Pulsed CVD Research Articles

Ultrasmall and Highly Dispersed Pt Entities Deposited on Mesoporous N-doped Carbon Nanospheres by Pulsed CVD for Improved HER.

Vapor-based deposition techniques are emerging approaches for the design of carbon-supported metal powder electrocatalysts with tailored catalyst entities, sizes, and dispersions. Herein, a pulsed CVD (Pt-pCVD) approach is employed to deposit different Pt entities on mesoporous N-doped carbon (MPNC) nanospheres to design high-performance hydrogen evolution reaction (HER) electrocatalysts. The influence of consecutive precursor pulse number (50-250) and deposition temperature (225-300°C) are investigated. The Pt-pCVD process results in highly dispersed ultrasmall Pt clusters (≈1nm in size) and Pt single atoms, while under certain conditions few larger Pt nanoparticles are formed. The best MPNC-Pt-pCVD electrocatalyst prepared in this work (250 pulses, 250°C) reveals a Pt HER mass activity of 22.2 ± 1.2Amg-1 Pt at -50mV versus the reversible hydrogen electrode (RHE), thereby outperforming a commercially available Pt/C electrocatalyst by 40% as a result of the increased Pt utilization. Remarkably, after optimization of the Pt electrode loading, an ultrahigh Pt mass activity of 56 ± 2Amg-1 Pt at -50mV versus RHE is found, which is among the highest Pt mass activities of Pt single atom and cluster-based electrocatalysts reported so far.

Low-k SiOx/AlOx Nanolaminate Dielectric on Dielectric Achieved by Hybrid Pulsed Chemical Vapor Deposition.

Selective and smooth low-k SiOx/AlOx nanolaminate dielectric on dielectric (DOD) was achieved by a hybrid water-free pulsed CVD process consisting of 50 pulses of ATSB (tris(2-butoxy)aluminum) at 330 °C and a 60 s TBS (tris(tert-butoxy)silanol) exposure at 200 °C. Aniline selective passivation was demonstrated on W surfaces in preference to Si3N4 and SiO2 at 300 °C. At 200 °C, TBS pulsed CVD exhibited no growth on W or SiO2, but its growth was catalyzed by AlOx. Using a two-temperature pulsed CVD process, ∼2.7 nm selective SiOx/AlOx nanolaminate was deposited on Si3N4 in preference to aniline passivated W. Nanoselectivity was confirmed and demonstrated on nanoscale W/SiO2 patterned samples by TEM analysis. For a 1:1 Si:Al ratio, a dielectric constant (k) value of 3.3 was measured. For a 2:1 Si:Al ratio, a dielectric constant (k) value of 2.5 was measured. The k value well below that of Al2O3 and SiO2 is consistent with the formation of a low-density, low-k SiO2/Al2O3 nanolaminate in a purely thermal process. This is the first report of a further thermal CVD process for deposition of a low-k dielectric and the first report for a selective low-k process on the nanoscale.

Development of gas-injected pulsed plasma CVD method using Ar/C2H2 mixed gas for ultra-high-rate diamond-like carbon deposition

A diamond-like carbon (DLC) fabrication method with a greater deposition rate and simple equipment configuration facilitates to introduce DLC coating technology to industrial processes. In this study, a gas-injected pulsed plasma CVD method using a single plasma source is proposed as an ultra-high-rate deposition method for DLC films. A gas mixture of Ar and C2H2 was injected into a vacuum chamber through a gas nozzle, and plasma in the chamber was generated by applying a negative pulse voltage to the substrate stage. The gas velocity in the chamber was calculated using computational fluid dynamics simulations. DLC films with a nanoindentation hardness of 17.5 GPa were fabricated on a limited area of a Si substrate at a deposition rate of 2480 nm min−1. The deposition rate of the DLC films can be further improved by optimizing the conditions of the Ar partial pressure ratio, gas velocity, and stage applied voltage.

