NEMS Fluid Sensors Based on Suspended Nanotubes and Nanowires-
The objective of this research is to explore the behaviors of Nanoelectro-mechanical system (NEMS) based sensors employing suspended single walled carbon nanotubes (SWNT) or metallic nanowires (MNW) in liquids. The approach is outlined as following: 1) Fabrication of NEMS sensors based on single suspended SWNT/MNW; 2) Systematic characterization of the important mechano-electrical behaviors (both resonant and non-resonant transient behaviors) of SWNT/MNW at a single-device level and 3) investigation of their dependence on various environments (in particular liquids). 4) Exploration of potential device applications, such as liquid characterization and molecules sensing.
Intellectual Merit: The research proposed here represents a vital step toward fundamental physical understanding of SWNT/MNW behaviors in liquid environments, which has been largely unexplored but is of great scientific and technological interests. More importantly, the potential integration of nanomechanical suspensions/resonators and micro/nano fluidics (two previously largely disjoint fields) creates exciting opportunities to explore new phenomena and to breed new applications in fresh directions.
Broader Impact: The versatile and robust NEMS fluid sensors proposed have great potentials to become a disruptive innovation with many critical applications in medicine, energy, environment and national security. In addition to research program, graduate and under-represented undergraduate students will be actively recruited to work on this cutting-edge research. Founded by the PI, the newly established Paslay Nanoscale Science and Engineering Educational Lab at Rice University will serve as a platform for outreach activities involving high school students and science teachers from the Houston Independent School District, and to also communicate findings from this research to the general public.
First of all, we have successfully demonstrated that at near room temperature, individual <111> single crystalline gold nanowires with 3-10 nanometers in diameter could be welded together within seconds by only making mechanical contact without any local heating process. High resolution transmission electron microscopy (HRTEM) imaging indicated that the joining quality was exceptional, with the two constituent nanowires forming the same crystalline orientation in the welding zone. Quantitative in situ tensile and electrical measurements confirmed that the strength of the as-welded nanowire was very close to that of the original nanowire, and the electrical properties of as-welded nanowires had little change for each successful welding. The rapid cold welding is attributed to mechanically assisted diffusion of surface atoms as well as the oriented attachment in gold nanowires. These results provide the first atomic scale visualization of the macroscopic cold welding process, and it is expected to have potential applications for future bottom-up assembly of metallic 1-D nanomaterials into large scale NEMS device arrays. A novel micromechanical device capable of accurately measure mechanical properties of low dimensional nanomaterials inside electron microscopes (SEM and TEM) were developed showing great potentials for probing material system at the extreme length scales. We also found that under uni-axial tensile loading, single crystalline ultrathin gold nanowires may fracture in two modes, displaying distinctively different fracture morphologies and ductility. In situ high resolution transmission electron microscopy (HRTEM) studies suggest that the unexpected brittle-like fracture was closely related to the observed twin structures, which is very different from surface dislocation nucleation/propagation mediated mechanism in ductile fracture mode. This finding has very important implication for robust design of functional NEMS devices based on suspended metallic nanowires. The PI hosted several high school student and several high school teachers during summer of 2007, 2009, 2010. One female high school student from Conroe High School and two male high school students from the Awty International School gained some first-hand research experiences from this project. The high school teachers were given a lecture on NEMS devices based on metallic nanowires and graphene after a one-week observation in the lab. The PI also served as a speaker for distinguished lecture series of Academy of Science and Health (Conroe, TX) and Academy of Science and Technology (Woodlands, TX). The audiences of over 100 are mostly high school students, their parents and general public who are interested in nanotechnology and nanomaterials. The PI has been collaborating with the UHD Scholar Academy of College of Science and Technology. The UHD Scholars Academy (UHDSA) is an academically competitive program in the College of Sciences and Technology at UHD that promotes scholarship and student success for undergraduate students majoring in Science, Technology, Engineering and Mathematics (STEM). There have been at least one UHDSA student performing nanomaterials and nanotechnology related research in Lou lab each summer since 2009. The partnership also includes providing UHDSA students fieldtrip access to several labs within the Rice University Department of Mechanical Engineering and Materials Science, as well as providing several seminar presentations at UHD focusing on graduate school information, careers, and real-world research avenues. Our presence at the annual UHD Scholars Academy Graduate School and Internship Fair will continue to attract more under-represented students to exciting research activities enabled by this project.
