Platelets In Diamond Research Articles

Making Use of Low‐Cost High‐Pressure–High‐Temperature‐Diamond Materials for Industry‐Type Quantum Sensor Device Applications

A cost‐effective approach to provide diamond platelets containing nitrogen vacancy center ensembles (NVs) in the range of ppm is investigated. Industry‐type high‐pressure–high‐temperature‐diamond type 1b containing a high number of interstitial nitrogen in the range of several tens of ppm are used and small diamond platelets (size ≈1 × 1 mm2, thickness ≈300 μm) are prepared by laser cutting and polishing. The nitrogen is converted into NV by means of high‐energy electron irradiation of 10 MeV and annealing at 900 °C. Variations in the irradiation dose between 0.5E18 1/cm2 and 2E18 1/cm2 result in different densities of NV. The diamond platelets are analyzed with regard to their nitrogen concentration and photoluminescence as well as optically detected magnetic resonance is used to investigate the usability for a NV‐based magnetometer. A method to calculate the ratio of negatively to neutrally charged NV (NV−/NV0) is proposed that uses the photoluminescence intensities of the spectrum at 575 and 638 nm, namely, the zero‐phonon lines of NV− and NV0.

CO2 reduction by visible-light-induced photoemission from heavily N-doped diamond nano-layer

While realizing carbon neutrality is an urgent priority, diamond materials with negative electron affinity (NEA) are considered productive sources of solvated electrons, which can help efficiently reduce CO2 in potential green chemistry applications. Recently, CO2 was photocatalytically reduced into CO by solvated electrons using commonly used H-terminated diamond with NEA under deep ultraviolet light irradiation. However, CO2 has never been reduced under visible-light irradiation, would be more practicable in the living environment, because of the wide band gap afforded by diamonds. In this study, electrons excited by visible light in heavily N-doped surface nano-layer of diamond platelets are emitted through the H-terminated surface with NEA toward a CO2-saturated aqueous solution, successfully reducing CO2 into CO. To this end, the B-doped p-type diamond films are grown by chemical vapor deposition on initial seed layers of detonation-synthesized nanodiamonds (DNDs). This approach allows incorporating the abundantly available N atoms in the DNDs into the surface nano-layer on the diamond platelets, resulting in the formation of an electron-excitation nano-layer having ≥1021 N atoms/cm3 and associated defects absorbing visible light. These results pave the way toward a new, energy-efficient technology for CO2 reduction with strong implications for achieving a carbon-negative society.

Novel configurations of VN4 and VN4H defects in diamond platelets: Structure, energetics and vibrational properties

Atomic structure and lattice dynamics properties of the novel configurations of VN4 and VN4H defects in combination with the {001} platelet structure in diamond are investigated by first-principles density functional techniques. We find that incorporation of B centers (VN4) in the platelet structure substantially reduce the formation energy of B centers by ~0.45 eV for both structure models, suggesting that they may tend to develop preferentially together with platelets. Moreover, our results provide evidence that VN4 centers in the platelet might be effective sinks for atomic hydrogen in diamond. Vibrational properties of the defective structures are computed by using the linear response density functional perturbation theory (DFPT). NH stretching modes for VN4H centers appear around 3221 (model 1) and 3095 (model 2) cm−1, suggesting that the experimental vibrational modes of 3085.4, 3107 and 3237 cm−1 observed in natural IaA/B diamonds could be attributed to the VN4H defects. Moreover, we observed that incorporation of VN4H centers quenches the platelet IR absorption, which is unconventional but important in understanding the platelet degradation phenomenon. Our calculations shed light on possible novel configurations of VN4H centers and platelets, which can be extrapolated to VN4H2 centers as well as to a more hybrid platelet structure, and elucidate the role of nitrogen and hydrogen in the development of platelet defects in diamond.

Imaging the atomic structure and local chemistry of platelets in natural type Ia diamond.

