Diamond nitrogen–vacancy (NV) centers possess long coherence times and stable fluorescence emission, and have therefore attracted widespread attention in fields such as quantum communication, biological fluorescence labeling, and precision sensing. However, the high refractive index of diamond causes most of the fluorescence from the color centers to be internally reflected, resulting in low fluorescence collection efficiency. To improve the utilization efficiency of fluorescence from diamond color centers, this work proposes a low‐cost and controllable method for fabricating nanocone array structures. By depositing a SiO 2 array mask, the effects of etching power and bias power on the morphologies of both the mask and the diamond were investigated. Subsequently, the regulatory mechanism of the O 2 /CF 4 mixed‐gas ratio on the etching behaviors of the mask and diamond was explored, and it was found that an increased CF 4 proportion is beneficial for reducing the cone angle of the nanocone structures. Optical characterization reveals that the fabricated diamond cone structure with a cone angle of 73° exhibits an approximately twofold increase in transmittance, while simultaneously enhancing the fluorescence intensities of both NV − and SiV − color centers. Compared with a diamond thin film, the fluorescence enhancement reaches 12.2 times for NV − centers and 11.7 times for SiV − centers. Finite‐difference time‐domain (FDTD) simulations further demonstrate that the cone structure can concentrate photons, thereby effectively improving the fluorescence collection efficiency of color centers. This work provides a feasible approach for the low‐cost fabrication of quantum sensing devices and for enhancing the sensitivity of quantum detection.

All-Diamond Transparent Solar-Blind UV Photodetector with Thin Boron-Doped Diamond Film as Electrodes

The electrical properties of diamond are modulated by impurity doping. Isolated substitutional boron atoms introduce holes; however, the fraction of electrically inactive boron atoms increases at higher doping concentrations. This has been attributed to boron aggregation and hydrogen passivation, although their structural identification based on atomic arrangement has yet to be experimentally verified. Here we show the origin of multiple chemical states in homoepitaxially grown boron-doped diamond thin films by analyzing the atomic environment of boron using spectro-photoelectron holography. Our analysis identifies boron dimers and boron-hydrogen complexes, with hydrogen occupying different atomic sites that give rise to distinct chemical shifts. These results suggest that hydrogen incorporation during growth leads to passivation of boron acceptors. We demonstrate that photoelectron holography serves as a promising tool for imaging hydrogen as well as determining the atomic sites of dopants.

Hydrogen implantation combined with bonding enables the transfer of large scale, single crystal thin films. This process, known as Smart Cut™, is well-established for silicon in the fabrication of SOI stacks but remains challenging for diamond due to its rough and non-planar surface hindering bonding. To improve bonding energy, surface activation bonding was used which led to a successful transfer of diamond thin films onto silicon with nearly 90% surface yield. However, the post-fracture diamond film exhibited a pyramidal surface topology. This particular topology is characterized by Raman spectroscopy, Cathodoluminescence, Scanning Electron Microscopy, Transmission Electron Microscopy, Atomic Force Microscopy, and Laue microdiffraction, and results from the formation of dihydrogen pressurized microcracks. The deformation of the crack walls causes the formation of vertical graphite sheets on the film's surface and induce plastic deformation in the underlying silicon substrate without compromising the diamond film's crystallinity or the bonding. Additionally, we propose a post-fracture surface cleaning method to obtain an epi-ready diamond film and to enable the reuse of the donor substrate. • High transfer rate of diamond film onto Si substrate using the Smart Cut™ process • Characterization of pyramidal surface morphology on the transferred diamond film • Cleaning process to recover a monocrystalline diamond surface suitable for epitaxial growth

Many quantum networking applications require efficient photonic interfaces to quantum memories which can be produced at scale and with high yield. Synthetic diamond offers unique potential for the implementation of this technology as it hosts color centers which retain coherent optical interfaces and long spin coherence times in nanophotonic structures. Here, we report a technique enabling wafer-scale processing of thin-film diamond that combines ion implantation and membrane liftoff, high-quality overgrowth, targeted color center implantation, and serial, high-throughput thermocompression bonding with yields approaching unity. The deterministic deposition of thin diamond membranes onto semiconductor substrates facilitates consistent integration of photonic crystal cavities with silicon-vacancy (SiV) quantum memories. We demonstrate reliable, strong coupling of SiVs to photons with cooperativities approaching 50. Furthermore, we show that photonic crystal cavities can be reliably fabricated across several membranes bonded to the same handling chip. Our platform enables modular fabrication where the photonic layer can be integrated with functionalized substrates featuring electronic control lines such as coplanar waveguides for microwave delivery. Finally, we implement passive optical packaging with sub-decibel insertion loss. Together, these advances pave the way to the scalable assembly of optically addressable quantum memory arrays which are a key building block for modular photonic quantum interconnects.

