High-pressure High-temperature Diamond Research Articles

Delayed luminescence and thermoluminescence in laboratory-grown diamonds

The “blue-green” phosphorescence/thermoluminescence is most commonly observed in diamonds following excitation at or above the indirect band gap and has been explained by a substitutional nitrogen-boron donor-acceptor pair recombination model. “Orange” and “red” phosphorescence have also been frequently observed in laboratory-grown near-colorless high-pressure high-temperature diamonds following optical excitation and their luminescence mechanisms are shown to be different from that of the blue-green phosphorescence. The physics of the orange and red luminescence and phosphorescence bands including the optical-excitation dependency (UV-NIR), temperature dependency (20K–573K), and related charge transfer process are investigated by a combination of self-built time-resolved imaging/spectroscopic techniques. In this paper, an alternative model for long-lived phosphorescence based on charge trapping is proposed to explain the orange phosphorescence/thermoluminescence band. Additionally, the red phosphorescence band is attributed to point defect, which possibly has a three-level phosphorescence system. Published by the American Physical Society 2024

Investigation of electrochemical fingerprints for Buzhong Yiqi Tang extract granules using diamond-graphene composite electrode

This study presents a novel electrochemical fingerprinting method for Buzhong Yiqi Tang extract granules using a diamond-graphene composite electrode. The electrode was fabricated through chemical vapor deposition of graphene on high-pressure high-temperature synthetic diamond, resulting in a few-layer graphene coating as confirmed by Raman spectroscopy (I₂D/IG ratio ≈ 1.2) and XPS analysis (78 % sp² C-C signal). Cyclic voltammetry revealed four anodic and three cathodic peaks, while differential pulse voltammetry provided enhanced resolution with eight distinct oxidation peaks. The method demonstrated high sensitivity (LODs 0.08–0.15 mg/mL) and good linearity (R² > 0.995) over a concentration range of 0.5–10 mg/mL. Comparison of fingerprints from individual herb extracts (Astragalus membranaceus, Panax ginseng, and Glycyrrhiza uralensis) elucidated the origins of major peaks in the Buzhong Yiqi Tang profile. Principal component analysis of fingerprints successfully differentiated between samples from three manufacturers, accounting for 87.3 % of total variance. Strong correlations (r > 0.92) were observed between key DPV peak intensities and HPLC-determined concentrations of traditional chemical markers. The rapid analysis time, minimal sample preparation, and holistic representation of multiple electroactive components make this approach a promising complement to existing chromatographic methods for quality assessment of traditional Chinese medicine formulations.

Compensation Ratio of Acceptor Centers in Different Growth Sectors of Boron-Doped High-Pressure High-Temperature Diamond

Compensation Ratio of Acceptor Centers in Different Growth Sectors of Boron-Doped High-Pressure High-Temperature Diamond

Comparative analysis: CapEx in diamond mining versus diamond growing, based on open data sources and experimental results

The diamond industry has long been associated with environmental and social problems, ranging from mining practices to ethical concerns related to diamond sourcing. In recent years, there has been a growing interest in lab-grown diamonds as a sustainable alternative for diamond consumers. However, the production of lab-grown diamonds has own challenges. This article examines the capital expenditures per annualized carat of rough diamonds obtained through mining and two fabrication methods: high-pressure high-temperature (HPHT) and microwave plasma-assisted chemical vapour deposition (MP CVD). Lab-grown diamonds produced using HPHT and MP CVD methods require significantly higher capital expenditures per annualized carat compare to mined diamonds. HPHT diamonds require on-time CapEx of 500–833 US$ per carat annually, while MP CVD diamonds demand 549–1648 US$ per carat annually. Finding ways to reduce production cost and increase efficiency will be crucial in realizing the potential of lab-grown diamonds as a sustainable alternative to mined diamonds.

