Algirdas Selskis

Nanocomposite films and coatings produced by interaction between graphite oxide and Congo red

Nanocomposite films and coatings were produced from the aqueous solutions containing different proportions of graphite oxide (GO) and Congo red by filtering through a polycarbonate membrane filter into alkaline media. They were examined by electron microscopy, Raman and FTIR spectroscopy, XRD, contact angle, and electrical conductivity measurements. It was established that the Congo red is able to interact through its amino groups with different functional groups of GO to form larger moieties composed of the nanoplatelets of GO. Raman spectroscopy revealed quinoid-like ring structure for dye adhering to the GO. In the case when the interaction occurs with the terminal functional groups located on the edges of the nanoplateletes of GO, larger crystallites in the nanocomposite are formed. The interaction between the Congo red and functional groups of GO situated in a basal plane leads to more compact structure of the nanocomposite. Pulsed laser treatment was used to reduce GO to graphene. Raman spectra of laser treated areas show positive effect of addition of the Congo red on the graphene yield in nanocomposite coatings after the laser treatment.

Synthesis and evolution of crystalline garnet phases in Y3Al5-xInxO12

In the present work the sinterability and microstructal evolution of mixed-metal Y3Al5-xInxO12 (0 ≤ x ≤ 2) (YAING) garnet powders synthesized by an aqueous sol-gel process were investigated. The synthesized samples were characterized by X-ray powder analysis (XRD). It was demonstrated that the formation of Y3Al5-xInxO12 garnets proceeds only within narrow substitutional range. Scanning electron microscopy was used to study the morphology and microstructure of the ceramic samples.

Effect of deposition method and substrate surface quality on laser-induced damage threshold for repetitive 13-ns and 130-fs pulses

A comparison of laser induced damage thresholds (LIDT) of ion assisted deposition (IAD) and standard electron beam deposition dielectric coatings on BK7 glass with different surface roughness was performed. Five types of high reflectance mirrors at 800 nm and two types of high reflectance mirrors at 1064 nm were tested. Mirror coatings were made of ZrO2 and SiO2. Automated LIDT measurements were performed according to the requirements of current ISO 11254-2 standard. Two lasers were used for the measurements: Nd:YAG (l = 1064 nm, t = 13 ns) and Ti:Sapphire (l = 800 nm, t = 130 fs ). All measurements were performed at 1-kHz pulse repetition rate (S-on-1 test). A fixed spot size was used for each laser. For 1064 nm it was ~ 70 um and for 800 nm ~ 500 um. The damage morphology and structure of coatings were characterized by an atomic force microscopy (AFM), Nomarski microscopy and X-ray diffraction (XRD).

Stereophotography and spatial surface reconstruction using scanning electron microscopy images

Abstract Three-dimensional reconstruction technique to fully characterize structural performance of solid materials is suggested. The three-dimensional sample data out of the SEM images taken from different angles were extrapolated, measured and interpreted. In stereometry, the technique of three dimensional SEM imaging is fairly straightforward. Selected specimen area is photographed using SEM imaging tools from two different angles. Tilting is performed using standard SEM manipulation tools. In some cases, the specimen must be rotated to such a position, in which the tilting is done on visual ordinate axis. The resulting images are combined in pairs using any three-dimensional anaglyph software available to produce an anaglyph image, which, in turn, can be analyzed using standard 3D glasses. To achieve finer results, extrapolation of spatial data was done from three or more sample images using visual reconstruction software applications. This technique for recovering spatial data from the SEM pictures (structure-from-motion) is the VisualSFM software, which is an application for spatial reconstruction using structure from sample motion. Using VisualSFM, the images are analyzed for matching points and the camera angle is guessed for each image. Any number of additional viewports can be added to VisualSFM software. Based on this input, a surface is reconstructed where the matching points intersect and a colour value is assigned. The software produces a cloud of points, which has to be processed externally. Freely available software, such as MeshLab can be used to join the point cloud to a mesh and, as a second step of reconstruction, apply surface properties to the mesh polygons. The gold particles were selected as model material for the spatial 3D surface reconstruction.

