Vladimir Fonoberov - Profile on Academia.edu (original) (raw)
Papers by Vladimir Fonoberov
Interfacial and Confined Optical Phonons in Wurtzite Nanocrystals
Moldavian Academy of Sciences, Institute of Applied Physics, Laboratory of Physical Kinetics (Aca... more Moldavian Academy of Sciences, Institute of Applied Physics, Laboratory of Physical Kinetics (Academic Str. 5, MD-2028, Kishinev) The defense will take place on December 18, 2002 at 2 p.m. in the framework of the meeting of the specialized Scientific Council .16 at the State University of Moldova (Mateevici Str. 60, MD-2009, Kishinev) The Ph.D. thesis and the abstract can be consulted at the library of the State University of Moldova, Mateevici Str. 60, Kishinev The abstract was mailed on November 14, 2002 Scientific Secretary of the specialized Scientific Council, Doctor of Physical and Mathematical Sciences V. Pleşca 3
Exciton radiative lifetime and the ``dead-layer'' effect in ZnO quantum dots
ZnO quantum dots (QDs) have recently attracted significant attention due to the proposed optoelec... more ZnO quantum dots (QDs) have recently attracted significant attention due to the proposed optoelectronic and nanoelectronic applications. We theoretically investigated the exciton radiative lifetime and the thickness of the ``dead-layer'' (layer where exciton does not penetrate) for ZnO QDs with radii from 1 to 3 nm [1]. Our calculations show that the dead layer formed near the QD surface is rather thick for ZnO QDs, what is attributed to the large hole-electron effective mass ratio in ZnO. The excited exciton states are also investigated as a function of the ZnO QD size. The small radiative lifetime and thick dead layer found in ZnO QDs can be beneficial for device applications owing to better luminescence and isolation of the exciton from surface defects [2]. The obtained results can be used for the optimization of ZnO QD arrays for optoelectronic applications. The authors acknowledge the support of MARCO and its Functional Engineered Nano Architectonics (FENA) Focus Center...
Journal of Nanoelectronics and Optoelectronics, 2006
We present a review of the recent theoretical and experimental investigation of excitonic and pho... more We present a review of the recent theoretical and experimental investigation of excitonic and phonon states in ZnO quantum dots. A small dielectric constant in ZnO leads to very large exciton binding energies, while wurtzite crystal structure results in unique phonon spectra different from those in cubic crystals. The exciton energies and radiative lifetimes are determined in the intermediate quantum confinement regime, which is pertinent to a variety of realistic ZnO quantum dots produced by wet chemistry methods. An analytical model for the interface and confined polar optical phonons is presented for spheroidal quantum dots of different size and barrier materials. The experimental part of the review covers results of the nonresonant and resonant Raman spectroscopy and photoluminescence study of ZnO quantum dots with sizes comparable to or larger than the exciton diameter in ZnO. The origins of the Raman phonon shifts and the mechanisms of the carrier recombination in ZnO quantum dots are discussed in detail. The reviewed properties of ZnO quantum dots are important for the proposed optoelectronic applications of these nanostructures.
Properties of GaN and ZnO quantum dots
... Quantum Dots Vladimir A. Fonoberov, Alexander A. Balandin Nano-Device Laboratory, Department ... more ... Quantum Dots Vladimir A. Fonoberov, Alexander A. Balandin Nano-Device Laboratory, Department of Electrical Engineering, University of CaliforniaRiverside, Riverside, CA, USA ... kx l kx + k⊥ x h k⊥ x 3 kx + 3 ky + ky − 3 kx 3 kx + 3 kz + kz − 3 kx ...
