Bilayer transition metal chalcogenides (TMDs) have gradually attracted a great deal of attention due to the higher density of states and carrier mobility than monolayer TMDs. Controlling the uniformity of the layer number is very crucial because it will intensively influence the physical properties. However, it is difficult to synthesize equal-bilayer (EB) TMDs with two identical layers via a normal layer-by-layer strategy. Most reported bilayer TMDs are not uniform and such unequal bilayers would introduce a sizable Schottky barrier, resulting in the low carrier mobility. Here, a nucleationetching strategy is proposed to grow EB-MoSe 2 by chemical vapor deposition (CVD), which breaks the limitations of normal layer-by-layer strategy. The second layer is preferentially formed beneath the first layer rather than above, and a different etching phenomenon is also observed, which occurs more preferentially at the overlapping grain boundary sites on the top layer. The obtained EB-MoSe 2 flakes are 3R-stack with high crystal quality. Furthermore, the contact between EB-MoSe 2 and metal electrodes is greatly improved, thereby EB-MoSe 2 transistors exhibit an order of magnitude higher carrier mobility (104 cm 2 V −1 s −1 ) than that of UEB-MoSe 2 transistors (12 cm 2 V −1 s −1 ). This value is also at a relatively high level compared with reported results. Our work offers a feasible strategy for the synthesis of EB-TMDs with high carrier mobility, which is meaningful for developing highperformance 2D optoelectronic devices.

Jiamei Chen

Maolin Chen

Xing Xin

Wei Xin

Weizhen Liu

Youzhe Bao

Mengfan Ding

Peng Li

Jiangang Ma

Haiyang Xu

Yichun Liu

ACS Nano

ACS NANO 每月出版一次，是一个国际论坛，用于交流有关化学、生物学、材料科学、物理学和工程学接口的纳米科学和纳米技术研究的综合文章。此外，该期刊有助于促进这些研究社区的科学家之间的交流，以开发新的研究机会，通过新发现推进该领域，并接触各级科学家。ACS NANO 发表关于合成、组装、表征、理论和模拟纳米结构（纳米材料和组件、纳米器件和自组装结构）、纳米生物技术、纳米制造、纳米科学和纳米技术的方法和工具，以及自组装和定向组装。除了全面的原创研究文章外，ACS NANO 还提供全面的评论，对前沿研究的看法，与纳米科学和纳米技术思想领袖的对话，以及对纳米科学和纳米技术的未来提供独特观点的主题讨论。

ACS Nano is a monthly international journal that serves as a forum for the exchange of comprehensive articles on research in nanoscience and nanotechnology at the interfaces of chemistry, biology, materials science, physics, and engineering. The journal facilitates communication among scientists in these research communities to develop new research opportunities, advance the field through new discoveries, and engage scientists at all levels. ACS Nano publishes articles on the synthesis, assembly, characterization, theory, and simulation of nanostructures (including nanomaterials and components, nanodevices, and self-assembled structures), nanobiotechnology, nanofabrication, and methodologies and tools in nanoscience and nanotechnology. In addition to comprehensive original research articles, ACS Nano offers extensive reviews, perspectives on cutting-edge research, dialogues with thought leaders in nanoscience and nanotechnology, and thematic discussions that provide unique insights into the future of the field.

《ACS Nano》是一本每月出版的国际期刊，旨在交流关于化学、生物学、材料科学、物理学和工程学交叉领域的纳米科学与纳米技术研究的综合性文章。该期刊促进了研究社区科学家之间的交流，帮助开发新的研究机会，推动领域的进展，并吸引各级科学家参与。期刊内容涵盖合成、组装、表征、理论与模拟纳米结构（包括纳米材料、组件、纳米器件和自组装结构）、纳米生物技术、纳米制造、以及纳米科学与纳米技术的方法和工具。此外，《ACS Nano》还发表全面的原创研究文章，提供对前沿研究的评论，与纳米科学与纳米技术领域的思想领袖进行对话，并就纳米科学与纳米技术的未来提供独特的主题讨论。

Category	Quartile
材料科学	1
材料科学, 化学综合	1
材料科学, 物理化学	1
材料科学, 材料科学综合	1
材料科学, 纳米科技	1

Equal-Bilayer MoSe₂ Grown by a Nucleation-Etching Strategy with High Carrier Mobility

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Category	Quartile
NANOSCIENCE & NANOTECHNOLOGY	1

Equal-Bilayer MoSe2 Grown by a Nucleation-Etching Strategy with High Carrier Mobility

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Equal-Bilayer MoSe₂ Grown by a Nucleation-Etching Strategy with High Carrier Mobility