Aberration corrected high resolution transmission electron microscope:

Teaching

 

We have recently acquired one state of the art aberration corrected high resolution transmission electron microscope (TITAN3TM 80-300) from FEI Company, Netherland. This particular microscope has both Cs corrector (spherical aberration, for HRTEM) and probe corrector (for HAADF-STEM) in order to achieve spatial resolution ~ 0.8 Å during imaging of crystals. Acceleration voltage can be varied between 80 kV to 300 kV. Besides, this microscope is equipped with EELS, EDX and energy filter components. In EELS mode, energy resolution better than 0.2 eV allows studying fine details of electronic structure near and extended regions of the absorption edge, providing wide range of information such as coordination, charge state, bonding environment, electronic charge density etc for an atom. Capability in simultaneous imaging in the sub-angstrom level and spectroscopy (atom by atom) is an extremely powerful tool to get direct insight into many of the concepts and controversial issues associated with solid state physics through structure (both crystallographic and electronic) and property correlation.

 
 

Figure 1:

(a) Cs corrected HAADF-STEM image on Si <110> (left) and Ge <112> (right), (b) after subtraction of the zero-loss peak, band gap thresholds can be measured as well as the energy shift due to the AI doping in AlGaAs (courtesy to FEI).

EELS from magnetic thin film and nanostructures:


EELS can also be utilized to obtain both magnetic linear and circular dichroic signals from ferromagnetic and paramagnetic materials in order to experimentally evaluate the origin of magnetization in complex magnetic materials. Aberration corrected microscopy allows us to select very small specific area of a given sample to deduce such properties. This new technique might unravel the complexity in phase separation in highly correlated electron systems, complete understanding of certain magnetic phenomena in manganites, dilute magnetic semiconductors, metamagnetic materials and ferromagnetic/antiferromagnetic interfaces in magnetic multilayers which are important for the rapidly growing field of spintronics. Electron magnetic circular dichroism (EMCD) in a TEM is a new idea and more work need to be done both in experimentation and simulation before it can be turned into practice.

Focused Ion beam (FIB):


Dual beam focused ion milling can be used to prepare very thin electron transparent TEM foil. This can also be used to machining materials at micron and nanometer scale. Micromanipulator arrangement allows transferring very small size sample to the required position which can then be used for various studies.

 
 

ZnO:

We are now actively engaged in p-doping and magnetism in ZnO in thin film form for application in bi-polar devices and spintronics. We are trying to understand the issues using unique capability of our TITAN microscope.