Shift In Band Position Research Articles

Leak-out spectroscopy as alternative method to rare-gas tagging for the Renner-Teller perturbed HCCH+ and DCCD+ ions.

Infrared messenger-tagging predissociation action spectroscopy (IRPD) is a well-established technique to record vibrational spectra of reactive molecular ions. One of its major drawbacks is that the spectrum of the messenger-ion complex is taken instead of that of the bare ion. In particular for small open-shell species, such as the Renner-Teller (RT) affected HCCH+ and DCCD+, the attachment of the tag may have a significant impact on the spectral features. Here we present the application of the novel leak-out spectroscopy (LOS) as a tag-free method to record the cis-bending of the HCCH+ (∼700 cm-1) and DCCD+ cations (∼520 cm-1), using a cryogenic ion trap end user station at the FELIX laboratory. We demonstrate that the obtained LOS spectrum is equivalent to a previously recorded laser-induced reactions (LIR) spectrum of HCCH+. The bending modes are the energetically lowest-lying vibrational modes targeted with LOS so far, showing its potential as a universal broadband spectroscopic technique. Furthermore, we have investigated the effect of the rare gas attachment by recording the vibrational spectra of Ne- and Ar-tagged HCCH+. We found that the Ne-attachment led to a shift in band positions and change in relative intensities, while the Ar-attachment even led to a complete quenching of the RT splitting, showing the importance of using a tag-free method for RT affected systems. The results are interpreted with the help of high-level ab initio calculations in combination with an effective Hamiltonian approach.

Defect-Induced Modulation of a 2D ZnO/Graphene Heterostructure: Exploring Structural and Electronic Transformations

This paper presents a theoretical study on the effects of selected defects (oxygen vacancies and substitutional FeZn atoms) on the structural and electronic properties of a 2D ZnO/graphene heterostructure. Spin-polarized Hubbard- and dispersion-corrected density functional theory (DFT) was used to optimize the geometrical configurations of the heterostructure and to analyze the equilibrium distance, interlayer distance, adhesion energy, and bond lengths. Charge density difference (CDD) analysis and band structure calculations were also performed to study the electronic properties of the heterostructure. The results show that the presence of defects affects the interlayer distance and adhesion energy, with structures including oxygen vacancies and FeZn substitutional atoms having the strongest interaction with graphene. It is demonstrated that the oxygen vacancies generate localized defect states in the ZnO bandgap and lead to a shift of both valence and conduction band positions, affecting the Schottky barrier. In contrast, Fe dopants induce strong spin polarization and high spin density localized on Fe atoms and their adjacent oxygen neighbors as well as the spin asymmetry of Schottky barriers in 2D ZnO/graphene. This study presents a comprehensive investigation into the effects of graphene on the electronic and adsorption properties of 2D ZnO/graphene heterostructures. The changes in electronic properties induced by oxygen vacancies and Fe dopants can enhance the sensitivity and catalytic activity of the 2D ZnO/graphene system, making it a promising material for sensing and catalytic applications.

Band Position-independent Piezo-electrocatalysis for Ultrahigh CO2 Conversion.

Piezo-electrocatalysis as an emerging mechano-to-chemistry energy conversion technique opens multiple innovative opportunities and draws great interest over the past decade. However, the two potential mechanisms in piezo-electrocatalysis, i.e., screening charge effect and energy band theory, generally coexist in the most piezoelectrics, making the essential mechanism remain controversial. Here, for the first time, we distinguish the two mechanisms in piezo-electrocatalytic CO2 reduction reaction (PECRR) through a narrow-bandgap piezo-electrocatalyst strategy using MoS2 nanoflakes as demo. With conduction band of -0.12eV, the MoS2 nanoflakes are unsatisfied for CO2 -to-CO redox potential of -0.53eV, yet they achieve an ultrahigh CO yield of ∼ 543.1 μmol·g-1 ·h-1 in PECRR. Potential band position shifts under vibration are still unsatisfied with CO2 -to-CO potential verified by a combination analysis of theoretical investigation and piezo-photocatalytic experiment, further indicating that the mechanism of piezo-electrocatalysis is independent of band position. Besides, MoS2 nanoflakes exhibit unexpected intense "breathing" effect under vibration and enable the naked-eye-visible inhalation of CO2 gas, independently achieving the complete carbon cycle chain from CO2 capture to conversion. The CO2 inhalation and conversion processes in PECRR are revealed by a self-designed in situ reaction cell. This work brings new insights into the essential mechanism and surface reaction evolution of piezo-electrocatalysis. This article is protected by copyright. All rights reserved.

