Thermal vibration properties of nanometer-scale objects are critical for their application in devices such as nanomechanical resonators. An imaging method has been developed which allows the direct visualization of higher-order thermal vibration modes at room temperature, which have so far been inaccessible to observation due to their subangstrom amplitudes and the much stronger overlapped first mode. This technique, combining aberration-corrected scanning transmission electron microscopy with broad-band signal acquisition in the time domain, can display the amplitude distribution of several thermal vibration modes simultaneously by selecting specific frequency windows. This is showcased by mapping the first six thermal vibration modes of a singly clamped nanowire and comparing them to natural vibration mode profiles obtained by finite element calculations. This implementation furthers our understanding of the collective Brownian motion of nanostructures and extends the analysis capabilities of electron microscopy.
Keywords: High-speed signal acquisition; Nanowire; Scanning transmission electron microscopy; Thermal vibration.