Fabrication of large area sub-wavelength structures for anti-reflection optical film Reporter ﹕ Wen-Yu Lee Advisor ： Cheng-Hsin Chuang Department of Mechanical Engineering, Southern Taiwan University of Science and Technology, Tainan, Taiwan Date: 2013/03/05 製作具次波長結構之大面積抗反射光學元件

Outline 2 Introduction Experimental setup and results Anti-reflection film measurement Conclusions & Future works  Porous Anodic Alumina Oxide (AAO) Template  Nano imprinting process  The transmittance and reflectance measurement results  Comparing the results of different experiment parameters  Motivation  Types of Anti-reflection film

Outline 3 Introduction Experimental setup and results Anti-reflection film measurement Conclusions & Future works  Porous Anodic Alumina Oxide (AAO) Template  Nano imprinting process  The transmittance and reflectance measurement results  Comparing the results of different experiment parameters  Motivation  Types of Anti-reflection film

4 Motivation Reflection Low contrast Decreased conversion efficiency Low transmittance Disadvantages of light reflection n=1.5 Air n=1 n=1.5 n=1.1~1.4 10%

5 Antireflective coating technology – Multilayer coating Antireflective structure – Sub-wavelength structure (SWSs) Protective film Antireflection layer Substrate with hard coating Adhesive layer Separator The refractive index of multilayer (Ladder) High-cost facilities Types of Anti-reflection film

6 Antireflective structure - Sub-wavelength structure (SWSs)  Moth eye structures The reflective index of cylindrical SWSs The reflective index of cone-shape SWSs Information source : FINETECH JAPAN 2011 Multilayer coating The lowest reflection and broadband Sub-wavelength Structures(SWSs) The best optical characteristic Imprinting process Low-cost How to achieve broadband and omnidirectional antireflection with low cost process?

7 Types of Sub-wavelength structures (SWSs) Colloidal lithography RIE Etching Langmuir, 2009, 25 (13), pp 7375–7382 Interference lithography Optics Communications 282 (2009) 434–438 Electron beam lithography BOE etching KOH etching Solar Energy Materials & Solar Cells 94 (2010) 629–633 Electron beam lithography Disadvantages Complex High-end facilities Costly Small size Nano imprinting technique Advantages Low-cost nano-scale mold Simple process The best optical characteristic Large area

Outline 8 Introduction Experimental setup and results Anti-reflection film measurement Conclusions & Future works  Porous Anodic Alumina Oxide (AAO) Template  Nano imprinting process  The transmittance and reflectance measurement results  Comparing the results of different experiment parameters  Motivation  Types of Anti-reflection film

9 Experimental – Fabrication of AAO template Procedures Acid cleaning pure Al foil 1 st anodization process Removed anodic oxide layer by acid 2 nd anodization process Pure aluminum Schematic of the cross section Process condition Constant voltage of 80V Oxalic acid solution (0.3M) Temperature at 4 ℃ Oxalic acid solution Phosphoric acid etching Platinum(Pt) Anodizing + etchig = 1 time (1 st cycle) Phosphoric acid solution (5wt%) Temperature at 32 ℃ Anodizing + etchig = 1 time (2 nd cycle)

10 Experimental result – Different 2 nd anodization time Top view High purity aluminum foil Cross section view 30sec45sec60sec 30sec45sec60sec Aspect ratio 1:1Aspect ratio 1:1.5Aspect ratio 1:2

11 Experimental result – Different 2 nd anodization time Top view Sputtering aluminum membrane with temper, widening time 10 min Cross section view 30sec45sec 30sec45sec Aspect ratio 1:1.2Aspect ratio 1:2.5

12 Experimental result – Different Pore widening time Top view 15min Aspect ratio 1:1.5 Cross section view 10min Aspect ratio 1:2.5 Sputtering aluminum membrane with temper, widening time 10 min

13 Experimental result – Compare the results of temper Anodizing time 45sec, widening time 15 min 5 ̊ C / min400 ̊ C, 4hr Rapid cooling 400 SEM images of AAO template Tempering status Tempering champer Without temperWith temper

14 Experimental process – Nano imprinting process AAO template with cone structure Schematic of nanoimprinting process by using UV exposure technique. AAO template Nano imprinting Process UV curable PET substrate Anti-reflection Film PET substrate Sub-wavelength structures RollerUV light AAO template Anti-reflection Film

Experimental result – Nano imprinting process by using AAO template AAO template SWSs Aluminum substrate 45sec, 10min Aspect ratio 1:1 Sputtering Al membrane (without temper) 45sec, 15min Sputtering Al membrane 30sec, 10min Sputtering Al membrane 45sec, 15min Sputtering Al membrane Aspect ratio 1:1 Aspect ratio 1:1.5 Aspect ratio 1:2

Outline 16 Introduction Experimental setup and results Anti-reflection film measurement Conclusions & Future works  Porous Anodic Alumina Oxide (AAO) Template  Nano imprinting process  The transmittance and reflectance measurement results  Comparing the results of different experiment parameters  Motivation  Types of Anti-reflection film

17 Optical measurements results – Transmittance (%) Transmittance and of the glass plate with/without SWSs 89.7% 91.8% 92.9% 94.2% 95.1% Aspect ratio increased

18 Optical measurements results – Reflectance (%) Reflectance and of the glass plate with/without the SWSs 60 ̊ 45 ̊ 30 ̊ 15 ̊ 5 ̊ Wavelength (nm) Reflectance (%) Incident light angles 1% 0.14% 0.16% 0.26% 0.64% Aspect ratio increased

Outline 19 Introduction Experimental setup and results Anti-reflection film measurement Conclusions & Future works  Porous Anodic Alumina Oxide (AAO) Template  Nano imprinting process  The transmittance and reflectance measurement results  Comparing the results of different experiment parameters  Motivation  Types of Anti-reflection film

20 Conclusions This study successfully fabricated the large area AAO template by using homemade Circulate-coolded etching system. In the fabrication of large area cone-shape AAO template, we could control the different depth characteristics of anodic alumina by phosphoric acid etching process and anodization parameters. We have successfully produced sub-wavelength structures(SWSs) on glass plant by using hot embossing with AAO template In the optical measurement results, the average transmittance of glass plate with SWSs was 96.5% and the reflection was reduced from 5.71% to 0.2%. Due to the contact angle of high-aspect-ratio SWSs film exceeded 110°, the surface energy is much lower than bare glass whose contact angle is 25°. Consequently, a SWSs film could possess the self-cleaning effect.

21 Thanks for your attention!