The electrical resistivity under hydrostatic pressure up to 1.0 GPa, Hall effect, magnetoresistan... more The electrical resistivity under hydrostatic pressure up to 1.0 GPa, Hall effect, magnetoresistance, and thermoelectric power are measured over the temperature range from 1.5 to 300 K for both, orthorhombic γ-Mo4O11 and monoclinic η-Mo4O11 crystals with quasi-two-dimensional structures. All these properties show anomalies associated with the charge density wave (CDW) transition; particularly the hydrostatic pressure enhances the CDW instabilities through the increased electron–phonon interaction and partial nesting of the Fermi surfaces. It is also found that both, electrons and holes contribute to the conduction processes, for which a qualitative discussion is made. Der elektrische Widerstand unter hydrostatischem Druck bis 1,0 GPa, Halleffekt, magnetische Widerstandsanderung und Thermospannung werden bei Temperaturen von 1,5 bis 300 K fur rhombische γ-Mo4O11- und monokline η-Mo4O11-Kristalle mit quasi-zwei-dimensionaler Struktur gemessen. Alle Transporterscheinungen zeigen die mit dem Ladungsdichtewellen (LDW)-Ubergang assoziierten Anomalien; besonders der hydrostatische Druck erhoht die LDW-Instabilitaten durch die angewachsene Elektron–Phonon-Wechselwirkung und partielle Schachtelung der Fermi-Flachen. Es wird auch gefunden, das sowohl die Elektronen als auch die Locher zum Leitungsprozes beitragen; dafur wird eine qualitative Diskussion gegeben.
Herein, we investigate the performance of single- and multiparametric luminescence thermometry fo... more Herein, we investigate the performance of single- and multiparametric luminescence thermometry founded on the temperature-dependent spectral features of Ca6BaP4O17:Mn5+ near-infrared emission. The material was prepared by a conventional steady-state synthesis, and its photoluminescence emission was measured from 7500 to 10,000 cm−1 over the 293–373 K temperature range in 5 K increments. The spectra are composed of the emissions from 1E → 3A2 and 3T2 → 3A2 electronic transitions and Stokes and anti-Stokes vibronic sidebands at 320 cm−1 and 800 cm−1 from the maximum of 1E → 3A2 emission. Upon temperature increase, the 3T2 and Stokes bands gained in intensity while the maximum of 1E emission band is redshifted. We introduced the procedure for the linearization and feature scaling of input variables for linear multiparametric regression. Then, we experimentally determined accuracies and precisions of the luminescence thermometry based on luminescence intensity ratios between emissions f...
Negative thermal quenching of intrinsic BiFeO3 semiconductor nanoparticles for ratiometric lumine... more Negative thermal quenching of intrinsic BiFeO3 semiconductor nanoparticles for ratiometric luminescence thermometry with 2.5% K−1 relative sensitivity and 0.2 K temperature resolution.
In this work, the potential of Li1.8Na0.2TiO3:Mn 4+ for the lifetime-based luminescence thermomet... more In this work, the potential of Li1.8Na0.2TiO3:Mn 4+ for the lifetime-based luminescence thermometry is assessed. The material is prepared by the solid-state reaction of Li2CO3, Na2CO3, and nanostructured TiO2 at 800°C, and its monoclinic structure (space group C2/c) is confirmed by X-ray diffraction analysis. In this host, Mn 4+ provides strong absorption around 330 nm and 500 nm due to 4 A2g → 4 T1g and 4 A2g → 4 T2g electric dipole forbidden and spinallowed electron transitions, respectively, and emits around 679 nm on account of 2 Eg → 4 A2g spin forbidden electron transition. Temperature dependences of emission intensity and emission decay are measured over the 10-350 K range. Due to the low value of energy of 4 T2g level (20000 cm-1), the strong emission quenching starts at low-temperatures which favors the use of this material for the luminescence thermometry. It is demonstrated that the quite large value of relative sensitivity (2.6% K-1 @340 K) facilitates temperature measurements with temperature resolution better than 0.1 K, and with the excellent repeatability.
