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  • 351.
    Magnuson, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics II.
    Wilhelmsson, Ola
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Mattesini, Maurizio
    Li, Sa
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Högberg, Hans
    Hultman, Lars
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Anisotropy in the electronic structure of V2GeC investigated by soft x-ray emission spectroscopy and first-principles theory2008In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 3, p. 035117-Article in journal (Refereed)
    Abstract [en]

    Theanisotropy of the electronic structure of ternary nanolaminate V2GeC isinvestigated by bulk-sensitive soft x-ray emission spectroscopy. The measured polarization-dependentemission spectra of V L2,3, C K, Ge M1, and Ge M2,3 in V2GeCare compared with those from monocarbide VC and pure Ge.The experimental emission spectra are interpreted with calculated spectra usingab initio density-functional theory including dipole transition matrix elements. Differenttypes of covalent chemical bond regions are revealed: V 3d-C 2p bondingat −3.8  eV, Ge 4p-C 2p bonding at −6  eV, and Ge 4p-C 2s interaction mediatedvia the V 3d orbitals at −11  eV below the Fermi level.We find that the anisotropic effects are high for the4p valence states and the shallow 3d core levels ofGe, while relatively small anisotropy is detected for the V 3dstates. The macroscopic properties of the V2GeC nanolaminate result from the chemical bonds with the anisotropic pattern as shown in this work.

  • 352.
    Magnuson, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Wilhelmsson, Ola
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Palmquist, Jens Petter
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Jansson, Ulf
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Mattesini, M.
    Departamento de Física de la Tierra, Astronomía y Astrofísica I, Universidad Complutense de Madrid, E-28040, Spain.
    Li, S.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Eriksson, Olle
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Electronic structure and chemical bonding in Ti2AlC investigated by soft x-ray emission spectroscopy2006In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 19, article id 195108Article in journal (Refereed)
    Abstract [en]

    The electronic structure of the nanolaminated transition metal carbide Ti2AlC has been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured Ti L, C K, and Al L emission spectra are compared with calculated spectra using ab initio density-functional theory including dipole matrix elements. The detailed investigation of the electronic structure and chemical bonding provides increased understanding of the physical properties of this type of nanolaminates. Three different types of bond regions are identified: The relatively weak Ti 3d-Al 3p bond 1 eV below the Fermi level and the Ti 3d-C 2p and Ti 3d-C 2s bonds which are stronger and deeper in energy are observed around 2.5 and 10 eV below the Fermi level, respectively. A strongly modified spectral shape of the 3s final states in comparison to pure Al is detected for the intercalated Al monolayers indirectly reflecting the Ti 3d-Al 3p hybridization. The differences between the electronic and crystal structures of Ti2AlC, Ti3AlC2, and TiC are discussed in relation to the number of Al layers per Ti layer in the two former systems and the corresponding change of the unusual materials properties.

  • 353.
    Mahabal, Manasi S.
    et al.
    HPT Arts & RYK Sci Coll, Dept Phys, Nasik 422005, Maharashtra, India..
    Deshpande, Mrinalini D.
    HPT Arts & RYK Sci Coll, Dept Phys, Nasik 422005, Maharashtra, India..
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kang, Tae Won
    Dongguk Univ, Dept Phys, Seoul 100715, South Korea..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rare earth functionalization effect in optical response of ZnO nano clusters2016In: European Physical Journal D: Atomic, Molecular and Optical Physics, ISSN 1434-6060, E-ISSN 1434-6079, Vol. 70, no 3, article id 63Article in journal (Refereed)
    Abstract [en]

    The electronic structure of rare earth (RE) doped Zn12O12 clusters - namely, REZn11O12 and RE2Zn10O12 with RE = Nd, Eu and Gd have been investigated within the framework of density functional theory formalism. Doping of a RE atom is found to be energetically favorable in this zinc oxide cluster. We have found that the cage structure of the host cluster Zn12O12 does not change significantly by the substitutional doping of a RE atom on Zn sites. The magnetic coupling between RE ions in the host cluster is found to be ferromagnetic. The static polarizabilities and optical properties of the RE doped Zn12O12 clusters have been studied based on the time dependent density functional theory. With RE doping, the polarizability increases as compared to that of the host cluster. The analysis of the optical absorption spectra indicate that the f electrons in RE doped clusters are significantly more involved in low-energy transitions. For Eu doped clusters give rise to more quenched oscillator strengths as compared to that of Nd and Gd doped zinc oxide clusters. With the increase in number of RE atoms, the red shift is observed in the optical spectrum of the zinc oxide cluster.

  • 354.
    Mahabal, Manasi S.
    et al.
    HPT Arts & RYK Sci Coll, Dept Phys, Nasik 422005, Maharashtra, India..
    Deshpande, Mrinalini D.
    HPT Arts & RYK Sci Coll, Dept Phys, Nasik 422005, Maharashtra, India..
    Hussain, Tanveer
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden.;Univ Queensland, Australian Inst Bioengn & Nanotechnol, Ctr Theoret & Computat Mol Sci, Brisbane, Qld 4072, Australia..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden..
    Sensing Characteristics of a Graphene-like Boron Carbide Monolayer towards Selected Toxic Gases2015In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 16, no 16, p. 3511-3517Article in journal (Refereed)
    Abstract [en]

    By using first-principles calculations based on density functional theory, we study the adsorption efficiency of a BC3 sheet for various gases, such as CO, CO2, NO, NO2, and NH3. The optimal adsorption position and orientation of these gas molecules on the BC3 surface is determined and the adsorption energies are calculated. Among the gas molecules, CO2 is predicted to be weakly adsorbed on the graphene-like BC3 sheet, whereas the NH3 gas molecule shows a strong interaction with the BC3 sheet. The charge transfer between the molecules and the sheet is discussed in terms of Bader charge analysis and density of states. The calculated work function of BC3 in the presence of CO, CO2, and NO is greater than that of a bare BC3 sheet. The decrease in the work function of BC3 sheets in the presence of NO2 and NH3 further explains the affinity of the sheet towards the gas molecules. The energy gap of the BC3 sheets is sensitive to the adsorption of the gas molecules, which implies possible future applications in gas sensors.

