Non-volatile Bipolar Resistive Memory Switching inSingle Crystalline NiO Heterostructured Nanowires
Keisuke Oka, Takeshi Yanagida*, Kazuki Nagashima, Hidekazu Tanaka and Tomoji Kawai*.
Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 5670047 (Japan)
E-mail: yanagi32@sanken.osaka -u.ac.jp, kawai@sanken.osaka-u.ac.jp.
Supporting Information

Intensity (a.u.)

MgO
(200)

20NiO
(200)
42.7

30

40

50

43.0

60

43.3

70

80

2θ (degree)
Figure S1. XRD data of the NiO/MgO heterostructured nanowires grown on MgO (100) single
crystal substrate. The NiO shell layer was formed at 10 Pa of the oxygen pressure and 800oC of thegrowth temperature.

Figure S1 shows the XRD data of the NiO/MgO heterostructured nanowires grown on MgO (100)single crystal substrate. The formation conditions for the NiO shell layers were 10 Pa of the oxygenpressure and 800oC of the growth temperature, respectively. The presence of the NiO (200) peak clearly
indicates the preferential orientation of the NiO heterostructured nanowires along the direction

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perpendicular to the MgO single crystal substrate. Thus the NiO shell layers were epitaxially grown onthe MgO core nanowires. The single crystalline nature of NiO heterostructured nanowires was further
confirmed by performing the high-resolution TEM analysis as shown in Figure S2. The HRTEM image
clearly indicates the single crystalline nature of fabricated NiO heterostructured nanowires.

(a)

(b)
MgO

50nm

NiO

Figure S2. HRTEM images of NiO/MgO heterostructured nanowire.

Figure S3. Schematic diagram of C-AFM measurement system.
Figure S3 shows the schematic diagram of C-AFM measurements employed. The used cantilever wasconductive Ir/Pt coated Si (Nanoworld). The C-AFM measurements were performed at the nanowire
position around 1000nm away from Pt electrode. The Pt electrode was fabricated by using the mask ofcleavage Si substrate. The external resistance (1GΩ) was used to prevent the permanent breakdown ofS2

the NiO heterostructured nanowires when SET occurs. The C-AFM measurements were always
performed after confirming the exact location of the NiO heterostructured nanowires using nondestructive tapping-mode. The typical cross-sectional area of NiO in the heterostructured nanowires
was 10-3µm2. The formation conditions for NiO shell layers were 300C of the growth temperature and0.1Pa of the oxygen pressure, considering the NiO conductivity in previous investigations using NiOhetero-thin films 20. We have performed several experiments to confirm the occurrence of the resistive
switching within the NiO layer. First, the I-V measurement between the substrate and the electrode wasperformed, which exhibited only noise-level current below 10-12A. Second, the I-V measurement usingmore conductive NiO layer grown under reduced atmosphere (300C of the temperature and 10-3Pa of theoxygen pressure: see also the reference 18) was performed. We confirmed the bipolar resistive switchingwith the lower ON/OFF ratio and the increase of the measured current on the OFF state. This resultclearly indicates the contribution of NiO layer conductivity on the measured I-V data. Third, the I-V
measurement on bare MgO nanowire was performed. Only noise-level current below 10-12A wasobtained due to the insulating nature of MgO. In addition, the initial resistance of the device- 1011Ω wasalmost consistent with the resistance estimated theoretically from the NiO thin film resistivity. 18
Furthermore the switching electric field of the nanowire device was almost consistent with the switching
electric field of the NiO epitaxial thin film devices with the bipolar switching. Thus these experimental
results consistently indicate the occurrence of the resistive switching within the NiO layer. Figure S4
shows the I-V curves for two cycles, the retention and the endurance data of the device. The retention
time was at least over 104s, and the endurance was confirmed for 6 cycles until the Pt coating on theAFM tip was deteriorated due to applying the high voltage sweep. These data clearly indicate the nonvolatile memory effect of the device. The switching is not a threshold switching, in which there is nonon-volatile memory effect. In such case, the resistance of the device is always high once after theapplied voltage was stopped. On the other hand, in our case after the SET process, the low resistance ofthe device was kept as long as the voltage sweep was performed on the same polarity. This memory
effect was kept even if the voltage sweep was applied once after the applied voltage was stopped. Once

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applying the inverse polarity voltage sweep, the RESET process appeared. Thus observed phenomenon
is a bistable memory switching.
(a)

(b)

(c)
(a)

1011

Resistance (ƒ )¶Resistance (ƒ )¶1012

Off state

1010
109
108 0
10

On state

101102

103

104

Time (second)1012 (b)Off state

1011
1010
109

On state

108 012 3
4 56
Number of Cycle (#)

7Figure S4. I-V curves, retention and endurance data of the device.

Supporting information in References(4)Kim, D. C.; Seo, S.; Ahn, S. E.; Suh, D.–S.; Lee, M. J.; Park, B.-H.; Yoo, I. K.; Baek, I. G.; Kim,H.-J.; Yim, E. K.; Lee, J. E.; Park, S. O.; Kim, H. S.; Chung, U-In.; Moon, J. T.; Ryu, B. I. Appl.
Phys. Lett. 2006, 88, 202102.

(14)

Ahn, S.-E.; Lee, M.-J.; Park, Y.; Kang, B. S.; Lee, C. B.; Kim, K. H.; Seo, S.; Suh, S.-S.; Kim
D.-C.; Hur, J.; Xianyu, W.; Stefanovich, G.; Yin, H.; Yoo, I.-K.; Lee, J.-H.; Park, J.-B.; Baek, I.G.; Park, B. H. Adv. Mater. 2008, 20, 924-928.

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