Blue-Shifted SPR of Au Nanoparticles with Ordering of Carbon by Dense Ionization and Thermal Treatment

Thin films of carbon-containing Au nanoparticles (NPs), prepared by the co-sputtering using a neutral Ar atom beam, were irradiated by 120 MeV Ag ions and also annealed, separately, at increasing temperatures in inert atmosphere. The surface plasmon resonance (SPR) band of the nanocomposite film was observed to be blue shifted (～50 nm) in both cases, with increasing fluence and temperature. The structural changes of Au NPs embedded in amorphous carbon matrix were investigated using X-ray diffraction and transmission electron microscopy. A growth of Au NPs was observed with increasing fluence and also with increasing temperature. A percolation of Au NPs was observed at 500 °C. A growth of Au NPs with ion irradiation is explained in the framework of a thermal spike model. Raman spectroscopy revealed the ordering of a-C thin films with increasing fluence and temperature, which is ascribed to a change of refractive index and the blue shift of the SPR band.     

Plasmonic and Nonlinear Optical Absorption Properties of Ag:ZrO2 Nanocomposite Thin Films

Ag nanoparticles (NPs) embedded in a zirconium oxide matrix in the form of Ag:ZrO₂ nanocomposite (NC) thin films were synthesized by using the sol–gel technique followed by thermal annealing. With the varying of the concentration of Ag precursor and annealing conditions, average sizes (diameters) of Ag nanoparticles (NPs) in the nanocomposite film have been varied from 7 to 20 nm. UV–VIS absorption studies reveal the surface plasmon resonance (SPR)-induced absorption in the visible region, and the SPR peak intensity increases with the increasing of the Ag precursor as well as with the annealing duration. A red shift in SPR peak position with the increase in the Ag precursor concentration confirms the growth of Ag NPs. Surface topographies of these NC films showed that deposited films are dense, uniform, and intact during the variation in annealing conditions. The magnitude and sign of absorptive nonlinearities were measured near the SPR of the Ag NPs with an open-aperture z-scan technique using a nanosecond-pulsed laser. Saturable optical absorption in NC films was identified having saturation intensities in the order of 10¹² W/m². Such values of saturation intensities with the possibility of size-dependent tuning could enable these NC films to be used in nanophotonic applications.     

Improving Efficiency of TiO<Subscript>2</Subscript>:Ag /Si Solar Cell Prepared by Pulsed Laser Deposition

Titanium dioxide (TiO₂) has been extensively studied and demonstrated to be suitable to enhance the efficiency of solar cell. In this work, TiO₂ is doped with silver nanoparticles (AgNP’s) on glass and the Si substrate by using Pulsed Laser Deposition (PLD) technique. UV–vis spectroscopy, X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Atomic Force Microscope (AFM), electrical conductivity (σ _dc), Hall coefficient (R_H), current–voltage (I–V), and capacity–voltage (C–V) characterizations have been used to examine the optical, the morphological, and the electrical properties of the films. It has been found that 5 wt.% (Ag) doped TiO₂ thin film has the most effect on efficiency of TiO₂:Ag /Si solar cell. The (I–V) characteristics showed that the (TiO₂) thin film enhances the efficiency of the (p–n) junction solar cell from 1.26 % pure TiO₂ to 7.19 % with doping of noble metal (Ag) representing improvement in the efficiency of solar cell leading to estimate empirical equations between efficiency, extinction coefficient, and energy band gap which have a total fit with the experimental data.     

