High-temperature Diamond Research Articles

Photodynamics and quantum efficiency of germanium vacancy color centers in diamond

Color centers in diamond—especially group IV defects—have been advanced as a viable solid-state platform for quantum photonics and information technologies. We investigate the photodynamics and characteristics of germanium-vacancy (GeV) centers hosted in high-pressure high-temperature diamond nanocrystals. Through back-focal plane imaging, we analyze the far-field radiation pattern of the investigated emitters and derive a crossed-dipole emission, which is strongly aligned along one axis. We use this information in combination with lifetime measurements to extract the decay rate statistics of the GeV emitters and determine their quantum efficiency, which we estimated to be ∼ ( 22 ± 2 ) % . Our results offer further insight into the photodynamic properties of the GeV center in nanodiamonds and confirm its suitability as a desirable system for quantum technologies.

Homoepitaxy Growth of Single Crystal Diamond under 300 torr Pressure in the MPCVD System.

The high-quality single crystal diamond (SCD) grown in the Microwave Plasma Chemical Vapor Deposition (MPCVD) system was studied. The CVD deposition reaction occurred in a 300 torr high pressure environment on a (100) plane High Pressure High Temperature (HPHT) diamond type II a substrate. The relationships among the chamber pressure, substrate surface temperature, and system microwave power were investigated. The surface morphology evolution with a series of different concentrations of the gas mixture was observed. It was found that a single lateral crystal growth occurred on the substrate edge and a systemic step flow rotation from the [100] to the [110] orientation was exhibited on the surface. The Raman spectroscopy and High Resolution X-Ray Diffractometry (HRXRD) prove that the homoepitaxy part from the original HPHT substrate shows a higher quality than the lateral growth region. A crystal lattice visual structural analysis was applied to describe the step flow rotation that originated from the temperature driven concentration difference of the C2H2 ion charged particles on the SCD center and edge.

Formation of two crystal modifications of Fe7C3−x at 5.5 GPa

The Fe–C system, which is widely used to grow commercial high-pressure–high-temperature diamond monocrystals, is rather complicated due to the formation of carbides. The carbide Fe3C is a normal run product, but the pressure at which Fe7C3 carbide becomes stable is a subject of discussion. This paper demonstrates the synthesis of Fe7C3 carbide and its detailed study using single-crystal and powder X-ray diffraction, as well as electron probe micro-analysis and scanning electron microscopy. The experiments were performed using a multiple-anvil high-pressure apparatus of `split-sphere' (BARS) type at a pressure of 5.5 GPa and a temperature of 1623 K. Our results show that in the Fe–C system, in addition to diamond, a phase that corresponds to the Fe7C3 carbide was synthesized. This means that both carbides (Fe7C3 and Fe3C) are stable at 5.5 GPa. Two crystal phases are described, Fe14C6 and Fe28C12−x . Fe14C6 is based on the well known rhombic structure of Fe7C3, while Fe28C12−x has a different packing order of Fe6C polyhedrons. The results obtained in this study should be taken into account when synthesizing and growing diamond at high pressures and temperatures in metal–carbon systems with a high iron content, as well as when conducting experimental studies on the synthesis of diamond directly from carbide.

Development of a Stable High-Temperature Diamond Thermistor Using Enhanced Supporting Designs

Diamond is an excellent material for a high-temperature thermistor given its superior material properties. Despite its long history of the development, diamond thermistor is not widely used for commercial sensors because it is difficult to maintain optimum conditions for the diamond thermistor to operate at high temperature ranges in a compact size. In this paper, we demonstrate methods to improve the practicality and the feasibility of the diamond thermistor, focusing on the supporting components. The diamond thermistor design, where the diamond is sandwiched between contact pads, is tested up to 700 °C and being characterized by the Steinhart–Hart equations. For temperatures higher than 700 °C, the design of the thermistor is improved by encasing it in a metal sheath tube that protects and seals the diamond thermistor. Our supporting components provide oxygen free environment and a sturdy structure for the sensor components in a compact size. The encased diamond thermistor operates up to 880 °C and shows stable performance in a cycling test between 880 °C and the room temperature. An additional long-term stability test is performed at various temperatures for 10-hour durations. The tests show that the metal sheath tube design enables the diamond thermistor to be used as a practical temperature sensor at high-temperature ranges.

