Research Assistant Positions in Materials Characterization by Atomic Force Microscopy: Higher-Order Modes and Nonlinear Vibrations
Faculty Advisor: Dr. J. Turner, Assistant Professor of Engineering Mechanics
Dr. Turner is seeking 2-3 highly motivated individuals to begin Graduate Research Assistantships. These students will be involved with research on the project, "Materials Characterization by Atomic Force Microscopy: Higher-Order Modes and Nonlinear Vibrations," supported by the US Air Force Office of Scientific Research. The assistantships carry full financial support including tuition, semester fees, health insurance, and monthly stipends ($1,000/month for the first two semesters). The academic performance of each appointee will be evaluated at the end of every semester to determine whether a continuation of the appointment and a stipend increase shall be awarded. Under normal circumstances, the maximum duration of each assistantship is three years for a Ph.D. student or two years for an MS student. Applicants who are not currently enrolled in the Engineering Mechanics Graduate Program must also complete the application for admission to the program and be qualified by the Department Graduate Admissions Committee. Students who are highly motivated to complete a Ph.D. degree in Engineering Mechanics at UNL are preferred. For further details, please contact Dr. Turner.
Project Description: Recent, dynamic imaging techniques have been developed to image and to measure material properties of specimens and microelectromechanical systems (MEMS) components using an Atomic Force Microscope (AFM). The AFM was originally developed for determining surface topography information with resolution on the order of atomic length scales. The tip-sample interaction force is a complex nonlinear function. The nonlinear vibrations of AFM cantilevers interacting with a specimen surface will be investigated as part of this project. Analytical techniques from nonlinear vibration theory will be used to examine the influence of specimen material properties on the response of the higher-order vibration modes. These techniques allow the mixing of frequencies and frequency-amplitude interactions to be examined explicitly. Numerical modeling of the system with numerical methods (finite element or finite difference) will be conducted in conjunction with the analytical research. In addition, extensive experimental work will be used to corroborate the predictions made from the analytical/numerical methods. The vibration response will be characterized in terms of materials parameters such as the elastic modulus of the specimen, adhesion, and damping. It is anticipated that new techniques will be developed for characterization of thin films and MEMS at the microscale. The combined analytical and experimental work will also provide new insight into the structure of the nonlinear interaction forces between the AFM tip and specimen surface.
