Electroassisted Transfer of Vertical Silicon Wire Arrays Using a Sacrificial Porous Silicon Layer

An electroassisted method is developed to transfer silicon (Si) wire arrays from the Si wafers on which they are grown to other substrates while maintaining their original properties and vertical alignment. First, electroassisted etching is used to form a sacrificial porous Si layer underneath the Si wires. Second, the porous Si layer is separated from the Si wafer by electropolishing, enabling the separation and transfer of the Si wires. The method is further expanded to develop a current-induced metal-assisted chemical etching technique for the facile and rapid synthesis of Si nanowires with axially modulated porosity

Three-Dimensional Hetero-Integration of Faceted GaN on Si Pillars for Efficient Light Energy Conversion Devices

An important pathway for cost-effective light energy conversion devices, such as solar cells and light emitting diodes, is to integrate III–V (<i>e</i>.<i>g</i>., GaN) materials on Si substrates. Such integration first necessitates growth of high crystalline III–V materials on Si, which has been the focus of many studies. However, the integration also requires that the final III–V/Si structure has a high light energy conversion efficiency. To accomplish these twin goals, we use single-crystalline microsized Si pillars as a seed layer to first grow faceted Si structures, which are then used for the heteroepitaxial growth of faceted GaN films. These faceted GaN films on Si have high crystallinity, and their threading dislocation density is similar to that of GaN grown on sapphire. In addition, the final faceted GaN/Si structure has great light absorption and extraction characteristics, leading to improved performance for GaN-on-Si light energy conversion devices

Simultaneously Efficient Light Absorption and Charge Separation in WO₃/BiVO₄ Core/Shell Nanowire Photoanode for Photoelectrochemical Water Oxidation

We report a scalably synthesized WO₃/BiVO₄ core/shell nanowire photoanode in which BiVO₄ is the primary light-absorber and WO₃ acts as an electron conductor. These core/shell nanowires achieve the highest product of light absorption and charge separation efficiencies among BiVO₄-based photoanodes to date and, even without an added catalyst, produce a photocurrent of 3.1 mA/cm² under simulated sunlight and an incident photon-to-current conversion efficiency of ∼60% at 300–450 nm, both at a potential of 1.23 V versus RHE

High-Performance Ultrathin BiVO₄ Photoanode on Textured Polydimethylsiloxane Substrates for Solar Water Splitting

Photoelectrochemical (PEC) water splitting devices rely on light-absorbers to absorb sunlight, and the photogenerated electrons and holes further react with water to generate hydrogen and oxygen. Fabricating light-absorbers on textured substrates offers alternative routes for optimizing their PEC performance. Textured substrates would greatly enhance both light absorption and surface reactions of photoanodes and thus reduce the total amount of light-absorbers needed. Herein, we report the fabrication of ultrathin BiVO₄ photoanode film on textured polydimethylsiloxane (PDMS) substrates by using a modified water-assisted transfer printing method. Significantly, a pristine BiVO₄ photoanode of only 80 nm thick shows a photocurrent density of 1.37 mA/cm² at 1.23 V_RHE on patterned PDMS substrates, which is further increased to ∼2.0 mA/cm² at 1.23 V_RHE when FeOOH oxygen evolution catalyst is added. We believe that our transfer printing method can be broadly applied to integrate photoelectrodes and other thin-film optoelectronic devices (e.g., solar cells and electronics) onto diverse textured substrates to enhance their performance

Biodegradable Elastomers and Silicon Nanomembranes/Nanoribbons for Stretchable, Transient Electronics, and Biosensors

Transient electronics represents an emerging class of technology that exploits materials and/or device constructs that are capable of physically disappearing or disintegrating in a controlled manner at programmed rates or times. Inorganic semiconductor nanomaterials such as silicon nanomembranes/nanoribbons provide attractive choices for active elements in transistors, diodes and other essential components of overall systems that dissolve completely by hydrolysis in biofluids or groundwater. We describe here materials, mechanics, and design layouts to achieve this type of technology in stretchable configurations with biodegradable elastomers for substrate/encapsulation layers. Experimental and theoretical results illuminate the mechanical properties under large strain deformation. Circuit characterization of complementary metal-oxide-semiconductor inverters and individual transistors under various levels of applied loads validates the design strategies. Examples of biosensors demonstrate possibilities for stretchable, transient devices in biomedical applications