Reverse-loop impedance profile in Bi2S3 quantum dots

Bismuth sulfide quantum dots (ϕ ∼ 12 nm) with two-dimensional platelet morphology synthesized using a simple aqueous colloidal method exhibit directional growth along 〈2 1 1〉 direction. Impedance characteristics of this two-dimensional quantum structure yields a characteristic semi-circular profile due to a classical Voigt element in addition to a semi-circle like loop in the negative imaginary part of the impedance Nyquist plot. The apparent inductive reverse-loop impedance profile observed, a distinguishing feature of this study can be explained on the basis of an unusual negative resistor–capacitor combination, realized due to relaxation of surface states in this technologically important semiconductor–quantum structure.