Gemologic and Spectroscopy Properties of Chinese High-Pressure High-Temperature Synthetic Diamond

Compared with the chemical vapor deposition method, the high-pressure and high-temperature (HPHT) method has some advantages, such as fast diamond crystal growth speed, mature technology and easy mass production. HPHT method synthetic diamond is widely used industrially, but gem-quality synthetic diamond from China has rarely been reported. In this work, the gem-quality diamond synthesized by State Key Laboratory of Superhard Materials, Jilin University, China (SKLSHM), using the cubic hinge press equipment by the HPHT method, was investigated by microscopy, field-emission scanning electron microscopy (FE-SEM) and Diamond View observations as well as infrared spectrometer, ultraviolet–visible spectrometer (UV spectrometer) and energy-dispersive x-ray fluorescence tests. FE-SEM observation showed that regular growth steps and obvious growth pits were common on the {100} surface, and they were consistent with the distribution of internal metal inclusions. In most cases, the {111} plane is significantly flatter than the {100} plane, which may be related to the surface atomic state. It also can be seen that the internal metal inclusions are easily aligned along the internal growth boundary,which may be due to the different growth rates of different crystal faces during diamond growth. The fluorescent image under Diamond View shows the special geometric growth zone structure. Cubes, octahedrons and rhombohedral dodecahedrons have different intensities of orange, yellow, blue and other uneven fluorescences, which can be used as the most important diagnostic evidence.

Evaluation of growth sector orientation changes of high B doped high pressure and high temperature diamond by high resolution electron backscatter diffraction study

The orientation of growth sectors of highly B doped p+ high pressure and high temperature (HPHT) substrates were investigated by high angular resolution electron backscatter diffraction (HR-EBSD). The lattice rotation mapping images of the areas across the 〈111〉 growth sector boundaries were measured. The crystal orientation was found to be inclined approximately 0.03° for [001] to [-1-10], compared with the [-1-11] growth sector area at a given location. Other orientation inclinations were observed such as 0.02° for [001] to [110] and 0.025° for [001] to [1-10]. The same phenomena were confirmed for the other two crystals. Conventionally, it has been recognized that a HPHT-grown crystal is a perfect single crystal, however, our results indicate that “twin boundaries” are formed between the growth sectors for p+ HPHT substrates. To meet the requirements for the power device wafer specifications, the establishment of growth technology is desirable in the near future.

Automated FTIR mapping of boron distribution in diamond

Type IIb diamonds are those that contain more boron than nitrogen. The presence of this uncompensated boron gives rise to absorption in the infrared part of the electromagnetic spectrum, extending into the visible region and often resulting in blue colouration. Here we report on the expansion of the DiaMap freeware (for the automated spectral deconvolution of Type I [nitrogen containing] diamonds) to work on Type IIb diamonds, returning concentrations from three boron-related absorption bands, and determining which band provides the most reliable value. The program uses the calibration coefficients of Collins (2010), which show good relative agreement between the three bands, but might require some further study to confirm their absolute accuracy to the uncompensated boron concentration. The methodology of DiaMap_IIb is applicable to all Type IIb diamonds, both natural and synthetic. Analysis of high-resolution Fourier-transform infrared (FTIR) maps of two high-pressure high-temperature (HPHT) synthetic diamonds using DiaMap_IIb, confirm the growth sector dependence of the boron incorporation. Partitioning of boron strongly favours the octahedral {111} sectors.

Magnetic resonance study of lightly boron-doped diamond

We report on 11B and 13C NMR nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) study of a lightly boron-doped microdiamond. 11B NMR shows two components assigned to boron atoms substituting carbon and those located within the conducting regions, respectively. The latter component demonstrates exceptionally short spin-lattice relaxation time (T1 = 2.4 ms) characteristic of conductive compounds. The total content of localized paramagnetic defects is 24 ppm, among them 12 ppm are due to substitutional nitrogen defects (P1). The P1 content is found to be much smaller than that usually observed in conventional high pressure—high temperature (HPHT) diamonds.

Boron–oxygen complex yields n-type surface layer in semiconducting diamond

Diamond is a wide-bandgap semiconductor possessing exceptional physical and chemical properties with the potential to miniaturize high-power electronics. Whereas boron-doped diamond (BDD) is a well-known p-type semiconductor, fabrication of practical diamond-based electronic devices awaits development of an effective n-type dopant with satisfactory electrical properties. Here we report the synthesis of n-type diamond, containing boron (B) and oxygen (O) complex defects. We obtain high carrier concentration (∼0.778 × 1021 cm-3) several orders of magnitude greater than previously obtained with sulfur or phosphorous, accompanied by high electrical conductivity. In high-pressure high-temperature (HPHT) boron-doped diamond single crystal we formed a boron-rich layer ∼1-1.5 μm thick in the {111} surface containing up to 1.4 atomic % B. We show that under certain HPHT conditions the boron dopants combine with oxygen defects to form B-O complexes that can be tuned by controlling the experimental parameters for diamond crystallization, thus giving rise to n-type conduction. First-principles calculations indicate that B3O and B4O complexes with low formation energies exhibit shallow donor levels, elucidating the mechanism of the n-type semiconducting behavior.

