Direct laser pruning of CdS(x)Se1-x nanobelts en route to a multicolored pattern with controlled functionalities.

CdS(x)Se(1-x) nanobelts are interesting nanostructured materials with a tunable band gap from 1.7 to 2.4 eV depending on the nanobelts' stoichiometry. On the basis of their chemical compositions, these nanobelts give out strong photoluminescence with unique color. In this work, we demonstrate that a direct focused laser beam irradiation was able to achieve localized modification of the chemical composition of the nanobelts. As a result, we could locally change the optical properties of these nanobelts. With a scanning laser beam, micropatterns with a wide range of fluorescence color could be created on a substrate covered with ternary nanobelts without a prepatterned mask. The laser modified nanobelts showed higher resistance to acid corrosion and these nanobelts exhibited more superior photoconductivity. The construction of micropatterns with functionality/color control within the sample would provide greater building blocks for photoelectronic applications.

Re-grown aligned carbon nanotubes with improved field emission.

In this work, a simple technique to improve the field emission property of multi-walled carbon nanotubes is presented. Re-grown multi-walled carbon nanotubes are grown on the same substrates after the as-grown multi-walled carbon nanotubes are transferred to other substrates using polydimethylsiloxane as intermediation. For the duration of the synthesis of the re-grown multi-walled carbon nanotubes, similar synthesis parameters used in growing the as-grown multi-walled carbon nanotubes are utilized. As a form of possible application, field emission studies show -2.6 times improvement in field enhancement factor and more uniform emission for the re-grown multi-walled carbon nanotubes. In addition, the turn-on field is reduced from 2.85 V/microm to 1.40 V/microm. Such significant improvements are attributed to new emission sites comprising of sharp carbonaceous impurities encompassing both tip and upper portion of the multi-walled carbon nanotubes. As such, this technique presents a viable route for the production of multi-walled carbon nanotubes with better field emission quality.

Micropatterning of porphyrin nanotubes thin film using focused laser writing.

We report an effective process to create micropatterns on a thin film of porphyrin nanotubes PNTs on Si substrate using focused laser beam. The optical properties of the newly synthesized porphyrin nanotubes are investigated and micropatterning is demonstrated using laser fabrication, an increasingly important tool in various fields of research. We made use of this laser cutting method to create interesting and useful two-dimensional patterned structures. The shapes and sizes of the structures created can be controlled by varying the power of the laser, angle of incident of the focused laser beam, the relative speed with which the laser beam traverse through the film and the magnification of objective lens used.

Nanoparticle fractionation using an aligned carbon nanotube array.

A technique utilizing the capillary assisted sieving capability of carbon nanotubes (CNTs) to achieve fractionation of nanoparticles of small size distribution is presented. By dipping aligned CNT arrays into a solution comprising different sized quantum dots (QDs), size-selective gradient decoration of QDs onto CNTs is achieved. The fractionating capability of CNTs is also demonstrated for poly-dispersed manganese doped zinc sulfide nanoparticles and QDs of varying sizes and chemical compositions, which we attribute to the size-selective sieving effect of CNTs. By controlling the terminating point for the flow of QDs across the CNT array, a QD size specific CNT/QD hybrid structure is achieved.

Capillarity-assisted assembly of carbon nanotube microstructures with organized initiations.

In this work, detailed studies of three different capillary-assisted techniques for the formations of large-scale multiwalled carbon-nanotube (MWNT)-based microstructures were presented. Using laser induced artificial vacancies, new insights into the effect of laser power, densities of MWNTs, and oxidation process dependencies for the creations of MWNT polygons were presented. With organized initiations, MWNT pillars were crafted out of MWNT arrays and 0.21 pL of water was found to produce sufficient force to bring about 14.7 mum deflections of a 9.19 x 9.19 x 24.1 mum(3) pillar, thereby allowing well-controlled formations of three-dimensional top-gathering MWNTs. Lastly, by twisting densified MWNT microbelts, 14 times improvements in resistivity as compared to undensified MWNT microwalls were achieved. Through prepatterning, the amount of twisting effect could be controlled, and this in turn allowed control of the resistance of the densified MWNT microwalls. These new insights and techniques presented could further encourage the use of self-organized MWNT structures with initiation as a flexible and viable route for the implementations of carbon-nanotube-based electronic devices.

