Diamond Materials Research Articles

Spectral tuning of diamond photonic crystal slabs by deposition of a thin layer with silicon vacancy centers

Abstract The controlled extraction of light from diamond optical color centers is essential for their practical prospective applications as single photon sources in quantum communications and as biomedical sensors in biosensing. Photonic crystal (PhC) structures can be employed to enhance the collection efficiency from these centers by directing the extracted light towards the detector. However, PhCs must be fabricated with nanoscale precision, which is extremely challenging to achieve for current materials and nanostructuring technologies. Imperfections inherently lead to spectral mismatch of the extraction (leaky) modes with color center emission lines. Here, we demonstrate a new and simple two-step method for fabricating diamond PhC slabs with leaky modes overlapping the emission line of the silicon vacancy (SiV) centers. In the first step, the PhC structure with leaky modes blue shifted from the SiV emission line is fabricated in a nanocrystalline diamond without SiV centers. A thin layer of SiV-rich diamond is then deposited over the PhC slab so that the spectral position of the PhC leaky modes is adjusted to the emission line of the SiV centers, thereby avoiding the need for nanoscale precision of the structuring method. An intensity enhancement of the zero-phonon line of the SiV centers by a factor of nine is achieved. The color centers in the thin surface layer are beneficial for sensing applications and their properties can also be further controlled by the diamond surface chemistry. The demonstrated PhC tuning method can also be easily adapted to other optical centers and photonic structures of different types in diamond and other materials.

Large Area Diamond Disk Growth Experiments and Thermomechanical Investigations for the Broadband Brewster Window in DEMO

An electron cyclotron system (ECS) is required in the European DEMO fusion reactor for plasma heating, magnetohydrodynamic control, especially the suppression of neoclassical tearing modes (NTMs), and thermal instability control. Microwave beams of 2 MW, generated by gyrotrons, shall propagate through corrugated HE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> waveguides (WGs) of 63.5-mm inner diameter and finally reach specific locations in the plasma by a dedicated set of mirrors. The deployment of the beam may be done either by angular steering, i.e., tilting moveable mirrors, or by frequency steering, i.e., tuning the gyrotron frequency. In the last option, for long pulse operations, broadband optical grade diamond windows are required as confinement and/or vacuum barriers both at the torus and the gyrotron side. The Brewster-angle window represents a promising solution due to its intrinsic simplicity. However, the WG aperture imposes a minimum Ø180 mm for the disk at the Brewster-angle of 67.2° for diamond. This is an ambitious target, considering 140 mm as the state of the art. First, this article shows the very promising results of diamond growth experiments carried out by Diamond Materials GmbH with the first worldwide free-standing optical grade Ø180-mm disk having an average unpolished thickness of 1.3 mm. For the first time, one side of this large disk was polished and loss tangent measurements were performed at the center and over a large area. Then, the performance of the window featuring these large disks was characterized by a consistent set of thermomechanical analyses in view of the forthcoming window prototyping activity.

Micro-cantilever testing of diamond - silicon carbide interfaces in silicon carbide bonded diamond materials produced by reactive silicon infiltration

SiC-bonded diamond materials produced by pressureless reactive infiltration of diamond preforms with silicon show high hardness and wear resistance. These properties are due to the relatively high diamond volume content of approximately 50 vol% and the mechanically strong interface between diamond and SiC. To determine the bending strength of individual interfaces between diamond and SiC, micro-cantilevers were prepared by focused ion beam milling at 13 grain boundaries and in-situ bending tests were carried out in a scanning electron microscope. The determined strength of cantilevers showing interface fracture was 10.4 ± 4.0 GPa. Fracture surfaces were analyzed to verify the fracture behavior and initiation. In addition to fracture at the interface diamond/SiC, fracture occurred inside the SiC grains and at the SiC/silicon interface at comparable strength values. The results prove the high diamond/SiC-interface bonding strength.

