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- Creator:
- Wang, Danhao and Mi, Zetian
- Description:
- Wurtzite ferroelectrics possess transformative potential for next-generation microelectronics. A comprehensive understanding of their ferroelectric properties and domain energetics is crucial for tailoring their ferroelectric characteristics and exploiting their functional properties in practical devices. Despite burgeoning interest, the exact configurations, and electronic structures of domain walls in wurtzite ferroelectrics remain elusive. In this work, we elucidate the atomic configurations and electronic properties of electric-field-induced domain walls in ferroelectric ScGaN. By combining transmission electron microscopy and theoretical calculations, a novel charged domain wall with a buckled two-dimensional hexagonal phase is revealed. Density functional theory calculations confirm that such domain wall structures further give rise to unprecedented mid-gap states within the forbidden band. Quantitative analysis unveils a universal charge-compensation mechanism stabilizing antipolar domain walls in ferroelectric materials, wherein the polarization discontinuity at the 180º domain wall is compensated by the unbonded valence electrons. Furthermore, the reconfigurable conductivity of these domain walls is experimentally demonstrated, showcasing their potential for ultra-scaled device applications. Our findings represent a pivotal advancement in understanding the structural and electronic properties of wurtzite ferroelectric domain walls and lay the groundwork for fundamental physics studies and device applications.
- Keyword:
- Charged domain walls, Scanning transmission electron microscopy, and Density functional theory calculations
- Discipline:
- Science
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- Creator:
- Ye, Zhengwei and Mi, Zetian
- Description:
- Generation of C2+ compounds using sunlight, carbon dioxide, and water provides a promising path for carbon neutrality. The exploration of a catalyst to break the bottleneck of C-C coupling, for constructing a rational artificial photosynthesis integrated device, is at the core. Herein, based on operando spectroscopy measurements, theoretical calculations, and feedstock experiments, it is discovered that gold, in conjunction with iridium, can catalyze the reduction of CO2, achieving C-C coupling by insertion of CO2 into -CH3. Owing to a combination of optoelectronic and catalytic properties, the assembly of AuIr with InGaN nanowires on silicon (AuIr@InGaN NWs/Si) enables the achievement of a C2H6 activity of 58.8 mmol‧g-1‧h-1 with a turnover number of 54,595 over 60 hours. A light-to-fuels efficiency of ~0.59% for solar fuels production from CO2 and H2O is achieved without any other energy inputs. This work provides a carbon-negative path for producing higher order C compounds.
- Keyword:
- Carbon dioxide reduction and Photocatalysis
- Discipline:
- Science
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- Creator:
- Zhou, Peng and Mi, Zetian
- Description:
- Production of hydrogen fuel from sunlight and water offers one of the most promising pathways for carbon neutrality. Some solar hydrogen production approaches, e.g., photoelectrochemical water splitting, often requires corrosive electrolyte, limiting their performance stability and environmental sustainability. Alternatively, clean hydrogen can be produced directly from tap water, or seawater by wireless photocatalytic water splitting. The solar-to-hydrogen (STH) efficiency, however, is still lower than 3%. Herein, we have developed a unique strategy to overcome the efficiency bottleneck. A high STH efficiency of 9.2% was achieved by utilizing pure water, concentrated solar light, and visible-light-responsive InGaN photocatalyst. The success of this strategy was explained by the synergistic effects of promoting forward hydrogen-oxygen evolution and inhibiting the reverse hydrogen-oxygen recombination by operating at an optimal reaction temperature (~70 °C). Such an optimal temperature can be readily achieved by harvesting the previously wasted infrared light of the solar spectrum without other energy consumption. This temperature-dependent strategy also leads to the STH efficiencies of ~7% from the widely available tap water and seawater. A large-scale photocatalytic water splitting system with a natural solar light capacity of 257 W on a 4 cm × 4 cm photocatalyst wafer achieves a STH of 6.2% at ~70 oC. Our study offers a practical approach to produce hydrogen fuel efficiently from natural solar and water, overcoming some of the major barriers for green hydrogen economy.
- Keyword:
- photocatalysis, water splitting, and solar hydrogen
- Discipline:
- Science