Reversibly photoswitchable gratings prepared from azobenzene-modified tethered poly(methacrylic acid) brush as colored actuator

Journal Pre-proof Reversibly Photoswitchable Gratings Prepared from Azobenzene-Modified Tethered Poly(Methacrylic Acid) Brush as Colored Actuator Jian-Wei Guo, Bohr-Ran Huang, Juin-Yih Lai, Chien-Hsing Lu, Jem-Kun Chen

PII:

S0925-4005(19)31474-1

DOI:

https://doi.org/10.1016/j.snb.2019.127275

Reference:

SNB 127275

To appear in:

Sensors and Actuators: B. Chemical

Received Date:

18 June 2019

Revised Date:

5 September 2019

Accepted Date:

12 October 2019

Please cite this article as: Guo J-Wei, Huang B-Ran, Lai J-Yih, Lu C-Hsing, Chen J-Kun, Reversibly Photoswitchable Gratings Prepared from Azobenzene-Modified Tethered Poly(Methacrylic Acid) Brush as Colored Actuator, Sensors and Actuators: B. Chemical (2019), doi: https://doi.org/10.1016/j.snb.2019.127275

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Reversibly Photoswitchable Gratings Prepared from Azobenzene-Modified Tethered Poly(Methacrylic

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Acid) Brush as Colored Actuator

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Jian-Wei Guo1,2, Bohr-Ran Huang3, Juin-Yih Lai4, Chien-Hsing Lu5,6*, Jem-Kun Chen2*

School of Chemical Engineering & Light Industry, Guangdong University of Technology, Guangzhou, China

2

Department of Materials Science and Engineering, Taiwan Building Technology Center, National Taiwan University of Science and Technology,

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1

43, Sec. 4, Keelung Road, Taipei 10607, Taiwan, ROC

Graduate Institute of Electro-Optical Engineering and Department of Electronic Engineering, National Taiwan University of Science and

Technology, Taipei, Taiwan

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3

Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei 10607, Taiwan

5

Department of Obstetrics and Gynecology, Taichung Veterans General Hospital,

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4

Taichung, Taiwan, ROC 6

Department of Obstetrics and Gynecology, National Yang-Ming University School

of Medicine, Taipei, Taiwan, ROC *

To whom correspondence should be addressed.

Tel.: +886-2-27376523; Fax: +886-2-27376544

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E-mail: [email protected] (C.-H.L.); [email protected] (J.-K. Chen)

Highlights

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Facile fabrication process to prepare photoswitchable visualized platform is developed.

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Azo is blended with PAA brush with cationic surfactant groups to assign photoswitchable function. Geometry of PAA grating changes reversible with Azo structure under UV-light irradiation. Geometry of PAA grating changes result the visualized color changes under UV-light irradiation.

Abstract

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Color of Azo-PAA grating switches from yellow to red under irradiation of UV-light.

Line arrays of poly(methacrylic acid) brush gratings (PBGs) were prepared to hybridize azobenzene (Azo) cationic surfactants. The change in the free volume of the Azo unit between the cis-state and its trans counterpart under 365-nm irradiation resulted in geometrical-parameter variations of the PBGs. The effective refractive index (neff) of the PBGs changed from 1.202 to 1.245 under 365-nm irradiation. To observe the 2

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color change under 365-nm irradiation, the correlation between the reflection wavelength and the reflection angle at a diffraction order ranging from 1 to 5 was established to obtain the optimal observation angle. The PBG exhibited yellow light initially, which was observed at 60 –70 by

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the naked eye. This is consistent with our prediction. The yellow changed to red under irradiation at 365 nm and returned to yellow under irradiation at 460 nm. The photomechanical (contraction and expansion) color of the dry polymer brush was reversible with repeated irradiation

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cycles, indicating potential for applications in photomanipulable sensors or actuators.

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Keywords: PMAA brush; azobenzene; grating; photomanipulable; visualized platform

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1. Introduction

One end of polymer brushes is tethered to the surface, which comprises versatile stretched polymer chains [1−3]. They also exhibit significant

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physical and chemical property tunability through modification of the monomer types, functionalization of biomolecules, and changer of the polymerization conditions [4]. In particular, polymer brushes based on functional poly(methacrylic acid) (PMAA) have been studied as a

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framework for advanced biomaterials engineering [5]. The high sensitivity of carboxyl groups to ionization and ionic strength of the aqueous solution induce a swelling behavior with negative charges in PMAA, which results high responses to pH changes [6]. Furthermore, the richness

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of carboxyl groups allows the easy immobilization of PMAA to the functional molecules through vertical conjugation strategies [7]. Therefore, PMAA brushes have been considered for biosensor applications because of their flexibility and strength, three-dimensional (3D) architecture,

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and control of multilayer biomolecules [8]. Surface topography modulation with stimuli is a methodology for designing a smart coating and is prominently utilized in numerous fields of

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surface science and technology, including controlled wettability [9,10], friction [11,12], adhesion [13,14], and modification of the optical properties of surfaces [15,16]. Moreover, such stimuli-responsive surfaces have the characteristics of shape adjustment or roughness depending on their exposure to the environmental conditions. One of the most familiar exterior trigger candidates for such surface dynamic fluctuations is light, which can handle both contactless and spatially distinct areas on the sample surface. The incorporation of light-sensitive groups (i.e., azobenzene (Azo) units) into the thin films is a modest approach to designing photosensitive polymer films and has been widely studied for the last two decades in the application areas of reversible sensors, micro- and nanopatterning, light-powered electrical switches based on

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cargo-lifting Azo monolayers, and light-driven artificial muscles [17−20]. The reliability and accuracy of the photoresponsive behavior for applications in label-free detections have been proven by the development of commercial products with high throughput [21]. Additionally,

