XPS Valence Band Spectra Research Articles

Stacking-order independent inter-layer charge transfer in MBE-grown MoSe2 and WSe2 heterostructures

Stacking-order independent inter-layer charge transfer in MBE-grown MoSe2 and WSe2 heterostructures

Construction of PANI@V2O5-ZnIn2S4 Z-scheme heterojunction photocatalysts for highly effective degradation of industrial dyes and antibiotics

Construction of PANI@V2O5-ZnIn2S4 Z-scheme heterojunction photocatalysts for highly effective degradation of industrial dyes and antibiotics

(Invited) Consideration on Gate Stack Formation Processes of Ultrawide Bandgap Ga2O3 with SiO2 Dielectric Layer

MOSFETs on β-Ga2O3 are expected to be a high-efficient and cost-effective alternative option of high-voltage power devices. Taking account of the reliability and the large conduction-band offset against β-Ga2O3, it would be reasonable to employ SiO2 as the gate dieletric. In this study we investigated the effects of post-deposition annealing (PDA) on SiO2/β-Ga2O3 MOS gate stacks, in terms of the MOS electrical characteristics and the band alignment.β-Ga2O3 (001) wafers with ~2×1016 cm-3 n-type doped epitaxial layers were cleaned in diluted HF solution, and SiO2 films were deposited by electron-beam (EB) evaporation of Si in O2 ambient of ~1×10-2 Pa, followed by PDA at various temperatures from 600 to 1000℃ in either O2 or N2 ambient. Au was evaporated as gate electrode to form MOS capacitors. X-ray photoelectron spectroscopy (XPS) was conducted on the stacks with ~3nm-thick SiO2 for the evaluation of band alignment. Ultraviolet photoelectron spectroscopy (UPS) was also employed to determine the band diagram of β-Ga2O3 (001).Nearly-ideal capacitance-voltage characteristics were obtained for the MOS capacitor fabricated with O2-PDA at 1000℃. The interface state density (Dit) determined by conductance method decreased down to ~1010 cm-3 at the energy level of EC−0.2 eV by PDA at higher temperature. The hysteresis width (ΔVhys) of C-V curves was smaller for the samples annealed at higher temperatures. The flatband voltage (VFB) shift after O2-PDA resulted in VFB close to the ideal value estimated from the physical properties of Au and Ga2O3, suggesting that fixed charge density at the interface would be minimized. However, PDA in N2 at 1000℃ resulted in a negative shift of VFB, which indicates the formation of positive fixed charges in the stack. The beneficial influences of O2-PDA on those characteristics suggest that an oxygen deficiency introduced near the interface is one of the origins of interface defect states. It is noteworthy that Ga3d XPS on the surface of Ga2O3 substrate always shows a tailing in lower binding energy side, which is indicating oxygen deficiency on the surface. The intensity of this lower-binding-energy component reduced significantly when a bare-Ga2O3 substate was annealed in O2, however, it did not decrease efficiently even after O2-PDA when the surface was covered with SiO2. This is probably due to the oxygen rearrangement at SiO2/Ga2O3 interface determined by the difference of material properties of those oxides. This fact suggests that the Ga2O3 surface easily forms oxygen vacancies when it is covered with SiO2. This would be the reason why the formation of interface defect states is not suppressed without O2-PDA.Next the band diagram of β-Ga2O3 (001) substrate was investigated by UPS analysis where the energy level of valence band edge referring to the vacuum level was evaluted from the energy difference between minimum (cut-off) and maximum edges of the obtained kinetic energy spectra of photoelectrons. As a result we found the valence band edge of of β-Ga2O3 (001) was ~8.2 eV below the vacuum level, where the influences of O2 annealing at 1000℃ on the valence band edge energy level was limited to the shift within ~0.1eV. This would tell us the valence band offset between SiO2 and Ga2O3 should be around ~1.1eV, and the conduction band offset between them is to be around 2.8-2.9eV, by taking account of the well-reported SiO2 band diagram and assuming the bandgap of β-Ga2O3 as 4.7eV. On the other hand, the valence band offset estimated from the deconvolution of the XPS valence band spectrum for a ~3nm-thick SiO2/β-Ga2O3 stack from the energy edge difference between the deconvoluted spectra corresponding to SiO2 and Ga2O3, was a few hundreds of mV smaller than the above expected value (~1.1eV). This discrepancy is indicating the formation of an interface dipole layer between SiO2 and Ga2O3 with a pair of nagative and positive charges aligned at the interface to cause a shift in the band alignment. The magnitude of such dipole was indicated to be more significant (~0.5eV) for the stack after PDA at 1000℃, whereas it was less (0.2~0.3eV) after PDA at 600℃.In conclusion, we demonstrated that SiO2/β-Ga2O3 (001) MOS capacitors showed nearly-ideal electrical characteristics with significantly reduced interface defect density and small fixed charge density by applying O2-PDA. The band alignment of SiO2/β-Ga2O3 (001) MOS stack was clarified by photoelectron spectroscopy to confirm a very large conduction band offset of the stack, but an influence of the formation of interface dipole layer between SiO2 and Ga2O3 on the band alighment was also indicated.

