Nanoimprinting in Polymers and Applications in Cell Studies. Albert F. YEE Chemical Engineering & Materials Science UC Irvine

Transcription

1 Nanoimprinting in Polymers and Applications in Cell Studies Albert F. YEE Chemical Engineering & Materials Science UC Irvine

2 Presentation outline Motivation Reversal imprinting Soft inkpad imprinting on nonflat surfaces 3-D Structures Cell Studies 2

3 Why Fabricate Nanostructures? q Nanodevice elements may possess functions not found in microdevices Ø Quantum mechanical effects Ø Size-dependent electronic properties q Nanodevices are small Ø Large surface/volume ratio may mean higher sensitivity Ø Some nanodevices may operate at higher speeds and lower power q Nano-structures may be important in certain systems Ø Biological systems: cell differentiation and motility Ø Unusual surface properties such as superhydrophobicity q Nanofabrication can produce templates to assist selfassembly 3

4 Cicada wings are superhydrophobic 4

5 Cicada wings also kill bacteria on contact (Gram only) 5

6 We duplicated the bactericidal properties by nanoimprinting a synthetic polymer: E. coli were killed on acrylic surface with nano-pillars 6

7 Lithographic techniques for going below 50 nm: Many choices - with pros and cons q q q q q q Electron beam EUV lithography X-ray Ion Beam Optical Ø Liquid immersion Ø Chemically amplified resists Nanoimprint lithography (NIL) Ø Conventional nanoimprint lithography is sometimes known as NIL Ø Hot embossing Ø Step and flash Ø We will be discussing a new technique: reversal imprinting Ø Directed assembly: possibly more practical than self-assembly 7

8 Nanoimprint Lithography a) b) c) d) a) Fluorinated silane coating was applied to silicon mold b) Spin-coated 5% M.W. PMMA on glass c) Imprinted PMMA to silicon mold at 160 degc for 5 min. with 400 N of force in Jenoptik nanoimprinter d) Released mold from PMMA to yield nanostructures This leaves a residual polymer layer!

9 Nanoimprint Lithography (NIL) Ø Versatile, cost effective, flexible and high throughput (parallel) method for fabrication of down to 10 nm structures even over large areas (wafers) Applications in: Semiconductor memory Micro and nano fluidics Optical devices e.g. LEDs and lasers Life science, e.g. lab-on-a-chip systems, bio sensors Radio frequency components Renewable energy Security (holography, tags, etc.) Nanotechnology

10 Polymer Stamp Substrate A stamp is fabricated by electron beam lithography (EBL) and dry etching The stamp is pressed into a soft thermoplastic, thermosetting or UV-curable polymer on a substrate combined with heating or UV radiation The polymer is cured and the stamp release from substrate Residual imprint polymer under stamp protrusion removed by descum process Imprinted pattern transferred into substrate by dry etching

11 Direct Nanoimprinting of Metal Nanoparticles Ko, S. H., et. al, Nano letters, Vol. 7, No. 7, p1869, 2007

12 Nanoimprinted gold structures Minimum feature size is 450 nm because PDMS mold s poor resolution. (There is more room to be optimized) There is few residual material because of low viscosity of solution Ko, S. H., et. al, Nano letters, Vol. 7, No. 7, p1869, 2007

13 Nanoscale patterning on flexible substrate Park, I., et. al, Advanced Materials, Vol. 20, p489, 2008

14 Research in Nanoimprint Lithography Lab at UC Irvine Fabrication of 2-D and 3-D nanostructures Integration of functional nano-elements with nano- and micro- device structures Study of basic materials issues of nanostructures Core equipment Jenoptik Hex03 nanoimprinter Ø Imprinting force 200 kn Ø Max. temperature 220 C Ø Max. substrate size 180 mm dia. Ø Alignment accuracy ± 2 µm Applied Microstructures MVD-100 coater Ø Deposition of Low surface energy self assembled monolayer Ø Mold release layer 14

15 Reversal Nanoimprinting - Huang, X. D., L. R. Bao, X. Cheng, L. J. Guo, S. W. Pang, and A. F. Yee, J. Vac. Sci. Technol. B 20: , (2002)! q Spin coat polymer on mold, then transfer the material to substrate Ø Release treatment required for the mold Ø Proper selection of solvent for uniform coating on mold 15

