Showing papers by "Anvar A. Zakhidov published in 1994"
24 Jul 1994
TL;DR: In this article, the electrical and optical properties of both poly( p -phenylene) (PPP) and PPP-C 60 films prepared by evaporation methods have been studied in detail.
Abstract: Electrical and optical properties of both poly( p -phenylene) (PPP) and PPP-C 60 films prepared by evaporation methods have been studied in detail. Fluorescence and electroluminescence of PPP have been found to be influenced by incorporated C 60 . Photoconductivity and junction characteristics of PPP and PPP-C 60 have also been clarified.
41 citations
TL;DR: In this article, two other examples of such photocells in RO-PPV/C60 and PPP/C 60 heterojunctions and study their spectral characteristics are presented.
Abstract: We have found recently that thin film layered heterojunction between C60 and conducting polymer, like poly(3-alkylthiophene) (PAT) shows a photovoltaic effect due to photoinduced charge transfer at the interface. Here we describe two other examples of such photocells in RO-PPV/C60 and PPP/C60 heterojunctions and study their spectral characteristics. Contrary to conventional inorganic semiconductor p-n junction photocells, the C60-PAT junction can be rather viewed as molecular donor-acceptor (D-A) type photocell in which the processes of photogeneration and separation of charge carriers are quite distinct. In a p-n junction free electron-hole pairs are known to be primarily photogenerated at interband transition and then separated in the internal electric field of the barrier, while in D-A molecular photocell mainly neutral excitons are first created by light, with charges being primarily separated at the narrow interface region due to D-A type intermolecular charge transfer interactions. We analy...
28 citations
TL;DR: In this paper, the role of photoexcited polarons and charges solitons S+ in polymeric chains is discussed in terms of photo-induced charge transfer between PTMSiPA and C60.
24 citations
TL;DR: In this paper, the polarization double barrier (PDB) was introduced as a potential profile for electrons and holes at the interfaces of organic multilayered molecular structures (OMSs) due to the difference in polarization energies P of charge carriers in each layer.
23 citations
TL;DR: In this article, the effect of fullerene doping on photoluminescence in conducting polymer with non-degenerated ground state (NDGS CP) was investigated and it was shown that each C60 molecule acts as multiple trapping and recombination center for carriers.
Abstract: Earlier we found that photoluminescence (PL) in conducting polymer with non-degenerated ground state (NDGS CP) is quenched remarkably upon doping by small amount of fullerenes such as C60 and C70. Here we show that electroluminescence is quenched even much more stronger indicating that each C60 molecule acts as a multiple trapping and/or recombination center for carriers. On the other hand photoconductivity (PC) in NDGS CP and also in conducting polymer with degenerated ground state (DGS CP) such as polyacetylene derivatives is enhanced significantly upon fullerene doping at the excitation of (a) the wavelengths of the inter-band transition in conducting polymer and (b) allowed and (c) forbidden optical transitions in fullerene. Remarkable polarity effect is observed in the spectral response of enhanced photoconductivity, proving that positively charged mobile carriers in polymeric chains contribute to PC. The effect of persistent photoconductivity at room temperature is found in C60/CP (conducti...
19 citations
TL;DR: In this article, a review of Raman spectra of intramolecular and external modes in pristine and doped fullerene C 60 is given, and the expected changes of internuclear distances in the excited state of C 60 should be close to the form of the A g mode at 1468 cm −1.
15 citations
24 Jul 1994
TL;DR: In this article, self-localized excitations of conducting polymeric chain: exciton-polarous (Ex-P),solitons (S/spl deg/, S), polaron/bipolarons (P/BP) are shown to exhibit various types of interactions with the C/sub 60/ weak dopants, including charge transfer and Coulomb interactions.
Abstract: Summary form only given. Self-localized (SL) excitations of conducting polymeric chain: exciton-polarous (Ex-P),solitons (S/spl deg/, S), polaron/bipolarons (P/BP) are shown to exhibit various types of interactions with the C/sub 60/ weak dopants, (which have LUMO level within the band gap of conducting polymer) including charge transfer and Coulomb interactions. The self trapping of charges and excitation into string-type polaron/bipolarons within C/sub 60/ molecule plays important role in the stabilization of charge transfer from polymer chain to C/sub 60/ due to orientational suppression of backward electron recombination processes. We discuss the reactions of Ex-P dissociation at the neutral C/sub 60/ and the charged C/sub 60//sub -/ dopant: (Ex - P) + C/sub 60/ = P/sub +/ + C/sub 60//sub -/ , (Ex - P) + C/sub 60//sub -/ = P/sub +/ + C/sub 60//sub 2-/ as the origins for photoinduced charge transfer to C/sub 60/ with formation of charged P+s , which contribute to enhanced photoconductivity and photoluminescence quenching in C/sub 60/-doped conducting polymers. Here we analyse also other types of interactions and intercharging reactions between charged (P/BP, S) and neutral (S/spl deg/, Ex-P) excitations with P/BP on C/sub 60/ molecules intercalated between chains of conducting polymer and discuss in compsarison with our recent experimental results on electrochemically controlled charge transfer.
