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This paper presents a diamond gammavoltaic cell—a solid-state device that converts gamma radiation into electricity—with a novel design and promising capabilities. Gammavoltaics pose a unique challenge among radiovoltaics due to the highly penetrating nature of gamma rays. To adapt existing radiovoltaic and dosimeter designs by increasing their thickness risks throttling the flowing current due to an attendant increase in series resistance. The presented design partially decouples this relationship by creating a low-coverage hydrogen-terminated collection volume around the device, exploiting the transfer doping effect. This paper proves that hydrogen termination is necessary for the gammavoltaism exhibited. Data are then presented from current-voltage curves taken using synchrotron radiation over the range 50-150 keV. A drop in the series resistance over the range is discovered and linked to the transition from the photoelectric effect to Compton scattering. The cell produces an open-circuit voltage VOC = 0.8 V. Its short-circuit current ISC and maximum power Pmax are found to also depend on photon energy, reaching maxima at ∼150 keV, where ISC > 10 μA and Pmax > 3 μW, normalized in flux to 2 × 1011 γ.s−1. Groundwork is hence laid for developing this type of cell for micropower applications.

Low work function materials are desirable in many applications such as electron emission and photo-catalysis. We have studied low energy electron emission from low work function hydrogen terminated diamond surfaces via electron spectroscopy to gain insight into the mechanisms involved during electron excitation and emission. Electron emission was found to be dominated by electrons within the band gap energy region, allowed due to the negative electron affinity diamond surface, while sub-bandgap illu-mination was able to significantly increase emission current. Substantial upward surface band bending greater than 2 eV was observed for the diamond samples, which affect electron accumulation at the surfaces. Intra-bandgap states are shown to strongly influence electron emission behavior, which can have great implications for various energy conversion devices. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Thermionic emission relies on the low work function and negative electron affinity of the, often functionalized, surface of the emitting material. However, there is little understanding of the interplay between thermionic emission and temperature-driven dynamic surface transformation processes as these are not represented on the traditional Richardson-Dushman equation for thermionic emission. Here, we show a new model for thermionic emission that can reproduce the effect of dynamic surface changes on the electron emission and correlate the components of the thermionic emission with specific surface reconstruction phases on the surface of the emitter. We use hydrogenated100single-crystal and polycrystalline diamonds as thermionic emitters to validate our model, which shows excellent agreement with the experimental data and could be applicable to other emitting materials. Furthermore, we find that tailoring the coverage of specific structures of the C(100)-(2 × 1):H surface reconstruction could increase the thermionic emission of diamond by several orders of magnitude.

The aim of this work is to study the heating efficiency of refractory microstructures by excitation of surface plasmon polaritons in the far infrared that can be used for high-temperature applications. The work has designed metal grating couplers on molybdenum films to maximise the absorption of a 10.6 µm CO 2 laser light source. Molybdenum has been chosen since it is an industrial refractory metal combined with the fact that its optical properties in the far infrared are similar to gold but with stable high-temperature performance. Linear gratings have been used as plasmonic couplers on large area substrates produced by laser milling. Real-time absolute temperature measurements have been performed showing a 42% increase in the maximum achievable temperature from 702 to 985 K.

Thermionic emitting materials are relevant for several technological applications like electron guns, X-ray sources, or thermionic energy converters. As new materials and surface functionalisations that enable thermionic emission are developed, it is essential to be able to test them in a repeatable and reliable manner. Here, we present a CO 2 laser-heated system for thermionic tests that can be used to test the thermionic emission current of different materials regardless of the optical properties or form factor. Our system can reach sample temperatures of T ≈ 1000 °C and can follow pre-programmed heating profiles. Additionally, a double thermo-electrical decoupling provides a very low electrical noise environment while keeping the sample heat loss to a minimum. Experimental data on sample temperature and thermionic current from a hydrogen terminated single crystal diamond are presented and discussed.

We demonstrate diamond growth through microwave plasma-enhanced chemical vapor deposition using a sealed (static-mode) CH4/H2 process gas mixture. The growth experiments were complemented by spatially and spectrally resolved optical emission imaging measurements of electronically excited C2 and CH radicals in the hot plasma core. The as-grown material was characterized by Raman Spectroscopy and Scanning Electron Microscopy and shown to be typical of polycrystalline diamond grown using traditional methods. Moreover, this material was essentially indistinguishable from material grown using a tracked flow-mode of operation in which the input methane flow rate was progressively reduced to mimic the time evolving C2 emission intensities in the static-mode experiments. These proving static-mode studies demonstrate a ~30-fold improvement (cf. that achieved using standard flow-mode conditions) in the conversion efficiency of carbon in the input source gas into diamond, and we argue that further gains should be possible with appropriate reactor and process optimization. Static-flow growth could be particularly advantageous in the case of depositions using limited, expensive, hazardous, or environmentally damaging feedstock gases.

As model systems of poly(aniline), oligo(aniline)s have been previously predicted to exist in a number of isomeric forms, with positional, geometric and conformational isomerism possible. Here, monolayers of phenyl and alkyl-chain end-capped tetra(aniline)s in their half-oxidised emeraldine base (EB) state are thermally evaporated in ultra-high vacuum (UHV) conditions. Scanning tunneling microscopy (STM) is then used to directly visualize individual cis/trans isomers. The influence the observed isomerism has on the two-dimensional self-assembly of these conjugated systems is discussed. Gas-phase density functional theory (DFT) calculations are used to corroborate the experimental data, providing optimized structural data that corresponds well to the isomers observed by STM. The proof of the presence of these isomers provides the basis for understanding and gaining insight into the lack of well-defined self-assembled thin films and single crystals from aniline-based materials in their half-oxidised EB state. The assembly behavior and properties of molecular thin films are thus clearly and intractably linked, highlighting the importance of isomerism and material choice for organic thin film applications.

Self-organized 3D nanostructured architectures including quasi-ordered concentric hexagonal structures generated during the growth of single crystalline n-GaN substrates by hydride vapor phase epitaxy (HVPE) are reported. The study of as-grown samples by using Kelvin Probe Force Microscopy shows that the formation of self-organized architectures can be attributed to fine modulation of doping related to the spatial distribution of impurities. The specific features of nanostructured architectures involved have been brought to light by using electrochemical and photoelectrochemical etching techniques which are highly sensitive to local doping. The analysis of the results shows that the formation of self-organized spatial architectures in the process of HVPE is caused by the generation of V-pits and their subsequent overgrowth accompanied by the growth in variable direction. It is demonstrated for the first time that the electrical and luminescence properties of HVPE-grown GaN are spatially modulated throughout, including islands between overgrown V-pit regions. The dependence of doping upon growth direction is confirmed by the micro-cathodoluminescence characterization of HVPE-grown pencil-like microcrystals exposing various crystallographic planes along the tip. These results are indicative of new possibilities for defect engineering in gallium nitride and for three-dimensional spatial nanostructuring of this important electronic material by controlling the growth direction. (C) 2016 The Electrochemical Society. All rights reserved.