Li Yufen

Quantum confinement effect of fullerenes in silica aerogel

Fullerenes (C-60/C-70) were encased in silica aerogel by sol-gel process followed by supercritical drying technique. Visible light emission was observed from the composite under Ar+ laser (488 nm) excitation at room temperature. The luminescent intensity was found to decrease whilst being red shift with the increase of the fullerene content in the composite (from 0.05 up to 2.5 mol%). This can be interpreted with quantum confinement effect of fullerenes confined in networks of the nanoporous silica aerogel.

Time-Resolved Fluorescence Study of C60 Solution

Using a picosecond excitation source and a time-resolved streak camera detection system, the time-resolved fluorescence spectra of purified C60 have been recorded from toluene solution at room temperature. A fluorescence peak at about 730 nm was detected and its lifetime was directly determined to be 1.1±0.1 ns. Two fluorescence peaks obtained from the mixture of C60 and C70 at 676 and 696 nm were mainly related to C70 content.

A Novel Metal and Nonmetal Cluster Source Produced by Laser Ablation

We have developed a simple, novel cluster source with which intense beam of carbon and silver clusters were generated. The formation mechanism of the fullerene carbon clusters are discussed, and the velocity distribution of small carbon clusters was measured. The intensity distribution of silver clusters shows a distinct odd-even alternation, which agrees well with our previous theoretical predictions.

Structural Origin of the Formation of Odd-Numbered Carbon Clusters from Fullerene Derivatives

We report the mass spectrometric investigation on fullerence derivatives C60CH2, C60RH, C60R2(R= C6H5CO-) and C60On under the 308 nm laser ablation. In the negative ion mass spectra of C60CH2 C60R2, and C60On, odd-numbered clusters C57-, C55-, C53-, C51- are observed clearly in addition to the even-numbered fullerene fragment ions, while for the monoadduct C60RH, odd-numbered species can not be detected. In the positive ion channel, the fragmentation patterns of the three derivatives are similar. A mechanism related to the structural characteristics of the derivatives is supposed for the odd-numbered cluster formation. The 3-membered ring formed on the C60 cage is thought of to play a vital role for the formation of odd-numbered carbon clusters.

Stimulated Raman oscillation from the droplets by ultrashort laser pulse

We have measured the picosecond Stokes oscillation from CCl4, C6H6 and other droplets with about 70 micrometer diameter. The obtained oscillation can reach 8th order. The explanation for the differences between the Stokes oscillations with nanosecond and picosecond pumping is given.

Structures of Adatom Clusters on Ag(111) Surface by Genetic Algorithm

We study the structures of Ag adatom clusters supported on the metal Ag(111) surface using the genetic algorithm (GA). The atomic interactions are modelled by the surface-embedded-atom method. The lowest-energy structures of adatom clusters with sizes n = 3–20 are obtained, in which n = 7, 10, 12, 14, 16, 19 are the magic numbers. Furthermore, we give a series of structures with energies close to the lowest energy (the lower-energy isomers), and the structure features are studied in detail. Except for some magic clusters and small clusters, every configuration of adatom clusters generally has two distinct adsorption ways, so the isomers always appear in pairs.

A Molecular Dynamics Simulation of C60-C60 Collision

The formation process of C120-complex in C60-C60 collision has been clearly demonstrated by a molecular dynamics simulation. The complex, with a peanut-shell-like structure, is in a quite stable dynamical state. The results are consistent with recent observations.

Critical Size of a Crossover from Noncrystalline Icosahedra to Crystalline Cuboctahedra Structure for Copper Clusters

We present an estimation of a critical size of a crossover from icosahedral to bulk-like (cuboctahedral) structures for copper clusters by a semi-empirical calculation of cohesive energies for both icosahedral and cuboctahedral copper clusters. The results are consistent with available experimental observations.

Reversible Vertical Manipulations of Single Pt Adatom on Pt(111) Surface with a Triple-Apex Tip

With a triple-apex tip, we investigate theoretically the vertical manipulation of single Pt adatom on the Pt(111) surface. The adatom adsorbed on the fcc site of the flat Pt(111) surface can be transferred vertically to the tip by adjusting the tip height properly. Moreover, based on the strong vertical trapping ability and the relatively weak lateral trapping ability of the tip, we propose a simple method to realize a reversible vertical manipulation of the Pt adatom from the highly coordinated sites, the kink and the step sites, of the stepped Pt(111) surface. All the vertical manipulations are completed using only the atomic force between the tip and the adatom, without the electric field.

Magic Number Behaviour and Structures of Silicon Dioxide-Based Clusters

The lowest energy structures of (SiO2)nO2 cluster skeletons with size from n = 2 to 12 is investigated theoretically by genetic algorithm. The calculations based on the Tsuneyuki–Tsukada–Aoki–Matsui (TTAM) and Flikkema–Bromley (FB) potentials give the same result: n = 4 and n = 8 are the magic numbers in the virtual (SiO2)nO2 cluster sequence. This conclusion is in agreement with the experimental observation on the [(SiO2)nO2H3]− cluster sequence. The comparison of the present results with those from the density-functional-theory calculations on (SiO2)nO2H4 shows that addition of H atoms to the O terminals of (SiO2)nO2 clusters to form the complex (SiO2)nO2H4 clusters has only minor influence on the relative energies and the structures of different isomers. This means that the magic behaviour of the clusters [(SiO2)nO2H3]− (n = 4, 8) observed in our previous experiment is originated from the stability of the cluster skeletons (SiO2)nO2 (n = 4,8).