Petr Malý - Academia.edu (original) (raw)
Papers by Petr Malý
Physical Review B
We report on the theoretical and experimental investigation of valley-selective optical Stark and... more We report on the theoretical and experimental investigation of valley-selective optical Stark and Bloch-Siegert shifts of exciton resonances in monolayers WSe2 and MoS2 induced by strong cirularly polarized nonresonant optical fields. We predict and observe transient shifts of both 1sA and 1sB exciton transitions in the linear interaction regime. The theoretical description is based on semiconductor Bloch equations. The solutions of the equations are obtained with a modified perturbation technique, which takes into account many-body Coulomb interaction effects. These solutions allow to explain the polarization dependence of the shifts and calculate their values analytically. We found experimentally the limits of the applicability of the theoretical description by observing the transient exciton spectra change due to many-body effects at high field amplitudes of the driving wave.
Beilstein journal of nanotechnology, 2018
Phosphorus- and boron-doped silicon nanocrystals (Si NCs) embedded in silicon oxide matrix can be... more Phosphorus- and boron-doped silicon nanocrystals (Si NCs) embedded in silicon oxide matrix can be fabricated by plasma-enhanced chemical vapour deposition (PECVD). Conventionally, SiH and NO are used as precursor gasses, which inevitably leads to the incorporation of ≈10 atom % nitrogen, rendering the matrix a silicon oxynitride. Alternatively, SiH and O can be used, which allows for completely N-free silicon oxide. In this work, we investigate the properties of B- and P-incorporating Si NCs embedded in pure silicon oxide compared to silicon oxynitride by atom probe tomography (APT), low-temperature photoluminescence (PL), transient transmission (TT), and current-voltage (-) measurements. The results clearly show that no free carriers, neither from P- nor from B-doping, exist in the Si NCs, although in some configurations charge carriers can be generated by electric field ionization. The absence of free carriers in Si NCs ≤5 nm in diameter despite the presence of P- or B-atoms has s...
Springer Proceedings in Physics, 2014
The spin transfer torque (STT) is a non-relativistic phenomenon where angular momentum of spin po... more The spin transfer torque (STT) is a non-relativistic phenomenon where angular momentum of spin polarized carriers electrically injected into a ferromagnet from an external polarizer is transferred to the magnetization [1]. In the absence of an external polarizer a distinct phenomenon can occur in which carriers in a magnet under applied electric field develop a non-equilibrium spin polarization due to the relativistic spin-orbit coupling, resulting in a current induced spin-orbit torque (SOT) [1]. We show, using the experimental data observed in the ferromagnetic semiconductor (Ga,Mn)As, that there exists optical counterparts of STT (OSTT) [2] and SOT (OSOT) [3]. In OSTT a circularly polarized femtosecond pump laser pulse acts as the external polarizer and it induces a coherent magnetization precession due to the angular momentum transfer, in a direct analogy to the current induced STT [2]. The absence of an external polarizer in OSOT corresponds to photo-carrier excitations which are independent of the polarization of the pump laser pulses and the phenomenon relies on spin-orbit coupling of non-equilibrium carriers, as in the case of the current induced SOT [3]. Our work demonstrates the possibility to study the spin-transfer and spin-orbit torques on the sub-picosecond timescales using the optical pump-and-probe experimental technique.
