Krzysztof Fronc - Academia.edu (original) (raw)

Papers by Krzysztof Fronc

Low Temperature Physics - LOW TEMP PHYS, 1997

A comparison of field dependences of the meridional Kerr effect and magnetization leads to the co... more A comparison of field dependences of the meridional Kerr effect and magnetization leads to the conclusion that a noncollinear inhomogeneous magnetic state is formed in the surface layer of gadolinium in multilayered Gd/Fe films in a magnetic field. Experimental results are described by using a theoretical model predicting the formation of a noncollinear spin configuration in the surface Gd layer as a result of a spin-reorientation phase transition induced by the magnetic field.

Opto-Electronics Review, 2009

ABSTRACT Optical properties of an external cavity laser with a semiconductor optical amplifier an... more ABSTRACT Optical properties of an external cavity laser with a semiconductor optical amplifier and two diffraction gratings are described. The laser has been pigtailed and its emission showed two peaks in the output spectrum. The wavelength of the peaks, and in particular the spectral spacing between them, could be controlled by adjusting the reflecting elements in the system. The proposed double-frequency laser may be adopted as a signal source in terahertz generators.

Low Temperature Physics, 2012

ABSTRACT The magnetoelastic constants of epitaxial iron films prepared by dc magnetron sputtering... more ABSTRACT The magnetoelastic constants of epitaxial iron films prepared by dc magnetron sputtering on single crystal GaAs (001) substrate in argon atmosphere and covered with a protective Si layer have been investigated in the temperature range 10–300 K by means of the strain modulated ferromagnetic resonance. It has been shown that the magnetoelastic constants strongly depend on the thickness of the film. The surface components of the magnetoelastic constants have been determined and analyzed within the Néel and dipolar models. The proposed analysis of experimental data gives chance for deeper insight into mechanisms responsible for magnetostriction of iron thin films.

In this paper the physical properties of two types of Co-doped ZnO nanostructures: tetrapods and ... more In this paper the physical properties of two types of Co-doped ZnO nanostructures: tetrapods and nanofibers grown by a rapid thermal evaporation process and prepared by the electrospinning technique, respectively, were investigated and analyzed. Surface morphology of the samples was examined using scanning electron microscopy. X-ray diffraction measurements showed hexagonal wurtzite crystal structure of both types of investigated nanostructures. Both X-ray diffraction and Raman scattering data confirmed high phase purity of the samples. The magnetic properties studied with the use of the SQUID magnetometer confirmed a presence of ferromagnetic order in analyzed nanostructures. The observed photoluminescence spectra exhibited two groups of lines. The first one, in the ultraviolet spectral range, is due to the optical transitions close to ZnO band gap, the second one in the red region is most probably related to the Co 2+ d–d internal transitions. The influence of native defects on th...

Low-Dimensional Materials and Devices, 2015

ABSTRACT Semiconductor surface plays an important role in the technology of semiconductor devices... more ABSTRACT Semiconductor surface plays an important role in the technology of semiconductor devices. In the present work we report results of our deep-level transient spectroscopy (DLTS) investigations of surface defect states in nitrogen doped p-type CdTe layers grown by the molecular-beam epitaxy technique. We observed a deep-level trap associated with surface states, with the activation energy for hole emission of 0.33 eV. DLTS peak position in the spectra for this trap, and its ionization energy, strongly depend on the electric field. Our measurements allow to determine a mechanism responsible for the enhancement of hole emission rate from the traps as the phonon-assisted tunnel effect. Density of surface defect states significantly decreased as a result of passivation in ammonium sulfide. Capacitance-voltage measurements confirmed the results obtained by the DLTS technique.

Acta Physica Polonica A, 2007

We report on the photoluminescence studies of ZnO and ZnCdO nanowires grown on SiO 2 /Si substrat... more We report on the photoluminescence studies of ZnO and ZnCdO nanowires grown on SiO 2 /Si substrates by low-pressure vapor phase synthesis. X-ray diffraction and transmission electron microscopy measurements show that the crystallographic structure of these ZnO and ZnCdO nanowires is of wurtzite-type with a high crystal perfection. Surface morphology of samples was determined by scanning electron microscopy and atomic force microscopy. The photoluminescence spectra of as-grown nanowires, nanowires extracted from the substrate and deposited onto Si wafer, and nanowires dispersed in ethanol by sonication were investigated at room temperature and compared to each other. The temperature dependence of the near band-gap photoluminescence emitted by the as-grown nanowires was also measured and analyzed.

