Ultraviolet Photoelectron Spectroscopy Results Research Articles

Engineering of Schottky heterojunction in Ru@Bi2S3/Nb2C MXene based on work function with enhanced carrier separation for promoted sterilization

Within the illustrious and renowned MXene family, Niobium carbide (Nb2C) has astounded researchers by exhibiting an extraordinary level of photothermal conversion efficiency and photothermal stability, all while maintaining the possibility of biodegradability. However, the absence of band gaps hindered Nb2C as an attractive photoresponsive material for sterilization purposes. To overcome this obstacle, we engineered a Schottky heterojunction in Nb2C by introducing Ru and Bi2S3 based on the work function theory to generate an internal electric field (IEF) in Ru@Bi2S3/Nb2C, thus enhancing the photocatalytic sterilization performance by improving the charge transfer efficiency. The strategic doping of Ru also improved the carrier separation as an electron trap, apart from enhancing the light absorption efficiency by exploiting the Localized Surface Plasmon Resonance (LSPR). The results of Ultraviolet Photoelectron Spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) divulge the stark difference in work function, which facilitates the directional transfer of carrier and subsequently augments the formation of Schottky heterojunction. This unique structure which is beneficial to the generation of reactive oxygen species (ROS). As a result, the in vitro sterilizing efficiency of the Ru@Bi2S3/Nb2C exceeds 99.87%, and in vivo experiments demonstrated wound healing effects in mouse wound models. These results have confirmed the significant implications of Schottky heterojunction for the use of Nb2C in the biomedical sector.

Synthesis of Z-type spherical B-g-C3N4/Bi2WO6 heterojunctions for enhanced rhodamine B degradation

A spherical B-g-C3N4/Bi2WO6 heterojunction photocatalyst was synthesized using the hydrothermal coprecipitation method. Scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and ultraviolet–visible diffuse reflectance spectroscopy (DRS) showed that B-g-C3N4 was uniformly dispersed on the Bi2WO6 surface through a strong chemical bond, reducing the energy bandgap of Bi2WO6. The outcomes of the experiment regarding the photocatalytic degradation of rhodamine B (RhB) demonstrated a notable enhancement in the degradation rate for the 1:3 BCN/BWO composite. Specifically, the degradation rate was found to be 76 times greater than that of B-g-C3N4 and 7 times higher than that of Bi2WO6. Furthermore, a photocatalytic degradation mechanism was proposed based on the results of ultraviolet photoelectron spectroscopy (UPS) and free radical capture experiments. The direct Z-type B-g-C3N4/Bi2WO6 heterojunction structure promotes the effective separation of photogenerated carriers and enhances their oxidation-reduction ability.

Fe3O4/Co3O4–TiO2 S-scheme photocatalyst for degradation of organic pollutants and H2 production under natural sunlight

Sunlight responsible mono- and co-doped TiO2 nanoparticles (Con+ and Fen+) were prepared via sol–gel technique. The X-ray diffraction (XRD) results showed no phase change of TiO2 was observed after the addition of Con+ and Fen+ ions. Diffuse reflectance spectra (DRS) results showed a significant red-shift of the absorption edge after doping TiO2 by Con and Fen+ and the band gap energy reduced sharply from 3.10 to 1.72 eV. X-ray photoelectron spectroscopy (XPS) results emphasized the existence of multivalent states of Co2+, Co3+, Fe2+ and Fe3+. The results of ultraviolet photoelectron spectroscopy (UPS), work function, electron spin resonance (ESR) illustrated the Fe3O4/Co3O4–TiO2 formed of ternary heterojunctions. The photocatalytic performance of the prepared photocatalysts was determined for photodegradation of tetracycline (TC) and phenol (Pl) and production of hydrogen. The results illustrated the existence of multivalent states of Fe and Co ions (Co2+, Co3+, Fe2+ and Fe3+) together improved the solar light absorption, inhibited the recombination of photogenerated charges and consequently enhanced the photocatalytic efficiency of TiO2 compared with mono-doped TiO2 (Co3O4/TiO2 and Fe3O4/TiO2). The sample with 5%Fe3O4/Co3O4–TiO2 showed the highest photoactivity. The mineralization (TOC), photodegradation mechanism and reusability of prepared photocatalysts were also studied. The Fe3O4/Co3O4–TiO2 nanoparticles showed high photoactivity and stability and can be adopted as a promising materials for different environmental and H2 production applications.

