Type IIa Diamond Research Articles

Dedication

Dedication

Temperature effects on luminescence centers in natural type IIb diamonds

Blue diamonds are among the rarest and most valuable of naturally occurring gemstones. In this study, 12 rough naturally-sourced type IIb diamonds were subjected to HPHT annealing, three different irradiation energies, and then all were stepwise annealed from 200°C to 1100°C and the optical defects were documented by changes in phosphorescence and photoluminescence spectroscopy. Several optical features that are removed from natural type IIb diamonds by HPHT processing, such as 3H, 648.2nm peak, 776.4nm peak, and 660nm band (red) phosphorescence, can be reintroduced into these diamonds with subsequent electron irradiation and annealing at low-to-moderate temperatures. The thermal stability of these centers along with their spatial distribution provided additional insights into their configuration and distinguished them from nitrogen-bearing diamonds.

Optical and electronic properties of sub-surface conducting layers in diamond created by MeV B-implantation at elevated temperatures

Boron implantation with in-situ dynamic annealing is used to produce highly conductive sub-surface layers in type IIa (100) diamond plates for the search of a superconducting phase transition. Here, we demonstrate that high-fluence MeV ion-implantation, at elevated temperatures avoids graphitization and can be used to achieve doping densities of 6 at. %. In order to quantify the diamond crystal damage associated with implantation Raman spectroscopy was performed, demonstrating high temperature annealing recovers the lattice. Additionally, low-temperature electronic transport measurements show evidence of charge carrier densities close to the metal-insulator-transition. After electronic characterization, secondary ion mass spectrometry was performed to map out the ion profile of the implanted plates. The analysis shows close agreement with the simulated ion-profile assuming scaling factors that take into account an average change in diamond density due to device fabrication. Finally, the data show that boron diffusion is negligible during the high temperature annealing process.

Ferromagnetic-resonance induced electromotive forces in Ni81Fe19|p-type diamond

Abstract We report on direct-current (DC) electromotive forces (emfs) in a nickel-iron alloy ( Ni 81 Fe 19 ) | p -type diamond under the ferromagnetic resonance of the Ni81Fe19 layer at room temperature. The observed DC emfs take its maximum around the ferromagnetic resonant frequency of the Ni81Fe19, and their signs are reversed by reversing the direction of an externally-applied magnetic field; it shows that the observed DC emfs are spin-related emfs.

Magnetic properties of point defects in proton irradiated diamond

We investigate the magnetic properties of ultra-pure type-IIa diamond following irradiation with proton beams of ≈1–2MeV energy. SQUID magnetometry indicate the formation of Curie type paramagnetism according to the Curie law. Raman and Photoluminescence spectroscopy measurements show that the primary structural features created by proton irradiation are the centers: GR1, ND1, TR12 and 3H. The Stopping and Range of Ions in Matter (SRIM) Monte Carlo simulations together with SQUID observations show a strong correlation between vacancy production, proton fluence and the paramagnetic factor. At an average surface vacancy spacing of ≈1–1.6nm and bulk (peak) vacancy spacing of ≈0.3-0.5nm Curie paramagnetism is induced by formation of ND1 centres with an effective magnetic moment μeff~(0.1–0.2)μB. No evidence of long range magnetic ordering is observed in the temperature range 4.2-300K.

Numerical Study of Forced Convection of Nanofluid Flow Over a Backward Facing Step With a Corrugated Bottom Wall in the Presence of Different Shaped Obstacles

