Lee Takhee, Wang Wenyong, Reed M A
Department of Electrical Engineering, Yale University, New Haven, Connecticut 06520, USA.
Ann N Y Acad Sci. 2003 Dec;1006:21-35. doi: 10.1196/annals.1292.001.
Electron tunneling through self-assembled monolayers (SAMs) of alkanethiols was investigated using nanometer scale devices that allow temperature-dependent current-voltage, I(V, T), measurements. The I(V, T) measurement results show, for the first time, temperature-independent electron transport characteristics, proving direct tunneling as the transport mechanism in alkanethiol SAMs. The measured tunneling currents can be fitted with theoretical calculations using the modified rectangular barrier model of direct tunneling with a barrier height Phi(B) = 1.42 +/- 0.04 eV and a non-ideal barrier factor alpha = 0.65 +/- 0.01 (that may correspond to effective mass of 0.42 m). From the length-dependent conduction measurement on different alkanethiols of various lengths, the tunneling current exhibits exponential dependence on the molecular length, d, as I proportional, variant exp(-betad), where beta is a decay coefficient that was found to be bias-dependent and agrees with the existing theory of direct tunneling. A zero field decay coefficient beta(0) of 0.79 +/- 0.01 A(-1) was obtained.
利用能够进行与温度相关的电流-电压（I(V, T)）测量的纳米级器件，对通过链烷硫醇自组装单分子层（SAMs）的电子隧穿进行了研究。I(V, T)测量结果首次显示出与温度无关的电子输运特性，证明直接隧穿是链烷硫醇SAMs中的输运机制。所测量的隧穿电流可以用理论计算来拟合，该理论计算使用了直接隧穿的修正矩形势垒模型，其势垒高度Phi(B) = 1.42 +/- 0.04 eV，非理想势垒因子alpha = 0.65 +/- 0.01（这可能对应于有效质量为0.42 m）。通过对不同长度的各种链烷硫醇进行与长度相关的传导测量，隧穿电流表现出对分子长度d的指数依赖性，即I与exp(-betad)成正比，其中beta是一个衰减系数，发现它与偏置有关，并且与现有的直接隧穿理论一致。获得了零场衰减系数beta(0)为0.79 +/- 0.01 A(-1)。
