Recently, Artificial Neural Network that mimics the function of the human brain is becoming popular, which is demonstrated as a device and applied for voice recognition and image identification. Nonlinear classification is demonstrated by using a system with a disordered dopant atom network in silicon. ^[1] The nonlinearity of hopping conduction through a network of boron dopant atoms is clarified. However, the nonlinear properties emerged at low temperatures, and these devices are desired to work at room temperature for future applications. To achieve the nonlinear network at room temperature, organic molecules with an appropriate dopant was used as a possible candidate to examine the emergence of the higher conductivity.
Here, The PCBM ([6,6]-phenyl-C₆₁-butyric acid methyl ester) /Au molecule system is proposed. In Fig.1, when PCBM in higher concentration, which owns higher density, has a promoting effect on conductivity and shows earlier current than the lower one and without PCBM one under Au doping (ML= Monolayer). In the meantime, after stopping the Au deposition, the current of the whole molecule system dramatically decreases within one day, but it gradually decreases in the following days. Because after Au doping, the diffused Au has the tendency to be stable, the current is decreased during that period. The conductivity in the PCBM/Au molecule system is due to the density of the PCBM molecule and the Au diffusion in the PCBM layer, which produces the hopping site for the electrons. The hopping site will determine the conductivity and the nonlinearity in the molecule system. In conclusion, the density of the PCBM molecule and the Au diffusion in the molecule system have the influence of conductivity.
[1] T. Chen, et al., Nature 577, 341 (2020).