Endre søk
Begrens søket
1234 51 - 100 of 158
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 51.
    da Silva, A. Ferreira
    et al.
    Univ Fed Bahia, Inst Fis, BR-40210340 Salvador, BA, Brazil..
    Castro Meira, M. V.
    Univ Fed Bahia, Inst Fis, BR-40210340 Salvador, BA, Brazil.;CETEC Univ Fed Reconcavo Bahia, BR-44380000 Cruz Das Almas, BA, Brazil..
    Baldissera, Gustavo
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.). KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Gutman, N.
    Hebrew Univ Jerusalem, Racah Inst Phys, IL-91904 Jerusalem, Israel.;Hebrew Univ Jerusalem, Ctr Nanosci & Nanotechnol, IL-91904 Jerusalem, Israel..
    Sa'ar, A.
    Hebrew Univ Jerusalem, Racah Inst Phys, IL-91904 Jerusalem, Israel.;Hebrew Univ Jerusalem, Ctr Nanosci & Nanotechnol, IL-91904 Jerusalem, Israel..
    Klason, P.
    Gothenburg Univ, Dept Phys, SE-41296 Gothenburg, Sweden..
    Willander, M.
    Gothenburg Univ, Dept Phys, SE-41296 Gothenburg, Sweden.;Linkoping Univ, Dept Sci & Technol ITN, SE-60174 Norrkoping, Sweden..
    Canestraro, Carla
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Moreno, T. V.
    Univ Fed Parana, Dept Fis, BR-81531990 Curitiba, Parana, Brazil..
    Roman, L. S.
    Univ Fed Parana, Dept Fis, BR-81531990 Curitiba, Parana, Brazil..
    Growth, Electrical and Optical Properties of SnO2:F on ZnO, Si and Porous Si Structures2009Inngår i: NANOTECH CONFERENCE & EXPO 2009, VOL 1, TECHNICAL PROCEEDINGS: NANOTECHNOLOGY 2009: FABRICATION, PARTICLES, CHARACTERIZATION, MEMS, ELECTRONICS AND PHOTONICS / [ed] Laudon, M Romanowicz, B, CRC PRESS-TAYLOR & FRANCIS GROUP , 2009, s. 352-+Konferansepaper (Fagfellevurdert)
    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-S/C [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 x V, and electroluminescence intensity versus bias.

  • 52. da Silva, Antonio Ferreira
    et al.
    Pernot, Julien
    Contreras, Sylvie
    Sernelius, Bo E.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Camassel, Jean
    Electrical resistivity and metal-nonmetal transition in n-type doped 4H-SiC2006Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 24Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electrical resistivity of 4H-SiC doped with nitrogen is analyzed in the temperature range 10-700 K for nitrogen concentrations between 3.5x10(15) and 5x10(19) cm(-3). For the highest doped samples, a good agreement is found between the experimental resistivity and the values calculated from a generalized Drude approach at similar dopant concentration and temperature. From these results, the critical concentration (N-c) of nitrogen impurities which corresponds to the metal-nonmetal transition in 4H-SiC is deduced. We find N-c similar to 10(19) cm(-3).

  • 53. Dantas, N. S.
    et al.
    de Almeida, J. S.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    da Silva, A. F.
    Novel semiconducting materials for optoelectronic applications: Al1-xTlxN alloys2008Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, nr 12Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We proprose the ternary semiconducting Al1-xTlxN alloys as new material for optoelectronic applications. Ab initio calculations have been performed to study structural, electronic, and optical properties of the theoretically designed thallium-aluminum based nitride alloys. We found that the lattice constants vary linearly with thallium composition whereas the band gap and absorption edge span from ultraviolet to infrared energy region by increasing thallium content which make the predicted material interesting for infrared optical devices among other technological applications.

  • 54.
    David, Denis
    et al.
    Univ Fed Bahia, Inst Fis, Campus Ondina, BR-40210340 Salvador, BA, Brazil. lnoor, Hatim; Nur, Omer; Willander, Magnus.
    Alnoor, Hatim
    Silva Santana, Victor Mancir
    Bargiela, Pascal
    Nur, Omer
    Willander, Magnus
    Baldissera, Gustavo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Univ Oslo, Dept Phys, POB 1048 Blindern, NO-0316 Oslo, Norway.
    Silva, Antonio Ferreira
    Optical properties from photoelectron energy-loss spectroscopy of low-temperature aqueous chemically synthesized ZnO nanorods grown on Si2019Inngår i: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 34, nr 4, artikkel-id 045019Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The optical properties of zinc oxide (ZnO) nanorods (NRs) synthesized by the low-temperature aqueous chemical method on top of silicon (Si) substrate have been investigated by means of photoelectron energy loss spectroscopy (PEELS). The ZnO NRs were obtained by the low temperature aqueous chemical synthesis on top of Si substrate. The measured valence band, the dynamical dielectric functions and optical absorption of the material show a reasonable agreement when the trending and shape of the theoretical calculations are considered. A first-principle calculation based on density functional theory (DFT) was performed using the partially self-consistent GW approximation (scGW(0)) and compared to the experimental results. The application of these two techniques brings a new analysis of the electronic properties of this material. The experimental results regarding the density of states (DOS) obtained for the valence band using x-ray photoelectron spectroscopy (XPS) was found to be consistent with the theoretical calculated value. Due to this consistency, the same wavefunctions was then employed to calculate the dielectric function of the ZnO NRs. The experimentally extracted dielectric function was also consistent with the calculated values.

  • 55. Davydova, A.
    et al.
    Eriksson, J.
    Chen, R.
    Rudisch, K.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. University of Oslo, Norway.
    Scragg, J. J. S.
    Thio-olivine Mn2SiS4 thin films by reactive magnetron sputtering: Structural and optical properties with insights from first principles calculations2018Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 152, s. 110-118Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thio-olivines such as (Fe,Mn)2(Si,Ge)S4 have been proposed as candidate earth-abundant materials for single and multi-junction solar cells. In this work we present the first investigation of Mn2SiS4thin films prepared by reactive magnetron sputtering deposition, using a composition grading approach. Precursor instability in ambient conditions is observed, revealing the oxidation/hydrolysis of Si–S bonds from the as-deposited film as a blocking mechanism for the ternary compound formation. Structural, morphological and optical properties of the annealed Mn2SiS4 films are reported for the first time. Resulting Mn2SiS4 films have orthorhombic Pnma structure and are polycrystalline. Raman active modes at 325 nm excitation are observed at 262, 320, 400 and 464 cm−1. From room temperature photoluminescence at 532 nm excitation the band gap is estimated to be about 1.9 eV, but a high optical absorption coefficient of >104 cm−1 was only obtained at E > 2.8 eV. First principles calculations are used for better understanding of opto-electronic properties. From the calculations, Mn2SiS4 is suggested to have a band gap of about 1.73–1.86 eV depending on the magnetic configuration of Mn and slight indirect nature. The slow absorption onset is interpreted by strong anisotropy due to one of the components of the dielectric function.

