Showing papers on "Plasma-enhanced chemical vapor deposition published in 2021"

Carbon nanotubes: a review on properties, synthesis methods and applications in micro and nanotechnology

Abstract: This research article discusses the types of carbon nanotubes and some related properties, synthesis methods and applications. In this research article, the specificities of SWCNTs as well as MWCNTs are described along with the extraordinary properties of carbon nanotubes such as electrical conductance, resistivity, and thermal conductivity in the direction of axis of the tube. Overview of certain specific methods for the growth of carbon nanotubes has also been reviewed. Previously available methods for the formation of CNTs are also described which include: arc discharge, laser ablation, chemical vapor deposition (CVD) and plasma enhanced chemical vapor deposition (PECVD). Carbon nanotubes have a number of applications in the field of electronics, biomedicine, and chemical sensors etc. Some of the applications are also briefly described.

Revealing Structural Disorder in Hydrogenated Amorphous Silicon for a Low-Loss Photonic Platform at Visible Frequencies.

Abstract: The high refractive index of hydrogenated amorphous silicon (a-Si:H) at optical frequencies is an essential property for the efficient modulation of the phase and amplitude of light. However, substantial optical loss represented by its high extinction coefficient prevents it from being utilized widely. Here, the bonding configurations of a-Si:H are investigated, in order to manipulate the extinction coefficient and produce a material that is competitive with conventional transparent materials, such as titanium dioxide and gallium nitride. This is achieved by controlling the hydrogenation and silicon disorder by adjusting the chemical deposition conditions. The extinction coefficient of the low-loss a-Si:H reaches a minimum of 0.082 at the wavelength of 450 nm, which is lower than that of crystalline silicon (0.13). Beam-steering metasurfaces are demonstrated to validate the low-loss optical properties, reaching measured efficiencies of 42%, 62%, and 75% at the wavelengths of 450, 532, and 635 nm, respectively. Considering its compatibility with mature complementary metal-oxide-semiconductor processes, the low-loss a-Si:H will provide a platform for efficient photonic operating in the full visible regime.

Plasma-Enhanced Chemical Vapor Deposition of Two-Dimensional Materials for Applications.

Abstract: ConspectusSince the rise of two-dimensional (2D) materials, synthetic methods including mechanical exfoliation, solution synthesis, and chemical vapor deposition (CVD) have been developed. Mechanical exfoliation prepares randomly shaped materials with small size. Solution synthesis introduces impurities that degrade the performances. CVD is the most successful one for low-cost scalable preparation. However, when it comes to practical applications, disadvantages such as high operating temperature (∼1000 °C), probable usage of metal catalysts, contamination, defects, and interstices introduced by postgrowth transfer are not negligible. These are the reasons why plasma-enhanced CVD (PECVD), a method that enables catalyst-free in situ preparation at low temperature, is imperatively desirable.In this Account, we summarize our recent progress on controllable preparation of 2D materials by PECVD and their applications. We found that there was a competition between etching and nucleation and deposition in PECVD, making it highly controllable to obtain desired materials. Under different equilibrium states of the competition, various 2D materials with diverse morphologies and properties were prepared including pristine or nitrogen-doped graphene crystals, graphene quantum dots, graphene nanowalls, hexagonal boron nitride (h-BN), B-C-N ternary materials (BCxN), etc. We also used mild plasma to modify or treat 2D materials (e.g., WSe2) for desired properties.PECVD has advantages such as low temperature, transfer-free process, and industrial compatibility, which enable facile, scalable, and low-cost preparation of 2D materials with clean surfaces and interfaces directly on noncatalytic substrates. These merits significantly benefit the as-prepared materials in the applications. Field-effect transistors with high motilities were directly fabricated on graphene and nitrogen-doped graphene. By use of h-BN as the dielectric interfacial layer, both mobilities and saturated power densities of the devices were improved owing to the clean, closely contacted interface and enhanced interfacial thermal dissipation. High-quality materials and interfaces also enabled promising applications of these materials in photodetectors, pressure sensors, biochemical sensors, electronic skins, Raman enhancement, etc. To demonstrate the commercial applications, several prototypical devices were studied such as distributed pressure sensor arrays, touching module on a robot hand for braille recognition, and smart gloves for recording sign language. Finally, we discuss opportunities and challenges of PECVD as a comprehensive preparation methodology of 2D materials for future applications beyond traditional CVD.