High-frequency high-power DNP/EPR spectrometer operating at 7 T magnetic field

One of the most essential prerequisites for the development of pulse Dynamic Nuclear Polarization (DNP) is the ability to generate high-power coherent mm-wave pulses at the electron precession frequencies corresponding to the magnetic fields of modern high-resolution NMR spectrometers. As a major step towards achieving this goal, an Extended Interaction Klystron (EIK) pulse amplifier custom-built by the Communications and Power Industries, Inc. and producing up to 140 W at 197.8 GHz, was integrated with in-house built NMR/DNP/EPR spectrometer operating at 7 T magnetic field. The spectrometer employs a Thomas Keating, Ltd. quasioptical bridge to direct mm-waves into a homebuilt DNP probe incorporating photonic bandgap (PBG) resonators to further boost electronic B1e fields. Three-pulse electron spin echo nutation experiments were employed to characterize the B1e fields at the sample by operating the homodyne 198 GHz bridge in an induction mode. Room-temperature experiments with a single-crystal high-pressure, high-temperature (HPHT) diamond and a polystyrene film doped with BDPA radical yielded < 9 ns π/2 pulses at ca. 50 W specified EIK output at the corresponding resonance frequencies and the PBG resonator quality factor of Q≈300. DNP experiments carried out in a “gated” mode by supplying 20 μs mm-wave pulses every 1 ms yielded 13C solid-effect DNP with gains up to 20 for the polystyrene-BDPA sample at natural 13C abundance. For a single-crystal HPHT diamond, the gated DNP mode yielded almost the same 13C enhancement as a low-power continuous wave (CW) mode at 0.4 W, whereas no DNP effect was observed for the BDPA/polystyrene sample in the latter case. To illustrate the versatility of our upgraded DNP spectrometer, room-temperature Overhauser DNP enhancements of 7–14 for 31P NMR signal were demonstrated using a liquid droplet of 1 M tri-phenyl phosphine co-dissolved with 100 mM of BDPA in toluene‑d8.

On the peculiar EPR spectra of P1 centers at high (12-20 T) magnetic fields.

The most common lattice defect in high-pressure high-temperature (HPHT) diamonds is the nitrogen substitution (P1) center. This is a paramagnetic defect with a single unpaired electron spin coupled to a 14N nuclear spin forming an S = 1/2, I = 1 spin system. While P1 centers have been studied by electron paramagnetic resonance (EPR) spectroscopy for decades, only recently did their behavior at ultra-high (>12 T) magnetic fields become of interest. This is because P1 centers were recently found to be very efficient polarizing agents in dynamic nuclear polarization (DNP) experiments, which are typically carried out at high magnetic fields. The P1 ultra-high field EPR spectra show multiple peaks which the lower fields spectra do not. In this paper, we present an account of the EPR spectra of P1 centers at ultra-high fields and show that the more complex spectra at 12-20 T are the result of significant state mixing in the mS = +1/2 electron spin manifold. The state mixing is a result of fulfilling the cancellation condition, meaning the e-14N hyperfine interaction equals twice the Larmor frequency of the 14N nuclear spin. We illustrate the influence of the cancellation condition on the EPR spectra by comparing EPR spectra acquired at 6.9 and 13.8 T. While the former are similar to the consensus spectra observed at lower fields, the latter are very different. We present numerical simulations that quantitatively account for the experimental spectra at both 6.9 and 13.8 T. Finally, we use electron electron double resonance (ELDOR) measurements to show that the cancellation condition results in increased spectral diffusion in the 13.8 T spectrum. This work sheds light on the spin properties of P1 centers under DNP-characteristic conditions, which will be conducive to their efficient utilization in DNP.

Comparative of HPHT and CVD diamond: performance and defect analysis for alpha radiation detector