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ordered patterns, such as surface-relief gratings, are obtained for better technological significance and are commonly employed for spectral analysis and integrated optics. It has been demonstrated that one-dimensional (1D)/two-dimensional (2D) patterned gratings are the potential

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interests in microelectronic through variations in the phase, period, and orientation. Polymer brush gratings exhibit surface plasmon polaritons (SPPs) that are highly susceptible to slight deviations in the refractive index (RI) of the surface [22–24]. Periodic nanostructures and 1D/2D

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grating derivative-based plasmonic sensors have also been more attractive owing to their scalability and simplicity of the guided/slit [25]. Generally, SPPs are governed by the structural parameters of the single-slit system period and the order of resonance from the incidence angle of

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the transverse electric (TE) and transverse magnetic (TM) polarization [26]. The versatile and homogeneous grating structure can be effectively engineered to create more efficient SPPs with specifically intended chemical and physical stability, optical signals, etc. [27, 28]. Accordingly, the

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combination of plasmonic PMAA brush gratings (PBGs) and photoswitchable Azo molecules is worthy of full exploitation. In a previous study, an Azo polymer was synthesized to observe the light-induced reversible volume changes in thin films [29]. Azo units were bound within PBGs to amplify the photomechanical effect with SPPs. Azo units are contained within the line patterns to generate the maximum change in the geometrical parameters, such as the cross section, period, space, and scale, under ultraviolet (UV) irradiation, which should improve the photoresponsive efficiency significantly to exhibit reversibly light-induced color changes. Accordingly, the geometrical parameters vary under 365-nm irradiation and return to the initial state under 460-nm irradiation. The repeated cycles of irradiation produce reversible

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contraction/expansion processes and are accompanied by important changes in the filling factor, RI, and color. The PBGs offer the advantage of photoresponsive properties through geometrical parameters with light irradiation and greater possibilities for applications of a photomanipulable

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nanoactuator. 2. Experimental Section

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2.1 Materials

Single-crystal-grown Si wafers with a thickness and diameter of 1.5 and 6 inches, respectively, were procured from Hitachi, Inc. (Japan). As per

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previous experiments [30], the impurities—notably organic contaminants and dust particles—were effectively removed. Acros Organics Co. supplied the chemicals for graft polymerization, such as 2-bromo-2-methylpropionyl bromide (2B), 3-aminopropyltriethoxysilane (3A),

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triethylamine (TA), methacrylic acid (MAA), 1,1,4,7,7-pentamethyldiethylenetriamin (PMDETA), copper(I) bromide (CuBr), and copper(II) bromide (CuBr2), as well as a trimethylammonium bromide surfactant containing Azo (Figure 1). Azo-coupling was performed using 4-butylaniline with phenol, shadowed through a consequent reaction with trimethylamine and 1,6-dibromohexane used for quaternization, as

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explained elsewhere [31, 32]. The structure of Azo was identified via 1H nuclear magnetic resonance, as shown in Figure 1, with identification of protons, as follows: (a) 0.6, (b) 0.9, (c) 1.2, (g) 1.7, (d) 2.1, (i) 2.9, (f) 3.2, (g) 3.6, (h) 6.7, and 7.4 ppm. The surfactant was dissolved in Milli-Q water and kept under dark conditions for a few days to ensure the whole relaxation to the trans configuration. All experiments were performed at room temperature to avoid yellow light and early isomerization of the surfactant. The vacuum distillation process was conducted in advance for MAA, PMDETA, 3A, and 2B. The other chemicals and solvents used for the experiments were procured from Aldrich Chemical Co.

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(reagent-grade quality, used without further purification). 2.2 Preparation of Polymer Brush Line Array as Gratings

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The common approach followed for the grating fabrication uses the very-large-scale integration (VLSI) technique, which has been formerly explained [33]. The procedure of the fabrication method is schematically shown in Figure 2. Step A: The Si wafer was preserved in a thermal

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evaporator (Track MK-8) with hexamethyldisilazane (HMDS) at 90 °C for 30 s to convert the OH groups on the wafer surface into an inert film of Si(CH3)3 groups. Step B: For the patterned photoresist, I-line lithography was utilized to create trench arrays with 1, 2, and 3 m scales. Step

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C: The sample was exposed to O2 plasma treatment to form OH groups from the HMDS-treated-surface TCP 9400SE instrument (Lam Research Co, Ltd.). Step D: On the surface of the Si substrate, selective units of 3A were carefully fabricated onto the bare regions of the substrate, which

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was marked as Si-3A. After step D, the immersion of the sample in a solution containing tetrahydrofuran in 2% (v/v) TA solution and 2B at 20 °C for 8 h yielded a surface patterned with regions of halogen groups for atom-transfer radical-polymerization (ATRP), which was denoted as

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Si-3A-2B. Simultaneously, rinsing with the solvent helped to remove the retained photoresist from the HMDS-treated surface, leaving behind a chemically nanopatterned surface. Step E: ATRP was utilized for grafting patterned PMAA brushes on the initiator-modified surface of Si. For the preparation of PMAA brushes on the Si-3A-2B surface, a mixture of water and methanol was prepared with a ratio of 2:1, and PMDETA, CuBr, CuBr2, and MAA were added to it. The Si-3S-2B substrate was dropped into a deoxygenated solution with Ar at 90 °C for 15 min. After 4 h of polymerization, the unreacted monomer, non-grafted material, and catalyst were detached using a Soxhlet apparatus. The samples were dried under vacuum conditions at 60 °C for 20 min prior to use. These PMAA brushes grafted from 1-, 2-, and 3- m-scale trench arrays of the

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photoresists were denoted as PA1, PA2, and PA3, respectively. Step F: To render the brushes photosensitive, Azo was loaded into the PMAA brush at a 0.45 mM concentration of the solution, which is slightly lower than that of critical micelle concentration (CMC) [34]. Samples PA1,

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PA2, and PA3 after Azo immobilization were denoted as PA1-azo, PA2-azo, and PA3-azo, respectively. X-ray photoelectron spectroscopy (XPS) was conducted using a Scientific Theta Probe, UK. The sample morphology was investigated using atomic force microscopy (AFM; Veeco

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Dimension 5000 scanning probe microscope). The samples were irradiated at various wavelengths by employing either a solid-state laser operating at 375 nm (Oxxius) or a HeCd gas laser operating at 325 or 442 nm (Kimmon).