We perform analysis of data on crime and violence for 5,660 U.S. cities over the period of 2005-2... more We perform analysis of data on crime and violence for 5,660 U.S. cities over the period of 2005-2009 and uncover the following trends: 1) The proportion of law enforcement officers required to maintain a steady low level of criminal activity increases with the size of the population of the city; 2) The number of criminal/violent events per 1,000 inhabitants of
Physical Review B, 2001
In order to study heterostructures composed both of materials with strongly different parameters ... more In order to study heterostructures composed both of materials with strongly different parameters and of materials with narrow band gaps, we have developed an approach ͓E. P. Pokatilov et al., Phys. Rev. B 64, 245328 ͑2001͒, preceding paper͔͒, which combines the spherical eight-band effective-mass Hamiltonian and the Burt's envelope-function representation. Using this method, electron and hole states are calculated in CdS/HgS/CdS/H 2 O and CdTe/HgTe/CdTe/H 2 O quantum dot quantum-well heterostructures. Radial components of the wave functions of the lowest S and P electron and hole states in typical quantum dot quantum wells ͑QDQW's͒ are presented as a function of radius. The six-band-hole components of the radial wave functions of an electron in the eight-band model have amplitudes comparable with the amplitude of the corresponding two-band-electron component. This is a consequence of the coupling between the conduction and valence bands, which gives a strong nonparabolicity of the conduction band. At the same time, the two-band-electron component of the radial wave functions of a hole in the eight-band model is small compared with the amplitudes of the corresponding six-band-hole components. It is shown that in the CdS/HgS/CdS/H 2 O QDQW holes in the lowest states are strongly localized in the well region ͑HgS͒. On the contrary, electrons in this QDQW and both electron and holes in the CdTe/HgTe/CdTe/H 2 O QDQW are distributed through the entire dot. The importance of the developed theory for QDQW's is proven by the fact that in contrast to our rigorous eight-band model, there appear spurious states within the commonly used symmetrized eight-band model.
Physical Review B, 2001
We derive a nonsymmetrized 8-band effective-mass Hamiltonian for quantumdot heterostructures (QDH... more We derive a nonsymmetrized 8-band effective-mass Hamiltonian for quantumdot heterostructures (QDHs) in Burt's envelope-function representation. The 8×8 radial Hamiltonian and the boundary conditions for the Schrödinger equation are obtained for spherical QDHs. Boundary conditions for symmetrized and nonsymmetrized radial Hamiltonians are compared with each other and with connection rules that are commonly used to match the wave functions found from the bulk k ·p Hamiltonians of two adjacent materials. Electron and hole energy spectra in three spherical QDHs: HgS/CdS, InAs/GaAs, and GaAs/AlAs are calculated as a function of the quantum dot radius within the approximate symmetrized and exact nonsymmetrized 8×8 models. The parameters of dissymmetry are shown to influence the energy levels and the wave functions of an electron and a hole and, consequently, the energies of both intraband and interband transitions.
Physical Review B, 2002
We present a theoretical investigation of electron-hole and exciton energy spectra as well as osc... more We present a theoretical investigation of electron-hole and exciton energy spectra as well as oscillator strengths of optical transitions in colloidal CdS quantum dots ͑QD's͒ with spherical and tetrahedral shape. The Coulomb potential energy of the electron-hole system is treated taking into account the dielectric mismatch at the QD boundaries. Calculation of electron-hole energy spectrum and Coulomb potential energy in tetrahedral QD's is carried out using the finite difference method. It is shown that the bulk Coulomb potential energy with the dielectric constant of QD leads to lower exciton energy levels as compared to the Coulomb potential, which includes electron-hole interaction and self-action energies. The Coulomb potential changes the electron-hole pair energies without dielectric confinement contributions in such a way that the exciton ground state becomes active for optical transitions in dipole approximation for both tetrahedral and spherical QD's while the lowest electron-hole pair energy level is active for tetrahedral and passive for spherical QD's. The exciton binding energy in both types of QD's is enhanced by a factor of 2 in the presence of the dielectric mismatch. It is proven that the inclusion of the real QD shape and dielectric mismatch is important not only for the quantitative analysis but also for the qualitative description of optical properties of colloidal CdS QD's.