  • 56. de Almeida, J. S.
    et al.
    da Silva, A. J.
    Norman, P.
    Persson, Clas
    Ahuja, R.
    da Silva, A. F.
    Optical properties of donor-triad cluster in GaAs and GaN2002Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 81, nr 17, s. 3158-3160Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of the transition energy of three-donor clusters on far infrared absorption in n-type semiconductor materials has been investigated by a multiconfigurational self-consistent-field model calculation and applied to GaAs and GaN systems. We show that it is crucial to consider the many-particle correlation effects within three-donor clusters. With electron correlation taken into account, the present results support the interpretation of a very recent unidentified peak energy observed in absorption measurement of GaN as due to electronic transitions in these clusters. We also corroborate the suggestion that the X line in GaAs arises from such transitions.

  • 57.
    Doe, Maofeng
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Boström, Mathias
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Ultrathin nanosheet induced repulsive Casimir force with two transition pointsManuskript (preprint) (Annet vitenskapelig)
  • 58.
    Doe, Maofeng
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering. Department of Physics, University of Oslo, Norway .
    Analysis of the Semi local States in ZnO-InN Compounds2014Inngår i: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 14, nr 10, s. 4937-4943Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    ZnO alloys are extensively explored for the developments of optoelectronics. In this work we analyze the rather unconventional type of ZnO-based compound ZnOX (ZnO)(1y)Xy with X = InN. The compound forms alloy with ZnO and/or assembles cluster structures in the ZnO host. Importantly, this type of alloy benefits from being isovalent which implies a more stable crystalline structure, and at the same time it benefits from the oxynitride anion-alloying that alters the optoelectronic properties. Theoretical studies reveal that incorporating InN in ZnO strongly narrows the fundamental band gap energy Eg. For example, the (ZnO)(0.875)(InN)(0.125) alloy has the gap energy E-g = 2.20 eV = E-g(ZnO) 1.14 eV. The origin of this effect is a hybridization of the anion N 2p-like and O 2p-like orbitals. Intriguingly, the presence of InN nanoclusters enhances this effect and narrows the gap further, and moreover, the nanostructured configurations show more disperse energy distribution of the hybridized anion states compared with the random alloy. Nanoclustering affects the ZnO host more compared to structures with more random distribution of the InN dimers. On the basis of the different characters of the alloys and the nanostructures, we conclude that fine-tuned synthesizing of the (ZnO)(1-y)(InN)(y) alloys can be beneficial for a variety of novel nanosystems for optoelectronic and photoelectrochemical applications.

  • 59. Dong, C. L.
    et al.
    Persson, Clas
    KTH, Tidigare Institutioner, Materialvetenskap.
    Vayssieres, L.
    Augustsson, A.
    Schmitt, T.
    Mattesini, M.
    Ahuja, Rajeev
    KTH, Tidigare Institutioner, Materialvetenskap.
    Chang, C. L.
    Guo, J. H.
    Electronic structure of nanostructured ZnO from x-ray absorption and emission spectroscopy and the local density approximation2004Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, nr 19Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    O 1s absorption spectroscopy (XAS) and O Kalpha emission spectroscopy (XES) were performed to study the electronic structure of nanostructured ZnO. The band gap is determined by the combined absorption-emission spectrum. Resonantly excited XES spectra showing an energy dependence in the spectral shape reveal the selected excitations to the different Zn 3d, 4s, and 4p states in hybridization with O 2p states. The partial density of state obtained from local density approximation (LDA) and LDA+U calculations are compared with the experimental results. The LDA+U approach is suitable to correct LDA self-interaction error of the cation d states. The atomic eigenstates of 3d in zinc and 2p in oxygen are energetically close, which induces the strong interaction between Zn 3d and O 2p states. This anomalous valence band cation-d-anion-p hybridization is verified by taking into account the strong localization of the Zn 3d states.

  • 60.
    Dou, Maofeng
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Baldissera, Gustavo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Free exciton absorption in Ga1-xZnxN1-xOx alloys2012Inngår i: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 350, nr 1, s. 17-20Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 61.
    Dou, Maofeng
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Baldissera, Gustavo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    ZnO-InN nanostructures with tailored photocatalytic properties for overall water-splitting2013Inngår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 38, nr 36, s. 16727-16732Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 62.
    Dou, Maofeng
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Lou, Fei
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Optik och Fotonik, OFO.
    Boström, Mathias
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Brevik, Iver
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Casimir quantum levitation tuned by means of material properties and geometries2014Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 89, nr 20, s. 201407-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Casimir force between two surfaces is attractive in most cases. Although stable suspension of nano-objects has been achieved, the sophisticated geometries make them difficult to be merged with well-established thin film processes. We find that by introducing thin film surface coating on porous substrates, a repulsive to attractive force transition is achieved when the separations are increased in planar geometries, resulting in a stable suspension of two surfaces near the force transition separation. Both the magnitude of the force and the transition distance can be flexibly tailored though modifying the properties of the considered materials, that is, thin film thickness, doping concentration, and porosity. This stable suspension can be used to design new nanodevices with ultralow friction. Moreover, it might be convenient to merge this thin film coating approach with micro- and nanofabrication processes in the future.

  • 63.
    Dou, Maofeng
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Band gap reduction and dielectric function of Ga1-xZnxN1-xOx and In1-xZnxN1-xOx alloys2012Inngår i: Physica Status Solidi. A: Applications and Materials Science (Print), ISSN 1862-6300, Vol. 209, nr 1, s. 75-78Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The band gap reductions, dielectric functions and absorption coefficients of the Ga1-xZnxN1-xOx and In1-xZnxN1-xOx (x=0.00, 0.25, 0.50, 0.75, and 1.00) alloys were calculated, employing the partial self-consistent GW approximation. As a comparison, the local density approximation (LDA) and the Heyd-Scueria-Ernzerhof (HSE) hybrid functional were also used to calculate the gap reduction. Both Ga1-xZnxN1-xOx and In1-xZnxN1-xOx alloys show strong band gap bowing. As a result, the band gap energy in Ga1-xZnxN1-xOx is reduced by E-g(GaN) E-g (Ga1-xZnxN1-xOx) - 1.61, 2.01 and 1.91 eV for x=0.25, 0.50, and 0.75, respectively. This allows optoelectronic devices based on GaN and ZnO with more efficient absorption or emission of light in the visible light range. The calculated dielectric functions and absorption spectra demonstrate that the band gap reduction enhances the optical absorption around the 2.5 eV region. Interestingly, the In1-xZnxN1-xOx alloy with x=0.25 has the large optical absorption coefficient in the energy region 0.69-6.0 eV, and the alloy has very good absorption at 2-3 eV.

