Induced Charge Transfer Research Articles

Charging of Gold Atoms on Doped MgO and CaO: Identifying the Key Parameters by DFT Calculations

The use of transition metals (TM) as dopants is a versatile way to change the properties of oxides. One example is the possibility to induce charge transfer from the TM to species adsorbed on the oxide surface. In the case of wide-gap alkaline-earth oxides, such as MgO and CaO, the charge transfer is determined by the respective position of the energy levels of the impurity and the adsorbate and resides in the capability of the TM to be stabilized in various oxidation states. The structural and electronic properties of Cr- and Mo-doped MgO and CaO are investigated by density functional theory (DFT) calculations. Because of limitations of DFT in the description of band gaps and energy levels alignment, we compare the results obtained with standard GGA, GGA+U, and hybrid exchange-correlation functionals. The ability of the impurity ion to transfer one electron to the adsorbed species is considered for the case of electronegative Au adatoms. The study of the thermodynamic stability of the TM ions in combination with the formation of cation vacancies shows that Mo impurities are stable in the oxide lattice as Mo3+ or Mo4+ but can assume also higher oxidation states and are therefore able to transfer electrons to adsorbed gold. Conversely, Cr impurities are stabilized as Cr3+ and the high cost of further oxidation results in the absence of charge transfer to gold on both Cr-doped MgO and Cr-doped CaO.

Facile Modulation of Optical Properties of Diketonate-Containing Polymers by Regulating Complexation Ratios with Boron

We present the facile modulation of the optical properties of the conjugated polymers via polymer reactions. The polymers composed of diketonate and fluorene were prepared, and boron complexation was performed after polymer synthesis. By changing feed ratios of BF3·Et2O, which is a reagent to produce a boron diketonate complex, the series of polymers with various complexation ratios with boron at the diketonate unit can be obtained. These synthesized polymers showed diverse optical properties. In the solution states, the quantum yields of emission were greatly changed by the complexation ratios with boron. Accordingly, the polymers with complexation ratio of 21% present the largest intensity. In addition, the emission color can be tuned by changing the complexation ratios in the films. From blue to orange, the emissions were achieved. It was revealed that induced charge transfer between fluorene and boron diketonate should be the main path for the emission of the synthesized polymers.

Evolution of the thermoelectric performance in low Ca-doped layered cobaltite Bi2Sr2Co2Oy

We have synthesized a series of layered cobaltite Bi2Sr2−xCaxCo2Oy (0≤x≤0.3). Reduced resistivity was observed with x≤0.2 due to the possible chemical pressure induced charge transfer between the Bi2Sr2O4 layer and CoO2 layer. Enhanced thermoelectric power S was also observed in the Ca-doped samples with the largest S as for x=0.2. The variation of S(T) could reflect the change of electronic correlation or the modification of local density of states and band structure near the Fermi energy. In addition, magnetic measurements show that the samples with x=0.0 exhibit abnormal and abrupt changes, revealing a possible thermally excited spin-state transition. It is found that the thermoelectric performance is obviously enhanced by the low Ca-doping.

Facile UV-healable polyethylenimine–copper (C2H5N–Cu) supramolecular polymer networks

This study focuses on the development of facile polyethylenimine–copper (C2H5N–Cu) supramolecular polymer networks which upon mechanical damage are capable of reversible UV-induced self-repairs by the reformation of Cu–N coordination bonds. The chemical changes responsible for self-healing that leads to network remodeling include the formation of C2H5N–Cu complexes which, upon UV absorption, induce charge transfer between σ(N) bonding and dx2–y2(Cu) antibonding orbitals. The primary structural component responsible for network remodeling is the C2H5N–Cu coordination complex center that, upon UV exposure, undergoes square-planar-to-tetrahedral (D4h → Td) transition. The energy difference between dx2–y2 and dxz/yz orbitals during process change decreases significantly, enabling the σ(N) → dx2–y2(Cu) charge transfer and leading to energetically favorable Cu–N geometries. Manifested by virtually no temperature changes during UV-initiated self-healing, a unique feature of this network is the high efficiency of the damage–repair cycle resulting from the reversible conversion of electromagnetic radiation to chemical energy.

