CVD Diamond Plates Research Articles

Properties of near-colourless lightly boron doped CVD diamond

We report homoepitaxial growth of large sized lightly boron doped CVD diamond on HPHT diamond (100) substrates. Light boron doping was achieved by using a solid boron nitride disk as a substrate holder. Colourless boron doped diamonds with no macroscopic defects such as non-epitaxial crystallites over large areas of at least 4 × 4 mm2 and thicknesses as thin as 0.77 mm to thick layers of 1.5 mm were grown. The plates were subsequently separated from the substrates by laser cutting and polished. Hall Effect measurement at room temperature indicates that the free hole concentration, hole mobility and resistivity are ~1013 cm−3, 1550–2200 cm2 V−1 s−1 and 71–160 Ωcm, respectively. Infrared absorption spectroscopy was used to estimate the effective boron concentration in the plates. Raman/photoluminescence (λex = 514.5 nm) and UV–visible spectroscopy were used to characterize the high quality CVD diamond plates and we observe that nitrogen-related optical features are absent upon boron doping.

Wettability of Sn-Ti Alloys on Poly-Crystalline CVD Diamond Plates

In this paper,in-situwetting and spreading behaviours of the binary Sn-Ti alloys with Ti contents were investigated on poly-crystalline CVD diamond plates. The variation of contact angles at increasing temperatures indicated the wettability of Sn-Ti alloys were strongly influenced by the Ti contents. Addition of small amount of Ti (0.5 wt.%) dramatically reduced the contact angle of Sn-Ti alloys; while a relatively high Ti concentration (above 4 wt.%) induced the formation of large refractory intermetallics phase, which reduced the fluidity and impeded the spreading of Sn-Ti alloys.

Exploring constant substrate temperature and constant high pressure SCD growth using variable pocket holder depths

SCD substrates were successfully synthesized using an optimized pocket holder design. The pocket holder design creates an appropriate thermal environment to shield the diamond substrate from the intense microwave discharge. This substrate configuration allows for a polycrystalline diamond (PCD) rimless, uniform single crystal diamond (SCD) growth process. Square shaped pocket holders with a constant width but with varying depths were used. The SCD growth procedures were carried out via microwave plasma assisted chemical vapor deposition (MPACVD) in a 2.45GHz microwave cavity plasma reactor C at a constant pressure of 240Torr and high power density of ~500W/cm3. By continuously adjusting incident microwave power (Pinc), the substrate temperature (Ts) was held at 1020°C±5°C throughout the entire process cycle. Under these growth conditions, the crystal morphologies exhibited a smooth and flat surface. The average growth rate of the SCDs varied between 30 and 24μm/h as the pocket depth increased from 2.0 to 2.9mm. The PCD rim was eliminated for all pocket depths and the shape of the final, as grown, top SCD surface varied from a square to a circular shape as the pocket holder depth increased. When using the 2.0mm and 2.3mm pockets, the final top SCD surface area increased to almost twice the original HPHT diamond seed area and the lateral growth rate was slightly larger than the vertical growth rate. Birefringence imaging of the grown CVD diamond indicated low stress and SIMS analysis indicated nitrogen concentration levels in the freestanding, CVD diamond plates were in the range of 50ppb to 140ppb. Prime novelty statementSingle crystal diamond is grown by high power density, microwave plasma assisted chemical vapor deposition in a pocket holder held at a constant temperature of 1020°C, a constant pressure of 240Torr and with 5% CH4/H2. Experimental variables were pocket depth and deposition time. Thick, PCD rimless growth was achieved, and for shallow holders, top growth surface area gains of 1. 4–1.9 were demonstrated.

The diamond time of flight detector of the TOTEM experiment

This contribution describes the design and the performance of a novel timing detector developed by the TOTEM Collaboration. The detector will be installed inside the TOTEM Roman Pots (RPs) and will measure the Time-Of-Flight (TOF) of the protons produced in the central diffractive (CD) interactions at the LHC. In particular, the measurement of the proton TOF allows the determination of the vertex longitudinal position where the protons are produced, thus allowing the protons association with one of the vertices reconstructed by the CMS detectors. The TOF detector is based on single crystal CVD (scCVD) diamond plates and it is designed in order to measure the protons TOF with 50ps time resolution. To achieve this performance, a dedicated fast and low noise electronics for the signal amplification has been developed. Indeed, while diamond sensors have lower noise and faster signals than silicon sensors, the amount of charge released in the medium is lower. The digitization of the diamond signal is performed sampling the waveform at 10GSa/s with the SAMPIC chip. The performance of the first TOF detector installed in the LHC in November 2015 will be reported. An overview of the clock distribution system and of the control system which interfaces the timing detectors to the experiment DAQ is finally given.

