利用掃描探針顯微鏡分析二硒化錸之電性結構與厚度關係

Abstract

電子元件尺寸與厚度逐漸縮小，矽晶圓已經無法在奈米尺度下製作高效能場效電晶體，使得科學家轉移到二維結晶材料上尋找替代之電荷通道材料。本實驗主要利用掃描穿隧電子顯微鏡(scanning tunneling microscopy, STM)探討新穎二維材料之二硒化錸(rhenium diselenide, ReSe2)的能隙與其厚度關係。用機械撕貼法將二硒化錸放在摻雜氧化銦錫(Indium Tin Oxide, ITO)的導電玻璃基板上，並以STM尋找ReSe2薄片，掃描其影像圖以及掃描穿隧能譜圖(scanning tunneling spectroscopy, STS)，藉此分析二硒化錸的厚度與電子結構關係。 為了分辨出二硒化錸薄片，先觀察ITO玻璃表面形貌及電子結構，發現ITO導電玻璃表面有明顯顆粒組成小島嶼覆蓋整個表面，且其STS顯示出金屬電子結構不具有能隙。二硒化鉛表面在厚度高的薄片上能觀察到平整表面，且STS顯示明顯能隙。我們也使用原子力顯微鏡(Atomic Force Microscope, AFM)確認STM所觀察的表面形貌，確認此兩種顯微鏡所觀察到形貌相同。我們探討二硒化錸的能隙與厚度的關係，發現當二硒化錸厚度減少，其能隙將增加，此趨勢與文獻中理論預測相符。

In order to scale down electronic devices, scientists have paid much attention to new materials of two-dimensional (2D) materials like graphene and MoS2. In this experiment, we explore thickness dependency of electronic structures of the 2D material - rhenium diselenide (ReSe2) by scanning tunneling microscope (STM). We adopt mechanical exfoliation to disperse ReSe2 flakes on indium tin oxide (ITO) conductive glass. The morphology and the electronic structures of these ReSe2 flakes are investigated by STM and scanning tunneling spectroscopy (STS). The dependency between thickness and electronic structures of ReSe2 flakes is studied. In the beginning, we check the ITO surfaces. We find that the surface of the ITO conductive glass consists of islands which are formed by aggregated grains. Further, the STS measurements show that there are no bandgaps on the ITO surface. On the other hand, we observe flat surfaces on thick ReSe2 flakes and clear bandgaps on their surface. We also check surface morphology using atomic force microscope (AFM) and get the same conclusions. Finally, we learn that the thinner the thickness of ReSe2 is, the larger the bandgap of ReSe2 will be. The dependency of the bandgap of ReSe2 flakes on their thickness is qualitatively consistent with theoretical calculations.