Chemical vapor deposition and phase stability of pyrite on SiO2

Semiconducting pyrite (cubic-FeS2) is of great interest for photovoltaics, energy-storage and catalysis applications due its remarkable optical, electrochemical and catalytic properties in combination with its high abundance, low raw material cost and environmental benignancy. In addition, recent theoretical studies indicate that it is possible to synthesize two-dimensional (2D) FeS2 with atomic thickness, and 2D FeS2 possesses highly tunable electronic and magnetic properties that do not exist in its bulk form, enabling its application in nanoelectronics. Herein, we report the first growth of single-phase FeS2 on SiO2 substrates at temperatures between 300 degrees C and 600 degrees C by atmospheric pressure chemical vapor deposition (CVD). The temperature-dependent growth studies suggest that air-stable FeS2 crystals with 2D morphologies grow at 450 degrees C and above while smaller irregular-shaped FeS2 with low crystallinity and poor stability form at lower temperatures. We also demonstrate the patterned growth of 2D hexagonal crystals on SiO2 substrates using graphene as a template at 600 degrees C. Raman spectroscopy measurements in conjunction with ab initio density functional theory (DFT) calculations confirm that the growth up to 600 degrees C does not include any other phase than FeS2. Moreover, we show that laser-induced local phase transformations from FeS2 (pyrite phase) and FeS (troilite phase) can be monitored in-situ by the changes in Raman spectra. Our method paves the way toward scalable synthesis of phase-pure FeS2 crystals on SiO2 substrates, which is fully compatible with semiconductor processing. This method can be also further developed and adopted for the synthesis of atomically thin 2D FeS2 layers and their heterostructures with graphene that may bring enhanced or novel properties.