Structural modifications, optical response, and electrical conductivity mechanism of Bi2O3 doped in P2O5–V2O5–MoO3 nanocomposite glass systems

Structural, optical and electrical conductivity mechanism of four compositional series of xBi2O3-(1-x)(0.30P2O5–0.35V2O5–0.35MoO3) [x = 0.05, 0.15, 0.25, and 0.35] have been investigated. XRD pattern affirms the existence of nanocrystallites in the glassy network, which affects the structural, optical and electrical alterations. The structural variation leads to an increase in the density of all the glassy systems. The FTIR analysis reveals the shift of different band positions suggesting structural alterations. The electrical conductivity investigation reveals the decreasing values of ac and dc activation energy, which enhances the ac and dc conductivity. The validity of Mott's VRH model has been examined and the value of hopping energy has been estimated. The obtained DC conductivity spectra of all samples have been fitted with Greaves's model. The AC conductivity scaling model of Pan and Ghosh has been used to demonstrate the electrical conduction relaxation method. In the spectroscopic investigation, by deploying the Tauc's plot, the optical band gap energies of the studied glass compositions are estimated. The calculation of Urbach energy values allows us to estimate the disorders of glassy nanocomposites. Different spectroscopic parameters like refractive index, polarizability, reflection factor, and reflectivity have been studied.

Strain Adjustment Realizes the Photocatalytic Overall Water Splitting on Tetragonal Zircon BiVO4.

Overall water splitting to generate H2 and O2 is vital in solving energy problem. It is still a great challenge to seek efficient visible light photocatalyst to realize overall water splitting. In this work, the tetragonal zircon BiVO4 is prepared by epitaxial growth on FTO substrate and its overall water splitting reaction is studied. Under the influence of epitaxial strain, the conduction band position shifts negatively and beyond H+/H2 reduction potential (0 V vs NHE), which enables it to possess the photocatalytic hydrogen evolution activity. After loading cocatalysts, the overall water splitting (λ > 400 nm) is realized (H2: ≈65.7 µmol g−1 h−1, O2: ≈32.6 µmol g−1 h−1), and the value of solar hydrogen conversion efficiency is 0.012%. The single‐particle photoluminescence (PL) spectra and PL decay kinetics tests demonstrate the cocatalysts are beneficial to the separation and transfer of carriers. The new strategy of adjusting the band structure by strain is provided.

Core-Shell Nanostructured Ru@Ir-O Electrocatalysts for Superb Oxygen Evolution in Acid.

The design of highly active and durable catalysts for the sluggish anodic oxygen evolution reaction (OER) in acid remains an urgent yet challenging goal in water electrolysis. Herein, a core-shell nanostructured Ru@Ir-O catalyst with tensile strains and incorporated oxygens is introduced in the Ir shell that holds an extremely low OER overpotential of 238 mV at 10 mA cm-2 in acid. The material also shows a remarkable 78-fold higher mass activity than the conventional IrO2 at 1.55 V in 0.5 M H2 SO4 . Structural characterization and theoretical calculations reveal that the core-shell interaction and tensile strain cause band position shift and charge redistribution. These electronic factors furthermore optimize the bonding strength of O* and HOO* intermediates on the surface, yielding significantly boosted OER activity relative to the conventional IrO2 .

