Raman spectroscopy of diamond and doped diamond

Picometer-Scale Atomic Shifts Governing Subdisordered Structures in Diamond

Diamond is considered the most promising next-generation semiconductor material due to its excellent physical characteristics. It has been more than three decades since the discovery of a special structure named n-diamond. However, despite extensive efforts, its crystallographic structure and properties are still unclear. Here, we show that subdisordered structures in diamond provide an explanation for the structural feature of n-diamond. Monocrystalline diamond with subdisordered structures is synthesized via the chemical vapor deposition method. Atomic-resolution scanning transmission electron microscopy characterizations combined with the picometer-precision peak finder technology and diffraction simulations reveal that picometer-scale shifts of atoms within cells of diamond govern the subdisordered structures. First-principles calculations indicate that the bandgap of diamond decreases rapidly with increasing shifting distance, in accordance with experimental results. These findings clarify the crystallographic structure and electronic properties of n-diamond and provide new insights into the bandgap adjustment in diamond.

Selective SERS Detection of TATB Explosives Based on Hydroxy-Terminal Nanodiamond-Multilayer Graphene Substrate

Selective surface-enhanced Raman scattering (SERS) detection of target explosives with good reproducibility is very important for monitoring soldiers' health and ecological environment. Here, the specific charge transfer pathway was constructed between a stable nanodiamond-multilayer graphene (MGD) film substrate and the target explosives. Two-step wet chemical oxidation methods of H2O2 (30%) and HNO3 (65%) solutions were used to regulate the terminal structure of MGD films. The experimental results showed that the hydroxyl (-OH) functional groups are successfully modified on the surface of MGD thin films, and the MGD-OH substrates having good selectivity for 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) explosive in mixed solutions of the TATB, 2,2-dinitroethene-1,1-diamine, 2,4,6-trinitrotoluene, and 1,3,5-trinitroperhydro-1,3,5-triazine explosives compared with MGD substrates were demonstrated. Finally, first-principles density functional theory simulations revealed that the SERS enhancement of the MGD-OH substrate is mainly attributed to the transferred electrons between the -NO2 groups of TATB and the -OH groups of the MGD-OH substrate.

Multimodal fiber probe for simultaneous mid-infrared and Raman spectroscopy

A fiber probe has been developed that enables simultaneous acquisition of mid-infrared (MIR) and Raman spectra in the region of 3100-2600 cm-1. Multimodal measurement is based on a proposed ZrO2 crystal design at the tip of an attenuated total reflection (ATR) probe. Mid-infrared ATR spectra are obtained through a pair of chalcogenide infrared (CIR) fibers mounted at the base of the crystal. The probe enables both excitation and acquisition of a weak Raman signal from a portion of the sample in front of the crystal using an additional pair of silica fibers located in a plane perpendicular to the CIR fibers. The advantages of combining MIR and Raman spectra in a single probe have been discussed.

Comparing transmission- and epi-BCARS: a round robin on solid-state materials

Broadband coherent anti-Stokes Raman scattering (BCARS) is a powerful spectroscopy method combining high signal intensity with spectral sensitivity, enabling rapid imaging of heterogeneous samples in biomedical research and, more recently, in crystalline materials. However, BCARS encounters spectral distortion due to a setup-dependent non-resonant background (NRB). This study assesses BCARS reproducibility through a round robin experiment using two distinct BCARS setups and crystalline materials with varying structural complexity, including diamond, 6H-SiC, KDP, and KTP. The analysis compares setup-specific NRB correction procedures, detected and NRB-removed spectra, and mode assignment. We determine the influence of BCARS setup parameters like pump wavelength, pulse width, and detection geometry and provide a practical guide for optimizing BCARS setups for solid-state applications.

Super High-Concentration Si and N Doping of CVD Diamond Film by Thermal Decomposition of Silicon Nitride Substrate

The high-concentration N doping of diamond film is still a challenge since nitrogen is limited during diamond growth. In this work, a novel method combined with the thermal decomposition of silicon nitride was proposed to form the activated N and Si components in the reactor gas that surrounded the substrate, with which the high-concentration N and Si doping of diamond film was performed. Meanwhile, graphene oxide (GO) particles were also employed as an adsorbent to further increase the concentration of the N element in diamond film by capturing the more decomposed N components. All the as-deposited diamond films were characterized by scanning electron microscopy, energy dispersive spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. For the pure diamond film with a growth time of 0.5 h, the N and Si concentrations were 20.78 and 41.21 at%, respectively. For the GO-diamond film, they reached 47.47 and 21.66 at%, which set a new record for super high-concentration N doping of diamond film. Hence, thermal decomposition for the substrate can be regarded as a potential and alternative method to deposit the chemical vapor deposition (CVD) diamond film with high-concentration N, which be favorable for the widespread application of diamond in the electric field.

