High Island Densities in Pulsed Laser Deposition: Causes and Implications

By studying metal growth on Pt(111), we determine the reasons for the high island densities observed in pulsed laser deposition (PLD) compared to conventional thermal deposition. For homoepitaxy by PLD with moderate energies ($\lesssim 100\mathrm{eV}$) of the deposited ions, high island densities are caused by the high instantaneous flux of arriving particles. Additional nuclei are formed at high ion energies ($\gtrsim 200\mathrm{eV}$) by adatoms created by the impinging ions. For heteroepitaxy, the island density is also increased by intermixing (deposited material implanted in the surface), creating an inhomogeneous potential energy surface for diffusing atoms. We discuss implications for layer-by-layer growth and sputter deposition.

Figure 1

(a),(b) STM images of 0.014 ML Pt deposited on Pt(111) by PLD (STM at 80 K). (c) Experimental island densities labeled with the energies of the impinging Pt ions. Full and broken lines show calculated island densities for pulsed (10 pulses, $10\mu \mathrm{s}$ each, 10 Hz) and continuous (1 s) deposition. (d) Geometry of our PLD setup.

Figure 2

(a) STM image of 0.0056 ML Pt deposited on Pt(111) by PLD at 50 K ($E_{\mathrm{ion}}=90\mathrm{eV}$; STM at 5 K). The Pt(111) substrate lattice reconstructed from the CO sites is superimposed on (b). (c) Number of adatoms or clusters depending on the energy of the impinging Pt ions. $2\sigma$ error bars include counting statistics only. The broken line is a guide to the eye. (d) STM image of 0.2 ML deposited at 180 K ($E_{\mathrm{ion}}=130\mathrm{eV}$), showing vacancies in the substrate. The image was processed for better visibility of the atomic corrugation on the substrate and adatom islands.

Figure 3

STM images of (a),(b) 0.2 ML Co and (c) 0.2 ML Pt deposited on Pt(111) by PLD at 300 K. The insets show experimental (813 and 189 islands for Co and Pt, respectively) and calculated [19] island size distributions.

Figure 4

STM images of $12\pm 1\mathrm{ML}$ Pt deposited on Pt(111) by PLD at $\approx 100\mathrm{eV}$ kinetic energy (shown as if illuminated from the left). Insets show height distributions; the curve in (a) is the Poisson distribution arising in case of no interlayer mass transport.