Acta Physica Polonica A, 2007

Scanning tunneling spectroscopy was used to check the tunneling I−V characteristics of junctions ... more Scanning tunneling spectroscopy was used to check the tunneling I−V characteristics of junctions formed by n-ZnO nanowires deposited on Si substrates with n-and p-type electrical conductivity (i.e. n-ZnO nanowire/ n-Si and n-ZnO nanowire/p-Si junctions, respectively). Simultaneously, several phenomena which influence the measured I−V spectra were studied by atomic force microscopy. These influencing factors are: the deposition density of the nanowires, the possibility of surface modification by tip movement (difference in attraction forces between nanowires and the p-Si and n-Si) and the aging of the surface.

Materials Science Forum, 2001

ABSTRACT The in-plane magnetic anisotropy and interlayer coupling have been investigated in the F... more ABSTRACT The in-plane magnetic anisotropy and interlayer coupling have been investigated in the Fe/Si/Fe trilayers grown by de magnetron sputtering deposition on GaAs (001) substrates. The samples have been covered with thin Si cap layer. The measurements have been performed by means of ferromagnetic resonance (FMR) technique as a function of the orientation of dc magnetic field in plane of the film and at liquid helium and room temperatures. From these dependencies the in-plane cubic anisotropy constants as well as interlayer coupling constants are determined. It is shown that the uniaxial in-plane anisotropy has mainly magnetoelastic origin and directions of easy axes are different in both layers. Moreover, the anisotropy constants in both layers have different temperature dependencies related only to the differences in thermal expansion coefficients between Fe, Si and GaAs.

Physical Review B, 2015

We present photoluminescence studies of CdTe and Cd1−xMnxTe quantum dots grown in two adjacent la... more We present photoluminescence studies of CdTe and Cd1−xMnxTe quantum dots grown in two adjacent layers. We show that when the dots are 8 nm apart, their magnetooptical properties -Zeeman shifts and transition linewidths -are analogous to those of individual CdTe or Cd1−xMnxTe dots. When the dots are grown closer, at a distance of 4 nm, it becomes possible to tune the electron states to resonance and obtain a formation of a molecular state hybridized over the two dots. As a result of the resonant enhancement of the electron-Mn ion exchange interaction, spectroscopic signatures specific to spin-dependent inter-dot coupling appear. Namely, an anomalous increase of the Zeeman shift and a resonant increase in the transition linewidth are observed. A simple model calculation allows us to quantitatively reproduce the experimental results.

Phys. Chem. Chem. Phys., 2015

This study describes a new method of passivating ZnO nanofiber-based devices with a ZnS layer. Th... more This study describes a new method of passivating ZnO nanofiber-based devices with a ZnS layer. This one-step process was carried out in H2S gas at room temperature, and resulted in the formation of core/shell ZnO/ZnS nanofibers. This study presents the structural, optical and electrical properties of ZnO/ZnS nanofibers formed by a 2 nm ZnS sphalerite crystal shell covering a 5 nm ZnO wurtzite crystal core. The passivation process prevented free carriers from capture by oxygen molecules and significantly reduced the impact of O2 on nanostructure conductivity. The conductivity of the nanofibers was increased by three orders of magnitude after the sulfidation, the photoresponse time was reduced from 1500 s to 30 s, and the cathodoluminescence intensity increased with the sulfidation time thanks to the removal of ZnO surface defects by passivation. The ZnO/ZnS nanofibers were stable in water for over 30 days, and in phosphate buffers of acidic, neutral and alkaline pH for over 3 days. The by-products of the passivation process did not affect the conductivity of the devices. The potential of ZnO/ZnS nanofibers for protein biosensing is demonstrated using biotin and streptavidin as a model system. The presented ZnS shell preparation method can facilitate the construction of future sensors and protects the ZnO surface from dissolving in a biological environment.

Biosensors and Bioelectronics, 2015

A novel recognition unit of chemical sensor for selective determination of the inosine, renal dis... more A novel recognition unit of chemical sensor for selective determination of the inosine, renal disfunction biomarker, was devised and prepared. For that purpose, inosine-templated molecularly imprinted polymer (MIP) film was deposited on an extended-gate field-effect transistor (EG-FET) signal transducing unit. The MIP film was prepared by electrochemical polymerization of bis(bithiophene) derivatives bearing cytosine and boronic acid substituents, in the presence of the inosine template and a thiophene cross-linker. After MIP film deposition, the template was removed, and was confirmed by UV-visible spectroscopy. Subsequently, the film composition was characterized by spectroscopic techniques, and its morphology and thickness were determined by AFM. The finally MIP film-coated extended-gate fieldeffect transistor (EG-FET) was used for signal transduction. This combination is not widely studied in the literature, despite the fact that it allows for facile integration of electrodeposited MIP film with FET transducer.