Improved hydrophobicity of carbon nanotube arrays with micropatterning.

The hydrophobicity of vertically aligned multiwalled carbon nanotubes (MWCNTs) was improved through the creation of a parallel array of microwalls via a laser pruning technique. Changes to the hydrophobic nature of the patterned MWCNTs due to artificially induced roughness through variations in both the widths of the walls and the distance between adjacent walls, channel width, were investigated. The sample became more hydrophobic whenever water droplets landed on one microwall 7 or 13 microm in width. However, when a droplet bridged two microwalls, the surface became less hydrophobic. The optimal superhydrophobic MWCNT surface corresponded to a parallel array of microwalls with a width of 13 microm and a channel width of approximately 50 microm. Such findings could possibly serve as value-add for further developments in the creation of water-repelling CNT surfaces via micropatterning.

Multicolored carbon nanotubes: decorating patterned carbon nanotube microstructures with quantum dots.

In this work, techniques to create patterned array of multiwalled nanotube (MWNT) microstructures decorated with quantum dots (QDs) were presented. Using aligned array of intertwined MWNTs as the supporting template, a droplet of solution comprising QDs was deposited onto the MWNTs. When the solution evaporated away, QDs were left behind on the MWNT template. Coupled with the technique of laser pruning, a wide variety of QDs-decorated MWNT microstructures were created. In addition, the aligned array of MWNTs was found to be an effective nanosieve that could effectively sort out QDs with a size difference of approximately 0.5 nm. In this case, a droplet of solution comprising QDs of different sizes was placed on aligned array of MWNTs. As the solution spread across as well as trickled down the MWNTs, the smaller QDs were found to venture further and deeper into the MWNTs. Again coupled with laser pruning, fluorescence microscopy revealed multicolored MWNT microstructures due to preferential decoration of these QDs with difference sizes. As a result, multicolored/multicomponents hybrid functional materials were achieved.

Versatile transfer of aligned carbon nanotubes with polydimethylsiloxane as the intermediate.

A simple technique to transfer aligned multi-walled carbon nanotubes (MWCNTs) is demonstrated in this work. With polydimethylsiloxane (PDMS) as the transfer medium, as-grown or patterned MWCNT arrays are directly transferred onto a wide variety of Pt-coated substrates such as glossy paper, cloth, polymers, glass slides, and metal foils at low temperatures. The surface of the transferred CNTs is cleaner with better alignment, compared with the as-grown one. Furthermore, the transferred CNTs show strong adhesion and good electric contact with the target substrates. A maximal current density of ∼10(4) A cm(-2) has been achieved from the CNT interconnects prepared with this technique. Because of the lower density and open-ended structures, improved field emission performance has been obtained from CNTs transferred on polymers, based on which flexible emitter devices can be fabricated. In addition, the surface of transferred CNTs becomes more hydrophilic, with an averaged contact angle of 93.4 ± 5.8°, in contrast to the super-hydrophobic as-grown CNT surface (contact angle 151.6 ± 5.5°). With versatile properties and flexible applications, the technique provides a simple and cost-effective way towards future nanodevices based on CNTs.

Tailoring wettability change on aligned and patterned carbon nanotube films for selective assembly.

The effects of oxygen reactive ion etching (RIE) on the surface wettability of aligned carbon nanotube (CNT) films have been systematically investigated. It was found that 3 s of RIE treatment could change the surface of CNT films from hydrophobic to more hydrophilic. The degree of modification in the surface wettability of the film could be controlled by the flow rate of O2 gas during the RIE process. It is proposed that such a surface hydrophobicity change is related to the opened structure and functionalized tip of as-treated CNTs by oxygen reactive ions. More importantly, after the RIE treatment, focused laser pruning was utilized to trim the surface layer of treated CNTs and revert them back to a hydrophobic surface. Combined with the laser pruning technique and O2 RIE treatment, CNT templates with interlaced wettability surfaces in a stripe pattern have been fabricated. It has been demonstrated that this interlaced and structured wettability pattern can be used to selectively assemble microspheres or quantum dots on the aligned CNT films with desired patterns.