Participants - Group I

Christos G. Takoudis [PI]
Manish Singh [PhD]
Yi Yang [PhD]

Activities

A new commercially available iron source was identified for deposition of iron-based oxide films. Its thermal properties were characterized and its use as metalorganic precursor for low pressure chemical vapor deposition was demonstrated.

The new iron precursor was used with a bismuth source to successfully deposit BiFeO3 thin films using LPCVD after optimizing the processing conditions. Thin film deposition on platinized substrates at different temperatures (400-600 C) was carried out at. Material and electrical characterizations were done using various techniques.

Findings

Based on XPS anlaysis, the films were stoichiometric BiFeO3 and did not have any carbon impurities. Structural studies using XRD revealed peaks corresponding to only BiFeO3 indicating the phase-purity of the BiFeO3 films. The surface of the film was smooth and the grains looked round at higher magnification. The average lateral and vertical sizes of grains were measured to be about ~40 and ~20 nm, respectively. Charge retention behavior of the deposited BiFeO3 films was studied using dynamic contact electrostatic force microscopy (DC-EFM). An area of 55 μm2 was poled at +10 V. The polarization of the single-poled region remained invariable with time.

Participants - Group II

Siddhartha Ghosh [Co-PI]
Jiri Kabelac [PhD]

Activities

Dr. Ghosh’s group has been heavily involved with developing an in-situ real-time surface stoichiometry measurement set up for studying surface conditions as a function of growth conditions. They utilized total reflection angle x-ray spectroscopy to study the different x-ray lines from the surface constituent atoms. The relative intensity of the x-ray lines from various elements provides information on the surface stoichiometry. They also developed double perovskite multiferroic films which are highly ferroelectric but weakly magnetic. They are in the process of optimizing growth conditions and investigating several double perovskite material systems for further studies.

Findings

The recent relevant significant results have been:
1. Epitaxial growth of BiFeO3
2. Ferroelectric properties observed in BiFeO3
3. Ferromagnetic properties observed in Sr and Co doped BiFeO3

Preliminary hetero-epitaxy of BFO, which is one of the best candidates for ME multiferroic, on STO (001) substrates showed good epitaxial film quality (less defects, single crystal films) and ferroelectric and weak ferromagnetic behavior at room temperature. The ferromagnetism can be enhanced by straining the BFO films by using an underlying piezoelectric (such as BaTiO3) thin film.

Recent Publications

  1. M. Singh, Y. Yang, and C. G. Takoudis, "Low-pressure metalorganic chemical vapor deposition of Fe2O3 thin films on Si(100) using n-butylferrocene and oxygen," J. Electrochem. Soc., accepted (2008).
  2. J. Kabelac, S. Ghosh, P. Dobal and R. Katiyar, "rf oxygen plasma assisted molecular beam epitaxy growth of BiFeO3 thin films on SrTiO3 (001)," , J. Vac. Sci. Technol. B 25(3) 1049-1052  (2007). [View article]