Data synchronization in operando gas and heating TEM.

Time-resolved correlations of the environment, the reaction products, the energy transfer and the material structures during the reaction processes make operando gas and heating TEM more and more attractive in recent years. The time delays existing among parameter measurement locations need to be calibrated for valid correlations. Otherwise, erroneous conclusions would be drawn, such as over/under-estimating the critical temperatures, mismatching the structure and composition relationships to activities, and so on. Herein, we report on a method synchronizing the data from pre-, in- and post-TEM by measuring and calibrating the time delays involved. This method relies on the unique capability of on-chip calorimetry of the gas Nano-Reactor, which is intrinsically synchronized with the TEM imaging and spectroscopy data. The time delay is found to be dependent on the gas flow rate and pressure, and have little dependence on the gas type. A functional relationship fitted between the time delay and the gas flow rate and pressure can automate the time delay calibration and thus synchronize the data from different locations. Based on the investigations, we developed algorithms and scripts to enable the automatic data synchronization in operando gas and heating TEM in both real time experiments and post experiments.

Mapping Elevated Temperatures with a Micrometer Resolution Using the Luminescence of Chemically Stable Upconversion Nanoparticles.

The temperature-sensitive luminescence of nanoparticles enables their application as remote thermometers. The size of these nanothermometers makes them ideal to map temperatures with a high spatial resolution. However, high spatial resolution mapping of temperatures >373 K has remained challenging. Here, we realize nanothermometry with high spatial resolutions at elevated temperatures using chemically stable upconversion nanoparticles and confocal microscopy. We test this method on a microelectromechanical heater and study the temperature homogeneity. Our experiments reveal distortions in the luminescence spectra that are intrinsic to high-resolution measurements of samples with nanoscale photonic inhomogeneities. In particular, the spectra are affected by the high-power excitation as well as by scattering and reflection of the emitted light. The latter effect has an increasing impact at elevated temperatures. We present a procedure to correct these distortions. As a result, we extend the range of high-resolution nanothermometry beyond 500 K with a precision of 1-4 K. This work will improve the accuracy of nanothermometry not only in micro- and nanoelectronics but also in other fields with photonically inhomogeneous substrates.

In situ electrochemistry inside a TEM with controlled mass transport.

The field of electrochemistry promises solutions for the future energy crisis and environmental deterioration by developing optimized batteries, fuel-cells and catalysts. Combined with in situ transmission electron microscopy (TEM), it can reveal functional and structural changes. A drawback of this relatively young field is lack of reproducibility in controlling the liquid environment while retaining the imaging and analytical capabilities. Here, a platform for in situ electrochemical studies inside a TEM with a pressure-driven flow is presented, with the capability to control the flow direction and to ensure the liquid will always pass through the region of interest. As a result, the system offers the opportunity to define the mass transport and control the electric potential, giving access to the full kinetics of the redox reaction. In order to show the benefits of the system, copper dendrites are electrodeposited and show reliable electric potential control. Next, their morphology is changed by tuning the mass transport conditions. Finally, at a liquid thickness of approximately 100 nm, the diffraction pattern revealed the 1,1,1 planes of the copper crystals, indicating an atomic resolution down to 2.15 Å. Such control of the liquid thickness enabled elemental mapping, allowing us to distinguish the spatial distribution of different elements in liquid.

Enabling nanoscale flexoelectricity at extreme temperature by tuning cation diffusion.

Any dielectric material under a strain gradient presents flexoelectricity. Here, we synthesized 0.75 sodium bismuth titanate -0.25 strontium titanate (NBT-25ST) core-shell nanoparticles via a solid-state chemical reaction directly inside a transmission electron microscope (TEM) and observed domain-like nanoregions (DLNRs) up to an extreme temperature of 800 °C. We attribute this abnormal phenomenon to a chemically induced lattice strain gradient present in the core-shell nanoparticle. The strain gradient was generated by controlling the diffusion of strontium cations. By combining electrical biasing and temperature-dependent in situ TEM with phase field simulations, we analyzed the resulting strain gradient and local polarization distribution within a single nanoparticle. The analysis confirms that a local symmetry breaking, occurring due to a strain gradient (i.e. flexoelectricity), accounts for switchable polarization beyond the conventional temperature range of existing polar materials. We demonstrate that polar nanomaterials can be obtained through flexoelectricity at extreme temperature by tuning the cation diffusion.

Advanced microheater for in situ transmission electron microscopy; enabling unexplored analytical studies and extreme spatial stability.

In this work we present our advanced in situ heating sample carrier for transmission electron microscopy (TEM). The TEM is a powerful tool for materials characterization, especially when combined with micro electro-mechanical systems (MEMS). These deliver in situ stimuli such as heating, in which case temperatures up to 1300 °C can be reached with high temporal stability without affecting the original TEM spatial resolution: indeed, atomic resolution imaging can be routinely performed. Previously, the thermal expansion of suspended microheaters caused vertical displacement of the sample (bulging). As a result, changing temperatures required either continuous focus or stage adjustments, inducing resolution loss or mechanical drift, respectively. Moreover, those actions hinder the possibility to capture fast dynamic events. This new MEMS-based sample carrier, however, keeps the sample at constant z-position (no bulging) up to 700 °C. Furthermore, it enables energy dispersive x-ray spectroscopy (EDS) acquisition in the TEM up to an unmatched temperature of 1000 °C, with a drift rate down to 0.1 nm/min. Its viewable area of 850 µm2 features a temperature homogeneity up to 99.5%.