Patterned Carbon Nanotube Research Articles

Pulsed laser deposition-assisted patterning of aligned carbon nanotubes modified by focused laser beam for efficient field emission

Patterned carbon nanotube (CNT) arrays have been synthesized on patterned substrates created via pulsed laser deposition (PLD) of the precursor catalyst films with a mask. Arrays of CNTs in square and hexagonal patterns with tube lengths of 8 μm and 16 μm were created on silicon or quartz substrates, respectively. Using the method of laser cutting, as-grown CNT patterns were pruned by focused He–Ne laser beam. It is found that after pruning, CNTs tend to cluster together and form welded junctions. The comparison of field emission properties of CNTs before and after pruning shows that laser modification of CNT morphologies effectively enhanced the emission currents.

Electrophoretic deposition and field emission properties of patterned carbon nanotubes

Patterned carbon nanotubes on silicon substrates were obtained using electrophoretic method. The carbon nanotubes migrated towards the patterned silicon electrode in the electrophoresis suspension under the applied voltage. The carbon nanotubes arrays adhered well on the silicon substrates. The surface images of carbon nanotubes were observed by scanning electron microscopy. The field emission properties of the patterned carbon nanotubes were tested in a diode structure under a vacuum pressure below 5 × 10 −4 Pa. The measured emission area was about 1.0 mm 2. The emission current density up to 30 mA/cm 2 at an electric field of 8 V/μm has been obtained. The deposition of patterned carbon nanotubes by electrophoresis is an alternative method to prepare field emission arrays.

Guided neurite growth on patterned carbon nanotubes

A combination of microlithography and chemical vapor deposition is used to engineer patterned vertical multiwalled carbon nanotube substrates. They are used to demonstrate the formation of directed neuronal networks. Multiple substrate geometries and nanotube heights were fabricated to determine the most suitable combination for understanding the cell morphological changes. The interaction between the cell membrane and the nanotube substrate are visually characterized. The viability of the networks on the nanoscale substrates was observed.

High-resolution Raman microscopy of curled carbon nanotubes

Patterned carbon nanotube assemblies with bent nanotube bundles were investigated with combined atomic force microscopy and confocal Raman imaging spectroscopy to identify conditions of carbon nanotubes in the bent state. We showed that the tangential G mode on Raman spectra systematically shifts downward upon nanotube bending as was predicted earlier. This lower frequency shift is attributed to the tensile stress, which results in the loosening of C–C bonds in the outer nanotube walls.

Carbon nanotubes grown on different-sized rectangular patterns

Carbon nanotubes have been synthesized by chemical vapor deposition using a thin iron film as catalyst on the silicon substrate with different-sized rectangular patterns. It is found that the carbon nanotubes grow vertically to the substrate in a high density with a surface shape similar to that of the substrate when the line width of the patterns are larger than 1 μm, However, when the line width of the pattern is reduced to below 0.5 μm, carbon nanotubes cannot grow vertically anymore. This phenomenon might be caused by the relaxation of stress in catalyst film and the coalescence of the catalyst clusters to form particles or grains, which contributes to the migration of catalyst from edge to inner part during the nucleation process. These results are very useful for the fabrication of field-emission displays and other devices using patterned carbon nanotubes.

Liquid-phase fabrication of patterned carbon nanotube field emission cathodes

High-resolution electron field emission cathodes were fabricated at room temperature by a high throughput electrophoresis process using functionalized carbon nanotubes (CNTs). Well-defined and adherent CNT patterns with 20 μm feature size were achieved on a variety of substrates with fine control of the CNT morphology. The cathodes show uniform emission pattern across the entire surfaces and emission current with long-term stability. This room-temperature liquid-phase process is efficient and has no intrinsic limit on the deposition area. The emission characteristics of these cathodes compare favorably to those from other fabrication methods for CNT based field emission display applications.

