[Show abstract][Hide abstract] ABSTRACT: The microwave irradiation effects on purified HiPCO and CoMoCat single-walled carbon nanotube (SWNT) thin films are investigated.
The surface conductivities of the SWNT films are extracted from the measured THz transmission coefficients to provide a direct
indication of the metallic content in the films. The observed drastic conductivity decrease indicates a significant metallic
content reduction after the microwave irradiation. Two different laser excitations are applied for Raman spectroscopy to reveal
the response of different nanotube species. The Raman spectra of both HiPCO and CoMoCat thin films confirm the decrease of
metallic carbon nanotubes. The observed microwave-induced effects may potentially lead to a convenient scheme for demetalization
of single-walled carbon nanotube mixtures.
Full-text · Article · Feb 2011 · Applied Physics A
[Show abstract][Hide abstract] ABSTRACT: A major driving force behind the research of SWNT electronic properties is their potential in nanoelectronic applications. It has been predicted and experimentally verified that the electronic properties of metallic and semiconducting SWNTs are dependent on their diameter and chirality. With the increase in the density of integration, the length of SWNTs used in electronic devices is approaching submicrometer and nanometer scales. It is thus necessary to understand how the length affects the properties of SWNTs besides chirality and diameter. Here, we report that the dielectric response of metallic SWNTs decreases with length. Experimental investigation and numerical modeling determine that the apparent decrease in longitudinal dielectric polarization is due to higher defect density in shorter nanotubes.
Preview · Article · Jun 2009 · The Journal of Physical Chemistry C
[Show abstract][Hide abstract] ABSTRACT: Low-frequency dielectric polarization of single-walled carbon nanotubes (SWNTs) not only affects charge carrier transport in SWNT-based nanoelectronic devices but also determines their interaction with molecules, other nanomaterials, and external fields. Differential dielectric responses of metallic and semiconducting SWNTs are critical in electronic-type sorting of SWNTs. Here, we describe the measurement of low-frequency dielectric polarization of individual SWNTs without making electrical contacts to the nanotubes. Qualitative contrast is observed between metallic and semiconducting SWNTs due to drastically different longitudinal polarizabilities. This is developed into a facile assay for metallic and semiconducting contents in SWNT samples.
[Show abstract][Hide abstract] ABSTRACT: Carbon nanotubes have been considered as potential building blocks for nano-scale circuits in virtue of their unique mechanical and electrical properties. However, one of the biggest obstacles for massive production of nanotube circuits is the difficulty of separating semiconducting tubes from metallic tubes or vice versa. In this work, a convenient method which may be potentially employed to selectively remove metallic tubes using microwave induced breakdown is proposed and investigated. Carbon nanotube thin films deposited on glass and quartz substrates are placed in a commercial microwave oven and heated for up to several minutes. The radial breathing mode in Raman spectra on the nanotube samples before and after the microwave irradiation suggests that the metallic-to-semiconducting ratios are reduced by around 20%. Meanwhile, because in the thin film samples most of the nanotubes are entangled, smaller diameter nanotubes (both metallic and semiconducting) tend to be affected more. THz transmission measurements of these thin films are also performed before and after microwave irradiation. The significant increase of transmission after the microwave irradiation process confirms the loss of metallic tubes.