Electrodynamic Configurational Resonances in Nanocomposite Thin Films

Plasmonics - The thin films with embedded identical spheroidal nanoparticles (NPs) are studied in order to derive conditions of configurational resonances. These resonances are determined by the...     

Atomic Layer Deposition of Tin Monosulfide Thin Films

Thin film solar cells made from earth‐abundant, non‐toxic materials are needed to replace the current technology that uses Cu(In,Ga)(S,Se)₂ and CdTe, which contain scarce and toxic elements. One promising candidate absorber material is tin monosulfide (SnS). In this report, pure, stoichiometric, single‐phase SnS films were obtained by atomic layer deposition (ALD) using the reaction of bis(N,N′‐diisopropylacetamidinato)tin(II) [Sn(MeC(N‐ⁱPr)₂)₂] and hydrogen sulfide (H₂S) at low temperatures (100 to 200 °C). The direct optical band gap of SnS is around 1.3 eV and strong optical absorption (α > 10⁴ cm^?1) is observed throughout the visible and near‐infrared spectral regions. The films are p‐type semiconductors with carrier concentration on the order of 10¹⁶ cm^?3 and hole mobility 0.82–15.3 cm²V^?1s^?1 in the plane of the films. The electrical properties are anisotropic, with three times higher mobility in the direction through the film, compared to the in‐plane direction.     

Fluorescence Resonance Energy Transfer Near Thin Films on Surfaces

A theory is developed for resonant energy transfer between donor and acceptor molecules outside of a solid coated with a thin film. The energy transfer rate is expressed in terms of a second-rank tensor, allowing one to consider all possible orientations of the transition dipole moments of the molecules. The theory of images is employed to construct expressions valid in the near-field approximation. This theory is extended to the full electrodynamic theory valid over all distances. Connections are made between the expressions for the image charges and the Fresnel coefficients from optics. It is found that the energy transfer rates are strongly influenced by surface resonances, including the interfacial surface plasmons and the two-dimensional plasmon of a metallic film. The possibility of the film supporting Fabry–Perot resonator modes is discussed.     

Novel Covellite CuS Single-Crystal Thin Films for Optoelectronic Applications

Copper sulfide (CuS) thin films have been used in many applications such as solar cells, photo-thermal, electro-conductive, and microwave shielding. In this work, copper sulfide thin films were deposited on glass and silicon substrates by thermal evaporation of in situ synthesized CuS powder. XRD analysis of these films revealed a single-crystal structure, AFM measurements indicated the films have a surface roughness (14.1 nm) and agglomerates of multiple monocrystalline particles with average size (66 nm), and the optical properties were investigated by UV-Vis spectrophotometer showing the films have high transmission (>80%) in the visible region and low absorbance with wide energy gap (3.813 eV). This novel structure with outstanding optical properties makes it very promising optical materials in optoelectronics.

     

Optical and Photocatalytic Measurements of Co-TiO2 Nanoparticle Thin Films

Plasmonics - Co-TiO2 nanoparticle thin films were synthesized by sol-gel method. The structural properties of the synthesized sample were studied using FTIR, XRD, and TEM. XRD confirmed the...     

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.     

Reduced Graphene Oxide Thin Films as Ultrabarriers for Organic Electronics

Encapsulation of electronic devices based on organic materials that are prone to degradation even under normal atmospheric conditions with hermetic barriers is crucial for increasing their lifetime. A challenge is to develop ultrabarriers that are impermeable, flexible, and preferably transparent. Another important requirement is that they must be compatible with organic electronics fabrication schemes (i.e., must be solution processable, deposited at room temperature and be chemically inert). Here, a lifetime increase of 1300 h for poly(3‐hexylthiophene) (P3HT) films encapsulated by uniform and continuous thin (≈10 nm) films of reduced graphene oxide (rGO) is reported. This level of protection against oxygen/water vapor diffusion is substantially better than conventional polymeric barriers such as Cytop, which degrades after only 350 h despite being 400 nm thick. Analysis using atomic force microscopy, X‐ray photoelectron spectroscopy, and high‐resolution transmission electron microscopy suggest that the superior oxygen gas/moisture barrier property of rGO is due to the close interlayer distance packing and absence of pinholes within the impermeable sheets. These material properties can be correlated to the enhanced lag time of 500 h. The results provide new insight for the design of high‐performance and solution‐processable transparent ultrabarriers for a wide range of encapsulation applications.     

Optical Absorption Transitions in Mn Star-like Helical Sculptured Thin Films

Plasmonics - In this work, we have shown that by engineering of the morphology of a manganese thin film as a star-like helical sculptured thin film (pine tree shaped) (SHSTF), three broad band...     

Solvation Force and Confinement-Induced Phase Transitions of Model Ultra Thin Films

Abstract

The static (equilibrium) properties of atomically thin films confined between two surfaces are studied as a function of surface separation by Grand Canonical Monte Carlo and Molecular Dynamics simulations. A model was used, in which the fluid and wall species consist of two different Lennard-Jones rare gas atoms. This was designed to mimic the static SFA experiments in which it is known that epitaxy is not necessary for inducing an oscillatory solvation force in simple non polar liquids. We have been able to simulate, using this simple system, many aspects of the equilibrium properties observed in the experiments. The solvation force is an exponentially damped, periodic curve. All peaks of maximum amplitude in the solvation force correspond to solid-like structures. These structures melt in increasing the surface separation. A further increase in separation leads to the addition of a whole layer and the recrystallisation of the film. In addition this model displays an interesting phenomenon of confinement induced solid-solid phase transition. Two different stable packing (bcc and triclinic) can be observed in the bilayer film and a transition from one to the other occurs when the surface separation is changed. This phase change has been studied as a function of pressure and temperature. As compared to the simulations using a ‘commensurate’ model, in which the fluid and wall species are made of like atoms, the results obtained here are in much better agreement with experimental findings.     

