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  • Luo, Jun, et al. (författare)
  • Surface-energy triggered phase formation and epitaxy in nanometer-thick Ni1-xPtx silicide films
  • 2010
  • Ingår i: APPLIED PHYSICS LETTERS. - 0003-6951. ; 96:3, s. 031911
  • Tidskriftsartikel (refereegranskat)abstract
    • The formation of ultrathin silicide films of Ni1-xPtx at 450-850 degrees C is reported. Without Pt (x=0) and for t(Ni)andlt; 4 nm, epitaxially aligned NiSi2-y films readily grow and exhibit extraordinary morphological stability up to 800 degrees C. For t(Ni)andgt;= 4 nm, polycrystalline NiSi films form and agglomerate at lower temperatures for thinner films. Without Ni (x=1) and for t(Pt)=1-20 nm, the annealing behavior of the resulting PtSi films follows that for the NiSi films. The results for Ni1-xPtx of other compositions support the above observations. Surface energy is discussed as the cause responsible for the distinct behavior in phase formation and morphological stability.
  • Leisner, Peter, et al. (författare)
  • Influence of ultrasound and cathode rotation on the formation of intrinsic stress in Ni films during electrodeposition
  • 2011
  • Ingår i: Transactions of the Institute of Metal Finishing. - Institute of Metal Finishing. - 0020-2967. ; 89:3, s. 137-142
  • Tidskriftsartikel (refereegranskat)abstract
    • The influence of 25 kHz ultrasound and cathode rotation during electroplating of Ni films on Si wafers has been studied with respect to intrinsic stress formation. Current densities from 1.6 A dm-2 up to 28.3 A dm-2 were used in an additive-free Ni sulphamate electrolyte. In general more efficient agitation by either ultrasound or cathode rotation was found to reduce intrinsic stress towards compressive levels compared to conventional agitation with an electrolyte circulation pump. Further more, intrinsic stresses become less dependent on changes in current density. The latter effect is most pronounced for ultrasonic agitation. Structure analysis of samples deposited by ultrasonic agitation show dense deposits with initially smaller grains at high ultrasonic effect. Locally increased temperature at the substrates surface could be an important effect of ultrasound agitation.
  • Alling, Björn, 1980-, et al. (författare)
  • Mixing and decomposition thermodynamics of c-Ti1-xAlxN from first-principles calculations
  • 2007
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121. ; 75:045123
  • Tidskriftsartikel (refereegranskat)abstract
    • Wedescribe an efficient first-principles method that can be used tocalculate mixing enthalpies of transition metal nitrides with B1 structureand substitutional disorder at the metal sublattice. The technique isbased on the density functional theory. The independent sublattice modelis suggested for the treatment of disorder-induced local lattice relaxationeffects. It supplements the description of the substitutional disorder withinthe coherent potential approximation. We demonstrate the excellent accuracy ofthe method by comparison with calculations performed by means ofthe projector augumented wave method on supercells constructed as specialquasirandom structures. At the same time, the efficiency of thetechnique allows for total energy calculations on a very finemesh of concentrations which enables a reliable calculation of thesecond concentration derivative of the alloy total energy. This isa first step towards first-principles predictions of concentrations and temperatureintervals where the alloy decomposition proceeds via the spinodal mechanism.We thus calculate electronic structure, lattice parameter, and mixing enthalpiesof the quasibinary alloy c-Ti1−xAlxN. The lattice parameter follows Vegard'slaw at low fractions of AlN but deviates increasingly withincreasing Al content. We show that the asymmetry of themixing enthalpy and its second concentration derivative is associated withsubstantial variations of the electronic structure with alloy composition. Thephase diagram is constructed within the mean-field approximation.
