Plasma Chemical Vapor Deposition Research Articles

Diamond-coated quartz crystal microbalance sensors: Challenges in high yield production and enhanced detection of ethanol and sars-cov-2 proteins

This study presents the technological progress in the deposition of diamond thin films on quartz crystal microbalance (QCM) sensors. The linear antenna microwave plasma chemical vapour deposition (CVD) technique effectively grows thin diamond films on QCM substrates (Dia-QCM) differently oriented on the substrate holder in the deposition chamber, resulting in single-sided and double-sided coated QCMs. Each of these coated QCMs offers a distinctive advantage for sensing applications. The double-sided coated QCM sensors exhibited the most effective performance in ethanol detection, demonstrating approx. a 3-fold and 12-fold higher response than single-sided diamond-coated and bare gold QCM sensors, respectively. Furthermore, the single-sided Dia-QCM aptasensors demonstrated superior performance compared to bare gold QCM sensors, with a 2-fold higher response and a lower detection limit for S-RBD protein (LODDia-QCM = 0.09pg/mL vs. LODAu-QCM = 0.10pg/mL). In experiments conducted in human plasma, the Dia-QCM aptasensor demonstrated the ability to detect S-RBD protein at concentrations as low as 50pg/mL, with high percentage recoveries. These results highlight the potential of linear antenna microwave plasma CVD for the mass production of advanced diamond-coated QCM sensors with different diamond film morphologies (porous, micro- or nanocrystalline) for various applications.

Facile synthesis of novel nitrogen-doped diamond with excellent microwave absorption and thermal conductive performance

Herein, nitrogen doped polycrystalline diamond was prepared using the microwave plasma chemical vapor deposition (MPCVD) method with H2–CH4–N2 gas sources to achieve excellent electromagnetic (EM) wave absorption and thermal management properties. The effect of the nitrogen content (0 to 50 ppm) on its performance was studied. The 25-ppm nitrogen doped diamond demonstrated excellent EM wave absorption performance, achieving a minimum reflection loss (RLmin) of −44.8 dB at 6.7 GHz and a maximum effective absorption band (EAB) of 5.4 GHz (3.7–9.1 GHz). The superior absorption performance could be attributed to synergistic attenuation mechanisms including dipole and interface polarization, conduction loss, eddy current loss, and magnetic polarization, intensified by nitrogen vacancy centers. This multifunctional material, combining high thermal conductivity with effective low-frequency EM wave absorption, showed promise for applications in 5G communications and electronic devices.

Effect of substrate type on structural and electrochemical performance of vertical graphene nanosheets deposited by HWP-CVD

Vertical graphene nanosheets (VGs) were synthesized on Cu, Ti, Si, and C substrates by helicon wave plasma chemical vapor deposition (HWP-CVD) method using CH4/Ar as precursors. The obtained samples formed vertical orientation structures of nanosheets-graphene as the scanning electron microscopy and TEM images indicated. Specifically, the VGs grown on Cu substrate exhibit a parallel arrangement with a wall spacing of approximately 450 nm. This structural characteristic facilitates efficient ion exchange channels and promotes low resistance for electron transport. The effect of substrate type on the growth mechanism of VGs was discussed. The relationship between the microstructure and electrochemical performance of the VGs grown on different substrates was investigated. The charge transfer resistance of the VGs/Cu is 20.75 Ω, and the value of VGs/Ti, VGs/C and VGs/Si are 23.51 Ω, 33.76 Ω and 66.40 Ω, respectively. The robust vertical orientation structure of VGs holds promise for various applications, including catalyst support in fuel cells, conductive electrodes in photovoltaic cells, and energy storage devices like lithium-ion batteries and supercapacitors. This structural characteristic plays a pivotal role in advancing the development of next-generation energy storage technologies.