  • 355.
    Manotum, R.
    et al.
    Chulalongkorn Univ, Fac Sci, Dept Phys, Extreme Condit Phys Res Lab,Phys Energy Mat Res U, Bangkok 10330, Thailand;CHE, ThEP Ctr, 328 Si Ayuttaya Rd, Bangkok 10400, Thailand.
    Klinkla, R.
    Chulalongkorn Univ, Fac Sci, Dept Phys, Extreme Condit Phys Res Lab,Phys Energy Mat Res U, Bangkok 10330, Thailand;Rajamangala Univ Technol Isan, Fac Sci & Liberal Arts, Dept Appl Phys, Nakhon Ratchasima 30000, Thailand.
    Pinsook, U.
    Chulalongkorn Univ, Fac Sci, Dept Phys, Extreme Condit Phys Res Lab,Phys Energy Mat Res U, Bangkok 10330, Thailand;CHE, ThEP Ctr, 328 Si Ayuttaya Rd, Bangkok 10400, Thailand.
    Kotmool, K.
    Mahidol Wittayanusorn Sch, Dept Phys, Phutthamonthon 73170, Nakhon Pathom, Thailand.
    Tsuppayakorn-aek, P.
    Chulalongkorn Univ, Fac Sci, Dept Phys, Extreme Condit Phys Res Lab,Phys Energy Mat Res U, Bangkok 10330, Thailand;CHE, ThEP Ctr, 328 Si Ayuttaya Rd, Bangkok 10400, Thailand.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, S-10044 Stockholm, Sweden.
    Bovornratanaraks, T.
    Chulalongkorn Univ, Fac Sci, Dept Phys, Extreme Condit Phys Res Lab,Phys Energy Mat Res U, Bangkok 10330, Thailand;CHE, ThEP Ctr, 328 Si Ayuttaya Rd, Bangkok 10400, Thailand.
    Effect of pressure on the structure stability, electronic structure and band gap engineering in Zn16O1S152018In: COMPUTATIONAL CONDENSED MATTER, ISSN 2352-2143, Vol. 17, article id e00332Article in journal (Refereed)
    Abstract [en]

    Crystal structures and high pressure structural phase transitions of Zn16O1S15 have been investigated using density functional theory calculation. The two candidate high pressure structures namely Wurtzite and Zincblende were examined for theirs stability and properties up to 20 GPa. The co-exist phase of both structure which occurred during the different film growth conditions was fully explained. Phonon dispersion and the Born criteria reveal that Zincblende is only stable up to 10 GPa. Besides, Wurtzite structure yield no imaginary phonon frequencies and also satisfy the elastic constants sufficiency condition up to 20 GPa which indicated that the co-exist phase would eventually become the single Wurtzite structure above 10 GPa. The electronic structure and PDOS were also fully investigated using HSE06. The multiple band gap energy and mid O-3 state between fundamental ZnS band gap was revealed for the first time. The pressure effect on their electronic structure has been investigated for possible applications in adjustable optoelectronic device.

  • 356. Mao, Ho-Kwang
    et al.
    Ding, Yang
    Xiao, Yuming
    Chow, Paul
    Shu, Jinfu
    Lebegue, Sebastien
    Lazickif, Amy
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Electronic dynamics and plasmons of sodium under compression2011In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 108, no 51, p. 20434-20437Article in journal (Refereed)
    Abstract [en]

    Sodium, which has long been regarded as one of the simplest metals, displays a great deal of structural, optical, and electronic complexities under compression. We compressed pure Na in the body-centered cubic structure to 52 GPa and in the face-centered cubic structure from 64 to 97 GPa, and studied the plasmon excitations of both structures using the momentum-dependent inelastic X-ray scattering technique. The plasmon dispersion curves as a function of pressure were extrapolated to zero momentum with a quadratic approximation. As predicted by the simple free-electron model, the square of the zero-momentum plasmon energy increases linearly with densification of the body-centered cubic Na up to 1.5-fold. At further compressions and in face-centered cubic Na above 64 GPa, the linear relation curves progressively toward the density axis up to 3.7-fold densification at 97 GPa. Ab initio calculations indicate that the deviation is an expected behavior of Na remaining a simple metal.

  • 357. Mao, Wendy L.
    et al.
    Wang, Lin
    Ding, Yang
    Yang, Wenge
    Liu, Wenjun
    Kim, Duck Young
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Meng, Yue
    Sinogeikin, Stas
    Shu, Jinfu
    Mao, Ho-Kwang
    Distortions and stabilization of simple-cubic calcium at high pressure and low temperature2010In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 22, p. 9965-9968Article in journal (Refereed)
    Abstract [en]

    Ca-III, the first superconducting calcium phase under pressure, was identified as simple-cubic (sc) by previous X-ray diffraction (XRD) experiments. In contrast, all previous theoretical calculations showed that sc had a higher enthalpy than many proposed structures and had an imaginary (unstable) phonon branch. By using our newly developed submicrometer high-pressure single-crystal XRD, cryogenic high-pressure XRD, and theoretical calculations, we demonstrate that Ca-III is neither exactly sc nor any of the lower-enthalpy phases, but sustains the sc-like, primitive unit by a rhombohedral distortion at 300 K and a monoclinic distortion below 30 K. This surprising discovery reveals a scenario that the high-pressure structure of calcium does not go to the zero-temperature global enthalpy minimum but is dictated by high-temperature anharmonicity and low-temperature metastability fine-tuned with phonon stability at the local minimum.

  • 358. Marqués, M.
    et al.
    Osorio-Guillén, Jorge Mario
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Flórez, M.
    Recio, J. M.
    Pressure effects on the structure and vibrations of β- and γ-C3N42004In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 70, no 10, p. 104114-Article in journal (Refereed)
    Abstract [en]

    We present the results of an investigation on the pressure behavior of structural, bonding and vibrational properties of β- and γ-C3N4 phases. Emphasis is focused on the trends of the calculated properties along the A3N4 (A: C, Si, Ge) family. Geometry optimizations and electronic structure calculations are carried out in the framework of the local density functional theory using a planewave-pseudopotential scheme. The equilibrium cell geometry, the isothermal bulk modulus and its pressure derivatives have been evaluated for the two phases in a pressure range up to 400 GPa. The Bader’s Atoms in Molecules formalism is applied to characterize the chemical bonding and the atomic contributions to the bulk compressibility in β- and γ-A3N4 crystals. The calculated stability diagram reveals the occurrence of a hypothetical β-C3N4→γ-C3N4 phase transition around 370 GPa. Γ-point harmonic vibrational modes are computed at selected pressures within the density functional perturbation theory approach. In agreement with recent theoretical calculations, the comparison of the computed Raman vibrational frequencies with experimental estimations for β-C3N4 raises doubts on a previously reported synthesis of this structure. Pressure effects on the vibrational frequencies inform of a reduction of the P63∕m symmetry of the β phase at pressures around 60 GPa and contribute to look into the mechanical stability of the γ phase.

  • 359. Mattesini, M.
    et al.
    Belonoshko, A. B.
    Tkalcic, H.
    Buforn, E.
    Udias, A.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Candy Wrapper for the Earth's Inner Core2013In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 3, p. 2096-Article in journal (Refereed)
    Abstract [en]

    Recent global expansion of seismic data motivated a number of seismological studies of the Earth's inner core that proposed the existence of increasingly complex structure and anisotropy. In the meantime, new hypotheses of dynamic mechanisms have been put forward to interpret seismological results. Here, the nature of hemispherical dichotomy and anisotropy is re-investigated by bridging the observations of PKP(bc-df) differential travel-times with the iron bcc/hcp elastic properties computed from first-principles methods. The Candy Wrapper velocity model introduced here accounts for a dynamic picture of the inner core (i.e., the eastward drift of material), where different iron crystal shapes can be stabilized at the two hemispheres. We show that seismological data are best explained by a rather complicated, mosaic-like, structure of the inner core, where well-separated patches of different iron crystals compose the anisotropic western hemispherical region, and a conglomerate of almost indistinguishable iron phases builds-up the weakly anisotropic eastern side.

