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A newly developed nanopatterned broadband antireflective (AR) coating was fabricated on the front side of a glass/indium tin oxide/perovskite solar cell (PSC) by depositing a single interference layer onto a two-dimensional (2D)-patterned moth-eye-like nanostructure. The optimized developed AR nanostructure was simulated in a finite-difference time domain analysis. To realize the simulated developed AR nanostructure, we controlled the SiO2 moth-eye structure with various diameters and heights and a MgF2 single layer with varying thicknesses by sequentially performing nanosphere lithography, reactive ion etching, and electron-beam evaporation. Optimization of the developed AR nanostructure, which has a 100 nm-thick MgF2 film coated onto the SiO2 moth-eye-like nanostructure (diameter 165 nm and height 400 nm), minimizes the reflection loss throughout the visible range. As a result, the short-circuit current density (JSC) of the newly AR-coated PSC increases by 11.80%, while the open-circuit voltage (VOC) remains nearly constant. Therefore, the power conversion efficiency of the newly developed AR-decorated PSC increases by 12.50%, from 18.21% for a control sample to 20.48% for the optimum AR-coated sample. These results indicate that the newly developed MgF2/SiO2 AR nanostructure can provide an advanced platform technology that reduces the Fresnel loss and therefore increases the possibility of the commercialization of glass-based PSCs.

Metal-assisted chemical etching (MACE) has been widely explored for developing silicon (Si)-based energy and optical devices with its benefits for low-cost and large-area fabrication of Si nanostructures of high aspect ratios. Surface structures and properties of Si nanostructures fabricated through MACE are significantly affected by experimental and environmental conditions of etchings. Herein, we showed that surfaces and interfacial energy states of fabricated Si nanowires can be critically affected by oxidants of MACE etching solutions. Surfaces of fabricated Si nanowires are porous and their tips are fully covered with lots of Si nano-sized grains. Strongly increased photoluminescence (PL) intensities, compared to that of the crystalline Si substrate, are observed for MACE-fabricated Si nanowires due to interfacial energy states of Si and SiOx of Si nano-sized grains. These Si grains can be completely removed from the nanowires by an additional etching process of the anisotropic chemical etching (ACE) of Si to taper the nanowires and enhance light trapping of the nanowires. Compared with the MACE-fabricated Si nanowires, ACE-fabricated tapered Si nanowires have similar Raman and PL spectra to those of the crystalline Si substrate, indicating the successful removal of Si grains from the nanowire surfaces by the ACE process.

A newly developed nanopatterned broadband antireflective (AR) coating was fabricated on the front side of a glass/indium tin oxide/perovskite solar cell (PSC) by depositing a single interference layer onto a two-dimensional (2D)-patterned moth-eye-like nanostructure. The optimized developed AR nanostructure was simulated in a finite-difference time domain analysis. To realize the simulated developed AR nanostructure, we controlled the SiO

In contrast with the conventional in situ and ex situ methods for the preparation of polymer-based nanocomposites in which the polymer matrix (for both methods) and metal nanoparticles (for the ex situ method only) are prepared separately prior to being combined to form the composite, polyhedral gold nanocrystal/polymer composite film was successfully synthesized through combining the in situ formation of gold nanocrystals (AuNCs) and simultaneous polymerization of the polyelectrolytes from ionic liquids and surfactants under atmospheric pressure plasma. The composite film contained a large number of well-shaped polyhedral AuNCs. The AuNCs are stereoscopically distributed in the polyelectrolyte matrix without agglomeration. The size of the AuNCs prepared in a 3 mm deep reactor decreased along the cross section of the composite film from top to bottom, while they were uniform in size when they were prepared in a 5 mm deep reactor. In the presence of the Au precursors, the polymer film thickness increases to 7.03 μm, which is two-fold thicker than that of the polymer film prepared without adding Au precursors. Through the density functional theory (DFT) calculations, the critical role of Triton X100 was clearly demonstrated in the formation of the well-shaped AuNCs. The composite film exhibited the reduction of ∼66% in Young's modulus and the reduction of ∼44% in hardness compared to the neat polymer film. Finally, an appropriate mechanism is proposed for the formation of the polyhedral AuNC/polyelectrolyte composite film.

