Tsvetanka Babeva - Academia.edu (original) (raw)

Papers by Tsvetanka Babeva

Sensors

The blending approach (also known as the ex-situ approach) was used for the deposition of thin co... more The blending approach (also known as the ex-situ approach) was used for the deposition of thin composite films comprising poly(vinyl alcohol-graft-methyl acrylate) (PVA-g-PMA) and silver nanoparticles (AgNPs). Firstly, the copolymer aqueous dispersion was synthesized through the redox polymerization of methyl acrylate (MA) on poly(vinyl alcohol) (PVA) using ammonium cerium (IV) nitrate as the initiator. Then, AgNPs were synthesized through a “green” method using the water extract of lavender based on by-products of the essential oil industry, and then they were blended with the polymer. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to determine nanoparticle size, along with their stability over time in suspension, during the 30-day period. Thin films of the PVA-g-PMA copolymer, with different AgNP volume fractions varying between 0.008 and 0.260%, were deposited via the spin-coating method on Si substrates, and their optical properties were expl...

Coatings

In this paper, the aqueous copolymer dispersions of methyl (meth)acrylate-grafted poly(vinyl alco... more In this paper, the aqueous copolymer dispersions of methyl (meth)acrylate-grafted poly(vinyl alcohol) are in situ synthesized and studied as a promising platform for the deposition of thin films with advanced applications. A series of dispersions of the varied copolymer structure and composition are obtained at mild reaction conditions by carrying out a redox polymerization at a different monomer-to-PVA ratio and initiator concentration. The obtained colloidal particles are characterized by Fourier transformed infrared spectroscopy, nuclear magnetic resonance, dynamic light scattering, and transmission electron microscopy. The copolymer dispersions are further used for deposition of thin films on silicon substrates. The films are characterized optically through reflectance measurements and non-linear curve fitting. Their suitability for the optical sensing of acetone vapors is confirmed by reflectance measurements before and during their exposure to analyte vapors. The cross sensiti...

The 8th International Symposium on Sensor Science, 2021

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

The preparation of responsive multilayered structures with quarter-wave design based on layer-by-... more The preparation of responsive multilayered structures with quarter-wave design based on layer-by-layer deposition of sol-gel derived Nb 2 O 5 films and spin-coated MEL type zeolite is demonstrated. The refractive indices (n) and thicknesses (d) of the layers are determined using non-linear curve fitting of the measured reflectance spectra. Besides, the surface and cross-sectional features of the multilayered structures are characterized by scanning electron microscopy (SEM). The quasi-omnidirectional photonic band for the multilayered structures is predicted theoretically, and confirmed experimentally by reflectance measurements at oblique incidence with polarized light. The sensing properties of the multilayered structures toward acetone are studied by measuring transmittance spectra prior and after vapor exposure. Furthermore, the potential of the one-dimensional photonic crystals based on the multilayered structure consisting of Nb 2 O 5 and MEL type zeolite as a chemical sensor with optical read-out is discussed.

Influence of PEO, PDMAA and corresponding diand triblock copolymers on the optical properties of ... more Influence of PEO, PDMAA and corresponding diand triblock copolymers on the optical properties of niobia thin films R. Georgiev, L. Todorova, D. Christova, B. Georgieva, M. Vasileva and T. Babeva* 1 Institute of Optical Materials and Technologies “Acad. J. Malinowski”, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 109, 1113 Sofia, Bulgaria 2 Institute of Polymers, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 103-A, 1113 Sofia, Bulgaria

Photonics, 2021

In this study, an emphasis is put on vapor-sensitive Bragg stacks as an important class of optica... more In this study, an emphasis is put on vapor-sensitive Bragg stacks as an important class of optical sensors. All-niobia Bragg stacks were deposited by spin-coating of sol-gel Nb2O5 thin films alternated with mesoporous layers after proper design through optimization of operating wavelength and number of layers in the stack. Mesoporous Nb2O5 films with different morphology and identical structure were obtained using organic templates (Pluronics PE6200 and PE6800) and subsequent annealing. Transmittance measurements were performed as a detection method that offers technological simplicity and accuracy. It was demonstrated that stacks including PE6200 templated films exhibit higher sensitivity than stacks templated with PE6800. It was assumed and verified by computer-aided modelling of experimental data that mesoporous films prepared with addition of PE6200, although less porous, were more stable compared to those templated with PE6800, and did not collapse during the thermal treatment ...

