ID-12-P-3524 Novel functionalized MEMS devices for in-situ Electron Microscopy

MEMs-based in situ TEM holders for heating experiments do provide a large flexibility in performing heating experiments [1], because the virtually zero drift, very fast temperature changes (in millisecond) and accurate measurement of the real sample temperature. There are still questions on these heaters that have to be addressed: 1. How to get regular sample onto the MEMS chip ? 2. How to further reduce the drift induced by large temperature changes to study real dynamics 3. What is the temperature distribution? 4. How to improve accuracy of the temperature? 5. How to overcome bulging of the membrane that carries the sample ? Since a microheater in a MEMS device is small, e.g. 300 µm diameter, the sample has to be also small. Thus sample preparation has to be unconventional, if one want make full use of the microheater advantages. One approach is the “lift-out” method, developed for Dual Beams, in which a lamella is cut out from specimen and placed on the MEMS heater. Another approach is to cut by FIB lamella-like samples from a conventional TEM specimen prepared by PIPS or electrochemical polishing methods (Hui Wang, this conference). The drift of the MEMS-based heaters is in general very low, but if the temperature is changed over more that 50°C a significant drift can be present for several minutes, hampering HREM imaging. We will discuss novel designs of the heater chip in which this this problem can be reduced such that HREM recording remains possible throughout the jump in T. The temperature distribution over the heater cannot be completely prevented and it is in quite a number of experiments quite useful, for instance to repeat an experiment at a certain temperature with a particles that are further to the outside of the heater and thus at lower temperature. Thus if the exact temperature profile is known, then the temperature gradient is actually quite useful. The temperature gradient can be determined very well with Raman spectroscopy. Bulging of the membrane occurs due to the thermal expansion. For the SiN membranes that we are using, this bulging can be very significant, resulting in a change in focus if the temperature is changes. Such bulging can be calibrated and by coupling of the heater and TEM software a automatic correction can be made. We will discuss novel MEMS based heater chips, in which the bulging can be almost completely overcome in a specific temperature range. Also we will discuss additional functions designed into the MEMS based heater chips like contact lines for biasing experiment and gas and/or fluid in- and outlets. Also we will discuss a technology road map for MEMS based sample carriers enabling very sophisticated in-situ dynamic experiments in TEM. References 1. Van Huis, MA., et al, Adv. Materials, 21 (2009)