An antipodal tapered slot antenna (ATSA) is miniaturized by extending the lower operating frequency range using spidron-shaped slots and additional impedance-matching stubs at the tapered radiator. Simulation and measurement results show that the electrical size of the antenna, or the lowest matching frequency, is reduced by 56.4% when compared to a conventional ATSA with the same physical dimensions. The realized gain is also improved in the newly matched low-end operating frequency.

An arsenobetaine (AsB) standard solution with metrological traceability to the International System of Units was developed as a calibration standard for the quantitative analysis of AsB. An arsenic-specific mass balance method was established for the certification of the AsB standard solution. The accurate mass fraction of total arsenic in the solution was determined by instrumental neutron activation analysis with direct comparator method. Arsenic-containing impurities were evaluated by arsenic speciation analysis using liquid chromatography-inductively coupled plasma mass spectrometry (LC-ICP-MS). Two LC separation methods were adopted for comprehensive coverage of the impurities, which include the reversed-phase LC with ion-pairing and the cation exchange chromatography. The only arsenic-containing impurity observed by LC-ICP-MS was trace level of trimethylarsine oxide. The mass fraction of arsenic in the form of AsB was obtained by subtracting the arsenic mass fractions of the impurities from the total arsenic in the standard solution. The between-bottle inhomogeneity of AsB content in the standard solution was less than 0.7%, which was estimated from the relative standard deviation of the measurement results obtained from 10 representative sample bottles from a batch. The certified value of AsB and its expanded uncertainty as arsenic mass fraction were assigned to be (51.28 ± 1.17) mg/kg (k = 2 approximately at 95% level of confidence).

The argon atmospheric pressure plasma treatment is combined with the conventional sol-gel dip-coating process for fabricating ITO thin films to improve the electrical property of the ITO glass. The increase of the surface free energy of the ITO layer by plasma treatment improves the adhesion of the pre-annealed ITO layer, thereby increasing the thickness of the ITO film without significantly losing the light transmittance. While increasing the plasma treatment time up to 240 s, both the thickness and surface free energy of the ITO layer are increased, and the sheet resistance of the thin film is rapidly decreased. The ITO layer plasma-treated for 240 s with the thickness of 360 nm exhibits the lowest sheet resistance of 126.5 Ω/sq and the highest surface free energy of 79.45 mJ/m2. However, the increase of the plasma treatment time over 240 s do not affect the increase of film thickness, but the increase of sheet resistance. X-ray photoelectron spectroscopy depth profile reveals the decrease of the level of the oxygen vacancies with increasing plasma treatment time over 240 s. It results from the diffusion of oxygen from the surface into the bulk and explains the increase of the sheet resistance.

Putrescine and cadaverine are important volatile indicators for the evaluation of food spoilage. In this study, a metal-organic framework (MOF)-coated surface-enhanced Raman scattering (SERS) paper platform for the detection of putrescine and cadaverine is developed. Au@ zeolite imidazolate framework-8 (ZIF-8) SERS paper is fabricated by the coating of ZIF-8 layer on a Au nanoparticle-impregnated paper that is prepared by dry plasma reduction. The Au@ZIF-8 SERS paper is characterized by scanning electron microscope, energy-dispersive X-ray spectroscopy, X-ray diffraction, and N2 sorption isotherm. The ZIF-8 layer enables the accumulation of gaseous molecules and also provides enhancement of SERS signals. The fluorescence, SERS, and simulation results prove the improved detection ability of the Au@ZIF-8 platform for the volatile molecules. For the selective detection of putrescine and cadaverine, the Au@ZIF-8 SERS paper is functionalized with 4-mercatobenzaldehyde (4-MBA). The 4-MBA molecule acts as a Raman reporter and also a specific receptor for the volatile amine molecules. Using the intensity ratiometric detection of 4-MBA-functionalized Au@ZIF-8 SERS paper, putrescine and cadaverine are quantitatively detected with detection limits of 76.99 and 115.88 parts per billion, respectively. Furthermore, the detection of volatile amine molecules released from spoiled salmon, chicken, beef, and pork samples is demonstrated. It is anticipated that the MOF-coated SERS paper platforms will be applicable not only in food safety but other applications including disease diagnosis and environmental monitoring.

