Ethanol Chemical Vapor Deposition Research Articles

Graphene nanomesh as highly sensitive chemiresistor gas sensor.

Graphene is a one atom thick carbon allotrope with all surface atoms that has attracted significant attention as a promising material as the conduction channel of a field-effect transistor and chemical field-effect transistor sensors. However, the zero bandgap of semimetal graphene still limits its application for these devices. In this work, ethanol-chemical vapor deposition (CVD) of a grown p-type semiconducting large-area monolayer graphene film was patterned into a nanomesh by the combination of nanosphere lithography and reactive ion etching and evaluated as a field-effect transistor and chemiresistor gas sensors. The resulting neck-width of the synthesized nanomesh was about ∼20 nm and was comprised of the gap between polystyrene (PS) spheres that was formed during the reactive ion etching (RIE) process. The neck-width and the periodicities of the graphene nanomesh (GNM) could be easily controlled depending on the duration/power of the RIE and the size of the PS nanospheres. The fabricated GNM transistor device exhibited promising electronic properties featuring a high drive current and an I(ON)/I(OFF) ratio of about 6, significantly higher than its film counterpart. Similarly, when applied as a chemiresistor gas sensor at room temperature, the graphene nanomesh sensor showed excellent sensitivity toward NO(2) and NH(3), significantly higher than their film counterparts. The ethanol-based graphene nanomesh sensors exhibited sensitivities of about 4.32%/ppm in NO(2) and 0.71%/ppm in NH(3) with limits of detection of 15 and 160 ppb, respectively. Our demonstrated studies on controlling the neck width of the nanomesh would lead to further improvement of graphene-based transistors and sensors.

Growth of carbon nanotubes from titanium dioxide nanoparticles

We have demonstrated that titanium dioxide (TiO2) nanoparticle is an efficient catalyst for the growth of carbon nanotubes (CNTs). TiO2 nanoparticles can be generated either by sol–gel method or sputtering. Highly dense single-walled carbon nanotubes (SWNTs) and/or multi-walled CNTs can be produced by ethanol-chemical vapor deposition (EtOH-CVD) using those TiO2 nanoparticles as catalysts. XPS measurements further prove that the TiO2 nanoparticles are responsible for the nanotube growth. Sputtering approach for generating TiO2 nanoparticles provide a facile way for patterning SWNTs for various applications.

Fabrication of horizontally aligned ultra-long single-walled carbon nanotubes on Si substrates using the fast-heating chemical vapor deposition method

In this paper we study the growth of horizontally aligned ultra-long single-walled carbon nanotubes (SWCNTs) (5 mm) on oxidized silicon substrates by the fast-heating chemical vapor deposition (CVD) method. Ferric chloride (FeCl 3) and ethanol (C 2 H 5 OH) solution are used as catalyst and carbon source, respectively. The influence of growth conditions such as temperature, time and gas flow rates on the SWCNTs’ growth is studied in detail. The morphologies and structure of the SWCNTs are analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The experimental results demonstrate that by fast-heating CVD of ethanol at a temperature of 900 °C for 60 min, the SWCNTs have high quality. They are clean, ultra-long (mm), highly dense and as straight as parallel lines.

Fluidized Bed Chemical Vapor Deposition Synthesis of Carbon Nanotubes Using Different Fe–Co/Alumina Catalytic Powders

Catalytic particles, Iron-Cobalt supported on Alumina, with different metal compositions were investigated in fluidized bed chemical vapor deposition of Ethanol at 600°C to produce carbon nanotubes (CNTs). The characteristics of catalytic particles as well as product were studied using different analytical techniques. Results indicated that the dispersion of metallic nanoparticles was higher when small amounts of two kinds of metal were used. However, lowering of metal content was not always favored with respect to process efficiency. This study proved atomic ratio of the active metals in bimetallic catalyst is not an accurate specification, and mass ratio of the metals should be considered. Also, it was demonstrated that the characteristics of catalytic particles, such as pore structure and their size as well as distribution of the metallic nanoparticles, need to be suitably modified to get the desired quality and quantity of CNTs.

