Diamond Layers Research Articles

Operational Control of Substrates and Epitaxial Layers of Silicon Carbide and Diamond by IR Spectroscopy

A set of efficient operational methods for post-growth determination of the kinetic parameters of charge carriers and impurity concentration in silicon carbide and diamond substrates and epitaxial layers, as well as layer thicknesses, by analyzing infrared (IR) reflection and absorption spectra, is presented.

Pretreatment strategies of titanium substrates to modulate the electrochemical properties of CVD-grown Ti-doped diamond electrodes for dopamine detection

The identification of highly sensitive materials able to combine performance stability, relatively low cost, controllable and large area fabrication process is still a major bottleneck in the scientific community. Dopamine is considered a key indicator to monitor cardio and cerebrovascular diseases and its redox activeness makes electrochemical detection the most straightforward and promising sensing approach. Here we report the realization, by a simple yet effective approach, of diamond-based electrodes with a native selectivity towards dopamine. In details, three different substrate pretreatments, i.e., lapping, electropolishing and chemical etching, are adopted to tailor the morphological, structural, and sensing features of titanium doped diamond layers. SEM, AFM, Raman spectroscopy, XRD, XPS and I-V analyses demonstrate the features' modulation of the diamond layers being crucial for electrochemical and sensing performances, as confirmed by dopamine selectivity under ascorbic and uric acid interferents' excess. Furthermore, the controlled introduction of oxygen-containing groups enhances the dopamine sensitivity, lowering the detection limit from 6000 to 600 nM. In addition to giving an important insight on the physical-chemical growth processes, these preliminary results pave the way for the exploitation of these materials in a wide range of sensing applications, thanks to the non-toxicity and high surface tunability without post-synthesis treatments.

NV microscopy of thermally controlled stresses caused by thin Cr2O3 films.

Many modern applications, including quantum computing and quantum sensing, use substrate-film interfaces. Particularly, thin films of chromium or titanium and their oxides are commonly used to bind various structures, such as resonators, masks, or microwave antennas, to a diamond surface. Due to different thermal expansions of involved materials, such films and structures could produce significant stresses, which need to be measured or predicted. In this paper, we demonstrate imaging of stresses in the top layer of diamond with deposited structures of Cr2O3 at temperatures 19°C and 37°C by using stress-sensitive optically detected magnetic resonances (ODMR) in NV centers. We also calculated stresses in the diamond-film interface by using finite-element analysis and correlated them to measured ODMR frequency shifts. As predicted by the simulation, the measured high-contrast frequency-shift patterns are only due to thermal stresses, whose spin-stress coupling constant along the NV axis is 21±1 MHz/GPa, that is in agreement with constants previously obtained from single NV centers in diamond cantilever. We demonstrate that NV microscopy is a convenient platform for optically detecting and quantifying spatial distributions of stresses in diamond-based photonic devices with micrometer precision and propose thin films as a means for local application of temperature-controlled stresses. Our results also show that thin-film structures produce significant stresses in diamond substrates, which should be accounted for in NV-based applications.

Pressure Sensor Using a Hybrid Structure of a Magnetostrictive Layer and Nitrogen-Vacancy Centers in Diamond

Pressure Sensor Using a Hybrid Structure of a Magnetostrictive Layer and Nitrogen-Vacancy Centers in Diamond

Espresso Science: Laser-Based Diamond Thin-Film Waveguide Sensors for the Quantification of Caffeine.

Diamond thin-film waveguides with a nanocrystalline diamond layer of approximately 20 μm thickness were used in the mid-infrared regime in combination with quantum cascade lasers to detect the IR signature of caffeine. The diamond thin-film waveguides were fundamentally characterized with respect to their morphological properties via AFM and SEM. Theoretical simulations confirmed the feasibility of using a larger sensing area of approximately 50 mm2 compared to conventionally used strip waveguides. A comprehensive and comparative analysis confirmed the performance of the diamond thin-film-waveguide-based sensing system vs data obtained via conventional attenuated total reflection Fourier transform infrared spectroscopy using a single-bounce diamond internal reflection element. Hence, the utility of innovative diamond thin-film-waveguide-based sensors coupled with quantum cascade laser light sources has been confirmed as an innovative analytical tool, which may be used in a wide range of application scenarios, ranging from environmental to medical sensing, taking advantage of the robustness and inertness of nanocrystalline diamond.