Precise positioning of a plasmonic nanoparticle (NP) near a small dielectric surface is not only necessary for understanding gap-dependent interactions between a metal and dielectric but it is also a critical component in building ultrasensitive molecular rulers and force sensing devices. In this study we investigate the gap-dependent scattering of gold and silver NPs by controllably depositing them on an atomic force microscope (AFM) tip and monitoring their scattering within the evanescent field of a tin dioxide nanofiber waveguide. The enhanced distance-dependent scattering profiles due to plasmon-dielectric coupling effects show similar decays for both gold and silver NPs given the strong dependence of the coupling on the decaying power in the near-field. Experiments and simulations also demonstrate that the NPs attached to the AFM tips act as free NPs, eliminating optical interference typically observed from secondary dielectric substrates. With the ability to reproducibly place individual plasmonic NPs on an AFM tip, and optically monitor near-field plasmon-dielectric coupling effects, this approach allows a wide-variety of light-matter interactions studies to be carried out on other low-dimensional nanomaterials.

Summary Thin crystalline silicon (c-Si) showing outstanding flexibility has been considered as an active material for flexible solar cells. However, an effective photon management should be developed for thin c-Si, which shows severe light absorption loss. Here, we introduce random inverted-pyramidal polydimethylsiloxane (RIP-PDMS) films on the surface of the thin c-Si solar cell to simultaneously secure high absorption and flexibility. Attaching the RIP-PDMS film on the front surface of the device can significantly reduce surface reflection; near-infrared light recycling can be further improved by attaching a metal-coated RIP-PDMS film on the rear surface of the device. Notably, thin c-Si solar cells with RIP-PDMS films have an efficiency of 18.4% and exhibit a constant efficiency during 1,000 repeated bending tests with a bending radius of 10 mm. Also, finite-difference time-domain simulations confirm that the RIP-PDMS films increase the light diffusion and optical path length inside the c-Si.

Ultrasensitive nanomechanical instruments, including the atomic force microscope (AFM)1-4 and optical and magnetic tweezers5-8, have helped shed new light on the complex mechanical environments of biological processes. However, it is difficult to scale down the size of these instruments due to their feedback mechanisms9, which, if overcome, would enable high-density nanomechanical probing inside materials. A variety of molecular force probes including mechanophores10, quantum dots11, fluorescent pairs12,13 and molecular rotors14-16 have been designed to measure intracellular stresses; however, fluorescence-based techniques can have short operating times due to photo-instability and it is still challenging to quantify the forces with high spatial and mechanical resolution. Here, we develop a compact nanofibre optic force transducer (NOFT) that utilizes strong near-field plasmon-dielectric interactions to measure local forces with a sensitivity of

We report gap-dependent strong SERS enhancements and plasmonic couplings of hole/sphere nanostructures. The structure shows uniform sensitivity of less than 10% over the entire substrate, which comes from uniform narrow gaps over the substrate.

