Production and Defect Engineering of MoO3-x Pseudo-Layers for Electronic Applications

Abstract

Mechanical exfoliation produces high-quality, defect-free two-dimensional (2D) layers and enables rapid prototyping. However, its inherently low throughput severely limits its viability for large-scale device manufacturing. Addressing this scalability issue, this work presents a robust strategy for the synthesis and defect engineering of MoO3-x pseudo-layers, which are integrated into field-effect transistor (FET) templates for electrical characterization and evaluation of their potential for electronic applications. The synthesis approach relies on the generation of a MoO3-x colloidal dispersion by exfoliating α-MoO3 bulk crystals using pulsed laser ablation in liquid (PLAL). The resulting colloid is subsequently deposited by drop-casting onto pre-patterned bottom-contact, bottom-gate FET templates, forming a continuous pseudo-layer within the device channel. Post-deposition annealing in air at 300 °C significantly enhances the structural order of the pseudo-layers, while reducing their electrical conductivity and suppressing hysteresis effects, as confirmed by X-ray diffraction, Raman spectroscopy, and I-V measurements. This behavior is attributed to the rearrangement of nanostructures within the pseudo-layer, which likely enhances interparticle connectivity and leads to a more efficient charge transport. Concurrently, the partial recovery of exfoliation-induced defects - particularly oxygen vacancies - contributes to the observed decrease in electrical conductivity. Defect engineering through vacuum annealing and ion implantation increases the conductivity of the pseudo-layers by several orders of magnitude, demonstrating effective modulation of the carrier density. Additionally, following thermal treatment in air, a clear modulation of the pseudo-layer resistance with applied gate voltage is observed, consistent with n-type semiconductor behavior. An electron mobility of 1.27 cm2 V-1 s-1 is achieved, representing an order-of-magnitude improvement compared to FET devices fabricated from 2D-MoO3 crystals originating from the same bulk source. Although the overall FET performance remains limited, this improvement in electron mobility, achieved through potentially scalable solution processing and standard microfabrication and annealing processes, underscores the potential of 2D-MoO3 for electronic device applications.