Measurement of the complex permittivity of polycrystalline diamond by the resonator method in the millimeter range

An improved resonator method is developed, which allows for a change in the resonator coupling coefficient at insertion of the sample during the measurement of the imaginary part of the material permittivity. The method makes it possible to measure small samples. The permittivity at a frequency of 27GHz is measured for rods made of polycrystalline CVD diamond plates of 57 and 100mm in diameter grown in the microwave plasma in methane−hydrogen mixtures, and the loss tangent tan δ is determined at a level of the order of 10−3.

Diamond sensor arrays for neutron detection: Preamplifier signal dependence on sensor array configuration

Experimental verification of simulated results of series and parallel diamond detector arrays is reported. Eight commercially available electronic grade single crystal CVD diamond plates were used in series and parallel array configurations and were characterized through alpha particle and neutron exposures. It was found that a series array of diamond detectors is inherently limited due to the impedances of the diamond plates. Plutonium–beryllium neutron exposures were conducted with each of these diamond plates and on a parallel array of all eight diamond plates. It was found that the detection efficiency scaled linearly with the number of plates and that the pulse height from the preamplifier was not affected by the parallel array configuration. However, the additional capacitance introduced to the charge sensitive preamplifier indicates that there is a limitation to the total size that can be realized with a parallel diamond sensor array before significant signal degradation occurs.

On the Diffusion Profile at the Brazed Interface between Active Filler Metal and CVD Diamond Plates

Diamonds films have characteristics that are interesting for many optical applications, such as transparency to ultraviolet, visible and infrared light. These applications include use in detectors and windows in processes that involve high temperatures, microelectronics applications and wear-resistant components [. Polycrystalline diamond films can be made in the vapor phase at low-pressure, relatively low temperatures and in the form of auto-supported films, using the CVD process (Chemical Vapor Deposition) [. These films have a significant number of industrial applications, but often have problems with adhesion to metallic substrates. Diamond films can be deposited directly over some metals, but other techniques, such as brazing, can be used [.

Strength of optical quality polycrystalline CVD diamond

The three-point loading method is used to the measure the fracture strength σ f of polycrystalline CVD diamond plates with thickness in the range of h = 0.06–1.0 mm. Optical quality samples grown in a microwave plasma using CH4-H2 gas mixtures show an inherently nonuniform structure, the crystallite size varying (increasing) by 1–2 orders of magnitude in traversing from the substrate side to growth side. The value of σ f approaches ≈ 2200 MPa for the thinnest film when the fine-grained (substrate) side is under tensile stress, reducing with plate thickness down to ≈ 600 MPa at h ≈1000 μm. The strength is approximately a factor of two lower for the substrate side under tensile stress. In general, the material tested follows Hall-Petch relationship—a stress increase with grain size reduction. The fracture statistics are analyzed using a Weibull distribution, and a Weibull modulus m of 6.4 and 4.5 is found for the growth and substrate side under tension, respectively. Young’s modulus E = 1072 ± 153 GPa for polycrystalline diamond is evaluated from the same tests.

Diamond X-ray Photodiode for White and Monochromatic SR beams.

High purity, single crystal CVD diamond plates are screened for quality and instrumented into a sensor assembly for quantitative characterization of flux and position sensitivity. Initial investigations have yielded encouraging results and have led to further development. Several limiting complications are observed and discussed, as well as mitigations thereof. For example, diamond quality requirements for x-ray diodes include low nitrogen impurity and crystallographic defectivity. Thin electrode windows and electronic readout performance are ultimately also critical to device performance. Promising features observed so far from prototype devices include calculable responsivity, flux linearity, position sensitivity and timing performance. Recent results from testing in high flux and high speed applications are described.

Large Single Crystal Diamond Plates Produced by Microwave Plasma CVD

Recent developments in producing large single crystal CVD diamond plates are reviewed. The developments consist of synthesis of large single crystal diamond and production of single crystal diamond plates from the bulk diamond by the lift-off process. Combining these developments, half-inch single crystal CVD diamond plates have been successfully produced.

