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Tantalum nitride (Ta3N5) is a visible-light-responsive semiconductor that may be capable of achieving the 10% solar-to-hydrogen (STH) efficiency required to allow the commercialization of water splitting systems. However, despite immense research efforts, the highest STH efficiency yet reported for photoanodes based on Ta3N5-nanorods (NRs) is only 2.7%. Therefore, it is imperative to build a theoretical foundation that explains the various loss mechanisms and their correlations with structural and material properties, so as to optimize the performance of this material. The present work devised a detailed numerical model based on an in-depth analysis of the performance characteristics of photoanodes made from either Ba-doped or undoped Ta3N5-NRs. This experimentally calibrated optoelectrical modelling enabled predictions of various factors related to performance loss, including optical effects, charge carrier recombination and resistive loss. Certain physical parameters, such as charge carrier lifetime, diffusion length, hole extraction rate from the NR surfaces to the electrolyte and the series resistance of the photoanode, could also be calculated. The results show that the enhanced performance obtained with Ba doping can be primarily attributed to increases in the carrier lifetime and diffusion length. The present model was recalibrated using experimental data from the literature to examine hidden effects of the NRs’ dimensions on optical and recombination losses. On this basis, various design principles are presented herein that should allow the fabrication of efficient Ta3N5-NRs photoanodes for commercial STH production.

Heterostructure-based photoanodes have been investigated to enhance light absorption and promote the generation and extraction of charge carriers for efficient solar-to-hydrogen energy conversion. ...

In the field of micro/nanofluidics, the channel open/close valves are among the most important technologies for switching and partitioning actions and integration of various operations into fluidic circuits. While several types of valves have been developed in microfluidics, few are capable in nanofluidics. In this study, we proposed a femtoliter (fL) volume nanochannel open/close valve fabricated in glass substrates. The valve consists of a shallow, circular and stepped-bottom valve chamber connected to nanochannels and an actuator. Even with tiny deformation occurring at the nanolevel in glass, an open/closed state of a nanochannel (10-1000 nm) can be achieved. We designed a fL-valve based on an analytical material deformation model, and developed a valve fabrication process. We then verified the open/closed state of the valve using a 308 fL-valve chamber with a four-stepped nanostructure fitting an arc-shape of deflected glass, confirmed its stability and durability over 50 open/close operations, and succeeded in stopping/flowing an aqueous solution at 209 fL s-1 under a 100 kPa pressure in a 900 nm nanochannel with a fast response of ∼0.65 s. A leak flow from the closed valve was sufficiently small even at a 490 kPa pressure-driven flow. Since the developed fL-valve can be applied to various nanofluidic devices made of glass and other rigid materials such as plastic, it is expected that this work will contribute significantly to the development of novel integrated micro/nanofluidics chemical systems for use in various applications, such as single cell/single molecule analysis.

Photocatalytic splitting of water under solar light has proved itself to be a promising approach toward the utilization of solar energy and the generation of environmentally friendly fuel in a form of hydrogen. In this work, we demonstrate highly efficient solar-to-hydrogen conversion efficiency of 7.7% by photovoltaic–photoelectrochemical (PV–PEC) device based on hybrid MAPbI3 perovskite PV cell and WO3/BiVO4 core–shell nanorods PEC cell tandem that utilizes spectral splitting approach. Although BiVO4 is characterized by intrinsically high recombination rate of photogenerated carriers, this is not an issue for WO3/BiVO4 core–shell nanorods, where highly conductive WO3 cores are combined with extremely thin absorber BiVO4 shell layer. Since the BiVO4 layer is thinner than the characteristic carrier diffusion length, the photogenerated charge carriers are separated at the WO3/BiVO4 heterojunction before their recombination. Also, such architecture provides sufficient optical thickness even for extremely thin BiVO4 layer due to efficient light trapping in the core–shell WO3/BiVO4 nanorods with high aspect ratio. We also demonstrate that the concept of fill factor can be used to compare I–V characteristics of different photoanodes regarding their optimization for PV/PEC tandem devices.

