Selective Growth Of Carbon Nanotubes Research Articles

Growth kinetics of single-walled carbon nanotubes with a (2n, n) chirality selection.

The growth kinetics play key roles in determining the chirality distribution of the grown single-walled carbon nanotubes (SWCNTs). However, the lack of comprehensive understandings on the SWCNT's growth mechanism at the atomic scale greatly hinders SWCNT chirality-selective synthesis. Here, we establish a general model, where the dislocation theory is a specific case, to describe the etching agent-dependent growth kinetics of SWCNTs on solid catalyst particles. In particular, the growth kinetics of SWCNTs in the absence of etching agent is validated by both in situ environmental transmission electron microscopy and ex situ chemical vapor deposition growth of SWCNTs. On the basis of the new theory of SWCNT's growth kinetics, we successfully explained the selective growth of (2n, n) SWCNTs. This study provides another degree of freedom for SWCNT controlled synthesis and opens a new strategy to achieve chirality-selective synthesis of (2n, n) SWCNTs using solid catalysts.

Temperature-dependent selective growth of carbon nanotubes in Si/SiO2 structures for field emitter array applications

Temperature-dependent selective growth of Carbon Nanotubes (CNTs) in Si/SiO2 structures using ferrocene/xylene volatile catalyst source and its application in Field Emitter Array (FEA) is demonstrated in this work. CNTs are grown directly on Si/SiO2 substrates by volatile catalyst source (Ferrocene/Xylene) Chemical Vapor Deposition (CVD) technique and the effect of growth temperatures (760–880°C) on CNT height and crystallinity has been studied. Selective growth of CNTs on Si substrates is achieved at 790°C growth temperature. Using the obtained selective growth condition, CNT FEAs are fabricated by growing CNT bundles selectively on the Si surface of the pre-fabricated SiO2 pits on a Si wafer. Field emission current density above 100mA/cm2 is obtained from inter-pit separation distances of 4–10μm. These results show the potential of ferrocene/xylene catalyst source in achieving selective growth of CNTs in Si/SiO2 structures for FEA application.

Selective growth of carbon nanotubes on boron-doped diamond for electrochemical biosensor application

Selective growth of MWCNTs on boron-doped diamond electrode was introduced and their electrochemical properties and glucose biosensing performances were reported.

Selective growth of carbon nanotubes on the substrate dependently active iron nano-particles

We propose a selective growth of carbon nanotubes (CNTs) on the substrate dependently active iron nano-particle (Fe-NP) catalysts. Fe-NPs synthesized by thermal decomposition of iron pentacarbonyl-oleic acid complex were used as catalysts for the growth of CNTs. While the Fe-NPs deposited on the metal substrate maintain their catalytic property for the growth of CNTs, those deposited on the silicon oxide substrate transform to oxidized state resulting in losing their catalytic property. Although all the Fe-NPs might be oxidized even on the metal patterns, oxidized Fe-NPs deposited only on the metal line would be reduced selectively by the hydrogen gas used as carrier gas in this CVD system. Consequently, CNTs were grown only at the Fe-NPs on the metal substrate selectively. Therefore, we could grow CNTs selectively by patterning the substrate without additional patterning process for the catalyst layer.

Modification of Silicon Substrate Using Low-Energy Proton Beam for Selective Growth of CNTs

A 3 keV low-energy proton beam was used to irradiate a silicon substrate for selective modification. The water contact angle measurement, chemical etching test with HF and the auger electron spectroscopy were used to investigate the chemical properties and the material composition of the proton beam-irradiated silicon substrate. The proton beam-irradiated silicon substrate was covered with a silicon oxide layer of about 60-70 angstroms due to the incorporation of oxygen molecules after exposure to ambient air. The silicon oxide layer produced by the proton beam was highly resistant to HF treatment which typically used to remove the silicon oxide on a substrate, and the surface of it was more hydrophilic than the native silicon oxide removed silicon surface with Si-H surface group. For the selective growth of carbon nanotubes (CNTs), the silicon oxide pattern was easily fabricated via proton beam irradiation when the silicon substrate was covered with a shadow mask. The Fe-Mo bimetallic catalysts for the growth of CNTs were adsorbed onto the silicon oxide layer, which is more hydrophilic than the silicon surface. The CNTs were grown on the patterned substrate using a chemical vapor deposition method, and it was confirmed by scanning electron microscopy.