The shift to an industrial ecosystem that operates with abundant water and sunlight on the earth is essential to the sustainability of mankind. One effort to do this is to produce freshwater utilizing solar energy, called solar steam generation. Here, we develop a dual-function ecosystem of the 3-dimensional conical structure consisted of multi-walled carbon nanotubes (MWNTs), which utilizes the solar energy to produce the fresh water from any pollutated water or saline water at the massive production rate and to generate the high electric power of hundreds mW·m-2 using evaporation-enhanced capillary water stream of the structure under ambient daylight conditions. Since this cone-shaped fluidic nanogenerator (CFN) acquires all energy required from the environment, it will find immediate applications in providing electricity and freshwater for living and system maintenance in water-abundant isolated locations such as islands or wetlands. The CFN of MWNTs has advantages in solar steam generation because it can be more exposed to the environment due to its high surface curvature and because it can be thermally isolated from the cold water by the inside air-pocket. A single CFN of which vertical projection area is 0.64 cm2 can show high water evaporation rate of 1.6 kg·m-2·h at 20 °C. Multilayers of functionalized MWNTs can have advantages in fluidic nanogenerator which can harvest large electric power with high open-circuit voltage (Voc) and current density (Jsc) by the double layer interaction of MWNTs with ions flowing in the evaporation-induced capillary water stream. The CFN of MWNTs can produce strong electric power due to the capillary water stream induced by the solar steam under 1 sun irradiation (1 kW·m-2) and the single CFN produces electric powers of 120.7 mW·m-2 (Voc: 0.5V, Jsc: 0.12 mA·cm-2) at the saline water and of 505.69 mW·m-2 (Voc:0.64 V, Jsc: 0.59 mA·cm-2) at the 0.6 M KCl aqueous solution.

We experimentally demonstrate that plasmonic nanoparticles embedded in the evanescent field of subwavelength optical waveguides (WGs) are highly sensitive to distances normal to the propagation of light, showing an ~10× increase in spatial resolution compared to the optical field decay of the WG. The scattering cross-section of the Au nanoparticle is increased by the plasmon-dielectric coupling interaction when the nanoparticle is placed near the dielectric surface of the WG, and the decay of the scattering signal is enhanced, showing angstrom level distance sensitivity within 10 nm from the WG. Numerical studies with the finite-difference time-domain (FDTD) method correlate well with the experimental results. To demonstrate real-time monitoring of a single molecule stretching in the evanescent field, we linked individual single-stranded DNA molecules between the WG and plasmonic nanoparticles and pushed on the nanoparticles with fluidic forces. The simple design and ease of obtaining optical feedback on molecular displacements makes our approach ideal for new in situ force sensing devices, imaging technologies, and high-throughput molecular analysis.

Optical antennas interface an object with optical radiation and boost the absorption and emission of light by the objects through the antenna modes. It has been much desired to enhance both excitation and emission processes of the quantum emitters as well as to interface multiwavelength channels for many nano-optical applications. Here we report the experimental implementation of an optical antenna operating in the full visible range via surface plasmon currents induced in a defect-free single-crystalline Ag nanowire (NW). With its atomically flat surface, the long Ag NW reliably establishes multiple plasmonic resonances and produces a unique rainbow antenna radiation in the Fresnel region. Detailed antenna radiation properties, such as radiating near-field patterns and polarization states, were experimentally examined and precisely analyzed by numerical simulations and antenna theory. The multiresonant Ag NW nanoantenna will find superb applications in nano-optical spectroscopy, high-resolution nanoimaging, photovoltaics, and nonlinear signal conversion.

We report for the first time the synthesis of niobium dioxide nanowires on a sapphire substrate by chemical vapor transport method. We identified single crystalline nature of as-synthesized nanowires by scanning electron microscopy and transmission electron microscopy. Niobium dioxide nanowires with their large surface-to-volume ratio and high activities can be employed for electrochemical catalysts and immunosensors. The Raman spectrum of niobium dioxide nanowires also confirmed their identity.

We report that twin-free single-crystalline Pd nanowire (NW) arrays grow epitaxially in a selected pattern on a substrate. Parallel aligned Pd NWs are synthesized on a SrTiO(3) (110) substrate in a very high density. On a SrTiO(3) (001) substrate, Pd NWs grow horizontally in two perpendicular directions. Vertical Pd NWs are synthesized instead of horizontal NWs when a c-cut sapphire substrate is employed. We reveal that the atomic structure of the substrate surface determines the geometry and orientation of seeds, which in turn direct the growth patterns of the NWs. The interface energy between the NW material and the substrate is also critical in determining the NW growth pattern. Polarization-dependent localized surface plasmon resonance of as-synthesized epitaxial Pd NW arrays is investigated for application as a plasmonic platform.

