Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
The Fabrication of YBa 2 Cu 3 O 7- Superconducting Thin Film on SrTiO 3 Buffered Si Substrate by PED
Z. Mutlu 1 *, M. Yilmaz 1 , Y. G. Mutlu 1 , O. Dogan 1
1 Department of Physics, Selcuk University, A. K. Education Faculty, Konya 42090 Turkey
Abstract- A superconducting YBa 2 Cu 3 O 7- (YBCO) thin film has been produced by pulsed electron deposition (PED) which is an essential and
low-cost physical deposition technique of high quality superconducting films. The crystalline structure, surface morphology and microstructure
of thin films have been characterized with x-ray diffractometer (XRD), atomic force microscope (AFM) and scanning electron microscope
(SEM).
The method of pulsed electron deposition (PED) has
recently become an alternative to PLD as a means for
producing thin films. PED shares some of the same
advantages that characterize PLD for vacuum deposition.
Among these are modest requirements for vacuum, easy
control of film thickness, easy set-up, multicomponent film
stoichiometry nearly identical to target material, and a
relatively high deposition rate with low consumption of target
materials. In addition, PED works for UV-transparent
materials where PLD might fail [1]. Moreover, PED has a
significant cost advantage over PLD because of the much
lower cost of the electron source compared to the cost of the
excimer laser typically used in PLD.
The aim of this study is to determine some properties of
YBCO thin film and STO buffer layer deposited by PED
process. We have reported a detailed study of the
superconducting layer of YBCO on STO buffered Si substrate
and the buffer layer of STO on Si substrate.
Using PED, several research groups have successfully
grown YBCO thin films on STO [4], LaAlO 3 [2] and Ni-W [3]
substrates. However, a study of the deposition of YBCO
on STO buffered Si substrate by PED has not yet been
realised. Our research has thus been focused on the possibility
of fabricating the YBCO thin film on STO buffered Si
substrate by PED.
PED electron beam source from Neocera Inc. (PEBS–20
Model) was used to fabricate YBCO superconducting lms on
STO buffered substrates. Deposition conditions are the
following: the base pressure of 5x10 –6 Torr, 13 kV
accelerating voltage, 5000 total shots and 5 Hz electron
repetition rate. The distance between target and substrate was
10 cm. STO thin film was first deposited on Si at substrate
temparature of 890 o C in O 2 pressure of 16 mTorr. Then
YBCO thin film was deposited on the top of STO thin film at
substrate temparature of 890 o C in O 2 pressure of 15 mTorr.
After deposition, deposited films were cooled to room
temparature in ambient of high oxygen pressure.
The surface structure and surface morphology of the film
was investigated by AFM. Fig.1 shows typical 3-dimensional
AFM image of the YBCO film on STO buffered Si substrate.
The values of root-mean-square (Rms) and average (Ra)
surface roughness have been measured ~ 27 nm and ~ 22 nm,
respectively. The droplets were observed on the film surface.
The droplets sizes were measured directly from AFM scans of
the film. The average size of the droplets is about 0,098 μm in
diameters.
Figure 1. Typical 3-dimensional atomic force microscope image of
the surface of an YBCO film at deposited 890 o C (scan area: 1.0x1.0
μm 2 ).
We observed the film surface is dense and free of cracks.
Surface particulates across the entire film were observed. The
size of these particulates is typically 1–3 μm in diameters. The
particulates might be secondary phases which are observed in
XRD. The presence of particulates on the surface of film
grown by PED is well known [3, 5].
The crystal structures of STO/Si and YBCO/STO/Si thin
films were characterized by XRD. The XRD results indicated
that YBCO was formed with complete c-axis orientation.
There are also two peaks of (110) and (003) of STO and the
peaks from Si of the substrate materials. The weak XRD peak
intensities show poor crystallinity of the YBCO thin film. The
crystallinity and superconductivity of YBCO film could be
hampered by the intermediate layer formed at the YBCO/STO
interface.
In summary, from the -2 XRD analysis of YBCO films,
(00l) diffraction peaks are obtained indicating they have a
poor c-axis oriented structure. SEM analysis show that the
films surfaces are crack-free but they have some particulates.
On AFM images, the droplets are clearly observed leading to a
rough surface. The measured experimental results are
compared with the results of other studies.
*Corresponding author: 0Hzmutlu@selcuk.edu.tr
[1] Mathis J.E., Christen H.M., Physica C: Superconductivity,
Vol:459, Iss:1-2 (2007), 47-51.
[2] Zhai H.Y., Christen H.M., Feenstra R., List F.A., Goyal A.,
Leonard K.J., Xu Y., Christen D.K., Venkataraman K., Maroni A.,
Mat. Res. Soc. Symp. Proc. Vol. EXS–3 (2004), USA.
[3] Gilioli E., Baldini M., Bindi M., Bissoli F., Calestani D., Patini
F., Rampino S., Rocca M., Zannella S., Woerdenweber R., J. of
Physics: Conference Series 97 (2008).
[4] Jiang Q.D., Matacotta F.C., Konijnenberg M.C., Mueller G., and
Schultheiss C., Thin Solid Films, 241:100 (1994).
[5] Kovaleski S.D., Gilgenbach R.M., Ang L.K., Lau Y.Y., J. of
Appl. Phys., Vol. 86, No. 12 (1999), 7129–7137.
6th Nanoscience and Nanotechnology Conference, zmir, 2010 416