In this paper, a numerical study of laminar forced convection of nanofluid flow over a backward facing step with a corrugated bottom wall in the presence of different shaped obstacles placed behind the step was performed. The bottom corrugated wall of the channel downstream of the step is isothermally heated and the other walls of the channel and obstacle surface are assumed to be adiabatic. The governing equations are solved with a finite-element method. The influences of the Reynolds number (between 10 and 200), solid volume fraction of the nanoparticle (between 0 and 0.05), and obstacle type (circular, square, and diamond shaped) on fluid flow and heat transfer are numerically investigated. It is observed that among different obstacles, the diamond shaped obstacle provides better local heat transfer enhancement characteristic in the vicinity of the step compared to the circular or square obstacle at high Reynolds number. Heat transfer enhancement of 6.66% is achieved in terms of maximum values with a diamond shaped obstacle compared to the no-obstacle case of the corrugated channel. Adding an obstacle deteriorates heat transfer in terms of average values for the backward facing step geometry with a corrugated wall. When the solid volume fraction of nanoparticle is increased, maximum and average heat transfer rate increase. Heat transfer enhancements of 7.45%, 7.42%, 6.94%, and 6.64% are obtained for the average values for circle, diamond, square, and no-obstacle cases, respectively, when solid volume fraction of 0.05 is compared to pure fluid.

Friction coefficient of diamond under conditions compatible with microelectromechanical systems applications

Because of its good tribological properties, diamond has been suggested to solve the known reliability issues in silicon MEMS components submitted to frictional contacts. An evaluation of self-mating diamond friction under a low load, representative of a number of MEMS applications, was undertaken. Results have shown that initial friction coefficients of 0.02–0.05 can be achieved, as reported in the literature. However, continuation of the test for an extended period of time invariably led to a strong increase of the friction coefficient. This phenomenon has been observed with different types of diamonds (mono-, micro-, or nano-crystalline), suggesting that it is a general behavior for diamond under our experimental conditions. A micro structuration of the surface prevented this phenomenon by limiting the increase of the contact area resulting from wear.

Design of elliptically-vibrating ultrasonic actuator for nanocoining

Nanocoining is a method of rapidly creating a cylindrical mold surface covered with features smaller than the wavelength of light. This mold can then be used in a roll-to-roll process to make surfaces whose functionality depends on the wavelength of the illumination. The die replaces the typical diamond tool used to produce overlapping grooves for applications such as reflective signs. The die has a face area approximately 20μm2 that has been patterned in an FIB. It is mounted on a 2D ultrasonic actuator and follows an elliptical path that matches the surface speed of the moving workpiece during the short contact time and creates approximately 6000 features per impact. The spacing of die indents is controlled by the speed of the diamond turning machine axes such that a small overlap exists from previous indents as the die spirals around and along the mold surface. Because the die is small, the indentations must occur rapidly to make nanocoining a feasible process. This work focuses on the design and control of a nominally 40kHz, 2D resonant actuator that is suitable for this process. A controller to automatically track resonance is described to maintain the elliptical motion during indentation. Methods of tuning the behavior of the actuator and maintaining a constant indent depth are proposed. Finally, 500nm pitch feature indents were created on a brass workpiece at 40kHz and scanning electron microscope (SEM) images of the features are provided.

A novel Fe–Cr–Nb matrix composite containing the TiB2 neutron absorber synthesized by mechanical alloying and final hot isostatic pressing (HIP) in the Ti-tubing

The Fe–Cr–Ti-Nb elemental powders were mechanically alloyed/ball milled with TiB2 and a small quantity of Y2O3 ceramic to synthesize a novel Fe-based alloy-ceramic powder composite that could be processed by hot isostatic pressing (HIP) for a perceived potential application as a neutron absorber in nuclear reactors. After ball milling for the 30–80 h duration relatively uniform powders with micrometric sizes were produced. With increasing milling time a fraction of TiB2 particles became covered with the much softer Fe-based alloy which resulted in the formation of a characteristic “core-mantel” structure. For the final HIP-ing process the mechanically alloyed powders were initially uniaxially pressed into rod-shaped compacts and then cold isostatically pressed (CIP-ed). Subsequently, the rod-shaped compacts were placed in the Ti-tubing and subjected to hot isostatic pressing (HIP) at 1150 °C/200 MPa pressure. The HIP-ing process resulted in the formation of the near-Ti and intermediate diffusional layers in the microstructure of HIP-ed samples which formed in accord with the Fe-Ti binary phase diagram. Those layers contain the phases such as α-Ti (HCP), the FeTi intermetallic and their hypo-eutectoid mixtures. In addition, needle-like particles were formed in both layers in accord with the Ti-B binary phase diagram. Nanohardness testing, using a Berkovich type diamond tip, shows that the nanohardness in the intermediate layer areas, corresponding to the composition of the hypo-eutectoid mixture of Ti-FeTi, equals 980.0 (±27.1) HV and correspondingly 1176.9 (±47.6) HV for the FeTi phase. The nanohardness in the sample's center in the areas with the fine mixture of Fe-based alloy and small TiB2 particles equals 1048.3 (±201.8) HV. The average microhardness of samples HIP-ed from powders milled for 30 and 80 h is 588 HV and 733 HV, respectively.