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2.3 Optical Model

The effective RI (neff) of the samples was relatable to the grating profile in a simple manner effective medium theory (EMT) for artificial

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dielectric elements [35]. According to the EMT, PBG can be considered as moderately mixed with PMAA and air. The grating profile related to the effective index can be used to fabricate artificial dielectric elements and be readily designed. Afterward, the solution of Maxwell’s equations

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to 1D subwavelength gratings with the applicable boundary conditions of the effective indices were attained numerically by several researchers [36]. Furthermore, according to the EMT, the index in the direction normal to the grating vectors of a 1D subwavelength grating is expressed as neff = [f1n12 + f2 n22]1/2,

(1)

where f1 and f2 are the fill factors for PMAA and air, respectively. In this particular case, the TM polarizations nTE and n indicate the 1D binary TM

relief grating and the effective refractive indices for TE, respectively. The different TM indices for the two polarization states indicate that the 1D subwavelength gratings exhibit birefringence [37]. For the 1D grating (Figure 3), the theory offers an expression for the ordinary and

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extraordinary indices, as follows: nTE2 = f1n12 + f2n22 2

－ M

= f1n1 2 + f2n2 2 . －

(3)

－

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nT

(2)

Equations (2) and (3) are well-known outcomes and have been often likened with rigorous calculations. Additionally, the Azo attachment to

3. Results and Discussion

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3.1 Surface Properties of PMAA-Azo Brushes

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the PBG was achieved with an neff obtained from the filling factor of PBGs.

The pristine chemical compositions during the surface modification of the Si(100) surface and Si surfaces at numerous stages were determined

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using XPS. The detailed XPS profiles of the samples at each stage have been described previously [38]. There was a local change under UV irradiation at 365 nm, where the hydrophobicity of the brush due to photoisomerization of the surfactant molecules changed from a more

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hydrophobic trans-state to a more hydrophilic cis-state. The line geometry could generate a split of the static water contact angles (SWCAs) along TE and TM polarizations [28, 30], which were parallel and perpendicular to the line geometry, respectively. Figure 4 displays the SWCAs of PA1-azo, PA2-azo, and PA3-azo along the TE and TM directions under irradiations at 365 nm as well as 460 nm. The SWCAs along the TM directions did not change significantly during the irradiations, indicating that the capillarity predominantly determined the SWCAs. The SWCAs along the TE direction changed from 116

3 to 78

4 after UV irradiation at 365 nm for PA1-azo, indicating that the transition of Azo units

from the hydrophobic trans-state to the hydrophilic cis-state occurred under the irradiation at 365 nm (Figure 4a). For PA2-azo and PA3-azo, the

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SWCA changes along the TE directions exhibited a trend similar to that for PA1-azo (Figures 4b and c). The observations suggested that the SWCA along the TE direction had a greater change than that along the TM direction under the irradiation at 365 nm. The SWCAs along the TE

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and TM directions recovered again under irradiation at 460 nm. In this process, it was found that the measurement time of the SWCAs should not exceed ∼10 s with high reversibility. The results suggest that the Azo units were sufficiently loaded within the PBGs, resulting in the

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photoresponsive behavior.

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3.2 Geometrical Change of Azo-loaded PBGs under Irradiations

Figure 5a shows the 2D and 3D AFM topographies of the photoresist templates possessing line arrays with resolutions of 1, 2, and 3 m. The trench texture of the photoresist exhibits a similar depth with various trench scales and grating periods. Furthermore, we used AFM to obtain the

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topographies of the PBGs (line arrays) with numerous structures. As depicted in Figure 5b, PA1 was fabricated successfully on the Si surface with a line scale of nearly 1 m inside a scanning area of 20 m × 20 m. The PA1 lines indicate a hill-like structure, with bottom and top

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widths of 2.103 m and 484 nm, respectively. The hill-like structure can be attributed to the collapse of the polymer brush due to the high aspect ratio. Moreover, the line patterns of PA1 had an average height of 118

8 nm without a clear space between the lines. The spaces between the

lines represented a polished Si surface, which predominantly reflected the incident light for generating the grating effect. The hill-like structure transformed into a trapezoid-like structure when the scales of the grafting sites were increased to 2 and 3 m. The PA2 and PA3 lines exhibited more uniform heights (120

4 nm and 121

4 nm, respectively) with clear spaces. The results suggest that the scale of the grafting site was not

significantly related to the height of grafting polymerization but to the uniformity of the polymer brush lines. After the brushes were loaded with 10

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Azo units, the height and cross-sectional area changed significantly, indicating the Azo loading (Figure 5c). Edges of lines may readily assemble more Azo units, resulting in the appearance of a double-edge structure. Figure 5d shows AFM images of PA1-azo, PA2-azo, and PA3-azo