Micro-Machining of Diamond, Sapphire and Fused Silica Glass Using a Pulsed Nano-Second Nd:YVO4 Laser

Optically transparent materials are being found in an ever-increasing array of technological applications within industries, such as automotive and communications. These industries are beginning to realize the importance of implementing surface engineering techniques to enhance the surface properties of materials. On account of the importance of surface engineering, this paper details the use of a relatively inexpensive diode-pumped solid state (DPSS) Nd:YVO4 laser to modify the surfaces of fused silica glass, diamond, and sapphire on a micrometre scale. Using threshold fluence analysis, it was identified that, for this particular laser system, the threshold fluence for diamond and sapphire ranged between 10 Jcm−2 and 35 Jcm−2 for a laser wavelength of 355 nm, dependent on the cumulative effects arising from the number of incident pulses. Through optical microscopy and scanning electron microscopy, it was found that the quality of processing resulting from the Nd:YVO4 laser varied with each of the materials. For fused silica glass, considerable cracking and deformation occurred. For sapphire, good quality features were produced, albeit with the formation of debris, indicating the requirement for post-processing to remove the observed debris. The diamond material gave rise to the best quality results, with extremely well defined micrometre features and minimal debris formation, comparative to alternative techniques such as femtosecond laser surface engineering.

Optoelectronics of Color Centers in Diamond and Silicon Carbide: From Single‐Photon Luminescence to Electrically Controlled Spin Qubits

AbstractColor centers in diamond, silicon carbide, and related materials have recently emerged as one of the most promising platforms for quantum technology applications. These optically active point defects in the crystal lattice demonstrate outstanding optical and spin properties at room and even higher temperatures, which can hardly be achieved using other quantum systems. For a long time, the host material was considered only as a mechanical carrier of color centers, and the fact that it is a semiconductor and, therefore, can contain high densities of electrons and holes, was ignored. However, recent studies have demonstrated that color centers can exchange electrons and holes with the valence or conduction bands of the host material, which enables novel functionalities, ranging from ultrabright electrically driven single‐photon sources to protected quantum memories. This review summarizes recent advances in understanding this interaction.

Diamond thin films integrated with flexible substrates and their physical, chemical and biological characteristics

Diamond has attracted tremendous attention in materials science and engineering, owing to its superior mechanical, thermal, electrical and optical properties. However, its applications in biomedical fields are constrained by its mechanical rigidity, high temperature fabrication and difficulties of integration with flexible platforms. In this paper, we develop a facile process to form large-area, freestanding diamond thin films and combine them with optoelectronic devices on flexible substrates. Obtained undoped diamond (UD) and boron doped diamond (BDD) films are comprehensively investigated, in terms of their structural, morphological, optical and electrochemical characteristics. On flexible substrates, electrically conductive BDD films are employed as an electrochemical sensor for dopamine detection in aqueous solutions, while optically transparent and thermally conductive UD films can effectively promote heat dissipation of microscale light-emitting diodes. Finally, in vitro cytotoxicity study demonstrates the desirable biocompatibility of these diamond films. The presented techniques remove barriers in the manufacturing and heterogeneous integration of freestanding thin-film diamond materials, and provide promising paths to their broad applications in flexible biointegrated systems.

Efficient microspark erosion-assisted machining of a monocrystalline microdiamond stylus using a heat-avoidance path

Monocrystalline diamond possesses covalent bonding making diamond extremely hard and difficult to machine. In this study, a microdiamond stylus typically used in measuring surface roughness is machined to exemplify the proposed ‘microspark erosion-assisted machining with heat-avoidance path’ technique. Based on the high thermal conductivity and weak electrical conductivity of boron-doped monocrystalline diamond, high-frequency pulsed discharge plasma is employed to efficiently perform microspark erosion machining on an extremely hard monocrystalline diamond blank. It was found that the pulse-on time and servo voltage respectively affect erosion plasma length and the erosion gap during diamond machining. Also, the safety distance and safety height of the erosion path dominate heat transfer to filler metal. These factors all affect the firmness of the brazed diamond blank on the substrate. Three mechanisms for removing carbon atoms from the diamond blank surface were observed. They are vaporization, melting, and graphitization of carbon atoms. This graphitized carbon atoms have weak electrical conductivity, which is conducive to inducing the wire-electrode to generate a greater electric field and secondary discharging, facilitating removal of additional carbon atoms. Experimental results indicate that a microdiamond stylus prototype with a tip of 10 μm can be safely formed using a ‘microspark erosion-assisted machining with heat-avoidance path’ technique, creating 93.7% repeatability of the minimum residual stylus diameter. The tangential micro-grinding facilitates the stylus tip to receive grinding from the grinding wheel's maximum tangential speed and create the precision microdiamond stylus with 1 μm in tip-radius. The applied microspark erosion-assisted machining had a diamond material removal rate that was 54% more efficient than conventional grinding of a commercial microdiamond stylus. The formed microdiamond stylus was inspected by Raman spectroscopy and verified by the surface roughness standard gauge to be up to industry standards.