  • 360. Mattesini, M
    et al.
    Buforn, E
    Udias, A
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    An ab initio study of S-substituted iron-nickel-silicon alloy at the Earth's inner core pressure2008In: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 28, no 4, p. 437-441Article in journal (Refereed)
    Abstract [en]

    The thermodynamic stability of S-substituting Si into a bcc Fe0.80Ni0.05SxSi(0.15-x) random alloy, with x=0.025 n (n=0-- 4), was investigated up to 350GPa by using an ab initio density functional method based on the full charge density-exact muffin-tin orbital-coherent potential approximation scheme. From the analysis of the calculated H values, we suggest that the FeNiSSi stoichiometry with zero sulphur content always behaves as the most stable system along the whole pressure range of 0-350GPa. As a general tendency, we found that the alloys with 6.8-8.1wt.% Si are energetically more stable than those with lower silicon content, thus supporting the dissolution mechanism for the Earth's inner core compositional model.

  • 361. Mattesini, Maurizio
    et al.
    Belonoshko, Anatoly B.
    Buforn, Elisa
    Ramirez, Maria
    Simak, Sergei I.
    Udias, Agustin
    Mao, Ho-Kwang
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Hemispherical anisotropic patterns of the Earth's inner core2010In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 21, p. 9507-9512Article in journal (Refereed)
    Abstract [en]

    It has been shown that the Earth's inner core has an axisymmetric anisotropic structure with seismic waves traveling similar to 3% faster along polar paths than along equatorial directions. Hemispherical anisotropic patterns of the solid Earth's core are rather complex, and the commonly used hexagonal-close-packed iron phase might be insufficient to account for seismological observations. We show that the data we collected are in good agreement with the presence of two anisotropically specular east and west core hemispheres. The detected travel-time anomalies can only be disclosed by a lattice-preferred orientation of a body-centered-cubic iron aggregate, having a fraction of their [111] crystal axes parallel to the Earth's rotation axis. This is compelling evidence for the presence of a body-centered-cubic Fe phase at the top of the Earth's inner core.

  • 362.
    Meresse, Y
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Heathman, S
    Le, Bihan T
    Rebizant, J
    Brooks, Michael S. S.
    Ahuja, Rajeev
    X-ray diffraction studies of AuCu3-type neptunium compounds under pressure2000In: JOURNAL OF ALLOYS AND COMPOUNDS, ISSN 0925-8388, Vol. 296, no 1-2, p. 27-32Article in journal (Refereed)
    Abstract [en]

    NpX3 (AuCu3-type structure) compounds with X=Al, Ga, Ge, In and Sn were studied up to 50 GPa using the energy dispersive X-ray diffraction (EDXRD) technique. No structural phase transitions were observed for any of the compounds studied up to the highest

  • 363. Miao, Naihua
    et al.
    Sa, Baisheng
    Zhou, Jian
    Sun, Zhimei
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mechanical properties and electronic structure of the incompressible rhenium carbides and nitrides: A first-principles study2011In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 151, no 23, p. 1842-1845Article in journal (Refereed)
    Abstract [en]

    By means of first-principles calculations, the structural stability, mechanical properties and electronic structure of the newly synthesized incompressible Re(2)C, Re(2)N, Re(3)N and an analogous compound Re(3)C have been investigated. Our results agree well with the available experimental and theoretical data. The proposed Re(3)C is shown to be energetically, mechanically and dynamically stable and also incompressible. Furthermore, it is suggested that the incompressibility of these compounds is originated from the strong covalent bonding character with the hybridization of 5d orbital of Re and the 2p orbital of C or N, and a zigzag topology of interconnected bonds, e.g., Re-Re, Re-C or Re-N bonding.

  • 364. Miao, Naihua
    et al.
    Sa, Baisheng
    Zhou, Jian
    Sun, Zhimei
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    First-principles investigation on the phase stability and chemical bonding of mInSb.nInTe phase-change random alloys2010In: Solid State Communications, ISSN 0038-1098, E-ISSN 1879-2766, Vol. 150, no 29-30, p. 1375-1377Article in journal (Refereed)
    Abstract [en]

    The phase stability and bond character of mInSb.nInTe (m = 1, n = 2 or 3) phase-change materials have been investigated by means of ab initio calculations. The results show that In3SbTe2 (IST312) is a metastable phase and is less stable than In4Sb1Te3 (IST413). IST312 will decompose into InSb and InTe as analyzed by formation energies. The chemical bonding in IST312 is rather inhomogeneous, i.e. strong and weak In-Sb or In-Te bonded pairs observed in IST312, which is similar to the available phase-change materials and may lead to its easy phase-change. While in IST413, the bond strengths of In-Sb or In-Te are identical. The present results will provide a fundamental understanding on the phase stability and chemical bonding of mInSb.nInTe (m = 1, n = 2 or 3) alloys and may be applied to develop new InSbTe based phase-change materials.

  • 365. Miao, Naihua
    et al.
    Sa, Baisheng
    Zhou, Jian
    Xu, Lihua
    Sun, Zhimei
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Investigation on Ge5-x Sb (x) Te-5 phase-change materials by first-principles method2010In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 99, no 4, p. 961-964Article in journal (Refereed)
    Abstract [en]

    The structure stability and chemical bonding of Ge5-x Sb (x) Te-5 (x=0,1,2) phase-change alloys were studied by ab initio calculations. By analyzing formation energies, density of states and electron localization function, we have shown that the chemical bonding character of Ge4Sb1Te5 is quite similar to that of GeTe and hence a NaCl crystalline state is expected. The introduction of extra electrons by Sb in Ge4Sb1Te5 and Ge3Sb2Te5 results in states at the Fermi Level. With increasing Sb contents as in Ge3Sb2Te5, the chemical bonding becomes rather inhomogeneous.

  • 366.
    Minakshi, M.
    et al.
    Murdoch Univ, Sch Engn & Informat Technol, Perth, WA, Australia.
    Watcharatharapong, Teeraphat
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    A combined theoretical and experimental approach of a new ternary metal oxide in molybdate composite for hybrid energy storage capacitors2018In: APL MATERIALS, ISSN 2166-532X, Vol. 6, no 4, article id 047701Article in journal (Refereed)
    Abstract [en]

    Sustainable energy sources require an efficient energy storage system possessing excellent electrochemical properties. The better understanding of possible crystal configurations and the development of a new ternary metal oxide in molybdate composite as an electrode for hybrid capacitors can lead to an efficient energy storage system. Here, we reported a new ternary metal oxide in molybdate composite [(Mn1/3Co1/3Ni1/3)MoO4] prepared by simple combustion synthesis with an extended voltage window (1.8 V vs. Carbon) resulting in excellent specific capacity 35 C g−1 (58 F g−1) and energy density (50 Wh kg−1 at 500 W kg−1) for a two electrode system in an aqueous NaOH electrolyte. The binding energies measured for Mn, Co, and Ni 2p are consistent with the literature, and with the metal ions being present as M(II), implying that the oxidation states of the transition metals are unchanged. The experimental findings are correlated well through density functional theory based electronic structure calculations. Our reported work on the ternary metal oxide studies (Mn1/3Co1/3Ni1/3)MoO4 suggests that will be an added value to the materials for energy storage.

