Ishida Takao, Mizutani Wataru, Liang Tien-Tzu, Azehara Hiroaki, Miyake Koji, Sasaki Shinya, Tokumoto Hiroshi
Institute of Mechanical Systems Engineering, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan.
Ann N Y Acad Sci. 2003 Dec;1006:164-86. doi: 10.1196/annals.1292.011.
The electrical conduction of self-assembled monolayers (SAMs) made from conjugated molecules was measured using conductive probe atomic force microscopy (CP-AFM), with a focus on the molecular structural effect on conduction. First, the electrical conduction of SAMs made from phenylene oligomer SAMs was measured. The resistances through the monolayers increased exponentially with an increase in molecular length and the decay constants of transconductance beta were about 0.45 to 0.61 A(-1) measured at lower bias region. We further investigated the influence of applied load on the resistances. The resistances through terphenyl SAMs increased with an increase in the applied load up to 14 nN. Second, using an insertion technique into insulating alkanethiol SAMs, the electrical conduction of single conjugated terphenyl methanethiol and oligo(para-phenylenevinylene) (OPV) molecules embedded into insulating alkanethiol SAMs were measured. Electrical currents through these single molecules of OPVs were estimated to be larger than those through single terphenyl molecules, suggesting that the OPV structure can increase the electrical conduction of single molecules. Third, apparent negative differential resistance (NDR) was observed at higher bias measurements of SAMs. The appearance of NDR might be related to roughness of SAM surface, because apparent NDR was often observed on rough surfaces. In any case, the tip-molecule contact condition strongly affected carrier transport through metal tip/SAM/metal junction.
利用导电探针原子力显微镜（CP-AFM）测量了由共轭分子制成的自组装单分子层（SAMs）的导电情况，重点研究了分子结构对导电的影响。首先，测量了由亚苯基低聚物SAMs制成的SAMs的导电情况。穿过单分子层的电阻随着分子长度的增加呈指数增加，在低偏置区域测量的跨导衰减常数β约为0.45至0.61 A⁻¹。我们进一步研究了外加负载对电阻的影响。穿过三联苯SAMs的电阻随着外加负载增加到14 nN而增加。其次，使用插入绝缘链烷硫醇SAMs的技术，测量了嵌入绝缘链烷硫醇SAMs中的单个共轭三联苯甲硫醇和聚对苯撑乙烯（OPV）分子的导电情况。估计通过这些单个OPV分子的电流大于通过单个三联苯分子的电流，这表明OPV结构可以增加单个分子的导电性。第三，在SAMs的高偏置测量中观察到明显的负微分电阻（NDR）。NDR的出现可能与SAM表面的粗糙度有关，因为在粗糙表面上经常观察到明显的NDR。无论如何，针尖-分子接触条件强烈影响通过金属针尖/SAM/金属结的载流子传输。
