Superconducting properties of multilayered thin film structure of YBCO with NiO and CoO fabricated by pulsed laser deposition
This thesis attempts to investigate theoretical aspect of transport properties and experimental preparation of Yttrium Barium Copper Oxide (YBCO) single layer and multilayer thin films. Theoretical discussion on possible electrical transport properties on the basis of important experimental facts...
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| Format: | Thesis |
| Language: | English |
| Published: |
2015
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/68163/1/FS%202015%2076%20IR.pdf |
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| Summary: | This thesis attempts to investigate theoretical aspect of transport properties and
experimental preparation of Yttrium Barium Copper Oxide (YBCO) single layer and
multilayer thin films. Theoretical discussion on possible electrical transport properties
on the basis of important experimental facts to satisfy the requirements of practical
YBCO devices applications have not been addressed. The Pulsed Laser Deposition
(PLD) is one of the techniques that is used to develop fine quality epitaxial thin films. In
this research the bulk YBCO and NiO doped YBCO are prepared by different methods
namely solid state reaction method and co precipitation method. The simulation
modeling of laser plasma dynamics has been done in Matlab 2012 and different
parameters have been proposed under the light of theoretical modeling. The theoretical
transport properties have also been modeled which may provide some important
utilization in electronic devices.
The doping of NiO at Yttrium sites of the six samples with ratio from 0 - 0.1 exhibited
tetragonal structure in pure while the orthorhombic structure in doped samples. The
same orthorhombic structure has been found with decreased Tc values when the NiO has
been added. AC susceptibility results indicate that the introduction of NiO during the
final processing of YBCO bulk targets can decrease the Tc from 78-88K.
Then PLD experiments were carried out on two different setups with different ranges of
substrate heating systems, the former has 0-500ºC while other has 0-800ºC under oxygen
and nitrogen ambient.
The undertaken work involves two distinct studies, firstly, the YBCO epitaxial films
and buffer layers have been probed numerically with the help of computer simulations.
The simulations revealed the transport properties of the deposited YBCO thin films and
analyzed the laser plasma dynamics and transport properties like resistive versus magnetic field and temperature, susceptibility measurements, the activation energy
versus current density and high temperature thermal factor.
The electrical transport properties of YBCO thin film have been investigated using
different physical techniques. The physical transport properties were also estimated with
temperature and magnetic fields limits using thermally-activated flux flow model with
some modifications. The results of present simulation modelling have indicated that the
magnitude of activation energy depends on temperature and magnetic field. The
simulations revealed thickness dependent physical transport properties including
electrical and magnetic properties of deposited YBCO thin films. The results have
indicated that the temperature depends on the pinning energy and can be used to
improve the superconducting properties (Tc) of the YBCO single layers thin films.
The YBCO thin film have been experimentally fabricated in PLD system with substrate
heater (> 750ºC) annealed in-situ for the 30 minutes after the deposition under oxygen
ambient. The heating and cooling rate for annealing the deposited sample was 3ºC/min,
and 2ºC/min, respectively to improve the quality of film layer. The YBCO target used in
those experiment were prepared by amorphous phase epitaxy method. The same
procedure for the YBCO/NiO(CoO) double layer and YBCO/NiO(CoO)/YBCO triple
layer have been adopted.
The results produce in the other PLD system with lower substrate heating system and
ex-situ annealing via tubular furnace has not improved the quality of the layers either
used by increasing heating rate and decreasing cooling rate. All the XRD diffraction
peaks observed in bulk samples are also seen in the films.
The XRD patterns have indicated that the crystalline quality of the thin film samples
prepared by Amorphous phase epitaxy was better than those with co-precipitation
method. Furthermore, based on FESEM images, it has proven that thicker and high
substrate heating can absorb more oxygen and improve the surface layer. |
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