Polycrystalline Chemical Vapor Deposition Diamond Research Articles

Development of the Beam Conditions Monitoring Prime system for beam abort and luminosity monitoring in ATLAS based on a segmented polycrystalline CVD diamond system and dedicated front-end ASIC

The High Luminosity upgrade of Large Hadron Collider (HL-LHC) will increase the LHC luminosity and with it the density of particles on the detector by an order of magnitude. For protecting the inner silicon detectors of the ATLAS experiment and for monitoring the delivered luminosity, a radiation hard beam monitor was developed based on polycrystalline Chemical Vapor Deposition (pCVD) diamond detectors and a new dedicated rad-hard front-end ASIC. Due to the large range of particle flux through the detector, flexibility is very important. To satisfy the requirements imposed by the HL-LHC, our solution is based on segmenting diamond sensors into devices of varying size and reading them out with new multichannel readout ASICs divided into two independent parts — each of them serving one of the tasks of the system. This paper describes the system design including detectors, electronics, mechanics and services and presents preliminary results from the most recent detectors fabricated, using our prototype ASIC with data from beam tests at CERN.

Latest results from the RD42 collaboration on the radiation tolerance of polycrystalline diamond detectors

As nuclear and particle physics facilities move to higher intensities, the detectors used there must be more radiation tolerant. Diamond is in use at many facilities due to its inherent radiation tolerance and ease of use. In this article we present our radiation tolerance measurements of the highest quality polycrystalline Chemical Vapor Deposition (pCVD) diamond material for irradiations from a range of proton energies, pions and neutrons up to a fluence of 2×1016particles/cm2. We have measured the damage constant as a function of energy and particle species and compared it with theoretical models. We also present measurements of the rate dependence of pulse height for non-irradiated and irradiated pCVD diamond pad and pixel detectors, including detectors tested over a range of particle fluxes up to 20 MHz/cm2 with both pad and pixel readout electronics. Our test beam results indicate a 2% upper limit to the pulse height dependence of unirradiated and neutron irradiated pCVD diamond detectors leading to the conclusion that the pulse height in pCVD diamond detectors is, at most, minimally dependent on the particle flux.

High pressure and high temperature treatment of chemical vapor deposited polycrystalline diamond: From opaque to transparent

The enhanced optical properties of chemical vapor deposited (CVD) diamond have been pursued in academia and industry for many applications. However, the barrier of CVD technology limits the application field of diamond. Herein, the performance of CVD polycrystalline diamond thick films was improved by high-pressure and high-temperature (HPHT) treatment. The microstructures of CVD polycrystalline diamond films before and after HPHT treatments were thoroughly examined using optical microscope, UV–visible and infrared absorption, Raman spectroscopy, scanning electron microscope (SEM) and transmission electron microscope (TEM). It is found that the transparency of the CVD samples at 10 GPa increases dramatically with processing temperatures, from the original opacity to almost full optical transparency. Through spectroscopic and microstructural analyses, the modification mechanism of CVD polycrystalline diamond under HPHT conditions is proposed. The results show that the HPHT treatment can significantly enhance the optical properties of the starting CVD polycrystalline diamond films.

Transitions in polycrystalline diamond probed by steady state, modulated and transient surface photovoltage spectroscopy

Numerous electronic transitions in polycrystalline chemical vapor deposition diamond with characteristic nucleation and growth sides were obtained by highly sensitive surface photovoltage (SPV) spectroscopy in dc (Kelvin probe), ac (modulated) and ac (transient) regimes from near infrared to deep ultraviolet. In the dc regime, defect transitions D1 to D8 were detected at 0.8–0.9, 1, 1.37, 1.78, 2.27, 3.15, 4.2 and 5.42 eV, respectively. Hints for more transitions were found for measurements in the ac (modulated) regime in the range near D3. SPV measurements in the ac (transient) regime showed the importance of disorder for relaxation of SPV signals excited at different photon energies. Phonon assisted transitions were observed at E g− E x− hν LA,LO, E g− E x + hν LA,LO and E g− E x + hν TO. The developed SPV techniques are suitable for applications in research and quality control not only for diamond but also for any other semiconductor with ultra-wide bandgap.