The possibility of formation of a fully spin-polarized 2D electron gas at the SrMnO 3 =ðLaMnO 3 Þ... more The possibility of formation of a fully spin-polarized 2D electron gas at the SrMnO 3 =ðLaMnO 3 Þ 1 = SrMnO 3 heterostructure is predicted from density-functional calculations. The LaðdÞ electrons become confined in the direction normal to the interface in the electrostatic potential well of the positively charged layer of La atoms, acting as electron donors. These electrons mediate a ferromagnetic alignment of the Mn t 2g spins near the interface via Zener double exchange and become, in turn, spin-polarized due to the internal magnetic fields of the Mn moments.
The near-infrared luminescence of Ca6Ba(PO4)4O:Mn5+ is demonstrated and explained. When excited i... more The near-infrared luminescence of Ca6Ba(PO4)4O:Mn5+ is demonstrated and explained. When excited into the broad and strong absorption band that spans the 500–1000 nm spectral range, this phosphor provides an ultranarrow (FWHM = 5 nm) emission centered at 1140 nm that originates from a spin-forbidden 1E → 3A2 transition with a 37.5% internal quantum efficiency and an excited-state lifetime of about 350 μs. We derived the crystal field and Racah parameters and calculated the appropriate Tanabe–Sugano diagram for this phosphor. We found that 1E emission quenches due to the thermally-assisted cross-over with the 3T2 state and that the relatively high Debye temperature of 783 K of Ca6Ba(PO4)4O facilitates efficient emission. Since Ca6Ba(PO4)4O also provides efficient yellow emission of the Eu2+ dopant, we calculated and explained its electronic band structure, the partial and total density of states, effective Mulliken charges of all ions, elastic constants, Debye temperature, and vibrati...
Employing X-ray magnetic circular dichroism (XMCD), angle-resolved photoemission spectroscopy (AR... more Employing X-ray magnetic circular dichroism (XMCD), angle-resolved photoemission spectroscopy (ARPES), and momentum-resolved density fluctuation (MRDF) theory, the magnetic and electronic properties of ultrathin NdNiO 3 (NNO) film in proximity to ferromagnetic (FM) La 0.67 Sr 0.33 MnO 3 (LSMO) layer are investigated. The experimental data shows the direct magnetic coupling between the nickelate film and the manganite layer which causes an unusual ferromagnetic (FM) phase in NNO. Moreover, it is shown the metal-insulator transition in the NNO layer, identified by an abrupt suppression of ARPES spectral weight near the Fermi level (E F), is absent. This observation suggests that the insulating AFM ground state is quenched in proximity to the FM layer. Combining the experimental data (XMCD and AREPS) with the momentum-resolved density fluctuation calculation (MRDF) reveals a direct link between the MIT and the magnetic orders in NNO systems. This work demonstrates that the proximity layer order can be broadly used to modify physical properties and enrich the phase diagram of RENiO 3 (RE = rare-earth element).
We investigate the band structure of BaBiO_{3}, an insulating parent compound of doped high-T_{c}... more We investigate the band structure of BaBiO_{3}, an insulating parent compound of doped high-T_{c} superconductors, using in situ angle-resolved photoemission spectroscopy on thin films. The data compare favorably overall with density functional theory calculations within the local density approximation, demonstrating that electron correlations are weak. The bands exhibit Brillouin zone folding consistent with known BiO_{6} breathing distortions. Though the distortions are often thought to coincide with Bi^{3+}/Bi^{5+} charge ordering, core level spectra show that bismuth is monovalent. We further demonstrate that the bands closest to the Fermi level are primarily oxygen derived, while the bismuth 6s states mostly contribute to dispersive bands at deeper binding energy. The results support a model of Bi-O charge transfer in which hole pairs are localized on combinations of the O 2p orbitals.
