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Oxygen-terminated type IIa (OT-IIa) diamond with oxygen suspended in the form of a ketone bond (C O) was synthesized via acid treatment. The Fermi level at 3.23 eV below the conduction band minimum for the OT-IIa diamond surface was measured experimentally, while that at 0.97 eV for the bulk was calculated theoretically. An acceptor model of the surface states was developed, employed, and combined with an upward-bending band diagram to compensate this energetic band difference between the surface and bulk of OT-IIa diamond. A Schottky barrier height of 3.15 eV between gold and the OT-IIa diamond was also measured. In addition, we also inferred the downward-bending band diagram for the surface of oxygen-terminated p-type diamond doped with boron. This work complements the semiconductor theory concerning diamond and will be helpful to analyze and improve the performance of devices based on oxygen-terminated diamond.

It has been widely accepted that conversion between negatively charged nitrogen-vacancy (NV−) center and neutral nitrogen-vacancy (NV0) center can be realized with the Fermi level crossing the transition level corresponding to the ground state of NV−. In this study, a suppressing effect was observed in the emission of NV− center; however, emission of NV0 center was not observed to be increasing as expected and was stable when lowering of the Fermi level was induced by a Schottky junction between gold and oxygen-terminated diamond containing NV centers. The relationship between the thickness of the depletion layer as well as that of the suppression layer, appearing when the Fermi level shifted below the ground state level of NV−, and the donor concentration was derived. Moreover, a model based on the assumption that an intermediate transition level (nonfluorescence state) existed between the ground state energy levels of NV− and NV0, was proposed to explain why suppressed NV− did not convert to NV0. The results of this study will aid in further understanding of the characteristics of NV centers. In addition, a Schottky junction can be developed to determine the charge state of unknown color centers and facilitate study of defects in diamonds.

An interdigital electrode of 200-nm thickness, 160-μm spacing, and 160-μm width was fabricated on one side of a diamond fabricated by chemical vapor deposition. A gold contact of 200-nm thickness was deposited on the back side of the diamond. The back contact and one half of the interdigital electrode were connected by a switch. Higher responsivity and higher detectivity were observed when the back electrode contact was activated. The results of electrical field simulation showed that a stronger electrical field formed over the diamond region in the device with the back electrode than in that without the back electrode. This indicated that the detector performance improvement could be attributed to the higher carrier collection efficiency achieved with the back electrode, particularly under ultraviolet (UV) light at certain wavelengths, which have longer attenuation lengths in diamond. This structure could also be applied to UV detectors based on other wide-band-gap semiconductors.

We report magnetic alignment of single-crystalline microdiamonds with aid of superparamagnetic magnetite in polymeric composites and their material properties. The silicone composite containing aligned microdiamonds shows interesting properties in alignment direction, including enhancement of thermal conductivity, 250% higher than that of randomly dispersed counterpart at a low loading of 5.1 vol%. Composites with aligned diamond exhibited enhanced thermal conductivity and electrical insulation compared with matrix, and are attractive for application as thermal interface materials in the semiconductor industry, though the introduction of magnetite had part of negative effect on electrical resistivity of composites. A two-level model that accounts first-order interaction between particles to calculate effective thermal conductivity of composites with aligned microdiamonds, is found to fit accurately absolute value and tendency of thermal conductivity for composites with aligned particles. Utilizing the modelling procedure, the volume fraction of microdiamonds within chains is 0.3, which is smaller than 0.698 predicted for ideal body-centered-tetragonal arrangement of particles. This suggested that thermal conductivity of composites can be enhanced further by improving microstructures within particle chains.

A highly selective anisotropic etching method for single-crystal diamond was investigated. After a thin film of Fe was deposited on the diamond surface, it was processed in H plasma activated by microwave plasma-assisted-chemical vapor deposition (MPCVD). Spurred by the high catalytic activity of Fe, the diamond was easily etched, with masked areas (i.e., with no Fe deposition) remaining smooth or barely damaged. The etch rate was 180 nm min−1. This method provides a simple and alternative way for diamond processing and patterning.

Diamond micro powders have been synthesized by chemical vapor deposition via etching a graphite substrate in hydrogen microwave plasma, without a hydrocarbon (methane) gas addition. The graphite temperature, varying from 700 to 1000 °C, was found to significantly affect the diamond nucleation and growth, the growth rate of the diamond particles increasing from 2.4 to ≈ 4 μm/h with the temperature. The diamond powders had a better crystalline quality at the substrate temperature of 900 °C. Because of low adhesion of the deposited grit to the substrate the particles can be collected easily and mechanically disaggregated. The average size of ≈ 12 μm of the dispersed particles grown for 5 h, was determined with a laser particle size analyzer, while the maximum grain size estimated with electron microscopy, varied between 12 and ≈ 20 μm. The particle's surface exhibited many micro-pyramids with sharp tips, that could be beneficial for abrasive applications. X-ray diffraction and Raman spectroscopy revealed high purity and quality of the diamond powders.

