Formation of Multilayer Cu Islands Embedded beneath the Surface of Graphite: Characterization and Fundamental Insights

Abstract

We present an extensive experimental study of the conditions under which Cu forms encapsulated islands under the top surface layers of graphite, as a result of physical vapor deposition of Cu on argon-ionbombarded graphite. When the substrate is held at 800 K during deposition, conditions are optimal for formation of encapsulated multilayer Cu islands. Deposition temperatures below 600 K favor adsorbed Cu clusters, while deposition temperatures above 800 K favor a different type of feature that is probably a singlelayer intercalated Cu island. The multilayer Cu islands are characterized with respect to size and shape, thickness and continuity of the graphitic overlayer, relationship to graphite steps, and stability in air. The experimental techniques are scanning tunneling microscopy and X-ray photoelectron spectroscopy. We also present an extensive study using density functional theory to compare stabilities of a wide variety of configurations of Cu atoms, Cu clusters, and Cu layers on/under the graphite surface. The only configuration that is significantly more stable under the graphite surface than on top of it, is a single Cu atom. This analysis leads us to conclude that formation of encapsulated Cu islands is kinetically driven, rather than thermodynamically driven.

Shapes of Fe nanocrystals encapsulated at the graphite surface

“…Specifically, for Fe, h max =9 nm, whereas for Cu, h max =43 nm, so the Fe islands do not grow as tall. Second, for Cu, some islands have round tops rather than flat tops [10] whereas for Fe, only flat tops are observed. For Cu, the largest islands tend to have round tops, so these two differences may be related, e.g.…”

“…Necessary conditions for Fe encapsulation include (i) activating the graphite surface with atomic-scale defects via Ar + ion bombardment, and (ii) depositing Fe on the activated graphite surface that is held at elevated temperature (T dep ). Our group has demonstrated that these conditions are effective for encapsulating a variety of metals, including Cu [10], Ru [11], and Dy [9]. Fe encapsulation is operational in a narrow T dep window of 875-900 K, with 900 K being the optimal temperature where the extent of encapsulation is high with minimal bare Fe on top of graphite [12].…”

“…This is challenging, since 2D materials have intrinsically low surface energies, so metals tend to grow on top of them as 3D clusters [7]. It is therefore attractive to consider synthesis strategies wherein metal morphologies are kinetically-limited [8], or the metal morphology is constrained (and stabilized) by intercalation, to promote the 2D morphology.Elsewhere, we have reported that metal nanoclusters can be synthesized at the surface of the 3D van der Waals material, graphite, in an intercalated form if two conditions are met [9][10][11][12]. First, the graphite surface must be ion bombarded to introduce defects that can act as entry portals for the metal atoms.…”

“…Elsewhere, we have reported that metal nanoclusters can be synthesized at the surface of the 3D van der Waals material, graphite, in an intercalated form if two conditions are met [9][10][11][12]. First, the graphite surface must be ion bombarded to introduce defects that can act as entry portals for the metal atoms.…”

Adsorption, intercalation, diffusion, and adhesion of Cu at the 2H−MoS2 (0001) surface from first-principles calculations

“…One key goal of our analysis is to assess the relative stability of a single Cu atom adsorbed on the surface of 2H-MoS 2 (0001) versus intercalated underneath the surface. To this end, we calculate the Cu chemical potential defined as [30,31]…”