14 citations
TL;DR: In this paper, photo-induced charge transfer between conducting polymers and fullerenes is discussed in terms of photoinduced charges photoseparation at the interface, taking into account the excitation of the wavelengths of the interband transition.
Abstract: Photoluminescence in conducting polymer with non-degenerated ground state (NDGS CP) such as polythiophene derivatives, poly(p-phenylene vinylene) derivatives and polyfluorene derivatives is quenched remarkably upon doping by fullerenes such as C60 and C70. On the other hand photoconductivity in NDGS CP and also in conducting polymer with degenerated ground state (DGS CP) such as polyacetylene derivatives is enhanced remarkably upon fullerene doping at the excitation of the wavelengths of the inter-band transition in conducting polymer and allowed and forbidden optical transitions in fullerene. Remarkable polarity effect is observed in the spectral response of enhanced photoconductivity. Conducting polymer/C60 layer interface exhibits also unique junction characteristics demonstrating sizable photovoltaic effect due to charges photoseparation at the interface. These unique characteristics are discussed in terms of photo-induced charge transfer between conducting polymers and fullerenes, taking int...
12 citations
24 Jul 1994
TL;DR: In this paper, the C60/poly(isothianaphthene) (PITN) heterojunction device was fabricated and its electrical characteristics and photo-irradiation effects were investigated.
Abstract: The C60/poly(isothianaphthene) (PITN) heterojunction device was fabricated and its electrical characteristics and photoirradiation effects were investigated. This device has current-rectifying function. Upon photoirradiation, both forward and backward currents were enhanced, and photovoltaic effects was also appeared. These results were discussed in terms of charge transfer between C60 and PITN in the ground state and photoexcited state.
10 citations
Journal Article•
TL;DR: In this article, a review of Raman spectra of intramolecular and external modes in pristine and doped fullerene C 60 is given, and the expected changes of internuclear distances in the excited state of C 60 should be close to the form of the A g mode at 1468 cm −1.
Abstract: Abstract A review of our investigations of Raman spectra of intramolecular and external modes in pristine and doped fullerene C 60 is given. Experimental results are compared with group-theoretical predictions. In low-frequency spectra of M 6 C 60 new bands are found that we have assigned to external modes. An interpretation of M 6 C 60 external modes and lattice dynamics calculations are carried out. From an analysis of the excitation profile of resonant Raman spectra it is found that expected changes of internuclear distances in the excited state of C 60 should be close to the form of the A g mode at 1468 cm −1 . Moreover, a destructive interference of A g modes in M 3 C 60 and M 6 C 60 is observed. The essential broadening, a shift and the Fano lineshape of low-frequency intramolecular H g bands in metallic M 3 C 60 are found. A narrowing of these bands in insulating C 60 and M 6 C 60 indicates the strong electron-phonon interaction of H g Jahn-Teller modes. An estimation of the electron-phonon coupling constants for some modes is given. A possible origin of low-energy electronic excitations appearing in M 3 C 60 resonant Raman spectra at λ i = 1064 nm excitation is discussed.
10 citations
TL;DR: In this article, the evolution of superconducting phase of sodium doped C 60 prepared from sodium azide is studied upon heat treatment by means of low field signal (LFS) of microwave absorption combined with conventional ESR.
24 Jul 1994
TL;DR: In this paper, photoexcitation in both conducting polymers and fullerene, photoinduced excitons, solitons and polarons and also their transfer between conducting polymer and fullein were discussed.
Abstract: Summary form only given. Optical properties of conducting polymers such as absorption spectrum, photoluminescence, electroluminescence, photo-magnetic effect, photoconductivity and their dynamics change drastically upon doping of small amount of fullerene. Electrical and optical characteristics of junctions based on conducting polymers and fullerene are also anomalous. It should be mentioned that these unique photophysical properties and their dynamics are dependent on the molecular structure of conducting polymer (non-degenerated polymers such as polythiophene derivatives or degenerated polymers such as polyacetylene derivatives) and also on fullerenes (C60,C70,C76). These novel results are discussed in terms of photoexcitation in both conducting polymers and fullerene, photoinduced excitons, solitons, polarons and also their transfer between conducting polymers and fullerene by taking into account the electronic energy states of conducting polymers and fullerene.
