Type IIa Diamond Research Articles

Robust dynamical decoupling for arbitrary quantum states of a single NV center in diamond

Dynamical decoupling is a powerful technique for extending the coherence time (T2) of qubits. We apply this technique to the electron spin qubit of a single nitrogen-vacancy center in type-IIa diamond. In a crystal with natural abundance of 13C nuclear spins, we extend the decoherence time up to 2.2 ms. This is close to the T1 value of this NV center (4 ms). Since dynamical decoupling must perform well for arbitrary initial conditions, we measured the dependence on the initial state and compared the performance of different sequences with respect to initial state dependence and robustness to experimental imperfections.

Structural analysis of dislocations in type-IIa single-crystal diamond

High-quality crystals with flat surfaces and low defect densities are required in order to realize stable high performance in diamond-based power devices. Type-IIa single-crystal diamond that has no inclusions is thought to have potential as a defectless substrate. However, with today's crystal growth methods, there exist many dislocations in the type-IIa diamond, and thus this potential remains unrealized. In this paper, we describe the identification of dislocations in type-IIa diamond using X-ray topography. From the quantitative dislocation density analysis, it is estimated that the half of the dislocations are 45° dislocations and one-fourth of the dislocations are edge dislocations and 60° dislocations.

Silver nanoclusters decked diamond thin film as a substrate for surface-enhanced Raman scattering

Modified diamondthin filmsurfaces are proven candidates for bio-sensoric applications. A typical polycrystalline diamond thin film surface decked with silver (Ag) nanoclusters is found to be suitable for surface-enhanced Raman scattering (SERS). Simple and time effective procedures are used to fabricate Ag nanoclusters/diamond/silicon structure. Standard Rhodamine 6G probe molecules are used to access the SERS activity of the test surface. The observed SERS activity is explained in terms of predominant electromagnetic enhancement mechanism. This work is expected to benefit SERS based bio-sensing with diamond as the core sensing material.

A Study of the relationship between brown colour and extended defects in diamond using core-loss electron energy loss spectroscopy

There is strong evidence to support the theory that the vacancy cluster, a by-product of dislocation interaction, is the extended defect responsible for brown colour in natural type IIa diamonds. A characteristic of these open volume structures is the hybridised sp2 bonding of the 3-fold coordinated carbon atoms that line their cage-like surfaces. When present in sufficiently large concentrations the sp2 bonds alter the electronic and optical properties of type IIa diamond dramatically. Similar sp2 bond concentrations are found in dark brown CVD diamond, although the defects in this material appear much larger in size than in the natural diamond. In this study we employ core-loss electron energy loss spectroscopy (EELS) and aberration corrected scanning transmission electron microscopy (AC-STEM) to compare the relative sp2 content of brown coloured natural type IIa diamonds and dark brown CVD diamonds, using 100% sp2 bonded graphite as a reference. The effect of high-pressure high-temperature (HPHT) treatment on sp2 content is also investigated.

Origin of temperature plateaus in laser-heated diamond anvil cell experiments

Many high-pressure high-temperature studies using laser-heated diamond cells have documented plateaus in the increase of temperature with increasing laser power or with time. By modeling heat transfer in typical laser-heated diamond anvil cell experiments, we demonstrate that latent heat due to melting or other phase transformation is unlikely to be the source of observed plateaus in any previously published studies, regardless of whether pulsed or continuous lasers were used. Rather, large increases (∼10-fold) in thermal conductivity can explain some of the plateaus, and modest increases in reflectivity (tens of percent) can explain any or all of them. Modeling also shows that the sub-microsecond timescale of heating employed in recent pulsed heating experiments is fast enough compared to heat transport into and through typical insulations, but too slow compared to heat transport into metallic laser absorbers themselves to allow the detection of a large plateau due to latent heat of fusion. Four new designs are suggested for future experiments that could use the simple observation of a latent heat-induced plateau to provide reliable high-pressure melting data.

SU-E-T-153: Detector-Grade CVD Diamond for Radiotherapy Dosimetry.