An ultraviolet (UV) detector on single crystal chemical vapor deposition (CVD) diamond with three-dimensional (3D) metal electrodes, is designed, and fabricated with the aim to improve collection efficiency of photo-induced carriers. Interdigitated Ti/Au electrodes were formed within 10 μm deep groove etched in diamond to ensure a more uniform field pattern in the diamond bulk. In the preliminary tests the groove-shaped 3D device performance was compared to a detector with a conventional planar structure on the same material at applied electric field of 1 V/μm. It is found that the responsivity of the 3D electrode structure in the spectral range of 220–280 nm is up to 50% higher than that for the planar structure.

Polycrystalline CVD diamond typically has inhomogeneous structure in cross section, with grain size monotonically increasing from bottom (nucleation) side to top (growth) side, this resulting in a significant difference in local thermal conductivity in the layers adjacent to the two surfaces. The polycrystalline diamond films with both sides of similar structure with coarse-grains are of interest for thermal management applications. Here, we produced a double-side coarse-grain polycrystalline diamond film by microwave plasma assisted chemical vapor deposition (MPCVD), by a repeated diamond growth on nucleation side of a primary free-standing film. The grain size, texture, morphology and phase purity of the samples were characterized with SEM, XRD and Raman spectroscopy, while the thermal conductivity (TC) perpendicularly to the film plane was measured by a laser flash technique in the temperature range of 250–400 K. The thermal conductivity of a single layer and bi-layered films are found to be almost identical, while the local TC values for latter on both sides are expected to become similar. A simple model discretizing the film in two regions, “poor” and “good” diamond layers, is considered to explain the observed TC temperature dependences.

As thermal interface materials, polymers are limited by its low thermal conductivity. In this work, a three-dimensional bi-network structure consisting of chemical vapor deposition graphene foam and close-stacked nanodiamonds was constructed in epoxy matrix via a template method. The obtained composites exhibit interesting properties: significant thermal conductivity enhanced efficiency per unit of fillers (74.33%) based on pure epoxy matrix, and excellent electrical conductivity (0.256 S/cm) compared with epoxy matrix (4.58exp-14 S/cm). Finite Element Analysis based on the design of the dual networks was carried out to confirm the heat transfer mechanism, and it is proved that composites with GF/ND bi-network have a lower temperature gradient. That provides a novel insight of improvement method for thermal conductivity by construction of a three-dimension bi-network structure.

Smart materials with self-healing properties that can heal themselves with restored mechanical performance are highly desired. Herein, a transparent healable PDMS (HPDMS) elastomer based on imine bonds is successfully prepared from amino-modified polydimethylsiloxane (PDMS) and 1,4-diformylbenzene (DFB) through a simple method. The concentration of DFB has a great effect on the gelation process. The elastomer features an outstanding optical transmittance (more than 80%) over the full visible light region. The results of TGA and DSC indicate that the HPDMS elastomer is highly flexible at room temperature and can be used in a wide temperature range. The presence of imine bonding and the formation of Schiff base linkages is proved by the FT-IR and Raman spectra. The reversible imine bond can promote the contact of the fracture surfaces and result in quick and repeatable self-healing without any external intervention such as heat or light. Furthermore, the elastomer exhibits excellent recyclability and reprocessability. Besides, the adhesion test reveals the potential of the elastomer in application as adhesives. We anticipate that this strategy can be employed to prepare a transparent PDMS elastomer with mechanical strength, stretchable, and excellent self-healing properties.

A UV detector based on a planar quadrant electrode structure with a 100-μm isolating cross-gap deposited on chemical vapor deposition diamond was fabricated. An asymmetrical behavior was observed for the amplitude of photocurrent when in forward and reverse bias. A linear relationship between the sum of the photocurrents at biases U and −U, and the light spot position was also observed. The aim of this study is to clarify the mechanism underlying this asymmetrical behavior and exhibit its potential application based on this behavior. A mechanism involving lowering of the contact barrier height between gold and i-diamond by carrier generation upon UV illumination was adopted to account for the photocurrent behavior and confirmed when an opposite asymmetrical photocurrent behavior was observed in other samples. In addition, position-sensitive detection performance, based on this asymmetrical photocurrent behavior, was preliminarily studied. The results exhibited the potential for application as a position-sensitive detector.