退火温度对聚对苯乙炔MOPPV-ZnSe量子点复合材料太阳电池性能影响

According to high photoelectric conversion performance of quantum dot composite material,we use in situ condensation method to prepare polymer / poly( 2-methoxyl-5-octyloxy)-1,4-phenylenevinylene( MOPPV)-ZnSe quantum dot composites. X-ray diffraction,transmission electron microscope,UV-Vis absorption spectroscopy were employed to study their characteristics. The results indicate that MOPPV and ZnSe quantum dots forming a coating or mosaic structure which can be effectively combined,and ZnSe quantum dots keep good crystallinity,each with an average size of 4 nm in the composite,producing the light induced charge transfer phenomenon. The absorption spectra of the composite have a few red-shift with the increasing of the annealing temperature. The study of composite photoelectric performance indicates that it gradually shows obvious characteristic of diode,the power conversion efficiency reaches the maximum of 0. 3726% at the temperature of 160 ℃.

Polyimide memory: a pithy guideline for future applications

Polymeric materials for use in memory devices have attracted significant scientific interest due to their several advantages, such as low cost, solution processability, high mechanical strength, and possible development of three-dimensional stacking devices. Taking into account the heat resistance for the device fabrication process, polyimides (PIs) are one of the most attractive polymers for memory applications due to their high thermal stability and mechanical strength. In recent years, a large number of studies have revealed that almost all kinds of memory properties from volatile to non-volatile memory can be produced by optimizing the chemical structure of the PIs. Several mechanisms have been discussed in order to explain the switching properties. Among them, two major theories, field induced charge transfer (CT) and filament formation, are thought to explain the phenomena in the PI system. In this article, recent studies of functional polyimides (PIs) for memory applications are reviewed, mostly focusing on the mechanism underlying the switching phenomena. In addition, some progress in the fabrication process for developing high density storage will also be reviewed.

Effect of carbon nanotubes on the properties of polymer MOPPV-PbSe quantum dot composites

According to single-walled carbon nanotube good conductivity, baryon transmission performance, and high photoelectric conversion performance of quantum dot composite material, in this letter, we use in situ condensation method to prepare polymer/poly (2-methoxy, 5-oc-toxy)-1, 4-phenylenevinylene (MOPPV)-single walled carbon nanotubes/PbSe quantum dot composites and use X-ray diffraction, transmission electron microscope, UV-vis absorption spectroscopy to study their characteristics. The results indicate that MOPPV, SWNT and PbSe quantum dots can be effectively combined, especially the SWNT and MOPPV form a network structure in MOPPV matrix, and PbSe quantum dots, each with an average size of 5.75 nm, can be dispersed to form a coating or mosaic structure in the polymer substrate of MOPPV-SWNT, producing the light induced charge transfer phenomenon. The study of composite photoelectric performance shows that when the polymer MOPPV, SWNT, PbSe have their mass ratio of 1: 0.3: 1, the composite photoelectric performance is best: open circuit voltage is 0.556 V, short circuit current is 2.133 mA, fill factor is 34.48%, conversion efficiency is 0.452%. Compared with the polymer MOPPV-PbSe quantum dots composite materials, the optoelectronic properties are increased by 2-3 times.

