| 摘要: | 隨著摩爾定律逐漸逼近物理極限，傳統藉由電晶體幾何微縮以提升效能的策略，受到量子穿隧、短通道效應與功耗密度等問題的嚴重限制。後摩爾時代的發展因此轉向材料創新與異質整合，以尋求具備更小厚度與更佳界面品質的新型通道材料。二維材料因其原子級厚度、無懸鍵結構及可透過凡德瓦力進行堆疊的特性，成為探索低維電子結構與功能性異質結構的重要平台。其中，透過硫族元素取代反應調控二維材料的電子結構，提供了一條可在原子尺度上實現能隙、自旋軌道耦合與物性工程化的有效途徑。
本研究聚焦於 PtSe2、PtTe2 系統中的硫族元素取代行為，利用分子束磊晶 (Molecular Beam Epitaxy, MBE)成長不同層數的 PtSe2、PtTe2 薄膜及其異質結構，並結合反射式高能電子繞射（Reflection high-energy electron diffraction, RHEED）與角解析光電子能譜（Angle-Resolved Photoemission Spectroscopy, ARPES），系統性探討取代反應在不同堆疊順序與化學環境下的行為。我們發現，在 Te-rich 環境中，PtSe2 會發生完整的 Se→Te 取代反應並轉變為 PtTe2，且取代反應可沿薄膜表面垂直向與平行方向同時進行。相對地，PtTe2處於Se-rich環境並不會發生取代反應。我們運用嘗試成長PtSe2/PtTe2，結果顯示當 PtSe2 位於異質結構上層，即便處於 Se-rich 環境，PtSe2可穩定存在於此異質結構上層不發生取代反應；而我們嘗試成長PtTe2/PtSe2當 PtTe2異質結構則發現， Te-rich 成長條件會觸發下層 PtSe2 的取代反應，使異質結構等效為層數增加的 PtTe2。本研究結果指出，在設計二維過渡金屬硫化物(Transition metal dichalcogenides, TMDCSs)異質結構時，硫族元素取代反應的介入必須被視為關鍵因素，並為未來低維材料異質整合與可工程化設計提供重要指引。
;As Moore’s law approaches its fundamental physical limits, the conventional strategy of enhancing device performance through geometric scaling of transistors has been increasingly constrained by quantum tunneling, short-channel effects, and rising power density. Consequently, the focus of post-Moore electronics has shifted toward materials innovation and heterogeneous integration, aiming to identify new channel materials with reduced thickness and superior interface quality. Two-dimensional materials, characterized by their atomic-scale thickness, absence of dangling bonds, and ability to form heterostructures via van der Waals stacking, provide an exceptional platform for exploring low-dimensional electronic structures and functional heterostructures. Among various approaches, chalcogen substitution reactions offer an effective route to engineer the electronic structure of 2D materials at the atomic scale, enabling tunability of the band gap, spin–orbit coupling strength, and related physical properties.
In this work, we focus on chalcogen substitution in the PtSe2、PtTe2 system. Thin films of PtSe2, PtTe2, and their heterostructures with controlled layer thicknesses were grown by molecular beam epitaxy, and the substitution behavior under different stacking sequences and chemical environments was systematically investigated using reflection high-energy electron diffraction and angle-resolved photoemission spectroscopy. We find that under Te-rich conditions, PtSe2 undergoes a complete Se→Te substitution and transforms into PtTe2, with the substitution reaction propagating both vertically across the film thickness and laterally within the plane. In contrast, when PtSe2 is positioned as the top layer under Se-rich conditions, the heterostructure remains chemically stable and exhibits only electronic hybridization without substitution. When PtTe2 is placed on top, however, the Te-rich growth environment triggers substitution in the underlying PtSe2, rendering the heterostructure electronically equivalent to a thicker PtTe2 film. These results demonstrate that chalcogen substitution must be explicitly considered in the design of 2D TMDCs heterostructures and provide important guidelines for low-dimensional materials integration and heterostructure engineering. |