STUDY OF THE STRUCTURE AND PROPERTIES OF THE SURFACE OF HARD ALLOY VK10KS AFTER TWO-COMPONENT ELECTRICAL EXPLOSION TREATMENT WITH SYNTHETIC DIAMONDS

The article presents the results of studies of the VK10KS hard alloy after two-component electroexplosive treatment (EVL) with synthetic diamonds. Aluminum was used as the exploding conductor. The choice of aluminum is based on the experimental data of a number of researchers who note that in order to increase the strength properties of hard alloys at elevated temperatures, it is necessary that particles with a size of hundredths of a micron of ultrafine α-Al2O3 be present in the cobalt binder. Thus, the addition of aluminum to the bond significantly increases the hardness, wear resistance and bending strength. The essence of the EVL is the accumulation of energy by a battery of impulse capacitors up to 10 kJ and its subsequent discharge for 100 μs through a conductor that experiences explosive destruction. In this case, the treated surface is heated and saturated with explosion products, followed by self- hardening due to heat removal to the environment and deep into the material. To increase the hardening effect, a powder sample of synthetic diamond powder AC2 weighing 60 mg was additionally added to the explosion area. It was experimentally revealed that alloying the surface of the VK10KS hard alloy with the products of aluminum electric explosion with a sample of diamond powder did not lead to the formation of a hardened diamond-type layer. During processing, the diamond powder trans-formed into graphite. Despite the fact that the diamond layer was not formed, surface hardening of the VK10KS hard alloy occurred after the electric explosion of diamond powder with aluminum as a conductor. The thickness of the hardened surface layer is about 15 µm with a nanohardness of 24000 MPa, which is 2 times higher compared to the initial state. The increase in hardness is associated with the refinement of phases in the surface layer and the formation of W2C and α-Al2O3 type carbides. The surface roughness of machined carbide inserts does not exceed the values corresponding to the technical requirements.The study of the cobalt binder in the heat-affected zone after two-component EVL found that the cobalt binder is additionally alloyed with tungsten, carbon, aluminum, which are part of the explosive materials and the base. Additional alloying of the cobalt binder will lead to its hardening, which will positively affect the service life of tungsten carbide hard alloys in general.

C+ ion implanted single crystal diamond with amorphous surface for efficient oxygen evolution catalysis

Oxygen evolution reaction (OER) is critical in water splitting for green hydrogen gas production due to its sluggish kinetics; however, commercial OER catalysts commonly suffer from high cost, low catalytic activity and poor stability. Herein, we developed a C+ ion implantation method to modify single crystal diamond, and the resultant surface amorphous layer not only raised the active site number but also increased the content of the C=O group, thus significantly improving the OER activity. The C+ ion implanted high-temperature and high-pressure (C+-HTHP) and chemical vapor deposition (C+-CVD) diamonds both exhibit low OER overpotential with η10 of 317 mV and 325 mV respectively, superior to those of HTHP diamond (360 mV), CVD diamond (395 mV) and RuO2 (364 mV). The potentiostatic testing shows that the C+ implanted diamonds almost didn't undergo the rise of OER overpotential upon catalysis for more than 12 h at a current density of 10 mA cm−2, suggesting a high catalytic stability, owing to the strong bonding between single crystal diamond and amorphous carbon layer. For the first time, we utilized carbon ion implantation to prepare diamond-based high-performance OER catalyst, which broadens the understanding of carbon-based materials in OER catalysis.

Study of preparation and cutting performance of a chemical vapor deposition diamond coated cutting tool

The thermal stability of the traditional polycrystalline diamond compact (PDC) cutting tool is significantly reduced due to the presence of Cobalt (Co), and the surface quality of the machined material was degrades after cutting . However, the removal of Co results in pores formation on PDC surface, thus reducing the material's hardness and wear resistance. The chemical vapor deposition (CVD) diamond coated cutting tool exhibits poor adhesion at the film-base interface, resulting in short service life. To overcome these issues, this study suggests a method for depositing a CVD diamond coating directly on the surface of a polycrystalline diamond layer following the decobalt treatment of PDC. The influence of the distance between filament and substrate on the performance of the CVD diamond coating cutting tool was investigated. Further, a comparison of four cutting tools including traditional PDC, decobalt PDC, CVD diamond coated cemented carbide, and the CVD diamond coated was carried out in terms of wear resistance, hardness, bonding strength, and cutting performance. The developed CVD diamond coated cutting tool can provide excellent performance and real-time applications.

