A ZERO-POWER, HIGH-THROUGHPUT MICRO, NANOPARTICLE
PRINTING VIA GRAVITY-DRIVEN FORMATION of PICOLITER-SCALE
DROPLETS
Sun Choi1*, Arash Jamshidi1, Tae Joon Seok1, Tarek I. Zohdi1, Ming C. Wu1 and Albert P. Pisano1
1
University of California at Berkeley, USA
ABSTRACT
We report a zero-power, gravity and surface tension mediated method to generate and print picoliter-scale droplets for
high-throughput, size-tunable printing of micro, nanoparticle assemblies. High-throughput, picoliter-scale droplets are printed
by a single step, contact-transferring of the droplets through microporous nanomembrane of a printing head. Rapid evaporative self-assembly of the particles on a hydrophobic surface leads to printing a large array of various microparticles and nanoparticles assemblies of tunable sizes and resolutions. Finally, size-tunable, uniform large arrays of gold nanoparticle assemblies for Surface Enhanced Raman Spectroscopy (SERS) are created. This technology offers a straightforward, efficient
methodology to manufacture nanophotonic and nanoelectrical devices in a controllable way with low power and material consumption.
KEYWORDS: Surface tension, Gravity, Printing, Microparticle, Nanoparticle
INTRODUCTION
In cutting-edge nanotechnology, significant efforts are made to manipulate, locate and print micro, nanoparticles in targeted area for numerous applications such as three-dimensional photonic crystals[1-3], circuitry of printed electronics on flexible substrates[4,5], conductometric[6-8], and plasmonic-based biochemical sensors[9,10]. Conventional approaches to print
micro, nanoparticles - inkjet printing[11], electrohydrodynamic jet printing[12], dip-pen lithography[13], gravure printing[14], template assisted evaporative self-assembly[15] or atomic force microscopy (AFM) tip-based contact printing[16] –
have been achieving a number of milestones in certain applications, however, still suffering from many obstacles as listed:
high power consumption,[11,12] complicated and costly set-up,[11-13] low throughput,[11-13] limit of pattern size and resolution[11-16] and difficulties in an accurate alignment with other features.[11-16] In addition, controlling pattern size of various types of micro, nanoparticle has been a huge challenge because feature sizes and resolutions of existing technologies are
significantly limited by composition of inks or volume fraction of particles. These obstacles are preventing nanoparticle-based
nanoplasmonic or nanoelectronic devices from being manufactured in a controllable way with low processing time and cost.
THEORY
Multiple droplets are printed on a flat, hydrophobic surface by a single step, contact-transferring of multiple droplets extruded from the microporous membrane of a printing head driven by gravity and following rapid evaporative self-assembly of
the particles as illustrated in Figure 1.
Figure 1: Schematics of printing procedure. (a) Serial printing processes. Gravity-driven extrusion of pico-liter scale droplets are transferred to the substrate via pinch-off processes. Rapid evaporative self-assembly of the particles form 3D structure. (b,c) A high-throughput printing head. A 200 nanometer-thick microporous membrane is fabricated by applying microfabrication technologies to SOI wafer. (d) A global printing system. A printing head is attached to conventional
978-0-9798064-4-5/µTAS 2011/$20©11CBMS-0001
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15th International Conference on
Miniaturized Systems for Chemistry and Life Sciences
October 2-6, 2011, Seattle, Washington, USA
photolithography tool. 3-axis micron-precision stage and embedded optics enable an accurate alignment of patterning.
EXPERIMENTAL
A printing head – handling wafer complex was attached to a mask holder of uv-exposure system for contact- photolithography via vacuum. The mask holder was inserted to the system and a substrate for printing was loaded to the stage. After
loading the substrate, the alignment of the printing head to the patterns on the substrate wafer was performed and the spacing
gap between the printing head and the substrate was controlled and placed by taking advantage of the embedded electronics of
the system. The micro, nanoparticle suspension was injected to the reservoir of the printing head. The contact of the extruded
membrane of the printing head was performed by driving the mask holder to the substrate. After 1 second of the contact, the
printing head was driven back to the original position and the evaporation of the printed droplets were observed in-real time
by optical microscope embedded in the printing system in case the concentration of the suspension was sufficiently low to be
transparent. After the evaporation of the droplets was completed, the substrate with printed patterns was unloaded.
