Pure Diamond Research Articles

Comparison of α particle detectors based on single-crystal diamond films grown in two types of gas atmospheres by microwave plasma-assisted chemical vapor deposition

Chemical vapor deposition (CVD)-grown diamond films have been developed as irradiation-resistant materials to replace or upgrade current detectors for use in extreme radiation environments. However, their sensitivity in practical applications has been inhibited by space charge stability issues caused by defects and impurities in pure diamond crystal materials. In this study, two high-quality CVD-grown single-crystal diamond (SCD) detectors with low content of nitrogen impurities were fabricated and characterized. The intrinsic properties of the SCD samples were characterized using Raman spectroscopy, stereomicroscopy, and X-ray diffraction with the rocking curve mode, cathode luminescence (CL), and infrared and ultraviolet-visible-near infrared spectroscopies. After packaging the detectors, the dark current and energy resolution under α particle irradiation were investigated. Dark currents of less than 5 pA at 100 V were obtained after annealing the electrodes, which is comparable with the optimal value previously reported. The detector that uses a diamond film with higher nitrogen content showed poor energy resolution, whereas the detector with more dislocations showed poor charge collection efficiency (CCE). This demonstrates that the nitrogen content in diamond has a significant effect on the energy resolution of detectors, while the dislocations in diamond largely contribute to the poor CCE of detectors.

Calculation of Surface Properties of Cubic and Hexagonal Crystals through Molecular Statics Simulations

Surface property is an important factor that is widely considered in crystal growth and design. It is also found to play a critical role in changing the constitutive law seen in the classical elasticity theory for nanomaterials. Through molecular static simulations, this work presents the calculation of surface properties (surface energy density, surface stress and surface stiffness) of some typical cubic and hexagonal crystals: face-centered-cubic (FCC) pure metals (Cu, Ni, Pd and Ag), body-centered-cubic (BCC) pure metals (Mo and W), diamond Si, zincblende GaAs and GaN, hexagonal-close-packed (HCP) pure metals (Mg, Zr and Ti), and wurzite GaN. Sound agreements of the bulk and surface properties between this work and the literature are found. New results are first reported for the surface stiffness of BCC pure metals, surface stress and surface stiffness of HCP pure metals, Si, GaAs and GaN. Comparative studies of the surface properties are carried out to uncover trends in their behaviors. The results in this work could be helpful to the investigation of material properties and structure performances of crystals.

TRIBOLOGICAL PROPERTIES OF THE CARBON AND NITROGEN-BASED HARD FILMS SLIDING AGAINST THE NICKEL-BASED SUPERALLOY

This study is focused on the tribological properties of micro- and nano-crystalline diamond (MCD and NCD), non-hydrogenated and hydrogenated diamond-like carbon (DLC and DLC-H) and nitrogen-based (CrN, TiN and TiAlN) coatings sliding against the super alloy Inconel 718, in terms of the maximal and average coefficients of frictions (COFs), the worn morphologies and the specific wear rates, by the rotating ball-on-plate configuration under dry condition. The results show that the nitrogen-based films show comparable COFs and wear rates with the WC–Co substrates. The DLC and DLC-H show lower COFs compared with the nitrogen-based films. Furthermore, their wear resistance is limited due to their low thickness compared with MCD and NCD, which have the same elemental composition. The DLC-H coating exhibits much lower wear rate compared with the DLC coating, which may be derived from the passivation of dangling bonds by the linking of H to C atoms. The MCD and NCD films show the lowest average COFs and mild wear after tribotests, due to their high hardness and low adhesive strength between pure diamond and the super alloy. Among all the tested films, the NCD film-based tribopair presents the lowest maximal and average COFs, tiny wear debris particles, mild wear of ball and plate without scratching grooves, indicating that the NCD film may be suitable to be deposited on cutting tools for super alloy machining.