Nanomaterials, 2021

In this study, thin composite films of a sol–gel Nb2O5 matrix doped with coal fly ash Na-X zeolit... more In this study, thin composite films of a sol–gel Nb2O5 matrix doped with coal fly ash Na-X zeolites were deposited by the spin-coating method. Fly ash of lignite coal collected from the electrostatic precipitators of one of the biggest TPPs in Bulgaria was used as a raw material for obtaining zeolites. Zeolite Na-X was synthesized by ultrasonic-assisted double stage fusion-hydrothermal alkaline conversion of coal fly ash. In order to improve the optical quality and sensing properties of the deposited thin films, synthesized zeolites were wet-milled for 60, 120, and 540 s prior to film deposition. The surface morphology of zeolite powders was studied both by scanning electron microscopy and transmission electron microscopy, while their porosity was investigated by N2-physisorption. Refractive index, extinction coefficient, and thickness of the films were determined through fitting of their reflectance spectra. The sensing ability of thin films towards acetone vapors was tested by mea...

7th International Electronic Conference on Sensors and Applications, 2020

In this paper, the possibility to design flexible humidity sensors by spin-coating of moisture-se... more In this paper, the possibility to design flexible humidity sensors by spin-coating of moisture-sensitive polymer on three types of substrates-poly(ethylene terephthalate) (PET), polylactide (PLA) and composite polysiloxane is investigated. The optical properties, surface morphology and roughness of the substrates covered with polymer are studied by transmittance measurements and surface profiling, respectively. Thin polymer films of amphiphilic copolymer obtained by partial acetalization of poly(vinyl alcohol) are used as humidity sensitive media. The sensing properties are probed through transmittance measurements at different levels of relative humidity (RH). The influence of substrate type is studied by comparing the hysteresis of flexible sensors with those that are deposited on glass substrates.

Sensors, 2021

Thin spin-coated polymer films of amphiphilic copolymer obtained by partial acetalization of poly... more Thin spin-coated polymer films of amphiphilic copolymer obtained by partial acetalization of poly (vinyl alcohol) are used as humidity-sensitive media. They are deposited on polymer substrate (PET) in order to obtain a flexible humidity sensor. Pre-metallization of substrate is implemented for increasing the optical contrast of the sensor, thus improving the sensitivity. The morphology of the sensors is studied by surface profiling, while the transparency of the sensor is controlled by transmittance measurements. The sensing behavior is evaluated through monitoring of transmittance values at different levels of relative humidity gradually changing in the range 5–95% and the influence of up to 1000 bending deformations is estimated by determining the hysteresis and sensitivity of the flexible sensor after each set of deformations. The successful development of a flexible sensor for optical monitoring of humidity in a wide humidity range is demonstrated and discussed.

Proceedings of 2nd Coatings and Interfaces Web Conference, 2020

Thin, homogeneous ZrO2 films were obtained by spin coating method from ZrOCl2 8H2O solution, modi... more Thin, homogeneous ZrO2 films were obtained by spin coating method from ZrOCl2 8H2O solution, modified with polyethylene glycol (PEG) (Mw = 400). The films have thickness of 80 nm and refractive index of about 1.45, which varied with the amount of added PEG. The thermal behaviour of the precursor was studied with thermogravimetry and differential thermal analysis (TG-DTA). The X-ray diffraction (XRD) analysis revealed the presence of a mixture of monoclinic and tetragonal ZrO2 polycrystalline phases with nanosized crystallites. The formation of hydrogen bonds among the organic and inorganic components was proved by means of Fourier transform infrared spectroscopy (FT-IR) analysis, while the different defect centres were investigated with electron paramagnetic resonance (EPR) spectroscopy. The scanning electron microscopy (SEM) images showed that the samples are dense and crack-free, with ganglia-like nanostructure. It was established that the addition of polymer resulted in the introduction of free volume in the films, which also varied with the content of PEG in the precursor solution.