The growth of carbon nanotube with chemical vapor deposition under different process parameters

Whether the active catalytic species are in a liquid, solid phase, surface premelting or surface processes during CNT or other nanowire growth are controversial. In order to explore the mechanism for catalytically grown carbon nanotube (CNT), the mechanism for CNT grown under different temperatures was proposed tentatively. With ethanol chemical vapor deposition (CVD), carbon n.anotubes (CNTs) were synthesized controllably on Si substrates using cobalt (Co) as a catalyst. The effects of the Co particle size, growth temperature and ethanol pressure on CNT growth were investigated. A different dependence of CNT growth on the Co particle size at different ranges of the growth temperature was found.

X-ray photoelectron spectroscopy study on Fe and Co catalysts during the first stages of ethanol chemical vapor deposition for single-walled carbon nanotube growth

Optimized chemical vapor deposition processes for single-walled carbon nanotube (SWCNT) can lead to the growth of dense, vertically aligned, mm-long forests of SWCNTs. Precise control of the growth process is however still difficult, mainly because of poor understanding of the interplay between catalyst, substrate and reaction gas. In this paper we use x-ray photoelectron spectroscopy (XPS) to study the interplay between Fe or Co catalysts, SiO2 and Al2O3 substrates and ethanol during the first stages of SWCNT forest growth. With XPS we observe that ethanol oxidizes Fe catalysts at carbon nanotube (CNT) growth temperatures, which leads to reduced carbon nanotube growth. Ethanol needs to be decomposed by a hot filament or other technique to create a reducing atmosphere and reactive carbon species in order to grow vertically aligned single-walled carbon nanotubes from Fe catalysts. Furthermore, we show that Al2O3, unlike SiO2, plays an active role in CNT growth using ethanol CVD. From our study we conclude that metallic Fe on Al2O3 is the most optimal catalyst/substrate combination for high-yield SWCNT forest growth, using hot filament CVD with ethanol as the carbon containing gas.

Fractal Carbon Films Prepared by Chemical Vapor Deposition

Fractal carbon films deposited on copper plate by ethanol chemical vapor deposition are reported. In order to prepare fractal carbon films, iron nitrate was employed as catalyst precursor, copper plate as substrate, and ethanol as carbon source materials. The as-prepared carbon films were characterized by employing scanning electron microscopy and Raman spectroscopy. The thickness of the film was a few micrometers. According to Raman spectrum, we know the films exhibit low graphitization. According to SEM observation, we find that there are many protuberances with nanometer scale tips on the film surface. Due to direct growth on metal substrate and many nanometer scale tips, it has potential application that is fit for electron source in vacuum devices.

Self-Assembly of Carbon Nanotubes via Ethanol Chemical Vapor Deposition for the Synthesis of Gas Chromatography Columns

The synthesis of the gas chromatography stationary phase by molecular self-assembly of carbon nanotubes (CNTs) via a novel ethanol chemical vapor deposition process is presented. A major advantage is that ethanol was found to be an excellent carbon source that generated highly pure multiwalled carbon nanotubes with very little nontubular carbon impurities. The nanotubes were not vertically aligned but lay flat out on the column surface in a randomly distributed configuration. The CNT phase was able to separate a wide range of organic compounds with diverse polarity and volatility, where the number of plates per meter ranged from 900 to 1280. It also showed classical chromatographic behavior and good precision.

Temperature and time dependence study of single-walled carbon nanotube growth by catalytic chemical vapor deposition

The temperature and time dependence of single-walled carbon nanotube (SWCNT) growth by chemical vapor deposition of ethanol on Fe 2O 3/MgO catalyst are compared at both low (∼27 Pa) and atmospheric pressure limits. SWCNTs are synthesized in two reactors with different geometries and operating pressures and are characterized by Raman spectroscopy. Both reactors show SWCNT growth within a relatively narrow temperature window of 700–850 °C, with an optimum growth time of 35 min for the cold wall reactor and 75 min for the quartz tube reactor. A kinetic model comprising of ethanol decomposition, SWCNT formation, and water etching is developed to better understand the growth mechanism. The existence of a temperature window and an optimum growth time in both reactors can be well described by the kinetic model. Simulation results suggest that the temperature and time dependence can be explained by the competition between the growth of SWCNTs and that of amorphous carbon.

