Abstract
Heteroatom doping is a widely used method for the modification of the electronic and chemical properties of graphene. A low-pressure chemical vapor deposition technique (CVD) is used here to grow pure, nitrogen-doped and phosphorous-doped few-layer graphene films from methane, acetonitrile and methane-phosphine mixture, respectively. The electronic structure of the films transferred onto SiO2/Si wafers by wet etching of copper substrates is studied by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy using a synchrotron radiation source. Annealing in an ultra-high vacuum at ca. 773 K allows for the removal of impurities formed on the surface of films during the synthesis and transfer procedure and changes the chemical state of nitrogen in nitrogen-doped graphene. Core level XPS spectra detect a low n-type doping of graphene film when nitrogen or phosphorous atoms are incorporated in the lattice. The electrical sheet resistance increases in the order: graphene < P-graphene < N-graphene. This tendency is related to the density of defects evaluated from the ratio of intensities of Raman peaks, valence band XPS and NEXAFS spectroscopy data.
Highlights
Planar graphene sheets possessing a good electrical conductivity and mechanical strength as well as transparency and flexibility are very attractive for advanced electronics and energy applications [1,2].The chemical vapor deposition (CVD) method provides a scalable synthesis of the sheets on different catalytic substrates, and copper is among the cheapest ones [3]
It is assumed that the growth of a few layers on a copper substrate is due to the penetration of feeding gas molecules between copper and underlayer graphene [7]
We report the synthesis of few-layer graphene films on copper substrates using low pressures of a gaseous mixture of CH4 /H2 at 1323 K, CH3 CN/H2 at 1123 K (N-graphene) and CH4 /PH3 /H2 at 1173 K (P-graphene)
Summary
Planar graphene sheets possessing a good electrical conductivity and mechanical strength as well as transparency and flexibility are very attractive for advanced electronics and energy applications [1,2].The chemical vapor deposition (CVD) method provides a scalable synthesis of the sheets on different catalytic substrates, and copper is among the cheapest ones [3]. Precursor carbon-containing molecules decompose at the substrate and the obtained species form the graphene domains that coalescence over the synthesis yields a continuous polycrystalline graphene layer [4]. The low solubility of carbon in copper allows the production of large area graphene monolayers on the substrates [5]. It is assumed that the growth of a few layers on a copper substrate is due to the penetration of feeding gas molecules between copper and underlayer graphene [7]. It becomes possible when edges of graphene sheet are not in tight contact with copper
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