Engineering the electronic band structure of two-dimensional electron liquids (2DELs) confined at... more Engineering the electronic band structure of two-dimensional electron liquids (2DELs) confined at the surface or interface of transition metal oxides is key to unlocking their full potential. Here we describe a new approach to tailoring the electronic structure of an oxide surface 2DEL demonstrating the lateral modulation of electronic states with atomic scale precision on an unprecedented length scale comparable to the Fermi wavelength. To this end, we use pulsed laser deposition to grow anatase TiO2 films terminated by a (1 × 4) in-plane surface reconstruction. Employing photo-stimulated chemical surface doping we induce 2DELs with tunable carrier densities that are confined within a few TiO2 layers below the surface. Subsequent in-situ angle resolved photoemission experiments demonstrate that the (1 × 4) surface reconstruction provides a periodic lateral perturbation of the electron liquid. This causes strong backfolding of the electronic bands, opening of unidirectional gaps and...
Scanning tunneling spectroscopy has been a window into the (sub)atomic world for more than two de... more Scanning tunneling spectroscopy has been a window into the (sub)atomic world for more than two decades now, but the wealth of information that this technique offers seem yet to be exploited to it's maximum. In this thesis it is tried to optimize STM and, more precisely, STS techniques for the investigation of transition metal oxides, especially ones that exhibit interesting correlated structural and electronic phenomena like Pr$_{1-x}$Ca$_{x}$MnO$_{3}$ and LaAlO$_{3}$/SrTiO$_{3}$ system; the first is an insulator characterized by intriguing magnetic and charge-ordered phases, and the second is unique example of 2D electron gas, confined to the buried interface between two band-insulators. To this purpose, different numerical methods are proposed, which greatly help the handling of the data obtained in STS measurements. This approach allowed to determine important correlations between structural and electronic properties of the TMO surfaces/interfaces
Material properties can be controlled via strain, pressure, chemical composition, or dimensionali... more Material properties can be controlled via strain, pressure, chemical composition, or dimensionality. Nickelates are particularly susceptible due to their strong variations of the electronic and magnetic properties on such external stimuli. Here, we analyze the photoinduced dynamics in a single crystalline NdNiO 3 film upon excitation across the electronic gap. Using time-resolved reflectivity and resonant x-ray diffraction, we show that the pump pulse induces an insulator-to-metal transition, accompanied by the melting of the charge order. Finally, we compare our results with similar studies in manganites and show that the same model can be used to describe the dynamics in nickelates, hinting towards a unified description of these photoinduced electronic ordering phase transitions. V
We studied the structural, magnetic and transport properties of LaAlO 3 /EuTiO 3 /SrTiO 3 heteros... more We studied the structural, magnetic and transport properties of LaAlO 3 /EuTiO 3 /SrTiO 3 heterostructures grown by Pulsed Laser Deposition. The samples have been characterized in-situ by electron diffraction and scanning probe microscopy and ex-situ by transport measurements and x-ray absorption spectroscopy. LaAlO 3 /EuTiO 3 /SrTiO 3 films show a ferromagnetic transition at K related to the ordering of Eu 2+ spins, even in samples characterized by just two EuTiO 3 unit cells. A finite metallic conductivity is observed only in the case of samples composed by one or two Eu-TiO 3 unit cells and, simultaneously, by a LaAlO 3 thickness equal or above 4 unit cells. The role of ferromagnetic Eu-TiO 3 on the transport properties of -doped LaAlO 3 /EuTiO 3 /SrTiO 3 is critically discussed.
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms, 2005
The quantitative surface composition analysis with low energy ion scattering (LEIS), which is the... more The quantitative surface composition analysis with low energy ion scattering (LEIS), which is the experimental technique with the information depth that can be restricted to the first atomic layer, is often obstructed by the experimental problems. A novel approach is presented in order to calculate the influence of the optics of the energy analyzer and the geometric primary ion beam
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms, 2007
The inelastic energy losses of He + ions singly scattered from polycrystalline chromium (Cr) surf... more The inelastic energy losses of He + ions singly scattered from polycrystalline chromium (Cr) surface in the 0.7-2.0 keV energy range were experimentally investigated in this work. The energy spectra of ions scattered to 90°were measured. The peak corresponding to singly scattered ions is resolved into two Gaussians. The one at higher energies (elastic peak) corresponds to the He + ions that were not neutralized along the trajectory, while that at lower energy (inelastic peak) is attributed to the He + ions that were neutralized while approaching the surface and then reionized during the violent collision with Cr surface atoms. The difference between the positions of these Gaussians is a measure of the inelastic energy losses caused by the projectile reionization. These discrete inelastic losses are interpreted using the model of Tsuneyuki and Tsukada. It was observed that the energy difference between the elastic and inelastic peak increases with the incident ion energy. The elastic and inelastic peak intensities depend on the incoming angle and the character of this dependence abruptly changes for the incident ion energies in the range 1350-1400 eV, which cannot be explained by the existing theoretical models.