Simplified CVD route to near-zero thickness silicon nitride films

Silicon nitride (SiNx, x ∼ 1) thin films were deposited by chemical vapor deposition on silicon oxide (SiO2) substrates by combining controlled pulses of the precursor 1,3,5-tri(isopropyl)cyclotrisilazane (TICZ, C9H27N3Si3) with a continuous ammonia (NH3) plasma. This plasma-assisted pulsed CVD (PPCVD) process enables the integration of the nanoscale thickness and uniformity control achieved in atomic layer deposition with the efficiency of plasma-enhanced CVD (PE-CVD). TICZ was selected because it is a nonpyrophoric stable liquid with a high vapor pressure (∼133 Pa at 70 °C) and could act as a single source for SiNx with both high Si and N contents. An optimized PPCVD process window was identified consisting of a substrate temperature of 350 °C, a TICZ pulse of ≤0.2 s, and a TICZ purge pulse ≥10 s in a continuous direct NH3 plasma at a NH3 flow rate and a power of 40 SCCM and 3000 W, respectively. The as-deposited films were analyzed by x-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry. XPS analysis confirmed the absence of any C inclusion and demonstrated the existence of the 1:1 Si:N ratio. In situ, real-time ellipsometry measurements indicated that SiNx growth occurred in a typical PE-CVD regime. They also yielded an as-grown SiNx average refractive index of ∼1.75.

Design of Organic-Free Superhydrophobic TiO2 with Ultraviolet Stability or Ultraviolet-Induced Switchable Wettability.

Superhydrophobic TiO2 with great application potential is mainly obtained by surface modification with low surface energy organics, which is easily degraded under sunlight irradiation, which results in the loss of superhydrophobic properties. Herein, we developed a room-temperature pulsed chemical vapor deposition (pulsed CVD) method to develop amorphous TiO2-deposited TiO2 nanoparticles. The ultraviolet stability/ultraviolet-induced reversible wettability switch had been simultaneously realized by different and controllable deposition cycles of amorphous TiO2. The superhydrophobic properties of the organic-free TiO2 were determined by the micrometer-nanometer-sub-nanometer multiscale structure, the multiscale pore structure, and the large Young's contact angle resulting from carboxylic acid adsorption. Also, we found that the adsorption rate and adsorption stability of oxygen and water at the surface oxygen vacancies were the key to facilitate the reversible switching between superhydrophilic and superhydrophobic states, which was well demonstrated by experimental characterization and theoretical simulation. In addition, we also found that the resistance of dense amorphous TiO2 films on the TiO2 surface to the migration of photogenerated electrons and holes was the key to maintain the stable superhydrophobic properties of superhydrophobic TiO2 under ultraviolet illumination. The powders were strongly ground and the coating surface was rubbed on the surface of the sandpaper, which still maintained superhydrophobic properties, providing favorable conditions for the application of superhydrophobic TiO2. This work modulates the ultraviolet stability and dark/ultraviolet-induced switchable superhydrophobicity/superhydrophilicity of coated TiO2 by simply adjusting the number of deposition times in a pulsed CVD process for the first time, thus contributing to the development of organic-free superhydrophobic TiO2.

Near-Room-Temperature Soft Plasma Pulsed Deposition of SiCxNy from 1,3,5-tri(isopropyl)cyclotrisilazane

The silicon-nitrogen material system, primarily in the form of silicon nitride (SiNx) and silicon silicon carbo-nitride (SiNxCy) (where 0<x<1.33 and 0<y<1) continues to witness tremendous research and development interest. This interest is driven by its highly desirable combination of physical, mechanical, electrical, and optoelectronic properties, making it one of the most useful materials in integrated circuitry (IC) applications. However, the drive towards more complex and smaller IC and hetero-device structures is significantly challenging established SiNx deposition methodologies. Low thermal exposure during fabrication of the device structures is becoming essential due to the complexity and thermally fragile nature of these structures, where temperature changes can induce undesirable reactions within substructures. Furthermore, with the thickness of films approaching atomic dimensions, thermally-induced migration, in addition to electromigration, can significantly alter film properties and performance. Another consideration is the desire to move towards more flexible substrates, such as plastic or polymer substrates, which typically cannot withstand the same process temperatures as traditional substrates, such as Si or GaN. Given these emerging thermal budget limitations, work by the present investigators has focused on the development and optimization of a remote plasma-activated ALD and/or pulsed CVD process for SiNxCy at exceptionally low temperatures as protective coatings on thermally and chemically fragile substrates such as polymers and plastics. In this presentation, results are presented for low temperature remote plasma-activated pulsed CVD (P-CVD) SiNxCy using 1,3,5-triisopropylcyclotrisilazane (C9H27Si3N3, TICZ) as source precursor. This presentation will provide the following: (i) the process window for deposition of SiNxCy through the P-CVD decomposition of TICZ as a single-source precursor without a co-reactant and using ammonia (NH3) as co-reactant; (ii) the lowest deposition temperature that can be achieved using this process; (iii) the chemical, compositional, morphological, and structural properties of the resulting films as function of processing parameters, with particular emphasis on film composition, density, etch rate, and structure (amorphous versus crystalline); (iv) the effects of the process on thermally and chemically fragile substrates, such as polymers and plastics; and (v) how to deposit good quality SiNxCy while maintaining the structural and chemical integrity of such substrates, including in particular at the film-substrate interface? The instantaneous growth of the SiNxCy film on multiple types of substrates during the remote plasma pulse of the P-CVD process was observed by in-situ, real-time, ellipsometry (an example is provided in Figure 1) and the resulting films were further analyzed by XPS and wet etch rate studies. Figure 1

