| 1. |
- Grennberg, Helena, et al.
(författare)
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Functionalization and Area-Selective Deposition of Magnetic Carbon-Coated Iron Nanoparticles from Solution
- 2011
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Ingår i: Journal of Nanotechnology. - : Hindawi publishing. - 1687-9503 .- 1687-9511. ; , s. 342368-
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Tidskriftsartikel (refereegranskat)abstract
- A route to area-selective deposition of carbon-coated iron nanoparticles, involving chemical modification of the surface of the particles, is described. Partial oxidative etching of the coating introduces carboxylic groups, which then are esterified. The functionalized particles can be selectively deposited on the Si areas of Si/SiO2 substrates by a simple dipping procedure. Nanoparticles and nanoassemblies have been analyzed using SEM, TEM, and XPS.
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| 2. |
- Lewin, Erik, et al.
(författare)
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Industrialisation Study of Nanocomposite nc-TiC/a-C Coatings for Electrical Contact Applications
- 2009
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Ingår i: Plasma Processes and Polymers. - : WILEY-VCH Verlag GmbH & Co. - 1612-8850. ; 6:S1, s. S928-S934
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Tidskriftsartikel (refereegranskat)abstract
- Nanocomposite nc-TiC/a-C coatings were prepared by non-reactive magnetron sputtering in industrial scale equipment, under varying deposition conditions in order to investigate upscaling and possible industrialisation. The coatings were found to have similar microstructure and performance compared to previous laboratory scale experiments. The samples were characterised with XRD, XPS and SEM as well with ball-on-disc, nanoindentation and electrical measurements. Coatings containing a small fraction of a-C matrix phase were found to have promising both electrical properties (rho < 400 mu Omega cm and contact resistances down to 0.34 m Omega at 40 N) and tribological properties (f < 0.3 for 10 000 laps).
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| 3. |
- Lewin, Erik, 1979-
(författare)
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Design of carbide-based nanocomposite coatings
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis research on synthesis, microstructure and properties of carbide-based coatings is reported. These coatings are electrically conducting, and can be tailored for high hardness, low friction and wear, along with load-adaptive behaviour. Tailoring these properties is achieved by controlling the relative phase content of the material. Coatings have been synthesised by dc magnetron sputtering, and their structures have been characterised, mainly by X-ray photoelectron spectroscopy and X-ray diffraction.It has been shown that nanocomposites comprising of a nanocrystalline transition metal carbide (nc-MeCx, Me = Ti, Nb or V) and an amorphous carbon (a-C) matrix can result in low contact resistance in electrical contacts. Such materials also exhibit low friction and high resistance to wear, making them especially suitable for application in sliding contacts. The lowest contact resistance is attained for small amounts of the amorphous carbon phase.It has been shown that specific bonding structures are present in the interface between nc-TiCx and the a-C phases in the nanocomposite. It was found in particular that Ti3d and C2p states are involved, and that considerable charge transfer occurs across the interface, thereby influencing the structure of the carbide.Further design possibilities were demonstrated for TiCx-based nanocomposites by alloying them with weakly carbide-forming metals, i.e., Me = Ni, Cu or Pt. Metastable supersaturated solid solution carbides, (T1-xMex)Cy, were identified to result from this alloying process. The destabilisation of the TiCx-phase leads to changes in the phase distribution in the deposited nanocomposites, thus providing further control over the amount of carbon phase formed. Additional design possibilities became available through the decomposition of the metastable (Ti1-xMex)Cy phase through an appropriate choice of annealing conditions, yielding either more carbon phase or a new metallic phase involving Me. This alloying concept was also studied theoretically for all 3d transition metals using DFT techniques.It has also been demonstrated that Ar-ion etching (commonly used in the analysis of carbide based nanocomposites) can seriously influence the result of the analysis, especially for materials containing metastable phases. This implies that more sophisticated methods, or considerable care are needed in making these analyses, and that many of the earlier published results could well be in error.
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| 4. |
- Eklund, Per, et al.
