11:30 〜 11:45
▲ [21a-W641-10] Hysteresis of the Electrostatic Potential of (GeTe)2 Sb2Te3 Superlattice Grains Measured by Scanning Probe Spectroscopy
キーワード：chalcogenide crystal superlattice,scanning probe mycroscopy,surface potential
Interfacial phase-change memory topological materials such as (GeTe)/(Sb2Te3) superlattices (SL) have been attracting much attention as the promising candidate material for next generation of nonvolatile memory.[1] Resistivity switching in the SL films occurs through crystal-to-crystal phase transition involving displacement of atoms, and results in change of the crystal symmetry.[1] Here, to recognize an effect of external electric field, we measured the surface electrostatic potential of SL films employing the multimode scanning probe microscope (MSPM).
We measured films consisting of 11-nm-thick [(GeTe)2/(Sb2Te3)]4 prepared by sputtering on Si(001) and W(50 nm)/Si(001) substrates at 240oC. In our setup, a sharp metal tip is attached to a quartz resonator (qLER) for detecting the probe-sample force through a shift of the resonance frequency (Δf) in the non-contact mode. Change in the surface electrostatic potential of the SL films was obtained from the contact potential difference (CPD) voltage measured after applying an external voltage of 2.0 – 3.2 V to the SPM probe for 15 – 50 ms. Here, the CPD voltage was derived from Δf -Vs spectra taken in forward and backward voltage-sweep directions in a lift-off mode in ultrahigh vacuum at room temperature.
The CPD difference between forward and backward sweeps was positive and independent on the probe position along a 10-nm-thick Sb2Te3 crystal film. A hysteresis in the CPD voltage was 60 mV at an offset of 0.7 nm and ~400 mV at -0.2 nm. This fact indicates stronger polarization of the film at short distance, resembling behavior of a ferroelectric films. In a SL film on W/Si substrates, the voltage-induced polarization was negative and took place for certain grains. The work was supported by Japan Science and Technology Agency (JST/CREST).
[1] J. Tominaga et al., Adv. Mater. Interfaces 1 (2014) 1300027.
We measured films consisting of 11-nm-thick [(GeTe)2/(Sb2Te3)]4 prepared by sputtering on Si(001) and W(50 nm)/Si(001) substrates at 240oC. In our setup, a sharp metal tip is attached to a quartz resonator (qLER) for detecting the probe-sample force through a shift of the resonance frequency (Δf) in the non-contact mode. Change in the surface electrostatic potential of the SL films was obtained from the contact potential difference (CPD) voltage measured after applying an external voltage of 2.0 – 3.2 V to the SPM probe for 15 – 50 ms. Here, the CPD voltage was derived from Δf -Vs spectra taken in forward and backward voltage-sweep directions in a lift-off mode in ultrahigh vacuum at room temperature.
The CPD difference between forward and backward sweeps was positive and independent on the probe position along a 10-nm-thick Sb2Te3 crystal film. A hysteresis in the CPD voltage was 60 mV at an offset of 0.7 nm and ~400 mV at -0.2 nm. This fact indicates stronger polarization of the film at short distance, resembling behavior of a ferroelectric films. In a SL film on W/Si substrates, the voltage-induced polarization was negative and took place for certain grains. The work was supported by Japan Science and Technology Agency (JST/CREST).
[1] J. Tominaga et al., Adv. Mater. Interfaces 1 (2014) 1300027.