To evaluate the use of commercially available detector-grade synthetic diamond films made via chemical vapor deposition (CVD) as x- ray detectors for radiotherapy dosimetry. A detector was fabricated using high-quality single crystal CVD diamond films (0.5 × 3 × 3 mm̂3) with 0.4 mm̂3 sensitive volumes, which were encapsulated with PMMA. The detector was placed in a (30 × 30 × 30 cm̂3) PTW water phantom. Six- and ten-MV photons from an Elekta Synergy linac were measured using an SSD of 90 cm and typically a 10-cm phantom depth with a 10 × 10 cm̂2 field size in the central axis of the beam. Data acquisition was performed using a PTW UNIDOS E electrometer with a 100-V bias. The detector was evaluated by measuring leakage current, priming dose, response dynamics, dose linearity, dependence on dose rate, percent depth dose (6 and 10 MV photons) and output factors. Some measurements were compared with a Si diode detector, 0.04 and/or 0.13-cc ion chamber(s). Leakage currents were negligible (∼1 pA) given the overall average sensitivity of the material (680 nC/Gy at 100 V). Detector current rise and fall times were < 2 s. Dose measurements up to 5 Gy were linear. A slight dependence on nominal dose rates up to 500 MU/min was seen with Fowler fitting parameter delta = 0.981. Percent depth dose profiles compared well to a 0.13-cc ion chamber up to 25 cm depths for 10-MV photons. Output factors measured well for field widths 5-15 cm; below 5 cm, differences are seen between all four different detectors as expected. The type of diamond tested has potential to be used for small field dosimetry due to its small sensitive volume and high sensitivity. Further experiments are ongoing and detector packaging is yet to be optimized.

Influence of CeO&lt;sub&gt;2&lt;/sub&gt; and Sintering Parameters on the Performance of Vitrified Bond Diamond Abrasive

A kind of vitrified bond was selected to be sintered with diamond powders to prepare diamond abrasive. The effect of the additive of CeO2 and sintering parameters on the performance of vitrified bond diamond abrasive was investigated. The mechanical properties of diamond abrasives were tested on ZMC-Ⅱ type diamond static strength tester and the interfacial bonding states between diamond powders and vitrified bonds were studied by Scanning Electron Microscopy (SEM). The results indicated that CeO2 improved the performance of diamond abrasive by means of strengthening the bonding between diamond grits and vitrified bond. The admirable diamond abrasive was achieved when the sample was sintered at 800°C holding for 120min.

Boron doped diamond electrodes based on porous Ti substrates

The boron doped diamond (BDD) electrodes were fabricated as a novel type of porous conductive diamond by hot filament chemical vapor deposition (HFCVD) technique. The challenge for the composite material is the stability, and diamond growth parameters should be optimized in order to cover entirely the substrate surface. The high-quality porous BDD electrodes were prepared by added high concentration of boron in the reaction compartment at the initial stage to inhibit the formation of TiC interlayer. With the characterization of SEM and XRD, it can be found that the substrate surface including the bottom, surface and wall in the pores was entirely covered by boron doped diamond film, and the crystalline type of diamond almost was crystal plane (111). The electrochemical characteristics of the BDD electrodes were investigated by the CV and large potential windows could be observed. Boron element influences the interlayer formation, the high concentration of doped boron can inhibit the formation of TiC, and addition of boron is favored for adhesion enhancement.

A Microscopy and FTIR and PL Spectra Study of Polycrystalline Diamonds from Mengyin Kimberlite Pipes

The results of a microscopy and FTIR and PL spectra study of the natural polycrystalline diamonds from the Mengyin kimberlite pipes show that they can be classified as the euhedral faceted polycrystalline diamonds (EFPCDs) and anhedral rounded polycrystalline diamonds (ARPCDs). Different diamond grains or their points were formed in different conditions or processes. They were not formed in diamond nucleation stage, but in the diamond growth period. They probably originated from the relatively deeper mantle and were formed in the environment like the peridotitic (P) type diamond single crystals. The EFPCDs did not undergo a remarkable dissolution process during their formation and were possibly fast formed shortly before the kimberlite eruption. The ARPCDs not only were formed at a higher temperature than the EFPCDs but also underwent a notable dissolution process and had been stored relatively longer in the mantle. Fluids or melts probably participated in the formation of the ARPCDs or modified them during the period of their storage in the mantle.