Currently, the high-purity single crystal diamond preparation is still a challenging task, which restricts the application of diamond in electronics. In this paper, the chemical vapor deposition (CVD) IIa type single crystal diamond was prepared on the IIa type high pressure high temperature (HPHT) substrate by combining the chamber design with the plasma purifying technology, and the performance of diamond detectors using both IIa type single crystal diamonds were compared based on the defect analysis. The dislocations in diamonds were directly observed by synchrotron radiation X-ray white-beam topography. The CVD diamond shows the comparatively low dislocation density resulting from the high-quality HPHT diamond substrate. No observable NV impurity could be found in photoluminescence (PL) spectrum. The trace impurity of substitutional nitrogen (Ns) was characterized by electron paramagnetic resonance (EPR). It shows the very low concentration in the CVD diamond (2.1 ppb) compared with the several tens ppb in HPHT diamond. This value is comparable with the electronic-grade diamond reported by Element Six. Furthermore, both of the HPHT and CVD single crystal diamonds were packaged as the α-particle radiation detectors with the typical sandwich structure and used Ni/Al (50 nm/500 nm) as metal electrodes. The energy resolution of HPHT and CVD diamond detectors were 2.04% and 0.86%, respectively. Based on Schottky contact and defect regulation, at 0 voltage, the CVD diamond detector achieved response of α-particle radiation and the charge collection efficiency (CCE) was 10.76%. Under positive voltage, the CCE of HPHT and CVD diamond detectors were 38.11% and 86.65%, respectively. The deep level trapping effect of Ns impurities on charge carriers resulted in low CCE of HPHT diamond detector. The spatial polarization effect caused by defects leaded to the formation of an internal electric field, which was the main reason affecting the transport of charge carriers in CVD diamond.

Basic characteristics of synthetic-diamond scintillator

To extend the use of diamond detectors to particle detail analysis and the development of radiation monitoring applications, we conducted a study on synthetic-diamond scintillators, which have so far not been sufficiently evaluated. To understand the basic characteristics of scintillators, we measured the luminescence characteristics of two types of commercially available synthetic diamonds manufactured via high-pressure high-temperature (HPHT) and chemical vapor deposition (CVD) methods. The color center of each diamond was identified by measuring the radio-luminescence spectrum under X-ray excitation, and the scintillation light waveform was measured by irradiating α-rays and β-rays. The light yield of the HPHT diamond with a nitrogen concentration less than 200 ppm had a higher emission than that of the CVD diamond with a nitrogen concentration of less than 1 ppm; the light yield for the former was estimated to be (5.5 ± 0.5) × 104 ph/MeV. Because of the significant light yield and physical properties of diamonds, unique particle detectors can be achieved.

New surface features on high-pressure high-temperature diamond octahedrons observed by confocal laser scanning microscope

New surface features on high-pressure high-temperature diamond octahedrons observed by confocal laser scanning microscope

Improving the Performance of HPHT-Diamond Detectors for Pulsed X-Ray Dosimetry Using the Synchronous Detection Technique

A single-crystal diamond sample grown by high-pressure high-temperature (HPHT) technique was used for the fabrication of a metal–semiconductor–metal (MSM) photoconductor. The sample quality was evaluated by means of spectral photocurrent measurements highlighting the presence of a significant density of defect states within the diamond bandgap, responsible for trap-mediated conduction mechanisms. The photoconductor was fully characterized under 6 MeV pulsed X-rays, sourced by a medical linear accelerator (LINAC), in the 0.05–20 Gy and 0.017–0.100 Gy/s dose (D) and dose-rate (DR) ranges, respectively. Photocurrent measurements performed with a conventional precision electrometer showed that the detector performance is strongly affected by charge-trapping phenomena, resulting in a sublinear dependence with the DR (power-law dependence with an exponent of 0.86). Measurements were repeated in the same experimental conditions by coupling the detector to a specifically developed gated integrator, allowing for a synchronous integration of photocurrent pulses (limited to 40 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <inline-formula> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> </i> s) centered on each impinging X-ray pulse. In this case, the detector photoresponse showed an excellent linearity with both the D and the DR (power-law dependence with 1.0009 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 0.0004 and 1.009 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 0.005 exponents, respectively). Significantly, the proposed synchronous integration technique is then able to mitigate the detrimental effect that defects have on detector performance. The proposed method paves, therefore, the way to the exploitation of HPHT diamond as a low-cost alternative to single-crystal chemical vapor deposition (CVD)-diamond for the fabrication of accurate and linear X-ray dosimeters.