STRUCTURAL, ELECTRONIC AND OPTICAL PROPERTIES OF THIOPHENE AND THIENOTHIOPHENE CONTAINING DIKETO-PYRROLO-PYRROLES (DPPs) IN POLAR APROTIC SOLVENTS

Thiophene (T) and thienothiophene (TT) containing 2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione (DPP) compounds were prepared according to the succinic ester route from the corresponding heterocyclic nitrile precursors. As is typical of most DPP pigments, the new compounds showed high thermal stability and could be obtained in pure form as determined by elemental analysis. The bulk properties and molecular structure of the compounds were further characterized by thin film, powder XRD and solid state CP-MAS 13 C NMR. Density functional theory (DFT) and time-dependent (TD) DFT were employed to study the geometric and electronic structures of these molecules in the ground state. The optical properties were investigated by UV-Vis absorption and fluorescence spectroscopies in dimethylsulfoxide (DMSO) and N,N-dimethylacetamide (DMA), which revealed that the absorption maximum of the thiophene diketo-pyrrolo-pyrroles (TDPP) and thienothiophene diketo-pyrrolo-pyrroles (TTDPP) in solution were red shifted up to 25 nm and 60 nm, respectively, relative to Pigment Red 255 (PhDPP), while a new absorption band appeared at longer wavelengths in N-methyl pyrolidone (NMP) and N,N′-dimethylpropylene urea (DMPU) which is ascribed to solvent induced charge transfer (CT) complex. The molecular conformations and absorption spectra of TDPP and TTDPP were characterized by quantum chemical methods in order to better understand the observed behavior.

A tetrastable naphthalenediimide: anion induced charge transfer, single and double electron transfer for combinational logic gates

Herein we demonstrate the formation of the first tetrastable naphthalenediimide (NDI, 1a) molecule having multiple distinctly readable outputs. Differential response of 1a to fluoride anions induces intramolecular charge transfer (ICT), single/double electron transfer (SET/DET) leading to a set of combinational logic gates for the first time with a NDI moiety.

Fowler–Nordheim Tunneling Induced Charge Transfer Plasmons between Nearly Touching Nanoparticles

Reducing the gap between two metal nanoparticles down to atomic dimensions uncovers novel plasmon resonant modes. Of particular interest is a mode known as the charge transfer plasmon (CTP). This mode has been experimentally observed in touching nanoparticles, where charges can shuttle between the nanoparticles via a conductive path. However, the CTP mode for nearly touching nanoparticles has only been predicted theoretically to occur via direct tunneling when the gap is reduced to ~0.4 nm. Because of challenges in fabricating and characterizing gaps at these dimensions, experiments have been unable to provide evidence for this plasmon mode that is supported by tunneling. In this work, we consider an alternative tunneling process, that is, the well-known Fowler-Nordheim (FN) tunneling that occurs at high electric fields, and apply it for the first time in the theoretical investigation of plasmon resonances between nearly touching nanoparticles. This new approach relaxes the requirements on gap dimensions, and intuitively suggests that with a sufficiently high-intensity irradiation, the CTP can be excited via FN tunneling for a range of subnanometer gaps. The unique feature of FN tunneling induced CTP is the ability to turn on and off the charge transfer by varying the intensity of an external light source, and this could inspire the development of novel quantum devices.

Dual-Mechanism-Controlled Ternary Memory Devices Fabricated by Random Copolymers with Pendent Carbazole and Nitro-Azobenzene

In the designed copolymers of poly(9-(4-vinyl benzyl)-9H-carbazole) (PVCz)-random-poly(1-(4-nitro-azo-phenyl)-pyrrole-2, 5-dione) (PMIDO3), carbazole donor and nitro-azobenzene acceptor are introduced into the lateral chains to induce charge transfer under an electric field, and the resulting copolymers have a progressive increase in the nitrogen content to induce filamentary conduction. The fabricated devices with a simple sandwich configuration distinctively exhibit three conductivity states when a negative bias is applied which can be encoded as “0”, “1” and “2” for future ternary data storage. The fabricated devices could endure 108 read cycles and showed a long retention time of 104 s. It is worth noting that the switch-OFF voltages and the OFF-currents are significantly affected by the MIDO3 content within the polymers. The experimental results indicate that charge transfer between the donor and acceptor is responsible for the first switching and the second switching can be attributed to the filamentary rupture. This approach of achieving devices with multistable states through combination of different switching mechanisms in one device may provide a framework for the design and selection of multilevel electrical memory materials in future research.

