An ibuprofen tablet was characterized by x-ray photoelectron spectroscopy. The sample was fixed to a stainless-steel sample holder with a copper double-sided adhesive tape. Survey spectra, C 1s, O 1s, N 1s, Si 2p, and Na 1s core level spectra were acquired. The results showed the presence of carbon and oxygen, elements that are part of the chemical structure of ibuprofen; however, these can also be part of the excipients. In addition, nitrogen, silicon, and sodium were detected, which are associated with excipients.

A spectrum deconvolution method based on grey relational analysis

The extensive usage of X-ray spectroscopies in studying complex material systems is not only intended to reveal underlying mechanisms that govern physical phenomena, but also used in applied studies focused on an insight-driven performance improvement of a wide range of devices. However, the traditional analysis methods for X-ray spectroscopic data are rather time-consuming and sensitive to errors in data pre-processing (e.g., normalization or background subtraction). In this study, a method based on grey relational analysis, a multi-variable statistical method, is proposed to analyze and extract information from X-ray spectroscopic data. As a showcase, the valence bands of microcrystalline silicon suboxides probed by hard X-ray photoelectron spectroscopy (HAXPES) were investigated. The results obtained by the proposed method agree well with conventionally derived composition information (e.g., curve fit of Si 2p core level of the silicon suboxides). Furthermore, the uncertainty of chemical compositions derived by the proposed method is smaller than that of traditional analysis methods (e.g., the least square fit), when artificial linear functions are introduced to simulate the errors in data pre-processing. This suggests that the proposed method is capable of providing more reliable and accurate results, especially for data containing significant noise contributions or that is subject to inconsistent data pre-processing. Since the proposed method is less experience-driven and error-prone, it offers a novel approach for automate data analysis, which is of great interest for various applications, such as studying combinatorial material “libraries”.

C–Si bonded two-dimensional hole gas diamond MOSFET with normally-off operation and wide temperature range stability

A C–Si bonded SiO2/diamond interface is formed under a SiO2 mask during the selective diamond growth at a high temperature in a H2 atmosphere including methane (5%). A few monolayers with C–Si bonding at the SiO2/diamond surface are confirmed through X-ray photoelectron spectroscopy at the C1s and Si2p core levels from 290 eV to 271 eV and 107 eV–95 eV, respectively. In addition, secondary ion mass spectroscopy results suggest that the C–Si bonds, and not C–H bonds, are majority at the interface and are mainly responsible for the field effect transistor (FET) operation. Two-dimensional hole gas C–Si diamond metal–oxide–semiconductor FET (MOSFETs) are fabricated using the C–Si diamond sub-surface as a p-channel. The MOSFETs in which the actual length from the source to the drain (LSD) is 12 μm–6 μm show appreciable field-effect mobility (e.g. 140 cm2V−1s−1 at LSD = 12 μm and 300 K) and normally-off operation. The wide temperature characteristics of the C–Si MOSFETs are confirmed and the device shows high stability, and a high on/off ratio of 106 is maintained at 673 K. The C–Si bonding at the SiO2/diamond interface provide a lower interface state density which makes the MOSFET show high drain current density and field-effect mobility with normally-off operation.

Sildenafil tablet analyzed by XPS

Sildenafil tablet was analyzed by x-ray photoelectron spectroscopy. Sample was fixed to a stainless-steel sample holder with a copper double-sided adhesive tape. Survey spectrum, C 1s, O 1s, N 1s, S 2p, Si 2p, Mg 1s, and Na 1s core levels spectra were acquired. Results showed the presence of carbon, oxygen, nitrogen, and sulfur, elements that constitute sildenafil; however, carbon and oxygen are also found in other ingredients (excipients). Additionally, the presence of silicon, sodium, and magnesium is associated with excipients.

Drastic change in surface electronic properties and creation of a new carbon-based nanostructure on the vicinal SiC(111)-4° surface

Novel carbon based nanostructure on the vicinal SiC(111)-4° surface has been found as effect of Cs adsorption. The SiC(111)-4°sample was grown by method of epitaxy of low-defect unstressed nanoscaled silicon carbide films on vicinal Si(111)-4° substrate. Electronic structure of the SiC(111)-4° surface and the Cs/SiC(111)-4°interface has been detailed studied in situ in an ultrahigh vacuum using synchrotron-based photoelectron spectroscopy. The C 1s and Si 2p core level spectra have been investigated as a function of Cs submonolayer coverage. A unique fine structure of the C 1s core level spectrum was revealed to appear under Cs atomic layer deposition. The effect was ascertained and shown to be originated from the interaction of the silicon vacancy with adsorbed Cs atoms that leads to both the redistribution of electron density and surface reconstruction with formation of a new type of the C-enriched aromatic-like nanostructure.

GaP/Si(0 0 1) interface study by XPS in combination with Ar gas cluster ion beam sputtering

The study of the chemical composition of buried interfaces by X-ray photoelectron spectroscopy (XPS) is limited by the inelastic mean free path of emitted photoelectrons (PE). Soft X-ray sources (AlKα) are generally suitable for careful probing of surfaces or very thin films. Here we applied gas cluster ion beam sputtering in combination with in-situ XPS (GCIB-XPS) to analyze buried GaP/Si(0 0 1) heterointerfaces. The GCIB method was used to dig a crater into the 20 nm thick GaP(0 0 1) film. We found optimal parameters for GCIB sputtering and achieved interface layers without severe damage. Destructive effects, i.e. broadening of core level peaks, could not be completely avoided, however, and the formation of metallic Ga on the GaP surface was observed. PE spectra of the sputtered heterostructures were compared with corresponding reference spectra of sputtered bulk crystals. Interface contributions to the intensity of phosphorus and sillicon core level peaks were revealed: interface components are shifted to high binding energies of P 2p Si 2p core levels. Similar results were obtained on 4 nm thick GaP/Si(0 0 1) by XPS. Finally, a top-to-bottom concept for buried semiconductor interfaces studies by GCIB-XPS is demonstrated.

