Growth of Cerium Oxide Buffer Layers and Superconducting thin films on Silicon

Abstract

Films of CeO2 have been grown on Si and glass substrates using the laser ablation deposition technique. X-ray diffraction measurements for the films deposited on glass indicated that they are the same as films grown on Si covered with the native oxide. This evidence supports a picture in which chemical rather than crystal-lographic effects constrain the film growth. The crystal quality for films grown on Si was shown to improve with increasing film thickness away from the amorphous layer. Low cooling rates as well as reduced film thickness were effective in avoiding the formation of micro-cracks. The surface morphology was shown to be dependent on the laser wave-length as well as the oxygen partial pressure. Thin films of YBa2Cu3O7δ could easily be grown on CeO2/Si showing c-axis orientation, whereas the growth of BiSrCaCuO (2212) on CeO2/Si resulted in the two films mixing with each other.

Scanning electron microscopy investigation of laser ablated oxide targets

“…The laser repetition rate was 1 Hz, the angle of incidence measured from the surface normal was 30 • and the number of subsequent laser pulses directed to the same location was varied from 1 to 100. The peak fluence was varied from 2 to 4 J cm −2 , values usually employed to grow thin films [12][13][14]. Some irradiations were also performed with an excimer laser (KrF, λ = 248 nm, 20 ns pulse duration) at similar fluences.…”

“…The morphology and the structural, electrical and optical properties of the ZnO, CeO 2 and PZT films grown by PLD under optimum conditions have been presented in detail elsewhere [12][13][14]. Investigations of the surface morphology of the targets before and after laser irradiation were performed using SEM.…”

“…There is still much controversy concerning the mechanisms of droplet formation, there having been several suggestions so far [7][8][9][10][11]. In our previous studies [12][13][14] we tentatively suggested, following the initial idea of Gagliano and Paek [7] and the experimental results obtained when depositing ZnO, CeO 2 and Pb(Ti 0.5 Zr 0.5 )O 3 (PZT) films, that the majority of these droplets observed on the surface of films grown using longer wavelength lasers (hν < E g , the material optical bandgap, which is 3.3 eV, 3.6 eV and 3.7 eV for ZnO, CeO 2 and PZT, respectively) were caused by explosive boiling due to a subsurface superheating (SSSH) effect.…”