  • Gao, Xindong, et al. (författare)
  • Epitaxy of Ultrathin NiSi2 Films with Predetermined Thickness
  • 2011
  • Ingår i: Electrochemical and solid-state letters. - 1099-0062. ; 14:7, s. H268-H270
  • Tidskriftsartikel (refereegranskat)abstract
    • This letter presents a proof-of-concept process for tunable, self-limiting growth of ultrathin epitaxial NiSi2 films on Si (100). The process starts with metal sputter-deposition, followed by wet etching and then silicidation. By ionizing a fraction of the sputtered Ni atoms and biasing the Si substrate, the amount of Ni atoms incorporated in the substrate after wet etching can be controlled. As a result, the thickness of the NiSi2 films is increased from 4.7 to 7.2 nm by changing the nominal substrate bias from 0 to 600 V. The NiSi2 films are characterized by a specific resistivity around 50 mu Omega cm.
  • Hultman, Lars, et al. (författare)
  • Interface structure in superhard TiN-SiN nanolaminates and nanocomposites : film growth experiments and ab initio calculations
  • 2007
  • Ingår i: Physical Review. B. - 1098-0121 (print) 1550-235x (online). ; 75:15, s. 155437
  • Tidskriftsartikel (refereegranskat)abstract
    • Nanostructured materials—the subject of much of contemporary materials research—are defined by internal interfaces, the nature of which is largely unknown. Yet, the interfaces determine the properties of nanocomposites and nanolaminates. An example is nanocomposites with extreme hardness<img src="http://scitation.aip.org/stockgif3/ges.gif" />70–90  GPa, which is of the order of, or higher than, diamond. The Ti-Si-N system, in particular, is attracting attention for the synthesis of such superhard materials. In this case, the nanocomposite structure consists of TiN nanocrystallites encapsulated in a fully percolated SiNx “tissue phase” (1 to 2 monolayers thick) that is assumed to be amorphous. Here, we show that the interfacial tissue phase can be crystalline, and even epitaxial with complex surface reconstructions. Using in situ structural analyses combined with ab initio calculations, we find that SiNx layers grow epitaxially, giving rise to strong interfacial bonding, on both TiN(001) and TiN(111) surfaces. In addition, TiN overlayers grow epitaxially on SiNx/TiN(001) bilayers in nanolaminate structures. These results provide insight into the development of design rules for new nanostructured materials.
  • Lu, Jun, et al. (författare)
  • On Epitaxy of Ultrathin Ni1-xPtx Silicide Films on Si(001)
  • 2010
  • Ingår i: Electrochemical and solid-state letters. - 1099-0062. ; 13:10, s. H360-H362
  • Tidskriftsartikel (refereegranskat)abstract
    • Epitaxial Ni(Pt)Si2-y (y &lt; 1) films readily grow upon thermal treatment of 2 nm thick Ni and Ni0.96Pt0.04 films deposited on Si(001). For annealing at 500 degrees C, the films are 5.4-5.6 nm thick with 61-70 mu cm in resistivity. At 750 degrees C, the epitaxial Ni(Pt)Si2-y films become 6.1-6.2 nm thick with a resistivity of 42-44 mu cm. Structural analysis reveals twins, facet wedges, and thickness inhomogeneities in the films grown at 500 degrees C. For higher temperature, an almost defect-free NiSi2-y film with a flat and sharp interface is formed. The presence of Pt makes the aforementioned imperfections more persistent.
  • Luo, Jun, et al. (författare)
  • On Different Process Schemes for MOSFETs With a Controllable NiSi-Based Metallic Source/Drain
  • 2011
  • Ingår i: IEEE Transactions on Electron Devices. - 0018-9383. ; 58:7, s. 1898-1906
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper focuses on different silicidation schemes toward a controllable NiSi-based metallic source/drain (MSD) process with restricted lateral encroachment of NiSi. These schemes include thickness control of Ni, Ni-Pt alloying, and two-step annealing. Experimental results show that all the three process schemes can give rise to effective control of lateral encroachment during Ni silicidation. By controlling t(Ni), NiSi-based MSD metal-oxide-semiconductor field-effect transistors (MOSFETs) of gate length L-G = 55 nm are readily realized on ultrathin-body silicon-on-insulator substrates with 20-nm surface Si thickness. With the aid of dopant segregation (DS) to modifying the Schottky barrier heights of NiSi, both n- and p-type MSD MOSFETs show significant performance improvement, compared to reference devices without DS.
