Traditional Chemical Vapor Deposition Research Articles

Preparation of Three-Dimensional Graphene Foams Using Powder Metallurgy Templates.

A simple and scalable method which combines traditional powder metallurgy and chemical vapor deposition is developed for the synthesis of mesoporous free-standing 3D graphene foams. The powder metallurgy templates for 3D graphene foams (PMT-GFs) consist of particle-like carbon shells which are connected by multilayered graphene that shows high specific surface area (1080 m(2) g(-1)), good crystallization, good electrical conductivity (13.8 S cm(-1)), and a mechanically robust structure. The PMT-GFs did not break under direct flushing with DI water, and they were able to recover after being compressed. These properties indicate promising applications of PMT-GFs for fields requiring 3D carbon frameworks such as in energy-based electrodes and mechanical dampening.

Synthesis of Layer‐Tunable Graphene: A Combined Kinetic Implantation and Thermal Ejection Approach

Layer‐tunable graphene has attracted broad interest for its potentials in nanoelectronics applications. However, synthesis of layer‐tunable graphene by using traditional chemical vapor deposition method still remains a great challenge due to the complex experimental parameters and the carbon precipitation process. Herein, by performing ion implantation into a Ni/Cu bilayer substrate, the number of graphene layers, especially single or double layer, can be controlled precisely by adjusting the carbon ion implant fluence. The growth mechanism of the layer‐tunable graphene is revealed by monitoring the growth process, it is observed that the entire implanted carbon atoms can be expelled toward the substrate surface and thus graphene with designed layer number can be obtained. Such a growth mechanism is further confirmed by theoretical calculations. The proposed approach for the synthesis of layer‐tunable graphene offers more flexibility in the experimental conditions. Being a core technology in microelectronics processing, ion implantation can be readily implemented in production lines and is expected to expedite the application of graphene to nanoelectronics.

Growth of tapered silica nanowires with a shallow U-shaped vapor chamber: Growth mechanism and structural and optical properties

Traditional chemical vapor deposition method modified with a shallow U-shaped vapor chamber has been used to synthesize tapered bamboo shoot-like (BS-like) amorphous SiO2 nanowires (NWs) on Si (100) substrates without catalyst. The key innovation of this approach lies in a creation of swirling flow of the reactant vapors during the growth, which leads to a harvest of tapered silica NWs with lengths up to several microns. The unique structures and corresponding luminescence properties of the BS-like NWs were studied and their relationship with the evaporated active reactants was explored. A thermodynamic model that considers the critical role of the vapor flow during the growth is proposed to understand the structural and optical features. The shallow U-shaped vapor chamber-aided approach may provide a viable way to tailor novel structure of NWs for potential applications in nano-devices.

Challenges with Industrialization of Atomic Layer Deposition of Silicon Nitride

Scaling of next generation logic and memory semiconductor devices requires conformal thin films on high aspect ratio features at low deposition temperatures (<500ºC). Atomic layer deposition (ALD) is an ideal method for depositing these films and is currently being used in high volume manufacturing (HVM) to deposit high-k dielectric materials (HfO2, ZrO2, etc.) as well as the more traditional dielectrics silicon oxide (SiO2) and silicon nitride (SiNx). With the notable exception of silicon nitride, all of these films can be deposited at sufficiently low temperatures to satisfy the integration requirements while maintaining reasonable throughput and cost. In the HVM environment, silicon nitride ALD has historically been deposited in large furnaces operating at high temperatures, and although both plasma and thermal deposition of silicon nitride have been reported at low temperatures1-2, translation of these low temperature R&D films into HVM films has been challenging.In this presentation, we discuss some of the challenges faced with addressing the requirements associated with bringing low temperature ALD SiNx into HVM, which include achieving high wafer throughput and low per wafer cost, while simultaneously keeping the resistance of the film to multiple downstream etches and cleans, which may include exposure to hydrofluoric acid (HF). Generic to all ALD processes is the high cost of the precursors relative to traditional chemical vapor deposition (CVD); in the case of SiNx, this is exacerbated by the relative low “reactivity to cost ratio” of available silicon precursors. Cost can partially be addressed with chlorosilane precursors, but the chlorine byproducts create challenges with deposition chamber materials and effluent management. Low reactivity of the silicon precursors poses challenges with respect to process design; the choice of spatial ALD vs. temporal ALD and isobaric vs. non-isobaric deposition sequences affects the final cost and throughput. Lastly, the use of plasmas in ALD poses challenges for achieving isotropic film properties over the complex topography on today’s semiconductor substrates.

