Gas-Phase Nanoparticle Formation During PLD of YBCO
"Gas-Phase Nanoparticle Formation and Transport During Pulsed Laser Deposition of Y1Ba2Cu3O7-d" D. B. Geohegan, A. A. Puretzky, and D.J. Rader. Appl. Phys. Lett. 74, 3788 (1999).
Do nanoparticles form in the gas-phase during PLD (Pulsed Laser Deposition) of thin films? If so, they can become incorporated as inclusions in the growing film. This question has remained unanswered, principally because the necessary diagnostic techniques had not been applied.
These images show (top row) the laser plasma as it penetrates the 200 mTorr of oxygen to collide with a room temperature substrate. Laser-induced fluorescence (LIF) is used to excite ground-state YO and BaO molecules at the same times (second row). After colliding with the heater (see third row) a cloud of stopped oxides, illuminated by LIF, gives rise to nanoparticles, which are detected using Rayleigh scattering (RS) at very long times. At high temperatures, (lower row) the heater causes the nanoparticles to move away before they are fully formed, thereby limiting possible incorporation in the growing film.
"Gas-phase nanoparticle formation and transport during pulsed laser deposition of Y1Ba2Cu3O7 – d"
D. B. Geohegan, A. A. Puretzky, and D. J. Rader
Appl.Phys. Lett. 74, 3788 (1999) .
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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. © 1999 American Institute of Physics.