Growth and evaluation of self-standing CVD diamond single crystals on off-axis (001) surface of HP/HT type IIa substrates

As part of the development of diamond radiation detectors for energy spectrometry, quality improvement of CVD diamond single crystals was conducted mainly by measures of single diamond substrates. To suppress stress resulting from unconformity of lattice spacing between a substrate and a grown layer, which sometimes causes breakage, HP/HT type IIa diamond single-crystal substrates were adopted, and it resulted successfully. In addition an off-axis (001) surface was fabricated on the substrate to reduce abnormal growth. A lift-off method was adopted to reuse the HP/HT type IIa substrate with an off-axis (001) surface. Judging from peaks caused by free exciton recombination in cathode luminescence spectra, growth conditions more strongly affected the diamond crystal quality than substrates of any kind. Energy resolution of 0.6% for alpha particles was obtained by one CVD diamond single crystal. Charge collection efficiency of approximately 100% and 95% for holes and electrons was achieved. Step bunching caused by residual gas was observed on the grown CVD diamond surface. From the perspective of charge carriers' transportation measurement, the reduction of residual gas and optimization of growth conditions are indispensable.

Photoluminescence studies of 515.8 nm, 533.5 nm and 580 nm centres in electron irradiated type IIa diamond

A series of irradiations has been performed mainly on some very high purity CVD single crystal diamonds but also on some other diamond specimens at various electron doses and dose rates. The electron energies were sufficient to cause atomic displacements creating vacancies and self-interstitials in the irradiated samples. The 515.8nm, 533.5nm and 580nm centres were commonly observed in low temperature photoluminescence examination of electron-irradiated type IIa diamonds. Details of their spectra indicate that they are all related to interstitial complexes.

Synthetic diamond opens windows into the deep Earth

As a result of its singular strength and exceptional transparency, diamond plays a unique role in laboratory studies of materials under extreme pressures and temperatures. Historically, the quality and size of the diamond used have been limited to that available from nature. However, researchers can now synthesize various types of diamonds in the laboratory that are harder, tougher, and larger than those available natural diamonds. The physical properties and features of these diamonds allow scientists to study materials at pressure‐temperature conditions ranging from those at Earth's surface to those at the very center of the Earth. In essence, these synthetic diamonds offer new windows into the deep Earth.

Lattice structure of a freestanding nitrogen doped large single crystal diamond plate fabricated using the lift-off process: X-ray diffraction studies

Lattice structures of freestanding, large (~9×9mm) nitrogen doped single crystal (SC) diamond plates were investigated mainly by X-ray diffraction including a reciprocal space mapping (RSM) method. After a plasma-chemical-vapor-deposited thick homoepitaxial diamond film was grown at a high-speed on type-Ib (001) diamond, a SC freestanding diamond plate was fabricated by separation of the substrate from the film by a lift-off process using high-energy ion implantation. Due to the use of the lift-off process, there is a thin (~1.6μm in thickness) residual diamond substrate on the back-face of the freestanding plate. It was found that only in the case of the X-ray incidence on the back-face, the RSM around (113) diffraction pattern displayed a long streaky pattern along the [001] direction. This indicates a gradual lattice expansion only along the growth direction. The maximum value of the lattice expansion was approximately +0.7%. Such a lattice expansion probably occurs around the interface between the thin residual substrate and the film.

Structural and optical characterization of thick and thin polycrystalline diamond films deposited by microwave plasma activated CVD

Preliminary results of growth of thin diamond film in a recently installed 3 kW capacity microwave plasma activated CVD (MW-PACVD) system are being reported. The films were deposited on Si (100) substrate at 850°C using methane and hydrogen mixture at 1·5 kW MW power. The grown polycrystalline films were characterized by micro-Raman, transmission electron microscope (TEM), spectrophotometer and atomic force microscope (AFM). The results were compared with that of a thicker diamond film grown elsewhere in a same make MW-PACVD system at relatively higher power densities. The presence of a sharp Raman peak at 1332 cm − 1 confirmed the growth of diamond, and transmission spectra showed typical diamond film characteristics in both the samples. Typical twin bands and also a quintuplet twinned crystal were observed in TEM, further it was found that the twinned region in thin sample composed of very fine platelet like structure.