On the Dependence of Band Alignment of SiO₂/Si Stack on SiO₂ Thickness: Extrinsic Or Intrinsic?

The dependence of band alignment of SiO 2 /Si stack on SiO 2 thickness is restudied. The band structure of SiO 2 /Si stack is investigated by time-dependent X-ray photoelectron spectroscopy (XPS) with and without electron-compensation technology. The binding energy difference ΔSi_2p between Si 2p core-levels of SiO 2 and Si, measured without electron-compensation, is found larger than that with electron-compensation, owning to the charging effect. And more severe charging effect induces larger ΔSi_2p. The ΔSi_2p measured with electron-compensation technology, however, is scarcely affected by the charging effect and thus accurate band alignment can be obtained. The band alignment of SiO 2 /Si stack is found to be SiO 2 thickness dependent. And this dependence is attributed to the gap states on the SiO 2 surface and their lower charge neutrality level than the Fermi level of Si substrate, resulting in electron transfer from Si to SiO 2 and electric potential distribution across the SiO 2 . As a result, the experimentally obtained dependence of ΔSi_2p on SiO 2 thickness with electron-compensation is intrinsic. The proposed explanation about the XPS results further confirms the feasibility of the gap state theory in demonstrating the band lineup of hetero-structures.

Aromatic-Like Carbon Nanostructures Created on the Vicinal SiC Surfaces

Electronic structure of the ultrathin Cs, Ba/SiC(111)-4°, 8° interfaces have been studied in situ in an ultrahigh vacuum using synchrotron-based photoelectron spectroscopy. Change in the C 1s and Si 2p core level spectra was studied upon the adsorption of Cs or Ba within the submonolayer coverage range. The formation of a new, previously unknown carbon nanostructure was revealed under adsorption of Cs or Ba atoms. Data show that the nanostructure is formed exclusively on SiC vicinal surfaces in the presence of stabilizing adsorbed metal atoms, such as Cs or Ba atoms. It is established that the carbon nanostructure consists of carbon rings, in which chemical bonds are similar in nature to the bonds inherent in aromatic compounds.

Impact of annealing temperature on band-alignment of PLD grown Ga2O3/Si (100) heterointerface

Cost-effective integration with existing silicon CMOS electronics has been one of the primary motivations for most of the emerging non-silicon devices. In this context, β-gallium oxide (Ga2O3) films were deposited on Si (100) substrate using pulsed laser deposition (PLD) technique in this research. After deposition, samples were further annealed at 600 °C and 800 °C under vacuum. X-ray diffractometer (XRD) was employed to observe the crystallinity variation due to the annealing. The crystallinity of samples degrades with annealing at 600 °C and an incremental improvement in crystallinity was again exhibited at 800 °C due to the possible rearrangement of the Ga and O atoms to their optimal sites. Further, x-ray photoelectron spectroscopy (XPS) was used for identification of elements and chemical composition. XPS results were also analyzed to locate the position of Ga 2p and Si 2p core levels and calculate the valance band offset (VBO) at Ga2O3/Si interface. Reflected electron energy loss spectroscopy (REELS) and ultraviolet photoelectron spectroscopy (UPS) were utilized to calculate the bandgap and work function, respectively. Moreover, valance band maxima and Fermi level position of the as-deposited and annealed samples were calculated using UPS. The bandgaps for the as-deposited, annealed samples at 600 °C and 800 °C were estimated to be 4.72 ± 0.05, 4.52 ± 0.05, and 4.48 ± 0.05 eV, respectively. Consequently, the work function of the sample increases with annealing due to increase in the oxygen vacancies and resulting bandgap narrowing. The band offsets (valance band, conduction band) were determined to be (3.35 ± 0.05 eV, 0.26 ± 0.02 eV), (3.55 ± 0.05 eV, 0.15 ± 0.02 eV) and (3.54 ± 0.05 eV, 0.17 ± 0.02 eV) for the as-deposited, annealed samples at 600 °C and 800 °C, respectively. This optimization of band alignment with annealing temperature shall be very useful for controlling the carrier transport at the interface for Ga2O3/Si based devices. Thus, a trade-off is to be performed between VBO and crystallinity of the Ga2O3/Si to operate the devices efficiently and reliably respectively.

Direct Observation of Conductive Polymer Induced Inversion Layer in n‐Si and Correlation to Solar Cell Performance

AbstractHeterojunctions formed by ultrathin conductive polymer [poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate)—PEDOT:PSS] films and n‐type crystalline silicon are investigated by photoelectron spectroscopy. Large shifts of Si 2p core levels upon PEDOT:PSS deposition provide evidence that a dopant‐free p–n junction, i.e., an inversion layer, is formed within Si. Among the investigated PEDOT:PSS formulations, the largest induced band bending within Si (0.71 eV) is found for PH1000 (high PEDOT content) combined with a wetting agent and the solvent additive dimethyl sulfoxide (DMSO). Without DMSO, the induced band bending is reduced, as is also the case with a PEDOT:PSS formulation with higher PSS content. The interfacial energy level alignment correlates well with the characteristics of PEDOT:PSS/n‐Si solar cells, where high polymer conductivity and sufficient Si‐passivation are also required to achieve high power conversion efficiency.