1. 磁流體實驗

2. Role of magnetic fluids In the early 20 th century Solid state physics   Nanoparticles Nanostructured materials Nanodevices Nanoparticles Nanostructured materials Nanodevices Nanoscale science & technology 1960 ~ Including Soft Materials : Fluids Liquid crystals Polymers Emusions Colloids Including Soft Materials : Fluids Liquid crystals Polymers Emusions Colloids Condensed matter physics   Magnetic fluids

3. Outline What Is Magnetic Fluids (Ferrofluids) ? Properties of Magnetic Fluids Properties of Magnetic Fluid Thin Films under Magnetic Fields (perpendicular/parallel) Ordered Structures of Magnetic Fluid Films Optical Properties of Magnetic Fluid Films Outlook What Is Magnetic Fluids (Ferrofluids) ? Properties of Magnetic Fluids Properties of Magnetic Fluid Thin Films under Magnetic Fields (perpendicular/parallel) Ordered Structures of Magnetic Fluid Films Optical Properties of Magnetic Fluid Films Outlook

4.  100 Å Magnetic particleSurfactant ( 界面活性劑 ) Liquid Carrier What Is Magnetic Fluids (Ferrofluids) ?

5. Properties of Magnetic Fluids Fundamental Properties - Magnetic Characterizations - H  I/r I = 0 I  0

6. - Thermal Conductivity - Magnetic fluid has good thermal conductivity. (Air: 26.2 mW/m/k @ T = 300 K)

7. - Loudspeaker (high thermal conductivity of MF) - Applications

8. Oil Magnets Magnetic fluid Liquid Research Ltd. - Sealing of magnetic fluids - S N High-pressure region Low-pressure region MF

9. - Other Applications Inkjet printing : coding (magnetic particles) Surface polishing (nanoparticles) Most applications are focused on mechanical purposes. Applications in bio-medical and optical- electronics are new interesting topics

10. Preparation of Magnetic Fluids Fe 3 O 4 Dextran Water mixing NH 4 OH co-precipitate, Fe 3 O 4 removing salt residue & large particles removing unbound dextran coating centrifugal gel filtration chromatography homogeneous water- based Fe 3 O 4 magnetic fluid dextran H2OH2O FeCl 2 & FeCl 3

11. FeCl 2 + FeCl 3 +8NaOH → Fe(OH) 2 + Fe(OH) 3 + 8NaCl Fe(OH) 2 + 2Fe(OH) 3 → Fe 3 O 4 + 4 H 2 O

12. Properties of Magnetic Fluid Thin Films under Magnetic Fields (perpendicular/parallel) Ordered Structures of Magnetic Fluid Films Under Perpendicular Magnetic Fields Under Parallel Magnetic Fields Optical Properties of Magnetic Fluid Films Magnetochromatics (perpendicular) Birefringence (parallel) Transmittance (perpendicular/parallel) Refractive Index (perpendicular)

13. H  H.E. Horng et al., JAP, 81, 4275(1997) APL, 75, 2196(1999) APL, 79, 2360(2001) Magneti c fluid Si wafer/ glass Top View glass - Formation of Ordered Structure in a Magnetic Fluid Film -

14. Ordered Structures of Magnetic Fluid Films Under Perpendicular Magnetic Fields Magnetic fluid film Magnetic fluid Au - Observation of Ordered Structure in a Magnetic Fluid Film -

15. H = 53 Oe, d = 5.14  m H =200 Oe, d = 3.36  m H = 77 Oe, d = 3.36  m H = 210 Oe, d = 3.27  m H = 34 Oe H = 560 Oe, d = 2.37  mH =630 Oe, d = 2.37  m H = 0 Oe 5  m M s = 5.6 emu/g, T = 18.0  C, dH/dt = 5 Oe/s, L = 6  m HH  ~1  m, h~6  m  10 7 ~ 10 8 particles

16. Fast Fourier Transformation H  10  m The ordered structure is characterized by d (distance between two neighboring columns, d varies from submicron to several  m): d = 2  /k r H.E. Horng et al., JAP, 81, 4275(1997) APL, 75, 2196(1999) APL, 79, 2360(2001) 磁點排列成 六角形分佈

17. Sweep rate Film thickness Concentration Temperature Material. - Control Parameters for the Magnetically Tunable Ordered Structure - Well-controlled and tunable ordered structure Important Result:

18. Magnetochromatic Effects in Magnetic Fluid Thin Films H.E. Horng, Chin-Yih Hong, Wai Bong Yeung, and H.C. Yang Cover page of Applied Optics, Vol. 37, 1 May(1998)

19. Magnetochromatics (perpendicular) A: PC B : Camera C: Solenoid D : Magnetic fluid film E : Mirror F : Telescope G : White source H :Current source I : Lens J : Aperture C E G H F G D B A I J I H.E. Horng et al., Appl. Opt., 37, 2674(1998) JAP, 83, 6771(1998) JAP, 88, 5904(2000) Optical Properties of Magnetic Fluid Films

20. H = 50 Oe (d = 2.34  m) H = 100 Oe (d = 2.26  m) H = 200 Oe (d = 1.64  m) - Controllable Magnetochromatics -

21. Under Parallel Magnetic Fields

22. - Periodic one dimensional grating - H = 200 Oe dH/dt = 100 Oe/s W = 10 μm L = 1.5 μm M s = 17.6 emu/g t d = 3 min Δx = 1.45 μm H 10  m xx

23. Magnetochromatics of the Magnetic Fluid Film under a Dynamic Magnetic Field Herng-Er Horng, S.Y. Yang, S.L. Lee, Chin-Yih Hong, and H.C. Yang Appl. Phys. Lett., 79, 350 (2001) H (Oe) 60200  = 15.2 o

24. Tunable Refractive index Experimental setup The critical angle of the total reflection at interface can be determined precisely. The refractive index of the magnetic fluid films via S.Y. Yang, Y.F. Chen, H.E. Horng, Chin-Yih Hong, W.S. Tse, and H.C. Yang, APL, 81, 4931(2002)

25. Applications of Magnetic Fluids Future Works We have well controlled and understood the ordered structures and the optical properties of the magnetic fluid thin films.

26. Magnetic Field Dependent n MF (H) 10  m  m The n MF is increased under a higher field. The increase in n MF is suggested to be due to the column formation.

27. Working Principle Magnetic fluid core (a) H = 0, n core > n MF, total reflection occurs (b) H  0, n core < n MF, total reflection vanishes cladding I H=0 IH0IH0 I H  0 < I H=0

28. Modulation of Transmitted Light Intensity Transmission loss = (I T -I T,H=0 )/I T,H=0 H (Oe) L = 796  m M s = 0.61 emu/g Transmission loss (%)

29. H  Transmission axis Polarizer Sample He-Ne laser ( = 632.8 nm) - Experimental Setup E in E out w/0.01 o resolution  Analyzer Transmission axis 

30. - Magnetic Field Dependent C-M Rotation -  - H  = 45 o  - 

31.  - H  = 45 o

32.  - H

33. Summary The refractive index of magnetic fluid films can well manipulated. The feasibility of the magnetic-fluid-based optical modulator and switch is demonstrated.

34. Conclusions Magnetically labeled immunoassay Photonic Crystal Modulator CWDM Switch What else? Magnetic fluids