Kinetic pathways leading to layer-by-layer growth from hyperthermal atoms: A multibillion time step molecular dynamics study

We employ multibillion time step embedded-atom molecular dynamics simulations to investigate the homoepitaxial growth of Pt(111) from hyperthermal Pt atoms $(E_{\mathrm{Pt}}=0.2–50\mathrm{eV})$ using deposition fluxes approaching experimental conditions. Calculated antiphase diffraction intensity oscillations, based on adatom coverages as a function of time, reveal a transition from a three-dimensional multilayer growth mode with $E_{\mathrm{Pt}}<20\mathrm{eV}$ to a layer-by-layer growth with $E_{\mathrm{Pt}}\ge 20\mathrm{eV}$. We isolate the effects of irradiation-induced processes and thermally activated mass transport during deposition in order to identify the mechanisms responsible for promoting layer-by-layer growth. Direct evidence is provided to show that the observed transition in growth modes is primarily due to irradiation-induced processes which occur during the $10\mathrm{ps}$ following the arrival of each hyperthermal atom. The kinetic pathways leading to the transition involve both enhanced intralayer and interlayer adatom transport, direct incorporation of energetic atoms into clusters, and cluster disruption leading to increased terrace supersaturation.

Figure 1

(Color) Left side: Normalized antiphase diffraction scattering intensity vs deposited layer thickness during Pt(111) homoepitaxy using Pt atoms with incident energies $E_{\mathrm{Pt}}$ of (a) $0.2\mathrm{eV}$ (thermal deposition), (b) $10\mathrm{eV}$, (c) $15\mathrm{eV}$, and (d) $20\mathrm{eV}$. The deposition rate $R$ is $10{\mathrm{ns}}^{-1}$. Right side: Plan-view images showing the corresponding Pt(111) surface topographies after deposition of 2.5 and 5.0 ML. Atoms in the first, second, third, and fourth deposited layers are brown, yellow, green, and blue, respectively.

Figure 2

[(a) and (b)] Histograms showing averaged intra- and interlayer mass transport distances per atom during consecutive $10\mathrm{ps}$ intervals following the deposition of a Pt atom with $E_{\mathrm{Pt}}=0.2$, 5, 25, and $50\mathrm{eV}$ on Pt(111). Mass transport values are expressed in units of $l$, the separation between adjacent fcc and hcp surface sites, and $d$, the interlayer spacing in the [111] direction.

Figure 3

[(a) and (b)] Average irradiation-induced intra- and interlayer mass transport distances per atom as a function of the incident Pt energy $E_{\mathrm{Pt}}$ during deposition on Pt(111). The intra- and interlayer components are expressed in terms of the distance between adjacent fcc and hcp surface sites $\left(l\right)$ and the interlayer spacing $\left(d\right)$ in the [111] direction. The horizontal dashed line in (a) represents the average intralayer thermal migration distance.

Figure 4

(Color) Left side: Normalized antiphase diffraction intensity during energetic Pt deposition on Pt(111) with $E_{\mathrm{Pt}}=25\mathrm{eV}$ and atom arrival rates $R$ of (a) $10{\mathrm{ns}}^{-1}$ and (b) $1{\mathrm{ns}}^{-1}$. Right side: Plan-view images from video files showing the corresponding Pt(111) surface morphology after deposition of 1.0 and 3.0 ML. Substrate surface and first, second, third, and fourth deposited layers are gray, brown, yellow, green, and blue, respectively.

Figure 5

Average intra- and interlayer mass transport distances plotted as a function of time intervals ($10\mathrm{ps}$ each) between two consecutive impacts during deposition of $E_{\mathrm{Pt}}=25\mathrm{eV}$ Pt atoms on Pt(111) with atom arrival rates $R$ of [(a) and (b)] $10{\mathrm{ns}}^{-1}$ and [(c) and (d)] $1{\mathrm{ns}}^{-1}$. The intra- and interlayer components are expressed in terms of the distance between adjacent fcc and hcp surface sites $\left(l\right)$ and the interlayer spacing $\left(d\right)$ in the [111] direction.