二维二碲化钒的化学气相沉积法制备及电、磁性能研究

Layered material VTe2 has distinct physical properties, such as room temperature ferromagnetism and charge density wave (CDW) phase transition. It is an ideal platform for studying two-dimensional (2D) magnetism and magneto-optical and magneto-electrical properties. However, the preparation of few layer and monolayer VTe2 has rarely been reported. The lack of preparation methods seriously hinders the study of its physical properties, especially magnetic properties. A sublimed-salt assisted low-temperature chemical vapor deposition method will be developed in this project. By optimizing the growth parameters, understanding the relationship of growth parameters with the growth process, large-area, high-quality, few-layer and single-layer VTe2 crystals will be grown. Based on the those few-layer and monolayer VTe2, Hall devices will be fabricated. And the electrical and magnetic properties of VTe2 with different thickness will be measured. The intrinsic electrical and magnetic properties of VTe2 will be studied. The relationship of Curie temperature with thickness of VTe2 will be studied, and the influence of thickness on its magnetism will be explored. The CDW phase transition mechanism will be further explored by precisely characterization of its structure before and after phase transition, and the relationship between magnetism and CDW phase transition will be explored. Finally, the magnetic properties of VTe2 will be tuned by doping of other elements. This project will be of great significance to the preparation of 2D magnetic nanomaterials and the development of spintronics.

层状材料VTe2具有室温铁磁序及电荷密度波（CDW）相变等丰富的物理特性，是研究二维磁性，及磁-光、磁-电器件的理想平台。然而，少层及单层VTe2的制备鲜有报道，制备方法的缺失严重阻碍其物性尤其铁磁性的研究。本课题将开发一种升华盐辅助低温化学气相沉积法，通过优化生长条件，深入理解各生长参数对其生长过程的影响，最终实现大面积、高质量、少层及单层VTe2的制备。基于少层及单层的VTe2，构筑霍尔器件，用物性测量系统（PPMS）对不同厚度VTe2进行电学、磁学测试，研究其本征电学磁学性质等，解决VTe2的铁磁居里温度与其厚度的相关性，探明二维尺度对其铁磁性的影响。结合CDW相变前后结构的精确表征探明其相变机理，理清铁磁性与CDW相变的关系。最后，通过掺杂实现对VTe2的磁性与CDW相变的调控。本研究将对促进二维铁磁性纳米材料的制备及自旋电子学的发展具有重要意义。

层状VTe2材料具有室温铁磁及性电荷密度波等丰富的物理特性，是研究二维材料物性的理想平台，引起了研究人员的广泛关注与兴趣。本项目采用升华盐辅助化学气相沉积法制备了层状VTe2单晶纳米片，并对其结构进行了表征。低温电输运测试发现，该二维层状晶体低温下无长程磁序，表现出近藤效应输运特性，表明该材料存在局域磁矩。第一性原理计算表明，局域磁矩由VTe2晶体层间插入的钒离子导致。此外，通过升华盐辅助化学气相沉积法，我们发现并制备了一类新型的层状二维铁硫族化合物晶体（FeSe2和FeTe2）并对他们的低温输运特性进行了研究。发现纯相的层状二维FeSe2晶体表现出金属性，同时该晶体在低温11K左右会发生相变。最后，我们进一步扩展了升华盐辅助化学气相沉积法，将传统的磁性物质Fe3O4制备成超薄二维结构。该超薄二维Fe3O4纳米晶体具有高温亚铁磁性，居里温度高达858K，与块体材料相当，说明随着厚度的降低，其居里温度未发生明显下降。这为二维磁性研究以及反常霍尔效应的研究提供了很好的材料基础。