Simultaneous solution-based generation and characterization of crystalline bismuth thin film by femtosecond laser spectroscopy

Abstract

We demonstrate generation and characterization of crystalline bismuth thin film from triphenyl bismuth in methanol. Upon ultraviolet (267 nm) femtosecond laser irradiation of the solution, a thin film of elemental bismuth forms on the inner side of the sample cuvette, confirmed by detection of the coherent A1g optical phonon mode of crystalline bismuth at ∼90 cm−1. Probe pulses at 267 and 400 nm are used to elucidate the excited state potential energy surface and photochemical reaction coordinate of triphenyl bismuth in solution with femtosecond resolution. The observed phonon mode blueshifts with increasing irradiation time, likely due to the gradual thickening of nascent bismuth thin film to ∼80 nm in 90 min. From transient absorption with the 400 nm probe, we observe a dominant ∼4 ps decay time constant of the excited-state absorption signal, which is attributed to a characteristic metal-ligand bond-weakening/breaking intermediate enroute to crystalline metallic thin film from the solution precursor molecules. Our versatile optical setup thus opens an appealing avenue to characterize the laser-induced crystallization process in situ and prepare high-quality thin films and nanopatterns directly from solution phase.