Direct nonlinear parameter estimation method for a phase generated carrier position sensor.

Phase generated carrier (PGC) is widely applied in interferometric phase estimation for distance, vibration and velocity measurements. However, traditional PGC methods suffer from nonlinear effects, causing limitations to demodulation of signal. Modified PGC methods, such as ellipse fitting algorithm (EFA), resolves these issues, but usually requires additional phase shift. With our proposed method in this paper, only one period of signal and one test point is required to attain accurate depth of phase modulation and phase. We use a photodiode to calibrate light intensity in data acquisition, and develop a Levenburg-Marquadt algorithm to estimate values of PGC parameters. An improved algorithm is also proposed to avoid local optimization based on prior information to ensure measurement stability. Less than 5 × 10-3 rad phase measurement uncertainty and over 55 dB Signal to Noise and Distortion Ratio (SINAD) is obtained in experiment.

All layers patterned conical nanostructured thin-film silicon solar cells for light-trapping efficiency improvement.

Thin-film silicon solar cells (TSSC) has received great attention due to its advantages of low cost and eco-friendly. However, traditional single-layer patterned solar cells (SPSC) still fall short in light-trapping efficiency. This article presents an all layers patterned (ALP) conical nanostructured TSSC to enhance the low absorption caused by the thin absorption layers. The Finite-Difference Time-Domain result shows that a photocurrent density up to 41.27 mA/cm2 can be obtained for the structure, which is 31.39% higher than that of the SPSC. An electrical optimization simulation of doping concentration was carried out on the parameters of the optically optimal structure of the model. The power conversion efficiency is 17.15%, which is 1.72 times higher than that of the planar structure. These results demonstrate a success for the potential and prospect of the fully patterned nanostructures in thin-film photovoltaic devices.

Large-scale pattern transfer based on non-through-hole AAO self-supporting membranes.

Fabricating large-scale nanoarrays is a significant and challenging work in the field of nanometer devices. Anodic aluminum oxide (AAO) membrane is considered as a promising mask due to its inherent advantages such as low-cost and tunable pore diameter. However, there are few reports on the use of non-through-hole large-area AAO membrane as a mask. Due to its higher mechanical strength, non-through-hole AAO membrane has the advantage of self-supporting for large-area fabrication. Herein, we present a robust approach to transferring nanopattern to substrates with high fidelity by using the non-through-hole AAO membrane as an etching mask. A novel two-step inductively coupled plasma (ICP) etching method is adopted. The morphological evolution of the AAO during ICP etching is systematically investigated. The aspect ratio of the AAO can be quantitatively controlled by adjusting etching time. The AAO nanopore arrays with an area of 7.1 cm2 are successfully transferred to gallium nitride wafer to enhance photoluminescence. The luminous intensity of the nano-array LED with a pore diameter of 400 nm and a depth of 150 nm is improved by 3.4 times compared with the LED without the nano-array. This method extends the opportunities for AAO mask to serve as generic templates for novel applications that are previously impractical due to the difficulty of large-scale nano-pattern transfer.

Fabrication of GaN truncated nanocone array using a pre-deposited metallic nano-hemispheres template for efficient solar water splitting.

The GaN truncated nanocone is an excellent candidate for better photoelectrochemical efficiency than other GaN nanostructures. Here the highly ordered GaN truncated nanocone array was fabricated using a pre-deposited metallic nano-hemispheres template on a wafer scale. The highly ordered profiles of pre-deposited metallic nano-hemispheres template were defined by anodic aluminum oxide (AAO) masks through electron beam evaporation. The formation mechanism for the profiles of nano-hemispheres and GaN truncated nanocones were investigated. The results elucidate that proper selection of AAO parameters enables controllability of desired profiles and depth of Cr nano-hemispheres template, further controllability of desired profiles and depth of the GaN truncated nanocones. The optical and photoelectrochemical characterizations show the substantial improvements in ultraviolet light absorption and photoelectrochemical efficiency with photocurrent density by 300% times with respect to planar counterpart. The presented synthetic strategy will pave the way towards low-cost and mass production of GaN truncated nanocone photoelectrode for efficient photocatalysis.

Accurate characterization of nanoimprinted resist patterns using Mueller matrix ellipsometry.

In order to control nanoimprint lithography processes to achieve good fidelity, accurate characterization of structural parameters of nanoimprinted resist patterns is highly desirable. Among the possible techniques, optical scatterometry is relatively ideal due to its high throughput, low cost, and minimal sample damage. Compared with conventional optical scatterometry, which is usually based on reflectometry and ellipsometry and obtains at most two ellipsometric angles, Mueller matrix ellipsometry (MME) based scatterometry can provide up to 16 quantities of a 4 × 4 Mueller matrix in each measurement and can thereby acquire much more useful information about the sample. In addition, MME has different measurement accuracy in different measurement configurations. It is expected that much more accurate characterization of nanoimprinted resist patterns can be achieved by choosing appropriate measurement configurations and fully using the rich information hidden in the measured Mueller matrices. Accordingly, nanoimprinted resist patterns were characterized using an in-house developed Mueller matrix ellipsometer in this work. We have experimentally demonstrated that not only more accurate quantification of line width, line height, sidewall angle, and residual layer thickness of nanoimprinted resist patterns can be achieved, but also the residual layer thickness variation over the illumination spot can be directly determined, when performing MME measurements in the optimal configuration and meanwhile incorporating depolarization effects into the optical model. The comparison of MME-extracted imprinted resist profiles has also indicated excellent imprint pattern fidelity.

