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  • 251.
    Huang, Shuo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Quantum-Mechanical Modeling of High-Entropy Alloys2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    High-entropy alloys (HEAs) consisting of multi-principal elements open up a near-infinite compositional space for materials design. Extensive attention has been put on HEAs, and interesting structural, physical and chemical properties are being continuously revealed. Based on first-principle theory, here we focus on the fundamental characteristics of HEAs, as well as on the optimization and prediction of alternative alloy with promising technological applications.

    The relative phase stability of different-types of HEAs is investigated from the minimum of structural energy, and the composition-, temperature-, and ordering-induced phase transformations are presented. The elastic properties are discussed through the single-crystal and polycrystalline elastic moduli by making use of a series of phenomenological models. The competition between full slip, twinning, and stacking fault in face-centered cubic HEAs is analyzed by studying the generalized stacking fault energy. The magnetic characteristics are provided through the Heisenberg Hamiltonian model in connection with Monte-Carlo simulation, and the Curie temperature of a large number of cubic HEAs is mapped out with the help of mean-filed approximation. The thermal expansion behavior is estimated by using the Debye-Grüneisen model.

    This work provides some fundamental and pioneering theoretical points of view to understand the intrinsic physical mechanisms in HEAs, and reveals alternative opportunities for optimizing and designing properties of materials. The challenge of comprehending the observed complex behavior behind the multi-component nature of HEAs is great, on the other hand, the potential to enhance the underlying theoretical understanding is remarkable.

  • 252.
    Huang, Shuo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Theoretical Investigations of High-Entropy Alloys2017Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    High-entropy alloys (HEAs) are composed of multi-principal elements with equal or near-equal concentrations, which open up a vast compositional space for alloy design. Based on first-principle theory, we focus on the fundamental characteristics of the reported HEAs, as well as on the optimization and prediction of alternative HEAs with promising technological applications.

    The ab initio calculations presented in the thesis confirm and predict the relatively structural stability of different HEAs, and discuss the composition and temperature-induced phase transformations. The elastic behavior of several HEAs are evaluated through the single-crystal and polycrystalline elastic moduli by making use of a series of phenomenological models. The competition between dislocation full slip, twinning, and martensitic transformation during plastic deformation of HEAs with face-centered cubic phase are analyzed by studying the generalized stacking fault energy. The magnetic moments and magnetic exchange interactions for selected HEAs are calculated, and then applied in the Heisenberg Hamiltonian model in connection with Monte-Carlo simulations to get further insight into the magnetic characteristics including Curie point. The Debye-Grüneisen model is used to estimate the temperature variation of the thermal expansion coefficient.

    This work provides specific theoretical points of view to try to understand the intrinsic physical mechanisms behind the observed complex behavior in multi-component systems, and reveals some opportunities for designing and optimizing the properties of materials

  • 253.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Holmstrom, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Eriksson, Olle
    Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Orebro Univ, Sch Sci & Technol, SE-70182 Orebro, Sweden..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ; Wigner Res Ctr Phys.
    Mapping the magnetic transition temperatures for medium- and high-entropy alloys2018Inngår i: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 95, s. 80-84Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Tailorable magnetic state near room temperature is very promising for several technological, including magnetocaloric applications. Here using first-principle alloy theory, we determine the Curie temperature (T-C) of a number of equiatomic medium- and high-entropy alloys with solid solution phases. All calculations are performed at the computed lattice parameters, which are in line with the available experimental data. Theory predicts a large crystal structure dependence of T-C, which explains the experimental observations under specified conditions. The sensitivity of the magnetic state to the crystal lattice is reflected by the magnetic exchange interactions entering the Heisenberg Hamiltonian. The analysis of the effect of composition on T-C allows researchers to explore chemistry-dependent trends and design new multi-component alloys with pre-assigned magnetic properties.

  • 254.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Huang, He
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Science and Technology on Surface Physics and Chemistry Laboratory, Mianyang, 621900, PR China.
    Li, Wei
    Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, SE-75120, Uppsala, Sweden.
    Kim, Dongyoo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics, Pukyung National University, Busan, 608-737, Republic of Korea.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Holmström, E.
    Kwon, S. K.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Twinning in metastable high-entropy alloys2018Inngår i: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, nr 1, artikkel-id 2381Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Twinning is a fundamental mechanism behind the simultaneous increase of strength and ductility in medium- and high-entropy alloys, but its operation is not yet well understood, which limits their exploitation. Since many high-entropy alloys showing outstanding mechanical properties are actually thermodynamically unstable at ambient and cryogenic conditions, the observed twinning challenges the existing phenomenological and theoretical plasticity models. Here, we adopt a transparent approach based on effective energy barriers in combination with first-principle calculations to shed light on the origin of twinning in high-entropy alloys. We demonstrate that twinning can be the primary deformation mode in metastable face-centered cubic alloys with a fraction that surpasses the previously established upper limit. The present advance in plasticity of metals opens opportunities for tailoring the mechanical response in engineering materials by optimizing metastable twinning in high-entropy alloys. 

  • 255.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Holmström, E.
    Kwon, S. K.
    Eriksson, O.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Uppsala, Sweden; Sandvik Coromant R&D, Stockholm, Sweden.
    Plastic deformation transition in FeCrCoNiAlx high-entropy alloys2019Inngår i: Materials Research Letters, ISSN 2166-3831, Vol. 7, nr 11, s. 439-445Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The competition between plastic deformation mechanisms in FeCrCoNiAlx high-entropy alloys is explored as a function of temperature by first-principle theory. Investigating the generalized stacking fault energy, we identify a strong interplay between the magnetic and chemical effects. At cryogenic conditions (ferromagnetic state), full-slip is accompanied by martensitic transformation, whereas increasing temperature towards room-temperature (paramagnetic state) changes the deformation mechanism to full-slip plus twinning. Alloying with Al reduces the susceptibility for stacking fault formation in the ferromagnetic state and promotes twinning in the paramagnetic state. The present advance in magneto-plasticity reveals new opportunities for tailoring the mechanical response in high-entropy alloys. IMPACT STATEMENT: Magnetic state critically affects the γ-surface of FeCrCoNiAlx and is responsible for the emergence of the exceptional metastable twinning phenomena at room temperature.

  • 256.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Holmström, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Vitos, Levente
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Uppsala Univ, Dept Phys & Astron, Div Mat Theory, SE-75120 Uppsala, Sweden.;Inst Solid State Phys & Opt, Wigner Res Ctr Phys, H-1525 Budapest, Hungary..
    Phase-transition assisted mechanical behavior of TiZrHfTax high-entropy alloys2018Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 8, artikkel-id 12576Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent developments of high-entropy alloys with high strength and high ductility draw attention to the metastability-engineering strategy. Using first-principle theory, here we demonstrate that reducing the Ta level in the refractory TiZrHfTax system destabilizes the body-centered cubic (bcc) phase and leads to the appearance of the hexagonal close-packed (hcp) phase embedded in the bcc matrix. The alloying-induced features of the elastic parameters for the cubic and hexagonal structures are mapped out in details, and strong sensitivity to the crystal lattice and chemistry is revealed. Results show softening of the bcc matrix with decreasing Ta concentration which ensures ductile behavior. However, the elastically nearly isotropic hcp precipitates possess enhanced resistance against shear which promotes strengthening of the TiZrHfTax dual-phase system. The present atomic-level insight provides strong evidence to the experimental observation, and emphasizes the significance of quantum-design for advanced multi-phase high-entropy alloys with excellent strength-ductility combinations.