Journal of Applied Physics, 2014
Superlattices of Si-rich silicon nitride and Si 3 N 4 are prepared by plasma-enhanced chemical va... more Superlattices of Si-rich silicon nitride and Si 3 N 4 are prepared by plasma-enhanced chemical vapor deposition and, subsequently, annealed at 1150 C to form size-controlled Si nanocrystals (Si NCs) embedded in amorphous Si 3 N 4. Despite well defined structural properties, photoluminescence spectroscopy (PL) reveals inconsistencies with the typically applied model of quantum confined excitons in nitride-embedded Si NCs. Time-resolved PL measurements demonstrate 10 5 times faster time-constants than typical for the indirect band structure of Si NCs. Furthermore, a pure Si 3 N 4 reference sample exhibits a similar PL peak as the Si NC samples. The origin of this luminescence is discussed in detail on the basis of radiative defects and Si 3 N 4 band tail states in combination with optical absorption measurements. The apparent absence of PL from the Si NCs is explained conclusively using electron spin resonance data from the Si/Si 3 N 4 interface defect literature. In addition, the role of Si 3 N 4 valence band tail states as potential hole traps is discussed. Most strikingly, the PL peak blueshift with decreasing NC size, which is often observed in literature and typically attributed to quantum confinement (QC), is identified as optical artifact by transfer matrix method simulations of the PL spectra. Finally, criteria for a critical examination of a potential QC-related origin of the PL from Si 3 N 4-embedded Si NCs are suggested.
Physical Review B, 1996
We report on a detailed study of the dynamics of photoexcited carriers in red-emitting porous sil... more We report on a detailed study of the dynamics of photoexcited carriers in red-emitting porous silicon at room temperature after excitation by 532-nm picosecond laser pulses. Experimental techniques of time-resolved absorption ͑pump and probe͒ and photoluminescence are used to cover a very large time interval 10 Ϫ11-10 Ϫ4 s. The dynamics exhibits fast and slow components. The fast component ͑ϳ10 Ϫ10 s͒ is interpreted as a bimolecular recombination of free carriers in the core of nanometer-sized silicon nanocrystallites, and the slow component ͑ϳ10 Ϫ4 s͒ originates in the recombination of carriers rapidly trapped in the surface localized states. We propose a rate-equation model which enables us to describe well the complete photoexcited-carrier dynamics from picoseconds to hundreds of microseconds. Our results strongly support the key role of localized states on the surface of a Si network in the steady-state red photoluminescence of porous silicon. ͓S0163-1829͑96͒01935-2͔
Journal of Applied Physics, 2014
Hybrid diamond-organic interfaces are considered attractive for diverse applications ranging from... more Hybrid diamond-organic interfaces are considered attractive for diverse applications ranging from electronics and energy conversion to medicine. Here we use time-resolved and time-integrated photoluminescence spectroscopy in visible spectral range (380-700 nm) to study electronic processes in H-terminated nanocrystalline diamond films (NCD) with 150 nm thin, electrochemically deposited polypyrrole (PPy) layer. We observe changes in dynamics of NCD photoluminescence as well as in its time-integrated spectra after polymer deposition. The effect is reversible. We propose a model where the PPy layer on the NCD surface promotes spatial separation of photo-generated charge carriers both in non-diamond carbon phase and in bulk diamond. By comparing different NCD thicknesses we show that the effect goes as much as 200 nm deep inside the NCD film.
The Journal of Physical Chemistry A, 1998
The excited-state structure and energy-transfer dynamics, including their dependence on temperatu... more The excited-state structure and energy-transfer dynamics, including their dependence on temperature and redox conditions, were studied in chlorosomes of the green sulfur bacterium Chlorobium tepidum at low temperatures by two independent methods: spectral hole burning in absorption and fluorescence spectra and isotropic one-color pump-probe spectroscopy with ∼100 fs resolution. Hole-burning experiments show that the lowest excited state (LES) of BChl c aggregates is distributed within approximately 760-800 nm, while higher excitonic states of BChl c (with absorption maximum at 750 nm) possess the main oscillator strength. The excited-state lifetime determined from hole-burning experiments at anaerobic conditions was 5.75 ps and most likely reflects energy transfer between BChl c clusters. Isotropic one-color absorption difference signals were measured from 720 to 790 nm at temperatures ranging from 5 to 65 K, revealing BChl c photobleaching and stimulated emission kinetics with four major components, with lifetimes of 200-300 fs, 1.7-1.8 ps, 5.4-5.9 ps, and 30-40 ps at anaerobic conditions. The lifetimes are attributed to different relaxation processes of BChl c, taking into account their different spectral distributions as well as limitations arising from results of hole burning. Evidence for at least two spectral forms of BChl c in chlorosome is reported. There is a striking similarity between the spectrum and kinetics of the 5.4-5.9 ps component with those of the LES determined from hole burning. A pronounced change of isotropic decays was observed at around 50 K. The temperature dependence of the isotropic decays is correlated with temperature-dependent changes of BChl c fluorescence emission. Further, the temperature decrease leads to an increase in the relative amplitude of the 200-300 fs component. At aerobic conditions, both hole burning and pump-probe spectroscopy show that the lifetime of the LES shortens to ∼2.6 ps, as a result of excitation quenching by a mechanism presumably protecting the cells against superoxide-induced damage. This mechanism operates on at least two levels, the second one being characterized by a 14-16 ps lifetime.
Thin Solid Films, 1995
We report in detail on the picosecond dynamics of photoexcited charge carriers in size-controlled... more We report in detail on the picosecond dynamics of photoexcited charge carriers in size-controlled silicon nanocrystals in silicon nanocrystal/Si 3 N 4 superlattices. The samples were prepared using plasma enhanced chemical vapor deposition and subsequent thermally induced phase separation. The pump and probe transmission technique was used to monitor directly the initial (picosecond) carrier dynamics. The transient transmission signal (decay time about 2 ps) was found to be independent of the nanocrystal size, pump pulse intensity and wavelength from the interval 400 to 700 nm. The signal is attributed to the dynamics of photoexcited carriers captured on the K 0 centers in Si 3 N 4. V
Solid State Communications, 1994
![Research paper thumbnail of Publisher's Note: “High precision magnetic linear dichroism measurements in (Ga,Mn)As” [Rev. Sci. Instrum. 83, 123108 (2012)]](https://attachments.academia-assets.com/103492073/thumbnails/1.jpg)
](Review of Scientific Instruments, 2013
Review of Scientific Instruments, 2012
Investigation of magnetic materials using the first-order magneto-optical Kerr effects (MOKE) is ... more Investigation of magnetic materials using the first-order magneto-optical Kerr effects (MOKE) is well established and is frequently used in the literature. On the other hand, the utilization of the second-order (or quadratic) magneto-optical (MO) effects for the material research is rather rare. This is due to the small magnitude of quadratic MO signals and the fact that the signals are even in magnetization (i.e., they do not change a sign when the magnetization orientation is flipped), which makes it difficult to separate second-order MO signals from various experimental artifacts. In 2005 a giant quadratic MO effect-magnetic linear dichroism (MLD)-was observed in the ferromagnetic semiconductor (Ga,Mn)As. This discovery not only provided a new experimental tool for the investigation of in-plane magnetization dynamics in (Ga,Mn)As using light at normal incidence, but it also motivated the development of experimental techniques for the measurement of second-order MO effects in general. In this paper we compare four different experimental techniques that can be used to measure MLD and to separate it from experimental artifacts. We show that the most reliable results are obtained when the harmonic dependence of MLD on a mutual orientation of magnetization and light polarization plane is used together with the in-situ rotation of the sample followed by the magnetic field-induced rotation of magnetization. Using this technique we measure the MLD spectra of (Ga,Mn)As in a broad spectral range from 0.1 eV to 2.7 eV and we observe that MLD has a comparable magnitude as polar MOKE signals in this material.
physica status solidi c, 2011
We report on ultrafast photoluminescence (PL) spectroscopy of blue and red-emitting silicon nanos... more We report on ultrafast photoluminescence (PL) spectroscopy of blue and red-emitting silicon nanostructures. We prepared samples of porous Si with different dominating PL bands in time-integrated PL spectrum. These samples show also striking differences in ultrafast PL dynamics. For the red-emitting samples we observe rapid PL onset followed by a two-exponential decay, which is spectrally dependent. For the blue-emitting porous Si the PL builds up several picoseconds and decays mono-exponentially with spectrally independent PL rise and decay times. Our results indicate that a dominant part of the blue and red emission comes from two distinct species with different energy states structures. This is furthermore supported by two-photon absorption induced PL mea-surements. The two-photon and one-photon absorption induced PL spectra, which are identical for the red-emitting samples, differ substantially for the blue-emitting ones. However, polarization properties of PL suggest that the blue PL band originates from several overlapping PL bands with sample-dependent importance. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi c, 2006
Abstract We report on the ultrafast photoluminescence dynamics in silicon nanocrystals measured b... more Abstract We report on the ultrafast photoluminescence dynamics in silicon nanocrystals measured by femtosecond up-conversion technique. The samples were prepared by embedding porous silicon grains in a sol-gel derived SiO 2 matrix. Efficient initial relaxation of the excess energy of photoexcited carriers with the effective rate≥ 4 eV/ps was observed. The ultrafast photoluminescence decay (about 400 fs) was interpreted in terms of quenching the interior exciton radiative recombination by fast carrier trapping on the nanocrystal ...
physica status solidi (b), 2001
ABSTRACT The dynamics of absorption bleaching in CdS nanocrystalline thin films were studied in t... more ABSTRACT The dynamics of absorption bleaching in CdS nanocrystalline thin films were studied in the temperature interval 10–300 K and three distinct decay time constants (sub-ps, ps, and ns) were identified. We interpreted the dynamics in terms of three groups of nanocrystals with specific defects and showed that two of them are related. A close link between the temperature behaviour of the photoluminescence efficiency and that of the relative amplitude of the nanosecond component was observed and an explanation based on a microscopical model was proposed. The optical nonlinearities were studied by self-diffraction technique. A dephasing time constant shorter than 80 fs and a value of |γ3| ≈ 6 × 10—16 m2 V—2 were obtained.
![Research paper thumbnail of Erratum to “Spectral and dynamical study of nonlinear luminescence from silicon nanocrystals excited by ultrashort pulses” [Physica E, 41(6) (2009) 959–962]](https://attachments.academia-assets.com/103492053/thumbnails/1.jpg)
](Physica E: Low-dimensional Systems and Nanostructures, 2009
Journal of Non-Crystalline Solids, 1998
Samples of a-Si:H having a wide gap G 2.1 eV were prepared using routine rf glow discharge decomp... more Samples of a-Si:H having a wide gap G 2.1 eV were prepared using routine rf glow discharge decomposition of silane Ž. SiH strongly diluted with He. Also, microwave electron-cyclotron-resonance plasma-enhanced chemical-vapour-deposi-4 tion was used to prepare wide-gap a-Si:H via decomposition of He diluted SiH. The wide-gap a-Si:H samples, containing 4 above 30 at.% of hydrogen, exhibit visible photoluminescence at room temperature. From the temperature dependence of photoluminescence intensity and from the observed shift of the maximum with temperature we deduce that the customary model of radiative recombination of carriers localised in tail states is not directly applicable to the case of wide-gap a-Si:H. Ž. Instead, we propose that the photoluminescence arises in parallel from tail states and from isolated extrinsic centres. Electroluminescence results obtained on a p-in structure with wide-gap a-Si:H are reported.
Journal of Nanoscience and Nanotechnology, 2012
Journal of Nanoscience and Nanotechnology, 2010
ABSTRACT Multicolour photochromism of Ag-TiO2 nanocomposite material was found several years ago ... more ABSTRACT Multicolour photochromism of Ag-TiO2 nanocomposite material was found several years ago but its microscopic origin is still ambiguous. We study the initial stages of the effect of light exposure on extinction spectrum of this material prepared by photocatalytic technique. We propose a simple model to analyse the experimental data that suggests that the extinction changes are due to a pure shift of the plasmon resonance of silver nanoparticles after light exposure. The homogeneous spectral widths (100-200 meV) of plasmon resonance of individual classes of nanoparticles were found to increase with the resonance frequency.
Journal of Luminescence, 1997
... JOURNAL OF LUMINESCENCE ELSEVIER Journal of Luminescence 7274 (1997) 375376 Effect of photoda... more ... JOURNAL OF LUMINESCENCE ELSEVIER Journal of Luminescence 7274 (1997) 375376 Effect of photodarkening on picosecond photoluminescence m CdSSedoped glasses P. Nemec, F. Trojanek, S. Santhi, P. Maly ... Excitation by picosecond 532 nm (1) or 626 nm (2) pulse. ...
Physical Review B
We report on the theoretical and experimental investigation of valley-selective optical Stark and... more We report on the theoretical and experimental investigation of valley-selective optical Stark and Bloch-Siegert shifts of exciton resonances in monolayers WSe2 and MoS2 induced by strong cirularly polarized nonresonant optical fields. We predict and observe transient shifts of both 1sA and 1sB exciton transitions in the linear interaction regime. The theoretical description is based on semiconductor Bloch equations. The solutions of the equations are obtained with a modified perturbation technique, which takes into account many-body Coulomb interaction effects. These solutions allow to explain the polarization dependence of the shifts and calculate their values analytically. We found experimentally the limits of the applicability of the theoretical description by observing the transient exciton spectra change due to many-body effects at high field amplitudes of the driving wave.
Beilstein journal of nanotechnology, 2018
Phosphorus- and boron-doped silicon nanocrystals (Si NCs) embedded in silicon oxide matrix can be... more Phosphorus- and boron-doped silicon nanocrystals (Si NCs) embedded in silicon oxide matrix can be fabricated by plasma-enhanced chemical vapour deposition (PECVD). Conventionally, SiH and NO are used as precursor gasses, which inevitably leads to the incorporation of ≈10 atom % nitrogen, rendering the matrix a silicon oxynitride. Alternatively, SiH and O can be used, which allows for completely N-free silicon oxide. In this work, we investigate the properties of B- and P-incorporating Si NCs embedded in pure silicon oxide compared to silicon oxynitride by atom probe tomography (APT), low-temperature photoluminescence (PL), transient transmission (TT), and current-voltage (-) measurements. The results clearly show that no free carriers, neither from P- nor from B-doping, exist in the Si NCs, although in some configurations charge carriers can be generated by electric field ionization. The absence of free carriers in Si NCs ≤5 nm in diameter despite the presence of P- or B-atoms has s...
Springer Proceedings in Physics, 2014
The spin transfer torque (STT) is a non-relativistic phenomenon where angular momentum of spin po... more The spin transfer torque (STT) is a non-relativistic phenomenon where angular momentum of spin polarized carriers electrically injected into a ferromagnet from an external polarizer is transferred to the magnetization [1]. In the absence of an external polarizer a distinct phenomenon can occur in which carriers in a magnet under applied electric field develop a non-equilibrium spin polarization due to the relativistic spin-orbit coupling, resulting in a current induced spin-orbit torque (SOT) [1]. We show, using the experimental data observed in the ferromagnetic semiconductor (Ga,Mn)As, that there exists optical counterparts of STT (OSTT) [2] and SOT (OSOT) [3]. In OSTT a circularly polarized femtosecond pump laser pulse acts as the external polarizer and it induces a coherent magnetization precession due to the angular momentum transfer, in a direct analogy to the current induced STT [2]. The absence of an external polarizer in OSOT corresponds to photo-carrier excitations which are independent of the polarization of the pump laser pulses and the phenomenon relies on spin-orbit coupling of non-equilibrium carriers, as in the case of the current induced SOT [3]. Our work demonstrates the possibility to study the spin-transfer and spin-orbit torques on the sub-picosecond timescales using the optical pump-and-probe experimental technique.
Journal of Applied Physics, 2014
Superlattices of Si-rich silicon nitride and Si 3 N 4 are prepared by plasma-enhanced chemical va... more Superlattices of Si-rich silicon nitride and Si 3 N 4 are prepared by plasma-enhanced chemical vapor deposition and, subsequently, annealed at 1150 C to form size-controlled Si nanocrystals (Si NCs) embedded in amorphous Si 3 N 4. Despite well defined structural properties, photoluminescence spectroscopy (PL) reveals inconsistencies with the typically applied model of quantum confined excitons in nitride-embedded Si NCs. Time-resolved PL measurements demonstrate 10 5 times faster time-constants than typical for the indirect band structure of Si NCs. Furthermore, a pure Si 3 N 4 reference sample exhibits a similar PL peak as the Si NC samples. The origin of this luminescence is discussed in detail on the basis of radiative defects and Si 3 N 4 band tail states in combination with optical absorption measurements. The apparent absence of PL from the Si NCs is explained conclusively using electron spin resonance data from the Si/Si 3 N 4 interface defect literature. In addition, the role of Si 3 N 4 valence band tail states as potential hole traps is discussed. Most strikingly, the PL peak blueshift with decreasing NC size, which is often observed in literature and typically attributed to quantum confinement (QC), is identified as optical artifact by transfer matrix method simulations of the PL spectra. Finally, criteria for a critical examination of a potential QC-related origin of the PL from Si 3 N 4-embedded Si NCs are suggested.
Physical Review B, 1996
We report on a detailed study of the dynamics of photoexcited carriers in red-emitting porous sil... more We report on a detailed study of the dynamics of photoexcited carriers in red-emitting porous silicon at room temperature after excitation by 532-nm picosecond laser pulses. Experimental techniques of time-resolved absorption ͑pump and probe͒ and photoluminescence are used to cover a very large time interval 10 Ϫ11-10 Ϫ4 s. The dynamics exhibits fast and slow components. The fast component ͑ϳ10 Ϫ10 s͒ is interpreted as a bimolecular recombination of free carriers in the core of nanometer-sized silicon nanocrystallites, and the slow component ͑ϳ10 Ϫ4 s͒ originates in the recombination of carriers rapidly trapped in the surface localized states. We propose a rate-equation model which enables us to describe well the complete photoexcited-carrier dynamics from picoseconds to hundreds of microseconds. Our results strongly support the key role of localized states on the surface of a Si network in the steady-state red photoluminescence of porous silicon. ͓S0163-1829͑96͒01935-2͔
Journal of Applied Physics, 2014
Hybrid diamond-organic interfaces are considered attractive for diverse applications ranging from... more Hybrid diamond-organic interfaces are considered attractive for diverse applications ranging from electronics and energy conversion to medicine. Here we use time-resolved and time-integrated photoluminescence spectroscopy in visible spectral range (380-700 nm) to study electronic processes in H-terminated nanocrystalline diamond films (NCD) with 150 nm thin, electrochemically deposited polypyrrole (PPy) layer. We observe changes in dynamics of NCD photoluminescence as well as in its time-integrated spectra after polymer deposition. The effect is reversible. We propose a model where the PPy layer on the NCD surface promotes spatial separation of photo-generated charge carriers both in non-diamond carbon phase and in bulk diamond. By comparing different NCD thicknesses we show that the effect goes as much as 200 nm deep inside the NCD film.
The Journal of Physical Chemistry A, 1998
The excited-state structure and energy-transfer dynamics, including their dependence on temperatu... more The excited-state structure and energy-transfer dynamics, including their dependence on temperature and redox conditions, were studied in chlorosomes of the green sulfur bacterium Chlorobium tepidum at low temperatures by two independent methods: spectral hole burning in absorption and fluorescence spectra and isotropic one-color pump-probe spectroscopy with ∼100 fs resolution. Hole-burning experiments show that the lowest excited state (LES) of BChl c aggregates is distributed within approximately 760-800 nm, while higher excitonic states of BChl c (with absorption maximum at 750 nm) possess the main oscillator strength. The excited-state lifetime determined from hole-burning experiments at anaerobic conditions was 5.75 ps and most likely reflects energy transfer between BChl c clusters. Isotropic one-color absorption difference signals were measured from 720 to 790 nm at temperatures ranging from 5 to 65 K, revealing BChl c photobleaching and stimulated emission kinetics with four major components, with lifetimes of 200-300 fs, 1.7-1.8 ps, 5.4-5.9 ps, and 30-40 ps at anaerobic conditions. The lifetimes are attributed to different relaxation processes of BChl c, taking into account their different spectral distributions as well as limitations arising from results of hole burning. Evidence for at least two spectral forms of BChl c in chlorosome is reported. There is a striking similarity between the spectrum and kinetics of the 5.4-5.9 ps component with those of the LES determined from hole burning. A pronounced change of isotropic decays was observed at around 50 K. The temperature dependence of the isotropic decays is correlated with temperature-dependent changes of BChl c fluorescence emission. Further, the temperature decrease leads to an increase in the relative amplitude of the 200-300 fs component. At aerobic conditions, both hole burning and pump-probe spectroscopy show that the lifetime of the LES shortens to ∼2.6 ps, as a result of excitation quenching by a mechanism presumably protecting the cells against superoxide-induced damage. This mechanism operates on at least two levels, the second one being characterized by a 14-16 ps lifetime.