Photoresponse of Carbon Nanofiber-Based Photodetector and Its Enhancement on CuNi Nanoparticle Adsorption.

We explore the photodetection properties of a carbon nanofiber (CNF)-based p-CNF/n-Si heterojunction device in the 400-800 nm wavelength range and investigate the changes brought in by adsorption of CuNi (CN) nanoparticles on the CNFs. The nanoparticles and CN-CNF nanocomposites were synthesized by using chemical hydrothermal routes. The p-type semiconducting nature of the CNFs and nanocomposites was determined using X-ray photoelectron (XPS) and UV-vis spectroscopies. The p-CNF/n-Si device is found to be better than many carbon-nanotube-based devices in terms of its peak responsivity (0.6 A/W) and gain (1.6), with an acceptably moderate peak detectivity (1.3 × 109 Jones) at 450 nm and a -5 V bias. The p-CN-CNF/n-Si device displays an appreciable enhancement in the photoresponse with respect to the p-CNF/n-Si device, with a peak responsivity of 2.8 A/W, peak detectivity of 9.4 × 109 Jones, and gain of 8. With the aid of valence band XPS and Raman spectra, the enhancement is explainable in terms of a CN to CNF charge transfer and the resulting increase in the built-in potential at the heterojunction.

Valence band XPS spectra of K silicate glasses: Effect of HOMO energies on K, Na and Li leach rates, activation energies and reaction mechanism

Valence band XPS spectra of K silicate glasses: Effect of HOMO energies on K, Na and Li leach rates, activation energies and reaction mechanism

High-efficiency photocatalyst based on Au nanoparticles loaded on defective ZnO nanorods

High-efficiency photocatalyst based on Au nanoparticles loaded on defective ZnO nanorods

Synthesis of Novel MOF‐Based BixTiy‐BTC and Bi1Ti3‐BTC/Fe3O4 Photocatalysts and Their Application in the Degradation of UDMH in Wastewater

AbstractRemoval of organic pollutants from wastewater remains a significant challenge. Hence, we report a series of novel MOFs based BixTiy‐BTC photocatalysts synthesized by hydrothermal method for decontamination of 1,1‐Dimethylhydrazine (UDMH). The preparation parameters of MOFs were optimized, the best catalytic performance was achieved by adjusting the Bi/Ti molar ratio to 1 : 3, with Bi1Ti3‐BTC a photocurrent density of 0.35 mA/cm2 was reached. The morphology and composition of the materials were analyzed, titanium doping increased the specific surface area. Bi1Ti3‐BTC was loaded with magnetic nano‐Fe3O4, which prevented agglomeration of Bi1Ti3‐BTC and increased the specific surface area, thus improving photocatalytic activity. The band gap structure of the semiconductor materials was estimated by UV‐Vis and XPS valence band spectra, while the separation efficiency of photogenerated carriers was investigated by photocurrent density and PL (Photoluminescence) spectrum. The photocatalytic degradation rate of UDMH rapidly decreased after addition of EDTA, indicating that h+ was the main active species in the photocatalytic degradation process. The photocatalytic removal efficiency of UDMH with Bi1Ti3‐BTC/Fe3O4 at a concentration of 0.5 g/L reached 97.58 % after illumination for 180 min, and after 210 min near quantitative degradation was observed.