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recorded after the irradiation at 365 nm for 5 min. The changes in the geometrical parameters for PA1, PA2, PA3, PA1-azo, PA2-azo, and PA3-azo under irradiation at 365 and 460 nm are presented in Table 1 to evaluate the change in filling factor of PMAA (f1). The effective RI (neff),

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which is related to the grating effect, was calculated using the filling factor. After 460-nm irradiation, these PBGs returned to the initial structure, which was similar to the structure in Figure 5c, indicating the reversible photoresponsive behavior (Figure 5e). The changes in the geometrical

Aazo,365 1, Aazo, 460

(4)

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Et

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parameters of the Azo-loaded PBGs were exploited to calculate the efficiency of the Azo transition, Et, as follows:

where Aazo,365 and Aazo,460 represent the cross-sectional areas of the Azo-loaded PBGs under 365- and 460-nm irradiation, respectively. In a previous study, the light-induced behavior of the polymer brushes was investigated with changes in the roughness and thickness [39, 40]. The

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changes in the geometrical parameters of the brush lines after exposure to the surfactant solution for 16 h are presented in Table 1. Generally, the cross section of a line is a rectangle that can be used to evaluate the filling factor readily. In our case, the cross-sectional area of a line exhibited an irregular shape. Therefore, the geometrical parameters, including the top width (Wt), bottom width (Wb), period (P), space (S), and cross-sectional area (A) of a line, based on the AFM data, of these PBGs were utilized to determine Et, the filling factor, and neff

precisely [41].

Our results suggested that the expansion of Azo-loaded PBGs appeared predominantly in the cross-sectional area of the stripes. PA1-azo exhibited the highest Et because it had the largest contact area to bind with Azo units. 11

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3.3 Optical Performance of Azo-Loaded PBGs Under Irradiations

The RI of the PMAA thin film at 590 nm was recorded as approximately 1.59, which is consistent with previous studies [42, 43], as a standard

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value to measure the RI of the PBGs with spectroscopic ellipsometry. According to the geometrical parameters in Table 1, f1 was obtained to calculate the theoretical neff using Eq. (1). The neff of the PBG without Azo loading did not change significantly under the irradiations, indicating

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that no environmental factor, such as a thermal effect, influenced the results. The change of neff was predominantly relative to the optical property [44]. Figure 6a presents the f1 and neff of the Azo-modified PBGs plotted in terms of the strip scale. The PGBs could be regarded as a

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mixture interface of PMAA and air, resulting in the decrease of the RI. As expected, PA1-azo exhibited the greatest change in neff after UV irradiation at 365 nm. Moreover, under irradiation at λ = 460 nm, the neff recovered again when the cis-state of the Azo surfactant experienced a

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photoisomerization change to the trans-form. The Azo-loaded PBGs irradiated with UV interference patterns were distorted after the polarization of incoming light or the distribution of intensity. In this case, the refractive indices along the TM and TE polarizations, i.e., nTM and nTE,

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respectively, were evaluated during the irradiation. Figure 6b shows the nTM and nTE obtained via ellipsometry along the directions of the TM and TE polarized modes using Eqs. (2) and (3) for the Azo-modified PBGs plotted in terms of the strip scale. Both nTE and nTM increased after 365-nm irradiation. The color, which was reflected by the PBGs, was dependent on the observation angle because of the TM and TE polarization. The nTM and nTE of the Azo-loaded PBGs could be switched to higher values after UV irradiation at 365 nm; they returned to approximately the initial vales after UV irradiation at 460 nm. The physical mechanism of enhanced transmission/absorption has been widely studied using micro/nanostructures for applications [42, 45]. When light impinging the sample at an incident angle is linearly polarized, with s perpendicular

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to the plane of incidence or p parallel to the electric-field vibration, the reflected light is also s-polarized or p-polarized. It is universally accepted that the reflecting wavelength (RW) anomaly is responsible for the occurrence of the physical mechanism in these grating structures or SPPs [46].

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The grating angles at a certain disappearance or emergence of the diffraction orders in the RW anomaly induce a difference in the values of the transmittance, reflectance, and absorptance spectra of subwavelength grating structures. The occurrence of the RW anomaly can be predicted

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using the following equation: 2

2

P

sin

cos 2

0,

(5)

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P

j

where λ represents the reflection wavelength; P represents the grating period;

for PA1-azo, PA2-azo, and PA3-azo. For PA1-azo, the RW ranged

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represents the diffraction order. Figure 7 displays the dependence of RW on

represents the angle of incidence as well as reflection, and j

from 421 to 1834 nm at a reflection angle of 10 , indicating that the PBG exhibited various colors, which were observed at 10 by the naked eye

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(Figure 7a). The RW converged gradually when the reflection angle was increased to 90 , indicating that the PBGs exhibited a more stable color at a larger observation angle. Therefore, an observation angle of 60 –70 was selected to observe the RW in the range of 400 to 700 nm for PA1-azo. Additionally, the reflection angle that could obtain the visible wavelength from the PA2-azo surface merely ranged from 80 to 89 , indicating a narrow window for observing the color change by the naked eye (Figure 7b). The RW of PA3-azo was outside of the visible wavelength range, and the color could not be readily observed by the naked eye (Figure 7c). The intensity of the RW for gratings decays with the increase of diffraction order. The RW at a diffraction order of >5 may not appear with a sufficient intensity to be identified by the naked eye.

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Figure 7d displays photographs of PA1-azo during UV irradiation at 365 nm in real time, which were obtained at 65 of the observation angle. PA1-azo was prepared into a 1 cm × 1 cm die using a lithography method with a mask. The Azo-loaded PBG exhibited a yellow color before UV

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irradiation at 365 nm, which is consistent with the prediction. The sample exhibited a mixture of yellow and red colors under UV irradiation at 365 nm for 90 s, which became completely red after 180 s of irradiation at 365 nm. Therefore, the angle of observation and the period were fixed

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feasibly in our case.