Fluorescent HPHT nanodiamonds have disk- and rod-like shapes

Fluorescent nanodiamonds (FNDs) containing nitrogen-vacancy (NV) centers can be used as nanoscale sensors for temperature and electromagnetic fields and find increasing application in many areas of science and technology from biology to quantum metrology. Decreasing the separation between the NV centers and their sensing target often enhances the measurement sensitivity. FND shape strongly affects this distance from NV centers to the particle surface and therefore properties such as brightness and fluorescence spectrum, and can limit sensor applications. Here, we demonstrate that FNDs made from high-pressure high-temperature (HPHT) diamond have predominantly disk-like shapes. Using single-particle atomic force microscopy in combination with ensemble X-ray and light scattering techniques, we show that a typical FND in the 50–150 nm size range has an aspect ratio of three i.e. is three times thinner (e.g. in z) than it is wide (e.g. in the x-y plane). This high aspect ratio of FNDs is important for many quantum sensing measurements as it will enable enhanced sensitivities compared to spherical or other isotropic particle geometries. We investigate FND shape, fluorescence properties, T1 spin relaxation time and T1 fluorescence contrast as functions of particle size and discuss the implications of FND particle shape on quantum sensing applications.

Morphological and Surface Microtopographic Features of HPHT-Grown Diamond Crystals with Contact Twinning

Gem-grade twinned high-pressure high-temperature (HPHT) synthetic diamond crystals are rare. Hence, few investigations on their morphological features and formation have been reported. In this article, the morphological and surface microtopographic features of HPHT synthetic-diamond crystals contact twinning is detailed and investigated. It indicates that twins of diamond forming and nucleating during the early stages of the growth and the development of {100} and {111} growth sectors on either side of such boundaries proceeds independently, which affects the final morphology of the diamond crystals. According to the different features of crystal macroscopic morphological properties, two kinds of twin model have been established. The formation of twin crystals changed the lattice of diamonds with face-centered cubic dimensions. The type of diamond lattice at the twin boundary is hexagonal and closely packed, which has potential for further developing the application of synthetic diamond twin crystals.

Complete analysis of dislocations in single crystal diamonds

In this study, we applied dislocation analysis to X-ray topography images to identify the complete dislocation information for two typical high-pressure high-temperature diamond crystals, IIa and Ib. Almost all dislocation line vectors of both crystals were identified for the first time. For IIa crystal, it was confirmed that up to 84% of the dislocations have 〈101〉 vectors. For Ib crystal, up to 71% of the dislocations have 〈112〉, 〈121〉, and 〈211〉 vectors. Both [110] and [1-10] with zero components of the c-axis are the major Burgers vectors. Regarding the types of dislocation, the major types were edge types, which were approximately 47% and 65% for IIa and Ib crystals, respectively. In addition, screw, 60° and 73° type on the IIa, and 30°, 35°, and 73° type on Ib were identified. Complete analysis of dislocations will give important information for the diamond growth and reduction of the dislocations.

Superluminescence in the phonon wing of the photoluminescence spectrum of NV centres in diamond optically pumped at λ = 532 nm

Superluminescence of NV centres with a band peaking at λ = 718 nm in the phonon wing of the photoluminescence spectrum of a high-pressure high-temperature (HPHT) diamond sample under pulsed optical excitation at λ = 532 nm with an intensity of 2 – 46 MW cm−2 is demonstrated. Superluminescence is observed in the diamond crystal region containing 6 ppm NV centres and 150 ppm substituent nitrogen; it is absent in the crystal part with a lower nitrogen content. Superluminescence pulses are observed on the leading edge of the optical excitation pulse at λ = 532 nm and have an FWHM value of 4 ns. The enhancement of the photoluminescence of NV centres is suggested to be due to the total internal reflection in the diamond plate (waveguide effect).

Digital micro-photogrammetry in analysis and modeling habit and sectoral structure of real high-pressure high-temperature single-crystal diamonds.

We demonstrate the potential of using digital stereo micro-photogrammetry for the analysis and modeling of the habit and sectoral structure of real high-pressure high-temperature single-crystal diamonds. A prototype scanning system with a resolution of 5μm has been implemented based on a digital single-lens reflex camera, making it possible to create highly accurate reproductions of crystal shapes with a minimum size of 4mm. This method makes it possible to monitor the effect of actual conditions on the physical processes of crystal growth, which is a useful advance for the development of active device elements based on semiconductor diamonds.

Characterization of the nitrogen state in HPHT diamonds grown in an Fe–C melt with a low sulfur addition

This paper reports the results of high-pressure high-temperature (HPHT) diamonds growing in an Fe–C melt with introduction of 1 wt% sulfur.

