Horizontally-aligned Carbon Nanotubes Research Articles

Frequency analysis of carbon and silicon nanosheet with surface effects

• FE modeling of surface effects in Si, Graphene–Silicon and SWCNT-Silicon nanosheet . • Numerical analysis of HACNTs on silicon substrate and its effect on frequency. • Development of analytical model to find frequency of HACNTs arrays on silicon. Silicon-based microelectromechanical system (MEMS) and nanoelectromechanical systems (NEMS) have been used to design and fabricate sensitive sensors and actuators. Recent research trends show that graphene and carbon nanotubes (CNTs) have been used to change the surface properties of silicon-based MEMS and NEMS to improve different mechanical, optical and electrical properties of silicon-based composites. In this paper, we focus on analyzing the vibrational characteristics of silicon-based devices when the surface of silicon is coated with single-layer graphene and horizontally aligned carbon nanotubes (HACNTs). To perform the analysis, we use multi-scale finite element approach for developing graphene–silicon nanocomposites (GSNCs) and carbon nanotube-silicon nanocomposites (CSNC) composites in which interface layer of silicon with graphene or CNT is modeled using bonded contact element. Subsequently, we performed modal analysis to find the first transverse mode frequency of GSNC and CSNC composites for beam with smaller as well as longer lengths. The numerical model is compared with classical beam theory with and without surface effect. For GSNCs composites, we take a fixed-free case with lengths in the range of (20 Å–120 Å) and (400 Å–2000 Å), respectively. For CSNC composites, CNT diameter is varied from (5 Å–30 Å) for single walled nanotube . Subsequently, we analyze the influence of HACNTs-on-silicon on its vibrational characteristics. The analysis presented in the paper demonstrate that GSNCs offer a higher bending stiffness compared to single layer graphene (SLGs) and isolated silicon nanosheet which lead to higher natural frequency. A similar trend is found in the case of HACNTs on silicon NS when the number of tubes increases.

An ex-situ method to convert vertically aligned carbon nanotubes array to horizontally aligned carbon nanotubes mat

Carbon nanotubes (CNTs) have been attracted by the researchers for their extraordinary properties and wide applications in various fields. Among numerous types of CNTs, the horizontally aligned CNTs (HACNTs) has shown many advantages due to its nano-structural features and proper arrangements. HACNTs open new opportunity in the field of microwave, nanoelectronics, and heat dissipation system. This article reports the study on the post-growth processing technique (mechanical) to transform vertically aligned carbon nanotubes (VACNTs) array into HACNTs mat. The above technique has been named as micromechanical rolling (M2R) that uses a rotating rigid cylinder to bend and align the individual nanotubes in the VACNTs array. The process yielded remarkably arranged (horizontal) nanotubes with a resultant smooth surface. Various process parameters such as tool rotational speed, lateral speed, and step size were investigated in this study to achieve the smooth surface of HACNTs array. It was observed that the minimum surface roughness of Ra = 4 nm was achieved with 2000 rpm of the tool’s rotational speed, 1 mm min−1 of lateral speed and 1 μm of step size.

The light-switching conductance of an anisotropic azobenzene-based polymer close-packed on horizontally aligned carbon nanotubes

We present an anisotropic photo-responsive film of azobenzene–poly(methyl methacrylate) (Azo–PMMA) close-packed on the sidewalls of horizontally aligned carbon nanotubes (HACNTs), showing anisotropic conductance and light-switching properties.

Controlled synthesis and property of horizontally aligned carbon nanotubes

Horizontally aligned carbon nanotubes (HACNTs) refers to the horizontally aligned CNT arrays grown and parallel on flat substrates, with relatively large intertube distances. Due to their perfect structures, excellent properties and lengths up to millimeters, even centimeters, HACNTs show great potential as building blocks for transparent displays, nano electronics, quantum lines, field emission transistors, superstrong tethers, and aeronautics and aerospace materials, etc. Great development was obtained on the study of ultralong CNTs during the past decade. In this review, we summarize the recent progress on the growth mechanism, structure-controlled synthesis, optical visualization, controllable manipulation, mechanical, electrical and thermal properties, as well as the superlubricity between the shells of HACNTs. First we review the growth mechanism of ultralong CNTs, pointing out the key for obtaining CNTs with perfect structures, extraordinary properties and macroscale lengths. We then discuss the controlled synthesis of ultralong CNTs with various chirality, diameters, lengths, and morphologies, etc. After that, we discuss the optical visualization, controllable manipulation, structure and property characterization, and superlubricity of HACNTs. Finally, an outlook is presented to shed light on the future study of ultralong CNTs.

