Multistage growth of monocrystalline ZnO nanowires and twin-nanorods: oriented attachment and role of the spontaneous polarization force

Abstract

Our understanding of crystal growth mechanisms has changed deeply in the past few decades. Particularly, the oriented attachment of intermediate nanoparticles has been accepted to be a crucial crystal growth mechanism that is distinct from the traditional one involving nucleation and Ostwald ripening. However the details of the oriented attachment process are not readily observed experimentally, and little is known about the driving force and the dynamics involved in oriented attachment. In this respect, ZnO is an ideal material because it possesses strong spontaneous polarization which may easily drive oriented attachment during its crystal growth. We study experimentally and theoretically the complete crystal growth process (from primitive amorphous nanoclusters to ultimate single nanocrystals) of one-dimensional ZnO nanocrystals growing in water/ethanol at high temperatures. The results reveal that both axial (along the direction of the polarization axis) and lateral oriented attachment of the intermediates occurs during the growth process of the one-dimensional ZnO nanocrystals. Calculation based on the force and interaction model reveals that the axial oriented attachment driven by the spontaneous polarization force dominates the crystal growth of ZnO nanocrystals, and the van der Waals force also plays a role in driving oriented attachment. The study shows that oriented attachment of intermediate nanoparticle ensembles induces formation of the symmetric twin-nanorods. These results improve our understanding of the growth mechanism of nanocrystals in a liquid medium.

Direction-specific interaction forces underlying zinc oxide crystal growth by oriented attachment

“…Since its discovery in natural systems 2 , 3 there has been growing interest in exploiting oriented attachment to construct hierarchically structured crystalline materials. Examples include metals such as Au 7 and Ag 8 , alloys such as ZnTe 9 , Pt-Ni, Pt-Cu, and Pt-Fe 10 , 11 , metal oxides such as ZnO 12 , 13 , TiO 2 3 , MnO 14 , and α-Fe 2 O 3 15 , metal sulfides such as PbS 16 , ZnS 17 , Ag 2 S 18 , and CdS 18 , 19 , and metal selenides such as PbSe 20 , CdSe 19 , NiSe 2 21 . Furthermore, surfactants have been widely used in experiments to facilitate oriented particle assembly via preferential adsorption on crystal surfaces.…”

“…It has been used to fabricate nanogenerators 33 , solar cells 34 , 35 , LEDs 36 , and photo sensors 37 , and as a photocatalyst to degrade organic pollutants 38 . Both theoretical calculations and experimental data have indicated the ZnO nanocrystals oriented aggregate through the (001)/(002) surface to form the rod-like single crystals 12 , 13 , 39 . Thus our study focuses on Zn-terminated ZnO(0001) interaction with its partner O-terminated ZnO(000 ) face as a model oriented attachment system.…”

A New Functional Composite for Photovoltaic and Sensor Applications

“…The precursor anatase TiO 2 that was in the particle form successively transformed into nanorod on increasing the hydrothermal reaction duration from 12 to 48 h. This structural transformation could have happened by Ostwald ripening during which many small crystals slowly disappear, except for a few that grow larger at the expense of the small crystals, which act as fuel for the growth of bigger crystals. [ 28–30 ] Kolen'ko et al. reported the synthesis of nanorods in one step by hydrothermal treatment in a NaOH solution followed by an acid treatment to produce sodium‐free nanorods.…”

Surface Chemistry Affects the Efficacy of the Hydration Force between Two ZnO(101̅0) Surfaces

“…The surface chemistry of ZnO(101̅ 0) exposed up to several water layers is well characterized, and both experimental and theoretical studies find congruent results. 13,14 Although ZnO(0001) basal surfaces are a more likely candidate than (101̅ 0) for OA in experiments, 2,15 the study of latter avoids the complexity of reconstruction to eliminate the dipole on the former surface. Specifically, different reconstruction mechanisms have been revealed for Zn-and Oterminated (0001) surfaces, 16−20 and a large discrepancy exists between experiments and calculations in terms of how much dissociation of adsorbed water occurs on the O-terminated surface.…”