Change search
Refine search result
1 - 12 of 12
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the 'Create feeds' function.
  • 1.
    Baldissera, Gustavo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Oslo, Norway.
    Understanding the optical properties of ZnO1-xSx and ZnO1-xSex alloys2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 119, no 4, article id 045704Article in journal (Refereed)
    Abstract [en]

    ZnO1-xYx with chalcogen element Y exhibits intriguing optoelectronic properties as the alloying strongly impacts the band-gap energy E-g(x). In this work, we analyze and compare the electronic structures and the dielectric responses of Zn(O,S) and Zn(O, Se) alloys by means of the density functional theory and the partially self-consistent GW approach. We model the crystalline stability from the total energies, and the results indicate that Zn(O, S) is more stable as alloy than Zn(O, Se). We demonstrate also that ion relaxation strongly affects total energies, and that the band-gap bowing depends primarily on local relaxation of the bonds. Moreover, we show that the composition dependent band-gap needs to be analyzed by the band anti-crossing model for small alloying concentration, while the alloying band-bowing model is accurate for strong alloying. We find that the Se-based alloys have a stronger change in the band-gap energy (for instance, Delta E-g(0.50) = E-g(ZnO) -(E)g(x = 0.50) approximate to 2.2 eV) compared with that of the S-based alloy (Delta E-g(0.50) = 1.2 eV), mainly due to a stronger relaxation of the Zn-anion bonds that affects the electronic structure near the band edges. The optical properties of the alloys are discussed in terms of the complex dielectric function epsilon(omega) = epsilon(1)(omega) + i epsilon(2)(omega) and the absorption coefficient alpha(omega). While the large band-gap bowing directly impacts the low-energy absorption spectra, the high-frequency dielectric constant epsilon(infinity) is correlated to the intensity of the dielectric response at energies above 4 eV. Therefore, the dielectric constant is only weakly affected by the non-linear band-gap variation. Despite strong structural relaxation, the high absorption coefficients of the alloys demonstrate that the alloys have well-behaved optoelectronic properties.

  • 2.
    Baldissera, Gustavo
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Oslo University, Norway.
    Vacancy induced magnetism in WO32013In: European Physical Journal B: Condensed Matter Physics, ISSN 1434-6028, E-ISSN 1434-6036, Vol. 86, no 6, p. 273-Article in journal (Refereed)
    Abstract [en]

    The possibility to obtain ferromagnetic (FM) phase from native defects in WO3 is investigated by theoretically analyzing six different crystalline structures. The local magnetic moment from vacancies is calculated using the projector augmented wave method in combination with the local spin density approximation including a Coulomb correction (LSDA + U) of the W d-states. We find that tungsten vacancies V-W can induce a magnetic phase of similar to 3.5 mu(B)/V-W with a local magnetic moment on the oxygen atoms of at most similar to 1 mu(B)/V-W, whereas corresponding oxygen vacancies V-O have no impact on the magnetic coupling. Intriguingly, although the six crystalline structures have very comparable bonds, the magnetic moment generated by the cation vacancies is different, showing higher local magnetic moments for WO3 structures with low crystalline symmetry. The results indicate that WO3:V-W cannot induce a hole-mediated FM phase, and instead V-W in WO3 induces a local magnetic moment on the unpaired states at surrounding O atoms.

  • 3. Boström, Mathias
    et al.
    Sernelius, Bo E.
    Baldissera, Gustavo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ninham, Barry W.
    Casimir-Lifshitz interaction between ZnO and SiO2 nanorods in bromobenzene turns repulsive at intermediate separations due to retardation effects2012In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 4, p. 044702-Article in journal (Refereed)
    Abstract [en]

    We consider the interaction between a ZnO nanorod and a SiO2 nanorod in bromobenzene. Using optical data for the interacting objects and ambient we calculate the force (from short-range attractive van der Waals force to intermediate-range repulsive Casimir-Lifshitz force to long-range entropically driven attraction). The nonretarded van der Waals interaction is attractive at all separations. We demonstrate a retardation-driven repulsion at intermediate separations. At short separations (in the nonretarded limit) and at large separations (in the classical limit) the interaction is attractive. These effects can be understood from an analysis of multiple crossings of the dielectric functions of the three media as functions of imaginary frequencies.