Interactions in Al2O3 - graphene oxide composite: XPS study

The structure of an aluminum oxide/graphene oxide (GO) composite was studied using X-ray photoelectron spectroscopy (XPS). High-energy resolved XPS measurements of Al 2p-core level spectra revealed the formation of Al–O–C bonds, which indicated the occurrence of interfacial reactions between Al2O3 and GO in the process of composite synthesis. An increase in intensity in the near-edge region of XPS valence band (VB) spectrum was observed with increasing GO concentration, indicating possible contribution of the electronic states of carbon. Filling the electronic states on the edge of VB allows to associate GO doping with the loss of dielectric properties of the original Al2O3 compound. Addition of graphene oxide to Al2O3 ceramics changed conductive properties of the composite due to formation of new chemical bonds.

Significant reduction of thermomagnetic hysteresis in NdMn2-x Ag x Si2 (0 ≤ x ≤ 0.4) alloys

ABSTRACT In this research, the single-phase tetragon NdMn2-x Ag x Si2 (0 ≤ x ≤ 0.4) alloys were prepared. It was found that the phase transition temperature was decreased by evaluating Ag substitution, which was attributed to the enhancement of orbital hybridization. The thermomagnetic hysteresis disappears for x ≥ 0.2. For Δμ0H of 0–7 T, the values of the maximum magnetic entropy change (the relative cooling power) are 22.2 J/kgK (420.7 J/kg), 20.1 J/kgK (500.5 J/kg), 19.9 J/kgK (552.8 J/kg) and 12.0 J/kgK (300.0 J/kg) in NdMn2-x Ag x Si2 (x = 0, 0.2, 0.3 and 0.4) alloys. The XPS valence band spectra indicate that the density of electron and the hybridization effect is enhanced by increasing the substitution amount of Ag. This is attributed to the fact that the atomic radius of Ag is larger than that of Mn, resulting in the strengthening of the covalent bond between Ag and Si.

Highly Selective NH3 Sensor Based on MoS2/WS2 Heterojunction

In this paper, the heterostructure of MoS2/WS2 was prepared by a hydrothermal method; the n-n heterostructure was demonstrated using TEM combined with Mott-Schottky analysis. The valence and conduction band positions were further identified by the XPS valence band spectra. The NH3-sensing properties were assessed at room temperature by changing the mass ratio of the MoS2 and WS2 components. The 50 wt%-MoS2/WS2 sample exhibited the best performance, with a peak response of 23643% to NH3 at a concentration of 500 ppm, a minimum detection limit of 20 ppm, and a fast recovery time of 2.6 s. Furthermore, the composites-based sensors demonstrated an excellent humidity immune property with less than one order of magnitude in the humidity range of 11–95% RH, revealing the practical application value of these sensors. These results suggest that the MoS2/WS2 heterojunction is an intriguing candidate for fabricating NH3 sensors.

Construction of Ag deposited g-C3N4 loaded Co[sbnd]Al LDH ternary composites with aim of pharmaceutical wastewater treatment:Pathways and mechanism for ciprofloxacin degradation

Construction of Ag deposited g-C3N4 loaded Co[sbnd]Al LDH ternary composites with aim of pharmaceutical wastewater treatment:Pathways and mechanism for ciprofloxacin degradation

Ni12P5-Supported Marigold-Shaped CdIn2S4: A 2D/3D Non-Noble-Metal Catalyst for Visible-Light-Driven Hydrogen Production