  • 367.
    Mir, Showkat H.
    et al.
    Cent Univ Gujarat, Sch Nano Sci, Sect 30, Gandhinagar 382030, India..
    Chakraborty, Sudip
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wärnå, John
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Narayan, Som
    Maharaja Sayajirao Univ Baroda, Fac Sci, Dept Phys, Vadodara 390002, India..
    Jha, Prakash C.
    Cent Univ Gujarat, Ctr Appl Chem, Sect 30, Gandhinagar 382030, India..
    Jha, Prafulla K.
    Maharaja Sayajirao Univ Baroda, Fac Sci, Dept Phys, Vadodara 390002, India..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    A comparative study of hydrogen evolution reaction on pseudo-monolayer WS2 and PtS2: insights based on the density functional theory2017In: Catalysis Science & Technology, ISSN 2044-4753, E-ISSN 2044-4761, Vol. 7, no 3, p. 687-692Article in journal (Refereed)
    Abstract [en]

    In this study, we investigated the catalytic activity of ultrathin PtS2 and WS2 nanostructures for the hydrogen evolution reaction by electronic structure calculations based on the spin-polarised density functional theory. We also explored the effect of van der Waals interactions on the surface-adsorbate interactions. Using the adsorption free energy of H-2 as an activity descriptor, we tuned the photocatalytic water splitting activity of PtS2 and WS2 by functionalizing the individual systems with different transition metals such as Ru, Rh, Pd, Ag, Ir, Au, and Hg. The density of states was calculated along with the band structure to find the effect of different dopants on the fundamental band gap, which is one of the primary parameters in the photocatalytic water splitting.

  • 368.
    Mir, Showkat H.
    et al.
    Cent Univ Gujarat, Ctr Nano Sci, Gandhinagar 382030, India..
    Jha, Prakash C.
    Cent Univ Gujarat, Sch Chem Sci, Gandhinagar 382030, India..
    Islam, Muhammed Shafiqul
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Banarjee, Amitava
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dabhi, Shweta D.
    Maharaja Krishnakumarsinhji Bhavnagar Univ, Dept Phys, Bhavnagar 364001, Gujarat, India..
    Jha, Prafulla K.
    Maharaja Sayajirao Univ Baroda, Dept Phys, Fac Sci, Vadodara 390002, India..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Static and Dynamical Properties of heavy actinide Monopnictides of Lutetium2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 29309Article in journal (Refereed)
    Abstract [en]

    In this work, density functional theory within the framework of generalized gradient approximation has been used to investigate the structural, elastic, mechanical, and phonon properties of lutetium monopnictides in rock-salt crystal structure. The spin orbit coupling and Hubbard-U corrections are included to correctly predict the essential properties of these compounds. The elastic constants, Young's modulus E, Poisson's ratio v, shear modulus G, anisotropy factor A and Pugh's ratio are computed. We found that all lutetium monopnictides are anisotropic and show brittle character. From the wave velocities along [100], [110] and [111] directions, melting temperature of lutetium monopnictides are predicted. Dynamical stability of these monopnictides has been studied by density functional perturbation theory.

  • 369.
    Modin, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Kvashnina, K. O.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics II.
    Butorin, Sergei. M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
    Werme, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics II.
    Nordgren, Joseph
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics II.
    Arapan, Sergiu
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Fallberg, A.
    Ottosson, Mikael
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry.
    Electronic structure of Cu3N films studied by soft x-ray spectroscopy2008In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 20, no 23, p. 235212-Article in journal (Refereed)
    Abstract [en]

    Soft x- ray emission spectroscopy was used to characterize the electronic structure of seven copper nitride films, one synthesized with atomic layer deposition ( ALD) and six grown with chemical vapor deposition ( CVD) at different preparation temperatures. Interpretation of the x- ray emission spectra was supported by calculations of the electronic structure for bulk pure Cu3N and Cu3N with: an excess of Cu atoms, oxygen or carbon impurities, and N vacancies. The calculations are shown to describe the experimental spectra quite well. Analysis of the x- ray spectra suggests that films grown in copper rich environments and above a cut- off temperature of approximately 360 degrees C have a growing fraction of copper enriched areas, while films prepared below this temperature do not have these areas with excess copper.

  • 370. Music, D.
    et al.
    Sun, Z.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Schneider, Jochen M.
    Electronic structure of M2AlC(0001) surfaces (M = Ti, V, Cr)2006In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 18, no 39, p. 8877-8881Article in journal (Refereed)
    Abstract [en]

    We have studied the correlation between the valence electron configuration and the electronic structure of M2AlC(0001) surfaces (M = Ti, V, Cr) using ab initio calculations. Based on our surface energy data, we find that the Al termination is the most stable configuration. As the M valence electron population is increased, the surface energy increases. This can be understood by analysing the valence electron concentration induced changes of the electronic structure. Antibonding states are present as Ti is substituted by Cr in M2AlC(0001). These results are of relevance for vapour phase condensation as well as oxidation.

  • 371. Music, D.
    et al.
    Sun, Zhimei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Schneider, J. M.
    Surface energy of M(2)AC(0001) determined by density functional theory (M = Ti, V, Cr; A = Al, Ga, Ge)2007In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 601, no 4, p. 896-899Article in journal (Refereed)
    Abstract [en]

    We have studied the correlation between the valence electron configuration and the electronic structure of M(2)AC(0001) surfaces (M = Ti, V, Cr; A = Al, Ga, Ge) by density functional theory. The A surface termination is the most stable configuration for all systems studied according to our surface energy data. As the M valence electron population is increased, the surface energy increases by 22% and 12% for A = Al and Ga, respectively, while it decreases by 29% for A = Ge. This can be understood by evaluating the valence electron concentration induced changes in the surface density of states. Antibonding surface Md-Ap states are present as Ti is substituted by Cr in M(2)AC(0001) for A = Al and Ga, while antibonding surface Md-Ap states are not present as Ti is substituted by Cr in M2GeC(0001).

  • 372. Music, Denis
    et al.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Schneider, Jochen M.
    Electronic structure and lattice dynamics of CaPd3B studied by first-principles methods2006In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 356, no 3, p. 251-254Article in journal (Refereed)
    Abstract [en]

    Using first-principles methods, we have studied the electronic structure and lattice dynamics of CaPd3B and compared them to isostructural MgNi3C- CaPd3B possesses less electronic states at the Fermi level, but more phonon modes at low frequencies, than MgNi3C. According to the phonon density of states, low frequency acoustic modes are dominated by Pd states, corresponding to Ni in MgNi3C. Furthermore, these Pd modes show soft phonons, which may be significant for second-order phase transitions. Based on the comparison to MgNi3C, we suggest that the properties of these two compounds may be similar.

