Review: understanding the properties of amorphous materials with high-performance computing methods

Exploring semiconductor potential: novel boron-based Ti3AlC2 and Ti4AlN3 MAX phase composites with tunable band gaps

This research focuses on synthesizing chemically and thermally stable novel in situ Ti4AlN3 and Ti3AlC2 MAX phase reinforced boron-based composites using hot pressed and inert sintering processes, enabling a sizeable and wider bandgap for semiconductor applications. The study found that the MAX phase is formed from 0.2% to 2.9% in fabricated samples with increasing sintering temperatures from 950 °C to 1325 °C. As the sintering temperature increases, the percentage of crystallinity in Ti4AlN3 MAX phase reinforced boron-based composites increases from 69.14% to 89.88%, while in Ti3AlC2 MAX phase reinforced boron-based composites, it increases from 71.02% to 77.86%. And the energy bandgap shows a declining trend from 2.33 eV to 1.78 eV for Ti4AlB2N sample composites and 2.60 eV to 2.40 for Ti4AlB2C sample composites. The UV-vis test for boron-based Ti4AlN3 and Ti3AlC2 MAX phase composites shows an absorbance rate ranging from 0.065 a.u. to 0.63 a.u. and 0.008 to 2.4 a.u. respectively with increasing sintering temperature. Tuning these bandgap variations for Ti4AlN3 and Ti3AlC2 MAX phase reinforced boron-based composites with sintering temperature allows for customization of the material's optical absorption and emission spectra, which is important for semiconductor properties and for electronic and optoelectronic devices.

On the Structure of Oxygen Deficient Amorphous Oxide Films

Understanding defects in amorphous oxide films and heterostructures is vital to improving performance of microelectronic devices, thin-film transistors, and electrocatalysis. However, to what extent the structure and properties of point defects in amorphous solids are similar to those in the crystalline phase are still debated. The validity of this analogy and the experimental and theoretical evidence of the effects of oxygen deficiency in amorphous oxide films are critically discussed. The authors start with the meaning and significance of defect models, such as "oxygen vacancy" in crystalline oxides, and then introduce experimental and computational methods used to study intrinsic defects in amorphous oxides and discuss their limitations and challenges. To test the validity of existing defect models, ab initio molecular dynamics is used with a non-local density functional to model the structure and electronic properties of oxygen-deficient amorphous alumina. Unlike some previous studies, the formation of deep defect states in the bandgap caused by the oxygen deficiency is found. Apart from atomistic structures analogous to crystal vacancies, the formation of more stable defect states characterized by the bond formation between under-coordinated Al ions is shown. The limitations of such defect models and how they may be overcome in simulations are discussed.