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海歸學(xué)者發(fā)起的公益學(xué)術(shù)平臺(tái)

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交流學(xué)術(shù)，偶爾風(fēng)月

來(lái)自中國(guó)西湖大學(xué)工學(xué)院的李文彬教授團(tuán)隊(duì)利用第一性原理計(jì)算方法，系統(tǒng)研究并闡明了曲率對(duì)鉬基和鎢基過(guò)渡金屬二硫化物(TMDC) 一維范德華異質(zhì)結(jié)中能帶對(duì)齊的影響。該研究發(fā)現(xiàn)，對(duì)于單獨(dú)的TMDC納米管，隨著納米管直徑的縮小，其導(dǎo)帶底能量呈現(xiàn)單調(diào)下降的趨勢(shì)，而價(jià)帶頂能量先下降再上升。這一現(xiàn)象源自曲率誘導(dǎo)的撓曲電效應(yīng)以及納米管周向固有拉伸應(yīng)變的協(xié)同作用。相較于絕大多數(shù)TMDC二維范德華異質(zhì)結(jié)所呈現(xiàn)的II型能帶對(duì)齊，對(duì)于TMDC一維范德華異質(zhì)結(jié)，在曲率影響納米管帶邊能級(jí)的基礎(chǔ)上，撓曲電電壓導(dǎo)致的管間耦合可使MoSe₂@WS₂, MoTe₂@MoSe₂, 以及MoTe₂@WS₂等多個(gè)異質(zhì)結(jié)體系在不同曲率下出現(xiàn)從II型到 I型能帶對(duì)齊類(lèi)型的轉(zhuǎn)變，如圖2所示。因此，通過(guò)曲率的控制，TMDC一維范德華異質(zhì)結(jié)有可能在同一材料體系中實(shí)現(xiàn)發(fā)光和光探測(cè)功能的集成。該研究為理解一維范德華異質(zhì)結(jié)中的能帶對(duì)齊奠定了重要的理論基礎(chǔ)，并為合理設(shè)計(jì)一維同軸TMDC范德華異質(zhì)結(jié)鋪平了道路。

圖1：常見(jiàn)的半導(dǎo)體能帶對(duì)齊類(lèi)型：跨騎 (I型), 交錯(cuò) (II型)，以及錯(cuò)層 (III型)。紅色和藍(lán)色分別代表半導(dǎo)體材料的導(dǎo)帶和價(jià)帶。

圖2：曲率導(dǎo)致的過(guò)渡金屬二硫化物（TMDC）一維范德華異質(zhì)結(jié)能帶對(duì)齊類(lèi)型轉(zhuǎn)變的示意圖。當(dāng)TMDC納米管的管徑（D）減小時(shí)，一些異質(zhì)結(jié)體系的能帶對(duì)齊類(lèi)型可發(fā)生從II型到I型的轉(zhuǎn)變。

Curvature-controlled band alignment transition in 1D van der Waals heterostructures

Shu Zhao, Chunxia Yang, Ziye Zhu, Xiaoping Yao & Wenbin Lig

The effect of curvature on the band alignment of one-dimensional (1D) van der Waals (vdW) transition metal dichalcogenide (TMDC) heterostructures is studied by comprehensive first-principles calculations. We find that, as the diameter of a TMDC nanotube decreases, the combined effect of curvature-induced flexoelectricity and circumferential tensile strain causes a rapid lowering of the conduction band minimum, whereas the valence band maximum exhibits an initial lowering before rising. As individual TMDC nanotubes form coaxial heterostructures, the concerted effect of diameter-dependent band-edge levels and intertube coupling via flexovoltage can result in a transition of intertube band alignment from Type II to Type I in multiple heterostructural systems, including large-diameter MoSe2@WS2, MoTe2@MoSe2, and MoTe2@WS2 heterostructures. These results lay down a foundation for the rational design of 1D vdW heterostructures.