Enantioselective Molecular Detection by Surface Enhanced Raman Scattering at Chiral Gold Helicoids on Grating Surfaces.

Distinct advantages of surface enhanced Raman scattering (SERS) in molecular detection can benefit the enantioselective discrimination of specific molecular configurations. However, many of the recent methods still lack versatility and require customized anchors to chemically interact with the studied analyte. In this work, we propose the utilization of helicoid-shaped chiral gold nanoparticles arranged in an ordered array on a gold grating surface for enantioselective SERS recognition. This arrangement ensured a homogeneous distribution of chiral plasmonic hot spots and facilitated the enhancement of the SERS response of targeted analytes through plasmon coupling between gold helicoid multimers (formed in the grating valleys) and adjacent regions of the gold grating. Naproxen enantiomers (R(+) and S(-)) were employed as model compounds, revealing a clear dependence of their SERS response on the chirality of the gold helicoids. Additionally, propranolol and penicillamine enantiomers were used to validate the universality of the proposed approach. Finally, numerical simulations were conducted to elucidate the roles of intensified local electric field and optical helicity density on the SERS signal intensity and on the chirality of the nanoparticles and enantiomers. Unlike previously reported methods, our approach relies on the excitation of a chiral plasmonic near-field and its interaction with the chiral environment of analyte molecules, obviating the need for the enantioselective entrapment of targeted molecules. Moreover, our method is not limited to specific analyte classes and can be applied to a broad range of chiral molecules.

Black Titanium Oxide/Activated TaS2 Flakes Photoelectrode for Plasmon Assisted Hydrogen Evolution at Neutral pH at High Current Density.

A heterojunction photo-electrode(s) consisting of porous black titanium oxide (bTiO2) and electrochemically self-activated TaS2 flakes is proposed and utilized for hydrogen evolution reaction (HER). The self-activated TaS2 flakes provide abundant catalytic sites for HER and the porous bTiO2, prepared by electrochemical anodization and subsequent reduction serves as an efficient light absorber, providing electrons for HER. Additionally, Au nanostructures are introduced between bTiO2 and TaS2 to facilitate the charge transfer and plasmon-triggering ability of the structure created. After structure optimization, high HER catalytic activity at acidic pH and excellent HER activity at neutral pH are achieved at high current densities. In particular, with the utilization of bTiO2@TaS2 photoelectrode (neutral electrolyte, sunlight illumination) current densities of 250 and 500 mA cm-2 are achieved at overpotentials of 433, and 689 mV, respectively, both exceeding the "benchmark" Pt. The addition of gold nanostructures further reduces the overpotential to 360 and 543 mV at 250 and 500 mA cm-2, respectively. The stability of the prepared electrodes is investigated and found to be satisfying within 24 h of performance at high current densities. The proposed system offers an excellent potential alternative to Pt for the development of green hydrogen production on an industrial scale.

Microstructure and physical properties of black-aluminum antireflective films.

The microstructure and physical properties of reflective and black aluminum were compared for layers of different thicknesses deposited by magnetron sputtering on fused silica substrates. Reflective Al layers followed the Volmer-Weber growth mechanism classically observed for polycrystalline metal films. On the contrary, the extra nitrogen gas used to deposit the black aluminum layers modified the growth mechanism and changed the film morphologies. Nitrogen cumulated in the grain boundaries, favoring the pinning effect and stopping crystallite growth. High defect concentration, especially vacancies, led to strong columnar growth. Properties reported for black aluminum tend to be promising for sensors and emissivity applications.

Surface Enhancement Using Black Coatings for Sensor Applications.

The resolution of a quartz crystal microbalance (QCM) is particularly crucial for gas sensor applications where low concentrations are detected. This resolution can be improved by increasing the effective surface of QCM electrodes and, thereby, enhancing their sensitivity. For this purpose, various researchers have investigated the use of micro-structured materials with promising results. Herein, we propose the use of easy-to-manufacture metal blacks that are highly structured even on a nanoscale level and thus provide more bonding sites for gas analytes. Two different black metals with thicknesses of 280 nm, black aluminum (B-Al) and black gold (B-Au), were deposited onto the sensor surface to improve the sensitivity following the Sauerbrey equation. Both layers present a high surface roughness due to their cauliflower morphology structure. A high response (i.e., resonant frequency shift) of these QCM sensors coated with a black metal layer was obtained. Two gaseous analytes, H2O vapor and EtOH vapor, at different concentrations, are tested, and a distinct improvement of sensitivity is observed for the QCM sensors coated with a black metal layer compared to the blank ones, without strong side effects on resonance frequency stability or mechanical quality factor. An approximately 10 times higher sensitivity to EtOH gas is reported for the QCM coated with a black gold layer compared to the blank QCM sensor.

