Exciton Localization of High-Quality ZnO/Mg_<i>x</i>Zn_1–<i>x</i>O Multiple Quantum Wells on Si (111) with a Y₂O₃ Buffer Layer

We report the structural and optical properties of ten-period ZnO/Mg_<i>x</i>Zn_1–<i>x</i>O multiple quantum wells (MQWs) prepared on the most widely used semiconductor material, Si. The introduction of a nanometer thick high-k Y₂O₃ transition layer between Si (111) substrate and a ZnO buffer layer significantly improves the structural perfection of the MQWs grown on top of it. The high structural quality of the ZnO/Mg_<i>x</i>Zn_1–<i>x</i>O MQWs is evidenced by the appearance of pronounced high order satellite peaks in X-ray crystal truncation rods; high resolution cross-sectional transmission electron microscopy images also confirmed the regularly arranged well and barrier layers. When the well width is less than ∼2.7 nm, the quantum-confined Stark effect in MQWs can be negligible. Not only the increasing exciton-binding energy but also reducing exciton–phonon coupling determined in temperature-dependent photoluminescence spectra indicate quantum-size effect. Our results demonstrate that ZnO/Mg_<i>x</i>Zn_1–<i>x</i>O MQWs integrated on Si have great potential in UV optoelectronic device applications

Real-Time Observation of Anion Reaction in High Performance Al Ion Batteries

Recently, aluminum ion batteries (AIBs) have attracted great attention across the globe by virtue of their massive gravimetric and volumetric capacities in addition to their high abundance. Though carbon derivatives are excellent cathodes for AIBs, there is much room for further development. In this study, flexuous graphite (FG) was synthesized by a simple thermal shock treatment, and for the first time, an Al/FG battery was applied as a cathode for AIBs to reveal the real-time intercalation of AlCl4– into FG with high flexibility by using in-situ scanning electron microscope (SEM) measurements exclusively. Similarly, in-situ X-ray diffraction (XRD) and in-situ Raman techniques have been used to understand the anomalous electrochemical behavior of FG. It was found that FG adopts a unique integrated intercalation–adsorption mechanism where it follows an intercalation mechanism potential above 1.5 V and an adsorption mechanism potential below 1.5 V. This unique integrated intercalation–adsorption mechanism allows FG to exhibit superior properties, like high capacity (≥140 mAh/g), remarkable long-term stability (over 8000 cycles), excellent rate retention (93 mAh/g at 7.5 A/g), and extremely rapid charging and slow discharging