Direct scanning tunneling microscope detection of laser induced ultrasonic pulses with nanometer resolution

We show the use of scanning tunneling microscope (STM) with a self-designed wide-bandwidth current preamplifier (50 MHz) for direct registration of ultrasonic pulses induced by nanosecond laser pulses in substrate. The changes in tip–sample separation caused by ultrasonic vibrations are seen as perturbations in tunneling current. At moderate incident laser pulse energy of 1–2 mJ ultrasonic waves in glass rod and silica wafer were observed. This wide-band signal, low noise registration in addition with nanometer spatial resolution of a STM opens new possibilities in investigations of ultrasonic near-field distribution, elastic material properties on a nanometer scale, and measurements of the ultrasound velocity in laser ultrasonics.