Enhancement of infrared absorption of biomolecules absorbed on single-wall carbon nanotubes and graphene nanosheets

Surface-enhanced infrared absorption effect was shown for graphene for the first time. Comparative analysis of the effect was carried out for thymine (Thy), one of the bases of DNA, absorbed on single-wall carbon nanotubes (SWCNT) and graphene sheets. The enhancement factor in the case of SWCNT was generally greater in comparison with that obtained for graphene sheets. Its value for SWCNT was up to six and the largest enhancement factors were found for vibrations of CH, C−OH , and C−N bonds. The maximum enhancement factor in the case of graphene sheets equal to 3.7 was found for ring and deformational vibrations of N-H bonds. The obtained experimental data allowed us to suppose that H-bonds influence the interaction between SWCNT and Thy in Thy-SWCNT/Au, while the chemically induced charge transfer is probably dominant in the case of Thy-graphene/Au.

Disorder induced semiconductor to metal transition and modifications of grain boundaries in nanocrystalline zinc oxide thin film

This paper report on the disorder induced semiconductor to metal transition (SMT) and modifications of grain boundaries in nanocrystalline zinc oxide thin film. Disorder is induced using energetic ion irradiation. It eliminates the possibility of impurities induced transition. However, it is revealed that some critical concentration of defects is needed for inducing such kind of SMT at certain critical temperature. Above room temperature, the current-voltage characteristics in reverse bias attributes some interesting phenomenon, such as electric field induced charge transfer, charge trapping, and diffusion of defects. The transition is explained by the defects induced disorder and strain in ZnO crystallites created by high density of electronic excitations.

Identifying the magnetoconductance responses by the induced charge transfer complex states in pentacene-based diodes

We investigate the magnetoconductance (MC) responses in photocurrent, unipolar injection, and bipolar injection regimes in pentacene-based diodes. Both photocurrent and bipolar injection contributed MC responses show large difference in MC line shape, which are attributed to triplet-polaron interaction modulated by the magnetic field dependent singlet fission and the intersystem crossing of the polaron pair, respectively. By blending 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane into pentacene, all the MC responses are suppressed but the MC response at unipolar injection regime is enhanced, which is attributed to the induced charge transfer complex states (CT complex states). This work identify the MC responses between single carrier contributed MC and exciton related MC by the induced CT complex states.

Electrochemically induced charge transfer in platinum–silicon heterosystems

AbstractElectrochemical cyclovoltammetry experiments were carried out on the platinum surface of a platinum–silicon thin‐film device in sulfuric acid. The internal electronic barrier of the device allows the separation of ground state and excited state charge transfer events released by the electrochemical surface reaction. The traces of the device current show similar features as the cyclovoltammogram and can be discussed in terms of small deviations from the equilibrium state of the thin platinum film. The device current plotted as a function of the electrode potential shows a well‐defined shift of the baseline when hydrogen is adsorbed. This baseline shift may be originated by an adsorbate‐induced change of the chemical potential of the platinum film, thus influencing the internal field in the device (up to values of 23 mV).magnified imagePlot of the electrochemical current and the device current as functions of the electrode potential.

Memory and Photovoltaic Elements in Organic Field Effect Transistors with Donor/Acceptor Planar-Hetero Junction Interfaces

Interfacial charge transfer at organic/organic planar-hetero junctions allows access to device structures that create new opportunities for flexible electronic devices. Fundamental characteristics of a pentacene/[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) interface are explored via a comprehensive study of charge transfer between these two materials using the field-effect transistor (FET) geometry both in the dark and under illumination. Organic memory elements in a field effect transistor are demonstrated for a device fabricated with a pentacene/PCBM interface. Electric field induced charge transfer at the interface, in the dark, induced a nonvolatile memory effect with a large hysteresis characterized by a memory window of 43 V in the transfer characteristics. A photoinduced threshold voltage shift induced by exciton dissociation at the interface, in the absence of a gate electric field, is consistent with the formation of the photoinduced conducting channel in pentacene.