Nanodiamonds Doped with Manganese for Applications in Magnetic Resonance Imaging

Nanodiamonds (NDs) are emerging with great potential in biomedical applications like biomarking through fluorescence and magnetic resonance imaging (MRI), targeted drug delivery, and cancer therapy. The magnetic and optical properties of NDs could be tuned by selective doping. Therefore, we report multifunctional manganese-incorporated NDs (Mn-NDs) fabricated by Mn ion implantation. The fluorescent properties of Mn-NDs were tuned by inducing the defects by ion implantation and enhancing the residual nitrogen vacancy density achieved by a two-step annealing process. The cytotoxicity of Mn-NDs was investigated using NCTC clone 929 cells, and the results revealed no cytotoxicity effect. Mn-NDs have demonstrated dual mode contrast enhancement for both T ₁- and T ₂-weighted in vitro MR imaging. Furthermore, Mn-NDs have illustrated a significant increase in longitudinal relaxivity (fivefold) and transversal relaxivity (17-fold) compared to the as-received NDs. Mn-NDs are employed to investigate their ability for in vivo MR imaging by intraperitoneal (ip) injection of Mn-NDs into mice with liver tumors. After 2.5 h of ip injection, the enhancement of contrast in T ₁- and T ₂-weighted images has been observed via the accumulation of Mn-NDs in liver tumors of mice. Therefore, Mn-NDs have great potential for in vivo imaging by MR imaging in cancer therapy.

Electron density and thermal motion of diamond at elevated temperatures

The electron density and thermal motion of diamond are determined at nine temperatures between 100 K and 1000 K via synchrotron powder X-ray diffraction (PXRD) data collected on a high-accuracy detector system. Decoupling of the thermal motion from the thermally smeared electron density is performed via an iterative Wilson-Hansen-Coppens-Rietveld procedure using theoretical static structure factors from density functional theory (DFT) calculations. The thermal motion is found to be harmonic and isotropic in the explored temperature range, and excellent agreement is observed between experimental atomic displacement parameters (ADPs) and those obtained via theoretical harmonic phonon calculations (HPC), even at 1000 K. The Debye temperature of diamond is determined experimentally to be Θ_D = 1883 (35) K. A topological analysis of the electron density explores the temperature dependency of the electron density at the bond critical point. The properties are found to be constant throughout the temperature range. The robustness of the electron density confirms the validity of the crystallographic convolution approximation for diamond in the explored temperature range.

Laser induced white emission of diamond

Laser-induced white emission of diamond was investigated under irradiation with a focused beam of an infrared laser diode. It is a surface-related coherent emission, characterized by an excitation threshold and an exponential dependence on pumping laser power. The mechanism of white emission is discussed in terms of multiphoton ionization of carbon atoms in an irradiated spot. The excitation power dependence of white emission intensity has demonstrated hysteresis loop behavior. This phenomenon could be useful in new broadband laser sources and optical information storage.

Effects of Boron Doping on the Bulk and Surface Acoustic Phonons in Single-Crystal Diamond

We report the results of the investigation of bulk and surface acoustic phonons in the undoped and boron-doped single-crystal diamond films using the Brillouin-Mandelstam light scattering spectroscopy. The evolution of the optical phonons in the same set of samples was monitored with Raman spectroscopy. It was found that the frequency and the group velocity of acoustic phonons decrease nonmonotonically with the increasing boron doping concentration, revealing pronounced phonon softening. The change in the velocity of the shear-horizontal and the high-frequency pseudo-longitudinal acoustic phonons in the degenerately doped diamond, as compared to that in the undoped diamond, was as large as ∼15% and ∼12%, respectively. As a result of boron doping, the velocity of the bulk longitudinal and transverse acoustic phonons decreased correspondingly. The frequency of the optical phonons was unaffected at low boron concentration but experienced a strong decrease at the high doping level. The density-functional-theory calculations of the phonon band structure for the pristine and highly doped samples confirm the phonon softening as a result of boron doping in diamond. The obtained results have important implications for thermal transport in heavily doped diamond, which is a promising material for ultra-wide-band-gap electronics.

Ultrasmall Nanodiamonds: Perspectives and Questions

Nanodiamonds are at the heart of a plethora of emerging applications in areas ranging from nanocomposites and tribology to nanomedicine and quantum sensing. The development of alternative synthesis methods, a better understanding, and the availability of ultrasmall nanodiamonds of less than 3 nm size with a precisely engineered composition, including the particle surface and atomic defects in the diamond crystal lattice, would mark a leap forward for many existing and future applications. Yet today, we are unable to accurately control nanodiamond composition at the atomic scale, nor can we reliably create and isolate particles in this size range. In this perspective, we discuss recent advances, challenges, and opportunities in the synthesis, characterization, and application of ultrasmall nanodiamonds. We particularly focus on the advantages of bottom-up synthesis of these particles and critically assess the physicochemical properties of ultrasmall nanodiamonds, which significantly differ from those of larger particles and bulk diamond.

Scanning Deposition Method for Large-Area Diamond Film Synthesis Using Multiple Microwave Plasma Sources

The demand for synthetic diamonds and research on their use in next-generation semiconductor devices have recently increased. Microwave plasma chemical vapor deposition (MPCVD) is considered one of the most promising techniques for the mass production of large-sized and high-quality single-, micro- and nanocrystalline diamond films. Although the low-pressure resonant cavity MPCVD method can synthesize high-quality diamonds, improvements are needed in terms of the resulting area. In this study, a large-area diamond synthesis method was developed by arranging several point plasma sources capable of processing a small area and scanning a wafer. A unit combination of three plasma sources afforded a diamond film thickness uniformity of ±6.25% at a wafer width of 70 mm with a power of 700 W for each plasma source. Even distribution of the diamond grains in a size range of 0.1–1 μm on the thin-film surface was verified using field-emission scanning electron microscopy. Therefore, the proposed novel diamond synthesis method can be theoretically expanded to achieve large-area films.