Effect of thermal annealing on the structural and optical properties of tris‐(8‐hydroxyquinoline)aluminum(III) (Alq3) films

Tris‐(8‐hydroxyquionoline)aluminum (Alq₃) was synthesized and coated on to a glass substrate using the dip coating method. The structural and optical properties of the Alq₃ film after thermal annealing from 50°C to 300°C in 50° steps was studied. The films have been prepared with 2 to 16 layers (42–324 nm). The thickness and thermal annealing of Alq₃ films were optimized for maximum luminescence yield. The Fourier transform infrared spectrum confirms the formation of quinoline with absorption in the region 700 ? 500/cm. Partial sublimation and decomposition of quinoline ion was observed with the Alq₃ films annealed at 300°C. The X‐ray diffraction pattern of the Alq₃ film annealed at 50°C to 150°C reveals the amorphous nature of the films. The Alq₃ film annealed above 150°C were crystalline nature. Film annealed at 150°C exhibits a photoluminescence intensity maximum at 512 nm when excited at 390 nm. The Alq₃ thin film deposited with 10 layers (220 nm) at 150°C exhibited maximum luminescence yield. Copyright © 2014 John Wiley & Sons, Ltd.     

Highest Efficiency Plasmonic Polycrystalline Silicon Thin-Film Solar Cells by Optimization of Plasmonic Nanoparticle Fabrication

Excitation of surface plasmons in metallic nanoparticles is a promising method for increasing the light absorption in solar cells and hence the cell photocurrent. Comprehensive optimization of a nanoparticle fabrication process for enhanced performance of polycrystalline silicon thin-film solar cells is presented. Three factors were studied: the Ag precursor film thickness, annealing temperature and time. The thickness of the precursor film was 10, 14 and 20 nm; annealing temperature was 190, 200, 230 and 260 °C; and annealing time was varied between 20 and 95 min. Performance enhancement due to light-scattering by nanoparticles was calculated by comparing absorption, short-circuit current density and energy conversion efficiency in solar cells with and without nanoparticles formed under different process conditions. Nanoparticles formed from 14-nm-thick Ag precursor film annealed at 230 °C for 53 min result in the highest absorption enhancement in the 700–1,100 nm wavelength range, in the highest enhancement of total short-circuit current density. The highest photocurrent enhancement was 33.5 %, which was achieved by the cell with the highest absorption enhancement in the 700–1,100 nm range. The plasmonic cell efficiency of 5.32 % was achieved without a back reflector and 5.95 % with the back reflector; which is the highest reported efficiency for plasmonic thin-film solar cells.     

C<Subscript>60</Subscript> fullerene affects elastic properties and osmoregulation reactions of human lymphocytes

The influence of aqueous solution of pristine C₆₀ fullerene (C₆₀FAS) on functional activity of lymphocytes from a healthy person was studied for the first time. By means of atomic force microscopy, it was found that C₆₀FAS in a concentration of 0.1 mg/ml increases the stiffness of the lymphocyte membrane by 41 % (p < 0.05) and lowers the functional activity of the plasmalemma surface, thereby constraining the use of its membrane material in physiological reactions using a hypotonic model in vitro. However, a cell retains the ability to regulate its volume and demonstrates relative resistance to hypo-osmotic stress. The resistance of lymphocytes in hypo-osmotic medium is facilitated by activation of the nucleus by C₆₀ fullerene particles, which regulates the implementation of two consistent phases of an increase and decrease of cell volume, thereby retaining cell viability. All these indicate the impact of C₆₀ fullerene on the cellular nucleus.     

Toward High‐Temperature Stability of PTB7‐Based Bulk Heterojunction Solar Cells: Impact of Fullerene Size and Solvent Additive