Journal of Applied Physics, 2015

We demonstrate an efficient method to engineer the quantum confinement in a system of two quantum... more We demonstrate an efficient method to engineer the quantum confinement in a system of two quantum dots grown in a vertical stack. We achieve this by using materials with a different lattice constant for the growth of the outer and inner barriers. We monitor the resulting dot morphology with transmission electron microscopy studies and correlate the results with ensemble quantum dot photoluminescence. Furthermore, we embed the double quantum dots into diode structures and study photoluminescence as a function of bias voltage. We show that in properly engineered structures, it is possible to achieve a resonance of the hole states by tuning the energy levels with electric field. At the resonance, we observe signatures of a formation of a molecular state, hybridized over the two dots. arXiv:1502.03592v1 [cond-mat.mes-hall]

In this study, a ZnO nanofiber biosensor design is reported. ZnO nanofibers were obtained by elec... more In this study, a ZnO nanofiber biosensor design is reported. ZnO nanofibers were obtained by electrospinning process followed by calcination. As a novel fabrication method, amorphous thin film of AlN x deposited by reactive magnetron sputtering, was proposed as a protective and stabilizing layer in subsequent technological processes. This allowed to use photolithography techniques for fabrication of the electrospun ZnO nanofibers sensor structures which is first time reported. The wet etching of AlN protective layer, Ti/Au ohmic contacts to ZnO fibers and polyimide passivating film have completed the design. Topography of the sensor structure was investigated using AFM and SEM. I-V measurements made for electrical characterization of ohmic contacts and nanofibers in different solutions environments including biological agent are reported.

In the presented work, ZnO nanofiber sensor structures designed and fabricated using a standard m... more In the presented work, ZnO nanofiber sensor structures designed and fabricated using a standard microelectronic device technology were studied. The structures in the configuration of a resistor with chemically active ZnO multiple nanofibers deposited by electrospinning method were prepared. Investigation of inclusion in the process reactive-ly sputtered AlN insulating film to improve the robustness of the nanofibres on the substrate was undertaken. Selective wet chemical etching of AlN film using photoresist developers and a photoresist mask to define the sensor active area was studied. The Ti/Au ohmic contacts were fabricated using the lift-off photolithography process. To-pography of the sensor structure details was investigated using AFM. Electrical charac-terization by means of I-V measurements was made. Sensitivity to the physiologically relevant concentration of Bovine Serum Albumin in water solution was shown.

Tenth International School on Quantum Electronics: Laser Physics and Applications, 1999

ABSTRACT We present an experimental study of fine structure (fs)- mixing in the 52D state of Rb, ... more ABSTRACT We present an experimental study of fine structure (fs)- mixing in the 52D state of Rb, and details of construction and performance of an external cavity cw diode laser, developed to provide a light source at 778 nm for two-photon excitation of Rb(52D). Cross section for the fs-mixing Rb(52D5/2) yields Rb(52D3/2) in collisions with the ground state Rb(52S1/2) atoms was found to be 5.8 +/- 1.9 (DOT) 10-14 cm2.

We show that by means of an electric field we can tune the energy levels in vertical quantum dot ... more We show that by means of an electric field we can tune the energy levels in vertical quantum dot pairs and study transitions related to recombination of direct and indirect excitons. With decreasing the reverse bias, we observe both the blue-and red-shifted indirect exciton transitions. Based on the band profile of our device, we conclude that the former corresponds to the recombination of the electron and hole localized in the top and the bottom dot, respectively and the latter is related to the recombination of the electron and hole localized in the bottom and the top dot, respectively.

The Ninth International Conference on Advanced Semiconductor Devices and Mircosystems, 2012

In the present study determination of the impact of various gas atmospheres on the surface potent... more In the present study determination of the impact of various gas atmospheres on the surface potential distribution of the electrospun ZnO nanofiber was carried out. Analysis of surface properties was performed using a Scanning Surface Potential Microscopy (SSPM). Obtained results proved homogeneity of the electrical and structural properties along the fiber. The effect of majority carriers depletion in metal oxides in oxidizing gas atmospheres was confirmed by changing the surface potential distribution of the fibers. Measurements performed in dry and humid atmosphere of nitrogen and air could clarify the role of water vapor on the properties of ZnO fibers.