... Communication. Electrical and Optical Characteristics of Ta 2 O 5 Thin Films Deposited by Ele... more ... Communication. Electrical and Optical Characteristics of Ta 2 O 5 Thin Films Deposited by Electron-Beam Vapor Deposition. Zhana Todorova 1,* ,; Nikolay Donkov 1 ,; Zoran Ristić 2 ,; Nenad Bundaleski 2 ,; Suzana Petrović 2 ,; Mario Petkov 1. ... D. Spassov, Appl. Surf. Sci. ...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007
Nichrome coatings have been deposited using the d.c. sputtering of the target (80% Ni-20% Cr wt.)... more Nichrome coatings have been deposited using the d.c. sputtering of the target (80% Ni-20% Cr wt.) by Ar + ions at a working pressure of 10 À1 Pa and at room temperature. After the air exposure of samples at room temperature, their phase composition and structure was studied by X-ray diffraction, while the surface elemental composition was determined by low energy ion scattering (LEIS) and Auger electron spectroscopy (AES). AES has been also used for the bulk composition analysis. There is a significant difference between the compositions of the surface and of the bulk. Surface segregation of chromium was observed using both LEIS and AES, and it was found that the chromium concentration increases with that of oxygen adsorbed at the surface during the air exposure. The nichrome surface composition is qualitatively the same as in the case of its exposure to O 2 at room temperature, but significantly different from that of the thermally annealed nichrome to 400°C in air.
The electrical resistivity under hydrostatic pressure up to 1.0 GPa, Hall effect, magnetoresistan... more The electrical resistivity under hydrostatic pressure up to 1.0 GPa, Hall effect, magnetoresistance, and thermoelectric power are measured over the temperature range from 1.5 to 300 K for both, orthorhombic γ-Mo4O11 and monoclinic η-Mo4O11 crystals with quasi-two-dimensional structures. All these properties show anomalies associated with the charge density wave (CDW) transition; particularly the hydrostatic pressure enhances the CDW instabilities through the increased electron–phonon interaction and partial nesting of the Fermi surfaces. It is also found that both, electrons and holes contribute to the conduction processes, for which a qualitative discussion is made. Der elektrische Widerstand unter hydrostatischem Druck bis 1,0 GPa, Halleffekt, magnetische Widerstandsanderung und Thermospannung werden bei Temperaturen von 1,5 bis 300 K fur rhombische γ-Mo4O11- und monokline η-Mo4O11-Kristalle mit quasi-zwei-dimensionaler Struktur gemessen. Alle Transporterscheinungen zeigen die mit dem Ladungsdichtewellen (LDW)-Ubergang assoziierten Anomalien; besonders der hydrostatische Druck erhoht die LDW-Instabilitaten durch die angewachsene Elektron–Phonon-Wechselwirkung und partielle Schachtelung der Fermi-Flachen. Es wird auch gefunden, das sowohl die Elektronen als auch die Locher zum Leitungsprozes beitragen; dafur wird eine qualitative Diskussion gegeben.
