Development and Application of Membraneless Electron Microscopy

Abstract

Transmission electron microscopy (TEM) is an important tool for the characterization of materials as it can provide clear understanding of the relationship between structure, property and composition of nanomaterials. For this, the in-situ TEM analysis is performed and requires specially manufactured sample holders. In particular, those designed to carry out electrical biasing can be used to understand not just the I-V characteristics but also the failure mechanism, structure-property relationship, Joule heating dynamics, electromigration, field emission properties, etc. at the nanoscale.

The platforms holding the sample in most modern in-situ TEM holders rely on an insulating ceramic membrane which needs to be (almost) transparent to the imaging electron beam. Electrodes are defined through lithography and patterned on this membrane. Unfortunately, the presence of this membranes introduces several limitations such as electrostatic charging, reduction of image contrast and poor mechanical stability. To circumvent this issue it is necessary to fabricate a novel type of sample platform which does not rely on the presence of a membrane.

In this work, novel membraneless sample-holding platforms were designed and manufactured using advanced microfabrication methods and tools. Besides fitting into an array of analytical tools, the novel platforms (or “chips”) can be subjected to thermal and/or chemical processing without compromising their function or structure.

To test these, the electrical response of one-, two- and zero-dimensional nanoparticles were studied. Firstly, we investigated current-induced modifications in silver nanowires and expandable graphite flakes and studied various phenomenon involved. Along with these, corresponding ex-situ studies were also performed. Next, graphene oxide was explored as an alternative support platform for in-situ TEM. We successfully achieved temperature as high as 2000o C by Joule heating of graphene oxide. Furthermore, this graphene oxide platform was used as a heater and chemical processing substrate for investigating thermal stability and synthesis of inorganic nanoparticles, respectively.