Homoepitaxial growth of device-grade GaAs using low-pressure remote plasma CVD

We have achieved the growth of high-quality, homoepitaxial 100 GaAs thin films at 0.5 mbar and 500 °C using a Remote Plasma Chemical Vapor Deposition (RP-CVD) reactor. With this process, we demonstrate a film growth rate up to 3 μm/h, comparable to the conventional MOCVD technique. The resulting films exhibit structural characteristics close to those of commercial GaAs wafers, with excellent crystalline quality as confirmed by SAED patterns and XRD rocking-curve measurements for the 004 peak with a FWHM of 0.004°. AFM measurements reveal a surface roughness of 0.2 nm, similar to that of a polished wafer. Analysis of the chemical composition – as determined through XPS surface and depth-profiled measurements – indicates that the film is homogeneous, with a constant III/V ratio of 1 throughout the whole layer, and has no detectable carbon or oxygen contamination. Additionally, the films demonstrate a sharp photoluminescence peak (FWHM of 55 meV), a p-type doping concentration of 1.1018 cm−3, and a hole mobility of 172 cm2 V⁻1.s⁻1. This work thus demonstrates a cost-effective growth method for III-V devices, enabled by the reduced gas consumption (only a few sccm, compared to tens of L/min in MOCVD) in RP-CVD operation at low pressure.

Growth of homoepitaxial single crystal diamond by microwave plasma CVD in H2-CH4-O2 gas mixtures at high microwave power densities

Single crystal diamond growth by microwave plasma assisted CVD in oxygen-containing gas mixtures is attractive in view of possibility to realize a prolonged non-stoped synthesis process and to minimize defects and impurities in the produced material. We studied the homoepitaxial diamond growth on (100) oriented substrates in H2-CH4-O2 environment at high pressures (300 Torr) and high microwave power density (≈400 W/cm3) at variable O2 content (up to 3.5 %) in the plasma. A low-coherence optical interferometry and optical emission (OE) spectroscopy was used to measure in situ the growth rate and probe the plasma chemistry, respectively. Depending on CH4 content the growth rate dependence on the concentration [O2] either shows a maximum at certain [O2], or a monotonic decline, up to complete stop of the growth at some critical O2 percentage (specific for each methane content) in the mixture. We found CH, Hβ, C2 and C3 lines in OE spectra from the plasma to monotonically quenched with O2 adding, particularly, disappearance of the C2 line coincidences with growth rate going to zero. High-quality homoepitaxial diamond layers were produced at moderate growth rate at optimal gas composition and characterized with Raman spectroscopy. Moreover, a significant reduction in the stress on (111) oriented substrates owing to O2 addition was observed.

Observation of thickness-independent ultrafast relaxation times in MPCVD few-layer graphene

Graphene presents unique optoelectronic properties, making it attractive for the development of a wide range of new and advanced technological applications such as high-speed photodetectors and all-optical modulators. The study and control of the generated carriers in graphene, namely their ultrafast relaxation dynamics, are of great importance for these applications. Here, we report the ultrafast relaxation times of photogenerated carriers in few-layer graphene grown by microwave plasma chemical vapour deposition. Graphene samples with 3, 5 and 6 layers were studied by degenerate femtosecond optical pump-probe spectroscopy. We observed a fast relaxation constant on the order of 120−180fs and a slow relaxation constant below 1 ps, associated with carrier-carrier scattering and carrier-phonon scattering processes, respectively. These results suggest that small variations in the number of graphene layers do not affect the dynamics.

Nitrogen‐Induced Microcrystalline‐to‐Nanocrystalline Structure Transition in Diamond Films Grown by Microwave Plasma Chemical Vapor Deposition: Comparison of N2 and NH3 Precursors

The structure and properties of polycrystalline chemical vapor deposition (CVD) diamond coatings grown by microwave plasma CVD in H2–CH4 mixtures can be effectively controlled by nitrogen admixture in the process gas. Here, a comparative study of adding nitrogen from different precursors, N2 and ammonia NH3, in concentrations up to 0.4%vol on grain size, texture, surface roughness, and sp2/sp3 ratio of the produced films on Si substrates is performed. A transition from microcrystalline to smooth nanocrystalline diamond structure is found to occur at a certain concentration of the precursor, for NH3 this threshold concentration being much lower, 0.02–0.1%, than for N2. The higher activity of ammonia is associated with easier formation of cyano radicals in the plasma as detected with optical emission spectroscopy, in accord with the lower bond‐dissociation energy for NH3 compared to N2. On the contrary, a smaller addition (0.004%) of either N2 or NH3 promotes almost doubling of the growth rate, while preserving the microcrystalline structure of the film. The results establish ammonia as a convenient alternative precursor to commonly used N2 added in the plasma for the diamond film structure modifications.