  • 373.
    Nabi, Z.
    et al.
    Univ Djillali Liabes Sidi Bel Abbes, Dept Phys, Lab Catalysis & React Syst, Sidi Bel Abbes 22000, Algeria..
    Amari, S.
    Univ Djillali Liabes Sidi Bel Abbes, Dept Phys, Lab Modelisat & Simulat Sci Mat, Sidi Bel Abbes 22000, Algeria..
    Mecabih, S.
    Univ Djillali Liabes Sidi Bel Abbes, Dept Phys, Lab Modelisat & Simulat Sci Mat, Sidi Bel Abbes 22000, Algeria..
    Zaoui, A.
    Univ Djillali Liabes Sidi Bel Abbes, Dept Phys, Lab Modelisat & Simulat Sci Mat, Sidi Bel Abbes 22000, Algeria..
    Abbar, B.
    Univ Djillali Liabes Sidi Bel Abbes, Dept Phys, Lab Modelisat & Simulat Sci Mat, Sidi Bel Abbes 22000, Algeria..
    Bouhafs, B.
    Univ Djillali Liabes Sidi Bel Abbes, Dept Phys, Lab Modelisat & Simulat Sci Mat, Sidi Bel Abbes 22000, Algeria..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ferromagnetism in CdOX (X = Mn and N) with and without intrinsic point defects: A density functional theory2013In: RESULTS IN PHYSICS, ISSN 2211-3797, Vol. 3, p. 205-208Article in journal (Refereed)
    Abstract [en]

    The purpose of this study is to further understanding of the structural, electronic, magnetic properties of CdO doped with transition metal (Mn) and non metal element (N). The calculations are performed by the developed full-potential augmented plane wave plus local orbitals method within the spin density functional theory. As exchange-correlation potential we used the generalized gradient approximation (GGA) form. Moreover, the electronic structure study for our compounds was performed with and without oxygen deficiency. We treated the ferromagnetic and antiferromagnetic states and we found that all compounds are stable in the ferromagnetic structure, and all doped materials CdO:Mn and CdO: N adopt the half metallic character. In addition, we notice that the oxygen vacancy destroyed the ferromagnetism in N doped CdO, while Mn doped CdO becomes semiconductor.

  • 374.
    Nabi, Z.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Vitos, Levente
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics. Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics IV.
    Ab initio calculation of elastic properties of solid He under pressure2005In: Physical Review B, Vol. 72, p. 172102-Article in journal (Refereed)
  • 375.
    Naqvi, S. Rabab
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hussain, T.
    Univ Queensland, Australian Inst Bioengn & Nanotechnol, Ctr Theoret & Computat Mol Sci, Brisbane, Qld 4072, Australia..
    Panigrahi, P.
    Hindustan Univ, Ctr Clean Energy & Nano Convergence CENCON, Madras, Tamil Nadu, India..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Manipulating energy storage characteristics of ultrathin boron carbide monolayer under varied scandium doping2017In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 7, no 14, p. 8598-8605Article in journal (Refereed)
    Abstract [en]

    We report, for the first time we believe, a detailed investigation on hydrogen storage efficiency of scandium (Sc) decorated boron carbide (BC3) sheets using spin-polarized density functional theory (DFT). We analyzed the energetics of Sc adsorption and explored the most favorable adsorption sites of Sc on BC3 sheets with 3.12%, 6.25%, and 12.5% coverage effects. Our investigations revealed that Sc strongly binds on pristine BC3 sheet, with a minimum binding energy of similar to 5 eV, which is robust enough to hinder Sc-Sc metal clustering. Sc, the lightest transition metal, adsorbs a large number of H-2 molecules per atom, resulting in a reasonable storage capacity. With 12.5% Sc-coverage, functionalized BC3 sheets could attain a H2 storage capacity of 5.5 wt% with binding energies suitable for a practical H-2 storage medium.

  • 376.
    Naqvi, Syeda Rabab
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hussain, T.
    Univ Queensland, Australian Inst Bioengn & Nanotechnol, Ctr Theoret & Computat Mol Sci, Brisbane, Qld 4072, Australia..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Exploring Doping Characteristics of Various Adatoms on Single-Layer Stanene2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 14, p. 7667-7676Article in journal (Refereed)
    Abstract [en]

    We have performed first-principles calculations based on density functional theory to investigate the doping characteristics of 31 different adatoms on stanene monolayer, which includes the elements of alkali metals (AM), alkaline earth metals (AEM), transition metals (TMs), and groups III-VII. The most stable configurations of all the dopants have been explored by calculating and comparing binding energies of all the possible binding sites. To comment on the uniform distribution of adatoms on stanene, the adsorption energies (E-ads) of adatoms have been compared with their experimental cohesive energies (E-c,) in the bulk phase.A further comparison reveals that the binding energies of most of the studied adatoms on stanene are much stronger than other group IV monolayers. Apart from structural and binding characteristics, bond lengths, adatom adatom distance, charge-transfer mechanism, electronic properties, and work function have also been explored in pristine and doped monolayers. The strong adsorption of adatoms on stanene, tunable electronic properties, and formation of dumbbell structures in the case of AEM and TM shows that doped stanene sheets are worth further exploration.

  • 377.
    Naqvi, Syeda Rabab
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hussain, Tanveer
    Univ Queensland, Australian Inst Bioengn & Nanotechnol, Ctr Theoret & Computat Mol Sci, Brisbane, Australia.
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, Stockholm, Sweden.
    Metallized siligraphene nanosheets (SiC7) as high capacity hydrogen storage materials2018In: Nano Reseach, ISSN 1998-0124, E-ISSN 1998-0000, Vol. 11, no 7, p. 3802-3813Article in journal (Refereed)
    Abstract [en]

    A planar honeycomb monolayer of siligraphene (SiC7) could be a prospective medium for clean energy storage due to its light weight, and its remarkable mechanical and unique electronic properties. By employing van der Waals-induced first principles calculations based on density functional theory (DFT), we have explored the structural, electronic, and hydrogen (H-2) storage characteristics of SiC7 sheets decorated with various light metals. The binding energies of lithium (Li), sodium (Na), potassium (K), magnesium (Mg), calcium (Ca),scandium (Sc), and titanium (Ti) dopants on a SiC7 monolayer were studied at various doping concentrations, and found to be strong enough to counteract the metal clustering effect. We further verified the stabilities of the metallized SiC7 sheets at room temperature using ab initio molecular dynamics (MD) simulations. Bader charge analysis revealed that upon adsorption, due to the difference in electronegativity, all the metal adatoms donated a fraction of their electronic charges to the SiC7 sheet. Each partially charged metal center on the SiC(7)sheets could bind a maximum of 4 to 5 H-2 molecules. A high H-2 gravimetric density was achieved for several dopants at a doping concentration of 12.50%. The H-2 binding energies were found to fall within the ideal range of 0.2-0.6 eV. Based on these findings, we propose that metal-doped SiC7 sheets can operate as efficient H-2 storage media under ambient conditions.