Effects of compound diamond slurry with graphene for lapping of sapphire wafers

Recently, sapphire has been used in a wide range of applications including optics, consumer electronics, and especially the rapidly growing LED wafer manufacturing. This paper investigates effects of a novel compound slurry composed of micron scaled diamond abrasives and various nano-platelets of graphene oxide (GO) for improving lapping performance of c-plane single-crystal aluminum oxide (Al2O3) sapphire wafers. Four kinds of graphenes including GO, reduced graphene oxide (RGO), ML-RGO (laminate), and MF-RGO (few-layer) are added into the diamond slurry to achieve compound slurries. Those compound slurries have been prepared with various graphene weight fractions in the range of 0.3 to 2.0 wt%, by LP (low power) or HP (high power) ultrasonication with different time spans in the range of 10 min to 48 h to adjust size of GOs. For the lapping process conducted by 10-min HP ultrasonicated GO (2.0 wt%)/diamond slurry, combination of medium down force pressure and the highest platen rotation speed of 45 kPa/80 rpm results in highest material removal rate (MRR) of 926.73 nm/min, which is 324% higher than MRR by pure diamond slurry. It is caused by high reactivity of GOs with sapphire wafer. As lapped at pressure/speed of 45 kPa/70 rpm by ultrasonicated GO (0.5 wt%)/diamond compound slurry, the average surface roughness Ra of wafer can reach 7.19 nm, which is 0.7% lower than 7.24 nm by pure diamond slurry. Experimental results demonstrate that the optimized planarization of sapphire wafer with high MRR and low surface roughness can be achieved using the GO compound slurry when the mechanical removal effect and the chemical reaction mechanism are in synergistic equilibrium. The XPS and EDS analyses clearly support the material removal model that a reactant aluminum carbonate layer and a residual carbon layer exist and both are efficiently removed by diamond abrasives. Results of this study can be applied to further explore high volume production of CMP of sapphire wafers.

First-principles calculations of co-doping impurities in diamond

Diamond co-doping with B and P, As atoms are investigated separately by using first-principles density functional theory (DFT) based on the stable structure of diamond. The formation energy and ionization energy corresponding to all doping diamond are studied. And the most stable co-doping structures with the lowest formation energy are obtained. Besides, the band structures and the densities of states of the doping diamond are discussed. It can be found that the double-acceptor-donor center complexes and acceptor-donor-acceptor center complexes are more likely to be formed than the donor-acceptor-donor center complexes and acceptor-double-donor center complexes. The introduction of B atoms can improve the solubility of P and As impurities in diamond. It is also found that the intermediate band minimum and the valence band maximum are located at the same k-point of G. Compared with pure diamond, the direct bandgap of co-doping impurities in diamond is reduced. Ionization energies of diamond with double-acceptor-donor center complexes are much smaller than that of the B-doping diamond. This indicates that B-B-As and B- B-P co-doping complexes structures are a better choice for the p-type diamond.

First‐Principles Studies of Ti‐Related Defects in Diamond

The transition metal‐related centers of diamond exhibit good properties. Herein, a first‐principles method based on density functional theory (DFT) is used to study single‐doped Ti‐related point defect structures and codoped structures of Ti and B or N, which possibly exist in diamond; the electronic structure and formation energy are also calculated. The results from structural calculations show that Ti is more likely to be located adjacent to a vacancy to form a TiV structure, which is more stable than other configurations. Ti doping introduces impurity levels into the pure diamond band gap, and the possible energy level transitions are determined. The results from the calculations of the codoped system show that the incorporation of N or B atoms is beneficial for the formation of defect structures and that the incorporation of N optimizes the energy band structure of the defects. When a substitutional Ti atom is located adjacent to a B atom and forms a Ti–B structure, and when four N atoms replace the corresponding neighboring C atoms around TiV to form a TiV–4N structure (which is similar to the NE8 configuration), the structure shows a better energy band structure, which presents new color centers.