Figure 8 presents the neff in real time over four stages: from 0 to 60 s in the absence of UV irradiation, within 6 min of irradiation at 365 nm,

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within 8 min of irradiation at 460 nm, and within 1.5 min in the absence of UV irradiation. With the irradiation at 365 nm, the neff of PA1-azo increased constantly to the maximum value. The time required to attain the plateau of neff was correlated with the photostationary state, which

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was reached after 3 min of irradiation (shorter than the time in a previous study [37]). We observed approximately linear increases in neff from 1.202 to 1.245 on the surface upon switching on the 365-nm radiation for 3 min; it decreased gradually from 1.245 to 1.208 under irradiation at

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460 nm for 8 min, reaching a minimum of neff. The transition rate from the trans-state to the cis-state was higher than that from the cis-state to the trans-state for the Azo units. The results suggest that the cis-sate of the Azo units possessed a greater interaction with PMAA chains because of the hydrophobicity, resulting in the retardation of the transition. Note that neff did not completely return to its original value within 1.5 min after the irradiation was switched off. The UV irradiation may have generated a thermal effect, resulting in a gradual decrease after it was switched off.

4. Conclusions

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We employed a “grafting from” system consisting of an ATRP approach and VLSI processes for preparing definite PBGs to load Azo units. The photosensitive Azo units were loaded into the PBGs to induce geometrical variations using irradiation with two wavelengths: UV light (λ = 365

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nm) and blue light (λ = 460 nm). The highest degree of light-induced change occurred at the smallest grating period of PBGs with the alteration of the effective RI. According to the dependence of the RW on the reflection angle, the color of PBGs could be predicted at various diffraction

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orders. The change in the RIs resulted in various colors ranging from yellow to red, which were observable by the unaided eye, under irradiation at 365 nm. This study offers an exact methodology to combine polymer brush gratings and photoresponsive components to achieve surface

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modification for applications in photomanipulable sensors or actuators. Acknowledgements

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Funding: This work was supported by the Ministry of Science and Technology of the Republic of China [grant number 106-2221-E-011-135-MY3] and the Taiwan Building Technology Center from The Featured Areas Research Center Program within the

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framework of the Higher Education Sprout Project by the Ministry of Education in Taiwan.

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K.V. Sreekanth, J.K. Chua, V.M. Murukeshan, Interferometric lithography for nanoscale feature patterning: a comparative analysis between laser interference, evanescent wave interference, and surface plasmon interference, Appl. Opt. 49 (2010) 6710−6717.

of the donor moiety, Dyes Pigm. 150 (2018) 89–96.

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S. Yamada, J. Bessho, H. Nakasato, O. Tsutsumi, Color tuning donor–acceptor-type azobenzene dyes by controlling the molecular geometry

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J.N. Anker, W.P. Hall, O.L. Nilam, C. Shah, J. Zhao, R.P. Van Duyne, Biosensing with plasmonic nanosensors, Nat. Mater. 7 (2008) 442–453.

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J. Chen, G. Zhou, C. Chang, A. Lee, F. Chang, Label-free DNA detection using two-dimensional periodic relief grating as a visualized platform for diagnosis of breast cancer recurrence after surgery, Biosens. Bioelectron. 54 (2014) 35–41.

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A.M. Craciun, M. Focsan, L.Gaina, S. Astilean, Enhanced one- and two-photon excited fluorescence of cationic (phenothiazinyl)vinyl-pyridinium chromophore attached to polyelectrolyte-coated gold nanorods, Dyes Pigm. 136 (2017) 24–30. J.K. Chen, J.H. Wang, C.C. Cheng, J.Y. Chang, Reversibly thermoswitchable two-dimensional periodic gratings prepared from tethered poly(N‑isopropylacrylamide) on silicon surfaces, ACS Appl. Mater. Interfaces 5 (2013) 2959−2966. T.W. Ebbesen, H.J. Lezec, H.F. Ghaemi, T. Thio, P.A. Wolff, Extraordinary optical transmission through sub-wavelength hole arrays, Nature 391 (1998) 667–669.

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M. Grande, R. Marani, F. Portincasa, G. Morea, V. Petruzzelli, A.D. Orazio, V. Marrocco D. de Ceglia, M.A.Vincenti, Asymmetric plasmonic grating for optical sensing of thin layers of organic materials, Sensor. Actuat. B-Chem. 160 (2011) 1056–1062.

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W.T. Chena, S.S. Lib, J.P. Chua, K.C. Fengc, J.K. Chen, Fabrication of ordered metallic glass nanotube arrays for label-free biosensing with diffractive reflectance, Biosens. Bioelectron. 102 (2018) 129–135.

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J.R. Zeng, C.C. Cheng, A.W. Lee, P.L. Wei, J.-K. Chen, Visualization platform of one-dimensional gratings of tethered polyvinyltetrazole brushes on silicon surfaces for sensing of Cr(III), Microchim. Acta 184 (2017) 2723–2730.

Macromolecules 38 (2005) 10566–10570.

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M.O. Tanchak, C.J. Barrett, Light-induced reversible volume changes in thin films of azo polymers: the photomechanical effect,

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J.K. Chen, J.H. Wang, S.K. Fan, J.Y. Chang, pH-Responsive one-dimensional periodic relief grating of polymer brush–gold nanoassemblies on silicon surface, ACS Appl. Mater. Interfaces 4 (2012) 1935–1947.

