Suspended Graphene Membranes to Control Au Nucleation and Growth

Abstract

Control of nucleation sites is an important goal in materials growth: nuclei in regular arrays may show emergent photonic or electronic behavior, and once the nuclei coalesce into thin films, the nucleation density influences parameters such as surface roughness, stress, and grain boundary structure. Tailoring substrate properties to control nucleation is therefore a powerful tool for designing functional thin films and nanomaterials. Here, we examine nucleation control for metals deposited on two-dimensional materials in a situation where substrate effects are absent and heterogeneous nucleation sites are minimized. Through quantification of faceted, epitaxial Au island nucleation on graphene, we show that ultralow nucleation densities with nuclei several micrometers apart can be achieved on suspended graphene under conditions where we measure 2–3 orders of magnitude higher nucleation density on the adjacent supported substrate. We estimate diffusion distances using nucleation theory and find a strong sensitivity of nucleation and diffusion to suspended graphene thickness. Finally, we discuss the role of surface roughness as the main factor determining nucleation density on clean free-standing graphene.

Metal Films on Two-Dimensional Materials: van der Waals Contacts and Raman Enhancement

“…The root-mean-square roughness ( R rms ) value calculated for SiO 2 is consistent with previous studies . The relatively high roughness of SiO 2 suppresses adatom surface diffusion and provides ample opportunities for nucleation and growth of grains. , …”

“…Related parameters such as nucleation density ( N , represented as grains per μm 2 ), diffusivity, diffusion length, and activation energy for diffusion can be estimated from mean field diffusion theory. ,, For 2D island growth, N is proportional to diffusivity ( D ) of the metal atom as N ∝ true( 1 D true) i / i + 2 , where i is the critical radii for nucleation. ,, The diffusivity is related to the activation energy of diffusion ( E d ), and we can estimate using D ∝ e − normalΔ E / kT , where k is Boltzmann’s constant, T is temperature, and Δ E is the diffusion barrier . Combining these proportionalities allows nucleation density to be related to the activation energy via N ∝ exp ( i i + 2 E d italickT ) .…”

“…Combining these proportionalities allows nucleation density to be related to the activation energy via N ∝ exp ( i i + 2 E d italickT ) . The diffusion length of adatom on the surface is L D = 1 N . We estimate N from the number of individual grains per unit area in the AFM images.…”

Metal functionalization of two-dimensional nanomaterials for electrochemical carbon dioxide reduction

“…[71][72][73] Other methods such as thermal evaporation and atomic layer deposition can also be used to prepare the metal-functionalized graphene. [74][75][76] Various metal elements, such as Fe, Co, Ni, Cu, Zn, Sn, Ru, Ag, Os, Pt, and Au, can be used to functionalize graphene for electrocatalytic CO 2 reduction. In these elements, Fe, Ni, Zn, Ag, and Au can promote the reduction of CO 2 to CO. 43,73,[77][78][79][80][81] Co, In, and Sn show higher intrinsic activity and selectivity toward the formation of HCOOH.…”

“…71–73 Other methods such as thermal evaporation and atomic layer deposition can also be used to prepare the metal-functionalized graphene. 74–76…”