  • 257.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Holmström, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Wigner Res Ctr Phys, Inst Solid State Phys & Opt, H-1525 Budapest, Hungary.;Uppsala Univ, Div Mat Theory, Dept Phys & Astron, SE-75120 Uppsala, Sweden..
    Strengthening Induced by MagnetoChemical Transition in Al-Doped Fe-Cr-Co-Ni High-Entropy Alloys2018Inngår i: Physical Review Applied, E-ISSN 2331-7019, Vol. 10, nr 6, artikkel-id 064033Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Alloys with adjustable mechanical performance are of fundamental interest in material designs. Here, we investigate the magnetic- and chemical-ordering behavior of the ferromagnetic Fe-Cr-Co-Ni-Al-x (1 <= x <= 2.5) high-entropy alloys with the help of first-principle alloy theory. The lattice constants and the single- and polycrystalline elastic parameters for partially ordered and random structures are considered. In contrast to the trend found for the completely disordered phase, we demonstrate that ordering driven primarily by Al results in an enhanced Young's modulus, especially at high-Al concentrations, which is in line with the observed increase of the hardness for systems with a body-centered-cubic underlying lattice. The results suggest that outstanding strength and ductility can be realized by proper control of the ordering level in single- and multiphase high-entropy alloys.

  • 258.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Bergqvist, Lars
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Holmström, E.
    Varga, L. K.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Wigner Research Centre for Physics, Hungary; Uppsala University, Sweden.
    Mechanism of magnetic transition in FeCrCoNi-based high entropy alloys2016Inngår i: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 103, s. 71-74Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    First-principles alloy theory and Monte-Carlo simulations are performed to investigate the magnetic properties of FeCrCoNiAlx high entropy alloys. Results show that face-centered-cubic (fcc) and body-centered-cubic (bcc) structures possess significantly different magnetic behaviors uncovering that the alloy's Curie temperature is controlled by the stability of the Al-induced single phase or fcc-bcc dual-phase. We show that the appearance of the bcc phase with increasing Al content brings about the observed transition from the paramagnetic state for FeCrCoNi to the ferromagnetic state for FeCrCoNiAl at room-temperature. Similar mechanism is predicted to give rise to room-temperature ferromagnetism in FeCrCoNiGa high entropy alloy.

  • 259.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Lu, Song
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Tian, Fuyang
    Univ Sci & Technol Beijing, Dept Phys, Beijing 100083, Peoples R China..
    Shen, Jiang
    Univ Sci & Technol Beijing, Dept Phys, Beijing 100083, Peoples R China..
    Holmstrom, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, SE-75120 Uppsala, Sweden.
    Temperature dependent stacking fault energy of FeCrCoNiMn high entropy alloy2015Inngår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 108, s. 44-47Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stacking fault energy (SFE) of paramagnetic FeCrCoNiMn high entropy alloy is investigated as a function of temperature via ab initio calculations. We divide the SFE into three major contributions: chemical, magnetic and strain parts. Structural energies, local magnetic moments and elastic moduli are used to estimate the effect of temperature on each term. The present results explain the recently reported twinning observed below room-temperature and predict the occurrence of the hexagonal phase at cryogenic conditions.

  • 260.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Li, Xiaoqing
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Huang, He
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Sci & Technol Surface Phys & Chem Lab, Mianyang 621900, Peoples R China..
    Holmström, Erik
    Sandvik Coromant R&D, S-12680 Stockholm, Sweden..
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Div Mat Theory, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Wigner Res Ctr Phys, Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Mechanical performance of FeCrCoMnAlx high-entropy alloys from first-principle2018Inngår i: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 210, s. 37-42Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The elastic parameters and ideal tensile strength in the 10011 direction for the body-centered cubic solid solution phase of FeCrCoMnAlx (0.6 <= x <= 1.5) high-entropy alloys are determined using first-principle alloy theory. Based on the estimated theoretical Curie temperatures, all alloys considered here are predicted to order ferromagnetically at room temperature. The mechanical behaviors are analyzed through the single-crystal and polycrystalline elastic moduli, Pugh ratio, and Debye temperature by making use of a series of phenomenological models. High ideal tensile strength is found for the equiatomic FeCrCoMnAl system, and the intrinsic strength increases with decreasing Al content.

  • 261.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Tian, F.
    Vitos, Levente
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Elasticity of high-entropy alloys from ab initio theory2018Inngår i: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 33, nr 19, s. 2938-2953Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-entropy alloys (HEAs) consisting of multiprincipal elements have demonstrated many interesting structural, physical, and chemical properties for a wide range of applications. This article is a review of the current theoretical research on the elastic parameters of HEAs. The performance of various ab initio-based computational models (effective medium and supercell approaches) is carefully analyzed. Representative theoretical elastic parameters of different HEAs, including single-crystal elastic constants, polycrystalline elastic moduli, elastic anisotropy, and Debye temperature, are presented and discussed. For comparison, simple mixtures of the elastic moduli of pure elements are calculated and contrasted with the ab initio results. The present work provides a reference for future theoretical investigation of the micromechanical properties of systems based on HEAs. Copyright

  • 262.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Vida, Adam
    Heczel, Anita
    Holmstrom, Erik
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Thermal Expansion, Elastic and Magnetic Properties of FeCoNiCu-Based High-Entropy Alloys Using First-Principle Theory2017Inngår i: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 69, nr 11, s. 2107-2112Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effects of V, Cr, and Mn on the magnetic, elastic, and thermal properties of FeCoNiCu high-entropy alloy are studied by using the exact muffin-tin orbitals method in combination with the coherent potential approximation. The calculated lattice parameters and Curie temperatures in the face-centered-cubic structure are in line with the available experimental and theoretical data. A significant change in the magnetic behavior is revealed when adding equimolar V, Cr, and Mn to the host composition. The three independent single-crystal elastic constants are computed using a finite strain technique, and the polycrystalline elasticity parameters including shear modulus, Young's modulus, Pugh ratio, Poisson's ratio, and elastic anisotropy are derived and discussed. The effects of temperature on the structural parameters are determined by making use of the Debye-Gruneisen model. It is found that FeCoNiCuCr possesses a slightly larger thermal expansion coefficient than do the other alloys considered here.

  • 263.
    Huang, Shuo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vida, Á.
    Li, Wei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Molnár, David
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Dalarna University, Sweden.
    Kyun Kwon, S.
    Holmström, E.
    Varga, B.
    Károly Varga, L.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Thermal expansion in FeCrCoNiGa high-entropy alloy from theory and experiment2017Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 110, nr 24, artikkel-id 241902Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    First-principle alloy theory and key experimental techniques are applied to determine the thermal expansion of FeCrCoNiGa high-entropy alloy. The magnetic transition, observed at 649 K, is accompanied by a significant increase in the thermal expansion coefficient. The phase stability is analyzed as a function of temperature via the calculated free energies accounting for the structural, magnetic, electronic, vibrational and configurational contributions. The single- and polycrystal elastic modulus for the ferro- and paramagnetic states of the face-centered and body-centered cubic phases are presented. By combining the measured and theoretically predicted temperature-dependent lattice parameters, we reveal the structural and magnetic origin of the observed anomalous thermal expansion behavior.

