Induced crystallization and enhanced light absorption and optical conduction in WO3 flms via pulsed laser welding technique

Abstract

Herein amorphous WO3 thin flms prepared by the thermal evaporation technique under a vacuum pressure of 10−5 mbar are treated via pulsed laser welding technique (PLW) in an argon atmosphere. An induced crystallization process within one second for a spot of diameter of 2 mm is achieved via this technique. The crystalline flms exhibited hexagonal structure and showed cuboid grains of dimensions of (length×width) 4.6× 1.1 (μm)2 . In addition, the PLW treated tungsten oxide thin flms exhibited enhanced light absorbability reaching 90 times at 3.09 eV. Moreover in addition to the existing indirect energy band gap (3.50 eV) of WO3 flms, the PLW treatment resulted in formation of another direct energy band gap of value of 1.92 eV. The pulsed laser welding of the WO3 flms increased the optical conductivity of the flms by 66 times and shifted the plasmon frequency from 0.19 to 6.99 GHz. The free charge carrier density also increased by two orders of magnitude. On the other hand, the impedance spectroscopy studies have shown domination of negative capacitance efect in samples treated with PLW technique. The conversion of the structure of the flms from amorphous to polycrystalline that is associated with enhanced light absorption and improved optical conduction which is achieved within 41 s for a large area of 1.25 cm2 of the flms is accounted as a smart new approach for improving the physical properties of thin flms.