Microsensors for in situ electron microscopy applications
With the ongoing miniaturisation of devices, the interest in characterising nanoscale physical properties has strongly increased. To further advance the field of nanotechnology new scientific tools are required. High resolution imaging is one of the key components and when combined with existing characterisation tools such as Atomic Force Microscopy (AFM), Scanning Tunnelling Microscopy (STM) and nanoindentation, this enables direct imaging of real time responses and the possibility to locally probe for instance an individual nanotube. For nanoscale studies, electron microscopy and in particular Transmission Electron Microscopy (TEM) is one of the few tools with sufficiently high imaging resolution. The main challenge of such in situ instruments is the restricted space available in the millimetre sized pole piece gap of a TEM.
In this work the design, fabrication and integration of two types of in situ TEM sensors is presented. The sensors are used in an in situ TEM-Nanoindentation and an in situ TEM-AFM system, providing direct and continuous force measurements. The nanoindenter force sensor utilises capacitive read out and the AFM sensor read out is based on piezoresistive detection. Both sensors were fabricated using silicon micromachining. Silicon micromachined devices have the advantage of inherently small footprint, which makes them suitable for the millimetre sized pole piece gap of the TEM. The nanoindenter force sensor operates in force ranges up to 4.5 mN and a resolution of 0.3 µN has been measured in the TEM. The AFM sensor has a force range up to 3 µN with a resolution of 15 nN at 5 kHz bandwidth. Both sensor geometries are designed such that they fit in most TEM models.
The force sensors have been integrated into TEM-Nanoindenter and TEM-AFM specimen holders. The systems have been evaluated with measurements on aluminium film and nanowires. Furthermore, the AFM sensor has also been used inside a Scanning Electron Microscope (SEM) and an Environmental SEM. Studies of tool steel and living yeast cells have been performed. These measurements verify proper operation and demonstrate possible application areas of the TEM-Nanoindenter and the TEM-AFM.
In situ TEM