Plasmon-enhanced Förster energy transfer in Langmuir-Blodgett films based on organic dyes

The effect of plasmon resonance of silver island films (SIF) on the interlayer Förster resonance energy transfer (FRET) between xanthene and oxazine dye molecules was studied. It has been shown that the enhancement of FRET can be controlled by changing in the distance between the donor-acceptor system and the SIF. The maximum increase in energy transfer efficiency (EET) by a factor of 2.6 was recorded at a distance of 6 nm from the SIF. The assumption was made that an increase in EET can be associated with both the direct appearance of a plasmon-enhanced rate constant of energy transfer and an increase in the quantum yield of the energy donor in direct contact with the SIF. The results can serve as a basis for studying of photoinduced processes in hybrid materials such as “organic dye-plasmon nanoparticles”, to increase the photosensitivity of solar cells in the visible region of the spectrum, and for the studying of photobiological processes, as well as to create materials with desired properties, sensors and light energy converters.

Surface plasmon-polaritons in deformed graphene excited by attenuated total internal reflection

In the present work we theoretically investigated the excitation of surface plasmon-polaritons (SPPs) in deformed graphene by attenuated total reflection method. We considered the Otto geometry for SPPs excitation in graphene. Efficiency of SPPs excitation strongly depends on the SPPs propagation direction. The frequency and the incident angle of the most effective excitation of SPPs strongly depend on the polarization of the incident light. Our results may open up the new possibilities for strain-induced molding flow of light at nanoscales.

Improvement of the photoinduced birefringence in azopolymer PAZO doped with TiO2 nanoparticles via thermal treatment

We present a study of the photoinduced birefringence in nanocomposite films of the azopolymer PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfon amido]-1,2-ethanediyl, sodium salt]) doped with TiO2 nanoparticles (NP) with different concentrations before and after thermal annealing. The NP represent nanopowder with primary particle size 21 nm. The concentration of the NP was varied from 0% (non-doped azopolymer film) to 5 wt%. The thermal process, applied to the nanocomposite films, includes 1 h heating at 200°C. Previous studies of PAZO show that the polymer is stable up to 270°C. We study the dependence of the maximal birefringence induced with He-Cd laser (λ= 442 nm) on the concentration of the TiO2 NP in the azopolymer thin films as well as thermal effect on the absorbance spectra of the thin films. As indicated by our results, the birefringence is higher for the thermally annealed samples. An increase of the photoinduced birefringence is also observed for the nanocomposite layers with 1% NP for the non-annealed films, and with 2% NP for the annealed films.

Particle contamination monitoring in the backscattering light experiment for LISA

In the context of space-based optics, contamination due to particle deposition on the optics is inevitable and constitutes a critical issue. This gets more challenging for the sensitive heterodyne measurements of the Laser Interferometer Space Antenna (LISA), the space-based gravitational wave observatory to be launched in 2034. Therefore, table-top experiments need to be developed for a better understanding of how micrometer to millimeter sized dust particles, present on optical surfaces, affect LISA measurements. In this work, we present an experimental setup for the simultaneous measurement of the coherent backscattering and the monitoring of particles deposition on the optics to be tested. The results of the first measurements are presented and discussed in this article.

Preparation and characterization of sintered clay ceramic membranes water filters

Metal oxide ceramic is getting more attention in current times due to their unique pore structures, hydrophilic surfaces, high chemical, thermal and mechanical stabilities which offer avenues for application in water treatment. This paper presents the results of an experimental study on the effects of different ratios of clay, grog, sawdust and bone char on efficiency of ceramic composite water filters. Filter of different designs were developed from clay (50, 60, 70, 75 and 80) |%|, sawdust (15, 25, and 35) |%|, grog (5 and 15) |%| bone char and 5|%| ratios by volume and sintered at temperature of 900°C for 6 hours. The Phase and functional group identification of sintered filter investigated with x-ray diffraction and infrared spectroscopy revealed the presence of mixed phase and hydroxyl functional group on the surface of sintered filter. Field emission scanning electron microscopy (FESEM) revealed the porous nature of the microstructures of the sintered filter elements. The superior ceramic water filter design (C900-50-15-35) with total porosity 35.89±0.04|%|, flow rate 2.05±0.41|%| and the percent E coli, nitrite and fluoride removal efficiency: 99.6±0.40 |%|, 81.17±0.22|%| and 96.4±0.42|%| were obtained from this work. Porosity evaluated by BET study for C900-50-15-35 demonstrated an average pore size and surface area of 5 |nm | and 7.30|m2/g|, respectively.

