Asta Guobienė | Kaunas University of Technology (original) (raw)

Papers by Asta Guobienė

Nanomaterials

Biosensors based on graphene field-effect transistors (G-FET) for detecting COVID-19 spike S prot... more Biosensors based on graphene field-effect transistors (G-FET) for detecting COVID-19 spike S protein and its receptor ACE2 were reported. The graphene, directly synthesized on SiO2/Si substrate by microwave plasma-enhanced chemical vapor deposition (MW-PECVD), was used for FET biosensor fabrication. The commercial graphene, CVD-grown on a copper substrate and subsequently transferred onto a glass substrate, was applied for comparison purposes. The graphene structure and surface morphology were studied by Raman scattering spectroscopy and atomic force microscope. Graphene surfaces were functionalized by an aromatic molecule PBASE (1-pyrenebutanoic acid succinimidyl ester), and subsequent immobilization of the receptor angiotensin-converting enzyme 2 (ACE2) was performed. A microfluidic system was developed, and transfer curves of liquid-gated FET were measured after each graphene surface modification procedure to investigate ACE2 immobilization by varying its concentration and subseq...

American Journal of Applied Sciences, 2010

In this study, attempts had been made to synthesize silver (Ag)/Poly Vinylpyrolidone (PVP) nanopa... more In this study, attempts had been made to synthesize silver (Ag)/Poly Vinylpyrolidone (PVP) nanoparticles by ionizing radiation and at the same time overcoming some of the disadvantages previously reported by other methods such as impurities, solvent toxicity, size and distribution control and difficulty in their preparation that limits their commercialization potential. Approach: The use of this alternative method overcomes some unfavorable characteristics like long tedious and costly process, uncontrolled size and distribution. The advantages of radiation processing of the materials relative to other methods are; no metallic catalyst is required; (gives pure product), no oxidizing or reducing agent is required, the process occurs at a liquid or/and solid-state condition, fast and inexpensive, environmental friendly with controllable acquisitions. Results: Ag/PVP nanoparticles were successfully prepared in one-step by γ-irradiation technique in an aqueous system at room temperature and under ambient pressure. The Transmission of Electron Microscopy (TEM) of the asprepared product particles ranged from 100 to around 8 nm depend on the irradiation dose value, which showed a good distribution with a controlled size as dose changed. The presence of PVP polymer was considered as an important reason that influenced the shape and distribution. The band gap energy was calculated from the UV-VIS absorption spectra. Thermal analysis TGA showed that the composite had a higher degradation temperature than the PVP alone. Conclusion: This result indicated that AgNO 3 can effectively dope PVP and enhance the optical and thermal properties. In addition, γ-irradiation is an effective technique for preparing inorganic/organic nanocomposites.

Optical Materials, Aug 1, 2023

Proceedings of SPIE, Apr 30, 2010

ABSTRACT In the recent years fundamental research involving the nanodimensional materials has rec... more ABSTRACT 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.

Materials, Feb 7, 2020

In the present research, hydrogen-free diamond like carbon films with embedded copper nanoparticl... more In the present research, hydrogen-free diamond like carbon films with embedded copper nanoparticles (DLC:Cu) were grown by simultaneous DC magnetron sputtering of the graphite and copper targets. X-ray photoelectron spectroscopy was used to define the composition of the samples. Atomic force microscopy studies of diamond, like carbon films containing different amount of copper, revealed wide range of the surface morphologies as well as sizes and shapes of the embedded copper nanoclusters. Raman scattering spectra of all the DLC:Cu films investigated were typical for diamond-like carbon (including samples containing more than 60 at.% of copper). sp 3 /sp 2 carbon bond ratio in the films decreased with the increase of the Cu amount in the films. According to the optical absorbance measurements, the surface plasmon resonance related absorption peak of DLC:Cu films was only detected in the films containing ≥28.45 at.% Cu. For the diamond like carbon films containing more than 40 at.% Cu, a further increase of Cu amount in the nanocomposite resulted in minor changes of the absorbance spectra. Some correlation between the changes of the samples surface morphology as well as phase structure and optical absorbance spectra of the films was found. In all cases, reverse-saturable absorption of the DLC:Cu films was observed. For some DLC:Cu films damage of the sample occurred at higher light fluences that can be related to the heating that is caused by the surface plasmon resonance effect.

