着色斜め蒸着膜の光学的性質～無機偏光膜への応用

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1 Anisotropy in the Optical Absorption of Metal-insulator Obliquely Deposited Thin Films The Application for an Inorganic Polarizer Motofumi Suzuki, Yasunori Taga Abstract An attempt has been made to clarify the anisotropy in the optical absorption and nanostructure of thin films prepared by oblique codeposition of Ag and an insulator (SiO 2 or Ta 2 O 5 ). At a low concentration of Ag, the columnar structure grows toward the incident direction of vapor flux of the insulator, and Ag is dispersed in that structure as small metallic particles. The optical transmittance is strongly dependent on the angle of incidence of the light, the degree of polarization of incident light and the refractive index of the insulator. These properties can be mainly interpreted in terms of the plasma resonance of free electrons in the small Ag particles embedded in the biaxial matrix. Furthermore, an inhomogeneous distribution of Ag particles is obtained when the Ag is deposited from the side of the normal to the film surface opposite to that of the incident direction of the insulator. As the result, the optical anisotropy is enhanced, and useful polarization and angular selective properties have been achieved. The anisotropic optical absorption of metal and insulator hybrid films can be used as an inorganic polarizer. R&D Vol. 29 No. 2 ( )

2 Motohiro and Taga Smith 2 2 Leamy and Dirks Keitoku Ag SiO 2 2 Ag Ta 2 O (a) 2(b) λ x' y' z' ε mx' ε my' ε mz' y'ε mx' < ε my' < ε mz' z' Jones Maxwell- Garnett ε j' ( ω ) ε M (ω)(1+ 2f )+2ε mj (1 f ) ε j (ω)=ε mj,(j = x, y, z ) ε M (ω)(1 f )+2ε mj (2+ f ) (1) R&D Vol. 29 No. 2 ( )

3 ε M (ω) ; f ; Cu Ag Au Drude 2 iω pτ ε M (ω)=1+ (2) ω (1 iωτ) ω ; ω p τ ; ; Ag hω p = 6.5eV τ = s Ag 5% ε mx' = 1.10 ε mz' = 1.45 z'45 SiO 2 0.5µm θ = 0 ±60 p x' z' θfig. 1 z' log 10 ( 1/T ) T2 ε mx' = 1.10 ε mz' = 1.45 Ag θ p s s (a) s Fig. 2p 21 Ag Schematic showing the system used to model thin film optical properties. The film parallels the x y plane. The x', y', z' system has each axis parallel to one of the optical axes defined by the columns. The calculated absorbance for p-polarized light. The angle of incidence θ is 60 for spectrum A, 0 for spectrum B and 60 for C. Each spectrum is shifted by 40. (Ref. 8) R&D Vol. 29 No. 2 ( )

4 . Ag Ag ( SiO 2 Ta 2 O 5 ) W SiO 2 Si Agα Ag α Ag θ Ag Ag 20cm 50cm Ag 0.6 1µm ( TEM ) NaCl 50nm Torr Ag SiO 2 Ag Si O ( atoms/cm 2 ) Ag SiO 2 O Si 2 Ag SiO 2 3% 6% 32% Ag Ta 2 O 5 AgAg Ta 2 O 5 TEM ( FE SEM ) TEM SEM NaCl SiO 2 Si SEM 300 < λ < 1240nm ( ) 2 ( ) Fig. 1 ( z' ) ( x' ) ( y' ) 2 y p s p 60 < θ < 60 s 0 < θ < 60 s 60 < θ < 60 Schematic showing the geometry for codeposition. The deposition angle of SiO 2 or Ta 2 O 5 is fixed at 70, while that of Ag is. Ag SiO 2 2 FE SEM α Ag = 60 [Fig. 4(a)] α Ag = 30 [Fig. 4(b)] SiO 2 40 SiO 2 α Ag = 60 TEM R&D Vol. 29 No. 2 ( )

$Scanning electron micrographs of the cross section of obliquely codeposited Ag SiO 2 thin films fractured parallel to the plane of incidence of the SiO 2 vapor beam for the sample prepared with$ 8, 9) Transmission electron micrograph for the obliquely codeposited Ag SiO 2 thin film prepared with α Ag = 60. The small near spherical particles are agglomerations of Ag. (Refs.

8, 9) Transmission electron micrograph for the obliquely codeposited Ag SiO 2 thin film prepared with α Ag = 60. The small near spherical particles are agglomerations of Ag. (Refs.

