Evidence For Charge Transfer Research Articles

New compound XeN14 with high energy density

As a high-energy density material, polymeric nitrogen has attracted considerable attention, while the exceptionally high synthesis pressure hinders its studies and applications. A significant discovery indicates that the insertion of noble gas elements can effectively reduce the synthesis pressure of polymeric nitrogen compounds. This work utilized the particle swarm optimization algorithm and first-principles calculations to extensively explore the stoichiometry of Xe–N compounds under high pressures. Two phases of XeN14, P6mm and P-62m, have been discovered, which are energetically more stable than the basic mixture of Xe and N2. Evidence of charge transfer between Xe and N was found, verifying that Xe plays a crucial role in forming polymeric nitrogen compounds. These two compounds are kinetically stable at pressures ranging from 50 to 200 GPa and exhibit semiconductor properties. A unique channel-like structure was discovered in the P6mm phase. The energy densities of P6mm and P-62m phases are 7.39 and 7.59 kJ/g, respectively, significantly exceeding those of TNT (Trinitrotoluene) and HMX (Octogen), indicating their potential as high-energy density materials.

Unraveling quantum coherences mediating primary charge transfer processes in photosystem II reaction center.

Photosystem II (PSII) reaction center (RC) is a unique complex that is capable of efficiently separating electronic charges across the membrane. The primary energy- and charge-transfer (CT) processes occur on comparable ultrafast timescales, which makes it extremely challenging to understand the fundamental mechanism responsible for the near-unity quantum efficiency of the transfer. Here, we elucidate the role of quantum coherences in the ultrafast energy and CT in the PSII RC by performing two-dimensional (2D) electronic spectroscopy at the cryogenic temperature of 20 kelvin, which captures the distinct underlying quantum coherences. Specifically, we uncover the electronic and vibrational coherences along with their lifetimes during the primary ultrafast processes of energy and CT. We construct an excitonic model that provides evidence for coherent energy and CT at low temperature in the 2D electronic spectra. The principles could provide valuable guidelines for creating artificial photosystems with exploitation of system-bath coupling and control of coherences to optimize the photon conversion efficiency to specific functions.

Evidence of charge transfer across the organic-inorganic hetero-junction based visible light driven photo-catalyst

Organic-inorganic hetero-junction based catalysts with efficient charge separation ability for superior photo-catalytic activity have been developed by chemical methods. Titanium dioxide (TiO2) and polypyrrole (PPy) as single photo-catalyst have been investigated and compared with TiO2/PPy hetero-junction composite. TiO2/PPy composite has enhanced efficiency for the degradation of toxic organic dye methylene blue (MB) through the charge transfer route. Broad curves in UV-Vis spectra arise due to polaron and bipolaron in PPy and TiO2/PPy composite. The de-localized polaron (Landé g factor value of 1.99) was further detected by electron spin resonance (ESR). The effect of polaron-bipolaron on the structure of as-synthesized PPy and TiO2/PPy composite has been explored by Raman spectroscopy. The oxidation state of different species and electronic structures below the Fermi level has been investigated by x-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS), which provides molecular orbitals insight and charge transfer state across the hetero-junction TiO2/PPy composite. Collectively, UPS and UV-Vis spectroscopy gives the energy positions (valence/ HOMO band and conduction band (C.B.)/LUMO) for TiO2 and PPy having straggled type band alignment which confirms the hetero junction in the composite.

Switching on/off molybdenum nitride catalytic activity in ammonia synthesis through modulating metal-support interaction.

