Growth evolution of rapid grown aligned carbon nanotube forests without water vapor on Fe/Al 2O 3/SiO 2/Si substrate

Impact of dynamic density decay of growing carbon nanotube forests on electrical resistivity

Single-step CVD growth of high-density carbon nanotube forests on metallic Ti coatings through catalyst engineering

This study examined the correlation between the thickness of the iron catalyst film deposited by e-beam evaporation and carbon nanotube (CNT) growth by water-assisted chemical vapour deposition. The number of walls and the alignment of the CNTs in the CNT forest could be controlled by the iron thickness. High resolution transmission electron microscopy was used to examine the catalyst size distribution and individual CNT structure. Atomic force microscopy was used to analyse the surface roughness. The correlation between the surface roughness, catalyst agglomeration, number of walls in the CNT and the alignment of the CNTs in the CNT forest was established. The CNTs grown on an iron catalyst ranging in thickness from 0.1 to 0.5 nm were well aligned with 2–4 walls. On the other hand, the CNTs grown on an iron catalyst ranging in thickness from 0.6 to 1 nm were less well aligned with 4–10 walls. The CNTs grown on an iron catalyst >1 nm in thickness were misaligned with 8–16 walls. The significance of these experimental trends is discussed within the framework of the clusters aggregation and Van der Waals interaction.

This paper presents direct growth of horizontally-aligned carbon nanotubes (CNTs) between two predefined various inter-spacing up to tens of microns of electrodes (pads) and its use as CNT field-effect transistors (CNT-FETs). Using the conventional photolithography technique followed by thin film evaporation and lift off, the catalytic electrodes (pads) were prepared, consisting of Pt, Al and Fe triple layers on SiO2/Si substrate. The grown CNTs were horizontally-aligned across the catalytic electrodes on the modified gold image furnace hot stage (thermal CVD) at 800 degrees C by using an alcohol vapor as the carbon source. Scanning and transmission electron microcopies (SEM/TEM) were used to observe the structure, growth direction and density of CNTs, while Raman spectrum analysis was used to indicate the degree of amorphous impurity and diameter of CNTs. Both single- and multi-wall CNTs with diameters of 1.1-2.2 nm were obtained and the CNT density was controlled by thickness of Fe catalytic layer. Following horizontally-aligned growth of CNTs, the electrical properties of back-gate CNT-FETs were measured and showd p-type conduction behaviors of FET.

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Carbon nanotubes (CNTs) are solid carbon allotropes that feature high strength and high transport capabilities. When large populations of CNTs are synthesized simultaneously, they self-assemble into vertically oriented CNT forests (also called CNT arrays or CNT turfs). In the current work, three-dimensional CNT forest microstructures are engineered by selectively activating CNT growth on specific regions of a patterned substrate. The process is realized using a combination of two distinct chemical vapor deposition (CVD) processes in concert with silicon substrates independently patterned with regions of alumina, iron, or alumina and iron. The CVD process of both techniques require a catalyst nanoparticle to facilitate CNT growth and a hydrocarbon gaseous precursor. Floating catalyst CVD, a process in which CNT catalyst is delivered to a substrate in the vapor state, is compatible with oxide-coated substrates and not compatible with bare silicon surfaces. Fixed catalyst CVD utilizes a static iron film catalyst layer to support CNT synthesis. Regions of alumina support selective CNT forest growth with floating catalyst CVD, while regions of layered Al2O3/Fe support both fixed and floating catalyst growth when the fixed catalyst is activated first. By selectively and sequentially activating specific regions of a lithographically-defined substrate using the various CVD processes, complex 3D microstructures are demonstrated. The resultant CNT forest microstructures are characterized using scanning electron microscopy (SEM) and nanoindentation. Atomic force microscopy is used to analyze the behavior of the fixed iron catalyst during the high temperatures required for CVD processing.

Carbon nanotubes (CNTs) were synthesized by catalytic decomposition of acetylene over Fe, Ni and Fe–Ni catalysts supported on alumina. The growth of CNTs was carried out at various reaction conditions. The growth density and diameter of CNTs could be controlled by varying the catalyst composition and the growth parameters. The growth density of CNTs increased with increasing the activation time of catalysts in H2 atmosphere and/or decreasing acetylene concentration. At 600 °C, higher density of CNTs was observed at 60 min for higher Fe containing catalyst, whereas at 90 min for higher Ni containing catalyst. The growth density of CNTs highly increased with increasing reaction time from 30 to 60 min. For all the catalysts, the diameter of CNTs decreased with increasing growth time further mainly due to hydrogen etching. Bimetallic catalysts produced narrower diameter CNTs than single metal catalysts. The growth of CNTs followed the tip growth mode and the CNTs were multi-walled CNTs.

