錳摻雜硒化鉛奈米陣列交互鏈間不同耦合強度電荷傳輸研究

Abstract

利用奈米晶粒做為組裝單元合成各種不同型態的奈米材料技術已經相當純熟。其中硒化鉛因其高熱電轉換效能等特性而被大幅研究，但是錳摻雜硒化鉛奈米陣列被合成至今，其電荷傳輸特性卻仍尚未被有系統地探討。所以此篇論文將針對錳摻雜硒化鉛奈米陣列交互鏈間不同耦合強度下，探究其電荷傳輸行為。 首先，我們利用標準的電子束微影技術於二氧化矽基板上製作兩個鈦金電極，接著利用介電泳動法（Dielectrophoresis），藉由調控不同參數，可將奈米陣列跨接於電極兩端而得到不同並聯根數之奈米陣列元件。奈米元件在進行電性量測前，必須藉由熱處理與化學處理方式去除陣列外之有機包覆層，以得到其本質特性；奈米陣列元件之電流與電壓關係曲線皆為線性關係，證明我們的處理方式，有效去除接點電阻影響。單根奈米陣列之變溫量測結果呈現一穿隧行為，亦即電阻值不隨溫度變化而改變；另一方面，在並聯根數較多的奈米陣列元件中，我們可以利用熱擾動導致穿隧傳輸理論（Fluctuation-induced tunneling）定性地成功解釋量測結果，並且發現隨著並聯根數的增加、耦合強度增強，穿隧機率隨之上升。最後，藉由量測磁電阻（Magnetoresistance）的效應，發現磁電阻變化率與並聯根數成一正相關，證明在糾結嚴重的奈米陣列中，受到耦合效應之影響，電荷於陣列與陣列間的傳輸是有可能發生的，自洽地與我們的假設符合。

Synthesizing various nanoscale materials and taking them as building blocks to realize the bottom-up technique have attracted considerable attention in the past decades. Owing to its particular semiconducting and thermoelectric properties, researches on PbSe dots have been reported extensively. Although the one-step preparation of 1D Pb1-xMnxSe corrugated nanoarrays (NAs) has been demonstrated, the intrinsic electrical transport property of this 1D NAs has not been systematically explored yet. This work focuses on charge transport in Pb1-xMnxSe NAs, and discusses weak and strong inter-chain coupling. The standard e-beam lithography technique was used to fabricate two Ti/Au electrodes, with a gap of 200-350 nm in width, on Si substrate, which were capped with a 150-nm thick SiO2 layer to prevent from any possible leakage currents through the substrate and were photolithographically pre-patterned with micrometer-scale electrodes. A dielectrophoresis technique with a sinusoidal wave (a frequency of 500 kHz and a voltage of 2-4 V) was implemented to move and position Pb1-xMnxSe NAs into the pre-patterned nanogap. Before electrical property measurements, all as-fabricated devices were treated both by thermal annealing and chemical methods to remove some excess capping ligands. Since current-voltage curves in all NA devices show a linear behavior, it is conjectured that the contact resistances are small enough to be neglected. The resistance of Pb1-xMnxSe NA as a function of temperature was measured from 300 K to 100 K to exhibit the electron transport manner. We observed that the electron transport of single Pb1-xMnxSe NA (for devices with few NAs in gap) exhibits a temperature independent tunneling behavior. On the other hand, the electron transport of entangled Pb1-xMnxSe NAs (for devices with hundred of overlapped NAs in gap) quantitatively follows the theory of fluctuation-induced tunneling. Moreover, by measuring the magnetoresistance (MR) in entangled NA devices, we found that the MR resistance increases with increasing magnetic field, indicating a transport path acrossing other NAs. This result corroborates that the electron transport between NAs is feasible and it is consistent with our hypothesis that the inter-NA coupling might affect the electron transport behavior.