Growth Dynamics of Photoinduced Phase Domain in Cyano-Complex Studied by Boundary Sensitive Raman Spectroscopy

Rubidium manganese hexacyanoferrate exhibits charge transfer phase transition from high temperature phase to low temperature phase at 230 K. This phase transition can also be triggered by light irradiation resonantly inducing charge transfer from Mn to Fe. In the present study, boundary sensitive Raman spectroscopy was performed for Rb0.94Mn[Fe(CN)6]0.98·0.2H2O in both cases of photoinduced and thermal phase transition. Since the frequencies of C≡N stretching vibration modes are very sensitive to the valence states of the adjacent metal ions, we can quantify the distribution of not only high and low temperature phase but also boundary configurations from the observed spectra. We obtained the time evolution of the fraction ratios of the valence states from the observed peak areas. In the case of photoinduced situation, the boundary increases up to 15% when high temperature phase diminishes to 55% of the initial fraction. This is quite different from the result in thermal phase transition where the boundary is created only 0.8% at the same high temperature phase fraction value. We conclude that many small domains are preferably created in photoinduced phase transition since the ratio of boundary is large, while large domains grow in thermal phase transition.

Femtosecond laser field induced modifications of electron-transfer processes in Ne+-He collisions

We demonstrate the presence of femtosecond laser induced charge transfer in Ne+-He collisions. Electron transfer in ion-atom collisions is considerably modified when the collision is embedded in a strong laser field with the laser intensity of ∼1015 W/cm2. The observed anisotropy of the He+ angular distribution confirms the prediction of early work that the capture probability varies significantly with the laser polarization angle.

Electrical transport of SiNWs array after covalent attachment of new organic functionalities

Modification of the electrical transport of a random network of silicon nanowires assembled on n-silicon support, after silicon nanowires functionalization by chlorination/alkylation procedure, is here described and discussed. We show that the organic functionalities induce charge transfer at single SiNW and produce doping-like effect that is kept in the random network too. The SiNWs network also presents a surface recombination velocity lower than that of bulk silicon. Interestingly, the functionalized silicon nanowires/n-Si junctions display photo-yield and open circuit voltages higher than those including oxidized silicon nanowire networks. Electrical properties stability in time of junctions embedding propenyl terminated silicon nanowires network and transport modification after secondary functionalization is also shown. These results suggest a possible route for the integration of functionalized Si nanowires, although randomly distributed, in stable large area photovoltaic or molecule sensitive based devices.

High-precision imaging of an encapsulated Lindqvist ion and correlation of its structure and symmetry with quantum chemical calculations

Low-voltage aberration-corrected transmission electron microscopy (AC-TEM) of discrete Lindqvist [W(6)O(19)](2-) polyoxometalate ions inserted from an ethanolic solution of [NBu(4)](2)[W(6)O(19)] into double walled carbon nanotubes (DWNTs) allows a higher precision structural study to be performed than previously reported. W atom column separations within the constituent W(6) tungsten cage can now be visualized with sufficient clarity that reliable correlation with structural predictions from density functional theory (DFT) can be achieved. Calculations performed on [W(6)O(19)](2-) anions encapsulated in carbon nanotubes show good agreement with measured separations between pairs of W(2) atom columns imaged within equatorial WO(6) polyhedral pairs and also single W atom positions located within individual axial WO(6) octahedra. Structural data from the tilted chiral encapsulating DWNT were also determined simultaneously with the anion structural measurements, allowing the influence of the conformation of the encapsulating tubule to be included in the DFT calculation and compared against that of other candidate encapsulating nanotubes. Additional DFT calculations performed using Li(+) cations as a model for the [NBu(4)](+) counterions indicate that the latter may help to induce charge transfer between the DWNT and the [W(6)O(19)](2-) ion and this may help to constrain the motion of the ion in situ.