第一原理研究：單軸應變對動態穩定及傳輸性質在拱形石墨烯奈米緞帶的影響

Abstract

石墨烯奈米帶（Graphene nanoribbons, GNRs）因其優異的材料特性，被視為未來電晶體通道材料的有望候選。提升載子遷移率是優化電晶體通道材料的主要目標之一。先前研究指出，在奈米帶邊緣引入凹槽（coved）結構能有效提升 GNR 的載子遷移率。然而，過去對載子遷移率的預測，多依賴於電子與長波長聲子之間散射的近似處理，使得凹槽結構與載子傳輸之間的關聯性仍不夠明確。本研究考慮電子與所有聲子模式之間的完整交互作用，以更準確地預測載子傳輸行為。透過此全面性的分析，我們得以辨識影響 GNR 電子傳輸的主要因素，並明確指出哪些電子—特定聲子模式的交互作用最為關鍵。研究結果顯示，隨著凹槽結構尺度的增加，電子—聲學模式（acoustic modes）之間的散射降低。此機制在凹槽石墨烯奈米帶（Coved-GNRs）與鋸齒石墨烯奈米帶（ZGNRs）中皆扮演重要角色。由於電子–聲子散射減弱，群速度增加，進而延長平均自由徑（mean free path, MFP），使 Coved-GNRs 的電子遷移率優於寬度相近的 ZGNRs。此外，應變工程對電子遷移率與電子熱導率（electronic thermal conductivity）展現相似的調控能力。縱向拉伸應變可降低電子–聲子散射率，提升兩者；而橫向拉伸應變則會增加散射率，導致兩者下降。綜合而言，本研究提出一套透過邊緣結構設計與應變工程提升 GNR 載子遷移率的策略，為未來先進奈米電子元件的材料優化提供新方向。

Graphene nanoribbons (GNRs) are being explored for their promising material properties that could play a crucial role in the development of future transistors. One of the main goals in optimizing transistor channel materials is to develop effective strategies for improving carrier mobility. Previous research has indicated that a coved structure at the edges of the ribbon can significantly improve carrier mobility in GNRs. However, predictions regarding carrier mobility have relied on approximations concerning electron scattering with long-wavelength acoustic phonon modes, leaving the relationship between the covered structure and carrier transport somewhat opaque. In this study, we account for all interactions between electrons and various phonon modes to provide a more accurate prediction of carrier transport. This comprehensive approach enables us to identify the key factors that impede electron transport in GNRs by determining which interactions between electrons and specific phonon modes are most influential. Our findings indicate that as the distance of the coved structure increases, electron-acoustic mode scattering decreases. This interaction plays a significant role in electron-phonon (el-ph) scattering in both coved graphene nanoribbons (Coved-GNRs) and zigzag graphene nanoribbons (ZGNRs). Consequently, the decrease in el-ph scattering leads to an increase in group velocity. These changes result in a longer mean free path (MFP) and a subsequent enhancement of electron mobility in Coved-GNRs, exceeding that of ZGNRs with comparable widths. Strain engineering demonstrates a similar influence on both electron mobility and electronic thermal conductivity. Longitudinal tensile strain enhances both properties by lowering the electron-phonon scattering rate, while transverse tensile strain has the opposite effect, diminishing both properties by increasing electron-phonon scattering. These findings pave the way for developing a strategy to improve carrier mobility in GNRs.