Fabrication and characterization of boron-doped nanocrystalline diamond-coated MEMS probes

Fabrication processes of thin boron-doped nanocrystalline diamond (B-NCD) films on silicon-based micro- and nano-electromechanical structures have been investigated. B-NCD films were deposited using microwave plasma assisted chemical vapour deposition method. The variation in B-NCD morphology, structure and optical parameters was particularly investigated. The use of truncated cone-shaped substrate holder enabled to grow thin fully encapsulated nanocrystalline diamond film with a thickness of approx. 60 nm and RMS roughness of 17 nm. Raman spectra present the typical boron-doped nanocrystalline diamond line recorded at 1148 cm−1. Moreover, the change in mechanical parameters of silicon cantilevers over-coated with boron-doped diamond films was investigated with laser vibrometer. The increase of resonance to frequency of over-coated cantilever is attributed to the change in spring constant caused by B-NCD coating. Topography and electrical parameters of boron-doped diamond films were investigated by tapping mode AFM and electrical mode of AFM–Kelvin probe force microscopy (KPFM). The crystallite–grain size was recorded at 153 and 238 nm for boron-doped film and undoped, respectively. Based on the contact potential difference data from the KPFM measurements, the work function of diamond layers was estimated. For the undoped diamond films, average CPD of 650 mV and for boron-doped layer 155 mV were achieved. Based on CPD values, the values of work functions were calculated as 4.65 and 5.15 eV for doped and undoped diamond film, respectively. Boron doping increases the carrier density and the conductivity of the material and, consequently, the Fermi level.

Surface morphology and structural types of natural impact apographitic diamonds

External and internal morphologies of natural impact apographitic diamonds (paramorphoses) have been studied. The (0001) surface morphology of the paramorphoses reflects their phase composition and the structural relationship of its constituting phases. Growth and etch figures together with the elements of crystal symmetry of lonsdaleite and diamond are developed on these surfaces. The crystal size of lonsdaleite is up to 100 nm, and that of diamond is up to 300 nm. Two types of structural relations between graphite, lonsdaleite, and diamond in the paramorphoses are observed: the first type (black, black-gray, colorless and yellowish paramorphoses): the (0001) graphite face is parallel to the (100) lonsdaleite face and parallel to (111) diamond; the second type (milky-white paramorphoses): the (0001) graphite is parallel to the (100) lonsdaleite and parallel to the (112) diamond. The first type of the paramorphoses contains lonsdaleite, diamond, graphite or diamond, lonsdaleite, the second type of the paramorphoses contains predominantly diamond. The direct phase transition of graphite → lonsdaleite and/or graphite →diamond occurred in the paramorphoses of the first type. A successive phase transition graphite → lonsdaleite → diamond was observed in the paramorphoses of the second type. The structure of the paramorphoses of this type shows characteristic features of recrystallization.

