Tuning carbon nanotube band gaps with strain

We show that the band structure of a carbon nanotube (NT) can be dramatically altered by mechanical strain. We employ an atomic force microscope tip to simultaneously vary the NT strain and to electrostatically gate the tube. We show that strain can open a band gap in a metallic NT and modify the band gap in a semiconducting NT. Theoretical work predicts that band gap changes can range between +/-100 meV per 1% stretch, depending on NT chirality, and our measurements are consistent with this predicted range.