Modulating the interaction between Mo nanoparticles and their support is an elegant approach to finely tune the structural, physico-chemical, redox and electronic properties of the active site. In this work, a series of molybdenum nitride catalysts supported on TiO2, and SBA-15 has been prepared and fully characterized. The results of characterization confirmed the high dispersion of Mo and the formation of small molybdenum nanoparticles in both the 10-Mo-N/SBA-15 and 10-Mo-N/TiO2 catalysts. In this context, we have shown that the catalytic activity of Mo species was strongly impacted by the nature of the catalytic support. Amongst the studied supports, SBA-15 was found to be the most appropriate for Mo dispersion. In comparison, when supported on a reducible oxide (TiO2), Mo species showed poor catalytic activity in both ammonia synthesis and decomposition and were prone to quick deactivation in the ammonia synthesis reaction. Evidence of charge transfer from the reducible support to the active phase, indicative of possible SMSI behaviour, has been observed by XPS and EPR. Differences in the oxidation states, redox behaviours, and electronic properties have been further studied by means of EPR, H2-TPR and H2-TPD.

Synthesis, morphological, structural, functional, optical and computational properties of nickel oxide nanoparticles using hydrothermal method

In this work, hydrothermal synthesis of NiO nanoparticles in aqueous solutions at higher temperatures was used. An investigation of its optical and electrical capabilities might be done in many ways. As a result, the size and structure of NiO nanoparticles were characterised using a scanning electron microscope. A powder X-ray diffractometer was used to measure experimentally the crystallite grain size and dislocation density, which were computed using the Scherer formula. The functional groups of the title nanoparticles were easily distinguishable in the FTIR spectrum. After optical absorption analyses, NiO nanoparticles were shown to have optimised UV-Visible transmittance. The density functional theory (B3LYP) was used to compute the bonding of molecular properties of NiO in the ground state using the basis sets 6-311+G (d, p) and 6-311++G (d, p). There is evidence of charge transfer in molecules based on the computed molecular electrostatic potential (MESP), Thermodynamic properties, HOMO and LUMO energies determined. The scientific applications of this NiO nanomaterial would be well served by this material.

Functionalization of Pristine, Metallic, and Semiconducting-SWCNTs by ZnO for Efficient Charge Carrier Transfer: Analysis through Critical Coagulation Concentration.

Noncovalent functionalization of single-walled carbon nanotubes (SWCNT) by semiconducting oxides is a majorly sought technique to retain individual properties while creating a synergetic effect for an efficient heterostructure charge transfer. Three types of electronically and optically different SWCNTs: metallic (m), semiconducting (s), and pristine (p) are functionalized by ZnO using a facile sonication method. The physicochemical and morphological properties of the ZnO-functionalized SWCNTs, m-SWCNT+ZnO, s-SWCNT+ZnO, and p-SWCNT+ZnO, are analyzed by advanced characterization techniques. Evidence of charge transfer between SWCNT and ZnO is observed with an increase in charge carrier lifetime from 3.31 ns (ZnO) to 4.76 ns (s-SWCNT+ZnO). To investigate the optimum interaction between SWCNTs and ZnO, critical coagulation concentrations (CCC) are determined using UV–vis absorption spectroscopy for m-SWCNT, s-SWCNT, and p-SWCNT using different molar concentrations of ZnO as the coagulant. The interaction and coagulation mechanisms are described by the modified DLVO theory. Due to the variation in dielectric values and electronic properties of SWCNTs, the CCC values obtained have differed: m-SWCNT (1.9 × 10–4), s-SWCNT (3.4 × 10–4), and p-SWCNT (2 × 10–4). An additional analysis of the aggregates and supernatants of the CCC experiments is also shown to give an insight into the interaction and coagulation processes, explaining the absence of influence exerted by sedimentation and centrifugation.

Predicting the structure configuration and Raman analysis of caffeine molecules encapsulated into single-walled carbon nanotubes: Evidence for charge transfer

A new hybrid nano-system constituted of a single-walled carbon nanotube (SWNT) filled by caffeine (Caff) molecule(s) is proposed as a potential candidate for organic solar cells. The stability of this hybrid system with either a single or two Caff molecule(s) encapsulated into SWNTs has been investigated. In particular, the optimal SWNT diameter is discussed for each configuration. Raman spectra have been calculated using an approach combining the density functional theory, molecular mechanics, bond polarizability model and the spectral moment’s method. We have analyzed the influence of the nanoconfinement on the Raman-active modes of Caff molecule and those of SWNT. The analysis of the nanoconfinement effect on the Raman active modes of Caff molecules and those of SWNTs (radial breathing mode (RBM) and tangential mode (TM)) confirm the structural stability and indicate an evidence for a charge transfer between the Caff molecules and the nanotubes.

