GaP/GaNP Heterojunctions for Efficient Solar‐Driven Water Oxidation

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137529/1/smll201603574_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137529/2/smll201603574.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137529/3/smll201603574-sup-0001-S1.pd

Ultra-Sharp Nanowire Arrays Natively Permeate, Record, and Stimulate Intracellular Activity in Neuronal and Cardiac Networks

Intracellular access with high spatiotemporal resolution can enhance our understanding of how neurons or cardiomyocytes regulate and orchestrate network activity, and how this activity can be affected with pharmacology or other interventional modalities. Nanoscale devices often employ electroporation to transiently permeate the cell membrane and record intracellular potentials, which tend to decrease rapidly to extracellular potential amplitudes with time. Here, we report innovative scalable, vertical, ultra-sharp nanowire arrays that are individually addressable to enable long-term, native recordings of intracellular potentials. We report large action potential amplitudes that are indicative of intracellular access from 3D tissue-like networks of neurons and cardiomyocytes across recording days and that do not decrease to extracellular amplitudes for the duration of the recording of several minutes. Our findings are validated with cross-sectional microscopy, pharmacology, and electrical interventions. Our experiments and simulations demonstrate that individual electrical addressability of nanowires is necessary for high-fidelity intracellular electrophysiological recordings. This study advances our understanding of and control over high-quality multi-channel intracellular recordings, and paves the way toward predictive, high-throughput, and low-cost electrophysiological drug screening platforms.Comment: Main manuscript: 33 pages, 4 figures, Supporting information: 43 pages, 27 figures, Submitted to Advanced Material

Advanced Microfabrication Technologies for Wearable Solar Energy Harvesting and Electrophysiology Monitoring Devices

Internet of Things (IoT) is becoming pervasive in our daily lives. Wearable technologies will expand the connectivity of IoT and will increase the interaction between technology and human body. Micro Electro-Mechanical Systems (MEMS) microfabrication techniques that involve bulk Si micromachining and thin film processing have allowed us to develop electronic systems that are based on Si and other advanced materials that are flexible, wearable, and implantable. Wearable and implantable electronics equipped with sensors enable us to perform real-time health monitoring from above and below the skin, respectively, and can replace conventional bulky electrophysiological monitoring devices and systems. Research efforts in wearables and implantables have intensified in the last decade tackling several aspects of the sensor technology, embedded signal processing and conditioning, energy harvesting, connectorization, functionality, longevity and reliability. However, there are still technical challenges that impose restrictions for their widespread adoption. On top of these challenges is the power source for the wearable or implantable device. Energy harvesting is expected to replace conventional battery systems that power wearables and implantables. In this dissertation, we focus on solar energy as an energy source for self-powered electronics. In Chapter 1, the motivation of the dissertation together with a brief survey of state of the art in flexible and wearable electronics with energy harvesting system and implantable medical devices are discussed. In Chapter 2, we disclose our parametric studies on solar cells with different microwire surface and array morphologies to understand the effect of surface passivation, surface crystal orientation on surface recombination and carrier collection on SiMW solar cells with radial p-n junctions as well as their emitter series resistances with an overall goal of maximizing their power conversion efficiencies. In Chapter 3, we present an approach for self-powered wearable electronics by means of the monolithic integration of SiMW solar cells with Si MOSFETs on a Silicon on Insulator (SOI) wafer that is subsequently transferred to flexible substrates. The fabrication details and its application to a voltage-controlled oscillator and electrophysiological monitoring are discussed. In Chapter 4, we discuss the details of the novel fabrication processes for the development of a stylet guided depth/laminar probe and of a surface electrocorticography (ECoG) grid that is fabricated with bio-compatible polymers (Polyimide and Parylene C) including their electrochemical characterization and their use in vivo for electrophysiological recordings in rats

Advanced Microfabrication Technologies for Wearable Solar Energy Harvesting and Electrophysiology Monitoring Devices

Internet of Things (IoT) is becoming pervasive in our daily lives. Wearable technologies will expand the connectivity of IoT and will increase the interaction between technology and human body. Micro Electro-Mechanical Systems (MEMS) microfabrication techniques that involve bulk Si micromachining and thin film processing have allowed us to develop electronic systems that are based on Si and other advanced materials that are flexible, wearable, and implantable. Wearable and implantable electronics equipped with sensors enable us to perform real-time health monitoring from above and below the skin, respectively, and can replace conventional bulky electrophysiological monitoring devices and systems. Research efforts in wearables and implantables have intensified in the last decade tackling several aspects of the sensor technology, embedded signal processing and conditioning, energy harvesting, connectorization, functionality, longevity and reliability. However, there are still technical challenges that impose restrictions for their widespread adoption. On top of these challenges is the power source for the wearable or implantable device. Energy harvesting is expected to replace conventional battery systems that power wearables and implantables. In this dissertation, we focus on solar energy as an energy source for self-powered electronics. In Chapter 1, the motivation of the dissertation together with a brief survey of state of the art in flexible and wearable electronics with energy harvesting system and implantable medical devices are discussed. In Chapter 2, we disclose our parametric studies on solar cells with different microwire surface and array morphologies to understand the effect of surface passivation, surface crystal orientation on surface recombination and carrier collection on SiMW solar cells with radial p-n junctions as well as their emitter series resistances with an overall goal of maximizing their power conversion efficiencies. In Chapter 3, we present an approach for self-powered wearable electronics by means of the monolithic integration of SiMW solar cells with Si MOSFETs on a Silicon on Insulator (SOI) wafer that is subsequently transferred to flexible substrates. The fabrication details and its application to a voltage-controlled oscillator and electrophysiological monitoring are discussed. In Chapter 4, we discuss the details of the novel fabrication processes for the development of a stylet guided depth/laminar probe and of a surface electrocorticography (ECoG) grid that is fabricated with bio-compatible polymers (Polyimide and Parylene C) including their electrochemical characterization and their use in vivo for electrophysiological recordings in rats