Dynamic Response Analysis of a Jack-up Leg with Pile-Soil Interaction

Using the substructure method, numerical models of pile-soil interaction of diagonal and diamond types of jack-up legs were developed for dynamic response analysis. Wave and current forces acting on the leg were calculated using the modified Morison equation. Wind load was computed using the DNV formula. Modal analysis was performed to estimate the eigenvalues of the structure. The Newmark-beta method was used to calculate the dynamic behaviors of the structure in the time domain analysis. Maximum displacement and bending stress were computed for each type of leg. Reliability analysis was carried out for both types of legs to obtain a reliability index for the uncertainty of input wave periods.

Effect of depth of Buried-In Tungsten Electrodes on Single Crystal Diamond Photodetector

AbstractThe performance of new type three dimensional buried-in electrode structure ultraviolet photodetector fabricated on single crystal diamond epitaxial layer was investigated. The epitaxial layer was grown on high-pressure-high-temperature Ib-type diamond substrate. Then the buried-in electrodes with different depths were formed by oxygen plasma reactive ion etching method and radio frequency magnetron sputtering technique on this diamond layer. Compared with that of traditional planar electrode photodetector, the responsivity of buried-in electrode photodetector shows higher value, which reaches the highest when the electrode depth is 100 nm.

Studying the effect of hydrogen on diamond growth by adding C10H10Fe under high pressures and high temperatures

ABSTRACTIn this paper, hydrogen-doped industrial diamonds and gem diamonds were synthesized in the Fe–Ni–C system with C10H10Fe additive, high pressures and high temperatures range of 5.2–6.2 GPa and 1250–1460°C. Experimental results indicate similar effect of hydrogen on these two types of diamonds: with the increasing content of C10H10Fe added in diamond growth environment, temperature is a crucial factor that sensitively affects the hydrogen-doped diamond crystallization. The temperature region for high-quality diamond growth becomes higher and the morphology of diamond crystal changes from cube-octahedral to octahedral. The defects on the {100} surfaces of diamond are more than those on the {111} surfaces. Fourier transform infrared spectroscopy (FTIR) results indicate that the hydrogen atoms enter into the diamond crystal lattice from {100} faces more easily. Most interestingly, under low temperature, nitrogen atoms can also easily enter into the diamond crystal lattice from {100} faces cooperated with hydrogen atoms.

Effects of cavity size on the growth of hexahedral type-Ib gem-diamond single crystals

In the paper, using the one-seed method and multiseed method separately, the hexahedral type-Ib diamonds are synthesized in a cubic anvil under high pressure and high temperature. This cubic anvil is of 550 mm hydraulic cylinder with the sample chambers of 14 mm or 26 mm in diameter under 5.6 GPa and 1200-1400 ℃. The FeNiMnCo alloy is chosen as catalyst. The high-quality abrasive diamonds each with a diameter of 0.9 mm are used as seed crystals. High purity-graphite powder (99.99%, purity) is selected as the carbon source. The effects of cavity size on the growth of hexahedral type-Ib Gem-diamond single crystal are studied carefully. The Relationship between oil pressure and synthesis pressure is obtained in our studies. When the pressure is transmitted the same distance, in the catalyst melt, the pressure loss is less than in the pressure transmitting medium. By expanding synthesis cavity size, the pressure transmission efficiency of the oil pressure increases significantly, which can be attributed to the transmission distance shortening in the pressure transmitting medium and transmission distance lengthening in the catalyst melt. Using the 14 mm synthesis cavity, by the one-seed method, the 5 mm grade diamond single crystals of cubo-octahedral shape are synthesized, but the 5 mm grade diamond single crystals of perfectly hexahedral shape could not be synthesized. Choosing the 14 mm synthesis cavity, by the five-seed method, the 3 mm grade diamond single crystals in the center each present a perfectly hexahedral shape, but each outside of the crystals exhibits a cubo-octahedral shape. According to the application requirement for the type-Ib hexahedral diamond single crystal with a size of 3.0-3.5 mm on an industrial diamond single crystal tool, the diamond single crystals of perfect hexahedral shape are synthesized by the multiseed method. Using the 26 mm synthesis cavity, many 3 mm grade diamond single crystals of perfectly hexahedral shape are synthesized in one synthesis cavity. In our studies, up to 14 diamond single crystals of perfect hexahedral shape are synthesized in one synthesis cavity by the multiseed method. We find that the uniformity of temperature field of the 26 mm synthesis cavity is better than that of the 14 mm synthesis cavity, so the 26 mm synthesis cavity is suitable for growing 3 mm grade diamond single crystals of perfect hexahedral shape by the multiseed method. In 35 h growth time, the overall growth rate of the 26 mm synthesis cavity (25.2 mg/h) synthesizing 14 diamonds in one time (9.4 mg/h) is 2.68 times that of the 14 mm synthesis cavity by five-seed method. Moreover, the Raman spectra of the synthesized high-quality hexahedral type-Ib diamond single crystals and natural diamond single crystal indicate that the structure and quality of the synthesized high-quality diamond single crystal is better than that of a natural diamond.

