EventsDr. Mehmet Yılmaz

Tensile Testing MEMS Devices for in-situ Mechanics and Strain Engineering Characterization of Nanomaterials

Developing the experimental capabilities in order to characterize and understand the mechanical properties, and properties that are coupled with mechanics, have many important implications in energy and information technology related research fields. First, there are many novel nanomaterials that need to be explored for their mechanical, and coupled field properties. Second, these novel, as well as some of the widely studied nanomaterials need to be statistically characterized for their mechanical, and coupled field properties. Furthermore, in materials science and engineering, there is a gap that needs to be connected between the theoretical and computational predictions of the properties of the materials, and experimental validation of these predicted material properties. Last but not least, there are variations even between the obtained experimental results. Hence, it is very important to be able to experimentally measure the mechanical and coupled field properties of nanomaterials with great care and repeatable consistency. However, the experiments are very difficult to perform because of the small dimensions of the test samples. Nevertheless, several research groups have made significant progress towards measuring the mechanical and coupled field properties of interest of a wide range of nanomaterials.

In this seminar, I am going to give the details of an experimental platform that addresses the items stated above. I am going to present the details of an extremely generalized approach that I designed, and developed. For the realization of the platform, I used batch-compatible and monolithic microfabrication approaches. These microfabrication approaches are the first of its kind with the capability to integrate such small dimensional confined volume gold test samples (7 µm long, ~200 nm wide, and ~40 nm thick) and microelectromechanical systems (MEMS) with suspended and mobile mechanical parts. The developed platform is a uniaxial tension test MEMS device for in-situ scanning electron microscope (SEM) experiments. The MEMS device is composed of a comb-actuator, and two displacement sensors. The purpose of the platform is to mechanically characterize nanoscale test samples that are located between the two displacement sensors of the MEMS device. Sub-pixel resolution digital image correlation (DIC) on as-taken (i.e. raw or unprocessed) SEM micrographs is used as displacement tracking and displacement extraction technique in order to quantitatively characterize nominal stress – nominal strain behavior of the tested samples. From the nominal stress – nominal strain behavior of the tested nanoscale specimens, I experimentally obtained Young’s modulus, and ultimate tensile strength of polycrystalline ultra-thin gold samples. In addition, I obtained the Young’s modulus, ultimate tensile strength, and critical resolved shear stress values of single crystal materials. More important, I developed a generalized experimental method to obtain the elastic strain as well as the plastic strain ranges of the tested materials.

This MEMS platform can be adapted to a wide range of strain engineering applications of functional nanomaterials using a wide range of advanced in-situ characterization tools such as transmission electron microscopy (TEM), scanning probe microscopy (SPM), Raman spectroscopy, etc. As a demonstration of this claim, I am going to briefly present my progress on one of the MEMS devices that is microfabricated to extract the I-V curves of functional nanomaterials while the materials are under dynamically controlled strain states.

UNAM_Seminar_Figure_Mehmet_Yilmaz_v2

a) In-situ SEM tensile testing MEMS device, b) Nanoscale sample that is batch-compatible integrated to the MEMS device, c) Nominal stress – nominal strain diagram of the tested polycrystalline gold sample.

About The Speaker

MehmetYilmaz-bio

Mehmet Yilmaz is a post-doctoral researcher at National Nanotechnology Research Center (UNAM) at Bilkent University. In spirit, he is an academician, scientist, engineer, inventor, and entrepreneur.

Mehmet Yilmaz received the B.S. degree (with high honors) from Izmir Institute of Technology, the M.S. degree from Koc University, and the Ph.D. degree from Columbia University, all in mechanical engineering. After his Ph.D. degree studies, he joined IBM Microelectronics Division at Albany Nanotechnology Research and Development Center, in New York, Albany.

During his M.S. and Ph.D. degree studies, Mehmet Yilmaz specialized in design and microfabrication of MEMS and integration of MEMS with nanostructures. During his Ph.D. degree studies, he also specialized in nanomechanical characterization of materials in-situ scanning electron microscope (SEM). During his time at IBM Microelectronics Division, he worked on developing reactive ion etching (RIE) processes for via patterning, and developing new integration schemes for 10 nm and 7 nm technology nodes, and silicon 3D integration (3Di) technologies. He is a co-inventor of two U.S. patents from the research and development efforts during his time at IBM.

Mehmet Yilmaz is interested in mechanical characterization, elastic strain engineering, understanding, and tuning the material properties at small length scales for energy and information technology applications, and developing new unit processes and integration processes for batch-compatible nanofabricated, high yield, MEMS and NEMS devices for energy, information technology, and health applications.