Three different procedures are used to deposit aluminium onto O‐terminated (100) and (111) boron‐doped diamond, with the aim of producing a thermally stable surface with low work function and negative electron affinity. The methods are 1) deposition of a > 20 nm film of Al by high‐vacuum evaporation followed by HCl acid wash to remove excess metallic Al, 2) deposition of <3 Å of Al by atomic layer deposition, and 3) thin‐film deposition of Al by electron beam evaporation. The surface structure, work function, and electron affinity are investigated after annealing at temperatures of 300, 600, and 800 °C. Except for loss of excess O upon first heating, the Al + O surfaces remain stable up to 800 °C. The electron affinity values are generally between 0.0 and −1.0 eV, and the work function is generally 4.5 ± 0.5 eV, depending upon the deposition method, coverage, and annealing temperature. The values are in broad agreement with those predicted by computer simulations of Al + O (sub)monolayers on a diamond surface.
This article reports on a technique for patterning diamond nanogrit which utilizes commercial ink-jet printer technology. Diamond nanogrit as small as 50 nm has been successfully printed onto substrates of glass, silicon, copper, and fused quartz. The technique has been used to demonstrate a quick and simple means to seed patterned. nanocrystalline diamond films onto candidate substrates of potentially any conceivable size or shape.
Cu2ZnSn(S,Se)4 (CZTSSe) is a promising material for thin-film photovoltaics, however, the open-circuit voltage (VOC) deficit of CZTSSe prevents the device performance from exceeding 13% conversion efficiency. CZTSSe is a heavily compensated material that is rich in point defects and prone to the formation of secondary phases. The landscape of these defects is complex and some mitigation is possible by employing non-stoichiometric conditions. Another route used to reduce the effects of undesirable defects is the doping and alloying of the material to suppress certain defects and improve crystallization, such as with germanium. The majority of works deposit Ge adjacent to a stacked metallic precursor deposited by physical vapour deposition before annealing in a selenium rich atmosphere. Here, we use an established hot-injection process to synthesise Cu2ZnSnS4 nanocrystals of a pre-determined composition, which are subsequently doped with Ge during selenisation to aid recrystallisation and reduce the effects of Sn species. Through Ge incorporation, we demonstrate structural changes with a negligible change in the energy bandgap but substantial increases in the crystallinity and grain morphology, which are associated with a Ge-Se growth mechanism, and gains in both the VOC and conversion efficiency. We use surface energy-filtered photoelectron emission microscopy (EF-PEEM) to map the surface work function terrains and show an improved electronic landscape, which we attribute to a reduction in the segregation of low local effective work function (LEWF) Sn(II) chalcogenide phases.
This paper presents results obtained from Finite Difference Time Domain (FDTD) and Transfer Matrix Method (TMM) modelling of nickel thin-films. It is shown that by adding a periodic grating to the surface of the nickel we can dramatically increase its optical absorption over the 300 nm-1000 nm spectral range at normal incidence. The main aim of this work is to maximise the optical absorption of a thin nickel film as part of a solar-thermal energy conversion device.
We present measured optical absorptivity, emissivity, and maximum solar-heated temperatures for micropatterned molybdenum. The molybdenum samples were fabricated using laser micromachining and characterized using an integrating sphere and an infrared microscope. In-air solar simulator-heated temperature results for the molybdenum samples with different microstructures are presented, and COMSOL modeling is then used to predict in-vacuum maximum temperatures. A vacuum chamber was developed to reduce the convection heat loss with a mount designed to minimize conduction loss, and a maximum measured temperature of 413°C was obtained.
Diamond-based thermionic emission devices could provide a means to produce clean and renewable energy through direct heat-to-electrical energy conversion. Hindering progress of the technology are the thermionic output current and threshold temperature of the emitter cathode. In this report, we study the effects on thermionic emission caused by in-situ exposure of the diamond cathode to beta radiation. Nitrogen-doped diamond thin films were grown by microwave plasma chemical vapour deposition on molybdenum substrates. The hydrogen-terminated nano-crystalline diamond was studied using a vacuum diode setup with a 63Ni beta radiation source-embedded anode, which produced a 2.7-fold increase in emission current compared to a 59Ni-embedded control. The emission threshold temperature was also examined to further assess the enhancement of thermionic emission, with 63Ni lowering the threshold temperature by an average of 58 ± 11 oC compared to the 59Ni control. Various mechanisms for the enhancement are discussed, with a satisfactory explanation remaining elusive. Nevertheless, one possibility is discussed involving excitation of pre-existing conduction band electrons that may skew their energy distribution toward higher energies.
Microscopic and macroscopic field emission properties of amorphic diamond films on n- and p-type silicon substrates were studied by combined scanning tunneling microscopy/spectroscopy and integral field emission I–V measurements. Microscopic scanning tunneling spectroscopy showed that amorphic diamond films on n-Si have lower threshold voltage and higher emission current than amorphic diamond films on p-Si. The observed rectification characteristics suggest that amorphic diamond on n-Si is an ideal forward-biased p-n junction cold cathode emitter; however, there is no significant difference between these two structures by integral field emission I–V measurements. Conversion of the smooth amorphic diamond film into porous sp3/sp2 composites with sharp features under electric fields higher than 50 V/μm, followed by preferred electron emission from the porous composite sites of high transconductance, was believed to be the cause.
Low resistivity (~3-24 this http URL) with tunable n- and p-type phase pure Cu2O thin films have been grown by pulsed laser deposition at 25-200 0C by varying the background oxygen partial pressure (O2pp). Capacitance data obtained by electrochemical impedance spectroscopy was used to determine the conductivity (n- or p-type), carrier density, and flat band potentials for samples grown on indium tin oxide (ITO) at 25 0C. The Hall mobility of the n- and p-type Cu2O was estimated to be ~ 0.85 cm2.V-1s-1 and ~ 4.78 cm2.V-1s-1 respectively for samples grown on quartz substrate at 25 0C. An elevated substrate temperature ~ 200 0C with O2pp = 2 - 3 mTorr yielded p-type Cu2O films with six orders of magnitude higher resistivities in the range ~ 9 - 49 this http URL and mobilities in the range ~ 13.5 - 22.2 cm2.V-1s-1. UV-Vis-NIR diffuse reflectance spectroscopy showed optical bandgaps of Cu2O films in the range of 1.76 to 2.15 eV depending on O2pp. Thin films grown at oxygen-rich conditions O2pp > 7 mTorr yielded mixed-phase copper oxide irrespective of the substrate temperatures and upon air annealing at 550 0C for 1 hour completely converted to CuO phase with n-type semiconducting properties (~12 this http URL, ~1.50 cm2.V-1s-1). The as-grown p- and n-type Cu2O showed rectification and a photovoltaic (PV) response in solid junctions with n-ZnO and p-Si electrodes respectively. Our findings may create new opportunities for devising Cu2O based junctions requiring low process temperatures.
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