Samples of YBa2Cu3O7 were prepared by sol-gel, co-precipitation, and solid state processes. Sol-gel samples were prepared from a solution of yttrium, barium, and copper nitrates dissolved in ethylene glycol, co-precipitated samples were made by the amorphous citrate method, and solid state samples were prepared by conventional high temperature reaction of the appropriate metal oxides and carbonates. The sol-gel process was shown to yield superconducting samples of superior Meissner effect, critical current, and critical field. The co-precipitated samples contain impurities that affect the critical properties. The sol-gel and co-precipitated processes yield materials with well-formed, plate-like particles with a fairly uniform size of about 10 μm. The grains in the solid state sample are smaller but have a much wider distribution of sizes than the samples prepared by solution methods.
Microstructures of polycrystalline diamond thin films deposited on silicon (100) substrates which were pretreated by (a) wet polishing, (b) dry polishing, (c) sonication and (d) acid etching, respectively, have been studied by scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HREM). The thin films were deposited by using a Hot Filament Assisted Chemical Vapor Deposition (HFCVD) technique, with a methane to hydrogen ratio of 0.5%. Atomic Force Microscopy (AFM) was used to characterize substrate surfaces after the different pretreatments. The wet and dry polishing produced substrates with scratch type of defects while the sonication and acid etching caused pit type of defects. Planar and cross-sectional SEM studies indicated that diamond films on the wet and dry polished surfaces were continuous and had a high density of nucleation sites while the films on the sonicated and acid etched surfaces were discontinuous in nature under the same deposition time (8 hours) and condition. Cross-sectional HREM studies did not reveal any intermediate layers such as SiC and amorphous carbon between the thin films and substrates. Tungsten carbide nano-sized crystals, however, were observed to be dispersed at the interface region. These particles were believed to be formed during carburizing a fresh tungsten filament and deposited on the substrate during initial stage of growth.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.