Houjin Huang

The third-order non-linear optical response of the endohedral metallofullerene Dy@C82

Abstract Dy@C 82 has been prepared by an efficient solvent extraction procedure and characterized by negative-ion desorption chemical ionization mass spectrometry and UV-VIS–near-IR absorption. Degenerate four-wave-mixing measurements on the CS 2 solution of Dy@C 82 were performed using 70 ps laser pulses at 0.532 μm. The magnitude of the second hyperpolarizability γ 1111 of the Dy@C 82 molecule was (3.0±0.5)×10 −30 esu at 0.532 μm. The resonant enhancement and the electron transfer from the trapped dysprosium to the C 82 cage are suggested to bring about its larger non-linear optical response relative to the empty fullerene. The experimental results are in good agreement with our calculations based on an extended Su–Schrieffer–Heeger model and the sum-over-state method.

Nonlinear optical response of the higher fullerene C90- a comparison with C60

Abstract Degenerate four-wave-mixing measurements on C 90 in CS 2 with different concentrations were performed using 70 ps laser pulses at 0.532 μm. The dependence of the conjugate signal intensity on the incident laser power and the concentration of C 90 were investigated. By optimizing experimental parameters, the second hyperpolarizability γ 1111 of C 90 was determined to be (1.8 ± 0.6) × 10 −30 esu, which is approximately eight times that of the C 60 molecule measured under identical conditions. Our results are in accord with the theoretical prediction that higher fullerenes should show larger nonlinear optical responses.

C60 INDUCED PHOTOLUMINESCENCE OF A SILICA MOLECULAR SIEVE

The optical properties of the regular, 3-nm-wide hexagonal channels of the mesoporous silica molecular sieve (MCM–41) containing C60 are reported. Besides an intensive photoluminescence response at 642 nm from confined C60, a more intensive photoluminescence at 484 nm has been observed, which is considered to result from the passivation of silica zeolite with C60. Our studies indicate that both the properties of guest and host can be modified due to the interaction at the interface of them.

Magnetoresistance in arrays of fine graphite powders with nearest-neighbor tunneling conduction

Abstract Resistance of samples prepared by compressing submicron graphite powders was measured in the temperature range 1.8–300xa0K and magnetic field up to 4.5 T. The temperature dependence of resistance for some samples is satisfactorily described by a fluctuation-induced tunneling model R∝ exp [T 1 /(T+T 2 )] . In others resistance follows a power law R∝1/T α with α close to 1, and we propose a phonon-assisted bunch hopping (or tunneling) model for this case. The dominating mechanism is determined by the effective tunneling distance. Magnetoresistance (MR) is dominantly positive, with mesoscopic oscillations at low fields, in the fluctuation-induced tunneling regime, and has a negative component in the phonon-assisted bunch hopping regime. Our results confirm the existence of negative MR in systems with nearest-neighbor tunneling conduction and point the conditions for this effect. We interpret NMR as due to shifting of discrete electron levels towards the Fermi level in the magnetic field, which enhances the phonon-assisted bunch hopping.

Preparation and characterization of the endohedral metallofullerene Lu@C-82

Abstract A new metallofullerene Lu@C 82 has been isolated with good purity using polar solvent extraction and HPLC techniques. XPS, EPR and UV–Vis–Nir spectroscopic techniques are employed to characterize the mono-metallofullerene Lu@C 82 . Our results suggest that the encaged Lu atom donates approximately three electrons to the carbon cage.

Scanning tunneling microscopy of endohedral metallofullerene Lu–C82 on C60 film

Endohedral metallofullerene Lu–C82 molecules adsorbed on C60 film have been investigated by an ultra-high-vacuum scanning tunneling microscopy. The C60 film was obtained by depositing 2–3 ML of C60 molecules on a highly oriented pyrolytic graphite surface. The as-deposited Lu–C82 molecules were observed to form various structures on the C60 film. The nucleation behavior of Lu–C82 was compared with that of Nd–C82 and Tb–C82 on the C60 film. These structures were explained based on the interactions of Lu–C82–C60, Lu–C82–Lu–C82, and Lu–C82 scanning tunneling microscopy tip.

Self-assembled Co3(BO3)2/surfactant nanostructured multilayers

Co3(BO3)2/surfactant composites have been prepared by the controlled precipitation of aqueous cobalt cations together with surfactant. The composite shows a layered structure as determined by x-ray diffraction, in which the Co3(BO3)2 layers of about 6 A in thickness are in alternation with surfactant bilayers. The temperature-dependent magnetization measured in the zero-field-cooled (ZFC) and field-cooled (FC) processes and the AC-magnetic susceptibility measured at different frequencies indicate that there is a freezing temperature at low temperature (<6 K) and the temperature is weakly frequency dependent. A clear difference between thermal remanent magnetization (TRM) and isothermal remanent magnetization (IRM) was observed at 2 K. All the experimental observations suggest that the multilayers are spinglass in nature.