Three-Dimensional Polymeric Mechanical Metamaterials Fabricated

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Three-dimensional Polymeric Mechanical Metamaterials Fabricated by Multi-beam Interference Lithography with the Assistance of Plasma Etching Da-Young Kang, Wooju Lee, Dongchoul Kim, and Jun Hyuk Moon Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.6b02176 • Publication Date (Web): 28 Jul 2016 Downloaded from http://pubs.acs.org on July 30, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Langmuir is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Three-dimensional Polymeric Mechanical Metamaterials Fabricated by Multi-beam Interference Lithography with the Assistance of Plasma Etching Da-Young Kang, †[a] Wooju Lee, †[b] Dongchoul Kim,*[b] and Jun Hyuk Moon*[a] [a] Department of Chemical and Biomolecular Engineering, Sogang University, Seoul 121-742, South Korea [b] Department of Mechanical Engineering, Sogang University, Seoul 121-742, South Korea †

These authors contributed equally to this work.

RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required according to the journal that you are submitting your paper to) Corresponding author, E-mail: [email protected]

1

ACS Paragon Plus Environment

Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT The pentamode structure is a type of mechanical metamaterial that displays dramatically different bulk and shear modulus responses. In this study, a face-centered cubic (FCC) polymeric microstructure was fabricated by using SU8 negative-type photoresists and multibeam interference exposure. Isotropic plasma etching is used to control the solid-volume fraction; for the first time, we obtained a structure with the minimum solid-volume fraction as low as 15 % that still exhibited high structural integrity. Using this method, we reduced the width of atom-to-atom connections by up to 40 nm. We characterize the effect of the connection area on the anisotropy of the mechanical properties using simulations. Nanoindentation measurements were also conducted to evaluate the energy dissipation by varying the connection area. The Young’s/shear modulus ratio is 5 times higher for the etched microstructure than that of the bulk SU8 materials. The use of interference lithography may enable the properties of microscale materials to be engineered for various applications, such as MEMS.

KEYWORDS Three-dimensional polymeric structure, Interference lithography, Metamaterials

2


Page 2 of 24

Page 3 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

INTRODUCTION Mechanical metamaterials are materials that exhibit rare mechanical properties that are not found in nature. The term can also refer to materials whose mechanical properties are predominantly determined by their macroscopic geometrical structure rather than the material composition.1-4 For example, Bertoldi et al. have demonstrated materials with negative Poisson’s ratios using 2D periodic macroporous structures.5-6 Zheng et al. have reported an octet truss structure comprising a tetrakaidecahedron unit whose structural stiffness remains relatively constant with decreasing density.2 The pentamode structure is a type of mechanical meta-material first proposed by Milton et al. in 1995.7 This structure has an exceptionally high bulk modulus but a small shear modulus; therefore, despite being a solid, it behaves like a fluid. The ‘penta’ prefix is applied (5) because of the 6 diagonal elements in the elastic tensor, of which only one is zero. Wegener et al. first fabricated this structure by using direct-laser-writing lithography; the resulting structure exhibited diamond symmetry, with a double-truncated cone connecting the basis atoms.8-9 The pentamode structure displayed dramatically different bulk and shear modulus responses as the area of cone-to-cone contact decreased. This change occurs because the applied force is more concentrated in the connection, thus reducing the connection area. Consequently, in this regime, the elastic properties are affected by the connection regardless of the volume fraction of the structure.8, 10 However, most of the structures demonstrated previous were on a submillimeter length scale, and thus, their application to, for example, MEMS or NEMS is limited. The research presented here demonstrates the design of a 3D lattice polymeric structure by interference lithography.11 Interference lithography uses light interference as an alternative to

3


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

the photomask used in photolithography. The most important attribute of this technique is that it can produce 3D lattice structures with micrometer resolution. Moreover, unlike for the direct-writing method, the 3D structure is developed by one-shot exposure, enabling the highthroughput fabrication of 3D microstructures.12-15 Thomas et al. have previously reported the mechanical properties of a cube-symmetric structure fabricated by this approach; they were also able to change the solid-volume fraction and study its relationship with the mechanical properties.16-18 However, as we also observed here, the control of the solid volume fraction is rather limited by only controlling the lithography process condition. This study uses the isotropic plasma etching as an alternative method for the control of the solid-volume fraction; we achieve a minimum solid-volume fraction of as low as 15 % and could accordingly reduce the width of atom-to-atom connections by up to 40 nm. We then characterize the effect of the area on the anisotropy of the mechanical properties, mainly via simulations. The nanoindentation measurement was also conducted to evaluate the energy dissipation by varying the connection area. The etched microstructure exhibits a 5 times higher Young’s/shear modulus ratio than that of the bulk SU8 materials.