Diamond and Related Materials, Aug 1, 2022

Nanomaterials, May 11, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Thin Solid Films, Jul 1, 2012

ABSTRACT Chromium (Cr) thin films were deposited on float glass using electron beam (e-beam) phys... more ABSTRACT Chromium (Cr) thin films were deposited on float glass using electron beam (e-beam) physical vapor deposition and radio frequency (RF) magnetron sputtering techniques. Surface morphology of these Cr films was studied using atomic force microscopy (AFM). The e-beam deposited Cr films consisted of isolated surface mounds while in RF sputtered samples, these mounds combined to form larger islands. Lower surface adhesive properties were observed for e-beam deposited films, as determined from AFM force–distance curves, presumably due to the nanostructural differences. Similar amounts of adsorbed atmospheric carbonaceous contaminants and water vapor were detected on samples deposited using both methods with e-beam deposited samples having additional carbide species, as determined by X-ray photoelectron spectroscopy data. The dominant crystallographic plane in both e-beam deposited and RF sputtered Cr thin films was (110) of body-centered cubic Cr metal structure as determined from X-ray diffraction data. Weak (211) reflection was also observed in RF sputtered samples and was attributed to a different thin Cr film condensation and growth mechanism which resulted in nanostructural differences between films deposited using two different methods.

Thin Solid Films, Jul 1, 2013

In this study SiOx containing amorphous hydrogenated carbon (a-C:H/SiOx) and nitrogen-doped a-C:H... more In this study SiOx containing amorphous hydrogenated carbon (a-C:H/SiOx) and nitrogen-doped a-C:H/SiOx (a-C:H:N/SiOx) films were deposited on polyvinylpyrrolidone (PVP) templates of variable thickness using a Hall-type closed drift ion beam source with constant irradiation parameters. A detailed surface characterization was followed using atomic force microscopy (AFM) topography images, surface morphology parameters, height distribution histograms and bearing ratio curves with hybrid parameters. The AFM analysis directly showed that the a-C:H/SiOx/PVP and a-C:H:N/SiOx/PVP composite films represent different morphologies with characteristic surface textures. Surface adhesive properties were evaluated by measuring the force required to separate the AFM tip from the surface by means of AFM force-distance curves. The variance in adhesion force detected was lower for a-C:H/SiOx/PVP composite films due to lower structural homogeneity of the surfaces. Fourier transform infrared spectroscopy analysis was performed to study the blend behavior of PVP upon a-C:H/SiOx and a-C:H:N/SiOx direct ion beam deposition. It was determined that interfacial interactions of PVP with the direct ion beam induced changes in the carbonyl group of the PVP and are dependent on the carrier gas used for the synthesis of the amorphous hydrogenated carbon films.

Bibliogr.: p. 268 (8 pavad.)Vytauto Didžiojo universitetasŽemės ūkio akademij

Superlattices and Microstructures, 2014

ABSTRACT Abstract Graphene oxide (GO) has been recognized as an important intermediate compound f... more ABSTRACT Abstract Graphene oxide (GO) has been recognized as an important intermediate compound for a potential low-cost large-scale graphene-like film fabrication. In this work, graphene oxide multilayer films deposited on glass substrate were reduced using different thermal reduction methods, including low-temperature annealing, flame-induced and laser reduction, and the corresponding surface morphology and structural properties were investigated. These graphene oxide thermal reduction methods strongly affected surface morphology and differently facilitated structural and chemical transformations of graphene oxide. As evidenced by Raman measurements, thermal annealing and laser reduction of graphene oxide produced more ordered graphene-like structure multilayer films. However, surface morphological differences were observed and attributed to the different de-oxidation mechanisms of GO. This Letter provides an important systematic comparison between the GO reduction methods and thermally-driven structural changes they provide to the reduced GO multilayer films obtained.

