Detection of charge dynamics of a tetraphenylporphyrin particle using GaAs-based nanowire enhanced by particle–metal tip capacitive coupling

Abstract

We investigate a detection technique of charge dynamics of a molecular particle using a GaAs-based nanowire where the charge sensitivity is locally enhanced by particle-metal tip capacitive coupling. By equivalent circuit analysis, it was clarified that the nanowire channel potential becomes sensitive to the molecular particle on the nanowire when the particle is capacitively coupled with a metal tip. The concept was demonstrated using a GaAs-based nanowire with tetraphenylporphyrin (TPP) particles on its surface and a measurement system integrating an atomic force microscope (AFM) and a dynamic current measurement monitor/spectrum analyzer. When the metal tip was in contact with a TPP particle on the nanowire under an appropriate tip bias condition, random telegraph signal (RTS) noise was imposed on the nanowire current, suggesting the increase in sensitivity to the charge state of the particle by the metal tip contact. We discussed the origin of the RTS noise through analysis of the time constant of RTS noise, RTS amplitude, and noise spectrum.

Current timer switch in a GaAs-based nanowire coupled with polyoxometalate nanoparticle and conductive AFM tip

“…A clear current step was observed for each bias condition; the current was constant for about 60 seconds from the start of tip biasing and then decreased abruptly. This current timer switch was not seen in the nanowire with tetraphenylporphine (TPP) NPs 23) . On the other hand, similarities were observed between the current timer switch and the reported charge threshold property of the POM NP-CNT complex 15) .…”

“…1(b). The nanowire functioned as a high-sensitive and high-speed charge detector [23][24][25] . The sample was set in an AFM system with a conductive-tip cantilever.…”

“…Its low-noise property is more ideal than the MOS-type Si device 29) and CNT device 30) . From our understanding of these devices, [31][32][33][34][35] we determined that the GaAs-based nanowire device possessed singleelectron charge sensitivity 23,24) . The nanowire length L was 4 µm.…”

“…This distinct current change could not be explained by the electrostatic effect from the tip on the nanowire channel. Considering the charge sensitivity of the nanowire [22][23][24][25] , over 200 electrons were necessary to charge the NP for explaining the observed current change around 1 µA.…”

“…In this paper, we demonstrate a current timer switch in a GaAs-based nanowire coupled with a POM NP, which is based on the charge dynamics of POM. We observed the timer function using our dynamic charge detection system [22][23][24] . In this study, atmospheric humidity of the system was precisely controlled to clarify the effect of the environment.…”