5 Scanning electron micrographs of the cross section of obliquely codeposited Ag SiO 2 thin films fractured parallel to the plane of incidence of the SiO 2 vapor beam for the sample prepared with (a) α Ag = 60 and (b) α Ag = 30. Arrows indicate the direction of incident Ag and SiO 2 vapor fluxes. The samples were observed without a conductive coating. (Refs. 8, 9) Transmission electron micrograph for the obliquely codeposited Ag SiO 2 thin film prepared with α Ag = 60. The small near spherical particles are agglomerations of Ag. (Refs. 8, 9) 20nmSEM TEM X Ag Fig. 4(a)(b) α Ag α Ag = 60 Ag SiO 2 [Fig. 4(a)]α Ag = 30 [Fig. 4(b)] AgAg α Ag SiO 2 Ag SiO 2 Ag SiO 2 AgAg Ag α Ag = 60 Ag Ag Ag α Ag = 30 Ag Ag α Ag = eVp [Fig. 6(a)] s p R&D Vol. 29 No. 2 ( )

Fig. 2 Fig. 2 p 2 1 20 < θ < 20 θ < 20 θ > 20 θ 2.8eV θ 3.4eV Fig. 22 p v F τ Ag 50nm 2Ag 20nm (2) τ Fig. 2 τ = 0.

Arrows indicate the plasma resonance energy corresponding to the principle dielectric constants of the matrix.

$For this sample, the volume fraction of Ag is 4% and the thickness is 0.71µm. (Ref.$

6 Fig. 2 Fig. 2 p < θ < 20 θ < 20 θ > 20 θ 2.8eV θ 3.4eV Fig. 22 p v F τ Ag 50nm 2Ag 20nm (2) τ Fig. 2 τ = s 2 Contour map of the absorbance for p polarized light for the same sample as in Fig. 6. Arrows indicate the plasma resonance energy corresponding to the principle dielectric constants of the matrix. Typical absorbance spectra for the obliquely codeposited Ag SiO 2 thin film prepared with α Ag = 60 for (a) p-polarized light and (b) s polarized light. The spectra A, B, C, D, and E are measured at θ = 60, 30, 0, 30, 60, respectively. For this sample, the volume fraction of Ag is 4% and the thickness is 0.71µm. (Ref. 8) The calculated absorbance spectrum for p polarized light. The small size effect is taken into account. (Ref. 8) R&D Vol. 29 No. 2 ( )

7 1 / 60 20nm 1 Ag TEM Ag Ag Si O Ag TEM SiO x H 2 O O 2 α Ag = 30 2 Ag SiO 2 Ag Ag (a) α Ag = 60 (b) α Ag = 30 θ = ±45 p θ = 45 s Ag 6% 1µm 330 < λ < 600nm λ > 500nmFig. 92 α Ag = 60 α Ag = 30 α Ag T u (θ )= T p(θ )+T s (θ ) 2 P(θ )= T p(θ ) T s (θ ) T p (θ )+T s (θ ) (3) (4) t (θ )= T p(θ )+T p ( θ),(θ >0) 2 Π(θ )= T p(θ ) T p ( θ),(θ >0) T p (θ )+T p ( θ) T u (θ ) P(θ ) T u (θ ) P(θ ) T u (θ ) = 0.5 P(θ ) = 1 t(θ ) Π(θ ) (a) α Ag = 60 α Ag = 30 λ = 600 nmt u (45 ) P(45 ) Fig. 10(b)t(45 ) Π(45 ) Ag T u tag (5) (6) T p (θ ) ; θp T s (θ ) ; θs Typical transmittance spectra for the obliquely codeposited Ag SiO 2 thin films prepared with (a) α Ag = 60, (b) α Ag = 30. The measurements were performed at θ = 45 for p polarized light (solid line), at θ = 45 for p polarized light (dashed line), and θ = 45 for s polarized light (dashed and dotted line). (Refs. 8, 9) R&D Vol. 29 No. 2 ( )

8 r (θ)= logt p(θ ) (7) logt s (θ ) r(θ)t u P r(θ) p s (1) (2) r(45 ) = 4.0 r(45 ) = 2.0 t Π T u P Fig. 10(b) (1) (2) logt p (+45 )/logt p ( 45 ) = α Ag = 60 α Ag = 30 (1) (2) Ag Agα Ag α Ag Ag α Ag = Ag α Ag = 60 Ag SEM [Fig. 4(a)] Ag α Ag = 60 Ag α Ag = 60 Fig. 9(a)λ = 600nm θ = 45 T p (45 )/T s (45 ) = 35 T p (45 )/T p ( 45 ) = 130p s 2% The relation between (a) T u (45 ), and P(45 ), and t(45 ) and Π(45 ) for the Ag-SiO 2 obliquely deposited thin films prepared with α Ag = 60 ( ) and α Ag = 30 ( ). The lines in (a) represent constant dichroic ratio r, line (1) r = 4.0, line (2) r = 2.0. In a similar manner, the lines in (b) indicate log Tp(45 )/log Tp( 45 ) = 5.0 [line(1)] and 2.5 [line(2)]. (Ref. 8) The angular dependence of the transmittance of p polarized light ( ) and s polarized light ( ) measured at λ = 600nm for the same sample as in Fig. 9(a). (Refs. 8, 9) R&D Vol. 29 No. 2 ( )

