Can Europium Atoms form Luminescent Centres in Diamond: A combined Theoretical-Experimental Study

The incorporation of Eu into the diamond lattice is investigated in a combined theoretical-experimental study. The large size of the Eu ion induces a strain on the host lattice, which is minimal for the Eu-vacancy complex. The oxidation state of Eu is calculated to be 3+ for all defect models considered. In contrast, the total charge of the defect-complexes is shown to be negative -1.5 to -2.3 electron. Hybrid-functional electronic-band-structures show the luminescence of the Eu defect to be strongly dependent on the local defect geometry. The 4-coordinated Eu substitutional dopant is the most promising candidate to present the typical Eu3+ luminescence, while the 6-coordinated Eu-vacancy complex is expected not to present any luminescent behaviour. Preliminary experimental results on the treatment of diamond films with Eu-containing precursor indicate the possible incorporation of Eu into diamond films treated by drop-casting. Changes in the PL spectrum, with the main luminescent peak shifting from approximately 614 nm to 611 nm after the growth plasma exposure, and the appearance of a shoulder peak at 625 nm indicate the potential incorporation. Drop-casting treatment with an electronegative polymer material was shown not to be necessary to observe the Eu signature following the plasma exposure, and increased the background luminescence.Comment: 12 pages, 7 figures, 5 table

Direct observation of electron emission from grain boundaries in CVD diamond by PeakForce-controlled tunnelling atomic force microscopy

AbstractA detailed investigation of electron emission from a set of chemical vapour deposited (CVD) diamond films is reported using high-resolution PeakForce-controlled tunnelling atomic force microscopy (PF-TUNA). Electron field emission originates preferentially from the grain boundaries in low-conductivity polycrystalline diamond samples, and not from the top of features or sharp edges. Samples with smaller grains and more grain boundaries, such as nanocrystalline diamond, produce a higher emission current over a more uniform area than diamond samples with larger grain size. Light doping with N, B or P increases the grain conductivity, with the result that the emitting grain-boundary sites become broader as the emission begins to creep up the grain sidewalls. For heavy B doping, where the grains are now more conducting than the grain boundaries, emission comes from both the grain boundaries and the grains almost equally. Lightly P-doped diamond samples show emission from step-edges on the (111) surfaces. Emission intensity was time dependent, with the measured current dropping to ∼10% of its initial value ∼30h after removal from the CVD chamber. This decrease is ascribed to the build-up of adsorbates on the surface along with an increase in the surface conductivity due to surface transfer doping

High phosphorous incorporation in (100)-oriented MP CVD diamond growth

Diamond n-type layers are crucial for the development of a new bipolar diamond-based electronic technology. However, the difficulties to incorporate impurity atoms into the diamond lattice make its growth a stage of technological research still in progress. Phosphorus doping has been carried out successfully on (111)-oriented diamond substrates, reaching high concentrations and good reproducibility. Nevertheless, such reproducible results have not been obtained for the (100) growth orientations yet, even though the (100) substrate orientation is still the most used diamond substrate for electronic applications. In this study, three samples are grown by microwave plasma-enhanced chemical vapor deposition on diamond (100)-oriented high pressure high temperature substrates. All samples are deposited with the same growth conditions except methane, which was varied between 1.5 % and 3.5 %. A different growth mechanism is observed for each of the methane content used. The step flow growth mechanism shows increased phosphorus incorporation, determined by cathodoluminescence (CL) in cross sectional view in focused ion beam preparations. This sample also shows a less rough surface and no crystal defects observable by transmission electron microscopy (TEM). That is why these growth conditions are used for the fabrication of the n-type layer of a p+/p−/n stack. Ellipsometry and TEM measurements on this sample yield a high growth rate of 3.5 μm/h with a phosphorus concentration of 4 × 1017 cm−3, estimated by CL spectroscopy. The sample shows a low density of surface defects, observed by optical microscopy. However, TEM observations show dislocations with 1/2 a〈110〉 burger vector and stacking faults with 1/3 〈111〉 displacement vector. © 2023 The Author(s

Laser-Patternable Graphene Field Emitters for Plasma Displays

This paper presents a plasma display device (PDD) based on laser-induced graphene nanoribbons (LIGNs), which were directly fabricated on polyimide sheets. Superior field electron emission (FEE) characteristics, viz. a low turn-on field of 0.44 V/μm and a large field enhancement factor of 4578, were achieved for the LIGNs. Utilizing LIGNs as a cathode in a PDD showed excellent plasma illumination characteristics with a prolonged plasma lifetime stability. Moreover, the LIGN cathodes were directly laser-patternable. Such superior plasma illumination performance of LIGN-based PDDs has the potential to make a significant impact on display technology

Low-temperature transport in highly boron-doped nanocrystalline diamond

International audienceWe studied the transport properties of highly boron-doped nanocrystalline diamond thin films at temperatures down to 50 mK. The system undergoes a doping-induced metal-insulator transition with an interplay between intergranular conductance g and intragranular conductance g0, as expected for a granular system. The conduction mechanism in the case of the low-conductivity films close to the metal-insulator transition has a temperature dependence similar to Efros-Shklovskii type of hopping. On the metallic side of the transition, in the normal state, a logarithmic temperature dependence of the conductivity is observed, as expected for a metallic granular system. Metallic samples far away from the transition show similarities to heavily borondoped single-crystal diamond. Close to the transition, the behavior is richer. Global phase coherence leads in both cases to superconductivity also checked by ac susceptibility , but a peak in the low-temperature magnetoresistance measurements occurs for samples close to the transition. Corrections to the conductance according to superconducting fluctuations account for this negative magnetoresistance

Deposition of diamond films on single crystalline silicon carbide substrates

Silicon carbide (SiC) is a wide band gap material that is slowly but steadily asserting itself as a reliable alternative to silicon (Si) for high temperature electronics applications, in particular for the electrical vehicles industry. The passivation of SiC devices with diamond films is expected to decrease leakage currents and avoid premature breakdown of the devices, leading to more efficient devices. However, for an efficient passivation the interface between both materials needs to be virtually void free and high quality diamond films are required from the first stages of growth. In order to evaluate the impact of the deposition and seeding parameters in the properties of the deposits, diamond films were deposited on SiC substrates by hot filament chemical vapor deposition (HFCVD). Before the seeding step the substrates were exposed to diamond growth conditions (pre-treatment PT) and seeding was performed with a solution of detonation nanodiamond (DND) particles and with 6–12 and 40–60 μm grit. Diamond films were then grown at different temperatures and with different methane concentrations and the deposits were observed in a scanning electron microscope (SEM); their quality was assessed with Raman spectroscopy.publishe