Variations In Optical Emission Research Articles

Enhanced Photocurrent Generation in Proton‐Irradiated “Giant” CdSe/CdS Core/Shell Quantum Dots

AbstractGroup II–VI quantum dots (QDs) possess tunable electrical and optical properties that make them very attractive for high‐tech applications and power generation. The effects of proton irradiation on both the structural and physical properties of “giant” CdSe/CdS core–shell QDs (g‐CS QDs) are investigated. These experiments shed light on photoelectron delocalization in g‐CS QDs, where current linkages and strong variations in optical emission result from the spatial extension of the photoelectron wavefunctions over the conduction bands of CdSe and CdS. Monte Carlo simulations of ion–matter interactions show that the damaging rates can be set from the energy of impinging protons to promote the formation of structural defects in the core or shell. The formation of nanocavities is demonstrated after irradiation doses higher than ≈1017 H+ cm−2, while a continuous decrease in luminescence intensity is observed for increasing proton fluencies. This feature is accompanied by a concomitant lifetime decrease marking the rise of nonradiative phenomena and the occurrence of greater photocarrier transfers between CdS and CdSe. Current‐to‐voltage characterizations evidence that proton implantation can be implemented to enhance the photocurrent generation in g‐CS QDs. This increase is attributed to the delocalization of photoelectrons in the CdS shell, whose improvement is found to promote electron–hole pair separation.

Pulsed dc operation of a Penning-type opposed target magnetron

This article describes the medium frequency pulsed dc power operation of a Penning-type (opposed target) magnetron to sputter copper in an argon atmosphere. The current–voltage characteristics of the magnetron are detailed in dc and pulsed dc conditions. The variations in optical emission from the excited species in the plasma are measured as a function of time during the applied pulses. The intensity of the argon emissions closely follows the variations of the target voltage but the different behavior of the copper emissions shows some evidence of self-sputtering of the target by copper ions. The energy and flux of the ions arriving at the substrate are measured as a function of time and it is shown that during pulsed operation, as the pulse off-period is extended, there are large increases in ion energy and ion flux. The initial overshoots in the target voltage cause a rapid expansion of the plasma sheath at the analyzer probe and wide variations in plasma potential leading to an initial pulse of high energy ions during the first 500ns. The plasma potential then settles to ∼40eV and there is a second peak in ion flux at this energy with a peak at ∼4000ns due to the increased ion drift resulting from electron extraction from the target.