Atomic layer deposited V2O5 coatings: a promising cathode for Li-ion batteries

A modified, thermal atomic layer deposition process was employed for the pulsed chemical vapor deposition growth of vanadium pentoxide films using tetrakis (dimethylamino) vanadium and water as a co-reagent.Depositions were carried out at 350oC for 400 pulsed CVD cycles, and samples were subsequently annealed for 1hour at 400°C in air to form materials with enhanced cycling stability during the continuous lithium-ion intercala­tion/deintercalation processes. The diffusion coefficient was estimated to be 2.04x10-10 and 4.10x10-10 cm2 s-1 for the cathodic and anodic processes, respectively. These values are comparable or lower than those reported in the literature, indicating the capability of Li+ of getting access into the vanadium pentoxide framework at a fast rate. Overall, it presents a specific discharge capacity of 280 mAh g-1, capacity retention of 75 % after 10000 scans, a coulombic efficiency of 100 % for the first scan, dropping to 85 % for the 10000th scan, and specific energy of 523 Wh g-1.

Tuning the field emission of graphene-diamond hybrids by pulsed methane flow CVD

Integrating different carbon allotropes, namely graphene and nanocrystalline diamond, into a hybrid structure is highly desirable for a synergistic approach envisaging a field emission material. In this work, this was accomplished by a simultaneous synthesis of both allotropes by microwave plasma CVD on copper substrates, using a CH4 pulsed flow modulation strategy. This approach enabled tailoring the density (from 1.01 × 106 to 4.48 × 106/cm2) and diameter (from 1.06 to 3.09 μm) of nanocrystalline diamond clusters nucleated on the underlying graphene layer. Since morpho-structural aspects are critical regarding the field emission behavior, an exhaustive characterization was undertaken using scanning and transmission electron microscopy, Raman spectroscopy and optical profillometry.The field emission data were analyzed using the Fowler-Nordheim model and the electrical activation fields, ranging from ∼4.6 to ∼8.4 V/μm, were found to decrease with increasing NCD cluster content. Two emission regimes were observed, each corresponding to a distinct field enhancement factor, reaching values as high as 2204. The dependency of these factors with the total NCD cluster surface area suggests emission from both the background graphene and the protruded NCD clusters.

Application of Pulsed Chemical Vapor Deposited Tungsten Thin Film as a Nucleation Layer for Ultrahigh Aspect Ratio Tungsten-Plug Fill Process

Tungsten (W) thin film was deposited at 400 °C using pulsed chemical vapor deposition (pulsed CVD); film was then evaluated as a nucleation layer for W-plug deposition at the contact, with an ultrahigh aspect ratio of about 14~15 (top opening diameter: 240~250 nm, bottom diameter: 98~100 nm) for dynamic random access memory. The deposition stage of pulsed CVD has four steps resulting in one deposition cycle: (1) Reaction of WF6 with SiH4. (2) Inert gas purge. (3) SiH4 exposure without WF6 supply. (4) Inert gas purge while conventional CVD consists of the continuous reaction of WF6 and SiH4. The pulsed CVD-W film showed better conformality at contacts compared to that of conventional CVD-W nucleation layer. It was found that resistivities of films deposited by pulsed CVD were closely related with the phases formed and with the microstructure, as characterized by the grain size. A lower contact resistance was obtained by using pulsed CVD-W film as a nucleation layer compared to that of the conventional CVD-W nucleation layer, even though the former has a higher resistivity (~100 μΩ-cm) than that of the latter (~25 μΩ-cm). The plan-view scanning electron microscopy images after focused ion beam milling showed that the lower contact resistance of the pulsed CVD-W based W-plug fill scheme was mainly due to its better plug filling capability.

