Li-doped ZnO nanorods with single-crystal quality – non-classical crystallization and self-assembly into mesoporous materials

Abstract

The benefits and promise of nanoscale dimensions for the properties of (ceramic) semiconductors are widely known. 1-D nanostructures in particular have proven to be of extraordinary relevance due to their applicability in future electronic and optoelectronic devices. Key to successful technological implementation of semiconductor nanostructures is the control of their electronic properties via doping. Despite its tremendous importance, precise chemical doping of defined nano-objects has been addressed rarely so far. Frequent problems are the creation of secondary defects and related undesired property changes by incorporation of hetero-elements, and the difficulty in ensuring a uniform and precise positioning of the dopant in the nanocrystal lattice. Here, we present the synthesis of Li-doped zinc oxide nanorods, which possess excellent (single-crystal) quality. The method is based on a novel non-classical crystallization mechanism, comprising an unusually oriented disassembly step. Afterwards, the nanorods are incorporated into mesoporous layers using colloidal self-assembly. Proof-of-principle gas sensing measurements with these novel materials demonstrate the beneficial role of Li-doping, indicating not only better conductivity but also the occurrence of catalytic effects.

Nanoparticle shape anisotropy and photoluminescence properties: Europium containing ZnO as a Model Case

“…Because these metal cations should be incorporated into the lattice of the particles E@ZnO, we deploy a method, which has been developed by us in 2011. 79,80 ZnO is generated in a water-in-oil emulsion via a sol-gel route using a special organometallic precursor system. The mentioned molecular compounds have a heterocubane structure [MeZnOR] 4 (with R = alkyl), and precursor properties have been investigated extensively.…”

“…24,[83][84][85][86][87][88] ZnO formation in the emulsion based method proceeds via solidification of the emulsion droplets as amorphous particles, followed by morphogenesis induced by crystallization. 79,80 The described method can easily be applied towards the synthesis of ZnO nanorods (see also ESI-1 †). Because of the gelation of the emulsion droplets as a transition state, ions dissolved in the aqueous phase become entrapped inside the particles and are this way incorporated in the ZnO lattice (see Scheme 1).…”

“…The first important question to answer is, what the morphological effect of cations is, while the crystalline nanorods are forming. Thus, a series of metal cations with an ionic radius smaller (Li + , Al 3+ ), 80,89 close to (Cu + , Mn 2+ ) 90 or larger (Eu 3+ , La 3+ , Na + ) 62,91 compared to Zn 2+ (r = 0.74 Å) were selected and was applied at two different concentrations (χ metal = 0.03% and 0.7%). Furthermore, an experiment was performed with additional Zn 2+ dissolved in the emulsion droplets.…”

Hydrolysis of organometallic and metal–amide precursors: synthesis routes to oxo-bridged heterometallic complexes, metal-oxo clusters and metal oxide nanoparticles

“…More recently, Polarz and co-workers prepared highly crystalline Li doped ZnO nanorods by using an oil in water emulsion technique, in which the Zn precursor is added to the oil phase with Li salts dissolved in the aqueous phase. 232 Amorphous gel-like particles are initially formed, which crystallise into clusters of wurzite nanorods; the authors propose that this unusual growth process benefits from intimate doping as the Li ions are trapped in the vicinity of the growing ZnO structure. A single 7 Li solidstate NMR resonance was identified suggesting that Li + is replacing Zn 2+ within the lattice.…”

Lithium doping and photoluminescence properties of ZnO nanorods

“…Although there are few reports on Li doped ZnO thin films 13 and nanostructures. 14,15 Here in this letter, we report the growth and Li doping of ZnO NRs by a low temperature thermal decomposition method, which is a cost effective and rapid synthesis method for fabricating ZnO NRs. This growth method have some advantages compared with other growth methods, such as use of simple equipment, low temperature deposition, low cost, less hazardous, and does not require catalyst.…”