Defect-mediated, thermally-activated encapsulation of metals at the surface of graphite

Abstract

We show that 3 metals -Dy, Ru, and Cu -can form multilayer intercalated (encapsulated) islands at the graphite (0001) surface if 2 specific conditions are met: Defects are introduced on the graphite terraces to act as entry portals, and the metal deposition temperature is well above ambient. Focusing on Dy as a prototype, we show that surface encapsulation is much different than bulk intercalation, because the encapsulated metal takes the form of bulk-like rafts of multilayer Dy, rather than the dilute, single-layer structure known for the bulk compound. Carbon-covered metallic rafts even form for relatively unreactive metals (Ru and Cu) which have no known bulk intercalation compound. Defect-mediated, thermally-activated encapsulation of metals at the surface of graphite." Carbon 127 (2018): 305-311.ABSTRACT: We show that 3 metals -Dy, Ru, and Cu -can form multilayer intercalated (encapsulated) islands at the graphite(0001) surface if 2 specific conditions are met: Defects are introduced on the graphite terraces to act as entry portals, and the metal deposition temperature is well above ambient. Focusing on Dy as a prototype, we show that surface encapsulation is much different than bulk intercalation, because the encapsulated metal takes the form of bulk-like rafts of multilayer Dy, rather than the dilute, single-layer structure known for the bulk compound.Carbon-covered metallic rafts even form for relatively unreactive metals (Ru and Cu) which have no known bulk intercalation compound.

Shapes of Fe nanocrystals encapsulated at the graphite surface

“…We have considered the possibility that increasing D in the bending strain energy term might shift the upturn in d/h toward the right and toward better agreement with experiment. Increasing bending stiffness can be achieved by, for example, doubling the Young's modulus, Y, to 2.2 TPa in equation (8), or by adding a factor of two to the bending term in equation (9). Unfortunately, these have only a minor effect on d/h, and they enhance the downward dive in h/a with decreasing h. Neither of these changes improves agreement with experiment.…”

“…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.…”

Nucleation and growth kinetics for intercalated islands during deposition on layered materials with isolated pointlike surface defects

“…In general, nucleation of additional islands will also occur preferentially at locations away from existing islands. Motivation for the above scenario comes from recent experimental studies of the deposition at around 800 K of various metals, including Cs [4], Dy, Ru, and Cu [5], on a defective HOPG surface. In these studies, HOPG was sputtered by Ar + ions to produce damage in the form of local or pointlike surface defects.…”