Molecular Beam Epitaxy of Transition Metal (Ti-, V-, and Cr-) Tellurides: From Monolayer Ditellurides to Multilayer Self-Intercalation Compounds
Molecular Beam Epitaxy of Transition Metal (Ti-, V-, and Cr-) Tellurides: From Monolayer Ditellurides to Multilayer Self-Intercalation Compounds
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DOI：
10.1021/acsnano.0c02712
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发表时间：
2020-07-28
期刊：
影响因子：
17.1
通讯作者：
Batzill, Matthias
中科院分区：
文献类型：
--
作者：
Lasek, Kinga;Coelho, Paula Mariel;Batzill, Matthias
范德华外延材料生长技术在分离单层材料和合成超薄膜方面具有潜在的应用价值，而剥离或其他生长方法不易制备。本文研究了用分子束外延技术(MBE)在单层到少数层区域合成早期过渡金属(钛、钒、铬)碲化物。这些材料的层状双硫化物以其耐人寻味的量子和层相关性质而闻名。在这里，我们通过现场样品表征和与计算预测的比较表明，具有八面体1T结构的ML二硫代硫化物很容易生长，但对于多层膜，过渡金属二氢碳化物(TMDC)的形成与自插层化合物竞争。在较低的生长温度下，在ML区成功地合成了一种TMDC，它在体相中是亚稳定的，容易分解为插层化合物。在较高的生长温度或多层膜中，只能得到相当于块体Cr3Te4的插层化合物。ML VTe2更稳定，可以在ML区的较高生长温度下合成，但多层膜也会转化为与体相等效的V3Te4化合物。TiTe2是所研究的TMDCs中最稳定的；然而，对多层膜的详细分析也表明存在插层金属。计算表明，与钒、铬碲化物相比，碲化钛的TMDC层的插层引起的变形要小得多。这使得用扫描隧道显微镜识别插层材料对碲化钛来说更具挑战性。分子束外延生长的多层硫系化合物中自插层化合物的识别可以解释先前报道的分子束外延生长的早期过渡金属硫化物中观察到的晶格扭曲。另一方面，这些超薄极限的插层化合物本身就可以被认为是范德华材料。这类材料只能通过直接生长方法获得，但可以用作分子束外延范德华异质结的“构建块”。控制它们的生长是了解和研究这些材料性能的重要一步。
Material growth by van der Waals epitaxy has the potential to isolate monolayer (ML) materials and synthesize ultrathin films not easily prepared by exfoliation or other growth methods. Here, the synthesis of the early transition metal (Ti, V, and Cr) tellurides by molecular beam epitaxy (MBE) in the mono- to fewlayer regime is investigated. The layered ditellurides of these materials are known for their intriguing quantum- and layer dependent- properties. Here we show by a combination of in situ sample characterization and comparison with computational predictions that ML ditellurides with octahedral 1T structure are readily grown, but for multilayers, the transition metal dichalcogenide (TMDC) formation competes with self-intercalated compounds. CrTe2, a TMDC that is known to be metastable in bulk and easily decomposes into intercalation compounds, has been synthesized successfully in the ML regime at low growth temperatures. At elevated growth temperatures or for multilayers, only the intercalation compound, equivalent to a bulk Cr3Te4, could be obtained. ML VTe2 is more stable and can be synthesized at higher growth temperatures in the ML regime, but multilayers also convert to a bulk-equivalent V3Te4 compound. TiTe2 is the most stable of the TMDCs studied; nevertheless, a detailed analysis of multilayers also indicates the presence of intercalated metals. Computation suggests that the intercalation-induced distortion of the TMDC-layers is much reduced in Ti-telluride compared to V-, and Cr-telluride. This makes the identification of intercalated materials by scanning tunneling microscopy more challenging for Ti-telluride. The identification of self-intercalation compounds in MBE grown multilayer chalcogenides may explain observed lattice distortions in previously reported MBE grown early transition metal chalcogenides. On the other hand, these intercalation compounds in their ultrathin limit can be considered van der Waals materials in their own right. This class of materials is only accessible by direct growth methods but may be used as "building blocks" in MBE-grown van der Waals heterostructures. Controlling their growth is an important step for understanding and studying the properties of these materials.