  • 378.
    Naqvi, Syeda Rabab
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rao, Gollu Sankar
    Univ Basel, Dept Phys, CH-4056 Basel, Switzerland..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol KTH, Dept Mat & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Hussain, Tanveer
    Univ Queensland, Australian Inst Bioengn & Nanotechnol, Ctr Theoret & Computat Mol Sci, Brisbane, Qld 4072, Australia..
    Hexagonal Boron Nitride (h-BN) Sheets Decorated with OLi, ONa, and Li2F Molecules for Enhanced Energy Storage2017In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 18, no 5, p. 513-518Article in journal (Refereed)
    Abstract [en]

    First-principles electronic structure calculations were carried out on hexagonal boron nitride (h-BN) sheets functionalized with small molecules, such as OLi, ONa, and Li2F, to study their hydrogen (H-2) storage properties. We found that OLi and ONa strongly adsorb on h-BN sheets with reasonably large inter-adsorbent separations, which is desirable for H-2 storage. Ab initio molecular dynamics (MD) simulations further confirmed the structural stability of OLi-BN and ONa-BN systems at 400K. On the other hand, Li2F molecules form clusters over the surface of h-BN at higher temperatures. We performed a Bader charge investigation to explore the nature of binding between the functionalized molecules and h-BN sheets. The density of states (DOS) revealed that functionalized h-BN sheets become metallic with two-sided coverage of each type of molecules. Hydrogenation of OLi-BN and ONa-BN revealed that the functionalized systems adsorb multiple H-2 molecules around the Li and Na atoms, with H-2 adsorption energies ranging from 0.20 to 0.28eV, which is desirable for an efficient H-2 storage material.

  • 379.
    Niklasson, Gunnar A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Fasta tillståndets fysik.
    Ahuja, R
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Nanoteknologi och Funktionella material.
    Electronic states in intercalation materials studied by electrochemical techniques.2006In: Modern Phys. Lett.B, Vol. 20, p. 863-875Article in journal (Refereed)
  • 380.
    Niklasson, Gunnar A
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Fasta tillståndets fysik.
    Berggren, Lars
    Jonsson, A K
    Ahuja, R
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Skorodumova, N V
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Backholm, Jonas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Fasta tillståndets fysik.
    Strömme, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials. Nanoteknologi.
    Electrochemical studies of the electron states of disordered electrochromic oxides2006In: Solar Energy Materials & Solar Cells, Vol. 90, p. 385-394Article in journal (Refereed)
  • 381.
    Nisar, J
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Peng, X
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Stability of ferromagnetic phase in Fe-doped AlH32009In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 85, no 6, p. 67006-Article in journal (Refereed)
    Abstract [en]

    We have carried out a systematic theoretical investigation of Fe-doped AlH3 to study its magnetic properties and to assess the stability of the ferromagnetic phase in this material. All calculations were performed using the projector augmented-wave method and generalized-gradient approximation (GGA) as well as GGA+U. The magnetic moment is found to be constant at 1.1 mu(B) per Fe-atom in the ferromagnetic configuration for distances between adjacent Fe atoms varying from 3.25 angstrom to 7.41 angstrom. We conclude that the ferromagnetic phase in Fe-doped AlH3 is stable both for near and far configurations of Fe. The stability of the ferromagnetic phase is due to the holes created by Fe-doping and the larger level splitting of the interacting gap states within the ferromagnetic phase. Copyright (C) EPLA, 2009

  • 382.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Equation of state (EOS) and collapse of magnetism in iron-rich meteorites at high pressure by first-principles calculations2010In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 182, no 3-4, p. 175-178Article in journal (Refereed)
    Abstract [en]

    We have calculated electronic and structure properties, equation of state (EOS) and collapse of magnetism of different meteoritic materials at high pressure using density functional theory (DFT). The fully optimization structures are obtained by minimization of the total energy and atomic forces of iron-rich materials, which are in good agreement with the experiment. Phase transition of Fe2P (C22 type structure) barringerite into Fe2P (C23 type structure) allabogdanite is calculated to be 26 GPa. Collapse of magnetism (high spin-low spin) of some iron-rich materials are described at various pressures. It has been observed that the optimized equilibrium volume has been changed due to transition of non-magnetic to magnetic material at high pressure, so EOS parameters have also been changed. EOS parameters such as bulk modulus (B-o and derivative of bulk modulus with respect to pressure (B-o') for magnetic and non-magnetic configurations have been calculated by fitting E-V curves with Birch-Murnaghan equation, which confirm the experimental results. (C) 2010 Elsevier B.V. All rights reserved.

  • 383.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Structure behavior and equation of state (EOS) of Ni2P and (Fe1 x Nix)2P (allabogdanite) from First-principles calculations2010In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 295, no 3-4, p. 578-582Article in journal (Refereed)
    Abstract [en]

    First-principles calculations have been performed to determine the equations of state (EOS) and structural parameters of Ni2P, NiP2 (Pyrite type) and Ni-doped Fe2P (allabogdanite) at high pressures. Ni2P (C22) is less compressible than hcp Fe, Fe2P (C22) and Fe2P (C23), because of its higher bulk modulus, found to be in good agreement with experimental results. Phase transition from C22 to C23 phase in Ni2P has not been observed up to 50 GPa. We have studied the structure parameters and the bulk modulus of (Fe1-x Ni-x)(2)P (allabogdanite) in the concentration range (x=0-0.187) of a stability region of allabogdanite phase. Bulk modulus of (Fe1-x Ni)(2)P (allabogdanite) slightly increases with increase in doping concentration up to 18.75%. The resulting bulk modulus, however, is between Fe2P and Ni2P. Bulk modulus of Ni-doped Fe2P (C23) with maximum possible doping concentration is found to be larger than pure Fe2P (C23) by 7.6%.

  • 384.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Water Interaction with native defects on rutile TiO2 nanowire: Ab initio calculations2011In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 98, no 8, p. 083115-Article in journal (Refereed)
    Abstract [en]

    Adsorption of water molecules on stoichiometric and defective surfaces of rutile TiO2 nanowire oriented along the [(1) over bar 10] direction is investigated using density function theory calculations. We have investigated, in particular, O and Ti vacancies where energetic, structural, and electronic properties were evaluated. It was found that the water molecules interacting with O-vacancy undergo spontaneous dissociation, forming hydroxyl groups bound to Ti atoms and other OH groups formed by surface O and H-water. The same is not found in the case of perfect and Ti-vacancy containing nanowire. This dissociation of water molecules is due to charge transfer from neighboring Ti atom, which is polarized due to the O-vacancy.

  • 385.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Araújo, C. Moysés
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
    Structural, electronic and energetic properties of water adsorbed on beta-Si3N4 (0001) surface: First-principles calculations2010In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 604, no 5-6, p. 617-622Article in journal (Refereed)
    Abstract [en]

    Structural, energetic and electronic properties of water molecules adsorbed on beta-Si3N4 (0 00 1) surface, at various coverages, are investigated using density functional theory. At low coverages (0 <= 0.5), it is found that all H2O molecules undergo spontaneous dissociation forming hydroxyl (OH) and imino (NH) groups where the reactive sites are identified, a result shown for the first time using ab initio theory. For higher coverages (0 > 0.5), only partial dissociation takes place where some of the molecules stay intact being bound via H-bond in good agreement with experimental findings. The driving force for the water dissociation has been identified to be dangling bonds on lower coordinated N and Si surface atoms showing that not all surface atoms are reactive corroborating with previous experimental findings. (C) 2010 Elsevier B.V. All rights reserved.