In Situ Monitoring of Pulsed Laser Annealing of Eu-Doped Oxide Thin Films.

Eu3+-doped oxide thin films possess a great potential for several emerging applications in optics, optoelectronics, and sensors. The applications demand maximizing Eu3+ photoluminescence response. Eu-doped ZnO, TiO2, and Lu2O3 thin films were deposited by Pulsed Laser Deposition (PLD). Pulsed UV Laser Annealing (PLA) was utilized to modify the properties of the films. In situ monitoring of the evolution of optical properties (photoluminescence and transmittance) at PLA was realized to optimize efficiently PLA conditions. The changes in optical properties were related to structural, microstructural, and surface properties characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The substantial increase of Eu3+ emission was observed for all annealed materials. PLA induces crystallization of TiO2 and Lu2O3 amorphous matrix, while in the case of already nanocrystalline ZnO, rather surface smoothening0related grains' coalescence was observed.

Switchable PNIPAm/PPyNT Hydrogel for Smart Supercapacitors: External Control of Capacitance for Pulsed Energy Generation or Prolongation of Discharge Time.

Supercapacitors based on nonresponsive polymer hydrogels are gaining significant attention due to their fabrication simplicity and high potential for wearable electronics. However, the use of smart hydrogels in supercapacitor design remains unexplored. In this work, a smart externally controlled supercapacitor based on a temperature-responsive hydrogel doped with polypyrrole nanotubes (PPyNTs) is proposed. The redistribution of PPyNTs in the poly(N-isopropylacrylamide) (PNIPAm) hydrogel can be reversibly controlled by light illumination or temperature increase, leading to on-demand formation/disruption of the nanotube conductive network, due to release/entrapping of the nanotubes from PNIPAm globule volume on surface. The switchable material was introduced in a supercapacitor design as an active and smart electrode, responsible for external control of charge transport and storage. The created device showed a switchable supercapacitor performance with an ability to significantly and rapidly change capacity under heating/cooling or light illumination. The external trigger was applied for static or dynamic control of supercapacitor behavior: prolongation of discharge time (with constant electric loading) or vice-versa pronounced acceleration of supercapacitor discharge. The proposed smart material-based supercapacitor can find a range of attractive applications in backup energy storage or high power pulse generation.

New Insights towards High-Temperature Ethanol-Sensing Mechanism of ZnO-Based Chemiresistors.

In this work, we investigate ethanol (EtOH)-sensing mechanisms of a ZnO nanorod (NRs)-based chemiresistor using a near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS). First, the ZnO NRs-based sensor was constructed, showing good performance on interaction with 100 ppm of EtOH in the ambient air at 327 °C. Then, the same ZnO NRs film was investigated by NAP-XPS in the presence of 1 mbar oxygen, simulating the ambient air atmosphere and O2/EtOH mixture at the same temperature. The partial pressure of EtOH was 0.1 mbar, which corresponded to the partial pressure of 100 ppm of analytes in the ambient air. To better understand the EtOH-sensing mechanism, the NAP-XPS spectra were also studied on exposure to O2/EtOH/H2O and O2/MeCHO (MeCHO = acetaldehyde) mixtures. Our results revealed that the reaction of EtOH with chemisorbed oxygen on the surface of ZnO NRs follows the acetaldehyde pathway. It was also demonstrated that, during the sensing process, the surface becomes contaminated by different products of MeCHO decomposition, which decreases dc-sensor performance. However, the ac performance does not seem to be affected by this phenomenon.

Can Plasmon Change Reaction Path? Decomposition of Unsymmetrical Iodonium Salts as an Organic Probe.

