Conventional Thermal Chemical Vapor Deposition Research Articles

Synthesis of Nitrogen-Doped Graphene on Copper Nanowires for Efficient Thermal Conductivity and Stability by Using Conventional Thermal Chemical Vapor Deposition.

Cu nanowires (NWs) possess remarkable potential a slow-cost heat transfer material in modern electronic devices. However, Cu NWs with high aspect ratios undergo surface oxidation, resulting in performance degradation. A growth temperature of approximately <1000 °C is required for preventing the changing of Cu NW morphology by the melting of Cu NWs at over 1000 °C. In addition, nitrogen (N)-doped carbon materials coated on Cu NWs need the formation hindrance of oxides and high thermal conductivity of Cu NWs. Therefore, we investigated the N-doped graphene-coated Cu NWs (NG/Cu NWs) to enhance both the thermal conductivity and oxidation stability of Cu NWs. The Cu NWs were synthesized through an aqueous method, and ethylenediamine with an amine group induced the isotropic growth of Cu to produce Cu NWs. At that time, the amine group could be used as a growth source for the N-doped graphene on Cu NWs. To grow an N-doped graphene without changing the morphology of Cu NWs, we report a double-zone growth process at a low growth temperature of approximately 600 °C. Thermal-interface material measurements were conducted on the NG/Cu NWs to confirm their applicability as heat transfer materials. Our results show that the synthesis technology of N-doped graphene on Cu NWs could promote future research and applications of thermal interface materials in air-stable flexible electronic devices.

Quality improvement of fast-synthesized graphene films by rapid thermal chemical vapor deposition for mass production

The conventional thermal chemical vapor deposition (T-CVD) equipment takes a long time to synthesize a thin film, which is the stumbling block in the commercialization of monolayer graphene. Rapid thermal chemical vapor deposition (RT-CVD) equipment is suitable for rapid graphene synthesis on most surfaces of large area transition metals. The initial graphene domains synthesized by RT-CVD were visualized and compared with graphene synthesized by T-CVD. The number of graphene domains grown by RT-CVD was approximately 12.31% larger than those synthesized by T-CVD. The surface of the thermally treated metal substrate determines the density and shape of the graphene domains due to the reduced surface irregularities and hence flattens. As a result of the thermal treatment of the copper foil, the ID/IG value of RT-CVD graphene decreased by 12.5%. Thus, it was confirmed that the electrical characteristics were improved as the average value of the sheet resistance reduced by 15.8%.

Plasma enhanced synthesis of N doped vertically aligned carbon nanofibers on 3D graphene

Graphene and carbon nanotubes/fibers (CNT/CNF) hybrid structures are emerging as frontier materials for high‐efficiency electronics, energy storage, thermoelectric, and sensing applications owing to the utilization of extraordinary electrical and physical properties of both nanocarbon materials. Recent advances show a successful improvement in the structure and surface area of layered graphene by incorporating another dimension and structural form—three‐dimensional graphene (3DG). In this study, vertically aligned CNFs were grown using plasma enhanced chemical vapor deposition on a relatively new form of compressed 3DG. The latter was synthesized using a conventional thermal chemical vapor deposition. The resulting free‐standing hybrid material is in‐situ N doped during synthesis by ammonia plasma and is produced in the form of a hybrid paper. Characterization of this material was done using electrochemical and spectroscopic measurements. The N doped hybrid showed relatively higher surface area and improved areal current density in electrochemical measurements than compressed pristine 3DG, which makes it a potential candidate for use as an electrode material for supercapacitors, sensors, and electrochemical batteries.

Photoactive Zinc Ferrites Fabricated via Conventional CVD Approach

Owing to its narrow band gap and promising magnetic and photocatalytic properties, thin films of zinc ferrite (ZFO, ZnFe2O4) are appealing for fabrication of devices in magnetic recording media and photoelectrochemical cells. Herein we report for the first time the fabrication of photactive zinc ferrites via a solvent free, conventional CVD approach, and the resulting ZFO layers show promise as a photocatalyst in PEC water-splitting. For large scale applications, chemical vapor deposition (CVD) routes are appealing for thin film deposition; however, very little is known about ZFO synthesis following CVD processes. The challenge in precisely controlling the composition for multicomponent material systems, such as ZFO, via conventional thermal CVD is an issue that is caused mainly by the mismatch in thermal properties of the precursors. The approach of using two different classes of precursors for zinc and iron with a close match in thermal windows led to the formation of polycrystalline spinel type ZFO. Un...