  • 264. Hudl, Matthias
    et al.
    Haggstrom, Lennart
    Delczeg-Czirjak, Erna-Krisztina
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Hoglin, Viktor
    Sahlberg, Martin
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Eriksson, Olle
    Nordblad, Per
    Andersson, Yvonne
    Strongly enhanced magnetic moments in ferromagnetic FeMnP(0.5)Si(0.5)2011Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 99, nr 15, s. 152502-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The compound FeMnP(0.5)Si(0.5) has been studied by magnetic measurements, Mossbauer spectroscopy, and electronic structure and total energy calculations. An unexpectedly high magnetic hyperfine field for Fe atoms located at the tetrahedral Me(1) site in the Fe(2)P structure is found, The saturation moment derived from magnetic measurements corresponds to 4.4 mu(B)/f.u. at low temperatures, a value substantially higher than previously reported, but in accordance with the results from our electron structure calculations, This high saturation moment and the tunable first order ferromagnetic transition make the Fe(2-x)Mn(x)P(1-y)Si(y), system promising for magnetocaloric applications.

  • 265.
    Hudl, Matthias
    et al.
    Department of Engineering Sciences, Uppsala University.
    Nordblad, Per
    Department of Engineering Science, Uppsala University.
    Björkman, Torbjörn
    Department of Physics and Astronomy, Uppsala University.
    Eriksson, Olle
    Department of Physics and Astronomy, Uppsala University.
    Häggström, Lennart
    Department of Physics and Astronomy, Uppsala University.
    Sahlberg, Martin
    Department of Materials Chemistry, Uppsala Univeristy.
    Andersson, Yvonne
    Department of Materials Chemistry, Uppsala University.
    Delczeg-Czirjak, Erna Krisztina
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Vitos, Levente
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Order-disorder induced magnetic structures of FeMnP0.75Si0.252011Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 83, nr 13, s. 134420-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report on the synthesis and structural characterization of the magnetocaloric FeMnP0.75Si0.25 compound. Two types of samples (quenched and slowly cooled) were synthesized and characterized structurally and magnetically. We have found that minor changes in the degree of crystallographic order causes large changes in the magnetic properties. The slow-cooled sample, with a higher degree of order, is antiferromagnetic. The quenched sample has a net moment of 1.26 mu(B) per formula unit and ferrimagnetic behavior. Theoretical calculations give rather large values for the Fe and Mn magnetic moments, both when occupied on the tetrahedral and the pyramidal lattice sites.

  • 266. Hunter-Dunn, J.
    et al.
    Karis, O.
    Andersson, C.
    Carr, R.
    Abrikosov, I. A.
    Sanyal, B.
    Bergqvist, Lars
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Eriksson, Olle
    Vanishing Magnetic Interactions in Ferromagnetic Thin Films2005Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 94, s. 217202-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have used element-specific hysteresis measurements, based on the x-ray magnetic circular dichroism technique, to investigate magnetic trilayer structures composed of Fe and Ni layers. Within a critical regime we have discovered a class of structures in which the exchange interaction, the mechanism responsible for the macroscopic magnetism, can become vanishingly small. The experimental observations are supported by first principles theory and are explained as arising from a cancellation of several competing magnetic interactions. Hence, we have discovered a system with a novel exchange interaction between magnetic layers in direct contact that replaces the conventional exchange interaction in ferromagnets.

  • 267. Hussain, T.
    et al.
    Chakraborty, Sudip
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Metal-functionalized silicene for efficient hydrogen storage2013Inngår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 14, nr 15, s. 3463-3466Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    First-principles calculations based on density functional theory are used to investigate the electronic structure along with the stability, bonding mechanism, band gap, and charge transfer of metal-functionalized silicene to envisage its hydrogen-storage capacity. Various metal atoms including Li, Na, K, Be, Mg, and Ca are doped into the most stable configuration of silicene. The corresponding binding energies and charge-transfer mechanisms are discussed from the perspective of hydrogen-storage compatibility. The Li and Na metal dopants are found to be ideally suitable, not only for strong metal-to-substrate binding and uniform distribution over the substrate, but also for the high-capacity storage of hydrogen. The stabilities of both Li- and Na-functionalized silicene are also confirmed through molecular dynamics simulations. It is found that both of the alkali metals, Li+ and Na+, can adsorb five hydrogen molecules, attaining reasonably high storage capacities of 7.75 and 6.9 wt %, respectively, with average adsorption energies within the range suitable for practical hydrogen-storage applications. Hoovering up hydrogen: A systematic density functional theory investigation shows alkali-metal doped silicene to be a promising hydrogen-storage material. The preferential sites of the dopants, stabilities of the doped systems, the bonding mechanism, and the hydrogen storage capacities are calculated by using a variety of computational methods including the projector augmented wave method, the Perdew-Burke-Ernzerhof variant of the generalized gradient approximation, the Nosé-Hoover thermostat, and Bader charge analysis.

  • 268. Hussain, T.
    et al.
    De Sarkar, Abir
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Strain induced lithium functionalized graphane as a high capacity hydrogen storage material2012Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, nr 10, s. 103907-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Strain effects on the stability, electronic structure, and hydrogen storage capacity of lithium-doped graphane have been investigated by state-of-the-art first principles density functional theory. Molecular dynamics simulations have confirmed the stability of Li on graphane sheet when it is subject to 10% of tensile strain. Under biaxial asymmetric strain, the binding energy of Li of graphane (CH) sheet increases by 52% with respect to its bulk's cohesive energy. With 25% doping concentration of Li on CH sheet, the gravimetric density of hydrogen storage is found to reach up to 12.12 wt.%. The adsorption energies of H 2 are found to be within the range of practical H 2 storage applications.

  • 269. Hussain, T.
    et al.
    De Sarkar, Abir
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Maark, T. A.
    Sun, Weiwei
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Strain and doping effects on the energetics of hydrogen desorption from the MgH2 (001) surface2013Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 101, nr 2, s. 27006-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    On the basis of first-principles calculations we have systematically investigated the energetics of hydrogen desorption from the MgH2 (001) surface. Based on total energy and electronic structure calculations, two modes namely strain and doping of selected dopants (Al, Si, Ti) and the combined effect of both on the dehydrogenation energies (ΔH) of MgH2 (001) systems have been analyzed. The maximum improvement in ΔH has been obtained with the combined effect of doping and strain. Among all the dopants, Al gives the lowest value of ΔH when the system Al-MgH2 is subjected to a 7.5% biaxial symmetric strain whereas the Si-MgH2 systems show the least improvement in ΔH. The doping of Ti on MgH 2 (001) is also very beneficial even without strain. The reduction in ΔH is caused by the charge localization on the metal atoms, destabilization and the weakening of metal-hydrogen bonds.

