Density Of Nanoislands Research Articles

Self-assembled Ge/Si nanoislands: effect of argon flow and radio frequency power

The growth of a germanium–silicon (Ge/Si) heterostructure using radio frequency (rf) magnetron sputtering under optimized conditions is performed. High-density self-assembled Ge nanoislands ∼14 nm in size are obtained directly on Si(100) under 10 sccm argon (Ar) flow and 100 W rf power. The surface roughness and number density of nanoislands revealed by atomic force microscopy are found to be in the range of 3.7–0.6 nm and 45 × 102–20 × 102 μm−2, respectively. An increase in Ar flow and rf power leads to an enhancement of defects, anti-sputtering of the deposited islands and a decrease in the sample quality. X-ray diffraction is used to measure the strain, which is found to be close to the lattice misfit of Ge and Si. It shows the carefully controlled growth condition with minimum density of dislocation. Room temperature photoluminescence exhibits a very strong blue–violet peak at 3.2 eV, which is attributed to the transition from excited triplet level to grand-state singlet level.

<tex>$J_c$</tex>Enhancement in<tex>$rm YBa_2rm Cu_3rm O_rm x$</tex>Thin Films by Introduction of One-Dimensional Artificial Pinning Centers

A novel technology to introduce artificial pinning centers (APCs) into YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thin films prepared by pulsed laser deposition (PLD) was investigated for a drastic improvement of J/sub c/ in the films. Linear-like defects (one-dimensional APCs) were introduced perpendicular to the surface of the c-axis oriented films during the deposition process by using distributed Y/sub 2/O/sub 3/ nano-islands on substrates. The density of nano-islands was varied within 0.8-1.2/spl times/10/sup 10//cm/sup 2/ by PLD. A normalized resistivity as a function of temperature in magnetic fields shows a sharper resistivity drop for the film with APC, compared to pure YBCO film. J/sub c/ of the film with APC was also increased to 0.12 MA/cm/sup 2/ (77 K, B//c, 5 T), which was about two times higher than that of the pure YBCO film. The film had a very large J/sub c/ peak when the field was applied close to the c-axis. The peak J/sub c/ increased with the number density of Y/sub 2/O/sub 3/ nano-islands. This indicates that strong APCs parallel to the c-axis were incorporated into the YBCO film.