Polycrystalline diamond is a promising material for MEMS resonators due to its remarkable mechanical and electrical properties and compatibility with standard semiconductor manufacturing processes. However, the growth on non-diamond substrates is challenging, and a seeding process is needed to grow closed thin films. Hot filament chemical vapor deposition and reactive ion etching are powerful tools to deposit and micromachine diamond thin films on silicon substrates. In this paper, a polycrystalline diamond thin film with micrometer-sized grains is used to fabricate MEMS resonator devices, and quality factors are measured using laser Doppler vibrometry. The resonator’s bottom and top sides, as well as the cross sections, are investigated, and a substrate-near region with an elevated amount of non-diamond carbon bonds is identified with TEM in the energy-filtered transmission electron microscopy mode. By monitoring the quality factors of several resonance modes of 142 MEMS resonator devices, while a reactive ion etching treatment is performed at the bottom side of the resonators, we find an initial increase in the mean quality factor of all out-of-plane modes in the frequency spectrum from 20 to 500 kHz by nearly a factor of 3 after 28 min of back thinning of an initially 2.2 μm thick polycrystalline diamond thin film due to the reduction of the defect-rich substrate-near region. Even more, we find no correlation between surface roughness and quality factor, indicating losses at structural defects, such as grain boundaries and non-diamond carbon clusters, as dominant for energy dissipation.

Hydrogenated few layer graphene, also called thin film diamond, two-dimensional diamond or diamane are promising novel nano-materials with wide and direct band gap. A theoretical investigation is carried out to study the thermal and thermoelectric properties of hydrogenated graphene-based materials, namely graphane, bilayer (2LD), and trilayer diamane (3LD). Phonon dispersion relations, calculated within the harmonic approximation (HA), confirm their dynamical stability. The quasi-HA is then employed to assess the volume-dependent quantities, revealing positive thermal expansion coefficients for both diamane structures across the entire temperature range, in contrast to the negative expansion observed in graphane at low temperatures. The lattice thermal conductivity is obtained by solving the linearized Boltzmann transport equation using both the single-mode relaxation-time approximation and the exact iterative scheme which at 300 K, have values of 574, 1314, and 1282 W·m-1⋅K-1for graphane, 2LD, and 3LD, respectively. It highlights the influence of hydrogenation and interlayer bonding on the conductivity. Mode-resolved analysis indicates that low-frequency acoustic phonons are the primary contributors to heat conduction, with increased lifetimes in multilayered structures. Thermoelectric properties are evaluated within the constant relaxation-time approximation, revealing a significant enhancement of the Seebeck coefficient upon hydrogenation. Among the studied systems, 2LD displays the best thermoelectric performance, reaching a maximum figure of merit (ZT) of approximately12×10-3at room temperature. These results demonstrate the tunability of thermal transport and thermoelectric efficiency in hydrogenated graphene structures, underscoring their potential for nanoscale thermal management and energy conversion applications.

Abstract Polycrystalline diamond (PCD) thin films have been widely used as a coating material to enhance surface properties or protect against wear and tear. However, their implementation as an electronic material has been hindered by inconsistent semiconducting properties arising from their polycrystalline nature and associated processing challenges. In this study, the first demonstration of vertical Schottky barrier diodes fabricated using freestanding PCD membranes (PCDm) is presented, which addresses these limitations by enabling dual‐side access to the PCDm. The Schottky contact is formed on the high‐quality growth surface with larger grains and high sp 3 carbon content, while the ohmic contact is placed on the smoother, sp 2 ‐rich bottom side. This configuration enables distinct contact optimization on each surface, eliminating the trade‐offs encountered in conventional planar devices based on thin‐film PCD. The devices exhibit an excellent rectifying behavior with an on/off ratio of ≈10 3 and a breakdown field of 0.25 MV cm −1 —among the highest reported for PCD‐based Schottky barrier diodes. The result paves the way for the development of high‐performance electronic devices based on freestanding and transferable PCDm, positioning it as a cost‐effective and scalable wide‐bandgap semiconductor for next‐generation electronics.

Interfacial Microstructure and Thermal Properties of Diamond Thin Films Prepared on Si and SiC Substrates by Chemical Vapor Deposition

Diamond color centers are promising candidates for optically addressable quantum memories, which motivates the development of efficient photonic interfaces, often using nanophotonic cavities with narrow spectral line widths and small mode volumes. However, they require perfect spectral and spatial overlap between the cavity mode and quantum emitter, which is challenging. This is especially true for solid-state quantum emitters that are often randomly positioned and suffer from inhomogeneous broadening. Another approach to enhance light-matter interaction across large optical bandwidths and areas is using slow light waveguides. Here, we demonstrate diamond slow light photonic crystal (PhC) waveguides optically coupled to embedded silicon-vacancy (SiV) color centers. We use the recently developed thin-film diamond approach to fabricate fully suspended two-dimensional PhC waveguides. We demonstrate waveguide modes with high group indices up to 70 and observe Purcell-enhanced emissions of the SiVs. Our approach represents a practical diamond platform for robust spin-photon interfaces with color centers.

