Asta Guobiene

Morphological, structural and optical properties of MoO2 films electrodeposited on SnO2∣glass plate

AbstactMoO2 films were prepared by electrodeposition under potential controlled conditions from an aqueous alkaline solution of sodium molybdate.Optical microscopy showed that films of different morphology were deposited. The surface roughness and grain size were determined by atomic force microscopy. The characterization of as-deposited films by X-ray diffraction analysis revealed their amorphous nature. The optical constants of films were derived from transmittance spectra recorded in the 310–1100 nm wavelength range. All films were highly absorptive and showed a direct band to band transition. From the absorption edge data, the values of the optical band gap Eg and the Urbach energy EU were determined based on Tauc’s model. The influence of film thickness on the extinction coefficient k, refractive index n, absorption coefficient a and the band gap energy Eg was studied.

Periodical Microstructures Based on Novel Piezoelectric Material for Biomedical Applications.

A novel cantilever type piezoelectric sensing element was developed. Cost-effective and simple fabrication design allows the use of this element for various applications in the areas of biomedicine, pharmacy, environmental analysis and biosensing. This paper proposes a novel piezoelectric composite material whose basic element is PZT and a sensing platform where this material was integrated. Results showed that a designed novel cantilever-type element is able to generate a voltage of up to 80 µV at 50 Hz frequency. To use this element for sensing purposes, a four micron periodical microstructure was imprinted. Silver nanoparticles were precipitated on the grating to increase the sensitivity of the designed element, i.e., Surface Plasmon Resonance (SPR) effect appears in the element. To tackle some issues (a lack of sensitivity, signal delays) the element must have certain electronic and optical properties. One possible solution, proposed in this paper, is a combination of piezoelectricity and SPR in a single element.

Optical characterization of diffractive optical elements replicated in polymers

Due to relative ease and cost effectiveness with which planar polymeric structures can be fabricated, diffractive optical elements replication in polymeric substrates are receiving global attention for a myriad of planar photonic and optoelectronic applications including optical interconnects. In this work we present an optical laser control method to control replication of microperiodic profile structures in polymers. Diffraction efficiency of diffraction gratings (originally produced in silicon, quartz glass and in replicated polymer substrates) was measured experimentally and estimated using linear dimensions of gratings or replica defined by atomic force microscopy (AFM). Diffraction efficiency of periodic structure was used to control the surface relief formation during the combined ion etching of crystalline Si (100) and replication of this structure using UV light hardening and hot embossing. The main experimental results are compared with the computer simulations where the standard programme (PCGrate-SX6.0) was employed.

Influence of PZT Coating Thickness and Electrical Pole Alignment on Microresonator Properties

With increasing technical requirements in the design of microresonators, the development of new techniques for lightweight, simple, and inexpensive components becomes relevant. Lead zirconate titanate (PZT) is a powerful tool in the formation of these components, allowing a self-actuation or self-sensing capability. Different fabrication methods lead to the variation of the properties of the device itself. This research paper covers the fabrication of a novel PZT film and the investigations of its chemical, surface, and dynamic properties when film thickness is varied. A screen-printing technique was used for the formation of smooth films of 60 µm, 68 µm, and 25 µm thickness. A custom-made poling technique was applied to enhance the piezoelectric properties of the designed films. However, poling did not change any compositional or surface characteristics of the films; changes were only seen in the electrical ones. The results showed that a thinner poled PZT film having a chemical composition with the highest amount of copper and zirconium led to better electrical characteristics (generated voltage of 3.5 mV).

Sol-Gel Synthesis of Mesoporous TiO2 Films for Visible Light Sensitive TiO2/CdS Heterostructures

Mesoporous TiO2 films were prepared by template assisted sol-gel method and used as support for deposition of CdS particles on its surface to produce visible light sensitive nanocomposites. The influence of the surface morphology of mesoporous titania matrix onto the TiO2/CdS heterostructure formation was investigated using UV-Vis, IR, low-angle XRD, SEM and AFM methods.

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.

Mesoporous TiO2 and TiO2/ZnO/Ag films: Sol-Gel Synthesis, Photoelectrochemical and Photocatalytic Properties

TiO2 and TiO2/ZnO films with silver nanoparticles (Ag NP’s) distributed in the matrix and on the surface were characterized by TEM, AFM and UV-Vis spectroscopy. Direct photoelectrochemical investigations of the TiO2/Ag and TiO2/ZnO/Ag heterojunctions showed the cathodic shift of the flat-band potential position and the increase of photocurrent quantum yield in comparison with unmodified TiO2 electrodes. Photocatalytic activity of Ag/TiO2 and Ag/ TiO2/ZnO films estimated in the process of Rhodamine B dye degradation is coincides with photoelectrochemical data.