Proceedings of 2nd Coatings and Interfaces Web Conference, 2020

In this study, solid waste from coal combustion in thermal power plants (TPPs) was used for the s... more In this study, solid waste from coal combustion in thermal power plants (TPPs) was used for the synthesis of zeolite Na-X samples. They were prepared by the long-term alkaline atmospheric conversion of coal ash collected from the electrostatic precipitators in the TPP "AES Galabovo". When used in the form of thin films/layers, the optical detection of volatile organic compounds (VOCs) is possible due to a change in their reflectance spectra and color. In order to improve the sensing properties of synthesized zeolites, they were wet milled for 60 s and both milled and unmilled zeolites were used as dopants for the niobium oxide matrix in the form of thin films deposited by the spin-coating method on a silicon substrate. The surface morphology and structure of both zeolite powders were studied by scanning electron microscopy, while their size was determined by dynamic light scattering (DLS) spectra. Optical constants (refractive index, n, and extinction coefficient, k) and the thickness of the films were calculated from reflectance measurements. The change in the reflection coefficient ∆R of the films was determined from measured reflectance spectra prior to and after exposure to probe acetone molecules. An increase in the reaction of the films with milled zeolites to acetone, compared to the samples with unmilled zeolites, is demonstrated.

Coatings, 2020

This Special Issue is devoted on design and application of thin films and structures with special... more This Special Issue is devoted on design and application of thin films and structures with special emphasis on optical applications. It comprises ten papers, five featured and five regular papers, authored by respective scientists all over the world. Diverse materials are studied and their possible applications are demonstrated and discussed: transparent conductive coatings and structures from ZnO doped with Al and Ga and Ti-doped SnO2, polymer and nanosized zeolite thin films for optical sensing, TiO2 with linear and non-linear optical properties, organic diamagnetic materials, broadband optical coatings, CrWN glass molding coatings and silicon on insulator waveguides.

Coatings, 2020

A possible approach for enhancement of Poly(vinyl alcohol) (PVA) humidity-sensing performance usi... more A possible approach for enhancement of Poly(vinyl alcohol) (PVA) humidity-sensing performance using hydrophobically modified PVA copolymers is studied. Series of poly(vinylalcohol-co-vinylacetal)s (PVA–Ac) of acetal content in the range 18%–28% are synthesized by partial acetalization of hydroxyl groups of PVA with acetaldehyde and thin films are deposited by spin-coating using silicon substrates and glass substrates covered with Au–Pd thin film with thickness of 30 nm. Sensing properties are probed through reflectance measurements at relative humidity (RH) in the range 5%–95% RH. The influence of film thickness, post-deposition annealing temperature, and substrate type/configuration on hysteresis, sensitivity, and accuracy/resolution of humidity sensing is studied for partially acetalized PVA copolymer films, and comparison with neat PVA is made. Enhancement of sensing behavior through preparation of polymer–silica hybrids is demonstrated. The possibility of color sensing is discus...

The 6th International Electronic Conference on Sensors and Applications, 2019

Hydrophobically modified poly(vinyl alcohol)s of varied copolymer composition were tested as acti... more Hydrophobically modified poly(vinyl alcohol)s of varied copolymer composition were tested as active media for optical sensing of humidity. Copolymer thin films were deposited on silicon substrate using water-methanol solution in a volume ratio of 20:80 and concentration of 1 wt%. Films were subjected to low (60 °C) and moderate (180 °C) temperature annealing in order to study the temperature influence on optical and humidity sensing properties. Refractive index, extinction coefficient along with thickness of the films were determined by non-linear minimization of the goal function comprising measured and calculated reflectance spectra at normal light incidence. The humidity sensing ability of the films was studied through reflectance measurements at different humidity levels in the range 5–95 %RH. The influence of temperature annealing on optical and sensing properties was demonstrated and discussed.

Proceedings, 2018

Thin films from double hydrophilic copolymer of complex branched structures containing poly(N,N-d... more Thin films from double hydrophilic copolymer of complex branched structures containing poly(N,N-dimethyl acrylamide) and poly(ethylene oxide) blocks were used as humidity sensitive media, and two types of Bragg reflectors with different optical contrast and operating wavelengths were implemented as transducers of humidity changes. The required film thickness was pre-optimized through theoretical modelling in order to achieve the highest sensitivity. Single films and Bragg reflectors were characterized by transmittance measurements at different humidity levels in the range from 5% to 95% relative humidity. The influence of the number of the layers in the stack, the operating wavelength and optical contrast on sensitivity was studied. The potential and advantages of using top-covered Bragg reflectors as humidity sensors with simple optical read-out are demonstrated and discussed.