Polarization Transfer to External Nuclear Spins Using Ensembles of Nitrogen-Vacancy Centers

The nitrogen-vacancy (NV) centre in diamond has emerged as a candidate to non-invasively hyperpolarise nuclear spins in molecular systems to improve the sensitivity of nuclear magnetic resonance (NMR) experiments. Several promising proof of principle experiments have demonstrated small-scale polarisation transfer from single NVs to hydrogen spins outside the diamond. However, the scaling up of these results to the use of a dense NV ensemble, which is a necessary prerequisite for achieving realistic NMR sensitivity enhancement, has not yet been demonstrated. In this work, we present evidence for a polarising interaction between a shallow NV ensemble and external nuclear targets over a micrometre scale, and characterise the challenges in achieving useful polarisation enhancement. In the most favourable example of the interaction with hydrogen in a solid state target, a maximum polarisation transfer rate of $\approx 7500$ spins per second per NV is measured, averaged over an area containing order $10^6$ NVs. Reduced levels of polarisation efficiency are found for liquid state targets, where molecular diffusion limits the transfer. Through analysis via a theoretical model, we find that our results suggest implementation of this technique for NMR sensitivity enhancement is feasible following realistic diamond material improvements.

Performance analysis of diamond-based masers

Masers, the microwave analog of lasers, are an important class of devices that can be used to generate highly coherent and stable microwave signals as well as quantum-limited amplification of microwave photons. Recently, the interest in such devices has increased, probably owing to experiments demonstrating the successful operation at room temperature of solid-state maser employing defects in diamond. These defects, called nitrogen vacancy (NV) centers, are comprised of a negatively charged substitutional nitrogen that replaces one of the diamond crystal lattice’s carbons and a vacancy adjacent to the excluded carbon atom. The performance of diamond-based masers, in terms of gain, noise, bandwidth, frequency of operation, and saturation, greatly depends upon the specific diamond crystal composition and its geometry in the respective microwave device. The currently available data on these issues are scarce and sometimes conflicting. It is, therefore, important to provide additional experimental data, complemented by theoretical analysis, to further optimize the required diamond material and thus enhance the capabilities of diamond-based maser technology. The latter is currently limited to operate only as an oscillator at very small bandwidths, with low saturation power. Here, we provide experimental results on a set of important parameters affecting diamond maser operation, such as the population and linewidth of the electron spin energy levels of the NVs under light illumination, as well as their relaxation times for several different diamond material compositions. These results are then used to point out which diamond material compositions and crystal geometry may be best suitable for maser-type applications.

Diamond supercapacitors: Progress and perspectives

High performance supercapacitors (SCs) need to employ superior capacitor electrodes. Among various capacitor electrodes, diamond and related materials have been recognized as one of the best capacitor electrodes. This is because of their excellent stability, large potential windows, rich surface chemistry, varied surface terminations, and the possibility to enhance their surface areas. Herein, this article summarizes recent progress and achievements regarding the synthesis of nanostructures, particles, hybrid materials and pseudocapacitive composites of diamond and related materials. The applications of these materials for the SC construction are then overviewed. The performance of reported diamond electrical double layer capacitors, pseudocapacitors, redox-electrolyte-enhanced SCs, and metal-ion capacitors is reviewed in detail. Some diamond SC devices and demonstrators are highlighted. The future perspectives of diamond SCs are further outlined and discussed.

