High-Temperature and High-Speed Atomic Force Microscopy Using a qPlus Sensor in Liquid via Quadpod Scanner and...

Atomic-resolution imaging on molten metal/solid interfaces at temperatures above $200{}^{\circ }C$ was achieved using a high-temperature, high-speed atomic force microscope (AFM) equipped with a qPlus sensor. A tip-scanning high-speed Quadpod scanner for a large mass load of qPlus sensor ( $2.3g$ ) was developed to enhance thermal drift tolerance by high-speed scanning and thermal insulation from the heated specimen. This scanner has dominant resonant frequencies of $7.05\mathrm{kHz}$ (lateral) / $29.7\mathrm{kHz}$ (vertical) without a load. In addition, the Hybrid-Loop frequency demodulation technique for low-resonant-frequency ( $f_0$ ) sensors with a wider bandwidth than conventional phase-locked loop was also established, providing a demodulation bandwidth of $B_{\Delta f_{\mathrm{inst}}}\sim 0.26f_0$ without exceeding the theoretical noise of the input deflection signal. Combining these techniques enabled atomic-resolution imaging on the molten Ga/ ${\mathrm{PtGa}}_x$ interface at $\sim 210{}^{\circ }C$ . The topographic images obtained at $\sim 210{}^{\circ }C$ showed a relatively low-symmetry surface with an oblique lattice with a superstructure, which differed from the primitive rectangular lattice observed in the non-heated sample left at room temperature for $96h$ . This demonstrates that the developed high-temperature, high-speed AFM techniques for qPlus sensors enable visualization of non-aqueous liquid/solid interfaces above $200{}^{\circ }C$ at atomic resolution, which has various potential applications, such as injection modeling, soldering, and the fabrication of liquid-metal-based catalysts.