Selective Growth of Carbon Nanotubes using Two-step Etch Scheme for Semiconductor Via Interconnects

In the present work, a new approach is proposed for via interconnects of semiconductor devices, where multi-wall carbon nanotubes (MWCNTs) are used instead of conventional metals. In order to implement a selective growth of carbon nanotubes (CNTs) for via interconnect, the buried catalyst method is selected which is the most compatible with semiconductor processes. The cobalt catalyst for CNT growth is pre-deposited before via hole patterning, and to achieve the via etch stop on the thin catalyst layer (ca. 3nm), a novel 2-step etch scheme is designed; the first step is a conventional oxide etch while the second step chemically etches the silicon nitride layer to lower the damage of the catalyst layer. The results show that the 2-step etch scheme is a feasible candidate for the realization of CNT interconnects in conventional semiconductor devices.

Fuzzy-based Field-programmable Gate Array Implementation of a Power Quality Enhancement Strategy for ac-ac Converters

In the present work, a new approach is proposed for via interconnects of semiconductor devices, where multi-wall carbon nanotubes (MWCNTs) are used instead of conventional metals. In order to implement a selective growth of carbon nanotubes (CNTs) for via interconnect, the buried catalyst method is selected which is the most compatible with semiconductor processes. The cobalt catalyst for CNT growth is pre-deposited before via hole patterning, and to achieve the via etch stop on the thin catalyst layer (ca. 3nm), a novel 2-step etch scheme is designed; the first step is a conventional oxide etch while the second step chemically etches the silicon nitride layer to lower the damage of the catalyst layer. The results show that the 2-step etch scheme is a feasible candidate for the realization of CNT interconnects in conventional semiconductor devices.

Patterning of Catalysts for the Selective Growth of Carbon Nanotubes Using Laser Irradiation of Nickel Nitrate

We developed a simple method to produce patterned catalysts for the growth of carbon nanotubes (CNTs) on Si substrate using laser irradiation of Ni nitrate. We found that Ni nitrate can easily be decomposed into Ni oxide by KrF laser irradiation and that unexposed Ni nitrate can be removed using deionized (DI) water. Once we obtained patterned Ni oxide, we were able to synthesize multi-walled CNTs using a conventional thermal CVD. This new method does not require any photoresist or vacuum processes. Not only is the method compatible with low-temperature and large-area fabrication, it also significantly reduces the total processing steps required for conventional lithographic patterning technology. A detailed investigation of the decomposition process of this patterned catalyst and the microstructure of the patterned multi-walled CNTs was carried out using IR, SEM and TEM.

Recent Developments in Carbon Nanotube Sorting and Selective Growth

AbstractDue to their high carrier mobilities, electromigration resistance, and tailorable optical properties, carbon nanotubes are promising candidates for high-performance electronic and optoelectronic applications. However, traditional synthetic methods have lacked control over the structure and properties of carbon nanotubes. This polydispersity problem has confounded efforts to take carbon nanotubes from the research laboratory to the marketplace, especially for electronic and optoelectronic applications, where reliable and reproducible performance is paramount. In recent years, the research community has devoted significant effort to this issue, leading to substantial advances in the preparation of monodisperse carbon nanotube materials. This article highlights the most recent and promising developments from two perspectives: post-synthetic sorting and selective growth of carbon nanotubes of predetermined physical and electronic structure. These complementary approaches have yielded improved uniformity in carbon nanotube materials, resulting in impressive advances in carbon nanotube electronic and optoelectronic technology.

Realization of Highly Controllable Electrolysis Process by Application of Carbon NanoTubes in Field Effect Transistors