Effect of gamma irradiation, annealing on spectroscopic and thermal properties of some biopolymers – Gelatin

Modification of chemical structure of gelatin is an important point of research due to its extensive applications in food and package industry. Various methods are prescribed in literature for this purpose. Among them the radiation method is very important due to its easiness and economy. The authors have used gamma irradiation for this purpose and studied the effect of gamma irradiation and annealing on spectroscopic and thermal properties of gelatins. For this purpose spectroscopic (Electron spin resonance (ESR) and Fourier transform infrared (FTIR)), thermal (differential scanning calorimetry) and scanning electron microscope are used. ESR spectra of irradiated gelatin have shown quartet structure at room temperature and the signal is annealed by heating the irradiated gelatin. FTIR spectra of gelatin are recorded under different conditions. After irradiation, change in intensity and shift in band position is observed, which are associated with the chemical changes brought out by radiation. Gamma irradiation brings changes in thermal and surface morphology of gelatin.

Insight into the relationship between redox ability and separation efficiency via the case of α-Bi2O3/Bi5NO3O7

α-Bi2O3/Bi5NO3O7 heterojunctions are constructed, and show higher separation efficiency but lower photocatalytic activity. The reasons are related to the shift of energy band positions.

Tantalum-Doped TiO2 Prepared by Atomic Layer Deposition and Its Application in Perovskite Solar Cells.

Tantalum (Ta)-doped titanium oxide (TiO2) thin films are grown by plasma enhanced atomic layer deposition (PEALD), and used as both an electron transport layer and hole blocking compact layer of perovskite solar cells. The metal precursors of tantalum ethoxide and titanium isopropoxide are simultaneously injected into the deposition chamber. The Ta content is controlled by the temperature of the metal precursors. The experimental results show that the Ta incorporation introduces oxygen vacancies defects, accompanied by the reduced crystallinity and optical band gap. The PEALD Ta-doped films show a resistivity three orders of magnitude lower than undoped TiO2, even at a low Ta content (0.8–0.95 at.%). The ultraviolet photoelectron spectroscopy spectra reveal that Ta incorporation leads to a down shift of valance band and conduction positions, and this is helpful for the applications involving band alignment engineering. Finally, the perovskite solar cell with Ta-doped TiO2 electron transport layer demonstrates significantly improved fill factor and conversion efficiency as compared to that with the undoped TiO2 layer.

Highly effective gating of graphene on GaN

By using four-layered graphene/gallium nitride (GaN) Schottky diodes with an undoped GaN spacer, we demonstrate highly effective gating of graphene at low bias rendering this type of structure very promising for potential applications. An observed Raman G band position shift larger than 8.5 cm−1 corresponds to an increase in carrier concentration of about 1.2·1013 cm−2. The presence of a distinct G band splitting together with a narrow symmetric 2D band indicates turbostratic layer stacking and suggests the presence of a high potential gradient near the Schottky junction even at zero bias. An analysis based on electroreflectance measurements and a modified Richardson equation confirmed that graphene on n-GaN separated by an undoped GaN spacer behaves like a capacitor at reverse bias. At least 60% of G subband position shifts occur at forward bias, which is related to a rapid reduction of electric field near the Schottky junction. Our studies demonstrate the usefulness of few layer turbostratic graphene deposited on GaN for tracing electron–phonon coupling in graphene. Multilayer graphene also provides uniform and stable electric contacts. Moreover, the observed bias sensitive G band splitting can be used as an indicator of charge transfer in sensor applications in the low bias regime.

Perfluoro effect on the electronic excited states of para-benzoquinone revealed by experiment and theory

We report a comprehensive study on the electronic excited states of tetrafluoro-1,4-benzoquinone, through high-resolution vacuum ultraviolet photoabsorption spectroscopy and time-dependent density functional theory calculations performed within the nuclear ensemble approach. Absolute cross section values were experimentally determined in the 3.8-10.8 eV energy range. The present experimental results represent the highest resolution data yet reported for this molecule and reveal previously unresolved spectral structures. The interpretation of the results was made in close comparison with the available data for para-benzoquinone [Jones et al., J. Chem. Phys., 2017, 146, 184303]. While the dominant absorption features for both molecules arise from analogous π* ← π transitions, some remarkable differences have been identified. The perfluoro effect manifests in different ways: shifts in band positions and cross sections, appearance of features associated with excitations to σCF* orbitals, and spectrum broadening by quenching of either vibrational or Rydberg progressions. The level of agreement between experiment and theory is very satisfactory, yet that required the inclusion of nuclear quantum effects in the calculations. We have also discussed the role of temperature on the absorption spectrum, as well as the involvement of core-excited resonances in promoting dissociative electron attachment reactions in the 3-5 eV range.

