By using the self-consistent Born approximation, we investigate disorder effect induced by the short-range impurities on the band gap in two-dimensional Dirac systems with the higher order terms in momentum. Starting from the Bernevig-Hughes-Zhang (BHZ) model, we calculate the density of states as a function of the disorder strength. We show that due to quadratic corrections to the Dirac Hamiltonian, the band gap is always affected by the disorder even if the system is gapless in the clean limit. Finally, we explore the disorder effects by using an advanced effective Hamiltonian describing the side maxima of the valence subband in HgTe quantum wells. We show that the band gap and disorder-induced topological phase transition in the real structures may differ significantly from those predicted within the BHZ model.

The addition of hard fillers to a polymer matrix is a well-known process for achieving mechanical reinforcement. With a decrease in the size of the fillers, the contribution from polymer–particle nanometer-sized interfaces becomes significant, and these interfaces affect the mechanical performance of polymer nanocomposites (PNCs) beyond the limits established for conventional composites. However, the molecular mechanisms underlying the improvement in the mechanical performance of glassy PNCs remain unresolved, necessitating a deeper understanding of the structure–property relationships in these intrinsically heterogeneous systems. In this effort, by using Brillouin light scattering (BLS) and dynamic mechanical analysis (DMA), we demonstrated that adding shorter chains to a PNC prepared with high molecular weight polymers significantly improved the mechanical properties of the PNC in the glassy state. The strongest enhancement of mechanical properties occurred at an optimum concentration of short chains. This is in contrast to the behavior of the glass transition temperature of PNCs which shows a monotonic decrease with an increase in the concentration of shorter chains. Using experimental data and coarse-grained molecular dynamics (MD) simulations, we have identified the molecular mechanism leading to the observed nonmonotonic changes in mechanical reinforcement. This mechanism includes changes in the nanoscale organization at the interface combined with chain stretching amplified by the addition of the short chains. Overall, our approach paves a simple and cost-effective pathway to fabricating glassy PNCs with significantly improved mechanical properties that will fill various practical needs.

Hexagonal boron nitride (hBN) is attracting much attention due to its tremendous applications including nanophotonic and electronic devices, substrates for two-dimensional (2D) materials, heat management materials, etc. To achieve the best device performance, large area hBN single crystals are required. Herein, large area (>500 microns each) high-quality (defect density < 0.52/μm2) bulk hBN single crystals are grown from molten metal solutions with a temperature gradient. The narrow Raman linewidths of the intralayer E2g mode peak and the interlayer shear mode, the strong and sharp phonon-assisted transition photoluminescence peaks, and the high thermal conductivity demonstrate that the hBN produced by this method are high crystal quality with a low density of defects. Atomic force microscope images show that atomically flat layers of hBN can be produced by exfoliation. This study not only demonstrates a new strategy for growing large hBN single crystals, but also provides high quality thick and thin hBN layers for nano device applications