  • 64.
    Dou, Maofeng
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Comparative study of rutile and anatase SnO2 and TiO2: Band-edge structures, dielectric functions, and polaron effects2013Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, nr 8, s. 083703-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    SnO2 and TiO2 polymorphs (rutile and anatase) are oxides with similar crystal structures, comparable bond lengths, and electronic band-gap energies, but different optical and electronic properties. In this work, we have studied the origin of these differences from the band-edge structures and electron-phonon coupling. The band-edge structures, dielectric functions, and effective masses were calculated by means of a first-principles approach with the exchange-correlation described by a hybrid functional. The phonon frequencies were calculated using a finite displacement method with non-analytic correction, and the phonon contribution to the dielectric functions was modeled using a multi-phonon Lorentz model. The calculated band-edge structures show that the bottommost conduction bands are highly dispersive for SnO2 polymorphs but flat dispersive for TiO2 polymorphs because of the strongly localized Ti-3d states. Consequently, SnO2 polymorphs present small effective electron masses and a weak optical absorption, whereas the TiO2 polymorphs present a strong optical absorption and larger effective electron masses. Due to the strong ionic bonds, TiO2 have larger Born effective charges than that of SnO2, result in stronger polaron effect and larger average static dielectric constant epsilon(0). For example, epsilon(0) = 115 for rutile TiO2 whereas epsilon(0) = 9.5 for rutile SnO2. Moreover, it is interesting to note that the epsilon(0) in rutile TiO2 is much larger than in anatase TiO2 (epsilon(0) = 28) although they have the same chemical compositions, which related to the local structure distortion of the phases.

  • 65.
    Dou, Maofeng
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Nanostructured ZnO-X alloys with tailored optoelectronic properties for solar-energy technologies2013Inngår i: Materials Research Society Symposium Proceedings: Volume 1558, Materials Research Society, 2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Alloying ZnO with isovalent compounds allows tailoring the material's optoelectronic properties. In this work, we theoretically analyze the ZnO-based alloys ZnO-X ≡ (ZnO)1-x(X)x where X = GaN and InN, employing a first-principles Green's function method GW0 based on the density functional approach. Since the alloy compounds are isovalent to ZnO, we find relatively small distortion of the crystalline structure, however, nanocluster structures are expected to be present in the alloy. ZnO-X reveal intriguing optoelectronic properties. Incorporating GaN or InN in ZnO strongly narrows the energy gap. The band gap energy is reduced from Eg = 3.34 eV in intrinsic ZnO to ∼2.17 and ∼1.89 eV in ZnO-X by alloying ZnO with 25% GaN and InN, respectively. Moreover, clustering enhances the impact on the electronic structure, and the gap energy in ZnO-InN is further reduced to 0.7-1.5 eV if the 25% compound contains nanoclusters. The dielectric function - 2(ω) varies weakly in ZnO-GaN with respect to alloy composition, while it varies rather strongly in ZnO-InN. Hence, by properly growing and designing ZnO-X, the alloy can be optimized for a variety of novel integrated optoelectronic nano-systems.

  • 66.
    Dou, Maofeng
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Yu, Tianhang
    Jin, Shengming
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Adjusting the Electronic and Optical Properties of Mesoporous MCM-41 Materials by Ti Doping2013Inngår i: Sensor Letters, ISSN 1546-198X, Vol. 11, nr 8, s. 1530-1534Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Solid mesoporous materials with ordered pore structures can be used for catalysis, genome sequencing, and drug delivering etc. The common method of synthesizing Ti doped mesoporous silica is to use costly ethyl silicate and tetrabutyl titanate as inorganic sources. In this work, however, low cost water glass and TiCl4 were used as the inorganic sources. Pore structures were studied by small angle X-ray diffraction, transmission electron microscopy, and N-2 adsorption-desorption. This Ti doped mesoporous material has binary mesopore structures with preferable pore sizes of 2.60 and 3.85 nm, respectively. Results from the ultraviolet-visible spectroscopy as well as density functional calculation employing a screened hybrid functional indicate that the mespore matrix contains tetrahedral coordinated Ti dopants (Ti-Si) and oxygen vacancies (V-O). The electron transitions from occupied V-O to the unoccupied Ti-Si contribute to the red-shift of the optical absorption edge. The hybrid potential describes fairly accurately the electronic structure and optical absorption, and we find an overall good qualitative agreement with the experimental characterization.

  • 67. Fernandez, J. R. L.
    et al.
    Araujo, C. M.
    da Silva, A. F.
    Leite, J. R.
    Sernelius, B. E.
    Tabata, A.
    Abramof, E.
    Chitta, V. A.
    Persson, Clas
    Ahuja, R.
    Pepe, I.
    As, D. J.
    Frey, T.
    Schikora, D.
    Lischka, K.
    Electrical resistivity and band-gap shift of Si-doped GaN and metal-nonmetal transition in cubic GaN, InN and AlN systems2001Inngår i: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 231, nr 3, s. 420-427Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The critical impurity concentration N-c of the metal-nonmetal (MNM) transition for the cubic GaN, InN and AIN systems. is calculated using the following two different criteria: vanishing of the donor binding energy and the crossing point between the energies in the metallic and insulating phases. A dielectric function model with a Lorentz-Lorenz correction is used for the insulating phase. The InN presents an order of magnitude increase in N-c as compared to the other two systems. The electrical resistivity of the Si-donor system GaN is investigated theoretically and experimentally from room temperature down to 10K. It presents a metallic character above a certain high impurity concentration identified as N-c. The samples were grown by plasma assisted molecular beam epitaxy (MBE) on GaAs (0 0 1) substrate. The model calculation is carried out from a recently proposed generalized Drude approach (GDA) presenting a very good estimation for the metallic region. The band-gap shift (BGS) of Si-doped GaN has also been investigated above the MNM transition where this shift is observed. Theoretical and experimental results have a rough agreement in a range of impurity concentration of interest.

  • 68. Ferreira da Silva, A.
    et al.
    Chubaci, J. F. D.
    Matsuoka, M.
    Freitas, J. A.
    Tischler, J. G.
    Baldissera, Gustavo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. University of Oslo, Norway.
    Improved theoretical model of InN optical properties2014Inngår i: Physica Status Solidi (C) Current Topics in Solid State Physics, ISSN 1862-6351, Vol. 11, nr 3-4, s. 581-584Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 69. Ferreira Da Silva, A.
    et al.
    Meira, M. V. C.
    Freitas Jr., J. A.
    Baldissera, Gustavo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Gutman, N.
    Sa'ar, A.
    Klason, P.
    Willander, M.
    Growth, optical characterization and modeling of ZnO nanorods on Si, SiC and macroporous si structure2009Inngår i: Technical Proceedings of the 2009 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2009, CRC Press, 2009, s. 206-209Konferansepaper (Fagfellevurdert)
    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.

  • 70. Fiedler, Johannes
    et al.
    Thiyam, Priyadarshini
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering. University of Oslo, Norway.
    Kurumbail, Anurag
    Burger, Friedrich A.
    Walter, Michael
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. University of Oslo, Norway.
    Brevik, Iver
    Parsons, Drew F.
    Bostrom, Mathias
    Buhmann, Stefan Y.
    Effective Polarizability Models2017Inngår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 121, nr 51, s. 9742-9751Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Theories for the effective polarizability of a small particle in a medium are presented using different levels of approximation: we consider the virtual cavity, real cavity, and the hard-sphere models as well as a continuous interpolation of the latter two. We present the respective hard-sphere and-cavity radii as obtained from density-functional simulations as well as the resulting effective polarizabilities at discrete Matsubara frequencies. This enables us to account for macroscopic media in van der Waals interactions between molecules in water and their Casimir-Polder interaction with an interface.