AbstractWe have proposed, fabricated and tested a novel structure of Field-Effect Transistor (FET) combined with carbon nanotubes (CNT) to control the process of electrolysis. Our proposed device includes a conventional n-channel MOSFET, with a selective growth of carbon nanotubes in its drain region. MOSFET is made according to standard NMOS fabrication flow chart utilizing the advantage of a self-aligned process. The CNT growth is carried out in plasma and at a high temperature environment, so a thick layer of chromium (200nm) was deposited on the whole structure as a passivating layer to overcome MOSFET degradation caused by dopant escape. Afterward we deposited and patterned a thin layer of nickel (10nm) as the catalyst of CNT growth. The CNTs are grown in a DC-PECVD system. Following this step, we etched away the chromium layer completely. After the growth, the transistors needed an annealing treatment in Argon chamber at 500°C for 5 hours to retrieve their electrical behavior. We believe this happens because the atomic hydrogen can pass through the chromium layer and passivate the impurities and annealing in Argon chamber give them enough energy to leave the silicon.In this structure, the CNT collection is used as one-side electrode of electrolysis and the MOSFET acts as the current controller. We tested the structure to electrolyze a one molar mixture of water and salt and observed well-controlled current-voltage characteristics.

Selective Growth of Carbon Nanotubes on Printed Fe3O4 Nanoparticles

For selective growth of Carbon Nanotubes (CNTs) or Carbon Nanofibres (CNFs) a print technique was used to distribute the catalyst on the substrate surface. Suspensions of Fe3O4 nano-particles (NPs) (~ 15-20 nm) in chloroform (CHCl3) were prepared and printed by a soft nano-imprinting lithography process (NIL) on quartz and silicon substrates. After printing and evaporation of the solvent the catalyst distribution on the substrate surfaces was investigated. After different types of pre-treatments the hot-filament CVD followed depositing nanotubes and nanofibres.

Selective Growth of Carbon Nanotubes on Silicon from Electrodeposited Nickel Catalyst

Selective Growth of Carbon Nanotubes on Silicon from Electrodeposited Nickel Catalyst

Selective growth of carbon nanotubes using catalyst poisoning and geometric trench

This work suggests catalyst poisoning and geometric patterned approaches to selectively grow multiwall carbon nanotubes. Ferromagnetic particles as a catalyst for CNTs growth vanish when they are deposited over an aluminum thin film. Additionally, geometric features, such as trenches or cavities, are revealed to be capable of selectively ceasing the growth of CNTs even though catalytic thin films were covered on entire samples by an atmospheric thermal chemical vapor deposition technique.

Selective growth of carbon nanotube for via interconnects by oxidation and selective reduction of catalyst

We propose a selective growth approach of carbon nanotubes (CNTs) to prevent interface rupture in CNT via interconnects. Oxidation of the Ni catalyst layer is carried out before via hole patterning and the open hole area of the Ni layer is reduced by annealing in H2 ambient after via hole patterning. It is found that the present scheme provides robust selective growth of CNTs in the via hole and effectively prohibits the interface rupture due to the diffusion of carbon source into the Ni catalyst layer buried under the insulator.

Controlling the formation of nanoparticles for definite growth of carbon nanotubes for interconnect applications

Our interest is the integration of carbon nanotubes (CNT) in electronic devices (IC, NEMS). In the scope of this work, we present a study on the preparation of the catalyst Ni particles from ultrathin films and the synthesis of carbon nanotubes by the chemical vapour deposition method. For the preparation, we use a cold-wall CVD reactor especially designed for handling samples up to a size of a 4” wafer. We show the influence of different process conditions like temperature, initial layer thickness of catalyst and substrate on particle formation characterized by scanning electron microscopy (SEM). We show that the optimization of process conditions in the catalyst preparation phase is constitutive for dense CNT films. Regarding the application of CNTs as electrical interconnects, we studied the arrangement of nanoparticles on Al and TiN supporting layer. Furthermore, we fabricated the first test structures for the selective growth of CNTs out of contact holes on a Cu/TiN metallization layer system. The growth of multi-walled nanotubes (MWNTs) was performed with thermal CVD with ethylene as a precursor gas and hydrogen as supporting gas mixed in a nitrogen gas flow. The effects of growth condition on the quality and morphology of the CNTs were characterized by scanning electron microscopy, transmission electron microscopy (TEM) and Raman spectroscopy. The influence of temperature, gas composition and substrate on CNT growth will be presented. We managed to grow dense CNTs even at temperatures as low as 500 °C.

