Covalent heterostructures of ultrathin amorphous carbon nitride and Si for high-performance vertical photodiodes
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Controlled layer-by-layer assembly and structured coloration of Ti3C2Tz MXene/polyelectrolyte heterostructures
Structural color arises from light scattering rather than organic pigments and can be found in Nature, such as in bird feathers and butterfly wings. Synthetic materials can mimic Nature by leveraging materials with contrasting optical characteristics by controlling each materials’ spatial arrangement in a heterostructure. Two-dimensional MXene nanosheets are particularly interesting due to their unique optical properties, but MXenes have not been used directly as a structural colorant because it is challenging to control the spatial placement of MXenes at the nanometer level. Here, we report the emergence of structural color in layer-by-layer (LbL) assemblies of Ti3C2Tz MXene nanosheets and polyelectrolyte heterostructures with controlled block thicknesses. The block thickness and spatial placement of MXene are controlled by the assembly’s salt concentration and number of layer pairs. This work demonstrates that optical characteristics of MXene/polyelectrolyte heterostructures depend on MXene content and placement, while deepening the understanding of MXenes within structural color films.
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Electric heating methods are being developed and used to electrify industrial applications and lower their carbon emissions. Direct Joule resistive heating is an energy-efficient electric heating technique that has been widely tested at the bench scale and could replace some energy-intensive and carbon-intensive processes. In this Review, we discuss the use of flash Joule heating (FJH) in processes that are traditionally energy-intensive or carbon-intensive. FJH uses pulse current discharge to rapidly heat materials directly to a desired temperature; it has high-temperature capabilities (>3,000 °C), fast heating and cooling rates (>102 °C s−1), short duration (milliseconds to seconds) and high energy efficiency (~100%). Carbon materials and metastable inorganic materials can be synthesized using FJH from virgin materials and waste feedstocks. FJH is also applied in resource recovery (such as from e-waste) and waste upcycling. An emerging application is in environmental remediation, where FJH can be used to rapidly degrade perfluoroalkyl and polyfluoroalkyl substances and to remove or immobilize heavy metals in soil and solid wastes. Life-cycle and technoeconomic analyses suggest that FJH can reduce energy consumption and carbon emissions and be cost-efficient compared with existing methods. Bringing FJH to industrially relevant scales requires further equipment and engineering development.
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Crystallization of amorphous precursors into metastable crystals plays a fundamental role in the formation of new matter, from geological to biological processes in nature to the synthesis and development of new materials in the laboratory. Reliably predicting the outcome of such a process would enable new research directions in these areas, but has remained beyond the reach of molecular modeling or ab initio methods. Here we show that candidates for the crystallization products of amorphous precursors can be predicted in many inorganic systems by sampling the local structural motifs at the atomistic level using universal deep learning interatomic potentials. We show that this approach identifies, with high accuracy, the most likely crystal structures of the polymorphs that initially nucleate from amorphous precursors, across a diverse set of material systems, including polymorphic oxides, nitrides, carbides, fluorides, chlorides, chalcogenides and metal alloys.
Carbon-coating effect on the performance of photolithographically-structured Si nanowires for lithium-ion microbattery anodes
The applications of three-dimensional Si nanowire anodes in lithium-ion microbatteries have attracted great interest in the realization of high-capacity and integrated energy storage devices for microelectronics. Combining Si nanowires with carbon can improve the anode performance by aiding its mechanical stability during cycling. Here, we incorporate photolithography, cryogenic dry etching, and thermal evaporation as the commonly used methods in semiconductor technologies to fabricate carbon-coated Si nanowire anodes. The addition of amorphous carbon to Si nanowire anodes has an impact on increasing the initial areal capacity. However, a gradual decrease to 0.3 mAh cm−2 at the 100th cycle can be observed. The post-mortem analyses reveal different morphologies of Si nanowire anodes after cycling. It is indicated that carbon coating can help Si nanowires to suppress their volume expansion and reduce the excessively produced amorphous Si granules found in pristine Si nanowire anodes.
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