An underlying challenge here is a tradeoff between removing particles and pittings of Cu foil as a function of treatment time and acid concentration. A treatment time of 10 min and an acid concentration of 4 wt% were found to be optimal. Scanning electron microscopy (SEM) based mapping of a relatively large area (~0.2 mm 2 , Figures ) of graphene was used to analyze the particle density on the surface (Figure ). Acid treatment significantly reduced the density of particles. The population of particles smaller than 1 µm was reduced by 70%. Importantly, particles larger than 1 µm were eliminated. This is crucial for reducing cracks during graphene transfer because the macroscopic particles lead to pinhole defects during transfer. The acid treatment also smoothened grooves and scratches on the Cu foil. Optical microscopy images (Figure ) and profilometry mapping analysis (Figure , n, Figure ) demonstrate that graphene produced on acid-treated Cu foil has a significantly lower root mean square (RMS) surface roughness (150 nm) compared to that on as-received Cu foil (261 nm). Therefore, the two interventions, namely acid pretreatment and using the alumina tube in the CVD reactor, effectively reduced the surface contamination of graphene.