  • 71. Gonzalez-Borrero, P. P.
    et al.
    Sato, F.
    Medina, A. N.
    Baesso, M. L.
    Bento, A. C.
    Baldissera, Gustavo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Niklasson, G. A.
    Granqvist, C. G.
    da Silva, A. F.
    Optical band-gap determination of nanostructured WO3 film2010Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, nr 6Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 72. Guo, J. H.
    et al.
    Vayssieres, L.
    Persson, Clas
    Ahuja, R.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Nordgren, J.
    Polarization-dependent soft-x-ray absorption of a highly oriented ZnO microrod-array2005Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 17, nr 1, s. 235-240Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polarization-dependent x-ray absorption measurements were performed on a crystalline ZnO three-dimensional array consisting of highly oriented microrods as well as on particulate thin film consisting of monodisperse spherical nanoparticles. Strong anisotropic effects have been observed for the highly oriented ZnO rods, unlike for the isotropic spherical ones. Full-potential calculations of orbital-resolved x-ray absorption of a ZnO wurtzite periodic crystal, including the Zn 3d as part of the valence states, shows a very good agreement with the experimental findings. Comprehensive fundamental knowledge of the electronic structure of ZnO is obtained by probing and demonstrating the orbital symmetry of oxygen and its contribution to the conduction band of this important II-VI semiconductor.

  • 73. Guo, J. H.
    et al.
    Vayssieres, L.
    Persson, Clas
    Ahuja, R.
    Johansson, Börje
    Nordgren, J.
    Polarization-dependent soft-x-ray absorption of highly oriented ZnO microrod arrays2002Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 14, nr 28, s. 6969-6974Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polarization-dependent x-ray absorption measurements were performed on crystalline ZnO three-dimensional arrays consisting of highly oriented microrods as well as on particulate thin films consisting of monodisperse spherical nanoparticles. Strong anisotropic effects have been observed for the highly oriented ZnO rods, but not for the isotropic spherical nanoparticles. Full-potential calculations of the orbital-resolved x-ray absorption of a ZnO wurtzite periodic crystal, including Zn 3d among the valence states, show very good agreement with the experimental findings. Comprehensive fundamental knowledge of the electronic structure of ZnO is obtained by probing and demonstrating the orbital symmetry of oxygen and its contribution to the conduction band of this important II-VI semiconductor.

  • 74. Han, Sung-Ho
    et al.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hasoon, Falah S.
    Al-Thani, Hamda A.
    Hermann, Allen M.
    Levi, Dean H.
    Optical properties and electronic structures of (4CuInSe(2))(y)(CuIn5Se8)(1-y)2006Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, nr 8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Spectroscopic ellipsometric measurements of thin polycrystalline (4CuInSe(2))(y)(CuIn5Se8)(1-y) films reveal that there are important differences in optical properties and electronic structures between alpha-phase CuInSe2 and Cu-poor CuInSe2. We report the optical functions of thin-film polycrystalline (4CuInSe(2))(y)(CuIn5Se8)(1-y) and describe how they change depending on the degree of Cu deficiency. We find a reduction in the absorption strength in the spectral region of 1-3 eV for Cu-poor CuInSe2. This reduction can be explained in terms of density of the Cu 3d states in CuInSe2. Cu-poor CuInSe2 samples show an increase in band gap due to reduced p-d interaction. We find that the reduction in the amplitudes of E-0(A,B,C) transitions at the Gamma point and E-1(A,B) transitions at the N point are due to Cu deficiency. Local density approximation calculations with a modeled on-site self-interaction correction of the absorption coefficients of Cu8In8Se16 (CuInSe2), Cu5In9Se16 (CuIn3Se5-like), and Cu2In10Se16 (CuIn5Se8) are in good agreement with those of thin-film polycrystalline CuInSe2 samples with 24.1, 15.6, and 9.1 at. % Cu, respectively.

  • 75. Hones, K.
    et al.
    Eickenberg, M.
    Siebentritt, S.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Polarization of defect related optical transitions in chalcopyrites2008Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 93, nr 9Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the symmetry of shallow acceptors in Cu chalcopyrites by polarization dependent photoluminescence measurements and density functional calculations. We determine the influence of the band symmetry versus the site symmetry. The polarization of the emitted or absorbed light is parallel to the c-axis in the case of CuGaSe2 and perpendicular to the c-axis in the case of CuInSe2. The symmetry of the defects depends in each case on the symmetry of the topmost band. Neither does the site symmetry affect the defect symmetry nor do the defects change the symmetry of the band.

  • 76.
    Huang, Dan
    et al.
    Guangxi Univ, Guangxi Coll & Univ Key Lab Novel Energy Mat & Re, Guangxi Novel Battery Mat Res Ctr Engn Technol,Sc, Guangxi Key Lab Proc Non Ferrous Metall & Feature, Nanning 530004, Peoples R China.;Guilin Univ Elect Technol, Sch Mat Sci & Engn, Guangxi Collaborat Innovat Ctr Struct & Property, Guilin, Peoples R China..
    Jiang, Jing-Wen
    Guangxi Univ, Guangxi Coll & Univ Key Lab Novel Energy Mat & Re, Guangxi Novel Battery Mat Res Ctr Engn Technol,Sc, Guangxi Key Lab Proc Non Ferrous Metall & Feature, Nanning 530004, Peoples R China..
    Guo, Jin
    Guangxi Univ, Guangxi Coll & Univ Key Lab Novel Energy Mat & Re, Guangxi Novel Battery Mat Res Ctr Engn Technol,Sc, Guangxi Key Lab Proc Non Ferrous Metall & Feature, Nanning 530004, Peoples R China.;Guilin Univ Elect Technol, Sch Mat Sci & Engn, Guangxi Collaborat Innovat Ctr Struct & Property, Guilin, Peoples R China..
    Zhao, Yu-Jun
    South China Univ Technol, Dept Phys, Guangzhou 510640, Guangdong, Peoples R China.;South China Univ Technol, Key Lab Adv Energy Storage Mat Guangdong Prov, Guangzhou 510640, Guangdong, Peoples R China..
    Chen, Rongzhen
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    General rules of the sub-band gaps in group-IV (Si, Ge, and Sn)-doped I-III-VI2-type chalcopyrite compounds for intermediate band solar cell: A first-principles study2018Inngår i: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 236, s. 147-152Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, we have investigated Si, Ge and Sn doped at III-site(Ga or Al) in CuGaSe2, CuAlSe2, AgGaSe2, and AgAlSe2 as the candidates for intermediate band solar cell (IBSC), and demonstrated that the absolute energy levels of the intermediate band from a given group IV dopant in various Se-based chalcopyrite hosts do not show remarkable changes. This is resulted from the fact that the intermediate band originates from the same anti-bonding state of IV-s and Se-p states. The intermediate bands sequence of Ge* < Sn* < Si* from the different dopants in the same chalcopyrite host is explained by a simple model based on the atomic orbital energy and bond interaction. Furthermore, Sn-doped CuAlSe2 with the suitable main-gap and sub-gaps has been selected out as a potential candidate for IBSC, and alloying with isovalent cations to adjust to proper sub-band gaps has been demonstrated in Ge-doped (Ag,Cu)AlSe2 and Ag(Ga,Al)Se-2.( )