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D. Dumont, T.V. Galstian, S. Senkow, A.M. Ritcey, Liquid crystal photoalignment using new photoisomerisable langmuir-blodgett films, Mol. Cryst. Liq. Cryst. 375 (2002) 341–352. Y. Zakrevskyy, M. Richter, S. Zakrevska, N. Lomadze, R.V. Klitzing, S. Santer, Light-controlled reversible manipulation of microgel particle size using azobenzene-containing surfactant, Adv. Funct. Mater. 22 (2012) 5000–5009. H. Huang, J. Chen, M. Houng, Fabrication of two-dimensional periodic relief grating of tethered polystyrene on silicon surface as solvent sensors, Sensor. Actuat. B-Chem. 177 (2013) 833–840.

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R. Konradi, J. Rühe, Binding of oppositely charged surfactants to poly(methacrylic Acid) brushes, Macromolecules 38 (2005) 6140–6151. J. Chen, G. Zhou, C. Chang, Real-time multicolor antigen detection with chemoresponsive diffraction gratings of silicon oxide nanopillar

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arrays, Sensor. Actuat. B-Chem. 186 (2013) 802–810.

E. B. Grann, M. G. Moharam, D. A. Pommet, Artificial uniaxial and biaxial dielectrics with use of two-dimensional subwavelength binary

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gratings, J. Opt. Soc. Am. A 11 (1994) 2695–2703.

J. Chen, J. Wang, C. Cheng, J. Chang, F. Chang, Polarity-indicative two-dimensional periodic relief gratings of tethered poly(methyl

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methacrylate) on silicon surfaces for visualization in volatile organic compound sensing, Appl. Phys. Lett. 102 (2013) 151906. J.K. Chen, J.Y. Li, Synthesis of tethered poly(N-isopropylacrylamide) for detection of breast cancer recurrence DNA, J. Colloid Interface Sci.

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358 (2011) 454–461. A. Kopyshev, C.J. Galvin, R.R. Patil, J. Genzer, N. Lomadze, D. Feldmann, J. Zakrevski, S. Santer, Light-induced reversible change of

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roughness and thickness of photosensitive polymer brushes, ACS Appl. Mater. Interfaces 8 (2016) 19175–19184. Y. Zakrevskyy, J. Roxlau, G. Brezesinski, N. Lomadze, S. Santer, Photosensitive surfactants: micellization and interaction with DNA, J. Chem. Phys. 140 (2014) 044906.

J.K. Chen, B.J. Bai, pH-Switchable optical properties of the one-dimensional periodic grating of tethered poly(2-dimethylaminoethyl methacrylate) brushes on a silicon surface, J. Phys. Chem. C 115 (2011) 21341–21350. D. Pristinski, V. Kozlovskaya, S.A. Sukhishvili, Determination of film thickness and refractive index in one measurement of

21

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phase-modulated ellipsometry, J. Opt. Soc. Am. A. 23 (2006) 2639–2644.

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gold nanorods as pH-sensitive optical materials, Chem. Mater. 20 (2008) 7474–7485.

E.B. Grann, M.G. Moharam, D.A. Pommet, Artificial uniaxial and biaxial dielectrics with use of two-dimensional subwavelength binary

e-

gratings, J. Opt. Soc. Am. A 11 (1994) 2695.

J.J. Greffet, R. Carminati, K. Joulain, J.P. Mulet, S. Mainguy, Y. Chen, Coherent emission of light by thermal sources, Nature 416 (2002)

Pr

61–64.

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M.C. Hutley, D. Maystre, The total absorption of light by a diffraction grating, Opt. Commun. 19 (1976) 431–436.

22

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f

Jianwei Guo received his PhD from South China University of Technology, Guangzhou, China, and worked as a postdoctoral researcher in Northwestern Polytechnical University. His research interests focus on functional polymer materials, porous materials and biomaterials. He has

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worked on around 20 different projects funded by the Chinese national National Science Funds, Science & Technology Agency of Guangdong Province and Guangzhou Science & Technology Burea. He is a Technical Committee member in several National & International Conferences in

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the above fields and authored or co-authored over 100 publications in International Journals. Bohr-Ran Huang got his M.S. and Ph.D degree in Electrical Engineering from Michigan State University, East Lansing, U.S.A, 1986 and 1992,

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respectively. He was recruited to the graduate Institute of Electro-optical engineering and department of Electronic Engineering in National Taiwan University of Science and Technology (NTUST) since August, 2007. His multidisciplinary research areas are synthesis of nanomaterials

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(including carbon nano tubes, silicon nanowires, ZnO, WO3, and Nanodiamond), silicon based solar cells and nano-optoelectronic sensing devices. Currently, he has published more than 180 papers in referred journal publications and over 200 conference proceedings.

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Juin-Yih Lai was a graduate student at the Montana State University, from where he received his PhD degree in 1971. He then moved back to Taiwan, starting his teaching career in the Department of Chemical Engineering, Chung Yuan University (CYU). He is now the Honorary Chair Professor of Graduate Institute of Applied Science and Technology of National Taiwan University of Science and Technology. He has worked on developing novel membranes for separation processes and environmental and biomedical applications and investigating the structure-property-performance relationship of polymeric membranes. He has published more than 400 journal papers and received 43 patents. Chien-Hsing Lu received his MD degree from National Yang Ming Medical University in 1992 and Ph.D. degree in biomedical science from

23

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National Chun Hsing University in 2012. He is also a assistant professor of National Yang Ming Medical University since 2008. He also is a clinical associate professor of National Defense Medical Center since 2012. He has been section chief in the Department of OB/GYN in

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Taichung Veterans General Hospital since 2008, and is currently Chief of Gynecology. His major interests of studies focused on Diagnosis and treatment gynecologic oncology, translational research, and cancer biology.