Nucleation and growth dynamics of graphene grown by radio frequency plasma-enhanced chemical vapor deposition.

Abstract: We investigated the nucleation and grain growth of graphene grown on Cu through radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) at different temperatures. A reasonable shielding method for the placement of copper was employed to achieve graphene by RF-PECVD. The nucleation and growth of graphene grains during PECVD were strongly temperature dependent. A high growth temperature facilitated the growth of polycrystalline graphene grains with a large size (~ 2 μm), whereas low temperature induced the formation of nanocrystalline grains. At a moderate temperature (790 to 850 °C), both nanocrystalline and micron-scale polycrystalline graphene grew simultaneously on Cu within 60 s with 50 W RF plasma power. As the growth time increased, the large graphene grains preferentially nucleated and grew rapidly, followed by the nucleation and growth of nanograins. There was competition between the growth of the two grain sizes. In addition, a model of graphene nucleation and grain growth during PECVD at different temperatures was established.

Compositional, Structural, Morphological, and Optical Properties of ZnO Thin Films Prepared by PECVD Technique

Abstract: ZnO thin films were synthesized on silicon and glass substrates using the plasma-enhanced chemical vapor deposition (PECVD) technique. Three samples were prepared at substrates temperatures of 200, 300, and 400 °C. The surface chemical composition was analyzed by the use of X-Ray Photoelectron spectroscopy (XPS). Structural and morphological properties were studied by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Optical properties were carried out by UV-visible spectroscopy. XPS spectra showed typical peaks of Zn(2p3/2), Zn(2p1/2), and O(1s) of ZnO with a slight shift attributed to the substrate temperature. XRD analysis revealed hexagonal wurtzite phases with a preferred (002) growth orientation that improved with temperature. Calculation of grain size and dislocation density revealed the crystallization improvement of ZnO when the substrate temperature varied from 200 to 400 °C. SEM images of ZnO films showed textured surfaces composed of grains of spherical shape uniformly distributed. The transmittance yields are reaching 80%, and the values of the band-gap energy indicate that the ZnO films prepared by PECVD present transparent and semiconducting properties.

Surface-Functionalized Boron Nanoparticles with Reduced Oxide Content by Nonthermal Plasma Processing for Nanoenergetic Applications.

Abstract: The development of an in situ nonthermal plasma technology improved the oxidation and energy release of boron nanoparticles. We reduced the native oxide layer on the surface of boron nanoparticles (70 nm) by treatment in a nonthermal hydrogen plasma, followed by the formation of a passivation barrier by argon plasma-enhanced chemical vapor deposition (PECVD) using perfluorodecalin (C10F18). Both processes occur near room temperature, thus avoiding aggregation and sintering of the nanoparticles. High-resolution transmission electron microscopy (HRTEM), high-angular annular dark-field imaging (HAADF)-scanning TEM (STEM)-energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) demonstrated a significant reduction in surface oxide concentration due to hydrogen plasma treatment and the formation of a 2.5 nm thick passivation coating on the surface due to PECVD treatment. These results correlated with the thermal analysis results, which demonstrated a 19% increase in energy release and an increase in metallic boron content after 120 min of hydrogen plasma treatment and 15 min of PECVD of perfluorodecalin. The PECVD coating provided excellent passivation against air and humidity for 60 days. We conclude in situ nonthermal plasma reduction and passivation lead to the amelioration of energy release characteristics and the storage life of boron nanoparticles, benefits conducive for nanoenergetic applications.