Herein, we investigate the performance of single- and multiparametric luminescence thermometry fo... more Herein, we investigate the performance of single- and multiparametric luminescence thermometry founded on the temperature-dependent spectral features of Ca6BaP4O17:Mn5+ near-infrared emission. The material was prepared by a conventional steady-state synthesis, and its photoluminescence emission was measured from 7500 to 10,000 cm−1 over the 293–373 K temperature range in 5 K increments. The spectra are composed of the emissions from 1E → 3A2 and 3T2 → 3A2 electronic transitions and Stokes and anti-Stokes vibronic sidebands at 320 cm−1 and 800 cm−1 from the maximum of 1E → 3A2 emission. Upon temperature increase, the 3T2 and Stokes bands gained in intensity while the maximum of 1E emission band is redshifted. We introduced the procedure for the linearization and feature scaling of input variables for linear multiparametric regression. Then, we experimentally determined accuracies and precisions of the luminescence thermometry based on luminescence intensity ratios between emissions f...
Negative thermal quenching of intrinsic BiFeO3 semiconductor nanoparticles for ratiometric lumine... more Negative thermal quenching of intrinsic BiFeO3 semiconductor nanoparticles for ratiometric luminescence thermometry with 2.5% K−1 relative sensitivity and 0.2 K temperature resolution.
In this work, the potential of Li1.8Na0.2TiO3:Mn 4+ for the lifetime-based luminescence thermomet... more In this work, the potential of Li1.8Na0.2TiO3:Mn 4+ for the lifetime-based luminescence thermometry is assessed. The material is prepared by the solid-state reaction of Li2CO3, Na2CO3, and nanostructured TiO2 at 800°C, and its monoclinic structure (space group C2/c) is confirmed by X-ray diffraction analysis. In this host, Mn 4+ provides strong absorption around 330 nm and 500 nm due to 4 A2g → 4 T1g and 4 A2g → 4 T2g electric dipole forbidden and spinallowed electron transitions, respectively, and emits around 679 nm on account of 2 Eg → 4 A2g spin forbidden electron transition. Temperature dependences of emission intensity and emission decay are measured over the 10-350 K range. Due to the low value of energy of 4 T2g level (20000 cm-1), the strong emission quenching starts at low-temperatures which favors the use of this material for the luminescence thermometry. It is demonstrated that the quite large value of relative sensitivity (2.6% K-1 @340 K) facilitates temperature measurements with temperature resolution better than 0.1 K, and with the excellent repeatability.
The possibility of formation of a fully spin-polarized 2D electron gas at the SrMnO 3 =ðLaMnO 3 Þ... more The possibility of formation of a fully spin-polarized 2D electron gas at the SrMnO 3 =ðLaMnO 3 Þ 1 = SrMnO 3 heterostructure is predicted from density-functional calculations. The LaðdÞ electrons become confined in the direction normal to the interface in the electrostatic potential well of the positively charged layer of La atoms, acting as electron donors. These electrons mediate a ferromagnetic alignment of the Mn t 2g spins near the interface via Zener double exchange and become, in turn, spin-polarized due to the internal magnetic fields of the Mn moments.
The near-infrared luminescence of Ca6Ba(PO4)4O:Mn5+ is demonstrated and explained. When excited i... more The near-infrared luminescence of Ca6Ba(PO4)4O:Mn5+ is demonstrated and explained. When excited into the broad and strong absorption band that spans the 500–1000 nm spectral range, this phosphor provides an ultranarrow (FWHM = 5 nm) emission centered at 1140 nm that originates from a spin-forbidden 1E → 3A2 transition with a 37.5% internal quantum efficiency and an excited-state lifetime of about 350 μs. We derived the crystal field and Racah parameters and calculated the appropriate Tanabe–Sugano diagram for this phosphor. We found that 1E emission quenches due to the thermally-assisted cross-over with the 3T2 state and that the relatively high Debye temperature of 783 K of Ca6Ba(PO4)4O facilitates efficient emission. Since Ca6Ba(PO4)4O also provides efficient yellow emission of the Eu2+ dopant, we calculated and explained its electronic band structure, the partial and total density of states, effective Mulliken charges of all ions, elastic constants, Debye temperature, and vibrati...