Diamond Thin Film Coating on WC Substrate by HFCVD Method using Different Seeding Powders and Its Characterization

The formation of diamond thin solid film is studied by Hot Filament Chemical Vapor Deposition (HFCVD) by using different seeding powders on WC substrate. Here, we have deposited microcrystalline diamond (MCD) on SPUN cemented carbide (WC-Co) cutting tool insert using conventional HFCVD technique. The substrates were ultrasonically seeded with titanium, tungsten, molybdenum, diamond, combined diamond and tungsten powder at the same operation parameters to observe the difference in the growth of diamond by different seeding. Nucleation of diamond coating was studied after 40 minutes of coating with seeded substrate. The physical characteristics were studied by X-ray Diffraction (XRD).The Scanning Electron Microscope (SEM) was used to study the surface morphology. The diamond purity was studied with the help of Raman spectroscopy (RS). Reduction of cobalt percentage before and after pretreatment was studied by Energy Dispersive Spectroscopy (EDS). A very dense and uniform coating was deposited on the diamond powder seeded substrate. The nucleation density was found to be highest in diamond powder when compared with molybdenum and tungsten powder individually, because in initial stage the deposited material contains more sp2 content as compared to sp3 content. By using diamond and tungsten mixed powder the coating was uniform rather in case of only tungsten powder coating the discrete crystals were formed.

Fabrication and microstructural characterization of the diamond@amorphous carbon nanocomposite core/shell structure via in-situ polymerization

A novel diamond@carbon core/shell structure, constituting diamond as a hard core and carbon as a soft shell, was synthesized from resole resin and nanodiamond as the starting materials via in-situ polymerization and subsequently high-temperature carbonization. The diamond@carbon nanocomposite was characterized using field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectra, and Fourier transform infrared spectroscopy (FT-IR). The results indicated that the shell material are comprised of amorphous carbon. The thickness of carbon shell was controlled from 502.5 nm to 27 nm by adjusting the concentration of the nanodiamond. As confirmed by TEM, FT-IR and XPS, the diamond@carbon nanocomposite revealed a stable structure, due to the formation of the chemical bonding between diamond and carbon shell after calcination process. Overall, the diamond@carbon nanocomposite abrasives could lead to a reducted surface roughness and damage of SiC wafer comparing with the nanodiamond abrasives, due to the spring-like effect coming from the elastic component of the amorphous carbon shell. Moreover, the as-prepared nanoparticles exhibited better dispersion stability than the pure diamond in the pH range from 8 to 11. • Core/shell structured diamond@carbon, was synthesized via in-situ polymerization then high-temperature carbonization. • Core/shell structured diamond@carbon comprises of nanodiamond as a hard core and carbon as a soft shell. • The thickness of carbon shell was controlled from 502.5 to 27 nm by adjusting the concentration of the nanodiamond. • The composite abrasives led in a decreased surface roughness and surface damage compared with nanodiamond.

Direct conversion of carbon nanofibers into diamond nanofibers using nanosecond pulsed laser annealing.

Here, we show the direct conversion of carbon nanofibers (CNFs) into diamond nanofibers (DNFs) by irradiating CNFs with an ArF nanosecond laser at room temperature and atmospheric pressure. The nanosecond laser pulses melt the tips of CNFs into a highly undercooled state, and their subsequent quenching results in the formation of DNFs. This formation of DNFs is dependent on the degree of undercooling which is controlled by nanosecond laser energy density and one-dimensional heat flow characteristics in CNFs. The conversion process starts at the top and extends with the number of pulses. Therefore, our highly non-equilibrium nanosecond laser processing opens a new avenue for the synthesis of exciting pure and doped diamond structures at ambient temperatures and pressures for a variety of applications.

Boron-doped diamond with improved oxidation resistance

The oxidation behavior of pure and 0.2 wt% B-containing diamond powders was investigated by thermal analysis, SEM analysis, and Raman spectroscopy of partially oxidized diamonds. Boron-doped diamond exhibited a much higher oxidation stability than that of pure diamond. The maximum oxidation rate shifted from 773 °C for the pure diamond to 1118 °C for the B-doped diamond. SEM analysis of the surface of the partially oxidized diamonds revealed that the low boron content (0.2%) was sufficient for the formation of a protective B2O3 surface layer in the regions in which active oxidation took place. This layer was most probably the reason for the improved oxidation resistance.