Antimony doped SnO2 nanowire@C core-shell structure as a high-performance anode material for Lithium-ion Battery

Abstract: SnO2 is considered as one of the high specific capacity anode materials for Lithium-ion batteries. However, the low electrical conductivity of SnO2 limits its applications. This manuscript reports a simple and efficient approach for the synthesis of Sb-doped SnO2 nanowires (NWs) core and carbon shell structure which effectively enhances the electrical conductivity and electrochemical performance of SnO2 nanostructures. Sb doping was performed during the vapor-liquid-solid (VLS) synthesis of SnO2 NWs in a horizontal furnace. Subsequently, carbon nanolayer was coated on the NWs using the DC Plasma Enhanced Chemical Vapor Deposition (DC-PECVD) approach. The carbon-coated shell improves the Solid-Electrolyte Interphase (SEI) stability and alleviates the volume expansion of the anode electrode during charging and discharging. The Sb-doped SnO2 core carbon shell anode showed the superior specific capacity of 585 mAhg-1 after 100 cycles at the current density of 100 mA g-1, compared to the pure SnO2 NWs electrode. The cycle stability evaluation revealed that the discharge capacity of pure SnO2 NWs and Sb doped SnO2 NWs electrodes were dropped to 52 and 152 mAh g-1 after100th cycles. The process of Sb doping and carbon nano shielding of SnO2 nanostructures is proposed for noticeable improvement of the anode performance for SnO2 based materials.

Atomic layer deposition of vanadium oxide films for crystalline silicon solar cells

Abstract: Transition metal oxides (TMOs) are promising materials to develop selective contacts on high-efficiency crystalline silicon solar cells. Nevertheless, the standard deposition technique used for TMOs is thermal evaporation, which could add potential scalability problems to industrial photovoltaic fabrication processes. As an alternative, atomic layer deposition (ALD) is a thin film deposition technique already used for dielectric deposition in the semiconductor device industry that has a straightforward up scalable design. This work reports the results of vanadium oxide (V2O5) films deposited by ALD acting as a hole-selective contact for n-type crystalline silicon (c-Si) solar cell frontal transparent contact without the additional PECVD passivating layer. A reasonable specific contact resistance of 100 mΩ cm2 was measured by the transfer length method. In addition, measurements suggest the presence of an inversion layer at the c-Si/V2O5 interface with a sheet resistance of 15 kΩ sq−1. The strong band bending induced at the c-Si surface was confirmed through capacitance–voltage measurements with a built-in voltage value of 683 mV. Besides low contact resistance, vanadium oxide films provide excellent surface passivation with effective lifetime values of up to 800 μs. Finally, proof-of-concept both-side contacted solar cells exhibit efficiencies beyond 18%, shedding light on the possibilities of TMOs deposited by the atomic layer deposition technique.

Structure and gas separation properties of ultra-smooth PE-CVD silicon organic coated composite membranes

Abstract: The layer properties of plasma polymerized membranes produced in a microwave-excited PECVD process depend on the reactor properties, process characteristics and the properties of the substrate used In order to be able to control gas separation properties for specific applications, thin silicon based SiOCH coatings were deposited on PDMS substrates The influence of oxygen to monomer ratios and of microwave power input were investigated, as their variation in the process is generally known to have a significant influence on the formation of the layer structure Correlations between process parameters, coating properties and gas separation or membrane performance were evaluated by permeation measurements, structure analysis (FESEM, AFM) and chemical analysis (XPS, FTIR) The investigations show a strong dependence of the membranes gas separation properties on the adjusted PECVD process parameters It was possible to produce dense, ultra-smooth SiOCH coatings with ideal selectivities in the range of >40 for He/N2; 10 for He/CO2 and > 8 for CO2/N2

The impact of processing conditions and post-deposition oxidation on the opto-electrical properties of hydrogenated amorphous and nano-crystalline Germanium films

Abstract: Low-cost multijunction photovoltaic devices are the next step in the solar energy revolution. Adding a bottom junction with a low bandgap energy material through plasma enhanced chemical vapor deposition (PECVD) processing could potentially provide a low-cost boost in conversion efficiency. A logical candidate for this low bandgap material is germanium. In this work we investigate the growth of PECVD processed hydrogenated amorphous/nano-crystalline germanium (a/nc-Ge:H), by characterizing over 100 samples, processed with a wide range of deposition pressures, powers, temperatures and GeH4 dilution in hydrogen, using elemental analysis, vibrational analysis and analysis of the opto-electrical properties. We have identified a small processing window in which nc-Ge:H films are processed reproducibly. We also report on the strong correlation between the refractive index of the films and the presence- and extent of post-deposition oxidation. Notably, the oxidation generally increased the photoresponse of the films, as it results in a decrease of room temperature σ d by 1-3 orders of magnitude. However, oxidation results in an increase of the bandgap energy and therefore impedes the development of a low bandgap material. The lowest E 04 we report is about 1.1eV, with an E Tauc of 0.9eV and an σ ph / σ d of 3.4.

