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The techniques of positron annihilation spectroscopy have been applied to the study of well-characterized reservoir rock samples. In this article we focus primarily on sandstone and carbonate samples. We report (a) measurements of the Doppler broadening (DB) parameters and mean lifetime values (〈τ〉) of dry samples; (b) measurement of the DB parameters as a function of temperature from room temperature to 200 °C; and (c) observation of the outgassing of heated samples simultaneously with the DB measurements. We interpret the measurements in terms of positron annihilation with both valence and core electrons and discuss how the DB parameters depend on the major chemical constituents (lithology) and to a lesser degree on the structure of the samples. The major result of this work is that the positron parameters such DB parameters (S, SW, and W) and mean lifetime values are shown to be reproducible and reliable bulk properties of well-characterized rock samples and can be used to categorize rocks of geophysic...

We present optical, electrical, and structural properties of nitrogen-doped graphene grown on the Si face of 4H-SiC (0001) by chemical vapor deposition method using propane as the carbon precursor and N2 as the nitrogen source. The incorporation of nitrogen in the carbon lattice was confirmed by X-ray photoelectron spectroscopy. Angle-resolved photoemission spectroscopy shows carrier behavior characteristic for massless Dirac fermions and confirms the presence of a graphene monolayer in the investigated nitrogen-doped samples. The structural and electronic properties of the material were investigated by Raman spectroscopy. A systematical analysis of the graphene Raman spectra, including D, G, and 2D bands, was performed. In the case of nitrogen-doped samples, an electron concentration on the order of 5–10 × 1012 cm−2 was estimated based upon Raman and Hall effect measurements and no clear dependence of the carrier concentration on nitrogen concentration used during growth was observed. This high electron concentration can be interpreted as both due to the presence of nitrogen in graphitic-like positions of the graphene lattice as well as to the interaction with the substrate. A greater intensity of the Raman D band and increased inhomogeneity, as well as decreased electron mobility, observed for nitrogen-doped samples, indicate the formation of defects and a modification of the growth process induced by nitrogen doping.