Plasma-assisted Chemical Vapor Deposition Research Articles

Ultra-Efficient Heat Transport Across a "2.5D" All-Carbon sp2/sp3 Hybrid Interface.

Single- and few-layer graphene-based thermal interface materials (TIMs) with extraordinary high-temperature resistance and ultra-high thermal conductivity are very essential to develop the next-generation integrated circuits. However, the function of the as-prepared graphene-based TIMs would undergo severe degradation when being transferred to chips, as the interface between the TIMs and chips possesses a very small interfacial thermal conductance. Here, a "2.5D" all-carbon interface containing rich covalent bonding, namely a sp2/sp3 hybrid interfaces is designed and realized by a plasma-assisted chemical vapor deposition with a function of ultra-rapid quenching. The interfacial thermal conductance of the 2.5D interface is excitingly very high, up to 110-117 MWm-2 K-1 at graphene thickness of 12-25 nm, which is even more than 30 % higher than various metal/diamond contacts, and orders of magnitude higher than the existing all-carbon contacts. Atomic-level simulation confirm the key role of the efficient heat conduction via covalent C-C bonds, and reveal that the covalent-based heat transport could contribute 85 % to the total interfacial conduction at a hybridization degree of 22 at %. This study provides an efficient strategy to design and construct 2.5D all-carbon interfaces, which can be used to develop high performance all-carbon devices and circuits.

A multi-method study of femtosecond laser modification and ablation of amorphous hydrogenated carbon coatings

We present a study on femtosecond laser treatment of amorphous hydrogen-containing carbon coatings (a-C:H). The coatings were deposited on silicon wafers by a plasma-assisted chemical vapour deposition (PA-CVD), resulting in two different types of material with distinct properties (referred to as “absorbing” and “semi-transparent” coatings in the following). The samples were laser-treated with single fs-laser pulses (800 nm center wavelength, 35 fs pulse duration) in the ablative regime. Through a multi-method approach using topometry, Raman spectroscopy, and spectroscopic imaging ellipsometry, we can identify zones and thresholds of different fluence dependent effects and have access to the local dielectric function. The two coating materials react significantly different upon laser treatment. We determined the (non-ablative) modification threshold fluence for the absorbing coating as 3.6×10-2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$3.6\ imes {10}^{-2}$$\\end{document} Jcm−2 and its ablation threshold as 0.22 Jcm−2. The semi-transparent coating does not show such a low-fluence modification but exhibits a characteristic interference-based intra-film ablation mechanism with two distinguishable ablation thresholds at 0.25 and 0.28 Jcm−2, respectively. The combination of tailored layer materials and correlative imaging spectroscopic methods delivers new insights into the behaviour of materials when treated with ultrashort-pulse laser radiation.Graphical abstract

8-Inch Wafer Scale, Transfer-Free, High-Quality Monolayer Graphene Growth on Ti-Buffered Si (001) Substrates At 100 ºC via Plasma-Assisted Chemical Vapor Deposition

8-Inch Wafer Scale, Transfer-Free, High-Quality Monolayer Graphene Growth on Ti-Buffered Si (001) Substrates At 100 ºC via Plasma-Assisted Chemical Vapor Deposition

Electrochemical carboxylation: Green synthesis of atrolactic acid using boron-doped diamond electrodes

Electrochemical CO2 fixation is vital for sustainability in the chemical industry, yet the selective synthesis of multi-carbon products remains challenging. Organic electrosynthesis offers promise by enabling precise control over reaction conditions and facilitating novel reactivity patterns. One such technique, electrochemical carboxylation, involves coupling CO2 with organic molecules to produce carboxylic acids. Specifically, electro-carboxylation of acetophenone yields atrolactic acid, a valuable precursor for nonsteroidal anti-inflammatory drugs, providing a greener alternative to traditional production methods. This study focuses on the synthesis and characterization of boron-doped diamond (BDD) films using the microwave plasma-assisted chemical vapor deposition (MP-CVD) method and synthesized BDD electrodes were then used for the electrolytic carboxylation of acetophenone. Various analytical techniques, including X-ray diffraction (XRD), Raman spectroscopy, and laser microscopy, etc. were employed to characterize the BDD films. Various BDD films synthesized for different durations were utilized in the electrolytic carboxylation of acetophenone, with the highest yield of atrolactic acid (25 %) achieved using a BDD film synthesized over 6 h. Also, the effect of BDD surface modification i.e. oxygen and hydrogen terminated BDD on the synthesis of atrolactic acid was studied. Additionally, different electrolytes were employed in the synthesis process of atrolactic acid. A comparative study between Pt and BDD electrodes for the electrolytic carboxylation of acetophenone was conducted, and a mechanism for the formation of atrolactic acid was proposed.