The development of photocatalysts with high catalytic activity and high stability is one of the effective ways to alleviate the energy shortage. A simple hydrothermal method was used to deposit a two-dimensional (2D) non-precious-metal cocatalyst Ni12P5 on the surface of three-dimensional (3D) CdIn2S4 in situ. A 2D/3D Ni12P5/CdIn2S4 heterostructure with close contact was obtained in this work. Its hydrogen production activity can reach 5.01 mmol/g/h, which was about 18 times higher than that of pure CdIn2S4. The apparent quantum yield of 3% Ni12P5/CdIn2S4 at 400 nm was 23.5%. In addition, the band structures of Ni12P5 and CdIn2S4 were calculated according to the experimental data of UV–visible diffuse reflection, Mott–Schottky analysis, and XPS valence band spectrum characterization. With the help of XPS testing, the transfer direction of photogenerated electrons and holes in the composite catalyst was predicted, and then the possible photocatalytic mechanism was speculated.

Structure and mechanical properties of toughening B1 Ta1-xMoxN films with various Mo contents

Structure and mechanical properties of toughening B1 Ta1-xMoxN films with various Mo contents

Effect of Ni Substitution on the Structural, Magnetic, and Electronic Structure Properties of Gd0.4Tb0.6(Co1-xNix)2 Compounds.

The comprehensive research of magnetic and electronic structure properties of the new class of Gd0.4Tb0.6(Co1-xNix)2 compounds, crystallizing in the cubic Laves phase (C15), is reported. The magnetic study was completed with electrical resistivity and electronic structure investigations. The analysis of Arrott plots supplemented by a study of temperature dependency of Landau coefficients revealed that all compounds undergo a magnetic phase transition of the second type. Based on magnetic isotherms, magnetic entropy change (ΔSM) was determined for many values of the magnetic field change (μ0H), which varied from 0.1 to 7 T. For each compound, the ΔSM had a maximum around the Curie temperature. Both values of the |ΔSMmax| and relative cooling power RCP parameters increased with increasing nickel content. It is shown that structural disorder upon Co/Ni substitution influences some magnetic parameters. The magnetic moment values of Co atoms determined from different methods are quantitatively consistent. From the M(T) dependency, the exchange integrals JRR, JRT, and JTT between rare-earths (R) and transition metal (T) moments were evaluated within the mean-field theory (MFT) approach. The experimental study of the electronic structure performed with the use of the X-ray photoelectron spectroscopy (XPS) was completed by calculations using the full-potential linearized augmented plane waves (FP-LAPW) method based on the density functional theory (DFT). The calculations explained experimentally observed changes in the XPS valence band spectra upon the Ni/Co substitution.

TiO2 nanoparticles modified with ZnIn2S4 nanosheets and Co-Pi groups: Type II heterojunction and cocatalysts coexisted photoanode for efficient photoelectrochemical water splitting

The optimization of photoelectrode is the key issue for the efficient photoelectrochemical water splitting process. In this work, the TiO 2 photoanode is synthesized and modified with ZnIn 2 S 4 nanosheets and Co-Pi cocatalyst (TiO 2 /ZnIn 2 S 4 /Co-Pi) for a favorable photoelectrochemical performance. The synthesis and modification process of the TiO 2 photoanode are optimized. The physical and chemical characterizations indicate that the TiO 2 has a nano-cauliflower-like structure and rutile crystal form modified with a network hexagonal ZnIn 2 S 4 nanosheets and amorphous Co-Pi groups. After optimization of the hydrothermal and annealing process, the optimized TiO 2 photoanode manifests a photocurrent density of 1.82 mA cm −2 , 1.73-fold of the pristine TiO 2 photoanode (1.05 mA cm −2 ). With the surficial ZnIn 2 S 4 and Co-Pi modification, the photocurrent density of the TiO 2 /ZnIn 2 S 4 /Co-Pi photoanode is raised to 5.05 mA cm −2 , 5.32-fold of the optimized TiO 2 photoanode (1.82 mA cm −2 ). The applied bias photon-to-current efficiency, the charge separation and injection efficiencies of the TiO 2 /ZnIn 2 S 4 /Co-Pi photoanodes are 8.79, 3.40, and 1.64-folds of the optimized TiO 2 photoanode. Combined the Tauc plot, valence band XPS spectra, EIS and Mott-Schottky analysis, the PEC water splitting mechanism could be that: (i) the type II heterojunction formed by the TiO 2 and ZnIn 2 S 4 semiconductors improves the charge separation/injection efficiencies; (ii) the Co-Pi groups facilitate the oxygen evolution kinetics; (iii) the Co-Pi groups and 2D ZnIn 2 S 4 nanosheets synergistically enhance the charge separation efficiency. This investigation could offer a prospect of practical implementation for photoelectrochemical water splitting. • TiO 2 nanoparticles modified with ZnIn 2 S 4 nanosheets and Co-Pi groups are prepared. • Type II heterojunction by TiO 2 and ZnIn 2 S 4 to improve charge transfer efficiency. • Co-Pi cocatalyst facilitates the surface oxygen evolution reaction kinetics. • ZnIn 2 S 4 and Co-Pi synergistically improve charge separation efficiency.

