Optical properties of ordered carbon nanotube arrays grown in porous anodic alumina templates

John Zuidema,Timothy S Fisher,Xiulin Ruan

doi:10.1364/oe.21.022053

Abstract

We have synthesized ordered carbon nanotube (CNT) arrays in porous anodic alumina (PAA) matrix, and have characterized their total optical reflectance and bi-directional reflectance distribution function after each processing step of the microwave plasma chemical vapor deposition process (MPCVD). For a PAA sample without CNT growth, the reflectance shows an oscillating pattern with wavelength that agrees reasonably with a multilayer model. During the MPCVD process, heating the sample significantly reduces the reflectance by 30-40%, the plasma treatment reduces the reflectance by another 5-10%, and the CNT growth further reduces the reflectance by 2-3%. After an atomic layer deposition (ALD) process, the reflectance increases to the embedded CNT arrays. After etching and exposure of CNT tips, the reflectance almost returns to the original pattern with slightly higher reflectance. Bi-directional reflectance distribution function (BRDF) measurements show that the CNT-PAA surface is quite specular as indicated by a large lobe at the specular angle, while the secondary lobe can be attributed to surface roughness.

Highlights

In 1991, Iijima first grew carbon nanotubes using an arc-discharge method [1]
For a porous anodic alumina (PAA) sample without carbon nanotube (CNT) growth, the reflectance shows an oscillating pattern with wavelength that agrees reasonably with a multilayer model
During the microwave plasma chemical vapor deposition process (MPCVD) process, heating the sample significantly reduces the reflectance by 30-40%, the plasma treatment reduces the reflectance by another 5-10%, and the CNT growth further reduces the reflectance by 2-3%

Summary

Introduction

In 1991, Iijima first grew carbon nanotubes using an arc-discharge method [1]. Carbon nanotubes (CNTs) are composed of individual sheets of graphene, rolled up into cylinders that can be only a few nanometers thick. Many interesting optical properties have been observed in CNT arrays grown without a template, such as photonic crystal effects [2, 3], directional emission [4, 5], wavelength-selective emission and polarization-dependent reflection [6], and high absorptivity [7, 8]. The configuration of CNT arrays grown in PAA holds promise for electronic devices based on carbon nanotubes [10, 11]. The presence of CNTs can possibly modify the optical properties of the PAA or exhibit optical antenna effect. Well-ordered and high-yield CNT growth in porous anodic alumina (PAA) templates was established by varying conditions such as electrical bias and plasma treatments. Optical reflectance has been characterized on CNT arrays samples, and tunable thermal radiative properties in total reflectance and spectra have been observed

Growth and preparation of CNT arrays

Hemispherical reflectance of CNT arrays grown in PAA

Conclusions