Development of a System for Beam Abort and Luminosity Determination at the HL-LHC based on polycrystalline CVD diamond

The high luminosity upgrade of Large Hadron Collider will increase its luminosity by an order of magnitude increasing with it the density of particles on the detector. For protecting the inner detectors of experiments and for monitoring the delivered luminosity, a radiation hard beam monitor is being developed. Text describes the proposed system’s principles of operation and its design. It details on the poly-crystalline chemical vapor deposition diamonds as sensor material, a dedicated radiation hard ASIC, as well as on electronics and data processing. The latter finally offers beam abort and luminosity measurement functionalities of the system.

Radiation tolerance of diamond detectors

Diamond is used as detector material in high energy physics experiments due to its inherent radiation tolerance. The RD42 collaboration has measured the radiation tolerance of chemical vapour deposition (CVD) diamond against proton, pion, and neutron irradiation. Results of this study are summarized in this article. The radiation tolerance of diamond detectors can be further enhanced by using a 3D electrode geometry. We present preliminary results of a poly-crystalline CVD (pCVD) diamond detector with a 3D electrode geometry after irradiation and compare to planar devices of roughly the same thickness.

Plasma etching for carbon materials by inward RF plasma apparatus

ABSTRACT Diamond has high wear resistance and shape stability, and poly-crystalline chemical vapour deposition (CVD) diamond is difficult to mechanically process because of cleavage and wear anisotropy. On the other hand, diamond can be removed under an oxidising atmosphere with O2 as the etching gas by reactive ion etching which is processing using plasma. In this study, the fabrication of an inward radio frequency (RF) plasma apparatus and the possibility of a removal process for carbon materials such as CVD diamond film and graphite plate by using it were investigated. OES, confocal laser scanning microscope and Raman spectroscopy were used for the evaluation of the etching. It was confirmed that the inward RF plasma apparatus fabricated could be applied to plasma etching for carbon materials. In addition, it was suggested that carbon materials were etched as CO with O2 in the atmosphere, and amorphous structures were etched preferentially over crystalline ones.

Periodic nano ripple fabricated on diamond and its structure damage repair

Surface nanocrystallization and adjusting chemical compositions are anticipated to be effective strategies for exploring potential applications of diamond in physics, chemistry and biology. In this paper, the morphology evolution of a polycrystalline chemical vapor deposition diamond (PCD) under Ar+ ion beam bombardment was studied. Nano ripple was formed on the substrate. The characteristic sizes, including amplitude (A) and wavelength (W), of ripples could be adjusted by changing ion energy. Meanwhile, chemical compositions of the diamond surface after the bombardment were investigated by Raman spectrum and XPS. Amounts of lattice damage or defects appeared on the surface region of PCD due to a conversion of sp3 C to sp2 C during the ion bombardment. Moreover, high temperature annealing in vacuum was adopted to remove the damage layer. It was proved to be an effective means to restore diamond structure here and the ripple pattern could be still preserved after the thermal treatment. In addition, the variations of the sheet resistance of the PCD, which significantly increases as the increasing annealing time, offer a direct evidence to reveal the extent of restoration of diamond structure.

Highly uniform polycrystalline diamond coatings of three-dimensional structures

Diamond is highly desirable as a conformal thin-film coating for three-dimensional (3D) devices due to its extreme hardness, durability and biocompatibility, especially in the case of implantable medical devices and prosthetics. Recent advances in microwave plasma chemical vapour deposition (CVD) have enabled conformal coating of such 3D structures with nanodiamond films. However, these techniques have not been extended to micro-crystalline diamond, due to interactions between the 3D substrates and resonant microwave cavity. Here we demonstrate more uniform growth of CVD polycrystalline diamond (PCD) coatings on complex-shaped structures, with the use of in-cavity Faraday cages, to isolate the 3D sample from the microwave cavity. While this does disrupt the distribution of the microwave plasma, which surrounds the 3D structure, we show that growth of relatively uniform micro-crystalline and faceted PCD films is possible over the entirety of the exposed 3D sample surface. The resultant technique opens possibilities for the coating of complex 3D geometries with a wider range of diamond materials than has been possible to date.

