Type IIa Diamond Research Articles

High-pressure generation using high-purity synthetic type IIa diamond anvils

High-pressure generation tests were conducted using synthetic type IIa diamond anvils with various shapes and orientations, and their deformation and fracture were investigated under high pressure. The synthetic diamond anvils with bevelled culet of less than 50 μm in diameter can generate pressures of up to 200 GPa with good reproducibility and without emitting any luminescence. The pressure generating efficiency of the (111) diamond anvil is slightly higher than that of the (100) diamond anvil. At pressures higher than 200 GPa, however, both of the (100) and (111) synthetic diamond anvils emit strong luminescence due to plastic deformation. The plastic deformation seems to be caused by the steep cupping deformation in the culet, leading to fracture of the anvil.

Enhancement of Dopant Activation in B-Implanted Diamond by High-Temperature Annealing

In this paper, we present the effect of postimplantation high-temperature annealing at 1600 °C on electrical properties and lattice structures of B-implanted diamonds. B multiple ion implantation at 30–360 keV was performed to make a B box-profile of 5 ×1018 or 5 ×1019 cm-3 into high-pressure, high-temperature type IIa diamond substrates at 400 °C, followed by 1450 °C and higher temperature annealing at 1600 °C. Optical transmission spectra indicated that radiation damage was almost eliminated with an increase in annealing temperatures to 1600 °C in both samples. In the sample of 5 ×1018 cm-3, the hole concentration and the Hall mobility were 2 ×1013 cm-3 and 55 cm2 V-1 s-1 after 1450 °C annealing, respectively. By contrast, after 1600 °C annealing, their values increased to 6.5 ×1013 cm-3 and 82 cm2 V-1 s-1, respectively. The doping efficiency of the sample after 1600 °C annealing is ∼50%, which is the highest ever reported for B-implanted diamond. In the sample of 5 ×1019 cm-3, the band conduction of carriers was observed after 1450 °C annealing, while high-temperature annealing at 1600 °C resulted in the appearance of hopping conduction in the low-temperature region below 400 K. In cathodoluminescence spectra of the samples annealed at 1600 °C, the peak intensities around 780 nm, originating from radiation defects frequently observed in ion implanted diamond, decreased, while a broad band centering around 560 nm appeared. The results of this study suggest that high-temperature annealing over 1450 °C is effective for elimination of radiation damage and an increase in the acceptor concentration.

Characterization of crystallinity of a large self-standing homoepitaxial diamond film

We have investigated the crystallinity of a self-standing homoepitaxial diamond film grown at a high rate using a polarized optical microscope, X-ray rocking curves and X-ray topographs. The self-standing film was made by removing a synthetic type-Ib(001) substrate after the film growth using a “lift-off process”. The cross-nicol optical microscope image demonstrated that there exists strain spreading at a relatively large area in the film and the strain inherits over that in the substrate. From cross-sectional X-ray topographs, the dominant defects, observed as dotted patterns in plan-view topographs and micrographs, are dislocations extending along the film growth direction 〈001〉 and generating at the interface between the film and the substrate. The density of such defects counted from these measurements was ~ 1 × 10 3 cm − 2 . The dotted patterns observed in X-ray topographs of (220), (− 220) and (400) diffraction planes are almost the same with each other, suggesting that dominant line defects along 〈001〉 are mixed dislocations with a burgers vector directing between 〈001〉 and in-plane of the sample. The high resolution X-ray rocking curve showed that the peak is very sharp with full width at half maximum of 7.56″, which indicates that imperfection of our single-crystal diamond plate is almost the same as that of high-quality high-pressure high-temperature, synthetic type-Ib diamond.

Synthetic Diamond for Intracavity Thermal Management in Compact Solid-State Lasers

The intracavity use of newly developed low-birefringence synthetic diamond for thermal management in compact solid-state lasers is examined both experimentally and theoretically. A comparison - using single-crystal natural diamond as a base line - is made between synthetic, single-crystal diamond types: chemical vapor deposition and high pressure/high temperature grown diamond. The synthetic diamond samples are shown to possess significantly lower birefringence than often occurs in natural single-crystal diamond while maintaining the excellent thermal management properties and low insertion loss of natural diamond. Low threshold, high efficiency laser operation is demonstrated in polarization sensitive cavities incorporating intracavity synthetic diamond using both doped-dielectric and semiconductor gain elements. In addition, finite element analysis is used to demonstrate the potential of diamond to reduce thermal distortion and stress in doped-dielectric disk lasers. A 15 W Nd:GdVO4 disk laser utilizing diamond is demonstrated. These results highlight the potential of low birefringence synthetic diamond for intracavity thermal management applications in solid-state lasers.