Photoexcitation dynamics in hybrid associates of Ag2S quantum dots with methylene blue

The dynamics of electronic excitations in hybrid associates of Ag2S quantum dots with methylene blue (MB) molecules are studied by femtosecond transient absorption spectroscopy and nanosecond time-resolved spectroscopy. The situation is considered where the relative positions of the energy levels of the associate components allow photoinduced charge transfer. The luminescence quenching for MB+ cations and Ag2S quantum dots in the hybrid associates provides evidence for charge transfer, which is accompanied by a quick return of MB+ to the ground state (absorption is recovered). We propose that there is electron transfer from the MB LUMO level to the energy level of the luminescence center in the quantum dot. In this case, the bleaching band with a peak at 590 nm corresponding to the MBOH· form of the dye is formed at a subpicosecond time scale. The corresponding decay time is about 100 ps.

The investigation of 2D monolayers as potential chelation agents in Alzheimer’s disease

In this study, we conducted density functional theory calculations comparing the binding energy of the copper-amyloid-β complex to the binding energies of potential chelation materials. We used the first-coordination sphere of the truncated high-pH amyloid-β protein subject to computational limits. Binding energy and charge transfer calculations were evaluated for copper’s interaction with potential chelators: monolayer boron nitride, monolayer molybdenum disulfide, and monolayer silicene. Silicene produced the highest binding energies to copper, and the evidence of charge transfer between copper and the monolayer proves that a strong ionic bond is present. Although our three monolayers did not directly present chelation potential, the absolute differences between the binding energies of the silicene binding sites and the amyloid-β binding sites were minimal, proving that further research in silicene chelators may be useful for therapy in Alzheimer’s disease.

Evidence for charge transfer and proximate magnetism in graphene– α−RuCl3 heterostructures

We report a study of electronic transport in van der Waals heterostructures composed of flakes of the antiferromagnetic Mott insulator a-RuCl_3 placed on top of monolayer graphene Hall bars. While the zero-field transport shows a strong resemblance to that of isolated graphene, we find a consistently $p$-type Hall effect suggestive of multiband conduction, along with a non-monotonic and gate-voltage-dependent excursion of the resistivity at low temperatures that is reminiscent of transport in the presence of a magnetic phase transition. We interpret these data as evidence for charge transfer from graphene to a-RuCl_3 in an inhomogeneous device yielding both highly- and lightly-doped regions of graphene, while the latter shows a particular sensitivity to magnetism in the a-RuCl_3. Thus proximity to graphene is a means to access magnetic properties of thin layers of magnetic insulators.

2-Amino-6-methylpyridinium nitrophenolate nitrophenol

Organic co-crystals fashioned with two or more different constituents through intermolecular non-covalent interactions (hydrogen and halogen bonds) gain cumulative research considerations as of their applications in ambipolar charge transport, nonlinear optics (NLO), light-driven actuator, liquid crystal material and electronics industry. In this contribution, charge-transfer (CT) interactions and the corresponding physicochemical and nonlinear properties of bulk organic, CT co-crystal of 2-amino-6-methylpyridinium nitrophenolate nitrophenol (2A6MPNN) were comprehensively investigated. CT crystals were fabricated by the facile solvent evaporation strategy and crystallized with an extensive hydrogen bonding network existed between the aromatic donor (D) and acceptor (A). The organic salt formation of phenol–pyridine co-crystal was investigated by using 1H NMR, 13C NMR and FTIR. More importantly, we show that the CT interactions in co-crystals are related to their molecular packing which eventually leads to distinct optoelectronic properties. The convincing evidence for multiple CT was found by UV–Vis spectral measurements, i.e., both π–π and n–π* interactions (between 4-nitrophenol and 2-amino-6-methylpyridine) are simultaneously present and additionally new feature band arises at 408 nm. Remarkably, upon photoexcitation at 374 nm in the solid state, CT displays an unusual emission around 572 nm, which is probably attributed for the shallow traps of the ion pairs, along with a usual phenolate-centered green emission. Thermal analysis was performed using TG/DTA/DSC and Modulated DSC studies. NLO response on CT powder (for diverse particle sizes) indicates a phase matchability and NLO coefficient about 1.8-fold larger than that of urea.