Quartz crystal microbalance gas sensor with nanocrystalline diamond sensitive layer

Gas sensors based on a quartz crystal microbalance (QCM) coated with nanocrystalline diamond (NCD) were developed and tested on NH3, CO2, and humidity detection at room temperature and compared with the bare (uncoated) QCM. NCD films were directly grown on the QCM by a large-area pulsed linear-antenna microwave plasma CVD process from the CH4/CO2/H2 gas mixture at temperatures below 400 °C. The as-grown NCD films on QCM and reference Si substrates were characterized by scanning electron and atomic force microscopies as well as Raman and optical spectroscopies. The NCD-coated QCM gas sensors showed a reasonable performance with a stable repeatability to the tested gases. The response time of the tested diamond-coated sensor was fast (∼5 s). Moreover, we also observed higher sensitivity and better stability for NCD-coated QCM than for the bare QCM.

G0400303 パルスプラズマCVD法により作製したa-BC:H膜の血液適合性

G0400303 パルスプラズマCVD法により作製したa-BC:H膜の血液適合性

On the possibility to grow zinc oxide-based transparent conducting oxide films by hot-wire chemical vapor deposition

Hot-wire chemical vapor deposition (HW-CVD) was applied to grow zinc oxide (ZnO)-based transparent conducting oxide (TCO) films. Indium (In)-doped ZnO films were deposited using a cold wall pulsed liquid injection CVD system with three nichrome wires installed at a distance of 2 cm from the substrate holder. The wires were heated by an AC current in the range of 0–10 A. Zn and In 2,2,6,6-tetramethyl-3,5-heptanedionates dissolved in 1,2-dimethoxyethane were used as precursors. The hot wires had a marked effect on the growth rates of ZnO, In-doped ZnO, and In2O3 films; at a current of 6–10 A, growth rates were increased by a factor of ≈10–20 compared with those of traditional CVD at the same substrate temperature (400 °C). In-doped ZnO films with thickness of ≈150 nm deposited on sapphire-R grown at a wire current of 9 A exhibited a resistivity of ≈2 × 10−3 Ωcm and transparency of &amp;gt;90% in the visible spectral range. These initial results reveal the potential of HW-CVD for the growth of TCOs.

A study of diamond like carbon/chromium films deposited by microwave plasma activated chemical vapor deposition

Since metal interlayer improves the adhesion, a sequential method of deposition of diamond like carbon (DLC) on Cr has been tried. The Cr interlayer and DLC grown sequentially on Si (100) by pulsed DC magnetron sputtering and microwave plasma CVD (MPCVD), respectively, which resulted in intermixing of DLC and Cr on the upper part of Cr interlayer. The intermixed layer contains nanocrystals of CrC which most likely contributes to formation of a relatively hard (18GPa) DLC with high modulus (up to 320GPa) and improved adhesion.

그래핀 하부전극을 이용하여 BMNO 케페시터의 특성 향상을 위한 Ti Adhesion Layer의 효과

The Ti adhesion layers were deposited onto the glass substrate for transparent capacitors using <TEX>$Bi_2Mg_{2/3}Nb_{4/3}O_7$</TEX> (BMNO) dielectric thin films. Graphene was transferred onto the Ti/glass substrate after growing onto the Ni/<TEX>$SiO_2$</TEX>/Si using rapid-thermal pulse CVD (RTPCVD). The BMNO dielectric thin films were investigated for the microstructure, dielectric and leakage properties in the case of capacitors with and without Ti adhesion layers. Leakage current and dielectric properties were strongly dependent on the Ti adhesion layers grown for graphene bottom electrode.

Homogeneous Optical and Electronic Properties of Graphene Due to the Suppression of Multilayer Patches During CVD on Copper Foils

A synthesis method of strictly monolayer and fully homogeneous graphene across tens of centimeter squares, by chemical vapour deposition onto standard copper foils, is presented. The growth technique involves cyclic injection of a carbon precursor separated by idle times with constant hydrogen exposure. The formation of spurious multilayer patches, which accompanies the standard growth techniques based on continuous exposure to methane, is inhibited here, in a broad range of pressure and gas composition, including in two pressure regimes which are known to yield distinctive grain morphologies (dendritic versus hexagonal). Raman spectra confirm the absence of defects within the graphene films. A mechanism for growth/suppression of the multilayer patches based on the carbon storage at defective regions is proposed. The importance of multilayer suppression is highlighted in a comparative study showing the detrimental effect of patches on the performances of graphene transistors and on the optical transparency of stacked layers. The full‐layer graphene sheets are superiorly homogeneous in terms of their optical and electronic properties, and are thus suited for applications for high‐density integration as well as transparent electrodes with spatially continuous optical absorbance. Graphene transistors fabricated by the pulsed CVD method exhibit room‐temperature mobilities with a mean value of 5000 cm2 V−1 s−1.