TL;DR: In this paper, the IR spectra and the photoinduced absorption of polyhexylthiophene (PHT) doped with C60 were analyzed and the presence of C60 −n anions was observed by a mode at 1383 cm−1 and a broad electronic transition at 1.2 eV while most of the C60 molecules stay neutral.
Abstract: We report the IR spectra and the photoinduced absorption of polyhexylthiophene(PHT) doped with C60. The presence of C60 −n anions is observed in the IR spectra by a mode at 1383 cm−1 and a broad electronic transition at 1.2 eV, while most of the C60 molecules stay neutral. This is indicative that for a small fraction of C60 molecules, charge transfer occurs in the ground state. The photoinduced absorption spectra display a sharp transition at 1.15 eV peculiar to C60 monoanion, the spectral features change with fullerene concentration. The intensity of the polymer photoinduced bands increases 5-10 times due to photoinduced charge transfer to C60.
24 Jul 1994
TL;DR: In this article, the polarization double barrier (PDB) was proposed to increase the photoseparation efficiency of the three-layer molecular structure of the Jonor absorber acceptor (D-M-A) type.
Abstract: Summary form only given. Organic materials became recently attractive for possible application in photovoltaic devices. Either low molecular weight, molecular semiconductors, like merocyanine, or conjugated polymeric semiconductors have been demonstrated to show photovoltaic effect in various types of p-n or Schottky type devices. Recently we have demonstrated the sizable photovoltaic response in the heterojunvion of fullerene C/sub 60/ and conjugated polymer. However the efficiency of this photocells is still very low and not comparable with those of inorganic semiconducting photocell. Here we discuss one possibility to increase the photoseparation efficiency: at the interfaces of three-layered molecular structure of Jonor absorber acceptor (D-M-A) type the polarization double barriers (PDB) may appear due to difference in polarization energies of charge carriers in each layer: PD, PA/spl Lt//spl Lt/PM. Such PDBs originate in purely solid state effect and being properly combined with single molecular properties of D, A and M layers should lead to selective separation of photogenerated charge carriers enhancing the efficiency of D-M-A photocell.
TL;DR: In this article, the superconducting behavior of Ca doped C 60 prepared by calcium azide thermal decomposition is studied by low-field signal (LFS) microwave absorption and conventional ESR.
Abstract: Superconducting (SC) behavior of Ca doped C 60 prepared by calcium azide thermal decomposition is studied by low-field signal (LFS) microwave absorption and conventional ESR. SC phase is obtained for the sample prepared with nominal composition of Ca 6 C 60 and its volume fraction is significantly enlarged by annealing at 350–400°C for 2 h. It is suggested that the SC compound may have two SC phases with slightly different transition temperatures, T C1 (8.2–8.4 K) and T C2 (8.7–8.8 K). The SC 2 phase with higher T C2 is degraded by annealing at 450–500°C and converts to SC 1 . Degradation of SC 2 at high temperature is interpreted to be caused either by (1) thermal reaction of some intercalated Ca with quartz glass and/or (2) dissociation of (CaN) y or N y clusters in the octahedral sites of the Ca 5 (CaN) y C 60 or Ca 5 N y C 60 lattice.
24 Jul 1994
TL;DR: In this paper, the effects of higher fullerenes such as C 70 on electrical and optical properties of conducting polymers such as poly(3-alkylthiophene), poly(2,5-dialkoxy-p-phenylene vinylene) and poly(9,9-dialkylfluorene) have been studied and compared with those by C 60 doping.
Abstract: Doping effects of higher fullerenes such as C 70 on electrical and optical properties of conducting polymers such as poly(3-alkylthiophene), poly(2,5-dialkoxy-p-phenylene vinylene) and poly(9,9-dialkylfluorene) have been studied and compared with those by C 60 doping. Fluorescence intensity was quenched and photoconductivity was enhanced upon doping of higher fullerenes in the conducting polymers just as the case of C 60 doping. However, there also exist differences in detailed aspects in quenching of photoluminescence and enhancement of photoconductivity between C 60 doping and higher fullerenes dopings. These results are interpreted by taking into account the electronic energy states of C 60 and higher fullerenes.
