在大氣環境下帶電摩擦介面中單層石墨烯和單層六方氮化硼之吸附特性

Abstract

本實驗利用原子力顯微鏡（Atomic Force Microscopy, AFM）研究了二氧化矽基板上的單層石墨烯（Single Layer Graphene, SLG）和單層六方氮化硼（Hexagonal Boron Nitride, h-BN）在滑動摩擦起電區域下的吸附性質對濕度的變化。首先，我們使用導電式原子力顯微鏡（Conductive Atomic Force Microscopy, c-AFM），在大氣環境下通過帶有偏壓的探針摩擦SLG和h-BN表面，以建立滑動摩擦起電。我們改變五種不同的環境濕度來量測矽探針與摩擦區域間的吸附特性。我們的實驗結果顯示，在SLG表面使用正偏壓進行帶電摩擦後，由於摩擦過程中產生的結構缺陷，將使摩擦過的SLG表面與未摩擦之前相比產生較大的吸附力。然而，當使用負偏壓進行帶電摩擦時，摩擦過的SLG表面的吸附力會顯著高於使用零伏特和正偏壓摩擦後的表面。這是因為當我們施加負電壓進行帶電摩擦時，探針與探針表面間的奈米水橋將會被電解，產生的氫氧根將使得石墨烯表面被氧化並形成大量含氧官能團。這些含氧官能團將會吸收大氣中的水分子，使得矽探針與摩擦區域之間更容易產生毛細水橋並導致更大的吸附力。另一方面，當我們對h-BN表面施加負偏壓摩擦時，與正偏壓和零伏特摩擦後的表面相比，摩擦區域的吸附力沒有顯著差異，這表明h-BN表面沒有像SLG表面那樣發生官能基化的現象。我們的研究結果可能有助於將SLG和h-BN應用於具有帶電摩擦介面的奈米機電元件中。In this study, we investigated the adhesive properties of single-layer graphene (SLG) and single-layer hexagonal boron nitride (h-BN) on silicon dioxide substrates under sliding electrical contact using atomic force microscopy (AFM). First, we used conductive atomic force microscopy (c-AFM) to slide an electrically-biased c-AFM probe on the surfaces of SLG and h-BN, creating sliding electrical contact. We measured the adhesive properties of the rubbed areas on SLG and h-BN using a silicon AFM probe under various environmental humidity. Our results showed that after rubbing the SLG surface with a positive bias, the adhesive forces measured on the rubbed area were slightly higher than those on the untreated surface, due to the structural defects generated during the sliding process. However, when a negative bias was used during rubbing, the adhesive forces on the SLG surface were significantly higher than the forces measured on SLG treated with zero volts or positive bias. This increase in adhesive forces is attributed to the electrolytic reaction of the nano meniscus between the probe and the surface when a negative bias was used, generating hydroxyl (OH-) that will oxidize the SLG surface , leading to the formation of numerous oxygen-containing functional groups on the SLG surface. These oxygen-containing functional groups will easily absorb ambient water molecules that resulting in larger water menisci between the silicon AFM probe and the rubbed SLG surface, giving rise to larger adhesive forces. On the other hand, when a negative bias was applied to rub the h-BN surface, the adhesive force in the rubbed area showed no significant differences compared to the surfaces treated with positive bias and zero volts, indicating that no functionalization occurred on the h-BN surface as it did on the SLG surface. Our findings may aid in the application of SLG and h-BN in nano-devices that require sliding electrical contacts.