探索不同尺寸下金奈米顆粒的傳輸性質

Abstract

在本實驗中使用兩種不同顆粒大小的金顆粒分別為10 nm以及20 nm，而電極間距為200 nm - 600 nm，此實驗分為兩個部分探討，第一部分為探討金奈米顆粒的傳輸性質，我們量測溫度在300 - 30 K內電阻的變化，發現10 nm的電阻隨溫度下降而上升，20 nm的電阻約在250 K及190 K會有轉折點，分析在180 - 65 K時傳輸機制為最近鄰近跳越(nearest neighbor hopping)，而65 – 30 K為ES hopping，並由Monte Carlo擬合出的結果可得知兩種顆粒大小活化能、穿隧電導的相對關係。 第二部分為探討金顆粒在照光下會有甚麼反應，我們分別比較兩種顆粒大小的上升時間(rising time)、光電導。並量測雷射光瓦數改變與電流的關係，由此關係可以由power law得到兩種顆粒大小皆為好的感光材料，也發現光電流大小與電極間距有關。

Two different sizes of gold particles are used in this experiment. The average sizes are 10 and 20 nm. The gap of electrode was about 200 to 600 nm for all our devices. This experiment was divided into two parts which will be separately discussed in the following paragraph. In the first part, we discussed the electrical property of Au nanoparticles. We measure the temperature dependence of resistance at temperatures between 300 K and 30 K. We find out that the resistance of 10-nm-diameter device increases with a decrease of temperature. On the other hand, we observed two transitions at 190 and 250 K in 20-nm-diameter Au particle devices. The electron transport is described well by nearest neighbor hopping in the temperature range from 65 K to 180 K. In addition, it behaves as ES hopping transport at temperatures between 30 K and 65 K. The activation energy and tunneling conductance have been estimated through the Monte-Carlo nonlinear least square fitting. In the second part, we discussed the photoconductivity of Au nanoparticle assembled arrays. We compared the rising time and photoconductance between two different sizes of Au NPs and measured photocurrent under different power of laser excitation. By fitting the data with power law, we can find that Au nanoparticles are sensitive to light. The magnitude of photocurrent is dependent on the gap length between electrodes.