Annealed plasmonic Ag nanoparticle films for surface enhanced fluorescence substrate

In this work, the silver nanoparticle (Ag NP) films were deposited on glass slide by dc magnetron sputtering. The effect of annealing temperature on morphology and optical property were characterized by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and UV–Vis-NIR spectroscopy, respectively. From the results, the size and inter-particle distance of Ag NPs depend on annealing temperature. The localized surface plasmon resonance (LSPR) band position shift to the blue with the annealing temperature increased. The surface enhanced fluorescence (SEF) effect of the Ag NPs films was investigated by emission spectra of Rhodamine 6G (Rh6G) fluorescent molecules. It was found that the florescent intensity of R6G, corresponding to the diameter and surface roughness of Au NP films. Finally, the Ag NPs film substrate offer a cost-effective with non-lithography fabrication potentially applied in plasmonic sensor chips for biomedical and food safety applications.

The influence of the oxidant on structural and morphological properties of conductive polypyrrole

Polypyrrole was synthesized using chemical oxidation of monomer Pyrrole with ferric chloride as an oxidant. Series of reactions were carried out to accomplish different oxidant to monomer ratio. The synthesized black powders were characterized using different techniques like SEM, FTIR, and XRD. The bulk conductivity of the samples was measured using two probe conductivity measurement system. The conductivity of these samples at room temperature was ranging from 545.19 μS/cm to 215.78 μS/cm, as the oxidant to monomer ratio varied from 0.5 to 3. The morphology observed in SEM of these samples shows the different sizes of the globular particle of Polypyrrole. All the characteristic absorption bands of Polypyrrole were observed in the FTIR spectrum obtained from synthesized samples. A little shift in band position is observed because of various oxidants to the monomer ratio. The broad peak is observed between 20 and 30°in the XRD pattern, indicating the amorphous nature of Polypyrrole.

Boron-doped rutile TiO2/ anatase TiO2/ ZrTiO4 ternary heterojunction photocatalyst with optimized phase interface and band structure

To improve the photocatalytic performance of TiO2-based heterostructures, Z-scheme/Ⅱ-type rutile TiO2 (R)/anatase TiO2 (A)/ZrTiO4 ternary heterojunction photocatalyst was designed and prepared via a facile one-step calcining strategy. Phase interface and band structure of the materials were controlled and optimized by regulating R–TiO2/A–TiO2 mass ratio in the TiO2 (A, R)/ZrTiO4 structures using boron doping. The highest photocatalytic performance and excellent catalytic stability of Rhodamine B removal was observed from the heterojunction with a low R–TiO2/A–TiO2 mass ratio of 0.066, even after five testing cycles, accompanying with low photoluminescence intensity and electrochemical impedance, high photocurrent and charge carrier density (5.12 × 1022 cm−3), and a positive shift of valence band position (from +2.06 to + 2.16 eV). The increased photodegradation behaviour was due to the remarkably enhanced separation efficiency and improved redox ability of the photo-induced charge carriers as a result of the high content of oxygen vacancies and the formed anatase TiO2/rutile TiO2 Z-scheme heterojunction.

Raman Optical Activity of Glucose and Sorbose in Extended Wavenumber Range.

Raman optical activity (ROA) is pursued as a promising method for structural analyses of sugars in aqueous solutions. In the present study, experimental Raman and ROA spectra of glucose and sorbose obtained in an extended range (50-4000 cm-1 ) are interpreted using molecular dynamics and density functional theory, with the emphasis on CH stretching modes. A reasonable theoretical basis for spectral interpretation was obtained already at the harmonic level. Anharmonic corrections led to minor shifts of band positions (up to 25 cm-1 ) below 2000 cm-1 , while the CH stretching bands shifted more, by ∼180 cm-1 , and better reproduced the experiment. However, the anharmonicities could be included on a relatively low approximation level only, and they did not always improve the harmonic band shapes. The dependence on the structure and conformation shows that the CH stretching ROA spectral pattern is a sensitive marker useful in saccharide structure studies.