Liquid-phase fabrication of patterned carbon nanotube field emission cathodes

Liquid-phase fabrication of patterned carbon nanotube field emission cathodes

Fabrication of the aligned and patterned carbon nanotube field emitters using the anodic aluminum oxide nano-template on a Si wafer

Aligned and patterned carbon nanotubes (CNTs) have been fabricated via catalytic chemical vapor deposition (CVD) with anodic aluminum oxide (AAO) nano-template. AAO nano-templates were prepared on the Nb-patterned silicon wafer by anodization process. After the cobalt catalyst had been electrochemically deposited at the pore bottom of the AAO nano-template on Nb pattern, CNTs were grown by chemical vapor deposition of 10% acetylene and 20% hydrogen in an argon carrier gas at 650 °C. Selectively grown CNTs from Nb pattern, standing normally on the AAO nano-templates, were observed. The diameter of CNTs was 60–90 nm and similar to the diameter of AAO nano-template. The density of aligned CNTs was in the order of 10 7–10 8 cm −2. Preparation of AAO nano-template on Nb-patterned wafer and growth characteristics of CNTs in the AAO nano-template are presented. The field emission measurement on the patterned CNTs showed a turn-on field of 2.3 V/μm and a field enhancement factor of 4200.

Field emission of large-area and graphitized carbon nanotube array on anodic aluminum oxide template

Large-area, graphitized, and patterned carbon nanotube (CNT) arrays were prepared via cracking of ethylene on an open-ended anodized aluminum oxide (AAO) template that also served as a catalyst. With ion-milling and gold coating techniques, ohmic contact between the CNTs and electrode for field emission measurements was greatly improved. In both tip-plane and plane-plane field emitting experiments, the CNTs/AAO displayed a low turn-on field of ∼2.8 V/μm, a high maximum emitting current density of ∼24 mA/cm2, and a fairly good emitting stability.

Controllable preparation of patterns of aligned carbon nanotubes on metals and metal-coated silicon substrates

Patterns and alignment of carbon nanotubes (CNTs) are particularly important for fabricating functional devices such as field emitters, scanning probes, sensors, and nanoelectronics. In this paper, the effects of various metal substrates on CNT growth are studied. Depending on the different growth mechanisms associated with the various substrate surfaces, two- or three-dimensional micropatterns of aligned carbon nanotubes have been prepared via pyrolysis of iron(II) phthalocyanine. Patterns created on silicon substrates were obtained by photolithographic techniques. The prepared CNT patterns have resolutions down to the micrometer scale. Possible growth mechanisms of aligned carbon nanotubes on different metal surfaces are also discussed.

Selective Growth of Aligned Carbon Nanotubes on a Silver-Patterned Substrate by the Silver Mirror Reaction

It was found that carbon nanotubes prepared by the pyrolysis of iron(II) phthalocyanine (FePc) can selectively grow on a SiO2 surface when the SiO2 wafer is patterned by silver. A combination of the micro-contact printing (μCP) technique and chemical reaction (classical silver tollens reaction, also called silver mirror reaction) has been applied to generate a silver pattern with micro/nanoscale resolution on a quartz glass substrate (silver selectively deposits on hydrophilic regions), and an aligned carbon nanotubes (CNTs) pattern with the same resolution can be fabricated by the pyrolysis of FePc on the basis of the selective growth. This new method represents a great advantage of controlled fabrication of a micro/nanoscale aligned CNT pattern on a conducting surface (silver) by combination of soft-lithography and chemical approach for various device applications, requiring high-resolution pattern and conducting surface.

Electron emitters synthesized by selected area deposition of carbon nanotubes on silicon substrates

We have successfully attained patterned carbon nanotubes grown on two-dimensional Ni arrays of square blocks of various sizes on Si by a microwave-heated chemical vapor deposition process. The Ni blocks are either freestanding or isolated by the silicon dioxide. For patterned carbon nanotube emitters, grown on freestanding Ni blocks, the emission current–density increases with the size of the Ni blocks. To the contrary, patterned carbon nanotube emitters grown on 2 μm by 2 μm Ni blocks isolated by the silicon diode have exhibited an emission behavior as excellent as the un-patterned emitters; both emitters have very low turn-on and threshold fields being at ∼0.1 V/μm and ∼1.50 V/μm, respectively and can emit current density exceeding 120 mA/cm 2.

Ink-jet printing of nanoparticle catalyst for site-selective carbon nanotube growth

We report on site-selective growth of multiwalled carbon nanotubes (MWNTs) from a Co nanoparticle catalyst patterned by an ink-jet printing (IJP) technique. The dispersion of the Co nanoparticles was employed as “catalyst ink” for the IJP, and the catalyst pattern was subjected to chemical vapor deposition of acetylene gas. The patterned array of MWNTs was obtained with a dot size around 5–30 μm and showed field emission of electrons corresponding to the printed pattern. The present method offers a simple and powerful means to pattern carbon nanotubes at desired positions with any patterns.