Highly Stable Micromorph Tandem Solar Cells Fabricated by ECRCVD With Separate Silane Gas Inlets System

In this paper, hydrogenated amorphous silicon (a-Si:H) and microcrystalline silicon ( \(\mu \) c-Si:H) films are deposited by electron cyclotron resonance chemical vapor deposition with two separate silane gas inlets. One of the silane gases (S2) is introduced near the substrate region. Effects of S2 flow rate on film properties and solar cell performance are investigated in comparison to traditional plasma-enhanced chemical vapor deposition (PECVD). The results show that the introduction of S2 gas leads to: 1) significant reduction of higher order silane radicals participating film growth; 2) dense film structure with a low microstructure factor of 0.06; and 3) lower surface roughness of the interface between top a-Si:H and bottom \(\mu \) c-Si:H subcells of micromorph tandem cells, favoring bottom \(\mu \) c-Si:H deposition. Single-junction amorphous silicon solar cells show light-induced degradation (LID) of 7.8%, almost half of that observed in PECVD cells. Micromorph tandem solar cells show a 13.3% initial conversion efficiency and a 12.7% stabilized efficiency. Highly stabilized micromorph tandem solar cell with 4.7% LID can be achieved.

High-quality monolayer graphene synthesis on Pd foils via the suppression of multilayer growth at grain boundaries.

The segregation of carbon from metals in which carbon is highly soluble, such as Ni (≈1.1 atom% at 1000 °C), is a typical method for graphene growth; this method differs from the surface-catalyzed growth of graphene that occurs on other metals such as Cu (<0.04 atom%). It has not been established whether strictly monolayer graphene could be synthesized through the traditional chemical vapor deposition route on metals where carbon is highly soluble, such as Pd (≈3.5 atom%). In this work, this issue is investigated by suppressing the grain boundary segregation using a pretreatment comprising the annealing of the Pd foils; this method was motivated by the fact that the typical thick growths at the grain boundaries revealed that the grain boundary functions as the main segregation channel in polycrystalline metals. To evaluate the high crystallinity of the as-grown graphene, detailed atomic-scale characterization with scanning tunneling microscopy is performed.

Development of a Polysilicon Chemical Vapor Deposition Reactor Using the Computational Fluid Dynamics Method

A novel reactor with low energy consumption has been developed, based on the traditional polysilicon chemical vapor deposition (CVD) reactor; a three-dimensional computational fluid dynamics theoretical model to describe various transport phenomena in the reactor is proposed, which was verified by comparison of simulated results with industrial data for a traditional polysilicon CVD reactor. The velocity profile, temperature field, concentration distribution, and energy consumption of the traditional reactor and novel reactor were analyzed. The simulation results demonstrated that the flow pattern of the gas mixture in the novel reactor approximates a plug flow model, which is fundamentally different from that of the traditional reactor, and that the temperature field can be controlled by changing the novel reactor operating parameters. Because gas-phase temperatures in the novel reactor are controllable, silicon powder generation can greatly inhibited, allowing for greatly reduced contamination of the reactor inner wall (above 95%). Simulation results revealed that the energy consumption by the novel reactor could be greatly reduced as a result of lower radiation on the cleaner inner wall.

Progress in Catalytic Preparation of Carbon/Carbon Composites

This paper reviewed published research into catalytic fabrication techniques and recent progresses of carbon/carbon (C/C) composites. It’s described the catalytic chemical vapor deposition theory and reviewed the catalytic properties of different metal catalysts. Merits and demerits of the traditional chemical vapor deposition, improved chemical vapor deposition and other new rapid densification techniques were analyzed. The new densification techniques are to shorten the preparation cycle, but most of them are limited in the laboratory with application problems. Finally, the prospect on the application and development tendency of improved catalytic chemical vapor deposition technique is put forward in the rapid low cost fabrication of C/C composites in the future.