Particularities of pure and Al-doped ZnO nanostructures aerogels elaborated in supercritical isopropanol

Undoped and Al-doped ZnO nanoparticles are synthesized in supercritical isopropanol using zinc acetate di-hydrate, aluminum nitrates and methanol as precursor, dopant source and solvent, respectively. The atomic ratio [Al]/[Zn] is fixed to 3%. X-ray diffraction (XRD) results indicate that the synthesized ZnO nanoparticles possess hexagonal wurtzite structure. Al-doping of ZnO aerogel leads to the improvement of the crystalline quality due to the occupation of Zn2+ sites by Al3+ ions. The crystallites size is found to be 32 nm in pure ZnO and 50 nm in the doped aerogel. Fourier-transform infrared spectroscopy spectra reveal that the intensity of the absorption bands in ZnO decreases and the Zn-O vibration band position shifts towards higher wave numbers upon Al-doping. UV–Visible measurements show a reduction in the band gap and a shift towards long wavelength side of the absorbance with Al-doping. Scanning electron microscopy images reveal that aerogel grains are quasi-spherical in pure ZnO and have different and random forms of morphologies in the doped sample. Room temperature photoluminescence (PL) studies put into evidence that the PL emission peaks are influenced by the Al-doping, in particular, a decrease in the green emission at 535 nm is observed.

Investigation of the kieserite–szomolnokite solid-solution series, (Mg,Fe)SO4·H2O, with relevance to Mars: Crystal chemistry, FTIR, and Raman spectroscopy under ambient and martian temperature conditions

AbstractThe investigation of hydrous sulfate deposits and sulfate-cemented soils on the surface of Mars is one of the important topics in the recent scientific endeavor to retrieve detailed knowledge about the planetary water budget and surface weathering processes on our neighbor planet. Orbital visible/near-IR spectra of the surface of Mars indicate kieserite, MgSO4·H2O, as a dominant sulfate species at lower latitudes. However, given the Fe-rich composition of the martian surface, it is very probable that its actual composition lies at an intermediate value along the solid-solution series between the kieserite and szomolnokite (FeSO4·H2O) end-members. Despite the known existence of significant lattice parameter changes and spectral band position shifts between the two pure end-members, no detailed crystal chemical and spectroscopic investigation along the entire kieserite–szomolnokite solid solution range has been done yet.The present work proves for the first time the existence of a continuous kieserite–szomolnokite solid-solution series and provides detailed insight into the changes in lattice parameters, structural details, and positions of prominent bands in FTIR (5200–400 cm–1) and Raman (4000–100 cm–1) spectra in synthetic samples as the Fe/Mg ratio progresses, at both ambient as well as Mars-relevant lower temperatures. Additionally, an UV-Vis-NIR (29 000–3500 cm–1) crystal field spectrum of szomolnokite is presented to elucidate the influence of Fe2+-related bands on the overtone- and combination mode region.The kieserite–szomolnokite solid-solution series established in this work shows Vegard-type behavior, i.e., lattice parameters as well as spectral band positions change along linear trends. The detailed knowledge of these trends enables semi-quantitative estimations of the Fe/Mg ratio that can be applied to interpret martian monohydrated sulfates in data from remote sensing missions on a global scale as well as from in situ rover measurements. Given the knowledge of the surface temperature during spectral measurements, the established temperature behavior allows quantitative conclusions concerning the Fe/Mg ratio. Our understanding of the kieserite–szomolnokite solid-solution series will be well applicable to the Mars 2020 and ExoMars 2020 rover missions that will focus on near IR (0.9 to 3.5 μm) and, for the first time on Mars, Raman spectroscopy.

Photoelectrochemical Solar Water Splitting: The Role of the Carbon Nanomaterials in Bismuth Vanadate Composite Photoanodes toward Efficient Charge Separation and Transport.

