Cold-wall Chemical Vapor Deposition Research Articles

Growth of high quality, high density single-walled carbon nanotube forests on copper foils

We demonstrate the growth of high quality single-walled carbon nanotube (SWCNT) forests on commercial Cu foils by cold-wall chemical vapor deposition. Time-of-flight secondary ion mass spectrometry was employed to study the effect of annealing on the catalyst evolution with or without an AlOx barrier layer. X-ray photoelectron spectroscopy was used to investigate the chemical states of the catalyst and the barrier layer. SWCNT forests can be reproducibly grown on Cu foils sputter-coated with Al and Fe layers as thin as 6 nm and 0.4 nm, respectively. Al transforms into AlOx on exposure to air and during annealing. Most importantly, such a thin AlOx barrier layer ensures not only the growth of SWCNTs but also an Ohmic contact between the as grown SWCNTs and the Cu base as measured by a two-point probe station. The as-grown SWCNTs exhibit a bimodal distribution of diameters ranging from 0.6 to 4.5 nm, with two peaks centered at 0.8 nn and 2.6 nm, respectively.

Single-walled carbon nanotube growth on SiO2/Si using Rh catalysts by alcohol gas source chemical vapor deposition

We carried out single-walled carbon nanotube (SWCNT) growth on SiO2/Si substrates using Rh as catalysts by a cold-wall chemical vapor deposition (CVD) method in a high vacuum using a nozzle injector for the ethanol gas supply. By optimizing the ethanol pressure, we could grow SWCNTs at 600 and 700°C. Using transmission electron microscopy (TEM) and Raman spectroscopy, we determined the diameter distributions of the SWCNTs and found that the SWCNTs grown at 600°C have a narrow diameter distribution and that the diameters of most of SWCNTs are between 1.1 and 1.4nm. TEM observation showed that the SWCNT diameters are similar to the Rh catalyst particle sizes, and that the reduction in SWCNT diameter was caused by the decrease in catalyst size with decreasing temperature.

Single-walled carbon nanotube synthesis using Pt catalysts under low ethanol pressure via cold-wall chemical vapor deposition in high vacuum

We study single-walled carbon nanotube (SWCNT) growth from Pt catalysts by a cold-wall chemical vapor deposition (CVD) method in a high vacuum using a nozzle injector for the ethanol gas supply. By optimizing the ethanol pressure, we could grow SWCNTs between 330 and 700 °C, and the optimal ethanol pressure to obtain the highest SWCNT yield was reduced as the growth temperature decreased. Using transmission electron microscopy, Raman spectroscopy and photoluminescence measurements, we determined the diameters and chirality distribution of the SWCNTs and showed that the grown SWCNTs have a narrow chirality distribution and that the diameters of most SWCNTs were below 1.0 nm. In addition, based on the size distribution and the chemical states of Pt catalyst particles, we proposed a growth model of the SWCNTs.

Enhancement of Material Quality of (Si)GeSn Films Grown by SnCl4 Precursor

The (Si)GeSn films have been grown with and without carrier gases on Si substrate using a cold-wall ultra-high vacuum chemical vapor deposition system. Material characterization of the films grown with Ar carrier gas using X-ray diffraction and transmission electron microscopy shows achievement of higher quality films. Optical characterization of the films with photoluminescence shows enhancement in material quality of the films at 350 and 400ºC growth temperatures. Increase in the pressure results in higher Sn incorporation and higher photoluminescence intensity. Spectroscopic ellipsometry data confirms the change in the GeSn bandgap towards lower energies.

Re-growth of single-walled carbon nanotube by hot-wall and cold-wall chemical vapor deposition

Single-walled carbon nanotube (SWCNT) was synthesized from short nanotubes using chemical vapor deposition (CVD) and the associated factors affecting the re-growth of the SWCNT were both investigated and optimized. Long, dense nanotubes were prepared from a mixture of acetylene and ethanol on air-annealed ST-cut quartz substrates by hot-wall CVD. Raman and photoluminescence analyses of the resulting material demonstrated that SWCNT was generated from the initial seeds since the chiralities of the seeds were maintained in the re-grown SWCNT. The re-growth of SWCNT was also achieved by cold-wall CVD. In both CVD systems, the efficiency of SWCNT re-growth was largely determined by the pretreatment conditions and growth parameters. By varying these factors, the growth of SWCNT from seeds was controlled. The re-growth mechanism is discussed based on experimental observations.