DesigningOptimalBiasVoltageforRadiotherapy Diamond Dosimeter

Introduction: Recent developments of radiotherapy techniques, require high accuracy detectors to determine the delivered dose in a small area. Chemical vapor deposition (CVD) or naturally growth diamond detectors which are commercially available are good candidates for this purpose. In these detectors two electrodes with high different electrical potential are deposited on both sides of a diamond, and the incident radiation generates a current which indicates absorbed dose. However, the large band gap makes diamond an excellent electrical insulator, but care must be taken to eliminate the air ionization contribution to the photocurrent. For this reason, the device must operate in vacuum. In the other hand, patient’s safety needs a decrease in detector’s voltage. In this simulation study, it is indicated that the applied voltage can be decreased to about 50[V] without loss of dosimeter’s sensitivity. Materials and methods: In this work Weightfield2 software, which is a program to simulate current signals in a silicon or diamond detector was used. This program uses GEANT4 libraries to simulate the energy released by an interacting particle. Minimum Ionizing Particle (MIP) with a 250 micrometers thick pure diamond was used and then the bias voltage was increased from 1 [V] to 500 [V], then the curve of time response and current response of the sensor was observed as a function of bias voltage. Results: The results indicate that the applied voltage can reduce up to about 50 [V] with a reasonable 40 [ns] time response. This can be achieved by the benefit of high accuracy and fast Analog to Digital Converters (ADCs). Conclusion: With new generation of synthetic diamonds known as single crystal CVDs, which their characteristic is very similar to natural diamond, and with modern electric measuring devices, in contrast to the current sensors, it is possible to reduce the applied voltage of dosimeter electrodes to about 50 [V].

Thermal conductivity enhancement of phase change materials with 3D porous diamond foam for thermal energy storage

For thermal energy storage applications using phase change materials (PCMs), the power capacity is often limited by the low thermal conductivity (λPCM). Here, a three-dimensional (3D) diamond foam (DF) is proposed by template-directed chemical vapor deposition (CVD) on Cr-modified Cu foam as highly conductive filler for paraffin-based PCM. Results showed the foam substrate was completely covered by continuous diamond films with high quality. And it showed a faster thermal response than that of Cu foam (CF) and Cu disc, while only a little slower than that of free-standing diamond disc with the same thickness. The incorporation of interconnected diamond foam with the diamond volume fraction of only 1.3% in the composite phase change material represented a great thermal conductivity enhancement over the pure paraffin, CF/paraffin and diamond particles reinforced paraffin by a factor of 25.8, 1.62 and 13.88, respectively. The great enhancement of the thermal conductive property was mainly attributed to interconnected diamond networks with high thermal conductivity, which effectively reduced the phonon-phonon and phonon-boundary scatterings. Besides, the DF/paraffin composite PCM exhibited an improved shape stability and a fast heat charging rate with the latent heat of 124.7 J/g. The marriage of the excellent properties of diamond and the inherent advantages of the 3D interconnected structure makes the diamond foams potential components or act as reinforcements in the field of high-efficiency heat dissipation and thermal energy storage.

Precision micro-mechanical components in single crystal diamond by deep reactive ion etching

The outstanding material properties of single crystal diamond have been at the origin of the long-standing interest in its exploitation for engineering of high-performance micro- and nanosystems. In particular, the extreme mechanical hardness, the highest elastic modulus of any bulk material, low density, and the promise for low friction have spurred interest most notably for micro-mechanical and MEMS applications. While reactive ion etching of diamond has been reported previously, precision structuring of freestanding micro-mechanical components in single crystal diamond by deep reactive ion etching has hitherto remained elusive, related to limitations in the etch processes, such as the need of thick hard masks, micromasking effects, and limited etch rates. In this work, we report on an optimized reactive ion etching process of single crystal diamond overcoming several of these shortcomings at the same time, and present a robust and reliable method to produce fully released micro-mechanical components in single crystal diamond. Using an optimized Al/SiO2 hard mask and a high-intensity oxygen plasma etch process, we obtain etch rates exceeding 30 µm/h and hard mask selectivity better than 1:50. We demonstrate fully freestanding micro-mechanical components for mechanical watches made of pure single crystal diamond. The components with a thickness of 150 µm are defined by lithography and deep reactive ion etching, and exhibit sidewall angles of 82°–93° with surface roughness better than 200 nm rms, demonstrating the potential of this powerful technique for precision microstructuring of single crystal diamond.