Combustion of Methane in Microchannels
Volume 12: Micro and Nano Systems, Parts A and B, 2009
Combustion of Methane in Microchannels. [ASME Conference Proceedings 2009, 719 (2009)]. Sophie Lo... more Combustion of Methane in Microchannels. [ASME Conference Proceedings 2009, 719 (2009)]. Sophie Loire, Igor Mezić, Vladimir A. Fonoberov. Abstract. The interest in micropower generation using the high energy density provided ...
Modeling and Calibration of Energy Models for a DoD Building
Properties of polar optical phonons in wurtzite quantum dots
Wurtzite (WZ) ZnO and GaN quantum dots (QDs) have attracted significant attention as promising ca... more Wurtzite (WZ) ZnO and GaN quantum dots (QDs) have attracted significant attention as promising candidates for optoelectronic applications. To enable the interpretation of the optical response of such QDs, we derive an integral equation that defines both interface and confined polar optical phonon modes in WZ QDs of arbitrary shapes [1]. The analytical solution of the derived equation is found for spheroidal QDs [2]. While the frequency of the confined polar optical phonons in zincblende QDs is equal to that of the bulk crystal, the confined optical phonons in WZ QDs are shown to have a discrete spectrum of frequencies different from those of the bulk crystal. The obtained results have been proven useful for the accurate prediction of interface and confined optical phonon frequencies in the novel class of QDs. This research has been supported in part by the ONR Young Investigator Award to A.A.B. [1] V.A. Fonoberov and A.A. Balandin, Phys. Rev. B 70, in press (Dec. 15, 2004). [2] V.A....
Calibration of a Building Energy Model Considering Parametric Uncertainty
Radiative lifetime of excitons in ZnO nanocrystals: The dead-layer effect
Physical Review B, 2004
We theoretically investigate exciton states of colloidal nearly spherical ZnO nanocrystals with d... more We theoretically investigate exciton states of colloidal nearly spherical ZnO nanocrystals with diameters from 2nmto6nm . The sizes of considered ZnO nanocrystals are chosen to be slightly larger than the exciton Bohr radius of bulk ZnO. A number of characteristic features of excitons are revealed in this intermediate quantum confinement regime. The exciton center of mass is found to be prolate along the c axis of wurtzite ZnO and squeezed to the center of the ZnO nanocrystal, thus forming a dead layer near the nanocrystal surface. The thickness of the exciton dead layer is found to increase with the nanocrystal size reaching the value of about 1.6nm for the nanocrystal with diameter of 6nm . Based on our calculations we proposed an analytical approximation for the exciton radiative-lifetime dependence on radius R in ZnO nanocrystal written as tau0/[1+(R/R0)3] with tau0=73.4ps and R0=2.55nm . Presented results and proposed analytical approximation can be used for interpretation of experimental data, and optimization of ZnO quantum dot structures for optoelectronic applications.
Global sensitivity/uncertainty analysis for agent-based models
Reliability Engineering & System Safety, 2013
Physical Review B, 2004
We derive within the dielectric-continuum model an integral equation that defines interface and c... more We derive within the dielectric-continuum model an integral equation that defines interface and confined polar optical-phonon modes in nanocrystals with wurtzite crystal structure. It is demonstrated theoretically, that while the frequency of confined polar optical phonons in zincblende nanocrystals is equal to that of the bulk crystal phonons, the confined polar optical phonons in wurtzite nanocrystals have a discrete spectrum of frequencies different from those of the bulk crystal. The calculated frequencies of confined polar optical phonons in wurtzite ZnO nanocrystals are found to be in an excellent agreement with the experimental resonant Raman scattering spectra of spherical ZnO quantum dots.
Physical Review B, 2009
͑CO͒ 1−x ͑Ar͒ x mixtures physisorbed on graphite experimentally display a novel phenomenon of inc... more ͑CO͒ 1−x ͑Ar͒ x mixtures physisorbed on graphite experimentally display a novel phenomenon of increasing phase-transition temperature ͑stabilizing the system͒ with increasing Ar impurity concentration or uncertainty ͓H. Wiechert and K.-D. Kortmann, Surf. Sci. 441, 65 ͑1999͔͒. We develop a two-dimensional Ising-type model that accurately captures the phase transition and its temperature dependence. The anomaly in transition temperature is due to formation of pinwheel regions of CO around Ar atoms. The dilemma of whether the ground state is head-to-head or head-to-tail ordered is reconciled in favor of the latter. The phase-transition curve in the presence of uncertainty in Ar impurity is computed using Monte Carlo ͑MC͒ and probabilistic collocation method ͑PCM͒. PCM computes the first two moments Ϸ2000 times faster than MC.
physica status solidi (c), 2004
We derive analytically the interface and confined polar optical-phonon modes for spherical quantu... more We derive analytically the interface and confined polar optical-phonon modes for spherical quantum dots with wurtzite crystal structure. While the frequency of confined optical phonons in zincblende nanocrystals is equal to that of the bulk crystal phonons, the confined polar optical phonons in wurtzite nanocrystals are shown to have a discrete spectrum of frequencies different from those in bulk crystal. The calculated frequencies of confined polar optical phonons in wurtzite ZnO quantum dots are found to be in excellent agreement with experimental resonant Raman scattering data. The derived analytical expression for phonon modes can facilitate interpretation of experimental data obtained for ZnO quantum dots.
physica status solidi (b), 2004
Viruses of cylindrical shape have recently attracted attention as templates for assembly of nanos... more Viruses of cylindrical shape have recently attracted attention as templates for assembly of nanostructured materials and as elements of nanoelectronic circuits. We have calculated the dispersion relations for the lowest vibrational frequencies of the tobacco mosaic virus (TMV) and M13 bacteriophage immersed in air or water. The radial breathing modes of TMV and M13 viruses in air (water) are 1.85 cm -1 and 6.42 cm -1 (2.10 cm -1 and 6.12 cm -1 ), respectively. Elastic vibrations of the two viruses in water are damped with the quality factor of 3.6 for the radial breathing modes. , Fax: +1 951 827 2425 R68 V. A. Fonoberov and A. A. Balandin: Low-frequency vibrational modes of viruses
Journal of Physics: Condensed Matter, 2000
Electron and hole states are studied in quantum well wires (QWWs) with a rectangular cross sectio... more Electron and hole states are studied in quantum well wires (QWWs) with a rectangular cross section. A theoretical approach is developed, within which the electronic properties of a single QWW as well as of finite and infinite planar lattices of QWWs are analysed. It is demonstrated that the ratio of effective masses in the well and in the barrier influences the dispersion law of the electron motion along the QWW axis. A six-wire lattice is studied in detail. Edge states, which can be observed in optical spectra, are revealed, when the barrier heights are different inside and outside the lattice. The miniband structure is investigated for an infinite lattice of QWWs. The evolution of electron states is analysed when the number of QWWs in the lattice increases: 1 → 6 → ∞. The calculated electron-hole pair energies are in a good agreement with the experimental data on photoluminescence in the Ga 0.47 In 0.53 As/InP QWW. § Present address: photoluminescence excitation (PLE) spectra, and the effect of lateral confinement on the valence-band mixing has been studied in . The mixing in the conduction band of Vand T-shaped QWWs has been studied in . Strained V-shaped QWWs have been described in [9] by means of the eight-band k · p scheme. An impurity located at the axis of a cylindrical QWW has also been studied . The binding energy of a hydrogenic impurity in a cylindrical QWW has been calculated as a function of the location of the impurity with respect to the axis of the QWW . The effect of the shape of a cross section on the impurity binding energies for a QWW has been investigated in . A contribution of the polaron effect to the impurity binding energy in a cylindrical QWW has been analysed in .
Interfacial and Confined Optical Phonons in Wurtzite Nanocrystals
Moldavian Academy of Sciences, Institute of Applied Physics, Laboratory of Physical Kinetics (Aca... more Moldavian Academy of Sciences, Institute of Applied Physics, Laboratory of Physical Kinetics (Academic Str. 5, MD-2028, Kishinev) The defense will take place on December 18, 2002 at 2 p.m. in the framework of the meeting of the specialized Scientific Council .16 at the State University of Moldova (Mateevici Str. 60, MD-2009, Kishinev) The Ph.D. thesis and the abstract can be consulted at the library of the State University of Moldova, Mateevici Str. 60, Kishinev The abstract was mailed on November 14, 2002 Scientific Secretary of the specialized Scientific Council, Doctor of Physical and Mathematical Sciences V. Pleşca 3
Exciton radiative lifetime and the ``dead-layer'' effect in ZnO quantum dots
ZnO quantum dots (QDs) have recently attracted significant attention due to the proposed optoelec... more ZnO quantum dots (QDs) have recently attracted significant attention due to the proposed optoelectronic and nanoelectronic applications. We theoretically investigated the exciton radiative lifetime and the thickness of the ``dead-layer'' (layer where exciton does not penetrate) for ZnO QDs with radii from 1 to 3 nm [1]. Our calculations show that the dead layer formed near the QD surface is rather thick for ZnO QDs, what is attributed to the large hole-electron effective mass ratio in ZnO. The excited exciton states are also investigated as a function of the ZnO QD size. The small radiative lifetime and thick dead layer found in ZnO QDs can be beneficial for device applications owing to better luminescence and isolation of the exciton from surface defects [2]. The obtained results can be used for the optimization of ZnO QD arrays for optoelectronic applications. The authors acknowledge the support of MARCO and its Functional Engineered Nano Architectonics (FENA) Focus Center...
Journal of Nanoelectronics and Optoelectronics, 2006
We present a review of the recent theoretical and experimental investigation of excitonic and pho... more We present a review of the recent theoretical and experimental investigation of excitonic and phonon states in ZnO quantum dots. A small dielectric constant in ZnO leads to very large exciton binding energies, while wurtzite crystal structure results in unique phonon spectra different from those in cubic crystals. The exciton energies and radiative lifetimes are determined in the intermediate quantum confinement regime, which is pertinent to a variety of realistic ZnO quantum dots produced by wet chemistry methods. An analytical model for the interface and confined polar optical phonons is presented for spheroidal quantum dots of different size and barrier materials. The experimental part of the review covers results of the nonresonant and resonant Raman spectroscopy and photoluminescence study of ZnO quantum dots with sizes comparable to or larger than the exciton diameter in ZnO. The origins of the Raman phonon shifts and the mechanisms of the carrier recombination in ZnO quantum dots are discussed in detail. The reviewed properties of ZnO quantum dots are important for the proposed optoelectronic applications of these nanostructures.
Properties of GaN and ZnO quantum dots
... Quantum Dots Vladimir A. Fonoberov, Alexander A. Balandin Nano-Device Laboratory, Department ... more ... Quantum Dots Vladimir A. Fonoberov, Alexander A. Balandin Nano-Device Laboratory, Department of Electrical Engineering, University of CaliforniaRiverside, Riverside, CA, USA ... kx l kx + k⊥ x h k⊥ x 3 kx + 3 ky + ky − 3 kx 3 kx + 3 kz + kz − 3 kx ...
We perform analysis of data on crime and violence for 5,660 U.S. cities over the period of 2005-2... more We perform analysis of data on crime and violence for 5,660 U.S. cities over the period of 2005-2009 and uncover the following trends: 1) The proportion of law enforcement officers required to maintain a steady low level of criminal activity increases with the size of the population of the city; 2) The number of criminal/violent events per 1,000 inhabitants of
Physical Review B, 2001
In order to study heterostructures composed both of materials with strongly different parameters ... more In order to study heterostructures composed both of materials with strongly different parameters and of materials with narrow band gaps, we have developed an approach ͓E. P. Pokatilov et al., Phys. Rev. B 64, 245328 ͑2001͒, preceding paper͔͒, which combines the spherical eight-band effective-mass Hamiltonian and the Burt's envelope-function representation. Using this method, electron and hole states are calculated in CdS/HgS/CdS/H 2 O and CdTe/HgTe/CdTe/H 2 O quantum dot quantum-well heterostructures. Radial components of the wave functions of the lowest S and P electron and hole states in typical quantum dot quantum wells ͑QDQW's͒ are presented as a function of radius. The six-band-hole components of the radial wave functions of an electron in the eight-band model have amplitudes comparable with the amplitude of the corresponding two-band-electron component. This is a consequence of the coupling between the conduction and valence bands, which gives a strong nonparabolicity of the conduction band. At the same time, the two-band-electron component of the radial wave functions of a hole in the eight-band model is small compared with the amplitudes of the corresponding six-band-hole components. It is shown that in the CdS/HgS/CdS/H 2 O QDQW holes in the lowest states are strongly localized in the well region ͑HgS͒. On the contrary, electrons in this QDQW and both electron and holes in the CdTe/HgTe/CdTe/H 2 O QDQW are distributed through the entire dot. The importance of the developed theory for QDQW's is proven by the fact that in contrast to our rigorous eight-band model, there appear spurious states within the commonly used symmetrized eight-band model.
Physical Review B, 2001
We derive a nonsymmetrized 8-band effective-mass Hamiltonian for quantumdot heterostructures (QDH... more We derive a nonsymmetrized 8-band effective-mass Hamiltonian for quantumdot heterostructures (QDHs) in Burt's envelope-function representation. The 8×8 radial Hamiltonian and the boundary conditions for the Schrödinger equation are obtained for spherical QDHs. Boundary conditions for symmetrized and nonsymmetrized radial Hamiltonians are compared with each other and with connection rules that are commonly used to match the wave functions found from the bulk k ·p Hamiltonians of two adjacent materials. Electron and hole energy spectra in three spherical QDHs: HgS/CdS, InAs/GaAs, and GaAs/AlAs are calculated as a function of the quantum dot radius within the approximate symmetrized and exact nonsymmetrized 8×8 models. The parameters of dissymmetry are shown to influence the energy levels and the wave functions of an electron and a hole and, consequently, the energies of both intraband and interband transitions.
Physical Review B, 2002
We present a theoretical investigation of electron-hole and exciton energy spectra as well as osc... more We present a theoretical investigation of electron-hole and exciton energy spectra as well as oscillator strengths of optical transitions in colloidal CdS quantum dots ͑QD's͒ with spherical and tetrahedral shape. The Coulomb potential energy of the electron-hole system is treated taking into account the dielectric mismatch at the QD boundaries. Calculation of electron-hole energy spectrum and Coulomb potential energy in tetrahedral QD's is carried out using the finite difference method. It is shown that the bulk Coulomb potential energy with the dielectric constant of QD leads to lower exciton energy levels as compared to the Coulomb potential, which includes electron-hole interaction and self-action energies. The Coulomb potential changes the electron-hole pair energies without dielectric confinement contributions in such a way that the exciton ground state becomes active for optical transitions in dipole approximation for both tetrahedral and spherical QD's while the lowest electron-hole pair energy level is active for tetrahedral and passive for spherical QD's. The exciton binding energy in both types of QD's is enhanced by a factor of 2 in the presence of the dielectric mismatch. It is proven that the inclusion of the real QD shape and dielectric mismatch is important not only for the quantitative analysis but also for the qualitative description of optical properties of colloidal CdS QD's.
Combustion of Methane in Microchannels
Volume 12: Micro and Nano Systems, Parts A and B, 2009
Combustion of Methane in Microchannels. [ASME Conference Proceedings 2009, 719 (2009)]. Sophie Lo... more Combustion of Methane in Microchannels. [ASME Conference Proceedings 2009, 719 (2009)]. Sophie Loire, Igor Mezić, Vladimir A. Fonoberov. Abstract. The interest in micropower generation using the high energy density provided ...
Modeling and Calibration of Energy Models for a DoD Building
Properties of polar optical phonons in wurtzite quantum dots
Wurtzite (WZ) ZnO and GaN quantum dots (QDs) have attracted significant attention as promising ca... more Wurtzite (WZ) ZnO and GaN quantum dots (QDs) have attracted significant attention as promising candidates for optoelectronic applications. To enable the interpretation of the optical response of such QDs, we derive an integral equation that defines both interface and confined polar optical phonon modes in WZ QDs of arbitrary shapes [1]. The analytical solution of the derived equation is found for spheroidal QDs [2]. While the frequency of the confined polar optical phonons in zincblende QDs is equal to that of the bulk crystal, the confined optical phonons in WZ QDs are shown to have a discrete spectrum of frequencies different from those of the bulk crystal. The obtained results have been proven useful for the accurate prediction of interface and confined optical phonon frequencies in the novel class of QDs. This research has been supported in part by the ONR Young Investigator Award to A.A.B. [1] V.A. Fonoberov and A.A. Balandin, Phys. Rev. B 70, in press (Dec. 15, 2004). [2] V.A....
Calibration of a Building Energy Model Considering Parametric Uncertainty
Radiative lifetime of excitons in ZnO nanocrystals: The dead-layer effect
Physical Review B, 2004
We theoretically investigate exciton states of colloidal nearly spherical ZnO nanocrystals with d... more We theoretically investigate exciton states of colloidal nearly spherical ZnO nanocrystals with diameters from 2nmto6nm . The sizes of considered ZnO nanocrystals are chosen to be slightly larger than the exciton Bohr radius of bulk ZnO. A number of characteristic features of excitons are revealed in this intermediate quantum confinement regime. The exciton center of mass is found to be prolate along the c axis of wurtzite ZnO and squeezed to the center of the ZnO nanocrystal, thus forming a dead layer near the nanocrystal surface. The thickness of the exciton dead layer is found to increase with the nanocrystal size reaching the value of about 1.6nm for the nanocrystal with diameter of 6nm . Based on our calculations we proposed an analytical approximation for the exciton radiative-lifetime dependence on radius R in ZnO nanocrystal written as tau0/[1+(R/R0)3] with tau0=73.4ps and R0=2.55nm . Presented results and proposed analytical approximation can be used for interpretation of experimental data, and optimization of ZnO quantum dot structures for optoelectronic applications.
Global sensitivity/uncertainty analysis for agent-based models
Reliability Engineering & System Safety, 2013
Physical Review B, 2004
We derive within the dielectric-continuum model an integral equation that defines interface and c... more We derive within the dielectric-continuum model an integral equation that defines interface and confined polar optical-phonon modes in nanocrystals with wurtzite crystal structure. It is demonstrated theoretically, that while the frequency of confined polar optical phonons in zincblende nanocrystals is equal to that of the bulk crystal phonons, the confined polar optical phonons in wurtzite nanocrystals have a discrete spectrum of frequencies different from those of the bulk crystal. The calculated frequencies of confined polar optical phonons in wurtzite ZnO nanocrystals are found to be in an excellent agreement with the experimental resonant Raman scattering spectra of spherical ZnO quantum dots.
Physical Review B, 2009
͑CO͒ 1−x ͑Ar͒ x mixtures physisorbed on graphite experimentally display a novel phenomenon of inc... more ͑CO͒ 1−x ͑Ar͒ x mixtures physisorbed on graphite experimentally display a novel phenomenon of increasing phase-transition temperature ͑stabilizing the system͒ with increasing Ar impurity concentration or uncertainty ͓H. Wiechert and K.-D. Kortmann, Surf. Sci. 441, 65 ͑1999͔͒. We develop a two-dimensional Ising-type model that accurately captures the phase transition and its temperature dependence. The anomaly in transition temperature is due to formation of pinwheel regions of CO around Ar atoms. The dilemma of whether the ground state is head-to-head or head-to-tail ordered is reconciled in favor of the latter. The phase-transition curve in the presence of uncertainty in Ar impurity is computed using Monte Carlo ͑MC͒ and probabilistic collocation method ͑PCM͒. PCM computes the first two moments Ϸ2000 times faster than MC.
physica status solidi (c), 2004
We derive analytically the interface and confined polar optical-phonon modes for spherical quantu... more We derive analytically the interface and confined polar optical-phonon modes for spherical quantum dots with wurtzite crystal structure. While the frequency of confined optical phonons in zincblende nanocrystals is equal to that of the bulk crystal phonons, the confined polar optical phonons in wurtzite nanocrystals are shown to have a discrete spectrum of frequencies different from those in bulk crystal. The calculated frequencies of confined polar optical phonons in wurtzite ZnO quantum dots are found to be in excellent agreement with experimental resonant Raman scattering data. The derived analytical expression for phonon modes can facilitate interpretation of experimental data obtained for ZnO quantum dots.
physica status solidi (b), 2004
Viruses of cylindrical shape have recently attracted attention as templates for assembly of nanos... more Viruses of cylindrical shape have recently attracted attention as templates for assembly of nanostructured materials and as elements of nanoelectronic circuits. We have calculated the dispersion relations for the lowest vibrational frequencies of the tobacco mosaic virus (TMV) and M13 bacteriophage immersed in air or water. The radial breathing modes of TMV and M13 viruses in air (water) are 1.85 cm -1 and 6.42 cm -1 (2.10 cm -1 and 6.12 cm -1 ), respectively. Elastic vibrations of the two viruses in water are damped with the quality factor of 3.6 for the radial breathing modes. , Fax: +1 951 827 2425 R68 V. A. Fonoberov and A. A. Balandin: Low-frequency vibrational modes of viruses
Journal of Physics: Condensed Matter, 2000
Electron and hole states are studied in quantum well wires (QWWs) with a rectangular cross sectio... more Electron and hole states are studied in quantum well wires (QWWs) with a rectangular cross section. A theoretical approach is developed, within which the electronic properties of a single QWW as well as of finite and infinite planar lattices of QWWs are analysed. It is demonstrated that the ratio of effective masses in the well and in the barrier influences the dispersion law of the electron motion along the QWW axis. A six-wire lattice is studied in detail. Edge states, which can be observed in optical spectra, are revealed, when the barrier heights are different inside and outside the lattice. The miniband structure is investigated for an infinite lattice of QWWs. The evolution of electron states is analysed when the number of QWWs in the lattice increases: 1 → 6 → ∞. The calculated electron-hole pair energies are in a good agreement with the experimental data on photoluminescence in the Ga 0.47 In 0.53 As/InP QWW. § Present address: photoluminescence excitation (PLE) spectra, and the effect of lateral confinement on the valence-band mixing has been studied in . The mixing in the conduction band of Vand T-shaped QWWs has been studied in . Strained V-shaped QWWs have been described in [9] by means of the eight-band k · p scheme. An impurity located at the axis of a cylindrical QWW has also been studied . The binding energy of a hydrogenic impurity in a cylindrical QWW has been calculated as a function of the location of the impurity with respect to the axis of the QWW . The effect of the shape of a cross section on the impurity binding energies for a QWW has been investigated in . A contribution of the polaron effect to the impurity binding energy in a cylindrical QWW has been analysed in .