Lab-on-a-chip Channels Novel Manufacturing Method

Transcription

1 Lab-on-a-chip Channels Novel Manufacturing Method Alex A. Volinsky, Megan Pendergast, Ramakrishna Gunda University of South Florida, Department of Mechanical Engineering, Tampa, FL 33647, USA. ABSTRACT: This IREE supplement supported two graduate students and PI s travel to Jagiellonian University in Krakow, Poland as a part of the NSF Lab-on-a-chip Channels Novel Manufacturing Method project. The goal of the project is to manufacture microfluidic device channels based on the controlled thin film buckling delamination phenomenon. In Poland unique ultra-high vacuum equipment was utilized to study the fundamental aspects of thin film adhesion loss. In addition, pattern formation due to irradiation and wear were studied along with the effects of environment on materials wear. INTRODUCTION This ISEE award supplement is for the DMII project Lab-on-a-chip Channels Novel Manufacturing Method awarded to the University of South Florida. We are exploring a thin film buckling phenomenon as a manufacturing method for microchannels in a microfluidic device. Compressed films are prone to buckling and loss of adhesion from the substrate, forming channels. The process of microchannels formation by buckling can be controlled by tailoring the film stress and placing patterned adhesion weakening layers underneath the film. As a part of current NSF award we have demonstrated the feasibility of this approach. Prof. Marek Szymonski s group at Jagiellonian University in Krakow, Poland has built two unique ultra-high vacuum (UHV) scanning probe microscope (SPM) systems, in which fracture surfaces could be created and characterized. These tools along with other equipment helped to provide an understanding of the thin film delamination, radiation damage and wear processes. The research outcomes of the IREE project are the following: o Fracture surfaces were created and characterized in UHV o Semiconductor materials were irradiated with ion beam in UHV, and the resulting surface morphologies were studied;

2 2 o The effects of environment on materials wear were studied; o Eutectic reaction between Si and gold was observed in UHV; The educational outcomes of the IREE project are the following: o Graduate students and the PI learned how to operate state-of-the-art UHV equipment; o Graduate students and the PI learned how to operate Digital Instruments Dimension 3000 and Park Scientific CP-II AFM systems; o The group members attended seminars at a world-class university that were conducted in English; o The group members interacted with Polish and international researchers; o The group members participated in the 12 th International Conference on Organized Molecular Films in Krakow; o The PI co-organized a workshop on Nanomechanical Materials testing together with Hysitron Inc. and Prof. Szymonski s group, in which graduate students participated as well; o The PI visited AGH University of Science and Technology in Krakow, and discussed a possible joint research project with the Department of Materials Science and Ceramics. Information about Host Laboratory Jagiellonian University is the oldest establishment in Poland after the Catholic Church. It has state-of-the-art unique facilities and researchers. Prof. Szymonski s group is formed of 30 undergraduate and graduate students, as well as post-docs ( and It hosts several international researchers annually. During the group stay Prof. Szymonski hosted Dr. Om Prakash Sinha from the Amity Institute of Nanotechnology (India) under the Marie Curie Host Fellowship under the project Nano-engineering for Expertise and Development NEED within the 6th EU Framework Program. Name of Travelers Alex A. Volinsky (PI), Megan Pendergast (M.S. student), Ramakrishna Gunda (M.S. student) Dates of Travel May 2007-August 2007 RESEARCH ACTIVITIES AND ACCOMPLISHMENTS OF THE INTERNATIONAL COOPERATION Program of research carried out during international research experience Fracture surfaces between Si and W films were created in UHV and in ambient environments. It was discovered that interfaces are tougher in UHV vs. air, or water due to the higher surface energy; AFM and Hysitron ambient wear tests were conducted in water, air and nitrogen. It was found that the wear rate is non-linear (Figure 1a). Higher wear rate was observed in water vs. air in poly and single crystalline gold (Figure 1b);

3 1 µn 1.5 µn 80 Wear Depth, nm Wear Depth, nm a) Number of Scans Water 10 µn Oil 10 µn Air 10 µn b) 60 Number of Scans 100 Figure 1. a) Gold wear rate in nitrogen at 1 and 1.5 µn normal load; b) gold wear rate in water, oil and air at 10 µn normal load. Calcite and KBr single crystals were repeatedly scanned in AFM and Hysitron Triboindenter, which resulted in the periodic pattern formation in the form of ripples perpendicular to the long scan direction. Repeated scanning over a single line also formed ripples (Figure 2a); Au/Cr films on Si were heated in UHV and at 550 C a eutectic reaction between Au and Si was observed, which resulted in the spiral pattern formation (Figure 2b); b) 150 µm a) Figure 2. a) Wear-induced ripples in KBr single crystal; b) Eutectic pattern in Au/Cr/Si heated in UHV. InP was irradiated with an Ar+ ion beam in UHV, and the corn-type of pattern formed on the sample surface. The effects of the beam flux and energy were investigated. How the work on-site is related to the work of the current NSF award