A Study of the Radiation Tolerance of CVD Diamond to 70 MeV Protons, Fast Neutrons and 200 MeV Pions.

We measured the radiation tolerance of commercially available diamonds grown by the Chemical Vapor Deposition process by measuring the charge created by a 120 GeV hadron beam in a 50 pitch strip detector fabricated on each diamond sample before and after irradiation. We irradiated one group of samples with 70 MeV protons, a second group of samples with fast reactor neutrons (defined as energy greater than MeV), and a third group of samples with 200 MeV pions, in steps, to () × 1015 protons/cm2, () × 1016 neutrons/cm2, and () × 1014 pions/cm2, respectively. By observing the charge induced due to the separation of electron–hole pairs created by the passage of the hadron beam through each sample, on an event-by-event basis, as a function of irradiation fluence, we conclude all datasets can be described by a first-order damage equation and independently calculate the damage constant for 70 MeV protons, fast reactor neutrons, and 200 MeV pions. We find the damage constant for diamond irradiated with 70 MeV protons to be 10−18 cm2, the damage constant for diamond irradiated with fast reactor neutrons to be 10−18 cm2, and the damage constant for diamond irradiated with 200 MeV pions to be 10−18 cm2. The damage constants from this measurement were analyzed together with our previously published 24 GeV proton irradiation and 800 MeV proton irradiation damage constant data to derive the first comprehensive set of relative damage constants for Chemical Vapor Deposition diamond. We find 70 MeV protons are 2.60 ± 0.29 times more damaging than 24 GeV protons, fast reactor neutrons are 4.3 ± 0.4 times more damaging than 24 GeV protons, and 200 MeV pions are 3.2 ± 0.8 more damaging than 24 GeV protons. We also observe the measured data can be described by a universal damage curve for all proton, neutron, and pion irradiations we performed of Chemical Vapor Deposition diamond. Finally, we confirm the spatial uniformity of the collected charge increases with fluence for polycrystalline Chemical Vapor Deposition diamond, and this effect can also be described by a universal curve.

Influence of the grain size of CVD diamond on the thermal conductivity, material removal depth and surface roughness in nanosecond laser machining

Due to the exceptional thermal conductivity and material hardness, CVD diamonds have been ideal materials for cutting tools; however, the specific properties of CVD diamonds vary with the grain size. An experimental study was carried out on chemical vapor deposition (CVD) diamonds with varying grain sizes in laser processing. This study aims to analyze the behavior of polycrystalline CVD diamonds under different thermal processing based on its thermal conductivity model. The pit formed under a single laser pulse on the material with a small grain size is shallow and tiny, because of its small thermal conductivity, a value calculated using the established model. The results show that for laser-machined surface, the material with a small grain size can obtain a better machined surface but a small material-removal depth; conversely, material with a large grain size provided opposite experimental results. Additionally, reasonable laser parameters achieved the desired material-removal depth of up to or even exceeding 180 μm and surface roughness Sa as low as 0.2 μm. Overall, both the grain sizes of polycrystalline CVD diamonds and laser parameters affect the machining result. However, there are considerable obstacles in simultaneously achieving a good surface and massive material removal. Hence, a tradeoff between the two aspects is essential in an actual machining process, and this study provides some useful guidance to practitioners and academicians.

Impact of Peak Material Volume of Polycrystalline CVD Diamond Coatings on Dry Friction Against Aluminum

For economic and environmental reasons, dry forming is of increasing interest due to the shortening of process chains, cost savings and reduction of environmental pollution. The aim of these investigations is to examine to what extent chemical vapor deposited (CVD) diamond coatings are suitable for dry forming of aluminum and to identify the surface topology requirements for a low friction coefficient and low wear. Nine different surface topologies of CVD diamond coatings were tested in an oscillating ball-on-plate tribometer test against aluminum balls with a Hertzian contact stress of 759 MPa and 99,900 cycles. It could be concluded that the peak material volume (Vmp) of the diamond coating is the most important factor for achieving a low abrasion of aluminum as well as a low friction coefficient against aluminum. The Vmp should be smaller than 0.04 ml/m2. Microcrystalline CVD diamond with a post-treated surface has great potential for dry forming of aluminum.

