Scanning tunneling microscopy studies of conducting molybdenum oxide bronzes

Abstract

Compounds of the formula AxMozOy, known as molybdenum bronzes, display interesting quasi-low-dimensional electronic properties such as anisotropic conduction, superconductivity, and charge-density waves (CDW). Scanning tunneling microscopy studies have been performed on Na0.9Mo6O17, a purple bronze, and Rb0.3MoO3, a blue bronze, demonstrating that they can be imaged in air with near atomic resolution. Surface defects can be created on these bronzes exhibiting varied in-air stabilities. The interpretation of images is discussed with reference to the structures, CDWs, defect creation techniques, and relative defect stabilities.

Scanning probe microscopy of oxide surfaces: atomic structure and properties

“…No surface reconstructions were observed. Garfunkel et al [114,115] used STM to image the ab plane surfaces of Rb 0.3 MoO 3 (blue bronze) and Na 0.9 Mo 6 O 17 (purple bronze). For the Rb compound, the distortion of MoO 6 octahedra evident in XRD was observed in the surface structure.…”

“…It can distinguish between the atomic structure of a surface and the spatial variations in surface charge density when these variations have a period different from that of the atomic lattice. Attempts to image blue bronzes at room temperature have yielded high spatial resolution [113,115,116]. Walter et al [117] found no evidence for charge density waves at the surface below the Peierls transition temperature T P = 180 K. Brun et al [118,119] imaged Rb 0.3 MoO 3 (0 0 0 1) at ∼70 K at which temperature the charge density is superimposed at the atomic lattice (within the resolution of STM) and is evident as a super period of high contrast.…”