Formation mechanism and process investigation of nitrogen-vacancy centers in diamond fabricated by microwave plasma chemical vapor deposition

Neural probes targeting single neurons are instrumental in overcoming the ambiguity associated with population-averaged signals and the attenuation of extracellular signals to reveal the fundamental units of neural coding. However, current neural probes are limited by resolution, structural design, and micro/nanotechnology, making it challenging to penetrate single neurons in vivo to directly record various neural signals. Here, we report a multilayer carbon-structured nanoprobe (MLCNP) for intracellular electrophysiological and chemical recordings in vivo. The sensing layers, composed of graphene and feather-shaped carbon nanowires (FCNW), and the protective layer of nanodiamond are prepared via microwave plasma chemical vapor deposition. The controlled exposure of nanotips, roughening of FCNW sensing layers, and adsorption of Pt nanoparticles on their surface are achieved through microplasma jet branch etching (MPJBE). The multilayer carbon structures and the MPJBE treatment significantly enhance the cathodic charge, peak cathodic current and sensitivity to dissolved O2 of nanoprobes. The MLCNP with a tip diameter of approximately 70 nm and an exposed sensing area length of about 900 nm, demonstrates good cytocompatibility, minimal invasive damage, and selective O2-sensing capabilities. Finally, intracellular electrophysiological signals and variations in O2 concentration, along with other potential biochemical signals, are successfully recorded in vivo, and the effects of pain stimulation on electrophysiological spikes were analyzed. The developed nanoprobe based on the new materials and processes and its successful acquisition of electrical and biochemical signals at the single-neuron level in vivo, hold profound significance for a deeper understanding of the intrinsic mechanisms of the nervous system.

Gene mutation is one of the core pathogenic factors in numerous major diseases, making the detection of base mismatches resulting from these mutations critically important in both biological and clinical contexts. This study presents a high-performance boron-doped diamond solution-gated field-effect transistor (BDD-SGFET) biosensor, designed with a diamond microwire structure, for the label-free detection of base mismatches associated with EGFR gene mutations. The simulations examining the impact of variations in diamond microwire dimensions on the electrical properties of BDD-SGFET reveal that increasing the microwire width while reducing its length enhances the electrical performance of the device. Utilizing microwave plasma chemical vapor deposition (MPCVD), photolithography, and plasma etching, we successfully fabricated high-performance BDD-SGFETs featuring microwire structures that demonstrate outstanding transconductance, a reduced threshold voltage, and a limit of detection of 10 pM. Notably, the enhanced performance of the fabricated BDD-SGFET enables the successful identification of DNA molecules with two base-pair mismatches. Furthermore, the device exhibits impressive anti-interference capabilities and exceptional stability in complex environments. These findings highlight the significant potential of microscale BDD-SGFETs as rapid, label-free, and robust platforms for point-of-care testing in genetic mutation analysis pertinent to cancer diagnosis.

Selective-area growth of diamond is highly desirable for integrated electronics and thermal management, yet scalable patterning with controlled microstructure remains challenging. Here, we report a nucleation-engineered strategy for selective-area and wafer-scale diamond growth using microwave plasma chemical vapor deposition. By combining nanodiamond seeding with either conventional photolithography or a laser-defined peel-off masking process, diamond patterns are realized across length scales ranging from micrometers to full 2-in. wafers on Si and GaN substrates. We demonstrate that spatial variations in seeding density result in distinct growth regimes, producing fine-grained diamond with mixed orientations in densely seeded regions and large-grained, (111)-textured diamond in sparsely seeded regions through geometric and thermodynamic selection. The resulting patterned diamond films exhibit high crystalline quality, as confirmed by Raman spectroscopy and x-ray diffraction. As a proof-of-concept demonstration, selectively patterned diamond films are employed as heat spreaders on Si substrates, resulting in an operating temperature reduction of more than 23 °C compared to bare Si under identical electrical loading conditions. These results establish scalable selective-area diamond growth as an effective platform for microstructured thermal management and integrated device applications.

