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Oct 24, 2017 - transparent electrodes is to use ITO - metal - ITO (IMI) multilayer thin films, built up by a thin .... From Newton's second law ma = mx = Fdriving + ...
Outline Introduction Experimental Details Results and Discussion Conclusion

The Observation of Surface Plasmon Resonance Effect in ITO-Titanium-ITO Multilayer Thin Films on Glass Prepared by Magnetron Sputtering Turgay C ¸ oruhlu1 Necdet Aslan1 Tuba S ¸ en2 Kenan S¸ent¨ urk3 4 4 Rainer Lilischkis Peter Pokrowsky 1 2 3

Department of Physics, Yeditepe University, Istanbul, Turkey

Department of Mathematics, Beykent University, Istanbul, Turkey

Department of Energy Systems Engineering, Beykent University, Istanbul, Turkey 4

Mikrosystemstechnik, Hochschule Kaiserslautern, Zweibr¨ ucken, Germany

October 24, 2017

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion

Introduction ITO-metal-ITO Multilayers

Experimental Details

Results and Discussion Optical Characterization Surface Plasmon Resonance Lorentz and Drude Models Electrical Characterization

Conclusion References

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion ITO-metal-ITO Multilayers

Indium Tin Oxide (ITO) The most commonly used transparent conductive oxide (TCO) due to I high optical transmittance I low electrical resistivity Alternative TCO’s: AZO, GZO, TiO2 , CNT s, graphene One possibility for the further improvement of the conductivity of transparent electrodes is to use ITO − metal − ITO (IMI ) multilayer thin films, built up by a thin metal layer of about 10 nm thickness, embedded between two ITO layers. In this work, we have prepared ITO monolayers, and ITO − Titanium − ITO (ITI ) multilayer thin films on soda lime glass (SLG) and borosilicate glass (BK7) by magnetron sputtering, and characterized by using SEM, AFM, Spectroscopic ellipsometry, surface profilometer, photoluminescence and four point probe.

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion ITO-metal-ITO Multilayers

ITO-metal-ITO (IMI) Multilayers The transparency in the visible spectral range of such multi-layers is comparable to that of ITO films of the same thickness, while the sheet resistance decreases to about a quarter of the ITO value[1].

Figure 1: Single ITO layer (left) and IMI multilayer (right) with same thickness around 100 nm

90 − 100 nm is common for solar cells.

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion

ITO-Titanium-ITO Trilayer

Figure 2: ITO-metal-ITO Trilayer Structure

Step height was made for thickness measurements with DEKTAK. Color change resulted from step-height. To prevent back-reflection the rear of the glass was mechanically etched. T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion

Deposition Parameters Target Parameter

ITO

Metals

Base pressure (mTorr) Working pressure (mTorr) Working gas Power supply Power (W) Interelectrode distance (cm) Substrate

0.05 8 Ar RF 60 5 Glass (SLG or BK 7)

0.05 8 Ar DC 100 5

Table 1: Deposition Conditions

We have used RF for ITO to avoid cracking it.

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion Optical Characterization Surface Plasmon Resonance Lorentz and Drude M

Transmission Spectra [T (%) vs λ(nm)]

Figure 3: Single ITO layers with different thickness

Figure 4: ITI trilayers with different thickness and single ITO layer

The optical transparency increases as the thickness of the Ti increases. T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion Optical Characterization Surface Plasmon Resonance Lorentz and Drude M

AFM Analysis of ITI

Figure 5:

Figure 6:

Figure 7:

Figure 8: AFM images of the intermediate layer of ITI with different coating time (1, 2, 3 min) of Ti

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion Optical Characterization Surface Plasmon Resonance Lorentz and Drude M

Transmission Spectra [T (%) vs λ(nm)]

Figure 9: ITO and ITI thin films deposited on SLG (Numbers show Ti thickness)

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion Optical Characterization Surface Plasmon Resonance Lorentz and Drude M

Figure 10: ITO and ITI thin films deposited on BK7

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion Optical Characterization Surface Plasmon Resonance Lorentz and Drude M

In Figure 5: I The optical transmittance of ITI − 6 sample is even higher than ITO monolayer. This is attributed to the island growth of thin film. (The film is not continuous.) I The spectra of ITI − 8 and ITI − 10 are nearly the same. This can be attributed to surface plasmon resonance (SPR) effect of ITI. I The optical transmittance of ITI − 14 is the same with or greater than ITI − 12. This is also attributed to SPR effect of ITI. In Figure 6: I The optical transmittance of ITI − 6 sample is even higher than ITO monolayer. This can be explained by the island growth of thin film, too. I The optical transmittance of ITI − 14 is greater than ITI − 12. This is also attributed to SPR effect of ITI.