  • Magnuson, Martin, et al. (författare)
  • Electronic structure investigation of Ti3AlC2 , Ti3SiC2 , and Ti3GeC2 by soft x-ray emission spectroscopy
  • 2005
  • Ingår i: Physical Review B Condensed Matter. - 0163-1829. ; 72:24, s. 245101
  • Tidskriftsartikel (refereegranskat)abstract
    • The electronic structures of epitaxially grown films of Ti3AlC2 , Ti3SiC2 , and Ti3GeC2 have been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured high-resolution Ti L , C K , Al L , Si L , and Ge M emission spectra are compared with ab initio density-functional theory including core-to-valence dipole matrix elements. A qualitative agreement between experiment and theory is obtained. A weak covalent Ti-Al bond is manifested by a pronounced shoulder in the Ti L emission of Ti3AlC2 . As Al is replaced with Si or Ge, the shoulder disappears. For the buried Al and Si layers, strongly hybridized spectral shapes are detected in Ti3AlC2 and Ti3SiC2 , respectively. As a result of relaxation of the crystal structure and the increased charge-transfer from Ti to C, the Ti-C bonding is strengthened. The differences between the electronic structures are discussed in relation to the bonding in the nanolaminates and the corresponding change of materials properties.
  • Tengstrand, Olof, et al. (författare)
  • Structure and electrical properties of Nb-Ge-C nanocomposite coatings
  • 2014
  • Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - American Institute of Physics (AIP). - 0734-2101. ; 32:4, s. 041509
  • Tidskriftsartikel (refereegranskat)abstract
    • Nb-Ge-C nanocomposite thin films were deposited by dc magnetron sputtering using three elemental targets. The films consist of substoichiometric NbCx in a nanometer-thick matrix of amorphous C and Ge. Films with no Ge contain grains that are elongated in the growth direction with a (111) preferred crystallographic orientation. With the addition of similar to 12 at. % Ge, the grains are more equiaxed and exhibit a more random orientation. At even higher Ge contents, the structure also becomes denser. The porous structure of the low Ge content films result in O uptake from the ambient. With higher C content in the films both the amount of amorphous C and C/Nb-ratio increases. The contact resistance was measured by four-point technique as a function of contact force between 0 and 10 N. The lowest contact resistance (1.7 m Omega) is obtained at 10 N. The resistivity varies between 470 and 1700 mu Omega center dot cm depending on porosity and O content.
  • Höglund, Carina, et al. (författare)
  • Stability of (B4C)-B-10 thin films under neutron radiation
  • 2015
  • Ingår i: Radiation Physics and Chemistry. - Elsevier. - 0969-806X. ; 113, s. 14-19
  • Tidskriftsartikel (refereegranskat)abstract
    • Thin films of (B4C)-B-10 have shown to be very suitable as neutron-converting material in the next generation of neutron detectors, replacing the previous predominantly used He-3. In this contribution we show under realistic conditions that (B4C)-B-10 films are not damaged by the neutron irradiation and interactions, which they will be exposed to under many years in a neutron detector. 1 mu m thick (B4C)-B-10 thin films were deposited onto Al or Si substrates using dc magnetron sputtering. As-deposited films were exposed to a cold neutron beam with fluences of up to 1.1 x 10(14) cm(-2) and a mean wavelength of 6.9 angstrom. Both irradiated and as-deposited reference samples were characterized with time-of-flight elastic recoil detection analysis, scanning electron microscopy, transmission electron microscopy, X-ray photoemission spectroscopy, and X-ray diffraction. We show that only 1.8 ppm of the B-10 atoms were consumed and that the film composition does not change by the neutron interaction within the measurement accuracy. The irradiation does not deteriorate the film adhesion and there is no indication that it results in increased residual stress values of the as-deposited films of 0.095 GPa. From what is visible with the naked eye and down to atomic level studies, no change from the irradiation could be found using the above-mentioned characterization techniques.
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