RESULTS AND DISCUSSION
A large array (10 ~ 100 patterns) of various microparticles (silica, polystyrene microbeads) and nanoparticles (zinc oxide,
gold nanoparticles) assemblies of different sizes and resolutions are printed on a flat, hydrophobic substrate as shown in Figure 2-4. The size of patterns can be easily tuned from single particle-scale to high-aspect ratio, 3D structures of several hundred micro-meter scale with an accurate positioning.
Figure 2. SEM View of silica microparticle (particle diameter: 1 µm) patterns (pattern diameter: 10 µm pattern). (a) Global
view of high-throughput patterns (conc.: 5 wt %) (b) Individual view of a 3D pattern (c-e) Silica patterns with low concentrations (conc.: 1 wt %)
Figure 3. SEM View of zinc oxide nanoparticle (particle diameter: 30 nm) patterns. (a) Global view of high-throughput patterns (conc.: 40 wt %) (b) Individual view of a 3D pattern (conc.: 40 wt %, pattern diameter: 30 µm) (c) Global view of highthroughput patterns (conc.: 1 wt %) (d) Individual view of a 3D pattern (conc.: 1 wt %, pattern diameter: 8 µm)
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Figure 4. SEM View of gold nanoparticle (particle diameter: 100 nm) patterns with different sizes. (a) Pattern diameter: 30
µm (b) Pattern diameter: 10 µm (c) Pattern diameter: 3.7 µm (d) Pattern diameter: 1.7 µm
Finally, size-tunable patterns were fabricated for uniform, large arrays of gold nanoparticle assemblies for Surface Enhanced Raman Spectroscopy (SERS)-based chemical detection. Four different gold dots of different sizes are printed by various combinations of pore sizes of the printing head and nanoparticle concentrations. Patterns were immersed in trans-1,2bis(4-pyridyl)-ethylene (BPE) solution prior to the measurement. As shown in Figure 5, very strong SERS signal with high
enhancement factor was obtained by prepared samples and the signal is subjected to be tuned by controlling the pattern sizes.
Also, the uniformity of the printed patterns was explored by measuring SERS signal of a number of dots on the substrate.
SERS measurement was performed on 5 dots with 10 µm diameter and the uniformity of all 3 peaks was measured to be very
good (< 10 %). Also, SERS measurement on 50 dots with 3.7 µm diameter shows the uniformity around 10 ~ 30 % as summarized in Figure 6.
Figure 5. Surface Enhanced Raman Spectroscopy (SERS)-spectrum of trans-1,2-bis(4-pyridyl)-ethylene (BPE) moleculesabsorbed gold dot patterns of four different sizes. The signal intensity drastically increases as the diameter increases.
Figure 6. Uniformity characterization of printed gold pattern dots. Intensity variation of 50 gold dots (left, average diameter: 3.7 µm) and 5 gold dots (right, average diameter: 10 µm)
CONCLUSION
We developed a novel, zero-power printing system for micro, nanoparticle assemblies. A microporous nanomembrane
was used to dispense multiple picoliter scale droplets and fast centering of all particles via evaporative self-assembly of the
particles on a hydrophobic surface leads to a high-aspect ratio, high-throughput printing of various micro, nanoparticles in wa-
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ter-based suspension. Various features of the printing such as continuous printing, multiplex printing and an accurate alignment capability are demonstrated. Size-tunable, uniform metallic nanoparticle assemblies via printing show a great promise to
fabricate nanoplasmonic biochemical sensors in a more controllable way with low power-consumption, time and cost.
ACKNOWLEDGEMENTS
This work was supported by a grant (2009K000069) from Center for Nanoscale Mechatronics & Manufacturing (CNMM),
one of the 21st Century Frontier Research Programs, which are supported by Ministry of Education, Science and Technology,
Korea. S. Choi also gives thanks for his graduate fellowship from Samsung Scholarship Foundation.
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CONTACT
*S. Choi, tel: +1-510-5295845; [email protected]
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