Advances in Condensed Matter Physics, 2015

Thin Nb2O5films with tunable porosity are deposited by the sol-gel and evaporation induced self-a... more Thin Nb2O5films with tunable porosity are deposited by the sol-gel and evaporation induced self-assembly methods using organic template Pluronic PE6100 with different molar fractions with respect to NbCl5used as a precursor for synthesis of Nb sol. Surface morphology and structure of the films are studied by Transmission Electron Microscopy and Selected Area Electron Diffraction. The optical characterization of the films is carried out through reflectance spectra measurements of the films deposited on silicon substrates and theoretical modeling in order to obtain refractive index, extinction coefficient, and thickness of the films. The overall porosity of the films and the amount of adsorbed acetone vapors in the pores are quantified by means of Bruggeman effective medium approximation using already determined optical constants. The sensing properties of the samples are studied by measuring both the reflectance spectra and room-temperature photoluminescence spectra prior to and afte...

The preparation of responsive multilayered structures with quarter-wave design by layer-by-layer ... more The preparation of responsive multilayered structures with quarter-wave design by layer-by-layer deposition of sol-gel derived Nb2O5 films and spin-coated nanosized MEL type of zeolites is demonstrated. The refractive indices (n) and thicknesses (d) of the layers are determined using non-linear curve fitting of the measured reflectance spectra. The surface and cross-sectional morphologies of the multilayered structures are characterized by scanning electron microscopy (SEM). The quazi-omnidirectional photonic band is predicted theoretically and confirmed experimentally by reflectance measurements at oblique incidence with polarized light. The sensing properties of the structures are studied by measuring transmittance and reflectance spectra prior and after exposure to vapors of acetone. The enhancement of detection through high temperature annealing is demonstrated. Furthermore, the potential of the onedimensional photonic crystals from Nb2O5 and zeolites as a chemical sensor with o...

Photonic Crystals - Innovative Systems, Lasers and Waveguides, 2012

Sensors

The blending approach (also known as the ex-situ approach) was used for the deposition of thin co... more The blending approach (also known as the ex-situ approach) was used for the deposition of thin composite films comprising poly(vinyl alcohol-graft-methyl acrylate) (PVA-g-PMA) and silver nanoparticles (AgNPs). Firstly, the copolymer aqueous dispersion was synthesized through the redox polymerization of methyl acrylate (MA) on poly(vinyl alcohol) (PVA) using ammonium cerium (IV) nitrate as the initiator. Then, AgNPs were synthesized through a “green” method using the water extract of lavender based on by-products of the essential oil industry, and then they were blended with the polymer. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to determine nanoparticle size, along with their stability over time in suspension, during the 30-day period. Thin films of the PVA-g-PMA copolymer, with different AgNP volume fractions varying between 0.008 and 0.260%, were deposited via the spin-coating method on Si substrates, and their optical properties were expl...

Coatings

In this paper, the aqueous copolymer dispersions of methyl (meth)acrylate-grafted poly(vinyl alco... more In this paper, the aqueous copolymer dispersions of methyl (meth)acrylate-grafted poly(vinyl alcohol) are in situ synthesized and studied as a promising platform for the deposition of thin films with advanced applications. A series of dispersions of the varied copolymer structure and composition are obtained at mild reaction conditions by carrying out a redox polymerization at a different monomer-to-PVA ratio and initiator concentration. The obtained colloidal particles are characterized by Fourier transformed infrared spectroscopy, nuclear magnetic resonance, dynamic light scattering, and transmission electron microscopy. The copolymer dispersions are further used for deposition of thin films on silicon substrates. The films are characterized optically through reflectance measurements and non-linear curve fitting. Their suitability for the optical sensing of acetone vapors is confirmed by reflectance measurements before and during their exposure to analyte vapors. The cross sensiti...