4


Page 4 of 24

Page 5 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

EXPERIMENTAL SECTION Preparation of the 3D face-centered cubic (FCC) SU8 structure The photoresist was prepared by dissolving a SU8 (EPON SU8, Miller-Stephenson Chemical) resin and a photoinitiator (Irgacure 261, Ciba, 2 wt%) in γ–butyrolactone (Sigma-Aldrich). The negative photoresist of SU-8 was spin-coated at 2,000 rpm and subsequently soft-baked at 65°C for 10 min and then at 95°C for 10 min. Three-dimensional (3D) face-centered cubic (FCC) patterns were obtained via four-beam interference. A 532 nm laser beam (Nd:YVO4, Coherent) source was expanded by a factor of 10 using a Galilean beam expander (Thorlabs) and was then incident on a top-cut four-sided fused silica prism. The beam passed vertically through the top surface, with four more beams refracting through the side surfaces and focusing beneath the prism. The approximate unit wave vectors of each beam are k0 = [0.58 0.58 0.58], k1 = [0.96 0.19 0.19], k2 = [0.19 0.96 0.19], and k3 = [0.19 0.19 0.96]. The interference pattern was exposed onto the photoresist film, which was subsequently baked at 65°C and 95°C for a few minutes. The pattern development was achieved by soaking the exposed film in propylene glycol methyl ether acetate (Sigma-Aldrich). The thicknesses of the resulting patterns were measured to be 8 – 10 µm. The fabricated patterns were etched by plasma etching. The plasma etching (HARRICK) is operated under the RF power of 18W and the chamber pressure of 1600 mTorr. The plasma etching time was varied from 10 to 30 min. Characterization The pattern morphologies were examined by scanning electron microscopy (SEM, JEOL). Nanoindentation measurements were performed using a MTS XP (MTS Systems Corporation). The device was run in the depth-controlled mode using the indenter tip 5


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(Berkovich-type triangular pyramid, the area function: 24.56) loaded variety. The simulation was performed with the implicit solver of LS-DYNA (Livermore Software Technology Corporation). Briefly, the pattern morphologies obtained by SEM image were transformed into a finite element mesh using Mathematica. We constructed boundary conditions for the finite element analysis to describe a compression and shear test. A fixed boundary condition is applied to the constraint translation of the elements at the bottom of the structures. Then, a loading is applied at the top surface of the structures. In the case of compression simulation, the load is applied in the vertical direction to the top surface of the structure. In the shear loading simulations, a loading is applied in the tangential direction. The load magnitude is controlled so that the applied strain is less than 1%. Each modulus can be calculated after obtaining the deflections in the loaded direction. The size of geometry is 2.32×2.32×2.32 µm3 and each finite element model consists of at least 1.5 million elements. The material property of SU8 was employed; Young’s modulus and Poisson’s ratio of SU8 are 3.0 GPa and 0.22, respectively.

6


Page 6 of 24

Page 7 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

RESULTS AND DISCUSSION Four-beam interference lithography was used to fabricate 3D FCC polymeric microstructures. Briefly, an epoxy-based negative-tone photoresist (SU8) was coated on a substrate, and then, the laser interference pattern was built up by passing the laser beam through a top-cut threesided prism. The exposed photoresist was baked to induce the crosslinking reaction of the SU8 molecules and soaked in the developing solution; the crosslinked region was left behind after developing. A detailed description of the fabrication process can be found in our previous work.19 Typically, the exposure intensity was approximately 20 J/cm2, and the postexposure baking was applied at 65°C for 5 min and at 95°C for 1 min. An SEM image of the SU8 FCC structure is shown in Fig. 1a. The structure consisted of the cylindrical basis macroscopic atoms with the cylinder elongated in the [111] direction. The surface of the microstructure shows a (111) plane of the FCC lattice (see the inset figure of Fig. 1a). Here, the diameter of the cylinder of “macroscopic atoms” is denoted by D and the width of thin “connection” that connects the cylinders is denoted by d, as shown in Fig. 1b. The simulated surface and the 3D structure are obtained by the following interference equation and are shown in Fig. 1b and 1c, respectively. sin(-x + y + z) + sin(x – y + z) + sin(x + y - z) = t1

(1)

,where t1 is the threshold variable that controls the volume fraction enclosed by the surface at this level.20-21 Specifically, the value of t1 = 0.39 was used to approximate the surface of the structure shown in Fig. 1a. Subsequently, the modelled structure was used to simulate the mechanical properties of the structure.

