## 4 Conclusions  
In conclusion, we have demonstrated the synthesis of NbSe\({}_{2}\) flakes by the CVD approach via specifically controlled Se source distance from the center of the quartz (dSe) and the carrier gas ratio (H\({}_{2}\):N\({}_{2}\)). Concerning these efforts, we had successfully grown the NbSe\({}_{2}\) flakes with highly uniform, good shape distribution, controlling layers from 2 to 10 layers. Together, we proposed the NbO\({}_{\rm x}\)/NbSe\({}_{2}\) heterostructure memristor device based on the native NbO\({}_{\rm x}\) oxide on the interface of NbSe\({}_{2}\) flakes. Here, the NbO\({}_{\rm x}\) oxide layer acts as a memristive surface in the Au-NbO\({}_{\rm x}\)-Au lateral memristor device, in which oxygen vacancies form a conductive filament. Our memristor shows an LRS/HRS ratio of 20 and stable cyclic endurance properties at a low working voltage of 1 V. Furthermore, by retention test, non-volatile characteristics were confirmed at 3000 s. This systematic study of the NbO\({}_{\rm x}\)/NbSe\({}_{2}\) heterostructured memristor device is expected to open the possibilities of a viable next-generation memory device. Figure 4: NbO\({}_{\rm x}\)/NbSe\({}_{2}\) van der Waals memristive memory properties. (**a**) The schematic image of the NbO\({}_{\rm x}\)/NbSe\({}_{2}\) heterostructure memristor. On top of the multi-layer NbSe\({}_{2}\), NbO\({}_{\rm x}\) was formed. (**b**) Optical microscope image and corresponding atomic force microscopy (AFM) mapping images of the intrinsic NbSe\({}_{2}\) flake (top panel) and NbO\({}_{\rm x}\)-formed NbSe\({}_{2}\) flake (bottom panel). (**c**) The height profile of NbO\({}_{\rm x}\)/NbSe\({}_{2}\) and NbSe\({}_{2}\) heterostructures. It is increased by about 2 nm compared to intrinsic flakes (12 nm), which can prove the formation of the NbO\({}_{\rm x}\). (**d**) Typical current\(-\)voltage curves of the memristor. The inset figure is the corresponding memristor device. (**e**) Endurance characteristics against repeated resistance switching cycles under 0.1 V read voltage. (**f**) Retention properties of the memristor under 0.01 V read voltage. Non-volatile properties were observed over 3 min without any resistance switching. (**g**) Schematics of memristive switching mechanism by conductive filament formation and rupture processes via migration of oxygen vacancies. (**h**) Hysteresis variation of the NbO\({}_{\rm x}\)/NbSe\({}_{2}\) hetero memory device according to the oxidation period of the NbSe\({}_{2}\) flake in the air. **Supplementary Materials:** The following are available online at [[http://www.mdpi.com/2076-3417/10/21/7598/s1](http://www.mdpi.com/2076-3417/10/21/7598/s1)]([http://www.mdpi.com/2076-3417/10/21/7598/s1](http://www.mdpi.com/2076-3417/10/21/7598/s1)), Figure S1: The CVD growth condition for NbSe2 flakes; Figure S2: Raman mapping image according to E2g mode at 250 cm\({}^{-1}\) of the CVD-grown NbSe2; Figure S3: CVD NbSe2 growth tendency according to the optimization of carrier gas ratio (N2:H2); Figure S4: Electrical characteristics of various other CVD-grown NbSe2 flakes; Figure S5: The oxidization effect of the thin CVD-grown NbSe2 flake; Figure S6: Formation of channels in a memristor device structured with NbOx/NbSe2 heterostructure; Figure S7: Retention properties of the NbOx/NbSe2 memristor under 0.01-V read voltage; Figure S8: I-V curves of NbOx/NbSe2 memory devices, displayed on a double-logarithmic scale; Figure S9: I-V characteristic of NbOx/NbSe2 heterostructure memristor along with the influence of oxidation time (0-24 days); Figure S10: Electrical comparison of memristor under vacuum and ambient condition. Supplementary Note 1: Explanation of the conduction mechanism of our NbOx/NbSe2 memory device based on the SCLC mechanism; Supplementary Note 2: Explanation of the relationship between the exposure time and device performance. **Author Contributions:** Conceptualization, J.E.K., V.T.V., T.T.H.V., T.L.P. and W.J.Y. ; Data curation, J.E.K., V.T.V., T.T.H.V., T.L.P. and W.J.Y.