Nanomaterials

The development of economical and scalable methods for synthesizing high-quality graphene remains a pivotal challenge in materials science. This study presents an efficient approach for synthesizing turbostratic graphene with micron-sized domains from an accessible bioprecursor-activated charcoal—using fast Joule heating. We demonstrate that ultra-rapid thermal annealing (~16.2 kJ/g, up to 3000 K) triggers a phase transition from amorphous carbon to a highly graphitized structure. Comprehensive characterization via SEM, AFM, Raman spectroscopy, and XRD revealed the formation of large flakes with lateral dimensions up to 1.5 µm and thicknesses ranging from 4 to 200 nm. Raman mapping further uncovered a heterogeneous structure with alternating regions exhibiting different degrees of interlayer coupling, characteristic of turbostratic stacking. The key feature of the material is its turbostratic layer stacking, confirmed by the combination of XRD data showing an interlayer distance of 3.436 Å and Raman spectra characteristic of decoupled graphene layers. The synthesized material exhibits excellent electrical transport properties, with a bulk resistivity of 0.51 Ω·cm—an order of magnitude lower than that of the initial charcoal. These findings highlight the potential of the developed method for producing electrode materials for energy storage devices and conductive composites.

Transparent conductive films based on silver nanowire meshes have demonstrated significant potential as alternatives to conventional tin-doped indium oxide and fluorine-doped tin oxide thin films. However, these materials feature high junction resistance, poor damp heat (DH) stability, and weak mechanical adhesion to substrates, which are critical issues that must be addressed before any practical applications. In this paper, transparent conducting films composed of silver nanowire (AgNW) frameworks and amorphous indium zinc oxide (IZO) fillers were prepared by a spin-coating method. The AgNW-IZO composite films exhibited a higher conductivity and better DH stability and adhesion to substrates than that of their constituent parts alone. The lowest sheet resistance of the composite films was 3.3 ohm/sq with approximately 70% transparency in the visible spectrum. No degradation was observed after 8 months. The excellent DH stability and mechanical adhesion might facilitate applications of these AgNW-IZO composite films in optoelectronic devices. Furthermore, the composite electrode is shown to have potential as a transparent heater.

Gallium nitride (GaN)-based high electron mobility transistors (HEMTs) are pivotal for next-generation power-switching applications, but their reliability under high electric fields remains constrained by lattice mismatches and high dislocation densities in heterogeneous substrates. Herein, we systematically investigate the electrical performance and reliability of GaN-on-GaN HEMTs in comparison to conventional GaN-on-SiC HEMTs via DC characterization, reverse gate step stress, off-state drain step stress, and on-state electrical stress tests. Notably, the homogeneous epitaxial structure of GaN-on-GaN devices reduces dislocation density by 83.3% and minimizes initial tensile stress, which is obtained through HRXRD and Raman spectroscopy. The GaN-on-GaN HEMTs exhibit a record BFOM of 950 MW/cm², enabled by a low specific on-resistance (R_ON-SP) of 0.6 mΩ·cm² and a high breakdown voltage (BV) of 755 V. They withstand gate voltages up to −200 V and drain voltages beyond 200 V without significant degradation, whereas GaN-on-SiC HEMTs fail at −95 V (reverse gate stress) and 150 V (off-state drain stress). The reduced dislocation density suppresses leakage channels and defect-induced degradation, as confirmed by post-stress Schottky/transfer characteristics and Frenkel–Poole emission analysis. These findings establish GaN-on-GaN technology as a transformative solution for power electronics, offering a unique combination of high efficiency and long-term stability for demanding high-voltage applications.