  • 77. Huang, Dan
    et al.
    Jiang, Jing-Wen
    Guo, Jin
    Zhao, Yu-Jun
    Chen, Rongzhen
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Group-IV (Si, Ge, and Sn)-doped AgAlTe2 for intermediate band solar cell from first-principles study2017Inngår i: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 32, nr 6, s. 065007-065014, artikkel-id 065007Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Earlier studies of chalcopyrites as the absorber for intermediate band solar cells (IBSCs) mainly focused on Cu-based compounds, whose intermediate band is usually empty due to its intrinsic p-type conductivity. This is not beneficial to the two sub-bandgap absorptions. In this paper, we demonstrate that the intermediate bands in group IV (Si, Ge, and Sn) doped AgAlTe2 are delocalized and mainly contributed by the anti-bonding state of group-IV elements s state and Te-p state. Overall, we suggest that Sn-doped AgAlTe2 should be a promising absorber candidate for IBSCs based on the theoretical efficiency and defect stability.

  • 78.
    Huang, Dan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Band gap change induced by defect complexes in Cu2ZnSnS42013Inngår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 535, s. 265-269Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Understanding the impact on the electronic and optical properties of kesterite Cu2ZnSn(S,Se)(4) due to the presence of native defects is crucial for designing and manufacturing efficient solar cells. In this work, we complement earlier published theoretical studies by investigating the change in the Cu2ZnSnS4 band gap energy induced by the dominating isovalent (Zn (Cu) + Cu-Zn) and (Zn-Cu + V-Cu) defect complexes and the corresponding larger [(Zn-Cu + Cu-Zn)+(Zn-Cu + V-Cu)] complex. The study is based on the generalized gradient approximation with corrections for on-site Coulomb interactions (GGA + U) and the Heyd-Scuseria-Ernzerh hybrid functional method (HSE06) within the first-principles density functional theory. We find that (Zn-Cu + Cu-Zn) and (Zn-Cu + V-Cu) affect the band gap energies in an opposite way: (Zn-Cu + Cu-Zn) decreases the gap whereas (Zn-Cu + V-Cu) increases the gap. However, there is a strong correlation between these two defect complexes. The presence of the Cu-poor (Zn-Cu + V-Cu) defect complex lowers the formation energy of the antisite (Zn-Cu + Cu-Zn) defect complex in close configuration, and vice versa. Thereby, and considering the opposite effect on the band gap for (Zn-Cu + Cu-Zn) and (Zn-Cu + V-Cu), our results indicate that the band gap energy will be compensated and stabilized in Cu-poor Cu2ZnSnS4. We discuss the underlying mechanisms behind the band gap physics of the considered isovalent defect complexes.

  • 79.
    Huang, Dan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Photocatalyst AgInS2 for active overall water-splitting: A first-principles study2014Inngår i: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 591, s. 189-192Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic structure of photocatalyst AgInS2 has been investigated by first-principles calculation. Our results demonstrate that the band edge positions of chalcopyrite and orthorhombic AgInS2 straddle the water redox potentials. From the band offset calculation, we find that Ga-doping of AgInS2 shifts the conduction band minimum upwards, whereas Cu-doping of AgInS2 shifts the valence band maximum upwards. By (Ag,Cu)(In,Ga)S-2 alloying one can thereby tailor both the band edge positions and the band gap energy, and this effect provides an approach to optimize the band properties for overall water splitting.

  • 80.
    Huang, Dan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Stability of the bandgap in Cu-poor CuInSe22012Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 24, nr 45, s. 455503-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent photoluminescence studies report that the bandgap energy E-g approximate to 1.0 eV of CuInSe2 is stable for Cu-poor compounds [Cu]/[In] < 1, despite the fact that Cu vacancies and (In-Cu + 2V(Cu)) complexes increase the energy gap. In this work, the impact on E-g due to the presence of native defects is analyzed using a screened hybrid density functional approach. We demonstrate that the formation energy of neutral (Cu-In + In-Cu) anti-site dimers decreases for CuInSe2 compounds when [Cu]/[In] decreases. This is explained in terms of the octet rule for the Se atoms next to the (In-Cu + 2V(Cu)) defects. As a consequence, Cu-poor CuInSe2 involves the large [(In-Cu + 2V(Cu)) + (Cu-In + In-Cu)] complexes where the anti-site defects stabilize E-g, in agreement with experimental findings.

  • 81.
    Huang, Dan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Ju, Zhiping
    Dou, Maofeng
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Yao, Chunmei
    Guo, Jin
    Investigation on AgGaSe2 for water splitting from first-principles calculations2014Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 105, nr 3, s. 37007-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic structure of AgGaSe2 has been investigated as a photocatalyst candidate by first-principles calculation. Our results demonstrate that the band edge positions of bulk AgGaSe2 straddle the water redox potentials. From the band offset calculation, we find that Al-doping of AgGaSe2 shifts the conduction band minimum upwards, whereas Cu-doping of AgGaSe2 shifts the valence band maximum upwards. By (Ag, Cu)(Ga, Al)Se-2 alloying one can thereby tailor both the band edge positions and the band gap energy, and this effect provides an approach to optimize the band properties for overall water splitting. Moreover, AgGaSe2 forms a suitable junction with CuGaSe2 with a type-II band offset, which facilitates electron-hole separation. The AgGaSe2 and CuGaSe2 junction can be designed as a tandem photoelectrochemical device to improve the photocatalytic properties of the system.

  • 82. Ivanov, I. G.
    et al.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Henry, A.
    Janzén, E.
    Wave-function symmetry and the properties of shallow P donors in 4H SiC2009Inngår i: Silicon Carbide and Related Materials 2007, Pts 1 and 2, Trans Tech Publications Inc., 2009, s. 445-448Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A new investigation on the optical properties of the phosphorus-bound excitons is presented. Arguments are given in favor of the possibility of degenerate donor state for phosphorus substituting Si atom on hexagonal site. On the base of a simple model, it is shown that the experimental spectra also provide evidence in favor of this possibility. The possibility for violation of the Haynes rule in the case of phosphorus donors on the two inequivalent sites is indicated.

  • 83. Jayakumar, O. D.
    et al.
    Sudakar, C.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Salunke, H. G.
    Naik, R.
    Tyagi, A. K.
    Enhancement of ferromagnetic properties in Zn0.95Co0.05O nanoparticles by indium codoping: An experimental and theoretical study2010Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 97, nr 23, s. 232510-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nanoparticles of Zn0.95-xCo0.05InxO (x = 0.0 to 0.07) were synthesized by the pyrolitic reaction of sol-gels obtained from respective metal precursors. X-ray diffraction and high-resolution transmission electron microscopy studies confirm the formation of impurity-free wurtzite type ZnO structure for all the compositions. While pristine ZnO is diamagnetic, Zn0.95Co0.05O nanoparticles show weak paramagnetic behavior at room temperature. When "In." is codoped with Co with x = 0.0 to 0.07 in Zn0.95-xCo0.05InxO, a systematic increase in magnetic moment is observed up to x = 0.07. First-principles modeling supports that the ferromagnetic phase become more favorable at higher indium doping concentrations.