16 Three variations of reversal imprinting Huang, X. D., L. R. Bao, X. Cheng, L. J. Guo, S. W. Pang, and A. F. Yee, J. Vac. Sci. Technol. B 20: , (2002)! Whole layer transfer Reversal embossing Inking Mold Polymer T T g T > T g T T g 16

17 Advantages of reversal imprinting Imprinting on thin or flexible substrates Residue free patterns with inking Process T Tg Lower pressure and temperature No spin coating over existing structures Dry process: No polymer intermixing issues Ø Multiple layers possible! 17

18 (a) (b) (c) Examples of 3-D scaffolds (a) grating over channels; (b) closeup of (a); (c) Grating not covering channels; (d) 3-layer grating. By varying the spacing of the grating on each layer holes of arbitrary size can be created. (d) 18

19 Multi-layer 3-D structure with reversal imprinting L. R. Bao, X. Cheng, Huang, X. D., L. J. Guo, S. W. Pang, and A. F. Yee, J. Vac. Sci. Technol. B 20: , (2002)" 19

20 Multi-layer 3-D structure with reversal imprinting L. R. Bao, X. Cheng, Huang, X. D., L. J. Guo, S. W. Pang, and A. F. Yee, J. Vac. Sci. Technol. B 20: , (2002)" Compostion of layers PC, Tg 150 C PMMA, Tg 105 C Poly(t-butyl-acrylate), Tg 43 C 20

21 Imprint over Topography q Imprint over topography without the need for planarization 21

22 Formation of enclosed microchannels: Photoresist over Si (a) (b) photoresist photoresist Si substrate Si substrate (c) photoresist (d) photoresist Si substrate Si substrate Cross-section images of a photoresist film with whole-layer film over topography pattern on Si substrate (depth: 1.2 or 4.1 µm). 22

23 Imprinting with bio- and functional polymers: Plasticizers are incorporated into polymers without a distinct Tg Tan L, Kong YP, Pang SW, Yee AF, Imprinting of polymer at low temperature and pressure, JVST B 22: 2486, 2004 Polymer + plasticizer solution spin coated on PDMS mold Press at room temperature PEDOT without plasticizer, patterned at 10 MPa, 100 C Glycerol:PEDOT (by weight) = 1:1, patterned at 10 kpa, room temp. 23

24 Imprinted 3-D grating with sealed cavities Polymer coating on low surface energy mold Surface area also determines surface adhesion Grating Grating Closed cavities Si Closed Si 1 µm cavities 1 µm FDTS treated (low surface energy) FDTS treated (low surface energy) Material: PMMA (Mw 15k) Both molds (700 nm period mold and square mold) treated with FDTS Imprinted at 5 MPa and 150 C Transferred to substrate at 2 MPa and 80 C 24

25 Imprinted 3-D grating structure Polymer coating on medium surface energy mold 200 nm PEDS-FDTS treated (medium surface energy) FDTS treated (low surface energy) 200 nm Material: PMMA (Mw 15k) Si grating molds 700 nm pitch Imprinted at 4 MPa and 120 C Transferred to substrate at 1 MPa and 65 C 25

26 Template directed self-assembly of PS nano-particles 26

27 Micro-roll with nanotexture to simulate 3-D extra cellular matrix with controlled dimensions 350 nm 2 µm 27

28 Sample 3: Photoresist/Si with gratings, dots, grids SMC grew on, and along the edge of the photoresist patterns most cells elongated on gratings 28

29 Sample 3 Dots around cells were moved toward the cells-cells grew on top of the dots might have pulled the dots along during the migration Thinner lines were deformed appeared to be caused by cell contraction and migration 29

30 Sample 2: collagen coated SMC formed pattern-- two perpendicular lines 10x 30

31 Sample 1: PMMA/Si with submicron gratings SMC line-up and elongate along an axis (we cannot see the gratings) 31

32 MC3T3-E1 behavior on NANO structures " Migration assay: 110 nm 32

33 MC3T3-E1 behavior on NANO structures " Migration assay: 350 nm 33

34 MC3T3-E1 behavior on NANO structures " IF images 34