Doping-induced realignment of molecular levels at organic–organic heterojunctions

This article examines how the concept of alignment of charge neutrality levels (CNL) can be used to explain and predict interface dipole and molecular level offset at organic–organic (OO) heterojunctions. The application of the model of CNL alignment to interfaces between undoped materials is reviewed first. The model is then extended to explain the shift of the CNL upon electrical doping of an organic material, and the resulting change in interface dipole and molecular level alignment. This approach provides, at this point, the first comprehensive prediction of energetics at OO heterojunctions.     

Submillimeter wave induced resistance oscillations in ultra-high mobility two-dimensional electron systems

Submillimeter wave induced resistance oscillations in two ultra-high mobility GaAs/Al_0.24Ga_0.76As quantum well samples have been investigated by means of a backward wave oscillator and far-infrared laser at ³He temperatures. Subnikov–de Haas oscillation, submillimeter wave induced resistance oscillation, and magnetoplasmon resonance occur simultaneously in this frequency regime. The primary radiation induced resistance minimum shifts toward cyclotron resonance with increasing radiation frequency. The positions of these minima agree well with those of the magnetoplasmon resonance. The higher-order harmonics of the resistance oscillation remain around the multiples of the cyclotron resonance frequency. An in situ transmission measurement exhibits an asymmetric broadening of the cyclotron resonance, appearing as a combination of the cyclotron resonance and the magnetoplasmon resonance, but no features directly linked to the microwave induced resistance oscillation can be seen.     

The growth mechanism of pentacene-fullerene heteroepitaxial films

The growth of pentacene on C₆₀ film has been studied in real-time by low energy electron microscope. The standing-up phase overgrows on the lying-down phase at room temperature with increasing film thickness. At intermediate temperature we observed two distinct types of nucleation: an earlier nucleation of lying-down phase and a delayed nucleation of standing-up phase on the bare C₆₀ surface between islands of lying-down phase. Further thermal activation control enabled us to tune the types of nucleation and the standing-up phase without co-presence of the lying-down phase could be achieved above ∼70 °C.