Three-Dimensional Metal-Oxide Nanohelix Arrays Fabricated by Oblique Angle Deposition: Fabrication, Properties, and Applications

Three-dimensional (3D) nanostructured thin films have attracted great attention due to their novel physical, optical, and chemical properties, providing tremendous possibilities for future multifunctional systems and for exploring new physical phenomena. Among various techniques to fabricate 3D nanostructures, oblique angle deposition (OAD) is a very promising method for producing arrays of a variety of 3D nanostructures with excellent controllability, reproducibility, low cost, and compatibility with modern micro-electronic processes. This article presents a comprehensive overview of the principle of OAD, and unique structural and optical properties of OAD-fabricated thin films including excellent crystallinity, accurate tunability of refractive indices, and strong light scattering effect which can be utilized to remarkably enhance performances of various systems such as antireflection coatings, optical filters, photoelectrodes for solar-energy-harvesting cells, and sensing layers for various sensors.1114Ysciescopu

Highly stable, reactive and ultrapure nanoporous metallic films

Nanoporous metals possess unique properties attributed to their high surface area and interconnected nanoscale ligaments. They are mostly fabricated by wet synthetic methods involving solution-based dealloying processes whose purity is compromised by residual amounts of the less noble metal. Here, we demonstrate a novel dry synthesis method to produce nanoporous metals, which is based on the plasma treatment of metal nanoparticles formed by physical vapor deposition. Our approach is general and can be applied to many metals including non-noble ones. The resultant nanoporous metallic films are impurity-free and possess highly curved ligaments and nanopores. The metal films are remarkably robust with many catalytically active sites, which is highly promising for electrocatalytic applications.Comment: 40 pages (including 13 pages of supplementary information), 5 figures, submitte

Establishment of feeder-free culture system for human induced pluripotent stem cell on DAS nanocrystalline graphene

The maintenance of undifferentiated human pluripotent stem cells (hPSC) under xeno-free condition requires the use of human feeder cells or extracellular matrix (ECM) coating. However, human-derived sources may cause human pathogen contamination by viral or non-viral agents to the patients. Here we demonstrate feeder-free and xeno-free culture system for hPSC expansion using diffusion assisted synthesis-grown nanocrystalline graphene (DAS-NG), a synthetic non-biological nanomaterial which completely rule out the concern of human pathogen contamination. DAS-NG exhibited advanced biocompatibilities including surface nanoroughness, oxygen containing functional groups and hydrophilicity. hPSC cultured on DAS-NG could maintain pluripotency in vitro and in vivo, and especially cell adhesion-related gene expression profile was comparable to those of cultured on feeders, while hPSC cultured without DAS-NG differentiated spontaneously with high expression of somatic cell-enriched adhesion genes. This feeder-free and xeno-free culture method using DAS-NG will facilitate the generation of clinical-grade hPSC.ope

Gas sensing behaviors in metal-oxides-based nanoscale Schottky and hetero p-n junctions

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Highly-sensitive H2 sensor operating at room temperature using Pt/TiO2 nanoscale Schottky contacts

Despite growing demands for high performance hydrogen (H-2) sensors operating at low temperature, metal oxides-based H-2 sensors intrinsically require an elevated operating temperature due to a high activation energy for gas adsorption on metal oxides surface. Here, we present a highly-sensitive H-2 sensor operating even at room temperature, enabled by the Pt/TiO2 nanoscale Schottky contacts which utilizes sensitive modulation of the Schottky barrier height by dissociative H-2 adsorption on the catalytic Pt layer, followed by the dipole layer formation at the junction. Our device showed very high H-2 response and short response and recovery times at low temperatures which are attributed to the unique device architecture having the highly-porous nanoscale Schottky contacts facilitating the gas diffusion and dissociation, and the top-and-bottom electrodes configuration making effective current modulation. Based on our results, we propose Schottky contact-assisted H-2 sensing mechanisms and a promising approach to further improve H-2 sensing performance at room temperature. (C) 2016 Elsevier B.V. All rights reserved.1115sciescopu