7


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

As stated previously, earlier studies noted that minimizing the connection between the macroscopic atoms is a prerequisite for maximizing the anisotropy of the elastic modulus.8-10 Because the photoresist was of a negative-tone type, the volume fraction of the structure (and thereby the connection width) can be minimized by reducing the exposure dose and/or postexposure baking temperature or time in the lithography process. This reduction impeded the crosslinking reaction of the SU8, which allowed for a lower solid-volume (smaller d accordingly) of the patterned structure.18, 22 The surface SEM images of the FCC SU8 structure fabricated with the lower exposure doses of 16 and 12 J/cm2 compared with the dose used for the structure shown in Fig. 1a are shown in Fig. 2a and 2b, respectively. The values of d and D also decreased with the decreasing dose, with d decreasing more rapidly than D.20 Specifically, the D and d values for the structure prepared at 16 J/cm2 were 550 and 200 nm, respectively, which were 2% and 33% smaller than the values for the structure shown in Fig. 1a (20 J/cm2). However, we observed a disconnected structure between the macroscopic atoms when the dose was equal to or less than 12 J/cm2, as observed in Fig. 2b. Meanwhile, we also prepared a structure using shorter post-exposure baking time at 65°C of 5 min. In this case, the structure often contained non-uniform, defective regions caused by thin connections, as shown in Fig. 2c. Previously, the experimentally attainable solid-volume fraction was 30 – 40%, although the volume fraction can theoretically range from 15% to 44%.23 The solid volume fraction of the structure shown in Fig. 2a was estimated to be approximately 30% using the modeled structure shown in the inset. Thus, our experiment also confirms that reducing the connections by using mild condition of exposure dose and baking time may be less reproducible.

8


Page 8 of 24

Page 9 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Here, we employ oxygen plasma etching as an alternative method.24-25 Isotropic etching was achieved under a high-pressure oxygen and air mixture (approximately 1600 mTorr). The surface SEM images of the SU8 structures etched for 10, 20, and 30 min for the structure shown in Fig. 2a are shown in Fig. 3a, 3b, and 3c, respectively. The D and d values decrease with increasing etching time. Specifically, the d values obtained for 10 and 20 min of etching were approximately 50 and 40 nm, respectively. Thus, the d value decreased linearly with the etching time. However, after 30 min of etching, the structure was distorted because of the disconnection of the part of the connections, as shown in Fig. 3c. This result implies that using the etching, the d value can be further reduced relative to the structure controlled by the lithography process only. The etched structure was modeled using a modified interference equation. This model was used because the control of t1 in Eq. 1 provides a non-uniform variation of the normal distance. Greater variation was obtained at the connection than the atom, which does not describe the isotropic variation of the surface along the surface normal direction during the etching process. The modified level surfaces are given by:20 sin(-x + y + z) + sin(x – y + z) + sin(x + y – z) +c(cos(4x) + cos(4y) + cos (4z)) = t2 (2) ,where t2 is the threshold variable. Here, the introduction of the second term multiplied by the constant c allows for a uniform variation of a level surface along the surface normal direction. The inset image, which was obtained using Eq. 2 with t2 = 1.3 and c = 0.104, describes the structure well. The solid volume fraction of the sample shown in Fig. 3b was estimated to be approximately 15%. To the best of our knowledge, this is the lowest solid volume fraction value that has been achieved by the interference lithography technique. 9


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Here, the mechanical properties of Young’s modulus (E) and shear modulus (G) for the SU8 structures were obtained by simulation. The modulus was calculated using finite element analysis and the LS-DYNA implicit solver. The volumetric mesh of the structure, described by the level surface equation, was constructed using the Mimics software package (Materialise). Both E and G were determined by inducing a deflection under compression and shear stress; the compression was loaded in the vertical direction (111 direction), whereas the shear stress was applied in the bending direction. The load magnitude was used to obtain a strain of less than 1% to introduce the deformation. A fixed boundary condition was applied to constrain the translation of the elements at the bottom of the structure. The SU8 FCC structure shown in Fig. 1a was used as a reference with d = d0 = 300 nm. Then, d/d0 values of up to 0.67 were obtained by controlling the exposure dose, and d/d0 values of up to 0.13 were obtained by controlling the etching time. The modulus for the structures with 0.67 < d/d0 < 1 and d/d0 < 0.67 was obtained using a simulated structure described by Eqs. 1 and 2, respectively. The E/G ratios of the FCC structures with various d/d0 values are shown in Fig. 4. Here, both moduli were normalized by the modulus of the reference structure (the structure shown in Fig. 1a). All structures are made of the same polymer material, but their mechanical properties vary considerably based on the differences in their material volume. As d/d0 (i.e., the ratio of the connection width and the width of the reference structure) decreased, both E and G decreased; however, G decreased to a greatest extent than E. The structure was more susceptible to the shear force than to the compression force, in agreement with the trends found in the previous studies.16 Fig. 4b shows the energy distribution of the FCC structure according to the compression and shear stress. The red area with the high relative stress is