The experimental measurement of effective compressive modulus of carbon nanotube forests and the nature of deformation

Evaluating the forces generated during carbon nanotube forest growth and self-assembly

Direct growth of carbon nanotubes forests on carbon fibers to replace microporous layers in proton exchange membrane fuel cells

A nanoscale fabrication technique appropriate for milling carbon nanotube (CNT) forests is described. The technique utilizes an environmental scanning electron microscope (ESEM) operating with a low pressure water vapor ambient. In this technique, a portion of the electron beam interacts with the water vapor in the vicinity of the CNT sample, dissociating the water molecules into hydroxyl radicals and other species by radiolysis. The remainder of the electron beam interacts with the CNT forest sample, making it susceptible to oxidation from the chemical products of radiolysis. This technique may be used to trim a selected region of an individual CNT, or it may be used to remove hundreds of cubic microns of material by adjusting ESEM parameters. The machining resolution is similar to the imaging resolution of the ESEM itself. The technique produces only small quantities of carbon residue along the boundaries of the cutting zone, with minimal effect on the native structural morphology of the CNT forest.

In this work, we grow different types of carbon nanotube (CNT) forests directly on AlN-based electroacoustic biosensors and study their functionalization efficiency. CNTs are used to increase the effective surface area of the sensor, pursuing a better sensitivity, without increasing the sensor capacitance. Here we use a general method for CNT bio-functionalization with specific receptors for targeted species. First, we make them hydrophilic. Next, we cover them with alternating polymers. Finally, we incubate their surface in an N-hydroxysuccinimide biotin solution. To study the functionalization homogeneity along the CNT length, Streptavidin conjugated with fluorescein isothiocyanate is used as the targeted species for confocal fluorescence microscopy characterization.

In this paper, Vertically Aligned Carbon Nanotube (VACNT) forests are embedded into two different glass fibre/epoxy composite systems to study their sensing abilities to strain and temperature. Through a bottom-up approach, performing studies of the VACNT forest and its individual carbon nanotubes on the nano-, micro-, and mesoscale, the observed thermoresistive effect is determined to be due to fluctuation-assisted tunnelling, and the linear piezoresistive effect due to the intrinsic piezoresistivity of individual carbon nanotubes. The VACNT forests offer great freedom of placement into the structure and reproducibility of sensing sensitivity in both composite systems, independent of conductivity and volume fraction, producing a robust sensor to strain and temperature.

Desalination by membrane distillation (MD) using low‐grade or waste heat provides a potential route for sustainable water supply. Nonwetting, porous membranes that provide a selective pathway for water vapor over nonvolatile salt are at the core of MD desalination. Conventional water‐repelling MD membranes (i.e., hydrophobic and superhydrophobic membranes) fail to ensure long‐term desalination performance due to pore wetting and surface fouling. To address these challenges, a defect‐free carbon nanotube forest (CNTF) is engineered in situ on a porous electrospun silica fiber substrate. The engineered CNTF forms an ultrarough and porous interface structure, allowing outstanding wetting resistance against water in air and oil underwater. As a result of this antiwetting property, the composite CNTF membrane displays a stable water vapor flux and a near complete salt rejection (>99.9%) in the desalination of highly saline water containing low surface tension contaminants. The antimicrobial property of the composite CNTF membrane imparted by the unique forest‐like architecture and the oxidative effect of carbon nanotubes (CNTs) are further demonstrated. The results exemplify an effective strategy for engineering CNT architecture to elucidate the structure–property–performance relationship of the nanocomposite membranes and to guide the design of robust thermal desalination membranes.

Here we report a systematic study on the contact and sheet resistances of vertically aligned carbon nanotube (CNT) forest in gas sensing applications. Four different methods: (1) transfer length method (TLM), (2) contact chain method, (3) Kelvin method and (4) four-point probe method have been implemented. Experimental results show prototype CNT forest with the stripe-shape of 100 μm in height and 100 μm in width has a sheet resistance of 100 Ω/□ and contact resistance of less than 50 Ω for an area of 100×100 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Consistent measurement results from the four methods validate the reliability of this study. When such CNT samples were tested as resistor-based gas sensors, results show 0.5 ppm of NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> gas sensing resolution with a detection response time of one minute.

We show a simple technique to grow patterned carbon nanotube (CNT) forests by annealing the catalytic surface using copper patterns (as stencil or bridge) prior to, or during, CNT growth. We demonstrate that copper diffused into the iron catalyst and deactivated it, thus preventing CNT growth on the areas where the copper was present. This technique is a promising and simple way to pattern CNT forests since it does not require the usual lithography and lift-off of the catalyst. This catalyst deactivating overlayer principle can be extended to pattern other 1D nanostructures such as carbon nanofibers or nanowires and 2D nanostructures such as graphene or transition metal dichalcogenides using chemical vapor deposition (CVD).