Yueh-Lin Loo Ph.D.
||Department / Business Unit
||Department of Chemical Engineering
|The University of Texas at Austin
||State / Provence
Our principal interest is to understand how specific micro- and nanoscale structures are generated in soft, complex systems, and how these structures in turn affect macroscopic properties and device performance. With improved understanding on these materials, we hope to exploit their structure-property relationships in the development of various applications in advanced technologies. Research in this area can be further divided into three sub-topics:
(A) Nanoscale Structure Characterization and Application Development of New Multicomponent Polymers
The development of new synthetic chemistries, such as atom transfer radical polymerization (ATRP) and various other living free radical polymerization (LFRP) techniques has enabled the production of block copolymers other than the limited selection (e.g., styrene-diene type block copolymers) accessible through classical anionic polymerization. These LFRP routes will also allow flexible derivatization and functionalization, thereby opening the possibility of making a new library of block copolymers that were previously inaccessible. The diverse monomer chemistries amenable to this technique, coupled with the ease of polymerization, make living free radical synthesis an attractive means of producing block copolymers for nanotechnology-related applications.
Our group is interested in understanding the phase behavior and the structure-property relationships of these new materials. We expect these polymers to behave differently compared to model block copolymers that are made by anionic routes. In particular, block copolymers polymerized by living free radical routes generally have a broader chain length distribution. We would like to understand how this impacts phase behavior and macroscopic properties.
With better understanding of how structures develop in these systems and in turn how these structures affect macroscopic properties, we can begin to exploit these new materials for advanced applications. These block copolymers show great promise in a variety of technologies, including controlled-release applications and polymer-based opto-electronic devices.
(B) Soft Lithography and Novel Patterning Schemes for Plastic Electronics
Research in plastic electronics has been fueled by the promise of low-cost fabrication, lightweight construction, mechanical flexibility and durability as well as large-area coverage. Recently, researchers at Bell Laboratories, Lucent Technologies have successfully demonstrated the fabrication of the world’s first electronic paper comprising a 64 by 64 array of organic transistors on a flexible backplane. This and other emerging technologies in plastic electronics point out that new age organic-based electronics can potentially be commercialized for novel applications, especially in the area of large area flexible displays, as well as wearable and disposable electronics.
Our research in the area of plastic electronics is focused on the development of new patterning and fabrication processes that are integratable with current processing techniques. For example, we have recently developed a purely additive contact printing technique, nanotransfer printing (nTP), which has enabled the transfer of complex and intricate features with nanoscale resolution over large-areas. This technique is highly versatile; we can routinely transfer a wide variety of functional materials from a stamp onto a range of substrates at ambient conditions. Using nTP, we have fabricated functional high-performance organic transistors and inverter circuits, as well as metal-insulator-metal capacitors on plastic substrates. We hope to extend this contact printing technique to fabricate thin film microbatteries for powering organic devices and plastic circuits.
In collaboration with researchers at DuPont, we have also developed a solventless thermal imaging technique for printing large-area plastic circuits. The functional devices on plastic substrates were printed using a commercial printer with speeds up to 1000 cm2/min. Future research in this area will involve materials development: we hope to widen the library of functional materials that are printable using this technique. Additionally, we will be focusing on the parallel assembly of devices over large-areas and their characterization.
(C) Self-Assembled Monolayers for Nanotransfer Printing and Nanoscale Organic Electronics
We have recently extended nanotransfer printing (nTP) to transfer patterns onto III-V semiconductor (e.g., GaAs) surfaces. This variation of nTP exploits interfacial chemistries that rely on thiol-based self-assembled monolayers (SAMs). Using similar techniques, we have also successfully fabricated nanoscale organic two-terminal devices where SAMs make up the active layer. Unlike direct evaporation of metal contacts on SAMs, SAM-based nTP is highly reliable; we have been able to make a large number of functional nanodevices reproducibly in this manner. Yet, the SAM surface is not well-characterized and the interfacial chemistry that is involved in printing is not well-understood.
We intend to better understand the interfacial chemistry and characterize the morphology of the SAM surface using a variety of surface characterization techniques. Near Edge X-ray Absorption Fine Structure Spectroscopy (NEXAFS) experiments will be conducted at Brookhaven National Laboratories to examine the molecular orientation and packing of the SAM layer. Additionally, we will also be using X-ray Photoelectron Spectroscopy (XPS) to extract information about the SAM/substrate bonding chemistries. These experiments will be conducted in collaboration with research scientists at the National Institute of Science and Technology (NIST).
