Modulation of the crystal structure in quasi-one-dimensional solids induced by impurities: An atomic-force microscope study

An atomic-force microscope study of interstitial impurities in the quasi-one-dimensional charge-density-wave system ${\mathrm{NbSe}}_3$ at room temperature (in the normal phase) exhibits long-range periodic lattice modulations. The amplitudes and wavelengths are strong functions of the impurity concentration, and in the case of vanadium successive wavelengths of 6${\mathit{b}}_0$, 4${\mathit{b}}_0$, and 3${\mathit{b}}_0$ are observed. The drastic changes in the long-range structure of the system caused by small changes in the impurity concentration are an indication of the complex electric susceptibility of a system on the verge of becoming unstable against charge-density-wave formation.