Daole Yin

YBaCuO superconducting thin films with zero resistance at 84 K by multilayer deposition

YBaCuO superconducting thin films were prepared by multilayer deposition on different kinds of substrates. High Tc with an onset of 94 K and a zero resistance at 84 K has been obtained by deposition on pure ZrO2 substrates. The nature of zero resistance as well as the dR/dT characteristic above Tc and the influence of substrates are discussed.

Electron microscopy study of C60

The microstructural features of the powder C60 material have been studied by using scanning microscopy, electron diffraction, and high resolution electron microscopy. Scanning electron microscopy observation reveals that the grains in the samples are packed by extensively disordered crystallites as well as amorphous granules. Electron diffraction measurements have identified that the crystals of C60 have two kinds of structure, one is face‐centered‐cubic (fcc) with unit cell parameter a=1.41 nm, and the other has the hexagonal closest packed (hcp) structure with cell parameters a=0.958 nm and c=1.63 nm. High resolution electron microscopy as well as electron diffraction observations clearly show the random crystallites packing in the C60 grains.

Specific heat studies of high-Tc superconductor YBa2Cu3O7−x

Abstract Specific heat studies of the high-T c superconducting compound YBa 2 Cu 3 O 7− x with bulk transition temperature at 92K are reported. A distinct anomaly of electronic origin in the specific heat is observed with granular-like behavior corresponding to a Sommerfeld constant γ = 7±2mJ(moleCuK 2 ) ±1 Debye temperature ( φo ≈ 400K) is obtained by fitting the experimental data with the theoretical Debye specific heat.

Growth and structure of C60 thin films on NaCl, glass and mica substrates

Abstract We studied the growth and structure of C60 thin film condensed on NaCl, glass and mica substrates by transmission electron microscopy. Highly ordered, (111) textured and epitaxial thin films were obtained on (001) NaCl and mica respectively. Various deposition parameters including different substrate temperatures, deposition rates and film thicknesses were experimented with. The orientational order and nature of defects present in the films were assessed by electron diffraction, bright and dark field images. We ascribe the abnormal reflections in the electron diffraction patterns which had been thought by some workers to belong to the diffraction of an h.c.p. structure phase to the existence of stacking disorder in the f.c.c. structure.

Structural study on C60 material

Abstract The crystal structure and defect structures of C60 material have been studied by means of X-ray diffraction, high-resolution electron microscopy and electron diffraction. The diffraction measurements show that the C60 crystal has the face-centered cubic (fcc) structure with lattice parameter a=1.42 nm. High-resolution electron microscopy observations, combined with the analyses of selected area electron diffraction, indicate that the coherent twins situated in the {111} planes frequently appear in the C60 crystal. The disordered stacking along the 〈111〉 direction and other kinds of defects appearing in the new material have also been investigated. Upon in situ cooling and heating from 130 K to 700 K, the structural stability of the C60 crystal has been observed.

Study of microstructure and anomalous variation of resistivity in metal-C60 multilayer thin films

Abstract The structure and electrical transport properties of C60 thin films and some metal-C60 multilayer thin films were studied. We find the resistance decreases sharply when adding C60 on some specific metal layers. There are two possible explainations: one is the formation of a conduction layer of metal doped C60, the other is the bonding interfacial interaction between the metal and C60 layers, which may result a better continuous metal layer.

Study of microstructure of epitaxial fullerenes films

Abstract A comprehensive study was made on the structure of epitaxial thin films of C 60 and C 70 by means of transmission electron microscopy. Both the films show similar face-centered cubic structure and are epitaxial on (001) mica with close-packed plane parallel to the substrate surface. Two main kinds of defects-stacking faults and twins-were observed and are discussed. The effect of the remaining C 70 impurity on the crystal orientation of C 60 films was studied by comparing different samples made from high-purity fullerene and C 60 /C 70 mixtures. The results show that there is a higher density of planar defects in the films containing larger amounts of impurities: moreover, some faint anomalous reflections located at so-called 2a 0 fcc reciprocal lattice points were also detected, probably as a result of C 70 contamination. Finally, it is found that stacking disorders can be easily increased by keeping the high-quality pure C 60 film in air at room temperature for a few weeks, implying the instability of the crystal orientation of the epitaxial fullerene films.

Surface enhanced electronic transport. A new method to probe the possible interactions between C60 and non-alkali metals

Abstract By measuring the resistance in situ during the deposition of C 60 on ultrathin metal layers in a UHV system, we find the resistance decreases sharply in most cases. This enhanced electronic transport in metal—C 60 multilayers (bilayers), may be related to charge transfer from the metal to C 60 and surface bonding effects, and hence can be used as a new possible approach for probing the interfacial interactions between C 60 and metals.

Epitaxial thin films of C70: Growth and structure characterization

Abstract Epitaxial thin films of C 70 have been grown on (001) mica substrate by resistive evaporation at a vacuum pressure of about 10 -3 Pa. The orientational ordering and the nature of the defects presented in the films were assessed by transmission electron diffraction and electron microscopy. The fundamental structure of the C 70 crystals is face-centered cubic with the lattice parameter a 0 = 1.50 nm, but forbidden reflections resulted from hcp stacking were also detected which are usually appeared in the prior study of alloys with low stacking fault energy and the solid C 60 . Furthermore, we also studied the films deposited on (001) NaCl and Si single crystals and the results show these substrates promoted polycrystal growth under the same evaporation conditions where epitaxy was observed on mica.

Josephson effects observed in constricted YBaCuO films at liquid nitrogen temperature

Abstract The DC and AC Josephson effects have been observed in constricted superconducting Y-Ba-Cu-O films at liquid nitrogen temperature. The temperature dependence of the critical current was studied. It was found that I c ∝ (T c -T) 3 2 . The induced steps were seen in the I-V characteristics when the sample was irradiated by a microwave field. Separations between steps agrees with the Josephson relation.