The compacts of boron-doped synthetic diamond: Methods for the increasing of their electrochemical activity

Conducting diamond-compact electrode materials are obtained by graphite transformation to diamond at high pressure and high temperature (8–9 GPa, ~ 2500 К) in two- and three-component B4C–C (graphite), Pt–C, and Pt–C–B growth systems; their physical and electrochemical properties are studied. Results of voltametric studies are in good agreement with the electrochemical impedance spectroscopy data obtained in f-sweep and E-sweep modes. The compacts’ electroactivity can be improved in two ways: either extremely heavy doping with boron or adding with catalytically active metal, platinum. The boron content reached in the diamond compacts is as high as ~ 4 at %. The obtained compacts showed the highest electroactivity of all diamond, diamond-based, and diamond-like materials we have studied (by example of the reaction of anodic chlorine evolution from KCl solution). In compliance with the earlier found general trend for all studied diamond, diamond-based, and diamond-like materials, the increase in the material’s electroactivity occurs with the increasing of the compact doping level. The diamond electrode added with Pt in the Pt–C growth system behaves in the chloride-ion anodic oxidation reaction like a purely platinum one, with due allowance for the platinum actual amount at the electrode surface. The combined platinum and boron adding to the diamond grown in the Pt–C–B system produced electrodes electroactive with respect to the chloride-ion anodic oxidation reaction; the electroactivity increased with the increasing of the platinum content at the electrode surface.

In-Situ Nanotribological Properties of Ultrananocrystalline Diamond Films Investigated with Ambient Pressure Atomic Force Microscopy

The relationship between nanoscale friction and the surrounding environment has long been a critical issue in the field of nanotribology. Here, we utilized ambient pressure–atomic force microscopy to investigate the effect of environmental gas on nanoscale friction of ultrananocrystalline diamond (UNCD) films. The frictional forces were measured in an atomic force microscopy (AFM) chamber in the environmental range from an ultrahigh vacuum to near ambient pressure in the presence of oxygen, nitrogen, and water. We observed that friction increased with the pressure of the oxygen responsible for the oxidation of the surface of the UNCD, while that in nitrogen gas remained unchanged. Interestingly, friction decreased in water, due to the tribochemical reaction caused by surface passivation. When two diamond materials come into contact under water conditions, the water molecules are dissociated because of normal pressure between the AFM tip and diamond surface, and the dissociative water molecule adsorption passivates the surfaces of the diamond-coated tip and UNCD, resulting in a reduction of friction force. The chemical state of the UNCD surface in various environmental conditions was confirmed using near ambient pressure X-ray photoelectron spectroscopy. This result elucidates the role of vapor-phase oxygen and water in the tribological properties of carbon-based materials.

Comprehensive topography characterization of polycrystalline diamond coatings

The surface topography of diamond coatings strongly affects surface properties such as adhesion, friction, wear, and biocompatibility. However, the understanding of multi-scale topography, and its effect on properties, has been hindered by conventional measurement methods, which capture only a single length scale. Here, four different polycrystalline diamond coatings are characterized using transmission electron microscopy to assess the roughness down to the sub-nanometer scale. Then these measurements are combined, using the power spectral density (PSD), with conventional methods (stylus profilometry and atomic force microscopy) to characterize all scales of topography. The results demonstrate the critical importance of measuring topography across all length scales, especially because their PSDs cross over one another, such that a surface that is rougher at a larger scale may be smoother at a smaller scale and vice versa. Furthermore, these measurements reveal the connection between multi-scale topography and grain size, with characteristic scaling behavior at and slightly below the mean grain size, and self-affine fractal-like roughness at other length scales. At small (subgrain) scales, unpolished surfaces exhibit a common form of residual roughness that is self-affine in nature but difficult to detect with conventional methods. This approach of capturing topography from the atomic- to the macro-scale is termed comprehensive topography characterization, and all of the topography data from these surfaces has been made available for further analysis by experimentalists and theoreticians. Scientifically, this investigation has identified four characteristic regions of topography scaling in polycrystalline diamond materials.