Graphene-based carbon nano-fibers grown on thin-sheet sinter-locked Ni-fiber as self-supported electrodes for supercapacitors

A promising thin-sheet graphene-based carbon/Ni-fiber hybrid structure has been developed by the catalytic chemical vapor deposition of ethanol on a sinter-locked 3-dimensional network consisting of 5 vol.% 8-μm-nickel fibers. It is revealed that the graphene nano-sheets consisting of tens of graphene single-layers are stacked in one line to form mesopore-rich carbon nano-fibers (CNFs). One of the most promising is its use as electrodes in electrochemical devices. When employed in an electrochemical capacitor, this hybrid shows excellent capacitive behavior and delivers pleasing specific capacitance at high current density (e.g., 87–100 F/g @ 100–500 mA/g).

Dynamic Study of Gas-Phase Species during Single-Walled Carbon Nanotubes Production by Chemical Vapor Deposition of Ethanol

The gas-phase species of the reactions that take place during Carbon Nanotubes (CNTs) production by Chemical Vapor Deposition (CVD) of ethanol vapors has been investigated in the temperature range of 650 - 900oC. More specifically, the effluent gases were analyzed by mass spectrometry in correlation to time as a way to determine the reactions that occur during the process and their influence on the rate of carbon deposition, total yield and kind of CNTs produced. The experiments were carried out in a thermogravimetric CVD hot-wall reactor over a Fe2O3/Al2O3 catalyst and the final product was characterized with Scanning Electron Microscopy (SEM) and Raman spectroscopy. It was found that the optimal temperature towards the highest yield of Single-Walled Carbon Nanotubes (SWCNTs) was achieved at 800oC leading to SWCNTs of 0.8 to 1.0 nm diameter. It was also determined that the presence of catalyst is crucial not only for the formation of CNTs, but also for the decomposition of ethanol vapors.

Dynamic Study of Gas-Phase Species during Single-Walled Carbon Nanotubes Production by Chemical Vapor Deposition of Ethanol

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Catalyst-free growth of oriented single-walled carbon nanotubes on mica by ethanol chemical vapor deposition

In this letter, it is reported for the first time that single-walled carbon nanotubes (SWNTs) can grow on mica substrate without additional catalyst by chemical vapor deposition (CVD) using ethanol as carbon source. The single-wall structure was characterized by Raman spectra and AFM (Atomic Force Microscopy) measurements. The growth of carbon nanotubes on mica surface contributes to the small amount of iron oxide in bare mica. The uniform dispersion and nanosized Fe particles formed from the reduction of iron oxide favor for the growth of SWNTs. Horizontally aligned superlong SWNTs arrays can be successfully generated on the mica surface, which is proved to be guided by the gas flow and under “kite growth mechanism”. The mica is a machinable material which can be easily cut and made a narrow slit on, thus the nanotubes can traverse the slit which can be in millimeter scale and long suspended SWNTs can be generated. This will provide an opportunity to manipulate individual SWNT for various purposes.

Carbon Nanofibers Synthesized by Ethanol Catalytic Chemical Vapor Deposition

. Carbon nanofibers have been attracted many attentions for their potential applications in nanocomposites and electromagnetic wave-absorbing materials due to their remarkable mechanical, electrical and other properties. Ethanol as carbon source possesses low toxicity, easier storage and transportation. In this paper, we report ethanol catalytic chemical vapor deposition (ECCVD) for synthesizing carbon nanofibers. We utilized ferrocene as catalyst precursor and use ethanol as carbon source to synthesize carbon nanofibers by ethanol chemical vapor deposition. The deposits were characterized by employed scanning electron microscopy, transmission electron microscope and Raman spectroscopy.

Growth of Vertically Aligned Single-Walled Carbon Nanotubes on Alumina and Sapphire Substrates

The synthesis of vertically aligned carbon nanotubes with submillimeter-order heights was performed using ethanol chemical vapor deposition with Co catalysts supported on Al2O3 substrates. The effects of Al2O3 in the form of amorphous alumina and single-crystalline sapphire were investigated through a characterization of the Co catalyst particles on the substrates. An important effect of Al2O3 was found to be the production of highly dense and nanosized Co particles, owing to a low surface diffusivity.