Effects of carbon nanoparticle insertion on stress reduction in hydrogenated amorphous carbon films using plasma chemical vapor deposition

Stress reduction in hydrogenated amorphous carbon (a-C:H) films is of considerable interest for improving their performance as protective films. Herein, we reduced the compressive stress of the films by inserting carbon nanoparticles (CNPs) between two a-C:H layers to form an a-C:H/CNP/a-C:H sandwich structure using a system of plasma chemical vapor deposition (CVD). We measured the deposition features of the CNPs via transmission electron microscopy (TEM) and assessed the dependence of the stress on the thickness of the second a-C:H layer as a parameter of surface coverage, Cp. We represented the stress reduction as a function of Cp; mean size of large CNPs, and thickness of the first and second a-C:H layers. In addition, the surface and film morphologies were investigated using atomic force microscopy (AFM) and cross-sectional scanning electron microscopy (SEM). Compared with films without CNPs, those containing CNPs with 8.9 % Cp showed 36 % lower stress when the thickness of the second a-C:H layer was similar to that of the first (154 nm). The deposited CNPs exhibited two size groups, with mean sizes of the small and large CNPs of 5 and 16 nm, respectively. Stress reduction was strongly correlated with the distance between large CNPs. The insertion of CNPs between a-C:H films affects the surface morphology of the second layer, and the stress decreases when the growth stage of the film starts transitioning from three-dimensional (3D) to two-dimensional (2D).

Microcrystalline and nanocrystalline structure of diamond films grown by MPCVD with nitrogen additions: Study of transitional synthesis conditions

This research explores the complex influence of nitrogen concentration and substrate temperature on the resultant properties of polycrystalline diamond (PCD) films grown by microwave plasma chemical vapor deposition (CVD). In particular, we investigated the growth parameters to find the exact conditions for changing the morphology of the resulting film from microcrystalline (MCD) to nanocrystalline (NCD). A series of 2 µm-thick polycrystalline diamond films was grown on Si substrates in methane-hydrogen–nitrogen gas mixtures with varied: (i) nitrogen concentration (0–2 %) and (ii) substrate temperature (700–1050 °C). Comprehensive characterization techniques, including scanning electron microscopy (SEM), micro-Raman spectroscopy, and X-ray diffraction, were employed to assess the morphological, structural, and spectroscopic properties of the films. The study reveals that even minor additions of nitrogen significantly modulate secondary nucleation, impacting both film morphology and phase composition. Furthermore, substrate temperature emerges as another critical parameter, influencing the growth kinetics and crystallite size. The comparison of the characteristics of grown PCD films allowed us to find conditions for the formation of NCD films with minimal surface roughness and maximal growth rate: nitrogen concentration [N2] ≈ 0.2–0.5 % and temperature T ≈ 850–900 °C. These findings can be used to optimize the CVD synthesis parameters of PCD films for applications as protective or friction-reducing layers, as well as for superhard cutting tools and optical devices.

Dielectric behavior and defects of nitrogen-containing single crystal diamond films

Single crystal diamond (SCD) film, as a new substrate material, has attracted growing attention because of its low dielectric loss. The nitrogen was usually introduced into microwave plasma chemical vapor deposition (MPCVD) process in order to enhance the growth rate of SCD films. So SCD films with nitrogen were prepared by MPCVD compared with the undoped film. The impurities and defects of diamond films were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and photoluminescence spectroscopy (PL). The dielectric behavior of SCD films was measured using the LCR measurement in the frequency range of 1 kHz to 110 MHz. The results indicate that the primary dielectric loss in SCD films is conductivity loss and space charge polarization below 1 MHz, while the main dielectric loss is dipole orientation polarization and electronic relaxation polarization in the frequency range of 1 MHz to 110 MHz. Point defects like substitutional N+, NV− and SiV− exert a significant influence on polarization loss. This is essential to improve the growth of SCD with excellent dielectric properties.