Nanotwinned diamond cutting tool processed by femtosecond pulsed laser milling with trochoidal trajectory

Ultrahard nanotwinned diamond (nt-D) is an excellent diamond material with higher hardness, better fracture toughness and thermal stability than the commonly used single crystal diamond (SCD), thus it is considered as a promising tool material applied in ultra-precision cutting. However, extremely high hardness results in the fabrication of nt-D tool more difficult than SCD because of very low machining efficiency when using the conventional mechanical methods. Aiming to mass-produce of nt-D tool, the femtosecond pulsed laser milling technique was applied, and the related phase transition mechanism was explored during processing nt-D. Then, a trochoidal trajectory was proposed to acquire high forming accuracy and sharp edge in this study. It is found that the cubic diamond within nt-D was transformed into amorphization directly rather than graphitization under laser processing, which is attributed to the enhanced phase stability for nt-D. Furthermore, the nt-D surface integrity processed by laser was mainly restricted by diamond falling-off pits dewetting from grain boundary. Then, an optimized trochoidal trajectory method was proved to effectively decrease the depth of the falling-off pits and improve the surface integrity by the aid of laser pulse delay. Through the distribution calculation of pulse overlapping with the deduced theoretical equations and processing parameters optimization of galvanometer rotation, an nt-D cutting tool was successfully fabricated with smooth surface and sharp cutting edge. Finally, the wear mechanism, wear resistance and cutting performance of the as-fabricated nt-D tool were explored through cutting testing of hard polycrystalline MgF2. The results supported that nt-D tool exhibits better wear resistance and cutting performance than nanograined polycrystalline diamond (NPD) tool.

Room temperature direct bonding of diamond and InGaP in atmospheric air

A new technique of diamond and InGaP room temperature bonding in atmospheric air is reported. Diamond substrate cleaned with H2SO4/H2O2 mixture solution is bonded to InGaP exposed after removing the GaAs layer by the H2SO4/H2O2/H2O mixture solution. The bonding interface is free from interfacial voids and mechanical cracks. An atomic intermixing layer with a thickness of about 8 nm is formed at the bonding interface, which is composed of C, In, Ga, P, and O atoms. After annealing at 400 °C, no exfoliation occurred along the bonding interface. An increase of about 2 nm in the thickness of the atomic intermixing layer is observed, which plays a role in alleviating the thermal stress caused by the difference of the thermal expansion coefficient between diamond and InGaP. The bonding interface demonstrates high thermal stability to device fabrication processes. This bonding method has a large potential for bonding large diameter diamond and semiconductor materials.

Diamond with nitrogen: states, control, and applications

The burgeoning multi-field applications of diamond concurrently bring up a foremost consideration associated with nitrogen. Ubiquitous nitrogen in both natural and artificial diamond in most cases as disruptive impurity is undesirable for diamond material properties, eg deterioration in electrical performance. However, the feat of this most common element-nitrogen, can change diamond growth evolution, endow diamond fancy colors and even give quantum technology a solid boost. This perspective reviews the understanding and progress of nitrogen in diamond including natural occurring gemstones and their synthetic counterparts formed by high temperature high pressure (HPHT) and chemical vapor deposition (CVD) methods. The review paper covers a variety of topics ranging from the basis of physical state of nitrogen and its related defects as well as the resulting effects in diamond (including nitrogen termination on diamond surface), to precise control of nitrogen incorporation associated with selective post-treatments and finally to the practical utilization. Among the multitudinous potential nitrogen related centers, the nitrogen-vacancy (NV) defects in diamond have attracted particular interest and are still ceaselessly drawing extensive attentions for quantum frontiers advance.