Gaseous product mixture from Fischer-Tropsch synthesis as an efficient carbon feedstock for low temperature CVD growth of carbon nanotube carpets.

Low-temperature chemical vapor deposition (CVD) growth of carbon nanotube (CNT) carpets from Fe and Fe-Cu catalysts using a gaseous product mixture from Fischer-Tropsch synthesis (FTS-GP) as a superior carbon feedstock is demonstrated. This growth approach addresses a persistent issue of obtaining thick CNT carpets on temperature-sensitive substrates at low temperatures using a non-plasma CVD approach without catalyst pretreatment and/or preheating of the carbon feedstock. The efficiency of the process is evidenced by the highly dense, vertically aligned CNT structures from both Fe and Fe-Cu catalysts even at temperatures as low as 400 °C - a record low growth temperature for CNT carpets obtained via conventional thermal CVD. The grown CNTs exhibit a straight morphology with hollow interior and parallel graphitic planes along the tube walls. The apparent activation energies for CNT carpet growth on Fe and Fe-Cu catalysts are 0.71 and 0.54 eV, respectively. The synergistic effect of Fe and Cu show a strong dependence on the growth temperature, with Cu being more influential at temperatures higher than 450 °C. The low activation energies and long catalyst lifetimes observed are rationalized based on the unique composition of FTS-GP and Gibbs free energies for the decomposition reactions of the hydrocarbon components. The use of FTS-GP facilitates low-temperature growth of CNT carpets on traditional (alumina film) and nontraditional substrates (aluminum foil) and has the potential of enhancing CNT quality, catalyst lifetime, and scalability.

High growth rate chemical vapor deposition of graphene under low pressure by RF plasma assistance

High throughput synthesis of atomic layer graphene membrane by chemical vapor deposition (CVD) is one of key technologies to establish industrial applications. Here we report the details of the initial stage of graphene growth on copper substrate by radio frequency (RF) plasma-assisted CVD under low pressure and compare the nucleation rate and the growth rate with conventional thermal CVD. Two-dimensional growth rate of graphene by plasma-assisted CVD is 100 and 1000 times larger than that of thermal CVD at 950 °C and at 750 °C, respectively. It is found that graphene growth is governed by the diffusion of active carbon species on the copper surface with a very low activation energy of 0.4 eV at low-temperature(≦ 850 °C) and low pressure. The high growth rate of plasma-assisted CVD of graphene is discussed.

Interpretation of Ostwald ripening of catalytic nanoparticles based on the radial breathing mode in single-walled carbon nanotubes

Catalytic nanoparticle (NP) size is the crucial factor that determines carbon nanotube (CNT) diameter. Therefore, we explored the Ostwald ripening phenomenon of catalytic NPs from the radial breathing modes in resonant Raman spectra of synthesized single-walled CNTs (SWCNTs). SWCNTs were synthesized using chemically derived monodisperse Fe oxide catalytic NPs by a conventional thermal chemical vapor deposition system. The density of the NPs was manipulated by simply adjusting the spin-coating speed and cycle. The diameter distribution and tube type (SWCNTs or multi-walled CNTs) were thereby determined, which can be understood by density-dependent Ostwald ripening of the NPs. As a result, the diameter-selective growth of SWCNTs was successfully achieved, which will be useful for SWCNTs-based electronic applications.