Role of annealing temperature of nickel oxide (NiOx) as hole transport layer in work function alignment with perovskite

Use of inorganic charge transport layer has demonstrated relatively stable perovskite solar cells (PSCs). NiOx is the most widely used inorganic hole transport layer in inverted PSCs and different techniques and doping in this layer have been reported to improve the performance of these devices. This manuscript describes the synthesis of NiOx thin film which act as hole transport layer on glass substrate at the initial stage and PSC devices were fabricated at the secondary stage. Effect of post deposition annealing temperature on the composition, tuning of the work function and aligning it with perovskite work function increase the hole transport efficiency and improve the open circuit voltage of devices from 0.96 to 1.08 V is reported. Ultraviolet photoelectron spectroscopy results were used to check the change in work function and X-ray photoelectron spectroscopy to probe the underlying reason for improvement of devices are also included. The charge transfer efficiency is checked by the results of time resolved photoluminescence spectra is also given. Devices with NiOx as hole transport layer and ZnSe as electron transport layer are also described and performance of devices is also included in this manuscript.

Investigation of work function and chemical composition of thin films of borides and nitrides

Thin films of various borides, nitrides, and barium fluorides were tentatively deposited by pulsed laser deposition and by magnetron sputtering in order to develop the components of thermionic‐photovoltaic devices for the high‐temperature thermal to electrical conversion by solid state. To improve the device performance, the materials characterized by a low work function were selected. In the present work, the chemical composition and work function of obtained films were investigated by X‐ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy techniques. The values of work function were determined from the cut‐off in the He I valence band spectra. Different films were compared and estimated on the basis of X‐ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy results.

Improved performance and stability of inverted polymer solar cells with ammonium heptamolybdate acted as hole extraction layers via thermal annealing method

High-performance Inverted polymer solar cells (PSC) were fabricated with ammonium heptamolybdate (NH4)6Mo7O24−4H2O as hole extraction layer (HEL), and the blend of the poly(3-hexylthiophene) (P3HT):indene-C60 bisadduct (ICBA) as photoactive layer, using the structure of ITO/ZnO/P3HT:ICBA/(NH4)6Mo7O24/Ag. Correspondingly, the influence of different annealing time of ammonium heptamolybdate on carrier mobility and thus device performance were investigated. The power conversion efficiency (PCE) has been optimized from 4.12% to 6.24% after thermal annealing treatment of (NH4)6Mo7O24 layer at 130 °C for 15min. The results of ultraviolet photoelectron spectroscopy (UPS) curve clearly proven the increase of conduction-band minimum (CBM) and valence-band maximum (VBM) energy level of (NH4)6Mo7O24 layer upon thermal annealing, which is caused by the decrease of barrier potential between HOMO of P3HT and HEL. This obviously facilitate hole transport hole transport between HOMO levels of P3HT and HEL block electron transfer between LUMO levels of P3HT and Ag electrode. The space charge-limited current (SCLC) test has further confirmed the enhanced hole collection and transport capability of (NH4)6Mo7O24 after thermal annealing treatment.

Electronic properties of small molecule-diketopyrrolopyrrole derivatives and a correlation with the open circuit voltage in organic solar cells

The electronic properties of five diketopyrrolopyrrole (DPP) derivatives as a function of alkyl chains and conjugated frameworks were investigated. The results of ultraviolet photoelectron spectroscopy (UPS) and UV–vis absorption measurements show different ionization potentials (IPs), and optical band gaps. To investigate the relation between the IP and the open circuit voltage (VOC) of bulk heterojunction (BHJ) solar cells, the VOC of organic solar cells fabricated with DPP derivatives as the donor and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) as the acceptor were measured. The values between the IP of the DPP derivatives and VOC in BHJ devices exhibit linear relationship.