  • 270. Hussain, T.
    et al.
    Kaewmaraya, T.
    Chakraborty, S.
    Vovusha, H.
    Amornkitbamrung, V.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. King Abdullah University of Science and Technology (KAUST), Physical Science and Engineering Division (PSE), Thuwal, Saudi Arabia.
    Defected and Functionalized Germanene-based Nanosensors under Sulfur Comprising Gas Exposure2018Inngår i: ACS Sensors, ISSN 2379-3694, Vol. 3, nr 4, s. 867-874Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Efficient sensing of sulfur containing toxic gases like H2S and SO2 is of the utmost importance due to the adverse effects of these noxious gases. Absence of an efficient 2D-based nanosensor capable of anchoring H2S and SO2 with feasible binding and an apparent variation in electronic properties upon the exposure of gas molecules has motivated us to explore the promise of a germanene nanosheet (Ge-NS) for this purpose. In the present study, we have performed a comprehensive computational investigation by means of DFT-based first-principles calculations to envisage the structural, electronic, and gas sensing properties of pristine, defected, and metal substituted Ge-NSs. Our initial screening has revealed that although interaction of SO2 with pristine Ge-NSs is within the desirable range, H2S binding however falls below the required values to guarantee an effective sensing. To improve the binding characteristics, we have considered the interactions between H2S and SO2 with defected and metal substituted Ge-NS. The systematic removals of Ge atoms from a reasonably large super cell lead to monovacancy, divacancies, and trivacancies in Ge-NS. Similarly, different transition metals like As, Co, Cu, Fe, Ga, Ge, Ni, and Zn have been substituted into the monolayer to realize substituted Ge-NS. Our van der Waals corrected DFT calculations have concluded that the vacancy and substitution defects not only improve the binding characteristics but also enhance the sensing propensity of both H2S and SO2. The total and projected density of states show significant variations in electronic properties of pristine and defected Ge-NSs before and after the exposure to the gases, which are essential in constituting a signal to be detected by the external circuit of the sensor. We strongly believe that our present work would not only advance the knowledge towards the application of Ge-NS-based sensing but also provide motivation for the synthesis of such efficient nanosensor for H2S and SO2 based on Ge monolayer.

  • 271. Hussain, T.
    et al.
    Pathak, B.
    Maark, T. A.
    Ramzan, M.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Functionalization of graphane with alkali and alkaline-earth metals: An insulator-to-metallic transition2012Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 99, nr 4, s. 47004-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In view of interest in functionalized carbon nanostructures due to their potential applications in nanotechnology and nanoelectronics, we have performed a systematic and thorough density functional theory (DFT) study on the interaction of the elements in the first two groups of the periodic table with graphane (hydrogenated graphene) sheet. GGA approximation as employed in DFT has been used to study in detail the binding configuration, bond length, charge transfer and band gap of each of these adatoms doped graphane (CH) systems. To have a better understanding of the adatoms-CH interaction, different doping concentrations varying from 3.125% to 50% have been considered. A certain trend in binding strength, bond length and charge transfer has been found in the case of both alkali metal and alkaline-earth metal adatoms. In the case of alkali-metal adatoms at the low doping concentration of 3.125%, semiconductor behavior was found, whereas at doping higher than this the compound showed metallic behavior. In contrast, alkaline-earth metal-doped CH exhibited metallic behavior at all the doping concentrations.

  • 272. Hussain, T.
    et al.
    Pathak, B.
    Ramzan, M.
    Maark, T. A.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Calcium doped graphane as a hydrogen storage material2012Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 100, nr 18, s. 183902-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    On the basis of first principle density functional theory, we have studied the stability, electronic structure, and hydrogen storage capacity of a monolayer calcium doped graphane (CHCa). The stability of CHCa was further investigated using the ab initio molecular dynamics study. The binding energy of Ca on graphane sheet was found to be higher than its bulk cohesive energy, which indicates the stability of CHCa. It was observed that with a doping concentration of 11.11% of Ca on graphane sheet, a reasonably good H-2 storage capacity of 6 wt. % could be attained. The adsorption energies of H-2 were found to be 0.1 eV, within the range of practical H-2 storage applications.

  • 273.
    Hussain, T.
    et al.
    Univ Western Australia, Sch Mol Sci, Perth, WA 6009, Australia.;Univ Queensland, Ctr Theoret & Computat Mol Sci, Australian Inst Bioengn & Nanotechnol, Brisbane, Qld 4072, Australia..
    Vovusha, H.
    KAUST, Phys Sci & Engn Div PSE, Thuwal 239556900, Saudi Arabia..
    Kaewmaraya, T.
    Khon Kaen Univ, Integrated Nanotechnol Res Ctr, Dept Phys, Khon Kaen, Thailand..
    Karton, A.
    Univ Western Australia, Sch Mol Sci, Perth, WA 6009, Australia..
    Amornkitbamrung, V
    Khon Kaen Univ, Integrated Nanotechnol Res Ctr, Dept Phys, Khon Kaen, Thailand..
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, Box 516, S-75120 Uppsala, Sweden.
    Graphitic carbon nitride nano sheets functionalized with selected transition metal dopants: an efficient way to store CO22018Inngår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 29, nr 41, artikkel-id 415502Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Proficient capture of carbon dioxide (CO2) is considered to be a backbone for environment protection through countering the climate change caused by mounting carbon content. Here we present a comprehensive mechanism to design novel functional nanostructures capable of capturing a large amount of CO2 efficiently. By means of van der Waals corrected density functional theory calculations, we have studied the structural, electronic and CO2 storage properties of carbon nitride (g-C6N8) nano sheets functionalized with a range of transition metal (TM) dopants ranging from Sc to Zn. The considered TMs bind strongly to the nano sheets with binding energies exceeding their respective cohesive energies, thus abolishing the possibility of metal cluster formation. Uniformly dispersed TMs change the electronic properties of semiconducting g-C6N8 through the transfer of valence charges from the former to the latter. This leaves all the TM dopants with significant positive charges, which are beneficial for CO2 adsorption. We have found that each TM's dopants anchor a maximum of four CO2 molecules with suitable adsorption energies (-0.15 to -1.0 eV) for ambient condition applications. Thus g-C6N8 nano sheets functionalized with selected TMs could serve as an ideal sorbent for CO2 capture.

  • 274.
    Hussain, T.
    et al.
    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..
    Vovusha, H.
    KAUST, Phys Sci & Engn Div PSE, Thuwal 239556900, Saudi Arabia.;Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, Box 516, S-75120 Uppsala, Sweden..
    Umer, R.
    Univ Southern Queensland, Ctr Future Mat, Toowoomba, Qld 4350, Australia..
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Superior sensing affinities of acetone towards vacancy induced and metallized ZnO monolayers2018Inngår i: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 456, s. 711-716Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The sensing propensities of acetone molecule towards zinc oxide monolayers (ZnO-ML) have been studied by means of density functional theory (DFT) calculations. Our van der Waals induced first principles calculations revealed that pristine ZnO-ML barely binds acetone, which limits its application as acetone sensing materials. However the formation of vacancies and foreign element doping improves acetone binding drastically. Among several defects, divacancy, and metal doping Li, Sc and Ti functionalization on ZnO-ML has been found the most promising ones. Presence of dangling electrons and partial positive charges in case of vacancy-induced and metallized ZnO-ML respectively, is believed to enhance the binding of acetone on the monolayers. The acetone-ZnO binding behavior has been further explained through studying the electronic properties by density of states and charge transfer mechanism though Bader analysis. Thus defected and metallized ZnO-ML could be a promising nano sensor for efficient sensing/capture of acetone.

