Charge density waves in nanocrystalline thin films of blue bronze K0.3MoO3

Thin granular films of charge density wave (CDW) system K0.3MoO3 were prepared by pulsed laser deposition and investigated by various standard characterization methods such as GI-XRD, electric transport, TOF-ERDA, AFM and UV-vis spectroscopy. While all these methods indicate that the thin films consist of nanometer grains of K0.3MoO3, it is only the non-destructive femtosecond time-resolved spectroscopy (fsTRS) that demonstrates the charge density wave nature of the ground state and therefore proves directly the presence of K0.3MoO3. Furthermore, the comparison of the fsTRS data obtained in thin films and in single crystals shows the reduction of the charge density wave transition temperature and of the photoinduced signal strength in granular thin films in respect to single crystals, which is attributed to the granularity and crystal growth morphology. Our results establish fsTRS technique as the indispensible tool for the detection and characterization of complex ground states in nano-sized systems. Photoinduced reflectivity transients in a) bulk K0.3MoO3 and b) thin film of K0.3MoO3 on Al2O3 substrate as a function of temperature recorded at the same excitation density.