Tribological Performance of Diamond Films with Different Roughnesses of Silicon Nitride Substrates and Carbon Source Concentrations

Diamond films were deposited on silicon nitride (Si3N4) substrates with three different roughnesses using the method of hot-filament chemical vapor deposition (HFCVD). The tribological properties of the film were studied by changing the deposition time, deposition distance, and methane (CH4) concentration. The friction coefficient, delamination threshold load, and wear rate of the diamond films were tested and calculated using the reciprocating friction and wear test under dry friction conditions. The results show that, when the deposition time is 12 h, the bonding force of the film is the lowest and the friction coefficient is the largest (0.175, 0.438, and 0.342); the deposition distance has little effect on the friction performance. The friction coefficients (0.064, 0.107, and 0.093) of nano-diamond films (NCD) prepared at a 40 sccm CH4 concentration are smaller than those of micro-diamond films (MCD) prepared at a 16 sccm CH4 concentration. The load thresholds before delamination of Ra 0.4 μm substrate diamond film are as high as 40 N and 80 N, whereas the diamond films deposited on Ra 0.03 μm substrates have lower wear rates (4.68 × 10−4 mm3/mN, 5.34 × 10−4 mm3/mN) and low friction coefficients (0.119, 0.074, 0.175, and 0.064). Within a certain load range, the deposition of a diamond film on a Ra 0.03 μm Si3N4 substrate significantly reduces the friction coefficient and improves wear resistance. Diamond film can improve the friction performance of a workpiece and prolong its service life.

Advances in RF Glow Discharge Optical Emission Spectrometry Characterization of Intrinsic and Boron-Doped Diamond Coatings

Accurate determination of the effective doping range within diamond thin films is important for fine-tuning of electrical conductivity. Nevertheless, it is not easily attainable by the commonly adopted techniques. In this work, pulsed RF glow discharge optical emission spectrometry (GD-OES) combined with ultrafast sputtering (UFS) is applied for the first time to acquire elemental depth profiles of intrinsic diamond coatings and boron content bulk distribution in films. The GD-OES practical advances presented here enabled quick elemental profiling with noteworthy depth resolution and determination of the film interfaces. The erosion rates and layer thicknesses were measured using differential interferometric profiling (DIP), demonstrating a close correlation between the coating thickness and the carbon/hydrogen gas ratio. Moreover, DIP and the adopted semiquantification methodology revealed a nonhomogeneous bulk distribution of boron within the diamond crystalline structure, i.e., boron doping is both substitutional and interstitial within the diamond framework. DIP measurements also showed that effective boron doping is not linearly correlated to the increasing content introduced into the diamond coating. This is a finding well supported by X-ray diffraction (XRD) Rietveld refinement and X-ray photoelectron spectroscopy (XPS). This work demonstrates the advantage of applying advanced GD-OES operation modes due to its ease of use, affordability, accuracy, and high-speed depth profile analysis capability.

Determination and Monitoring of Quality Parameters: A Detailed Study of Optical Elements of a Lens-Based Raman Spectrometer

A lens-based Raman spectrometer is characterized by studying the optical elements in the optical path and we study the measure of aberration-diffraction effects. This is achieved by measuring the spectral resolution (SR) thus encompassing almost all optical elements of a spectrometer that are mostly responsible for such effects. An equation for SR is used to determine the quality factor Q which measures aberration/diffraction effects occurring in a spectrometer. We show how the quality factor changes with different spectrometer parameters such as grating groove density, the wavelength of excitation, pinhole width, charge-coupled device (CCD) pixel density, etc. This work provides an insight into the quality of a spectrometer and helps to monitor the performance of the spectrometer over a certain period. Commercially available spectrometers or home-built spectrometers are prone to misalignment in optical elements and can benefit from this work that allows maintaining the overall quality of the setup. Performing such experiments over a period helps to minimize the aberration/diffraction effects occurring as a result of time and maintaining the quality of measurements.

Thickness Impact on the Morphology, Strain Relaxation and Defects of Diamond Heteroepitaxially Grown on Ir/Al2O3 Substrates

This paper investigates the formation and propagation of defects in the heteroepitaxial growth of single-crystal diamond with a thick film achieving 500 µm on Ir (001)/Al₂O₃ substrate. The growth of diamond follows the Volmer-Weber mode, i.e., initially shows the islands and subsequently coalesces to closed films. The films' strain imposed by the substrate gradually relaxed as the film thickness increased. It was found that defects are mainly located at the diamond/Ir interface and are then mainly propagated along the [001] direction from the nucleation region. Etching pits along the [001] direction formed by H₂/O₂ plasma treatment were used to show defect distribution at the diamond/Ir/Al₂O₃ interface and in the diamond bulk, which revealed the reduction of etching pit density in diamond thick-film surface. These results show the evident impact of the thickness on the heteroepitaxially grown diamond films, which is of importance for various device applications.