A Au particle-on-wire system that can be used as a specific, sensitive, and multiplex DNA sensor is developed. A pattern formed by multiple Au nanowire sensors provides positional address and identification for each sensor. By using this system, multiplex sensing of target DNAs was possible in a quantitative manner with a detection limit of 10 pM. Target DNAs from reference bacteria and clinical isolates were successfully identified by this sensor system, enabling diagnostics for infectious diseases.

Graphene sheets formed by the reaction of carbon monoxide (CO) with aluminum sulfide (Al 2 S 3 ) at reaction temperatures > 800 °C were characterized by X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM). The graphene sheets, formed as CO was reduced to gaseous carbon by the reaction with Al 2 S 3 , in the temperature range 800 - 1100 °C, did not exhibit their characteristic XRD peaks because of the small number of graphene layers and/or low crystallinity of graphene sheets. Raman spectra of graphene sheets showed that the intensity ratio of the D band to the G band decreased and the 2D band was shifted to higher frequencies with increasing reaction temperature, indicating that the number of graphene layers increased with increasing reaction temperature.

Well-defined surface-enhanced Raman scattering (SERS) active systems were fabricated by single-crystalline noble metal nanowires. Crossed and parallel nanowire pairs were constructed by using a nanomanipulator to create SERS hot spots in the form of nanowire junction. SERS spectra of brilliant cresyl blue (BCB), p-mercaptoaniline (pMA), and p-mercaptobenzoic acid (pMBA) were observed at the junction of two nanowires. The SERS enhancement and polarization dependence are correlated well with the enhanced electric field intensities calculated by the finite difference time domain (FDTD) method for specific nanowire geometries. These simple and effective SERS active systems have a practical advantage that the hot spots can be readily located and visualized by an optical microscope. These well-defined SERS active systems based on noble metal nanowires can be further developed to find applications in a variety of biological and chemical sensing.

Fabricating well-defined and highly reproducible platforms for surface-enhanced Raman scattering (SERS) is very important in developing practical SERS sensors. We report a novel SERS platform composed of a single metallic nanowire (NW) on a metallic film. Optical excitation of this novel sandwich nanostructure provides a line of SERS hot spots (a SERS hot line) at the gap between the NW and the film. This single nanowire on a film (SNOF) architecture can be easily fabricated, and the position of hot spots can be conveniently located in situ by using an optical microscope during the SERS measurement. We show that high-quality SERS spectra from benzenethiol, brilliant cresyl blue, and single-stranded DNA can be obtained on a SNOF with reliable reproducibility, good time stability, and excellent sensitivity, and thus, SNOFs can potentially be employed as effective SERS sensors for label-free biomolecule detection. We also report detailed studies of polarization- and material-dependent SERS enhancement of the SNOF structure.

A clear understanding of the mechanical behavior of nanometer thick films on nanostructures, as well as developing versatile approaches to characterize their mechanical properties, are of great importance and may serve as the foundation for understanding and controlling molecular interactions at the interface of nanostructures. Here we report on the synthesis of thin, compressible polyethylene glycol (PEG) monolayers with a wet thickness of

Here we demonstrate a facile method of quantifying the decaying optical field surrounding free-standing tin dioxide (SnO(2)) nanofiber waveguides. Through the use of thin self-assembled polyelectrolyte coatings and fluorescent optical transmitters we map out the optical intensity as a function of distance with nanometer resolution.