Evidence for Charge Transfer at the Interface between Hybrid Phosphomolybdate and Epitaxial Graphene.

The interfacing of polyoxometalates and graphene can be considered to be an innovative way to generate hybrid structures that take advantage of the properties of both components. Polyoxometalates are redox-sensitive and photosensitive compounds with high temperature stability (up to 400 °C for some), showing tunable properties depending on the metal incorporated inside the complex. Graphene has a unique electronic band structure combined with good material properties for electrical and optical applications. The spontaneous, rather than electrochemical, functionalization of epitaxial graphene on SiC with Keggin phosphomolybdate derivative TBA3[PMo11O39{Sn(C6H4)C≡C(C6H4)N2}] (named K(Mo)Sn[N2(+)]) bearing a phenyl diazonium unit is investigated. Graphene decoration is evidenced by means of AFM, Raman, XPS, and cyclic voltammetry, indicating a successful immobilization of the polyoxomolybdate. The covalent bonding of the polyoxometalate to the graphene substrate can be deduced from the appearance of a D band in the Raman spectra and from the loss of mobility in the electrical conduction. High-resolution XPS spectra reveal an electron transfer from the graphene to the Mo complex. The comparison of charge-carrier density measurements before and after grafting supports the p-type doping effect, which is further evidenced by work function UPS measurements.

Double electron excitation in He ions interacting with an aluminum surface

Observation of Auger electron emission from Al under the impact of He ions, at energies below the excitation threshold of Al-Al collisions, gives evidence for charge transfer in He-Al collisions. Excitation of $2p$-shell electrons in Al is produced by vacancy transfer, following double excitation of He by promotion of its $1s$ level. Studies of ion scattering from surfaces currently neglect the double excitation of He. We discuss implications on the debate about electronic excitations and energy deposition, which is relevant to many fields, since helium ions are applied in the characterization and imaging of materials.

Understanding Solvent Effects on the Properties of Two-Dimensional Transition Metal Dichalcogenides.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have emerged as attractive direct bandgap semiconducting materials with remarkable properties. Recently, TMDC-based electronic and optoelectronic systems have been demonstrated with various chemical doping and functionalization approaches for modulating their physical properties and enhancing device performances. However, the dependence of intrinsic properties of TMDCs on diverse solvents, which are used necessarily in fabrication processes and chemical doping, remains largely unaddressed. Here we report a charge transfer mechanism in TMDCs by commonly used solvents such as chloroform, toluene, acetone, and 2-propanol, which significantly changes the physical properties of monolayer MoS2 and WSe2. We find that the relative difference in electronegativity between solvents and TMDCs drives the transfer of electrons from or to the TMDCs, which results in photoluminescence (PL) enhancement or quenching depending on the change of carrier density in TMDCs. The analysis of exciton and trion spectral weights in MoS2 as a function of solvent electronegativity provides evidence of charge transfer. Finally, conductive atomic force microscopy (C-AFM) on TMDCs before and after immersion in the solvents further supports the charge transfer mechanism and resulting changes in carrier density. Our results highlight the importance of selection of solvents for solution-processed 2D TMDC devices and systems.

Evidence for charge transfer from hydrogen molecular ions to copper atoms in a neon–hydrogen analytical glow discharge

We show initial evidence that analyte atoms can be ionized by asymmetric charge transfer (ACT) process involving molecular ions, (M2+-ACT) in analytical glow discharges.

