Carbon Nanotubes (CNTs)

By: Masoud Mahjouri-Samani

Limitations of current technology and demands for smaller, faster, more efficient and cost effective electronic and optical devices have provoked scientists and researchers around the world to find new materials which satisfy their needs. The extraordinary characteristics and properties of carbon nanotubes (CNTs) have made them promising candidates for fabricating nano-scale electronics and optical devices such as transistors and sensors.

Although tremendous progress has been made in the growth and fabrication of CNTs and CNT-based devices, CNT-based devices have not yet been mass-produced due to lack of sufficient methods for controlling the location, orientation and the type of the CNTs grown on the samples. Current synthesis techniques provide CNTs of different electronic types, including semiconductor, semimetal and metal, which play different roles in applied fields, such as molecular conductors for metallic tubes and transistors for semiconducting tubes. Therefore, controlled production of mono-dispersed CNTs with the same electronic properties is highly desired in developing CNT-based electronics and photonics.

Works have been reported attempting to achieve precise discerning of CNTs of different electronic properties, including preferential growth of s-CNTs, post-growth separation, and selective removal of metallic tubes. However, several drawbacks, such as liquid processing and polymer wrapping, degrade the quality of the CNTs and prevent their practical applications. Also, there are very limited investigations on the in-situ selective separation of CNTs deposited on solid substrates, which are frequently used in device fabrication. Therefore, a new approach is desired to achieve in-situ efficient separation of surface deposited CNTs according to their electronic properties and still preserve their pristine properties.

In this study, an optically controlled approach is developed to remove m-CNTs selectively from CNT mixtures deposited on SiO2 surfaces through well tuned laser irradiation process. The mechanism behind the process is attributed to the free electron movement and optical near-field effects under the electromagnetic field generated by the laser irradiation. Due to the distinct electronic properties, m-CNTs and s-CNTs react to the laser irradiation in different ways. For m-CNTs, existing electrons in conduction bands respond readily to the electromagnetic field from the laser irradiation. However, electrons in s-CNTs have to overcome the band-gaps by absorbing photons of matching energy and transit from valance bands to conduction bands. Therefore, m-CNTs are more responsive to the incident lights than the s-CNTs, and yield thermal effects. Through this process, m-CNTs were selectively heated and preferentially oxidized when exposed to air. This method demonstrates a simple and efficient approach for processing s-CNT based devices through optical selection.

The above brief overview was extracted from its original abstract and paper presented at The International Congress on Applications of Lasers & Electro-Optics (ICALEO) in Orlando, FL. To order a copy of the complete proceedings from this conference click here

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Steven Glover is a proud member of the LIA staff. When he is not at work he is actively involved in several charitable efforts.
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