Recently, carbon spectroscopy became very important due to the growing interest in the applications of new carbon allotropes, especially of 2D structures such as graphene and nanotubes. It is well known that the hybridization of carbon electrons defines most of the properties of these materials. Among the analytical techniques used for the identification of carbon allotropes is the spectroscopy of carbon Auger line, which involves the transitions of valence band electrons and can be excited by electron beam (AES) or X‐ray photons (XAES). From the shape of C KVV spectrum, it is possible not only to recognize the cases of pure sp2 and sp3 configurations but also to quantify their ratio in amorphous carbon films. In present work, an experimental study of three main allotropes of carbon: graphite, diamond, and graphene is reported. The average thickness of graphene was evaluated from the ratio of C 1s and substrate photoelectron peaks, registered at grazing angle. Carbon KVV spectra were investigated by using XAES and AES techniques. Obtained results were compared with the ones acquired for reference samples of graphite and monocrystalline diamond. In addition, some samples of hydrogenated diamond were analyzed. It was demonstrated that the comparison of C KVV spectra excited by electrons and X‐rays can be used for identification of graphene. Diamond‐like C KVV spectrum, observed in XAES experiments, is a very promising fingerprint of graphene. Obtained results are also compared with valence band spectra of graphene, diamonds and graphite that were acquired by using ultraviolet photoemission spectroscopy. Copyright © 2014 John Wiley & Sons, Ltd.

Black diamond is obtained by a controlled nanoscale periodic texturing of CVD diamond surface, able to drastically modify the interaction with solar radiation from optical transparency up to solar absorptance values even >90%. Surface texturing, performed by the use of an ultra-short pulse laser, is demonstrated to induce an intermediate band within the diamond bandgap supporting an efficient photoelectronic conversion of sub-bandgap photons (<5.5 eV). The intermediate band introduction results in an external quantum efficiency enhanced up to 800 nm wavelengths (and up two orders of magnitude larger than the starting transparent diamond film), without affecting the film transport capabilities. The optical and photoelectronic outstanding results open the path for future application of black diamond as a photon-enhanced thermionic emission cathode for solar concentrating systems, with advantages of excellent electronic properties combined with a potentially very low work function and high thermal stability

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Concentrating solar technologies represent economically viable alternatives to distributed PV since the optics production cost per unit surface is far lower than that of PV cells. The reduction of the active conversion area allows for expensive multijunction cells with efficiency as high as 45% to be used in concentrating PV (CPV). [1] However, CPV is struggling commercially because high-density arrangements are prevented by issues in excess heat removal. On the other hand, concentrating solar power (CSP) technologies, [2,3] based on transfer of high-temperature thermal energy through a fluid toward thermomechanical engines, are promising for large plants characterized by thermal-to-electric efficiency around 35%, with the important capabilities of energy cogeneration and storage.The solar thermionic-thermoelectric generator (ST 2 G) explored here takes the advantages of CSP and CPV to provide an effective alternative concept for future solar technologies by combining the hightemperature operations, typical of CSP, to the compactness, scalability, reliability, and long operating lifetime of the solid-state converters, typically used in CPV systems. By combining a thermionic energy converter (TEC), operating at high but practical temperatures (<1100 °C) that can be achieved with point-focus solar concentrators and the development of low-work-function materials, with a thermoelectric energy generator (TEG) thermally connected in series, the ST 2 G technology can meet requirements of economic cost-effectiveness guaranteed by high-temperature solid-state converters. [4] The thermionic-thermoelectric solid-state technology, characterized by solar-to-electric conversion efficiency feasibly >40%, is comprehensively proposed and discussed for conversion of concentrating solar power. For the first time, the related solar generator prototype is designed and fabricated by developing advanced materials functionalized for the specific application, such as thermally resistant hafnium carbide-based radiation absorbers, surface-textured at the nanoscale to obtain a solar absorptance >90%, and chemical vapor deposition diamond films, acting as lowwork-function (2.06 eV) thermionic emitters. Commercial thermoelectric generators and encapsulation vacuum components complete the prototype. The conversion efficiency is here evaluated under outdoor concentrated sunlight, demonstrating thermionic stage output power of 130 mW at 756 °C, combined to the maximum thermoelectric output power of 290 mW. The related solar-to-electric conversion efficiency is found to be 0.4%, but, once the net thermal flux fed to the conversion stages is considered, a thermal-toelectric efficiency of 6% is revealed. Factors affecting the performance of the present prototype are analyzed and discussed, as well as a strategy to rapidly overcome limitations, in order to prepare an efficient and highly competitive solid-state conversion alternative for future concentrating solar plants.