Molecular Circuits for Optoelectronics utilizing Carbon Nanotubes

在4.2K和室温范围内，作为波长、源/漏电压、第三端上的栅极电压和温度的函数，应在三端装置中测量跨越单个分子的光导。分子将通过两个单壁碳纳米管(SWNT)接触，它们通过自组装过程充当分子的介观源极/漏极接触。有机电路SWNT-分子-SWNT的长度为数百纳米，这使得可以通过标准的电子束光刻来接触器件，进而对局部侧门进行图案化。通过在侧栅上施加电压，分子中电子的能级可以通过静电改变。对于分子的光激发，我们使用了一个脉冲的、波长可调的激光系统，它允许测量分子吸收带附近的光导。使用脉冲激光系统而不是连续波激光系统可以最大限度地减少接触中的加热效应对分子传输特性的影响。此外，与金接触相比，单壁碳纳米管-分子接触区的原子重排预计只起到很小的作用。为了给出直接的实验证据表明只有一个分子被表征，我们计划对可光切换的分子，如偶氮苯或二苯乙烯，以及金属蛋白进行传输测量。光开关表现出由光激发引起的构象变化，这使得研究分子构象对输运性质的影响成为可能。同时，分子构象的成功和可逆转换表明，只有一个分子被连接并被光电学表征。另一方面，蛋白质可以通过扫描探针显微镜来验证它们的存在。

The photo-conductance across a single molecule shall be measured in a three-terminal device as a function of the wavelength, the source/drain voltage, a gate voltage on the third terminal and the temperature in the range of 4.2 K and room temperature. The molecules will be contacted by two single wall carbon nanotubes (SWNTs), which act as mesoscopic source/drain contacts to the molecule, via a self-assembly process. The organic circuit ¿SWNT-molecule-SWNT¿ has a length of several hundreds of nanometers, which allows contacting the device by standard e-beam lithography and in turn, patterning of local side-gates. By applying voltages to the side-gates, the energy levels of the electrons in the molecule can be altered electrostatically. For the photo-excitation of the molecule we utilize a pulsed, wavelengthtunable laser system, which allows measuring the photo-conductance close to the absorption bands of the molecule. Using a pulsed laser system instead of a continuous wave laser minimizes the influence of heating effects in the contacts on the transport properties of the molecule. In addition, atomic rearrangements in the SWNT-molecule contact region are expected to play only a minor role as compared to gold contacts. In order to give direct experimental evidence that only one molecule is being characterized, we plan transport measurements on photo-switchable molecules, such as azobenzene or stilbene, and also on metalloproteins. Photo-switches exhibit a conformational change induced by photo-excitation, which allows studying the effect of molecular conformation on the transport properties. At the same time, a successful and reversible switching of the molecular conformation demonstrates that just one molecule is being connected and characterized optoelectronically. Proteins, on the other hand, allow verification of their presence by scanning probe microscopy.