  • 275.
    Hussain, Tanveer
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Chakraborty, Sudip
    De Sarkar, Abir
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Enhancement of energy storage capacity of Mg functionalized silicene and silicane under external strain2014Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 105, nr 12, s. 123903-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electronic structure, stability, and hydrogen storage capacity of strain induced Mg functionalized silicene (SiMg) and silicane (SiHMg) monolayers have been studied by means of van der Waals induced first principles calculations. A drastic increase in the binding energy of Mg adatoms on both the monolayers under the biaxial symmetric strain of 10% ensures the uniform distribution of dopants over the substrates. A significant positive charge on each Mg accumulates a maximum of six H-2 molecules with H-2 storage capacity of 8.10% and 7.95% in case of SiMg and SiHMg, respectively. The average adsorption energy for H-2 molecules has been found ideal for practical H-2 storage materials.

  • 276.
    Hussain, Tanveer
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Chakraborty, Sudip
    Kang, T. W.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    BC3 Sheet Functionalized with Lithium-Rich Species Emerging as a Reversible Hydrogen Storage Material2015Inngår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 16, nr 3, s. 634-639Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The decoration of a BC3 monolayer with the polylithiated molecules CLi4 and OLi2 has been extensively investigated to study the hydrogen-storage efficiency of the materials by first principles electronic structure calculations. The binding energies of both lithiated species with the BC3 substrate are much higher than their respective cohesive energies, which confirms the stability of the doped systems. A significant positive charge on the Li atom in each of the dopants facilitates the adsorption of multiple H-2 molecules under the influence of electrostatic and van der Waals interactions. We observe a high H-2-storage capacity of 11.88 and 8.70 wt% for the BC3-CLi4 and BC3-OLi2 systems, respectively, making them promising candidates as efficient energy-storage systems.

  • 277. Hussain, Tanveer
    et al.
    De Sarkar, Abir
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Functionalization of hydrogenated graphene by polylithiated species for efficient hydrogen storage2014Inngår i: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 39, nr 6, s. 2560-2566Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The hydrogen (H-2) storage capacity of defected graphane (CH) functionalized by polylithiated species CLi3 and CLi4 has been investigated by means of first-principles DFT calculations. The stability and electronic structures of these potential H-2 storage materials have also been studied. The binding of these lithium rich species (CLi3, CLi4) to the CH sheet has been found to be strong enough to avoid clustering. The nature of bonding in C-Li and C-C has been revealed by Bader charge analysis. It has been found that when both sides of CH sheet are functionalized by polylithiated species, a storage capacity of more than 13 wt % can be achieved with adsorption energies of H-2 in the range of 0.25 eV-0.35 eV, which is suitable for an efficient H-2 storage.

  • 278. Hussain, Tanveer
    et al.
    De Sarkar, Abir
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Kang, Tae Won
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ahuja, Rajeev
    Dongguk University, South Korea .
    Hexagonal Boron Nitride Sheet Decorated by Polylithiated Species for Efficient and Reversible Hydrogen Storage2013Inngår i: Science of Advanced Materials, ISSN 1947-2935, Vol. 5, nr 12, s. 1960-1966Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the quest for promising hydrogen storage materials, we have performed first principles calculations on CLi3 and OLi2 decorated hexagonal boron nitride (h-BN), sheet. The strong binding of the polylithiated species to pristine and doped BN sheet and the large distance between these functionalized species ensure their uniform distribution over the sheet without being clustered. MD simulations have also confirmed the stabilities of both functionalized systems. Bader analysis and density of states reveals the bonding nature in the systems. A reasonably high H-2 storage capacity with the adsorption energies within the desired window suggests that these systems hold promise as efficient H-2 storage mediums.

  • 279.
    Hussain, Tanveer
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden and University of Queensland, Australia.
    Islam, M. S.
    Rao, G. S.
    Panigrahi, P.
    Gupta, D.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden and Dongguk University, Korea.
    Hydrogen storage properties of light metal adatoms (Li, Na) decorated fluorographene monolayer2015Inngår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 26, nr 27, artikkel-id 275401Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Owing to its high energy density, the potential of hydrogen (H-2) as an energy carrier has been immense, however its storage remains a big obstacle and calls for an efficient storage medium. By means of density functional theory (DFT) in spin polarized generalized gradient approximation (GGA), we have investigated the structural, electronic and hydrogen storage properties of a light alkali metal (Li, Na) functionalized fluorographene monolayer (FG). Metal adatoms bind to the FG with significantly high binding energy, much higher than their cohesive energies, which helps to achieve a uniform distribution of metal adatoms on the monolayer and consequently ensure reversibility. Due to a difference of electronegativities, each metal adatom transfers a substantial amount of its charge to the FG monolayer and attains a partial positive state, which facilitates the adsorption of multiple H-2 molecules around the adatoms by electrostatic as well as van der Waals interactions. To get a better description of H-2 adsorption energies with metal-doped systems, we have also performed calculations using van der Waals corrections. For both the functionalized systems, the results indicate a reasonably high H-2 storage capacity with H2 adsorption energies falling into the range for the practical applications.

  • 280. Hussain, Tanveer
    et al.
    Kaewmaraya, Thanayut
    Chakraborty, Sudip
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Defect and Substitution-Induced Silicene Sensor to Probe Toxic Gases2016Inngår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 120, nr 44, s. 25256-25262Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Structural, electronic, and gas-sensing properties of pure, defected, and substituted silicene monolayer have been studied using first-principles calculations based on density functional theory. The spin-polarized calculations with van der Waals effect taken into consideration have revealed that the pristine silicene sheet rarely adsorbs the CO2, H2S, and SO2 gas molecules, which restricts the gas-sensing application of this 2D material. However, inducing vacancy defect in silicene drastically changes the electronic properties, and as a consequence it also improves the binding of exposed gas molecules significantly. Our Bader charge analysis reveals that a considerable amount of charge is being transferred from the defected silicene to the gases, resulting in binding energy improvement between silicene and the gas molecules. The change in binding energies has further been explained by plotting density of states. In addition to the vacancy defects, we have also considered the substitution of Al, B, N, and S in silicene. We found that the sensing propensity of silicene is more sensitive to the vacancy defect, as compared with the impurities.