(författare)
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The Mn + 1AXn phases : Materials science and thin-film processing
- 2010
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 518:8, s. 1851-1878
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Forskningsöversikt (refereegranskat)abstract
- This article is a Critical review of the M(n + 1)AX(n) phases ("MAX phases", where n = 1, 2, or 3) from a materials science perspective. MAX phases are a class of hexagonal-structure ternary carbides and nitrides ("X") of a transition metal ("M") and an A-group element. The most well known are Ti2AlC, Ti3SiC2, and Ti4AlN3. There are similar to 60 MAX phases with at least 9 discovered in the last five years alone. What makes the MAX phases fascinating and potentially useful is their remarkable combination of chemical, physical, electrical, and mechanical properties, which in many ways combine the characteristics of metals and ceramics. For example, MAX phases are typically resistant to oxidation and corrosion, elastically stiff, but at the same time they exhibit high thermal and electrical conductivities and are machinable. These properties stem from an inherently nanolaminated crystal structure, with M1 + nXn slabs intercalated with pure A-element layers. The research on MAX phases has been accelerated by the introduction of thin-film processing methods. Magnetron sputtering and arc deposition have been employed to synthesize single-crystal material by epitaxial growth, which enables studies of fundamental material properties. However, the surface-initiated decomposition of M(n + 1)AX(n) thin films into MX compounds at temperatures of 1000-1100 degrees C is much lower than the decomposition temperatures typically reported for the corresponding bulk material. We also review the prospects for low-temperature synthesis, which is essential for deposition of MAX phases onto technologically important substrates. While deposition of MAX phases from the archetypical Ti-Si-C and Ti-Al-N systems typically requires synthesis temperatures of similar to 800 degrees C, recent results have demonstrated that V2GeC and Cr2AlC can be deposited at similar to 450 degrees C. Also, thermal spray of Ti2AlC powder has been used to produce thick coatings. We further treat progress in the use of first-principle calculations for predicting hypothetical MAX phases and their properties. Together with advances in processing and materials analysis, this progress has led to recent discoveries of numerous new MAX phases such as Ti4SiC3, Ta4AlC3. and Ti3SnC2. Finally, important future research directions are discussed. These include charting the unknown regions in phase diagrams to discover new equilibrium and metastable phases, as well as research challenges in understanding their physical properties, such as the effects of anisotropy, impurities, and vacancies on the electrical properties, and unexplored properties such as Superconductivity, magnetism, and optics.
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| 5. |
- Quinlan, Ronald A., et al.
(författare)
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Transfer of carbon nanosheet films to nongrowth, zero thermal budget substrates
- 2011
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Ingår i: Journal of Vacuum Science & Technology B. - : American Vacuum Society. - 1071-1023 .- 1520-8567. ; 29:3, s. 030602-
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Tidskriftsartikel (refereegranskat)abstract
- Carbon-based nanostructures and materials have become a popular subject of research due to their unique thermal, mechanical, electrical, and optical properties. For example, the strong C-C bonds of graphene-based systems allow for excellent thermal conduction at room temperature and the conjugation of the sp(2) lattice enables extremely high electron mobility. However, the use of carbon nanostructures as a component in polymer composites, sensors, mirco-electro-mechanical systems, and both rigid and flexible electronics has been limited by several factors, including the incompatibility with standard photolithography techniques, the high temperatures required for the nanostructure growth, and the presence of-or complication-of removing noncarbon species. Here, the authors report on a novel method for the transfer of carbon nanosheets to a low or zero thermal budget substrate while maintaining their original morphology and electrical properties. Four-point probe measurements' post-transfer shows the retention of in-plane conductivity and scanning electron microscopy reveals the preservation of the original vertical morphology. Raman spectroscopy measurements confirm the retention of the graphitic structure of the post-transfer nanosheet film. This new transfer technique builds on the ability to conformally coat nanosheets while maintaining the original ultrahigh surface area morphology and the ability to fully incorporate nanosheets into several polymers while maintaining the original nanostructure separation. For a demonstration of the usefulness of polymer filling, carbon nanosheets were used as an ultrahigh surface area electrode for the photoactive polymer poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] in proof of principle experiments of a nanosheet-based organic photovoltaic device.
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| 6. |
- Yang, Wenzhi, et al.