$Arrows indicate the plasma resonance energy corresponding to the principle dielectric constants of the matrix. For this sample, the volume fraction of Ag is 4% and the thickness is 0.75µm.$

9 2 SiO 2 1p 2 SiO 2 Ta 2 O 5 2 α Ag = 0 Ag Ta 2 O 5 p 1.8 ev 3.5 ev 2 θ < 0 θ > 0 2 SiO 2 Ag 2 Ag Ta 2 O 5 θ = ±45 p s θ = 45 p λ < 500 nmθ = 45 p λ > 500nms p θ < 0 θ > 0 θ < 0 Ag Ta 2 O 5. 2 Ag SiO 2 Ta 2 O 5 2 Ag Contour map of the absorbance for p polarized light for the sample prepared by oblique codeposition of Ag and Ta 2 O 5 with α Ag = 0. Arrows indicate the plasma resonance energy corresponding to the principle dielectric constants of the matrix. For this sample, the volume fraction of Ag is 4% and the thickness is 0.75µm. Typical transmittance spectra for the obliquely codeposited Ag Ta 2 O 5 thin film prepared with α Ag = 30. The measurements were performed at θ = 45 for p polarized light (solid line), at θ = 45 for p polarized light (dashed line), and θ = 45 for s polarized light (dashed and dotted line). For this sample, the volume fraction of Ag is 5% and the thickness is 0.65µm. R&D Vol. 29 No. 2 ( )

p s α Ag α Ag = 60 SEM Ag 2 SEM TEM 1) MotohiroT. and TagaY. Appl. Opt.(1989)2466 2) SmithG. B. Opt. Commun.(1989)279 3) SmithG. B. Appl. Opt.(1990)3685 4) MbiseG. SmithG. B.NiklassonG. A. and GranqvistC.

and TagaY. J. Appl. Phys.(1992)2848 9) SuzukiM. and TagaY. J. Non-Cryst. Solids (1992) 148 10) GenzelL. and MartinT. P. Surf. Sci.(1973) 33 ; KregU.AlthoffA. and PressmannH. Surf. Sci. (1981)308 11) MacleodH.

10 p s α Ag α Ag = 60 SEM Ag 2 SEM TEM 1) MotohiroT. and TagaY. Appl. Opt.(1989)2466 2) SmithG. B. Opt. Commun.(1989)279 3) SmithG. B. Appl. Opt.(1990)3685 4) MbiseG. SmithG. B.NiklassonG. A. and GranqvistC. G. Appl. Phys. Lett.(1989)987 5) DitchburnR. J. and SmithG. B. J. Appl. Phys.(1991) ) LeamyH. J. and DirksA. G. J. Appl. Phys.(1979) ) KeitokuS.KamimoriT. and GotoM. Jpn. J. Appl. Phys.(1986)1668 8) SuzukiM. and TagaY. J. Appl. Phys.(1992)2848 9) SuzukiM. and TagaY. J. Non-Cryst. Solids (1992) ) GenzelL. and MartinT. P. Surf. Sci.(1973) 33 ; KregU.AlthoffA. and PressmannH. Surf. Sci. (1981)308 11) MacleodH. A. J. Vac. Sci. Technol. A, (1986)418 12) JonesR. C. Phys. Rev.(1945)93 ; ) Maxwell-GarnettJ. C. Philos. Trans. R. Soc. London (1904)385 ; (1906)237 14) JohnsonP. B. and ChristyR. W. Phys. Rev. B, (1972) ) KidoY.KakenoM.YamadaK.KawamotoJ.Ohsawa H. and KawakamiT. J. Appl. Phys.(1985) ) DirksA. G. and LeamyH. J. Thin Solid Films(1977) ) ClippeP.EvrardR. and LucasA. A. Phys. Rev. B, (1976) ) QuintenM. and KrebigU. Surf. Sci. (1986) R&D Vol. 29 No. 2 ( )

42 1 Fig. 2. Li 2 B 4 O 7 crystals with 3inches and 4inches in diameter. Fig. 4. Transmission curve of Li 2 B 4 O 7 crystal. Fig. 5. Refractive index

$42 1 Fig. 2. Li 2 B 4 O 7 crystals with 3inches and 4inches in diameter. Fig. 4. Transmission curve of Li 2 B 4 O 7 crystal. Fig. 5. Refractive index$ MEMOIRS OF SHONAN INSTITUTE OF TECHNOLOGY Vol. 42, No. 1, 2008 Li 2 B 4 O 7 (LBO) *, ** * ** ** Optical Scatterer and Crystal Growth Technology of LBO Single Crystal For Development with Optical Application