Rational Modification of a Metallic Substrate for CVD Growth of Carbon Nanotubes

Citation: Li, X., Baker-Fales, M., Almkhelfe, H., Gaede, N. R., Harris, T. S., & Amama, P. B. (2018). Rational Modification of a Metallic Substrate for CVD Growth of Carbon Nanotubes. Scientific Reports, 8(1). https://doi.org/10.1038/s41598-018-22467-7Growth of high quality, dense carbon nanotube (CNT) arrays via catalytic chemical vapor deposition (CCVD) has been largely limited to catalysts supported on amorphous alumina or silica. To overcome the challenge of conducting CNT growth from catalysts supported on conductive substrates, we explored a two-step surface modification that involves ion beam bombardment to create surface porosity and deposition of a thin AlxOy barrier layer to make the surface basic. To test the efficacy of our approach on a non-oxide support, we focus on modification of 316 stainless steel (SS), a well-known inactive substrate for CNT growth. Our study reveals that ion beam bombardment of SS has the ability to reduce film thickness of the AlxOy barrier layer required to grow CNTs from Fe catalysts to ∼ 5 nm, which is within the threshold for the substrate to remain conductive. Additionally, catalysts supported on ion beam-damaged SS with the same AlxOy thickness show improved particle formation, catalyst stability, and CNT growth efficiency, as well as producing CNTs with higher quality and density. Under optimal reaction conditions, this modification approach can lead to CNT growth on other nontraditional substrates and potentially benefit applications that require CNTs be grown on a conductive substrate

Correlating electrical resistance to growth conditions for multiwalled carbon nanotubes

A correlation between growth temperature and electrical resistance of multiwalled carbon nanotubes MWNTs has been established by measuring the resistance of individual MWNTs grown by microwave plasma-enhanced chemical vapor deposition PECVD at 800, 900, and 950 °C. The lowest resistances were obtained mainly from MWNTs grown at 900 °C. The MWNT resistance is larger on average at lower 800 °C and higher 950 °C growth temperatures. The resistance of MWNTs correlated well with other MWNT quality indices obtained from Raman spectra. This study identifies a temperature window for growing higher-quality MWNTs with fewer defects and lower resistance by PECVD

Preferential Biofunctionalization of Carbon Nanotubes Grown by Microwave Plasma-Enhanced CVD

Multiwalled carbon nanotubes (CNTs) were grown by microwave plasma chemical vapor deposition using dendrimer-templated Fe nanoparticles as a catalyst. Variation of the de bias voltage and the calcination temperature of the dendrimer-templated Fe2O3 catalyst yielded a matrix of CNT arrays. Samples were immobilized with glucose oxidase, which were used for amperometric cyclic voltammetry experiments. Spectroscopic and electron microscopic characterizations indicate that enzyme adsorption per unit CNT area is higher for samples with lower quality, suggesting that CNTs with higher levels of defect densities are desirable for biosensing applications

Effects of Growth Temperature on Carbon Nanotube Array Thermal Interfaces

Due to their excellent compliance and high thermal conductivity, dry carbon nanotube (CNT) array interfaces are promising candidates to address the thermal management needs of power dense microelectronic components and devices. However, typical CNT growth temperatures 800°C limit the substrates available for direct CNT synthesis. A microwave plasma chemical vapor deposition and a shielded growth technique were used to synthesize CNT arrays at various temperatures on silicon wafers. Measured growth surface temperatures ranged from 500°C to 800°C. The room-temperature thermal resistances of interfaces created by placing the CNT covered wafers in contact with silver foil (silicon-CNT-silver) were measured using a photoacoustic technique to range from approximately 7 mm2°C/W to 19 mm2°C/W at moderate pressures. Thermal resistances increased as CNT array growth temperature decreased primarily due to a reduction in the average diameter of CNTs in the arrays

Wetting Behavior And Activity Of Catalyst Supports In Carbon Nanotube Carpet Growth

A simple, reliable, and non-destructive approach based on contact angle measurements is described for predicting the activity of catalyst supports in carbon nanotube (CNT) carpet growth. The basic component of the surface free energy of different alumina supports - determined from the van Oss-Good-Chaudhury model and the Young-Dupré equation - was found to correlate with the activity of Fe catalyst during water-assisted CVD growth of CNT carpets. © The Royal Society of Chemistry 2013

XPS and Raman characterization of single-walled carbon nanotubes grown from pretreated Fe2O3 nanoparticles

X-ray photoelectron (XPS) and Raman spectroscopic techniques have been used to study the influence of the annealing ambient (N2, Ar and H2) of nearly monodispersed Fe2O3 nanoparticles (mean size = 3.2 ± 1 nm) on the growth of carbon nanotubes by microwave plasma chemical vapour deposition. XPS characterization of the catalytic templates reveals that a N2 ambient reduces sintering of the Fe2O3 nanoparticles and confirms that the chemical phase involved in the nucleation of nanotubes is the metal state Fe0. Multi-excitation wavelength Raman spectroscopy (514, 574, 633 and 785 nm) reveals that the single-walled carbon nanotubes (SWCNTs) grown from N2-annealed catalyst nanoparticles range between 0.8 and 1.1 nm while SWCNTs grown from Ar-annealed catalyst nanoparticles exhibit a broader diameter distribution in the range 0.8–1.8 nm. The narrowness in the distribution of SWCNTs grown from the N2-annealed catalysts has been attributed to the enhanced stability of Fe2O3 nanoparticles in an N2 ambient

Dendrimer-assisted controlled growth of carbon nanotubes for enhanced thermal interface conductance

Multi-walled carbon nanotubes (MWCNTs) with systematically varied diameter distributions and defect densities were reproducibly grown from a modified catalyst structure templated in an amine-terminated fourth-generation poly(amidoamine) (PAMAM) dendrimer by microwave plasma-enhanced chemical vapor deposition. Thermal interface resistances of the vertically oriented MWCNT arrays as determined by a photoacoustic technique reveal a strong correlation with the quality as assessed by Raman spectroscopy. This study contributes not only to the development of an active catalyst via a wet chemical route for structure-controlled MWCNT growth, but also to the development of efficient and low-cost MWCNT-based thermal interface materials with thermal interface resistances

Freestanding vertically oriented single-walled carbon nanotubes synthesized using microwave plasma-enhanced CVD

Freestanding single-walled carbon nanotubes (SWCNTs) have been synthesized in a vertical direction, perpendicular to the growth substrate, using applied DC substrate bias in a microwave plasma-enhanced chemical vapor deposition (PECVD) synthesis process. The degree of alignment and spatial density of SWCNTs demonstrate a strong dependence on the magnitude of applied bias, with increased alignment and decreased density with increased bias. The unique synthesis environment created by the application of a negative substrate bias in PECVD aligns SWCNTs along electric field lines and decreases SWCNT density due to bombardment by positively charged hydrogen ions. Multi-excitation wavelength Raman spectroscopy reveals shifts in dominant RBM peaks with the application of dc bias. Use of this technique to orient SWCNTs in the vertical direction may allow for three-dimensional SWCNT-based device architectures

Measurement of metal/carbon nanotube contact resistance by adjusting contact length using laser ablation

A technique of measuring contact resistance between an individual nanotube and a deposited metallic film is described. Using laser ablation to sequentially shorten the contact length between a nanotube and the evaporated metallic film, the linear resistivity of the nanotube as well as the specific contact resistivity between the nanotube and metallic film can be determined. This technique can be generally used to measure the specific contact resistance that develops between a metallic film and a variety of different nanowires and nanotubes