Influence of Gold Nanoparticles on the Characteristics of Plasma Display Panels

This paper proposes a modified alternating current plasma display panel (PDP) in which gold nanoparticles are incorporated into a bare MgO layer to enhance the performance of the protective layer. The proposed structure's ion-induced secondary electron yield, which is expressed in a gamma value ( value) is greater than that of a bare MgO layer; as a result, the operating voltage decreases by 10 V to 20 V. The integration of emitted infrared (IR) light and the power density consumed by the discharge current are both increased, but the ratio of increment is greater for the case of the IR light. Consequently, IR efficacy is increased. The IR response time of the sustain discharge and the address discharge time lag are reduced by the enhanced wall charge accumulation characteristic and the exoelectron emission property. The results of ultraviolet photoelectron spectroscopy show that a MgO layer with Au nanoparticles has a lower work function than a conventional bare MgO layer. Furthermore, the structure that is not flattened by nanoparticles seems to enhance the secondary electron emission property of the MgO protective layer. Consequently, the value is enhanced by the two reasons previously mentioned.

Insertion of an organic interlayer for hole current enhancement in inverted organic light emitting devices

We report the enhancement of hole current density in the hole transport part of an inverted top-emission organic light emitted diode by applying an organic insertion layer of 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN). Poor hole transporting performance of Al/4,4′-bis(N-phenyl-1-naphthylamino)biphenyl (NPB)/indium tin oxide is greatly improved by the HAT-CN insertion between Al and NPB layer. The highest occupied molecular orbital level onset of the NPB bends toward Fermi level at the HAT-CN/NPB interface. This extra charge generation layer made of pure organic molecules substantially enhances hole injection from Al anode as revealed by the results of ultraviolet photoelectron spectroscopy and J-V measurement data.

The evolution of charge-induced gap states in degenerate and non-degenerate conjugated molecules and polymers as studied by photoelectron spectroscopy

We report the results of ultraviolet photoelectron spectroscopy (UPS) studies of the interaction between sodium and conjugated systems for a series of diphenylpolyees and diffrent oligomers of poly( p-phenylenevinylene) (PPV). The diphenylpolyenes include molecules containing two (i.e., stilbene) to 14 carbon atoms in the polyene part; stilbene itself can also be considered as a phenyl-capped monomer of PPV. Furthermore, a PPV oligomer with three phenylene units, as well as PPV itself, has been studied. The experimental results are interpreted with the help of quantum-chemical calculations using the Hartree-Fock semi-empirical Austin Model 1 (AM1) and valence-effective Hamiltonian (VEH) methods. An important result is that all the systems react strongly with sodium; at high doping levels two new doping-induced states are detected above the valence band edge of the pristine material. In the case of saturation-doped diphenylpolyenes (i.e., two sodiums per molecule), the new states can be discussed in terms of soliton-antisoliton pairs confined within the polyene part of the molecules; in contrast, the self-localized states induced in PPV and its oligomers have to be referred to as bipolarons.

Observation of nanometer ordering in multilayer films of pyromellitic dianhydride–oxydianiline using the scanning tunneling microscope and ultrahigh vacuum

We have obtained topographic images and spatially resolved spectroscopic information of uncoated pyromellitic dianhydride–oxydianiline (PMDA-ODA) films. We find that prolonged exposure to vacuum is a key to successful imaging of this nominally insulating film surface. It is postulated that water desorption from the film is responsible. This mechanism may apply to many other organic materials. Topographic results indicate that there is a fair amount of ordering in this polymer, at least for dip-coated films. Finally, we see that PMDA-ODA has low-density states very close to the pseudo-Fermi energy, in contrast to the wide band gap predicted by ultraviolet photoelectron spectroscopy results. This provides an explanation for the anomalous conductivity seen in these thin films.

Quantum chemistry study on the nature of the CO and H 2 activation over CuO-ZnO catalysts for methanol synthesis

