Measurements of electronic properties of interfaces with functional nanostructures by bias-voltage non-contact atomic force microscopy/spectroscopy

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The aim of this study is to analyze opto-electronic functional nanostructures on atomic scale, and their electronic and binding states to substrates using bias-voltage non-contact atomic force microscopy/spectroscopy. The results showed that, when we brought two pieces of condensed matter close to each other, and changed bias voltage across them, we can energetically tune the electronic states at the two surfaces through the change in electrostatic potential energy, resulting in resonating states, i.e. covalent bond. In addition, simultaneous measurements of interaction force with current between them implied that the possibility of evaluating collapse of tunneling barrier and analyzing the correlation between electronic conduction and force. Thus, we promoted the tip preparation techniques to improve the detection sensitivity of current and force. We cleaned Si tips on AFM cantilevers, and deposited Ge on them or touch heated Ge or Si substrates with the tip, and heated and/or applied bias voltage: this leads to growth of a nanopillar on the tip. We evaluated them with SEM, SAM and TEM. Moreover, we fabricated quartz force sensors and prepared Pt nanopillars on electrochemically etched Pt-It wire for the sensors. We observed π-conjugated molecules of 4,4"-diamino-p-terphenyl (DAT) deposited on Si(111)-7x7 on atomic scale and analyzed their electronic binding states by XPS. DAT has two amino groups at both ends of the linear molecule with potential to form π-conjugated molecules with a controlled length standing on Si substrates, which are vapor polymerized by depositing, e.g., 1,4-bis (4-formylstyryl) benzene alternatively with DAT. We observed that DAT was adsorbed preferentially on faulted half cells of the 7x7 reconstruction, and obtained evidence that one amino group is bound with Si substrate and the other is free at the end of DAT. Moreover, we concluded that the amino group binding with Si exhibited electric conduction to the substrate.