Diamond is becoming an increasingly popular substrate material in the semiconductor industry due to its high thermal conductivity and wide forbidden band characteristics. With the development of high-power electronic devices, the demand for large-area single-crystal diamond films is also dramatically increasing. Microwave plasma chemical vapor deposition (MPCVD) technology is the dominant method for producing high-quality diamond films due to its advantages of high controllability, fast deposition rate, and low contamination. Despite the excellent performance of MPCVD reactors in various aspects, the question of how to increase the plasma size while improving its homogeneity remains a challenge for device design and optimization. This paper proposes a method to expand the geometrical sizes of the TM01-mode MPCVD reactor while maintaining the mode’s axisymmetric homogeneity. The size-enlarged TM01-mode MPCVD reactor was first designed and optimized with electromagnetic simulations. A multiphysics model that accounted for the microwave field, hydrogen gas discharge, and energy conservation was proposed to evaluate the performance of the MPCVD reactor afterwards. The results demonstrate that the size-enlarged MPCVD reactor can generate a plasma sphere with a diameter of 4 inches while still maintaining TM01-mode single-mode transmission, either with or without plasma. Its outstanding robustness and adaptability underlie excellent potential for large-area diamond thin-film deposition.

ABSTRACT High‐density and uniform diamond nucleation is the key to achieving high‐quality heteroepitaxial diamond films. Herein, a femtosecond (fs) laser‐induced diamond nucleation method is proposed for heterogeneous growth of high‐quality diamond films on silicon substrates. Specifically, a uniform and regular microstructure is first induced on the silicon substrate surface by fs laser, and then a high‐density and uniform diamond nucleation is achieved on the silicon surface thanks to the anchoring effect of the microstructure, so that the heterogeneous growth of high‐quality diamond film on the silicon substrate is realized by microwave plasma chemical vapor deposition process. The experimental results show that fs laser‐induced diamond nucleation has higher nucleation density and more uniform nucleation distribution than conventional mechanical grinding diamond nucleation, thereby obtaining diamond films with better quality, thicker thickness, and lower surface roughness. Furthermore, the obtained silicon/diamond substrate is used as a heat sink for the heat dissipation of an LED. Compared with the LEDs with a Si substrate and without a heat dissipation substrate, the working temperature of the LED at 220 s is reduced by 18.4°C and 6.6°C, respectively, demonstrating the potential of heteroepitaxial diamond film on a silicon substrate in the field of chip thermal management.

This study investigates the synergistic effects of co-doping with ultralow-concentration nitrogen and trace carbon dioxide on the growth of polycrystalline diamond films via microwave plasma chemical vapor deposition (MPCVD). The films were characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and photoluminescence spectroscopy. Results indicate that trace nitrogen effectively promotes <111> oriented growth and enhances the deposition rate, whereas excessive nitrogen leads to the formation of defects such as pores and microcracks. The introduction of CO2 suppresses the formation of nitrogen-vacancy-related defects through a selective etching mechanism. Under co-doping conditions, diamond films with high growth rates, strong <111> texture, and superior thermal conductivity (up to 1863.94 W·m-1·K-1) were successfully synthesized, demonstrating significant potential for thermal management applications in high-power integrated circuits.

Diamond holds significant application potential in microwave and deep-space observation windows due to its exceptionally low dielectric loss. This study aims to systematically investigate the key factors influencing the dielectric loss tangent (tanδ) of single-crystal diamond (SCD) and to establish correlations between its dielectric properties and material characteristics. To this end, dielectric property measurements were performed on SCD samples synthesized using microwave plasma chemical vapor deposition (MPCVD) systems under different growth conditions. A comprehensive material characterization was carried out using birefringence microscopy, Raman spectroscopy, photoluminescence (PL), and X-ray diffraction (XRD) to analyze crystal quality, defect distribution, and strain. The experimental results show that the measured tanδ of the SCD samples reached a minimum value of 4.94 × 10&lt;sup&gt;-5&lt;/sup&gt;. Detailed analysis reveals that the dielectric loss in SCD is attributed to a combination of factors: the density and distribution of internal defects (e.g., vacancies and impurities), the presence of internal growth sectors and boundaries, and phonon polarization losses induced by lattice vibrations under an external electric field. It is conclusively identified that defect density is the predominant factor governing dielectric loss. Furthermore, the study demonstrates that as the test frequency increases, contributions from defect polarization and interfacial polarization at sector boundaries become more pronounced, leading to higher overall loss. Interestingly, it was found that certain periodic defect structures can partially suppress the phonon-polarization related loss mechanism, thereby contributing to a lower tanδ in some samples. In conclusion, this work elucidates the multi-faceted origins of dielectric loss in SCD and provides valuable insights and a methodological framework for guiding the synthesis and processing of diamond crystals with further enhanced dielectric properties for advanced microwave and terahertz applications.