The 8th International Symposium on Sensor Science, 2021

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

The preparation of responsive multilayered structures with quarter-wave design based on layer-by-... more The preparation of responsive multilayered structures with quarter-wave design based on layer-by-layer deposition of sol-gel derived Nb 2 O 5 films and spin-coated MEL type zeolite is demonstrated. The refractive indices (n) and thicknesses (d) of the layers are determined using non-linear curve fitting of the measured reflectance spectra. Besides, the surface and cross-sectional features of the multilayered structures are characterized by scanning electron microscopy (SEM). The quasi-omnidirectional photonic band for the multilayered structures is predicted theoretically, and confirmed experimentally by reflectance measurements at oblique incidence with polarized light. The sensing properties of the multilayered structures toward acetone are studied by measuring transmittance spectra prior and after vapor exposure. Furthermore, the potential of the one-dimensional photonic crystals based on the multilayered structure consisting of Nb 2 O 5 and MEL type zeolite as a chemical sensor with optical read-out is discussed.

Influence of PEO, PDMAA and corresponding diand triblock copolymers on the optical properties of ... more Influence of PEO, PDMAA and corresponding diand triblock copolymers on the optical properties of niobia thin films R. Georgiev, L. Todorova, D. Christova, B. Georgieva, M. Vasileva and T. Babeva* 1 Institute of Optical Materials and Technologies “Acad. J. Malinowski”, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 109, 1113 Sofia, Bulgaria 2 Institute of Polymers, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 103-A, 1113 Sofia, Bulgaria

Photonics, 2021

In this study, an emphasis is put on vapor-sensitive Bragg stacks as an important class of optica... more In this study, an emphasis is put on vapor-sensitive Bragg stacks as an important class of optical sensors. All-niobia Bragg stacks were deposited by spin-coating of sol-gel Nb2O5 thin films alternated with mesoporous layers after proper design through optimization of operating wavelength and number of layers in the stack. Mesoporous Nb2O5 films with different morphology and identical structure were obtained using organic templates (Pluronics PE6200 and PE6800) and subsequent annealing. Transmittance measurements were performed as a detection method that offers technological simplicity and accuracy. It was demonstrated that stacks including PE6200 templated films exhibit higher sensitivity than stacks templated with PE6800. It was assumed and verified by computer-aided modelling of experimental data that mesoporous films prepared with addition of PE6200, although less porous, were more stable compared to those templated with PE6800, and did not collapse during the thermal treatment ...

Nanomaterials, 2021

In this study, thin composite films of a sol–gel Nb2O5 matrix doped with coal fly ash Na-X zeolit... more In this study, thin composite films of a sol–gel Nb2O5 matrix doped with coal fly ash Na-X zeolites were deposited by the spin-coating method. Fly ash of lignite coal collected from the electrostatic precipitators of one of the biggest TPPs in Bulgaria was used as a raw material for obtaining zeolites. Zeolite Na-X was synthesized by ultrasonic-assisted double stage fusion-hydrothermal alkaline conversion of coal fly ash. In order to improve the optical quality and sensing properties of the deposited thin films, synthesized zeolites were wet-milled for 60, 120, and 540 s prior to film deposition. The surface morphology of zeolite powders was studied both by scanning electron microscopy and transmission electron microscopy, while their porosity was investigated by N2-physisorption. Refractive index, extinction coefficient, and thickness of the films were determined through fitting of their reflectance spectra. The sensing ability of thin films towards acetone vapors was tested by mea...

7th International Electronic Conference on Sensors and Applications, 2020

In this paper, the possibility to design flexible humidity sensors by spin-coating of moisture-se... more In this paper, the possibility to design flexible humidity sensors by spin-coating of moisture-sensitive polymer on three types of substrates-poly(ethylene terephthalate) (PET), polylactide (PLA) and composite polysiloxane is investigated. The optical properties, surface morphology and roughness of the substrates covered with polymer are studied by transmittance measurements and surface profiling, respectively. Thin polymer films of amphiphilic copolymer obtained by partial acetalization of poly(vinyl alcohol) are used as humidity sensitive media. The sensing properties are probed through transmittance measurements at different levels of relative humidity (RH). The influence of substrate type is studied by comparing the hysteresis of flexible sensors with those that are deposited on glass substrates.