Thin Solid Films, 1995
We report in detail on the picosecond dynamics of photoexcited charge carriers in size-controlled... more We report in detail on the picosecond dynamics of photoexcited charge carriers in size-controlled silicon nanocrystals in silicon nanocrystal/Si 3 N 4 superlattices. The samples were prepared using plasma enhanced chemical vapor deposition and subsequent thermally induced phase separation. The pump and probe transmission technique was used to monitor directly the initial (picosecond) carrier dynamics. The transient transmission signal (decay time about 2 ps) was found to be independent of the nanocrystal size, pump pulse intensity and wavelength from the interval 400 to 700 nm. The signal is attributed to the dynamics of photoexcited carriers captured on the K 0 centers in Si 3 N 4. V
Solid State Communications, 1994
Review of Scientific Instruments, 2013
Review of Scientific Instruments, 2012
Investigation of magnetic materials using the first-order magneto-optical Kerr effects (MOKE) is ... more Investigation of magnetic materials using the first-order magneto-optical Kerr effects (MOKE) is well established and is frequently used in the literature. On the other hand, the utilization of the second-order (or quadratic) magneto-optical (MO) effects for the material research is rather rare. This is due to the small magnitude of quadratic MO signals and the fact that the signals are even in magnetization (i.e., they do not change a sign when the magnetization orientation is flipped), which makes it difficult to separate second-order MO signals from various experimental artifacts. In 2005 a giant quadratic MO effect-magnetic linear dichroism (MLD)-was observed in the ferromagnetic semiconductor (Ga,Mn)As. This discovery not only provided a new experimental tool for the investigation of in-plane magnetization dynamics in (Ga,Mn)As using light at normal incidence, but it also motivated the development of experimental techniques for the measurement of second-order MO effects in general. In this paper we compare four different experimental techniques that can be used to measure MLD and to separate it from experimental artifacts. We show that the most reliable results are obtained when the harmonic dependence of MLD on a mutual orientation of magnetization and light polarization plane is used together with the in-situ rotation of the sample followed by the magnetic field-induced rotation of magnetization. Using this technique we measure the MLD spectra of (Ga,Mn)As in a broad spectral range from 0.1 eV to 2.7 eV and we observe that MLD has a comparable magnitude as polar MOKE signals in this material.
