Enhancement of reflectance of densified vertically aligned carbon nanotube forests

• Main Authors: Rana, Masud, M Razib, M Asyraf, Saleh, Tanveer, Asan Gani, Abdul Muthalif
• Format: Article
• Language: English; English
• Published: Korean Carbon Society 2016
• Subjects: T Technology (General)
• Online Access: http://irep.iium.edu.my/50573/1/%5B67-70%5D-11.pdf; http://irep.iium.edu.my/50573/4/50573-Enhancement%20of%20reflectance%20of%20densified%20vertically%20aligned%20carbon%20nanotube%20forests_SCOPUS.pdf; http://irep.iium.edu.my/50573/; http://carbonlett.org/PublishedPaper/year_eachList.asp?page_url=Current_Issues
• Institution: Universiti Islam Antarabangsa Malaysia

Vertically aligned carbon nanotubes (VACNTs), also known as a carbon nanotube (CNT) forest, are a porous material that is well known for its exceptional optical absorbance property. The reflectance from a VACNT forest has been reported to be as low as 0.045% [1,2]. It is known as the darkest material on Earth. Because of its remarkable material properties, it has various other applications as gas sensors [3], pressure sensors [4], temperature sensors [5], and strain sensors [6]. Recently, various efforts have been made to mechanically manipulate the vertical structure of the nanotubes in the CNT forest and to conduct their optical characterization [7,8]. Optical reflection from bare VACNTs has also been investigated at different wavelengths by Wąsik et al. [9]. Controlled densification by wetting of the CNT forest is another post processing technique that has been reported by other researchers [10]. A densification process is necessary to make the CNT forest useful as a future electronics interconnect [10]. However, no study has been done so far on the optical behavior of CNT forests densified by a wetting process. In this letter, for the first time, we investigate and explain the nature of the optical reflectance of densified VACNTs. Fig. 1 illustrates how the CNT forest is able to absorb most incident light. It was reported elsewhere that VACNT arrays are highly porous [11]. As a result, when incident light enters the bare CNT forest, it goes through several internal reflection-absorption cycles via individual nanotubes and finally makes its way out of the CNT forest as shown in Fig. 1b. Hence, a very low amount of light bounces back (approximately 0.045%) [1,2]. Mathematically, a simple model can be developed to estimate the final amount of light coming out of a CNT forest after several internal reflections; this process is explained by eq (1):