Angled Plan View Sample Preparation of Diamond Thin Films for Multiscale Analysis

This study synthesized boron-doped diamond (BDD) thin films using hot-filament chemical vapor deposition at different carbon-to-hydrogen (C/H) ratios in the range of 0.3-0.9%. The C/H ratio influence, a key parameter controlling the balance between diamond growth and hydrogen-assisted etching, was systematically investigated while maintaining other deposition parameters constant. Microstructural and electrochemical analysis revealed that increasing the C/H ratio from 0.3% to 0.7% led to a reduction in sp2-bonded carbon and enhanced the crystallinity of the diamond films. The improved conductivity under these conditions can be attributed to effective substitutional boron doping. Notably, the film deposited at a C/H ratio of 0.7% exhibited the highest electrical conductivity and the widest electrochemical potential window (2.88 V), thereby indicating excellent electrochemical stability. By contrast, at a C/H ratio of 0.9%, the excessively supplied carbon degraded the film quality and electrical and electrochemical performance, which was owing to the increased formation of sp2 carbon. In addition, this led to an elevated background current and a narrowed potential window. These results reveal that precise control of the C/H ratio is critical for optimizing the BDD electrode performance. Therefore, a C/H ratio of 0.7% provides the most favorable conditions for applications in advanced oxidation processes.

Nearly a quarter of a century ago, we wrote a review paper about the very new technology of chemical vapour deposition (CVD) of diamond thin films. We now update this review and bring the story up to date by describing the progress made-or not made-over the intervening years. Back in the 1990s and early 2000s, there was enormous excitement about the plethora of applications that were suddenly possible now that diamonds could be fabricated in the form of thin films. Diamond was hailed as the ultimate semiconductor, and it was believed that the few remaining problems would be quickly solved, leading to a new 'diamond age' of electronics. In reality, however, difficulty in making large-area diamond wafers and the elusiveness of a useful n-type dopant slowed progress substantially. Unsurprisingly, over the following decade, the enthusiasm and funding for diamonds faded, while competing materials forged ahead. But in the early 2010s, several new game-changing applications for diamonds were discovered, such as electrochemical electrodes, the nitrogen-vacancy (NV) centre defect that promised room-temperature quantum computers, and methods to grow large single-crystal gemstone-quality diamonds. These led to a resurgence in diamond research and a new hope that diamond might finally live up to its promise.This article is part of the theme issue 'Science into the next millennium: 25 years on'.

Transfer of diamond thin films using Smart Cut™ technology

Contamination from nearby bending magnet radiation hinders precise and accurate determination of the true beam center of undulator radiation. To solve this problem, a semi-nondestructive method was developed to visualize the detailed profile of a synchrotron radiation beam by using a thin diamond film as a scatterer. As the beam passed through the diamond film, scattered X-rays were imaged using a pinhole camera and measured with a two-dimensional silicon drift detector (SDD) scan. With this configuration, the beam center was accurately determined by visualizing the radiation pattern distribution for each energy level of a pink X-ray beam within an aperture size of 1.5 mm × 1.5 mm, shaped by a front-end slit (FES) positioned upstream of the monochromator. Additionally, by scanning the FES in two dimensions with a reduced aperture of 0.4 mm × 0.4 mm, energy-resolved images were successfully obtained using the SDD at a fixed position. These images revealed the profile of undulator radiation over a broad area (with an aperture extending up to 4 mm) in a pre-slit positioned upstream of the FES, demonstrating good alignment with SPECTRA calculations. This method effectively eliminates contamination from nearby bending magnet radiation, a significant issue in previous approaches, enabling a direct and highly accurate determination of the true beam center.

A flexible supercapacitor is expected to possess a high power density and excellent cycling life and thus is a promising candidate for energy storage units in wearable and portable electronic devices. However, the drawback of a low energy density must be solved. In this context, a novel two-dimensional flexible capacitor material, diamond cloth, is proposed, which was prepared by overgrowing carbon cloth with a thin boron-doped diamond (BDD) film with the aid of a microwave plasma-enhanced chemical vapor deposition technique. As characterized by means of field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy, such a diamond cloth features the characteristics of both conductive diamond films and carbon cloth. Namely, the exceptional chemical stability and good conductivity of the BDD film are combined with the high flexibility of carbon cloth, making diamond cloth a perfect capacitor electrode and exhibiting superior capacitance retention and cycling stability. An assembled symmetrical pseudocapacitor exhibits a specific capacitance of 81.94 mF cm–2 at a scan rate of 10 mV s–1, an extremely excellent capacitance retention of 99.59% even after 10,000 charging/discharging cycles, a maximal energy density of 45.96 μWh cm–2, and a maximal power density of 67.93 mW cm–2. Its performance exceeds that of most reported carbon-based supercapacitors. Furthermore, it demonstrates excellent mechanical flexibility, featuring the consistency of capacitance at different bending angles and the minimum capacitance retention of 97.14% for 500 bending cycles. Therefore, diamond cloth holds great potential for constructing energy storage units in wearable and portable electronic devices.

