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Sökning: swepub > Hultman Lars

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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.
  • Gao, Xindong, et al. (författare)
  • Epitaxy of Ultrathin NiSi2 Films with Predetermined Thickness
  • 2011
  • Ingår i: Electrochemical and solid-state letters. - 1099-0062 .- 1944-8775. ; 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. ; 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 .- 1944-8775. ; 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.
  • Nedfors, Nils, et al. (författare)
  • Reactive sputtering of NbCx-based nanocomposite coatings An up-scaling study
  • 2014
  • Ingår i: Surface & Coatings Technology. - Elsevier. - 0257-8972. ; 253, s. 100-108
  • Tidskriftsartikel (refereegranskat)abstract
    • Nanocomposite Nb-C coatings, with a C/Nb ratio of 0.93-1.59, have been deposited by reactive sputtering in a commercial sputtering system where the C is supplied from an acetylene gas at deposition rates of up to 200 nm/min. The coatings are compared to non-reactively sputtered Nb-C coatings deposited from Nb and C targets in lab-scale equipment at deposition rates two orders of magnitude lower. X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy are used to conclude that all coatings consist of nanoctystalline Nbc(x) grains (nc-NbCx) embedded in a matrix of amorphous C (a-C). The coating performance was evaluated in terms of their mechanical, tribological, and electrical properties. The chemical stability of the coatings was evaluated by exposure to a flowing mixture of corrosive gases. It is found that the coatings have comparable microstructure and performance to the coatings deposited by non-reactive sputtering. The high deposition rate and presence of different C-radicals on the coating surface during film growth for the reactively sputtered coatings are believed to result in a smaller NbCx grain size compared to the non-reactively sputtered coatings (reactive process: 10-3 nm, non-reactive process: similar to 75-3 nm). This difference results in a thinner a-C matrix of about 0.2 nm, which is not varying with C content for the reactively sputtered coatings. The thinner a-C matrix is reflected in coating properties, with a higher conductivity and slightly higher hardness. The coating richest in C content (C/Nb ratio 1.59) shows the lowest friction (0.23), wear rate (0.17 x 10(-6) mm(3)/mN), and contact resistance before (11 m Omega at 10 N) and after (30 m Omega at 10 N) the chemical stability test. These results imply that nc-NbCx/a-C coatings of this composition are a good candidate for electrical contact applications, and that up-scaling of the process is achievable.
  • 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
  • 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 ∼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 mΩ) is obtained at 10 N. The resistivity varies between 470 and 1700 μΩ·cm depending on porosity and O content.
  • Frodelius, Jenny, 1978-, et al. (författare)
  • Ti2AlC coatings deposited by High Velocity Oxy-Fuel spraying
  • 2008
  • Ingår i: Surface & Coatings Technology. - Elsevier. - 0257-8972. ; 202:24, s. 5976-5981
  • Tidskriftsartikel (refereegranskat)abstract
    • High Velocity Oxy-Fuel has been utilized to spray coatings from Ti2AlC (MAXTHAL 211®) powders. X-ray diffraction showed that the coatings consist predominantly of Ti2AlC with inclusions of the phases Ti3AlC2, TiC, and Al–Ti alloys. The fraction of Ti2AlC in coatings sprayed with a powder size of 38 μm was found to increase with decreasing power of the spraying flame as controlled by the total gas flow of H2 and O2. A more coarse powder (56 μm) is less sensitive to the total gas flow and retains higher volume fraction of MAX-phase in the coatings, however, at the expense of increasing porosity. X-ray pole figure measurements showed a preferred crystal orientation in the coatings with the Ti2AlC (000l) planes aligned to the substrate surface. Bending tests show a good adhesion to stainless steel substrates and indentation yields a hardness of 3–5 GPa for the coatings sprayed with a powder size of 38 μm.
  • Höglund, Carina, et al. (författare)
  • Growth and oxidization stability of cubic Zr1-xGdxN solid solution thin films
  • 2015
  • Ingår i: Journal of Applied Physics. - American Institute of Physics (AIP). - 0021-8979. ; 117:19, s. 195301
  • Tidskriftsartikel (refereegranskat)abstract
    • We report Zr1-xGdxN thin films deposited by magnetron sputter deposition. We show a solid solubility of the highly neutron absorbing GdN into ZrN along the whole compositional range, which is in excellent agreement with our recent predictions by first-principles calculations. An oxidization study in air shows that Zr1-xGdxN with x reaching from 1 to close to 0 fully oxidizes, but that the oxidization is slowed down by an increased amount of ZrN or stopped by applying a capping layer of ZrN. The crystalline quality of Zr0.5Gd0.5N films increases with substrate temperatures increasing from 100 degrees C to 900 degrees C.
  • 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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