The Effects of Catalyst Grain Sizes on the Diameter of MPECVD Grown Patterned Carbon Nanotubes

AbstractThe electronic structure and properties of carbon nanotubes (CNTs) strongly depend on their diameter and chirality. The well controlled CNTs diameter is becoming one of the challenges for their applications in microelectronics. In this paper, the patterned CNTs were produced by microwave plasma enhanced chemical vapor deposition technique using a metal catalyst of nickel. The correlation between the CNT diameter and the grain sizes of the nickel catalyst was examined. The experimental results show that nickel films converted to nickel particles when they were heated up. The diameter of CNTs increases with increasing grain sizes of the nickel particles, indicating that the CNT diameter can be controlled by controlling the grain sizes of the nickel catalyst.

Novel emission degradation behavior of patterned carbon nanotubes by field emission

Field emission behavior of photolithography-based patterned carbon nanotubes (PP-CNTs) was irreversibly degraded, showing a gradual turn-on voltage shift to the high voltage region as a result of field emission measurements. The PP-CNTs show a flat region in Fowler–Nordheim (F–N) plots, which can be attributed to residue-induced emission suppression. The observed degradation in field emission can be attributed to a subsequent degradation of carbon nanotubes emitters by a combination of the high electric-field-induced straightening out effect and the high current-induced burning of PP-CNTs. The local emission current and the stability of electron emission were observed in an attempt to investigate the residue effect of the PP-CNTs on the field emission behavior.

Two- and Three-Dimensional Alignment and Patterning of Carbon Nanotubes

Alignment or patterning of carbon nanotubes (CNTs) is particularly important for fabricating functional devices such as field emitters, nanophotonics, nanoelectronics, and ultrahydrophobic materials. This work briefly reviews recent progress on the synthesis of two-dimensional CNT patterns, and then particularly concentrates on describing the pillar-shaped fabrication and very interesting patterns of three-dimensionally aligned CNTs formed by pyrolysis of iron(II) phthalocyanine. The possible formation mechanism of the structures is discussed. The Figure shows the pillar-shaped alignment of three-dimensional CNTs.

Field emission from patterned carbon nanotube emitters produced by microwave plasma chemical vapor deposition

Large area carbon nanotube patterns were fabricated by microwave plasma chemical vapor deposition. The carbon nanotubes were grown on pre-patterned catalyst films. Scanning electron microscopy and Raman spectroscopy were used to characterize the structure of the carbon nanotubes. The carbon nanotubes were very uniform and approximately 100 nm in diameter. The Raman spectrum shows a good graphitization for the carbon nanotubes. Aligned growth was found on the pattern line area. Field emission characteristics of the patterns were characterized. A threshold field of 2.0 V/μm and emission current density of 1.1 mA/cm 2 at 3.6 V/μm were achieved. A clear and stable image showing the patterns were obtained.

Comparative study of the catalytic growth of patterned carbon nanotube films

Three different catalysts (Fe, Ni, Co nitrates dissolved in ethanol) were patterned on a SiO 2/Si substrate and multi-wall carbon nanotubes were grown by catalytic decomposition of acetylene. We compare the growth of the carbon nanostructures in the temperature range between 580°C and 1000°C. With our experimental setup the catalyst solutions of cobalt and nickel were found to be less efficient than the one of iron. An optimal production of multi-wall nanotubes was observed at temperatures between 650°C and 720°C with the iron solution as catalyst. We found a tendency towards thicker structures with higher temperatures. Finally, we suggest a mechanism for the growth of these carbon structures.

Tuning the Field Emission Properties of Patterned Carbon Nanotube Films

Tuning the electron emission properties of films containing carbon nanotubes is demonstrated. Microcontact printing is used to pattern silicon substrates with catalyst, which facilitates the growth of the carbon nanotubes by the chemical vapor deposition of acetylene. The catalyst is applied in liquid form to an elastomeric stamp prior to transfer to the substrate, and varying the concentration of the catalyst on the solution (“the ink”) directly influences the density of nanotubes on the patterned film.

Scanning field emission from patterned carbon nanotube films

The investigation of the field emission (FE) properties of carbon nanotube (CNT) films by a scanning anode FE apparatus, reveals a strong dependence on the density and morphology of the CNT deposit. Large differences between the microscopic and macroscopic current and emission site densities are observed, and explained in terms of a variation of the field enhancement factor β. As a consequence, the emitted current density can be optimized by tuning the density of CNTs. Films with medium densities (on the order of 107 emitters/cm2, according to electrostatic calculations) show the highest emitted current densities.