Employing X-ray magnetic circular dichroism (XMCD), angle-resolved photoemission spectroscopy (AR... more Employing X-ray magnetic circular dichroism (XMCD), angle-resolved photoemission spectroscopy (ARPES), and momentum-resolved density fluctuation (MRDF) theory, the magnetic and electronic properties of ultrathin NdNiO 3 (NNO) film in proximity to ferromagnetic (FM) La 0.67 Sr 0.33 MnO 3 (LSMO) layer are investigated. The experimental data shows the direct magnetic coupling between the nickelate film and the manganite layer which causes an unusual ferromagnetic (FM) phase in NNO. Moreover, it is shown the metal-insulator transition in the NNO layer, identified by an abrupt suppression of ARPES spectral weight near the Fermi level (E F), is absent. This observation suggests that the insulating AFM ground state is quenched in proximity to the FM layer. Combining the experimental data (XMCD and AREPS) with the momentum-resolved density fluctuation calculation (MRDF) reveals a direct link between the MIT and the magnetic orders in NNO systems. This work demonstrates that the proximity layer order can be broadly used to modify physical properties and enrich the phase diagram of RENiO 3 (RE = rare-earth element).
We investigate the band structure of BaBiO_{3}, an insulating parent compound of doped high-T_{c}... more We investigate the band structure of BaBiO_{3}, an insulating parent compound of doped high-T_{c} superconductors, using in situ angle-resolved photoemission spectroscopy on thin films. The data compare favorably overall with density functional theory calculations within the local density approximation, demonstrating that electron correlations are weak. The bands exhibit Brillouin zone folding consistent with known BiO_{6} breathing distortions. Though the distortions are often thought to coincide with Bi^{3+}/Bi^{5+} charge ordering, core level spectra show that bismuth is monovalent. We further demonstrate that the bands closest to the Fermi level are primarily oxygen derived, while the bismuth 6s states mostly contribute to dispersive bands at deeper binding energy. The results support a model of Bi-O charge transfer in which hole pairs are localized on combinations of the O 2p orbitals.
Engineering the electronic band structure of two-dimensional electron liquids (2DELs) confined at... more Engineering the electronic band structure of two-dimensional electron liquids (2DELs) confined at the surface or interface of transition metal oxides is key to unlocking their full potential. Here we describe a new approach to tailoring the electronic structure of an oxide surface 2DEL demonstrating the lateral modulation of electronic states with atomic scale precision on an unprecedented length scale comparable to the Fermi wavelength. To this end, we use pulsed laser deposition to grow anatase TiO2 films terminated by a (1 × 4) in-plane surface reconstruction. Employing photo-stimulated chemical surface doping we induce 2DELs with tunable carrier densities that are confined within a few TiO2 layers below the surface. Subsequent in-situ angle resolved photoemission experiments demonstrate that the (1 × 4) surface reconstruction provides a periodic lateral perturbation of the electron liquid. This causes strong backfolding of the electronic bands, opening of unidirectional gaps and...
Scanning tunneling spectroscopy has been a window into the (sub)atomic world for more than two de... more Scanning tunneling spectroscopy has been a window into the (sub)atomic world for more than two decades now, but the wealth of information that this technique offers seem yet to be exploited to it's maximum. In this thesis it is tried to optimize STM and, more precisely, STS techniques for the investigation of transition metal oxides, especially ones that exhibit interesting correlated structural and electronic phenomena like Pr$_{1-x}$Ca$_{x}$MnO$_{3}$ and LaAlO$_{3}$/SrTiO$_{3}$ system; the first is an insulator characterized by intriguing magnetic and charge-ordered phases, and the second is unique example of 2D electron gas, confined to the buried interface between two band-insulators. To this purpose, different numerical methods are proposed, which greatly help the handling of the data obtained in STS measurements. This approach allowed to determine important correlations between structural and electronic properties of the TMO surfaces/interfaces
Material properties can be controlled via strain, pressure, chemical composition, or dimensionali... more Material properties can be controlled via strain, pressure, chemical composition, or dimensionality. Nickelates are particularly susceptible due to their strong variations of the electronic and magnetic properties on such external stimuli. Here, we analyze the photoinduced dynamics in a single crystalline NdNiO 3 film upon excitation across the electronic gap. Using time-resolved reflectivity and resonant x-ray diffraction, we show that the pump pulse induces an insulator-to-metal transition, accompanied by the melting of the charge order. Finally, we compare our results with similar studies in manganites and show that the same model can be used to describe the dynamics in nickelates, hinting towards a unified description of these photoinduced electronic ordering phase transitions. V
We studied the structural, magnetic and transport properties of LaAlO 3 /EuTiO 3 /SrTiO 3 heteros... more We studied the structural, magnetic and transport properties of LaAlO 3 /EuTiO 3 /SrTiO 3 heterostructures grown by Pulsed Laser Deposition. The samples have been characterized in-situ by electron diffraction and scanning probe microscopy and ex-situ by transport measurements and x-ray absorption spectroscopy. LaAlO 3 /EuTiO 3 /SrTiO 3 films show a ferromagnetic transition at K related to the ordering of Eu 2+ spins, even in samples characterized by just two EuTiO 3 unit cells. A finite metallic conductivity is observed only in the case of samples composed by one or two Eu-TiO 3 unit cells and, simultaneously, by a LaAlO 3 thickness equal or above 4 unit cells. The role of ferromagnetic Eu-TiO 3 on the transport properties of -doped LaAlO 3 /EuTiO 3 /SrTiO 3 is critically discussed.
