Gas-phase nanoparticle formation and transport during pulsed laser deposition of Y1Ba2Cu3O7−d

The gas-phase growth and transport of nanoparticles are characterized at the low background oxygen pressures used for pulsed laser deposition of high-Tc Y1Ba2Cu3O7−d superconducting films. Onset times and pressures for gas-phase nanoparticle formation were determined by intensified charge-coupled device imaging and optical spectroscopy of laser-induced fluorescence from diatomic oxides and Rayleigh scattering from gas-suspended nanoparticles. Nanoparticles are detected for oxygen pressures above 175 mTorr at room temperature, with growth continuing during seconds within the cloud of stopped vapor near the heater surface. Elevated heater temperatures create background density gradients which result in reduced resistance to the initial plume expansion. The temperature gradient also moves nanoparticles away from the heater surface as they grow, effectively limiting the time and spatial confinement necessary for continued growth or aggregation, and inhibiting deposition by thermophoresis.