Selective-catalyst formation for carbon nanotube growth by local indentation pressure

We studied the selective formation of Co catalyst particles as a function of indentation pressure. We subjected a Co (8 nm thickness)/Si substrate pre-annealed at 600 °C to indentation processing. The catalytic function was confirmed in the indentations by the selective growth of carbon nanotubes (CNTs) at 800 °C. The number density of CNTs against the indentation pressure was investigated against indentation loads for two types of indenter: a Berkovich indenter with a ridge angle of 115° and a Berkovich indenter with a ridge angle of 90°. The pressures above 7 GPa applied by the former indenter enhanced Co atomization acting as a catalyst function for CNT growth (35 CNTs in one indentation). In contrast to this, the number of CNTs was markedly reduced when the latter indenter was used with pressures less than 3 GPa. The pop-out phenomenon was observed in unloading curves at pressures above 7 GPa. These results indicate that metastable Si promotes the self-aggregation of catalyst particles (Co) leading to the selective growth of CNTs within indentations at pressures above 7 GPa.

Submicron patterning of a catalyst film by scanning probe nanolithography for a selective chemical vapor deposition of carbon nanotubes

Submicrometric catalyst patterns have been fabricated by atomic force nanolithography and the subsequent selective growth of carbon nanotubes has been successfully verified. Rectangular stripes (∼350 nm wide) were engraved onto a polymethylmethacrylate film, deposited onto SiO2/Si, by polymer removal with atomic force microscopy nanoindentation. Metallic catalyst patterns were subsequently obtained after 3 nm Ni deposition and lift-off of the residual polymer. Multiwalled carbon nanotubes were then grown by thermal chemical vapor deposition onto the Ni stripes. The various steps of nanopatterning and of carbon nanotubes growth are also studied by scanning electron microscopy and Raman measurements.

Carbon nanotubes/SiC whiskers composite prepared by CVD method

Selective growth of carbon nanotubes (CNTs) on silicon carbide (SiC) substrate will create some new applications in composites and electronic devices by combining their mechanical and physical properties. Multi-walled CNTs were successfully grown on SiC whiskers using a conventional xylene–ferrocene chemical vapor deposition process. A thin oxide layer was created on the surface of the SiC whiskers by high-temperature annealing in air before CNT growth. The effect of catalyst morphology and chemistry on the growth of CNTs was analyzed. Our technique may be further applied to the controlled growth of CNTs on any other SiC substrates.

Position-selective growth of carbon nanotubes on Ni catalysts/Mo underlayers by thermal chemical vapor deposition

Position-selective growth of carbon nanotubes (CNTs) and vertically aligned CNTs (VACNTs) on patterned metal were prepared using thermal chemical vapor deposition (TCVD) and direct current (DC) plasma-enhanced chemical vapor deposition. We propose a new position-controlling method of CNTs by controlling not only the position of Ni as a catalyst, but also the morphology of Mo as an underlayer for the catalysts. Selective growth of CNTs was achieved at the edges of the patterned metal using TCVD. The minimum width of selectively grown CNTs, approximately 2.6 μm, was approximately one-eightieth that of the patterned metal, 200 μm. The VACNTs were synthesized using the PECVD method, but the VACNTs grew throughout the patterned metal. A position-controlled method of CNT growth was demonstrated in optimum conditions of the TCVD.

Carbon Nanotubes with Small and Tunable Diameters from Poly(ferrocenylsilane)-block-polysiloxane Diblock Copolymers

Iron-containing nanostructures produced from various self-assembled poly(ferrocenylsilane)-block-polysiloxane thin films are catalytically active for the initiation and growth of high density, small diameter carbon nanotubes (CNTs). Moreover, the tube diameter and density can be tuned by adjusting the chain lengths of the block copolymer. Iron-containing nanostructures from poly(ferrocenylmethylethylsilane)-b-poly(methylvinylsiloxane) polymer with 25 repeat units of an iron-containing segment and 265 repeat units of a non-iron-containing segment are able to produce CNTs with diameters around or less than 1 nm. Lithographically selective growth of CNTs across a large surface area has been demonstrated using this polymer system. Under the same growth condition, it has been found that the yield of defect-free CNTs varies with the size of the catalytically active nanostructures, which are dictated by the chain lengths of the two blocks. This result indicates that, for a specific-sized catalyst nanocluster, a unique set of growth conditions is required for synthesizing high yield, defect-free CNTs. This finding further addresses the importance of using uniform-sized catalyst-containing nanostructures for consistently achieving high-yield and high-quality CNTs with a minimum number of defects and amount of amorphous carbon.