Xiu-Neng Song

Formation and electronic transport properties of bimolecular junctions based on aromatic coupling

A systematic first-principles study on conductance-voltage characteristics of bi-(quasi)oligo(phenylene ethynylene)-monothiol molecular junctions reported by Wu et al (2008 Nat. Nanotechnol. 3 569) is presented. The so-called ortho- and para-conformations of the bimolecular junction are considered. Our calculation indicates that the bimolecular junction prefers to take the ortho-conformation because of its lower energy. The simulation supports the experimental findings that aromatic coupling between two molecules is strong enough to induce the formation of molecular junctions. By comparing with experimental results, structure parameters for a probable bimolecular junction are determined. The underlying mechanism for formation of the bimolecular junction and its electron transport is discussed.

Theoretical Identification of the Six Stable C84 Isomers by the IR, XPS and NEXAFS Spectra

Six stable C84 isomers satisfying isolated pentagon rule (IPR) have been theoretically identified by infrared (IR), X-ray photoelectron (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra. The XPS and NEXAFS spectra at the K-edge for all nonequivalent carbon atoms were simulated by the density functional theory method. NEXAFS spectra show stronger dependence than IR and XPS spectra on the six C84 isomers, which can be properly used for isomer identification. Furthermore, spectral components of total spectra for carbon atoms in different local environment have been explored.

Theoretical Identification of Three C66 Fullerene Isomers and Related Chlorinated Derivatives by X-ray Photoelectron Spectroscopy and Near-edge X-ray Absorption Fine Structure Spectroscopy

C 1s X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra for three C66 fullerene isomers and related chlorinated species have been calculated by density functional theory (DFT) method. The XPS spectra show isomer dependence for the three pristine C66 isomers but not for the chlorinated species. The NEXAFS spectra exhibit strong dependence on the structures of all the investigated molecules and thus can be well employed to identify the three C66 fullerene isomers and related chlorinated species. Both XPS and NEXAFS spectra of the chlorinated species present significant variations compared with the pristine fullerenes. The spectral components for carbon atoms of different local environments have been explored as well. The spectra for the carbon atoms connecting to chlorine atoms exhibit a significant blue shift compared to the others.

Identification of Four C40 Isomers by Means of a Theoretical XPS/NEXAFS Spectra Study

XPS and NEXAFS spectra of four stable C40 isomers [29( C2), 31( C s), 38( D2), and 39( D5 d)] have been investigated theoretically. We combined density functional theory and the full core hole potential method to simulate C 1s XPS and NEXAFS spectra for nonequivalent carbon atoms of four stable C40 fullerene isomers. The NEXAFS showed obvious dependence on the four C40 isomers, and XPS spectra are distinct for all four isomers, which can be employed to identify the four stable structures of C40. Furthermore, the individual components of the spectra according to different categories have been investigated, and the relationship between the spectra and the local structures of C atoms was also explored.

Distinguishing the six stable C36 fullerene isomers by means of soft X-ray spectroscopies at DFT level

ABSTRACT The six most stable isomers of C36 fullerene (8Cs-C36, 9C2v-C36, 11C2-C36, 12C2-C36, 14D2d-C36, 15D6h-C36) have been distinguished in theory by analysing their C1s X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra, which are both simulated by the combination of density functional theory and full-core-hole potential approximation. The NEXAFS spectra exhibit stronger sensitivity to the structures of studied C36 molecules than the XPS; it can be regarded as an effective technology to distinguish the isomers of C36 fullerene. In addition, the decomposed spectra describing the influence of Carbon atoms with different local environments to the total spectra have also been discussed in detail. The results show that the spectral differences are mainly due to the distinct combinations of the Carbon atoms. GRAPHICAL ABSTRACT

Theoretical studies on structures and spectral properties for two C86 isomers and their chlorinated derivatives

ABSTRACT The near-edge X-ray absorption fine structure (NEXAFS) spectra and the X-ray photoelectron spectroscopy (XPS), as well as the geometrical structures of two C isomers (C(16), C(17)) and their corresponding chlorinated derivatives (C(16) Cl, C(17)Cl) which were newly purified have been investigated by the density functional theory (DFT). The variations of molecular structure, electronic structure and simulated spectra for C isomers after chlorination have been illustrated. Then, the above-mentioned C isomers and their chlorinated derivatives have been identified by the NEXAFS and XPS spectra which show the dependence on the local structure. Furthermore, we have also traced the source of the features in the total spectra by the spectral exploration of each component, which is very helpful for the further study of newly captured fullerene isomers and their derivatives. In this manuscript, we have performed first-principles simulation of the C1s X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure spectra (NEXAFS) for two C86 fullerene isomers and the related chlorinated species. The variations of molecular structure, electronic structure and simulated spectra for C86 isomers after chlorination have been illustrated. The above-mentioned C86 isomers and their chlorinated derivatives were identified by the NEXAFS and XPS spectra which show strong dependence on the local structure. Furthermore, we have also traced the source of the features in the total spectra by the spectral exploration of each component. The investigations on newly synthesized fullerenes and derivatives are effectively valuable and stimulative for the experimental researches in future. GRAPHICAL ABSTRACT

Theoretical and experimental study of surface-enhanced raman scattering of 4,4'-bipyridine molecule on graphene

In present work, we investigated the surface-enhanced raman scattering(SERS) of 4,4’-bipyridine on Graphene surface with a quasi-analytical approach based on density functional perturbation theory(DFPT). Three different configurations were considered to simulate the adsorption structures on the Graphene surface. The interaction between 4,4’-bipyridine molecule and Graphene surface depends on the adsorption structure, which also results in the distinct spectroscopy. The relationship between the configurations and SERS spectroscopy were interpreted. We also performed the experimental SERS spectroscopy of 4,4’bipyridine molecule on Graphene. Comparing with the experimental SERS spectroscopy, the landscape of 4,4’-bipyridine on Graphene has been revealed.