10


Page 10 of 24

Page 11 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

concentrated at the connection, indicating that the maximum effective stress is loaded on the connection regardless of the force direction. The maximum effective stress under compression and shear stress is increased with decreasing d/d0. Specifically, the connection region exhibited a 3-fold higher stress under the applied shear stress than under the same strength of the applied compressive stress. This result shows that the compressive stress was more effectively relieved than the shear stress due to the geometric connectivity in the FCC lattice. The E/G ratio of 0.76 for bulk SU8 film was calculated by modeling the structure without pores. The E/G ratio of the reference FCC structure (d/d0 = 1) was approximately 2.5; this structure possesses the minimum d/d0 that can be attained by the control of the lithography process. The ratio increased up to 4.1 with decreasing d/d0. The maximum E/G ratio was 64% higher than that of the reference structure and 440% higher than that of the bulk SU8. Thus, these results indicate that the formation of the FCC network of SU8 remarkably enhances the anisotropy of the mechanical properties. Moreover, the FCC structure optimized by etching could further enhance the mechanical anisotropy. We conducted nanoindentation experiments to measure the mechanical properties. The triangular pyramid-type tip pressed the SU8 FCC film with a maximum load of 1.0 mN. Specifically, we evaluated the enclosed area in the load-displacement curves that corresponds to the energy dissipation by plastic deformation under a compressive load. The loaddisplacement curves of FCC structures with d/d0 = 1, 0.25, 0.13, and bulk SU8 film are shown in Fig. 5a. The values of energy dissipation normalized by the value of the reference structure are shown in Fig. 5b. Examination of Fig. 5 shows that energy dissipation increased with decreasing d/d0. The 80% decrease in d/d0, which is equivalent to the 99% volume 11


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

decrease, induces a 700% increase in the energy dissipation. Specifically, the decrease in the d/d0 of the structure from 0.25 to 0.13 (approximately 85% decrease in volume) that can be obtained by the etching process increases the energy dissipation by approximately 3 times. This result indicates that the SU8 FCC structure with the connection minimized absorbs stress at the same compressive load with remarkably higher efficiency or, in other words, is more conducive to deformation than the reference structure. Thus, this result corresponds to the finding of the simulation analysis described above that under compression, the stress is effectively absorbed throughout the structure. Previously, it has been reported that higher energy dissipation is obtained at a lower crosslinking density (lower material density) of patterned microstructures.23 Our result implies that energy dissipation is controlled by the connection width (or the volume fraction of structure) of the periodic microstructure.

12


Page 12 of 24

Page 13 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

CONCLUSIONS An FCC polymeric microstructure was fabricated using SU8 negative-type photoresists and multi-beam interference exposure. Following previous studies that found that the connection between the macroscopic atoms in the micropatterns controls the mechanical anisotropy, we experimentally control the volume (or width) of the atom-to-atom connections using a lithography process and oxygen plasma etching. The use of mild conditions in lithography to reduce the crosslinking of SU8 and thus the structure volume after the development has limitations. On the other hand, the use of plasma etching was a facile approach for reducing the connection width while maintaining the structural integrity. Specifically, we achieved an FCC microstructure with a solid-volume fraction of approximately 15% and a relative width d/d0 of 0.13. This volume fraction was considerably lower than those for the lithographically designed structures reported previously. To evaluate the mechanical anisotropy, we obtained the Young’s modulus (E) and shear modulus (G) of the structure and the E/G ratio. The simulated structure was defined by the iso-intensity level surface obtained from the interference equation. Specifically, the etched FCC structure was modeled by a modifiedinterference equation. Compared with the E/G value of bulk SU8 materials, the FCC SU8 structures exhibited up to a 5-fold higher value, which was attributed to the microstructure with a minimized atom-to-atom connection becoming less susceptible to the compressive stress. We also conducted the nanoindentation experiments to evaluate energy dissipation. Decreasing the connection in the microstructure was found to facilitate the stress conduction. Microstructures with various lattices are required to further investigate the relationship between mechanical anisotropy and structural topology. This type of microstructure can be

