Tuning ZnO nanorods photoluminescence through atmospheric plasma treatments

Abstract

Room temperature atmospheric plasma treatments are widely used to activate and control chemical functionalities at surfaces. Here, we investigated the effect of atmospheric pressure plasma jet (APPJ) treatments in reducing atmosphere (Ar/1‰ H2 mixture) on the photoluminescence (PL) properties of single crystal ZnO nanorods (NRs) grown through hydrothermal synthesis on fluorine-doped tin oxide glass substrates. The results were compared with a standard annealing process in air at 300 °C. Steady-state photoluminescence showed strong suppression of the defect emission in ZnO NRs for both plasma and thermal treatments. On the other side, the APPJ process induced an increase in PL quantum efficiency (QE), while the annealing does not show any improvement. The QE in the plasma treated samples was mainly determined by the near band-edge emission, which increased 5–6 fold compared to the as-prepared samples. This behavior suggests that the quenching of the defect emission is related to the substitution of hydrogen probably in zinc vacancies (VZn), while the enhancement of UV emission is due to doping originated by interstitial hydrogen (Hi), which diffuses out during annealing. Our results demonstrate that atmospheric pressure plasma can induce a similar hydrogen doping as ordinarily used vacuum processes and highlight that the APPJ treatments are not limited to the surfaces but can lead to subsurface modifications. APPJ processes at room temperature and under ambient air conditions are stable, convenient, and efficient methods, compared to thermal treatments to improve the optical and surface properties of ZnO NRs, and remarkably increase the efficiency of UV emission.

Stabilization of the Surface of ZnO Films and Elimination of the Aging Effect

“…Sheet resistance can be reduced by several orders of magnitude, due to the persistent photoconductivity effect, while resistivity is restored to high values after turning off UV radiation Materials 2021, 14, 6535 2 of 14 during the storage of samples under ambient conditions [17]. It has been shown that plasma treatment under a hydrogen atmosphere is an effective method for improving the electrical properties of ZnO films [18][19][20]. According to Dong et al, free carrier concentration and mobility in the ZnO can be varied from 1 × 10 17 cm −3 and 7 cm 2 V −1 s −1 in as-synthesized film up to 1 × 10 18 cm −3 and 39 cm 2 V −1 s −1 in the film treated in hydrogen plasma [19].…”

Tarnished silver–copper surfaces reduction using remote helium plasma at atmospheric pressure studied by means of high-resolution synchrotron x-ray photoelectron microscopy

“…In addition, since the reduction process is not limited to the topmost exposed layer, the electrons and hydrogen atoms are expected to migrate through the surface, as already speculated for copper oxides [7]. The migration of atomic hydrogen in polycrystalline structures, indeed, have been already observed and demonstrated a high mobility [38]. This means that some semiconductors will endure a spontaneous reduction process in contact with the afterglow while other will not endure such an electrochemical reaction.…”

Optical field coupling in ZnO nanorods decorated with silver plasmonic nanoparticles

“…In addition, low temperature and wet-chemical environment of the hydrothermally grown ZnO NRs and NWs tend to create severe native and intrinsic defects, which in turn can cause uncontrolled conductivity, lattice imperfections and fast electron-hole recombination rate 21 . Therefore, several solutions have been targeted to either modify the intrinsic crystalline properties of ZnO (annealing in different atmosphere, plasma treatment) and/or broaden its absorption profile through designing a combinatorial composite system via metal and non-metal doping [22][23][24][25][26][27] . In particular, coupling with noble metals is an effective approach to enhance the visible light absorption of wide bandgap semiconductors, which inherently can also assist the passivation of their intrinsic defects 6,7 .…”