Poly(methyl
methacrylate) (PMMA) is commonly used as a temporary
support layer for chemical vapor deposition (CVD) graphene transfer;
it is then removed by a chemical or thermal treatment. Regardless
of the method used for PMMA removal, polymer residues are left on
the graphene surface, which alter its intrinsic properties. A method
based on isotope labeling of PMMA and time-of-flight secondary ion
mass spectrometry (ToF-SIMS) has now been developed to identify, locate,
and quantify these residues. It is shown that vacuum annealing does
not completely remove the PMMA residues but, instead, transforms them
into amorphous carbon. In contrast, air annealing under optimized
conditions generates a PMMA-free surface with limited damage to the
graphene structure. This cleaned graphene surface demonstrates low
friction which is comparable with that of pristine graphene film.
Cu−N codoped TiO 2 anatase thin films with a nanocolumnar architecture have been synthesized by RF-magnetron sputtering and characterized by Raman, scanning electron spectroscopy, and X-photoelectron spectroscopy. Absorption, photoluminescence, and photoluminescence lifetimes of the prepared samples have been investigated to understand the dynamics of the photogenerated carriers in connection to both introduced defects and the modified TiO 2 band structure. At low concentrations Cu is mainly present as Cu + , while at higher concentrations the Cu 2+ oxidation state prevails. Nitrogen, at low concentration and without the presence of copper dopant, substitutionally replaces oxygen to form a O−Ti−N linkage. With increasing concentration, interstitial nitrogen and Ti−O−N and Ti−O−N−O linkages are observed. In all codoped samples nitrogen is present as both interstitial and substitutional dopant. From photoluminescence spectra it is observed that nitrogen, in cooperation with Cu, more heavily affects the oxide structure, through Ti−N linkages, in such a way to quench the TiO 2 exciton luminescence through charge trapping or energy transfer mechanisms. Time-resolved PL analysis evidenced that Cu−N codoping hinders the exciton radiative recombination in the anatase network, giving rise to increase of both the mean lifetime and trapping rate on defects at the nanocolumn surface.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.