13


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

used as a personnel protection armor23 and will be also promising for applications in metafluidics26 and acoustic imaging.27

Acknowledgements This work was supported by the grant from the National Research Foundation of Korea (Grant No. 2011-0030253) and the Industrial Strategic Technology Development Program (Grant No. 10041589) funded by the Ministry of Trade, Industry, and Energy (Korea). The Korea Basic Science Institute is also acknowledged for the SEM measurement.

14


Page 14 of 24

Page 15 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

REFERENCE (1) Lee, J. H.; Singer, J. P.; Thomas, E. L. Micro‐/Nanostructured Mechanical Metamaterials. Adv. Mater. 2012, 24 (36), 4782-4810. (2) Zheng, X.; Lee, H.; Weisgraber, T. H.; Shusteff, M.; Deotte, J. R.; Duoss, E.; Kuntz, J. D.; Biener, M. M.; Kucheyev, S. O.; Ge, Q. Ultra-light, Ultra-stiff Mechanical Metamaterials. Science 2014, 344 (6190), 1373-1377. (3) Rafsanjani, A.; Akbarzadeh, A.; Pasini, D. Snapping Mechanical Metamaterials under Tension. Adv. Mater. 2015, 27 (39), 5931-5935. (4) Nicolaou, Z. G.; Motter, A. E. Mechanical metamaterials with negative compressibility transitions. Nat. Mater. 2012, 11 (7), 608-613. (5) Bertoldi, K.; Reis, P. M.; Willshaw, S.; Mullin, T. Negative Poisson's ratio behavior induced by an elastic instability. Adv. Mater. 2010, 22 (3), 361-366. (6) Overvelde, J. T. B.; Shan, S.; Bertoldi, K. Compaction through buckling in 2D periodic, soft and porous structures: effect of pore shape. Adv. Mater. 2012, 24 (17), 2337-2342. (7) Milton, G. W.; Cherkaev, A. V. Which elasticity tensors are realizable? J. Eng. Mater. Tech. 1995, 117 (4), 483-493. (8) Kadic, M.; Bückmann, T.; Stenger, N.; Thiel, M.; Wegener, M. On the practicability of pentamode mechanical metamaterials. Appl. Phys. Lett. 2012, 100 (19), 191901. (9) Bückmann, T.; Stenger, N.; Kadic, M.; Kaschke, J.; Frölich, A.; Kennerknecht, T.; Eberl, C.; Thiel, M.; Wegener, M. Tailored 3D Mechanical Metamaterials Made by Dip‐in Direct‐ Laser‐Writing Optical Lithography. Adv. Mater. 2012, 24 (20), 2710-2714.

15


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(10) Schittny, R.; Bückmann, T.; Kadic, M.; Wegener, M. Elastic measurements on macroscopic three-dimensional pentamode metamaterials. Appl. Phys. Lett. 2013, 103 (23), 231905. (11) Berggren, K. K. Lithography. Nanoscale 2011, 3 (7), 2662-2662. (12) Moon, J. H.; Ford, J.; Yang, S. Fabricating three‐dimensional polymeric photonic structures by multi‐beam interference lithography. Polymer. Adv. Tech. 2006, 17 (2), 83-93. (13) Miklyaev, Y. V.; Meisel, D. C.; Blanco, A.; von Freymann, G.; Busch, K.; Koch, W.; Enkrich, C.; Deubel, M.; Wegener, M. Three-dimensional face-centered-cubic photonic crystal templates by laser holography: fabrication, optical characterization, and bandstructure calculations. Appl. Phys. Lett. 2003, 82 (8), 1284-1286. (14) Campbell, M.; Sharp, D. N.; Harrison, M. T.; Denning, R. G.; Turberfield, A. J. Fabrication of photonic crystals for the visible spectrum by holographic lithography. Nature 2000, 404 (6773), 53-56. (15) Xu, Q.; Lv, Y.; Dong, C.; Sreeprased, T. S.; Tian, A.; Zhang, H.; Tang, Y.; Yu, Z.; Li, N. Three-dimensional micro/nanoscale architectures: fabrication and applications. Nanoscale 2015, 7 (25), 10883-10895. (16) Maldovan, M.; Ullal, C. K.; Jang, J. H.; Thomas, E. L. Sub‐Micrometer Scale Periodic Porous Cellular Structures: Microframes Prepared by Holographic Interference Lithography. Adv. Mater. 2007, 19 (22), 3809-3813. (17) Wang, L.; Boyce, M. C.; Wen, C. Y.; Thomas, E. L. Plastic Dissipation Mechanisms in Periodic Microframe‐Structured Polymers. Adv. Funct. Mater. 2009, 19 (9), 1343-1350.

