Strain-induced metal-semiconductor transition observed in atomic carbon chains.

A. La Torre,J. -C. Charlier,W. Baaziz,A. Botello-Mendez,F. Banhart

doi:10.1038/ncomms7636

Abstract

Carbyne, the sp1-hybridized phase of carbon, is still a missing link in the family of carbon allotropes. While the bulk phases of carbyne remain elusive, the elementary constituents, that is, linear chains of carbon atoms, have already been observed using the electron microscope. Isolated atomic chains are highly interesting one-dimensional conductors that have stimulated considerable theoretical work. Experimental information, however, is still very limited. Here we show electrical measurements and first-principles transport calculations on monoatomic carbon chains. When the 1D system is under strain, the chains are semiconducting corresponding to the polyyne structure with alternating bond lengths. Conversely, when the chain is unstrained, the ohmic behaviour of metallic cumulene with uniform bond lengths is observed. This confirms the recent prediction of a metal–insulator transition that is induced by strain. The key role of the contacting leads explains the rectifying behaviour measured in monoatomic carbon chains in a nonsymmetric contact configuration.

Highlights

Carbyne, the sp1-hybridized phase of carbon, is still a missing link in the family of carbon allotropes
Two configurations have been proposed for carbyne as a onedimensional (1D) crystal, namely cumulene with double bonds over the whole chain ( 1⁄4 C 1⁄4 C 1⁄4 C 1⁄4 C 1⁄4 C 1⁄4 ) and polyyne with alternating single and triple bonds ( À CC À CC À C)
Chains of carbon atoms were unravelled from the graphitic material

Summary

Introduction

The sp1-hybridized phase of carbon, is still a missing link in the family of carbon allotropes. When the chain is unstrained, the ohmic behaviour of metallic cumulene with uniform bond lengths is observed This confirms the recent prediction of a metal–insulator transition that is induced by strain. A recent theoretical consideration suggested that the energetic gain by the Peierls instability in unstrained chains is so small that it can be overcompensated by zero-point vibrations[16] This is a most important result since it predicts that metallic cumulene exists and should prevail in mechanically relaxed chains. It is shown experimentally that unstrained chains are metallic, while strained chains exhibit a distinct semiconducting behaviour This confirms the recent prediction of a straininduced metal–semiconductor transition in carbyne[16]. Rectifying behaviour in the electrical conductivity is observed when the contacts are different

Methods

Results

Conclusion