Jiang Yan, Baben Moritz To, Lin Yuankun, Littler Chris, Syllaios A J, Neogi Arup, Philipose Usha
Department of Physics, University of North Texas, Denton, TX 76203, United States of America.
GTT-Technologies, D-52134 Herzogenrath, Germany.
Nanotechnology. 2021 Mar 25;32(24). doi: 10.1088/1361-6528/abedf0.
Though the positive role of alkali halides in realizing large area growth of transition metal dichalcogenide layers has been validated, the film-growth kinematics has not yet been fully established. This work presents a systematic analysis of the MoSmorphology for films grown under various pre-treatment conditions of the substrate with sodium chloride (NaCl). At an optimum NaCl concentration, the domain size of the monolayer increased by almost two orders of magnitude compared to alkali-free growth of MoS. The results show an inverse relationship between fractal dimension and areal coverage of the substrate with monolayers and multi-layers, respectively. Using the Fact-Sage software, the role of NaCl in determining the partial pressures of Mo- and S-based compounds in gaseous phase at the growth temperature is elucidated. The presence of alkali salts is shown to affect the domain size and film morphology by affecting the Mo and S partial pressures. Compared to alkali-free synthesis under the same growth conditions, MoSfilm growth assisted by NaCl results in ≈81% of the substrate covered by monolayers. Under ideal growth conditions, at an optimum NaCl concentration, nucleation was suppressed, and domains enlarged, resulting in large area growth of MoSmonolayers. No evidence of alkali or halogen atoms were found in the composition analysis of the films. On the basis of Raman spectroscopy and photoluminescence measurements, the MoSfilms were found to be of good crystalline quality.
尽管碱金属卤化物在实现大面积生长过渡金属二硫属化物层方面的积极作用已得到验证，但薄膜生长动力学尚未完全确立。这项工作对在氯化钠（NaCl）对衬底进行各种预处理条件下生长的薄膜的钼硫形态进行了系统分析。在最佳NaCl浓度下，与无碱生长的MoS相比，单层的畴尺寸增加了近两个数量级。结果表明，分形维数与单层和多层衬底的面积覆盖率分别呈反比关系。使用Fact-Sage软件，阐明了NaCl在确定生长温度下气相中基于钼和硫的化合物的分压方面的作用。结果表明，碱金属盐的存在通过影响钼和硫的分压来影响畴尺寸和薄膜形态。与相同生长条件下的无碱合成相比，NaCl辅助的MoS薄膜生长导致约81%的衬底被单层覆盖。在理想生长条件下，在最佳NaCl浓度下，成核受到抑制，畴扩大，从而实现了MoS单层的大面积生长。在薄膜的成分分析中未发现碱或卤素原子的迹象。基于拉曼光谱和光致发光测量，发现MoS薄膜具有良好的晶体质量。
