Comparison of SAM-Based Junctions with Ga2O3/EGaln Top Electrodes to Other Large-Area Tunneling Junctions
Comparison of SAM-Based Junctions with Ga2O3/EGaln Top Electrodes to Other Large-Area Tunneling Junctions
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DOI：
10.1021/jp303072a
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发表时间：
2012-07-05
影响因子：
3.7
通讯作者：
Whitesides, George M.
中科院分区：
文献类型：
--
作者：
Nijhuis, Christian A.;Reus, William F.;Whitesides, George M.
本文比较了基于自组装单层 (SAM) 的隧道结与使用两种不同程序制造的镓和铟液体共晶 (EGaIn) 的顶部电极获得的 J(V) 特性：(i) 在 PDMS 微通道中稳定 EGaIn 电极，以及 (ii) 将 EGaIn 电极悬挂在注射器尖端。 EGaIn 电极的这两种几何形状（至少在与空气接触时，其固态 Ga2O3 表面膜）产生无法区分的数据。该连接点采用 SCn-1CH3（n = 12、14、16 或 18）的 SAM，支撑在超扁平、模板剥离的银电极上。两种方法都能产生高产量的结点 (70-85%)，这些结点足够稳定，可以使用大量统计数据 (N = 400-1000) 进行 J(V) 测量。顶部电极稳定在微通道中的装置还可以测量 J(V) 作为温度的函数，几乎低至液氮温度 (T = 110-293 K)。 J(V) 特性与 T 无关，并且在低偏置状态（-0.10 至 0.10V）下呈线性；随着 SAM 厚度的增加，电流密度呈指数下降。这些观察结果表明，隧道效应是电荷穿过这些结传输的主要机制。两种方法给出的隧道衰减系数 beta 值类似于 1.0 n(C)(-1)（类似于 0.80 埃(-1)），指前因子 J(0)（这是一个包括接触电阻的常数），类似于 3.0 x 10(2) A/cm(2)。将两种方法使用 EGaIn 生成的结的电特性与其他测量电荷传输系统的结果进行比较表明，使用 EGaIn 电极生成的 β 值与文献中报告的一致值一致。尽管对于 J(0) 的值没有达成共识，但使用 Ga2O3/EGaIn 电极估计的 J(0) 值与文献中报告的其他值兼容。多个实验平台上 β 实验值的一致性提供了强有力的证据，证明 SAM 的结构（包括它们的分子和超分子结构以及它们与电极的界面）主导着两种类型 EGaIn 结中的电荷传输。这些结果表明，对 Ag-Ts-SAM//Ga2O3/EGaIn 结的 J(V) 特性的研究主要由 SAM 有机成分的结构决定，而不是由电极、Ga2O3 表面膜的电阻或金属的功函数引起的伪影决定。
This paper compares the J(V) characteristics obtained for self-assembled monolayer (SAM)-based tunneling junctions with top electrodes of the liquid eutectic of gallium and indium (EGaIn) fabricated using two different procedures: (i) stabilizing the EGaIn electrode in PDMS microchannels and (ii) suspending the EGaIn electrode from the tip of a syringe. These two geometries of the EGaIn electrode (with, at least when in contact with air, its solid Ga2O3 surface film) produce indistinguishable data. The junctions incorporated SAMs of SCn-1CH3 (with n = 12, 14, 16, or 18) supported on ultraflat, template-stripped silver electrodes. Both methods generated high yields of junctions (70-85%) that were stable enough to conduct measurements of J(V) with statistically large numbers of data (N = 400-1000). The devices with the top electrode stabilized in microchannels also made it possible to conduct measurements of J(V) as a function of temperature, almost down to liquid nitrogen temperatures (T = 110-293 K). The J(V) characteristics were independent of T, and linear in the low-bias regime (-0.10 to 0.10V); the current density decreased exponentially with increasing thickness of the SAM. These observations indicate that tunneling is the main mechanism of charge transport across these junctions. Both methods gave values of the tunneling decay coefficient, beta, of similar to 1.0 n(C)(-1) (similar to 0.80 angstrom(-1)), and the pre-exponential factor, J(0) (which is a constant that includes contact resistance), of similar to 3.0 x 10(2) A/cm(2). Comparison of the electrical characteristics of the junctions generated using EGaIn by both methods against the results of other systems for measuring charge transport indicated that the value of beta generated using EGaIn electrodes is compatible with the consensus of values reported in the literature. Although there is no consensus for the value of J(0), the value of J(0) estimated using the Ga2O3/EGaIn electrode is compatible with other values reported in the literature. The agreement of experimental values of beta across a number of experimental platforms provides strong evidence that the structures of the SAMs-including their molecular and supramolecular structure, and their interfaces with the electrodes-dominate charge transport in both types of EGaIn junctions. These results establish that studies of J(V) characteristics of Ag-Ts-SAM//Ga2O3/EGaIn junctions are dominated by the structure of the organic component of the SAM, and not by artifacts due to the electrodes, the resistance of the Ga2O3 surface film, or to the work functions of the metals.