Length-dependent transport in molecular junctions based on SAMs of alkanethiols and alkanedithiols: Effect of metal work function and applied bias on tunneling efficiency and contact resistance
Length-dependent transport in molecular junctions based on SAMs of alkanethiols and alkanedithiols: Effect of metal work function and applied bias on tunneling efficiency and contact resistance
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DOI：
10.1021/ja046274u
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发表时间：
2004-11-03
影响因子：
15
通讯作者：
Frisbie, CD
中科院分区：
文献类型：
--
作者：
Engelkes, VB;Beebe, JM;Frisbie, CD
纳米隧道结是通过接触Au-，Pt-，或Ag-涂层的原子力显微镜（AFM）的提示，以自组装单分子层（SAMS）的烷硫醇或烷二硫醇分子的多晶Au，Pt，或Ag基板。电流-电压迹线呈现S形行为，并随分子长度呈指数衰减，这是非共振隧穿的特征。长度依赖性衰减参数β被发现大约为1.1/碳原子（C-1）或0.88埃（-1），并且与施加的偏压（在+/-1.5 V的电压范围内）和电极功函数无关。相比之下，接触电阻，R-0，外推电阻与分子长度图显示了显着的下降与施加的偏压和增加电极功函数。观察到双结合的烷二硫醇结具有比单结合的烷二硫醇结低约1至2个数量级的接触电阻。然而，链烷硫醇和二硫醇结表现出相同的长度依赖性（P值）。电阻与长度的数据也用于计算每种类型的接触的透射率值（例如，Au-S-C、Au/CH 3等）以及每个C-C键的透射率（TC-C）。
Nanoscopic tunnel junctions were formed by contacting Au-, Pt-, or Ag-coated atomic force microscopy (AFM) tips to self-assembled monolayers (SAMS) of alkanethiol or alkanedithiol molecules on polycrystalline Au, Pt, or Ag substrates. Current-voltage traces exhibited sigmoidal behavior and an exponential attenuation with molecular length, characteristic of nonresonant tunneling. The length-dependent decay parameter, beta, was found to be approximately 1.1 per carbon atom (C-1) or 0.88 Angstrom(-1) and was independent of applied bias (over a voltage range of +/- 1.5 V) and electrode work function. In contrast, the contact resistance, R-0, extrapolated from resistance versus molecular length plots showed a notable decrease with both applied bias and increasing electrode work function. The doubly bound alkanedithiol junctions were observed to have a contact resistance approximately 1 to 2 orders of magnitude lower than the singly bound alkanethiol junctions. However, both alkanethiol and dithiol junctions exhibited the same length dependence (P value). The resistance versus length data were also used to calculate transmission values for each type of contact (e.g., Au-S-C, Au/CH3, etc.) and the transmission per C-C bond (TC-C).