Van der Waals epitaxy of nearly single-crystalline nitride films on amorphous graphene-glass wafer

Van der Waals epitaxy provides a fertile playground for the monolithic integration of various materials for advanced electronics and optoelectronics. Here, a previously unidentified nanorod-assisted van der Waals epitaxy is developed and nearly single-crystalline GaN films are first grown on amorphous silica glass substrates using a graphene interfacial layer. The epitaxial GaN-based light-emitting diode structures, with a record internal quantum efficiency, can be readily lifted off, becoming large-size flexible devices. Without the effects of the potential field from a single-crystalline substrate, we expect this approach to be equally applicable for high-quality growth of nitrides on arbitrary substrates. Our work provides a revolutionary technology for the growth of high-quality semiconductors, thus enabling the hetero-integration of highly mismatched material systems.

Stone–Wales defects preserve hyperuniformity in amorphous two-dimensional networks

Disordered hyperuniformity (DHU) is a recently discovered novel state of many-body systems that possesses vanishing normalized infinite-wavelength density fluctuations similar to a perfect crystal and an amorphous structure like a liquid or glass. Here, we discover a hyperuniformity-preserving topological transformation in two-dimensional (2D) network structures that involves continuous introduction of Stone–Wales (SW) defects. Specifically, the static structure factor S(k) of the resulting defected networks possesses the scaling S(k)∼kα for small wave number k, where 1≤α(p)≤2 monotonically decreases as the SW defect concentration p increases, reaches α≈1 at p≈0.12, and remains almost flat beyond this p. Our findings have important implications for amorphous 2D materials since the SW defects are well known to capture the salient feature of disorder in these materials. Verified by recently synthesized single-layer amorphous graphene, our network models reveal unique electronic transport mechanisms and mechanical behaviors associated with distinct classes of disorder in 2D materials.

Бозонный пик в аморфном графене в рамках модели устойчивых случайных матриц

We study the role of disorder in the force constants distribution on the acoustical and optical phonons in amorphous graphene. It is shown that for a sufficient strength of disorder the boson peak appears in the density of states. With increasing strength of disorder, the peak moves to low frequencies together with Yung modulus. For sufficiently small disorder we have the Van-Hove singularities in the vibration density of states. With increasing disorder, these singularities transform together to one boson peak. The first disappears optical phonons then the acoustical one. The same investigation was done for flexural modes. We show that these modes disappear in disorder in already weak perturbations and transforms to phonons.

Amorphous graphene: a constituent part of low density amorphous carbon

An 800-atom model of nano-porous carbon obtained from anab initiomethod. The topology is warped/wrapped amorphous graphene.