Influence of B/N co-doping on electrical and photoluminescence properties of CVD grown homoepitaxial diamond films

Boron doped diamond (BDD) has great potential in electrical, and electrochemical sensing applications. The growth parameters, substrates, and synthesis method play a vital role in the preparation of semiconducting BDD to metallic BDD. Doping of other elements along with boron (B) into diamond demonstrated improved efficacy of B doping and exceptional properties. In the present study, B and nitrogen (N) co-doped diamond has been synthesized on single crystalline diamond (SCD) IIa and SCD Ib substrates in a microwave plasma-assisted chemical vapor deposition process. The B/N co-doping into CVD diamond has been conducted at constant N flow of N/C ∼ 0.02 with three different B/C doping concentrations of B/C ∼ 2500 ppm, 5000 ppm, 7500 ppm. Atomic force microscopy topography depicted the flat and smooth surface with low surface roughness for low B doping, whereas surface features like hillock structures and un-epitaxial diamond crystals with high surface roughness were observed for high B doping concentrations. KPFM measurements revealed that the work function (4.74-4.94 eV) has not varied significantly for CVD diamond synthesized with different B/C concentrations. Raman spectroscopy measurements described the growth of high-quality diamond and photoluminescence studies revealed the formation of high-density nitrogen-vacancy centers in CVD diamond layers. X-ray photoelectron spectroscopy results confirmed the successful B doping and the increase in N doping with B doping concentration. The room temperature electrical resistance measurements of CVD diamond layers (B/C ∼ 7500 ppm) have shown the low resistance value ∼9.29 Ω for CVD diamond/SCD IIa, and the resistance value ∼16.55 Ω for CVD diamond/SCD Ib samples.

Impact of Methanol Concentration on Properties of Ultra-Nanocrystalline Diamond Films Grown by Hot-Filament Chemical Vapour Deposition

Diamond is a very interesting material with a wide range of properties, making it highly applicable, for example, in power electronics, chemo- and biosensors, tools' coatings, and heaters. Due to the high demand for this innovative material based on the properties it is already expected to have, it is important to obtain homogeneous diamond layers for specific applications. Doping is often chosen to modify the properties of layers. However, there is an alternative way to achieve this goal and it is shown in this publication. The presented research results reveal that the change in methanol content during the Hot Filament Chemical Vapour Deposition (HF CVD) process is a sufficient factor to tune the properties of deposited layers. This was confirmed by analysing the properties of the obtained layers, which were determined using Raman spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and an atomic force microscope (AFM), and the results were correlated with those of X-ray photoelectron spectroscopy (XPS). The results showed that the increasing of the concentration of methanol resulted in a slight decrease in the sp3 phase content. At the same time, the concentration of the -H, -OH, and =O groups increased with the increasing of the methanol concentration. This affirmed that by changing the content of methanol, it is possible to obtain layers with different properties.

Effect of Reactive Ion Etching on the Luminescence of GeV Color Centers in CVD Diamond Nanocrystals

The negatively charged germanium-vacancy GeV^- color centers in diamond nanocrystals are solid-state photon emitters suited for quantum information technologies, bio-sensing, and labeling applications. Due to the small Huang-Rhys factor, the GeV^--center zero-phonon line emission is expected to be very intensive and spectrally narrow. However, structural defects and the inhomogeneous distribution of local strains in the nanodiamonds result in the essential broadening of the ZPL. Therefore, clarification and elimination of the reasons for the broadening of the GeV^- center ZPL is an important problem. We report on the effect of reactive ion etching in oxygen plasma on the structure and luminescence properties of nanodiamonds grown by hot filament chemical vapor deposition. Emission of GeV^- color centers ensembles at about 602 nm in as-grown and etched nanodiamonds is probed using micro-photoluminescence and micro-Raman spectroscopy at room and liquid nitrogen temperature. We show that the etching removes the nanodiamond surface sp²-induced defects resulting in a reduction in the broad luminescence background and a narrowing of the diamond Raman band. The zero-phonon luminescence band of the ensemble of the GeV^- centers is a superposition of narrow lines originated most likely from the GeV^- center sub-ensembles under different uniaxial local strain conditions.

Enhancing electroanalytical performance of porous boron-doped diamond electrodes by increasing thickness for dopamine detection

Novel porous boron-doped diamond (BDD_porous)-based materials have attracted lots of research interest due to their enhanced detection ability and biocompatibility, favouring them for use in neuroscience. This study reports on morphological, spectral, and electrochemical characterisation of three BDD_porous electrodes of different thickness given by a number of deposited layers (2, 3 and 5). These were prepared using microwave plasma-enhanced chemical vapour deposition on SiO₂ nanofiber-based scaffolds. Further, the effect of number of layers and poly-l-lysine coating, commonly employed in neuron cultivation experiments, on sensing properties of the neurotransmitter dopamine in a pH 7.4 phosphate buffer media was investigated. The boron doping level of ∼2 × 10²¹ atoms cm^-3 and increased content of non-diamond (sp²) carbon in electrodes with more layers was evaluated by Raman spectroscopy. Cyclic voltammetric experiments revealed reduced working potential windows (from 2.4 V to 2.2 V), higher double-layer capacitance values (from 405 μF cm^-2 to 1060 μF cm^-2), enhanced rates of electron transfer kinetics and larger effective surface areas (from 5.04 mm² to 7.72 mm²), when the number of porous layers increases. For dopamine, a significant boost in analytical performance was recognized with increasing number of layers using square-wave voltammetry: the highest sensitivity of 574.1 μA μmol^-1 L was achieved on a BDD_porous electrode with five layers and dropped to 35.9 μA μmol^-1 L when the number of layers decreased to two. Consequently, the lowest detection limit of 0.20 μmol L^-1 was obtained on a BDD_porous electrode with five layers. Moreover, on porous electrodes, enhanced selectivity for dopamine detection in the presence of ascorbic acid and uric acid was demonstrated. The application of poly-l-lysine coating on porous electrode surface resulted in a decrease in dopamine peak currents by 17% and 60% for modification times of 1 h and 15 h, respectively. Hence, both examined parameters, the number of deposited porous layers and the presence of poly-l-lysine coating, were proved to considerably affect the characteristics and performance of BDD_porous electrodes.