Growth of single crystalline GeSn alloy epilayer on Gd2O3/Si (111) engineered insulating substrate using RF sputtering and solid phase epitaxy

The article showcases a low-cost, low-temperature deposition andHVMtechnique to develop single crystalline GeSn alloy epilayers on Gd2O3/Si (111) substrate. First, GeSn alloy amorphous layer is deposited on the insulating substrates using an Radio Frequency (RF) sputtering apparatus. Subsequently, an inductively coupled plasma-assisted chemical vapor deposition (ICP-CVD) process is used to deposit a SiO2 capping layer to protect against Sn out-diffusion during heat treatment. The samples are then subjected to solid phase epitaxy (SPE) at 450 °C, 550 °C, and 650 °C. Sample processed for SPE at 450 °C has weak crystallinity and only shows Type-A stacking. Those processed for SPE at 550 °C and 650 °C, on the other hand, have revealed formation of the single-crystalline GeSn alloy epilayer with Type-A and Type-B stacking. However, SPE at 650 °C revealed tin out-diffusion and segregation effects. This work is significant for enabling the preparation of high-Sn-content GeSn alloy epilayers on insulating Gd2O3/Si (111) substrates, as it requires the initial deposition of a GeSn amorphous alloy epilayer using RF sputtering. This advancement promises benefits which includes advantages such as lower operating voltage, reduced leakage current, and minimized parasitic and short-channel effects, making it ideal for advancing RF technology.

Roll-to-Roll SiOx Synthesis on Polyethylene Terephthalate Film by Atmospheric-Pressure Plasma-Assisted Chemical Vapor Deposition

Silicon oxide (SiOx) coatings are attracting significant attention and are widely used in industrial applications. They can be prepared by plasma-assisted chemical vapor deposition (PACVD). PACVD at atmospheric pressure (AP-PACVD) is often employed to synthesize SiOx coatings, but it has generally not been scaled up to an industrially viable level. In the present work, a SiOx coating was continuously deposited onto a polyethylene terephthalate film using industrial-scale roll-to-roll type AP-PACVD. 1,1,3,3-Tetramethyldisiloxane (TMDSO) and tetraethoxysilane (TEOS) were selected as precursors. The elemental compositions and chemical structures of the SiOx coatings were characterized, and oxygen and water-vapor transmission rates were measured. The SiOx coating using TEOS exhibited better barrier properties than that using TMDSO, corresponding to the high oxygen content, high SiO2 content, and high siloxane network content in the SiOx coating.

Nitrogen-Doped 3D-Graphene Advances Near-Infrared Photodetector for Logic Circuits and Image Sensors Overcoming 2D Limitations.

The limitations of two-dimensional (2D) graphene in broadband photodetector are overcome by integrating nitrogen (N) doping into three-dimensional (3D) structures within silicon (Si) via plasma-assisted chemical vapor deposition (PACVD) technology. This contributes to the construction of vertical Schottky heterojunction broad-spectrum photodetectors and applications in logic devices and image sensors. The natural nanoscale resonant cavity structure of 3D-graphene enhances photon capture efficiency, thereby increasing photocarrier generation. N-doping can fine-tune the electronic structure, advancing the Schottky barrier height and reducing dark current. The as-fabricated photodetector exhibits exceptional self-driven photoresponse, especially at 1550 nm, with an excellent photoresponsivity (79.6 A/W), specific detectivity (1013 Jones), and rapid response of 130 μs. Moreover, it enables logic circuits, high-resolution pattern image recognition, and broadband spectra recording across the visible to near-infrared range (400-1550 nm). This research will provide new views and technical support for the development and widespread application of high-performance semiconductor-based graphene broadband detectors.

