The development of commercially available flexible and wearable devices requires low‐operating‐voltage circuit and resistive random access memory (RRAM). This paper reports the preparation and performances of low‐operating‐voltage RRAM based on the interlayer‐spacing regulation of MoSe2. Twine‐jumble‐like MoSe2 clusters were synthesized via hydrothermal method. The average interlayer spacing in the clusters is higher than the value for bulk MoSe2 by 9.969%. The layer count of the MoSe2 sample predicted according to the experimental value of in the Raman spectroscopy is 1.403 while it is 2 regarding the characteristic of A1g peak and the existence of B2g peak, which is inconsistent with the results of scanning electron microscope and transmission electron microscope. Calculation of van der Waals force reveals that the twine‐jumble‐like MoSe2 should not be considered as a bi‐layer (or few‐layer) crystal, but as a cluster consisting of a numerous monolayer crystals. Compared with the conventional nanosized MoSe2, the SET/RESET voltages of the RRAM device based on the monolayer MoSe2 clusters are decreased by 4–10 times while the switching ratio and endurance are increased by 2–40 and 2–10 times respectively, which is due to that the interstitial radius in the monolayer MoSe2 clusters is higher than that of a silver ion.

To meet the need for preparing high-performance nano-optoelectronic devices based on single-layer MoS2, the effects of the heating method (one-step or two-step heating) and the temperature of the MoO3 source on the morphology, size, structure, and layers of an MoS2 crystal grown on a sapphire substrate using chemical vapor deposition are studied in this paper. The results show that MoS2 prepared by two-step heating (the heating of the S source starts when the temperature of the MoO3 source rises to 837 K) is superior over that of one-step heating (MoO3 and S are heated at the same time). One-step heating tends to form a mixture of MoO2 and MoS2. Neither too low nor too high of a heating temperature of MoO3 source is conducive to the formation of MoS2. When the temperature of MoO3 source is in the range of 1073 K to 1098 K, the size of MoS2 increases with the rise in temperature. A uniform large-sized triangle with a side length of 100 μm is obtained when the heating temperature of MoO3 is 1098 K. The triangular MoS2 crystals grown by the two-step heating method have a single-layer structure.

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