First-Principles, Physically Motivated Force Field for the Ionic Liquid [BMIM][BF4

Molecular simulations play an important role in establishing structure-property relations in complex fluids such as room-temperature ionic liquids. Classical force fields are the starting point when large systems or long times are of interest. These force fields must be not only accurate but also transferable. In this work, we report a physically motivated force field for the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) based on symmetry-adapted perturbation theory. The predictions (from molecular dynamics simulations) of the liquid density, enthalpy of vaporization, diffusion coefficients, viscosity, and conductivity are in excellent agreement with experiment, with no adjustable parameters. The explicit energy decomposition inherent in the force field enables a quantitative analysis of the important physical interactions in these systems. We find that polarization is crucial and there is little evidence of charge transfer. We also argue that the often used procedure of scaling down charges in molecular simulations of ionic liquids is unphysical for [BMIM][BF4]. Because all intermolecular interactions in the force field are parametrized from first-principles, we anticipate good transferability to other ionic liquid systems and physical conditions.

Visualized method of chemical enhancement mechanism on SERS and TERS

We review our developed visualization method of charge transfer (CT) for chemical enhancement mechanism on surface‐enhanced Raman scattering (SERS) and tip‐enhanced Raman spectroscopy (TERS). Firstly, we describe our visualization method of charge difference density, which provides direct visual evidence for photoinduced CT. And then, using the visualization method of CT, we interpreted the mechanism of SERS and TERS. Photoinduced charge transfer in the processes of SERS and TERS can be clearly seen. Our visualization method provides a visual and easy understanding way for the mechanism of SERS and TERS. Copyright © 2014 John Wiley & Sons, Ltd.

Charge transfer in rare earth oxide hybrid solar cells

Hybrid inorganic–organic solar cells typically combine a transition metal oxide and organic absorber to form the donor–acceptor pair. Here, we explore the use of a rare earth oxide to function as the inorganic component of a hybrid solar cell. Oxidized neodymium (Nd2O3) particles are combined with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) to form the solar cell active layer. The short circuit current and open circuit voltage are both enhanced compared to pure PCBM. In addition, the photoinduced absorption decay rate increases, and photobleaching is observed. This provides evidence for charge transfer between the organic and rare earth inorganic components.

Thermal/electron irradiation assisted coalescence of Sc3N@C80 fullerene in carbon nanotube and evidence of charge transfer between pristine/coalesced fullerenes and nanotubes

Sc3N@C80 fullerenes are inserted inside carbon nanotubes (CNTs). The results show that the thermal stability of Sc3N@C80 fullerenes is around 1200 °C for the fullerenes resting on the wall of CNTs. Internal fullerenes show stability up to 1300 °C, which portrays them as one of most stable types of fullerenes. Electron irradiation of the peapods at 90 kV leads to the formation of capsules inside the CNTs at 5 × 10(9) e nm(-2) electron dosage. This value is an order of magnitude higher than the threshold of electron-induced damage in C60 molecules. Electron energy loss spectroscopy confirms the presence of Sc atoms in capsules. Encapsulation of fullerenes and capsule formation changes the oxidation state of Sc atoms from +2.5 towards +3. This is an evidence of charge transfer between the fullerene/capsule cage and CNT walls.

Molecular structures of antitumor active Pd(II) and Pt(II) complexes of N,N-donor benzimidazole methyl ester

[MLCl2] · zH2O · C2H5OH (L = 2-[(1H-benzimidazol-2-ylmethyl)-amino]-benzoic acid methyl ester; M = Pd, z = 2; M = Pt, z = 0) complexes were synthesized as potential antitumor compounds and their structures were elucidated by elemental analysis and spectroscopic data. Theoretical molecular structures were investigated by the DFT/B3LYP method using the LANL2DZ basis set. The calculated molecular parameters, bond distances, and angles, revealed a square-planar geometry around the metal through pyridine-type nitrogen (Npy) of benzimidazole and the secondary amino group (NHsec). The lone pair interaction LP(2)O48 of ethanol with anti-bonding σ*(C(16)–H(29)) is an evidence for charge transfer from ethanol to platinum. The electronic movement and assignment of electronic spectra were carried out by TD-DFT calculations. The ligand in comparison to its metal complexes was screened for antibacterial activity and cytotoxicity.