Exploring the Microstructural Effect of FeCo Alloy on Carbon Microsphere Deposition and Enhanced Electromagnetic Wave Absorption.

The rational design of magnetic carbon composites, encompassing both their composition and microstructure, holds significant potential for achieving exceptional electromagnetic wave-absorbing materials (EAMs). In this study, FeCo@CM composites were efficiently fabricated through an advanced microwave plasma-assisted reduction chemical vapor deposition (MPARCVD) technique, offering high efficiency, low cost, and energy-saving benefits. By depositing graphitized carbon microspheres, the dielectric properties were significantly enhanced, resulting in improved electromagnetic wave absorption performances through optimized impedance matching and a synergistic effect with magnetic loss. A systematic investigation revealed that the laminar-stacked structure of FeCo exhibited superior properties compared to its spherical counterpart, supplying a higher number of exposed edges and enhanced catalytic activity, which facilitated the deposition of uniform and low-defect graphitized carbon microspheres. Consequently, the dielectric loss performance of the FeCo@CM composites was dramatically improved due to increased electrical conductivity and the formation of abundant heterogeneous interfaces. At a 40 wt% filling amount and a frequency of 7.84 GHz, the FeCo@CM composites achieved a minimum reflection loss value of -58.2 dB with an effective absorption bandwidth (fE) of 5.13 GHz. This study presents an effective strategy for developing high-performance EAMs.

Comparative analysis: CapEx in diamond mining versus diamond growing, based on open data sources and experimental results

The diamond industry has long been associated with environmental and social problems, ranging from mining practices to ethical concerns related to diamond sourcing. In recent years, there has been a growing interest in lab-grown diamonds as a sustainable alternative for diamond consumers. However, the production of lab-grown diamonds has own challenges. This article examines the capital expenditures per annualized carat of rough diamonds obtained through mining and two fabrication methods: high-pressure high-temperature (HPHT) and microwave plasma-assisted chemical vapour deposition (MP CVD). Lab-grown diamonds produced using HPHT and MP CVD methods require significantly higher capital expenditures per annualized carat compare to mined diamonds. HPHT diamonds require on-time CapEx of 500–833 US$ per carat annually, while MP CVD diamonds demand 549–1648 US$ per carat annually. Finding ways to reduce production cost and increase efficiency will be crucial in realizing the potential of lab-grown diamonds as a sustainable alternative to mined diamonds.

Annealing process and temperature effects on silicon-vacancy and germanium-vacancy centers in CVD grown polycrystalline diamond

The annealing treatment plays a crucial role in tailoring the properties of synthetic diamond materials, especially those doped with various elements in order to form specific color centers like nitrogen-vacancy (NV), silicon-vacancy (Si-V), germanium-vacancy (Ge-V), etc. This study delves into the annealing of 175 μm-thick Ge-doped polycrystalline diamond (PCD) films grown by microwave plasma-assisted chemical vapor deposition (MPCVD). Large-area PCD plate was cut into smaller equivalent 5 × 5 mm2 pieces, which were separately subjected to annealing in microwave plasma in H2 atmosphere, to annealing in vacuum or to annealing under high-pressure high-temperature conditions (HPHT, 5.9 GPa, 2000 °C). The structure, phase composition and photoluminescence (PL) of samples before and after various annealing processes were investigated. All applied types of annealing enhance both the Si-V and Ge-V lines in PL at room temperature. Increasing annealing temperature leads to gradual decrease of full widths at half-maxima (FWHM) of diamond Raman peak (1332.5 cm−1), as well as Si-V (738 nm) and Ge-V (602 nm) PL peaks. In addition, the limitations for each type of annealing are established. The obtained results are crucial for the design of CVD-grown Ge-doped and Si-doped PCD materials that can be used for applications in photonics such as single photon sources, biomarkers, as well as for the fabrication of optical diamond thermometers.