On the Stabilization of Carbynes Encapsulated in Penta-Graphene Nanotubes: a DFT Study

We carried out density functional theory calculations to investigate the electronic and structural properties of linear carbon chains (carbynes) encapsulated in armchair and zigzag penta-graphene (PGNT) nanotubes. Results showed that PGNTs-wrapped carbyne can present negative formation energies that tend to stabilize that encapsulated carbon chains. These chains were stabilized in their cumulene and polyyne forms, with slight dependence on tube diameter. As a general trend, the PGNT band structures are kept almost unchanged upon carbyne encapsulation. This finding indicates weak orbital interactions between the PGNT and the carbyne. No net charge was found in chains encapsulated on zigzag PGNTs. Schematic representation of a carbyne encapsulated in a pentagraphene nanotube.

The Undoped Polycrystalline Diamond Film-Electrical Transport Properties

The polycrystalline diamonds were synthesized on n-type single crystalline Si wafer by Hot Filament CVD method. The structural properties of the obtained diamond films were checked by X-ray diffraction and Raman spectroscopy. The conductivity of n-Si/p-diamond, sandwiched between two electrodes, was measured in the temperature range of 90–300 K in a closed cycle cryostat under vacuum. In the temperature range of (200–300 K), the experimental data of the conductivity were used to obtain the activation energies Ea which comes out to be in the range of 60–228 meV. In the low temperature region i.e., below 200 K, the conductivity increases very slowly with temperature, which indicates that the conduction occurs via Mott variable range hopping in the localized states near Fermi level. The densities of localized states in diamond films were calculated using Mott’s model and were found to be in the range of 9×1013 to 5×1014eV−1cm−3 depending on the diamond’s surface hydrogenation level. The Mott’s model allowed estimating primal parameters like average hopping range and hopping energy. It has been shown that the surface hydrogenation may play a crucial role in tuning transport properties.

Advances in laser-assisted conversion of polymeric and graphitic carbon into nanodiamond films

Nanodiamond (ND) synthesis by nanosecond laser irradiation has sparked tremendous scientific and technological interest. This review describes efforts to obtain cost-effective ND synthesis from polymers and carbon nanotubes (CNT) by the melting route. For polymers, ultraviolet (UV) irradiation triggers intricate photothermal and photochemical processes that result in photochemical degradation, subsequently generating an amorphous carbon film; this process is followed by melting and undercooling of the carbon film at rates exceeding 10⁹K s^-1. Multiple laser shots increase the absorption coefficient of PTFE, resulting in the growth of 〈110〉 oriented ND film. Multiple laser shots on CNTs result in pseudo topotactic diamond growth to form a diamond fiber. This technique is useful for fabricating 4-50 nm sized NDs. These NDs can further be employed as seed materials that are used in bulk epitaxial growth of microdiamonds using chemical vapor deposition, particularly for use with non-lattice matched substrates that formerly did not form continuous and adherent films. We also provide insights into biocompatible precursors for ND synthesis such as polybenzimidazole fiber. ND fabrication by UV irradiation of graphitic and polymeric carbon opens up a pathway for preparing selective coatings of polymer-diamond composites, doped nanodiamonds, and graphene composites for quantum computing and biomedical applications.

Ultrafast and Controllable Phase Evolution by Flash Joule Heating

Flash Joule heating (FJH), an advanced material synthesis technique, has been used for the production of high-quality carbon materials. Direct current discharge through the precursors by large capacitors has successfully converted carbon-based starting materials into bulk quantities of turbostratic graphene by the FJH process. However, the formation of other carbon allotropes, such as nanodiamonds and concentric carbon materials, as well as the covalent functionalization of different carbon allotropes by the FJH process, remains challenging. Here, we report the solvent-free FJH synthesis of three different fluorinated carbon allotropes: fluorinated nanodiamonds, fluorinated turbostratic graphene, and fluorinated concentric carbon. This is done by millisecond flashing of organic fluorine compounds and fluoride precursors. Spectroscopic analysis confirms the modification of the electronic states and the existence of various short-range and long-range orders in the different fluorinated carbon allotropes. The flash-time-dependent relationship is further demonstrated to control the phase evolution and product compositions.

Fabrication of a Micron-Scale Three-Dimensional Single Crystal Diamond Channel Using a Micro-Jet Water-Assisted Laser

Two types of a trench with conventional vertical and new reverse-V-shaped cross-sections were fabricated on single crystal diamond (SCD) substrate using a micro-jet water-assisted laser. In addition, a microwave plasma chemical vapor deposition device was used to produce multiple micrometer-sized channels using the epitaxial lateral overgrowth technique. Raman and SEM methods were applied to analyze both types of growth layer characterization. The hollowness of the microchannels was measured using an optical microscope. According to the findings, the epitaxial lateral overgrowth layer of the novel reverse-V-shaped trench produced improved SCD surface morphology and crystal quality.