The influence of droplet-based seeding of nanodiamond particles on the morphological, optical, and mechanical properties of diamond coatings on glass

This work investigates four different methods for the seeding of nanodiamond (ND) particles towards applying nanocrystalline diamond coatings on glass. The standard spin coating and dip coating are investigated together with two droplet-based techniques, ink-jet printing and ultrasonic spray coating (USSC). The application of these last two techniques for diamond coatings on glass is novel and is specifically designed for patterning and large area deposition, respectively. Comparing the seeding processes, their impact on the chemical vapor deposited nanocrystalline diamond (NCD) layers is unclear. Here, particularly the impact on the morphological, optical, and mechanical properties, are studied. In this work, borosilicate glass substrates were seeded, after which diamond layers were grown in a linear antenna microwave plasma-enhanced chemical vapor deposition reactor to thicknesses of 45, 100, and 500 nm. The coatings showed a roughness that is 2 to 3 times higher for the droplet-based seeding techniques compared to spin coating. It was found that the optical absorption coefficient for 100 nm thick samples prepared using USSC was 2400 cm−1 at the wavelength of 550 nm, compared to 1500 cm- 1 using spin and dip seeding techniques. The stress in the film was compressive as determined by curvature measurements. Sand-trickling tests on samples coated with 100 nm thick diamond films showed similar resistance against damaging for all seeding techniques without delamination. Therefore, the different techniques achieve mechanically competitive performance. On top USSC and ink-jet printing have the opportunity to fully cover substrates on large-scale flat and even 3D surfaces, or pattern fine structures, which is not possible for standard spin and dip coating. It can be concluded that diamond coatings on large glass plates for scratch resistance, and sensing due their somewhat higher roughness, are within reach using these innovative droplet-based seeding technologies.

Orientation of the NV centers are determined using the cylindrical vector beam array.

The determination of nitrogen-vacancy centers plays an important role in quantum information sensing. Efficiently and rapidly determining the orientation of multiple nitrogen-vacancy center s in a low-concentration diamond is challenging due to its size. Here, we solve this scientific problem by using an azimuthally polarized beam array as the incident beam. In this paper, the optical pen is used to modulate the position of beam array to excite distinctive fluorescence characterizing multiple and different orientations of nitrogen-vacancy centers. The important result is that in a low concentration diamond layer, the orientation of multiple NV centers can be judged except when they are too close within the diffraction limit. Hence, this efficient and rapid method has a good application prospect in quantum information sensing.

Analysis of boron- and phosphorus-doped diamond layers by glow discharge optical emission spectroscopy in argon and neon

Boron- and phosphorus-doped diamond layers were analysed by glow discharge optical emission spectroscopy. A methodology for quantitative depth profiling of layers was developed, based on multi-matrix calibration with a calibration model assuming matrix-independent emission yields. Factors affecting accuracy and sensitivity of analysis are discussed. Analysis of boron with the B I line at 208.959 nm yielded a satisfactory performance. Analysis of phosphorus with the P I line at 178.284 nm in an argon glow discharge is affected by an argon-related interference, which can be avoided by using a neon discharge. The use of which leads to an eightfold improvement in the phosphorus detection limit. A light interference effect affecting the analysis in transparent layers is described, indicating that layers are transparent far into the ultraviolet region.

Combined HF+MW CVD Approach for the Growth of Polycrystalline Diamond Films with Reduced Bow

A combination of two methods of chemical vapor deposition (CVD) of diamond films, microwave plasma–assisted (MW CVD) and hot filament (HF CVD), was used for the growth of 100 µm-thick polycrystalline diamond (PCD) layers on Si substrates. The bow of HF CVD and MW CVD films showed opposite convex\concave trends; thus, the combined material allowed reducing the overall bow by a factor of 2–3. Using MW CVD for the growth of the initial 25 µm-thick PCD layer allowed achieving much higher thermal conductivity of the combined 110 µm-thick film at 210 W/m·K in comparison to 130 W/m·K for the 93 µm-thick pure HF CVD film.

Two-dimensional spin systems in PECVD-grown diamond with tunable density and long coherence for enhanced quantum sensing and simulation

Systems of spins engineered with tunable density and reduced dimensionality enable a number of advancements in quantum sensing and simulation. Defects in diamond, such as nitrogen-vacancy (NV) centers and substitutional nitrogen (P1 centers), are particularly promising solid-state platforms to explore. However, the ability to controllably create coherent, two-dimensional spin systems and characterize their properties, such as density, depth confinement, and coherence, is an outstanding materials challenge. We present a refined approach to engineer dense (≳1 ppm ⋅ nm), 2D nitrogen, and NV layers in diamond using delta-doping during plasma-enhanced chemical vapor deposition epitaxial growth. We employ both traditional materials techniques, e.g., secondary ion mass spectrometry, alongside NV spin decoherence-based measurements to characterize the density and dimensionality of the P1 and NV layers. We find P1 densities of 5–10 ppm ⋅ nm, NV densities between 1 and 3.5 ppm ⋅ nm tuned via electron irradiation dosage, and depth confinement of the spin layer down to 1.6 nm. We also observe high (up to 0.74) ratios of NV to P1 centers and reproducibly long NV coherence times, dominated by dipolar interactions with the engineered P1 and NV spin baths.