High Quality Monolayer Graphene Synthesized by Resistive Heating Cold Wall Chemical Vapor Deposition.

Emerging flexible and wearable technologies such as healthcare electronics and energy-harvest devices could be transformed by the unique properties of graphene. The vision for a graphene-driven industrial revolution is motivating intensive research on the synthesis of (1) high quality and (2) low cost graphene. Hot-wall chemical vapour deposition (CVD) is one of the most competitive growth methods, but its long processing times are incompatible with production lines. Here we demonstrate the growth of high quality monolayer graphene using a technique that is 100 times faster than standard hot-wall CVD, resulting in 99% reduction in production costs. A thorough complementary study of Raman spectroscopy, atomic force microscopy, scanning electron microscopy and electrical magneto-transport measurements shows that our cold wall CVD-grown graphene is of comparable quality to that of natural graphene. Finally, we demonstrate the first transparent and flexible graphene capacitive touch-sensor that could enable the development of artificial skin for robots.

Direct Growth of Ge1−xSnx Films on Si Using a Cold-Wall Ultra-High Vacuum Chemical-Vapor-Deposition System

Germanium tin alloys were grown directly on Si substrate at low temperatures using a cold-wall ultra-high vacuum chemical vapor deposition system. Epitaxial growth was achieved by adopting commercial gas precursors of germane and stannic chloride without any carrier gases. The X-ray diffraction analysis showed the incorporation of Sn and that the Ge1-xSnx films are fully epitaxial and strain relaxed. Tin incorporation in the Ge matrix was found to vary from 1% to 7%. The scanning electron microscopy images and energy dispersive X-ray spectra maps show uniform Sn incorporation and continuous film growth. Investigation of deposition parameters shows that at high flow rates of stannic chloride the films were etched due to the production of HCl. The photoluminescence study shows the reduction of bandgap from 0.8 eV to 0.55 eV as a result of Sn incorporation.

Rapid CVD growth of millimetre-sized single crystal graphene using a cold-wall reactor

In this work we present a simple pathway to obtain large single-crystal graphene on copper (Cu) foils with high growth rates using a commercially available cold-wall chemical vapour deposition (CVD) reactor. We show that graphene nucleation density is drastically reduced and crystal growth is accelerated when: (i) using ex situ oxidized foils; (ii) performing annealing in an inert atmosphere prior to growth; (iii) enclosing the foils to lower the precursor impingement flux during growth. Growth rates as high as 14.7 and 17.5 μm min−1 are obtained on flat and folded foils, respectively. Thus, single-crystal grains with lateral size of about 1 mm can be obtained in just 1 h. The samples are characterized by optical microscopy, scanning electron microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy as well as selected area electron diffraction and low-energy electron diffraction, which confirm the high quality and homogeneity of the films. The development of a process for the quick production of large grain graphene in a commonly used commercial CVD reactor is a significant step towards an increased accessibility to millimetre-sized graphene crystals.

Growth Mechanism of Single-Walled Carbon Nanotubes from Pt Catalysts by Alcohol Catalytic CVD

ABSTRACTSingle-walled carbon nanotube (SWCNT) growth from Pt catalysts by an alcohol gas source method, a type of cold-wall chemical vapor deposition (CVD), was investigated. Raman results showed that the diameters of SWCNTs grown from Pt were below 1.2 nm, while transmission electron microscopy (TEM) showed that the diameters of most Pt catalyst particles were above 1.2 nm. This suggests that SWCNT diameters were smaller than Pt catalysts particles. X-ray photoelectron spectroscopy measurements showed that reduction of Pt particles occurred during the SWCNT growth. Based on these experimental data, growth mechanism of SWCNTs was discussed.

Water-assisted growth of uniform 100 mm diameter SWCNT arrays.

We report a simple method for growing high-quality single-walled carbon nanotube (SWCNT) arrays on 100 mm wafers via the addition of water vapor to highly purified gases during the CNT growth step. We show that adding a small amount of water during growth helps to create a uniform catalyst distribution and yields high-quality (Raman G/D of 26 ± 3), high-density (up to 6 × 10(11) cm(-2)) and uniform SWCNT arrays on 100 mm large wafers. We rationalize our finding by suggesting that the addition of water decreases catalyst mobility, preventing its coarsening at higher temperatures. We also report a new mechanism of catalyst inactivation in wafer-scale growth using ultrapurified gas sources by the formation of large, 5 ± 3 μm iron particles. We found such formations to be common for substrates with large temperature gradients, such as for wafers processed in a typical cold-wall chemical vapor deposition reactor.