16


Page 16 of 24

Page 17 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

(18) Jang, J. H.; Ullal, C. K.; Choi, T.; Lemieux, M. C.; Tsukruk, V. V.; Thomas, E. L. 3D Polymer Microframes That Exploit Length‐Scale‐Dependent Mechanical Behavior. Adv. Mater. 2006, 18 (16), 2123-2127. (19) Moon, J. H.; Yang, S. Chemical Aspects of Three-Dimensional Photonic Crystals. Chem. Rev. 2010, 110 (1), 547-574. (20) Moon, J. H.; Xu, Y.; Dan, Y.; Yang, S. M.; Johnson, A. T.; Yang, S. Triply Periodic Bicontinuous Structures as Templates for Photonic Crystals: A Pinch-off Problem. Adv. Mater. 2007, 19 (11), 1510-1514. (21) Lambert, C. A.; Radzilowski, L. H.; Thomas, E. L. Triply periodic level surfaces as models for cubic tricontinuous block copolymer morphologies. Philos. T. Roy. Soc. A. 1996, 2009-2023. (22) Zhu, X.; Xu, Y.; Yang, S. Distortion of 3D SU8 Photonic Structures Fabricated by Fourbeam Holographic Lithography with Umbrella Configuration. Opt. Express 2007, 15 (25), 16546-16560. (23) Lee, J.-H.; Wang, L.; Kooi, S.; Boyce, M. C.; Thomas, E. L. Enhanced energy dissipation in periodic epoxy nanoframes. Nano Lett. 2010, 10 (7), 2592-2597. (24) Di Mundo, R.; Troia, M.; Palumbo, F.; Trotta, M.; d'Agostino, R. Nano-texturing of Transparent Polymers with Plasma Etching: Tailoring Topography for a Low Reflectivity. Plasma Process Polym. 2012, 9 (10), 947-954. (25) Dai, W.; Ko, T.-J.; Oh, K. H.; Lee, K.-R.; Moon, M.-W. Ion-Beam Induced Surface Roughening of Poly-(methyl methacrylate) (PMMA) Tuned by a Mixture of Ar and O2 Ions. Plasma Process Polym. 2012, 9 (10), 975-983.

17


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(26) Fang, N.; Xi, D.; Xu, J.; Ambati, M.; Srituravanich, W.; Sun, C.; Zhang, X. Ultrasonic metamaterials with negative modulus. Nat. Mater. 2006, 5 (6), 452-456. (27) Zhu, J.; Christensen, J.; Jung, J.; Martin-Moreno, L.; Yin, X.; Fok, L.; Zhang, X.; Garcia-Vidal, F. J. A holey-structured metamaterial for acoustic deep-subwavelength imaging. Nat. Phys. 2011, 7 (1), 52-55.

18


Page 18 of 24

Page 19 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Figure 1. (a) SEM cross-sectional image of the SU8 FCC structure fabricated by interference lithography. Inset displays the magnified surface image with D = 560 nm and d = 300 nm. Simulated level surface of (b) surface and (c) 3D view of the corresponding FCC structure.

19


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2. SEM images of the FCC lattice fabricated under different fabrication conditions. Exposure dose was controlled from (a) 16 J/cm2 to (b) 12 J/cm2. PEB time was reduced to (c) 1 min.

20


Page 20 of 24

Page 21 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Figure 3. SEM images of the FCC structure treated by dry etching. The treatment time was (a) 10 min, (b) 20 min, and (c) 30 min.

21


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4. (a) Simulated compression (E) and shear modulus (G). E/G ratio is also displayed using the right axis. (b) Stress distribution of FCC structure of the SU8 FCC structure as a function of d/d0.

22


Page 22 of 24

Page 23 of 24

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Figure 5. (a) Load-displacement curves with maximum load of 1 mN. (b) Energy dissipation as a function of d/d0.

23


Langmuir

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

TOC graphic

24


Page 24 of 24

Three-Dimensional Polymeric Mechanical Metamaterials Fabricated

Recommend Documents