The use of fullerene as acceptor limits the thermal stability of organic solar cells at high temperatures as their diffusion inside the donor leads to phase separation via Ostwald ripening. Here it is reported that fullerene diffusion is fully suppressed at temperatures up to 140 °C in bulk heterojunctions based on the benzodithiophene‐based polymer (the poly[[4,8‐bis[(2‐ethylhexyl)oxy]‐benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]‐thieno[3,4‐b]thiophenediyl]], (PTB7) in combination with the fullerene derivative [6,6]‐phenyl‐C71‐butyric acid methyl ester (PC₇₀BM). The blend stability is found independently of the presence of diiodooctane (DIO) used to optimize nanostructuration and in contrast to PTB7 blends using the smaller fullerene derivative PC₇₀BM. The unprecedented thermal stability of PTB7:PC₇₀BM layers is addressed to local minima in the mixing enthalpy of the blend forming stable phases that inhibit fullerene diffusion. Importantly, although the nanoscale morphology of DIO processed blends is thermally stable, corresponding devices show strong performance losses under thermal stress. Only by the use of a high temperature annealing step removing residual DIO from the device, remarkably stable high efficiency solar cells with performance losses less than 10% after a continuous annealing at 140 °C over 3 days are obtained. These results pave the way toward high temperature stable polymer solar cells using fullerene acceptors.     

Effect of fullerenes C<Subscript>60</Subscript> on X-protein amyloids

The inhibitory effect of hydrated fullerene C₆₀ and the sodium salt of the fullerene polycarboxylic derivative C₆₀Cl(C₆H₄CH₂COONa)₅ on the formation of amyloid fibrils by X-protein in vitro has been studied by electron microscopy. It is shown that these compounds not only destroy mature amyloid fibrils but also prevent the formation of new fibrils. This property of fullerenes, which are nanoparticles, can be used to develop a novel medical nanotechnology in the therapy for amyloidoses.     

Tuning the Optical and Rheological Properties of Fullerene C<Subscript>60</Subscript>/Poly (Vinyl Pyrrolidone) Nanofluids via Inclusion of Nanogold

In this article, development of nanogold (NG) containing fullerene C₆₀ nanofluids (NFs) with poly (vinyl pyrrolidone) PVP polymer in water via a wet chemical route is reported and studied their rheo-optical properties. An inclusion of NG into a C₆₀:PVP nanofluid thus results in a gold (Au) surface plasmon resonance (SPR) enhanced π?→?π* C₆₀ (sp²) electron transition over 250–450 nm of absorption spectrum in water. Evolution of a broad Au-SPR band in the 450–750 nm region signifies that a controlled Au³⁺?→?Au reduction reaction had occurred on it and was carried in C₆₀:PVP NFs. The average maximum wavelength value has thus varied along with a molar extinction coefficient in a function of the Au-uploads and shape and size of the flocculates in the resulting Au:C₆₀-PVP NFs. A systematic rheological study performed on the Au:C₆₀-PVP NFs in water by varying the NG content up to 85.0 μM reveals a non-Newtonian behavior with an enhanced yield stress is a signature of Bingham flow. NG of different shapes serves as filler in C₆₀:PVP NFs so as it adapts tailored shear viscosity. The shear viscosity relaxes slowly to the base value on increasing the shear rate from 10 to 100 s^?1 as it leads to breaking up of soft Au:C₆₀-PVP assemblies into a fine structures. Synthesis of Au:C₆₀-PVP NFs with various Au-contents could be potential nanostructure hybrid composite materials for development of photovoltaic nanodevices.     

Influence of SiO<Subscript>2</Subscript> Spacer Layer Thickness on Performance of Plasmonic Textured Silicon Solar Cell

We investigated the effect of SiO₂ spacer layer thickness between the textured silicon surface and silver nanoparticles (Ag NPs) on solar cell performance using quantum efficiency analysis. Separation of Ag NPs from high index silicon with SiO₂ layer led to modified absorption and scattering cross-sections due to graded refractive index medium. The forward scattering from Ag NPs is very sensitive to SiO₂ layer thickness in plasmonic silicon cell performance due to the evanescent character of generated near-fields around the NPs. With the optimized ～30–40 nm SiO₂ spacer layer, we observed an enhancement of solar cell efficiency from ～8.7 to ～10 %, which is due to the photocurrent enhancement in the off-resonance surface plasmon region. We also estimated minority carrier diffusion lengths (L _eff) from internal quantum efficiency data, which are also sensitive to SiO₂ spacer layer thickness. We observed that the L _eff values are enhanced from ～356 to ～420 μm after placing Ag NPs on ～40 nm spacer layer due to improved forward (angular) scattering of light from the Ag NPs into silicon.     

