Chikako Sakai

Active voltage contrast imaging of cross-sectional surface of multilayer ceramic capacitor using helium ion microscopy

We studied active voltage contrast (AVC) imaging using helium ion microscopy (HIM). We observed secondary electron (SE) images of the cross-sectional surface of multilayer ceramic capacitors (MLCCs) with and without a voltage applied to the internal electrodes. When no voltage was applied, we obtained an image reflecting the material contrast between the Ni internal electrode region and the BaTiO3 dielectric region of the cross-sectional surface of the MLCC. When a voltage was applied, the electrical potential difference between the grounded and the positively biased internal electrodes affected the contrast (voltage contrast). Moreover, attenuation of the SE intensity from the grounded to the positively biased internal electrodes was observed in the dielectric region. Kelvin probe force microscopy (KPFM) measurements of the contact potential difference (CPD) were performed on the same sample. By using the AVC image from the HIM observation and the CPD image from the KPFM measurement, we could quantitativ...

System to measure accurate temperature dependence of electric conductivity down to 20 K in ultrahigh vacuum.

We have developed the new in situ electrical-conductivity measurement system which can be operated in ultrahigh vacuum (UHV) with accurate temperature measurement down to 20 K. This system is mainly composed of a new sample-holder fixing mechanism, a new movable conductivity-measurement mechanism, a cryostat, and two receptors for sample- and four-probe holders. Sample-holder is pushed strongly against the receptor, which is connected to a cryostat, by using this new sample-holder fixing mechanism to obtain high thermal conductivity. Test pieces on the sample-holders have been cooled down to about 20 K using this fixing mechanism, although they were cooled down to only about 60 K without this mechanism. Four probes are able to be touched to a sample surface using this new movable conductivity-measurement mechanism for measuring electrical conductivity after making film on substrates or obtaining clean surfaces by cleavage, flashing, and so on. Accurate temperature measurement is possible since the sample can be transferred with a thermocouple and∕or diode being attached directly to the sample. A single crystal of Bi-based copper oxide high-Tc superconductor (HTSC) was cleaved in UHV to obtain clean surface, and its superconducting critical temperature has been successfully measured in situ. The importance of in situ measurement of resistance in UHV was demonstrated for this HTSC before and after cesium (Cs) adsorption on its surface. The Tc onset increase and the Tc offset decrease by Cs adsorption were observed.

In situ voltage-application system for active voltage contrast imaging in helium ion microscope

In this study, the authors present a new method for electrical potential observation in which helium ion microscope (HIM) observations can be performed while applying a selected voltage (up to approximately +5 V) to a sample. The in situ voltage-application system is operated in a high vacuum HIM chamber and consists of a transfer rod, tilt joint, x-, y-, and z-axis mechanisms, and two probes at the end of the transfer rod. The new system was used to acquire a secondary electron (SE) images of the cross-sectional surfaces of a multilayer ceramic capacitor (MLCC) with voltages (from 0.5 to 5 V) applied to the internal electrodes of the MLCC. The active voltage contrast corresponding to the electrical potential in the SE images could be observed when the applied voltage was less than or equal to 1.5 V. This technique enables any voltage to be applied to the samples from outside the chamber and can be used to measure the nanometer-scale electrical potential distribution of Li-ion rechargeable batteries, solar cells, etc.In this study, the authors present a new method for electrical potential observation in which helium ion microscope (HIM) observations can be performed while applying a selected voltage (up to approximately +5 V) to a sample. The in situ voltage-application system is operated in a high vacuum HIM chamber and consists of a transfer rod, tilt joint, x-, y-, and z-axis mechanisms, and two probes at the end of the transfer rod. The new system was used to acquire a secondary electron (SE) images of the cross-sectional surfaces of a multilayer ceramic capacitor (MLCC) with voltages (from 0.5 to 5 V) applied to the internal electrodes of the MLCC. The active voltage contrast corresponding to the electrical potential in the SE images could be observed when the applied voltage was less than or equal to 1.5 V. This technique enables any voltage to be applied to the samples from outside the chamber and can be used to measure the nanometer-scale electrical potential distribution of Li-ion rechargeable batteries, sola...