The electronic and magnetic properties of transition metal dichalcogenides are known to be extremely sensitive to their structure. In this paper we study the effect of structure on the electronic and magnetic properties of mono- and bilayer $\mathrm{V}{\mathrm{Se}}_2$ films grown using molecular beam epitaxy. $\mathrm{V}{\mathrm{Se}}_2$ has recently attracted much attention due to reports of emergent ferromagnetism in the two-dimensional (2D) limit. To understand this compound, high-quality $1T$ and distorted $1T$ films were grown at temperatures of 200 °C and 450 °C, respectively, and studied using 4 K scanning tunneling microscopy and spectroscopy. The measured density of states and the charge density wave (CDW) patterns were compared to band structure and phonon dispersion calculations. Films in the $1T$ phase reveal different CDW patterns in the first layer compared to the second. Interestingly, we find the second layer of the $1T$ film shows a CDW pattern with $4a\times 4a$ periodicity which is the 2D version of the bulk CDW observed in this compound. Our phonon dispersion calculations confirm the presence of a soft phonon at the correct wave vector that leads to this CDW. In contrast, the first layer of distorted $1T$ phase films shows a strong stripe feature with varying periodicities, while the second layer displays no observable CDW pattern. Finally, we find that the monolayer $1T \mathrm{VS}{\mathrm{e}}_2$ film is weakly ferromagnetic, with ∼3.5 ${\mu }_B$ per unit similar to previous reports.

中文翻译：

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外延VSe2薄膜的结构，电子和磁性相关

已知过渡金属二卤化物的电子和磁性对它们的结构极为敏感。在本文中，我们研究了结构对单层和双层电子和磁性性质的影响$\mathrm{V}{硒}_2$ 使用分子束外延生长的薄膜。 $\mathrm{V}{硒}_2$由于出现了二维（2D）极限中的强铁磁性的报道，近来引起了很多关注。要了解这种化合物，高质量$\mathrm{1个}Ť$ 扭曲了 $\mathrm{1个}Ť$薄膜分别在200°C和450°C的温度下生长，并使用4 K扫描隧道显微镜和光谱学进行研究。将测得的状态密度和电荷密度波（CDW）模式与能带结构和声子色散计算进行了比较。电影中的$\mathrm{1个}Ť$与第二阶段相比，第一阶段显示出不同的CDW模式。有趣的是，我们发现$\mathrm{1个}Ť$ 影片显示CDW模式 $4\mathrm{一种}\times 4\mathrm{一种}$周期性，是此化合物中观察到的大体CDW的2D版本。我们的声子色散计算确定了导致该CDW的正确波矢处存在软声子。相比之下，第一层扭曲$\mathrm{1个}Ť$相膜显示出周期性变化的强条纹特征，而第二层则没有可见的CDW图案。最后，我们发现单层$\mathrm{1个}Ť \mathrm{VS}{\mathrm{Ë}}_2$ 薄膜是弱铁磁的，约为3.5 ${\mu }_{乙}$ 每单位类似于以前的报告。