In the past decades, many efforts have been devoted to characterizing {001} platelet defects in type Ia diamond. It is known that N is concentrated at the defect core. However, an accurate description of the atomic structure of the defect and the role that N plays in it is still unknown. Here, by using aberration-corrected transmission electron microscopy and electron energy-loss spectroscopy we have determined the atomic arrangement within platelet defects in a natural type Ia diamond and matched it to a prevalent theoretical model. The platelet has an anisotropic atomic structure with a zigzag ordering of defect pairs along the defect line. The electron energy-loss near-edge fine structure of both carbon K- and nitrogen K-edges obtained from the platelet core is consistent with a trigonal bonding arrangement at interstitial sites. The experimental observations support an interstitial aggregate mode of formation for platelet defects in natural diamond.

The relationship between platelet size and the B′ infrared peak of natural diamonds revisited

Platelets in diamond are extended planar defects that are thought to be generated during the nitrogen aggregation process in type Ia diamonds. They were subjected to intensive research during the 1980s and 1990s but the techniques used for observation of defects in diamond have improved since that time and new insights can be gained by further study. This study combines high resolution Fourier Transform Infrared (FTIR) analysis, with an emphasis on the main platelet peak, and transmission electron microscopic (TEM) imaging. By performing TEM and FTIR analyses on volumes of diamond that were closely spatially related it is shown that the average platelet diameter, D, follows the relationship D=ax−b where x is the position of the platelet peak in the infrared spectrum, a is a constant and b is the minimum position of the platelet peak. The best fit to the data is obtained if a value of b=1360cm−1 is used, giving a fitted value of a=221. The observed variation in infrared (IR) peak width can also be explained in terms of this relationship. Additionally, platelet morphology was found to vary according to diameter with large platelets being more elongated. The tendency to become more elongated can be described by the empirical equation AR=11.9D+19.6+0.4 where AR is the aspect ratio. Using the relationships established here, it will be possible to study platelet abundance and size as a function of parameters such as nitrogen concentration, nitrogen aggregation and diamond residence time in the mantle. This work therefore will open up new methods for constraining the geological history of diamonds of different parageneses and from different localities.

Electrochemical Property of Boron-Doped Heteroepitaxial Diamond Treated By Different Oxidation Method

Boron-doped diamond electrode is expected to realize high sensitive electrochemical sensors because of its unique properties such as wide potential window and low background current. Many studies of diamond electrochemistry have been already reported but most of these works were carried out using polycrystalline diamond. Because several crystal faces and many grain boundary exists, electrochemical reactions at the surface of polycrystalline diamond becomes complex. On the other hand, epitaxial diamond (nearly single crystal) is structurally uniform, we believe that boron-doped epitaxial diamond will be more ideal material in order to realize highly-sensitive and highly-reliable sensor. Furthermore, it is useful to clarify basic electrochemical reactions at the surface of diamond. Several studies have been already reported using boron-doped homoepitaxial diamond. In the case of homoepitaxial growth, HPHT (high pressure high temperature) diamond is used for substrate but available size of HPHT diamond is small and also costs much. On the other hand, heteroepitaxial growth is much easier to fabricate diamond in large size at low cost. From the viewpoint of practical use, studies on boron-doped heteroepitaxial diamond will be important. In this study, fundamental electrochemical property of hydrogen-terminated and oxygen-terminated boron-doped heteroepitaxial diamond was evaluated. There are several methods to change the surface termination of diamond from hydrogen to oxygen such as heat mixed acid, oxygen plasma, UV irradiation, anodic oxidation treatment. The treatment conditions were optimized at each method and the oxidation peak shift of potassium ferrocyanide was compared. First, non-doped epitaxial diamond(100) was grown on Ir(100)/MgO(100) substrate in thickness of 100 μm by direct current plasma enhanced chemical vapor deposition (PE-CVD) method. After the growth, Ir/MgO substrate was removed by acid treatment in order to fabricate free-standing diamond platelet. Finally, boron-doped epitaxial diamond was grown on non-doped epitaxial diamond at boron concentration of 5000 ppm. Oxidation peak potential of potassium ferrocyanide (5mM in 0.1 M sodium sulfate) was measured by cyclic voltammetry after oxidation treatment under defined condition. To optimize oxidation treatment condition, this operation was repeated until the peak potential becomes constant. For heat mixed acid treatment, sample was dipped in mixed acid (60% nitric acid:95% sulfuric acid = 3:1) at 523 K for 15 min. For anodic oxidation treatment, 0.5 M sulfuric acid was used for electrolyte and the potential was kept at 3.0 V for 5 s. From the X-ray diffraction measurement, single sharp peak at around 120 degrees which is due to diamond(004) was detected from 2theta-omega spectrum and four-fold symmetry peaks were detected from diamond{111} pole figure which indicates that the diamond was epitaxially grown on Ir/MgO substrate. When the sample was terminated by hydrogen, sharp oxidation and reduction peaks were observed from the cyclic voltammogram and its peak separation was around 70 mV which reflects a quasi-reversible reaction (very close to reversible reaction). Shift of oxidation peak was observed after both heat mixed acid and anodic oxidation treatment. By repeating heat mixed acid treatment for four times (total 60 min treatment), oxidation peak became constant and its potential was 0.42 V vs Ag/AgCl. On the other hand, repeating anodic oxidation treatment for six times (total 30 s treatment), the peak became constant at potential of 1.52 V. Heat mixed acid treatment is a well-known method to remove surface conductive layer of diamond but the peak potential at optimized treatment condition was extremely different between two methods which indicates that termination structure differs. Termination structures analyzed by X-ray photoelectron spectroscopy will be discussed. Furthermore, the results of other methods such as oxygen plasma and UV irradiation treatment will be also discussed.