Catalyst-free growth of readily detachable nanographene on alumina

We have grown graphene directly on alumina (Al2O3) substrates without catalysts using conventional thermal chemical vapor deposition. By choosing Al2O3 as a growth substrate, the polycrystallinity of graphene was enhanced to form nanometer-size dome-like grains, which ensured a statistically homogeneous electrical property of graphene over a large area. As-grown bilayer, the nanographene (nGr) film showed a sheet resistance of ∼3 kΩ □−1 with a standard deviation of ∼2.3% over 15 mm × 15 mm. Top- and bottom-gate nGr thin film transistors (TFTs) fabricated directly on the Al2O3 substrate exhibited field-effect mobilities of 89 and 41 cm2 V−1 s−1, respectively. Moreover, the grown nGr could be easily detached from the Al2O3 substrate due to weak adhesion between the nGr and Al2O3, which has abundant fixed charges. Dry-transfer of the grown nGr from the Al2O3 substrate was realized via spin-coating a polyimide (PI) or poly(4-vinylphenol) film and subsequently detaching the film together with the nGr film. The recycled substrates provided the nGr films with reproducibility. The nGr devices on a 3 μm-thick PI film were stable upon bending with a bending diameter of down to 6 mm.

Plasma-assisted growth and nitrogen doping of graphene films

Microwave plasmas were employed to synthesize single- or double-layer graphene sheets on copper foils using a solid carbon source, polymethylmetacrylate. The utilization of reactive plasmas enables the graphene growth at reduced temperatures as compared to conventional thermal chemical vapor deposition processes. The effects of substrate temperature on graphene quality were studied based on Raman analysis, and a reduction of defects at elevated temperature was observed. Moreover, a facile approach to incorporate nitrogen into graphene by plasma treatment in a nitrogen/hydrogen gas mixture was demonstrated, and most of the nitrogen atoms were verified to be pyridinelike in carbon network.

Remote Plasma Chemical Vapor Deposition of Carbon Nanotubes and Analysis of Plasma Effect

Remote plasma is an efficient method to synthesize carbon nanomaterials because it can avoid the damage due to ion bombardment and can supply active precursor species for their growth. We introduced dc plasma to the CH4 thermal chemical vapor deposition (CVD) of carbon nanotubes (CNTs) in order to decompose CH4 efficiently. The effect of the plasma was investigated through the gas contents observed by a quadrupole mass spectrometer and the quality of CNTs evaluated by Raman spectroscopy. High-quality single-walled CNTs grew on Al2O3/Fe/Al2O3 substrates, on which CNTs did not grow in conventional thermal CVD. The intensity ratio of the G peak to D peak in Raman spectra (G/D ratio) was 41.8. Since the CNT yield increased with the discharge voltage, the activation of precursors by the plasma seemed to promote the CNT growth significantly. At this time, C2Hx and C3Hx, produced in the plasma, also increased. Thus, they seemed to contribute to the CNT growth. The diameter of CNTs, as well as the CNT yield, increased with increasing discharge voltage. This indicated the presence of the optimum precursor supply rate depending on the size of catalyst particles to keep them active.

Synthesis of Bandgap-Controlled Semiconducting Single-Walled Carbon Nanotubes

Bandgap-controlled semiconducting single-walled carbon nanotubes (s-SWNTs) were synthesized using a uniquely designed catalytic layer (Al(2)O(3)/Fe/Al(2)O(3)) and conventional thermal chemical vapor deposition. Homogeneously sized Fe catalytic nanoparticles were prepared on the Al(2)O(3) layer and their sizes were controlled by simply modulating the annealing time via heat-driven diffusion and subsequent evaporation of Fe at 800 degrees C. Transmission electron microscopy and Raman spectroscopy revealed that the synthesized SWNTs diameter was manipulated from 1.4 to 0.8 nm with an extremely narrow diameter distribution below 0.1 nm as the annealing time is increased. As a result, the bandgap of semiconducting SWNTs was successfully controlled, ranging from 0.53 to 0.83 eV, with a sufficiently narrow energy distribution, which can be applied to field-effect transistors based on SWNTs.

