Meso-scale Nondestructive Observation System of Self-organized Dislocation Network using Scanning Electron Acoustic Microscopy

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In order to investigate internal structures generated by self-organized dislocation network in various kinds of materials and loading states, we have developed a nondestructive observation system using acoustic wave by the electron beam. In this system, heat wave is firstly generated on the surface of the specimen by the irradiation of blanking and focused electron beam of the Scanning Electron Microscope (SEM). Then the heat wave is transferred into sound wave, and it propagates within the specimen as elastic wave. Difference of the local thermal property of the material is converted into an electric signal by a piezoelectric transducer (PZT) attached onto the back side of the specimen. This system is called the scanning electron acoustic microscopy (SEAM). It makes us enable to observe both the surface of the specimen by SEM mode and the nondestructive inside structure by SEAM. A commercial amplifier is not enough to detect the electric signals by the PZT, because these signals are very feeble and high frequency. We developed a newly head amplifier using transistors. This head amplifier transforms an impedance and amplifies the electric signals. And we used an instrumentation amplifier to eliminate the noises from detected signals. Then the detected signals are amplified by a lock-in amplifier synchronized to the blanking frequency of an electron beam. The performance of this developed head amplifier seems to be excellent and it makes us enable to detect the electron acoustic signals sufficiently.We obtained ultrasonic signal by the SEAM using the Diamond Like Carbon (DLC) thin film laminated on single crystalline silicon wafer. And we developed a portrayal system that draws these signals as two dimensional phase-contrast images on the display.