Plasmon-assisted transformations of organic compounds represent a novel opportunity for conversion of light to chemical energy at room temperature. However, the mechanistic insights of interaction between plasmon energy and organic molecules is still under debate. Herein, we proposed a comprehensive study of the plasmon-assisted reaction mechanism using unsymmetric iodonium salts (ISs) as an organic probe. The experimental and theoretical analysis allow us to exclude the possible thermal effect or hot electron transfer. We found that plasmon interaction with unsymmetrical ISs led to the intramolecular excitation of electron followed by the regioselective cleavage of C-I bond with the formation of electron-rich radical species, which cannot be explained by the hot electron excitation or thermal effects. The high regioselectivity is explained by the direct excitation of electron to LUMO with the formation of a dissociative excited state according to quantum-chemical modeling, which provides novel opportunities for the fine control of reactivity using plasmon energy.

Application of Plasmon-Induced Lithography for Creation of a Residual-Free Pattern and Simple Surface Modifications.

Here, we propose a plasmon-induced redistribution of a thin polymer layer as a unique way for a residual layer-free lithographic approach. In particular, we demonstrate an ultrafast area-selective fabrication method using a low-intensity visible laser irradiation to direct the polymer mass flow, under the plasmon-active substrates. Plasmon-supported substrates were created by thermal annealing of Ag thin films and covered by thin polystyrene layers. Then, laser beam writing (LBW) was applied to introduce a surface tension gradient through the local plasmon heating. As a result, polystyrene was completely removed from the irradiated place, without any residual layer. The proposed approach does not require any additional development steps, such as solvent or plasma treatment. To demonstrate the advantages of the proposed technique, we implemented the LBW-patterned structures for further spatially selective surface functionalization, including the metal deposition, spontaneous thiol grafting, and electrochemical deposition of ordered polypyrrole array.

Phthalocyanine Photoregeneration for Low Power Consumption Chemiresistors.

It is well-known that the applicability of phthalocyanine chemiresistors suffers from long recovery time after NO2 exposure. This circumstance enforces the necessity to operate the sensors at elevated temperatures (150-200 °C), which shortens the sensor lifetime and increases its power consumption (regardless, a typical measurement period is longer than 15 min). In this paper, we propose a new method for fast and effective recovery by UV-vis illumination at a low temperature (55 °C). The method is based on short illumination following short NO2 exposure. To support and optimize the method, we investigated the effects of light in the wavelength and intensity ranges of 375-850 nm and 0.2-0.8 mW/mm2, respectively, on the rate of NO2 desorption from the phthalocyanine sensitive layer during the recovery period. This investigation was carried out for a set of phthalocyanine materials (ZnPc, CuPc, H2Pc, PbPc, and FePc) operating at slightly elevated temperatures (55-100 °C) and was further supported by the analysis of UV-vis and FTIR spectral changes. We found out that the light with the wavelength shorter than 550 nm significantly accelerates the NO2 desorption from ZnPc, CuPc, and FePc, and allows bringing the measurement period under 2 min and decreasing the sensor power consumption by 75%. Possible mechanisms of the light-stimulated desorption are discussed.

Methodology of evaluating the influence of the resistance of contact regions in the measurements of sheet resistance on stripes of ultrathin high-resistance materials.

The paper reviews the problems of measurement of sheet resistance of ultrathin high-resistance layers of organic semiconductors and the essential underlying problems. Particular attention is paid to potential influence of the resistance of contact regions on the results of direct measurement of sheet resistance of stripe-shaped layers. In this connection, we present a methodology of double length stripe resistance measurement (DLSRM), used above all to minimise the influence of contact regions on the measurement results. We deduce theoretical as well as practical possibilities of DLSRM in the diagnostics and quantitative characterisation of unsuitable or even faulty contacts on high-resistance layers. The application efficiency of the DLSRM method is documented by the results of sheet resistance measurement on zinc phthalocyanine with cathode sputtered planar contacts of noble metals (gold, platinum, or palladium). As expected, gold is the best contact material, but even in its application one cannot neglect the influence of contact regions. The presented method is universal and generally applicable to all materials where sheet resistance is the relevant parameter, and its assessment is based on measurements of the layer resistance in stripe arrangement.