Nanocrystalline thin films with charge density wave ground state

• Potassium blue bronze thin films were grown on Al2O3 and SrTiO3 substrates.
• Characterization methods showed presence of nano-particles in deposited films.
• Transition to collective mode in films was confirmed.
• Transition temperature proved to be lower in films than in the bulk.

Good understanding of how properties can be tuned by changing the size of material is a basic prerequisite for production of new materials with designed superior properties. Systems with charge density wave (CDW) as a type of coupled electronic-lattice instability (usually found in low dimensional materials) are especially interesting due to their exceptional properties such as giant dielectric constant, nonlinear transport, memory effects, unusual electro-mechanical and thermoelectric properties, all of conceptual importance in various thin film applications. On the other hand, CDW films open the door for studying of meso- and micro-scale aspects of CDW physics caused by finite size effects. Our previously produced thin granular films of CDW prototype system K0.3MoO3 (blue bronze) did not show evidence of CDW condensation in the electrical transport measurements, and femtosecond time-resolved spectroscopy was established as the most appropriate method for characterization of CDW ground state in those nanocrystalline grains. However, the new films prepared by improved pulsed laser deposition (PLD) set-up in optimal conditions and characterized by various standard methods such as GI-XRD, electric transport, TOF-ERDA, AFM and UV–vis spectroscopy exhibit better properties. Electrical resistance decreased by three orders of magnitude and an indication of the Peierls transition is found in films with the best texture, which means that we have achieved the first requirement for testing of other interesting CDW properties related to the size effect (and possible applications of these blue bronze films).