Diamond platelets produced by chemical vapor deposition

Diamond platelets of sub-micrometer size were obtained by chemical vapor deposition technique from CH4/H2 gas mixture activated by a direct current discharge. Comprehensive characterization of the diamond platelets was performed with use of scanning and transmission electron microscopy. The diamond platelet crystallites were found to be in the deposited material in form of stacked or isolated hexagonal platelets in combination with polyhedron crystallites. Six-fold rotational symmetry and composition of stacked (111) atom planes in the diamond platelets was revealed from analysis of the electron diffraction patterns. The structure and possible growth mechanisms of the platelets in the case of direct current plasma-enhanced chemical vapor deposition are discussed.

Heat Dissipation Interfaces Based on Vertically Aligned Diamond/Graphite Nanoplatelets.

Crystalline carbon-based materials are intrinsically chemically inert and good heat conductors, allowing their applications in a great variety of devices. A technological step forward in heat dissipators production can be given by tailoring the carbon phase microstructure, tuning the CVD synthesis conditions. In this work, a rapid bottom-up synthesis of vertically aligned hybrid material comprising diamond thin platelets covered by a crystalline graphite layer was developed. A single run was designed in order to produce a high aspect ratio nanostructured carbon material favoring the thermal dissipation under convection-governed conditions. The produced material was characterized by multiwavelength Raman spectroscopy and electron microscopy (scanning and transmission), and the macroscopic heat flux was evaluated. The results obtained confirm the enhancement of heat dissipation rate in the developed hybrid structures, when compared to smooth nanocrystalline diamond films.

Effect of Dose and Pressure on the Transformation from Neutron-Irradiated Graphite to Amorphous Diamond

We previously discovered a novel pathway for the transformation from highly orientated pyrolytic graphite foils irradiated with neutrons into amorphous diamond platelets. Here, we utilized graphite foils irradiated with a neutron dose of about a half of the previous study, and confirmed the pathway for the transformation. Raman spectrum of the irradiated graphite exhibits a broad amorphous one but still possessed weak G and D peaks, appearing in a less disordered state. The irradiated graphite foils were shock compressed at 46, 51 and 54 GPa. At 46 GPa, Raman spectra clearly show the G and D peaks but a weak photoluminescence appears. At 51 GPa, we can find transparent platelets with intense photoluminescence but no diamond Raman peak, implying the transformation to amorphous diamond. At 54 GPa, we obtained transparent platelets with intense photoluminescence and a small and broad diamond peak, suggesting the formation of nano-diamond.

Pathway for the Transformation from Highly Oriented Pyrolytic Graphite into Amorphous Diamond

We report the discovery of a novel pathway for the transformation from highly oriented pyrolytic graphite foils into amorphous diamond platelets. This pathway consists of three stages of neutron irradiation, shock compression, and rapid quenching. We obtained transparent platelets which show photoluminescence but no diamond Raman peak, similar to the case of amorphous diamond synthesized from C60 fullerene. Wigner defects formed by irradiation are considered to make a high density of diamond nucleation sites under shock compression, of which growth is suppressed by rapid quenching.