Raman Scattering Enhancement Based on High-Pressure High-Temperature Diamonds†

Raman Scattering Enhancement Based on High-Pressure High-Temperature Diamonds†

Magneto-optical spectra of the split nickel-vacancy defect in diamond

Nickel is a common impurity in high-pressure high-temperature diamond and may contaminate chemical vapor deposited diamond used for high-power electronics or quantum technology applications. Magneto-optical fingerprints of nickel have been known since decades, however, no consensus has been reached about the microscopic origins of nickel-related electron paramagnetic resonance, photoluminescence, and optically detected magnetic resonance spectra. The unknown nickel-related defect structures in diamond make it difficult to control them or harness them for a given application. As a consequence, nickel is considered as an impurity in diamond that should be avoided or its concentration should be minimized. Recent advances in the development of ab initio magneto-optical spectroscopy have significantly increased its accuracy and predictive power that can be employed for identification and in-depth characterization of paramagnetic color centers in diamond. In this study, we extend the accuracy of the ab initio magneto-optical spectroscopy tools towards self-consistent calculation of second-order spin-orbit coupling for paramagnetic color centers in solids. We apply the full arsenal of the ab initio magneto-optical spectroscopy tools to characterize the split nickel-vacancy defect in diamond which is one of the most stable nickel-related defect configurations. As a result, electron paramagnetic resonance and optical centers are positively identified in various charge states of the nickel-vacancy defect in diamond. In particular, the 1.40-eV optical center and the NIRIM-2 electron paramagnetic resonance center are identified as the single negative charge state of the split nickel-vacancy center. The defect possesses $S=\frac{1}{2}$ spin state with an orbital doublet ground state. We find that the coherence time of the ground-state spin is about 0.1 ms at cryogenic temperatures which can be optically initialized and readout by a $\mathrm{\ensuremath{\Lambda}}$-scheme protocol. Since the defect has inversion symmetry the optical signal is insensitive to the stray electric fields, which is an advantage for creating indistinguishable solid-state single-photon sources. We predict that the negatively charged nickel-vacancy defect has similar optical properties to those of the well-known silicon-vacancy defect in diamond but is superior in terms of electron spin coherence times. Our study resolves a few decades controversy about the nickel-related spectroscopy centers in diamond and turns nickel from an impurity to a resource in quantum technology applications.

Surface Morphology and Microstructure Evolution of Single Crystal Diamond during Different Homoepitaxial Growth Stages.

Homoepitaxial growth of step-flow single crystal diamond was performed by microwave plasma chemical vapor deposition system on high-pressure high-temperature diamond substrate. A coarse surface morphology with isolated particles was firstly deposited on diamond substrate as an interlayer under hillock growth model. Then, the growth model was changed to step-flow growth model for growing step-flow single crystal diamond layer on this hillock interlayer. Furthermore, the surface morphology evolution, cross-section and surface microstructure, and crystal quality of grown diamond were evaluated by scanning electron microscopy, high-resolution transmission electron microcopy, and Raman and photoluminescence spectroscopy. It was found that the surface morphology varied with deposition time under step-flow growth parameters. The cross-section topography exhibited obvious inhomogeneity in crystal structure. Additionally, the diamond growth mechanism from the microscopic point of view was revealed to illustrate the morphological and structural evolution.

Forbidden X-ray diffraction of highly B doped diamond substrate

The (222) forbidden diffraction of a highly B doped high-pressure high-temperature (HPHT) diamond crystal was investigated by precise mapping using synchrotron radiation X-ray diffraction. The intensity ratios of (222) to (111) were high, ranging from 20% to 36% for the high-density dislocation areas with stacking faults (SFs), whereas the intensity ratios for the low-density dislocation areas ranged from 11% to 20%. For the high-density dislocation areas, the intensity distribution was very high in the upper region, which might correspond to the dislocation density along the X-ray path. In contrast, the intensity ratio of high-quality undoped HPHT crystals ranged from 3.0% to 4.3%, which might be due to multiple reflections of the high-quality crystal. The substrate quality can be conveniently investigated prior to device fabrication by examining the intensity of the forbidden diffraction using laboratory X-ray diffraction equipment.