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IRG 2 Nugget Faculty involved in IRG 2 have pioneered the two chemical routes shown in Fig. 1 to synthesize epitaxial films for device applications. For the Chemical Solution Deposition
 

Summary: IRG 2 Nugget Faculty involved in IRG 2 have pioneered the two chemical routes shown in Fig.
1 to synthesize epitaxial films for device applications. For the Chemical Solution Deposition
(CSD) method (left), the solution is merely used as a vehicle to deposit, by either spin coating or
stamping, the desired elements on a single crystal substrate. During spinning, a solid, precursor
film forms, which decomposes into a polycrystalline film by heating. Provided that the lattice
mismatch is < 10 %, the amorphous material at the interface between the single crystal substrate
and the polycrystalline film transforms to nano-crystals with the same orientation as the substrate.
Increasing the temperature causes these orientated nano-crystals to consume the surrounding
polycrystalline material, thus converting the polycrystalline material into a single crystal thin
film. We have characterized the defects produced during this process, as a function of lattice
mismatch. The CSD method is currently under development at Oak Ridge National Lab for the
production of Reel to Reel superconducting wires (Ni substrate, La2Zr2O7 buffer, YBa2Cu3O7
supercond.)
Hydrothermal Epitaxy (right), the second route, the single crystal thin film is directly
synthesized on a substrate, in water, at temperatures 250 C. When the inorganic material is
within its field of stability, it precipitates from solution. IRG2 students have shown that epitaxy
initiates by the nucleation of crystallites at ledges on the single crystal substrate. The number
nuclei per unit area is related to the stability of the inorganic materials (temperature, pressure, pH,
precursor concentration, etc.). Nuclei grow together to form a single `crystal thin film' with a
high degree of orientation. Students have shown that the number of threading dislocations per

  

Source: Akhmedov, Azer - Department of Mathematics, University of California at Santa Barbara

 

Collections: Mathematics