The next-generation cooling devices are gradually being scaled to smaller than the size of high-performance microchips to enable local heat removal from small hot spots. Realization of a micro/nanofluidic heat pipe device is a challenging task, as it requires high condensation efficiency in an ultra-small space and sufficient liquid transport without employing any wick. Herein, we demonstrate a two-phase loop micro heat pipe device based on unique liquid properties in extended nanospace (10–1000 nm) to meet the growing demands of the miniaturization of electronics and optoelectronics. The device, which contains a small volume of liquid (tens of nanoliter) and does not require a wick, can be conveniently embedded in the microchip. The capillary condensation of water on nanopillars was investigated. The experimental results showed a significant enhancement of the condensation rate on nanopillars for a faster vapor–liquid phase transition. In addition, a streaming potential measurement was performed to evaluate the liquid transport during operation of the micro heat pipe device. This method enables the measurement of water flow rates through extended nanochannels without requiring probe molecules. The micro heat pipe device was verified to work properly. Finally, the cooling performance of the micro heat pipe device was quantitatively estimated, and improvements were proposed to achieve highly efficient cooling.

We have developed dry etching process of lithium niobate (LN) wafer using neutral loop discharge reactive ion etching (NLD-RIE) to fabricate both micro- and nano-channels for investigating proton diffusion enhancement in ferroelectric nanochannels. We have also developed low-temperature direct bonding process between LN wafers. Two-hundred parallel nanochannel array of 200-nm deep and wide and 400-μm long connected to two microchannels (width: 500 μm, depth: 5.9 μm) at the both ends were fabricated. We have succeeded in measuring the proton diffusion coefficient as high as 1.2×10−8 m2/s.

Autonomous micro/nano mechanical, chemical and biomedical sensors require persistent power sources scaled to their size. Realization of autonomous micro-power sources is a challenging task, as it requires combination of wireless energy supply, conversion, storage and delivery to the sensor. In this work, we realized solar light driven power source that consists of a micro fuel cell (μFC) and a photocatalytic micro fuel generator (μFG) integrated on a single microfluidic chip. The μFG produces hydrogen by photocatalytic water splitting under solar light. The hydrogen is then consumed by the μFC to generate electricity. Importantly, the byproduct water returns back to the photocatalytic μFG via recirculation loop without losses. Functionality of both devices relies on novel phenomena in extended-nano fluidic channels that ensure ultra-fast proton transport. As a proof of concept, we demonstrate that μFG/μFC source achieves remarkable energy density of ~17.2 mWh cm-2 at room temperature.

Nanostructured photoanodes based on well-separated and vertically oriented WO3 nanorods capped with extremely thin BiVO4 absorber layers are fabricated by the combination of Glancing Angle Deposition and normal physical sputtering techniques. The optimized WO3 -NRs/BiVO4 photoanode modified with Co-Pi oxygen evolution co-catalyst shows remarkably stable photocurrents of 3.2 and 5.1 mA/cm(2) at 1.23 V versus a reversible hydrogen electrode in a stable Na2 SO4 electrolyte under simulated solar light at the standard 1 Sun and concentrated 2 Suns illumination, respectively. The photocurrent enhancement is attributed to the faster charge separation in the electronically thin BiVO4 layer and significantly reduced charge recombination. The enhanced light trapping in the nanostructured WO3 -NRs/BiVO4 photoanode effectively increases the optical thickness of the BiVO4 layer and results in efficient absorption of the incident light.

Organic molecular dots were successfully produced by means of a nano second pulsed dye laser on glass and indium tin oxide (ITO) substrates, with sizes of several hundred nanometres. The method involves the transfer of organic molecules from the source Coumarin 6 (C6) and poly [2-methoxy, 5-(2′-ethyl-hexyloxy)-p-phenylene-venylene] (MEH-PPV) films onto a target material through a water filled space-gap using a laser induced molecular jet (LIMJ). In this way, the organic dots of Coumarin 6 and MEH-PPV molecules were successfully implanted onto the glass and ITO targets. The present results demonstrate the possibility to significantly improve photo electronic or photoelectric devices such as novel photonic crystal and molecular device sensors, and so on.