(författare)
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Stirring-induced aggregation of graphene in suspension
- 2011
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Ingår i: New Journal of Chemistry. - 1144-0546 .- 1369-9261. ; 35:4, s. 780-783
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Tidskriftsartikel (refereegranskat)abstract
- Graphene in suspension undergoes stirring-induced aggregation that leads to reversible agglomeration and folding/scrolling, all of which affects the Raman spectra; the findings are of importance in all solution-based protocols for graphene preparation and processing.
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| 7. |
- Lewin, Erik, et al.
(författare)
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Influence of sputter damage on the XPS analysis of metastable nanocomposite coatings
- 2009
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Ingår i: Surface & Coatings Technology. - : Elsevier B.V.. - 0257-8972 .- 1879-3347. ; 204:4, s. 455-462
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Tidskriftsartikel (refereegranskat)abstract
- X-ray photoelectron spectroscopy (XPS) is a standard method of determining chemical bonding in e.g. nanocomposites. We demonstrate that sputter-cleaning of the sample prior to analysis can substantially alter the attained information. We present an in-depth analysis of sputter damage on binary and ternary TiC-based coatings in the Ti–Ni–C system. XPS was performed after sputter etching with different ion energies (0.15–4 keV). Results are compared to data from the bulk of undamaged samples attained using high kinetic energy XPS. We observe substantial sputter damage, strongly dependent on sputter energies and coating stability. Metastable samples exhibit severe sputter damage after etching with 4 keV. Additional samples from other Ti–Me–C (Me = Al, Fe, Cu or Pt) systems were also examined, and notable sputter damage was observed. This suggests that accurate analysis of any metastable nanocomposite requires careful consideration of sputter damages.
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| 8. |
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| 9. |
- Magnuson, Martin, et al.
(författare)
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Electronic structure and chemical bonding in Ti4SiC3 investigated by soft x-ray emission spectroscopy and first-principles theory
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 74:20
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Tidskriftsartikel (refereegranskat)abstract
- Theelectronic structure in the new transition-metal carbide Ti4SiC3 has beeninvestigated by bulk-sensitive soft x-ray emission spectroscopy and compared tothe well-studied Ti3SiC2 and TiC systems. The measured high-resolution TiL, C K, and Si L x-ray emission spectra arediscussed with ab initio calculations based on density-functional theory includingcore-to-valence dipole matrix elements. The detailed investigations of the Ti-Cand Ti-Si chemical bonds provide increased understanding of the physicalproperties of these nanolaminates. A strongly modified spectral shape isdetected for the intercalated Si monolayers due to Si 3phybridization with the Ti 3d orbitals. As a result ofrelaxation of the crystal structure and the charge-transfer from Ti(and Si) to C, the strength of the Ti-C covalentbond is increased. The differences between the electronic and crystalstructures of Ti4SiC3 and Ti3SiC2 are discussed in relation tothe number of Si layers per Ti layer in thetwo systems and the corresponding change of materials properties.
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| 10. |
- Emmerlich, Jens, et al.
(författare)
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Thermal stability of Ti3SiC2 thin films
- 2007
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 55:4, s. 1479-1488
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Tidskriftsartikel (refereegranskat)abstract
- The thermal stability of Ti3SiC2(0 0 0 1) thin films is studied by in situ X-ray diffraction analysis during vacuum furnace annealing in combination with X-ray photoelectron spectroscopy, transmission electron microscopy and scanning transmission electron microscopy with energy dispersive X-ray analysis. The films are found to be stable during annealing at temperatures up to 1000 °C for 25 h. Annealing at 1100–1200 °C results in the rapid decomposition of Ti3SiC2 by Si out-diffusion along the basal planes via domain boundaries to the free surface with subsequent evaporation. As a consequence, the material shrinks by the relaxation of the Ti3C2 slabs and, it is proposed, by an in-diffusion of O into the empty Si-mirror planes. The phase transformation process is followed by the detwinning of the as-relaxed Ti3C2 slabs into (1 1 1)-oriented TiC0.67 layers, which begin recrystallizing at 1300 °C. Ab initio calculations are provided supporting the presented decomposition mechanisms.
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