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Optically excited plasmonic nanostructures exhibit unique capabilities to catalyze interfacial chemical transformations of molecules adsorbed on their surfaces in a regioselective manner through anomalous reaction pathways that are inaccessible under thermal conditions. The mechanistic complexity of plasmon-driven photocatalysis is intimately tied to a series of photophysical and photochemical processes associated with the radiative and non-radiative decay of localized plasmon resonances in metallic nanostructures. Plasmon-enhanced Raman spectroscopy combines ultrahigh detection sensitivity with unique time-resolving and molecular finger-printing capabilities, ideal for detailed kinetic and mechanistic studies of photocatalytic interfacial transformations of molecular adsorbates residing in the plasmonic hot spots. Through systematic case studies of several representative reactions, we demonstrate how plasmon-enhanced Raman spectroscopy can be judiciously utilized as a unique in situ spectroscopic tool to fine-resolve the detailed molecule-transforming processes on the surfaces of optically excited plasmonic nanostructures in real time during the photocatalytic reactions. We further epitomize the mechanistic insights gained from in situ plasmon-enhanced Raman spectroscopic measurements into several central materials design principles that can be employed to guide the rational optimization of the photocatalyst structures and the nanostructure-molecule interfaces for plasmon-mediated surface chemistry.

Although the intriguing plasmonic properties of noble metal nanoparticles originate from the collective oscillations of free electrons in the conduction band, nanoparticles of doped semiconductors may also exhibit metal-like, plasmonic features that are dictated by the resonantly excited free hole oscillations in the valence band. Here, we combine Au, a representative free electron metal, with copper sulfides, a class of plasmonic p-type semiconductors, in a core-shell nanoparticle geometry to construct dual-plasmonic hetero-nanostructures displaying unique multiplex optical characteristics dominated by plasmonic hole oscillations in the semiconductor shells, plasmonic electron oscillations in the metallic cores, and interband electronic transitions from the valence to conduction bands. Through deliberately designed colloidal synthesis, we are able to selectively grow nanoshells comprising copper sulfides of specifically targeted crystalline phases and Cu/S stoichiometries, such as covellite (CuS), digenite (Cu1.8S), and nonstoichiometric Cu2-xS, on the surfaces of Au nanoparticle cores. Our synthetic approach enables us not only to finely control the core and shell dimensions but also to systematically adjust the free hole concentrations in the semiconductor shells, which forms the keystone for the fine tuning of multiple optical resonance modes supported by these hybrid hetero-nanostructures. The dual-plasmonic Au@copper sulfide core-shell nanoparticles exhibit unique multimodal photothermal and photocatalytic behaviors upon selective photoexcitations of different optical transitions at their characteristic resonant frequencies, allowing us to quantitatively evaluate and rigorously compare the intrinsic photothermal and photocatalytic efficacies of multiple types of hot charge carriers, all photoexcited in the same hybrid nanoparticles but with distinct photophysical origins, excited-state lifetimes, energy distributions, and transfer pathways.

Raman spectroscopy was used to establish direct evidence of heterometallic metal centers in a metal-organic framework (MOF). The Cu3(BTC)2 MOF HKUST-1 (BTC3- = benzenetricarboxylate) was transmetalated by heating it in a solution of RhCl3 to substitute Rh2+ ions for Cu2+ ions in the dinuclear paddlewheel nodes of the framework. In addition to the Cu-Cu and Rh-Rh stretching modes, Raman spectra of (CuxRh1-x)3(BTC)2 show the Cu-Rh stretching mode, indicating that mixed-metal Cu-Rh nodes are formed after transmetalation. Density functional theory studies confirmed the assignment of a Raman peak at 285 cm-1 to the Cu-Rh stretching vibration. Electron paramagnetic resonance spectroscopy experiments further supported the conclusion that Rh2+ ions are substituted into the paddlewheel nodes of Cu3(BTC)2 to form an isostructural heterometallic MOF, and electron microscopy studies showed that Rh and Cu are homogeneously distributed in (CuxRh1-x)3(BTC)2 on the nanoscale.