Sensors, 2021

Thin spin-coated polymer films of amphiphilic copolymer obtained by partial acetalization of poly... more Thin spin-coated polymer films of amphiphilic copolymer obtained by partial acetalization of poly (vinyl alcohol) are used as humidity-sensitive media. They are deposited on polymer substrate (PET) in order to obtain a flexible humidity sensor. Pre-metallization of substrate is implemented for increasing the optical contrast of the sensor, thus improving the sensitivity. The morphology of the sensors is studied by surface profiling, while the transparency of the sensor is controlled by transmittance measurements. The sensing behavior is evaluated through monitoring of transmittance values at different levels of relative humidity gradually changing in the range 5–95% and the influence of up to 1000 bending deformations is estimated by determining the hysteresis and sensitivity of the flexible sensor after each set of deformations. The successful development of a flexible sensor for optical monitoring of humidity in a wide humidity range is demonstrated and discussed.

Proceedings of 2nd Coatings and Interfaces Web Conference, 2020

Thin, homogeneous ZrO2 films were obtained by spin coating method from ZrOCl2 8H2O solution, modi... more Thin, homogeneous ZrO2 films were obtained by spin coating method from ZrOCl2 8H2O solution, modified with polyethylene glycol (PEG) (Mw = 400). The films have thickness of 80 nm and refractive index of about 1.45, which varied with the amount of added PEG. The thermal behaviour of the precursor was studied with thermogravimetry and differential thermal analysis (TG-DTA). The X-ray diffraction (XRD) analysis revealed the presence of a mixture of monoclinic and tetragonal ZrO2 polycrystalline phases with nanosized crystallites. The formation of hydrogen bonds among the organic and inorganic components was proved by means of Fourier transform infrared spectroscopy (FT-IR) analysis, while the different defect centres were investigated with electron paramagnetic resonance (EPR) spectroscopy. The scanning electron microscopy (SEM) images showed that the samples are dense and crack-free, with ganglia-like nanostructure. It was established that the addition of polymer resulted in the introduction of free volume in the films, which also varied with the content of PEG in the precursor solution.

Proceedings of 2nd Coatings and Interfaces Web Conference, 2020

In this study, solid waste from coal combustion in thermal power plants (TPPs) was used for the s... more In this study, solid waste from coal combustion in thermal power plants (TPPs) was used for the synthesis of zeolite Na-X samples. They were prepared by the long-term alkaline atmospheric conversion of coal ash collected from the electrostatic precipitators in the TPP "AES Galabovo". When used in the form of thin films/layers, the optical detection of volatile organic compounds (VOCs) is possible due to a change in their reflectance spectra and color. In order to improve the sensing properties of synthesized zeolites, they were wet milled for 60 s and both milled and unmilled zeolites were used as dopants for the niobium oxide matrix in the form of thin films deposited by the spin-coating method on a silicon substrate. The surface morphology and structure of both zeolite powders were studied by scanning electron microscopy, while their size was determined by dynamic light scattering (DLS) spectra. Optical constants (refractive index, n, and extinction coefficient, k) and the thickness of the films were calculated from reflectance measurements. The change in the reflection coefficient ∆R of the films was determined from measured reflectance spectra prior to and after exposure to probe acetone molecules. An increase in the reaction of the films with milled zeolites to acetone, compared to the samples with unmilled zeolites, is demonstrated.

Coatings, 2020

This Special Issue is devoted on design and application of thin films and structures with special... more This Special Issue is devoted on design and application of thin films and structures with special emphasis on optical applications. It comprises ten papers, five featured and five regular papers, authored by respective scientists all over the world. Diverse materials are studied and their possible applications are demonstrated and discussed: transparent conductive coatings and structures from ZnO doped with Al and Ga and Ti-doped SnO2, polymer and nanosized zeolite thin films for optical sensing, TiO2 with linear and non-linear optical properties, organic diamagnetic materials, broadband optical coatings, CrWN glass molding coatings and silicon on insulator waveguides.

