A Comparative Characterization Study of Molybdenum Oxide Thin Films Grown Using Femtosecond and Nanosecond Pulsed Laser Deposition

Abstract

Group 6 transition metal oxide thin films are in large demand for photocatalysis, heterogeneous catalysis, fuel cell, battery and electronic applications. Pulsed laser deposition offers an inexpensive method for the preparation of nanostructured thin films that may be suitable for heterogeneous catalysis. We have synthesized molybdenum oxide thin films using two types of pulsed laser deposition (PLD). The first method utilizes femtosecond laser-based PLD (f-PLD) while the second method uses an excimer (nanosecond) laser-based PLD (n-PLD). The PLD films have been deposited using f-PLD and, separately, n-PLD on glass and silicon substrates and subsequently annealed to 450 °C for up to 20 hours in air using a Linkam stage. SEM, XRD and Raman spectroscopic characterization shows that the f-PLD films are substantially more textured and partially crystalline prior to annealing whereas the n-PLD-grown thin films are much smoother and predominantly amorphous. A 3-dimensional nano-crystalline structure is evident in the post-annealed f-PLD synthesized thin films, which is desirable for catalytic applications. XPS elemental analysis shows that the stoichiometry of the f-PLD and n-PLD thin films is consistent with the presence of MoO₂ and MoO₃. Our results are discussed in terms of thin film growth models suitable for f-PLD vs n-PLD.