The design of improved materials for orthopedic implants and bone tissue engineering scaffolds relies on materials mimicking the properties of bone. Calcium phosphate (Ca-PO4)-mineralized collagen fibrils arranged in a characteristic hierarchical structure constitute the building blocks of mineralized vertebrate tissues and control their biomechanical and biochemical properties. Large, flexible, acidic noncollagenous proteins (ANCPs) have been shown to influence collagen mineralization but little is known about mineralization mechanisms with the aid of small proteins. Osteocalcin (OCN) is a small, highly structured biomolecule known as a multifunctional hormone in its undercarboxylated form. Here, we examined the potential mechanism of collagen intrafibrillar mineralization in vitro mediated by OCN as a model protein. Rapid and random extrafibrillar mineralization of flakey Ca-PO4 particles was observed by transmission electron microscopy mainly on the outer surfaces of collagen fibrils of a preformed collagen scaffold in the absence of the protein. In contrast, the protein stabilized hydrated, spherical nanoclusters of Ca-PO4 on the outer surface of the fibrils, thereby retarding extrafibrillar mineralization. The nanoclusters then infiltrated the fibrils resulting in intrafibrillar mineralization with HAP crystals aligned with the fibrils. This mechanism is similar to that observed for unstructured ANCPs. Results of fibrillogenesis and immunogold labeling studies showed that OCN was associated primarily with the fibrils, consistent with ex vivo studies on mineralizing turkey tendon. The present findings contribute to expanding our understanding of collagen intrafibrillar mineralization and provide insight into design synthetic macromolecular matrices for orthopedic implants and bone regeneration.

Hydroxyapatite (HAP) is an extensively used orthopedic biomaterial because of its high biocompatibility and osteoconductivity. Implant-related infection is a major cause of orthopedic device failure. Previous research showed that silver-doped hydroxyapatite nanoparticles (Ag-HAP NPs) have prominent antimicrobial activity, but their biocompatibility and plasma protein response remained unexplored. Here we investigated the effects of synthesis conditions on Ag-HAP NP antimicrobial (

Nanostructured surfaces are known to provide excellent optical properties for various photonics devices. Fabrication of such nanoscale structures to germanium (Ge) surfaces by metal assisted chemical etching (MACE) is, however, challenging as Ge surface is highly reactive resulting often in micron-level rather than nanoscale structures. Here we show that by properly controlling the process, it is possible to confine the chemical reaction only to the vicinity of the metal nanoparticles and obtain nanostructures also in Ge. Furthermore, it is shown that controlling the density of the nanoparticles, concentration of oxidizing and dissolving agents as well as the etching time plays a crucial role in successful nanostructure formation. We also discuss the impact of high mobility of charge carriers on the chemical reactions taking place on Ge surfaces. As a result we propose a simple one-step MACE process that results in nanoscale structures with less than 10% surface reflectance in the wavelength region between 400 nm and 1600 nm. The method consumes only a small amount of Ge and is thus industrially viable and also applicable to thin Ge layers., Comment: 8 pages, 4 figures. Full citation details and link to manuscript published in Nanotechnology were added

Silicon solar cells are known to suffer from poor UV response because of high reflectance combined with recombination at the front side of the cell - including heavily doped emitter. While black silicon (b-Si) has proven to be excellent technology to overcome the reflectance losses, it has been challenging to integrate it to PERC cells with recombination-free emitter without compromising the optical properties. Here we show that no such tradeoffs are needed when using boron emitter with proper surface passivation. We demonstrate a b-Si emitter that has saturation current as low as 33 fA/cm2 resulting close to 100% EQE even down to 300 nm. This result should be interesting for the PV industry looking for further improvements in their current products.