Influence of binding material of PZT coating on microresonator's electrical and mechanical properties

Microresonators are fundamental components integrated in hosts of MEMS applications: covering the automotive sector, the telecommunication industry, electronic equipment for surface/material characterization and motion sensing, and etc. The aim of this paper is to investigate the mechanical and electrical properties of PZT film fabricated with three binding materials: polyvinyl butyral (PVB), polymethyl methacrylate (PMMA) and polystyrene (PS) and to evaluate applicability in control of microresonators Q factor. Micro particles of PZT powder were mixed with 20% solution of PVB, PMMA and PS in benzyl alcohol. For investigation of mechanical and electrical properties multilayer cantilevers were made. Obtained PZT and polymer paste was screen printed on copper (thickness 40 μm) using polyester monofilament screen meshes (layer thickness 50 μm) and dried for 30 min at 100°C. Electric dipoles of the PZT particles in composite material were aligned using high voltage generator (5 kV) and a custom–made holder. Electric field was held for 30 min. Surfaces of the applied films were investigated by Atomic Force Microscope NanoWizard(R)3 NanoScience. Dynamic and electrical characteristics of the multilayer were investigated using laser triangular displacement sensor LK-G3000. The measured vibration amplitude and generated electrical potential was collected with USB oscilloscope PicoScope 3424. As the results showed, these cantilevers were able to transform mechanical strain energy into electric potential and, v.v. However, roughness of PZT coatings with PMMA and PS were higher, what could be the reason of the worse quality of the top electrode. However, the main advantage of the created composite piezoelectric material is the possibility to apply it on any uniform or non-uniform vibrating surface and to transform low frequency vibrations into electricity.

Novel composite piezoelectric material for energy harvesting applications

Past few decades were concentrated on researches related to effective energy harvesting applied in modern technologies, MEMS or MOEMS systems. There are many methods for harvesting energy as, for example, usage of electromagnetic devices, but most dramatic changes were noticed in the usage of piezoelectric materials in small scale devices. Major limitation faced was too small generated power by piezoelectric materials or high resonant frequencies of such smallscale harvesters. In this research, novel composite piezoelectric material was created by mixing PZT powder with 20% solution of polyvinyl butyral in benzyl alcohol. Obtained paste was screen printed on copper foil using 325 mesh stainless steel screen and dried for 30 min at 100 °C. Polyvinyl butyral ensures good adhesion and flexibility of a new material at the conditions that requires strong binding. Five types of a composite piezoelectric material with different concentrations of PZT (40%, 50%, 60%, 70% and 80 %) were produced. As the results showed, these harvesters were able to transform mechanical strain energy into electric potential and, v.v. In experimental setup, electromagnetic shaker was used to excite energy harvester that is fixed in the custom-built clamp, while generated electric potential were registered with USB oscilloscope PICO 3424. The designed devices generate up to 80 μV at 50 Hz excitation. This property can be applied to power microsystem devices or to use them in portable electronics and wireless sensors. However, the main advantage of the created composite piezoelectric material is possibility to apply it on any uniform or nonuniform vibrating surface and to transform low frequency vibrations into electricity.

Investigation of optical properties of Ag: PMMA nanocomposite structures

In the recent years fundamental research involving the nanodimensional materials has received enormous momentum for observing and understanding new types of plasmonic materials and their physical phenomena occurring in the nanoscale. Mechanical and optical properties of these polymer based nanocomposite structures depend not only on type, dimensions and concentration of filler material, but also on a kind of polymer matrix used. By proper selection of polymer matrix and nanofillers, it is possible to engineer nanocomposite materials with certain favorable properties. One of the most striking features of nanocomposite materials is that they can expose unique optical properties that are not intrinsic to natural materials. In these researches, nanocomposite structures were formed using polymer (PMMA) as a matrix, and silver nanoparticles as fillers. By hot embossing procedure a diffraction grating was imprinted on formed layers. The effect of UV exposure time on nanocomposite structures morphology, optical (diffraction effectiveness, absorbance) and mechanical properties was investigated. Results were confirmed by UV-VIS spectrometer, Laser Diffractometer, PMT- 3 and AFM. Investigations proposed new nanocomposite structures as plasmonic materials with improved optical and mechanical properties, which may be applied for a number of technological applications: micro-electro-mechanical devices, optical devices, various plasmonic sensors, or even in DNA nanotechnology.