The synthesis of high-quality heteroepitaxial diamond films on iridium composite substrates is a critical step toward advancing diamond for electronic and optical applications. Microwave plasma chemical vapor deposition, combined with in situ optical emission spectroscopy, enables precise control over growth modes through plasma parameter tuning. In this study, we examine how methane concentration, microwave power, and gas pressure influence plasma species and, consequently, the growth modes of heteroepitaxial diamond by optical emission spectroscopy and scanning electron microscope. At low nucleation densities, increased methane concentrations promote the transition from faceted polyhedral to ballas structures, driven by elevated C2 radical concentrations in the plasma. Conversely, at higher nucleation densities, gas pressure, and substrate temperature dominate growth mode determination, leading to diverse morphologies, such as planar, polycrystalline, octahedral, and step-flow growth. These findings elucidate the interplay among plasma species, growth parameters, and growth mode, offering critical insights for optimizing growth conditions and preparing heteroepitaxial diamond films in a specific growth mode.

Direct diamond growth without pretreatment was demonstrated on MgO single-crystal substrates with (111), (110), and (100) surface orientations using microwave plasma chemical vapor deposition. Raman spectroscopy confirmed diamond formation only on MgO (111) and (110) substrates, with growth most pronounced on MgO (111), where the nucleation density exceeded 108 cm−2, leading to the formation of a free-standing diamond film. This orientation-dependent growth behavior was attributed to the polarity of the MgO crystal structure, as the (111) polar surface possesses a larger surface energy than the other orientations. Density functional theory calculations of CH3 radical adsorption energies on MgO surfaces further supported this, showing that the (111) surface had the largest adsorption energy. The present study demonstrates that diamond can be grown directly on insulating materials without pretreatment, thereby expanding the range of substrate materials suitable for diamond growth.

Microwave power and chamber pressure studies for single-crystalline diamond film growth using microwave plasma CVD

Nanocrystalline diamond (NCD) films were synthesized by microwave plasma chemical vapor deposition (MPCVD) from a CH4/Ar mixture on seedless p-type Si(111) substrates at 100–400 °C. Crystallinity was evaluated by X-ray diffraction (Cu Kα); bonding by Raman spectroscopy and X-ray photoelectron spectroscopy (XPS); morphology and thickness by scanning electron microscopy (SEM); defect states by thermoluminescence (TL). SEM shows continuous films with uniform thickness. XRD displays a broad (111) reflection near 2θ = 44°. Raman and XPS reveal temperature-dependent bonding: between 300 and 400 °C, the sp3 fraction increases relative to sp2. TL glow curves show peaks at 157 °C and 270 °C, indicating electron-trap centers. These results demonstrate hydrogen-free and seedless NCD growth at low substrate temperatures, supporting potential electronic and dosimetry applications requiring a low thermal load.

ABSTRACT Isotopically modified single‐crystal diamond films are of increasing interest to researchers in view of their potential applications in photonics and spintronics, including those based on the interaction between the nitrogen‐vacancy color centre and the nuclear spin of the 13 C isotope. Confocal Raman spectroscopy is a powerful tool for profiling 13 C/ 12 C bilayer structures, especially since the two isotopes have identical optical properties but very different Raman peak positions. We performed confocal Raman mapping of a series of epitaxial, isotopically enriched 13 C diamond layers (with a thickness ranging from 2 to 558 μm), which were grown by microwave plasma CVD on single‐crystal diamond substrates with a natural isotopic composition. We also quantified the confocality parameter of the optical scheme used. Experimentally, it has been shown that confocality increases from 2 μm (for opaque objects) to approximately 30 μm along the observation axis (the Z ‐axis, which is perpendicular to the sample surface) along the path of the exciting laser beam. Nevertheless, the position of the film/substrate interface can be defined with an accuracy of a few micrometres. Finally, we demonstrate the use of the same confocal system for depth profiling of silicon‐vacancy (SiV) color center, another important photon source, in the photoluminescence spectrum of 13 C diamond, and we found an accumulation of the SiV at the film/substrate interface.

Producing inch-scale, binder-free ultrahard diamond presents a formidable challenge due to the limitations of the conventional high-pressure and high-temperature method. Here, we report a customized microwave plasma chemical vapor deposition technique with high-frequency gas-switching control. By periodically introducing nitrogen, a transient local non-equilibrium growth mode is established, enabling the synthesis of free-standing ultrahard diamond wafers up to 3 mm thick and 5 inches in diameter. The wafers exhibit a Vickers hardness of ~208.3 GPa, comparable to the hardest nano-twinned diamonds, and show exceptional wear resistance—abrasive ratio ~7 times higher than polycrystalline diamond substrate. High-resolution transmission electron microscopy reveals an ultra-dense three-dimensional interlocked stacking fault network (density up to 4.3×10¹² cm⁻²), contributing to superior mechanical properties. This process also allows deposition on commonly used three-dimensional tool surfaces. This work provides a scalable strategy for producing ultrahard, inch-scale diamond suitable for demanding applications in precision machining, semiconductor and aerospace industries.