Method for Staining and Washing Thin Sections on Support Films

A procedure is described for staining large numbers of thin sections on support films for use with one-hole grids. The film is picked up, carried and protected using easily made plastic blocks. Loop-tipped forceps are then used to transfer tissue ribbons from the knife boat to the support film. A large number of tissue sections can then be stained and washed simultaneously in a modified Pyrex dish without damaging the film. After staining, the slot in the one-hole grid is centered over the tissue ribbon, and the grid is attached to the film. The method is suitable for serial reconstruction and the unobstructed viewing of large thin sections in the TEM.     

Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain such surfaces are described. The first approach is the preparation of single terminated perovskite SrTiO₃ (001) and DyScO₃ (110) substrates. Wet etching was used to selectively remove one of the two possible surface terminations, while an annealing step was used to increase the smoothness of the surface. The resulting single terminated surfaces allow for the heteroepitaxial growth of perovskite oxide thin films with high crystalline quality and well-defined interfaces between substrate and film. In the second approach, seed layers for epitaxial film growth on arbitrary substrates were created by Langmuir-Blodgett (LB) deposition of nanosheets. As model system Ca₂Nb₃O₁₀^- nanosheets were used, prepared by delamination of their layered parent compound HCa₂Nb₃O₁₀. A key advantage of creating seed layers with nanosheets is that relatively expensive and size-limited single crystalline substrates can be replaced by virtually any substrate material.     

Ag and Sn Nanoparticles to Enhance the Near-Infrared Absorbance of a-Si:H Thin Films

Silver (Ag) and tin (Sn) nanoparticles (NPs) were deposited by thermal evaporation onto heated glass substrates with a good control of size, shape and surface coverage. This process has the advantage of allowing the fabrication of thin-film solar cells with incorporated NPs without vacuum break, since it does not require chemical processes or post-deposition annealing. The X-ray diffraction, TEM and SEM properties are correlated with optical measurements and amorphous silicon hydrogenated (a-Si:H) films deposited on top of both types of NPs show enhanced absorbance in the near-infrared. The results are interpreted with electromagnetic modelling performed with Mie theory. A broad emission in the near-infrared region is considerably increased after covering the Ag nanoparticles with an a-Si:H layer. Such effect may be of interest for possible down-conversion mechanisms in novel photovoltaic devices.     

Silver Nanoparticle Effect on Spectral-Kinetic Properties of Thin Nickel Phthalocyanine Films

Plasmonics - We have investigated spectral and spectral-kinetic properties of hybrid plasmonic nanocomposites on silver nanoparticle monolayers and thin nickel phthalocyanine films. The...     

Plasmonic Control of Near-Interface Exciton Dynamics in Defect-Rich ZnO Thin Films

Zinc oxide (ZnO) is an attractive material for many electro-optical applications, but the control of impurities remains an issue in device fabrication. For this paper, the dynamics of defect states produced by annealing ZnO thin films at temperatures of 400–800 °C were probed by band-edge pump-probe spectroscopy in differential reflection and transmission. The distinction between the differential reflection and transmission spectra allowed for the analysis of ultrafast near-interface dynamics, which cannot be separated from the bulk thin-film dynamics by traditional ultrafast spectroscopies. In particular, simultaneous differential reflection and transmission spectroscopy provided clear evidence that the band-edge recombination dynamics in samples annealed at 400 °C were absent near the ZnO/substrate interface. However, the Purcell enhancement observed in Ag/ZnO heterostructures resulted in the dramatic emergence of the band-edge recombination signal nearly two orders of magnitude greater in intensity than the defect differential reflectivity. This indicates that the spatial range of the Purcell effect is at least twice as large as inferred from previous photoluminescence studies.     

Large Optical Nonlinearity of Surface Plasmon Modes on Thin Gold Films

We investigate the optical nonlinear effects of a long-range surface plasmon polariton mode propagating on a thin gold film. These effects may play a key role in the design of future nanophotonic circuits as they allow for the realization of active plasmonic elements. We demonstrate a significant enhancement of the transmission on a timescale below a millisecond as well as a phase shift exceeding 2π already for modest peak powers of 150 mW. On the contrary, slow effects suppress the transmission on a millisecond timescale.     

Towards Engineering Nanoporous Platinum Thin Films for Highly Efficient Catalytic Applications

Porous metals attract significant interest for use in diverse electrochemical catalytic applications. However the fabrication of scalable and controlled porous metal structures on the nanoscale, particularly with highly catalytic pure Pt, still remains a significant challenge. We demonstrate highly engineered nanoporous Pt thin films by the dealloying of a Pt‐Si binary alloy system with a predetermined alloy composition. Controlled pore dimensions and nanostructures are obtained by tailoring the Pt‐Si alloy composition followed by selective Si etching. As a result, isotropic open nanopores are formed in continuous Pt ligaments and the porosity becomes larger on increasing the Si/Pt atomic ratio, which leads to the formation of a higher surface area and active catalytic sites. The formed nanoporous Pt film shows a 32‐times‐higher catalytic activity than Pt/C catalysts, with a high current density and low charge‐transfer resistance during methanol electro‐oxidation. The results reported here open up possibilities to develop high‐performance and reliable catalytic electrodes in energy and environmental applications.