Geometric-kinematic model for reinforced concrete core drilling

Since diamond-impregnated tools have a big share on tools for construction, the development of more efficient ones is necessary in the near future. The drilling speed performance is one of the concerns during the development of new diamond-impregnated segments in concrete core drilling. However, observations only based on experiments can be very costly, considering a quite demanding amount of material and workforce. One of the solutions to overcome these issues is the development of a geometric-kinematic model (containing a kinematic process model, material model, and drilling force model) to simulate the tangential and normal forces of diamond-impregnated segments in core drilling process. Such model is regularly used in the literature for the simulation of a bonded-abrasives process. The main purpose of the geometric-kinematic model is to generate simulations for the concrete core drilling for the tool performance estimation. This allows an evaluation of the geometric characteristics’ (diamond morphology, orientation, size, and positioning) impact of diamond-impregnated segments and of drilling parameters on the drilling force. The geometric-kinematic model will use detailed segment descriptions with stochastic and deterministic variables. The drilling simulation delivers a consistent drilling forces prediction in Utliberg concrete and ASTM A615 steel at the frequently used core drilling feed window. Besides, the model shows the competence to evaluate the impact of a diamond layer characteristics (diamond size and number of rows), allowing the comparison of distinct diamond arrangements designs between each other.

A Ti‐Doped Chemical Vapor Deposition Diamond Device as Artificial Synapse for Neuromorphic Applications

AbstractThe great demand of multifunctional portable electronic products in daily life and the need of a large integration of memories with logic devices and sensors, have increased the interest in the identification of suitable materials for neuromorphic computing applications. Major innovations in this direction have been achieved by exploring materials belonging to different fields of applications and taking advantage of already consolidated deposition methods. Despite the great interest in the field and the large use in complementary applications such as sensing electrodes, neural and cellular interfaces, the use of diamond‐like materials in neuromorphic applications is still limited to a few examples. Herein, the development of a synaptic element based on high‐quality polycrystalline diamond layers containing Ti inclusions showing a marked and reproducible resistance switching behavior is reported. Realized by means of a hybrid chemical vapor deposition‐powder flowing technique, this titanium doped diamond shows a 3D polycrystalline organization that is characterized by globular grains of a few microns. The coupling of Raman spectroscopy, X‐ray photoelectron spectroscopy, and X‐ray diffraction analyses confirms the good quality of diamond phase and convincingly points out the inclusion of the titanium species within the diamond lattice.

Hot-filament CVD diamond coatings for optical applications

The demand for highly scratch resistant transparent coatings is motivated by the industrial sector of consumer goods for example for the protection of displays, touch-screens, watches, and all kinds of optical instruments. In a wide variety of applications, scratch-free and highly wear-resistant surfaces are the enabling factor for improvement of lifetime and thus sustainability of the products. Diamond with its unique properties such as the highest known hardness, low thermal expansion coefficient and chemical resistance (to acids and bases) [1,2] has outstanding potential for optical applications [3]. The use of thin ultrahard diamond layers with adapted optical properties is expected to enhance the resistance against abrasive wear to a new level. At Fraunhofer IST large-area Hot-Filament Chemical Vapor Deposition (HFCVD) processes have been developed [4,5] and now utilized for depositing highly uniform and transparent diamond coatings on optical components with sizes of up to 200 mm × 200 mm. The use of single-layer diamond coatings is investigated as well as the integration of diamond films into multilayer film stacks combining anti-reflective properties with mechanical stability (strength). Four-layer anti-reflective coatings (Si3N4/SiO2/Diamond/SiO2) entirely deposited with hot-filament/hot-wire processes and their optical and mechanical performance will be presented.