Wavelength-dependent visible light response in vertically aligned nanohelical TiO2-based Schottky diodes

Enhancements in photocatalytic performance under visible light have been reported by noble metal functionalization on nanostructured TiO2; however, the non-uniform and discrete distribution of metal nanoparticles on the TiO2 surface makes it difficult to directly clarify the optical and electrical mechanisms. Here, we investigate the light absorption and the charge separation at the metal/TiO2 Schottky junctions by using a unique device architecture with an array of TiO2 nanohelixes (NHs) forming Schottky junctions both with Au-top and Pt-bottom electrodes. Wavelength-dependent photocurrent measurements through the Pt/TiO2 NHs/Au structures revealed that the origin of the visible light absorption and the separation of photogenerated carriers is the internal photoemission at the metal/nanostructured TiO2 Schottky junctions. In addition, a huge persistent photoconductivity was observed by the time-dependent photocurrent measurement, implying a long lifetime of the photogenerated carriers before recombination. We believe that the results help one to understand the role of metal functionalization on TiO2 and hence to enhance the photocatalytic efficiency by utilizing appropriately designed Schottky junctions.111sciescopu

An array of metal oxides nanoscale hetero p-n junctions toward designable and highly-selective gas sensors

Nano-helical array of p-NiO/n-SnO2 p-n junctions with well-defined and highly-gas-accessible hetero-interfaces is presented for designable and highly selective gas sensors. The gas sensor having the nanoscale p-n junction sensing layer with a top-and-bottom electrodes configuration was fabricated by conventional photolithography and oblique-angle deposition. The unique device structure enables a predominant modulation in barrier height at the hetero-interfaces, consistent with simulation results, resulting in unusual-yet-promising sensing behaviors upon H-2 and NO2 exposure. Based on our experimental and simulation results, and the ability to fabricate a variety combination of metal oxides heterostructures with a reproducible and controllable way, we believe that it becomes possible to design and realize highly-selective sensor array electronic-noses optimized towards target gases on demand. (C) 2017 Elsevier B.V. All rights reserved.112Nsciescopu

An array of metal oxides nanoscale hetero p-n junctions toward designable and highly-selective gas sensors

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Etv2- and Fli1-Induced Vascular Progenitor Cells Enhance Functional Recovery in Ischemic Vascular Disease Model-Brief Report

Objective: Vascular progenitor cells (VPCs), which are able to differentiate into both endothelial cells and smooth muscle cells, have the potential for treatment of ischemic diseases. Generated by pluripotent stem cells, VPCs carry the risk of tumorigenicity in clinical application. This issue could be resolved by direct lineage conversion, the induction of functional cells from another lineage by using only lineage-restricted transcription factors. Here, we show that induced VPCs (iVPCs) can be generated from fibroblasts by ETS (E-twenty six) transcription factors, Etv2 and Fli1. Approach and Results: Mouse fibroblasts were infected with lentivirus encoding Etv2 and Fli1. Cell colonies appeared in Fli1- and Etv2/Fli1-infected groups and were mechanically picked. The identity of cell colonies was confirmed by proliferation assay and reverse-transcription polymerase chain reaction with vascular markers. Etv2/Fli1- infected cell colonies were sorted by CD144 (also known as CDH5, VE-cadherin). We defined that CD144-positive iVPCs maintained its own population and expanded stably at multiple passages. iVPCs could differentiate into functional endothelial cells and smooth muscle cells by a defined medium. The functionalities of iVPC-derived endothelial cells and smooth muscle cells were confirmed by analyzing LDL (low-density lipoprotein) uptake, carbachol-induced contraction, and tube formation in vitro. Transplantation of iVPCs into the ischemic hindlimb model enhanced blood flow without tumor formation in vivo. Human iVPCs were generated by human ETS transcription factors ETV2 and FLI1. Conclusions: We demonstrate that ischemic disease curable iVPCs, which have self-renewal and bipotency, can be generated from mouse fibroblasts by enforced ETS family transcription factors, Etv2 and Fli1 expression. Our simple strategy opens insights into stem cell-based ischemic disease therapy