[15p-P5-1~4] 9.3 Nanoelectronics

▲ [15p-P5-4] Analysis of Single Molecular Device with Quinoidal Fused Oligosilole Derivatives Based on Scanning Tunneling Microscopy and Scanning Tunneling Spectroscopy.

〇(D)SeungJoo Lee¹, Shuhei Urayama¹, Yasuo Azuma¹, Ryo Takano², Ryo Shintani², Kyoko Nozaki², Yutaka Majima¹ (1.Tokyo Tech., 2.Univ Tokyo.)

Keywords:Single Molecular Device, Scanning Tunneling Microscopy, Scanning Tunneling Spectroscopy

π-Conjugated molecules attract a great interest for the application to single molecular devices. In the molecular electronic device, the negative differential resistance (NDR) effect is a very useful function which is characterized by a reduced current with an increase of a voltage bias. With this NDR effect, devices such as molecular switch and memory operation can be proposed. [1] However, π-conjugated molecules often suffer from structural instability for change in their valence charge. Here, we introduce the Si-bridged quinoidal fused oligosilole derivatives, which have an 18π-conjugated structure with flat a molecular shape (Fig. 1).Because bulky substituents on the Si can effectively suppress molecular interactions, it can be very stable under the air ambient condition. We used the STM (scanning tunneling microscopy) and STS (scanning tunneling spectroscopy) for measuring the tunneling current on the individual molecule based on W-tip/vacuum/molecule/SAM/Au(111) structure at 100 K. Density functional theory calculation gives the molecular orbital information with discrete energy levels, such as HOMO and LUMO levels. [2] It notes that not only the STS results but also the solid-state device results indicate the clear and strong NDR peak at -1.8 V (Fig. 2). This NDR peak should be based on inter-molecular resonance tunneling. For analyzing the mechanism of this molecular device operation, we classified the electrical properties of both the single molecular and inter-molecular structure. Electrostatically, single molecular electrical property was described with double barrier tunneling junction. Moreover, double molecular electrical property was explained by inter-molecular resonance tunneling with NDR. Not only at 100 K, even under the room-temperature condition, this NDR effect was also clearly observed with PVR (Peak to Valley Ratio) of 2 (Fig. 2). While most of molecular devices work at low temperature, this molecular device has strong advantages of room temperature operation. However, it still has many challenges such as reduction of NDR peak voltage and high PVR value.