Intracavity diamond heatspreaders in lasers: the effects of birefringence

The birefringence of a number of commercially-available diamond platelets is assessed in the context of their use for intracavity thermal management in lasers. Although diamond is normally thought of as isotropic, significant birefringence is found to be present in some samples, with considerable variation from batch to batch, and in some cases across an individual sample. Nonetheless, low-loss operation is achieved in a laser cavity containing a Brewster element, either by rotating the sample or by using a diamond platelet with low birefringence.

Microstructural investigation of hexagonal-shaped diamond nanoplatelets grown by microwave plasma chemical vapor deposition

Diamond crystallites in hexagonal-shaped nanoplatelet morphology were synthesized in microwave plasma chemical vapor deposition (MPCVD) system using a CH 4/H 2 gas mixture with a ratio of 0.667%. Diamond nanoplatelets were deposited on (1 0 0) silicon substrate. The substrate was embedded within the plasma ball close to its center where the high temperature above 1100 °C was reached during the deposition. Surface morphologies and crystalline characteristics of the deposited diamond were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM observations clearly show that the diamond nanoplatelets exhibit hexagonal-shaped morphologies, and the thickness and the length are measured to be around 20–30 nm and several hundred nanometers, respectively. Also, SEM shows that the distribution of the nanoplatelet density gradually increases from the center to the corner of the sample. TEM with selected area electron diffraction shows that each platelet is a single crystalline diamond. Both 〈1 1 0〉 and 〈1 1 1〉 orientations of the diamond platelets are observed.

Stacking-Fault Based Microscopic Model for Platelets in Diamond

We propose a new model for {001} platelets in diamond based on the formation of a metastable stacking-fault. The core of the defect is a double layer of threefold coordinated sp2 carbon atoms embedded in the sp3 diamond matrix. The properties of the model were determined using ab initio calculations. All significant experimental signatures attributed to the platelets are fully accounted for. The model is also very appealing from the point of view of kinetics, since naturally occurring shearing processes will lead to the formation of the metastable fault.

1.3-μm GaInNAs surface-normal devices

The compatibility of GaInNAs/GaAs active regions with AlGaAs Bragg mirror technology opens up a range of surface-normal device formats for the spectral region around 1.3 μm. The authors report recent progress on the development of diode-pumped vertical external-cavity surface emitting lasers (VECSELs) and vertical cavity semiconductor optical amplifiers (VCSOAs) based on this technology. Pertinent performance characteristics are reported for GaInNAs 1.3-μm VECSELs capillary-bonded to diamond heatspreader platelets. In a conventional three-mirror air-spaced laser cavity up to 0.6 W of TEM00 output power was obtained. With the outer surface of the diamond platelet coated to form a dielectric output coupler mirror, it was possible to obtain the first monolithic microchip operation of a GaInNAs VECSEL, where a Gaussian beam with output power up to 120 mW was obtained. The influence of temperature on the performance of a six-quantum-well VCSOA with on-chip gain values of up to 16 dB was also reported. It reveals that on-chip gain of 9 dB can be achieved over a range of 85°C, allowing the amplifier characteristics to be tuned over more than 9.5 nm. Further investigations of the influence of optical feedback on the performance of these vertical amplifiers demonstrate that a three-mirror analysis explains the observed phenomena.

Characterization of diamond nanoplatelets

Diamond deposition at a temperature above 1000 °C was carried out in a microwave plasma chemical vapor deposition reactor using a 3% CH 4/H 2 gas mixture. A polycrystalline diamond substrate was coated with a thin film of nickel in 100-nm thickness before deposition. Electron microscopy characterization of electron diffraction, high-resolution imaging, and electron energy loss spectroscopy shows that the diamonds deposited exhibit regular shapes in triangles and parallelogram with well-faceted surfaces. These diamond platelets are single crystallites with a uniform thickness of approximately 30–70 nm and length of several hundred nanometers to a few micrometers. The platelet morphology suggests that it is formed by lateral growth. Also, it was found that the diamonds are covered with a 1 to 2-nm thick graphite films in epitaxy.