In Situ Raman Microdroplet Spectroelectrochemical Investigation of CuSCN Electrodeposited on Different Substrates

Systematic in situ Raman microdroplet spectroelectrochemical (Raman-μSEC) characterization of copper (I) thiocyanate (CuSCN) prepared using electrodeposition from aqueous solution on various substrates (carbon-based, F-doped SnO₂) is presented. CuSCN is a promising solid p-type inorganic semiconductor used in perovskite solar cells as a hole-transporting material. SEM characterization reveals that the CuSCN layers are homogenous with a thickness of ca. 550 nm. Raman spectra of dry CuSCN layers show that the SCN⁻ ion is predominantly bonded in the thiocyanate resonant form to copper through its S−end (Cu−S−C≡N). The double-layer capacitance of the CuSCN layers ranges from 0.3 mF/cm² on the boron-doped diamond to 0.8 mF/cm² on a glass-like carbon. In situ Raman-μSEC shows that, independently of the substrate type, all Raman vibrations from CuSCN and the substrate completely vanish in the potential range from 0 to −0.3 V vs. Ag/AgCl, caused by the formation of a passivation layer. At positive potentials (+0.5 V vs. Ag/AgCl), the bands corresponding to the CuSCN vibrations change their intensities compared to those in the as-prepared, dry layers. The changes concern mainly the Cu−SCN form, showing the dependence of the related vibrations on the substrate type and thus on the local environment modifying the delocalization on the Cu−S bond.

A detailed EIS study of boron doped diamond electrodes decorated with gold nanoparticles for high sensitivity mercury detection

This work compares the electrochemical impedance response of polished and unpolished boron doped diamond (BDD) electrodes, during mercury detection measurements. For each substrate type both bare electrodes and electrodes decorated with average diameter 30 nm AuNPs were used, to investigate the role of AuNPs during mercury sensing with diamond electrodes. In square wave anodic stripping voltammetry (SWASV) measurements for mercury detection, the mercury ions in the electrolyte are deposited onto, then stripped from the diamond electrode surface. To investigate the different electrode performances during these steps, the EIS measurements were made at the deposition and stripping potentials, alongside scans at open circuit potential for comparison. The performance of the electrodes is assessed in terms of their electron transfer rate (k₀). The electrodes decorated with AuNPs are shown to have lower capacitance and higher reactivity than the bare pBDD and BDD electrodes, until the mercury concentration in the electrolyte is < 500 µM, when the sp²/sp³ carbon ratio at the surface of the electrodes has a greater influence on the sensitivity for mercury detection than the presence of AuNPs.

Comparison of diamond nanoparticles captured on the floating and grounded membranes in the hot filament chemical vapor deposition process

Negatively charged diamond nanoparticles are known to be generated in the gas phase of the hot filament chemical vapor deposition (HFCVD) process. However, the structures of these nanoparticles remain unknown. Also, the effect of charging on the stability of nanodiamond structures has not been studied experimentally. Here, by installing a capturing apparatus in an HFCVD reactor, we succeeded in capturing nanoparticles on the floating and grounded SiO, carbon, and graphene membranes of a copper transmission electron microscope grid during HFCVD. We examined the effect of charge on the crystal structure of nanodiamonds captured for 10 s under various conditions and identified four carbon allotropes, which are i-carbon, hexagonal diamond, n-diamond, and cubic diamond, by analyzing 150 d-spacings of ∼100 nanoparticles for each membrane. Nanoparticles captured on the floating membrane consisted mainly of cubic diamond and n-diamond, whereas those captured on the grounded membrane consisted mainly of i-carbon. Diamond particles deposited for 8 h on the floating silicon (Si) substrate exhibited an octahedron shape with well-developed facets, and a high-intensity 1332 cm⁻¹ Raman peak, whereas diamond particles deposited on the grounded Si substrate showed a spherical shape partially covered with crystalline facets with a broad G-band Raman peak. These results indicate that charging stabilizes the diamond structure.

Various carbon allotropes were captured on the floating and grounded membrane.

The effect of pressure on synthetic diamond crystals at high temperatures and pressures in an Fe/Ni catalyst system

Pressure is a necessary condition for the growth of natural diamond.

Growth and characterization of diamond single crystals grown in the Fe–S–C system by the temperature gradient method

Diagram of the apparatus for the HPHT diamond synthesis: (a) alloy hammer + pyrophyllite assembly block; (b) sample assembly.

Influence of temperature on the electrochemical window of boron doped diamond: a comparison of commercially available electrodes

This work compares the electrochemical windows of polished and unpolished boron doped diamond (BDD) electrodes with hydrogen and oxygen terminations at a series of temperatures up to 125 °C. The experiment was run at 5 bar pressure to avoid complications due to bubble formation. An alternative method for determining the electrochemical window is compared to the most commonly used method, which defines the window at an arbitrary current density cut-off (J_cut-off) value. This arbitrary method is heavily influenced by the mass transport of the electrolyte and cannot be used to compare electrodes across literature where different J_cut-off values have been used. A linear fit method is described which is less affected by the experimental conditions in a given measurement system. This enables a more accurate comparison of the relative electrochemical window from various diamond electrode types from reported results. Through comparison of polished and unpolished BDD electrodes, with hydrogen and oxygen surface terminations, it is determined that the electrochemical window of BDD electrodes narrows as temperature increases; activation energies are reported.