Synthesis of Vertically Aligned Multi-Walled Carbon Nanotubes on Copper Substrates for Applications as Thermal Interface Materials

AbstractVertically aligned carbon nanotubes (VACNTs) grown on bulk copper substrate are of great importance for CNT real-life applications as thermal interface materials in microelectronic packaging. However, their reproducible synthesis has been a great challenge so far. In this study, by introducing a well-controlled conformal Al2O3 support layer on the bulk copper substrate by atomic layer deposition (ALD) prior to the deposition of the iron catalyst layer, we reproducibly synthesize VACNTs of good alignment and high quality on the copper substrate, using a conventional thermal chemical vapor deposition process. The alignment and the quality are characterized by scanning electronic microscopy and Raman spectroscopy, respectively. The roles of the conformal Al2O3 support layer are discussed. A kinetics-controlled growth mechanism is shown. This progress provides a viable VACNT commercial application for thermal management, on the basis of which, we show a recent progress on a state-of-art Si/VACNT/Cu assembling process, named “chemical anchoring”. The high quality of the VACNTs on the copper growth substrate and the covalent bonding formed between the VACNTs and the silicon mating substrate greatly reduces the thermal resistance of the VACNT-mediated thermal interface.

One-step grown aligned bulk carbon nanotubes by chloride mediated chemical vapor deposition

We found the easy and efficient synthesis method of the vertically aligned ultralong multiwalled nanotubes using iron chloride powder. The 2.1-mm-long bulk nanotubes can be grown by conventional thermal chemical vapor deposition on bare quartz surface with the single gas flow of acetylene for 20min. In addition to the high growth rate, the bulk of carbon nanotubes is easily spun into the yarn by pulling it out, and the present method also provides the coating ability with nanotubes as a new functionality of this nanomaterial.

Novel and Simple Synthesis Method for Submillimeter Long Vertically Aligned Single-Walled Carbon Nanotubes by No-Flow Alcohol Catalytic Chemical Vapor Deposition

Using a conventional thermal chemical vapor deposition (CVD) system, ethanol vapor was enclosed in a reactor, i.e., no flow, with Co/Mo dip-coated quartz substrates to synthesize submillimeter long vertically aligned single-walled carbon nanotube (SWNT) films successfully. The no-flow CVD method yielded an increase in film thickness of up to 0.11 mm compared with the normal flowing gas method for 30 min of synthesis. The thermal decomposition of ethanol was investigated using Fourier transform infrared spectroscopy and quadrupole mass spectrometry. At CVD temperatures, ethanol decomposed mainly into ethylene, acetylene, acetaldehyde, and water. Some of these molecules could enhance SWNT growth.

Growth of Single Crystalline ZnO Nanotubes and Nanosquids

ABSTRACTThe growth of ZnO nanotubes and nanosquids is obtained by conventional thermal chemical vapor deposition (CVD) without the use of catalysts or templates. Characterization of these ZnO nanostructures was conducted by X-ray powder diffraction (XRD), Field-emission scanning electron microscopy (FESEM), Raman spectroscopy, and photoluminescence (PL). Results indicate that these ZnO nanostructures maintain the crystalline structures of the bulk wurtzite ZnO crystals. Our results show that rapid cooling can be used to induce the formation of ZnO nanotubes and ZnO nanosquids. The self-assembly of these novel ZnO nanostructures are guided by the theory of nucleation and the vapor-solid crystal growth mechanism.

High-speed deposition of zirconia films by laser-induced plasma CVD

Chemical vapor deposition (CVD) has been commonly applied to prepare thin films. However, the application of CVD can be expanded to thick coatings such as thermal barrier coatings (TBCs) by accelerating deposition rates. In this paper, the recent development of high-speed deposition for yttria-stabilized zirconia (YSZ) films by conventional thermal CVD and plasma-enhanced CVD (PE-CVD) has been briefly reviewed. A laser CVD (LCVD) process has been recently developed attaining an extremely high deposition rate of 660 μm/h. Plasma emerged during the laser CVD, and the relating plasma diagnosis is described.