Efficient photocatalytic water splitting requires effective generation, separation and transfer of photo-induced charge carriers that can hardly be achieved simultaneously in a single material. Here we show that the effectiveness of each process can be separately maximized in a nanostructured heterojunction with extremely thin absorber layer. We demonstrate this concept on WO3/BiVO4+CoPi core-shell nanostructured photoanode that achieves near theoretical water splitting efficiency. BiVO4 is characterized by a high recombination rate of photogenerated carriers that have much shorter diffusion length than the thickness required for sufficient light absorption. This issue can be resolved by the combination of BiVO4 with more conductive WO3 nanorods in a form of core-shell heterojunction, where the BiVO4 absorber layer is thinner than the carrier diffusion length while it’s optical thickness is reestablished by light trapping in high aspect ratio nanostructures. Our photoanode demonstrates ultimate water splitting photocurrent of 6.72 mA cm−2 under 1 sun illumination at 1.23 VRHE that corresponds to ~90% of the theoretically possible value for BiVO4. We also demonstrate a self-biased operation of the photoanode in tandem with a double-junction GaAs/InGaAsP photovoltaic cell with stable water splitting photocurrent of 6.56 mA cm−2 that corresponds to the solar to hydrogen generation efficiency of 8.1%.

Perylene molecules have been successfully implanted onto borosilicate glass plates, forming fluorescent features of 420 nm in diameter, using a method involving laser induced molecular micro-jet ejection through a water layer. The technique utilises a polymer source film in which perylene molecules are dispersed, a borosilicate glass substrate as a target and a pulsed laser. The space gap between the source film and the target is filled with liquid water. Perylene molecules dispersed in the polymer source films are photo-excited using 4-ns laser pulses resulting in the ejection of the molecules from the source matrix after which they become implanted into the target after passing through the water layer. This new advanced implantation method, using a laser induced molecular micro-jet through water, gives fine spatial control for fixing functional organic molecules in a designated region on hard dielectric materials and will have application in the fabrication of molecular devices, molecular sensors, and opto-electronics.

A simple method for silicon microfabrication has been successfully developed. Polypropylene (PP) film as a resist was prepared on a surface of silicon (Si) (1 0 0) plate by an rf magnetron sputtering method. A pulsed laser light was focused and irradiated to the PP film and a part of the film was removed by laser ablation process in the spot at certain laser intensity. When the sample was immersed in a potassium hydroxide solution, etching occurred only at the part that the PP film was removed by laser ablation. These results raise the possibility of this method as a process for Si microfabrication.

Laser induced molecular implantation technique (LIMIT) has been used for site-controlled fabrication of pixel arrays of organic light-emitting diodes in a form of dots with a diameter of several micrometers. N,N'-Bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) dots, which were implanted into the poly(3,4-ethylene dioxythiophene)–poly(styrene sulphonate) (PEDOT–PSS) layer, act as recombination centers between the hole- and electron-transport layers in the indium tin oxide (ITO)/PEDOT–PSS/TPDdots/tris(8-hydroxyquinoline) aluminum (Alq3)/Mg–Ag sandwich structure, and illuminate intense green light. We studied fluorescence spectra of the implanted TPD dots and the dependence of their size and morphology on the intensity of a laser pulse, as well as the electroluminescence resulted from the organic light-emitting device (OLED) arrays. The site-controlled fabrication of such small OLEDs opens up an opportunity for production of electroluminescent devices with ultrahigh resolution.

We demonstrated highly efficient solar hydrogen generation via water splitting by photovoltaic–photoelectrochemical (PV–PEC) tandem device based on GaAs/InGaAsP (PV cell) and WO3/BiVO4 core/shell nanorods (PEC cell). We utilized extremely thin absorber (ETA) concept to design the WO3/BiVO4 core/shell heterojunction nanorods and obtained the highest efficiencies of generation, separation and transfer of the photo-induced charge carriers that are possible for the WO3/BiVO4 material combination. The PV–PEC tandem shows stable water splitting photocurrent of 6.56 mA·cm−2 under standard AM1.5G solar light that corresponds to the record solar-to-hydrogen (STH) conversion efficiency of 8.1%.

Here we report a way to induce the visible response of non-doped TiO2 in the photocatalytic electrochemical water splitting, which is achieved by utilizing the optical near-field (ONF) generated on nanorod TiO2. The visible response is attributed to the ONF-induced phonon-assisted excitation process, in which TiO2 is excited by sub-bandgap photons via phonon energy. Our approach directly gets involved in the excitation process without chemical modification of materials; accordingly it is expected to have few drawbacks on the photocatalytic performance. This study may offer another perspective on the development of solar harvesting materials.