Nanodiamond Thin Films on Titanium Substrates : Growth and Electrochemical Properties

A new type of electrically conducting nanosized diamond film deposit is grown on titanium substrates in a microwave plasma chemical vapor deposition process. The deposition process occurs at 80 Torr in a helium atmosphere with only hydrogen (1.95%) and methane (0.73%) admitted and yields a deposit growing approximately 0.5 μm h−1 thick. Electron microscopy indicates the formation of nanosized diamond platelets. The electrochemical properties of nanodiamond when immersed in aqueous electrolyte solution are explored for the system, the system, the oxidation of hydroquinone, ascorbic acid, and the oxidation of dihydronicotinamide adenine dinucleotide. Compared to boron-doped diamond materials, nanodiamond is a highly active electrode material with very low overpotentials for all redox systems studied. For ascorbic acid, diffusion-controlled oxidation is detected at potentials approximately 0.5 V more negative compared to those observed at boron-doped diamond electrodes. The electrical conductivity, high surface reactivity, and electrochemical characteristics are explained in terms of many defects and active surface sites. © 2002 The Electrochemical Society. All rights reserved.

Epitaxially grown free-standing diamond platelet

We obtained an epitaxially grown free-standing diamond platelet utilizing epitaxial diamond film formed on a {100} iridium surface using a d.c. plasma CVD process. Iridium was selected as a suitable substrate material for the heteroepitaxy of diamond based on original criteria. Confocal Raman spectroscopy revealed that the diamond platelet contained little or no non-diamond carbon. The obtained diamond platelet is transparent to visible light and cleavable along the 〈110〉 direction on the surface. The angles between the top surface and the cross-sectional surfaces are approximately 55°, almost equal to the theoretical angle of 54.74° between {100} and {111} planes in cubic crystals. Therefore, the cross-sectional surfaces would be {111} planes of a typical facet for single-crystalline diamond. This means that the diamond platelet we have formed has relatively good crystallinity.

Small aggregates of interstitials and models for platelets indiamond

By examining the structure of small clusters of self-interstitials indiamond using local-density-functional techniques, we have developedmodels for the planar defects called platelets. We present thestructures, energies and vibrational properties.

New mounting method of diamond monochromator for high brilliance synchrotron radiation

We have studied a new and reliable cooling method for diamond crystals in third generation light sources. In order to reduce the strain from brazing between the diamond monochromator and its Cu block cooling device, another diamond platelet was introduced as an interface. Using a finite element method program based on numerical thermal analysis, the mounting strain was estimated at 0.6 arcsec. Then data was confirmed through preliminary x-ray characterization using laboratory x-ray sources. The strain in the area exposed to a 1 mm×4 mm synchrotron radiation beam (absorbed power 100 W) was estimated by simulation at an acceptable 1.0 arcsec. Applying the new cooling method, the diamond crystal can tolerate synchrotron radiation power up to 100 W.

A new proposal for the structure of platelets in diamond

A new model is proposed for platelets in diamond that is based upon the unambiguously determined molecular structure of the EPR centre known as R1, which comprises two parallel [001] split interstitials at nearest neighbour positions in the (11̄0) plane. The new feature of the model is the structure of the “pillar”, which holds apart the two sides of the platelet, which comprises two R1 centres related by a displacement of ao/2 along [11̄0], linked by two covalent bonds. The two sides of the platelet are pushed apart by a measured distance of 0.40(1) ao: an approximate calculation for the proposed structure gives 0.40 ao. The pillar has a rectangular cross-section in the (001) plane, having dimensions 1/2 ao/2×ao/2: that its symmetry is only twofold about [001] could account for the fact that platelets are often elongated along one of the 〈110〉 axes. The pillar comprises basically carbon interstitials, but could accommodate randomly up to 50% nitrogen interstitials. In particular, the model indicates a clear method of nucleation and growth. The pillars are most likely to be arranged in a regular array in one of two ways. In units of ao/2, the unit cell is 3 units in one 〈110〉 direction, and 2 or 4 units in the perpendicular direction. In either case, the number of interstitials is 8/3 per a2o.