Pillared graphene represents a class of three-dimensional carbon nanotube architectures. Carbon nanotube conductive coatings are a prospective replacement. The two main methods of carbon nanotube functionalization are covalent and non-covalent modifications. Other potential materials include microwave dielectrics and carbon nanotube (CNT) composites. Another approached used carbon nanotube fiber yarns. This reduces the mean free path and reduces the thermal conductivity of nanotube structures. Optical absorption is routinely used to quantify quality of the carbon nanotube powders. Recently, carbon nanotube based electrodes have gained marked interest from the scientific community. This is relevant in carbon nanotube quantum dot systems. Consequently, Raman spectroscopy is probably the most popular technique of carbon nanotube characterization. One such example is the carbon nanotube nanomotor. Carbon nanotube nanomotors have also been produced. NIST RM 8281 is a mixture of three lengths of single-wall carbon nanotube. In theory, a nanotorus is a carbon nanotube bent into a torus (doughnut shape). This nanotube was grown inside a multi-walled carbon nanotube.