Dynamics of infrared excitations in boron doped diamond

We report on the investigation of relaxation dynamics of optical excitations in IIb high pressure high temperature (HPHT) diamond doped by natural boron and isotopically enriched 11boron. The measurements were performed with a pump-probe technique using short pump pulses from a wavelength-tunable infrared free electron laser. Lifetimes of excited boron states ranging from a few picoseconds to a few hundred picoseconds, have been derived from the obtained data. The relaxation rates depend on the pumped states, the pump intensity and the diamond lattice temperature. We discuss possible contributions to the optical and nonradiative intracenter relaxation rates observed in these experiments. Theoretical simulations support ultrafast relaxation by multiple phonon emission, for the electronic states with the energy gap exceeding the energy of optical phonon.

Development of a high temperature diamond anvil cell for x ray absorption experiments under extreme conditions

X-ray absorption spectroscopy (XAS) is presently a powerful and established tool to investigate solid and liquid matter at high pressure and high temperature (HP-HT). HP-HT XAS experiments rely on high pressure technology whose continuous development has extended the achievable range up to 100 GPa and more. In high pressure devices, high temperature conditions are typically obtained by using internal and external resistive heaters or by laser heating. We have recently developed a novel design for an internally heated diamond anvil cell (DAC) allowing XAS measurements under controlled high temperature conditions (tested up to about 1300 K). The sample in the new device can be rapidly heated or cooled (seconds or less) so the cell is suitable for studying melting/crystallization dynamics when coupled with a time-resolved XAS setup (second and sub-second ranges). Here we describe the internally heated DAC device which has been realized and tested in experiments on pure selenium at the energy dispersive ODE beamline of Synchrotron SOLEIL. We also present results obtained in XAS experiments of elemental Se using a large volume Paris-Edinburgh press, as an example of the relevance of structural studies of matter under extreme conditions.

Increased nitrogen-vacancy centre creation yield in diamond through electron beam irradiation at high temperature

The nitrogen-vacancy (NV) centre is a fluorescent defect in diamond that is of critical importance for applications from ensemble sensing to biolabelling. Hence, understanding and optimising the creation of NV centres in diamond is vital for technological progress in these areas. We demonstrate that simultaneous electron irradiation and annealing of a high-pressure high-temperature diamond sample increases the NV centre creation efficiency from substitutional nitrogen defects by up to 117% with respect to a sample where the processes are carried out consecutively, but using the same process parameters. This increase in fluorescence is supported by visible and infrared absorption spectroscopy experiments. Our results pave the way for a more efficient creation of NV centres in diamond as well as higher overall NV densities in the future.

Luminescent diamond window of the sandwich type for X-ray visualization

A two-layered diamond plate is proposed as a transparent X-ray window visualizer. The plate consists of a thick substrate of a synthetic single-crystal high-pressure high-temperature (HPHT) diamond on which a thin $${\sim }10\, {\mu }m$$ optically active layer of chemical vapor deposition (CVD) diamond doped with silicon and nitrogen, and is epitaxially grown. The photoluminescent properties of the diamond sandwich plate were studied under the influence of X-ray radiation before and after treatment of the plate with high-energy electrons and its thermal annealing. It was established that broadband luminescence with a maximum near 500 nm, associated with defects of the HPHT diamond substrate, dominates before electron treatment. The electron irradiation and subsequent annealing of the plate completely suppressed the broadband luminescence and significantly (by more than two orders of magnitude) increased emission intensity of nitrogen-vacancy centers (NV) in the CVD diamond layer. As a result, the luminescence of neutrally charged NV centers with a zero-phonon line at 575 nm became dominant. No luminescence of the silicon-vacancy (SiV) centers in the CVD diamond film was detected. The first results demonstrating the two-layered diamond plate as an X-ray visualizer are presented.

Multi-resonant photonic band-gap/saddle coil DNP probehead for static solid state NMR of microliter volume samples.