  • 84. Jayakumar, O. D.
    et al.
    Sudakar, C.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Sudarsan, V.
    Naik, R.
    Tyagi, A. K.
    Tunable Ferromagnetism accompanied by Morphology Control in Li-doped Zn0.97Ni0.03O2010Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, nr 41, s. 17428-17433Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report morphological and ferromagnetic property control in ZnO nanorod structures by an optimum doping of Ni and Li. Nanostructures of Zn0.97-xNi0.03LixO (x = 0, 0.03, 0.05, 0.08, and 0.10) are prepared by a solvothermal method. High aspect ratio (5-15) ZnO nanorods transform to particles (with 1-3 aspect ratio) influenced by 3 at. % Ni substitution in ZnO (Zn0.97Ni0.03O). It is remarkable to note that the Zn1.97Ni0.03O particles completely retain the nanorod shape with significantly increased aspect ratio (15-30) when 3 at.c/a Li ions are codoped in (Zn0.99Li0.03Ni0.30O). Li substitution tits enhances ferromagnetism with largest magnetization (0.8 emu.g(-1)) observed for Zn0.94Li0.03Ni0.03O. For Li concentration >3 at.%, the aspect ratio as well as the magnetization decreased considerably. These experimental observations are explained by first-principles modeling. At low Li-on-Zn acceptor concentrations, the total magnetization is increased by lower Ni d-state populations, whereas at higher Li concentrations the population of ZnO host states decreases the ferromagnetism by induced magnetic moments on the oxygens. We discuss the significant implications of these results on the nanorods structures of room temperature ferromagnetic materials, which are expected to play pivotal role in developing spintronic devices.

  • 85. Jayakumar, O. D.
    et al.
    Sudakar, C.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Sudarsan, V.
    Sakuntala, T.
    Naik, R.
    Tyagi, A. K.
    1D Morphology Stabilization and Enhanced Magnetic Properties of Co: ZnO Nanostructures on Codoping with Li: A Template-Free Synthesis2009Inngår i: Crystal Growth & Design, ISSN 1528-7483, E-ISSN 1528-7505, Vol. 9, nr 10, s. 4450-4455Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    ID natiostructures of Zn1-xCoxO (x = 0, 0.03 and 0.05) and Co and Li codoped ZnO (Zn0.85Li0.10Co0.05O) were prepared by a soft chemical method. We report a very interesting observation of morphological control and transformation of ZnO nanorods to spherical particles induced by Co substitution. It is also remarkable to note that the morphology completely reverts back to rod shape by Li incorporation. In addition to this unusual observation, the Li incorporation enhances the room-temperature ferromagnetic (RTFM) properties. These experimental observations are well-supported by theory work as well. These results are significant, as the I D RTFM will have implications in spintronic devices.

  • 86. Johansson, Malin B.
    et al.
    Baldissera, Gustavo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Valyukh, Iryna
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. 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 calculations2013Inngår i: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 25, nr 20, s. 205502-Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 87. Klein, T.
    et al.
    Achatz, P.
    Kacmarcik, J.
    Marcenat, C.
    Gustafsson, F.
    Marcus, J.
    Bustarret, E.
    Pernot, J.
    Omnes, F.
    Sernelius, Bo E.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    da Silva, A. Ferreira
    Cytermann, C.
    Metal-insulator transition and superconductivity in boron-doped diamond2007Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 75, nr 16, s. 165313-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on a detailed analysis of the transport properties and superconducting critical temperatures of boron-doped diamond films grown along the {100} direction. The system presents a metal-insulator transition (MIT) for a boron concentration (n(B)) on the order of n(c)similar to 4.5x10(20) cm(-3), in excellent agreement with numerical calculations. The temperature dependence of the conductivity and Hall effect can be well described by variable range hopping for n(B)< n(c) with a characteristic hopping temperature T-0 strongly reduced due to the proximity of the MIT. All metallic samples (i.e., for n(B)>n(c)) present a superconducting transition at low temperature. The zero-temperature conductivity sigma(0) deduced from fits to the data above the critical temperature (T-c) using a classical quantum interference formula scales as sigma(0)proportional to(n(B)/n(c)-1)(nu) with nu similar to 1. Large T-c values (>= 0.4 K) have been obtained for boron concentration down to n(B)/n(c)similar to 1.1 and T-c surprisingly mimics a (n(B)/n(c)-1)(1/2) law. Those high T-c values can be explained by a slow decrease of the electron-phonon coupling parameter lambda and a corresponding drop of the Coulomb pseudopotential mu(*) as n(B)-> n(c).

  • 88. Kulish, Vadym V.
    et al.
    Malyi, Oleksandr I.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering. University of Oslo, Norway.
    Wu, Ping
    Adsorption of metal adatoms on single-layer phosphorene2015Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, nr 2, s. 992-1000Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Single- or few-layer phosphorene is a novel two-dimensional direct-bandgap nanomaterial. Based on first-principles calculations, we present a systematic study on the binding energy, geometry, magnetic moment and electronic structure of 20 different adatoms adsorbed on phosphorene. The adatoms cover a wide range of valences, including s and p valence metals, 3d transition metals, noble metals, semiconductors, hydrogen and oxygen. We find that adsorbed adatoms produce a rich diversity of structural, electronic and magnetic properties. Our work demonstrates that phosphorene forms strong bonds with all studied adatoms while still preserving its structural integrity. The adsorption energies of adatoms on phosphorene are more than twice higher than on graphene, while the largest distortions of phosphorene are only similar to 0.1-0.2 angstrom. The charge carrier type in phosphorene can be widely tuned by adatom adsorption. The unique combination of high reactivity with good structural stability is very promising for potential applications of phosphorene.

  • 89. Kulish, Vadym V.
    et al.
    Malyi, Oleksandr I.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering. University of Oslo, Norway.
    Wu, Ping
    Phosphorene as an anode material for Na-ion batteries: a first-principles study2015Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, nr 21, s. 13921-13928Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We systematically investigate a novel two-dimensional nanomaterial, phosphorene, as an anode for Na-ion batteries. Using first-principles calculations, we determine the Na adsorption energy, specific capacity and Na diffusion barriers on monolayer phosphorene. We examine the main trends in the electronic structure and mechanical properties as a function of Na concentration. We find a favorable Na-phosphorene interaction with a high theoretical Na storage capacity. We find that Na-phosphorene undergoes semiconductor-metal transition at high Na concentration. Our results show that Na diffusion on phosphorene is fast and anisotropic with an energy barrier of only 0.04 eV. Owing to its high capacity, good stability, excellent electrical conductivity and high Na mobility, monolayer phosphorene is a very promising anode material for Na-ion batteries. The calculated performance in terms of specific capacity and diffusion barriers is compared to other layered 2D electrode materials, such as graphene, MoS2, and polysilane.