  • 4. Castro Meira, M. V.
    et al.
    Ferreira da Silva, A.
    Baldissera, Gustavo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Freitas, J. A., Jr.
    Gutman, N.
    Sa'ar, A.
    Nur, O.
    Willander, M.
    Optical characterization of ZnO nanopillars on Si and macroporous periodic Si structure2012In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 111, no 12, p. 123527-Article in journal (Refereed)
    Abstract [en]

    ZnO nanopillars were successfully grown using both the vapor-liquid-solid and the aqueous chemical growth methods on different substrates, such as quartz, n-, and p-type non-porous Si wafer (flat) and microporous periodic Si structure (MPSiS). Scanning electron microscopy was employed to compare sample morphologies. The absorption was calculated employing the GW(0) method, based on the local density approximation, and with the projector augmented wave approach. Experiment and theory show a reasonable agreement when the shape of the optical absorption is considered. The measured absorption of ZnO nanopillars, on different substrates, is lower than that observed for ZnO films on quartz substrate, in the energy gap spectral range. A strong effect of MPSiS substrates on ZnO nanopillar properties is observed. The photoluminescence technique was also employed as an optical characterization.

  • 5. Da Silva, A. F.
    et al.
    Meira, M. V. C.
    Baldissera, Gustavo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Gutman, N.
    Sáar, A.
    Klason, P.
    Willander, M.
    Canestraro, Carla D.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Universidade Federal do Paraná, Brazil .
    Moreno, T. V.
    Roman, L. S.
    Growth, electrical and optical properties of SnO2: F on ZnO, Si and porous Si structures2009In: Nanotechnology 2009: Fabrication, Particles, Characterization, MEMS, Electronics and Photonics - Technical Proceedings of the 2009 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2009, 2009, p. 352-355Conference paper (Refereed)
    Abstract [en]

    In this work we have analyzed the optical absorption of the ZnO and SnO2:F (FTO) films and applied them in porous silicon light-emitting diodes. The absorption and energy gap were calculated by employing the projector augmented wave method [1] within the local density approximation and with a modeled on-site self-interaction-like correction potential within the LDA+U SIC [2]. Experiment and theory show a good agreement when the optical absorption and optical energy gap are considered. A layer of FTO is deposited by spray pyrolysis on top of porous Si (PSi) or ZnO/(PSi) in order to make the LEDs. The morphology and roughness of the films are analyzed by Atomic Force Microscopy before and after the FTO deposition. The electrical and optical properties are studied by characteristics curves J × V, and electroluminescence intensity versus bias.

  • 6.
    Dou, Maofeng
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Baldissera, Gustavo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Free exciton absorption in Ga1-xZnxN1-xOx alloys2012In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 350, no 1, p. 17-20Article in journal (Refereed)
    Abstract [en]

    The optical properties of the Ga1-xZnxN1-xOx alloy (x=0.0, 0.25, 0.50, 0.75, and 1.00) are studied by first-principles means, employing the GW method to describe single-particle excitations and the Bethe-Salpeter equation (BSE) to model the two-particle exciton interactions. Intriguingly, we find that the band gaps of the Ga1-xZnxN1-xOx alloy are reduced significantly compared with that of bulk ZnO and GaN. By including the electron-hole interactions within the BSE approach, the imaginary part epsilon(2)(omega) of the dielectric function shows an optical absorption enhancement in the low energy region with the exciton peak below the band gap energy. By comparing the energy difference between the exciton absorption peaks E-ex and the energy gaps E-g, we qualitatively estimate that the strength of excitonic coupling is weaker in the Ga1-xZnxN1-xOx alloy than in both GaN and ZnO. Interestingly, the exciton absorption intensity increases with respect to ZnO content.