Alkali solutions are not suitable for texturing multi-crystalline silicon (mc-Si) wafer due to the anisotropic etching. In this study, a two-step alkali-etch process is developed to form a flat surface on the wafer, which can be quickly and nearly isotropically etched by immersion in a sodium hydroxide solution, followed by a sodium hydroxide-sodium hypochlorite solution. The etching process leads to the formation of homogenous nanostructure, thereby improving the cell's repeatability and performance by simultaneously increasing its short-circuit current and open-circuit voltage.

Metal-assisted chemical etching (MACE) enables efficient texturing of diamond-wire sawn multicrystalline silicon (mc-Si) wafers. However, the excellent optics are often sacrificed by polishing the surface to achieve better surface passivation with chemical-vapor-deposited (CVD) silicon nitride (SiNx). In this work, we show that a polishing step is not required when CVD SiNx is replaced with atomic-layer-deposited (ALD) aluminum oxide (Al2O3). Indeed, while polishing increases reflectance, it has in general only very modest effect on surface recombination velocity of ALD-passivated b-Si. Furthermore, since ALD Al2O3 is compatible with various surface morphologies due to its excellent conformality, the MACE parameters can be more freely adjusted. First, the concentration of silver nitrate (AgNO3) in AgNO3/H2O solution that is used to deposit Ag nanoparticles is shown to affect the final b-Si morphology. Instead of needle-shaped b-Si produced by 5 mmol/L AgNO3 concentration, two orders of magnitude lower AgNO3 concentration produces porous structures, which are more challenging to passivate. Additionally, we demonstrate that a separate Ag nanoparticle removal step in nitric acid (HNO3) is not a prerequisite for high carrier lifetime. Instead, Ag nanoparticles present during polishing in a HF/HNO3/H2O solution affect the final b-Si morphology by accelerating the etching of Si. The results demonstrate that no trade-offs are necessary between optical and electrical properties of MACE b-Si when using ALD.

International audience; MACE nano-texture process applicable for both single-and multi-crystalline diamond-wire sawn Si solar cells. ABSTRACT The photovoltaic (PV) industry requires efficient cutting of large single and multi-crystalline (sc-and mc-) silicon (Si) wafers. Historically multi-wire slurry sawing (MWSS) dominated, but the higher productivity of diamond-wire-sawing (DWS) holds promise for decreasing PV costs in the future. While surface texturing of DWS wafers is more complicated than of MWSS wafers, especially in mc-Si wafers, nanotexturing has been shown to overcome this challenge. While the benefit of nanotexturing is thus clearer in mc-Si, a universal nano-texture process that also works on sc-Si would simplify and reduce the investments costs of PV production-lines. In this paper, such a nano-texture process is developed using a metal-assisted chemical etch (MACE) technique. Step-by-step characterization of surface structure and reflectance of the MACE process is used after: 1) wafering, 2) standard acidic texturing etch, 3) silver nanoparticles deposition, and 4) MACE nanotexturing for both sc and mc-Si. The results show that the same MACE process works effectively for both sc-Si and mc-Si wafers. Finally, the nano-textured wafers are processed into PV cells in an industrial process line with conversion efficiencies of 19.4 % and 18.7%, for sc-Si and mc-Si solar cells, respectively.

Near-infrared (NIR) sensors find numerous applications within various industry fields, including optical communications and medical diagnostics. However, the state-of-the-art NIR sensors made of germanium (Ge) suffer from rather poor response, largely due to high reflection from the illuminated device surface. We demonstrate here a method to increase the sensitivity of Ge sensors by implementing nanostructures to the wafer surfaces. The absorbance of nanostructured Ge wafers is measured to be >99 % in the whole UV-VIS-NIR spectrum up to 1600 nm wavelength, which is a significant improvement to bare Ge wafers that reach absorption of only 63 % in maximum. The process is shown to be capable of producing uniform nanostructures covering full 100-mm-diameter substrates as well as wafers with etch mask openings of different sizes and shapes, which demonstrates its applicability to CMOS sensor manufacturing. The results imply that nanostructured Ge has potential to revolutionize the sensitivity of Ge-based sensors., Comment: Article published in Advanced Optical Materials. Complete citation details and link to the article published in the journal were added

