Extending in situ liquid phase transmission electron microscopy to etching of silica and the swelling-collapse of temperature sensitive polymer microgels

Abstract

The aim of the study described in this Thesis is the imaging of sensitive processes at the nanoscale, which is achieved by performing specialized experiments using either electron microscopy or light microscopy. The first set of studies (Chapters 3-5) focuses on the use of liquid cell transmission electron microscopy (LC-TEM). LC-TEM is a technique in the realm of in situ transmission electron microscopy (TEM) specialized in imaging liquid samples. TEM typically images samples suspended in high vacuum, which makes the imaging of colloidal and nanometric samples dispersed in their native state impossible. LC-TEM prevents the exposure of the liquid to the high vacuum of the microscope by encapsulating and sealing a thin liquid layer between two membranes. State of-the-art LC-TEM is performed with the use of dedicated sample holders, which not only seal the liquid layer but also allowing liquid through the sample and apply electric currents to the sample region. The development of MEMS-based chip technology as part of the encapsulation method of LC-TEM has allowed in recent years to perform in situ heating and electrochemistry experiments inside a liquid cell in real time. This research is focused at the study of processes taking place in colloidal systems happening in liquid. In the second part of this thesis described in Chapter 6, the focus of our research is switched to light microscopy. Confocal Scanning Light Microscopy (CSLM) is a technique that allows imaging of fluorescent samples by scanning a sample with a laser and rejecting out of focus light with a pinhole in the back-focal plane of the imaging lens to increase resolution. If fluorescent colloidal particles are dispersed in a solvent with a refractive index close to the refractive index of the colloids, CSLM can be used to image deep into samples and determine the mesoscopic order of colloidal systems at the single particle level.