  • 281. Hussain, Tanveer
    et al.
    Kaewmaraya, Thanayut
    Chakraborty, Sudip
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Dept Phys & Astron, Condensed Matter Theory Grp, S-75120 Uppsala.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Functionalization of hydrogenated silicene with alkali and alkaline earth metals for efficient hydrogen storage2013Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 15, nr 43, s. 18900-18905Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    First principles density functional theory has been employed to investigate the electronic structure along with the stability, bonding mechanism, band gap and charge transfer of metal functionalized hydrogenated silicene (SiH), or silicane, in order to envisage the hydrogen storage capacity. Various metal adatoms including Li, Na, K, Be, Mg and Ca have been doped on the most stable chair like configuration of silicane. The corresponding binding energies and charge transfer mechanism have been discussed from the perspective of H-2 storage ability. The Li and Na metal adatoms have been found to be ideally suitable not only for their strong metal to substrate binding and uniform distribution over the substrate but also for their high capacity for storage of hydrogen. The stability of both Li and Na functionalized SiH has also been confirmed by MD simulations. It was found that both Li+ and Na+ adsorbed four H-2 molecules attaining reasonably high storage capacities of 6.30 wt% and 5.40 wt% respectively with average adsorption energies lying within the range suitable for practical H-2 storage applications, in contrast with alkaline earth metals.

  • 282.
    Hussain, Tanveer
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ.
    Maark, Tuhina Adit
    Chakraborty, Sudip
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM). Uppsala Univ.
    Improvement in Hydrogen Desorption from - and -MgH2 upon Transition-Metal Doping2015Inngår i: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 16, nr 12, s. 2557-2561Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A thorough study of the structural, electronic, and hydrogen-desorption properties of - and -MgH2 phases substituted by selected transition metals (TMs) is performed through first-principles calculations based on density functional theory (DFT). The TMs considered herein include Sc, V, Fe, Co, Ni, Cu, Y, Zr, and Nb, which substitute for Mg at a doping concentration of 3.125% in both the hydrides. This insertion of TMs causes a variation in the cell volumes of - and -MgH2. The majority of the TM dopants decrease the lattice constants, with Ni resulting in the largest reduction. From the formation-energy calculations, it is predicted that except for Cu and Ni, the mixing of all the selected TM dopants with the MgH2 phases is exothermic. The selected TMs also influence the stability of both - and -MgH2 and cause destabilization by weakening the MgH bonds. Our results show that doping with certain TMs can facilitate desorption of hydrogen from - and -MgH2 at much lower temperatures than from their pure forms. The hydrogen adsorption strengths are also studied by density-of-states analysis.

  • 283. Hussain, Tanveer
    et al.
    Maark, Tuhina Adit
    De Sarkar, Abir
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Polylithiated (OLi2) functionalized graphane as a potential hydrogen storage material2012Inngår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 101, nr 24, s. 243902-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydrogen storage capacity, stability, bonding mechanism, and the electronic structure of polylithiated molecules (OLi2) functionalized graphane (CH) has been studied by means of first principle DFT. Molecular dynamics have confirmed the stability, while Bader charge analysis describes the bonding mechanism of OLi2 with CH. The binding energy of OLi2 on CH sheet has been found to be large enough to ensure its uniform distribution without any clustering. It has been found that each OLi2 unit can adsorb up to six H-2 molecules resulting into a storage capacity of 12.90 wt. % with adsorption energies within the range of practical H-2 storage application.

  • 284. Hussain, Tanveer
    et al.
    Maark, Tuhina Adit
    Pathak, Biswarup
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Department of Physics and Astronomy, Uppsala University, SE-751 20 Uppsala, Sweden .
    Improvement in the hydrogen desorption from MgH2 upon transition metals doping: A hybrid density functional calculations2013Inngår i: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 3, nr 10, s. 102117-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study deals with the investigations of structural, electronic and thermodynamic properties of MgH2 doped with selected transition metals (TMs) by means of hybrid density functional theory (PBE0). On the structural side, the calculated lattice parameters and equilibrium volumes increase in case of Sc, Zr and Y opposite to all the other dopants indicating volumetrically increased hydrogen density. Except Fe, all the dopants improve the kinetics of MgH2 by reducing the heat of adsorption with Cu, Nb, Ni and V proving more efficient than others studied TM's. The electronic properties have been studied by density of states and correlated with hydrogen adsorption energies.

  • 285. Hussain, Tanveer
    et al.
    Panigrahi, Puspamitra
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Enriching physisorption of H2S and NH3 gases on a graphane sheet by doping with Li adatoms2014Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, nr 17, s. 8100-8105Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have used density functional theory to investigate the adsorption efficiency of a hydrogenated graphene (graphane) sheet for H2S and NH3 gases. We find that neither the pristine graphane sheet nor the sheet defected by removing a few surface H atoms have sufficient affinity for either H2S or NH3 gas molecules. However, a graphane sheet doped with Li adatoms shows a strong sensing affinity for both the mentioned gas molecules. We have calculated the absorption energies with one [referred to as half coverage] molecule and two molecules [referred to as full coverage] for both gases with the Li-doped graphane sheet. We find that for both the gases, the calculated absorption energies are adequate enough to decide that the Li-doped graphane sheet is suitable for sensing H2S and NH3 gases. The Li-doped sheet shows a higher affinity for the NH3 gas compared to the H2S gas molecules due to a stronger Li(s)-N(p) hybridization compared to that of Li(s)-S(p). However, while going from the half coverage effect to the full coverage effect, the calculated binding energies show a decreasing trend for both the gases. The calculated work function of the Li-doped graphane sheet decreases while bringing the gas molecules within its vicinity, which explains the affinity of the sheet towards both the gas molecules.

  • 286.
    Hussain, Tanveer
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Panigrahi, Puspamitra
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Sensing propensity of a defected graphane sheet towards CO, H2O and NO22014Inngår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 25, nr 32, s. 325501-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have used density functional theory to investigate the sensing property of a hydrogenated graphene sheet (graphane) towards CO, H2O and NO2 gas molecules. Though the pristine graphane sheet is found not to have sufficient affinity towards the mentioned gas molecules, the defected sheet (removing few surface H atoms) has a strong affinity towards the gas molecules. While CO and H2O are found to be weakly physisorbed, the NO2 molecules are found to be strongly chemi-sorbed to the defected graphane sheet. With NO2, the N(p) and O(p) states are found to have strong hybridization with the most active C(p) states which lie at the defected site of the graphane sheet. While increasing the coverage effect of the mentioned gas molecules toward the defected sheet, the adsorption energies do not change significantly. At the same time, the work function of the defected graphane sheet shows an increasing trend while adsorbed with CO, H2O and NO2 gas molecules, opening up the possibilities for a future gas sensor.

  • 287. Hussain, Tanveer
    et al.
    Pathak, Biswarup
    Maark, Tuhina Adit
    Araujo, Carlos Moyses
    Scheicher, Ralph H.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ab initio study of lithium-doped graphane for hydrogen storage2011Inngår i: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 96, nr 2, s. 27013-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Based on the first-principle density functional calculations we predict that Li-doped graphane (prehydrogenated graphene) can be a potential candidate for hydrogen storage. The calculated Li-binding energy on graphane is significantly higher than the Li bulk's cohesive energy ruling out any possibility of cluster formations in the Li-doped graphane. Our study shows that even with very low concentration (5.56%) of Li doping, the Li-graphane sheet can achieve a reasonable hydrogen storage capacity of 3.23 wt.%. The van der Waals corrected H(2) binding energies fall within the range of 0.12-0.29 eV, suitable for practical H(2) storage applications.

