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

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.