The most critical condition for performing Dynamic Nuclear Polarization (DNP) NMR experiments is achieving sufficiently high electronic B1e fields over the sample at the matched EPR frequencies, which for modern high-resolution NMR instruments fall into the millimeter wave (mmW) range. Typically, mmWs are generated by powerful gyrotrons and/or extended interaction klystrons (EIKs) sources and then focused onto the sample by dielectric lenses. However, further development of DNP methods including new DNP pulse sequences may require B1e fields higher than one could achieve with the current mmW technology. In order to address the challenge of significantly enhancing the mmW field at the sample, we have constructed and tested one-dimensional photonic band-gap (PBG) mmW resonator that was incorporated inside a double-tuned radiofrequency (rf) NMR saddle coil. The photonic crystal is formed by stacking ceramic discs with alternating high and low dielectric constants and thicknesses of λ/4 or 3λ/4, where λ is the wavelength of the incident mmW field in the corresponding dielectric material. When the mmW frequency is within the band gap of the photonic crystal, a defect created in the middle of the crystal confines the mmW energy, thus forming a resonant structure. An aluminum mirror in the middle of the defect has been used to substitute one-half of the structure with its mirror image in order to reduce the resonator size and simplify its tuning. The latter is achieved by adjusting the width of the defect by moving the aluminum mirror with respect to the dielectric stack using a gear mechanism. The 1D PBG resonator was the key element for constructing a multi-resonant integrated DNP/NMR probehead operating at 190-199 GHz EPR/300 MHz 1H/75.5 MHz 13C NMR frequencies. Initial tests of the multi-resonant DNP/NMR probehead were carried out using a quasioptical mmW bridge and a Bruker Biospin Avance II spectrometer equipped with a standard Bruker 7 T wide-bore 89 mm magnet parked at 300.13 MHz 1H NMR frequency. The mmW bridge built with all solid-state active components allows for the frequency tuning between ca. 190 and ca. 199 GHz with the output power up to 27 dBm (0.5 W) at 192 GHz and up to 23 dBm (0.2 W) at 197.5 GHz. Room temperature DNP experiments with a synthetic single crystal high-pressure high-temperature (HPHT) diamond (0.3 × 0.3 × 3.0 mm3) demonstrated dramatic 1500-fold enhancement of 13C natural abundance NMR signal at full incident mmW power. Significant 13C DNP enhancement (of about 90) have been obtained at incident mmW powers of as low as <100 μW. Further tests of the resonator performance have been carried out with a thin (ca. 100 μm thickness) composite polystyrene-microdiamond film by controlling the average mmW power at the optimal DNP conditions via a gated mode of operation. From these experiments, the PBG resonator with loaded Q ≃ 250 and finesse F≈75 provides up to 12-fold or 11 db gain in the average mmW power vs. the non-resonant probehead configuration employing only a reflective mirror.

Study of the Structural and Morphological Properties of HPHT Diamond Substrates

The morphological and structural properties of a series of high-pressure high-temperature (HPHT) single-crystal diamond substrates are comprehensively studied by white-light optical interference microscopy, atomic-force microscopy, and X-ray diffraction analysis. Procedures that provide a means for characterizing the substrate parameters most critical for epitaxial application with the laboratory equipment are described. It is shown that the jewelry-type characterization of diamond substrates is insufficient to assess the possibility of their use for the epitaxial growth of chemical-vapor-deposited (CVD) diamond.

A theoretical study of substitutional boron–nitrogen clusters in diamond

Substitutional clusters of multiple light element dopants are a promising route to the elusive shallow donor in diamond. To understand the behaviour of co-dopants, this report presents an extensive first principles study of possible clusters of boron and nitrogen. We use periodic hybrid density functional calculations to predict the geometry, stability and electronic excitation energies of a range of clusters containing up to five N and/or B atoms. Excitation energies from hybrid calculations are compared to those from the empirical marker method, and are in good agreement.When a boron-rich or nitrogen-rich cluster consists of three to five atoms, the minority dopant element—a nitrogen or boron atom respectively—can be in either a central or peripheral position. We find B-rich clusters are most stable when N sits centrally, whereas N-rich clusters are most stable with B in a peripheral position. In the former case, excitation energies mimic those of the single boron acceptor, while the latter produce deep levels in the band-gap. Implications for probable clusters that would arise in high-pressure high-temperature co-doped diamond and their properties are discussed.