Effects of alloying elements on diamond/Cu interface properties based on first-principles calculations

Diamond/copper composites with high thermal conductivity and a variable thermal expansion coefficient are promising materials for thermal management applications. However, achieving the desired thermal conductivity of the composite material is difficult due to detachment or weak bonding between diamond and Cu. The interfacial properties of diamond/Cu composites can be improved using metal matrix alloying methods. In this study, we investigate the effects of alloying elements (B, Cr, Hf, Mo, Nb, Si, Ti, V, Zr) on the interfacial properties of diamond/Cu using first-principles calculations. Results showed that all alloying components could increase the interfacial bonding of diamond/Cu. Analysis of the electronic structure revealed that increased interfacial bonding strength after doping was the result of the stronger bonding of the alloying element atoms to the C atoms. The C atoms in the first layer of diamond at the interface formed wave peaks near the Fermi energy level after doping with B or Si atoms, facilitating electron–phonon interaction at the interface. The phonon properties of B4C and SiC were similar to those of diamond, which facilitated phonon–phonon coupling. B and Si were shown to be better alloying elements when interfacial bond strength and heat transfer were considered.

Geometric-kinematic model for wear simulation of diamond-impregnated segments in concrete core drilling

The main concerns during the development of new diamond-impregnated segments in concrete core drilling are the tool lifetime and its capacity to self-sharpen, since tool sharpening is, most of the time, not acceptable under the conditions on the construction site. However, development only based on experiments can be very costly, considering that the amount of material and workforce are quite demanding. One of the solutions to overcome these issues is the development of a geometric-kinematic model to simulate the wear of diamonds in the segments due to the core drilling process. The main purpose of the model is to simulate the reinforced concrete core drilling, providing an estimation of the diamond wear states proportion for the segment diamond layer. This can allow an evaluation of the geometric characteristics impact of diamond-impregnated segments (diamond size, geometry, pattern, etc.) and of drilling parameters on the tool self-sharpening capacity. A specialized kinematic model, process force model and diamond wear model are the main ingredients. For the model validation, diamond wear states characterization after core drilling tests are carried out. The wear simulation delivers a tendency of a diamond layer design in specific process conditions, providing orthogonal worn/fractured profile, number of active diamonds and number of diamond pull-outs.

A Capacitance Model for Front- and Back-Gate Threshold Voltage Computation of Ultra-Thin-Body and BOX Double-Insulating Silicon-on-Diamond MOSFET

In this paper, a capacitance model for near threshold voltage computation of Ultra-Thin-Body and BOX (UTBB) Double-Insulating (DI) Silicon-on-Diamond (SOD) MOSFET is proposed. The transistor has a second insulating layer on top of the first insulating layer of a conventional SOD MOSFET which partially covers the diamond layer. The device’s simulation results of the front- and back-gate threshold voltages and the computed model’s threshold voltages - in terms of gate oxide thickness, silicon film layer thickness, first and second insulating layer thicknesses - are compared. In addition, length of the source/drain overlap with the second insulating layer is varied and the device simulation results are compared with those of the model findings. Results of the aforesaid comparison are found to be promising; more than 20 mV change in front-gate threshold voltage is observed at the range of 5 nm to 43 nm. Moreover, the model is found to be applicable in computations of front- and back-gate threshold voltage of 22 nm DI UTBB SOD MOSFET for low drain voltages. Finally, the model’s physical findings present insight on the device’s parameters that directly influence the threshold voltage

Tungsten doped diamond shells for record neutron yield inertial confinement fusion experiments at the National Ignition Facility

We report on fabrication and characterization of layered, tungsten doped, spherical about 2 mm diameter microcrystalline diamond ablator shells for inertial confinement fusion (ICF) experiments at the National Ignition Facility. As previously reported, diamond ICF ablator shells can be fabricated by chemical vapor deposition (CVD) on solid spherical silicon mandrels using an ellipsoidal microwave plasma reactor. In the present work, we further developed these ablator shells by embedding a W-doped diamond layer sandwiched between two undoped diamond regions. W incorporation in diamond was achieved by adding tungsten hexacarbonyl to the CH4/H2 CVD feed gas. We observe that the W doping concentration decreases with increasing deposition rate which, in turn, is controlled by adjusting the total gas pressure. Cross sectional microstructural analysis reveals sharp interfaces between doped and undoped regions of the diamond shell and uniform W distribution with concentrations up to about 0.3 at.%. At higher W concentrations (>0.3 at.%) formation of tungsten carbide precipitates is observed. Using a 3‐shock 1.6 MJ laser pulse, the targets described in this work produced the first laser driven implosion to break the 1 × 1016 neutron yield barrier, followed by experiments (described in future publications) with similar targets and slightly more laser energy producing yields as high as 4 × 1017.