Enhanced Tribological Performance of CVD Diamond Films Enabled by Using Graphene Layers as Solid Lubricant

The present study reports the influence of graphene layers on the tribological performance of CVD diamond films when they are used as the solid lubricants. Friction tests are conducted on a ball-on-plate friction tester, where the stainless steel is used as the counterpart material. The CVD diamond film sample is a typical microcrystalline diamond (MCD) coating which is deposited on a flat tungsten carbide substrate using the hot filament chemical vapor deposition method (HFCVD). Besides the MCD sample, a polished MCD film (pMCD) and a polished tungsten carbide (pWC) are also adopted in frictional tests, aiming at illustrating the influence of the surface morphology, as well as the physical property, of the sample on the lubricative effect of graphene layers. The experimental results show that graphene layers can effectively reduce the coefficient of friction (COF), regardless of the samples. The MCD sample presents the lowest stable COF, which is 0.13, in dry sliding period when the graphene flakes are sparyed on the sliding interface; while the pMCD and pWC samples exhibit slightly higher COFs, which are 0.16 and 0.18, respectively. Comparatively, the COFs of these three samples obtained in dry sliding process without graphene are 0.20, 0.25 and 0.64. In additon, the MCD sample exhibits a much longer stable dry slidng process which is more than 5000 cycles. Comparatively, the other two tribo-pairs only exhibit a stable low-COF dry sliding period for around 2000 cycles. The reduction of COF could be attributed to the graphene flakes adhered on the sliding interface. It forms a layer of solid lubricative film with extremely low shear strength and significantly decreases the interactions between two contacted surfaces. The rugged surface of the MCD film provides sufficient clogging locations for graphene flakes, which allows the generated lubricative film enduring a long sliding duration. It can be arrived from this study that the tribological properties of the MCD film could be enhanced by simply adoping graphene layers as a solid lubricant. Furthermore, an improved performance of a variety of MCD coated cutting tools or mechanical components could be expected when they are utilized with graphene layers.

Synthesis and electrical properties study of Ib type diamond single crystal co-doped with boron and hydrogen under HPHT conditions