Review of Materials Science and Technological Applications of a Unique Transformational Multifunctional Ultrananocrystalline Diamond (UNCD) Coating

Microcrystalline Diamond (MCD) (grains ≥ 1 µm) and Nanocrystalline Diamond (NCD) (grains 20-900 nm) coatings have been grown using Microwave Plasma Chemical Vapor Deposition (MPCVD), exciting H2/CH4 gas, via microwave power, in evacuated chambers, producing C atoms, bonding on surfaces with sp3 C atoms diamond bonds. Alternatively, MCD/NCD films have been grown via Hot Filament Chemical Vapor Deposition (HFCVD), using ~2200°C hot filaments, cracking CH4 into C atoms. Auciello-Gruen-Krauss developed (1990s) a transformational MPCVD process, growing unique multifunctional Ultrananocrystalline Diamond (UNCDTM) coating (3-5 nm grains), using patented Ar/CH4 gas mixture. Subsequently, Auciello’s group developed HFCVD process with Ar/CH4/H2 and H2/CH4. Gases flowing though filaments heated to ~2300°C. UNCD coatings exhibit unique multifunctionalities, enabling new industrial/high-tech/medical products, namely: 1) UNCD-coated pump seals/bearings/AFM tips (marketed worldwide since 2009); 2) unique electrically conductive Nitrogen atoms-grain boundary incorporated N-UNCD-coating on commercial graphite / copper anodes anodes, enabling superior stable capacity energy/safer Li-ion batteries; 3) Unique water corrosion resistant/electrically conductive Boron-doped B-UNCD-coated metal electrodes, purifying water, via viruses/pathogens’ killing by Ozone (O3) molecules generation.; 4) Best biocompatible UNCD coating (made of C atoms in human DNA/cells life’s elements) enable new medical products (e.g., UNCD-coated Si-microchip implanted on retina, to restore partial vision to blind people; UNCD-coated Dental Implants (DI), eliminating oral fluids corrosion of metal-DIs (clinical trials in progress),; 5) UNCD-coated magnet, outside eye, attracts injected biocompatible superparamagnetic nanoparticles, reattaching retina on eye’s wall; 6) superhydrophobic UNCD coated polymer-valves, drain inner eyes’ fluid of people with glaucoma, inhibiting blindness.

Uniform carbon pillars array grown on boron doped diamond for high-performance supercapacitors and hydrogen evolution reactions

Carbon materials have marvelous ability in energy storage and microelectronics as a result of the high specific surface area and electrical conductivity. However, the low stability and the low power density caused by low potential window make it particularly difficult for their application in aqueous electrolysis. In this study, boron doped diamond (BDD) with wide potential window is used as substrate and Ni as catalyst to grow uniform carbon pillars (CP) by microwave plasma chemical vapor deposition method. The composite structure (CP/BDD) yields significant specific capacity (91.64 mF cm−2 at 0.1 mA cm−2) and cycling stability (92.3 % retention rate after 20,000 cycles) when used as the electrode of supercapacitors, superior to most of BDD-based electrodes. The prepared symmetrical supercapacitor devices maintain their excellent electrochemical performance characteristics (power density of 4.4 mW cm−2 and energy density of 13.4 μW h cm−2), as well as high cycling stability. In addition, the electrode has considerable application potential in electrochemical hydrogen production with low hydrogen evolution potential and small Tafel slope value. These results illustrate the potential of BDD based composites for using as energy storage electrodes for electronic products and energy conversion equipment.

Edge effect during microwave plasma chemical vapor deposition diamond-film: Multiphysics simulation and experimental verification

Edge effect during microwave plasma chemical vapor deposition diamond-film: Multiphysics simulation and experimental verification

A Comparison of the Tribological Properties of SiC Coatings Prepared via Atmospheric Plasma Spraying and Chemical Vapor Deposition for Carbon/Carbon Composites

