Paraffin-Enabled Compressive Folding of Two-Dimensional Materials with Controllable Broadening of the Electronic Band Gap.

Abstract

The capability to manipulate the size of the electronic band gap is of importance to semiconductor technology. Among these, a wide direct band gap is particularly helpful in optoelectronic devices due to the efficient utilization of blue and ultraviolet light. Here, we reported a paraffin-enabled compressive folding (PCF) strategy to widen the band gap of two-dimensional (2D) materials. Due to the large thermal expansion coefficient of paraffin, folded 2D materials can be achieved via thermal engineering of the paraffin-assisted transfer process. It can controllably introduce 0.2-1.3% compressive strain onto folded structures depending on the temperature differences and transfer the folding product to both rigid and soft substrates. Exemplified by MoS2, its folded multilayers demonstrated blue-shifts at direct gap transition peaks, six times stronger photoluminescence intensity, almost double mobility, and 20 times higher photoresponsivity over unfolded MoS2. This PCF strategy can attain controllable widening band gap of 2D materials, which will open up novel applications in optoelectronics.