The regulation mechanism of oxygen additives on diamond growth and residual boron by microwave plasma chemical vapor deposition

Devices based on ultrawide bandgap heterostructures are attracting increased attention for applications that require high fields or high-temperature environments. In this article, we demonstrate an ultrawide bandgap BN/AlN metal-insulator-semiconductor Schottky diode on single-crystal AlN substrates, where the AlN epilayers were grown via metalorganic chemical vapor deposition, and the BN layer was deposited using microwave plasma chemical vapor deposition. The BN/AlN heterostructure was characterized by x-ray photoelectron spectroscopy, transmission electron microscopy, and electron-energy-loss spectroscopy. Capacitance-frequency measurements indicated a low interface state density of 0.67–3.55 × 1011 eV−1 cm−2 at the BN/AlN interface. At forward bias, the device showed good rectifying behavior. At reverse bias, 2D variable range hopping and trap-assisted tunneling were found to be the dominant mechanisms. This work provides valuable guidance for developing ultrawide bandgap nitride heterostructures.

The behavior of precursor gases (H 2 and CH 4 ) in a microwave plasma chemical vapor deposition (MPCVD) system plays a critical role in growing diamond with good quality and at a higher growth rate. In this work, the effect of an additional gas flow outlet integrated into the substrate holder (modified gas flow configuration) on diamond quality and growth rate in a clamshell‐type MPCVD reactor is investigated through simulation and experiments. A simulation using 3D computational fluid dynamics incorporating the gas flow dynamics, thermal, and species transport phenomena is done to evaluate the velocity, temperature, and molar concentration profiles of H 2 and CH 4 over the substrate holder. The modified substrate holder is fabricated and tested experimentally alongside the existing substrate holder under identical deposition conditions: 4% CH 4 in an H 2 CH 4 gas mixture, 4.5 kW microwave power, and 100 Torr chamber pressure. The grown diamond samples are analyzed using Raman, photoluminescence, UV–visible, and Fourier‐transform infrared spectroscopic techniques. From the analysis, the diamond grown with the additional gas outlet shows higher crystallinity and transmittance with less crystal defects, and lower nitrogen concentration than the diamond crystal grown with the existing gas flow configuration. Notably, the growth rate remains unaffected by the modification.

The exceptional stiffness of diamond is strongly anisotropic due to its crystal structure, yet experimental quantification of Young's modulus along different orientations remains limited. Here, we present a direct measurement of elastic anisotropy in microwave plasma chemical vapor deposition (MPCVD) single-crystal diamond (SCD) by analyzing the resonance frequencies of cantilevers aligned along distinct crystallographic directions. The measured Young's modulus exhibited a minimum value of 1085 ± 21 GPa along the ⟨100⟩ direction and a maximum value of 1189 ± 22 GPa along the ⟨110⟩ direction. The compliance constants derived from the MPCVD-SCD differ substantially from previously reported values for natural diamonds and are more consistent with first-principles theoretical values. This method enables precise determination of orientation-dependent stiffness, revealing significant variation in Young's modulus across crystallographic axes. These insights are critical for the design of diamond-based micro- and nano-mechanical systems as well as other high-precision devices, where directional elasticity strongly influences performance.

Abstract Diamond with silicon vacancies has an important role as a promising single-photon source applicable in the quantum information field. However, in a microwave plasma chemical vapor deposition (MPCVD) system, due to the presence of unintentional silicon doping sources such as quartz windows, the behavior of silicon vacancy formation in silicon-doped diamond is complex. In this work, the underlying mechanism of formation of silicon vacancies by unintentional silicon doping in diamond is investigated from the perspective of growing surface kinetics in a two-gas-flow MPCVD system. This system is equipped with a novel susceptor geometry designed to deliver an additional gas flow directly onto the substrate surface. Increasing the concentration of growth doping substances on the substrate surface thereby enhances the efficiency of silicon vacancy formation in diamond. At the same time, by changing the substrate deposition angle the distribution of gas and plasma on the substrate surface is changed, thereby regulating the concentration and distribution of silicon vacancies formed by unintentional silicon doping. Experimental and computational results demonstrate that the difference in silicon vacancies formed by unintentional silicon doping in diamond depends on the substances present on the substrate surface and the distribution of plasma.

Effect of microwave electric field displacement on diamond deposition in microwave plasma chemical vapour deposition: a three-dimensional simulation study