This thesis investigates the integration of Transmission Electron Microscopy (TEM), Microelectromechanical Systems (MEMS)-based heaters, and Photonic Crystals (PhCs) for advanced materials characterization at the nanoscale. TEM is paired with MEMS-based microheaters to enable in-situ temperature control during atomic-resolution imaging, facilitating the study of temperature-dependent material properties. The work focuses on the fabrication of MEMS-based microheaters and the development of thin electron-transparent membranes using backside electron-beam lithography, allowing precise control over the heating process and enabling new capabilities in TEM experiments. Additionally, MEMS-based nanoreactors are designed for high-pressure in-situ TEM studies, providing insights into gas-material interactions and catalytic processes under realistic environmental conditions.

The thermal tuning of PhC cavities using elastomeric infills is also explored, demonstrating the potential for temperature-responsive optical devices. Finally, the integration of cathodoluminescence (CL) spectroscopy with TEM for the study of nitrogen-vacancy (NV) centres in diamond photonic crystals is presented, with a focus on overcoming challenges in fibre-diamond coupling and optimizing experimental conditions for NV detection.

This work advances the field of materials science, offering innovative solutions for high-resolution imaging, photonic device development, and their applications.

We present a technique to fabricate ultrathin (down to 20 nm) uniform electron transparent windows at dedicated locations in a SiN membrane for in situ transmission electron microscopy experiments. An electron-beam (e-beam) resist is spray-coated on the backside of the membrane in a KOH-etched cavity in silicon which is patterned using through-membrane electron-beam lithography. This is a controlled way to make transparent windows in membranes, whilst the topside of the membrane remains undamaged and retains its flatness. Our approach was optimized for MEMS-based heating chips but can be applied to any chip design. We show two different applications of this technique for (1) fabrication of a nanogap electrode by means of electromigration in thin free-standing metal films and (2) making low-noise graphene nanopore devices.

We have performed a range of in situ heating experiments of polycrystalline Bi films of 22-25 nm-thickness in a transmission electron microscope (TEM). This shows that it is possible to locally transform a polycrystalline thin film into a [111]-oriented single-crystalline film, whereby the unique feature is that the original thickness of the film is maintained, and the substrate used in our experiments is amorphous. The single-crystalline areas have been created by heating the Bi film to temperatures close to the melting temperature with additional heating by focusing of the electron beam (e-beam), which results in local melting of the film. The film does not collapse by dewetting, and upon subsequent cooling, the film transforms into a single-crystalline [111] oriented area. The observed phenomenon is attributed to the presence of a thin Bi-oxide layer on top of Bi film. We show that removal of the Bi-oxide layer by heating the film in a H₂ gas atmosphere results in changes in the Bi film thickness and dewetting upon in situ heating in the TEM.

In-situ TEM studies using an environmental cell (nanoreactor) play an important role in not just giving an understanding the corrosion mechanisms at a sub-micron scale, but also on the influence of heat-treatment on the microstructural change and corrosion behaviour of these alloys. One of the main requirements of for these in-situ TEM studies is the leak tightness of the nanoreactor. This is achieved by gluing the top and the bottom chips together with water glass or commercially available cyanoacrylate compounds. The drawback of this method is the chips are inseparable after the in-situ TEM study, making it impossible to carry out any further investigations on the same specimen. To overcome this drawback, we worked on upgrading the nanoreactor by redesigning the TEM holder to avoid gluing. This made it possible not only to assemble the nanoreactors in a more reliable way but also separate the two halves after the in-situ TEM study. This has opened up opportunities to carry out investigations like tomography, AFM measurements and other surface characterization studies on the same specimen, adding more to the mechanisms observed from the in-situ TEM studies.