The effects of deposition parameters on the grain morphology and wear mechanism of monolayer diamond grinding tools fabricated by hot filament CVD method

The hot filament chemical vapor deposition technique (HFCVD) is used to fabricate monolayer grinding tools with high quality diamond abrasive grains. The high pressure and high temperature (HPHT) diamond seeds are distributed on SiC substrate randomly by a spin coater machine. Then epitaxial growth of CVD diamonds is conducted on both seeds and substrate simultaneously. The heteroepitaxial diamond film on substrate serves as a bonding layer to anchor the seeds, and the homoepitaxial growth of the seeds leads to changes in their morphology, purity, as well as mechanical properties. The grown seeds can be used as abrasive grains of the grinding tools. In this work, a systematic study is presented into the effects of deposition parameters (substrate temperature, carbon concentration, reactive pressure, bias current) on the growth behavior of diamond seeds. As a result, it is found that the well-faceted single crystal diamond (SCD) grains can be grown at 800 °C, 4.5 KPa, carbon concentration of 1.5% and bias current of 2 A. Besides, the increase of temperature and decrease of pressure allow the changes from SCD grains to microcrystalline diamond (MCD) clusters or further, to nanocrystalline diamond (NCD) clusters, while the high bias current and carbon concentration promote the growth of dislocated planes and secondary nucleation. Moreover, it is found that the protrusion of the diamond abrasives can be controlled by the difference in growth rates between seeds and diamond bonding films under various conditions. Finally, the wear resistance of diamond grains is tested. Results show that the wear of SCD grains is dominated by a high rate of wear flat and few fractures, and the wear of MCD grains exhibits less wear flat but more fractures, while the NCD grains exhibit the worst wear resistance in terms of both fracture and wear flat.

Surface conductivity enhancement of H-terminated diamond based on the purified epitaxial diamond layer

Diamond-based semiconductor with high electrical conductivity is a key point in diamond device development. In this paper, a thin single crystal diamond layer of high quality was epitaxially grown on a commercial tool-grade diamond seed by incorporating active O atoms from the typical growth environment. Subsequently, the H-termination density was enhanced on the diamond surface by exposure to the pure hydrogen plasma, and the surface conductivity of H-terminated diamond was analyzed in detail. The thin epitaxial layers on the high-pressure high-temperature diamond seeds show lower resistance than the ones on the chemical vapor deposition diamond seeds, which could be comparable with the lowest values reported. After the thin diamond layers were grown with and without addition of O2, the carrier mobility in the conductive channel increased to almost 80 cm2 V−1 s−1 under O2 contained condition, much higher than those without O2 incorporation. The ionization scattering is dominant to the carrier mobility compared with the surface scattering. The higher carrier mobility is attributed to the lower impurity density in the epitaxial layer, which is because the active O atoms could purify the epitaxial layer by removing or reducing Si- and N-related impurities.

Highly stable and regenerative graphene–diamond hybrid electrochemical biosensor for fouling target dopamine detection

Graphene is widely recognized as a promising nanomaterial for the construction of high-performance electrochemical biosensors. However, the lack of strong interfacial forces between graphene and conductive substrates is a bottleneck in the fabrication of highly stable graphene electrodes. In this work, few-layer graphene was directly formed on a high pressure high temperature (HPHT) diamond substrate via sp3-to-sp2 conversion by catalytic thermal treatment and using diamond itself as the carbon source. The hybrid electrode prototype was also highly conductive and had a linear electrochemical response to dopamine in the concentration range of 5 μM – 2 mM, with a low detection limit of 200 nM. After prolonged and repeated exposure to dopamine, electrode fouling was observed which led to sensitivity degradation. Based on the strong interfacial bonding between graphene and HPHT diamond, regeneration of the fouled electrode and full performance recovery would be easily achieved by ultrasonic cleaning. The hybrid electrode is highly robust, and shows potential in its application to the detection of biofouling molecules, food processing and wastewater treatment.

Исследование структурных и морфологических свойств HPHT алмазных подложек

AbstractThe morphological and structural properties of a series of high-pressure high-temperature (HPHT) single-crystal diamond substrates are comprehensively studied by white-light optical interference microscopy, atomic-force microscopy, and X-ray diffraction analysis. Procedures that provide a means for characterizing the substrate parameters most critical for epitaxial application with the laboratory equipment are described. It is shown that the jewelry-type characterization of diamond substrates is insufficient to assess the possibility of their use for the epitaxial growth of chemical-vapor-deposited (CVD) diamond.