Electrochemical characteristics of nano-structure TiCN coatings on the tool steel deposited by PACVD in various solutions

This study investigates The electrochemical behavior of various nano-structure TiCN coatings prepared using a plasma-assisted chemical vapor deposition technique in acidic and alkaline solutions. The N2/Ar ratio was varied to explore its effect on the microstructure and electrochemical properties of coatings on the steel cold-work tool. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PP) measurements were carried out in various corrosive solutions. Field emission scanning electron microscopy and X-ray diffraction were also utilized to evaluate the microstructure and phase detection. The EIS results showed that the resistance of TiCN coatings increased by about 94.3 % based on the equiaxed structure and small size of the coating cluster in 3.5 % wt NaCl solution after 24 h. The lowest corrosion rate with a value of 5.9 µA cm−2 in Ringer's solution at 37 °C after 24 h was attributed to the TiCN coating with the N2/Ar ratio of 0.4 according to exhibiting the highest Ti content and changes in present phases. The N2/Ar ratio of 0.7 effectively increased the impedance resistance to 97.5 % based on PP test results in 3 M H2SO4 solution. This behavior was related to the lowest value of the C/N ratio and the highest coating thickness.

Dielectric properties of low-temperature-grown homoepitaxial (−201) β-Ga2O3 thin film by atmospheric pressure plasma-assisted CVD

The atmospheric pressure plasma-assisted chemical vapor deposition technique has successfully demonstrated unintentionally doped (UID) Ga2O3 growth at 350 °C. This technique allows independent and homogeneous multiple nuclei growth of Ga2O3, leading to three-dimensional grain growth at a rate of ⁓0.17 μm/h. In the study of Schottky barrier diodes, the Schottky-like current (I)–voltage (V) response shows typical behavior on Ga2O3. This is a good sign at an early stage of device development on the grown sample. The extracted barrier height of ⁓2.20 eV was higher, which may be due to unintentional PtOx formation on the Ga2O3 surface. Furthermore, the extracted capacitance (C)–voltage (V) depth profiling of the effective impurity concentration was nearly flat, ⁓1.5 × 1017 cm−3, in the unintentionally doped grown film. The effective impurity concentration is comparable to the UID carrier concentration of epitaxial films fabricated using the high temperature growth technique. Therefore, low-temperature-grown homoepitaxial Ga2O3 thin films grown by atmospheric pressure-plasma-assisted chemical vapor deposition can be used in future Ga2O3-based power device applications.

Fabrication of high-density nitrogen-vacancy (NV) center-enriched diamond particles through methyl trityl amine (C20H19N) seeding

Diamond particles (DPs) show promise for advanced applications in bioimaging and quantum sensing due to the presence of defect centers. This work reports a unique growth process for diamond particles composed of nitrogen-vacancy centers (NV-DPs) using a methyl trityl amine (C20H19N) diamondoid seed, which acts as a nitrogen source for NV creation. Growth was performed via microwave plasma-assisted chemical vapor deposition in a CH4/H2 plasma. Tantalum plates were chosen as the substrate to facilitate the release of the NV-rich DPs after growth. Raman spectra of NV-DPs grown at 550 °C showed a sharp, intense peak at ∼1334 cm−1, while those grown at 750 °C exhibited a broader, high intensity peak at 1336 cm−1. Photoluminescence revealed the formation of high-density NV centers, with the highest intensity for NV-DPs grown at 750 °C and 20 Torr. Optically detected magnetic resonance confirmed the presence of NV centers, especially for DPs grown at 750 °C. This seeding process enables precise nitrogen incorporation into diamond crystals to generate required spin properties by growing high-quality, well-faceted NV-DPs with customizable NV densities.

Enhancing SERS Sensitivity in N‐Graphene Hydrangea by Synergistic Charge‐Transfer and Excitation Light Absorption