Strain-less directed self-assembly of Si nanocrystals on patterned SiO2 substrate

Strain induced self-assembled Stranski-Krastanov growth of semiconductor islands on patterned substrate has shown great improvement of island size uniformity and spatial order. Here, we show self-assembled Volmer-Weber (V-W) growth of Si nanocrystals (NCs) on patterned SiO2 substrate via traditional chemical vapor deposition method under certain experimental configurations, induced by surface/interface energy competition without strain. A simplified two-dimensional theoretical model is developed to elucidate V-W island nucleation on the pattern substrate with varied morphologies, which shows good consistency with the experimental results. Our studies provide a general guidance for directing the growth and self-assembly of NCs on non-planar oxide substrates.

GaN-Based High-kPraseodymium Oxide Gate MISFETs withP2S5/(NH4)2SX+ UV Interface Treatment Technology

This study examines the praseodymium-oxide- (Pr2O3-) passivated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) with high dielectric constant in which the AlGaN Schottky layers are treated with P2S5/(NH4)2SX+ ultraviolet (UV) illumination. An electron-beam evaporated Pr2O3insulator is used instead of traditional plasma-assisted chemical vapor deposition (PECVD), in order to prevent plasma-induced damage to the AlGaN. In this work, the HEMTs are pretreated with P2S5/(NH4)2SXsolution and UV illumination before the gate insulator (Pr2O3) is deposited. Since stable sulfur that is bound to the Ga species can be obtained easily and surface oxygen atoms are reduced by the P2S5/(NH4)2SXpretreatment, the lowest leakage current is observed in MIS-HEMT. Additionally, a low flicker noise and a low surface roughness (0.38 nm) are also obtained using this novel process, which demonstrates its ability to reduce the surface states. Low gate leakage current Pr2O3and high-kAlGaN/GaN MIS-HEMTs, with P2S5/(NH4)2SX+ UV illumination treatment, are suited to low-noise applications, because of the electron-beam-evaporated insulator and the new chemical pretreatment.

Growth and Atomic-Scale Characterizations of Graphene on Multifaceted Textured Pt Foils Prepared by Chemical Vapor Deposition

The synthesis of centimeter-scale uniform graphene on Pt foils was accomplished via a traditional ambient pressure chemical vapor deposition (CVD) method. Using scanning electron microscopy (SEM) and Raman spectroscopy, we reveal the macroscopic continuity, the thickness, as well as the defect state of as-grown graphene. Of particular importance is that the Pt foils after CVD growth have multifaceted texture, which allows us to explore the substrate crystallography effect on the growth rate and the continuity of graphene. By virtue of atomically resolved scanning tunneling microscopy (STM), we conclude that graphene grows mainly in registry with the symmetries of Pt(111), Pt(110), and Pt(100) facets, leading to hexagonal lattices and striped superstructures. Nevertheless, the carbon lattices on interweaving facets with different identities are connected seamlessly, which ensure the graphene growth from nanometer to micrometer levels. With these results, another prototype for clarifying the preliminary growth mechanism of the CVD process is demonstrated as an analogue of graphene on Cu foils.

High electrical performance liquid-phase HBr oxidation gate insulator of InAlAs/InGaAs metamorphic MOS-mHEMT