Persistent positive and transient absolute negative photoconductivity observed in diamond photodetectors

Persistent photoconductivity and optical quenching phenomena in boron-doped homoepitaxial diamond thin films grown on type Ib (100) substrates were investigated. Boron doping induced positive persistent photoconductivity (PPPC) and photocurrent gain upon the illumination of deep ultraviolet (DUV) light. A deep defect with a thermal energy of around 1.37 eV was deduced from the results of thermally stimulated current measurements. An optical quenching experiment revealed a threshold photon energy of around 2 eV. The difference between the thermal and optical energies of the deep defect suggests a large lattice relaxation. An absolute transient negative photocurrent (TNPC) was observed for zero or weak electric fields with DUV light illumination after optically quenching the PPPC. The absolute TNPC was due to transient electron filling of the charged nitrogen in the substrate. The combination of the nitrogen in the substrate and the boron-related defects in the epilayer was apparently responsible for the PPPC and TNPC effects. Therefore, the overall photoresponse properties of a thin epilayer deposited on a type Ib diamond substrate can be tailored by adjusting the concentration of nitrogen in the substrate and of boron in the epilayer.

Controlled synthesis of diamond and carbon nanotubes on Ni-base alloy

A Ni-base alloy Inconel 600 has been used as substrate for growing two typical carbon thin film materials, diamond and carbon nanotubes (CNTs), in a hot filament chemical vapor deposition reactor with methane–hydrogen mixture. Under typical deposition conditions, the deposits formed on the as-polished alloy substrate comprise duplex layers, outer diamond layer and intermediate graphite layer. An Al thin film applied as an interlayer on the Inconel alloy effectively prevented the growth of intermediate graphite, and only a dense, adherent diamond film was deposited. When the substrate was negatively biased, a glow discharge was initiated and aligned carbon nanotubes were exclusively synthesized. No diamond was formed in this case.

P-n junction on high-pressure-high-temperature grown single crystal diamond: UV-emission spectra and electrical properties

Semiconductor p+-p-n structure has been created on synthetic single crystal IIb type diamond grown by high pressure temperature gradient method and doped with boron at growth process. 250 μm thick (001) cut plate was ion implanted by B, As and P at (1 − 1.3)·1016 cm-2. Electroluminescence spectra were investigated at different values of electrical voltage and current in regular and S-part of the current-voltage characteristics. Strong exciton recombination emission was observed at the current density up to 60 A*cm-2. The spectrum transforms at transition from regular conductivity to electrical avalanche breakdown regime. Simultaneously a set of sharp EL lines appears in the range of 327-652 nm on the A-band background. They tentatively attributed to superlumenscence effect.

Diamond particle shape: Its measurement and influence in abrasive wear

The classification of diamond particles in terms of their abrasive characteristics is addressed in this work. Specifically, diamond particles of different grades have been studied in terms of their shape to identify useful trends and correlations with experimental wear rate. Ten diamond types, typically used by the abrasives industry and exhibiting varied shape, were selected. They included highly geometric single crystals, crushed single crystals, and polycrystalline diamond particles, with nominal diameters of between 65 and 197 μm. Electronic boundary projections were obtained using a digital-camera-equipped optical microscope, which were then processed using proprietary software. The parameters calculated include: diameter (minimum, minor and maximum), aspect ratio, convexity and sharpness. Interesting correlations were found between convexity and sharpness that engendered both these parameters to be considered as useful measures of wear rate. This was reinforced by experimental wear tests, using grinding wheels manufactured from six of the 10 diamond types, which demonstrated excellent correlations of sharpness (0.991 correlation coefficient), and convexity (0.987 correlation coefficient), with the wear rate of a polyurethane workpiece.