Fullerene Nucleating Agents: A Route Towards Thermally Stable Photovoltaic Blends

The bulk‐heterojunction nanostructure of non‐crystalline polymer:fullerene blends has the tendency to rapidly coarsen when heated above its glass transition temperature, which represents an important degradation mechanism. We demonstrate that fullerene nucleating agents can be used to thermally arrest the nanostructure of photovoltaic blends that comprise a non‐crystalline thiophene‐quinoxaline copolymer and the widely used fullerene derivative [6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM). To this end, C₆₀ fullerene is employed to efficiently nucleate PCBM crystallization. Sub‐micrometer‐sized fullerene crystals are formed when as little as 2 wt% C₆₀ with respect to PCBM is added to the blend. These reach an average size of only 200 nanometers upon introduction of more than 8 wt% C₆₀. Solar cells based on C₆₀‐nucleated blends indicate significantly improved thermal stability of the bulk‐heterojunction nanostructure even after annealing at an elevated temperature of 130 °C, which lies above the glass transition temperature of the blend. Moreover, we find that various other compounds, including C₇₀ fullerene, single‐walled carbon nanotubes, and sodium benzoate, as well as a number of commercial nucleating agents—commonly used to clarify isotactic polypropylene—permit to control crystallization of the fullerene phase.     

Room Temperature NO<Subscript>2</Subscript> Gas Sensor Based on SnO<Subscript>2</Subscript>-WO<Subscript>3</Subscript> Thin Films

Metal oxide semiconductors (MOS) are important and promising materials in optoelectronics, and it has been widely used in various catalytic applications such as gas sensing due to its high reactivity with many gases. In current work, mixtures of SnO₂-WO₃ (1:1) were prepared to synthesize nanostructured thin films by pulsed laser deposition as gas sensors. The sensitivity of sensors was measured for a relatively low concentration (200 ppm) of NO₂ gas at room temperature; sensors prepared with target exposed to (200) laser shots have higher sensitivity with a maximum value of 96.49 % at time 65 s as compared with the sensors prepared with (150) laser shots where the sensitivity has a maximum value 71.82 % at time 110 s; XRD pattern shows a better crystalline and high intensity with increasing laser shots up to 200; scanning electron microscopy (SEM) micrographs show approximate homogeneity of grains that cover the substrate without cracks and pinholes with nanoparticles fall in micro and nanometer range 50–200 nm. The values of the direct band gap were found to be 2.07143 eV for films prepared with 150 laser shots and 2.02899 eV for films prepared with 200 laser shots which have higher absorbance than the former films due to the increment in thickness and particle size. Empirical equations between sensitivity and gas exposure time have been formulated with great coincidence with the experimental data.     

Partial characterization of a crude cold-active lipase from Rhodococcus cercidiphylli BZ22

Cold-active lipase production by the psychrophilic strain Rhodococcus cercidiphylli BZ22 isolated from hydrocarbon-contaminated alpine soil was investigated. Depending on the medium composition, high cell densities were observed at a temperature range of 1–10 °C in Luria–Bertani (LB) broth or 1–30 °C in Reasoner’s 2A (R2A). Maximum enzyme production was achieved at a cultivation temperature of 1–10 °C in LB medium. About 70–80 % of the secreted enzyme was bound to the cell and was highly active as a cell-immobilized lipase which exhibited good reusability; more than 60 % of the initial lipase activity was retained after five-fold reuse. The properties of the lipase produced by the investigated strain were compared with those of a mesophilic porcine pancreatic lipase (PPL). The thermal stability of the cell-immobilized bacterial lipase was higher than that of the extracellular enzyme. Highest activity was detected at 30 °C for the cell-immobilized enzyme and for PPL, while the extracellular enzyme displayed highest activity at 10–20 °C. The bacterial lipase hydrolyzed p-nitrophenyl (p-NP) esters with different acyl chain lengths (C₂–C₁₈). The highest hydrolytic activity was obtained with p-NP-butyrate (C₄) as substrate, while the highest substrate affinity was obtained with p-NP-dodecanoate (C₁₂) as substrate, indicating a clear preference of the enzyme for medium acyl chain lengths.     