Process-Induced Nanostructures on Anatase Single Crystals via Pulsed-Pressure MOCVD

The recent global pandemic of COVID-19 highlights the urgent need for practical applications of anti-microbial coatings on touch-surfaces. Nanostructured TiO₂ is a promising candidate for the passive reduction of transmission when applied to handles, push-plates and switches in hospitals. Here we report control of the nanostructure dimension of the mille-feuille crystal plates in anatase columnar crystals as a function of the coating thickness. This nanoplate thickness is key to achieving the large aspect ratio of surface area to migration path length. TiO₂ solid coatings were prepared by pulsed-pressure metalorganic chemical vapor deposition (pp-MOCVD) under the same deposition temperature and mass flux, with thickness ranging from 1.3-16 mm, by varying the number of precursor pulses. SEM and STEM were used to measure the mille-feuille plate width which is believed to be a key functional nano-dimension for photocatalytic activity. Competitive growth produces a larger columnar crystal diameter with thickness. The question is if the nano-dimension also increases with columnar crystal size. We report that the nano-dimension increases with the film thickness, ranging from 17-42 nm. The results of this study can be used to design a coating which has co-optimized thickness for durability and nano-dimension for enhanced photocatalytic properties.

Influence of Adhesive Strength, Fatigue Strength and Contact Mechanics on the Drilling Performance of Diamond Coating

Adhesive strength of the coating significantly affects the lifetime of the coating. However, it is still inevitable for the coating, even with strong adhesive strength, to peel off from the substrate after working for a while. In this work, fatigue and wear behaviors were employed to analyze the effect on the mechanics of coating and contribute to a fundamental understanding of peeling of the coating. A small-size Co-cemented tungsten carbide drill bit was selected as the examined substrate to fabricate the diamond coating. Roughening pretreatment with a diamond slurry combined with ultrasonic vibration was performed for the substrate surface to enhance adhesive strength. Meanwhile, a diamond coating without roughening pretreatment was also fabricated for comparison. The lifetime and quality of the coating were evaluated by the drilling test. Although the diamond coating could grow on the substrates with and without roughening pretreatment, the diamond coating with roughening pretreatment possessed a higher lifetime and stronger wear resistance than that without roughening pretreatment. We found that both substrates with and without roughening pretreatment exhibited a coarse surface, whereas the roughening pretreatment could remove the original machined surface of the substrate and thus make the near surface with numerous integrated crystalline grains become the new topmost surface. This increased the contact area and surface energy of the interface, leading to the improvement of adhesive strength. Finally, fatigue strength and contact mechanics were studied to trace the changes in the stress of the diamond coating in the whole process of drilling from a theoretical point of view. We suggest that fatigue strength and contact mechanics may play vital roles on the durability and peeling of the coating.

Electrochemical degradation of the antibiotic ciprofloxacin in a flow reactor using distinct BDD anodes: Reaction kinetics, identification and toxicity of the degradation products

The performances of distinct BDD anodes (boron doping of 100, 500 and 2500 ppm, with sp³/sp² carbon ratios of 215, 325, and 284, respectively) in the electrochemical degradation of ciprofloxacin - CIP (0.5 L of 50 mg L^-1 in 0.10 M Na₂SO₄, at 25 °C) were comparatively assessed using a recirculating flow system with a filter-press reactor. Performance was assessed by monitoring the CIP and total organic carbon (TOC) concentrations, oxidation intermediates, and antimicrobial activity against Escherichia coli as a function of electrolysis time. CIP removal was strongly affected by the solution pH (kept fixed), flow conditions, and current density; similar trends were obtained independently of the BDD anode used, but the BDD₁₀₀ anode yielded the best results. Enhanced mass transport was achieved at a low flow rate by promoting the solution turbulence within the reactor. The fastest complete CIP removal (within 20 min) was attained at j = 30 mA cm^-2, pH = 10.0, and q_V = 2.5 L min^-1 + bypass turbulence promotion. TOC removal was practically accomplished only after 10 h of electrolysis, with quite similar performances by the distinct BDD anodes. Five initial oxidation intermediates were identified (263 ≤ m/z ≤ 348), whereas only two terminal oxidation intermediates were detected (oxamic and formic acids). The antimicrobial activity of the electrolyzed CIP solution was almost completely removed within 10 h of electrolysis. The characteristics of the BDD anodes only had a marked effect on the CIP removal rate (best performance by the least-doped anode), contrasting with other data in the literature.

Diamond growth from organic compounds in hydrous fluids deep within the Earth

At subduction zones, most diamonds form by carbon saturation in hydrous fluids released from lithospheric plates on equilibration with mantle rocks. Although organic molecules are predicted among dissolved species which are the source for carbon in diamonds, their occurrence is not demonstrated in nature, and the physical model for crustal diamond formation is debated. Here, using Raman microspectroscopy, I determine the structure of carbon-based phases inside fluid inclusions in diamond-bearing rocks from the Alps. The results provide direct evidence that diamond surfaces are coated by sp²-, and sp³-bonded amorphous carbon and functional groups of carboxylic acids (e.g., carboxyl, carboxylate, methyl, and methylene), indicating the geosynthesis of organic compounds in deep hydrous fluids. Moreover, this study suggests diamond nucleation via metastable molecular precursors. As a possible scenario, with carbon saturation by reduction of carboxylate groups, I consider tetrahedral H-terminated C groups as templates for the growth of sp³-structured carbon.

