Organic-inorganic lead halide perovskite semiconductors have recently reignited the prospect of a tunable, solution-processed diode laser, which has the potential to impact a wide range of optoelectronic applications. Here, we demonstrate a metal-clad, second-order distributed feedback methylammonium lead iodide perovskite laser that marks a significant step toward this goal. Optically pumping this device with an InGaN diode laser at low temperature, we achieve lasing above a threshold pump intensity of 5 kW/cm(2) for durations up to ∼25 ns at repetition rates exceeding 2 MHz. We show that the lasing duration is not limited by thermal runaway and propose instead that lasing ceases under continuous pumping due to a photoinduced structural change in the perovskite that reduces the gain on a submicrosecond time scale. Our results indicate that the architecture demonstrated here could provide the foundation for electrically pumped lasing with a threshold current density Jth < 5 kA/cm(2) under sub-20 ns pulsed drive.
Electrochemical CO 2 reduction reaction (CO2RR) to formate is considered as one of the most promising routes for value-added fuels and chemical productions. The achievement of excellent activity and high Faradaic efficiency in a wide potential range is critical for mature applications. To this regard, we first employed density functional theory simulations to predict activity of Bi nanotubes and Bi nanosheets to CO2RR and selectivity toward formate. The theoretical thermodynamic analysis of the reaction energetics suggests that the limiting potential for CO 2 reduction to HCOOH decreases with the increase of the curvature, suggesting a wider potential window of Bi nanotubes for formate formation. Then, Bi nanotubes with highly curved surface were experimentally prepared, showing a large current density (−39.4 mA cm −2 at −1.1 V vs reversible hydrogen electrode (RHE)) for CO 2 reduction and a maximum formate selectivity of 97% at −1.0 V vs RHE. More importantly, compared with Bi nanosheets, an appreciable selectivity for formate was achieved on Bi nanotubes in a significantly wider potential window of ∼600 mV (selectivity > 80%). This research provides not only the CO2RR activity−surface structure relationship of metallic Bi but also an efficient strategy for the rational design of electrocatalysts with high activity and selectivity in a wide potential window for CO2RR, which is favorable for compatible application with varied types of photovoltaics and other renewable energy sources.
The electron energy band alignment between (100)Si and several complex transition/rare earth (RE) metal oxides (LaScO 3 , GdScO 3 , DyScO 3 , and LaAlO 3 , all in amorphous form) is determined using a combination of internal photoemission and photoconductivity measurements. The band gap width is nearly the same in all the oxides ͑5.6-5.7 eV͒ yielding the conduction and valence band offsets at the Si/oxide interface of 2.0± 0.1 and 2.5± 0.1 eV, respectively. However, band-tail states are observed and these are associated with Jahn-Teller relaxation of transition metal and RE cations which splits their d* states.
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