|[General Info] [Applications] [Techniques] [Types]|
-Single-Walled Nanotubes-Single-walled nanotubes usually have a diameter close to one nanometer, but a length that can be thousands of times as long. There are several different types of single-walled nanotubes. The way these subtypes are determined is based on how the graphene (a one-atom thick layer of graphite that makes up single-walled nanotubes) sheet is wrapped. A pair of indices (n and m) called the chiral vector represent the type of graphene wrap. In a “zigzag” nanotube, m=0. When n=m, the nanotube is called an “armchair” nanotube. Any other arrangement is called “chiral.” Single-walled nanotubes exhibit extraordinary electrical conductivity, which is not shown in multi-walled nanotubes. However, single-walled nanotubes remain expensive to produce (around $1500 a gram as of 2007).
-Multi-Walled Nanotubes-Multi-walled nanotubes consist of either a single-walled nanotube rolled in on itself (called the “Parchment” model, because it resembles a scroll of parchment or rolled up newspaper) or several single-walled nanotubes wrapped around each other (referred to as the “Russian Doll” model because of the way they are wrapped). Multi-walled nanotubes are very useful in filters.
-Nanotubes That Aren’t Quite Nanotubes-There are many shapes that a carbon nanotube could take. Some of the most popular are the torus, or nanotorus and the carbon nanobud. The nanotorus is shaped like a donut and has several interesting properties. One is an incredibly high magnetic moment (the strength of its magnetic system). The other is its thermal stability. The nanobud is a “combination” of a spherical fullerene (also called a buckeyball) and a single-walled carbon nanotube. These nanobuds have properties of both buckyballs and nanotubes, and are exceptional field emitters.