Growth of High Quality Spherical Diamond Film by DC Plasma Jet CVD

Spherical diamond film was deposited on molybdenum substrate by DC‐plasma jet CVD. Scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, and X‐ray diffraction (XRD) were used to observed morphology, purities and orientation evolution of spherical diamond film, respectively. The results show that grain size is compact, clear, uniform, continuous and no remarkable bigger grain. When nucleation begins, grain grows with random orientation; after nucleation, grain grows with certain orientation. Characteristic diamond (111), (220), (311) peaks were clearly observed and no graphite peak was detected, and (111) facets were dominant, which indicated diamond film was an obviously polycrystalline texture. At 1332.0 cm−1 with FWHM, there is a the typical diamond Raman spectra characteristic peaks, and polycrystalline graphite and amorphous graphite were not observed; thus, high quality spherical diamond films were prepared. Upon increasing methane concentration and temperature, grain size also increases, and diamond film has more local clusters and vacancy defects; there are more polycrystalline graphite and amorphous graphite, and diamond film quality was worse. Thus, for preparing high quality diamond film, it is necessary to optimize some parameters, such as methane concentration and substrate temperature.

Selectivity of a 50-mm diamond mesh knotless polyethylene codend for commercially important fish species in the Aegean Sea

Summary This research investigated effects of changing the diamond mesh size on codend selectivity in Mediterranean fisheries. The selectivity of a typical 50-mm diamond knotless polyethylene (PE) codend used in the Turkish fishery in the Aegean Sea was measured for commercially important species, in particular hake (Merluccius merluccius), horse mackerel (Trachurus trachurus), anglerfish (Lophius piscatorius) and John Dory (Zeus faber). Fishing trials were carried out on the commercial trawler ‘Hapuloglu’ between 9 and 12 December 2006 using a modified trawl net. Selectivity data were collected by the covered codend method and analysed by means of a logistic equation (Maximum Likelihood Method). The mean selectivity curve was estimated from individual hauls, taking between-haul variations into account. Mean mesh size of the codend was 49.4 mm as measured by digital calliper. Mean values for 50% retention length of hake and horse mackerel were estimated to be 11.4 and 15.6 cm total length; corresponding selection ranges were 4.1 and 5.5 cm respectively. The 50-mm diamond mesh codend showed adequate selectivity compared to the minimum landing size (MLS) for horse mackerel, while for hake it selected specimens in a size range far lower than the MLS. No selectivity values could be determined for anglerfish or John Dory. To design a more selective codend for the Turkish demersal trawl fishery, not only mesh size regulations but also other codend characteristics and netting material properties must be urgently considered.

New insights into the mechanism of CVD diamond growth: Single crystal diamond in MW PECVD reactors

CVD Diamond can now be deposited either in the form of single crystal homoepitaxial layers, or as polycrystalline films with crystal sizes ranging from mm, μm or nm, and with a variety of growth rates up to 100s of μm h − 1 depending upon deposition conditions. We previously developed a model which provides a coherent and unified picture that accounts for the observed growth rate, morphology, and crystal sizes, of all of these types of diamond. The model is based on competition between H atoms, CH 3 radicals and other C 1 radical species reacting with dangling bonds on the diamond surface. The approach leads to formulae for the diamond growth rate G and average crystallite size < d> that use as parameters the concentrations of H and CH x (0 ≤ x ≤ 3) near the growing diamond surface. We now extend the model to show that the basic approach can help explain the growth conditions required for single crystal diamond films at pressures of 100–200 Torr and high power densities.

Characterization of phosphorus-doped homoepitaxial (1 0 0) diamond films grown using high-power-density MWPCVD method with a conventional quartz-tube chamber

Phosphorus-doped n-type homoepitaxial diamond films have been successfully grown at high substrate temperatures (>1000 °C) on high-pressure/high-temperature-synthesized type-Ib single-crystalline diamond (1 0 0) substrates, by using a conventional microwave plasma chemical-vapor-deposition (CVD) system with high power densities. The deposition system employed in this work had an easily exchangeable 36 mm inner-diameter quartz-tube growth chamber. The homoepitaxial diamond films thus grown were characterized by means of Hall-effect measurements with an AC magnetic field, atomic force microscope observations and secondary ion mass spectrometry techniques. The dependences of the substrate temperature (≤1300 °C) and the P/C ratio in the source gas (≤9900 ppm) on the specimen features were investigated. The optimum substrate temperature deduced was ≈1160 °C, which was also applicable to the CVD growth of undoped homoepitaxial diamond layers. The n-type conductions with an activation energy ≈0.6 eV were observed for the specimens with amounts of the P atoms incorporated to ≈1.5 × 10 18 cm −3 whereas the doping efficiencies changed from ≈0.06% to ≈0.92% with the growth condition. Possible origins for these results are discussed in relation to the growth mechanism.