  • 90.
    Kumar, Mukesh
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Cu3BiS3 as a potential photovoltaic absorber with high optical efficiency2013Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, nr 6, s. 062109-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cu3BiS3 is a potential photovoltaic material. Employing a first-principles approach, we calculate the structural, electronic, and optical properties of Cu3BiS3, and we demonstrate that Cu3BiS3 is an indirect band gap semiconductor in contrast to similar chalcogenide semiconductors. The fundamental band gap energy is estimated to be E-g approximate to 1.5-1.7 eV. The analysis reveals that Cu3BiS3 has a much stronger absorption coefficient (>10(5) cm(-1)) compared to other Cu-S based materials like CuInS2 and Cu2ZnSnS4. This is explained by the presence of localized Bi 6p states in the band gap region, generating a flat lowest conduction band.

  • 91.
    Kumar, Mukesh
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Cu(Sb,Bi)(S,Se)2 as indium-free absorber material with high optical efficiency2014Inngår i: Energy Procedia: Volume 44, Pages 1-244 (2014) Proceedings of E-MRS Spring Meeting 2013 Symposium D Advanced Inorganic Materials and Structures for Photovoltaics 27-31 May 2013, Strasbourg, France, Elsevier, 2014, s. 176-183Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Ternary Cu(Sb,Bi)(S,Se)2 compounds such as CuSbS2, CuSbSe2, CuBiS2, and CuBiSe2, are potential photovoltaic materials that contain earth abundant and low-cost elements. Employing an atomistic first-principles modeling within the density function theory we calculate the electronic and optical properties of Cu(Sb,Bi)(S,Se)2 compounds. We find that these four materials have indirect fundamental band gaps in the range of 1.1-1.7 eV. The indirect gap nature is different to the previous experimental measurements (direct gap). Calculations reveal that these materials have strong optical absorption compared to chalcopyrite CuIn(S,Se)2 and kesterite Cu2ZnSn(S,Se)4. The strong absorption of these compounds is explained by the localized p-states of cation Sb/Bi in the lower region of conduction band. Thereby, ternary Cu(Sb,Bi)(S,Se) 2 compounds have the potential to be used as absorber material in thin-film PV technologies.

  • 92.
    Kumar, Mukesh
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    CuSbS2 and CuBiS2 as potential absorber materials for thin-film solar cells2013Inngår i: Journal of Renewable and Sustainable Energy, ISSN 1941-7012, E-ISSN 1941-7012, Vol. 5, nr 3, s. 031616-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The current thin-film photovoltaic (PV) technologies are dominated by CdTe and Cu(In,Ga)Se-2 compounds. However, due to the limited availably and toxicity of the elements in these technologies, the current research efforts are directed to search alternative earth abundant materials. Therefore, in this work, we analyze the CuSbS2 and CuBiS2 compounds as alternative absorber materials for future thin-film solar cells. Employing a first-principles approach within the density functional theory, we calculate the structural, electronic, and optical properties of CuSbS2 and CuBiS2 compounds. We show that these compounds have indirect fundamental band gap E-g = 1.5-1.7 eV. The indirect gap nature is different from the previous experimental measurements. However, due to the flat bands, the direct gap E-dg = 1.6-1.8 eV is suitable for solar energy technologies. Furthermore, calculations reveal that these compounds have strong absorption coefficients, which are about twice as large as in other Cu-S based PV materials like CuInS2 and Cu2ZnSnS4. Therefore, CuSbS2 and CuBiS2 have the potential to be used as absorber materials in thin-film PV technologies.

  • 93.
    Kumar, Mukesh
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Structural, electronic and optical properties of silver delafossite oxides: A first-principles study with hybrid functional2013Inngår i: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 422, s. 20-27Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ternary delafossite compounds are potential materials for optoelectronic devices. Employing a first-principles method, we calculate the structural, electronic, and optical properties of the silver based compounds AgMO2 (M=Al, Ga or In), which crystallize in delafossite structure. Our calculations show that these AgMO2 oxides have indirect band gaps and the gap energies are in the region of 1.6-3.0 eV whereas, the lowest direct band gap energies are estimated in the range of 2.6-4.3 eV. Furthermore, we find that AgMO2 compounds exhibit a strong anisotropy for the dielectric function and absorption spectra. The absorption onset for these compounds occurs well above the band gap energies. Overall, we show that the hybrid functional improves the lattice parameters and band gap energies and the calculated values are in good agreement with the experimental values.

  • 94.
    Kumar, Mukesh
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ternary Cu3BiY3 (Y = S, Se, and Te) for thin-film solar cells2013Inngår i: Mater Res Soc Symp Proc, 2013, s. 235-240Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Very recently, Cu3BiS3 has been suggested as an alternative material for photovoltaic (PV) thin-film technologies. In this work, we analyze the electronic and optical properties of Cu3BiY 3 with the anion elements Y = S, Se, and Te, employing a first-principles approach within the density function theory. We find that the three Cu2BiY3 compounds have indirect band gaps and the gap energies are in the region of 1.2-1.7 eV. The energy dispersions of the lowest conduction bands are small, and therefore the direct gap energies are only ∼0.1 eV larger than the fundamental gap energies. The flat conduction bands are explained by the presence of localized Bi p-states in the band gap region. Flat energy dispersion implies a large optical absorption, and the calculations reveal that the absorption coefficient of Cu3BiY 3 is larger than 105 cm-1 for photon energies of ∼2.5 eV. The absorption is stronger than other Cu-S based materials like CuInS2 and Cu2ZnSnS4. Thereby, Cu 3BiY3 has the potential to be a suitable material in thin-film PV technologies.

  • 95.
    Kumar, Mukesh
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zhao, Hanyue
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Cation vacancies in the alloy compounds of Cu2ZnSn(S1-xSex)(4) and CuIn(S1-xSex)(2)2013Inngår i: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 535, s. 318-321Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present work analyzes theoretically the formation energy of the cation vacancies V-Cu, V-In, V-Zn, and V-Sn in Cu2ZnSn(S1-xSex)(4) and CuIn(S1-xSex)(2) alloy compounds. An atomistic first-principles study is carried out by employing a generalized gradient approximation and a hybrid functional approach within the density functional theory, using the supercell approach to model the alloy compositions x = 0.00, 0.25, 0.50, 0.75, and 1.00. We find that the Cu vacancy is the most dominant cation vacancy with the lowest formation energy Delta H-f. The formation energy of V-Cu is very similar in both types of alloy compounds, while the formation energy of V-In in CuIn(S1-xSex)(2) is roughly the average value of the formation energies of V-Zn and V-Sn in Cu2ZnSn(S1-xSex)(4). Moreover, we find that the vacancy formation energies are larger in the S-rich compounds compared with the corresponding vacancies in the Se-rich compounds. The results suggest that the concentration of especially V-Cu can, to some extent, be controlled by anion alloying.