Materials Science Forum, 2001

Low Temperature Physics - LOW TEMP PHYS, 1997

A comparison of field dependences of the meridional Kerr effect and magnetization leads to the co... more A comparison of field dependences of the meridional Kerr effect and magnetization leads to the conclusion that a noncollinear inhomogeneous magnetic state is formed in the surface layer of gadolinium in multilayered Gd/Fe films in a magnetic field. Experimental results are described by using a theoretical model predicting the formation of a noncollinear spin configuration in the surface Gd layer as a result of a spin-reorientation phase transition induced by the magnetic field.

Opto-Electronics Review, 2009

ABSTRACT Optical properties of an external cavity laser with a semiconductor optical amplifier an... more ABSTRACT Optical properties of an external cavity laser with a semiconductor optical amplifier and two diffraction gratings are described. The laser has been pigtailed and its emission showed two peaks in the output spectrum. The wavelength of the peaks, and in particular the spectral spacing between them, could be controlled by adjusting the reflecting elements in the system. The proposed double-frequency laser may be adopted as a signal source in terahertz generators.

Low Temperature Physics, 2012

ABSTRACT The magnetoelastic constants of epitaxial iron films prepared by dc magnetron sputtering... more ABSTRACT The magnetoelastic constants of epitaxial iron films prepared by dc magnetron sputtering on single crystal GaAs (001) substrate in argon atmosphere and covered with a protective Si layer have been investigated in the temperature range 10–300 K by means of the strain modulated ferromagnetic resonance. It has been shown that the magnetoelastic constants strongly depend on the thickness of the film. The surface components of the magnetoelastic constants have been determined and analyzed within the Néel and dipolar models. The proposed analysis of experimental data gives chance for deeper insight into mechanisms responsible for magnetostriction of iron thin films.

In this paper the physical properties of two types of Co-doped ZnO nanostructures: tetrapods and ... more In this paper the physical properties of two types of Co-doped ZnO nanostructures: tetrapods and nanofibers grown by a rapid thermal evaporation process and prepared by the electrospinning technique, respectively, were investigated and analyzed. Surface morphology of the samples was examined using scanning electron microscopy. X-ray diffraction measurements showed hexagonal wurtzite crystal structure of both types of investigated nanostructures. Both X-ray diffraction and Raman scattering data confirmed high phase purity of the samples. The magnetic properties studied with the use of the SQUID magnetometer confirmed a presence of ferromagnetic order in analyzed nanostructures. The observed photoluminescence spectra exhibited two groups of lines. The first one, in the ultraviolet spectral range, is due to the optical transitions close to ZnO band gap, the second one in the red region is most probably related to the Co 2+ d–d internal transitions. The influence of native defects on th...

Low-Dimensional Materials and Devices, 2015

ABSTRACT Semiconductor surface plays an important role in the technology of semiconductor devices... more ABSTRACT Semiconductor surface plays an important role in the technology of semiconductor devices. In the present work we report results of our deep-level transient spectroscopy (DLTS) investigations of surface defect states in nitrogen doped p-type CdTe layers grown by the molecular-beam epitaxy technique. We observed a deep-level trap associated with surface states, with the activation energy for hole emission of 0.33 eV. DLTS peak position in the spectra for this trap, and its ionization energy, strongly depend on the electric field. Our measurements allow to determine a mechanism responsible for the enhancement of hole emission rate from the traps as the phonon-assisted tunnel effect. Density of surface defect states significantly decreased as a result of passivation in ammonium sulfide. Capacitance-voltage measurements confirmed the results obtained by the DLTS technique.

Acta Physica Polonica A, 2007

We report on the photoluminescence studies of ZnO and ZnCdO nanowires grown on SiO 2 /Si substrat... more We report on the photoluminescence studies of ZnO and ZnCdO nanowires grown on SiO 2 /Si substrates by low-pressure vapor phase synthesis. X-ray diffraction and transmission electron microscopy measurements show that the crystallographic structure of these ZnO and ZnCdO nanowires is of wurtzite-type with a high crystal perfection. Surface morphology of samples was determined by scanning electron microscopy and atomic force microscopy. The photoluminescence spectra of as-grown nanowires, nanowires extracted from the substrate and deposited onto Si wafer, and nanowires dispersed in ethanol by sonication were investigated at room temperature and compared to each other. The temperature dependence of the near band-gap photoluminescence emitted by the as-grown nanowires was also measured and analyzed.