Information about the SAM layer on a molecular length scale is crucial, especially for further development of the nTP and fabrication optimization of nanoscale devices that rely on molecular active layers. Our initial characterization will involve model SAMs that are based on simple alkane chains. With such information in hand, we intend to extend our investigation to examine semiconducting SAM layers. These molecules are especially interesting from the nanodevice fabrication prospective.
Ph.D. in Chemical Engineering, Princeton University, 2001; M.A. in Chemical Engineering, Princeton University, 1998; B.S.E. in Chemical Engineering, University of Pennsylvania, 1996
General Dynamics Endowed Faculty Fellow, 2005-present
Beckman Young Investigator Award, 2005
MIT’s Technology Review: “Top 100 Young Innovator”, 2004
ACS/Dreyfus PROGRESS Lectureship, Rising Stars Program, 2004
NSF CAREER Award, 2004
DuPont Young Professor, 2003
Camille and Henry Dreyfus New Faculty Award, 2002
Porter Ogden Jacobus Fellow, Princeton University, 2000-2001
Frank J. Padden Jr. Award for Excellence in Polymer Research, APS, 2000
• G.B. Blanchet, Y.-L. Loo, J.A. Rogers, F. Gao, C. Fincher, “Large-Area Printing of Organic Transistors,” Applied Physics Letters, 82, 463, 2003.
• Y.-L. Loo, J.W.P. Hsu, R.L. Willett, K.W. Baldwin, K.W. West, J.A. Rogers, “High-Resolution Transfer Printing on GaAs Surfaces with Alkane Dithiol Self-Assembled Monolayers,” Journal of Vacuum Science and Technology, 20, 2853, 2002.
• Y.-L. Loo, T. Someya, K.W. Baldwin, Z. Bao, P. Ho, A. Dodabalapur, H.E. Katz, J.A. Rogers, “Soft, Conformable Electrical Contacts for Organic Transistors: High-Resolution Circuits by Lamination,” Proceedings of the National Academy of Science, USA, 99, 10252, 2002.
• D. Bendejacq, V. Ponsinet, M. Joanicot, Y.-L. Loo, R.A. Register, “Well-Ordered Microdomain Structures in Polydisperse Polystyrene-Poly(acrylic acid) Diblock Copolymers from Controlled Free Radical Polymerization,” Macromolecules, 35, 6645, 2002.
• Y.-L. Loo, R.L. Willett, K.W. Baldwin, J.A. Rogers, “Nanoscale Patterning With a Stamp and a Surface Chemistry Mediated Transfer Process: Applications in Plastic Electronics,” Applied Physics Letters, 80, 562, 2002.
• Y.-L. Loo, R.L. Willett, K.W. Baldwin, J.A. Rogers, “Interfacial Chemistries for Nanoscale Transfer Printing,” Journal of the American Chemical Society, 124, 7654, 2002.
• Y.-L. Loo, R.A. Register, A.J. Ryan, “Modes of Crystallization in Block Copolymer Microdomains: Breakout, Templated, and Confined,” accepted by Macromolecules, 35, 2365, 2002.
• Y.-L. Loo, R. A. Register, A. J. Ryan, G. T. Dee, “Polymer Crystallization Confined in One, Two, and Three Dimensions,” Macromolecules, 34, 8968, 2001.
• D.A. Vega, J.M. Sebastian, Y.-L. Loo, R.A. Register, “Phase Behavior and Viscoelastic Properties of Entangled Block Copolymer Gels,” Journal of Polymer Science Part B: Polymer Physics, 39, 2183, 2001.
• Y.-L. Loo, R. A. Register, D. H. Adamson, “Polyethylene Crystal Orientation Induced by Block Copolymer Cylinders,” Macromolecules, 33, 8361, 2000.Y.-L. Loo, R. A. Register, D. H. Adamson, “Direct Imaging of Polyethylene Crystallites in Block Copolymer Microdomains,” Journal of Polymer Science Part B : Polymer Physics, 38, 2564, 2000.
• Y.-L. Loo, R. A. Register, A. J. Ryan, “Polymer Crystallization in 25 nm Spheres,” Physical Review Letters, 84, 4120, 2000.