그래핀 전극을 이용한 유연한 BMNO (Bi2Mg2/3Nb4/3O7) 캐패시터의 굽힘 특성

Graphene was fabricated onto Ni/Si substrate using a rapid-thermal pulse CVD and they were transferred onto the Ti/PES flexible substrate. For top electrode applications of the BMNO dielectric films, graphene was patterned using a argon plasma. Through an AFM image and a leakage current density of the BMNO films grown onto various bottom electrodes before and after bending test, BMNO films grown onto the graphene bottom electrode showed no change of the microstructure and the leakage current density after the bend.

Conformity of Aluminum Thin Films Deposited onto Micro‐Patterned Silicon Wafers by Pulsed Laser Deposition, Magnetron Sputtering, and CVD

AbstractComplex materials, exhibiting a cocktail of properties, are currently needed for many applications. In this context, new requirements arise in terms of materials processing, such as the synthesis of sub‐micrometer objects, or the coating and functionalization of complex surfaces of powders, porous materials, or micro‐patterned devices. Depending on the requirements, the aim may be to duplicate the original design of the surface, or to modify it (filling of holes etc.). Physical vapor deposition (PVD) and CVD are promising techniques for the deposition of thin films on such substrates. In order to compare the ability of various deposition techniques to coat complex surfaces, a micro‐patterned silicon wafer has been developed. In the present work, aluminum thin films are deposited on this model substrate by two PVD techniques; pulsed laser deposition (PLD) and magnetron sputtering (MS), and by metal‐organic (MO)CVD. Scanning electron microscopy (SEM) is performed in order to determine the microstructure and study the thickness conformity.

Effects of duty cycle on microstructure and corrosion behavior of TiC coatings prepared by DC pulsed plasma CVD

Titanium carbide coatings are deposited on hot-work steel (H11) by plasma-assisted chemical vapor deposition (PACVD) and the dependence of the corrosion behavior on fabrication parameters is investigated. Grazing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy (FESEM), Raman and electrochemical tests are used to study the structure as well as corrosion behaviors. Grazing incidence X-ray diffraction reveals the (200) plane implying that the TiC coatings are deposited via the kinetics-limited crystal growth mechanism and under thermodynamically stable conditions. The SEM results indicate that the formation of a homogeneous and uniform titanium carbide nanostructure coatings. Potentiodynamic and electrochemical impedance tests performed in 0.5M H2SO4 and 0.05M NaCl show that the TiC coating produced using a 40% duty cycle possesses high corrosion resistance in both media. The Rp values of the TiC coating (50% duty cycle) in 0.05M NaCl and the other TiC coating (40% duty cycle) in 0.5M H2SO4 are approximately four and sixteen orders of magnitude higher than that of the bare steel, respectively. Our results reveal that the duty cycles not only affect the structure and morphology of the coatings but also influence the electrochemical properties.

Erratum to: Alumina microtubes prepared via template-directed pulsed chemical vapor deposition (pulsed CVD)

Page 4817, Fig. 5 unfortunately comprises data on the residual weight of uncoated fibres that were assigned to incorrect values of the abscissa. The correct diagram is given below. The text passage on page 4818, column 1, paragraph 1, ‘‘The uncoated fibers start to lose weight at approximately 300 C, whereas the coated fibers start to lose weight at approximately 700 C.’’ should read instead: ‘‘The uncoated fibers start to lose weight at approximately 630 C, whereas the coated fibers start to lose weight at approximately 660 C.’’

Deposition of amorphous hydrogenated carbon films on Si and PMMA by pulsed direct-current plasma CVD

A pulse-modulated direct-current methane plasma is used to deposit amorphous hydrogenated carbon (a-C:H) films on Si and polymethyl methacrylate (PMMA) substrates. The structure and mechanical properties of the films are examined by applying a negative pulse bias voltage of 0.5 to 3 kV to the substrate at a pulse bias period of 100 to 200 μs. The deposition rate on both Si and PMMA increases with increasing the net input power, independent of the pulse period. The Raman spectra demonstrate that the films on Si are diamond-like carbon (DLC), while those on PMMA are polymer-like or soft amorphous carbon because of higher crystallinity of the sp 2 phase and lower nanoscale hardness. The residual compressive stress of the films on PMMA is constantly low ranging from 0 to 2 GPa due exclusively to high flexibility of PMMA, which causes the easy relief of the stress and thus the density decrease in the films.