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We investigate the re-exciting process of a soliton, a polaron and a bipolaron in conjugated polymers. For a soliton case, the processes S0+h?S?+P and S?+h?S0+P? will take place, where S0, S? and P? express a neutral soliton, charged solitons and charged polarons, respectively. For a polaron case, the processes P?+h?P+BP?2 will occur, where BP?2 expresses a charged bipolaron with two electronic units. For a bipolaron case, the processes BP?2+h?P?+P? and BP?2+h?BP?2+E0 are obtained.

Reverse polarization in polythiophene under an applied electric field has been studied in the framework of the tight-binding model. It is found that the applied electronic field has a great influence on the excited states of polythiophene. The effect of the heteroatoms on the polarization has been calculated and analysed carefully. It is indicated that a reverse polarization of biexcitons in polythiophene will be observed more easily. The heteroatoms increase this reversed polarization strength apparently.

Polaron tunnelling is studied in xPA/nPPP/xPA (PA for polyacetylene and PPP poly (p-phenylene)) triblock copolymer, which has a well–barrier–well structure. An extended tight-binding Hamiltonian including external electric field is adopted. Without electric field, the injected electrons would not extend over the whole copolymer chain but instead be confined in the segments of PA. This is different from the behaviour of the traditional semiconductors. It is found that the polaron can transfer to the potential barrier-PPP segment when the applied electric field reaches a certain value. The critical polaron tunnelling electric fields depend upon the lengths of PPP segments.

A tight-binding calculation to describe the triblock copolymer xPA(polyacetylene)/nPPP (poly(p-phenylene))/yPA or xPPP/nPA/yPPP is presented. The interfacial coupling between homopolymer segments is attributed to the hopping of π-electrons and the coupling of σ-bonds. The dependence of the band gap of triblock copolymers on the interfacial couplings or on the composite segment lengths is studied. The influence of composite segment lengths on the electron density is also studied. For nPPP/xPA/nPPP structures, the band gap varies with PA segment length over a wide range of 1.32-2.74eV. For nPA/xPPP/nPA structures, the band gap is invariant with PPP segment length. It is found that a spontaneous tunnelling phenomenon could take place in nPA/xPPP/nPA structures. Furthermore, the polaron caused by doping an electron into nPA/xPPP/nPA will tend to be confined in one of the well (PA) parts. This kind of confinement may increase the electron-hole recombination probability.

The electronic properties of xPA/nPPP/yPA sandwiched copolymers with a well-barrier-well structure have been studied by using a tight-binding calculation. It was found that the electronic properties of the neutral states of these sandwiched copolymers are sensitive to the constitutions of PPP and PA monomers and the interface coupling between PA and PPP. It is verified that the quantum tunnelling effect will occur at the lowest conductive state of xPA/nPPP/xPA copolymers.

The stopping power of an electron gas for hydrogen ions is calculated based on the full self-consistent nonlinear density-functional frame. Three different configurations of hydrogen ions are considered and a criterion to test the validity of the self-consistent calculation is proposed. Comparison of calculation with available experimental data shows good agreement.

Chemical adsorption and desorption of hydrogen atoms on single-walled carbon nanotubes (SWNTs) are investigated by using molecular dynamics simulations. It is found that the adsorption and desorption energy of hydrogen atoms depend on the hydrogen coverage and the diameter of the SWNTs. Hydrogen-adsorption geometry at the coverage of 1.0 is more energetically stable. The adsorption energy decreases with the increasing diameter of the armchair tubes. The adsorption and desorption energy of hydrogen atoms can be modified reversibly by externally radial deformation. The averaged C-H bond energy on the high curvature sites of the deformed tube increases with increasing radial deformation, while that on the low curvature sites decreases.

The impact parameter dependence of electronic energy loss for heavy ions colliding at low velocity with atoms has been studied using the shell-wise local electron-density model. Roothaan-Hartree-Fock wave functions are used to calculate the local electron density of the atoms studied. The Brandt-Kitagawa effective stopping power charge theory is modified to incorporate the effective charge obtained using Fermi-level scattering phase shift calculations based on the density-functional formalism. The theoretical results are compared with available experimental measurements.

