Electron postgrowth irradiation of platinum-containing nanostructures grown by electron-beam-induced deposition from Pt ( P F 3 ) 4Investigation of morphological changes in platinum-containing nanostructures created by electron-beam-induced deposition J.Focused electron beam induced depositions of nickel-containing materials obtained by using bis͑methylcyclopentadienyl͒nickel͑II͒ Ni͑C 5 H 4 CH 3 ͒ 2 and tetrakis͑trifluorophosphine͒nickel͑0͒ Ni͑PF 3 ͒ 4 as precursors, were compared in terms of chemical composition and electrical resistivity. Ni͑PF 3 ͒ 4 decomposed into higher Ni content materials than that obtained with Ni͑C 5 H 4 CH 3 ͒ 2 ͑typically 40 and 10 at. %, respectively͒. Attempts of increasing the Ni content by injecting controlled flows of molecular oxygen or hydrogen simultaneously to the precursor vapors resulted in all cases in the increase of incorporated oxygen only. The lowest electrical resistivities of 150 nm wide lines obtained from Ni͑C 5 H 4 CH 3 ͒ 2 and Ni͑PF 3 ͒ 4 were 1 and 1 ϫ 10 −3 ⍀ cm, respectively. The electrical resistivity of the latter lines showed an e ͑−T͒ dependence with temperature, typical of magnetic heterogeneous alloys and granular alloys containing insulating particles. Transmission electron microscopy investigations of a freestanding rod obtained from Ni͑PF 3 ͒ 4 showed a nanocrystalline structure of nickel grains surrounded by a partially amorphous cladding.
Al/SiC composites with volume fractions of SiC between 0.55 and 0.71 were made from identical tapped and vibrated powder preforms by squeeze casting (SC) and by two different setups for gas pressure infiltration (GPI), one that allows short (1-2 min) liquid metal/ ceramic contact time (fast GPI) and the other that operates with rather long contact time, i.e., 10-15 min, (slow GPI). Increased liquid metal-ceramic contact time is shown to be the key parameter for the resulting thermal and electrical conductivity in the Al/SiC composites for a given preform. While for the squeeze cast samples neither dissolution of the SiC nor formation of Al 4 C 3 was observed, the gas pressure assisted infiltration led inevitably to a reduced electrical and thermal conductivity of the matrix due to partial decomposition of SiC leading to Si in the matrix. Concomitantly, formation of Al 4 C 3 at the interface was observed in both sets of gas pressure infiltrated samples. Longer contact times lead to much higher levels of Si in the matrix and to more Al 4 C 3 formation at the interface. The difference in thermal conductivity between the SC samples and the fast GPI samples could be rationalized by the reduced matrix thermal conductivity only. On the other hand, in order to rationalize the thermal conductivity of the slow GPI a reduction in the metal/ceramic interface thermal conductance due to excessive Al 4 C 3 -formation had to be invoked. The CTE of the composites generally tended to decrease with increasing volume fraction of SiC except for the samples in which a large expansive drift was observed during the CTE measurement by thermal cycles. Such drift was essentially observed in the SC samples with high volume fraction of SiC while it was much smaller for the GPI samples. G. Sinicco-formerly an undergraduate student of É cole Polytechnique Fédérale de Lausanne, EPFL.
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