  • 7.
    Dou, Maofeng
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Baldissera, Gustavo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    ZnO-InN nanostructures with tailored photocatalytic properties for overall water-splitting2013In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 38, no 36, p. 16727-16732Article in journal (Refereed)
    Abstract [en]

    ZnO-based electrodes for one-step photocatalytic water splitting are designed by incorporating InN. The electronic and optical properties of (ZnO)(1-x)(InN)(x) alloys and ZnO with InN-like cluster formations ZnO:(InN)(x) are analyzed by means of first-principles approaches. We calculate the energy gaps E-g, the band-edge energies relative to the vacuum level, and the optical absorption, employing the GW(o) method to describe single-particle excitations and the Bethe-Salpeter equation to model the two-particle exciton interactions. For ZnO and InN, the valence-band maximum (VBM) is E-VBM approximate to -7.3 and -5.7 eV, and the energy gap is E-g approximate to 3.3 and 0.7 eV, respectively. Incorporating InN into ZnO, the random (ZnO)(1-x)(InN)(x) alloys up-shifts the VBM and down-shifts the conduction-band minimum (CBM). In addition, the presence of InN-like clusters enhances this effect and significantly narrows the band gap. For instance, the VBM and the energy gap for 12.5% InN are E-VBM approximate to -6.5 and -6.1 eV, and E-g approximate to 2.2 and 1.9 eV for the alloy and the cluster structure, respectively. This impact on the electronic structure favors thus visible light absorption. With proper nanoclusters, the band edges straddle the redox potential levels of H+/H-2 and O-2/H2O, suggesting that ZnO-InN nanostructures can enhance the photocatalytic activity for overall solar-driven water splitting.

  • 8. Ferreira da Silva, A.
    et al.
    Chubaci, J. F. D.
    Matsuoka, M.
    Freitas, J. A.
    Tischler, J. G.
    Baldissera, Gustavo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. University of Oslo, Norway.
    Improved theoretical model of InN optical properties2014In: Physica Status Solidi (C) Current Topics in Solid State Physics, ISSN 1862-6351, Vol. 11, no 3-4, p. 581-584Article in journal (Refereed)
    Abstract [en]

    The optical properties of InN are investigated theoretically by employing the projector augmented wave (PAW) method within Green's function and the screened Coulomb interaction approximation (GWo). The calculated results are compared to previously reported calculations which use local density approximation combined with the scissors-operator approximation. The results of the present calculation are compared with reported values of the InN bandgap and with low temperature near infrared luminescence measurements of InN films deposited by a modified Ion Beam Assisted Deposition technique.

  • 9. Ferreira Da Silva, A.
    et al.
    Meira, M. V. C.
    Freitas Jr., J. A.
    Baldissera, Gustavo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Gutman, N.
    Sa'ar, A.
    Klason, P.
    Willander, M.
    Growth, optical characterization and modeling of ZnO nanorods on Si, SiC and macroporous si structure2009In: Technical Proceedings of the 2009 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2009, CRC Press, 2009, p. 206-209Conference paper (Refereed)
    Abstract [en]

    Zinc Oxide (ZnO) and Silicon Carbide (SiC) are prominent materials with large applicability such as optoelectronic nanodevices and for instance ultraviolet detectors. There is lack of important information about optical transitions beyond the indirect band gap energy (BGE) of 4H-SÍC and even more for ZnO direct BGE grown on the former material. Using vapor-liquid-solid and the aqueous chemical growth methods we have grown ZnO nanorods on different substrates, such as quartz, n- and p-type porous silicon, and n-type 4H-SÍC. Scanning electron microscopy (SEM) was employed to compare sample morphologies. The absorption was calculated employing a projector augmented wave (PAW) method. The measured absorption of ZnO nanorods, on different substrates, is lower than that observed for ZnO films on quartz substrate, in the low energy spectral range. It is observed a strong effect of 4H-SÍC substrates on ZnO nanorod properties. Experiment and theory show a good agreement when the shape of the optical absorption is considered for both materials.

