單一原子層離子固體在矽晶面上的成長與奇特排列

Abstract

在本研究中，我們利用掃描穿遂電子顯微術來探討室溫下矽晶面上二維之單一原子層氯化鈉的電子結構與表面形貌。不同於傳統分子束磊晶方式，我們這次使用原子層沉積的方式來進行本次實驗。首先成長一層氯，形成氯/矽(100)-2 × 1的表面結構，接著再蒸鍍鈉原子在此表面上。由得到一系列隨著氯化鈉面積成長的STM影像，除了讓我們對其影像產生過程有更深一層的了解之外，對其依附成長機制也能獲得進一步的理解。從我們的實驗數據，可以歸納出下面幾點結論： (1)鈉原子會在氯/矽(100)-2 × 1面上遊走，然後沉積在已形成的二 維氯化鈉島嶼之邊緣位置。 (2)當鈉原子的量不足已形成單一原子層氯化鈉薄層時，為了使二維氯化鈉島嶼內部有效緩和氯化鈉與矽的晶格常數差異，氯連帶最表層矽原子的位置出現同相「之字型」的結構。從得到的STM影像可以推測此時的氯化鈉島嶼對STM探針而言，扮演著類似真空層般的角色。 (3)單一原子層氯化鈉形成時，氯化鈉彼此之間的作用力變強而與基底的連結與之前島嶼階段相比更為微弱，以類似地毯的方式依附在矽表面上，佔據態影像所顯示的訊號也由先前矽表面態轉變為氯化鈉態。

In this study‚ the electronic structure and morphology of single 2D NaCl layer heteroepitaxially grown on Si(100) are investigated by using scanning tunneling microscopy (STM) at room temperature. Instead of the conventional method of depositing NaCl molecules on the surface of semiconductor directly‚ we expose the clean Si(100) surface to Cl2 forming Cl/Si(100)-2 × 1 structure first and then evaporate sodium atoms on the Cl-saturated Si(100)-2 × 1 surface. Atomic resolved STM images for NaCl on the surface allow us not only to obtain further insight into the STM imaging process but also to clarify the heteroepitaxial growth process. From the experiment results, we conclude that： (1)The arriving sodium atoms migrate on the Cl/Si(100)-2 × 1 surface, and then are captured at the edge of 2D NaCl islands. (2)If the amount of sodium atoms is less than that of single atomic NaCl layer, then the topmost chlorine-terminated silicon layer within 2D NaCl islands forms an in-phase zig-zag structure in order to relax the lattice constant mismatch between NaCl and Si efficiently. According to the STM images, we also suggest that the NaCl layer is transparent to electron tunneling. (3)Because a strong binding exists within single atomic NaCl layer, the interaction between NaCl and Si will be weaker than the former islands stage. Therefore, the single atomic NaCl layer is just like a carpet attached on Si(100) surface, and the occupied tunneling signal convert Si(100) surface states into NaCl states.