Growth dynamics of vertically aligned single-walled carbon nanotubes from in situ measurements

An in situ optical absorbance measurement was used to study the growth dynamics of vertically aligned single-walled carbon nanotubes (VA-SWCNTs) synthesized by chemical vapor deposition of ethanol. The growth rate of the VA-SWCNT film was found to decay exponentially from an initial maximum, resulting in an effective growth time of approximately 15 min. Investigation of various growth conditions revealed an optimum pressure at which growth is maximized, and this pressure depends on the growth temperature. Below this optimum pressure the synthesis reaction is first-order, and the rate-limiting step is the arrival of ethanol at the catalyst. We also present a novel method for determining the burning temperature of low-mass materials, which combines the in situ absorbance measurement with controlled oxidation.

A temperature window for ethanol chemical vapor deposition of a carbon nanotube arraycatalyzed by Co particles

With ethanol chemical vapor deposition (CVD), vertically grown carbon nanotube(CNT) arrays were synthesized controllably on Si substrates, using cobalt (Co) asa catalyst. The effect of the Co particle size, growth temperature and ethanolpressure on nanotube growth has been investigated. It is shown that a verticallygrown nanotube array can be grown within a temperature window from 500 to700 °C. Our experiment offers a new route by which CNT arrays might be continuously andinexpensively produced at a relatively low temperature and also suggests that ethanol CVDis a potential method for low-temperature growth of CNTs.

Synthesis of Single-Walled Carbon Nanotube Networks on Silicon Nanowires

Single-walled carbon nanotubes (SWNTs) have been synthesized on silicon nanowires (SiNWs) by ethanol chemical vapor deposition (CVD) using Co catalysts nanoparticles. The surface SiOx layers assist the formation of catalyst nanoparticles on SiNWs by inhibiting the diffusion of Co to Si. Co-Si compounds have formed in SiNWs readily when the surface SiOx layers are very thin. Therefore, the yield of SWNTs is strongly influenced by the thickness of the surface SiOx layers of SiNWs.

Catalytic effects of production of carbon nanotubes in a thermogravimetric CVD reactor

Catalytic effects of the production of carbon nanotubes by chemical vapor deposition of ethanol are investigated. More specifically, the rate of deposition, total yield and physical characteristics of the product are examined with respect to physicochemical characteristics of the catalyst. The experiments were carried out at 800 °C in a thermogravimetric chemical vapor deposition (CVD) hot-wall reactor, which enables continuous monitoring of the evolution of carbon mass with time. The carbon precursor was ethanol vapors. Different types of catalytic substrates enriched with iron were employed and the effect of iron concentration and preparation method was studied. It was determined that an optimal iron content of the catalyst results in maximum yield and that yield depends on the preparation method of the catalyst. For a ratio of Al/Fe = 1/4 the yield reached approximately 400% of the initial catalyst weight, after 1 h of exposure to ethanol vapor. The final product was characterized with Scanning Electron Microscopy (SEM) and Raman spectroscopy. The results revealed the existence of high purity multi-wall carbon nanotubes, and the presence of single-wall carbon nanotubes with diameter ranging between 0.76 and 1.14 nm.

Growth of single-walled carbon nanotubes on silicon nanowires

Single-walled carbon nanotubes (SWNTs) have been grown on silicon nanowires (SiNWs) by ethanol chemical vapor deposition (CVD) with Co catalysts. We have found that a surface SiO x layer of SiNWs is necessary for the formation of active Co catalysts. In fact, the yield of the SWNT/SiNW heterojunctions gradually decreases as the thickness of the surface SiO x layer decreases. Since thin SiNWs are transparent to an electron beam, the Co nanoparticles on SiNWs can be easily observed as well as SWNTs by TEM. Therefore, the relationship between the diameters of each SWNT and its catalyst nanoparticle has been investigated. The diameters of SWNTs are equal to or slightly smaller than those of the catalyst nanoparticles.