Improvement of polymer properties for powder bed fusion by combining in situ PECVD nanoparticle synthesis and dry coating

Abstract: Polypropylene (PP) powders are coated with silica nanoparticles in a fluidized bed to improve the flow behavior of the powders and the processability in powder bed fusion. The nanoparticles are produced in situ via dusty plasma‐enhanced chemical vapor deposition (PECVD) in an atmospheric‐pressure Ar/O2 plasma jet fixed at the distributor plate of the fluidized bed. Hexamethyldisiloxane is used as a precursor of the nanoparticles. The influence of the oxygen concentration in the plasma gas and the number of treatment cycles on the chemical composition of the nanoparticles, the amount of nanoparticles deposited, and the flow properties of the coated PP powders is investigated. The chemical composition of the formed silica particles is determined by X‐ray photon spectroscopy and infrared spectroscopy. The results reveal that the composition of the nanoparticles is SiOxCy, that is, the portion of organic residues introduced by the precursor can be controlled by changing the oxygen concentration in the plasma gas. The mass of nanoparticles deposited on the polymer powder's surface, as determined by inductively coupled optical emission spectroscopy, shows a linear dependence of the number of cycles and the oxygen concentration in the plasma gas. A considerable improvement of the flow behavior of the PP powders is observed after PECVD treatment.

Preventing Corrosion of Aluminum Metal with Nanometer-Thick Films of Al 2 O 3 Capped with TiO 2 for Ultraviolet Plasmonics

Abstract: Extending plasmonics into the ultraviolet range imposes the use of aluminum to achieve the best optical performance. However, water corrosion is a major limiting issue for UV aluminum plasmonics, as this phenomenon occurs significantly faster in presence of UV light, even at low laser powers of a few microwatts. Here we assess the performance of nanometer-thick layers of various metal oxides deposited by atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD) on top of aluminum nanoapertures to protect the metal against UV photocorrosion. The combination of a 5 nm Al2O3 layer covered by a 5 nm TiO2 capping provides the best resistance performance, while a single 10 nm layer of SiO2 or HfO2 is a good alternative. We also report the influence of the laser wavelength, the laser operation mode and the pH of the solution. Properly choosing these conditions significantly extends the range of optical powers for which the aluminum nanostructures can be used. As application, we demonstrate the label-free detection of streptavidin proteins with improved signal to noise ratio. Our approach is also beneficial to promote the long-term stability of the aluminum nanostructures. Finding the appropriate nanoscale protection against aluminum corrosion is the key to enable the development of UV plasmonic applications in chemistry and biology.

Oxygen-Assisted Trimming Growth of Ultrahigh Vertical Graphene Films in a PECVD Process for Superior Energy Storage.

Abstract: Combining the advantages of a three-dimensional structure with intrinsic properties of graphene, vertical graphene (VG) synthesized by the plasma-enhanced chemical vapor deposition (PECVD) process has shown great promise to be applied to energy-storage electrodes. However, the practical application of the VG electrodes suffers from the limited height, which is mostly in a scale of few hundreds of nanometers, as shown in the previous studies. The reason for the unacceptable thin VG film deposition is believed to be the height saturation, stemming from the inevitable confluence of the VG flakes along with the deposition time. In this study, we developed an oxygen-assisted "trimming" process to eliminate the overfrondent graphene nanosheets thereby surmounting the saturation of the VG thickness during growth. In this approach, the height of the VGs reaches as high as 80 μm. Tested as supercapacitor electrodes, a desirable capacitance of 241.35 mF cm-2 is obtained by the VG films, indicating the superior electrochemical properties and the potential for applications in energy storage. It is worth noting, this thickness is by no means the maximum that can be achieved with our synthesis technique and higher capacitance can be achieved by conducting the circulating deposition-correction process in our work.