  • 10. Gonzalez-Borrero, P. P.
    et al.
    Sato, F.
    Medina, A. N.
    Baesso, M. L.
    Bento, A. C.
    Baldissera, Gustavo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Niklasson, G. A.
    Granqvist, C. G.
    da Silva, A. F.
    Optical band-gap determination of nanostructured WO3 film2010In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, no 6Article in journal (Refereed)
    Abstract [en]

    The optical band-gap energy of a nanostructured tungsten trioxide film is determined using the photoacoustic spectroscopy method under continuous light excitation. The mechanism of the photoacoustic signal generation is discussed. The band-gap energy is also computed by other methods. The absorption coefficient as well as the band-gap energy of three different crystal structures of tungsten trioxide is calculated by a first-principles Green's function approach using the projector augmented wave method. The theoretical study indicates that the cubic crystal structure shows good agreement with the experimental data.

  • 11. Johansson, Malin B.
    et al.
    Baldissera, Gustavo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Valyukh, Iryna
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. University of Oslo, Norway.
    Arwin, Hans
    Niklasson, Gunnar A.
    Österlund, Lars
    Electronic and optical properties of nanocrystalline WO3 thin films studied by optical spectroscopy and density functional calculations2013In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, no 20, p. 205502-Article in journal (Refereed)
    Abstract [en]

    The optical and electronic properties of nanocrystalline WO3 thin films prepared by reactive dc magnetron sputtering at different total pressures (P-tot) were studied by optical spectroscopy and density functional theory (DFT) calculations. Monoclinic films prepared at low P-tot show absorption in the near infrared due to polarons, which is attributed to a strained film structure. Analysis of the optical data yields band-gap energies E-g approximate to 3.1 eV, which increase with increasing P-tot by 0.1 eV, and correlate with the structural modifications of the films. The electronic structures of triclinic delta-WO3, and monoclinic gamma- and epsilon-WO3 were calculated using the Green function with screened Coulomb interaction (GW approach), and the local density approximation. The delta-WO3 and gamma-WO3 phases are found to have very similar electronic properties, with weak dispersion of the valence and conduction bands, consistent with a direct band-gap. Analysis of the joint density of states shows that the optical absorption around the band edge is composed of contributions from forbidden transitions (>3 eV) and allowed transitions (>3.8 eV). The calculations show that E-g in epsilon-WO3 is higher than in the delta-WO3 and gamma-WO3 phases, which provides an explanation for the P-tot dependence of the optical data.

  • 12.
    Kumar, Mukesh
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Environmental Remediation Materials Unit, National Institute for Materials Science, Japan .
    Baldissera, Gustavo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, C.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Department of Physics, University of Oslo, Norway .
    David, D. G. F.
    da Silva, M. V. S.
    Freitas, J. A., Jr.
    Tischler, J. G.
    Chubaci, J. F. D.
    Matsuoka, M.
    Ferreira da Silva, A.
    Bulk properties of InN films determined by experiments and theory2014In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 403, p. 124-127Article in journal (Refereed)
    Abstract [en]

    Built properties of InN are determined by combining experimental and theoretical studies. In this work, we produced high quality InN film deposited on GaN templates by a modified ion beam assisted deposition technique confirmed by low temperature photoluminescence and absorption. The density of states, real and imaginary parts of the complex dielectric function and the absorption coefficient are calculated by means of first principles beyond density functional theory. The quasi particle aspect is described in the framework of a quasi particle method (the GW approximation). The calculated band gap energy is similar to 0.8 eV whereas significance in the optical absorption occurs at similar to 1.2 eV, which are consistent with both luminescence and absorption results. The Bethe-Salpeter equation is utilized to model the two particle exciton interactions, revealing a strong excitonic peak just below the absorption edge of InN.

1 - 12 of 12
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf