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  • 351.
    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.

  • 352.
    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.

  • 353.
    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.

  • 354.
    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.

  • 355.
    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.

  • 356.
    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.

  • 357.
    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).

  • 358.
    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.

  • 359.
    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.

  • 360.
    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.

  • 361.
    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

  • 362. 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.

  • 363.
    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)
  • 364. 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)
  • 365.
    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.

  • 366.
    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)
  • 367. Oubelkacem, A.
    et al.
    Essaoudi, I.
    Ainane, A.
    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, Materials Theory.
    Dujardin, F.
    The Magnetic Properties of Multi-surface Transverse Ferroelectric Ising Thin Films2015In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, E-ISSN 1557-1947, Vol. 28, no 3, p. 877-883Article in journal (Refereed)
    Abstract [en]

    The effective field theory (EFT) based on the transverse Ising model (TIM) is used to study the layer and average polarizations of multi-surface ferroelectric thin film. The effects of the transverse fields and the exchange interactions on the polarization are discussed. It is obvious that the polarizations are affected explicitly by the TIM parameters, and the larger the exchange interactions, the larger the layer and average polarizations. Our theoretical predictions may be a reference for future work in studying the phase transition properties of ferroelectric thin films.

  • 368. Oubelkacem, A.
    et al.
    Essaoudi, I.
    Ainane, Abdelmajid
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Dujardin, F.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Effect of Seeding Layers on Hysteresis Loops and Phase Transition of the Ferroelectric Thin Film2015In: Ferroelectrics (Print), ISSN 0015-0193, E-ISSN 1563-5112, Vol. 478, no 1, p. 1-10Article in journal (Refereed)
    Abstract [en]

    The hysteresis loops and the transition properties of a ferroelectric (FE) thin film with seeding layers are studied using the effective field theory with a probability distribution technique that accounts for the self-spin correlation functions. The effect of the interaction parameters for the seeding layer on the hysteresis loops and phase diagram are also examined. We calculated the critical temperature and the polarization of the FE thin film for different seeding layer structures. We find that the seeding layer can greatly increase the Curie temperature and the polarization of the whole FE thin film. The hysteresis loops are obtained for some typical value of the exchange interaction and the transverse field for a film with one or two seeding layers.

  • 369.
    Ouyang, Tianhong
    et al.
    Shandong Univ, Minist Educ, Key Lab Liquid Solid Struct Evolut & Proc Mat, Jinan, Shandong, Peoples R China.;Shandong Univ, Suzhou Inst, Jinan, Shandong, Peoples R China..
    Qian, Zhao
    Shandong Univ, Minist Educ, Key Lab Liquid Solid Struct Evolut & Proc Mat, Jinan, Shandong, Peoples R China.;Shandong Univ, Suzhou Inst, Jinan, Shandong, Peoples R China..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Liu, Xiangfa
    Shandong Univ, Minist Educ, Key Lab Liquid Solid Struct Evolut & Proc Mat, Jinan, Shandong, Peoples R China.;Shandong Univ, Suzhou Inst, Jinan, Shandong, Peoples R China..
    First-principles investigation of CO adsorption on pristine, C-doped and N-vacancy defected hexagonal AlN nanosheets2018In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 439, p. 196-201Article in journal (Refereed)
    Abstract [en]

    The optimized atomic structures, energetics and electronic structures of toxic gas CO adsorption systems on pristine, C-doped and N-vacancy defected h-AlN nanosheets respectively have been investigated using Density functional theory (DFT-D2 method) to explore their potential gas detection or sensing capabilities. It is found that both the C-doping and the N-vacancy defect improve the CO adsorption energies of AlN nanosheet (from pure -3.847 eV to -5.192 eV and -4.959 eV). The absolute value of the system band gap change induced by adsorption of CO can be scaled up to 2.558 eV or 1.296 eV after C-doping or N-vacancy design respectively, which is evidently larger than the value of 0.350 eV for pristine material and will benefit the robustness of electronic signals in potential gas detection. Charge transfer mechanisms between CO and the AlN nanosheet have been presented by the Bader charge and differential charge density analysis to explore the deep origin of the underlying electronic structure changes. This theoretical study is proposed to predict and understand the CO adsorption properties of the pristine and defected h-AlN nanosheets and would help to guide experimentalists to develop better AlN-based two-dimensional materials for efficient gas detection or sensing applications in the future.

  • 370. Owens, Frank J.
    et al.
    Gupta, Amita
    Rao, K. V.
    Iqbal, Zafar
    Guillen, J. M. Osorio
    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.
    Guo, J. -H
    Unusual room temperature ferromagnetism in bulk sintered GaP doped with copper2007In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 43, no 6, p. 3043-3045Article in journal (Refereed)
    Abstract [en]

    Robust room temperature ferromagnetism is obtained in single phase Gallium Phosphide doped with Cu2+ prepared by simple solid state reaction route. The saturation magnetization at 300 K is 1.5 x 10(-2) emu/g and the coercivity was found to be 125 Oe. A strong ferromagnetic resonance signal confirms the long range magnetic order which persists to temperatures as high as 739 K. X-ray absorption spectroscopy (XAS) indicate that Cu is in a +2 state. Ab initio calculations also show that the ferromagnetic ordering is energetically favorable in Cu doped GaP. When the spin-orbit coupling is included we get an enhanced total magnetic moment of 0.31 mu(B) with a local moment on Cu 0.082 and on P 0.204 mu(B). per atom.

  • 371.
    Ozaki, N.
    et al.
    Osaka Univ, Grad Sch Engn, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan.;Osaka Univ, Photon Pioneers Ctr, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan..
    Nellis, W. J.
    Harvard Univ, Dept Phys, Cambridge, MA 02138 USA..
    Mashimo, T.
    Kumamoto Univ, Shock Wave & Condensed Matter Res Ctr, Kumamoto 8608555, Japan..
    Ramzan, Muhammad
    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. KTH Royal Inst Technol, Dept Mat Sci & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Kaewmaraya, Thanayut
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Kimura, T.
    Ehime Univ, Geodynam Res Ctr, Matsuyama, Ehime 7908577, Japan..
    Knudson, M.
    Sandia Natl Labs, POB 5800, Albuquerque, NM 87185 USA.;Washington State Univ, Inst Shock Phys, Pullman, WA 99164 USA..
    Miyanishi, K.
    Osaka Univ, Photon Pioneers Ctr, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan..
    Sakawa, Y.
    Osaka Univ, Inst Laser Engn, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan..
    Sano, T.
    Osaka Univ, Inst Laser Engn, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan..
    Kodama, R.
    Osaka Univ, Grad Sch Engn, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan.;Osaka Univ, Photon Pioneers Ctr, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan.;Osaka Univ, Inst Acad Initiat, 2-2 Yamadaoka, Suita, Osaka 5650871, Japan..
    Dynamic compression of dense oxide (Gd3Ga5O12) from 0.4 to 2.6 TPa: Universal Hugoniot of fluid metals2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 26000Article in journal (Refereed)
    Abstract [en]

    Materials at high pressures and temperatures are of great current interest for warm dense matter physics, planetary sciences, and inertial fusion energy research. Shock-compression equation-of-state data and optical reflectivities of the fluid dense oxide, Gcl(3)Ga(5)O(12) (GGG), were measured at extremely high pressures up to 2.6TPa (26 Mbar) generated by high-power laser irradiation and magnetically driven hypervelocity impacts. Above 0.75TPa, the GGG Hugoniot data approach/reach a universal linear line of fluid metals, and the optical reflectivity most likely reaches a constant value indicating that GGG undergoes a crossover from fluid semiconductor to poor metal with minimum metallic conductivity (MMC). These results suggest that most fluid compounds, e.g., strong planetary oxides, reach a common state on the universal Hugoniot of fluid metals (UHFM) with MMC at sufficiently extreme pressures and temperatures. The systematic behaviors of warm dense fluid would be useful benchmarks for developing theoretical equation-of-state and transport models in the warm dense matter regime in determining computational predictions.

  • 372.
    Pandey, Kavita
    et al.
    Pandit Deendayal Petr Univ, Sch Technol, Gandhinagar 382007, India..
    Singh, Deobrat
    SV Natl Inst Technol, Dept Appl Phys, Adv Mat Lab, Surat 395007, India..
    Gupta, S. K.
    St Xaviers Coll, Dept Phys, Computat Mat & Nanosci Grp, Ahmadabad 380009, Gujarat, India..
    Yadav, Pankaj
    Pandit Deendayal Petr Univ, Sch Technol, Gandhinagar 382007, India..
    Sonvane, Yogesh
    SV Natl Inst Technol, Dept Appl Phys, Adv Mat Lab, Surat 395007, India..
    Lukacevic, Igor
    Josip Juraj Strossmayer Univ Osijek, Dept Phys, Osijek 31000, Croatia..
    Kumar, Manjeet
    Incheon Natl Univ, Dept Elect Engn, Incheon 406772, South Korea..
    Kumar, Manoj
    Pandit Deendayal Petr Univ, Sch Technol, Gandhinagar 382007, India..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Improving electron transport in the hybrid perovskite solar cells using CaMnO3-based buffer layer2018In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 45, p. 287-297Article in journal (Refereed)
    Abstract [en]

    In the present article, the detailed analyses of interface properties and device performance of inorganic perovskite CaMnO3-based buffer layer hybrid perovskite solar cell have been undertaken. Analyses are based on ab initio simulations and macroscopic modelling. A thorough study of electronic and optical properties and interface charge dynamics revealed that CaMnO3 presents a better candidate for the electron transport material in thin film hole transporting material free hybrid perovskite solar cells with the planar architecture than the most common anatase TiO2. This result is founded on the more appropriate band gap and better band alignment with the hybrid perovskite, leading to the faster charge carrier mobility, improved charge transfer and reduced exciton recombination. The results from theoretical simulations are justified by the solar cell model, which explored the basic cell characteristics and parameters: open circuit voltage, short circuit current, fill factor and efficiency, as the functions of cell performance factors, like defect density, diffusion length, absorber layer thickness and band offset. Our model suggests an unoptimized device with a photo-conversion efficiency of almost 10% for the low defect concentrations under 10(15). With efficiency in the upper range for HTM free perovskite solar cells, we propose that the CaMnO3-based solar cell poses as an improvement upon the up to now most frequently used ones and provides important step toward their commercialisation.

  • 373.
    Panigrahi, P.
    et al.
    Hindustan Inst Technol & Sci, Clean Energy & Nano Convergence Ctr, Madras 603103, Tamil Nadu, India.
    Dhinakaran, A. K.
    Hindustan Inst Technol & Sci, Clean Energy & Nano Convergence Ctr, Madras 603103, Tamil Nadu, India.
    Naqvi, S. Rabab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Gollu, S. R.
    Nanyang Technol Univ, Sch Elect & Elect Engn, 50 Nanyang Ave, Singapore 639798, Singapore.
    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.
    Hussain, T.
    Univ Queensland, Australian Inst Bioengn & Nanotechnol, Ctr Theoret & Computat Mol Sci, Brisbane, Qld 4072, Australia;Univ Western Australia, Sch Mol Sci, Perth, WA 6009, Australia.
    Light metal decorated graphdiyne nanosheets for reversible hydrogen storage2018In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 29, no 35, article id 355401Article in journal (Refereed)
    Abstract [en]

    The sensitive nature of molecular hydrogen (H-2) interaction with the surfaces of pristine and functionalized nanostructures, especially two-dimensional materials, has been a subject of debate for a while now. An accurate approximation of the H-2 adsorption mechanism has vital significance for fields such as H2 storage applications. Owing to the importance of this issue, we have performed a comprehensive density functional theory (DFT) study by means of several different approximations to investigate the structural, electronic, charge transfer and energy storage properties of pristine and functionalized graphdiyne (GDY) nanosheets. The dopants considered here include the light metals Li, Na, K, Ca, Sc and Ti, which have a uniform distribution over GDY even at high doping concentration due to their strong binding and charge transfer mechanism. Upon 11% of metal functionalization, GDY changes into a metallic state from being a small band-gap semiconductor. Such situations turn the dopants to a partial positive state, which is favorable for adsorption of H-2 molecules. The adsorption mechanism of H-2 on GDY has been studied and compared by different methods like generalized gradient approximation, van der Waals density functional and DFT-D3 functionals. It has been established that each functionalized system anchors multiple H-2 molecules with adsorption energies that fall into a suitable range regardless of the functional used for approximations. A significantly high H-2 storage capacity would guarantee that light metal-doped GDY nanosheets could serve as efficient and reversible H-2 storage materials.

  • 374.
    Panigrahi, P.
    et al.
    Hindustan Inst Sci & Technol, Clean Energy & Nano Convergence Ctr, Madras 603103, Tamil Nadu, India.
    Naqvi, S. Rabab
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hankel, M.
    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.
    Hussain, T.
    Univ Queensland, Australian Inst Bioengn & Nanotechnol, Ctr Theoret & Computat Mol Sci, Brisbane, Qld 4072, Australia.
    Enriching the hydrogen storage capacity of carbon nanotube doped with polylithiated molecules2018In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 444, p. 467-473Article in journal (Refereed)
    Abstract [en]

    In a quest to find optimum materials for efficient storage of clean energy, we have performed first principles calculations to study the structural and energy storage properties of one-dimensional carbon nanotubes (CNTs) functionalized with polylithiated molecules (PLMs). Van der Waals corrected calculations disclosed that various PLMs like CLi, CLi2, CLi3, OLi, OLi2, OLi3, bind strongly to CNTs even at high doping concentrations ensuring a uniform distribution of dopants without forming clusters. Bader charge analysis reveals that each Li in all the PLMs attains a partial positive charge and transform into Li+ cations. This situation allows multiple H-2 molecules adsorbed with each Li+ through the polarization of incident H-2 molecules via electrostatic and van der Waals type of interaction. With a maximum doping concentration, that is 3CLi(2)/3CLi(3) and 3OLi(2)/3OLi(3) a maximum of 36 H-2 molecules could be adsorbed that corresponds to a reasonably high H-2 storage capacity with the adsorption energies in the range of -0.33 to -0.15 eV/H-2. This suits the ambient condition applications. (C) 2018 Elsevier B.V. All rights reserved.

  • 375.
    Panigrahi, Puspamitra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araujo, Carlos Moyses Graca
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hussain, Tanveer
    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.
    Crafting ferromagnetism in Mn-doped MgO surfaces with p-type defects2014In: Science and Technology of Advanced Materials, ISSN 1468-6996, E-ISSN 1878-5514, Vol. 15, no 3, p. 035008-Article in journal (Refereed)
    Abstract [en]

    We have employed first-principles calculations based on density functional theory (DFT) to investigate the underlying physics of unusual magnetism in Mn-doped MgO surface. We have studied two distinct scenarios. In the first one, two Mn atoms are substitutionally added to the surface, occupying the Mg sites. Both are stabilized in the Mn3+ valence state carrying a local moment of 4.3 mu(B) having a high-spin configuration. The magnetic interaction between the local moments display a very short-ranged characteristic, decaying very quickly with distance, and having antiferromagnetic ordering lower in energy. The energetics analysis also indicates that the Mn ions prefer to stay close to each other with an oxygen atom bridging the local interaction. In the second scenario, we started exploring the effect of native defects on the magnetism by crafting both Mg and O vacancies, which are p-and n-type defects, respectively. It is found that the electrons and holes affect the magnetic interaction between Mn ions in a totally different manner. The n-type defect leads to very similar magnetism, with the AFM configuration being energetically preferred. However, in the presence of Mg vacancy, the situation is quite different. The Mn atoms are further oxidized, giving rise to mixed Mn(d) ionic states. As a consequence, the Mn atoms couple ferromagnetically, when placed in the close configuration, and the obtained electronic structure is coherent with the double-exchange type of magnetic interaction. To guarantee the robustness of our results, we have benchmarked our calculations with three distinct theory levels, namely DFT-GGA, DFT-GGA+U and DFT-hybrid functionals. On the surface, the Mg vacancy displays lower formation energy occurring at higher concentrations. Therefore, our model systems can be the basis to explain a number of controversial results regarding transition metal doped oxides.

  • 376.
    Panigrahi, Puspamitra
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hussain, Tanveer
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Araujo, Carlos Moyses Graca
    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.
    Hole induced Jahn Teller distortion ensuing ferromagnetism in Mn-MgO: bulk, surface and one dimensional structures2014In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 26, no 26, p. 265801-Article in journal (Refereed)
    Abstract [en]

    Using density functional theory, we investigate the magnetic properties of Mn doped MgO in its bulk (3D), surface (2D) and one dimensional (1D) structures. At a low dilute limit (1.5 %), the Mn impurity behaves indifferent to its position in 3D but energetically prefers to be on one of the surfaces of 2D and 1D structures. At a higher dilute limit (3.1 %), the Mn impurities stabilizing at Mn-d((3+)) ionic states prefer to be in a close configuration (4.2 angstrom compared to 5.95 angstrom) and the antiferromagnetic ordering (AFM) between them is preferred over the ferromagnetic ordering. The n-type extrinsic defects (O vacancy), when introduced to Mn doped MgO structures, also result in similar AFM exchanges as between the Mn impurities. However, the p-type defects (Mg vacancy) in the Mn doped MgO structures result in a reduced magnetic moment for the Mn atoms and bring a significant Jahn Teller (JT)-type of distortion to the e(g) and t(2)g degenerate states of Mn-d((3+)) ions. The strong hybridization between distorted Mnd states and O-2p states results in a FM exchange coupling between the Mn ions, in all the three mentioned Mn doped MgO structures. As we move from 3D to 2D, to 1D structures, the influence of JT distortion decreases, reflecting a decreasing trend for the strength of the FM exchange coupling between the Mn atoms.

  • 377.
    Parlak, Onur
    et al.
    Stanford Univ, Dept Mat Sci & Engn, Stanford, CA 94305 USA.;Linkoping Univ, IFM, Biosensors & Bioelect Ctr, S-58183 Linkoping, Sweden..
    Mishra, Yogendra Kumar
    Univ Kiel, Funct Nanomat, Inst Mat Sci, Kaiserstr 2, D-24143 Kiel, Germany..
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Mecklenburg, Matthias
    Hamburg Univ Technol, Inst Polymers & Composites, Denickestr 15, D-21073 Hamburg, Germany..
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Keene, Scott
    Stanford Univ, Dept Mat Sci & Engn, Stanford, CA 94305 USA..
    Salleo, Alberto
    Stanford Univ, Dept Mat Sci & Engn, Stanford, CA 94305 USA..
    Schulte, Karl
    Hamburg Univ Technol, Inst Polymers & Composites, Denickestr 15, D-21073 Hamburg, Germany..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Adelung, Rainer
    Univ Kiel, Funct Nanomat, Inst Mat Sci, Kaiserstr 2, D-24143 Kiel, Germany..
    Turner, Anthony P. F.
    Linkoping Univ, IFM, Biosensors & Bioelect Ctr, S-58183 Linkoping, Sweden..
    Tiwari, Ashutosh
    Linkoping Univ, IFM, Biosensors & Bioelect Ctr, S-58183 Linkoping, Sweden.;UCS, Inst Adv Mat, IAAM, Mjardevi Sci Pk,Teknikringen 4A, S-58330 Linkoping, Sweden..
    Hierarchical Aerographite nano-microtubular tetrapodal networks based electrodes as lightweight supercapacitor2017In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 34, p. 570-577Article in journal (Refereed)
    Abstract [en]

    A great deal of interest has been paid to the application of carbon-based nano-and microstructured materials as electrodes due to their relatively low-cost production, abundance, large surface area, high chemical stability, wide operating temperature range, and ease of processing including many more excellent features. The nanostructured carbon materials usually offer various micro-textures due to their varying degrees of graphitisation, a rich variety in terms of dimensionality as well as morphologies, extremely large surface accessibility and high electrical conductivity, etc. The possibilities of activating them by chemical and physical methods allow these materials to be produced with further higher surface area and controlled distribution of pores from nanoscale upto macroscopic dimensions, which actually play the most crucial role towards construction of the efficient electrode/electrolyte interfaces for capacitive processes in energy storage applications. Development of new carbon materials with extremely high surface areas could exhibit significant potential in this context and motivated by this in present work, we report for the first time the utilization of ultralight and extremely porous nano-microtubular Aerographite tetrapodal network as a functional interface to probe the electrochemical properties for capacitive energy storage. A simple and robust electrode fabrication strategy based on surface functionalized Aerographite with optimum porosity leads to significantly high specific capacitance (640 F/g) with high energy (14.2 Wh/kg) and power densities (9.67x103 W/kg) which has been discussed in detail.

  • 378.
    Pathak, Biswarup
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Löfås, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Prasongkit, Jariyanee
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    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.
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Double-functionalized nanopore-embedded gold electrodes for rapid DNA sequencing2012In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, no 2, p. 023701-Article in journal (Refereed)
    Abstract [en]

    We have studied the effect of double-functionalization on gold electrodes for improving nanopore-based DNA sequencing. The functionalizing molecular probes are, respectively, capable of temporarily forming hydrogen bonds with both the nucleobase part and the phosphate group of the target DNA, thus potentially minimizing the structural fluctuations of a single-stranded DNA molecule passing between the gold electrodes. The results of our first-principles study indicate that the proposed setup yields current signals that differ by at least 1 order of magnitude for the four different nucleic acid bases, thus offering the possibility to electrically distinguish them.

  • 379.
    Pathak, Biswarup
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pradhan, Kalpataru
    Hussain, Tanveer
    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.
    Jena, Purusottam
    Functionalized Boranes for Hydrogen Storage2012In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 13, no 1, p. 300-304Article in journal (Refereed)
    Abstract [en]

    Using density functional theory, the generalized gradient approximation for the exchange-correlation potential and MollerPlesset perturbation theory we study the hydrogen uptake of Li- and Mg-doped boranes. Specifically, we calculate the structures and binding energies of hydrogen molecules sequentially attached to LiB6H7, LiB12H13, Li2B6H6, Li2B12H12, MgB6H6, and MgB12H12. Up to three H2 molecules can be bound quasi-molecularly to each of the metal cations with binding energies per H2 molecule ranging between 0.07 eV and 0.27 eV. The corresponding gravimetric densities lie in the range of 3.49 to 12 wt %, not counting the H atoms bound chemically to the B atoms.

  • 380.
    Pathak, Biswarup
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Samanta, Devleena
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jena, Purusottam
    Borane Derivatives: A New Class of Super- and Hyperhalogens2011In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 12, no 13, p. 2422-2427Article in journal (Refereed)
    Abstract [en]

    Super- and hyperhalogens are a class of highly electronegative species whose electron affinities far exceed those of halogen atoms and are important to the chemical industry as oxidizing agents, biocatalysts, and building blocks of salts. Using the well-known Wade-Mingos rule for describing the stability of closo-boranes B(n)H(n)(2-) and state-of-the-art theoretical methods, we show that a new class of super-and hyperhalogens, guided by this rule, can be formed by tailoring the size and composition of borane derivatives. Unlike conventional superhalogens, in which a central metal atom is surrounded by halogen atoms, the superhalogens formed according to the Wade-Mingos rule do not have to have either halogen or metal atoms. We demonstrate this by using B(12)H(13) and its isoelectronic cluster CB(11)H(12) as examples. We also show that while conventional superhalogens containing alkali atoms require at least two halogen atoms, a single borane-like moiety is sufficient to give M(B(12)H(12)) clusters (M = Li, Na, K, Rb, Cs) superhalogen properties. In addition, hyperhalogens can be formed by using the above superhalogens as building blocks. Examples include M(B(12)H(13))(2) and M(CB(11)H(12))(2) (M = Li-Cs). This finding opens the door to an untapped source of superhalogens and weakly coordinating anions with potential applications.

  • 381.
    Peng, Xiangyang
    et al.
    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.
    Epitaxial graphene monolayer and bilayers on Ru(0001): Ab initio calculations2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 4, p. 045425-Article in journal (Refereed)
    Abstract [en]

    We studied very large graphene/Ru systems by ab initio calculations. It is shown that the graphene monolayer on Ru is nearly flat rather than strongly corrugated. The large corrugation is found to be unfavorable and disagrees with the observed bias dependence of scanning tunnel microscope images. The C-Ru bonds are metallic instead of covalent. A new moire structure arises between graphene bilayers and the generally supposed Bernal stacking is broken. The second layer has higher density of C atoms and is slightly corrugated. While the electronic states of the first graphene layer are shifted down by about 1 eV, the electronic structure of the second one resembles that of the free graphene, in good agreement with the experiments.

  • 382. Peng, Xiangyang
    et al.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Non-transition-metal doped diluted magnetic semiconductors2009In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 94, no 10, p. 102504-Article in journal (Refereed)
    Abstract [en]

    Based on first-principles calculations, we have investigated the magnetic properties of non-transition-metal doped semiconductors Al(N,X) and Zn(O,X), where X is a first row atom. It is revealed that the dopant can remain magnetic only if it is less electronegative than the substituted host anion atom and the dopant 2p states are located within the energy gap of the host. The calculated magnetic moment per dopant in mu(B) is the atomic number difference between the dopant and the host anion atom. The global magnetic order is determined by the hole number, the interaction between the 2p dopant states and their exchange splitting. It is found that the Curie temperature is highest when the atomic number of the dopant is smaller than that of the anion by two.

  • 383.
    Peng, Xiangyang
    et al.
    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.
    Symmetry Breaking Induced Bandgap in Epitaxial Graphene Layers on SiC2008In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 8, no 12, p. 4464-4468Article in journal (Refereed)
    Abstract [en]

    By performing density-functional calculations, we have investigated the electronic bandgap of single epitaxial and multiepitaxial graphene layers on SiC. The calculations show that a defect-free graphene layer above the carbon buffer layer is very flat and no bandgap is found in the Dirac bands. By introducing a finite density of Stone-Wales defects in the graphene layer(s), we find that a bandgap is opened and decreases as the thickness of graphene layers increases, in good agreement with experiments. The band splitting and the charge distribution vary greatly with the number of graphene layers. The bandgap opening is due to the symmetry breaking within the single graphene layer. The narrowing of the bandgap in multiple graphene layers is induced by interlayer interaction.

  • 384. Persson, C
    et al.
    Dong, C L
    Vayssieres, L
    Augustsson, Andreas
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics II. Physics IV.
    Schmitt, Thorsten
    Mattesini, M
    Ahuja, Rajeev
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics II. Physics IV.
    Nordgren, Joseph
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Physics, Department of Physics. Department of Physics and Materials Science, Physics II. Physics IV.
    Chang, C L
    da Silva, A F
    Guo, Jinghua
    X-ray absorption and emission spectroscopy of ZnO nanoparticle and highly oriented ZnO microrod arrays2006In: Microelectronics Journal, Vol. 37, no 8, p. 686-689Article in journal (Refereed)
  • 385. Phatak, Nishad A.
    et al.
    Kulkarni, Shrinivas R.
    Drozd, Vadym
    Saxena, Surendra K.
    Deng, Liwei
    Fei, Yingwei
    Hu, Jingzhu
    Luo, Wei
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Condensed Matter Theory.
    Synthesis and compressive behavior of Cr2GeC up to 48 GPa2008In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 463, no 1-2, p. 220-225Article in journal (Refereed)
    Abstract [en]

    M(n+1)AX(n) compounds have gathered huge momentum because of its exciting properties. In this paper we report the synthesis of ternary layered ceramic Cr2GeC, a 211 M(n+1)AX(n) compound by hot-pressing. Scanning electron microscopy and X-ray diffraction have been employed to characterize the new synthesized phase. High-pressure compressibility of Cr2GeC were measured using diamond anvil cell and synchrotron C radiation at room temperature up to 48 GPa. No phase transformation was observed in the experimental pressure range. The bulk modulus of Cr2GeC calculated using the Birch-Murnaghan equation of state is 169 +/- 3 GPa, with K' = 3.05 +/- 0.15.

  • 386.
    Philippe, Bertrand
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Jacobsson, T. Jesper
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry. École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
    Correa-Baena, Juan-Pablo
    École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; Massachusetts Institute of Technology, Cambridge, USA .
    Jena, Naresh K.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Banerjee, Amitava
    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.
    Cappel, Ute B.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hagfeldt, Anders
    École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland.
    Odelius, Michael
    Stockholm University, Stockholm, Sweden.
    Rensmo, Håkan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics.
    Valence Level Character in a Mixed Perovskite Material and Determination of the Valence Band Maximum from Photoelectron Spectroscopy: Variation with Photon Energy2017In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 48, p. 26655-26666Article in journal (Refereed)
    Abstract [en]

    A better understanding of the electronic structure of perovskite materials used in photovoltaic devices is essential for their development and optimization. In this investigation, synchrotron based photoelectron spectroscopy (PES) was used to experimentally delineate the character and energy position of the valence band structures of a mixed perovskite. The valence band was measured using PES with photon energies ranging from UPS (21.2 eV) to hard X-rays (up to 4,000 eV) and by taking the variation of the photoionization cross-sections into account, we could experimentally determine the inorganic and organic contributions. The experiments were compared to theoretical calculations to further distinguish the role of the different anions in the electronic structure. The investigation also includes a thorough study of the valence band maximum (VBM) and its position in relation to the Fermi level, which is crucial for the design and optimization of complete solar cells and their functional properties.

  • 387.
    Pietzsch, Annette
    et al.
    MAXlab, Lund University.
    Nisar, Jawad
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Jamstorp, Erik
    Gråsjö, Johan
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy.
    Kennedy, Brian
    Hennies, Franz
    Arhammar, Cecilia
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Rubensson, Jan-Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
    Kaolinite: defect states define material properties-a soft x-ray and first principles study of the band gap2015In: Journal of Electron Spectroscopy and Related Phenomena, ISSN 0368-2048, E-ISSN 1873-2526, Vol. 202, p. 11-15Article in journal (Refereed)
  • 388. Pinsook, Udomsilp
    et al.
    Scheicher, Ralph H
    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, Physics IV.
    Hannongbua, Supot
    Internal vibrations of the Li(NH3)4+ complex analyzed from ab initio, density functional theory, and the classical spring network model2008In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 112, no 24, p. 5323-5326Article in journal (Refereed)
    Abstract [en]

    We report our theoretical findings regarding internal vibrations of the Li(NH3)4+ complex which have been studied using three different methods, namely, a classical spring network model, density functional theory, and ab initio Hartree−Fock plus Møller−Plesset correlation energy correction truncated at second-order. The equilibrium Li···N and N···N distances are found to be 2.12 and 3.47 Å, respectively, in good agreement with the experimental data. The theoretically determined vibrational frequencies of the lowest modes are in good agreement with those extracted from inelastic X-ray scattering measurements. From group theory considerations, the internal vibrations of Li(NH3)4+ complexes resemble those of a tetrahedral object. Further experimental investigation is suggested.

  • 389. Prasongkit, Jariyanee
    et al.
    Amorim, Rodrigo G.
    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.
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Amornkitbamrung, Vittaya
    Highly Sensitive and Selective Gas Detection Based on Silicene2015In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 119, no 29, p. 16934-16940Article in journal (Refereed)
    Abstract [en]

    Recent advances in the fabrication of silicene devices have raised exciting prospects for practical applications such as gas sensing. We investigated the gas detection performance of silicene nanosensors for four different gases (NO, NO2, NH3, and CO) in terms of sensitivity and selectivity, employing density functional theory and nonequilibrium Greens function method. The structural configurations, adsorption sites, binding energies and charge transfer of all studied gas molecules on silicene nanosensors are systematically discussed in this work. Our results indicate that pristine silicene exhibits strong sensitivity for NO and NO2, while it appears incapable of sensing CO and NH3. In an attempt to overcome sensitivity limitations due to weak van der Waals interaction of those latter gas molecules on the device, we doped pristine silicene with either B or N atoms, leading to enhanced binding energy as well as charge transfer, and subsequently a significant improvement of sensitivity. A distinction between the four studied gases based on the silicene devices appears possible, and thus these promise to be next-generation nanosensors for highly sensitive and selective gas detection.

  • 390.
    Prasongkit, Jariyanee
    et al.
    Nakhon Phanom Univ, Div Phys, Fac Sci, Nakhon Phanom 48000, Thailand.;NanotecKKU Ctr Excellence Adv Nanomat Energy Prod, Khon Kaen 40002, Thailand..
    Feliciano, Gustavo T.
    Univ Estadual Paulista UNESP, Inst Chem, Dept Phys Chem, Araraquara, SP, Brazil..
    Rocha, Alexandre R.
    Univ Estadual Paulista UNESP, Inst Fis Teor, Sao Paulo, SP, Brazil..
    He, Yuhui
    Huazhong Univ Sci & Technol, Sch Opt & Elect Informat, Wuhan 430074, Peoples R China..
    Osotchan, Tanakorn
    Mahidol Univ, Dept Phys, Fac Sci, Bangkok 10400, Thailand..
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Royal Inst Technol, Dept Mat & Engn, Appl Mat Phys, SE-10044 Stockholm, Sweden..
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Theoretical assessment of feasibility to sequence DNA through interlayer electronic tunneling transport at aligned nanopores in bilayer graphene2015In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, article id 17560Article in journal (Refereed)
    Abstract [en]

    Fast, cost effective, single-shot DNA sequencing could be the prelude of a new era in genetics. As DNA encodes the information for the production of proteins in all known living beings on Earth, determining the nucleobase sequences is the first and necessary step in that direction. Graphene-based nanopore devices hold great promise for next-generation DNA sequencing. In this work, we develop a novel approach for sequencing DNA using bilayer graphene to read the interlayer conductance through the layers in the presence of target nucleobases. Classical molecular dynamics simulations of DNA translocation through the pore were performed to trace the nucleobase trajectories and evaluate the interaction between the nucleobases and the nanopore. This interaction stabilizes the bases in different orientations, resulting in smaller fluctuations of the nucleobases inside the pore. We assessed the performance of a bilayer graphene nanopore setup for the purpose of DNA sequencing by employing density functional theory and non-equilibrium Green's function method to investigate the interlayer conductance of nucleobases coupling simultaneously to the top and bottom graphene layers. The obtained conductance is significantly affected by the presence of DNA in the bilayer graphene nanopore, allowing us to analyze DNA sequences.

  • 391.
    Prasongkit, Jariyanee
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    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.
    Conductance of linear carbon wires bridging carbon nanotubesManuscript (preprint) (Other academic)
    Abstract [en]

    The cumulenes bridging two-dimensional electrodes provide a model for interconnecting molecular electronics circuit with one of the most conductive molecular wires known. In recent experiments cumulene molecules bridging graphene sheets were observed [PRL 102, 205501 (2009)], thus demonstrating the mechanical way of producing cumulenes. Appearance of carbon wires: cumulenes and polynes, is also feasible between graphene sheets or carbon nanotubes (CNTs). In this work, we study structure and conductance of these wires  suspended between CNTs of different chirality (zigzag and armchair), and graphene sheets (infinite radii CNTs) and corresponding conductance variation upon stretching. We find the geometrical structures of the carbon wire bridging CNT similar to the experimentally observed in the carbon wires obtained between graphene electrodes. We show a capability to modulate the conductance by changing bridging sites between the carbon wire and CNT without breaking the wire. Observed current modulation via cumulene wire stretching/elongation together with CNT stability makes it a promising candidate for mechano-switching device in molecular nanoelectronics.

  • 392.
    Prasongkit, Jariyanee
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    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.
    Mechano-switching devices from carbon wire-carbon nanotube junctions2013In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 87, no 15, p. 155434-155442Article in journal (Refereed)
    Abstract [en]

    Well-known conductive molecular wires, such as cumulene or polyyne, provide a model for interconnectingmolecular electronics circuits. In recent experiments, the appearance of carbon wire bridging between twodimensional electrodes, i.e., graphene sheets, was observed [C. Jinet al.,Phys. Rev. Lett.102, 205501 (2009)], thusdemonstrating a mechanical way of producing cumulene. In this work, we studied the structure and conductanceof carbon wire suspended between carbon nanotubes (CNTs) of different chiralities (zigzag and armchair), andcorresponding conductance variation upon stretching. We found that the geometric structure of the carbon wirebridging CNTs was similar to the experimentally observed structures in carbon wire obtained between grapheneelectrodes. We show a way to modulate conductance by changing bridging sites between carbon wire and CNTswithout breaking the wire. Observed current modulation via cumulene wire stretching or elongation together withCNT junction stability makes this a promising candidate for use in mechano-switching devices for molecularnanoelectronics.

  • 393.
    Prasongkit, Jariyanee
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    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.
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Theoretical Study of Electronic Transport through DNA Nucleotides in a Double-Functionalized Graphene Nanogap2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 29, p. 15421-15428Article in journal (Refereed)
    Abstract [en]

    Graphene nanogaps and nanopores show potential for the purpose of electrical DNA sequencing, in particular because single-base resolution appears to be readily achievable. Here, we evaluated from first principles the advantages of a nanogap setup with functionalized graphene edges. To this end, we employed density functional theory and the non-equilibrium Green's function method to investigate the transverse conductance properties of the four nucleotides occurring in DNA when located between opposing functionalized graphene electrodes. In particular, we determined the electrical tunneling current variation as a function of the applied bias and analyzed the associated differential conductance at a voltage which appears suitable to distinguish between the four nucleotides. Intriguingly, we predict for one of the nucleotides (deoxyguanosine monophosphate) a negative differential resistance effect.

  • 394.
    Prasongkit, Jariyanee
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    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.
    Scheicher, Ralph H.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Transverse Conductance of DNA Nucleotides in a Graphene Nanogap from First Principles2011In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 11, no 5, p. 1941-1945Article in journal (Refereed)
    Abstract [en]

    The fabrication of nanopores in atomically thin graphene has recently been achieved, and translocation of DNA has been demonstrated. Taken together with an earlier proposal to use graphene nanogaps for the purpose of DNA sequencing, this approach can resolve the technical problem of achieving single-base resolution in electronic nucleobase detection. We have theoretically evaluated the performance of a graphene nanogap setup for the purpose of whole-genome sequencing, by employing density functional theory and the nonequilibrium Green's function method to investigate the transverse conductance properties of nucleotides inside the gap. In particular, we determined the electrical tunneling current variation at finite bias due to changes in the nucleotides orientation and lateral position. Although the resulting tunneling current is found to fluctuate over several orders of magnitude, a distinction between the four DNA bases appears possible, thus ranking the approach promising for rapid whole-genome sequencing applications.

  • 395.
    Prasongkit, Jariyanee
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Scheicher, Ralph
    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.
    Transport properties of nucleotides in a graphene nanogap for DNA sequencing2010In: ElecMol’10 5th International Meeting on Molecular Electronics December 6-10, 2010, 2010, p. 86-86Conference paper (Other academic)
  • 396.
    Prasongkit, Jariyanee
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wendin, G.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Cumulene molecular wire conductance from first principles2010In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 11, p. 115404-Article in journal (Refereed)
    Abstract [en]

    We present first principles calculations of current-voltage characteristics (IVC) and conductance of Au(111):S-2-cumulene-S-2:Au(111) molecular wire junctions with realistic contacts. The transport properties are calculated using full self-consistent ab initio nonequilibrium Green's function density-functional theory methods under external bias. The conductance of the cumulene wires shows oscillatory behavior depending on the number of carbon atoms (double bonds). Among all conjugated oligomers, we find that cumulene wires with odd number of carbon atoms yield the highest conductance with metalliclike ballistic transport behavior. The reason is the high density of states in broad lowest unoccupied molecular orbital levels spanning the Fermi level of the electrodes. The transmission spectrum and the conductance depend only weakly on applied bias, and the IVC is nearly linear over a bias region of +/- 1 V. Cumulene wires are therefore potential candidates for metallic connections in nanoelectronic applications.

  • 397.
    Prasongkit, Jariyanee
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Grigoriev, Anton
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Wendin, Goran
    Department of Microtechnology and Nanoscience-MC2, Chalmers University of Technology.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Interference effects in phtalocyanine controlled by H-H tautomerization: Potential two-terminal unimolecular electronic switch2011In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 84, no 16, p. 165437-Article in journal (Refereed)
    Abstract [en]

    We investigate the electrical transport properties of two hydrogen tautomer configurations of phthalocyanine (H2Pc) connected to cumulene and gold leads. Hydrogen tautomerization affects the electronic state of H2Pc by switching the character of molecular orbitals with the same symmetry close to the Fermi level. The near degeneracy between the HOMO and HOMO-1 leads to pronounced interference effects, causing a large change in current for the two tautomer configurations, especially in the low-bias regime. Two types of planar junctions are considered: cumulene-H2Pc-cumulene and gold-H2Pc-gold. Both demonstrate a prominent difference in molecular conductance between ON and OFF states. In addition, junctions with gold leads show pronounced negative differential resistance (NDR) at high bias voltage, as well as weak NDR at intermediate bias.

  • 398.
    Qian, Zhao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    De Sarkar, Abir
    Maark, Tuhina Adit
    Jiang, Xue
    Deshpande, Mrinalini D.
    Bououdina, Mohamed
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Pure and Li-doped NiTiH: Potential anode materials for Li-ion rechargeable batteries2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 3, p. 033902-Article in journal (Refereed)
    Abstract [en]

    Pure and Li-doped NiTiH hydrides have been explored for their potential applications as anode materials for Li-ion batteries using density functional theory. The diffusion of Li-ion through pure NiTiH lattice has revealed a big enhancement at 600 K with the diffusion coefficient estimated to be 2.3 x 10(-10) m(2) s(-1) or so. The most thermodynamically stable Li-doped NiTiH material has been ascertained, which evidently shows enhanced electrochemical capacity and a minor increase in voltage and unit-cell volume with respect to pure NiTiH.

  • 399.
    Qian, Zhao
    et al.
    Shandong Univ, Shandong, Peoples R China.
    Guo, Weimin
    Shandong Univ, Shandong, Peoples R China.
    Jiang, Guanzhong
    Shandong Univ, Shandong, Peoples R China.
    Xu, Shaokun
    Shandong Univ, Shandong, Peoples R China.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. KTH, Stockholm, Sweden.
    Liu, Xiangfa
    Shandong Univ, Shandong, Peoples R China.
    Revisiting Mg-Mg2Ni System from Electronic Perspective2017In: METALS, ISSN 2075-4701, Vol. 7, no 11, article id 489Article in journal (Refereed)
    Abstract [en]

    Both Mg and Mg2Ni are promising electrode materials in conversion-type secondary batteries. Earlier studies have shown their single-phase prospects in electro-devices, while in this work, we have quantitatively reported the electronic properties of their dual-phase materials, that is, Mg-Mg2Ni alloys, and analyzed the underlying reasons behind the property changes of materials. The hypoeutectic Mg-Mg2Ni alloys are found to be evidently more conductive than the hypereutectic Mg-Mg2Ni system. The density functional theory (DFT) calculations give the intrinsic origin of electronic structures of both Mg2Ni and Mg. The morphology of quasi-nanoscale eutectics is another factor that can affect the electronic properties of the investigated alloy system; that is, the electrical property change of the investigated alloys system is due to a combination of the intrinsic property difference between the two constituting phases and the change of eutectic microstructures that affect electron scattering. In addition, regarding the Mg-Mg2Ni alloy design for device applications, the electronic property and mechanical aspect should be well balanced.

  • 400.
    Qian, Zhao
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Hudson, M. Sterlin Leo
    Raghubanshi, Himanshu
    Scheicher, Ralph H.
    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.
    Araújo, C. Moysés
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Blomqvist, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Johansson, Börje
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Srivastava, O. N.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
    Excellent Catalytic Effects of Graphene Nanofibers on Hydrogen Release of Sodium alanate2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 20, p. 10861-10866Article in journal (Refereed)
    Abstract [en]

    One of the most technically challenging barriers to the widespread commercialization of hydrogen-fueled devices and vehicles remains hydrogen storage. More environmentally friendly and effective nonmetal catalysts are required to improve hydrogen sorption. In this paper, through a combination of experiment and theory, we evaluate and explore the catalytic effects of layered graphene nanofibers toward hydrogen release of light metal hydrides such as sodium alanate. Graphene nanofibers, especially the helical kind, are found to considerably improve hydrogen release from NaAlH4, which is of significance for the further enhancement of this practical material for environmentally friendly and effective hydrogen storage applications. Using density functional theory, we find that carbon sheet edges, regardless of whether they are of zigzag or armchair type, can weaken Al-H bonds in sodium alanate, which is believed to be due to a combination of NaAlH4 destabilization and dissociation product stabilization. The helical form of graphene nanofibers, with larger surface area and curved configuration, appears to benefit the functionalization of carbon sheet edges. We believe that our combined experimental and theoretical study will stimulate more explorations of other microporous or mesoporous nanomaterials with an abundance of exposed carbon edges in the application of practical complex light metal hydride systems.

567891011 351 - 400 of 547
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