First-principles computation of the electronic structure and optical properties of Tl3PbBr5 and TlPb2Br5: Application of the TB-mBJ+U+SOC technique

Results of computation of the electronic structure of low-temperature (LT) orthorhombic (space group P212121) and high-temperature (HT) tetragonal (space group P41) polymorphous forms of Tl3PbBr5 as well as of TlPb2Br5 (monoclinic space group P21/c) compound as compared to the experimental XPS studies of these bromides are presented. Our results indicate that the best correspondence of the theoretical total density of states and the experimental XPS valence-band spectrum is detected when the computations are carried out employing the augmented plane wave + local orbitals method within a Density Functional Theory (DFT) formalism and using the modified Becke-Johnson (mBJ) functional as refined by Tran-Blaha and considering also the Hubbard correction parameter U for strongly correlated d electrons associated with Tl and Pb atoms and spin-orbit coupling (SOC) effect (TB-mBJ + U + SOC technique). Based on these findings, using the mBJ + U + SOC technique, we study in detail partial densities of states of LT- and HT-modifications of Tl3PbBr5 and of TlPb2Br5. Furthermore, for the above ternary bromides, for the first time, the main optical properties were calculated.

Ge incorporation in kesterite thin films by solution processing route: An in-depth study of structural and optoelectronic properties

Herein, we report a promising solution-processing method for the controlled incorporation of germanium (Ge) into Cu 2 ZnSnS 4 (CZTS) films using a nontoxic molecular ink. The effect of Ge concentration on structural, optical, electrical and electronic properties of the films were systematically investigated. The successful Ge alloying in CZTS was confirmed by XRD analysis and exploring the sensitivity of Raman scattering. The as-synthesized Cu 2 ZnSn 1- x Ge x S 4 (CZTGS; x = 0, 0.1, 0.15, 0.2 and 0.25) films exhibit strong absorption in the visible region with the gradual increment in the band gap energy from 1.46 to 1.61 eV by increasing x from 0 to 0.25. A decrease in Urbach energy at higher [Ge]/[Sn + Ge] ratio supports the reduction of overall disorder into the system. The information about the correct oxidation states of the constituent elements and optimal chemical composition of the CZTGS films was obtained from X-ray photoelectron spectroscopy (XPS). The decrease in Sn II /Sn IV signal ratio with the increase in Ge further supports the suppression of deep-trap Sn Zn antisite defects. The XPS valence band spectra reveal that the position of valence band maximum ascended from 0.09 to 0.15 eV with increasing Ge content in the films. Several relevant optical constants were determined of the CZTGS films which are important for applications in solar cell devices as well as for simulation purpose. • Highly stable Cu 2 ZnSn 1−x Ge x S 4 (0 ≤ x ≤ 0.25) thin films were obtained by molecular ink approach. • Ge incorporation in kesterite lattice reduces the Urbach energy. • Dielectric loss in kesterite films is decreased by increasing Ge/Sn ratio. • XPS valence band spectra reveals the ascendance of valence band maximum with Ge.