Coatings, 2020

A possible approach for enhancement of Poly(vinyl alcohol) (PVA) humidity-sensing performance usi... more A possible approach for enhancement of Poly(vinyl alcohol) (PVA) humidity-sensing performance using hydrophobically modified PVA copolymers is studied. Series of poly(vinylalcohol-co-vinylacetal)s (PVA–Ac) of acetal content in the range 18%–28% are synthesized by partial acetalization of hydroxyl groups of PVA with acetaldehyde and thin films are deposited by spin-coating using silicon substrates and glass substrates covered with Au–Pd thin film with thickness of 30 nm. Sensing properties are probed through reflectance measurements at relative humidity (RH) in the range 5%–95% RH. The influence of film thickness, post-deposition annealing temperature, and substrate type/configuration on hysteresis, sensitivity, and accuracy/resolution of humidity sensing is studied for partially acetalized PVA copolymer films, and comparison with neat PVA is made. Enhancement of sensing behavior through preparation of polymer–silica hybrids is demonstrated. The possibility of color sensing is discus...

The 6th International Electronic Conference on Sensors and Applications, 2019

Hydrophobically modified poly(vinyl alcohol)s of varied copolymer composition were tested as acti... more Hydrophobically modified poly(vinyl alcohol)s of varied copolymer composition were tested as active media for optical sensing of humidity. Copolymer thin films were deposited on silicon substrate using water-methanol solution in a volume ratio of 20:80 and concentration of 1 wt%. Films were subjected to low (60 °C) and moderate (180 °C) temperature annealing in order to study the temperature influence on optical and humidity sensing properties. Refractive index, extinction coefficient along with thickness of the films were determined by non-linear minimization of the goal function comprising measured and calculated reflectance spectra at normal light incidence. The humidity sensing ability of the films was studied through reflectance measurements at different humidity levels in the range 5–95 %RH. The influence of temperature annealing on optical and sensing properties was demonstrated and discussed.

Proceedings, 2018

Thin films from double hydrophilic copolymer of complex branched structures containing poly(N,N-d... more Thin films from double hydrophilic copolymer of complex branched structures containing poly(N,N-dimethyl acrylamide) and poly(ethylene oxide) blocks were used as humidity sensitive media, and two types of Bragg reflectors with different optical contrast and operating wavelengths were implemented as transducers of humidity changes. The required film thickness was pre-optimized through theoretical modelling in order to achieve the highest sensitivity. Single films and Bragg reflectors were characterized by transmittance measurements at different humidity levels in the range from 5% to 95% relative humidity. The influence of the number of the layers in the stack, the operating wavelength and optical contrast on sensitivity was studied. The potential and advantages of using top-covered Bragg reflectors as humidity sensors with simple optical read-out are demonstrated and discussed.

Advances in Condensed Matter Physics, 2015

Thin Nb2O5films with tunable porosity are deposited by the sol-gel and evaporation induced self-a... more Thin Nb2O5films with tunable porosity are deposited by the sol-gel and evaporation induced self-assembly methods using organic template Pluronic PE6100 with different molar fractions with respect to NbCl5used as a precursor for synthesis of Nb sol. Surface morphology and structure of the films are studied by Transmission Electron Microscopy and Selected Area Electron Diffraction. The optical characterization of the films is carried out through reflectance spectra measurements of the films deposited on silicon substrates and theoretical modeling in order to obtain refractive index, extinction coefficient, and thickness of the films. The overall porosity of the films and the amount of adsorbed acetone vapors in the pores are quantified by means of Bruggeman effective medium approximation using already determined optical constants. The sensing properties of the samples are studied by measuring both the reflectance spectra and room-temperature photoluminescence spectra prior to and afte...

The preparation of responsive multilayered structures with quarter-wave design by layer-by-layer ... more The preparation of responsive multilayered structures with quarter-wave design by layer-by-layer deposition of sol-gel derived Nb2O5 films and spin-coated nanosized MEL type of zeolites is demonstrated. The refractive indices (n) and thicknesses (d) of the layers are determined using non-linear curve fitting of the measured reflectance spectra. The surface and cross-sectional morphologies of the multilayered structures are characterized by scanning electron microscopy (SEM). The quazi-omnidirectional photonic band is predicted theoretically and confirmed experimentally by reflectance measurements at oblique incidence with polarized light. The sensing properties of the structures are studied by measuring transmittance and reflectance spectra prior and after exposure to vapors of acetone. The enhancement of detection through high temperature annealing is demonstrated. Furthermore, the potential of the onedimensional photonic crystals from Nb2O5 and zeolites as a chemical sensor with o...

Photonic Crystals - Innovative Systems, Lasers and Waveguides, 2012