The microstructure, mechanical performance, and tribological properties of SiC ceramic coatings prepared via atmospheric plasma spraying (APS) and chemical vapor deposition (CVD) method were compared to provide good anti-wear protection for carbon/carbon composites. The surface morphology of the APS-SiC coating was characterized as having a porous structure, whilst the CVD-SiC coating presented with many pyramidal-shaped crystals constituting the surface. The APS-SiC coating consists of a dominating SiC phase and a small fraction of the Si phase, while the XRD pattern of the CVD-SiC coating mainly consists of the SiC phase. The dense crystalline microstructure of the CVD-SiC coating made it possess a higher hardness and Young’s modulus at 31.0 GPa and 275 GPa, respectively. The higher H/E and H3/E2 parameters of the CVD-SiC coating implied that it exhibited better plastic resistance, which is also beneficial for anti-wear properties. The scratch test reflected the critical loads of the spallation of the APS-SiC coating and CVD-SiC coating, which were evaluated to be 25.9 N and 36.4 N, respectively. In the tribological test, the friction coefficient of the APS-SiC coating showed obvious fluctuations at high load due to damage to the SiC coating. The wear mechanism of the APS-SiC coating was dominated by abrasive wear and fatigue wear, while CVD-SiC was mainly dominated by abrasive wear. The wear rate of the CVD-SiC coating was far below that of the APS-SiC coating, suggesting the better wear-resistance of the CVD-SiC coating.

Enhanced etching of GaN with N2 gas addition during CVD diamond growth

Diamond on GaN materials processing is not straight-forward, as GaN is susceptible to a quasi-pure hydrogen CVD plasma etching. 1%, 3% and 5% N2 gas was gradually added to the H2 gas with fixed 6% CH4 in the recipe to promote the growth of diamond nanocrystals. Different types of microstructures were produced, with addition of nitrogen to the precursor gas recipe. Nitrogen gas changes the diamond film microstructure from faceted to spherical grains, with signs of GaN etching. The FWHM of the sp3 carbon Raman peak was calculated to be 6.5 cm−1, when there was no nitrogen gas in the precursor recipe, which deteriorates to a large extent after successive addition of N2. Fourier transform infrared spectroscopy (FTIR) showed a strong presence of the nitrogen related defects (peak positions at 1190 and 1299 cm−1) inside the nanocrystalline diamond (NCD) films grown with N2 addition. GaN layer etching from the base substrate by the CVD plasma was clearly evidenced by energy dispersive X-ray spectra (EDS) of the deposited films. Al elemental EDS peaks from the base sapphire substrate were observed for the films grown with nitrogen addition, but no Ga EDS peaks were detected. X-ray diffraction (XRD) micrographs further supported the enhanced GaN etching phenomenon. The electrical resistivity of the uncoated GaN was initially measured to be 22.2 Ω-cm. However, the resistivity rose to 1.59 × 106 Ω-cm after the nitrogen assisted film deposition; due to the GaN etching - thereby exposing the underlying insulating sapphire substrate.

(Invited) Preparation of N-Type and P-Type Doped Single Crystal Diamonds with Laser-Induced Doping and Microwave Plasma Chemical Vapor Deposition

In this study, n-type doped single crystal diamonds were successfully prepared under normal temperature and pressure conditions using laser-induced doping. 248nm pulsed laser beams with nanosecond duration were irradiated on the single crystal diamond substrate immersing in an 85% phosphoric acid solution and it introduced phosphorus doping to form an n-type doped thin layer. The resistivity of the doped region significantly decreased compared to that of the single crystal diamond. After depositing a titanium electrode, the resistivity of the doped film obtained by Van der Pauw Technique was determined to be 1.3×10-6 Ω·m. Raman spectroscopy confirmed the absence of carbon or graphite phases in the laser-induced doped diamond, indicating that the enhanced conductivity was due to phosphorus incorporation.Furthermore, p-type doped single crystal diamonds were successfully prepared by introducing boron during the growth process using Microwave Plasma Chemical Vapor Deposition（MPCVD）. It was demonstrated that the proposed technique can introduce impurities into single crystal diamonds to form doped conductive thin layers, which has potential applications in the field of microdevices and integrated circuits.

Spectroscopic analysis of pulsed-mode plasma with argon addition for diamond growth

The advancement of high-speed growth technology for large-scale single-crystal diamonds is desired. In the widely used microwave plasma chemical vapor deposition method, the gas temperature in the plasma atmosphere significantly contributes to the generation of reactive radicals and enhancement of crystal growth. However, the impact of electron-dominated reactions in the plasma on the crystal growth remains unclear. In this study, we actively controlled the plasma environment by adding argon gas and adopting microwave pulse modulation to generate the plasma. We estimated the gas temperature and electron density of the plasma using optical emission spectroscopy. Our results implied that an increase in gas temperature alone hardly explained the enhancement of the growth rate by the argon addition or pulse modulation. In addition to the increase in the electron density due to the argon addition and pulse modulation, gas-phase chemical reaction calculations showed that the radical production enhancement became remarkable under an electron density higher than a threshold (1017 m−3). Therefore, the enhancement of the growth rate mentioned above may be attributed to electron-dominated reactions in the discharge region. These findings suggest that increasing the electron density can further improve the growth rate and potentially enable diamond synthesis at lower temperatures than traditional methods.

