Exceptionally Small Statistical Variations in the Transport Properties of Metal-Molecule-Metal Junctions Composed of 80 Oligophenylene Dithiol Molecules.
Exceptionally Small Statistical Variations in the Transport Properties of Metal-Molecule-Metal Junctions Composed of 80 Oligophenylene Dithiol Molecules.
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DOI：
10.1021/jacs.7b01918
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发表时间：
2017-04
影响因子：
15
通讯作者：
Zuoti Xie;I. Bâldea;A. Demissie;Christopher E. Smith;Yanfei Wu;G. Haugstad;C. Frisbie
中科院分区：
文献类型：
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作者：
Zuoti Xie;I. Bâldea;A. Demissie;Christopher E. Smith;Yanfei Wu;G. Haugstad;C. Frisbie
在分子电子学领域的许多测量中，特别是在室温下基于单分子结的测量中，出现了宽度与最可能值相当甚至更大的非常宽的电阻(R)直方图的强随机波动。在这里，我们发现含有80个聚苯基二硫醇分子（OPDn, 1≤n≤4）并联连接的分子结显示出较小的相对统计偏差-δR/R≈25%，仅经过~ 200次独立测量-我们定量分析了这些偏差的来源。这些结是通过导电探针原子力显微镜（CP-AFM）制成的，其中镀有Au的尖端与Au上自组装的opd单层（SAM）接触。利用接触力学和直接测量分子表面覆盖率、尖端半径、尖端- sam粘附力(F)和样品弹性模量(E)，我们发现尖端- sam接触面积约为25 nm2，对应于结中约80个分子。利用I-V数据和解析输运模型补充这些信息，我们能够定量地描述R中δR偏差的来源：即δN（结中分子数量的偏差），δε（优势分子轨道能量位置的偏差）和δΓ（分子-电极耦合的偏差）。我们的主要成果有：(1)直接测定N；(2)表明CP-AFM结的δN/N非常小（≤2%），δε和δΓ对δR的贡献最大；(3)证明仅经过~ 200次测量的δR/R比大多数基于bbb1000次测量的单分子断裂结的报告要小得多。总的来说，这些结果突出了由数十个平行分子组成的结的出色再现性，这可能对继续努力构建健壮的分子器件很重要。
Strong stochastic fluctuations witnessed as very broad resistance (R) histograms with widths comparable to or even larger than the most probable values characterize many measurements in the field of molecular electronics, particularly those measurements based on single molecule junctions at room temperature. Here we show that molecular junctions containing 80 oligophenylene dithiol molecules (OPDn, 1 ≤ n ≤ 4) connected in parallel display small relative statistical deviations-δR/R ≈ 25% after only ∼200 independent measurements-and we analyze the sources of these deviations quantitatively. The junctions are made by conducting probe atomic force microscopy (CP-AFM) in which an Au-coated tip contacts a self-assembled monolayer (SAM) of OPDs on Au. Using contact mechanics and direct measurements of the molecular surface coverage, the tip radius, tip-SAM adhesion force (F), and sample elastic modulus (E), we find that the tip-SAM contact area is approximately 25 nm2, corresponding to about 80 molecules in the junction. Supplementing this information with I-V data and an analytic transport model, we are able to quantitatively describe the sources of deviations δR in R: namely, δN (deviations in the number of molecules in the junction), δε (deviations in energetic position of the dominant molecular orbital), and δΓ (deviations in molecule-electrode coupling). Our main results are (1) direct determination of N; (2) demonstration that δN/N for CP-AFM junctions is remarkably small (≤2%) and that the largest contributions to δR are δε and δΓ; (3) demonstration that δR/R after only ∼200 measurements is substantially smaller than most reports based on >1000 measurements for single molecule break junctions. Overall, these results highlight the excellent reproducibility of junctions composed of tens of parallel molecules, which may be important for continued efforts to build robust molecular devices.