Substrate Temperature Effect on Microstructure,Optical, and Glucose Sensing Characteristics of Pulsed Laser Deposited Silver Nanoparticles

This work reports the substrate temperature-influenced change in the structural, morphological, optical, and glucose sensing properties of silver (Ag) nanoparticles (NPs) deposited on p-type Si (100) wafers. AgNP films grown at temperatures ranging from RT to 600 °C clearly show a dependence of orientation texture and surface morphology on substrate temperature (T _s). As T _s increases from RT towards 600 °C, the preferred orientation of AgNP film changes from (111) to (200). The AgNPs size, that is T _s-dependent, reaches the maximum value at T _s = 300 °C. This result is attributed to restructuring of AgNPs texture. Moreover, the AgNP shape also changes from ellipsoid to sphere as T _s increases from RT to 600 °C. Surface plasmon enhancement in photoluminescence intensity is observed with increase in T _s. It is found also that the AgNP film deposited at 300 °C has considerable reflectance reduction relative to the silicon substrate, in wavelength range of 300–800 nm and a progressive red shift of localized surface plasmon resonances caused by the adding of increasing quantities of glucose has been observed. As a proof of concept, we also demonstrate the capability of grown AgNP substrates for glucose detection based on surface enhanced Raman spectroscopy in physiological concentration range with short integration time 10 s, varying with T _s.     

Linking Vertical Bulk‐Heterojunction Composition and Transient Photocurrent Dynamics in Organic Solar Cells with Solution‐Processed MoOx Contact Layers

It is demonstrated that a combination of microsecond transient photocurrent measurements and film morphology characterization can be used to identify a charge‐carrier blocking layer within polymer:fullerene bulk‐heterojunction solar cells. Solution‐processed molybdenum oxide (s‐MoO_x) interlayers are used to control the morphology of the bulk‐heterojunction. By selecting either a low‐ or high‐temperature annealing (70 °C or 150 °C) for the s‐MoO_x layer, a well‐performing device is fabricated with an ideally interconnected, high‐efficiency morphology, or a device is fabricated in which the fullerene phase segregates near the hole extracting contact preventing efficient charge extraction. By probing the photocurrent dynamics of these two contrasting model systems as a function of excitation voltage and light intensity, the optoelectronic responses of the solar cells are correlated with the vertical phase composition of the polymer:fullerene active layer, which is known from dynamic secondary‐ion mass spectroscopy (DSIMS). Numerical simulations are used to verify and understand the experimental results. The result is a method to detect poor morphologies in operating organic solar cells.     

Antiamyloid properties of fullerene C<Subscript>60</Subscript> derivatives

A comparative estimation of the ability of complexes of fullerene C₆₀ with polyvinylpyrrolidone and fullerene C₆₀ derivatives (the sodium salt of the polycarboxylic derivative of fullerene C₆₀, sodium fullerenolate), has been carried out. The fullerenes destroyed amyloid fibrils of the Aβ(1–42) peptide of the brain and the muscle X-protein. A study of the effect of fullerenes on muscle actin showed that complexes of fullerene C₆₀ with polyvinylpyrrolidone and sodium fullerenolate did not prevent the filament formation of actin, nor did they destroy its filaments in vitro. Conversely, sodium salt of the polycarboxylic derivative of fullerene C₆₀ destroyed actin filaments and prevented their formation. It was concluded that sodium fullerenolate and complexes of fullerene C₆₀ with polyvinylpyrrolidone are the most effective antiamyloid compounds among the fullerenes examined.     