Self-consistent charge-discrete variation-X α (SCC-DV-X α) quantum chemical calculations were used to study the nature of the activation of CO and H 2 on CuO-ZnO catalysts for methanol synthesis. Based on X-ray photoelectron spectroscopy, electron spin resonance and temperature programmed desorption mass spectrometry investigations (L.F. Chen and K.H. Huang, J. Catal. (in Chinese), 10 (1989) 14; W.J. Lai and K.H. Huang, J. Chem. Phys. (in Chinese), 3 (2) (1990) 86.) into CO and H 2 activation adsorption, a model of CO adsorption on the CuO-ZnO cluster and a model of H 2 adsorption on the (101̄0) surface cluster of ZnO were proposed. The results show that CO is terminally bonded to the Cu atom of the CuO-ZnO cluster and its activation is caused through transfer of 0.30 electrons from the σ molecular orbitais of CO to the Cu and back-donation of 0.23 electrons from Cu to the lowest unfilled 2π ∗ orbital of the adsorbed CO molecule. Moreover, DV-X α calculations for the Zn 8O 8 cluster model on the (101̄0) surface of ZnO for the proposed adsorption of the hydrogen species show that the density of states of Zn 8O 8 is in good agreement with known ultraviolet photoelectron spectroscopy results. The lowest unoccupied molecular orbital (LUMO) of cluster model is mainly composed of surface states Zn(4s + 4p), and consists of a linear combination of the sp 3 hybridized orbitals centred on the surface Zn ions and directed from the surface along the tetrahedral direction. The highest occupied molecular orbital (HOMO) is mainly made up of a 2p x + 2p y + 2p z surface orbital on O 2p. Both frontier orbitals play a role in H − or H 0 adsorption on Zn 2+ and H 0 or H + adsorption on O 2−. The calculations also show that H 2 adsorbs heterolytically on ZnO, yielding Zn 2+-H − and O 2−-H +, which are consistent with the IR spectra.

A model of ethylene and acetylene adsorption on the (111) surfaces of platinum and nickel

Despite the application of a variety of surface sensitive techniques to the adsorption of simple hydrocarbons on well characterized metallic surfaces, no consistent picture has appeared. We review briefly the published spectroscopic results of ultraviolet photoelectron spectroscopy (UPS) and electron energy loss spectroscopy (EELS) which probe, respectively, the electronic and vibrational structure of the surface-molecular complex, and we consider appropriate free molecular analogues, not only in their ground state but also in their first excited states. A simplified approach to determine the chemisorption geometry from UPS level shifts and EELS is presented. The technique allows an isolation of distortion induced shifts from the total relaxation shift, and we find that the true relaxation shift is rather constant, approximately 2.1 eV for the cases considered. These shifts can then be used to estimate the distance of the molecule to the surface. We concentrate primarily on four systems, C 2H 2 and C 2H 4 on Ni(111) and Pt(111), adsorbed at low temperature (below the onset of dissociation). Depending on the metal, the hydrocarbon can adsorb in a di-σ arrangement or with a distortion resembling the lowest energy configuration of the first excited state of the free molecule. We also consider briefly C 2H 4 on Ag and Cu in which no distortion occurs. The distortions that resemble the first excited states might occur as a consequence of donation of bonding (backbonding) electrons from (to) the normally filled π (empty π ∗) to (from) the empty (filled) d-band states of the metal. The net effect on the hydrocarbon to partially empty the π level and fill the π ∗ level, is analogous to a low excitation of the free molecule, π → π ∗. For C 2H 4 (planar in the ground state), the lowest excitation is the triplet T-state (3–4 eV) of minimal energy for a 90° twisted configuration with a lengthened C-C bond. Acetylene is a linear molecule in the ground state, but cis- or trans-bent for the triplet excitations, ~ a (5.2 eV) or ~ b (6.0 eV), respectively. Chemisorbed geometries derived from these configurations seem possible for C 2H 4 on Ni(111) and C 2H 2 on Pt(111), while interchanging the adsorbates and substrates gives di-σ bonding, (sp 3 hybridization), as proposed previously in the literature. For C 2H 4 on Ni(111), two of the hydrogens are twisted into the surface which leads to a softening of the CH vibrational frequency. For the four systems considered, the data are consistent with the C-C bond essentially parallel to the surface, but tilted orientations are not ruled out. While the models are clearly oversimplified, they suggest an interesting point of departure for likely chemisorption geometries. Also, some intriguing correspondences to the (presumed) location of the normally empty π ∗ level and the d-band are noted.

The importance of the surface density of states in the photoemission spectra of the alkali and alkaline earth metals

Ultraviolet photoelectron spectroscopy results are shown to distinguish between the surface and bulk electronic structure of a simple metal. The spectra from Sr at low photon energies (long escape depth) is described by the bulk electronic structure; the spectra at ≈10 eV (short escape depth) is described by the surface electronic structure.