Crystallographically Defined Silicon Macropore Membranes

Laser ablation with nanosecond-pulsed Nd:YAG laser irradiation combined with anisotropic alkaline etching of Si wafers creates 4-20 μm macropores that extend all the way through the wafer. The walls of these macropores are crystallographically defined by the interaction of the anisotropy of the etchant with the orientation of the single-crystal silicon substrate: rectangular/octagonal on Si(001), parallelepiped on Si(110), triangular/hexagonal on Si(111). Laser ablation can create pillars with peak-tovalley heights of over 100 μm. However, with nanosecondpulsed irradiation at 532 nm, the majority of this height is created by growth above the original plane of the substrate whereas for 355 nm irradiation, the majority of the height is located below the initial plane of the substrate. Repeated cycles of ablation and alkaline etching are required for membrane formation. Therefore, irradiating with 355 nm maintained better the crystallographically defined nature of the through-pores whereas irradiation at 532 nm led to more significant pore merging and less regularity in the macropore shapes. Texturing of the substrates with alkaline-etching induced pyramids or near-field modulation of the laser intensity by diffraction off of a grid or grating is used to modulate the growth of ablation pillars and the resulting macropores. Texturing causes the macropores to be more uniform and significantly improves the yield of macropores. The size range of these macropores may make them useful in single-cell biological studies.

Optical interferometry and photoacoustics as in-situ techniques to characterize the porous silicon formation: a review

Porous Silicon (PSi) is a groundbreaking material because its physicochemical properties can be customized through its porosity. This means that monitoring and control of the growing parameters allows the fabrication of PSi-based systems with controlled properties. Interferometry and photoacoustics are non -invasive, non - contact, real-time (in-situ) techniques used to characterize the phenomena that takes place during the formation of PSi. This work presents the mathematical and experimental aspects related to the implementation of the techniques mentioned above, which are meant to characterize the PSi growth in fluoride-based electrolyte media. These methods can determine macroscopic parameters of PSi such as thickness, porosity profile trough effective medium approximation (EMA), refractive index, etching rate, and RMS roughness under 100 nm. The monitoring ability of these techniques is strongly dependent on the wavelength of radiation used. However, it is possible to monitor thickness from λ0/4 to ∼ 1/ α0, where α0 is the optical absorption coefficient at λ0. Also, these techniques can be implemented as feedback control on the etching processes for fabrication of PSi.

Covalent grafting of graphene oxide on functionalized macroporous silicon

Graphene oxide (GO) is a single-atom-thick and two-dimensional carbon material that has attracted great attention because of its remarkable electronic, mechanical, chemical and thermal properties. GO could be an ideal substrate for the development of label-free optical biosensors, however, its weak photoluminescence (PL) strongly limits the use for this purpose. In this study, we developed a covalent chemical strategy in order to obtain a hybrid GO-macroporous silicon (PSi) structure for biomedical applications. The realized structure was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM)water contact angle (WCA) measurements, Fourier transform infrared spectroscopy (FTIR) and label- free optical methods based on spectroscopic reflectometry and PL analysis. Investigations showed that the hybrid structure is suitable as a transducer material for biosensing applications due to its peculiar optical properties resulting from the combination of GO and PSi.

Porous Materials for Immune Modulation

Biocompatible materials have a great potential to engineer immunology towards therapeutic applications. Among them, porous materials have attracted much attention for immune modulation due to their unique porous structure. The large surface area and pore space offer high loading capacity for various payloads including peptides, proteins and even cells. We first introduce recent developments in the porous particles that can deliver immunomodulatory agents to antigen presenting cells for immunomodulation. Then, we review recent developments in the porous implants that can act as a cellattracting/ delivering platform to generate artificial immunomodulatory environments in the body. Lastly, we summarize recent findings of immunogenic porous materials that can induce strong immune responses without additional adjuvants. We also discuss future direction of porous materials to enhance their immunomodulatory potential for immunotherapeutic applications.

Electrodeposition and characterization of one-dimensional CuInSe2 nanostructures in mesoporous silicon templates

In this work, the electrodeposition and characterization of 1D CuInSe2 (CIS) nanostructures formed by the assistance of porous silicon (PSi) templates is presented. The formation of CIS was found to be potential dependent on the specific substrate being used. The filling process of the pores of PSi template was studied directly by the current transient response during electrodeposition of nanostructured CIS and results were compared with FESEM images. CIS nanostructures were fully characterized by using FE-SEM, FIB, XRD, and Raman spectroscopy, in order to know their physical properties.