We report a systematic study of light coupling at junctions of overlapping SnO(2) nanofiber waveguides (WGs) as a function of gap separation and guided wavelength. The junctions were assembled on silica substrates using micromanipulation techniques and the gap separation was controlled by depositing thin self-assembled polyelectrolyte coatings at the fiber junctions. We demonstrate that the coupling efficiency is strongly dependent on the gap separation, showing strong fluctuations (0.1 dB/nm) in the power transfer when the separation between nanofibers changes by as little as 2 nm. Experimental results correlate well with numerical simulations using three-dimensional finite-difference time-domain techniques. To demonstrate the feasibility of using coupled nanofiber WGs to modulate light, we encased the junctions in an environment-responsive matrix and exposed the junctions to gaseous vapor. The nanofiber junctions show an ~95% (or ~80%) modulation of the guided 450 nm (or 510 nm) light upon interaction with the gaseous molecules. The results reveal a unique nanofiber-based sensing scheme that does not require a change in the refractive index to detect stimuli, suggesting these structures could play important roles in localized sensing devices including force-based measurements or novel chemically induced light modulators.

We report an ultrasensitive and selective single nanowire-on-film (SNOF) surface-enhanced resonance Raman scattering (SERRS) sensor for Hg 2 + detection based on structure- switching double stranded DNAs (dsDNAs). Binding of Hg 2 + induces conformational changes of the dsDNAs and let a Raman reporter get close to the SNOF structure, thereby turning on SERRS signal. The well-defined SNOF structure provides a detection limit of 100 pm with improved accuracy in Hg 2 + detection. This sensor is stable over a considerable amount of time and reusable after simple treatment. Since this SNOF sensor is composed of a single Au NW on a film, development of a multiplex sensor would be possible by employing NWs modified by multi- ple kinds of aptamers.

We report a new type of mo- lecular sensor using a Au nanowire (NW)-Au nanoparticles (NPs) conju- gated system. The Au NW-NPs struc- ture is fabricated by the self-assembly of biotinylated Au NPs on a biotinylat- ed Au NW through avidin; this creates hot spots between NW and NPs that strongly enhance the Raman signal. The number of the Au NPs attached to the NW is reproducibly proportional to the concentration of the avidin, and is also proportional to the measured sur- face-enhanced Raman scattering (SERS) signals. Since this well-defined NW-NPs conjugated sensor is only a few micrometer long, we expect that development of multiplex nanobiosen- sor of a few tens micrometer size would become feasible by combining individually modified multiple Au NWs together on one substrate.

Tyramine and its monohydrated clusters have been investigated by several laser spectroscopic methods in a pulsed molecular beam. The conformational structures and their effects on hydration have been revealed by resonant two-photon ionization (R2PI), UV-UV ion-dip, and ab initio calculations. UV rotational band contour spectra of the S1-- S0 origin bands enabled determination of ethylamine side chain conformations for all seven stable conformers of tyramine. When coexpanding tyramine with a mixture of Ar and water vapor, we have found two kinds of conformational effects on hydration. One is sensitive to conformation of the ethylamine chain and the other to the orientation of the OH group, particularly in the most stable pair of conformers. UV-UV ion-dip spectra detected seven stable conformers of the monohydrated clusters, of which hydrogen-bonding structures, spectral shifts, and origin band intensity distributions are well explained by considering tyramine as a hybrid of phenylethylamine (PEA) and phenol. Monohydration of the most stable gauche conformer pair (cis and trans) of tyramine leads to more detailed conformational assignments regarding the orientation of the phenolic OH group. Cyclic hydrogen-bonding linkage formed in the monohydrated cluster pair is found to be sensitive to the orientation of the phenolic OH group. One of the cluster pair, in which tyramine has the gauche-cis conformation, is more stabilized by the cyclic hydrogen bonding and its origin band intensity becomes stronger than that of the other.

We report vapor-phase synthesis of single-crystalline free-standing Ag nanowires and polarized surface-enhanced Raman scattering (SERS) of a single nanowire, as a first step toward fabrication of well-controlled nanobiosensors employing the SERS technique.

When particles are smaller than wavelength of incident light, the light can be considered as static field. We calculate the electric field enhancement by plasmon in the gap between two paralled metallic nano wires.