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Jem-Kun Chen received his BS (1996) and MS (1998) in Chemical Engineering from National Tsing Hua University (Taiwan) and his Ph.D. (2003) in Applied Chemistry from National Chiao Tung University (Taiwan). From 2003 to 2004 he was a postdoctoral fellow with Professor

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Samukawa in the Department of Fluid Science at Touhoku University, Sendai (Japan), where he investigated the fabrication and analysis of quantum dots and nanodisks. In 2005 he joined the Department of Biomechatronics Engineering at Ping-tung University (Taiwan) as an

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Assistant Professor. Since 2006 he has been an Assistant Professor of Polymer Engineering at National Taiwan University of Science and Technology. He was an Associate Professor of Materials Science and Engineering at National Taiwan University of Science and Technology

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from 2009 to 2012. In 2013 he was promoted to Professor of Materials Science and Engineering at National Taiwan University of Science and Technology. His current research emphasizes the processing, characterization, modeling, and optimization of polymer brush devices for optical and biological sensors. He has published more than 150 research articles in SCI journals.

24

i

a

g

N

i

e

O N

h

f

pr

i

oo

f

Figure 1: 1H NMR spectrum of Azo in D2O.

c

e

b

N

d

e-

e

8

Jo ur

na l

Pr

e

7.5

7

6.5

6

5.5

5

4.5

4

3.5

3

ppm

25

2.5

2

1.5

1

0.5

0

f oo

Figure 2: Schematic representation of the immobilization of Azo on PBGs with photoresponsive behavior. (A) Si wafer treated with HMDS in a

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thermal evaporator. (B)Photoresist spin-coated onto the Si surface presenting Si(CH3)3 groups. I-line lithography used to pattern the photoresist with a trench array. (C) OPT used to chemically modify the exposed regions presenting Si(OCH3)3 groups and to convert

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the topographic photoresist pattern into a chemical surface pattern. Photoresist removed through treatment with solvent. (D)3A selectively assembled onto regions of the OPT-treated Si surface. 2B selectively reacted with 3A-treated Si surface to form the initiator.

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(E) Sample grafting via surface-initiated ATRP of MAA from the functionalized areas as PBGs. (F) Immobilization of Azo on the

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na l

PBGs. The Azo-modified PBGs exhibit photoresponsive behavior resulting in significant change in the geometrical parameters.

26

OH

OH

OH

F

Si wafer A

H 3C

CH3

Si H 3C

O

CH3

Si CH3

OOC

CH3

H 3C

CH3

Si H 3C

O

O

CH3

Si CH3

O

CH3

B

I-line

Resist CH3

H 3C

CH3

Si H 3C

O

CH3

CH3

Si CH3

O

H 3C

CH3

Si H 3C

O

CH3

CH3

Si CH3

O

OOC

Si wafer

Si H3C

O

CH3

365 nm irradiation

Br

Br

C

OOC

OOC

Isotropic Oxygen Plasma

CH3

H3C

Si OH OH OH

O

CH3

OH OH OH

O

Si wafer

OH OH OH

Br H C CH3 C O NH (CH2)3 O Si O O O

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Br H C CH3 C O NH (CH2)3 O Si O O O

COO

OOC

COO

COO

OOC

D Br H C CH3 C O NH (CH2)3 O Si O O O

OOC

OOC

CH3

Si

na l

CH3

Resist

Br OOC

COO

COO

H 3C

460 nm irradiation

Pr

Si wafer

Resist

Br

COO

pr

Si wafer

OOC

Br

COO OOC COO COO COO OOC OOC OOC COO COO COO OOC OOC OOC COO COO COO H C CH H C CH3 H C CH3 3 C O C O C O NH NH NH (CH2)3 (CH2)3 (CH2)3 O O O Si Si Si O O O O O O O O O OOC

Si H3C

O

OOC

Br COO

CH3

e-

CH3

f

OH

oo

OH

OOC

COO

OOC

COO

COO

OOC

OOC

COO

OOC COO

COO

COO

Si wafer E

OOC

Br

OOC

COO

Br

COO

OOC

Br

COO OOC COO COO COO OOC OOC OOC COO COO COO OOC OOC OOC COO COO COO H C CH3 H C CH3 H C CH3 C O C O C O NH NH NH (CH2)3 (CH2)3 (CH2)3 O O O Si Si Si O O O O O O O O O OOC

OOC

Si wafer

H C CH3 C O NH (CH2)3 O Si O O O

H C CH3 C O NH (CH2)3 O Si O O O

H C CH3 C O NH (CH2)3 O Si O O O

Si wafer

=

=

Cis-Azo Trans-Azo

27

f oo

pr

Figure 3: Grating with geometrical parameters including a grating period (P), width (w) and height (h) for TM and TE polarized modes.

e-

Z

h

Jo ur

X

na l

Pr

Y

P

w

f1P = w f2P=1-w

28

oo

f

Figure 4: Images of water contact angles of (a) PA1-azo, (b) PA2-azo and (c)PA3-azo along TM and TE directions under irradiations at 365 and

(a) TM

TE

h h ’

(c) TM

Pr

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h ’

TE

na l

h

h

h ’

(b) TM

e-

pr

460 nm.

h h ’

TE

h

h

h ’

h ’

29

f oo pr

Figure 5: 2D, 3D AFM height images (20 μm × 20 μm) and cross-section profile of (a)photoresist with 1, 2, 3 m scale trench array, (b) PA1,

Pr

e-

PA2, PA3, (c) PA1-azo, PA2-azo, PA3-azo, and (c) after irradiation at (d) 365 and (e) 460 nm.