Surface and Coatings Technology, 2008

SiO x doped diamond-like carbon (DLC) films were synthesized by direct ion beam from hexamethyldi... more SiO x doped diamond-like carbon (DLC) films were synthesized by direct ion beam from hexamethyldisiloxane vapor. Effects of ion beam energy were studied. Variation of atomic concentration of the oxygen versus carbon with ion energy has been observed. Raman scattering spectroscopy didn't indicate essential changes in structure of the films deposited at different ion beam energies. The synthesized films were atomically smooth. Depending on the ion energy the refractive index of the SiO x doped diamond-like carbon films varied within 2.1-2.5 and increased with increase of energy. The contact angle with water for all samples was only 61-64°.

Surface and Coatings Technology, 2006

In this work, we present structural and compositional analysis of silver layers on PET and relati... more In this work, we present structural and compositional analysis of silver layers on PET and relation between the stress level and process conditions. The silver thin films (1 μm thickness) were deposited on PET (25 μm thickness) by electron beam evaporation in vacuum at different substrate temperatures (20, 40, 80 and 120°C). The size of the crystal grain was obtained from the peak width of X-ray diffraction using the two major models known and employed in bulk materials: the integral breadth and the Warren-Averbach methods. The classical sin 2 ψ method of Xray diffraction was used to measure the residual stresses in fine grained polycrystalline materials. The influence of metal coverage on interface composition, structure, morphology, and particle size of Ag/PET films has been studied employing X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM) and X-ray diffraction (XRD). According to the AFM and XRD, the structural changes in the polymer occurring above the glass transition temperature of PET (T g ≈ 80°C) may contribute to the morphological and stress changes in the Ag/PET system.

Experimental Techniques, 2008

Acta Physica Polonica A, 2013

The surface plasmon resonance evaluation of colloidal metal nanoparticles, synthesized in organic... more The surface plasmon resonance evaluation of colloidal metal nanoparticles, synthesized in organic medium, is reported in this work. Metal salts were dissolved in dioxane/AOT solution and reduced by hydrazine hydrate under vigorous stirring. Optical properties of obtained colloidal nanoparticles were investigated by UVVIS spectroscopy. Theoretical predictions of optical properties of metal nanoparticles were made by means of the Mie theory and the Drude free-electron model. Geometrical parameters and distribution of metal nanoparticles in colloidal solutions were characterized by atomic force microscopy. The results show that Ag, Cu, and Co nanoparticles, synthesized in organic medium distinguish plasmonic properties. Surface plasmon resonance bands were obtained in all cases: Ag at 430 nm, Cu at 570 nm, Co at 350 nm (SPR1) and 430 nm (SPR2). Comparing theoretical evaluation of nanoparticles size with atomic force microscopy analysis, we can assume that our calculations are accurate. It was found that dominating nanoparticles diameter in Ag colloidal solution is ≈ 150 nm, in Cu colloidal solution is ≈ 7080 nm and in Co colloidal solution is ≈ 150 nm. It can be concluded that nanoparticles with enhanced plasmonic properties synthesized in organic medium can be widely used in order to increase eciency of various optical elements.

Nanomaterials, Mar 20, 2023

RSC Advances

In the present research, graphene was synthesized directly on a Si(100) substrate via combining d... more In the present research, graphene was synthesized directly on a Si(100) substrate via combining direct microwave plasma-enhanced chemical vapor deposition and protective enclosure.

Surface and Coatings Technology, 2022

Applied Surface Science, 2021

Journal of Vibroengineering, 2014

This paper presents the investigation of surface morphology, wetting and chemical properties of t... more This paper presents the investigation of surface morphology, wetting and chemical properties of the nanocomposite Al/SiO2 film, which can be used as a shock generated vibration isolator for microelectromechanical devices. AFM analysis shows that two-step prepared Al/SiO2 composite film has regular nanoisland type surface topography provided by SiO2 nanospheres. EDS analysis confirms that SiO2 nanospheres are well distributed on the substrate. Carbon found in the composition of composite film can be attributed to the residuals of organic compounds used for the preparation of SiO2 nanospheres. FTIR analysis confirms formation of the Si-O and Si-OH functional groups and the presence of –CH3 stretching group can be related to the improved non-wetting behavior of the composite.