Impact of micron-sized diamond particles on barrier cells of the human small intestine

Diamond and diamond-like materials have shown great potential in variety of biomedical applications, such as coatings for implantable materials, drug delivery systems or tools for bioimaging. Due to the outstanding features of diamond like low chemical reactivity and unique physical properties, as well as unprecedented biocompatibility, the future for development of that kind of material in terms of biomedicine is still very promising. Despite the general low toxicity of diamond, it is of huge importance to monitor effects resulting from different nano- and microforms of diamond showing distinct properties in comparison to their bulk counterpart. Systematic studies of biocompatibility and toxicity should always be strong requirements for understanding and mitigating potential health hazards. Also the size, shape, and surface chemistry should be thoroughly investigated as such particles' properties greatly affect particle internalization and stand for their ultimate toxicity towards cells. Here we aimed to assess the influence of micron-sized diamond particles on epithelial cells of the human small intestine (FHs 74 Int). These cells constitute the barrier between the gastrointestinal tract and internal environment of the human body, thus serving as one of the first routes of exposure to drugs or particles administered orally. We employed various microscopic methods to observe epithelial cells after exposure to microdiamond particles, evaluating cell movement, particle uptake, cell viability, apoptosis, and formation of micronuclei. We observed uptake and accumulation of microdiamond particles by cells during and after exposure in time-dependent manner. Microdiamond particles were neither cytotoxic nor genotoxic to epithelial cells, and the rate of apoptosis was not significantly different than that of untreated control cells, however it should be of high importance to monitor cell responses to diamond particles when used in specific biomedical applications. Our studies demonstrated that microdiamond particles even at very low concentration can be effectively accumulated inside cells and show no harmful effects on barrier intestinal cells. This renders them very promising candidate for drug delivery systems, competitive towards diamond particles of nano size that are in general more prone to evoke toxic effects due to their much smaller size. We strongly believe that the use of microdiamonds in biomedical field, especially as drug carriers is still undervalued, and should be developed with the same attention as is paid for diamonds of nano size.

Microwave Plasma Chemical Vapor Deposition of Diamond and Novel Superhard Materials

Microwave Plasma Chemical Vapor Deposition of Diamond and Novel Superhard Materials

Fourier-transform infrared spectroscopy for analysis of diamond materials of different origin

The study of impurity composition of diamond materials is an important element of their classification for use in various fields of science and technology. Many physical (thermal and electrical conductivity, optical purity), mechanical (hardness and strength) and aesthetic (color grade and clarity) properties of diamond depend on the presence of impurities in their structure; therefore, it is important to quickly and reliably determine each impurity in diamond. In this work, the method of FTIR spectroscopy is proposed as an express method for determining the impurity composition of diamonds. We examined three types of diamond materials: single crystal natural diamonds (before and after heat treatment), single crystal synthetic HPHT-diamonds and synthetic polycrystalline diamond CVD-films. We have established that the used technique allows to determine impurities in single crystals of natural and synthetic origin reliably and effectively, while the study of polycrystalline thin films is best performed using spectrophotometry.

Deep-level impurities hyperdoped diamond: a first-principles calculations

A hyperdoped diamond material is engineered by first-principles calculations in this work. Several deep-level elements, such as S, Se, Te, Co, Au, V, Ni, are chosen as dopants in the diamond. The formation energy results show that the substitutional configuration of the dopants is more stable than the interstitial ones. The substitutional configurations of chalcogen dopants (S, Se, Te) can introduce a nearly filled intermediate band (IB) in the upper half of the bandgap of the diamond. The substitutional configurations of several transition metals, such as Co, Au, V, Ni, and Cu, can form partially filled IB(s) near the center of the bandgap, which is more appropriate than that formed by the chalcogens. The dielectric function results indicate that all of these deep-level elements can lead to the sub-bandgap absorption and the absorption range and intensity vary dramatically with different dopants. Among these dopants, Co, Au, and Cu exhibit a special strong sub-bandgap absorption in a longer wavelength range, which would make the material to be an excellent photoelectric device. With reducing the concentration of the transition metal dopants, the IBs in the bandgap are narrower and tend to separate from each other and the sub-bandgap absorptions reduce sharply. Our conclusions imply that the photoelectric properties of the novel diamond material would be modulated by changing the dopant types and concentrations.