Simultaneous Observation of Surface Morphology and Dielectric Properties using Non-Contact Scanning Nonlinear Dielectric
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0966-T09-08
Simultaneous Observation of Surface Morphology and Dielectric Properties using NonContact Scanning Nonlinear Dielectric Microscopy with Atomic Resolution Ryusuke Hirose and Yasuo Cho R. I. E. C., Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, 980-8577, Japan
ABSTRACT Recently, we have developed Non-Contact Scanning Nonlinear Dielectric Microscopy (NC-SNDM) with a new height-control technique utilizing higher order nonlinear dielectric constant detection (ε(4) signal). In theoretically, NC-SNDM has quite high height sensitivity against the gap between tip and sample as well as STM technique and the simultaneous observation of the topography and ferroelectric polarization (local dipole moment) distribution with atomic resolution has been expected. To confirm such performance of NC-SNDM with atomic resolution, UHV-SNDM was developed and Si(111) cleaned surface was chosen as a specimen. As a result, we have succeeded in observing Si(111) 7x7 atomic structure. Moreover, distribution of tunneling current and lowest order nonlinear dielectric signal ε(3) could be observed simultaneously. To the best our knowledge, this is the first successful demonstration of the atomic resolution achievement in dielectric microscopy techniques.
INTRODUCTION Scanning Nonlinear Dielectric Microscopy (SNDM) has been developed as the technique for observing the local dielectric properties of material surface. This microscopy can measure the higher order nonlinear dielectric constants ε(4) and ε(5) as well as the lowest order nonlinear dielectric constant ε(3) which contains the polarization information [1, 2]. Recently, we have developed Non-Contact Scanning Nonlinear Dielectric Microscopy (NC-SNDM) [3]. NCSNDM utilizes the higher-order nonlinear dielectric signal ε(4) for control of the non-contact state (tip-sample gap control), and simultaneous detection of the lowest order nonlinear dielectric constant, ε(3), and the linear dielectric constant, ε(2). Thus, NC-SNDM can observe both topography and dielectric properties of materials including insulators. From calculated results, it has been expected that NC-SNDM has higher sensitivity to the gap between a tip and a specimen than Scanning Tunneling Microscopy (STM), and will also have lateral atomic resolution. However, there have been theoretical reports that deny atomic resolution in dielectric microscopy techniques including Scanning Capacitance Microscopy (SCM) [4, 5]. In this paper, we have developed a NC-SNDM system operated in ultra-high vacuum, in order to prove that NC-SNDM has a real atomic resolution. Using this microscopic technique, we have succeeded in observing the Si(111)7×7 atomic structure.
PRINCIPLE The system diagram of the NC-SNDM apparatus is shown in Figure 1. The metal probe is connected to the inductance and capacitance (LC) resonator and the probe oscillator is tuned to this resonance frequency. As an alternating electric field Ep (= Epcos(ωp)) is applied between the probe tip and the lower electrode of the specimen, the oscillating frequency of
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