Control Of Nucleation Sites Research Articles

Suspended Graphene Membranes to Control Au Nucleation and Growth.

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.

Area selective OMCVD of gold and palladium on self-assembled organic monolayers : Control of nucleation sites

The area selective organometallic chemical vapor deposition (OMCVD) of gold and palladium onto self-assembled monolayers (SAMs) of ω-functionalized long chain alkanethiols and 4'-functionalized biphenylthiols was investigated. Trimethylphosphine-methylgold (Me 3 PAuMe) and cyclopentadienyl-allyl-palladium (Cp(allyl)Pd) were used as organometallic precursors. X-ray photoelectron spectroscopy (XPS) revealed that in both cases nucleation occurs selectively only on thiol terminated surfaces even at very mild conditions whereas nucleation is inhibited on methyl- and hydroxy-terminated SAMs. It has been shown that it is possible to control the number of gold clusters per area by depositing gold onto mixed SAMs consisting of biphenylthiol and 4'-biphenyldithiol with varying molar ratios.

Nucleation and Growth of Crystalline Silicon Films on Glass for Solar Cells

Understanding nucleation and growth of crystalline Si films on glass is of prime importance in order to tailor and optimize semiconductor properties for electronic devices such as solar cells. Commercial glass limits the maximum processing temperature of Si films to 600 C. Solid phase and laser crystallization, or a combination of both techniques, are thus primarily used to crystallize Si films on glass. While random nucleation and growth processes always result in the formation of a log± normal size distribution, control of nucleation sites allows one to determine the location of grain growth or even the crystallographic orientation of grains. Via sequential lateral solidification using a copper vapor laser, we obtain Si crystallites on glass of several tens of mm in length.