Polymer-templated electrodeposition of Ag nanosheets assemblies array as reproducible surface-enhanced Raman scattering substrate.

Position-configurable, reproducible, vertically aligned nanosheets assemblies (ANAs) arrays are fabricated by polymer-templated electrodeposition method at room temperature. Here, nanoimprint lithography is utilized to fabricate polymer template on the fluorine-doped tin oxide substrate for the purpose of evenly tuning the location of Ag nanostructures. Subsequently, vertically aligned ANAs can be achieved at the bottom of each hole via electrodeposition in a mixed aqueous solution of AgNO3 and citric acid. To obtain uniform ANAs array, we have systematically investigated the factors that influenced the electrodeposition. It was found that the formation of uniform ANAs arrays is strongly depended on the seeding layer, citric acid concentration, electrodeposition potential and time. The as-synthesized ANAs array exhibited a remarkable SERS activity and Raman signal reproducibility to rhodamine 6G, a concentration down to 10(-13) M can be identified. Our results revealed that the ANAs array is a highly desirable candidate as the reliable enhancer for high performance SERS analysis.

Self-assembly of Au nanocrystals into large-area 3-D ordered flexible superlattice nanostructures arrays for ultrasensitive trace multi-hazard detection.

Plasmonic nanoparticles that self-assemble into highly ordered superlattice nanostructures hold substantial promise for facilitating ultra-trace surface-enhanced Raman scattering (SERS) detection. Herein, we propose a boiling-point evaporation method to synthesize ordered monocrystal-like superlattice Au nanostructures (OML-Au NTs) with a polyhedral morphology. Combined with thermal nanoimprint technology, OML-Au NTs were directly transferred to impact-resistant polystyrene (IPS) flexible SERS substrates, the obtained flexible substrates (donated as OML-Au NTs/IPS) detection limit for R6G molecules as low as 10-13 M. These results were confirmed by simulating the electromagnetic field distribution of ordered/unordered two-dimensional single-layer and three-dimensional aggregated gold nanostructures. The OML-Au NTs/IPS substrates were successfully used to detect and quantify three commonly-used agricultural pesticides, achieving detection limits as low as 10-11 M and 10-12 M, and in situ real-time detection limit reached 0.24 pg/cm2 for thiram on apple peels, which was 3 orders of magnitude lower than the current detection limit. In addition, the Raman intensity from multiple locations showed a relative standard deviation lower than 7 %, exhibiting the reliability necessary for practical applications. As a result, this research demonstrates a highly reproducible method to enable the development of plasmonic nanomaterials with flexible superstructures.

High Anti-Reflection Large-Scale Cup-Shaped Nano-Pillar Arrays via Thin Film Anodic Aluminum Oxide Replication.

Surface anti-reflection (AR) with nanometer-scaled texture has shown excellent light trapping performance involving optical devices. In this work, we developed a simple and lithography-free structure replication process to obtain large scale surface cup-shaped nano-pillar (CSNP) arrays for the first time. A method of depositing was used for pattern transfer based on PMMA pre-coated through-hole anodic aluminum oxide (AAO) thin film (~500 nm), and eventually, the uniformity of the transferred nanostructures was guaranteed. From the spectrum (250 nm~2000 nm) dependent measurements, the CSNP nanostructured Si showed excellent AR performance when compared with that of the single-polished Si. Moreover, the CSNP was found to be polarization insensitive and less dependent on incidence angles (≤80°) over the whole spectrum. To further prove the excellent antireflective properties of the CSNP structure, thin film solar cell models were built and studied. The maximum value of Jph for CSNP solar cells shows obvious improvement comparing with that of the cylinder, cone and parabola structured ones. Specifically, in comparison with the optimized Si3N4 thin film solar cell, an increment of 54.64% has been achieved for the CSNP thin film solar cell.

Stable Resistive Switching in ZnO/PVA:MoS2 Bilayer Memristor.

Reliability of nonvolatile resistive switching devices is the key point for practical applications of next-generation nonvolatile memories. Nowadays, nanostructured organic/inorganic heterojunction composites have gained wide attention due to their application potential in terms of large scalability and low-cost fabrication technique. In this study, the interaction between polyvinyl alcohol (PVA) and two-dimensional material molybdenum disulfide (MoS2) with different mixing ratios was investigated. The result confirms that the optimal ratio of PVA:MoS2 is 4:1, which presents an excellent resistive switching behavior. Moreover, we propose a resistive switching model of Ag/ZnO/PVA:MoS2/ITO bilayer structure, which inserts the ZnO as the protective layer between the electrode and the composite film. Compared with the device without ZnO layer structure, the resistive switching performance of Ag/ZnO/PVA:MoS2/ITO was improved greatly. Furthermore, a large resistive memory window up to 104 was observed in the Ag/ZnO/PVA:MoS2/ITO device, which enhanced at least three orders of magnitude more than the Ag/PVA:MoS2/ITO device. The proposed nanostructured Ag/ZnO/PVA:MoS2/ITO device has shown great application potential for the nonvolatile multilevel data storage memory.