Acta Physica Polonica A, 2007

Scanning tunneling spectroscopy was used to check the tunneling I−V characteristics of junctions ... more Scanning tunneling spectroscopy was used to check the tunneling I−V characteristics of junctions formed by n-ZnO nanowires deposited on Si substrates with n-and p-type electrical conductivity (i.e. n-ZnO nanowire/ n-Si and n-ZnO nanowire/p-Si junctions, respectively). Simultaneously, several phenomena which influence the measured I−V spectra were studied by atomic force microscopy. These influencing factors are: the deposition density of the nanowires, the possibility of surface modification by tip movement (difference in attraction forces between nanowires and the p-Si and n-Si) and the aging of the surface.

Materials Science Forum, 2001

ABSTRACT The in-plane magnetic anisotropy and interlayer coupling have been investigated in the F... more ABSTRACT The in-plane magnetic anisotropy and interlayer coupling have been investigated in the Fe/Si/Fe trilayers grown by de magnetron sputtering deposition on GaAs (001) substrates. The samples have been covered with thin Si cap layer. The measurements have been performed by means of ferromagnetic resonance (FMR) technique as a function of the orientation of dc magnetic field in plane of the film and at liquid helium and room temperatures. From these dependencies the in-plane cubic anisotropy constants as well as interlayer coupling constants are determined. It is shown that the uniaxial in-plane anisotropy has mainly magnetoelastic origin and directions of easy axes are different in both layers. Moreover, the anisotropy constants in both layers have different temperature dependencies related only to the differences in thermal expansion coefficients between Fe, Si and GaAs.

Physical Review B, 2015

We present photoluminescence studies of CdTe and Cd1−xMnxTe quantum dots grown in two adjacent la... more We present photoluminescence studies of CdTe and Cd1−xMnxTe quantum dots grown in two adjacent layers. We show that when the dots are 8 nm apart, their magnetooptical properties -Zeeman shifts and transition linewidths -are analogous to those of individual CdTe or Cd1−xMnxTe dots. When the dots are grown closer, at a distance of 4 nm, it becomes possible to tune the electron states to resonance and obtain a formation of a molecular state hybridized over the two dots. As a result of the resonant enhancement of the electron-Mn ion exchange interaction, spectroscopic signatures specific to spin-dependent inter-dot coupling appear. Namely, an anomalous increase of the Zeeman shift and a resonant increase in the transition linewidth are observed. A simple model calculation allows us to quantitatively reproduce the experimental results.

Phys. Chem. Chem. Phys., 2015

This study describes a new method of passivating ZnO nanofiber-based devices with a ZnS layer. Th... more This study describes a new method of passivating ZnO nanofiber-based devices with a ZnS layer. This one-step process was carried out in H2S gas at room temperature, and resulted in the formation of core/shell ZnO/ZnS nanofibers. This study presents the structural, optical and electrical properties of ZnO/ZnS nanofibers formed by a 2 nm ZnS sphalerite crystal shell covering a 5 nm ZnO wurtzite crystal core. The passivation process prevented free carriers from capture by oxygen molecules and significantly reduced the impact of O2 on nanostructure conductivity. The conductivity of the nanofibers was increased by three orders of magnitude after the sulfidation, the photoresponse time was reduced from 1500 s to 30 s, and the cathodoluminescence intensity increased with the sulfidation time thanks to the removal of ZnO surface defects by passivation. The ZnO/ZnS nanofibers were stable in water for over 30 days, and in phosphate buffers of acidic, neutral and alkaline pH for over 3 days. The by-products of the passivation process did not affect the conductivity of the devices. The potential of ZnO/ZnS nanofibers for protein biosensing is demonstrated using biotin and streptavidin as a model system. The presented ZnS shell preparation method can facilitate the construction of future sensors and protects the ZnO surface from dissolving in a biological environment.

Biosensors and Bioelectronics, 2015

A novel recognition unit of chemical sensor for selective determination of the inosine, renal dis... more A novel recognition unit of chemical sensor for selective determination of the inosine, renal disfunction biomarker, was devised and prepared. For that purpose, inosine-templated molecularly imprinted polymer (MIP) film was deposited on an extended-gate field-effect transistor (EG-FET) signal transducing unit. The MIP film was prepared by electrochemical polymerization of bis(bithiophene) derivatives bearing cytosine and boronic acid substituents, in the presence of the inosine template and a thiophene cross-linker. After MIP film deposition, the template was removed, and was confirmed by UV-visible spectroscopy. Subsequently, the film composition was characterized by spectroscopic techniques, and its morphology and thickness were determined by AFM. The finally MIP film-coated extended-gate fieldeffect transistor (EG-FET) was used for signal transduction. This combination is not widely studied in the literature, despite the fact that it allows for facile integration of electrodeposited MIP film with FET transducer.

Journal of Applied Physics, 2015

We demonstrate an efficient method to engineer the quantum confinement in a system of two quantum... more We demonstrate an efficient method to engineer the quantum confinement in a system of two quantum dots grown in a vertical stack. We achieve this by using materials with a different lattice constant for the growth of the outer and inner barriers. We monitor the resulting dot morphology with transmission electron microscopy studies and correlate the results with ensemble quantum dot photoluminescence. Furthermore, we embed the double quantum dots into diode structures and study photoluminescence as a function of bias voltage. We show that in properly engineered structures, it is possible to achieve a resonance of the hole states by tuning the energy levels with electric field. At the resonance, we observe signatures of a formation of a molecular state, hybridized over the two dots. arXiv:1502.03592v1 [cond-mat.mes-hall]

In this study, a ZnO nanofiber biosensor design is reported. ZnO nanofibers were obtained by elec... more In this study, a ZnO nanofiber biosensor design is reported. ZnO nanofibers were obtained by electrospinning process followed by calcination. As a novel fabrication method, amorphous thin film of AlN x deposited by reactive magnetron sputtering, was proposed as a protective and stabilizing layer in subsequent technological processes. This allowed to use photolithography techniques for fabrication of the electrospun ZnO nanofibers sensor structures which is first time reported. The wet etching of AlN protective layer, Ti/Au ohmic contacts to ZnO fibers and polyimide passivating film have completed the design. Topography of the sensor structure was investigated using AFM and SEM. I-V measurements made for electrical characterization of ohmic contacts and nanofibers in different solutions environments including biological agent are reported.

In the presented work, ZnO nanofiber sensor structures designed and fabricated using a standard m... more In the presented work, ZnO nanofiber sensor structures designed and fabricated using a standard microelectronic device technology were studied. The structures in the configuration of a resistor with chemically active ZnO multiple nanofibers deposited by electrospinning method were prepared. Investigation of inclusion in the process reactive-ly sputtered AlN insulating film to improve the robustness of the nanofibres on the substrate was undertaken. Selective wet chemical etching of AlN film using photoresist developers and a photoresist mask to define the sensor active area was studied. The Ti/Au ohmic contacts were fabricated using the lift-off photolithography process. To-pography of the sensor structure details was investigated using AFM. Electrical charac-terization by means of I-V measurements was made. Sensitivity to the physiologically relevant concentration of Bovine Serum Albumin in water solution was shown.

Tenth International School on Quantum Electronics: Laser Physics and Applications, 1999

ABSTRACT We present an experimental study of fine structure (fs)- mixing in the 52D state of Rb, ... more ABSTRACT We present an experimental study of fine structure (fs)- mixing in the 52D state of Rb, and details of construction and performance of an external cavity cw diode laser, developed to provide a light source at 778 nm for two-photon excitation of Rb(52D). Cross section for the fs-mixing Rb(52D5/2) yields Rb(52D3/2) in collisions with the ground state Rb(52S1/2) atoms was found to be 5.8 +/- 1.9 (DOT) 10-14 cm2.

We show that by means of an electric field we can tune the energy levels in vertical quantum dot ... more We show that by means of an electric field we can tune the energy levels in vertical quantum dot pairs and study transitions related to recombination of direct and indirect excitons. With decreasing the reverse bias, we observe both the blue-and red-shifted indirect exciton transitions. Based on the band profile of our device, we conclude that the former corresponds to the recombination of the electron and hole localized in the top and the bottom dot, respectively and the latter is related to the recombination of the electron and hole localized in the bottom and the top dot, respectively.

The Ninth International Conference on Advanced Semiconductor Devices and Mircosystems, 2012

In the present study determination of the impact of various gas atmospheres on the surface potent... more In the present study determination of the impact of various gas atmospheres on the surface potential distribution of the electrospun ZnO nanofiber was carried out. Analysis of surface properties was performed using a Scanning Surface Potential Microscopy (SSPM). Obtained results proved homogeneity of the electrical and structural properties along the fiber. The effect of majority carriers depletion in metal oxides in oxidizing gas atmospheres was confirmed by changing the surface potential distribution of the fibers. Measurements performed in dry and humid atmosphere of nitrogen and air could clarify the role of water vapor on the properties of ZnO fibers.

Materials Science Forum, 2001