Surface‐enhanced Raman scattering (SERS) is a versatile spectroscopic technique, which plays a crucial role in enhancing analytical sensitivity, investigating interfacial reaction mechanisms, enabling biosensing, and fostering efficient catalysis. Currently, the common SERS substrates are primarily metal nanostructures, which entail high manufacturing costs, complex processes, and the metal surface undergo change over time and with environmental conditions. These issues limit the development of SERS technology. In this work, a nitrogen‐doped graphene (N‐graphene) hydrangea was synthesized on a silicon (Si) substrate using plasma‐assisted chemical vapor deposition (PACVD), forming an N‐graphene hydrangea/Si hybrid structure as a SERS substrate. This substrate offers the advantages of high stability, ultra‐sensitivity, and reusability. The three‐dimensional nano‐cavity structure of graphene can increase the interaction between light and graphene, resulting in an increased localized electric field. Combining theoretical simulation analysis, the introduction of nitrogen (N) elements adjusts the Fermi level of graphene, promoting efficient charge transfer. In practical scenarios, Di(2‐ethylhexyl) phthalate (DEHP), a commonly used plasticizer, has raised concerns due to its potential as an endocrine disruptor and carcinogen. The as‐prepared SERS substrate achieves a remarkable detection limit of as low as 10−8 m for DEHP, providing significant support for environmental conservation and human health.

GaSe/<i>β</i>-Ga<sub>2</sub>O<sub>3</sub> heterojunction based self-powered solar-blind ultraviolet photoelectric detector

UV photodetectors have the advantages of high sensitivity and fast response speed. As an ultra-wide bandgap semiconductor, gallium oxide (Ga<sub>2</sub>O<sub>3</sub>) plays an extremely important role in detecting deep ultraviolet. It can form a typical type-II heterostructure with GaSe, promoting carrier separation and transport. In this work, Ga<sub>2</sub>O<sub>3</sub> epitaxial films are grown on sapphire substrates by plasma-assisted chemical vapor deposition (PECVD). The GaSe films and GaSe/<i>β</i>-Ga<sub>2</sub>O<sub>3</sub> heterojunction photodetectors are grown on gallium oxide films by Bridgeman technology. The detector has a good response to deep ultraviolet light, the dark current of the device is only 1.83 pA at 8 V, and the photocurrent reaches 6.5 nA at 254 nm. The UVC/Visible (254 nm/600 nm) has a high rejection ratio of about 354. At very small light intensities, the responsivity and detection can reach 1.49 mA/W and 6.65 × 10<sup>11</sup> Jones, respectively. At the same time, due to the photovoltaic effect formed by the space charge region at the junction interface, the detector exhibits self-powered supply performance at zero bias voltage, and the open-circuit voltage is 0.2 V. In addition, the detector has a very good sensitivity. The device can respond quickly, whether it is irradiated with different light intensities under constant voltage, or with different voltages under constant light intensity. It can respond within milliseconds under a bias voltage of 10 V. This work demonstrates the enormous potential of heterojunctions in photoelectric detection by analyzing the photophysical and interface physical issues involved in heterojunction photodetectors, and provides a possibility for detecting the deep ultraviolet of gallium oxide.

Fabrication of polycrystalline phosphorus-doped diamond electrodes from red phosphorus.

Polycrystalline phosphorus-doped diamond was fabricated by the quartz-tube-type microwave plasma-assisted chemical vapor deposition method. Significantly, red phosphorus was used as a source of phosphorous, instead of PH3. Phosphorus-doped diamond electrodes with hydrogen-terminated and oxygen-terminated surfaces were investigated for the redox reactions of K3[Fe(CN)6] and [Ru(NH3)6]Cl3. The carrier concentration was estimated as 2.1-5.3 × 1018 cm-3 from electrochemical impedance measurements. Polycrystalline phosphorus-doped diamond shows great promise as chemical electrode materials.

Effect of plasma modulation on the nucleation and crystal evolution of nanodiamond seeds during CVD diamond growth

This study investigated the effect of plasma modulation on the nucleation and crystal evolution of nanodiamond seeds during chemical vapor deposition (CVD) diamond growth. To this end, secondary nucleation and growth of nanodiamond seeds on a mirror-polished silicon (100) substrate in nitrogen, oxygen, and nitrogen–oxygen co-doping environments were investigated using a 5500-W microwave plasma-assisted CVD (MPCVD) reactor. Plasma diagnosis was performed to determine the impact of auxiliary gas addition on plasma modulation using optical emission spectroscopy (OES). The results demonstrate that although nitrogen doping can promote secondary nucleation and growth of nanocrystalline diamond (NCD), it leads to the formation of twinned crystal defects and NCD aggregates, which reduce the quality of diamond growth. Similarly, although a small amount of oxygen doping can promote the competitive growth of nanodiamond seed crystals and catalyze the transition of diamond from the (111) to (220), excessive oxygen can inhibit diamond nucleation and growth. However, controlled plasma modulation can be achieved through appropriate nitrogen and oxygen additions. This study provides theoretical and experimental data for diamond nucleation, grain size, and orientation regulation in CVD diamond growth, and it can serve as a reference for studies on NCD and coatings. Furthermore, this study provides new insights into the growth of nitrogen–oxygen co-doped diamond films.

