Custom-made holey graphene via scanning probe block co-polymer lithography.

Samar A Alsudir,Edreese H Alsharaeh,Abdulaziz M Almalik,Roa S Fardous,Ali H Alhasan,Shahla Alsoughayer

doi:10.1039/d1na00769f

Abstract

Oxidative chemical etching of metal nanoparticles (NPs) to produce holey graphene (hG) suffers from the presence of aggregated NPs on the graphene surface triggering heterogeneous etching rates and thereby producing irregular sized holes. To encounter such a challenge, we investigated the use of scanning probe block co-polymer lithography (SPBCL) to fabricate precisely positioned silver nanoparticles (AgNPs) on graphene surfaces with exquisite control over the NP size to prevent their aggregation and consequently produce uniformly distributed holes after oxidative chemical etching. SPBCL experiments were carried out via printing an ink suspension consisting of poly(ethylene oxide-b-2-vinylpyridine) and silver nitrate on a graphene surface in a selected pattern under controlled environmental and instrumental parameters followed by thermal annealing in a gaseous environment to fabricate AgNPs. Scanning electron microscopy revealed the uniform size distribution of AgNPs on the graphene surface with minimal to no aggregation. Four main sizes of AgNPs were obtained (37 ± 3, 45 ± 3, 54 ± 2, and 64 ± 3 nm) via controlling the printing force, z-piezo extension, and dwell time. Energy dispersive X-ray spectroscopy analysis validated the existence of elemental Ag on the graphene surface. Subsequent chemical etching of AgNPs using nitric acid (HNO3) with the aid of sonication and mechanical agitation produced holes of uniform size distribution generating hG. The obtained ID/IG ratios ≤ 0.96 measured by Raman spectroscopy were lower than those commonly reported for GO (ID/IG > 1), indicating the removal of more defective C atoms during the etching process to produce hG while preserving the remaining C atoms in ordered or crystalline structures. Indeed, SPBCL could be utilized to fabricate uniformly distributed AgNPs of controlled sizes on graphene surfaces to ultimately produce hG of uniform hole size distribution.

Highlights

Among various carbon nanostructures, holey graphene has attracted considerable interest owing to its exceptional properties including excellent electrical conductivity, large specific surface area, and superior chemical/electrochemical stability surpassing its pristine graphene form[1,2]
scanning probe block co-polymer lithography (SPBCL)-defined polymeric nanoreactors govern the size of fabricated features via confining NP nucleation and growth, which are primarily affected by the hydrophobicity of the substrate, the printing force, z-piezo extension, and dwell time along with the conditions utilized during the subsequent thermal annealing step[36]
Probe sonication was carried out using continuous mode at 60% amplitude while applying various sonication times (1-4 hrs) to examine the output graphene flakes against a commercially available graphene suspended in PVP:Dettol hand soap (DHS) aqueous dispersion and probe sonicated for 1 hr

Summary

Introduction

Holey graphene (hG) has attracted considerable interest owing to its exceptional properties including excellent electrical conductivity, large specific surface area, and superior chemical/electrochemical stability surpassing its pristine graphene form[1,2]. Graphene hydrophobicity[31], thermal stability (≤600°C)[32], and electrical conductivity[33] are the determinant properties that could permit the use of SPBCL to fabricate uniformly distributed AgNPs on its surface. To self-assemble graphene flakes into a uniform layer, graphene in PVP: DHS (1 mL) was diluted with EtOH (5 mL), sonicated for 15 min, and injected in a timely manner into DDW (12 mL).

Results

Conclusion