Cu 3 N layers with a thickness of 40 nm were deposited by reactive sputtering using Ar: 10% N 2 and 100% N 2 , after which they were annealed under NH 3 /H 2 between 300 and 500 °C. These exhibited distinct maxima in differential transmission at ∼2.46, 2.30, 2.05, and 1.9 eV on a picosecond time scale, as shown by ultrafast pump-probe spectroscopy. We show that the maxima at 1.9 and 2.05 eV correspond to the M and R direct energy band gaps of bulk Cu 3 N. In contrast, the higher energy maxima at 2.46 and 2.30 eV are related to the occurrence of strained Cu 3 N in the vicinity of the surface due to surface oxidation upon exposure to the ambient. This is corroborated by the fact that we observed a suppression of the high energy maxima at 2.46 and 2.30 eV by increasing the thickness of the Cu 3 N layers from 40 to 80 nm, which also rules out intervalley transfer. It is also consistent with the fact that we observed a suppression of the low-energy peaks at 1.9 and 2.05 eV upon the intentional incorporation of oxygen during the deposition of Cu 3−x N 1−x O x . We describe these findings in conjunction with density functional theory calculations of the electronic band structure of Cu 3 N and Cu 3−x N 1−x O x , from which we find that oxygen is preferably incorporated as a shallow donor without giving rise to midgap states and may be used to tailor the direct energy band gaps of this defect-tolerant semiconductor, which in turn is important in the context of solar cells.

Raman spectroscopy is applied for the non‐destructive characterisation of the graphite which is used as solid lubricant in the friction material of semi‐metallic brake pads in vehicles. The characteristics (intensity, position, width) of the main Raman bands assigned to vibrational modes of the graphitic honeycomb structure (G‐band) and to defects (D‐band) are proved useful probes of the quality and wear status of the graphite lubricant because they are sensitive to the structural disorder. It is found that wear of the graphite lubricant proceeds in two stages: transformation of crystalline to nanocrystalline graphite and subsequent amorphisation. Moreover, the intensity of the defect‐related D′ peak is also used in order to obtain information about the nature of the defects.

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The third harmonic generation (THG) of graphite layers on paper substrate upon excitation with intense (up to 100 kV cm−1) narrowband terahertz (THz) pulses is studied. Highest THG efficiencies are comparable with those of chemical vapor deposition‐grown single‐layer graphene. Samples are hand drawn, using commercially available pencils. The THG response shows high sensitivity regarding the hatching direction relative to the THz polarization orientation. Using Raman spectroscopy, the occurrence of graphene‐like structures in the samples is confirmed. The findings demonstrate the feasibility of virtually no‐cost and easy‐to‐fabricate materials for THz nonlinear optics.

CuO nanowires with diameters between 100 and 200 nm, lengths up to 10 µm and a uniform distribution have been grown at 600°C under 100 ml/min O2 on 15 mm...