  • 288. Hussain, Tanveer
    et al.
    Vovusha, Hakkim
    Kaewmaraya, Thanayut
    Amornkitbamrung, Vittaya
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Adsorption characteristics of DNA nucleobases, aromatic amino acids and heterocyclic molecules on silicene and germanene monolayers2018Inngår i: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 255, s. 2713-2720Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Binding of DNA/RNA nucleobases, aromatic amino acids and heterocyclic molecules on two-dimensional silicene and germanene sheets have been investigated for the application of sensing of biomolecules using first principle density functional theory calculations. Binding energy range for nucleobases, amino acids and heterocyclic molecules with both the sheets have been found to be (0.43-1.16 eV), (0.70-1.58 eV) and (0.22-0.96 eV) respectively, which along with the binding distances show that these molecules bind to both sheets by physisorption and chemisorption process. The exchange of electric charges between the monolayers and the incident molecules has been examined by means of Bader charge analysis. It has been observed that the introduction of DNA/RNA nucleobases, aromatic amino acids and heterocyclic molecules alters the electronic properties of both silicene and germanene nano sheets as studied by plotting the total (TDOS) and partial (PDOS) density of states. The DOS plots reveal the variation in the band gaps of both silicene and germanene caused by the introduction of studied molecules. Based on the obtained results we suggest that both silicene and germanene monolayers in their pristine form could be useful for sensing of biomolecules.

  • 289.
    Huttmann, Felix
    et al.
    Univ Cologne, Inst Phys 2, Zulpicher Str 77, D-50937 Cologne, Germany..
    Rothenbach, Nico
    Univ Duisburg Essen, Fak Phys, Lotharstr 1, D-47057 Duisburg, Germany.;Ctr Nanointegrat Duisburg Essen CENIDE, Lotharstr 1, D-47057 Duisburg, Germany..
    Kraus, Stefan
    Univ Cologne, Inst Phys 2, Zulpicher Str 77, D-50937 Cologne, Germany..
    Ollefs, Katharina
    Univ Duisburg Essen, Fak Phys, Lotharstr 1, D-47057 Duisburg, Germany.;Ctr Nanointegrat Duisburg Essen CENIDE, Lotharstr 1, D-47057 Duisburg, Germany..
    Arruda, Lucas M.
    Free Univ Berlin, Inst Expt Phys, Arnimallee 14, D-14195 Berlin, Germany..
    Bernien, Matthias
    Free Univ Berlin, Inst Expt Phys, Arnimallee 14, D-14195 Berlin, Germany..
    Thonig, Danny
    Uppsala Univ, Dept Phys & Astron, Mat Theory, SE-75120 Uppsala, Sweden..
    Delin, Anna
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Fransson, Jonas
    Uppsala Univ, Dept Phys & Astron, Mat Theory, SE-75120 Uppsala, Sweden..
    Kummer, Kurt
    European Synchrotron Radiat Facil, 71 Ave Martyrs,CS40220, F-38043 Grenoble 9, France..
    Brookes, Nicholas B.
    European Synchrotron Radiat Facil, 71 Ave Martyrs,CS40220, F-38043 Grenoble 9, France..
    Eriksson, Olle
    Uppsala Univ, Dept Phys & Astron, Mat Theory, SE-75120 Uppsala, Sweden.;Orebro Univ, Sch Sci & Technol, SE-70182 Orebro, Sweden..
    Kuch, Wolfgang
    Free Univ Berlin, Inst Expt Phys, Arnimallee 14, D-14195 Berlin, Germany..
    Michely, Thomas
    Univ Cologne, Inst Phys 2, Zulpicher Str 77, D-50937 Cologne, Germany..
    Wende, Heiko
    Univ Duisburg Essen, Fak Phys, Lotharstr 1, D-47057 Duisburg, Germany.;Ctr Nanointegrat Duisburg Essen CENIDE, Lotharstr 1, D-47057 Duisburg, Germany..
    Europium Cyclooctatetraene Nanowire Carpets: A Low-Dimensional, Organometallic, and Ferromagnetic Insulator2019Inngår i: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, nr 5, s. 911-917Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We investigate the magnetic and electronic properties of europium cyclooctatetraene (EuCot) nanowires by means of low-temperature X-ray magnetic circular dichroism (XMCD) and scanning tunneling microscopy (STM) and spectroscopy (STS). The EuCot nanowires are prepared in situ on a graphene surface. STS measurements identify EuCot as an insulator with a minority band gap of 2.3 eV. By means of Eu M-5,M-4 edge XMCD, orbital and spin magnetic moments of (-0.1 +/- 0.3)mu(B) and (+7.0 +/- 0.6)mu(B), respectively, were determined. Field-dependent measurements of the XMCD signal at the Eu M-5 edge show hysteresis for grazing X-ray incidence at 5 K, thus confirming EuCot as a ferromagnetic material. Our density functional theory calculations reproduce the experimentally observed minority band gap. Modeling the experimental results theoretically, we find that the effective interatomic exchange interaction between Eu atoms is on the order of millielectronvolts, that magnetocrystalline anisotropy energy is roughly half as big, and that dipolar energy is approximately ten times lower.

  • 290. Hwang, Choongyu
    et al.
    Kim, Duck Young
    Siegel, D. A.
    Chan, Kevin T.
    Noffsinger, J.
    Fedorov, A. V.
    Cohen, Marvin L.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Neaton, J. B.
    Lanzara, A.
    Ytterbium-driven strong enhancement of electron-phonon coupling in graphene2014Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, nr 11, s. 115417-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a high-resolution angle-resolved photoemission spectroscopy study in conjunction with first-principles calculations to investigate how the interaction of electrons with phonons in graphene is modified by the presence of Yb. We find that the charges transferred from Yb to the graphene layer hybridize with the graphene pi bands, leading to a strong enhancement of the electron-phonon interaction. Specifically, the electron-phonon coupling constant is increased by as much as a factor of 10 upon the introduction of Yb with respect to as-grown graphene (<= 0.05). The observed coupling constant constitutes the highest value ever measured for graphene and suggests that the hybridization between graphene and the adatoms might be a critical parameter in realizing superconducting graphene.

  • 291. Isaev, E. I.
    et al.
    Ahuja, R.
    Simak, S. I.
    Lichtenstein, A. I.
    Vekilov, Y. K.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Abrikosov, I. A.
    Anomalously enhanced superconductivity and ab initio lattice dynamics in transition metal carbides and nitrides2005Inngår i: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, nr 6Artikkel i tidsskrift (Fagfellevurdert)
  • 292. Isaev, E. I.
    et al.
    Simak, S. I.
    Abrikosov, I. A.
    Ahuja, R.
    Vekilov, Yu Kh
    Katsnelson, M. I.
    Lichtenstein, A. I.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Phonon related properties of transition metals, their carbides, and nitrides: A first-principles study2007Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 101, nr 12Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Lattice dynamics of body-centered cubic (bcc) V-b-VIb group transition metals (TM), and B1-type monocarbides and mononitrides of IIIb-VIb transition metals are studied by means of first-principles density functional perturbation theory, ultra soft pseudopotentials, and generalized gradient approximation to the exchange-correlation functional. Ground state parameters of transition metals and their compounds are correctly reproduced with the generated ultrasoft pseudopotentials. The calculated phonon spectra of the bcc metals are in excellent agreement with results of inelastic neutron scattering experiments. We show that the superconductivity of transition metal carbides (TMC) and transition metal nitrides (TMN) is related to peculiarities of the phonon spectra, and the anomalies of the spectra are connected to the number of valence electrons in crystals. The calculated electron-phonon interaction constants for TM, TMC, and TMN are in excellent agreement with experimentally determined values. Phonon spectra for a number of monocarbides and mononitrides of transition metals within the cubic NaCl- and hexagonal WC-type structures are predicted. Ideal stoichiometric B1 crystals of ScC, YC, and VC are predicted to be dynamically stable and superconducting materials. We also conclude that YN is a semiconductor.