Plasma‐enhanced chemical vapor deposition (PECVD)‐assisted growth of undoped Q‐carbon films over a large area for wafer‐scale integration of diamond thin films and related structures is reported. A detailed mechanism is proposed to describe the formation of Q‐carbon via the low‐energy ion bombardment in the PECVD process. The energy of these ions is just adequate to generate a Frenkel pair, which facilitates the conversion of twofold coordinated sp2 carbon units in the as‐deposited carbon layer to fourfold sp3‐bonded tetrahedral carbon units in Q‐carbon but does not induce damage to the formed structure. This enhances the sp3 content and the atomic number density due to the random packing of tetrahedral units in the Q‐carbon structure. The cluster of four tetrahedra leads to the formation of the diamond unit cell, which provides a nucleus for diamond growth. Thus, large‐area diamond films can be grown by seeding with Q‐carbon layers. Further, attributed to its unique structure, it is shown that Q‐carbon is ferromagnetism at room temperature, while the untreated amorphous carbon is diamagnetic. With the thickness of Q‐carbon less than 10 nm, epitaxial growth of diamond films can be achieved via domain‐matching epitaxy. Wafer‐scale integration of Q‐carbon opens up new avenues to develop diamond‐based heterostructures.

This study presents a semiconducting optoelectronic system for light-controlled non-genetic neuronal stimulation using visible light. The system architecture is entirely wireless, comprising a thin film of nitrogen-doped ultrananocrystalline diamond directly grown on a semiconducting silicon substrate. When immersed in a physiological medium and subjected to pulsed illumination in the visible (595nm) or near-infrared wavelength (808nm) range, charge accumulation at the device-medium interface induces a transient ionic displacement current capable of electrically stimulating neurons with high temporal resolution. With a measured photoresponsivity of 7.5mA W-1, the efficacy of this biointerface is demonstrated through optoelectronic stimulation of degenerate rat retinas using 595nm irradiation, pulse durations of 50-500ms, and irradiance levels of 1.1-4.3mW mm-2, all below the safe ocular threshold. This work presents the pioneering utilization of a diamond-based optoelectronic platform, capable of generating sufficiently large photocurrents for neuronal stimulation in the retina.

This study presents the technological progress in the deposition of diamond thin films on quartz crystal microbalance (QCM) sensors. The linear antenna microwave plasma chemical vapour deposition (CVD) technique effectively grows thin diamond films on QCM substrates (Dia-QCM) differently oriented on the substrate holder in the deposition chamber, resulting in single-sided and double-sided coated QCMs. Each of these coated QCMs offers a distinctive advantage for sensing applications. The double-sided coated QCM sensors exhibited the most effective performance in ethanol detection, demonstrating approx. a 3-fold and 12-fold higher response than single-sided diamond-coated and bare gold QCM sensors, respectively. Furthermore, the single-sided Dia-QCM aptasensors demonstrated superior performance compared to bare gold QCM sensors, with a 2-fold higher response and a lower detection limit for S-RBD protein (LODDia-QCM = 0.09pg/mL vs. LODAu-QCM = 0.10pg/mL). In experiments conducted in human plasma, the Dia-QCM aptasensor demonstrated the ability to detect S-RBD protein at concentrations as low as 50pg/mL, with high percentage recoveries. These results highlight the potential of linear antenna microwave plasma CVD for the mass production of advanced diamond-coated QCM sensors with different diamond film morphologies (porous, micro- or nanocrystalline) for various applications.

Nitrogen-doped quenched-produced diamond (N-doped Q-dia) thin films were deposited onto a titanium substrate by coaxial arc plasma deposition (CAPD). The N-doped Q-dia thin film was successfully synthesized at room temperature without peeling. Its performance as an electrode material in aqueous solutions was investigated. The overpotential for the hydrogen evolution reaction was 0.35 V higher than the conventional boron-doped diamond (BDD) electrode. The kinetics of reversible electron transfer for redox species were comparable to the BDD electrode. We have demonstrated the N-doped Q-dia thin films have promising potential as a competitive and alternative electrode material to BDD films for electrochemical applications.