Photoelectrochemical performance of bismuth vanadate (BiVO4) photoanode is limited by poor charge separation and transport properties. The roles of carbon nanotube, reduced graphene oxide, or graphitic carbon nitride in BiVO4 composite photoanode were investigated toward enhancing light absorption and reducing overall impedance during photoelectrochemical water oxidation process. X-ray diffraction and Tauc analysis showed that BiVO4 retains its monoclinic phase, n-type semiconductor nature, and band gap in all carbon nanomaterials-incorporated composite photoanodes. It was observed that the carbon nanomaterials incorporation in BiVO4 film increases its surface porosity, ultimately leading to enhanced light absorption. The BiVO4 photoanode with reduced graphene oxide and graphitic carbon nitride showed same bulk charge separation efficiency, whereas the latter showed better charge transfer. It was found that the graphitic carbon nitride formed composite with BiVO4 to provide enhanced light absorption efficiency, i.e., 89% in 350-505 nm range. The BiVO4 with graphitic carbon nitride photoanode showed the best performance with a photocurrent of 2.2 mA cm-2, charge separation efficiency of 67%, and photocurrent of 4.0 mA cm-2 with cobalt-phosphate surface catalyst at 1.23 VRHE for water oxidation under 1 sun illumination. The Mott-Schottky and impedance measurements confirmed the shift of conduction band position toward hydrogen reduction potential and reduction in film resistance, respectively, with carbon nanomaterials addition, and the shift was most significant for graphitic carbon nitride. It is concluded that by concomitant formation of junction during photoanode fabrication between carbon nanomaterials, BiVO4, and fluorine-doped tin oxide glass substrate, better charge separation, transport, and light absorption can be achieved.

Physical characterization of cytochrome c- and vitamin B12-doped DNA thin films

DNA can be useful in the field of biological and physical sciences due to its unique features, e.g., molecular recognition and self-assembly. Here, we fabricated cytochrome C (Cy)- and vitamin B12 (VB)-doped DNA thin films via a drop-casting method and explored their chemical and optoelectronic characteristics. Fourier transform infrared (FTIR), Raman, absorption, photoluminescence (PL), and electrical measurements were used to estimate critical concentrations of Cy and VB (where extremes of measured quantities occurred) in a fixed DNA concentration. These measurements focused on chemical interactions, binding modes, energy transfer mechanism, and electrical characteristics of the Cy- and VB-doped DNA thin films. We noticed that FTIR absorbance and Raman (UV–Vis) band intensities were increased (decreased), with an increase in the Cy concentration of up to 1.5 μM (= critical concentration of Cy) and a VB concentration of up to 3 mM (= critical concentration of VB) in DNA thin films. Significant band intensity changes and band position shifts of FTIR, Raman, and UV–Vis spectra were observed by varying concentrations of Cy and VB in DNA thin films. These changes provided the evidence of interaction between DNA and Cy (VB) via electrostatic bonding and intercalation interactions. The PL spectra exhibited strong red emissions at 612 nm. The changes of PL intensities revealed that effective energy transfer occurred between the VB and DNA up to critical concentration of VB, due to proper binding of VB. Finally, the current extremes for Cy- and VB-doped DNA thin films were observed at 1.5 μM of Cy and 3 mM of VB, respectively, which agreed well with the other characteristics.

Plant extract: safe way for fabrication silver nanoparticles

A safe approach for fabrication silver nanoparticles has established. In this approach a grape fruit peel extract was employed to serve as a capping agent to reduce the aggregation process of Ag nanoparticles. The formation of Ag nanocrystal was confirmed by the color change from yellow to brownish red after 24-hour incubation. The red shift of SPR band position (∼455 nm) compared to the bulk silver (420 nm) indicates the formation of silver nanoparticles. The size and morphology of Ag nanoparticles were characterized by scanning electron microscopy. The SEM images revealed that the prepared Ag nanoparticles have a diameter of 50-70 nm, while the cubic-like shapes are dominated. Fourier Transform Infrared Spectroscopy (FT-IR) was employed to characterize the prepared Ag nanoparticles.