A molecular dynamics simulation method is used to study the growth of narrow single-wall carbon nanotubes. It is found that the growth temperature and the species of small carbon clusters in the feedstock are important for the quality of the nanotubes grown. There is a temperature range of 1000-1500 K in which the narrow armchair single-wall carbon nanotubes can grow rapidly via adduction of C2 dimers, even without the existence of catalysts. The narrow zigzag tubes cannot keep open-ended growth. If the feedstock consists of various species of carbon clusters, the tubes cannot keep open-ended growth. At higher temperatures, the narrow nanotubes close rapidly in the noncatalytic environment, and the products grown are fullerene-like capsules. PACS: 61. 46. +w, 36. 40. -c

We give a brief introduction to the oxide (ZnO, TiO2, In2O3, SnO2, etc.)-based magnetic semiconductors from fundamental material aspects through fascinating magnetic, transport, and optical properties, particularly at room temperature, to promising device applications. The origin of the observed ferromagnetism is also discussed, with a special focus on first-principles investigations of the exchange interactions between transition metal dopants in oxide-based magnetic semiconductors.

Titanium oxide ceramics doped with niobium is synthesized in reduced atmosphere at 1200 ℃ by conventional solid-state reaction technique. From their crystal structures determined by the powder X-ray diffraction(XRD), the samples have multiple-phase with low Nb concentration, but they have single tetragonal rutile phase when Nb content is larger than 0.02. The electrical conductivities, the Seebeck coefficients and the thermal conductivities of the samples with single phase are measured at a temperature range between room temperature and 900 K. The electrical conductivity and the Seebeck coefficient show non-metallic behaviors. According to the fitting, it is found that the samples show thermal-activation mechanism at low temperatures and small-polaron hopping conduction mechanism at high temperatures. Moreover, the analyses of XRD, electrical conductivity and Seebeck coefficient show that the concentration of oxygen vacancy decreases with Nb content increasing. Thermal conductivity decreases with temperature increasing, dominating by lattice thermal conductivity. In the measurement region, the figure of merit (ZT) reaches a highest value of 0.19 at 873 K in the Ti0.98Nb0.02O2- sample.

Zn1−xFexO inhomogeneous oxide magnetic semiconductor films with high Fe concentration are prepared by sputtering, and fast annealing is carried out at different temperatures. It is found that magnetic properties are greatly modulated by controlling the composition inhomogeneity and subsequently fast annealing. Both ferromagnetic and paramagnetic components are found to coexist in the as-deposited Zn1−xFexO magnetic semiconductor. In particular, the antiferromagnetic coupling between the neighbouring local ferromagnetic regions is found in the as-deposited Zn0.23Fe0.77 O film, and the antiferromagnetic coupling strength increases with increasing temperature from 110 K to 300 K. We believe that this unusual antiferromagnetic coupling is mediated by thermally activated hopping carriers.

The possibility of forming cascading energy levels in SrTiO3 by doping Bi and Cu as an example is analyzed by using the density-functional-theory based first principles calculations of the electronic structure. The results show that both Bi doping and Cu doping can introduce a defect level in the forbidden band，and Co-doping of Bi and Cu can introduce two defect levels in the forbidden band. Electrons at the top of valence band can transit to the bottom of conduction band through a cascade transition process. Using the nonradiative transition model，we point out that the probability of electronic transition from the valence band to the conduction band through a cascade transition is much higher than that of direct transition from the valence band to the conduction band. The cascade transitions can effectively increase the carrier concentration in the conduction band.

The Xα method is applied to study the spin-polarized electronic structures and atomic magnetic moments of clusters La8-xBaxCuO6 in the compound La2-yBayCuO4.This paper shows that Cu magnetic moment in La2CuO4 is 0.37μB, which is in better agreement with the experimental value(0.48±0.15μB). Ba substitution lowers the structure symmetry, removes molecular orbital degeneracy, and hence strengthens orbital hybridization and weakens quasi-two-dimensional feature, which enhance the coupling between Cu-O layer and the neighbormg layers and influence the charge transfer. These changes strongly affect the properties of carriers. Holes are introduced due to Ba substitution and they mainly enter into O sites, a few d-electronic holes enter into Cu sites, which causes important effects on the density of states, atomic magnetic moment and valence states of Cu and O in Cu-O layers. The results confirm that the holes are not always beneficial to the superconductivity. At the beginning the holes are beneficial to the superconductivity; they can decrease the superconductivity when more holes are introduced. This paper can explain that the transition temperature of high-temperature superconductive oxides changes with the variation of the doping level.

In our calculations of lattice vibration, one acoustic and three optical branche s were found to compose the phonon vibrating spectrum. Some isolated modes with frequencies lying outside the continuum branches aise under the defect states. These localized modes result in the sharp peaks in the infrared absorption and Raman spectra.

Intrinsic charge transfer in mixed halide compounds PtXxX′1-x was studied in the framework of the two-band extended Pielerls-Hubbard model. It was found that the number of transferred charges can be a fraction times of the electronic charge. The maximum amount of transferred charges occurs at a certain x for a given mixed compound.