Microwave plasma reactor design for high pressure and high power density diamond synthesis

The design and performance of an improved microwave plasma assisted chemical vapor deposition (MPACVD) reactor is described. This reactor operates with high power densities and at pressures up to 300torr. Differences from earlier MPACVD reactor designs [4] include an increase in applicator and dome size and the excitation of the applicator with a new “hybrid “TM0/TEM001” mode. The reactor is experimentally evaluated by synthesizing single crystal diamond (SCD) at pressures from 180 to 300torr with absorbed power densities between 400 and 1000W/cm3. Without N2 addition SCD growth rates as high as 75μm/h were observed. A SCD growth window between 950°C and 1300°C was identified and within this growth window growth rates were 1.2 to 2.5 times greater than the corresponding growth rates for earlier reactor designs. SCD characterization by micro-Raman spectroscopy, SIMS, and by IR-UV transmission spectroscopy indicated that the synthesized SCD quality is that of type IIa diamond.

Synthesis and characterization of the Gem-diamond by temperature gradient method

At pressure 5.0-5.7 GPa and temperature 1250-1600 ℃, the conditions of synthesis Gem-diamond are reported using FeNiMnCo catalyst by temperature gradient method (TGM), and the P-T phase diagram is given. Temperature field and carbon concentration gradient are simulated based on finite element method (FEM). The results of simulation and experiment show that type-I temperature field is suitable for growing high-quality large sheet-shaped Gem-diamond and small tower-shaped Gem-diamond; however, choosing type-II temperature field, both large sheet-shaped Gem-diamond and large tower-shaped Gem-diamond can be synthesized (type-Ib diamond and boron-doped diamond). On this basis, the growth speed and crystal quality are found to be determined by the carbon concentration gradient, and the rule that high-quality Gem-diamond can be synthesized when temperature field is suitable for the size and shape of diamond growing is given. The pressure and temperature regions for {110} and {113} faces to exist are studied. According to the analysis of Fourier infrared spectroscopy, it is found that the nitrogen concentrations in type-Ib and boron-doped diamonds synthesized by FeNiMnCo catalyst, which are due to the influence of Fe element, are lower than that of normal diamond. The diamond with low nitrogen can be used as an optical material with better transmission characteristics.

Boron in natural type IIb blue diamonds: Chemical and spectroscopic measurements

The presence of boron in the structure of diamond is rare in nature, and even when present, reported values are ≤0.5 ppm. This study used various spectroscopic methods and time-of-fight (ToF-) SIMS to characterize and analyze for boron in natural type IIb blue diamonds, including the well-known Hope and the Blue Heart diamonds, and on one high-pressure, high-temperature annealed natural stone. Infrared spectroscopy measurements reveal uncompensated boron values as large as 1.72 ± 0.15 ppm, which is significantly higher than the previously reported maximum of 0.5 ppm. ToF-SIMS analyses gave spot total boron concentrations as high as 8.4 ± 1.1 ppm for the Hope diamond to less than 0.08 ppm in other blue diamonds. By comparison, a type Ia diamond did not show detectable boron. ToF-SIMS analyses revealed strong zoning of boron in some diamonds, which was confirmed by mapping the uncompensated boron using synchrotron infrared spectroscopy. This greater range of boron concentrations compared to previous studies might be explained by the larger number of natural diamonds analyzed here, 78, compared to &lt;10 samples reported in the literature. The samples in this study are all gem-quality diamonds, including some Intense to Fancy-Deep blue diamonds; color intensity, however, only loosely correlates with the boron content. Boron is also likely responsible for the phosphorescence emissions of type IIb diamonds, in the red at 660 nm and in the blue-green at 500 nm. Our results are consistent with previous work suggesting that the emissions are caused by donor-acceptor pair recombination processes involving boron and other defects. The exact nature of the phosphorescence processes is still not fully understood, but likely involves complex steps of charge carrier trapping and detrapping.

