運用原子力顯微鏡操控奈米金粒子

Abstract

原子力顯微鏡被應用在研究表面結構、探針和表面間的交互作用力及奈米等級的操控已經很多年。目前技術上已經可以在平面上移動奈米粒子，但卻很少相關研究說明如何精準定位且操作奈米粒子在立體環境中，且在之前的研究中，成功率僅有5-7%。在此利用原子力顯微鏡的探針當作機械手臂，定位並操控奈米金粒子到相隔約10奈米的兩塊電極上，並使成功率達到20%左右。 實驗透過三種方式，將奈米金粒子利用探針放置到電極的邊緣，藉由原子力顯微鏡的奈米等級的精準度。第一，利用奈米金-探針和奈米金-金表面之間不同的作用力，使奈米金粒子留在表面上。第二，藉由將奈米金粒子灑在特定位置上後，運用探針接觸表面的模式推動奈米金粒子到電極邊緣上。第三，隨著探針靠近表面時，施加電壓於電極，使其表面帶電荷並能吸引奈米金粒子。整個放置奈米金粒子的過程可以透過力曲線即時觀察，所有的操作都是使用原子力顯微鏡機台內建軟體，軟體會自動補償機台所造成的錯誤。 實驗結果發現，選擇具有較小的針尖、彈性常數和共振頻率能獲得較好的解析度和奈米金粒子的操控-Type C；環境相對濕度控制在30 % 能減少探針受到毛細作用的影響，並獲得較準確的力曲線圖；下壓深度必須小於20 nm，避免對探針及表面造成損傷，透過調整相關參數，達到最佳化的奈米操控。主要有四種力會影響奈米金粒子的操控，凡德瓦力、庫倫作用力、毛細作用力和分子間作用力。我們認為奈米金粒子和探針及表面的分子間作用力可能是主要影響因素。 此方法可以在一般室溫環境下使用，並且不需要額外的套件配合，可以適用在任何系統上，運用這個方法可以製作出帶有奈米金粒子的奈米元件，並且可以更近一步的了解如何控制奈米等級的物體，製作俱生物相容性的介面和不同的奈米結構。

Atomic force microscope (AFM) have been applied to scan surface topography, tip-substrate force measurements and nanoscale manipulation for years. It is now technically possible to move nanoparticles on a plane, but still very hard to manipulate nanoparticles with precision and accuracy on a three-dimension place. In previous work, the success rate for positioning the GNPs on the electrode is about 5-7%. Here, we report a method for the application of atomic force microscope to manipulate and position nanometer-sized gold particles into a nanogap between two electrodes. The success rate have elevated to 20%. An individual GNPs are brought onto the edge of the electrode by AFM tip with nanometer precision. There are three ways to accomplish the goal. First, direct deposition nanoparticles on a desire place is achieved by approaching to the surface very close with the GNPs-tip. Second, manipulation GNPs which has already spread on the surface to the locating place. Third, applying bias on surface when GNPs-tip approach to the sample. The process of positioning GNPs on the electrode can be monitored in real time by acquiring force-distance curve. All of this method are under control of software that compensate for instrument errors. The result shows that tip with small radius, low spring constant and low resonance frequencies are essential for acquiring better resolution and manipulating nanoparticles. Controlling the relative humidity at 30% can reduce the influence of capillary effect and get more accurate force-distance curve. The indentation depth must small than 20nm for preventing sample damage or considerable tip-wear. There are four possible forces influence the deposition of GNPs - van der Waals forces, Coulomb interaction of outer-shell electron or applying bias on tip/substrate, capillary effect and intermolecular force in different materials. We suppose that the intermolecular forces, as the main point in positioning GNPs. This method can conduct in ambient air, room temperature and do not need any additional equipment. It can be applied to any system. Using this technic we can fabricate a nanoparticle-charged device, investigating the controlled manipulation of nanoscale objects, creating a biocompatible interface and constructing different nanostructures.