Very large cathode current and long term stability of vacuum sealed tubes with engrafted-carbon-nanotube emitters

Abstract For the future commercial applications of carbon nanotubes (CNTs) in high power vacuum microwave amplifiers or compact X-ray tubes, we have attempted to fabricate engrafted CNT field emitters on a metallic substrate using both screen printing and chemical vapor deposition. Cobalt nano-grains are doped in the printed CNT paste and act as the catalyst for the engrafted growth of CNTs by the cold wall chemical vapor deposition. Stable cathode current (~ 30 mA) from a small area (~ 1.5 mm 2 ) of engrafted CNT emitters was measured in a vacuum-sealed diode tube. High current density (> 1.6A/cm 2 ) has also gotten in the vacuum sealed tube in which the emitters spread about 0.78 mm 2 after an aging process that lasts more than 12 h in DC mode with the water cooling of the anode.

Large and stable emission current from synthesized carbon nanotube/fiber network

In order to obtain a large and stable electron field emission current, the carbon nanotubes have been synthesized on carbon fibers by cold wall chemical vapor deposition method. In the hierarchical nanostructures, carbon fibers are entangled together to form a conductive network, it could provide excellent electron transmission and adhesion property between electrode and emitters, dispersed clusters of carbon nanotubes with smaller diameters have been synthesized on the top of carbon fibers as field emitters, this kind of emitter distribution could alleviate electrostatic shielding effect and protect emitters from being wholly destroyed. Field emission properties of this kind of carbon nanotube/fiber network have been tested, up to 30 mA emission current at an applied electric field of 6.4 V/μm was emitted from as-prepared hierarchical nanostructures. Small current degradation at large emission current output by DC power operation indicated that carbon nanotube/fiber network could be a promising candidate for field emission electron source.

Single-Walled Carbon Nanotube Growth with Narrow Diameter Distribution from Pt Catalysts by Alcohol Gas Source Method

ABSTRACTSingle-walled carbon nanotube (SWCNT) growth were carried out on SiO2/Si substrates using Pt catalysts at different temperatures, from 400°C to 700°C, under various ethanol pressures by an alcohol gas source method, a type of cold-wall chemical vapor deposition (CVD). Raman measurements showed that the optimal ethanol pressure decreased as the growth temperature was reduced, and that SWCNTs grew even at 400°C by optimizing the ethanol pressure to 1×10-5 Pa in a high vacuum system. Compared to the SWCNTs grown from Co catalysts, the diameters of SWCNTs grown from Pt were smaller, irrespective of the growth temperature. In addition, both the SWCNT diameter and the distribution became narrower by reducing the growth temperature and we obtained small-diameter SWCNTs of which the diameters were less than 1 nm using Pt catalysts.

Low Temperature Homoepitaxial Growth of 4H-SiC on 4° Off-Axis Carbon-Face Substrate Using BTMSM Source

Homoepitaxial 4H-SiC thin films were grown on (0 0 0 -1) C-face substrate by cold-wall chemical vapor deposition (CVD) using bis-trimethylsilylmethane (BTMSM, C7H20Si2) precursor. Because of the polarity difference of C-face and (0 0 0 1) Si-face, epitaxial growth conditions of C-face was quite different from those of Si-face. To improve the quality of C-face epitaxial films, effects of epitaxial growth conditions on surface morphology and crystallinity of epitaxial films were investigated.

Preparation of Pyrolytic Carbon Coating from Acetylene by Cold Wall Chemical Vapour Deposition Process

Preparation of Pyrolytic Carbon Coating from Acetylene by Cold Wall Chemical Vapour Deposition Process

Few-Layer Graphene Direct Deposition on Ni andCu Foil by Cold-Wall Chemical Vapor Deposition

We report an alternative synthesis process, cold-wall thermal chemical vapor deposition (CVD), is replied to directly deposit single-layer and few-layer graphene films on Ar plasma treated Ni and Cu foils using CH4 as carbon source. Through optimizing the process parameters, large scale single-layer graphene grown on Ni foil is comparable to that grown on Cu foil. The graphene films were able to be transferred to other substrates such as SiO2/Si, flexible transparent PET and verified by optical microscopy, Raman microscopy and scanning electron microscopy. The sheet resistance and transmission of the transferred graphene films on PET substrate were also discussed.

