ZnO micro/nanocrystals grown by laser assisted flow deposition

Abstract

Laser assisted flow deposition (LAFD) is a very high yield method based on a vapor-solid mechanism, allowing the production of ZnO crystals in a very short time. The LAFD was used in the growth of different morphologies (nanoparticles, tetrapods and microrods) of ZnO micro/nanocrystals and their microstructural characterization confirms the excellent crystallinity of the wurtzite structure. The optical properties of the as-grown ZnO crystals investigated by low temperature photoluminescence (PL) evidence a well-structured near band edge emission (NBE) due to the recombination of free (FX), surface (SX) and donor bound (D 0 X) excitons. Among the most representative emission lines, the 3.31 eV transition was found to occur in the stacking faults-free microrods. The luminescence behavior observed in H passivated samples suggests a closer relationship between this optical center and the presence of surface states.Besides the unintentionally doped micro/nanocrystals, ZnO/Ag and ZnO/carbon nanotubes (CNT) hybrid structures were processed by LAFD. The former aims at the incorporation of silver as a p-type dopant and the latter envisaging photovoltaic applications. Silver-related spherical particles were found to be inhomogeneously distributed at the microrods surface, accumulating at the rods tips and promoting the ZnO nanorods re-nucleation. Despite the fact that energy dispersive X-ray measurements suggest that a fraction of the silver could be incorporated in the ZnO rods, no new related luminescence lines or bands were observed when compared with the as-grown samples. For the case of the ZnO/CNT composites two main approaches were adopted: i) a direct deposition of ZnO particles on the surface of vertically aligned multi-walled carbon nanotubes (VACNTs) forests without employing any additional catalyst and ii) new ZnO/CNT hybrids were developed as buckypaper nanocomposites. The use of the LAFD technique in the first approach preserves the CNTs structure and alignment and avoids the collapse of the VACNTs array, which is a major advantage of this method. On the other hand, LAFD grown ZnO nanoparticles and tetrapods were used to produce ZnO/CNT buckypaper nanocomposites. When compared with the as-grown samples the PL spectra of the composites structures behave differently. For the case of the ZnO/VACNTs no changes on the peak position and spectral shape were observed. Only an enhancement of the overall luminescence was found to occur. On contrary, for the buckypaper nanocomposites notable changes on the spectral shape and peak position were observed, likely due to distinct surface band bending effects for the ZnO nanoparticles and tetrapods embedded in the CNTs.

Insights on luminescence quenching of ZnO tetrapods in the detection of hCG

“…It is worth to comment that different spots of the samples were probed to evaluate their structural uniformity and similar spectra were recorded in all cases. Sharp and well-defined peaks, as the ones observed here, are typically an indication of the high degree of crystallinity of the samples, indicating the high crystalline quality of the LAFDproduced ZnO [44,46,47]. As can be seen from the spectra, no significant differences were observed in the spectral shape of the Raman spectra with the surface modification procedures.…”

“…The branches of the same TP present similar dimensions and morphology. However TPs with different sizes (Figure 2 (b) can be found in the same growth batch due to the high temperature gradient inside the growth chamber [36,44]. Dimensions from hundreds of nanometres to a few micrometres were measured for the length of the branches, while the diameter of the wider part is always in the nm range [36].…”

Stiff Diamond/Buckypaper Carbon Hybrids

“…CNT buckypapers mixed with diamond particles in a weight ratio of 2:1 were prepared in isopropyl alcohol (IPA, ≥99.8%, Sigma-Aldrich) following six main steps . (1) CNT suspensions of 1 g L –1 were dispersed by high-speed shearing for 30 min (IKA T25-Ultra-Turrax, 20 500 rpm) with a shear force of 96 Pa to eliminate big CNT agglomerates.…”

“…CNT buckypapers mixed with diamond particles in a weight ratio of 2:1 were prepared in isopropyl alcohol (IPA, ≥99.8%, Sigma-Aldrich) following six main steps 18 . (i) CNT suspensions of 1 g.l -1 were dispersed by high-speed shearing for 30 min (IKA T25-Ultra-Turrax, 20,500 rpm) with a shear force of 96 Pa to eliminate big CNT agglomerates; (ii) The CNT suspension was sonicated (Selecta, 60 kHz, 200 W) for 60 min to yield mixtures of individualized CNTs and small sized agglomerates (< 3 µm) 19 .…”

Dual Transduction of H2O2 Detection Using ZnO/Laser-Induced Graphene Composites

“…The as-prepared LIG was then carefully scraped from the polyimide substrate with the aid of a razor blade, resulting in a fine powder (see a schematic representation in Figure 1). ZnO was produced by laser-assisted flow deposition, whose detailed description can be found elsewhere [71][72][73]. In brief, LAFD is a technique based on a thermal evaporation process that uses a highly focused CO2 laser ( 200 W, Spectron Laser Corp, Azusa, CA, USA) as the heating source.…”