Sol-gel synthesis and study of neodymium substitution effects in Co-Al-Nd-O system with possible applications as novel inorganic pigments

AbstractIn the present work, the formation of cobalt aluminium spinel (CoAl2O4) as well as novel cobalt neodymium-aluminates with nominal compositions of CoAl1.75Nd0.25O4, CoAl1.5Nd0.5O4 and CoAlNdO4 by an aqueous sol-gel process and the sinterability of the products are investigated. The metal ions, generated by dissolving starting materials of metals in the diluted acetic acid were complexed by 1,2-ethanediol to obtain the precursors for the mixed metal ceramics. The phase purity of the synthesized compounds was characterized by powder X-ray diffraction analysis and infrared spectroscopy. The microstructural evolution and morphological features of the products were studied by scanning electron microscopy and atomic force microscopy, which together with the optical characterization of these new compounds showed that the sol-gel-derived materials could be successfully used as effective cobalt-based ceramic pigments.

Advanced design of UV waveplates based on nano-structured thin films

Optical elements for polarization control are one of the main parts in advanced laser systems. The state and intensity of polarized light is typically controlled by optical elements, namely waveplates. Polymers, solid or liquid crystals and other materials with anisotropic refractive index can be used for production of waveplates. Unfortunately, most of aforementioned materials are fragile, unstable when environmental conditions changes, difficult to apply in microsystems and has low resistance to laser radiation. Retarders, fabricated by evaporation process, do not consist any of these drawbacks. In order to manufacture such optical components with high quality, characterisation of deposition parameters are essential. A serial bi-deposition method was employed to coat anisotropic layers for polarisation control. Such waveplate can be deposited on micro optics or other optical elements, essentially improving compact optical systems. The range of available materials is limited by absorption losses for waveplates in UV spectral region. Therefore, the investigation was accomplished with four eligible candidates – TiO2, LaF3, Al2O3 and SiO2. Structural (XPS, XRD) and optical (spectrophotometry, ellipsometry) analysis have shown Al2O3 and SiO2 as the most applicable materials for UV spectral region.

New generation all-silica based optical elements for high power laser systems

Laser resistance of optical elements is one of the major topics in photonics. Various routes have been taken to improve optical coatings, including, but not limited by, materials engineering and optimisation of electric field distribution in multilayers. During the decades of research, it was found, that high band-gap materials, such as silica, are highly resistant to laser light. Unfortunately, only the production of anti-reflection coatings of all-silica materials are presented to this day. A novel route will be presented in materials engineering, capable to manufacture high reflection optical elements using only SiO2 material and GLancing Angle Deposition (GLAD) method. The technique involves the deposition of columnar structure and tailoring the refractive index of silica material throughout the coating thickness. A numerous analysis indicate the superior properties of GLAD coatings when compared with standard methods for Bragg mirrors production. Several groups of optical components are presented including anti-reflection coatings and Bragg mirrors. Structural and optical characterisation of the method have been performed and compared with standard methods. All researches indicate the possibility of new generation coatings for high power laser systems.

Optical Properties of HfO 2 Thin Films Grown by Atomic Layer Deposition

Atomic layer deposition was used to grow HfO2 thin films at different process temperatures. Optical constants and laser induced damage thresholds were determined and compared with thin films deposited by ion beam sputtering technology.

Investigation of Electrocatalytic Activity of the Nanostructured Au-Cu Catalyst Deposited on the Titanium Surface towards Borohydride Oxidation

Sodium borohydride (NaBH4) is characterized by interesting options for electrochemical power generation as a source of hydrogen or anodic fuel for direct borohydride fuel cells (DBFC) and batteries. In recent years the DBFCs are being developed especially for portable power supply. An active search for costeffective catalysts is still in progress. A simple way for fabrication of the nanostructured Au(Cu)/Ti catalysts by a two-step process which involves electroless copper deposition followed by a spontaneous Au displacement from the chloro-complex solution is presented herein. The morphology and composition of fabricated catalysts were characterized using field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDAX). The electrochemical behavior of the fabricated nano-Au(Cu)/Ti and Cu/Ti catalysts was examined by means of cyclic voltammetry (CV). The electrocatalytic activity of the catalysts towards the oxidation of BH4 ions was compared with that of bare Au electrode. Well-adherent gold-coated copper films (Au/Cu), with particles of a few nanometers in size have been fabricated on the titanium surface by immersion of Cu/Ti electrode into the gold-containing solution for various time periods as testified in Fig. 1. Electroless copper deposited on the titanium surface produced a layer of polycrystalline copper with the average size of crystallites ca. 1 μm. Notably the thickness of the electroless copper layer was about 1.5 μm. The Au particles appear as bright crystallites of cubic form of 10 up to 50 nm in size and are homogeneously dispersed on the copper surface (Fig. 1, b-d).