  • 386.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jiang, Xue
    Pathak, Biswarup
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Zhao, Jijun
    Kang, Tae Won
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Semiconducting allotrope of graphene2012In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 23, no 38, p. 385704-Article in journal (Refereed)
    Abstract [en]

    From first-principles calculations, we predict a planar stable graphene allotrope composed of a periodic array of tetragonal and octagonal (4, 8) carbon rings. The stability of this sheet is predicted from the room-temperature molecular dynamics study and the electronic structure is studied using state-of-the-art calculations such as the hybrid density functional and the GW approach. Moreover, the mechanical properties of (4, 8) carbon sheet are evaluated from the Young's modulus and intrinsic strength calculations. We find this is a stable planar semiconducting carbon sheet with a bandgap between 0.43 and 1.01 eV and whose mechanical properties are as good as graphene's.

  • 387.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pathak, Biswarup
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Screened hybrid density functional study on Sr2Nb2O7 for visible light photocatalysis2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 18, p. 181903-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of pure Sr2Nb2O7 and its electronic band position are being aligned with respect to the water oxidation/reduction potential level using hybrid functional (HSE06) theory. The experimental band gap (3.90 eV) of pure Sr2Nb2O7 can be reproduced (3.92 eV) using this level of theory. The cationic-anionic co-doping (Mo-N) in layered perovskite Sr2Nb2O7 structure reduces the band gap significantly, and its electronic band position is excellent for the visible-light photocatalysis. The respective cationic and anionic mono-doped systems create an occupied or unoccupied impurity states in the band gap, which can reduce the efficiency of the photocatalysis.

  • 388.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pathak, Biswarup
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wang, Baochang
    Kang, Tae Won
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hole mediated coupling in Sr2Nb2O7 for visible light photocatalysis2012In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, no 14, p. 4891-4897Article in journal (Refereed)
    Abstract [en]

    The band gap reduction and effective utilization of visible solar light are possible by introducing the anionic hole–hole mediated coupling in Sr2Nb2O7. By using the first principles calculations, we have investigated the mono- and co-anionic doping (S, N and C) in layered perovskite Sr2Nb2O7 for the visible-light photocatalysis. Our electronic structure and optical absorption study shows that the mono- (N and S) and co-anionic doped (N–N and C–S) Sr2Nb2O7 systems are promising materials for the visible light photocatalysis. The calculated binding energies show that if the hole–hole mediated coupling could be introduced, the co-doped systems would be more stable than their respective mono-doped systems. Optical absorption curves indicate that doping S, (N–N) and (C–S) in Sr2Nb2O7 can harvest a longer wavelength of the visible light spectrum as compared to the pure Sr2Nb2O7 for efficient photocatalysis.

  • 389.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Peng, Xiangyang
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Origin of ferromagnetism in molybdenum dioxide from ab initio calculations2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 1, p. 012402-Article in journal (Refereed)
    Abstract [en]

    We have performed spin-polarized calculations of the unexpected ferromagnetism in ultrathin films of molybdenum dioxide (MoO2) within the framework of density-functional theory. It is found that the ideal bulk MoO2 is metallic and nonmagnetic. Bulk MoO2 with Mo vacancy, O vacancy, Mo interstitial, or O interstitial remains to be nonmagnetic. Using slab calculation, we observed ferromagnetism in both oxygen-rich and -poor MoO2 (100) surfaces with average surface magnetic moment 1.53 and 0.69(mu B) per surface Mo atom, respectively. The partial density of states of surface Mo atom at the Fermi level (E-F) is much larger than that of the Mo atom in the center of the slab and in bulk MoO2, which indicates that ferromagnetism in surface (100) is due to Stoner instability. Enrichment of oxygen at the surface is found to be more favorable for ferromagnetism in MoO2 (100). The 2p states of surface oxygen atoms are significantly hybridized with the 4d states of Mo atoms and are appreciably spin polarized.

  • 390.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Peng, Xiangyang
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kang, T. W.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Stabilizing the defect-induced dilute magnetic semiconductors: Li-doping in GaN with Ga vacancies2011In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 93, no 5, p. 57006-Article in journal (Refereed)
    Abstract [en]

    By means of first-principles calculations, we have investigated the effects of various Li-doping on the exchange interaction and the formation energy in bulk GaN with Ga vacancies. Although the Ga vacancies can induce ferromagnetism in GaN, their formation energy is rather high. Our calculations show that Li-doping can effectively tune the formation energy of Ga vacancies. It is revealed that the stabilizing effect depends on whether the number of holes is increased or decreased after Li-doping. When Li atoms substitutes for N atoms or occupies the interstitial sites, the holes are reduced and the formation energy of Ga vacancies is lowered. In contrast, Li substituting for Ga generates additional holes in the system, leading to an enhancement of the formation energy of Ga vacancies and making the system less stable.

  • 391.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Silva, Luciana Almeida
    Instituto de Quimica, Universidade Federal da Bahia.
    Almeida, Cristiane Gomes
    Instituto de Quimica, Universidade Federal da Bahia.
    Mascarenhas, Artur José Santos
    Instituto de Quimica, Universidade Federal da Bahia.
    Wang, Baochang
    Department of Materials and Engineering, Royal Institute of Technology (KTH).
    Araújo, Carlos Moysés
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pepe, Iuri
    Instituto de Física, Universidade Federal da Bahia.
    Almeida, Jailton Souza de
    Instituto de Física, Universidade Federal da Bahia.
    Silva, Antonio Ferreira da
    Instituto de Física, Universidade Federal da Bahia.
    Study of electronic and optical properties of BiTaO4 for photocatalysis2012In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 9, no 7, p. 1593-1596Article in journal (Refereed)
    Abstract [en]

    We present the optical absorption spectrum of BiTaO4 using the photo acoustic spectroscopy (PAS) technique and first principle approach. Band gap have been estimated 2.65 and 2.45 eV using PAS method and DFT calculations, respectively. Position of reduction and oxidation level with respect to vacuum level are identified, which shows that BiTaO4 can be used as photocatalyst for hydrogen production. Electronic structure is explained by plotting total density of states (TDOS).

  • 392.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wang, B. C.
    Pathak, Biswarup
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kang, T. W.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mo- and N-doped BiNbO(4) for photocatalysis applications2011In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 99, no 5, p. 051909-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of pure BiNbO(4) has been calculated and their electronic band positions have been aligned with respect to the water oxidation/reduction potential. The effect of cationic (Mo), anionic (N), and co-doping (Mo-N) on BiNbO(4) has been studied and discussed with respect to the standard redox potential levels. Our results show that co-doping of Mo and N in BiNbO(4) reduces the band gap up to 31.8%, thus making it a potential candidate for the photocatalysis of water for hydrogen production. The relative stability between the mono-and co-doped BiNbO(4) materials show that co-doped material is more stable and feasible in comparison to the mono-doped materials.

