Electron beam lithography-assisted fabrication of Au nano-dot array as a substrate of a correlated AFM and confocal Raman spectroscopy

This paper documents a study of an Au nano-dot array that was fabricated by electron beam lithography on a glass wafer. The patterns that had features of 100nm dots in diameter with a 2-mum pitch comprised a total area of 200x200mum(2). The dot-shaped Cr underlayer was open to the air after developing Poly(methyl methacrylate) (PMMA). When dipped into the Cr etchant, the exposed Cr layer was eliminated from the glass wafer in a short period of time. In order to ultimately fabricate the Ti/Au dot arrays, Ti and Au were deposited onto the arrays with a thickness of 2 and 40nm, respectively. The lift-off procedure was carried out in the Cr etchant using sonication in order to completely remove the residual Cr/PMMA layer. The fabricated Au nano-dot array was then immersed in an Ag enhancing solution and then into an ethanol solution containing (N-(6-(Biotinamido)hexyl)-3'-(2'-pyridyldithio)-propionamide (Biotin-HPDP). The substrate was analyzed using a correlated atomic force microscopy (AFM) and confocal Raman spectroscopy. Through this procedure, position-dependent surface-enhanced Raman spectroscopy (SERS) signals could be obtained.     

Effect of deposition temperature on dielectric properties of PECVD Ta2O5 thin film

Tantalum oxide film formation by plasma-enhanced chemical vapour deposition (PECVD) using TaCl₅ as a source material was examined. The effects of deposition temperature on the formation, structure and electric properties of the Ta₂O₅ film were investigated for Al/Ta₂O₅/ p-Si (MTS) capacitors. The deposition rate and refractive index increased with increasing deposition temperature. It was found that the structure of Ta₂O₅ deposited by PECVD was amorphous as-deposited. However, crystalline -Ta₂O₅ of hexagonal structure was formed by a 700 °C, 1 h heat treatment in argon. Capacitance and relative dielectric constant of the PECVD Ta₂O₅ were found to be 2.54 fF m^–2 and 23.5, respectively. The PECVD films obtained in this study have higher dielectric constants and remarkably better general film characteristics than those obtained by other deposition methods.     

Preparation of PbTiO3 thin films using an alkoxide-alkanolamine sol-gel system

The stable range of PbTiO₃ sol and the processing conditions of uniform thin films were investigated using a solution of titanium isopropoxide, three kinds of alkanolamines (monoethanolamine, diethanolamine, triethanolamine), lead acetate trihydrate and isopropanol. Depending on the sol state with various alkanolamine/alkoxide molar ratios, diethanolamine (DEA) was very effective in preparing uniform and dense oxide films through room-temperature reaction, owing to its superior stability during the hydrolysis and condensation reaction. Perovskite PbTiO₃ thin films were obtained on oxidized silicon wafer above 550 °C and completely pure films were obtained at 650 °C using DEA as a complexing agent. The dielectric constant and loss tangent of these thin films fired at 650 °C for 30 min were found to be 240 and 0.01 at 1 kHz, respectively.     

Correlated Quantum Phenomena of Spin–Orbit Coupled Perovskite Oxide Heterostructures: Cases of SrRuO3 and SrIrO3 Based Artificial Superlattices

Unexpected, yet useful functionalities emerge when two or more materials merge coherently. Artificial oxide superlattices realize atomic and crystal structures that are not available in nature, thus providing controllable correlated quantum phenomena. This review focuses on 4d and 5d perovskite oxide superlattices, in which the spin–orbit coupling plays a significant role compared with conventional 3d oxide superlattices. Modulations in crystal structures with octahedral distortion, phonon engineering, electronic structures, spin orderings, and dimensionality control are discussed for 4d oxide superlattices. Atomic and magnetic structures, J_eff = 1/2 pseudospin and charge fluctuations, and the integration of topology and correlation are discussed for 5d oxide superlattices. This review provides insights into how correlated quantum phenomena arise from the deliberate design of superlattice structures that give birth to novel functionalities.     

Rational Design and Synthesis of Extremely Efficient Macroporous CoSe2–CNT Composite Microspheres for Hydrogen Evolution Reaction

