Advanced Hybrid GaN/ZnO Nanoarchitectured Microtubes for Fluorescent Micromotors Driven by UV Light

Abstract

The development of functional microstructures with designed hierarchical and complex morphologies and large free active surfaces offers new potential for improvement of the pristine microstructures properties by the synergistic combination of microscopic as well as nanoscopic effects. In this contribution, dedicated methods of transmission electron microscopy (TEM) including tomography are used to characterize the complex hierarchically structured hybrid GaN/ZnO:Au microtubes containing a dense nanowire network on their interior. The presence of an epitaxially stabilized and chemically extremely stable ultrathin layer of ZnO on the inner wall of the produced GaN microtubes is evidenced. Gold nanoparticles initially trigger the catalytic growth of solid solution phase (Ga1–xZnx)(N1–xOx) nanowires into the interior space of the microtube, which are found to be terminated by AuGa‐alloy nanodots coated in a shell of amorphous GaOx species after the hydride vapor phase epitaxy process. The structural characterization suggests that this hierarchical design of GaN/ZnO microtubes could offer the potential to exhibit improved photocatalytic properties, which are initially demonstrated under UV light irradiation. As a proof of concept, the produced microtubes are used as photocatalytic micromotors in the presence of hydrogen peroxide solution with luminescent properties, which are appealing for future environmental applications and active matter fundamental studies.

Highly Porous and Ultra-Lightweight Aero-Ga2O3: Enhancement of Photocatalytic Activity by Noble Metals

“…However, an array of Ga 2 O 3 nanowires (NWs) terminated by Au nanoparticles grows inside the Ga 2 O 3 microtubes during the HVPE on sacrificial ZnO microtetrapods, as illustrated in Figure 3 b. The growth of these nanowires was elucidated in detail in a previous paper [ 43 ]. It was shown that the confined reaction conditions during the HVPE process and hydrothermal dissolution of ZnO lead to the metal-catalytic vapor–liquid–solid (VLS) growth of NWs.…”

“…Following this, the second coating is deposited on the aero-GaN architecture before the annealing is performed for the transformation of aero-GaN into aero-Ga 2 O 3 . Thin gold or platinum films were deposited in a Cressington 108 Sputter Coater machine as described in a previous paper [ 43 ]. The thermal treatment leads to the structuring of the initially continuous metal film and to the formation of hybrid photocatalysts.…”

Electrochemistry‐Based Light‐Emitting Mobile Systems

“…In the majority of examples of fluorescent swimmers, motion is achieved via bubble‐propulsion, enabled by the catalytic [67] or photocatalytic [68] disproportionation of hydrogen peroxide or by the spontaneous reduction of water on the surface of Mg or Zn [69–71] . In addition to self‐propulsion, motion control can be also obtained by embedding ferromagnetic components [72] .…”

“…An interesting approach to produce fluorescence emission is the incorporation of fluorophores inside the swimmer structure. For example, hybrid nanostructures made of GaN/ZnO/Au have been reported as photocatalytic self‐propelled light emitting swimmers [68] . Under UV irradiation these devices show a strong blue fluorescence due to the hybrid GaN/ZnO structure.…”

Asymmetry controlled dynamic behavior of autonomous chemiluminescent Janus microswimmers

“…17,18 In this context, an interesting concept is the design of swimmers that couple mechanical motion and light emission, which enables or facilitates their tracking in real time. Recently, light emitting dynamic systems made out of luminescent materials 19,20 or based on microelectronics (LEDs) have been described. [21][22][23][24][25] In these cases, bubble propulsion or electrokinetic mechanisms cause mechanical motion, whereas photon emission is ensured either by the intrinsic composition of the luminescent object under illumination or by a local voltage difference generated at the poles of the electronic devices.…”