High pressure structural behavior and synthesis ofZr2SC

A high pressure study of Zr2SC using synchrotron x-ray diffraction and a Mao–Bell type diamond anvil cell hasbeen performed up to a pressure of 46 GPa at room temperature. No phasetransformation has been observed up to this pressure. It is found that thecompression along the two axes is almost identical up to 15 GPa, thereafter thec-axisshows a slightly higher compressibility. The third order Birch–Murnaghan equation of state was usedto fit the experimental pressure–volume data, from which the isothermal bulk modulus was obtained asKT = 186(4) GPa with apressure derivative K′T = 4.0. The sample was synthesized using the piston cylinder technique and was found tobe predominantly single phase after it was characterized by scanning electronmicroscopy equipped with an energy dispersive spectrometer and by synchrotron x-raydiffraction. The lattice parameters calculated from the x-ray diffraction werea0 = 3.406(2) and c0 = 12.138(4).

Polycrystalline Columnar Diamond Film Deposited on Spherical Substrate by DC Arc Plasma CVD

Diamond film was deposited on spherical molybdenum substrate by DC arc plasma CVD method. Diamond film morphology, purities and orientation evolution, obtained from atomic force microscopy, scanning electron microscopy, Raman spectroscopy, X ray diffraction respectively, has showed that grains on the growth surface are compact, continuous and uniform. Characteristic diamond (111), (220), (311) peaks were found and (111) facets were predominant. It revealed that diamond film was polycrystalline texture characteristic. There is a typical diamond Raman spectrum peaks at 1332.0 cm-1, and not graphite and amorphous carbon characteristic peak. High purity diamond film was deposited. When methane concentration was increased, diamond film has more local clusters and vacancy defects such as voids, graphite inclusion, and hydrogen cluster. Therefore, some important parameters such as methane concentration and substrate temperature should be optimized in depositing diamond film.

The presence of defects and their influence on the performance of CVD diamond as an α-particle radiation sensing element

Three types of diamonds produced by chemical vapour deposition (CVD) and broadly classified as detector grade, optical grade and single crystal were evaluated in terms of their response to α-particle radiation when used as detection elements. It is well known that the presence of defects in diamond, including CVD specimens, not only dictates but also affects the response of diamond to radiation in different ways. In this investigation tools such as electron spin resonance (ESR), thermo-luminescence (TL), Raman spectroscopy and ultraviolet (UV) spectroscopy were used to probe each of the samples, which were then graded on α-particle radiation detection performance. The presentation discusses the presence of defects identifiable by the techniques used and correlates the radiation performances of the three types of crystals to their presence.

Channel mobility evaluation for diamond MOSFETs using gate-to-channel capacitance measurement

In this work, the channel mobility ( μ ch) of diamond metal-oxide-semiconductor field-effect transistors (MOSFETs) with hole accumulation layer channels was evaluated from the gate-to-channel capacitance and drain conductance for the first time. The FET structure was utilized for the capacitance–voltage (C–V) measurement, and the gate-to-channel capacitance ( C GC) under the forward bias condition was proportional to the gate area, as in the case of Si MOSFETs. For the accurate evaluation of the drain conductance, diamond MOSFETs were fabricated on IIa-type diamond films with low boron concentrations (< 10 14cm − 3). In a 60-μm gate-length diamond MOSFET, a μ ch of 145cm 2/Vs was obtained, which is comparable to that of a SiC inversion layer.

