Mrs Bfo Bt Nano Sphere Lithography

Fabrication and characterization of epitaxial BiFeO3 - BaTiO3 nano scale hybrids using nanosphere lithography V. Rajasekarakumar, S. Bhattacharyya and Ram S. Katiyar Department of Physics, University of Puerto Rico, San Juan PR 00931

INTRODUCTION
Materials with coupled electric, magnetic, and structural order parameters are called as biferroics.
Biferroic materials present opportunities for potential applications in information storage, the emerging field of spintronics, and sensors.
Development of this new generation of materials have enriched significantly our basic understanding of the underlying mechanisms of ferroelectricity and ferromagnetism as well.
As the demand for higher device-density pushes the existing processing techniques to their limits, ordered nanostructures become more welcome for the futuristic multifunctional devices coupling these interesting properties at a nanometer level.
. Self-assembled nanostructures have attracted particular attention in recent years due to their potential applications in economic and versatile patterning of a wide variety of materials at the nanometer scale with tunable array size and density.

PRESENT WORK
Fabrication of template layers using self-assembled array of polystyrene spheres (PS) beads.
The monolayer formation of the template forming spheres on SrTiO3 was verified using cross sectional SEM and AFM.
BiFeO3 –BaTiO3 thin films with a thickness range form 50 –100 nm were deposited on these porous templates layers by pulsed laser deposition technique.
The BiFeO3 –BaTiO3 nano-islands obtained from 460 nm diameter PS templates were observed from SEM and AFM measurements.
X-ray diffraction studies showed the formation of crystalline and epitaxial BFO-BT on both SrTiO3 and on SrRuO3/SrTiO3 heterostructures.
The feasibility to produce nanostructures with less than 50 nm lateral sizes have been verified in laser ablated Pt using PS diameter of 100-200 nm.

Fabrication of nanostructures Si Substrate Heated at 4000C for 1 hour in O2 atmosphere

Si02 Substrate Coating of PS dispersed in water

PS beads on Substrate Deposition of BFO-BT

Coating material on PS template layer PS beads removal by etching

Nano Pattern of BFOBFO- BT

 The voids formed by monolayer arrangement of PS beads are triangular.  Pattern formed had array of triangular islands.

CHALLENGES  Obtaining continuous monolayer of polystyrene was difficult

SEM micrograph of polystyrene on Si substrate

To get the nano pattern by removing the polystyrene and getting undisturbed periodic pattern is crucial. SEM micrograph of etched polystyrene on Si substrate

Successful formation of monolayer  Monolayer was obtained by tailoring the processing parameters.

SEM micrograph of polystyrene monolayer on Si substrate

 Formation of Monolayer was verified by the crosssectional SEM. 500 nm CrossCross-sectional SEM micrograph of polystyrene on Si substrate

Coatings on monolayer of polystyrene 30 nm of platinum coated on monolayer of polystyrene (PS 100).

AFM of Platinum coated polystyrene monolayer on SiO2 /Si substrate

3-D AFM of Platinum coated polystyrene monolayer on SiO2 /Si substrate

Nano patterns of different Metals- Focus on size reduction Nano pattern of Gold  size of nano dots - 120 nm  size of PS sphere - 460nm.

AFM of nanonano-islands of Au on SiO2 /Si substrate

Nano pattern of Platinum  size of nano dots - 30 nm  size of PS sphere - 100nm.

AFM of nanonano-islands of Platinum on SiO2 /Si substrate

Nano patterns using different deposition techniques The double image probably due to the variation in the angle between the substrate normal and the incoming flux during the deposition.

AFM of nanonano-patterns of Pt by PLD on SiO2 /Si substrate.

 DC sputtering gave good quality nanopattern. nano dot of the size 30 nm was obtained  Template of PS100nm .

AFM of nanonano-patterns of Pt by DC sputtering 2 on SiO /Si substrate.

Nano patterns of BFO-BT ( BiFeO3 – BaTiO3)  Template layer of PS-460nm on SiO2/ Si substrate

AFM of PSPS- 460nm template on SiO2 /Si substrate.

 BFO-BT nano dots of 120 nm size obtained on SiO2/ Si substrate  BFO-BT deposited by PLD  Deposition pressure- 100 mT. AFM of nanonano-patterns of BFOBFO-BT on SiO2 /Si substrate.

Nano patterns of BFO-BT ( BiFeO3 – BaTiO3) on STO

 BFO-BT nano patterns obtained on STO substrate  BFO-BT deposited by PLD Deposition pressure- 100 mT.  Efforts are underway to get the clear and continuous patterns. AFM of nanonano-patterns of BFOBFO-BT on STO substrate.

X-Ray Diffraction Substrate Temp: R.T

0

(012)

RT+ A650 C

Annealing Temp : 650 0C_ 1hr

35

40

45

50

55

60

2θ

Intensity (a.u)

XRD of BFOBFO-BT film on SiO2 / Si substrate

STO (200)

30

BFO-BT (204)

25

STO (100)

20

Annealing attmosphere: O2 BFO-BT (102)

*

(018)

(024)

(104)

*

Intensity (a.u)

Deposition press: 100 mT

0

RT+ 650 C

BFO-BT/SRO/STO

BFO-BT/STO SRO/STO

20

25

30

35

40

45

50

55

60

2θ

XRD of BFOBFO-BT film on STO, SRO/STO substrates

XPS- Analysis  XPS showed the presence of Bi, Fe,O,Ba&Ti in the nano structure.  Observed valency Fe 3+

XPSXPS-Spectra for the nanostructured BFOBFO-BT on SiO2 / Si substrate

XPSXPS-Spectra for the nanostructured BFOBFO-BT on STO substrate

CONCLUSION
Continous monolayer of polystyrene template layer have been optimised successfully.
Nano patterns of different metal have been tried and successfully formed the patterns of nanodots of platinum of 30 nm size using the PS- 100nm template layer.
BFO-BT ( BiFeO3 – BaTiO3) nano patterns with the dot size of 120 nm was obtained using PS-460nm template.
BFO-BT ( BiFeO3 – BaTiO3) nano patterns were formed in SiO2/ Si and Strontium Titanate (STO) substrates.
Fabrication of nano structures with BiFeO3 –BaTiO3 was found to depend on the thickness of the film and the choice of the substrates. ACKNOWLEDGEMENTS This work was supported by the project NCC#-1034. The help of Mr. José Ortiz Morales and Esteban Fachini in SEM and XPS measurements is gratefully acknowledged.