Utilizing Electrical Characteristics of Individual Nanotube Devices to Study the Charge Transfer between CdSe Quantum Dots and Double-Walled Nanotubes

To study the charge transfer between cadmium selenide (CdSe) quantum dots (QDs) and double-walled nanotubes (DWNTs), various sizes of CdSe–ligand–DWNT structures are synthesized, and field-effect transistors from individual functionalized DWNTs rather than networks of the same are fabricated. From the electrical measurements, two distinct electron transfer mechanisms from the QD system to the nanotube are identified. By the formation of the CdSe–ligand–DWNT heterostructure, an effectively n-doped nanotube is created due to the smaller work function of CdSe as compared with that of the nanotube. In addition, once the QD–DWNT system is exposed to laser light, further electron transfer from the QD through the ligand, specifically, 4-mercaptophenol (MTH), to the nanotube occurs and a clear QD size-dependent tunneling process is observed. The detailed analysis of a large set of devices and the particular methodology employed here for the first time allowed for extracting a wavelength and quantum dot size-dependent charge transfer efficiency—a quantity that is evaluated for the first time through electrical measurement.