Diamonds can give us clues to the processes regulating deep carbon transport within the Earth. Here, the author discovers evidence from diamond coatings that organic compounds exist at great depth in Earth’s interior, and furthermore, that organic molecules may provide scaffolds for diamond nucleation and growth.

One-Step Preparation Method of Flexible Metafilms on the Water-Oil Interface: Self-Assembly Surface Plasmon Structures for Surface-Enhanced Raman Scattering Detection

The present study demonstrated a one-step method for the first time to fabricate self-assembled gold nanoparticle (AuNP) metafilms at the water-toluene interface by adding polystyrene-polyisoprene-polystyrene as the support layer. The thiolated polyethylene glycol and ethanol were used to tune the surface charge density on the AuNPs, constructing a balanced situation at the water-toluene interface. The flexible (AuNP) metafilm can be easily obtained after evaporation of the toluene phase and further used as a surface-enhanced Raman scattering (SERS) substrate for trace thiram detection. The SERS sensitivity was tested using standard Raman probes such as crystal violet and malachite green, both with the detect concentration reaching 1 × 10^-11 M. Moreover, the excellent reproducibility and elastic properties make the metafilm promising in practical detection. Hence, the trace thiram detection on an orange pericarp was inspected with the detection limit of 0.5 ppm (1 × 10^-6 M) as well as a favorable linearity relation with a correlation coefficient of 0.979, exactly matching the realistic application requirements.

Direct conversion of carbon nanofibers into diamond nanofibers using nanosecond pulsed laser annealing

Here, we show the direct conversion of carbon nanofibers (CNFs) into diamond nanofibers (DNFs) by irradiating CNFs with an ArF nanosecond laser at room temperature and atmospheric pressure. The nanosecond laser pulses melt the tips of CNFs into a highly undercooled state, and their subsequent quenching results in the formation of DNFs. This formation of DNFs is dependent on the degree of undercooling which is controlled by nanosecond laser energy density and one-dimensional heat flow characteristics in CNFs. The conversion process starts at the top and extends with the number of pulses. Therefore, our highly non-equilibrium nanosecond laser processing opens a new avenue for the synthesis of exciting pure and doped diamond structures at ambient temperatures and pressures for a variety of applications.

Direct conversion of carbon nanofibers and nanotubes into diamond nanofibers and the subsequent growth of large-sized diamonds

We report a pulsed laser annealing method to convert carbon fibers and nanotubes into diamond fibers at ambient temperature and pressure in air. The conversion of carbon nanofibers and nanotubes into diamond nanofibers involves melting in a super undercooled state using nanosecond laser pulses, and quenching rapidly to convert into phase-pure diamond. The conversion process occurs at ambient temperature and pressure, and can be carried out in air. The structure of diamond fibers has been confirmed by selected-area electron diffraction in transmission electron microscopy, electron-back-scatter-diffraction in high-resolution scanning electron microscopy, all showing characteristic diffraction lines for the diamond structure. The bonding characteristics were determined by Raman spectroscopy with a strong peak near 1332 cm-1, and high-resolution electron-energy-loss spectroscopy in transmission electron microscopy with a characteristic peak at 292 eV for σ* for sp3 bonding and the absence of π* for sp2 bonding. The Raman peak at 1332 cm-1 downshifts to 1321 cm-1 for diamond nanofibers due to the phonon confinement in nanodiamonds. These laser-treated carbon fibers with diamond seeds are used to grow larger diamond crystallites further by using standard hot-filament chemical vapor deposition (HFCVD). We compare these results with those obtained without laser treating the carbon fibers. The details of diamond conversion and HFCVD growth are presented in this paper.

Diamond/Porous Titanium Nitride Electrodes With Superior Electrochemical Performance for Neural Interfacing

Robust devices for chronic neural stimulation demand electrode materials which exhibit high charge injection (Q_inj) capacity and long-term stability. Boron-doped diamond (BDD) electrodes have shown promise for neural stimulation applications, but their practical applications remain limited due to the poor charge transfer capability of diamond. In this work, we present an attractive approach to produce BDD electrodes with exceptionally high surface area using porous titanium nitride (TiN) as interlayer template. The TiN deposition parameters were systematically varied to fabricate a range of porous electrodes, which were subsequently coated by a BDD thin-film. The electrodes were investigated by surface analysis methods and electrochemical techniques before and after BDD deposition. Cyclic voltammetry (CV) measurements showed a wide potential window in saline solution (between −1.3 and 1.2 V vs. Ag/AgCl). Electrodes with the highest thickness and porosity exhibited the lowest impedance magnitude and a charge storage capacity (CSC) of 253 mC/cm², which largely exceeds the values previously reported for porous BDD electrodes. Electrodes with relatively thinner and less porous coatings displayed the highest pulsing capacitances (C_pulse), which would be more favorable for stimulation applications. Although BDD/TiN electrodes displayed a higher impedance magnitude and a lower C_pulse as compared to the bare TiN electrodes, the wider potential window likely allows for higher Q_inj without reaching unsafe potentials. The remarkable reduction in the impedance and improvement in the charge transfer capacity, together with the known properties of BDD films, makes this type of coating as an ideal candidate for development of reliable devices for chronic neural interfacing.