Measurement of optical absorption in polycrystalline CVD diamond plates by the phase photothermal method at a wavelength of 10.6 μm

A highly-efficient phase photothermal method is developed for quantitative measurements of the small optical absorption coefficient in thin plates made of highly transparent materials in which bulk losses significantly exceed surface losses. The bulk absorption coefficient at 10.6 μm is estimated in polycrystalline diamond plates grown from the vapour phase (a CVD diamond). The results are compared with those for natural and synthetic diamond single crystals and with the concentrations of nitrogen and hydrogen impurities. The absorption coefficient of the best samples of the CVD diamond did not exceed 0.06 cm-1, which, taking into account the high thermal conductivity of the CVD diamond (1800–2200 W mK-1 at room temperature), makes this material attractive for fabricating output windows of high-power CO2 lasers, especially for manufacturing large-size optics.

Dry machining of silicon–aluminium alloys with CVD diamond brazed and directly coated Si 3N 4 ceramic tools

Silicon–aluminium alloys (Al–Si), with Si contents up to 20%, are important materials in automotive and aeronautical industries due to their low density and high wear resistance. The turning of these alloys has been done mainly by superhard tools like polycrystalline diamond (PCD). CVD diamond either as thin coatings on silicon nitride ceramics or as thick brazed tips on hard metals is alternative material. In this work, CVD diamond thin films were grown on Si 3N 4 ceramic substrates and thick CVD diamond plates were brazed onto WC–Co tools. These different inserts were used in dry turning of silicon–aluminium alloys with 12 wt% and 18 wt% Si. Both directly diamond coated and brazed tools are able to machine the Al-12 wt% Si alloy with negligible wear. In turning of Al-18 wt% Si, sharp edged tools yield lower cutting forces than the chamfered ones, with the occurrence of tool failure at about 500 and 100 m, respectively. CVD brazed tools proved to be able for dry turning this hypereutectic alloy, keeping the cutting forces below 60 N. Minimal wear was observed after 1500 m of cutting length, mainly caused by diamond chipping at the flank face.

Synthesis of large single crystal diamond plates by high rate homoepitaxial growth using microwave plasma CVD and lift-off process

A process of making a large, thick single crystal CVD diamond plates has been developed. This process consists of high rate homoepitaxial growth of CVD diamond and subsequent lift-off process using ion implantation. By using this process, single crystal CVD diamond plates with the size of about 10 × 10 × 0.2–0.45 mm 3 have been successfully fabricated. The crystallinity of the CVD diamond plates has been evaluated by X-ray topography, polarized light microscopy and high resolution X-ray diffraction. The results indicate the pretreatment of the seed substrate has strong effect on the crystallinity of the CVD diamond plates.

Single Crystal CVD Diamond growth and characterizations

ABSTRACTDue to its radiation harness, single crystal CVD diamond is a remarkable material for the construction of detectors used in hadron physics and for medical therapy. In this work, single crystal CVD diamond plates were grown in a microwave plasma reactor, using home design substrate holder and a relatively high pressure. Optical Emission Spectroscopy was employed during the MW-PECVD growth to characterize excited species present in the plasma and to detect the presence of residual gases such as nitrogen which is unsuitable for detector's applications.The samples were characterized using various methods such as Raman spectroscopy, photoluminescence (PL), photocurrent spectroscopy, Raman mapping, birefringence microscopy, optical microscopy and also AFM. The best sample, exhibits a FWHM for the 1332 cm−1 Raman peak about 1.6 cm−1. Room temperature PL spectra showed no N–related luminescence, confirming the high quality of the grown single crystal diamond.

N-type P-doped polycrystalline diamond

Here we present first data on P-doped polycrystalline diamond prepared by in-situ doping with phosphine. By optimisation of the growth conditions and use of polished polycrystalline CVD diamond plates we were able to incorporate P actively in the grains of polycrystalline films and to prepare n-type diamond, as confirmed by Hall measurements. We studied the P-incorporation in variously oriented grains by cathodoluminescence. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The absorption investigation in CVD-diamond plates and windows at 50–200 GHz

Absorption investigations into a number of CVD-diamond plates, as well as absorption investigations into the output windows of megawatt gyrotrons in the range of frequencies 50–200 GHz have been carried out. Significant additional surface absorption was found and its influence was defined. The theory for measurement of this additional absorption was developed. The possible mechanism of microwave absorption in CVD-diamond is briefly discussed.