Diamond is well known for its excellent properties, such as its hardness, high thermal conductivity, high electron and hole mobility, high breakdown field strength and large band gap (5.4 eV), which has been extensively used in many fields. However, its application in semiconductor area needs to be further understood, because it is irreplaceable by conventional semiconductor materials, especially in the extreme working conditions. In order to obtain diamond semiconductor with excellent electrical performances, diamond crystals co-doped with boron (B) and hydrogen (H) are synthesized in an FeNi-C system by temperature gradient growth (TGG) at pressure 6.0 GPa and temperature 1600 K. Fourier infrared spectra (FTIR) measurements displayed that H is the formation of sp3 CH2-antisymmetric and sp3 -CH2-symmetric vibrations in the obtained diamond. Furthermore, the corresponding absorption peaks of H element are located at 2920 cm-1 and 2850 cm-1, respectively. Hall effects measurements demonstrated that the co-doped diamond exhibited that p- type material semiconductor performance, and the conductivity of the co-doped diamond is significantly enhanced comparing tocompared with the conductivity of the B-doping diamond. The results indicated that the Hall mobility mobilities is nearly equivalent between B-doped and co-doped diamond crystals are nearly equivalent, while the concentrations of the carriers and conductivity of the co-doped diamonds are higher than those of the B-doped diamond crystals. It is also noticed that the nitrogen concentration of the co-doped diamond decreases obviously, when the H and B are introduced into the diamond structure. Additionally, the change of the conductivity is investigated by first-principles calculation. In the B-doping diamond, two impurity levels are located in the forbidden band with small gaps. These impurity states above the Fermi level couldcan trap the photo-excited electrons, while those below Fermi level can trap the photo-excited vacancies, improving the transfer of the photo-excited carriers to the reactive sites. With the H co-doped diamond, the two impurity states moved to the valance band maximum and merged into each other, which extends the valance band and improves the charge transfer efficiency. From the perspective of energy band, for the co-doped of B and N atoms co-doped diamond, the impurity states are contributed by N/B-2p states while the overlop and splitting of N/B-2p in the band gap appeared. For the H co-doped diamond, the splitting of the N/B-2p states vanishes and shifts to the lower energy level, which was due to the fact that the excess charge transferred from N to H. The calculation results above are in qualitatively agreement with experimental results. We hope that this investigation would be meaningful for the application of diamond in semiconductor field.

Surface damage mechanism of WC/Co and RB-SiC/Si composites under high spindle speed grinding (HSSG)

The surface damage mechanisms of WC/Co and Reaction-bonded SiC/Si (RB-SiC/Si) composites under high spindle speed grinding (HSSG) were investigated in the present work. Sharp edge loss and grit splintering were identified as two typical diamond wheel wear mechanisms. Plastic scratching grooves, Co extrusion and WC dislodgement were generated on the machined surface of WC/Co after grinding, while micro-pits of varied sizes at the phase boundaries and plastic scratching grooves were the main surface characteristics for RB-SiC/Si. Moreover, it was found that non-uniform surface finish at different radial positions resulted from the increase in material removal rate for both WC/Co and RB-SiC/Si, and the simulated results based on Soneys' model mostly corresponded with the measured outcomes. In addition, obvious relative wheel-workpiece vibration induced surface waviness was found, and its effect on the surface profile was analyzed for the wheel edge profile considered, which differed with that from single point diamond machining (SPDT).

Switching between two types of auxetic behavior of two-dimensional periodic cells with square rotation

Auxetic materials and related systems with negative Poisson's ratios have recently received physical and mathematical interest. Their mechanical properties induced by particular solid deformations are expected to allow remarkable advances to be made in the field of engineering. In our previous study, we proposed a structural unit that transforms into two types of diamond- and square-patterned cells and discussed its bi-stiffness property [Proc. R. Soc. A 469, 20130063 (2013)]. In this study, we applied the structural concept to a periodic framework. In numerical analyses with cell deflection, we revealed that the modified structure with periodicity has a similar switching mechanism and exhibits interesting post-switching behaviors with nonlinear elasticity.

Effects of hydrogen on diamond single crystal synthesized under high pressure and high temperature

In this paper, diamond single crystals doped with LiH and boron additives were synthesized in [Formula: see text]–[Formula: see text] system under high pressure and high temperature. Under the fixed pressure condition, we found that the synthesis temperature increased slightly after the addition of LiH in the synthesis system. The {100}-orientated surface morphology was investigated by scanning electron microscopy (SEM). The nitrogen concentration in the obtained diamond was analyzed and evaluated using Fourier transmission infrared spectroscopy (FTIR). Furthermore, the electrical properties of Ib-type and boron-doped diamond before and after hydrogenation using Hall effect measurement, which suggested that the conductivity of diamond co-doped with hydrogen and boron was obviously enhanced than that of boron-doped diamond.