Spin density wave in organic ferromagnets with open ends was studied and the results were compared with that in a closed organic ferromagnet ring. It was found that an end-open chain structure is unfavorable for the formation of the ferromagnetic ground. The competition of electron-electron interactions and the π-electron-radical spin couplings and their different effect on the SDW in the main chain were discussed.

The stabilities of one-dimensional conducting polymer chains with finte lengths have been studied in the frame work of the SSH tight-binding model.Three kinds of boundary conditions have been proposed to stabilize the dimerized structure of the chains.It was found that the natural boundary condition or the end-fixed boundary condition is applicable for getting a result to fit the observed photo-absorption of polyacetylene with short (N

With a local potential of site-impurity in the frame work of the SSH model, the Coulomb effect of the dopant ions on the vibrational modes around the charged-soliton in doped poly-acetylene has been studied. The calculated results showed that the Goldstone theorem will be destroyed and the translation mode g1 will be pined by the dopant potential. At the same time, a new even-parity mode g′ 1 has been found. The appearance of g1 and g′1 interpret well the broad peak at 930 cm-1. In addition, other localized modes have also been discussed.

The stability of soliton pairs and the electronic energy level structures in a doped poly-acetylene chain have been studied under natural boundary conditiono. In the Itamiltanian usel an end point potential was added to the SHH model, and the screened Coulomb potential of impurities and e-e interaetion on the tattice points were also indndelincluded. The caleulated results Show that, as the range of coulomb interaction is long enongh, stable soliton pairs are formel in the chain, and the stability is enlanced by the influce of the ends the gap width becomes narrow with the increase of chain length. But the deplndence of transition energg from soliton level to band bottom on chain length is not very signicant.

Based on the fact of the existance of a small amount itinerant electrons, a new theoretical model giving rise to magneto-crystalline anisotropy in compound Nd2Fe14B is presented in this paper. It is proposed that a combined effect on Nd-ion coming from both the crystal field of ligands and the electric field of itinerant electrons results in the anisotropy in the compound. An approach of calculating the interaction between itinerant electrons and central Nd-ion is given. The magneto-crystalline anisotropy of Nd-ion and its temperature dependences are calculated based on the model. The results are in good agreement with the experiments, and also give explanation to the spin reorientation phenomenon in the compound.

The electron correlation and soliton in polyacetylene have been studied with the CBF method. By considering the complete electron-electron interaction, we concluded that the stable static configuration of a PA chain with odd atoms and a single electric charge is a soliton. With the increase of e-e interaction strength U and interaction range α/β the localization of soliton is enhanced, and the soliton creation energy is reduced, so although the e-e interaction is considered, the conclusion that soliton is main charged carrier in high conducting polymers is still tenable.

The compositionally modulated FeBSi/Si amorphous films were prepared by rf sputtering. The saturation magnetization of modulated films decreases exponentially with increase of the thickness of Si layers. This is caused by the dead layers. The M?ssbauer spectra measurements showed that the dead layers are the paramagnetic phase formed by the interdiffusion of Fe and Si atoms at the interfaces. The size effect was observed in the FeBSi/Si films. The size effect depends only on the thickness of FeBSi layers, and the dead layer effect depends on both the FeBSi layer thickness and Si layer thickness.

Production of amorphous alloy layer in pure polycrystalline iron thin film by boron ion implantatiom has been studied and interesting phenomena have been observed such as the magnetic coercive field of the film decreases non-monotonously with increasing ion dose, etc. The possible mechanisms of the phenomena have been discussed.

The permeability of polycrystalline iron thin films implanted with different doses of boron ions rises nonmonotonously with increasing dose, while the 57Fe conversion electron Mossbauer spectra of the films have shown the formation of amorphous metallic alloy. The results favour the critical defect density model of amorphous state formation.

The electronic structures of Si (111) surface have been studied by means of molecular orbital theory of SCF-CNDO with the cluster model treatment. The calculated results show that: (1) The distribution and transfer of net charges in thesurface have localized characters at the atomic orbitals. Also, the T30, T3+ and T3-defect forms do not exist easily in practical system. (2) The electronic structures can be discribed with the stoohastic potential, from which one can find out the adsorption site and learn the adsorption dynamic process of ion and ionic molecules adsorbed on the Si (111) surface. (3) The surface states mainly appear in the region from the top of valence band to the centre of gap, and is strongly localized at the atomic orbitals. The above-mentioned results are consistent with some experimental discoveries.