Silver nanoparticles supported on graphitization micro-diamond as an electrocatalyst in alkaline medium

Graphitization micro-diamond composites are prepared by spark plasma sintering and which was modified by Ag nanoparticles subsequently. The samples are characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller analysis and Raman spectroscopy. Results show that the 1400-15 min diamond/graphite composite with core/shell structure has a more suitable thickness of graphite layer than other sintered samples. The silver nanoparticles are dispersed on the surface of graphitization micro-diamond in the form of elemental silver, with a size of approximately 15 nm. Electrocatalyst activities are investigated by cyclic voltammetry, linear sweep voltammetry, chronoamperometry and electrochemical impedance spectroscopy techniques. The test of the rotating disk electrode reveals the electrons transfer number of Ag/1400-15 min is about 3.90. Compared with pure micro diamond and 1400-15 min diamond/graphite composite, Ag/1400-15 min composites shows superior electrocatalytic activity and durability because of Ag particles facilitating charge transfer, and the core/shell structure of diamond/graphite can provide more active sites during the electrochemical reaction. The present results highly promise the silver-modified graphitization micro-diamond composite as a potential electrocatalyst.

Reduction of Thermal Conductivity in Nanowires by Combined Engineering of Crystal Phase and Isotope Disorder.

Nanowires are a versatile platform to investigate and harness phonon and thermal transport phenomena in nanoscale systems. With this perspective, we demonstrate herein the use of crystal phase and mass disorder as effective degrees of freedom to manipulate the behavior of phonons and control the flow of local heat in silicon nanowires. The investigated nanowires consist of isotopically pure and isotopically mixed nanowires bearing either a pure diamond cubic or a cubic-rhombohedral polytypic crystal phase. The nanowires with tailor-made isotopic compositions were grown using isotopically enriched silane precursors 28SiH4, 29SiH4, and 30SiH4 with purities better than 99.9%. The analysis of polytypic nanowires revealed ordered and modulated inclusions of lamellar rhombohedral silicon phases toward the center in otherwise diamond-cubic lattice with negligible interphase biaxial strain. Raman nanothermometry was employed to investigate the rate at which the local temperature of single suspended nanowires evolves in response to locally generated heat. Our analysis shows that the lattice thermal conductivity in nanowires can be tuned over a broad range by combining the effects of isotope disorder and the nature and degree of polytypism on phonon scattering. We found that the thermal conductivity can be reduced by up to ∼40% relative to that of isotopically pure nanowires, with the lowest value being recorded for the rhombohedral phase in isotopically mixed 28Si x30Si1- x nanowires with composition close to the highest mass disorder ( x ∼ 0.5). These results shed new light on the fundamentals of nanoscale thermal transport and lay the groundwork to design innovative phononic devices.

Application of rocking-scan method to detect the low-content diamonds in a complex mixture

A method for detecting large-size diamonds with low content in a complex mixture was described. Phase identification via conventional X-ray diffraction method is unsuitable because of the large-size and low-content characteristics of the diamonds. Thus, we proposed a convenient approach (i.e., rocking scan) for assessing the presence of low-content diamonds in a complex mixture. A thorough rocking scan of the (111), (220), and (311) planes revealed the presence of low-content diamonds prepared by reducing dense carbon dioxide with alkali metals. This procedure can be successfully applied to several standard mixture samples prepared by mixing α-SiO2, α-Al2O3, graphite, and pure diamond powders, which are commercially available. We estimated that the detection limit was at or below the 0.1 wt% level by using the proposed method under the current condition. This method is straightforward, routinized, and may be specifically developed to satisfy the requirements of public and private institutions for a rapid identification of other mixture phases, of which the large-size and low-content characteristics do not allow an instant phase identification by conventional X-ray diffraction methods.