Uniquely structured CoSe₂–carbon nanotube (CNT) composite microspheres with optimized morphology for the hydrogen‐evolution reaction (HER) are prepared by spray pyrolysis and subsequent selenization. The ultrafine CoSe₂ nanocrystals uniformly decorate the entire macroporous CNT backbone in CoSe₂–CNT composite microspheres. The macroporous CNT backbone strongly improves the electrocatalytic activity of CoSe₂ by improving the electrical conductivity and minimizing the growth of CoSe₂ nanocrystals during the synthesis process. In addition, the macroporous structure resulting from the CNT backbone improves the electrocatalytic activity of the CoSe₂–CNT microspheres by increasing the removal rate of generated H₂ and minimizing the polarization of the electrode during HER. The CoSe₂–CNT composite microspheres demonstrate excellent catalytic activity for HER in an acidic medium (10 mA cm^?2 at an overpotential of ≈174 mV). The bare CoSe₂ powders exhibit moderate HER activity, with an overpotential of 226 mV at 10 mA cm^?2. The Tafel slopes for the CoSe₂–CNT composite and bare CoSe₂ powders are 37.8 and 58.9 mV dec^?1, respectively. The CoSe₂–CNT composite microspheres have a slightly larger Tafel slope than that of commercial carbon‐supported platinum nanoparticles, which is 30.2 mV dec^–1.     

Broadband Light Absorption and Efficient Charge Separation Using a Light Scattering Layer with Mixed Cavities for High‐Performance Perovskite Photovoltaic Cells with Stability

CH₃NH₃PbI₃ is one of the promising light sensitizers for perovskite photovoltaic cells, but a thick layer is required to enhance light absorption in the long‐wavelength regime ranging from PbI₂ absorption edge (500 nm) to its optical band‐gap edge (780 nm) in visible light. Meanwhile, the thick perovskite layer suppresses visible‐light absorption in the short wavelengths below 500 nm and charge extraction capability of electron–hole pairs produced upon light absorption. Herein, we find that a new light scattering layer with the mixed cavities of sizes in 100 and 200 nm between transparent fluorine‐doped tin oxide and mesoporous titanium dioxide electron transport layer enables full absorption of short‐wavelength photons (λ < 500 nm) to the perovskite along with enhanced absorption of long‐wavelength photons (500 nm < λ < 780 nm). Moreover, the light‐driven electric field is proven to allow efficient charge extraction upon light absorption, thereby leading to the increased photocurrent density as well as the fill factor prompted by the slow recombination rate. Additionally, the photocurrent density of the cell with a light scattering layer of mixed cavities is stabilized due to suppressed charge accumulation. Consequently, this work provides a new route to realize broadband light harvesting of visible light for high‐performance perovskite photovoltaic cells.     

Plasmon Enhanced Fluorescence Based on Porphyrin–Peptoid Hybridized Gold Nanoparticle Platform

A porphyrin–peptoid‐hybridized silica‐coated gold nanoparticle is developed, which is inspired by the protein–chlorophyll ensemble found in photosynthetic antenna. In the natural antenna, chlorophylls are integrated into dense assemblies that are supported by frameworks of proteins, which ensure optimal pigment arrangement for effective light harvesting. In the subject platform, porphyrins are conjugated to the peptoid helix scaffold in a structurally well‐defined alignments and subsequently immobilized on the surface of nanoparticles. This prevents intermolecular aggregation among porphyrins and allows high resolution analysis of the effect of porphyrin configuration on the optical properties of the system. Interestingly, under the influence of plasmon from the gold nanoparticle core, the fluorescence of porphyrin is enhanced up to 24‐fold at the wavelength where the plasmon resonance matches the porphyrin excitation wavelength. In addition, differences in porphyrin configuration result in spectral modification of their fluorescence emissions. Particularly, the peptoid bearing two porphyrins at a distance of 6 Å shows the most significant alteration in fluorescence. The platform can facilitate extensive studies on the relationship between porphyrin arrangement design and their photophysical interaction in antenna complexes.     

Designing Metallic and Insulating Nanocrystal Heterostructures to Fabricate Highly Sensitive and Solution Processed Strain Gauges for Wearable Sensors

All‐solution processed, high‐performance wearable strain sensors are demonstrated using heterostructure nanocrystal (NC) solids. By incorporating insulating artificial atoms of CdSe quantum dot NCs into metallic artificial atoms of Au NC thin film matrix, metal–insulator heterostructures are designed. This hybrid structure results in a shift close to the percolation threshold, modifying the charge transport mechanism and enhancing sensitivity in accordance with the site percolation theory. The number of electrical pathways is also manipulated by creating nanocracks to further increase its sensitivity, inspired from the bond percolation theory. The combination of the two strategies achieves gauge factor up to 5045, the highest sensitivity recorded among NC‐based strain gauges. These strain sensors show high reliability, durability, frequency stability, and negligible hysteresis. The fundamental charge transport behavior of these NC solids is investigated and the combined site and bond percolation theory is developed to illuminate the origin of their enhanced sensitivity. Finally, all NC‐based and solution‐processed strain gauge sensor arrays are fabricated, which effectively measure the motion of each finger joint, the pulse of heart rate, and the movement of vocal cords of human. This work provides a pathway for designing low‐cost and high‐performance electronic skin or wearable devices.