physica status solidi c, 2011
We report on ultrafast photoluminescence (PL) spectroscopy of blue and red-emitting silicon nanos... more We report on ultrafast photoluminescence (PL) spectroscopy of blue and red-emitting silicon nanostructures. We prepared samples of porous Si with different dominating PL bands in time-integrated PL spectrum. These samples show also striking differences in ultrafast PL dynamics. For the red-emitting samples we observe rapid PL onset followed by a two-exponential decay, which is spectrally dependent. For the blue-emitting porous Si the PL builds up several picoseconds and decays mono-exponentially with spectrally independent PL rise and decay times. Our results indicate that a dominant part of the blue and red emission comes from two distinct species with different energy states structures. This is furthermore supported by two-photon absorption induced PL mea-surements. The two-photon and one-photon absorption induced PL spectra, which are identical for the red-emitting samples, differ substantially for the blue-emitting ones. However, polarization properties of PL suggest that the blue PL band originates from several overlapping PL bands with sample-dependent importance. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi c, 2006
Abstract We report on the ultrafast photoluminescence dynamics in silicon nanocrystals measured b... more Abstract We report on the ultrafast photoluminescence dynamics in silicon nanocrystals measured by femtosecond up-conversion technique. The samples were prepared by embedding porous silicon grains in a sol-gel derived SiO 2 matrix. Efficient initial relaxation of the excess energy of photoexcited carriers with the effective rate≥ 4 eV/ps was observed. The ultrafast photoluminescence decay (about 400 fs) was interpreted in terms of quenching the interior exciton radiative recombination by fast carrier trapping on the nanocrystal ...
physica status solidi (b), 2001
ABSTRACT The dynamics of absorption bleaching in CdS nanocrystalline thin films were studied in t... more ABSTRACT The dynamics of absorption bleaching in CdS nanocrystalline thin films were studied in the temperature interval 10–300 K and three distinct decay time constants (sub-ps, ps, and ns) were identified. We interpreted the dynamics in terms of three groups of nanocrystals with specific defects and showed that two of them are related. A close link between the temperature behaviour of the photoluminescence efficiency and that of the relative amplitude of the nanosecond component was observed and an explanation based on a microscopical model was proposed. The optical nonlinearities were studied by self-diffraction technique. A dephasing time constant shorter than 80 fs and a value of |γ3| ≈ 6 × 10—16 m2 V—2 were obtained.
Physica E: Low-dimensional Systems and Nanostructures, 2009
Journal of Non-Crystalline Solids, 1998
Samples of a-Si:H having a wide gap G 2.1 eV were prepared using routine rf glow discharge decomp... more Samples of a-Si:H having a wide gap G 2.1 eV were prepared using routine rf glow discharge decomposition of silane Ž. SiH strongly diluted with He. Also, microwave electron-cyclotron-resonance plasma-enhanced chemical-vapour-deposi-4 tion was used to prepare wide-gap a-Si:H via decomposition of He diluted SiH. The wide-gap a-Si:H samples, containing 4 above 30 at.% of hydrogen, exhibit visible photoluminescence at room temperature. From the temperature dependence of photoluminescence intensity and from the observed shift of the maximum with temperature we deduce that the customary model of radiative recombination of carriers localised in tail states is not directly applicable to the case of wide-gap a-Si:H. Ž. Instead, we propose that the photoluminescence arises in parallel from tail states and from isolated extrinsic centres. Electroluminescence results obtained on a p-in structure with wide-gap a-Si:H are reported.
Journal of Nanoscience and Nanotechnology, 2012
Journal of Nanoscience and Nanotechnology, 2010
ABSTRACT Multicolour photochromism of Ag-TiO2 nanocomposite material was found several years ago ... more ABSTRACT Multicolour photochromism of Ag-TiO2 nanocomposite material was found several years ago but its microscopic origin is still ambiguous. We study the initial stages of the effect of light exposure on extinction spectrum of this material prepared by photocatalytic technique. We propose a simple model to analyse the experimental data that suggests that the extinction changes are due to a pure shift of the plasmon resonance of silver nanoparticles after light exposure. The homogeneous spectral widths (100-200 meV) of plasmon resonance of individual classes of nanoparticles were found to increase with the resonance frequency.
Journal of Luminescence, 1997
... JOURNAL OF LUMINESCENCE ELSEVIER Journal of Luminescence 7274 (1997) 375376 Effect of photoda... more ... JOURNAL OF LUMINESCENCE ELSEVIER Journal of Luminescence 7274 (1997) 375376 Effect of photodarkening on picosecond photoluminescence m CdSSedoped glasses P. Nemec, F. Trojanek, S. Santhi, P. Maly ... Excitation by picosecond 532 nm (1) or 626 nm (2) pulse. ...