Single-walled carbon nanotube synthesis on SiO2/Si substrates at very low pressures by the alcohol gas source method using a Pt catalyst

A platinum catalyst was used for single-walled carbon nanotube (SWCNT) growth on SiO2/Si substrates using an alcohol gas source method, a type of cold-wall chemical vapor deposition. Compared to Co, a conventional transition metal catalyst, the optimal ethanol pressure was considerably reduced in the growth at 700°C, and SWCNTs could be grown even at an ambient ethanol pressure of 1×10−5Pa. Raman spectroscopy measurements showed that the G/Si ratios of SWCNTs grown at 700°C with the Pt catalyst under an ethanol pressure between 1×10−4 and 1×10−1Pa was larger than that grown with Co catalyst under optimal conditions (700°C, 1×10−1Pa), indicating that the Pt catalyst is suitable for SWCNT growth under a low ethanol pressure. In addition, the diameter distributions of SWCNTs grown with the Pt catalyst were narrower than those grown with the Co catalyst. Taking into account the results by transmission electron microscopy observation, the diameter reduction was caused by the smaller migration distance of Pt on the substrate. Based on these results, we discuss the growth mechanism of SWCNTs from the Pt catalyst.

Chemical Vapor Deposition of Boron Phosphide Thin Films

ABSTRACTBoron Phosphide (BP) is a promising material for use as a room temperature semiconductor detector of thermal neutrons. The absorption of a thermal neutron by a 10B nucleus in BP can yield 2.3MeV of energy which in solid state BP can yield ∼0.5 million electron-hole pairs that would be detectable with minimal amplification in a device. BP thin films are grown according to the net reaction below in a cold wall chemical vapor deposition (CVD) reactor: Thin film depositions are performed using diborane and phosphine with a balance of hydrogen gas at near atmospheric pressure with RF induction heating. The resultant BP films are characterized by Raman, XRD, SEM, TEM and TEM-EELS for chemical composition, surface and bulk morphology. BP growths on Si and SiC substrates are compared. SiC provides reduced lattice mismatch for growth of BP and growth of heteroepitaxial BP on SiC will be discussed.

Development of a Laser-Assisted Chemical Vapor Deposition System for the Growth of Carbon Nanotubes

We developed the chemical vapor deposition (CVD) system in which the pulsed UV laser (a fourth-harmonic Nd:YAG laser, λ = 266 nm, pulse width = 4.3 ns, repetition frequency = 10 Hz) can be introduced. This CVD system is based on the cold-wall thermal CVD. The substrate, on which the growth catalysts are deposited, can be heated by resistance heating and be irradiated with UV laser. We used a commonly-used Fe/Co supported on zeolite catalyst for carbon nanotube growth. The catalyst was coated on a 10 mm × 10 mm Si substrate. Ethanol gas was used as a carbon source. In the CVD process, the substrate is heated by resistance heating at 300 o C, then ethanol gas is supplied in the CVD chamber with the pressure around 1000 Pa, after that the laser is irradiated to the substrate. We have examined the dependence of the laser fluence on the grown carbon nanotubes (CNTs). The growth area and growth amount of CNTs depend on the laser fluence. CNTs were synthesized at the laser spot with the laser fluence of 0.05 J/cm 2 .

Thin Single-Walled Carbon Nanotubes with Narrow Diameter Distribution Grown by Cold-Wall Chemical Vapor Deposition Combined with Co Nanoparticle Deposition

We have grown thin single-walled carbon nanotubes (SWNTs) with a narrow diameter distribution using the arc-discharge plasma (ADP) technique for Co catalyst metal deposition and a cold-wall chemical vapor deposition (CVD) system for SWNT growth. The diameters of the SWNTs ranged from 0.79 to 1.07 nm. In addition to depositing small and uniform-sized metal catalyst nanoparticles by the ADP technique, decreasing the growth temperature using the cold-wall CVD system seemed to suppress the aggregation of the metal catalyst nanoparitcles leading to SWNTs with small diameters of narrow distribution.