TL;DR: In this paper, the ground state of the polaronic state in a quasi-one-dimensional polymer via local hopping at the points of the closest interchain separation was investigated with a discrete two-chain model, which can be applicable also to the strong electron-phonon coupling and small radius polaron case.
TL;DR: In this article, the authors investigated hydrogen uptake effects on the properties of metallic K 3 C 60 by means of ESR and superconductivity measurements and showed that superconductivities are not influenced by hydrogen uptake.
24 Jul 1994
TL;DR: In this paper, a thermal decomposition of CaN6 and the evolution of its superconducting properties by low field (LFS) microwave absorption and conventional ESR was studied.
Abstract: Summary form only given. We have prepared C/sub ax/C/sub 60/ by thermal decomposition of CaN6 and studied the X-evolution of its superconducting properties by low field (LFS) microwave absorption and conventional ESR. Superconducting phase is found at x=5 and also x=6 (with lower fraction) with Tc = 8.4-8.8K. The results of the annealing at different temperature (300-450 /spl deg/C) and of aging effect on the intensity of LFS (and hence the amount of superconducting fraction) and ESR g-value and linewidths are presented. Preliminary results on the C/sub 13/ isotope effect on superconducting T/sub c/ in C/sub a5/C/sub 60/ are also discussed.
TL;DR: In this article, the isotope effect on the superconducting transition temperature is reexamined in the model proposed by Chakravarty et al. where phonons modulate the electron-electron attraction energy on molecules.
Abstract: The isotope effect on the superconducting transition temperature is reexamined in the model proposed by Chakravarty et al. where phonons modulate the electron-electron attraction energy on ${\mathrm{C}}_{60}$ molecules. We find additional contributions to the effective interaction that increase the magnitude of the isotope shift. One of these contributions, which is nonadiabatic, has a stronger dependence on the intermolecular motion of electrons, which could result in an enhanced isotope effect in disordered samples.
24 Jul 1994
TL;DR: In this paper, the thermal stability of superconducting sodium-nitrogen-C 60 compound prepared from sodium azide has been studied after high temperature treatment by means of low-field signal of microwave absorption(LFS).
Abstract: Thermal stability of superconducting sodium-nitrogen-C 60 compound prepared from sodium azide has been studied after high temperature treatment by means of low-field signal of microwave absorption(LFS). The LFS amplitude decreased in a short time by high temperature (350∼400°C) annealing. The critical temperature Tc decreased smoothly from about 16K down to zero, indicating continuous change of superconducting composition and the average lattice constant.
24 Jul 1994
TL;DR: In this paper, diffusion-limited reactions of A + B /spl rarr/ 0 type on one-dimensional lattice (10E5 sites with PBC ) in the presence of particle source ( photogeneration of unlike charged solitons ) has been studied by using of proposed biased random walking model.
Abstract: Summary form only given. Diffusion-limited reactions of A + B /spl rarr/ 0 type on one-dimensional lattice ( 10E5 sites with PBC ) in the presence of particle source ( photogeneration of unlike charged solitons ) has been studied by using of proposed biased random walking model. The particles distribution has been studied by using of pair-correlation functions. The dependences of steady-state concentrations and relaxation times on the system parameters - rate of photogeneration, external electric field have been obtained. The phenomenon of stochastic aggregation of unlike charged particles has been found in case of random initial particles distribution. The results have been compared with analytical and experimental data on photoinduced conductivity in oriebted (CH)/sub x/.
TL;DR: In this paper, weak dopants, such as C60, may provide various types of interactions with self-localized excitations of conducting polymer (CP) chains: solitons (S), polaron/bipolarons (P/BP) or excitonpolarons (Ex), whose electronic levels are also located deeply inside the gap.
Abstract: Weak dopants, like C60, (which have LUMO level within the band gap of conducting polymer (CP)) may provide various types of interactions with self-localized (SL) excitations of CP chain: solitons (S˚, S), polaron/bipolarons (P/BP) or excitonpolarons (Ex), whose electronic levels are also located deeply inside the gap. In the present paper we analyse some types of interactions: 1) “Chemical reaction” type charge transfer (CT) processes between charged (P/BP, S) and neutral (S˚, Ex) excitations with C60 molecules intercallated between chains of CP. We stress the important role of SL states of C60 molecule itself: string type polarons (Pc) and bipolarons BP2- c in ttie stabilisation of this reactions through reorientations of string P− c/BP2- c relatively to CP chains resulting ui suppression of backward CT recombination. 2) The C60 mediated interchain hoping of electrons is considered withitin Holstein-Rashba molecular chain polaron approximation, which allows to find exact analytical solutions for...