Growth of YBa₂Cu₃O_7-deltathin films in pulsed laser deposition: influence of target, substrate and deposition rate

Abstract

The growth of smooth, high quality, c -axis thin films of optimally doped YBa2 Cu3 O7- on (001) MgO substrates has been studied using pulsed laser deposition. The films were characterized with Auger spectroscopy, x-ray diffraction, self-inductance and four-probe resistance techniques. We have found an interesting interaction between deposition rate, substrate topography and target oxygenation in the determination of film quality. The best films are produced with dense underoxygenated targets at low laser repetition rates (1 Hz) on very smooth substrates; the optimal deposition parameters for these are given. Atomic force microscopy shows spiral growth formations with a unit-cell edge height. Oriented outgrowths observed on some films are attributed to heat-modified substrate surface morphology. a -axis films also have been grown using PrBa2 Cu3 Ox template layers.

Significant tunability of thin film functionalities enabled by manipulating magnetic and structural nano-domains

“…4,34,68,74 , films deposited at low repetition rates had smoother surfaces, which is in opposite to our results provided in Table I. However in those works, the roughness was studied on thicker films (> 200 nm) with highly developed surface structures containing outgrowths, holes, pinholes and other defects formed due to incomplete island coalescence of relatively thick films 4,34 or stress-guided surface roughening after complete coalescence 5,33,35 .…”

“…68 and 71 , the laser frequency was varied by one order of magnitude (between 1 and 10 Hz and between 5 and 50 Hz, respectively), but, in contrast to our results, it did not affect the growth mode or the island size (i.e., the structure of films did not obey Eq. 1).…”

“…Therefore, the kinetic energy of adatoms in Refs. 68 and 71 was substantially higher and resulted in larger diffusion coefficients D s than in our work. Thus, all diffusionguided processes (i.e., 3D island formation and growth) were rapid and likely completed between the laser pulses for the laser repetition rates studied in Refs.…”

“…In Ref. 68 and 71 , the deposition was performed at the background oxygen pressure of P O2 112 mTorr (which is by a factor of 2.7 lower than in our work), as well as with target-substrate distances of 55 mm in Ref. 68 and 35 mm in Ref.…”

“…Thus, all diffusionguided processes (i.e., 3D island formation and growth) were rapid and likely completed between the laser pulses for the laser repetition rates studied in Refs. 68 and 71 . In contrast, the smaller D s enables us to effectively control the surface structure by varying time between laser pulses in agreement with Eq.…”