Multi‐Layered Triboelectric Nanogenerators with Controllable Multiple Spikes for Low‐Power Artificial Synaptic Devices

Abstract In the domains of wearable electronics, robotics, and the Internet of Things, there is a demand for devices with low power consumption and the capability of multiplex sensing, memory, and learning. Triboelectric nanogenerators (TENGs) offer remarkable versatility in this regard, particularly when integrated with synaptic transistors that mimic biological synapses. However, conventional TENGs, generating only two spikes per cycle, have limitations when used in synaptic devices requiring repetitive high‐frequency gating signals to perform various synaptic plasticity functions. Herein, a multi‐layered micropatterned TENG (M‐TENG) consisting of a polydimethylsiloxane (PDMS) film and a composite film that includes 1H,1H,2H,2H‐perfluorooctyltrichlorosilane/BaTiO3/PDMS are proposed. The M‐TENG generates multiple spikes from a single touch by utilizing separate triboelectric charges at the multiple friction layers, along with a contact/separation delay achieved by distinct spacers between layers. This configuration allows the maximum triboelectric output charge of M‐TENG to reach up to 7.52 nC, compared to 3.69 nC for a single‐layered TENG. Furthermore, by integrating M‐TENGs with an organic electrochemical transistor, the spike number multiplication property of M‐TENGs is leveraged to demonstrate an artificial synaptic device with low energy consumption. As a proof‐of‐concept application, a robotic hand is operated through continuous memory training under repeated stimulations, successfully emulating long‐term plasticity

Atomic scale analysis of the enhanced electro- and photo-catalytic activity in high-index faceted porous NiO nanowires.

Catalysts play a significant role in clean renewable hydrogen fuel generation through water splitting reaction as the surface of most semiconductors proper for water splitting has poor performance for hydrogen gas evolution. The catalytic performance strongly depends on the atomic arrangement at the surface, which necessitates the correlation of the surface structure to the catalytic activity in well-controlled catalyst surfaces. Herein, we report a novel catalytic performance of simple-synthesized porous NiO nanowires (NWs) as catalyst/co-catalyst for the hydrogen evolution reaction (HER). The correlation of catalytic activity and atomic/surface structure is investigated by detailed high resolution transmission electron microscopy (HRTEM) exhibiting a strong dependence of NiO NW photo- and electrocatalytic HER performance on the density of exposed high-index-facet (HIF) atoms, which corroborates with theoretical calculations. Significantly, the optimized porous NiO NWs offer long-term electrocatalytic stability of over one day and 45 times higher photocatalytic hydrogen production compared to commercial NiO nanoparticles. Our results open new perspectives in the search for the development of structurally stable and chemically active semiconductor-based catalysts for cost-effective and efficient hydrogen fuel production at large scale

Atomic scale analysis of the enhanced electro- and photo-catalytic activity in high-index faceted porous NiO nanowires.

Catalysts play a significant role in clean renewable hydrogen fuel generation through water splitting reaction as the surface of most semiconductors proper for water splitting has poor performance for hydrogen gas evolution. The catalytic performance strongly depends on the atomic arrangement at the surface, which necessitates the correlation of the surface structure to the catalytic activity in well-controlled catalyst surfaces. Herein, we report a novel catalytic performance of simple-synthesized porous NiO nanowires (NWs) as catalyst/co-catalyst for the hydrogen evolution reaction (HER). The correlation of catalytic activity and atomic/surface structure is investigated by detailed high resolution transmission electron microscopy (HRTEM) exhibiting a strong dependence of NiO NW photo- and electrocatalytic HER performance on the density of exposed high-index-facet (HIF) atoms, which corroborates with theoretical calculations. Significantly, the optimized porous NiO NWs offer long-term electrocatalytic stability of over one day and 45 times higher photocatalytic hydrogen production compared to commercial NiO nanoparticles. Our results open new perspectives in the search for the development of structurally stable and chemically active semiconductor-based catalysts for cost-effective and efficient hydrogen fuel production at large scale