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion Optical Characterization Surface Plasmon Resonance Lorentz and Drude M

Island Growth of Thin Films

Figure 11: Volmer-Weber type (3D or island) thin film growth

After an initial nucleation, an island structure was constructed, which grew and then coalesced with each other (Volmer-Weber type[3]) T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion Optical Characterization Surface Plasmon Resonance Lorentz and Drude M

Surface Plasmon Resonance The thickness correspondent to the formation of a continuous film (depending on the metal, the deposition process and the substrate, could be around 6 − 15 nm) the light is able to excite a surface plasmon on the metal film surface (at lower thicknesses you have separated clusters, not a continuous surface, so the surface plasmon could not exist, maybe some ”cluster” plasmon). The light wave (in the resonant wavelength range) penetrates in the metal film, and its tail excites a similar plasmon on the other surface of the metal film. The two plasmons are resonant, therefore a strong wave emerges from the other side of the metal film. In this way the light wave, instead of being absorbed, causes a resonance and emerge on the other side of the film amplificated (or much less absorbed). The result is that the light in that wavelength range is transmitted with very low absorption on the other side of the metal film. When you increase the metal thickness further, the two surfaces are more distant and therefore the first surface plasmon is not able to excite the surface on the other side [2].

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion Optical Characterization Surface Plasmon Resonance Lorentz and Drude M

From Newton’s second law ma = m¨ x = Fdriving + Fdamping + Fspring = qE − mγ x˙ − mω02 x where x, m, q, γ, ω0 and ω are the electron’s displacement, electron’s effective mass, the charge of an electron, the damping factor, the resonance or natural frequency and the frequency of the incident light. We will solve: eE0 iωt e (1) x¨ + γ x˙ + ω02 x = − m where we have used E = E (t) = E0 e iωt . To find solution, we assume x(t) = Ae iωt where A is a constant. Substituting x˙ and x¨ into Equation 1 to get 1 eE0 m ω02 − ω 2 − iγω 1 eE0 x(t) = e iωt m ω02 − ω 2 − iγω A=

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion Optical Characterization Surface Plasmon Resonance Lorentz and Drude M

Since ex is the polarization of one oscillator, the total polarization per unit volume is thus P = N0 ex =

ωp2 1 N0 e 2 iωt E e = 0 E 0 m ω02 − ω 2 − iγω ω02 − ω 2 − iγω

where we have used the definition of plasma frequency, ωp , ωp2 =

N0 e 2 . m0

The polarization is related to the electrical field through the electrical permittivity P = χ0 E Therefore

ωp2 − ω 2 − iγω and the relative dielectric constant  = 0 r is χ=

ω02

r = 1 + χ = 1 +

ωp2 = 1 + i2 ω02 − ω 2 − iγω

where 1 and 2 are the real and imaginary parts of r . T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion Optical Characterization Surface Plasmon Resonance Lorentz and Drude M

Complex Refractive Index Hence, 1 = 1 +

ωp2 (ω02 − ω 2 ) − ω 2 )2 + γ 2 ω 2

(ω02

,

2 =

(ω02

ωp2 γω . − ω 2 )2 + γ 2 ω 2

The complex refractive index (N = n + ik) can be calculated from r as N=



r

or n 2 − k 2 = 1

,

2nk = 2

where n and k are the refractive index and absorption coefficient. If there is no spring term (ω0 = 0), Lorentz model reduces to Drude model.

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion Optical Characterization Surface Plasmon Resonance Lorentz and Drude M

Quality Factor for SPR Quality factor (Qf ) is defined as ε1 ε2 Figure 8 shows the Qf spectrum of Ti. Figure 9 shows the Qf spectra of Ag, Cu, and Ti together. Comparing to Cu and Ag , Qf (Ti) is quite smaller, therefore, it is very interesting that we observe the effect with Titanium. This also show that Ti is not oxidized.

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion Optical Characterization Surface Plasmon Resonance Lorentz and Drude M

Quality Factor of Ti

Figure 12: SPR of Titanium T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion Optical Characterization Surface Plasmon Resonance Lorentz and Drude M

Comparison of Quality Factor of Ag, Cu, and Ti

SPR effect ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt Figure 13: Comparison of SPR ofonAg, Cu and Ti

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

Outline Introduction Experimental Details Results and Discussion Conclusion Optical Characterization Surface Plasmon Resonance Lorentz and Drude M

Sheet Resistance and Conductivity The sheet resistances of ITO monolayers and ITI multilayers have been measured by means of four-probe method. It is known that σ=

1 ρ

and

U π ρ = R = d I `n 2 where σ, ρ, R , U, I and d are the conductivity, resistivity, sheet resistance, voltage, current, and the thickness of the film, respectively [4]. We have found that R(ITI ) 1 = R(ITO) 3

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion References

Outlook In this study I In this work, indium tin oxide (ITO) monolayer and ITO-Titanium-ITO (ITI) multilayers have been prepared on glass by using magnetron sputtering. Electrical and optical properties have been investigated. I The discrepancy in results is attributed to surface plasmon resonance (SPR) effect. I For the first time, we have demonstrated that titanium (in ITO-Ti-ITO) shows SPR effect. SPR Spectroscopy: non-invasive technique to study biological molecules

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion References

C. Guillen and J.Herrero, Thin Solid Films 420 (2011) 1-17. YS Park et al., J. of the Electrochemical Society 156 (2009). Y. Shigesato et al., Vacuum 59 (2000) 614-621. L. B. Valdes, Proceedings of IRE 42 (1954) 420-427.

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt

Outline Introduction Experimental Details Results and Discussion Conclusion References

Thank you for your attention! [email protected]

T. C ¸ oruhlu et al. (32nd S ¸¨IS ¸ ECAM Glass Symposium, 2017, Istanbul)

SPR effect on ITO-Titanium-ITO Multilayers Prepared by Magnetron Sputt