  • 293. Isaev, E. I.
    et al.
    Skorodumova, N. V.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Vekilov, Y. K.
    Johansson, Börje
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Dynamical stability of Fe-H in the Earth's mantle and core regions2007Inngår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 104, nr 22, s. 9168-9171Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The core extends from the depth of 2,900 km to the center of the Earth and is composed mainly of an iron-rich alloy with nickel, with 10% of the mass comprised of lighter elements like hydrogen, but the exact composition is uncertain. We present a quantum mechanical first-principles study of the dynamical stability of FeH phases and their phonon densities of states at high pressure. Our free-energy calculations reveal a phonon-driven stabilization of dhcp FeH at low pressures, thus resolving the present contradiction between experimental observations and theoretical predictions. Calculations reveal a complex phase diagram for FeH under pressure with a dhcp -> hcp -> fcc sequence of structural transitions.

  • 294. Islam, M. S.
    et al.
    Hussain, Tanveer
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden, Univ Queensland, Australia.
    Rao, G. S.
    Panigrahi, P.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Augmenting the sensing aptitude of hydrogenated graphene by crafting with defects and dopants2016Inngår i: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 228, s. 317-321Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Density functional theory (DFT) level calculations were performed to study the interaction of hydrogenated graphene (CH) monolayer towards methane (CH4) gas molecules. The structural, electronic and gas sensing properties of pure, defected and light metal-doped CH monolayer were investigated. For the pristine CH, the estimated binding energy of CH4 fell short of the desired physisorption range and limit its gas sensing application at ambient conditions. However, upon crafting defects on pure CH layer by introducing hydrogen vacancies, a sharp increase in adsorption energies were observed when the CH4 molecules approached the defected sites of CH. Further, the effect of metal doping was studied by uniformly distributing light metal adatoms on CH monolayer which significantly enhanced the CH4 adsorption. To have better accuracy in calculating adsorption energies, we have incorporated van der Waals type corrections to our calculations for these weakly interacting systems.

  • 295. Jafri, S. H. M.
    et al.
    Blom, T.
    Leifer, K.
    Stromme, M.
    Lofas, H.
    Grigoriev, A.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Welch, K.
    Assessment of a nanoparticle bridge platform for molecular electronics measurements2010Inngår i: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 21, nr 43, s. 435204-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A combination of electron beam lithography, photolithography and focused ion beam milling was used to create a nanogap platform, which was bridged by gold nanoparticles in order to make electrical measurements and assess the platform under ambient conditions. Non-functionalized electrodes were tested to determine the intrinsic response of the platform and it was found that creating devices in ambient conditions requires careful cleaning and awareness of the contributions contaminants may make to measurements. The platform was then used to make measurements on octanethiol (OT) and biphenyldithiol (BPDT) molecules by functionalizing the nanoelectrodes with the molecules prior to bridging the nanogap with nanoparticles. Measurements on OT show that it is possible to make measurements on relatively small numbers of molecules, but that a large variation in response can be expected when one of the metal-molecule junctions is physisorbed, which was partially explained by attachment of OT molecules to different sites on the surface of the Au electrode using a density functional theory calculation. On the other hand, when dealing with BPDT, high yields for device creation are very difficult to achieve under ambient conditions. Significant hysteresis in the I-V curves of BPDT was also observed, which was attributed primarily to voltage induced changes at the interface between the molecule and the metal.

  • 296. Jafri, S. H. M.
    et al.
    Lofas, H.
    Fransson, J.
    Blom, T.
    Grigoriev, A.
    Wallner, A.
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    Ottosson, H.
    Leifer, K.
    Identification of vibrational signatures from short chains of interlinked molecule-nanoparticle junctions obtained by inelastic electron tunnelling spectroscopy2013Inngår i: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 5, nr 11, s. 4673-4677Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Short chains containing a series of metal-molecule-nanoparticle nanojunctions are a nano-material system with the potential to give electrical signatures close to those from single molecule experiments while enabling us to build portable devices on a chip. Inelastic electron tunnelling spectroscopy (IETS) measurements provide one of the most characteristic electrical signals of single and few molecules. In interlinked molecule-nanoparticle (NP) chains containing typically 5-7 molecules in a chain, the spectrum is expected to be a superposition of the vibrational signatures of individual molecules. We have established a stable and reproducible molecule-AuNP multi-junction by placing a few 1,8-octanedithiol (ODT) molecules onto a versatile and portable nanoparticle-nanoelectrode platform and measured for the first time vibrational molecular signatures at complex and coupled few-molecule-NP junctions. From quantum transport calculations, we model the IETS spectra and identify vibrational modes as well as the number of molecules contributing to the electron transport in the measured spectra.

  • 297. Jafri, S. Hassan M.
    et al.
    Lofas, Henrik
    Blom, Tobias
    Wallner, Andreas
    Grigoriev, Anton
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala Univ, Dept Phys & Astron, SE-75120 Uppsala, Sweden.
    Ottosson, Henrik
    Leifer, Klaus
    Nano-fabrication of molecular electronic junctions by targeted modification of metal-molecule bonds2015Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 5, artikkel-id 14431Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Reproducibility, stability and the coupling between electrical and molecular properties are central challenges in the field of molecular electronics. The field not only needs devices that fulfill these criteria but they also need to be up-scalable to application size. In this work, few-molecule based electronics devices with reproducible electrical characteristics are demonstrated. Our previously reported 5 nm gold nanoparticles (AuNP) coated with omega-triphenylmethyl (trityl) protected 1,8-octanedithiol molecules are trapped in between sub-20 nm gap spacing gold nanoelectrodes forming AuNP-molecule network. When the trityl groups are removed, reproducible devices and stable Au-thiol junctions are established on both ends of the alkane segment. The resistance of more than 50 devices is reduced by orders of magnitude as well as a reduction of the spread in the resistance histogram is observed. By density functional theory calculations the orders of magnitude decrease in resistance can be explained and supported by TEM observations thus indicating that the resistance changes and strongly improved resistance spread are related to the establishment of reproducible and stable metal-molecule bonds. The same experimental sequence is carried out using 1,6-hexanedithiol functionalized AuNPs. The average resistances as a function of molecular length, demonstrated herein, are comparable to the one found in single molecule devices.

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

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

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

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

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

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

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