J. Puišo

Growth of PbS thin films on silicon substrate by SILAR technique

Lead sulfide thin films were grown on (100)Si and (111)Si crystalline substrates by successive ionic layer adsorption and reaction, (SILAR), technique from solution phase at room temperature and normal pressure. The stress development, crystallinity and crystallite size, morphology and roughness and composition of the films were characterized as a function of the film thickness. The PbS thin films were polycrystalline and cubic. The residual stress in PbS was tensile and changed depending on the growth mode and thickness of the PbS films.

Biosynthesis of silver nanoparticles using lingonberry and cranberry juices and their antimicrobial activity

In this study lingonberry and cranberry juices were used for silver nanoparticle synthesis. The berry juices were characterized by total phenolics, total anthocyanins and benzoic acid content, respectively 1.9-2.7mg/ml, 55.2-83.4mg/l and 590.8-889.2mg/l. The synthesis of silver nanoparticles was performed at room temperature assisting in solutions irradiated by ultraviolet for 30min. Ultraviolet-visible (UV-vis) spectroscopy and microscopy confirmed the formation of nanoparticles as well as the dark red color of colloid of silver samples showed the formation of stable nanoparticles. Broad localized surface plasmon resonance (LSPR) peaks in UV-vis spectra indicated the formation of polydispersive silver nanoparticles and LSPR was observed at 485nm and 520nm for the silver nanoparticles synthesis using lingonberry and cranberry juices, respectively. The antimicrobial activity of silver nanoparticles was determined against the reference strains of microorganisms that could be found in food products: Staphylococcus aureus ATCC 25923, Salmonella typhimurium ATCC 13076, Listeria monocytogenes ATCC 19111, Bacillus cereus ATCC 11778, Escherichia coli ATCC 25922, Bacillus subtilis ATCC 6633, Candida albicans ATCC 10231 and foodborne B. cereus producing and non-producing enterotoxins. Silver nanoparticles showed a broad spectrum of antimicrobial activity and were most active against S. aureus ATCC 25923, B. subtilis ATCC 6633 and B. cereus ATCC 11778 reference cultures, and less active against C. albicans ATCC 10231 and foodborne B. cereus. It can be concluded that lingonberry and cranberry juices could be used as bioreductants for silver ions.

Synthesis and characterization of silver nanoparticles

Silver nanoparticles have received considerable attention due to their attractive physical and chemical properties. The surface plasmon resonance and large effective scattering cross section of individual silver nanoparticles make them ideal candidates for molecular labeling, where phenomena such as surface enhance Raman scattering (SERS) can be exploited. In addition, silver nanoparticles have recently been shown to be a promising antimicrobial material. In the present research silver colloid was produced by sodium citrate reduction. The colloidal silver was incorporated by dip-coating to the polymer substrate. X-Ray Fluorescence Spectroscopy (XRF), Atomic force microscopy (AFM), ultraviolet-visible spectroscopy (UV-VIS ) and SERS indicate that the produced structures include metallic crystalline silver nanoparticles. The surface plasmon resonance peak in absorption spectra of silver particles showed an absorption maximum at 420-500 nm. The silver - polymer nanocomposites structures with selective light properties as a result of plasmon resonance shifting in the UV-VIS wavelength region were produced.

The Polymeric Layers Formation by Sorption from Organic Solutions

The formation and morphology of polymethylmethacrylate (PMMA) films on crystalline silicon Si (100), quartz glass and polyethyleneterepftalate (PET) substrates exposed to plasma processing by immersion into toluene solution, was investigated exper imentally. The dependence on the type and conditions of substrate processing was studied by lase r ellipsometry, Fourier transform infrared spectroscopy, and atomic force microscopy. It i s shown, that as a result of sorption processes and interaction between the polymer macromolecule s and the substrate surface, the thin polymeric layers are formed with a structure determ ined by the substrate properties. The morphology of thin film has a tendency to nanostructurisation, and as a r esult periodic nanostructures can be formed. Introduction Understanding of polymer adsorption and film growth on inorganic substrates is of great interest for science and technology. Various methods are used to deposit polymers on substrates. Sorption of polymer molecules on the substrate [2] from dilute solutions allows very thin polymer layers, of thickness comparable to the size of the macromolecules to be forme d. Th properties of the film deposited using this method is defined by the properties of surface, and the kinetics of removing of molecules of solvent from the film. It is known that polymer films with a thickness less than about double the radius of gyration of an unperturbed chain, 2Rg, can be defi n d as two-dimensional ultra thin films [1-3]. The flexible polymer chain in an ultra thin film is in a non-equilibrium state, since the conformational entropy of an individual chain in the constrained thin re g ons is reduced as compared to that of a three-dimensional solid state [3,4]. Obviously macromolecules adsorbed on the surface have certain 2 D mob ility and during removal of a solvent, depending on the concentration of the cross linking, can cause cha nges in the morphology of the film. Combination of the process of condensation of macromol ecules combined with the moist air blown parallel to the surface appears a very simple and flexible way to make materials with the regular 3D structure [5]. Air flow, coupled w ith convection currents on the solution surface due to evaporation, drives the ordering or packing of the water droplets into hexagonally packed arrays. It is shown [5] that the process depends on the presence of atmospheric moisture and the observed structure is a result of the formation and subsequent crystallization of “breath figures”. Similar pictures on the nanoscale were observe d for the polystyrene and polymethylmethacrylate formed on the crystalline silicon [9]. The aim of this study is to investigate regularities of the P MMA films formation depending on the properties of substrate, but selecting substrates with different r oughness and thermal conductivity such as crystalline silicon, quartz glass and polyethylenetere pf alate (PET) and applying evaporation of solvent in standard conditions with no extra moisture or air blowing. Solid State Phenomena Online: 2003-06-20 ISSN: 1662-9779, Vol. 94, pp 265-270 doi:10.4028/www.scientific.net/SSP.94.265