Highly Phosphatized Magnetic Catalyst with Electron Transfer Induced by Quaternary Synergy for Efficient Dehydrogenation of Ammonia Borane.

Exploitation of high-efficiency and low-cost catalysts for dehydrogenation of the ideal hydrogen storage material (ammonia borane) can effectively promote the development of hydrogen economy. Here, we report an efficient and economical non-noble-metal magnetic catalyst (Ni0.23Co0.19P0.58@NHPC900) with nanoparticles uniformly distributed on MOF-derived (metal-organic framework) nitrogen-doped hierarchical porous carbon (NHPC900) by a one-step in situ synthesis method. The catalyst has achieved a superior initial total turnover frequency (TOF) of 125.2 molH2·molcat-1·min-1. Based on isotopic analyses and ion effects, we further obtain an unprecedentedly higher TOF of 282.4 molH2·molcat-1·min-1, the highest among non-noble-metal heterogeneous systems. Through experiments and theoretical studies, we confirm that the highly doped phosphorus component leads to a C-P-Ni-Co quaternary synergy in the catalyst. Then, the induced strong electron transfer and increased partial charge can reduce the reaction energy barrier, strengthen the adsorption of ammonia borane, and ultimately result in superior catalytic performance. The proposed mechanisms and strategies are helpful to develop non-noble-metal catalysts for practical applications of hydrogen energy systems in the future.

Experimental dataset of nanoporous GaN photoelectrode supported on patterned sapphire substrates for photoelectrochemical water splitting.

GaN is one of the most promising materials for high PEC efficiency to produce clean, renewable hydrogen in an ecofriendly manner (Ebaid et al., 2015; Kamimura et al., 2017; Yang et al., 2018; Ohkawa et al., 2013). Trough assays of nanoporous gallium nitride (GaN) photoelectrode, we recently demonstrated an improved PEC efficiency and photocurrent density of nanoporous GaN photoelectrode by 470% times with respect to planar counterpart (Li et al., 2019). Here, we report original data acquired under UV-visible spectrometer, X-ray diffraction (XRD), room temperature PL measurements and PEC measurements, based on the characterization of different sapphire substrate, different GaN samples and different GaN photoelectrodes. The optical properties and photoelectrochemical properties of the corresponding samples and possible mechanisms are presented, which is freely available (Li et al., 2019). The data can be valuable for researchers interested in photoelectrochemical water splitting, as well as to researchers developing fabrication of nanoporous photoelectrode. For more insight please see the research article "A nanoporous GaN photoelectrode on patterned sapphire substrates for high-efficiency photoelectrochemical water splitting", https://doi.org/10.1016/j.jallcom.2019.06.234.

Electrokinetic Supercapacitor for Simultaneous Harvesting and Storage of Mechanical Energy.

Energy harvesting and storage are two distinct processes that are generally achieved using two separated parts based on different physical and chemical principles. Here we report a self-charging electrokinetic supercapacitor that directly couples the energy harvesting and storage processes into one device. The device consists of two identical carbon nanotube/titanium electrodes, separated by a piece of anodic aluminum oxide nanochannels membrane. Pressure-driven electrolyte flow through the nanochannels generates streaming potential, which can be used to charge the capacitive electrodes, accomplishing simultaneous energy generation and storage. The device stores electric charge density of 0.4 mC cm-2 after fully charging under pressure of 2.5 bar. This work may offer a train of thought for the development of a new type of energy unit for self-powered systems.

Direct Tailoring the Si Substrate for Antireflection via Random Nanohole Nanoimprint.

In this paper, a 2 inch random nanohole Si template with hole diameter of 36-97 nm is employed for direct tailoring the Si substrate for antireflection. The random nanohole Si template is fabricated from the natural self-organization process and can be used repeatedly in nanoimprint lithography (NIL). The surface roughness induced from the nanohole structured surface enhanced the antiadhesion property (contact angle of 128°) of the Si template for high accuracy soft mold replication. The random nanohole structured polymer/Si substrate has a surface fluctuation of ~3 nm, which ensures a uniform and effective pattern transfer from resist to substrate. The reflectivity of the random nanohole structured Si substrate decreases from around 34% to less than 5% with the hole aspect ratio within 3.0 in the wavelength region of 400-800 nm. This method is simple, cheap, repeatable in large area and compatible with the high volume production lines.

Memristor-integrated voltage-stabilizing supercapacitor system.

Voltage-stabilized supercapacitors: A single supercapacitor formed with PCBM/Pt/IPS nanorod-array electrodes is designed and delivers enhanced areal capacitance, capacitance retention, and excellent electrical stability under bending, while a significant voltage-decrease is observed during the discharging process. Once integrated with the memristor, the memristor-integrated supercapacitor systems deliver an extremely low voltage-drop, indicating greatly enhanced voltage-stabilizing features.