(a) 1 m

1 m

1 m

20

20

20

15

15

15

10

10

na l

10

5

5 0 0

800

20 μm

15

10

5

0

0

800

10

5

15

400

400

4

2

8

6

(b)

10

14

12

16

18 μm

0 nm 0

4

2

6

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0 nm 0

8

10

20

10

10

5

0 nm

0

0

0

20

μm

μm

15

10

5

150

2

4

6

8

10

12

14

16

18 μm

16

18 μm

2

4

4

2

6

8

14

18 μm

16

20

10

10 5

5 20

μm 15

10

0

0

5

0

150

8

12

10

15

0

6

0 nm 0

200 nm

0 nm 0

400

15

5

15

14

800

20 μm

15

10

5

0

20

15

150

12

0

200 nm

200 nm

20

5

20 μm

10

12

14

16

18

μm

0 nm 0

2

4

6

8

10

30

12

14

16

18

μm

300 nm

20

20

0

0 nm

2

4

10

6

8

10

12

14

16

20

0 μm

5

4

2

6

10

8

12

450 nm

20

20

14

16

18 μm

nm 0

Pr

15

10

2

4

6

8

10

12

14

16

nm 0

(e)

14

16

18 μm

10

5

10 5 0

0

4

2

6

8

10

12

14

16

0

18 μm

4

2

6

μm

8

10

12

14

16

18

μm

14

16

18

μm

300 nm

300 nm

300 nm

12

0 nm

0

18 μm

15

400

0

400

0

20

μm

0

5

10

na l

0 nm

20

0 μm

8

20

10

0

6

15

5

5

4

2

450 nm

15

10

10

0

e-

450 nm

5 15

0 μm

5

0 0

18 μm

15

400

10

300

(d)

20

15

0

300

0 nm 0

15

0 μm

5

5

pr

10

10

5 20

15

15

10

10 5

250

20

15

15

20

300 nm

oo

300 nm

f

(c)

20

20

Jo ur 20

15

10

5

300

0

15

10

10 5

20

20

15

15

0 μm

15

10

10

5

5

μm

20

0

5

0

250

μm 15

10

0

5

0

250

nm

0 nm

0

2

4

6

8

10

12

14

16

18 μm

0

0

2

4

6

8

10

12

14

16

18

μm

0 nm 0

2

4

6

8

10

12

Figure 6: Values of (a) f1 and neff , and (b) nTE and nTM plotted in term of stripe scale after 365 and 460 nm irradiation. 31

f oo

(a)

1.25

pr

0.61

e-

0.59 1.23

n eff

Pr

f 1 0.57

365 nm irradiation

1.21

0.53 1.5

2.5

Jo ur

0.5

na l

0.55

1.19

3.5

Strip Scale ( m)

(b)

32

f

1.29

UV irradiation

1.27

1.35 1.25 n TM

e-

n TE

pr

1.37

oo

1.39

1.33 UV irradiation

Pr

1.23

1.31

1.21

0.5

1.5

na l

1.29 2.5

3.5

Jo ur

Stripe Scale ( m)

Figure 7: Dependence of RW in term of reflection angle at the diffractive order from 1 to 5 for (a) PA1-azo, (b) PA2-azo and (c) PA3-azo. (d) Photographs of PA1-azo during the irradiation at 365 nm for 3 min.

33

oo

f

(a)

j=2

j=3

j=4

e-

j=5

1.5 1

Pr

RW ( m)

2

j=1

pr

2.5

0 10

30

na l

0.5

50

70

90

(b)

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Reflection Angle (degree)

34

f oo

4.5

3.5

2.5

j=2

j=3

j=4

j=5

e-

RW ( m)

3

j=1

pr

4

2

Pr

1.5 1

0 10

30

na l

0.5 50

70

90

(c)

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Reflection Angle (degree)

35

f oo

18

14 j=1

j=2

j=3

j=4

e-

10

j=5

8

Pr

RW ( m)

12

pr

16

6

2 0 30

50

70

90

Jo ur

10

na l

4

Reflection Angle (degree)

(d)

36

f 90 s

180 s

oo

365 nm

Pr

e-

pr

365 nm

na l

Figure 8: neff of PA1-azo in real time over three stages: from 0 to 60 s in the absence of irradiation, within 6 min of switching on the irradiation at

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365 nm, within 8 min of switching on the irradiation at 460 nm, and within 1.5 min of switching off irradiation.

37

f oo

1.26

pr

1.25

1.23

Pr

1.22 1.21

460 nm irraiation

na l

365 nm irraiation

1.2 1.19

Jo ur

n eff

e-

1.24

0

200

400 600 Time (s)

800

1000

38

f oo

Table 1 Geometrical parameters of PBGs and Azo-loaded PBGs under irradiation at 365 and 460 nm, obtained via AFM over the area of 20 μm ×

sample code

h (nm)

Wb (nm)

Wt (nm)

S (nm)

PA1

118

8

1816

12

484

288

PA2

120

4

2805

10

1724

PA3

121

4

3858

8

2945

PA1-azo

268

5

2295

16

824

PA2-azo

263

4

3265

12

2012

3

1684

PA3-azo

258

4

4003

12

3126

3

2142

2

Et

135700

135732

-

4951

2

271740

271755

-

6243

2

411582

411598

-

2561

3

417946

305070.1

0.37

3

4949

2

693926

564167.5

0.23

3

6145

2

919641

779356.8

0.18

4

2382 266

Aazo,460 (nm2)

3

2146

3

7

Jo ur

na l

4

Aazo,365 (nm2)

2564

6

Pr

2

P ( m)

e-

3

pr

20 μm.

39