Molecular Junctions Stabilized Manually via Tactile Feedback for the Measurements of Single–Molecule Conductance

掃描式穿隧顯微術斷裂接合法(scanning tunneling microscopy break junction, STM BJ )是常用來量測單分子電性的方法，需重覆以探針對表面進行上千次的撞拉動作，以獲得大量的單分子導電訊號進行統計。又因撞拉為動態的過程，使得分子架接於電極兩端的時間極為短暫(ms)，而無法長時間觀測同一單分子的導電值。因此該實驗所統計出的單分子導電值，所代表的是各個同類分子在不同時間下所呈現的導電性之集合結果，而不是來自於同一分子的電性表現。 因此，本論文研究方向是建構出一個能夠長時間穩定量測單分子電性的方法，主要特性是維持分子接點的穩定性，進而獲取單分子在導電性上所呈現的資訊。針對亞甲基個數為六及八的飽和烷雙硫醇分子做探討，在金探針與金表面間施加固定偏壓，透過手調式作用力控制器(PicoAngler)使金探針接觸分子膜，藉由PicoAngler固定探針與分子間的作用力變化，以維持分子與電極的間距，穩定此分子接點，進而長時間量測單分子導電值。相較於STM BJ，此方法除了能穩定且長時間(數十秒)進行單分子電性的量測，更可藉由少次的量測結果，解析出單一分子的電性表現。The ultimate goal of molecular electronics is the construction of electronic circuit devices from individual molecules and the electron transport through single molecules is crucial to molecular devices. The factors that influence electron transport depend not only on molecules themself but also the detail of molecule-electrode contacts. The latter is considered to be the least controllable aspect of experiments would cause conductance variability due to the contact geometry in molecular junctions. In the scanning tunneling microscopy break junction (STM BJ) method, continuous tip retraction would lead to contact conformation changes, we try to establish a stable contact between the molecule and metal probes and ensure that not the properties of an ensemble but a single molecule are been found. The results presented here is the studies of the single molecular conductance for the self-assembled monolayers (SAMs) of hexanedithiol and octanedithiol (SH-(CH2)n-HS, n=6 and 8) molecules onto Au electrodes by the conductive atomic force microscopy and the PicoAngler. By utilizing the PicoAngler with a force-feedback knob for manual control of the fixed tip-substrate spacing, which can stabilize the molecular junction, our method can not only construct the conductance histogram without the preselection process, but also receive the experimental results similar to the previous reports