Reactive wetting of Sn-V solder alloys on polycrystalline CVD diamond

In this paper, the reactive wetting of polycrystalline chemical vapour deposition (CVD) diamond by a novel Sn-V solder alloy was critically examined using the sessile drop method. It has been found the Sn-V solder alloys start to spread on the CVD diamond at around 600 °C. Moreover, 0.5 wt% addition of V is adequate to induce an outstanding spreading of Sn-V active solder alloys on CVD diamond; while the original V content in Sn-V alloys has a negligible influence on final contact angles after wetting at 950 °C. The spreading kinetics of Sn-3V alloy on CVD diamond can be described using the classical chemical reaction-limited model at 700–850 °C. However, ultrafast adsorption of V element to the fresh diamond surface was evidenced by the formation of precursor film on the periphery of solidified Sn-V droplets. Hence, both interface reaction and adsorption of active element are accountable for the reactive spreading of Sn-V alloy on CVD diamond, especially during the early stage of spreading at relatively low temperatures. Results obtained in this study are therefore significant for not only the development of diamond bonding technique, but also the understanding of reactive wetting of metals on diamond and other carbonous materials.

New test beam results of 3D and pad detectors constructed with poly-crystalline CVD diamond

Chemical Vapour Deposition (CVD) diamond is being considered as a material for particle detectors in a harsh radiation environment. This article presents beam test results of 3D pixel detectors fabricated with poly-crystalline CVD diamonds. The cells of the devices had a size of 50µm×50µm with columns 2.6µm in diameter. The cells were ganged in a 3×2 and 5×1 pattern to match the layouts of the pixel read-out electronics currently used in the CMS and ATLAS experiments at the Large Hadron Collider, respectively. In beam tests, using tracks reconstructed with a high precision tracking telescope, a tracking efficiency of 99.3% was achieved. The efficiency of both devices plateaus at a bias voltage of 30V. Also irradiated poly-crystalline CVD diamond pad detectors were investigated. In high rate beam tests with particle fluxes up to 20MHz/cm2 and irradiations up to 8 ⋅ 1015n/cm2 it was shown that the pulse height of irradiated poly-crystalline CVD diamonds does not depend on flux to the O2%.

Study of Electrode Fabrication in Diamond with a Femto‐Second Laser

Diamond is a radiation hard material, which makes it suitable for its use in high energy physics experiments as a particle detector. To further reduce the effects of radiation damage, diamond detectors can be fabricated by inscribing graphitic electrodes perpendicular to the surface—the so‐called 3D detectors. This can be done via processing with a femtosecond laser. Herein, a systematic study of the cross section of the graphitic wires inscribed into diamond is shown as a function of laser pulse energy, stage translational speed and, for the first time, polarization for a single crystal and polycrystalline chemical vapour deposition (CVD) diamond samples. No dependence of the electrode width with speed polarization and sample for the same pulse energies within uncertainties are observed. The graphitic content of the electrodes is studied in terms of Raman spectrometry: no clear dependence on the fabrication parameters studied is observed.

A study of the radiation tolerance of poly-crystalline and single-crystalline CVD diamond to 800 MeV and 24 GeV protons

We have measured the radiation tolerance of poly-crystalline and single-crystalline diamonds grown by the chemical vapor deposition (CVD) process by measuring the charge collected before and after irradiation in a 50 m pitch strip detector fabricated on each diamond sample. We irradiated one group of sensors with 800 MeV protons, and a second group of sensors with 24 GeV protons, in steps, to protons cm−2 and protons cm−2 respectively. We observe the sum of mean drift paths for electrons and holes for both poly-crystalline CVD diamond and single-crystalline CVD diamond decreases with irradiation fluence from its initial value according to a simple damage curve characterized by a damage constant for each irradiation energy and the irradiation fluence. We find for each irradiation energy the damage constant, for poly-crystalline CVD diamond to be the same within statistical errors as the damage constant for single-crystalline CVD diamond. We find the damage constant for diamond irradiated with 24 GeV protons to be and the damage constant for diamond irradiated with 800 MeV protons to be . Moreover, we observe the pulse height decreases with fluence for poly-crystalline CVD material and within statistical errors does not change with fluence for single-crystalline CVD material for both 24 GeV proton irradiation and 800 MeV proton irradiation. Finally, we have measured the uniformity of each sample as a function of fluence and observed that for poly-crystalline CVD diamond the samples become more uniform with fluence while for single-crystalline CVD diamond the uniformity does not change with fluence.

