Microporous poly- and monocrystalline diamond films produced from chemical vapor deposited diamond-germanium composites

We report on a novel method for porous diamond fabrication, which is based on the synthesis of diamond-germanium composite films followed by etching of Ge component. The composites were grown by microwave plasma assisted CVD in CH4-H2-GeH4 mixtures on (100) silicon, microcrystalline- and single-crystal diamond substrates. The structure and the phase composition of the films before and after the etching were analyzed with scanning electron microscopy and Raman spectroscopy. The films revealed a bright emission of GeV color centers due to diamond doping with Ge, as evidenced by photoluminescence spectroscopy. The possible applications of the porous diamond films include thermal management, surfaces with superhydrophobic properties, chromatography, supercapacitors etc

Luminescent diamond composites

Diamond is valuable material with extraordinary high thermal conductivity and transparency in a wide spectral range from UV to IR and longer wavelengths. Defects and impurities in the diamond lattice can absorb and emit light at wavelengths specific for each of such “color centers.” Particularly, the vacancy-related defects in diamond, such as nitrogen-vacancy (NV) or silicon-vacancy (SiV) centers, are actively investigated due to their potential for biomedicine, quantum optics, local thermometry and magnetometry. Although a great variety of different color centers in diamond are discovered, only a limited number of those point defects can be reliably reproduced in synthetic diamond, obtained either by chemical vapor deposition (CVD) or high-pressure high-temperature (HPHT). An alternative approach to producing luminescent diamond-based materials is to integrate stable non-diamond sources of luminescence in the form of nano- or microparticles of foreign materials into the pristine diamond. The produced diamond composites possess excellent properties of diamond combined with optical emission characteristics, which cannot be provided with intrinsic defects in diamond. The good candidates for the materials of such impurities are well-investigated fluorides and oxides doped by rare-earth elements (RE) or other luminescent chalcogenides such as sulfides, selenides and tellurides. Here we briefly review recent achievements in fabrication and properties of these new luminescent diamond-RE composites, compare them with luminescent properties of doped diamond, and outline prospects for applications of the luminescent diamond composites for photonics, markers, monitors of high-power synchrotron, X-ray beams and X-ray lasers

Fabry-Perot Pressure Sensors Based on Polycrystalline Diamond Membranes

Pressure sensors based on diamond membranes were designed and tested for gas pressure measurement up to 6.8 MPa. The diamond film (2” diameter, 6 μm thickness)—grown by microwave plasma chemical vapor deposition on a silicon substrate—was a starting material to produce an array of membranes with different diameters in the 130–400 μm range, in order to optimize the sensor performance. Each 5 mm × 5 mm sensing element was obtained by subsequent silicon slicing. The fixed film thickness, full-scale pressure range, and sensor sensitivity were established by a proper design of the diameter of diamond membrane which represents the sensing element for differential pressure measurement. The pressure-induced deflection of the membrane was optically measured using a Fabry-Pérot interferometer formed by a single mode optical fiber front surface and the deflecting diamond film surface. The optical response of the system was numerically simulated using geometry and the elastic properties of the diamond diaphragm, and was compared with the experiments. Depending on the diamond membrane’s diameter, the fabricated sensors displayed a good modulation depth of response over different full-scale ranges, from 3 to 300 bar. In view of the excellent mechanical, thermal, and chemical properties of diamond, such pressure sensors could be useful for performance in a harsh environment

Thin Diamond Film on Silicon Substrates for Pressure Sensor Fabrication

Thin polycrystalline diamond films chemically vapor deposited on thinned silicon substrates were used as membranes for pressure sensor fabrication by means of selective chemical etching of silicon. The sensing element is based on a simple low-finesse Fabry–Pérot (FP) interferometer. The FP cavity is defined by the end-face of a single mode fiber and the diamond diaphragm surface. Hence, pressure is evaluated by measuring the cavity length by an optoelectronic system coupled to the single mode fiber. Exploiting the excellent properties of Chemical Vapor Deposition (CVD) diamond, in terms of high hardness, low thermal expansion, and ultra-high thermal conductivity, the realized sensors have been characterized up to 16.5 MPa at room temperature. Preliminary characterizations demonstrate the feasibility of such diamond-on-Si membrane structure for pressure transduction. The proposed sensing system represents a valid alternative to conventional solutions, overcoming the drawback related to electromagnetic interference on the acquired weak signals generated by standard piezoelectric sensors

Laser Ablated Nanocrystalline Diamond Membrane for Infrared Applications

We are reporting on laser microstructuring of thin nanocrystalline diamond membranes, for the first time. To demonstrate the possibility of microstructuring, we fabricated a diamond membrane, of 9 μm thickness, with a two-dimensional periodic array of closely located chiral elements. We describe the fabrication technique and present the results of the measurements of the infrared transmission spectra of the fabricated membrane. We theoretically studied the reflection, transmission, and absorption spectra of a model structure that approximates the fabricated chiral metamembrane. We show that the metamembrane supports quasiguided modes, which appear in the optical spectra due to grating-assisted diffraction of the guided modes to the far field. Due to the C4 symmetry, the structure demonstrates circular dichroism in transmission. The developed technique can find applications in infrared photonics since diamond is transparent at wavelengths >6 μm and has record values of hardness. It paves the way for creation of new-generation infrared filters for circular polarization

Morphology of Diamond Layers Grown on Different Facets of Single Crystal Diamond Substrates by a Microwave Plasma CVD in CH4-H2-N2 Gas Mixtures

Epitaxial growth of diamond films on different facets of synthetic IIa-type single crystal (SC) high-pressure high temperature (HPHT) diamond substrate by a microwave plasma CVD in CH4-H2-N2 gas mixture with the high concentration (4%) of nitrogen is studied. A beveled SC diamond embraced with low-index {100}, {110}, {111}, {211}, and {311} faces was used as the substrate. Only the {100} face is found to sustain homoepitaxial growth at the present experimental parameters, while nanocrystalline diamond (NCD) films are produced on other planes. This observation is important for the choice of appropriate growth parameters, in particular, for the production of bi-layer or multilayer NCD-on-microcrystalline diamond (MCD) superhard coatings on tools when the deposition of continuous conformal NCD film on all facet is required. The development of the film morphology with growth time is examined with SEM. The structure of hillocks, with or without polycrystalline aggregates, that appear on {100} face is analyzed, and the stress field (up to 0.4 GPa) within the hillocks is evaluated based on high-resolution mapping of photoluminescence spectra of nitrogen-vacancy NV optical centers in the film