  • 393.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wang, Baochang
    Araujo, Carlos Moyses
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    da Silva, Antonio Ferreira
    Kang, Tae Won
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Band gap engineering by anion doping in the photocatalyst BiTaO4: First principle calculations2012In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 37, no 4, p. 3014-3018Article in journal (Refereed)
    Abstract [en]

    We have shown the effect of mono and co-doping of non-metallic anion atoms on the electronic structure in BiTaO4 using the first-principles method. It can improve the photocatalytic efficiency for hydrogen production in the presence of visible sunlight. It is found that the band gap of BiTaO4 has been reduced significantly up to 54% with different nonmetallic doping. Electronic structure analysis shows that the doping of nitrogen is able to reduce the band gap of BiTaO4 due to the impurity N 2p state at the upper edge of the valence band. In case of C or C-S doped BiTaO4, double occupied (filled) states have been observed deep inside the band gap of BiTaO4. The large reduction of band gap has been achieved, which increases the visible light absorption. These results indicate that the doping of non-metallic element in BiTaO4 is a promising candidate for the photocatalyst due to its reasonable band gap.

  • 394.
    Nisar, Jawad
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Århammar, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jämstorp, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Optical gap and native point defects in kaolinite studied by the GGA-PBE, HSE functional, and GW approaches2011In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 84, no 7, p. 075120-Article in journal (Refereed)
    Abstract [en]

    The electronic structure of kaolinite with and without intrinsic defects has been studied by the Perdew-Burke-Ernzerhof (PBE) and Heyd-Scuseria-Ernzerhof (HSE) functionals and by the G(0)W(0) approach. The band gap of defect-free kaolinite was estimated to between 6.2 and 8.2 eV. Analysis of the formation energy of native point defects in kaolinite was carried out under different growth conditions. When the PBE defect formation energy as a function of temperature is considered, the hydroxyl vacancy is compensated by a hydrogen vacancy at a formation energy of 0.45 eV at oxygen-rich and hydrogen-poor conditions. The hydroxyl vacancy acts as a donor whereas the hydrogen vacancy acts as an acceptor, both inducing states in the band gap. The HSE06 hybrid functional increases the defect formation energy and tends to localize and move these states away from the band edges, as compared to the other two methods. Our results imply that intrinsic defects will tune the band gap of kaolinite and influence properties related to its band structure such as the cation retention capability and drug release.

  • 395.
    Nisar, Jawat
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Topalian, Zareh
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    De Sarkar, Abir
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Österlund, Lars
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    TiO2‑Based Gas Sensor: A Possible Application to SO22013In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 5, no 17, p. 8516-8522Article in journal (Refereed)
    Abstract [en]

    Fixation of SO2 molecules on anatase TiO2 surfaceswith defects have been investigated by first-principles densityfunctional theory (DFT) calculations and in situ Fourier transforminfrared (FTIR) surface spectroscopy on porous TiO2 films. Intrinsicoxygen-vacancy defects, which are formed on TiO2(001) andTiO2(101) surfaces by ultraviolet (UV) light irradiation and atelevated temperatures, are found to be most effective in anchoringthe SO2 gas molecules to the TiO2 surfaces. Both TiO2(101) andTiO2(001) surfaces with oxygen vacancies are found to exhibit higherSO2 adsorption energies in the DFT calculations. The adsorptionmechanism of SO2 is explained on the basis of electronic structure,charge transfer between the molecule and the surface, and the oxidation state of the adsorbed molecule. The theoretical findingsare corroborated by FTIR experiments. Moreover, the (001) surface with oxygen vacancies is found to bind SO2 gas moleculesmore strongly, as compared to the (101) surface. Higher concentration of oxygen vacancies on the TiO2 surfaces is found tosignificantly increase the adsorption energy. The results shed new insight into the sensing properties of TiO2-based gas sensors

  • 396. O'Byrne, Justin P.
    et al.
    Li, Zhonglai
    Tobin, Joseph M.
    Larsson, J. Andreas
    Larsson, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Holmes, Justin D.
    Growth of Carbon Nanotubes from Heterometallic Palladium and Copper Catalysts2010In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 114, no 18, p. 8115-8119Article in journal (Refereed)
    Abstract [en]

    Bamboo-structured carbon nanotubes (BCNTs) were synthesized with MgO-supported Pd and Cu catalysts, doped with either Mo or W, by the catalytic chemical vapor decomposition of methane. No nanotubes were observed to grow from the catalysts in the absence of the dopant metals. Additionally, the level of dopant in the catalysts was found to strongly affect the morphology of carbon produced. Amorphous carbon was generated on a 10 wt % Cu/5 wt % W (2:1) catalyst, while BCNTs were produced on 20 wt % Cu/5 wt W (4:1) and a 30 wt % Cu/5 wt W (6:1) catalysts. A pure Pd catalyst produced carbon nanofibres (CNFs), while BCNTs were able to grow from Pd/Mo catalysts. Density functional theory simulations show that the composite Cu/W and Pd/Mo bimetallic particles which generated BCNTs have similar binding energies to carbon, and comparable to metals such as Fe, Co, and Ni which are traditionally used to grow CNTs by chemical vapor deposition.

  • 397.
    Orthaber, Andreas
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Löfås, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Physics.
    Öberg, Elisabet
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wallner, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Jafri, S.Hassan M
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Santoni, Marie-Pierre
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Leifer, Klaus
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Ottosson, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC.
    Ott, Sascha
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Molecular Biomimetics.
    Cooperative Gold Nanoparticle Stabilization by Acetylenic Phosphaalkenes2015In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 54, no 36, p. 10634-10638Article in journal (Refereed)
  • 398. Osorio-Guillen, J.M.
    et al.
    Simak, S.I.
    Wang, Y.
    Johansson, Börje
    Ahuja, Rajeev
    Bonding and elastic properties of superconducting MgB$_2$2002In: Solid State Communications, ISSN 0038-1098, Vol. 123, no 6-7, p. 257-262Article in journal (Refereed)
  • 399.
    Osorio-Guillén, J. M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Structural phase transitions in heavy alkali metal under pressure2004In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 5, no 9, p. 1411-11415Article in journal (Refereed)
    Abstract [en]

    We performed a theoretical study of the crystal structures of cesium and rubidium under high compressions. Our results confirm the recent high-pressure experimental observations of new complex crystal structures for the Cs III and Rb III phases. The calculated transition pressures agree extremely well with the measured data. Thus, it is now certain that the famous isostructural phase transition in cesium is actually a new crystallographic phase transition. A d-orbital occupation number of about 0.52 is crucial for the occurrence of these complex structures.

  • 400.
    Osorio-Guillén, J. M.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
    Simak, S. I.
    Wang, Y.
    Johansson, Börje
    Ahuja, Rajeev
    Bonding and elastic properties of superconducting MgB22002In: Sol. Stat. Comm., Vol. 123, p. 257-Article in journal (Refereed)
567891011 351 - 400 of 599
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