  • 96.
    Kumar, Mukesh
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Zhao, Hanyue
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering.
    Study of band-structure, optical properties and native defects in A IBIIIO2 (AI = Cu or Ag, B III = Al, Ga or In) delafossites2013Inngår i: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 28, nr 6, s. 065003-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work, employing a first-principles approach, the structural, electronic, optical, as well as the defect physics of AIB IIIO2 (AI = Cu or Ag, BIII = Al, Ga or In) compounds are discussed. We show that all these delafossite compounds have indirect band gaps with gap energy in the range = 1.6-3.6 eV. We also estimate the lowest direct band gap energies to be in the range = 2.6-4.0 eV. Optical characteristics reveal that AIBIIIO2 compounds exhibit a significant anisotropy for both the real and imaginary parts of the dielectric function. Furthermore, we find that absorption onset for these compounds is energetically well above (&gt;1.5 eV) the fundamental band gaps. Moreover, we demonstrate that the copper delafossites have larger absorption coefficients compared to the corresponding BIII cation silver delafossites in the visible range. Defect calculations reveal that Cu or Ag vacancy has the lowest formation energy followed by the O vacancy while the BIII cation vacancy has the highest formation energy.

  • 97.
    Kumpulainen, Atte
    et al.
    KTH, Tidigare Institutioner, Kemi.
    Persson, Clas
    KTH, Tidigare Institutioner, Materialvetenskap.
    Eriksson, Jan Christer
    KTH, Tidigare Institutioner, Kemi.
    n-decyl-glucopyranoside and n-decyl-maltopyranoside Gibbs monolayers. Phase changes in the dilute liquid-expanded range2004Inngår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 20, nr 24, s. 10534-10541Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Surface tension isotherms were recorded for n-decyl-beta-(D)-glucopyranoside (Glu) and n-deCyl-beta-(D)-maltopyranoside (Mal) solutions at temperatures of 8,22, and 29degreesC. Comparison was made with isotherms of n-deCyl-beta-(D)-thiomaltopyranoside (S-Mal) at 22 degreesC. In addition to the transition from the gaseous to the liquid-expanded (LE) state, a second transition was observed in the early stages of the LE regime for Glu, Mal, and S-Mal at room temperature. The adsorption isotherm of Mal and Glu obtained at 22 degreesC shows the presence of an adsorption step at an average area/molecule of about 79 Angstrom(2) between, approximately, 0.02 and 0.1 mM (the critical micelle concentration (cmc) is 2 mM) and 0.015 and 0.03 mM (the cmc is 2 mM), respectively. Similarly, for S-Mal an adsorption plateau is observed at 70 Angstrom(2) between 0.01 and 0.03 mM (the cmc is 0.7 mM). From the temperature dependence of the surface tension, we have seen that there are considerable differences in the adsorption of Glu and Mal. For Mal, the adsorption plateau is also observed at 29 degreesC at around 79 Angstrom(2), whereas Glu exhibits no adsorption plateau at this temperature. At 8 degreesC, both Mal and Glu exhibit saturation behaviour in the dilute part of the liquid-expanded range, but at this temperature the average molecular areas are lower than at 22 degreesC: around 66 Angstrom(2) for Glu and 75 Angstrom(2) for Mal. Thus, the temperature sensitivity of Glu is considerably greater than for Mal in this range. The saturation regime coincides with a pronounced surface entropy minimum for Mal. The transition in the dilute liquid-expanded range supposedly occurs from a state with deformed surface micelles arranged in a hexagonal pattern, referred to as the granular range, to a true LE monolayer with a fluid hydrocarbon tail layer covering the entire surface.

  • 98. Kuznetsova, T. V.
    et al.
    Grebennikov, V. I.
    Zhao, Hanyue
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Derks, C.
    Taubitz, C.
    Neumann, M.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kuznetsov, M. V.
    Bodnar, I. V.
    Martin, R. W.
    Yakushev, M. V.
    A photoelectron spectroscopy study of the electronic structure evolution in CuInSe2-related compounds at changing copper content2012Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, nr 11, s. 111607-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Evolution of the valence-band structure at gradually increasing copper content has been analysed by x-ray photoelectron spectroscopy (XPS) in In2Se3, CuIn5Se8, CuIn3Se5, and CuInSe2 single crystals. A comparison of these spectra with calculated total and angular-momentum resolved density-of-states (DOS) revealed the main trends of this evolution. The formation of the theoretically predicted gap between the bonding and non-bonding states has been observed in both experimental XPS spectra and theoretical DOS.

  • 99. Lany, S.
    et al.
    Zhao, Y. J.
    Persson, Clas
    Zunger, A.
    Halogen n-type doping of chalcopyrite semiconductors2005Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 86, nr 4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We theoretically identify the chemical thermodynamic boundary conditions that will produce n-type CuInSe2 via halogen doping. Remarkably, we find that due to the low formation energies of the intrinsic defects, V-Cu and In-Cu in CuInSe2, the growth conditions that maximize the halogen donor incorporation do not yield n-type conductivity, whereas the conditions that maximize the concentration of the intrinsic donor In-Cu do yield n-type conductivity. Under the latter conditions, however, the contribution of the halogen donors to the net donor concentration stays significantly below that of In-Cu.

  • 100. Larsson, J.
    et al.
    Persson, Clas
    Tengvall, P.
    Lundqvist-Gustafsson, H.
    Anti-inflammatory effects of a titanium-peroxy gel: Role of oxygen metabolites and apoptosis2004Inngår i: Journal of Biomedical Materials Research, ISSN 0021-9304, E-ISSN 1097-4636, Vol. 68A, nr 3, s. 448-457Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Polymorphonuclear neutrophils (PMN) are among the first inflammatory cells to arrive at an implant interface, where they encounter with the foreign material and may produce reactive oxygen species (ROS). During the interaction between titanium and ROS, titanium-peroxy (Ti-peroxy) compounds may be formed. We used a Ti-peroxy gel, made from titanium and hydrogen peroxide, to study the effects of Ti-peroxy compounds on PMN. In the absence of serum, the Ti-peroxy gel decreased the oxidative response of PMN to yeast and PMA and reduced PMN apoptosis without inducing necrosis. These effects could not be ascribed to the release of hydrogen peroxide from the Ti-peroxy gel, because a steady-state hydrogen peroxide producing system failed to mimic the effects of the gel. The effects were similarly unaffected when PMN were preincubated with beta(2)-integrin antibodies, questioning the involvement of adhesion molecules. Nevertheless, when a filter was used to separate the Ti-peroxy gel from the cells, the gel effect on PMN life span was abolished, pointing to a contact-dependent mechanism. In the presence of serum, the Ti-peroxy gel had no effect on the PMN oxidative response and life span, but appeared rather inert. In summary, this study demonstrates that the Ti-peroxy gel has potentially anti-inflammatory properties through a combined peroxide and physical contact effect, supporting the notion that interactions between titanium and inflammatory cells are responsible for the good performance of titanium in vivo.

1234 51 - 100 of 158
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf