Iryna Golovina | Drexel University (original) (raw)

Papers by Iryna Golovina

Acta Materialia, 2021

Abstract Electrically tunable dielectric thin films in active circuits and systems are challenged... more Abstract Electrically tunable dielectric thin films in active circuits and systems are challenged by capacitance-induced delays and impedance matching requiring a lower dielectric constant. Here an approach to increasing the intrinsic tunability of compounds containing TiO6 octahedra by considering the influence of different connectivity among these octahedra is presented. Such connectivity variants in nanocrystalline monoclinic BaTi2O5 thin films enable a two orders of magnitude enhancement in Ti anharmonic interaction, thereby permitting a ≈ 65% decrease in dielectric constant to 70 at room temperature without sacrificing tunability. Edge-sharing TiO6 octahedra possess a much shorter Ti-Ti distance of only 2.91 A as compared to the perovskite structure (~4 A), permitting large field-induced structural re-arrangement and intrinsic tunability.

Ferroelectrics, 1994

The temperature dependence of Mn EPR spectrum in Sn2P2Se6 ferroelectric has been obtained. The ma... more The temperature dependence of Mn EPR spectrum in Sn2P2Se6 ferroelectric has been obtained. The magnitude of resonant magnetic field is shown to depend on the crystalline field constants ratio B2 /B2 not on their absolute values, if B2 B2 ≥ gβH· The Mn EPR line intensity decreses in temperature range 140⩽ ⩽ T ⩽ 192 K. The temperature of EPR

Nanoscale Research Letters, 2017

Physics of the Solid State, 2006

ABSTRACT The photoluminescence, electroluminescence, and electron paramagnetic resonance spectra ... more ABSTRACT The photoluminescence, electroluminescence, and electron paramagnetic resonance spectra of ZnS powders thermally doped with CuCl are investigated. The processes occurring in the material during simultaneous annealing of ZnS and CuCl are discussed, and the influence of the annealing conditions on the formation of the CuS and Cu2S phases in zinc sulfide is analyzed. It is shown that the concentration ratio of the blue luminescence centers to the green luminescence centers and the concentration of Mn2+ paramagnetic centers in the phosphor prepared can be controlled by varying the rate of heating of the material to the annealing temperature. A technique based on low-temperature annealing is conceptualized and developed for synthesizing materials that, as rule, can be produced only through high-temperature annealing.

Journal of Applied Physics, 2013

Journal of Materials Chemistry C

We report on the formation of epitaxial perovskite oxide superlattice structures by atomic layer ... more We report on the formation of epitaxial perovskite oxide superlattice structures by atomic layer deposition (ALD), which are integrated monolithically on Si wafers using a template layer of SrTiO3 deposited by hybrid molecular beam epitaxy.

Physics of The Solid State, 1995

Physics of the Solid State, 1998

physica status solidi (b), 2012

physica status solidi (b), 2012

Nanoscale, 2018

Traditionally, the ferroelectric Curie temperature can be manipulated by chemical substitution, e... more Traditionally, the ferroelectric Curie temperature can be manipulated by chemical substitution, e.g., in Ba1−xSrxTiO3 as one of the archetypical representatives. Here, we show a novel approach to tune the ferroelectric phase transition applicable for nanostructured thin films. We demonstrate this effect in nanograined BaTiO3 films. Based on an enhanced metastable cation solubility with Ba/Ti-ratios of 0.8 to 1.06,
a significant shift of the phase transition temperature is discovered. The transition temperature increases linearly from 212 K to 350 K with increasing Ba/Ti ratio. For all Ba/Ti ratios, a completely diffused phase
transition is present resulting in a negligible temperature sensitivity of the dielectric constant. Schottky defects are identified as the driving force behind the off-stoichiometry and the shift of the phase transition temperature as they locally induce lattice strain. Complementary temperature dependent Raman experiments reveal the presence of the hexagonal polymorph in addition to the perovskite phase in all cases. Interestingly, the hexagonal BaTiO3 influences the structural transformation on the Ba-rich side, while on the Ti-rich side no changes for the hexagonal polymorph at the ferroelectric transition temperature are observed. This concerted structural change of both polymorphs on the Ba-rich side causes a broad phase transition region spanning over a wide range up to 420 K including the transition temperature of 350 K obtained from dielectric measurements. These findings are promising for fine adjustment of the phase transition temperature and low temperature coefficient of permittivity.

Nanoscale, 2018

Thin films of ≈50 nm thickness with Ba/Ti-ratios ranging from 0.8 to 1.06 were prepared by deposi... more Thin films of ≈50 nm thickness with Ba/Ti-ratios ranging from 0.8 to 1.06 were prepared by depositing alternating layers of Ba(OH)2 and TiO2. Annealing at 750 °C promoted the solid–solid transformation into polycrystalline BaTiO3 films containing a mixture of the perovskite and the hexagonal polymorphs with average crystallite sizes smaller than 14 nm and without impurity phases. This, together with an increase of the cubic lattice parameters for Ba-rich films, suggests an extended metastable solubility range for the perovskite-phase in these nanocrystalline thin films on both sides of the stoichiometric composition. Mapping of the cation distribution utilizing energy-filtered transmission electron microscopy corroborates defect accommodation within the BaTiO3 grains. While the cation off-stoichiometry in thermodynamic equilibrium is negligible for BaTiO3, the metastable extended solubility range in the thin films can be directly correlated to the low annealing temperature and nanocrystalline nature. The leakage current behavior can be explained by the formation of Schottky defects for nonstoichiometric films, and the cation ratio has a distinct impact on the dielectric properties: while excess-BaO has a marginal detrimental effect on the permittivity, the dielectric constant declines rapidly by more than 50% towards the Ti-rich side. The present findings highlight the importance of compositional control for the synthesis of nanocrystalline BaTiO3 thin films, in particular for low annealing and/or deposition temperatures. Our synthesis approach using alternating layers of Ba(OH)2 and TiO2 provides a route to precisely control the cation stoichiometry.

J. Mater. Chem. C, 2018

An investigation of the influence of annealing conditions on the carrier transport, leakage curre... more An investigation of the influence of annealing conditions on the carrier transport, leakage current and dielectric properties of ALD-grown amorphous Bi–Fe–O thin films after their crystallization into BiFeO 3 is presented. Whereas the interface-limited Schottky emission mechanism is dominant in 70 nm thick Fe-rich films after relatively short annealing, a space-charge-limited conduction mechanism is dominant in stoichiometric films with a thickness of 215 nm independent of the annealing conditions. Interestingly, prolonged annealing of the thin films also results in space charge limited conduction. Analysis of the changes in dielectric properties, on one hand, and the film composition, microstructure and morphology, on the other hand, reveal the key role of grain boundary interfaces for the conductivity of the polycrystalline ALD-grown BiFeO 3 thin films. Extended annealing in oxygen results in 2–3 orders-of-magnitude reduction in leakage current accompanied by decreases in dielectric loss, highlighting the importance of optimizing annealing conditions for any applications of BiFeO 3 thin films.

J. Phys. Chem. C, 2017

A superlattice approach for the atomic layer deposition of polycrystalline BaTiO3 thin films is p... more A superlattice approach for the atomic layer deposition of polycrystalline BaTiO3 thin films is presented as an example for an effective route to produce high-quality complex oxide films with excellent thickness and compositional control. This method effectively mitigates any undesirable reactions between the different precursors and allows an individual optimization of the reaction conditions for the Ba−O and the Ti−O subcycles. By growth of nanometer thick alternating
Ba(OH)2 and TiO2 layers, the advantages of binary oxide atomic layer deposition are transferred into the synthesis of ternary compounds, permitting extremely high control of the cation ratio and superior uniformity. Whereas the Ba(OH)2 layers are partially crystalline after the deposition, the TiO2 layers remain mostly amorphous. The layers react to polycrystalline, polymorph BaTiO3 above 500 °C, releasing H2O. This solid-state reaction is accompanied by an abrupt decrease in film thickness. Transmission electron microscopy and Raman spectroscopy reveal the presence of hexagonal BaTiO3 in addition to the perovskite phase in the annealed films. The microstructure with relatively small grains of ∼70 Å and different phases is a direct consequence of the abrupt formation reaction. The electrical properties transition from the initially highly insulating dielectric semiamorphous superlattice into a polycrystalline BaTiO3 thin film with a dielectric constant of 117 and a dielectric loss of 0.001 at 1 MHz after annealing at 600 °C in air, which, together with the suppression of ferroelectricity at room temperature,
are very appealing properties for voltage tunable devices.

ChemPhysChem, 2017

We report on the growth of polycrystalline BiFeO3 thin films on SiO2/Si(001) and Pt(111) substrat... more We report on the growth of polycrystalline BiFeO3 thin films on SiO2/Si(001) and Pt(111) substrates by atomic layer deposition using the precursors ferrocene, triphenyl-bismuth, and ozone. By growing alternating layers of Fe2O3 and Bi2O3, we employ a superlattice approach and demonstrate an efficient control of the cation stoichiometry. The superlattice decay and the resulting formation of polycrystalline BiFeO3 films are studied by in situ X-ray diffraction, in situ X-ray photoelectron spectroscopy, and transmission electron microscopy. No intermediate ternary phases are formed and BiFeO3 crystallization is initiated in the Bi2O3 layers at 450 °C following the diffusion-driven intermixing of the cations. Our study of the BiFeO3 formation provides an insight into the complex interplay between microstructural evolution, grain growth, and bismuth oxide evaporation, with implications for optimization of ferroelectric properties.

Nanoscale Research Letters , 2017

Nanoparticles of potassium tantalate (KTaO3) and potassium niobate (KNbO3) were synthesized by ox... more Nanoparticles of potassium tantalate (KTaO3) and potassium niobate (KNbO3) were synthesized by oxidation of metallic tantalum in molten potassium nitrate with the addition of potassium hydroxide. Magnetization curves obtained on these ferroelectric nanoparticles exhibit a weak ferromagnetism, while these compounds are nonmagnetic in a bulk. The experimental data are used as a start point for theoretical calculations. We consider a microscopic mechanism that leads to the emerging of a ferromagnetic ordering in ferroelectric nanoparticles. Our approach is based on the percolation of magnetic polarons assuming the dominant role of the oxygen vacancies. It describes the formation of surface magnetic polarons, in which an exchange interaction between electrons trapped in oxygen vacancies is mediated by magnetic impurity Fe3+ ions. The dependences of percolation radius on concentration of the oxygen vacancies and magnetic defects are determined in the framework of percolation theory.

Acta Materialia, 2021

Abstract Electrically tunable dielectric thin films in active circuits and systems are challenged... more Abstract Electrically tunable dielectric thin films in active circuits and systems are challenged by capacitance-induced delays and impedance matching requiring a lower dielectric constant. Here an approach to increasing the intrinsic tunability of compounds containing TiO6 octahedra by considering the influence of different connectivity among these octahedra is presented. Such connectivity variants in nanocrystalline monoclinic BaTi2O5 thin films enable a two orders of magnitude enhancement in Ti anharmonic interaction, thereby permitting a ≈ 65% decrease in dielectric constant to 70 at room temperature without sacrificing tunability. Edge-sharing TiO6 octahedra possess a much shorter Ti-Ti distance of only 2.91 A as compared to the perovskite structure (~4 A), permitting large field-induced structural re-arrangement and intrinsic tunability.

Ferroelectrics, 1994

The temperature dependence of Mn EPR spectrum in Sn2P2Se6 ferroelectric has been obtained. The ma... more The temperature dependence of Mn EPR spectrum in Sn2P2Se6 ferroelectric has been obtained. The magnitude of resonant magnetic field is shown to depend on the crystalline field constants ratio B2 /B2 not on their absolute values, if B2 B2 ≥ gβH· The Mn EPR line intensity decreses in temperature range 140⩽ ⩽ T ⩽ 192 K. The temperature of EPR

Nanoscale Research Letters, 2017

Physics of the Solid State, 2006

ABSTRACT The photoluminescence, electroluminescence, and electron paramagnetic resonance spectra ... more ABSTRACT The photoluminescence, electroluminescence, and electron paramagnetic resonance spectra of ZnS powders thermally doped with CuCl are investigated. The processes occurring in the material during simultaneous annealing of ZnS and CuCl are discussed, and the influence of the annealing conditions on the formation of the CuS and Cu2S phases in zinc sulfide is analyzed. It is shown that the concentration ratio of the blue luminescence centers to the green luminescence centers and the concentration of Mn2+ paramagnetic centers in the phosphor prepared can be controlled by varying the rate of heating of the material to the annealing temperature. A technique based on low-temperature annealing is conceptualized and developed for synthesizing materials that, as rule, can be produced only through high-temperature annealing.

Journal of Applied Physics, 2013

Journal of Materials Chemistry C

We report on the formation of epitaxial perovskite oxide superlattice structures by atomic layer ... more We report on the formation of epitaxial perovskite oxide superlattice structures by atomic layer deposition (ALD), which are integrated monolithically on Si wafers using a template layer of SrTiO3 deposited by hybrid molecular beam epitaxy.

Physics of The Solid State, 1995

Physics of the Solid State, 1998

physica status solidi (b), 2012

physica status solidi (b), 2012

Nanoscale, 2018

Traditionally, the ferroelectric Curie temperature can be manipulated by chemical substitution, e... more Traditionally, the ferroelectric Curie temperature can be manipulated by chemical substitution, e.g., in Ba1−xSrxTiO3 as one of the archetypical representatives. Here, we show a novel approach to tune the ferroelectric phase transition applicable for nanostructured thin films. We demonstrate this effect in nanograined BaTiO3 films. Based on an enhanced metastable cation solubility with Ba/Ti-ratios of 0.8 to 1.06,
a significant shift of the phase transition temperature is discovered. The transition temperature increases linearly from 212 K to 350 K with increasing Ba/Ti ratio. For all Ba/Ti ratios, a completely diffused phase
transition is present resulting in a negligible temperature sensitivity of the dielectric constant. Schottky defects are identified as the driving force behind the off-stoichiometry and the shift of the phase transition temperature as they locally induce lattice strain. Complementary temperature dependent Raman experiments reveal the presence of the hexagonal polymorph in addition to the perovskite phase in all cases. Interestingly, the hexagonal BaTiO3 influences the structural transformation on the Ba-rich side, while on the Ti-rich side no changes for the hexagonal polymorph at the ferroelectric transition temperature are observed. This concerted structural change of both polymorphs on the Ba-rich side causes a broad phase transition region spanning over a wide range up to 420 K including the transition temperature of 350 K obtained from dielectric measurements. These findings are promising for fine adjustment of the phase transition temperature and low temperature coefficient of permittivity.

Nanoscale, 2018

Thin films of ≈50 nm thickness with Ba/Ti-ratios ranging from 0.8 to 1.06 were prepared by deposi... more Thin films of ≈50 nm thickness with Ba/Ti-ratios ranging from 0.8 to 1.06 were prepared by depositing alternating layers of Ba(OH)2 and TiO2. Annealing at 750 °C promoted the solid–solid transformation into polycrystalline BaTiO3 films containing a mixture of the perovskite and the hexagonal polymorphs with average crystallite sizes smaller than 14 nm and without impurity phases. This, together with an increase of the cubic lattice parameters for Ba-rich films, suggests an extended metastable solubility range for the perovskite-phase in these nanocrystalline thin films on both sides of the stoichiometric composition. Mapping of the cation distribution utilizing energy-filtered transmission electron microscopy corroborates defect accommodation within the BaTiO3 grains. While the cation off-stoichiometry in thermodynamic equilibrium is negligible for BaTiO3, the metastable extended solubility range in the thin films can be directly correlated to the low annealing temperature and nanocrystalline nature. The leakage current behavior can be explained by the formation of Schottky defects for nonstoichiometric films, and the cation ratio has a distinct impact on the dielectric properties: while excess-BaO has a marginal detrimental effect on the permittivity, the dielectric constant declines rapidly by more than 50% towards the Ti-rich side. The present findings highlight the importance of compositional control for the synthesis of nanocrystalline BaTiO3 thin films, in particular for low annealing and/or deposition temperatures. Our synthesis approach using alternating layers of Ba(OH)2 and TiO2 provides a route to precisely control the cation stoichiometry.

J. Mater. Chem. C, 2018

An investigation of the influence of annealing conditions on the carrier transport, leakage curre... more An investigation of the influence of annealing conditions on the carrier transport, leakage current and dielectric properties of ALD-grown amorphous Bi–Fe–O thin films after their crystallization into BiFeO 3 is presented. Whereas the interface-limited Schottky emission mechanism is dominant in 70 nm thick Fe-rich films after relatively short annealing, a space-charge-limited conduction mechanism is dominant in stoichiometric films with a thickness of 215 nm independent of the annealing conditions. Interestingly, prolonged annealing of the thin films also results in space charge limited conduction. Analysis of the changes in dielectric properties, on one hand, and the film composition, microstructure and morphology, on the other hand, reveal the key role of grain boundary interfaces for the conductivity of the polycrystalline ALD-grown BiFeO 3 thin films. Extended annealing in oxygen results in 2–3 orders-of-magnitude reduction in leakage current accompanied by decreases in dielectric loss, highlighting the importance of optimizing annealing conditions for any applications of BiFeO 3 thin films.

J. Phys. Chem. C, 2017

A superlattice approach for the atomic layer deposition of polycrystalline BaTiO3 thin films is p... more A superlattice approach for the atomic layer deposition of polycrystalline BaTiO3 thin films is presented as an example for an effective route to produce high-quality complex oxide films with excellent thickness and compositional control. This method effectively mitigates any undesirable reactions between the different precursors and allows an individual optimization of the reaction conditions for the Ba−O and the Ti−O subcycles. By growth of nanometer thick alternating
Ba(OH)2 and TiO2 layers, the advantages of binary oxide atomic layer deposition are transferred into the synthesis of ternary compounds, permitting extremely high control of the cation ratio and superior uniformity. Whereas the Ba(OH)2 layers are partially crystalline after the deposition, the TiO2 layers remain mostly amorphous. The layers react to polycrystalline, polymorph BaTiO3 above 500 °C, releasing H2O. This solid-state reaction is accompanied by an abrupt decrease in film thickness. Transmission electron microscopy and Raman spectroscopy reveal the presence of hexagonal BaTiO3 in addition to the perovskite phase in the annealed films. The microstructure with relatively small grains of ∼70 Å and different phases is a direct consequence of the abrupt formation reaction. The electrical properties transition from the initially highly insulating dielectric semiamorphous superlattice into a polycrystalline BaTiO3 thin film with a dielectric constant of 117 and a dielectric loss of 0.001 at 1 MHz after annealing at 600 °C in air, which, together with the suppression of ferroelectricity at room temperature,
are very appealing properties for voltage tunable devices.

ChemPhysChem, 2017

We report on the growth of polycrystalline BiFeO3 thin films on SiO2/Si(001) and Pt(111) substrat... more We report on the growth of polycrystalline BiFeO3 thin films on SiO2/Si(001) and Pt(111) substrates by atomic layer deposition using the precursors ferrocene, triphenyl-bismuth, and ozone. By growing alternating layers of Fe2O3 and Bi2O3, we employ a superlattice approach and demonstrate an efficient control of the cation stoichiometry. The superlattice decay and the resulting formation of polycrystalline BiFeO3 films are studied by in situ X-ray diffraction, in situ X-ray photoelectron spectroscopy, and transmission electron microscopy. No intermediate ternary phases are formed and BiFeO3 crystallization is initiated in the Bi2O3 layers at 450 °C following the diffusion-driven intermixing of the cations. Our study of the BiFeO3 formation provides an insight into the complex interplay between microstructural evolution, grain growth, and bismuth oxide evaporation, with implications for optimization of ferroelectric properties.

Nanoscale Research Letters , 2017

Nanoparticles of potassium tantalate (KTaO3) and potassium niobate (KNbO3) were synthesized by ox... more Nanoparticles of potassium tantalate (KTaO3) and potassium niobate (KNbO3) were synthesized by oxidation of metallic tantalum in molten potassium nitrate with the addition of potassium hydroxide. Magnetization curves obtained on these ferroelectric nanoparticles exhibit a weak ferromagnetism, while these compounds are nonmagnetic in a bulk. The experimental data are used as a start point for theoretical calculations. We consider a microscopic mechanism that leads to the emerging of a ferromagnetic ordering in ferroelectric nanoparticles. Our approach is based on the percolation of magnetic polarons assuming the dominant role of the oxygen vacancies. It describes the formation of surface magnetic polarons, in which an exchange interaction between electrons trapped in oxygen vacancies is mediated by magnetic impurity Fe3+ ions. The dependences of percolation radius on concentration of the oxygen vacancies and magnetic defects are determined in the framework of percolation theory.