The InAlAs/InGaAs metal–oxide–semiconductor metamorphic high electron mobility transistors (MOS-mHEMTs) were demonstrated by using liquid-phase HBr treatment technology to form a high-quality gate insulator layer. In this study, liquid-phase HBr treatment technology was used instead of traditional plasma-assisted chemical vapor deposition (PECVD) because the proposed technology can prevent the device from plasma-induced damage. The novel HBr + ultraviolet (UV) illumination treated InGaAs provided a lower surface states such that MOS structure can be efficiently obtained. Besides, based on the atomic force microscopy (AFM) measurement, the native oxides film formed by HBr + UV illumination treatment also provided a better surface roughness compared to traditional NH 4OH and only HBr treatment solutions. It is beneficial for reducing the surface traps and lowering the leakage current in MOS-mHEMTs. Based on the flicker noise and load-pull power measurement results, HBr + UV treatment mHEMT achieved a low flicker noise at high current level and the power-added efficiency can be enhanced up to 9%. Therefore, the novel liquid phase method of HBr + UV illumination treatment exhibited a highly potential for low noise microwave power device applications.

Deposition of platinum patterns by a liquid process

In contrast to the traditional chemical vapor deposition technique under high vacuum, we introduce a deposition method in liquid to prepare Pt patterns on substrate near 100 °C by seed growth.

A NOVEL SPINNING DISC CONTINUOUS STIR TANK AND SETTLER REACTOR (SDCSTR) MODEL FOR CONTINUOUS SYNTHESIS OF TITANIA: A PHENOMENOLOGICAL MODEL

A novel phenomenological spinning disc continuous stir tank and settler reactor (SDCSTR) has been modeled for continuous synthesis of titania from its chloride precursor and water in which the desired polymorph, particle size, and distribution are controlled by the characteristics of the atomized inlet reagents, disc, and tank stir rate. This energy-efficient reactor generates seeding nuclei in the aerosol reacting volume that are then deployed for heterogeneous nucleation and particle growth in the metastable reacting volume of the aqueous (sol) process. Once at steady state, the enhanced TiO2 nanoparticles due to the OH−–H+ chemisorbed on the surface (with surface energy 0.5 < σ < 2.11 N/m) are continuously withdrawn at a rate equivalent to the particle settling rate from the settler. This reactor model eliminates the energy intensity required in traditional chemical vapor deposition (CVD) and aerosol reactors and provides better control for particle growth and size distribution by increasing particle residence time in the metastable zone of the aqueous (sol) reaction stage.

High-k praseodymium oxide passivated AlGaN/GaN MOSFETs using P 2S 5/(NH 4) 2S X + UV interface treatment

This study elucidates the praseodymium oxide (Pr 2O 3)-passivated AlGaN/GaN metal–oxide–semiconductor high electron mobility transistors (MOS-HEMTs) with high dielectric constant, and with their AlGaN Schottky layers treated with P 2S 5/(NH 4) 2S X + ultraviolet (UV) illumination. An electron-beam evaporated Pr 2O 3 insulator is used, instead of traditional plasma-assisted chemical vapor deposition (PECVD), to prevent plasma-induced damage on AlGaN. In this work, the HEMTs were pretreated by P 2S 5/(NH 4) 2S X solution and UV illumination before the gate insulator (Pr 2O 3) was deposited. Since stable sulfur that is bound to the Ga species can be efficiently obtained and surface oxygen atoms were reduced by P 2S 5/(NH 4) 2S X pretreatment, the lowest leakage current was observed in MOS-HEMT. Additionally, a low flicker noise and a low surface roughness (1.1 nm) were also obtained using this novel process, to demonstrate its ability to reduce the surface states. Low gate leakage current Pr 2O 3, high-k AlGaN/GaN MOS-HEMTs, under P 2S 5/(NH 4) 2S X + UV illumination treatment are suited to low-noise applications because of its electron-beam-evaporated insulator and the new chemical pretreatment.

Polycrystalline Silicon–Germanium Films Prepared by Aluminum-Induced Crystallization

The thin films were deposited on Al-coated glass and single-crystal Si substrates by traditional plasma-enhanced chemical vapor deposition with the mixture of , , and Ar at a low temperature of . The structure of the films was characterized by X-ray diffraction, Raman spectra, field-effect scanning electron microscopy, and atomic force microscopy. It showed that the Al layer was a very effective crystallization precursor for preparing the thin films. The polycrystalline thin films were the easiest to be formed when . Moreover, the (111) interplanar spacing values of the stress-free poly- thin films, with a lower concentration of crystallographic defects, were in accord with Vegard’s law. The grain size was sensitive to the annealing temperature and the Ge content. And, there was no surface roughening in the aluminum-induced crystallization poly- .

