The effect of 200 MeV Ag ion irradiation on thick films ofYBCO grown by the diffusion reaction technique has been studied. Magnetization at 40 K marks a substantial change in the critical current density (J c ) of the irradiated sample when compared with unirradiated ones. The critical current density was estimated from the widths of magnetization loops using Bean's critical state model. The enhancement of J c from 1.06 × 10 5 to 2.5 × 10 5 A/cm 2 with irradiation up to a fluence of 5 × 10 11 ions/cm 2 in YBCO samples is associated with an increase in the flux pinning created by the irradiation-induced columnar defects. In excess Y 2 O 3 (10 wt%) to YBCO, the J c increases in the pristine sample to 1.33 × 10 5 A/cm 2 but decreases with increasing fluence. This may be due to an excess of defects, overlapping of defected zones and weakening of the pinning barriers. Further studies using X-ray diffraction and a scanning electron microscope reveal microstructural changes in the irradiated samples.

Y 1−x Ca x Ba 2 Cu 3 O 7−δ (x = 0.1) + Y 2 O 3 (10 wt%) composite thick film has been prepared by the diffusion reaction technique. Samples are irradiated with 200 MeV Ag ions. X-ray diffraction and scanning electron microscopy reveal microstructural changes in the irradiated samples. The enhancement of the critical current density (J c ) from 1.4 × 10 4 to 6.7 × 10 4 A/cm 2 with irradiation in YCaBCO samples is observed, indicating that flux pinning increases due to the creation of columnar defects induced by irradiation. On addition of Y 2 O 3 to YCaBCO, J c increases to 8.3 × 10 4 A/cm 2 . The insulating inclusions of Y 2 O 3 cause J c to increase by the process of flux pinning in the unirradiated YCABCO/Y 2 O 3 composite. However, J c starts decreasing for YCABCO/Y 2 O 3 composite with the increase in ion fluence. The main mechanism of the decrease in the critical current density is the reduction in the effective pinning potential, which is caused by an increase in the defect concentration.

The influence of concentration and size of sp 2 cluster on the transport properties and electron field emissions of amorphous carbon films have been investigated. The observed insulating to metallic behaviour from reduced activation energy derived from transport measurement and threshold field for electron emission of a-C films can be explained in terms of improvements in the connectivity between sp 2 clusters. The connectivity is resulted by the cluster concentration and size. The concentration and size of sp 2 content cluster is regulated by the coalescence of carbon globules into clusters, which evolves with deposition conditions.

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