Yawning is an important indicator of drivers’ drowsiness or fatigue. Techniques for automatic detection of driver’s yawning have been developed for use as a component of driver fatigue monitoring system. However, detecting driver’s yawning event accurately in real-time is still a challenging task, in particular in applications such as driver fatigue detection, illumination conditions vary in a broad range, driver facial features vary in size, shape, texture and degrees of distortion. In this paper, we present a deep neural network model built using transfer learning and sequential learning from yawning video clips as well as augmented images for yawning detection. As a result, unlike many other methods that follow a sequence of processes such as face ROI detection, eye/nose/mouth positioning and mouth open/close determination, the proposed yawning detection system detect yawning events directly from video images without requiring any facial part positions. The system is robust to variations in object scales, positions and subject view angles. The system has been evaluated on publicly available yawning data sets, YawDD and NTHU-DDD, as well as a data set containing challenging yawning videos. The experimental results show that the proposed yawning detection system has the capability of detecting yawning events in high precision even when face turns away from camera up to 70 degrees, while exhibiting capability of being scale- and spatial-invariant. In addition, the model demonstrates the capability of discriminating yawning events very well from the actions involving mouth opening-closing motions such as talking and laughing.

Tightly coupled LTE---Wi-Fi networks have emerged as a promising solution for improving capacity and coverage of wireless networks. Different architectures which realize this integration include LTE---Wi-Fi radio level interworking with IPSec tunnel (LWIP) and LTE---Wi-Fi Aggregation (LWA). In this paper, we firstly have described the structure of LWIP and stated its specific implement process. Then we have designed and implemented three different scenes to compare the performance differences between LWIP and LTE/WLAN. Simulation results demonstrate that the performances of LWIP are better than separate LTE and WLAN.

In this work, we demonstrate a facile route for the synthesis of nanostructured SnO2/C composites for lithium-ion batteries. The anode materials were prepared via a one-pot solvothermal approach and then calcination in a highly pure nitrogen atmosphere. The composited was composed of amor- phous carbon and nanocrystalline SnO2 by the X-ray diffraction (XRD) analysis, and the content of carbon was calculated according to the thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) images revealed that the diameter of these as-prepared spheres varied from 50 to 60 nm. A systematic study has been carried out to examine the effect of carbon content upon lithium-ion battery performance. The electrochemical results showed that SnO2/C nanocomposite could achieve 1197.5 mAh/g reversible capacity and 55.11% initial coulombic efficiency, and 190% capacity retention after 50 cycles compared to the SnO2 nanoparticles of 940.6 mAh/g at a current density 0.2 C in the voltage range of 0.01-3.0 V. These improvements can be ascribed to the carbon, which can enhance the conductivity of SnO2, suppress the aggregation of active particles, and increase their structural stability during cycling.

Mass production of diamond-wire-sawn (DWS) multicrystalline silicon (mc-Si) solar cells reached a significant point of maturity through utilization of metal-catalyzed chemical etching (MCCE). However, nanotextured DWS mc-Si solar cells usually produced with Ag-MCCE still suffer from certain drawbacks, such as remaining saw marks, color differences among grains, and slight decreases in the open-circuit voltage (Voc). In this work, we show that unoriented Cu-based MCCE (Cu-MCCE) not only depresses the saw marks and color differences but also introduces random shallow pits, which act as artificial defects that can be easily converted into a submicron texture using conventional HNO3/HF etching. Moreover, we demonstrate that the efficiency of DWS mc-Si solar cells produced with the Cu-MCCE process is greater than 19%, with improved Voc resulting from better surface passivation. This cost-effective Cu-MCCE method is, therefore, of significant potential for the photovoltaic industry.