Enhanced growth rates of N-type phosphorus-doped polycrystalline diamond via in-liquid microwave plasma CVD

Phosphorus-doped diamond (PDD) exhibits excellent properties, making it suitable for a wide range of applications, such as electronic devices and electrodes. Here, we report the first synthesis of PDD by in-liquid microwave plasma CVD (IL-MPCVD) under high-pressure and low-power conditions. A mixture of methanol (MeOH) and ethanol (EtOH) with triethyl phosphate ((C2H5)3PO4) and (P/C = 1000 ppm) was used for the PDD deposition. Samples were characterized by laser microscopy, Raman spectroscopy, and glow discharge optical emission spectroscopy. Notably, PDD was successfully produced at a growth rate of 280 μm/h, which is two orders of magnitude higher than conventional CVD methods. Additionally, cyclic voltammetry (CV) and impedance spectroscopy (EIS) were used to evaluate the electrochemical properties of PDD. As a result, we confirmed the wide potential window characteristic of conductive diamond and determined that the donor density was [P] = 3.8 × 1017cm⁻³. Therefore, it is clear that IL-MPCVD is applicable for very high growth rates in the CVD process for PDD synthesis.

Microstructure control and mechanical properties of ultra-nanocrystalline diamond films

Ultra-nanocrystalline diamond (UNCD) films exhibit excellent mechanical properties because of their unique structure, such as small grain size and high grain boundary ratio. The effect of nitrogen atoms in nitrogen-doped UNCD films on their structure and mechanical properties deserves in-depth study. In this study, we focus on the microstructure control of UNCD films and its effect on the mechanical properties. Ultra-nanocrystalline diamond films were prepared using microwave plasma chemical vapor deposition under varying nitrogen flow rates. It was observed that the hardness and elastic modulus of UNCD films initially increased and then decreased with the increase of nitrogen flow rate. The structure of UNCD films was characterized using transmission electron microscopy and the crystal quality was analyzed through Raman spectroscopy. Nitrogen-interstitial atom defects were identified in the photoluminescence spectra. These defects contribute to shorter interatomic bonds and enhance the covalent bonds in the crystalline structure, resulting in an increase in hardness. The sp2/sp3 ratio and effective nitrogen atom concentration in the UNCD film were analyzed by X-ray photoelectron spectroscopy. The results indicate that an increase in the effective nitrogen atom concentration corresponds with a notable reduction in grain size, which is simultaneously accompanied by a rise in the number of grain boundaries. Meanwhile, the increase of sp2 content in the UNCD leads to the increase of grain boundary width and density, resulting in the increase of hardness and elastic modulus. This work provides theoretical basis and experimental guidance for the development of high performance UNCD films through precisely regulating the microstructure.

Evaluation of the effect of oxygen addition on charge carrier transport properties in single-crystal diamond growth

The effects of oxygen addition during single-crystal diamond growth by microwave plasma CVD method on crystal surface morphology and charge carrier transport properties were evaluated. Diamond single-crystals were homoepitaxially grown on (001) surface of high-pressure and high-temperature (HPHT) synthesized type IIa single-crystal diamond substrates with a fixed methane concentration of 1 % and oxygen concentrations of 0–0.8 %. Inverted pyramid-shaped pits were generated as the oxygen concentration increased. The free exciton recombination emission intensity in the cathodoluminescence spectrum reached a maximum at oxygen concentration of 0.5 %. The samples with oxygen concentrations of 0.5 % and 0.8 % showed excellent charge collection efficiency and energy resolution. On the other hand, the mobility-lifetime (μτ) product was only (7.1 ± 1.7) × 10−5 cm2/V, which is approximately 1/4 of that of the sample with 0.2 % methane and no oxygen addition.