Diamond Schottky p-i-n diodes for high power RF receiver protectors

Abstract: The electrical characteristics of diamond Schottky p-i-n diodes grown by plasma enhanced chemical vapor deposition have been measured from DC to 25 GHz and used to extract the small-signal parameters for a lumped-element compact model. The model accurately reproduces the forward and reverse bias DC characteristics, the capacitance-voltage behavior, as well as the insertion and reflection loss. The high thermal conductivity of diamond makes the diodes ideally suited for high power radar receiver protector applications. We demonstrate that under forward bias a single diode can provide 14 dB of input power attenuation. For self-biased limiter applications, a two-stage circuit with back-to-back diodes has been simulated using the diode model to show > 20 dB of attenuation at an input power of 50 dBm.

Depositing chromium oxide film on alumina ceramics enhances the surface flashover performance in vacuum via PECVD

Abstract: Surface flashover seriously restricts the electrical performance of insulating system in vacuum. Surface properties of the insulating materials are the key factors affecting the electrical property along the surface. In this paper, Atmospheric-Pressure Plasma Enhanced Chemical Vapor Deposition (AP-PECVD) is used to deposit chromium oxide film on alumina ceramics to improve its flashover voltage in vacuum. Chromium acetylacetonate and argon are used as the precursor and working gas, respectively. A homemade ultrasonic atomizer and gas distribution system are used to ensure the uniformity during the AP-PECVD. For comparison, deposition experiments are both carried out at atmospheric and sub-atmospheric pressures. The experimental results show that the surface flashover voltages in 10−4 Pa are increased by 20% and 26% after the PECVD at atmospheric and sub-atmospheric pressures, respectively. The physicochemical and electrical property indicates that more shallow traps are introduced into the surface of alumina ceramics. The initial potential of the deposited sample decreases by 36% after the AP-PEVCD. Therefore, the deposition of chromium oxide films on alumina ceramics by AP-PECVD can effectively inhibit the surface charge accumulation and improve the surface flashover voltage in vacuum by reducing the trap energy level and its density. Based on the SEEA (secondary electron avalanche) theory and the distribution of the surface traps, the effects of chromium oxide films deposited on alumina ceramics are summarized for the application of vacuum insulation. The feasibility of depositing chromium oxide films to improve the vacuum surface flashover voltage of alumina ceramics by PECVD is proved. The process of the PECVD at atmospheric pressure is flexible, which provides a promising technical support for enhancing surface flashover for other insulating materials.

Excellent Passivation of n‐Type Silicon Surfaces Enabled by Pulsed‐Flow Plasma‐Enhanced Chemical Vapor Deposition of Phosphorus Oxide Capped by Aluminum Oxide

Abstract: Phosphorus oxide (POx) capped by aluminum oxide (Al2O3), prepared by atomic layer deposition (ALD), has recently been introduced as a surface passivation scheme for planar n‐type FZ silicon. In this work, a fast pulsed‐flow plasma‐enhanced chemical vapor deposition (PECVD) process for the POx layer is introduced, making it possible to increase the POx deposition rate significantly while maintaining the POx/Al2O3 passivation quality. An excellent surface passivation is realized on n‐type planar FZ and Cz substrates (J0 = 3.0 fA cm−2). Furthermore, it is demonstrated that the POx/Al2O3 stack can passivate textured surfaces and that the application of an additional PECVD SiNx capping layer renders the stack stable to a firing treatment that is typically used in fire‐through contact formation (J0 = 12 fA cm−2). The excellent surface passivation is enabled by a high positive fixed charge density (Qf ≈ 4 × 1012 cm−2) and an ultralow interface defect density (Dit ≈ 5 × 1010 eV−1 cm−2). Finally, outstanding passivation is demonstrated on textured silicon with a heavy n+ surface doping, as is used in solar cells, on par with alnealed SiO2. These findings indicate that POx/Al2O3 is a highly suited passivation scheme for n‐type silicon surfaces in typical industrial solar cells.