carbon nanotube
/ KAR-bun NAN-oh-tyoob /
Take a sheet of paper and roll it into a drinking straw. Now imagine that sheet is graphene — a single layer of carbon atoms — and the straw is so narrow that thousands of them laid side by side would barely span the width of a human hair. That tiny rolled-up tube is a carbon nanotube.
A carbon nanotube is exactly that: a graphene sheet curled into a seamless hollow cylinder, sometimes capped at the ends like a closed test tube. The strong carbon bonds that make graphene tough now run all the way around the cylinder, so the tube is one of the stiffest and strongest materials known for its weight. Curiously, the way the honeycomb pattern is angled as it wraps — the 'roll-up direction' — decides whether a given tube conducts electricity like a metal or behaves like a semiconductor.
Carbon nanotubes matter because they pack remarkable strength, light weight, and tunable electrical behavior into a single object only a nanometer or so wide, making them candidates for ultra-strong fibers, tiny transistors, and conductive films. The honest caveat is that real batches are messy: they come out as a tangled mix of metallic and semiconducting tubes of different sizes, and sorting them cleanly remains hard, which has limited their use in precise electronics.
A bundle of carbon nanotubes can be hundreds of times stronger than steel of the same weight. Engineers have woven them into fibers and conductive sheets, and they are a favorite thought-experiment material for the cable of a hypothetical space elevator.
Pound for pound, carbon nanotubes are among the strongest materials ever measured.
A carbon nanotube is often called a one-dimensional material: electrons can travel freely along its length but are wrapped tightly around its tiny circumference, so for them only the length truly counts as a direction to move.