Study of Broadband Tunable Properties of Surface Plasmon Resonances of Noble Metal Nanoparticles Using Mie Scattering Theory: Plasmonic Perovskite Interaction

We suggest semi-analytical approach to study the optical properties of noble metal nanoparticles and their interaction to the perovskite material (methyl ammonia lead halide: CH₃NH₃PbI₃). Metal nanoparticles embedded in perovskite matrix exhibits broadband surface plasmon resonances, and the tunability of these plasmonic resonances is highly sensitive to particle size. The calculation of optical cross section have been done using Mie scattering theory which is applicable to arbitrary size and spherical-shape metal nanoparticles. We have taken five different radii ranging from 15 to 100 nm to understand the plasmonic resonances and its spectral width in the wavelength range 300 to 800 nm. Out of these noble metal nanoparticles, silver have highest scattering efficiency nearly of the order of 18 for the case of 15 nm radii at resonance wavelength 613 nm. Our finding reveals a new concept to understand the applications of plasmonic resonances in order to enhance the photon absorption inside the thin film of perovskite.     

Magnetophoretic harvesting of freshwater microalgae using polypyrrole/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocomposite and its reusability

A magnetophoretic harvesting agent, a polypyrrole/Fe₃O₄ magnetic nanocomposite, is proposed as a cost and energy efficient alternative to recover biomass of the microalgae Botryococcus braunii, Chlorella protothecoides, and Chlorella vulgaris from their culture media. The maximal recovery efficiency reached almost 99 % for B. braunii, 92.4 % for C. protothecoides, and 90.8 % for C. vulgaris. The maximum adsorption capacity (Q ₀) of the magnetic nanocomposite for B. braunii (63.49 mg dry biomass mg^?1 PPy/Fe₃O₄) was higher than that for C. protothecoides (43.91 mg dry biomass mg^?1 PPy/Fe₃O₄) and C. vulgaris (39.98 mg dry biomass mg^?1 PPy/Fe₃O₄). The highest harvesting efficiency for all the studied microalgae were at pH 10.0, and measurement of zeta-potential confirmed that the flocculation was induced by charge neutralization. This study showed that polypyrrole/Fe₃O₄ can be a promising flocculant due to its high efficacy, low dose requirements, short settling time, its integrity with cells, and with great potential for saving energy because of its recyclability.     

Plasmonic Perovskite Solar Cells Utilizing Au@SiO<Subscript>2</Subscript> Core-Shell Nanoparticles

The role of Au@SiO₂ core-shell nanoparticles on optical properties of perovskite solar cells has been explored using both the theoretical computations and the experiments. A quasi-static model is used to study the surface plasmon resonances (SPRs) of Au@SiO₂ core-shell nanospheres. Au@SiO₂ core-shell nanoparticles, with varying shell thickness and core radius, were assumed to be embedded in methylammonium lead triiodide (CH₃NH₃PbI₃) perovskite active layer. Enhanced absorption in the active layer is obtained due to the near-field plasmonic effect of the embedded core-shell nanoparticles. Theoretical modelling shows that a shell thickness of 1 nm and core diameter of 20 nm provide absorption enhancement in the orange-red region of the electromagnetic spectrum. Experiments performed using ～20-nm-sized Au@SiO₂ core-shell nanoparticles (with a shell thickness of ～1 nm) clearly demonstrate the enhanced absorption and the resulting enhancement in photocurrent due to the plasmonic effects. An efficiency enhancement of over 18 % is obtained for the best plasmonic perovskite solar cell containing Au@SiO₂ nanoparticles in Au@SiO₂-TiO₂ weight ratio of ～1 %. Incident photon-to-current conversion efficiency (IPCE) data also showed enhancement in photocurrent for the plasmonic device. The quasi-static modelling approach provides a good correlation between theory and experiment.