Diamond windows and domes: flexural strength and thermal shock

Ring-on-ring flexural strength measurements performed on free-standing specimens of chemically vapor-deposited (CVD) diamond indicate that if fracture originates at the nucleation surface, the strength is thickness independent and best described as follows: characteristic strength of approximately 300 MPa; and a Weibull modulus of approximately three. In a test configuration that puts the growth surface in tension, the strength decreases with increasing thickness and drops to less than 100 MPa for specimens thicker than 0.5 mm. These strengths are much lower than anticipated and therefore, invalidate earlier speculations on the thermal shock resistance capability of CVD-diamond windows and domes. The purpose of this contribution is to evaluate the results of strength measurements and to provide an updated assessment of the thermal shock performance. In this context, it is essential to keep in mind that the transient stress intensity critically depends on the nature of the heat flow as characterized by the Biot number. Considering that any viable sensor window must also be able to withstand the mechanical stresses induced by aerodynamic pressure, it is demonstrated that in a thermally thin regime, CVD-diamond plates or shells have unmatched figures of merit, which is of significance because presently available infrared-transmitting window/dome materials for the long-wavelength IR may not be able to handle the thermo-structural loads encountered on projected flight trajectories.

Wettability studies of reactive brazing alloys on CVD diamond plates

Wettability of both the diamond and the insert surfaces by the filler metal in CVD diamond brazed-on cutting tools is a key condition for good brazing strength. The brazing process of CVD diamond thick plates still has to be improved, namely on the influence of the brazing alloy composition and of the substrate surface finishing quality in wettability. In this study, contact angle measurements were performed in a dedicated high vacuum furnace coupled with a video recording system. Diamond films with different thickness (75<t<300 μm), and thus having distinct grain sizes and roughness, were grown with fixed conditions by the MPCVD technique on Si substrates and chemically detached for wettability experiments. Roughness parameters were evaluated by profilometry and AFM, which was used to observe the grown diamond surfaces of the self-standing films. The reactive Ag–Cu–Ti brazing system was investigated. Results showed a very good wettability in the temperature range 800–850°C, namely for the diamond surface where a minimal contact angle of 10° was reached. A Ti-rich thin reaction layer (0.5–0.8 μm) was detected at the drop side of the substrate/brazing alloy interface in both substrate materials, proving the affinity of Ti to carbon. The influence of the diamond roughness on the contact angle θR is notable, obeying a linear dependence of the type cosθR=cosθ0+k cosθ0·(Ra/G)2, where Ra and G, the grain size, are related to asperity height and width, respectively. This relationship is based on the well-known Wenzel equation that correlates the real contact angle to the surface area increasing with roughness.

Laser machining of CVD diamond: chemical and structural alteration effects

Nd:YAG laser (1064 nm) and ArF laser (193 nm) surface machining of 400 μm thick, free-standing CVD diamond plates produced photon interaction zones which were chemically and structurally altered. A significant H loss and change in CC bonding environment were observed in the Nd:YAG laser-processed specimens, while ArF laser processing exhibited less H depletion and structural alteration on a less extensive spatial scale. These results are related to the different interaction mechanisms of Nd:YAG and ArF laser photons with diamond.

Laser damage testing of CVD-grown diamond windows

Laser-induced damage threshold (LIDT) measurements have been made on bulk polycrystalline (BP) CVD diamond plates using 0.532, 1.06 and 10.6 μm radiation and compared with measurements on natural type IIa diamond samples. Using 10.6 μm radiation, damage thresholds for BP CVD diamond have been measured as 5.6–12.7 MW mm −2 (29–66 J cm −2) using a 50 ns laser spike. These values compare with measurements in type IIa diamond of 12.5–18.5 MW mm −2 made in this study, and values of 3.5–40 MW mm −2 reported elsewhere. The LIDTs measured show a strong correlation with bulk absorption, which is significant at 0.532 μm, and with sample surface finish, but poor correlation with the carbonaceous inclusions found in the samples. Extrapolation from the d.c. dielectric breakdown threshold to the time domain of interest would suggest that, in both current CVD diamond and type IIa single-crystal natural diamond, the damage threshold is being substantially reduced by material or sample imperfections.