Growth of primary motor neurons on horizontally aligned carbon nanotube thin films and striped patterns

Objective. Carbon nanotubes (CNTs) are attractive for use in peripheral nerve interfaces because of their unique combination of strength, flexibility, electrical conductivity and nanoscale surface texture. Here we investigated the growth of motor neurons on thin films of horizontally aligned CNTs (HACNTs). Approach. We cultured primary embryonic rat motor neurons on HACNTs and performed statistical analysis of the length and orientation of neurites. We next presented motor neurons with substrates of alternating stripes of HACNTs and SiO2. Main results. The neurons survived on HACNT substrates for up to eight days, which was the full duration of our experiments. Statistical analysis of the length and orientation of neurites indicated that the longest neurites on HACNTs tended to align with the CNT direction, although the average neurite length was similar between HACNTs and glass control substrates. We observed that when motor neurons were presented with alternating stripes of HACNTs and SiO2, the proportion of neurons on HACNTs increases over time, suggesting that neurons selectively migrate toward and adhere to the HACNT surface. Significance. The behavior of motor neurons on CNTs has not been previously investigated, and we show that aligned CNTs could provide a viable interface material to motor neurons. Combined with emerging techniques to build complex hierarchical structures of CNTs, our results suggest that organised CNTs could be incorporated into nerve grafts that use physical and electrical cues to guide regenerating axons.

Synthesis and electroconductivity of epoxy/aligned CNTs composites

An efficient method is described of growing of vertically aligned carbon nanotubes (VANTs) densely packed on a large area with uniform height up to 1mm. The method is based on injection of active solution of ferrocene in cyclohexane into reactor during the growth process. We also describe a method of ER/VANTs composite preparation based on infiltration of epoxy resin (ER) liquid monomer into arrays of the VANTs forest with polymerization followed. Further on we describe a press-and-draw method to reorient VANTs into horizontally aligned carbon nanotubes (HANTs) in the liquid composite precursor. The electrical conductivities up to 0.6S/cm in ER/VANTs and up to 0.85S/cm in ER/HANTs are obtained.

Horizontally-aligned carbon nanotubes arrays and their interactions with liquid crystal molecules: Physical characteristics and display applications

We report on the physical characteristics of horizonthally-grown Single-Walled Carbon Nanotubes (h-al-SWNT) arrays and their potential use as transparent and conducting alignment layer for liquid crystals display devices. Microscopy (SEM and AFM), spectroscopic (Raman) and electrical investigations demonstrate the strong anisotropy of h-al-SWNT arrays. Optical measurements show that h-al-SWNTs are efficient alignment layers for Liquid Crystal (LC) molecules allowing the fabrication of optical wave plates. Interactions between h-al-SWNT arrays and LC molecules are also investigated evidencing the weak azimuthal anchoring energy at the interface, which, in turn, leads to LC devices with a high pretilt angle. The electro-optical reponses of h-al-SWNT/LC cells demonstrate that h-al-SWNT arrays are efficient nanostructured electrodes with potential use for the combined replacement of Indium Tin Oxyde and polymeric alignment layers in conventional displays.

Direct Growth of Horizontally Aligned Carbon Nanotubes between Electrodes and Its Application to Field-Effect Transistors

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.

Flexible High‐Conductivity Carbon‐Nanotube Interconnects Made by Rolling and Printing

Applications of carbon nanotubes (CNTs) in flexible and complementary metal-oxide-semiconductor (CMOS)-based electronic and energy devices are impeded due to typically low CNT areal densities, growth temperatures that are incompatible with device substrates, and challenges in large-area alignment and interconnection. A scalable method for continuous fabrication and transfer printing of dense horizontally aligned CNT (HA-CNT) ribbon interconnects is presented. The process combines vertically aligned CNT (VA-CNT) growth by thermal chemical vapor deposition, a novel mechanical rolling process to transform the VA-CNTs to HA-CNTs, and adhesion-controlled transfer printing without needing a carrier film. The rolling force determines the HA-CNT packing fraction and the HA-CNTs are processed by conventional lithography. An electrical resistivity of 2 mOmega . cm is measured for ribbons having 800-nm thickness, while the resistivity of copper is 100 times lower, a value that exceeds most CNT assemblies made to date, and significant improvements can be made in CNT structural quality. This rolling and printing process could be scaled to full wafer areas and more complex architectures such as continuous CNT sheets and multidirectional patterns could be achieved by straightforward design of the CNT growth process and/or multiple rolling and printing sequences.

Growth of the large area horizontally-aligned carbon nanotubes by ECR-CVD

For potential applications of carbon nanotubes (CNTs) as connectors in microelectronic devices, the process to synthesize the large area horizontally-aligned CNTs on 100 mm (4 inch) Si wafers was developed, using electron cyclotron resonance chemical vapor deposition, with CH 4 and H 2 as the source gases and Co as the catalyst. The results show that vertical and horizontal CNTs can be obtained by manipulating the electric field applied on the substrate and flow direction of the gases. In the present deposition conditions, the horizontal CNTs show better field emission properties than vertical CNTs. This may be due to the blocking effect of catalysts at the tips and to the diminishment of the effective emission area from defects of vertical CNTs body.