Type of event:
Audience / Guests:
Yasuo Cho (Research Institute of Electrical Communication, Tohoku University, Sendai 980-8577, Japan)
In recent years, Prof. Cho’s group has developed and reported the use of scanning nonlinear dielectric microscopy (SNDM) for the measurement of the microscopic distribution of dielectric polarization. Since the technique senses the dielectric polarity of the specimen at the atomic scale, it can resolve a single electric dipole moment of an atom.
In this presentation, SNDM with super-high resolution is reported. First, non-contact SNDM (NC-SNDM) is proposed. Using NC-SNDM, the electric dipole moment distribution of Si atoms on Si(111)7x7 surface can be observed by NC-SNDM under ultrahigh vacuum conditions. The dc-bias voltage dependence of the atomic dipole moment on Si(111)7x7 surface was measured and the directions and the magnitudes of dipole moments of Si atoms on the surface were revealed. Moreover, a method based on tip-sample capacitance detection and bias feedback is proposed which is only sensitive to polarization- or dipole-induced potentials, unlike Kelvin probe force microscopy. This method is called scanning nonlinear dielectric potentiometory (SNDP). Using SNDP, pristine and hydrogen-intercalated graphene synthesized on a 4H-SiC(0001) substrate were investigated. Permanent dipole moments were detected at the pristine graphene-SiC interface. These originate from the covalent bonds of carbon atoms of the so-called buffer layer to the substrate. Hydrogen intercalation at the interface eliminates these covalent bonds and the original quasi-(6 × 6) corrugation, which indicates the conversion of the buffer layer into a second graphene layer by the termination of Si bonds at the interface. SNDP images suggest that a certain portion of the Si dangling bonds remains even after hydrogen intercalation. These bonds are thought to act as charged impurities reducing the carrier mobility in hydrogen-intercalated graphene on SiC.
Next, as an application of SNDM, an ultrahigh-density ferroelectric data storage system using SNDM as a pickup device is presented that uses congruent lithium tantalate single crystals as a ferroelectric recording medium. A summarization made up of newest experimental data for ferroelectric high-density data storage is reported.
Yasuo Cho graduated in 1980 from Tohoku University with a degree in electrical engineering. In 1985 he became a research associate at the Research Institute of Electrical Communication at Tohoku University. In 1990, he received an associate professorship from Yamaguchi University. He then became an associate professor in 1997 and a full professor in 2001 at the Research Institute of Electrical Communication at Tohoku University. During this time, his main research interests included nonlinear phenomena in ferroelectric materials and their applications, research on scanning nonlinear dielectric microscopy (SNDM), and research on using SNDM in next-generation ultrahigh density ferroelectric data storage (SNDM ferroelectric probe memory).