Structural and electronic properties of two-dimensional (110) diamond nanofilms by first-principles calculations

Based on the first-principles calculations, we investigate the structural and electronic properties of pure and hydrogenated two-dimensional (2D) (110)-oriented diamond nanofilms related to the layer number (n). After structural optimization, for the pure (110) diamond nanofilms at n = 1 and 2, the original buckling 2D diamonds reconstruct into the planar graphene. For the pure 2D diamond films at n ≥ 3 and the cases of semi-hydrogenated and full-hydrogenated 2D diamond nanofilms, the original diamond structures are energetically favorable to be maintained. The calculated electronic properties of these optimized structures show that the pure and semi-hydrogenated 2D diamond nanofilms have metallic characteristics, and the full-hydrogenated structures are semiconductors. It theoretically demonstrates that the n and surface functionalization could effectively modulate the structural and electronic properties of the 2D atomically thick (110) diamond nanofilms, revealing their applications in numerous practical fields especially fabricating low-dimensional optoelectronic devices.

N-type B-S co-doping and S doping in diamond from first principles

The S-doped diamond and B-S co-doped diamond at different concentrations were investigated by the density functional theory (DFT) to explore the possibility to achieve effective and shallow donors in diamond. We found for the first time that the Valence Band maximum (VBM) and the Intermediate Band (IB) minimum of B-S co-doped diamond are located at the same κ-point Γ, which is quite different from the indirect energy gap of S-doped diamond and pure diamond. Although the simulated ionization energy of B-S defect is deeper than that of S defect, the impurities formation energy is much lower than that of S defect. It suggests that the introduction of B help improve the solubility of S in diamond. Besides, the electron effective mass of IB of B-S co-doped diamond is much smaller than that of the S-doped diamond, which may lead to conductivity promotion for diamond. Comparison of the density of states in both cases, it is found that the S-3p states are responsible for conduction band, as well as the B-2p states of B-S co-doped diamond have a little contribution to its conduction band. It can conclude that with the assistance of B, S is a suitable shallow donor impurity in diamond.

Hardness and thermal stability enhancement of polycrystalline diamond compact through additive hexagonal boron nitride

Hexagonal boron nitride (hBN) was used as the additive in improving the hardness and thermal stability of polycrystalline diamond compact under high temperature and high pressure. Indentation testing on diamond/cubic boron nitride (cBN) composites indicated a Vickers hardness of 96±7GPa, rivaling the hardness of monocrystal diamond. Thermal gravimetric analysis (TGA) suggested that the composites of diamond/cBN are thermally stable in air up to ∼910°C which is higher than that of pure polycrystalline diamond compact (∼750°C). Raman, TGA, x-ray photoelectron spectroscopic and microstructure analyses all revealed the features of diamond/cBN composition beyond both diamond and cBN.

Controlling Directional Liquid Motion on Micro- and Nanocrystalline Diamond/β-SiC Composite Gradient Films

In this Article, we report the synthesis of micro- and nanocrystalline diamond/β-SiC composite gradient films, using a hot filament chemical vapor deposition (HFCVD) technique and its application as a robust and chemically inert means to actuate water and hazardous liquids. As revealed by scanning electron microscopy, the composition of the surface changed gradually from pure nanocrystalline diamond (hydrophobic) to a nanocrystalline β-SiC surface (hydrophilic). Transmission electron microscopy and Raman spectroscopy were employed to determine the presence of diamond, graphite, and β-SiC phases. The as-prepared gradient films were evaluated for their ability to actuate water. Indeed, water was transported via the gradient from the hydrophobic (hydrogen-terminated diamond) to the hydrophilic side (hydroxyl-terminated β-SiC) of the gradient surface. The driving distance and velocity of water is pivotally influenced by the surface roughness. The nanogradient surface showed significant promise as the lower roughness combined with the longer gradient yields in transport distances of up to 3.7 mm, with a maximum droplet velocity of nearly 250 mm/s measured by a high-speed camera. As diamond and β-SiC are chemically inert, the gradient surfaces can be used to drive hazardous liquids and reactive mixtures, which was signified by the actuation of hydrochloric acid and sodium hydroxide solution. We envision that the diamond/β-SiC gradient surface has high potential as an actuator for water transport in microfluidic devices, DNA sensors, and implants, which induce guided cell growth.