Narrowband photoluminescence of Tin-Vacancy colour centres inSn-doped chemical vapour deposition diamond microcrystals.

Tin-Vacancy (Sn-V) colour centres in diamond have a spin coherence time in the millisecond range at temperatures of 2 K, so they are promising to be used in diamond-based quantum optical devices. However, the incorporation of large Sn atoms into a dense diamond lattice is a non-trivial problem. The objective of our work is to use microwave plasma-assisted chemical vapour deposition (CVD) to grow Sn-doped diamond with submicron SnO2 particles as a solid-state source of impurity. Well-faceted diamond microcrystals with sizes of afewmicrometres were formed on AlN substrates. The photoluminescence (PL) signal with zero-phonon line (ZPL) peak for Sn-V centre at ≈620 nm was measured at room temperature (RT) and at 7 K. The peak width (full width at half-maximum) was measured to be 1.1-1.7 nm at RT and ≈0.05 nm at 7 K. The observed variations of ZPL shape and position, in particular, narrowing of PL peak at RT and formation of single-line fine structure at low-T, are attributed to strain in the crystallites. The diamond doping with Sn via CVD process offers a new route to from Sn-V colour centre in the bulk of the diamond crystallites. This article is part of the Theo Murphy meeting issue 'Diamond for quantum applications'.

Influence of process parameters including the confining magnetic field of a plasma beam source on the deposition of N‐doped hydrogenated carbon films

Electrically conductive nitrogen‐doped hydrogenated carbon films (a‐C:H:N) were deposited using a nitrogenacetylene gas mixture by plasma‐assisted chemical vapor deposition (PACVD). A capacitively coupled plasma beam source was used for the depositions. The plasma is excited by a radio‐frequency (RF) discharge and confined by Helmholtz magnetic coils, resulting in an increase in plasma density. The ion energy, as well as the deposition rate, can be controlled by the choice of the size of the coupling electrode, i.e. the ratio of cathode-to‐anode area, the electric current at the Helmholtz magnet coils, the total gas pressure and the RF power. The interdependence of these process parameters on the ion energy and the deposition rate has been studied in detail in this work. Hardness and electrical resistivity were measured on the deposited a‐C:H:N films.

Dual low pressure plasma process for SiCN:H thin films deposition: A comparative study

SiCN:H thin films have large possibilities of applications due to their versatile chemical and physical properties. Plasma Assisted Chemical Vapor Deposition (PACVD) process is widely used for SiCN:H deposition. Here we discuss on the potentialities of dual Electron Cyclotron Resonance (ECR) and Radio Frequency Magnetron Sputtering (rf MS) plasmas coupling for SiCN:H deposition in Ar/N2/Si(CH3)4 gas mixture. The study is carried out by varying the autopolarisation voltage Vbias of the silicon target. ECR plasma gives low deposition growth rate about 50 nm/h. The films are transparent. SiCN nanopillars with high aspect ratio are obtained. Rf MS plasma gives high deposition growth rate up to 2200 nm/h. The films are opaque in the near UV and transparent in the visible depending on their thickness. The optical index at 630 nm is 1.95, the Tauc's band gap is 3.0 eV and do not change with Vbias. Dual ECR/rf MS plasma gives high deposition growth rate up to 2300 nm/h. The films are transparent. The optical index varies between 1.7 and 2.05 at 630 nm and the Tauc's band gap decreases linearly between 4.75 and 3.4 eV with Vbias. Dual ECR/rf MS plasma coupling is a very promising PACVD process for thin films deposition.