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms, 2005
The quantitative surface composition analysis with low energy ion scattering (LEIS), which is the... more The quantitative surface composition analysis with low energy ion scattering (LEIS), which is the experimental technique with the information depth that can be restricted to the first atomic layer, is often obstructed by the experimental problems. A novel approach is presented in order to calculate the influence of the optics of the energy analyzer and the geometric primary ion beam
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms, 2007
The inelastic energy losses of He + ions singly scattered from polycrystalline chromium (Cr) surf... more The inelastic energy losses of He + ions singly scattered from polycrystalline chromium (Cr) surface in the 0.7-2.0 keV energy range were experimentally investigated in this work. The energy spectra of ions scattered to 90°were measured. The peak corresponding to singly scattered ions is resolved into two Gaussians. The one at higher energies (elastic peak) corresponds to the He + ions that were not neutralized along the trajectory, while that at lower energy (inelastic peak) is attributed to the He + ions that were neutralized while approaching the surface and then reionized during the violent collision with Cr surface atoms. The difference between the positions of these Gaussians is a measure of the inelastic energy losses caused by the projectile reionization. These discrete inelastic losses are interpreted using the model of Tsuneyuki and Tsukada. It was observed that the energy difference between the elastic and inelastic peak increases with the incident ion energy. The elastic and inelastic peak intensities depend on the incoming angle and the character of this dependence abruptly changes for the incident ion energies in the range 1350-1400 eV, which cannot be explained by the existing theoretical models.
... Communication. Electrical and Optical Characteristics of Ta 2 O 5 Thin Films Deposited by Ele... more ... Communication. Electrical and Optical Characteristics of Ta 2 O 5 Thin Films Deposited by Electron-Beam Vapor Deposition. Zhana Todorova 1,* ,; Nikolay Donkov 1 ,; Zoran Ristić 2 ,; Nenad Bundaleski 2 ,; Suzana Petrović 2 ,; Mario Petkov 1. ... D. Spassov, Appl. Surf. Sci. ...
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007
Nichrome coatings have been deposited using the d.c. sputtering of the target (80% Ni-20% Cr wt.)... more Nichrome coatings have been deposited using the d.c. sputtering of the target (80% Ni-20% Cr wt.) by Ar + ions at a working pressure of 10 À1 Pa and at room temperature. After the air exposure of samples at room temperature, their phase composition and structure was studied by X-ray diffraction, while the surface elemental composition was determined by low energy ion scattering (LEIS) and Auger electron spectroscopy (AES). AES has been also used for the bulk composition analysis. There is a significant difference between the compositions of the surface and of the bulk. Surface segregation of chromium was observed using both LEIS and AES, and it was found that the chromium concentration increases with that of oxygen adsorbed at the surface during the air exposure. The nichrome surface composition is qualitatively the same as in the case of its exposure to O 2 at room temperature, but significantly different from that of the thermally annealed nichrome to 400°C in air.
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Papers by Zoran Ristic