Highly (111)-textured diamond film growth with high nucleation density

In a traditional hot-filament chemical vapor deposition (HF-CVD) system, highly (111)-textured diamond film was deposited on Si (111) substrate treated by diamond powder ultrasonic scratching or other methods. The relationship between the (111)-textured diamond film growth and the nucleation density has been discussed. The morphologies and structures of the films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy.

Hydrogen-free CVD diamond synthesis with graphite rod heating

A wide-band-gap semiconductor diamond has recently emerged as an important and promising material for a wide field of optoelectronic and electronic applications. In traditional chemical vapor deposition (CVD) diamond synthesis on a substrate, such as silicon single crystal, hydrogen radicals were thought to be inevitable. In this work, we synthesized diamond particles of wide-band-gap semiconductor on a substrate without flammable hydrogen gas. With our work, safer and easier diamond synthesis was realized. In our present technique, we call it “hydrogen-free diamond synthesis”. The graphite rods were used as heaters and, at the same time, carbon sources. In argon (99.99%; 4N), high-purity argon (6N), helium (4N5) or nitrogen (4N) atmosphere, without hydrogen gas, diamond particles were synthesized with the graphite rod heating method for the first time in the world. One-micrometer-diameter particles in argon gas, 0.8 μm particles in high-purity argon, 0.6 μm particles in helium, and 0.4 μm particles in nitrogen, were all confirmed as diamond with the SEM photographs and Raman spectroscopy; results will be reported in this paper.

Micro-Porous Nickel Produced by Powder Metallurgy

Micro-porous nickel (Ni) with an open cell structure was fabricated by a special powder metallurgical process, which includes the adding of a space-holding material. The average pore size of the micro-porous Ni samples approximated 30 μm and 150 μm, and the porosity ranged from 60 % to 80 %. The porous characteristics of the Ni samples were observed using scanning electron microscopy (SEM) and the mechanical properties were evaluated using compressive tests. For comparison, porous Ni samples with a macro-porous structure prepared by both powder metallurgy (pore size 800 μm) and the traditional chemical vapour deposition (CVD) method (pore size 1300 μm) were also presented. Results indicated that the porous Ni samples with a micro-porous structure exhibited different deformation behaviour and dramatically increased mechanical properties, compared to those of the macro-porous Ni samples.

Fabrication of a “Soft” Membrane Electrode Assembly Using Layer‐by‐Layer Technology

AbstractA new type of thin‐film electrode that does not utilize conducting polymers or traditional metal or chemical vapor deposition methods has been developed to create ultrathin flexible electrodes for fuel cells. Using the layer‐by‐layer (LbL) technique, carbon–polymer electrodes have been assembled from polyelectrolytes and stable carbon colloidal dispersions. Thin‐film LbL polyelectrolyte–carbon electrodes (LPCEs) have been successfully assembled atop both metallic and non‐metallic, porous and non‐porous substrates. These electrodes exhibit high electronic conductivities of 2–4 S cm–1, and their porous structure provides ionic conductivities in the range of 10–4 to 10–3 S cm–1. The electrodes show remarkable stability towards oxidizing, acidic, or delaminating basic solutions. In particular, an LPCE consisting of poly(diallyldimethyl ammonium chloride)/poly(2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid)/carbon–platinum assembled on a porous stainless steel support yields an open‐circuit potential similar to that of a pure platinum electrode. With LbL carbon–polymer electrodes, the membrane‐electrode assembly (MEA) in a fuel cell can be made several times thinner, assume multiple geometries, and hence be more compact. The mechanism for LPCE deposition, electrode structure, and miniaturization will be presented and discussed, and demonstrations of the LbL electrodes in a traditional Nafion‐based proton fuel cell and the first demonstration of a thin‐film hydrogen–air “soft” fuel cell fully constructed using multilayer assembly are described.