ON ENABLING NANOCRYSTALLINE DIAMOND FOR DEVICE USE: NOVEL ION BEAM METHODOLOGY AND THE REALIZATION OF SHALLOW N-TYPE DIAMOND

AbstractDespite the many superior attributes of diamond, electronic device performance to date has fallen well behind theoretical expectation. The potential realization of highly efficient electronic polycrystalline diamond devices has been more than limited by certain technological challenges such as maintaining efficient/shallow n-type doping without higher density of defects or incorporation of sp2 bonded carbon as a result of doping(during ion implantation process). Specific n-type diamond reports demonstrating phosphorus doping (with activation energy reported in the range of 485 meV to 600 meV in (100) oriented systems have been particularly problematic as a lower solubility is found as compared to (111) oriented synthesis efforts, in addition to the reported self-compensating nature. Amongst the previous reports of Phosphorus-doped diamond nearly all experimental reports to date show visual crystallographic dislocation/pitting on the (100) facet with even moderate doping where dislocations have been observed to be incorporated into the bulk volume during growth. These dislocations, which are known carrier scattering sites, subsequently lower mobility rendering poor conductance and high resistivity. Due to this well-known sensitivity of phosphorus incorporation to the crystal quality, typically lower in polycrystalline than homoepitaxial films, polycrystalline-based experimental reports have been largely absent. With respect to Phosphorus in-situ doping based efforts, rendered films demonstrate both the visually identifiable pitting and electronically identifiable poor conduction characteristic, and with respect to ion beam doping efforts, complete graphitic flaking at even moderate doses (i.e. greater than 3x1017cm−3). Motivated by these shortcomings and the success of recent experimentation, we present the methodology and data from our recent successful fabrication of polycrystalline diamond P+-i-N junction (diode) with high crystal quality, high power handling capability, high current density, low threshold voltage, and ohmic contact, under room temperature operation, previously undemonstrated across all diamond material types. The superior electrical performance of the device was obtained by novel ion beam methodology designed to resolve previously unaddressed issues relating to n-type doping of diamond materials. A high current density of approximately 104 A/cm2 is attained at 20V forward bias.

Growth and High Pressure Investigation of (C&lt;sub&gt;60&lt;/sub&gt;)&lt;sub&gt;n&lt;/sub&gt;@SWNT

The (C60)n@SWNT (peapod) samples were prepared by vapor diffusion method. We performed the high pressure Raman measurements on the peapod samples by using a Mao-Bell type diamond anvil cell (DAC). In the In situ high pressure experiments, the peapod samples were exposed under UV laser line irradiation. The polymerization of C60 molecules in SWNT cave under both laser irradiation and pressure effects has been studied. The Raman spectra of the released samples from high pressure indicated that C60s form one-dimensional orthorhombic polymer. For the Raman measurements, two different excitation wavelengths were used, 325 nm laser and 830 nm laser.

Ion beam forming of a shell type natural single crystal diamond stylus and sharpening of it by swinging a conical type diamond stylus

Natural single crystal diamond is used as a source material for diamond stylus employed in instruments for surface roughness measurement, and also used as diamond probe for AFMs due to ultra-high strength, ultra-high hardness, very-low friction coefficient, and so on. During the sharpening of diamond tools, facet formations at the tip and ripple formations at the cutting face (or at the tip's face) become problematic. We have successfully employed ion beam processing for the sharpening of diamond tools with small apex angles without any formation of facet or ripples. However, the sharpening conditions are limited to small areas only. Therefore, we introduced a new technique where a sample is swung during ion beam sharpening process to expand the processed area. We applied the technique for sharpening of a conical type diamond stylus and forming of a shell type diamond stylus by 1keV Ar+ ion beam at the swing angles of ±60° and ±90° respectively. Result shows that the facet or ripples were not formed on the processed surface. A simulation method is also developed for predicting the profile changes of diamond tools during ion beam machining at different swing angles.