Low-temperature wetting mechanisms of polycrystalline chemical vapour deposition (CVD) diamond by Sn-Ti solder alloys

Synthetic diamond is an important carbonous material that has widespread applications ranging from machine tools to the next-generation wafer of powder devices. Understanding of its wetting behaviours is therefore essential for the development of the highly required diamond bonding technique. In this paper, the wettability and spreading kinetics of Sn-Ti solder alloys were systematically investigated on polycrystalline chemical vapour deposition (CVD) diamond using the sessile drop method. In situ examination of contact angles at continuously elevated temperatures indicated that wetting of the CVD diamond by Sn-Ti solder alloys commenced at temperatures well below the bonding temperatures of conventional filler alloys. An excellent wetting of Sn-Ti solder alloy on the CVD diamond was induced by the addition of a small amount of Ti (0.5 wt%). It was also revealed that the spreading process of Sn-Ti alloys on the CVD diamond was initially controlled by the Ti adsorption at the wetting triple line. Enhancing the Ti adsorption at the wetting triple line could effectively improve the low-temperature wettability of Sn-Ti alloys on the CVD diamond, such as the case of 600 °C in this work, at which the possibility of surface corrosion and thermal damage of diamond devices can be substantially reduced.

Searching for a dark photon with PADME at LNF: status of the active diamond target

PADME (Positron Annihilation into Dark Matter Experiment) is an experiment that will search for the production of a dark photon A ′ from the annihilation of a positron beam on a thin diamond target. It will use the 550 MeV positron beam of the Beam Test Facility (BTF) of the Laboratori Nazionali di Frascati (LNF) of INFN. According to the PADME design, the region of sensitivity is M A ′ ≤ 23.7 MeV/c 2 and ϵ 2 > 1 0 − 6 , where M A ′ and ϵ are the dark photon mass and the A ′ γ mixing parameter. This paper presents the status of the active diamond target, in particular the assembly of two 32 channel targets of polycrystalline Chemical Vapor Deposition (CVD) diamond, one with graphitic strips and another with traditional CrAu strips.

Study on fabrication of PCD micro-milling tool by picosecond pulsed laser

For the purpose of processing some forms of diamond, such as polycrystalline diamond (PCD) and chemical vapor deposition diamond, picosecond pulsed laser (PSPL) has the decisive advantage of wear-free material removal. This availability of picosecond pulsed laser sources enables the efficient applications of cutting diamond to generate sharp and regular cutting edge. Therefore, in this study, picosecond pulsed laser is used to fabricate polycrystalline diamond (PCD) micro tool. In order to optimize the picosecond pulsed laser processing, the effects of PSPL cutting parameters including the pulse energy, pulse pitch, and grain size of PCD on the cutting results are investigated. The results indicate the grain size has the greatest impact on the cutting edge radius and pulse energy has great effect on the processed surface of PCD. The results prove that PSPL is a better choice for precision fabrication of PCD micro tool. Finally, the fabrication of PCD micro tools by PSPL has been demonstrated.

Composition of volatile components in the polycrystalline CVD diamond (by coupled gas chromatographic–mass spectrometric analysis)

The results of gas chromatography–mass spectrometry (GC–MS) demonstrate that the volatiles captured by diamond grown by chemical vapour deposition (CVD) technology contain hydrocarbons and their derivatives (72.2 rel. %). We have identified aliphatic (paraffins and olefins), cyclic (naphthenes and arenes) and oxygenated (alcohols, aldehydes, ketones and carboxylic acids) hydrocarbons, as well as nitrogenated and sulfonated compounds. Water, negligible amounts of CO2 and Ar were also detected among the volatile components.