Chemical Vapor Deposition of Cerium Oxide Films from a Cerium Alkoxide Precursor

The cerium(IV) alkoxide complex Ce(OCMe2-i-Pr)4, a volatile, nonfluorinated source of cerium, was used as a chemical vapor deposition precursor to cerium oxide films. A conventional thermal chemical vapor deposition process deposited cerium(IV) oxide films from Ce(OCMe2-i-Pr)4 on silicon, glass, quartz, lanthanum aluminum oxide (001), and roll-textured nickel (001) substrates at low substrate temperatures (<550 °C). The films were highly oriented when the depositions were carried out on lanthanum aluminum oxide and textured nickel substrates. An X-ray crystallographic study of Ce(OCMe2-i-Pr)4, which melts at just below room temperature, shows that it is a loosely bound dimer in the solid state with five-coordinate cerium centers and two bridging alkoxide ligands. The synthesis and X-ray crystal structures of Ce(OCMe2-i-Pr)4(DMAP)2 (DMAP = 4-(dimethylamino)pyridine) and Ce2(OCMe2-i-Pr)5(acac)3 are also reported. The cerium atoms in Ce(OCMe2-i-Pr)4(DMAP)2 and Ce2(OCMe2-i-Pr)5(acac)3 have, respectively, distorted octahedral and pentagonal bipyramidal coordination geometries.

Thermal barrier coatings produced by chemical vapor deposition

Yttria stabilized zirconia (YSZ) can be employed as thermal barrier coatings (TBCs) on Ni-based super alloys in gas turbines and aircraft engines. The YSZ coatings have been fabricated by atmospheric plasma spraying or electron-beam physical vapor deposition. The increase in operation temperature of gas turbines demands another fabrication process to obtain high quality TBCs. Chemical vapor deposition (CVD) can be an alternative route to prepare TBCs due to excellent conformal coverage and columnar microstructure. This paper reviews the fabrication of YSZ films by conventional thermal CVD and plasma CVD intended for TBCs. A new laser CVD developed by our group with a high deposition rate of 660 µμh-1 was also briefly introduced.

Synchronously Excited Discrete Chemical Vapor Deposition of Ta2 O 5

A versatile chemical vapor deposition (CVD) technique is proposed which has two noteworthy technical features: (i) alternate or intermittent introduction of source vapors followed by evacuation and (ii) one or more excitations synchronized with the sequence of vapor introduction. Since it can select and identify the place and time for the occurrence of reactions and excitation among source molecules, this technique also promises to be valuable in investigating the use of conventional CVD processes with unfamiliar materials. In this work, the technique is used to investigate the conventional photo and thermal CVD processes of tantalum pentoxide film using tantalum pentachloride and oxygen. The results indicate that significant deposition occurs even without the vapor phase reactions among source vapors and that photoexcitation of the substrate surface greatly enhances film deposition. In the course of the investigation, it was observed that temporary photoexcitation and ozone supply produced a high rate of film deposition even at temperatures lower than 300°C.

Wide area windowless disk plasma lamp of uniform intensity for use in microelectronic film processing

A wide area windowless plasma disk excited by a soft vacuum electron beam provides a wide area uniform source of vacuum ultraviolet (VUV) photons as well as atomic radicals. Hydrogen and oxygen when excited by the soft vacuum electron beam, emit strong atomic resonance radiation at 121.6 and 130 nm, respectively; in fact up to 8% of the total applied discharge power is emitted as VUV photons. The spatial uniformity of the atomic VUV resonance radiation approaches 6% across a disk 19 cm in diameter. The density of atomic oxygen species generated in the plasma disk has also been experimentally determined using an established polymer film etch rate method as well as with a conventional silver thin film sensor. We employ the disk plasma in a windowless configuration to achieve lower temperature chemical vapor deposition (CVD) than conventional thermal CVD. The VUV photon flux as well as the radical and excited atomic gas species emitted from the lamp can assist dissociation of feedstock reactant gases as well as assist heterogeneous surface reactions and increase surface mobility of absorbed species allowing for lower temperature CVD. Thin films of an aluminum nitride and hydrogenated amorphous silicon have been deposited at temperature between 100–400 °C. The deposited films show improvement over other plasma and photo-assisted CVD processes in the film quality achieved, the area covered, the substrate temperature required, and the maximum deposition rates that are possible. In situ generation of arsine (AH3) and unsaturated arsenic hydrides AsHx (x≤2) have also been achieved by placing elemental arsenic in an environment rich in atomic hydrogen created from the disk–plasma source.