4 4 Prof. Szymonski s group provided state-of-the-art UHV equipment to the IREE project group members to study surface effects during fracture, which lead to a better understanding of the thin film fracture process utilized in manufacturing of the microfluidic device channels; It was observed that thin film interfaces are weaker in the presence of moisture, which could be utilized for the film tunable adhesion and release-on-demand; Megan Pendergast (one of the graduate students) and the PI had access to an AFM system for three months, which had a capability of performing in-situ tests in fluids. We also modified this equipment for purging gases, and conducted wear experiments on gold and KBr. General interaction between researchers Each US IREE project participant occupied an office with a Polish researcher, which really helped the interaction. Alex Volinsky shared an office with Dr. Yanusz Budzioch, an expert in UHV systems, Megan Pendergast shared an office with Dr. Piotr Cyganik, an expert in self-assembled monolayers, and Ramakrishna Gunda shared an office with Dr. Om Prakash Sinha, an exchange researcher from Amity Institute of Nanotechnology in India, an expert in UHV systems. The research group would go to lunch and discuss scientific matters daily. The Jagiellonian University also organized events, which included the University Spring Picnic, and a guided tour to the Collegium Maius, museum operated by the Jagiellonian University. There were also multiple interactions on the personal level. For example, the PI went on the hiking trip with researchers from the Polish Academy of Sciences. BROADER IMPACTS OF THE INTERNATIONAL TRAVEL The IREE participants were integrated into a diverse international research group for three months. For Megan Pendergast this was the first trip outside of the US. According to her, if not for this project, she would have never traveled to Poland. Every part of staying in Krakow was unique, ranging from professional to cultural activities. This summer the city celebrated its 750 th anniversary. There were daily cultural events that we attended, which ranged from special museum exhibits to public performances and concerts. The group also conducted additional experiments that broaden the scope of the original proposal. The fact that materials have higher wear rate in water vs. air is technologically significant, and requires further study. Also, we conducted irradiation experiments, which may lead to new ways of forming patterns in materials. As a result of the joint project a journal publication is currently under preparation. Based on the gathered results, the PI gave a presentation at the International Workshop on the Frontiers of the Nanomechanical Testing, NanoPol ( DISCUSSION AND SUMMARY As a result of this IREE project, graduate students and the PI learned how to operate statof-the-art UHV and ambient SPM equipment. The group conducted experiments with

5 fracture surfaces in UHV, air and nitrogen. Interfaces were found to be tougher in UHV due to higher surface energies of the non-contaminated fracture surfaces. We developed techniques to conduct environmental wear tests using AFM and Hysitron Triboindenter, and found that materials exhibit higher wear rate in the presence of moisture. Pattern formation due to surface irradiation and solid state reaction was also investigated, which broaden the original research project goals. IREE program is extremely valuable, as it exposes researchers to international collaborations early in their career. The IREE trip could also be viewed as a recruitment opportunity for international graduate students. Participation of undergraduate students could also be encouraged through REU support. ACKNOWLEDGEMENTS Alex Volinsky, Megan Pendergast and Ramakrishna Gunda would like to acknowledge the NSF grant CMMI from which this IREE project was supported from. Alex Volinsky would also like to acknowledge the Marie Curie Host Fellowship under the project Nano-engineering for Expertise and Development NEED within the 6th EU Framework Program, which brought him to Prof. M. Szymonski s group in the summer of The authors would also like to acknowledge the tremendous help from multiple members of Prof. Szymonski s group with arranging accommodations in Krakow, Poland, and for sharing their state-of-the-art research facilities, and numerous valuable discussions. BRIEF BIOGRAPHIES OF RESEARCHERS Alex A. Volinsky received the Engineering degree in Metals Processing from Moscow State University of Aviation Technology (MATI) in He received Ph.D. degree in Materials Science and Engineering from the University of Minnesota in Following four years at Motorola he became an Assistant Professor of Mechanical Engineering at the University of South Florida in His research interests include thin films processing, mechanical properties and characterization, adhesion and fracture of thin films, nanoindentation, pattern formation, irradiated materials properties and X-Ray diffraction. Megan Pendergast is currently in the 5 year BSME - MSME program at the University of South Florida with an expected graduation date in May Her research under Assistant Professor Dr. Alex A. Volinsky deals with nanopatterning and mechanical properties of materials. She performs wear tests using Hysitron Triboindentor and contact mode Atomic Force Microscope on a variety of materials ranging from single crystal KBr to sputtered gold films. Ramakrishna Gunda received the B.E. degree in Mechanical Engineering from Andhra University, India in He received the M.E. degree in Welding

6 6 Engineering from National Institute of Technology, Tiruchirapalli, India in He worked as a research assistant from 2003 to 2006 in Nanotribology lab, Department of Mechanical Engineering in Indian Institute of Science (IISc), Bangalore, India. During his tenure in IISc, he worked on characterization and measurement of mechanical properties of TiN thin films on steel substrate using Nanoindentation technique. His research interests include Nanomechanics of materials. He is currently working on a project which deals with formation of Nano-ripples on the single crystal materials and Nano-wear.