Periodic structures modified with silver nanoparticles for novel plasmonic application

Forming structures similar to or smaller than the optical wavelength offers a wide range of possibilities to modify the optical properties of materials. Tunable optical nanostructures can be applied as materials for surface-enhanced spectroscopy, optical filters, plasmonic devices, and sensors. In this work we present experimental results on technology and properties of periodical, polymer based optical structures modified by ordered adsorption of silver nanoparticles. These structures were formed combining UV hardening and dip coating from colloidal solutions. We have investigated the influence of silver nanoparticles assembly on the ambient conditions (deposition temperature and time) and surface features (periodicities and shape) of the template micro structures. Optical absorbance as well as morphology of the structures containing silver nanoparticles were investigated by UV-VIS spectroscopy, AFM, SEM and optical microscopy. The influence of silver nanoparticles on the optical properties of the structures was investigated by polarized light spectroscopy (Grating Light Reflection Spectroscopy - GLRS). From the results of this study we propose a low cost procedure for fabricating structures that could be potentially new type of plasmonic sensors exploiting surface enhanced plasmon resonance in silver nano structures.

CdS-PbS Multilayer Thin Films Grown by the SILAR Method

The successive ionic layer adsorption and reaction (SILAR) technique was used to grow double layer structures of CdS-PbS. The growth of thin films by the SILAR technique from diluted aqueous solutions was achieved, ionic layer by ionic layer, at room temperature and normal pressure. The thin films on silicon were characterized by XRD, AFM, XPS. It was established that a double layer could be grown on crystalline silicon and that the morphology and crystallinity of the films could be controlled by changing the lead precursor.

Oxygen Plasma Processing of Silicon and Silica Substrates for Thin Films of Polymer Blends

The influence of plasma processing of silica and crystalline silicon substrates on the formation of polymeric layers of PS/PMMA blends by sorption from 50 vol. % concentration toluene solutions was analyzed. The morphology dependence of PS/ PMMA blend films on the type and condition of substrate processing was studied by X-ray photoelectron spectroscopy (XPS), ellipsometry and atomic force microscopy (AFM). It was shown that reduction of carbon and oxygen components from the surface contaminants as well as the existence of a nonstoichiometric SiOx layer on the Si surface contributed to the hydrophilicity of the substrate. These processes can be used to produce thin nanostructured polymer blend films.

The Influence of the Pretreatment of Si Substrate on the Growth of PbS Thin Films in the SILAR Technique

The successive ionic layer adsorption and reaction (SILAR) te chnique used to deposit PbS, involved the growth of thin films from dilute solutions (0.2M Pb(CH 3OO)2 as lead and 0.4 M CH3CSNH2 (Thioacetamide) as sulphur precursor) ionic layer by ionic layer at room temperature and normal pressure. The growth of the PbS thin film on Si was charact erized by XRD and AFM. The effect of the Si substrate pretreatment (by concentrated H 2SO4 +H2O2 „piranha” or by HF) on the film growth has been studied. After HF pretreatment the PbS fi lm growth had a more clear 3D mode as compared with growth after H 2SO4 +H2O2 treatment.

Synthesis and Characterization of Silver-Poly(Methylmethacrylate) Nanocomposite

Silver nanoparticles and polymethylmethacrylate (PMMA) nanocomposite was prepared in situ by photo-induced thermal reduction method. The interfacial interaction of Ag nanoparticles and PMMA polymer is investigated using Fourier transform infrared spectroscopy (FTIR). Optical properties of Ag/PMMA films were characterized by UV-Vis and FTIR absorption spectroscopy. Effects of the UV and heat-treatment time on the formation of silver nanoparticles in PMMA matric matrix were studied in detail. These investigations proposed new nanocomposite structures. They can be defined as plasmonic materials with improved optical properties. Ag/PMMA structures may found a number of technological applications: in optical devices, various plasmonic sensors or even in nanomedicine.

Design and fabrication of piezoelectric nanocomposite structures for microdevice applications

Abstract. We present a new group of piezoelectric nanocomposite thin films based on integrating piezoelectric material poly(vinylidene fluoride) and nanoparticles of barium titanate in a matrix of an organic polymer poly(methyl methacrylate). Implementation of piezoelectric properties in designed new nanocomposites allows us not only to increase the sensitivity and functionality of the overall system, where this material is used, but also to expand the application fields in sensing and actuating systems. Results implied that new nanostructures fabricated by nanoimprint lithography exhibit good piezoelectric, surface, and mechanical properties and allow independent control of tribological properties. Formed nanocomposite systems were integrated in designing optical components employed in medicine for sensing applications.