Anomalous high pressure behaviour in nanosized rare earth sesquioxides

We report Raman spectroscopic studies of the nanosized rare earth sesquioxides, namely yttrium sesquioxide(Y2O3), gadoliniumsesquioxide (Gd2O3) andsamarium sesquioxide (Sm2O3), under high pressure. The samples were characterized using x-ray diffraction,Raman spectroscopy and atomic force microscopy at atmospheric pressures.Y2O3 andGd2O3 were found to be cubicat ambient, while Sm2O3 was found to be predominantly cubic with a small fraction of monoclinicphase. The strongest Raman peaks are observed at 379, 344 and363 cm−1, respectively,for Y2O3, Sm2O3 and Gd2O3. All the samples were found to be nanosized with 50–90 nm particle sizes. Thehigh pressures were generated using a Mao–Bell type diamond anvil cell and aconventional laser Raman spectrometer is used to monitor the pressure-induced changes.Y2O3 seems to undergo a crystalline to partial amorphous transition whenpressurized up to about 19 GPa, with traces of hexagonal phase. However, onrelease of pressure, the hexagonal phase develops into the dominant phase.Gd2O3 is alsoseen to develop into a mixture of amorphous and hexagonal phases on pressurizing. However, on release ofpressure Gd2O3 does not show any change and the transformation is found to be irreversible. On the other hand,Sm2O3 shows a weakening of cubic phase peaks while monoclinic phase peaks gain intensity up toabout a pressure of 6.79 GPa. However, thereafter the monoclinic phase peaks alsoreduce in intensity and mostly disordering sets in which does not show significantreversal as the pressure is released. The results obtained are discussed in detail.

Fabrication and characterization of single crystal semiconductive diamond tip for combined scanning tunneling microscopy

Boron-doped type IIb diamond single crystal synthesized by the temperature gradient method under high pressure–high temperature (HPHT) conditions is proposed as a material for the tip of scanning nanoindentation–scanning tunneling microscopy (SN-STM) technique. Sequence of the procedures covering growing crystals with predetermined physical properties, selection of the synthesized crystals with the desired habit and their precise shaping in the form of Berkovich pyramid have been developed. Results of experimental studies demonstrated fabricated tip's ability to conduct combined nanoscale characterization of surface using indentation and scanning with the same tip.

Occurrence of the Si–V defect center in natural colorless gem diamonds

The Si–V defect center in diamond (737 nm; 1.682 eV) was long thought to occur only in chemical vapor deposition (CVD)-grown or Si-doped HPHT-grown synthetic diamonds. We report, for the first time, the occurrence of the Si–V defect in ten gem-quality colorless natural diamonds. Many of these samples, including type IIa and Ia diamonds, contained included crystals of olivine (Fo 93–95) and garnet (Ca–Mg-rich), proving their natural origin. The 737 nm photoluminescence feature (actually a doublet at 736.5 and 736.9 nm at 77 K) occurred in association with several additional and previously unreported peaks at 524.4, 550.4, 554.3, 557.9, 558.2, 573.5, 593.3, 594.8, and 714.7 nm, as well as two series of peaks in the ranges 535–539 and 644–652 nm. The intensities of the associated peaks were proportional to the 737 features, suggesting their association with Si as well. Based on olivine (Fo 0.93–0.95) and garnet inclusion (Ca, Mg-rich) chemistry, these diamonds are peridotitic in nature, likely having formed in the upper mantle. The source of the Si remains unclear. Care must be taken to avoid confusion between these natural Si–V diamonds and CVD synthetic diamonds with Si–V features. Fortunately, many of the commonly reported CVD identification features are absent from natural Si–V diamonds, facilitating the separation.

The presence of defects and their influence on the performance of CVD diamond as an α-particle radiation sensing element

Three types of diamonds produced by chemical vapor deposition (CVD) and broadly classified as detector grade, optical grade and single crystal were evaluated in terms of their response to α-particle radiation when used as detection elements. It is well known that the presence of defects in diamond, including CVD specimens, not only dictates but also affects the response of diamond to radiation in different ways. In this investigation, tools such as electron spin resonance (ESR), thermo-luminescence (TL), Raman spectroscopy and ultraviolet (UV) spectroscopy were used to probe each of the samples, which were then graded on their performance as α-particle radiation detectors. The presentation discusses the presence of defects identifiable by the techniques used and correlates the radiation performances of the three types of crystals to their presence.