High-temperature orthorhombic phase of Cu2HgGeS4: Electronic structure and principal optical constants as evidenced from the experiment and theory

We report on successful synthesis of single-phase high-temperature (HT) orthorhombic modification of Cu2HgGeS4 and studies of its electronic and optical properties from a viewpoint of experiment and theory. In particular, we have made measurements of the XPS core-level and valence-band spectra of the HT-Cu2HgGeS4 modification and calculated density of states. The calculations are carried out within a framework of density functional theory and using varieties of techniques. We have realized that the best agreement of the theory and experiment is observed when we use in the calculations the modified Becke-Johnson (mBJ) functional as refined by Tran-Blaha and consider also the Hubbard correction parameter U and spin-orbit coupling (SOC). The calculations demonstrate that main contributions of sulfur 3p states occur near the topmost and upper part of the HT-Cu2HgGeS4 valence band, copper 3d states dominate in its central part, the lower part is prevailed by contributions of mercury 6s and germanium 4p states, whereas near the valence band bottom the biggest contributions come from mercury 5d states. The theoretical predictions are verified experimentally. The calculations reveal that the HT-Cu2HgGeS4 modification is a direct band gap semiconductor. The principal optical constants are elucidated following first-principles calculations of the quaternary sulfide under consideration.

0D/2D/2D ZnFe2O4/Bi2O2CO3/BiOBr double Z-scheme heterojunctions for the removal of tetracycline antibiotics by permonosulfate activation: Photocatalytic and non-photocatalytic mechanisms, radical and non-radical pathways

• Efficient removal of TCs was achieved by the catalyst/sunlight/PMS systems. • The double Z-scheme heterojunction structure was proved by multiple characterizations and DFT calculation. • 1 O 2 was the dominant species for TCs degradation rather than SO 4 ·− or ·OH. • Photocatalytic and non-photocatalytic processes were distinguished. • Radical and non-radical pathways were also elucidated. A series of environmental-friendly and cost-effective 0D/2D/2D ZnFe 2 O 4 /Bi 2 O 2 CO 3 /BiOBr double Z-scheme heterojunctions (abbreviated as xZnCB) were fabricated by a hydrothermal method using an electrostatic self-assembly strategy. The removal efficiencies toward tetracycline (TC), oxytetracycline (OTC), and doxycycline (DOX) were 93%, 90.1%, and 89.4% in 10ZnCB/sunlight/permonosulfate (PMS) systems within 20 min, and the degradation rate constants of 10ZnCB were 5.7–8.2 times higher than those of ZnFe 2 O 4 and 2.6–2.9 times higher than those of Bi 2 O 2 CO 3 /BiOBr (CB) under the same conditions. XPS valence band spectra, quenching experiments, EPR measurements, and density functional theory (DFT) calculations demonstrated the existence of the double Z-scheme heterojunctions. The coexistence of radical and non-radical pathways caused by photocatalytic and non-photocatalytic degradation mechanisms was also elucidated. PMS was effectively activated by a photoinduced e − , · O 2 − , and Fe(II)/Fe(III) pathway, and active species including · O 2 − , 1 O 2 , SO 4 · − , · OH, and h + participated in the catalytic processes. Unexpectedly, 1 O 2 , and · OH were determined to be the primary species during the degradation processes instead of SO 4 · − . Recycling experiments, metal leaching measurements, and TC degradation experiments in the secondary effluent demonstrated the excellent catalytic and structural properties of these xZnCB hybrid materials.

XPS ON Mn₀.₉₅Dy₀.₀₅NiSb HEUSLER ALLOY

XPS results on Mn0.95Dy0.05NiSb Heusler alloy are presented. The compound is single phase with a C1b type cubic structure. All the experimental results suggest that the rare earth atoms entered in the lattice and they are not forming second phases. An exchange splitting of Mn 3s core-level spectrum of about 4.6 eV was shown, giving a direct evidence of the local magnetic moments on Mn sites. The Ni 3d states are giving the major contribution to the XPS valence band spectra. The Ni 3d satellite peak situated around 6 eV was attributed to the fact that the Ni 3d states in the valence band are not fully occupied. However, the Ni 3d band is almost full in this alloy and the Stoner criterion for the existence of a magnetic moment on Ni sites is no longer fulfilled.