Controlled Synthesis of Single‐Crystalline ZnO Nanoflakes on Arbitrary Substrates at Ambient Conditions

Abstract

www.particle-journal.com www.MaterialsViews.com COMMUNICATIONsubstrates for 2D morphology-controlled ZnO nanostructure growth. Graphene is a 2D carbon nanostructure, which has been studied extensively in recent years due its remarkable mechanical, optical, and electronic properties. [ 13 ] These properties makes graphene a promising candidate for many potential applications including electronic and optical devices. Graphene electrodes with nanostructures can also be applied as synergistic electrodes for different fl exible and transparent conducting devices. The growth mechanism of the synthesized 2D ZnO nanostructures is studied in detail with the help of scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). Based on the data, we believe that ZnO nanofl akes are oriented along (0001) plane and grow laterally along (0110) plane. Furthermore, the electrical and optical data show excellent conduction and transmission properties, respectively. Our synthesis method is a low-cost, low-temperature, scalable, and potentially high-throughput process, which can be further extended for the synthesis of wide range of other 2D materials for different applications in electronics and optoelectronics devices.We used zinc nitrate hexahydrate [ZNH; Zn(NO 3 )·6H 2 O] and hexamethylenetetramine [HMT; (CH 2 ) 6 ·N 4 ] (both from SigmaAldrich) for the sonochemical synthesis of ZnO nanofl akes. [ 12 ] ZNH provides Zn 2+ ions and H 2 O molecules in the solution provide O 2− ions. HMT has been used as a shape-inducing polymer in ZnO nanowire growth as polymer as it attaches to the nonpolar facets of ZnO cutting the supply of Zn 2+ ions, thus allowing the growth of ZnO in only <0001> direction. [ 14 ] However, the shape of the nanostructures strongly depends on the concentration of ZNH/HMT solutions, which affects the precipitation mechanism of the oxide. [ 15,16 ] It was observed that as the concentration of ZNH/HMT aqueous solution increased, the length of the ZnO nanorods decreased. [ 15 ] In the present case, the concentration of the precursors is increased by 10-20 times and the sonication amplitude is increased by 20% compared with the earlier process. [ 12 ] The process temperature does not exceed 70 ° C, as amplitude of the sonication is increased. At the higher concentrations used in this process and fast reaction rates achieved under sonication, HMT releases large amounts of OH − and NH 4 + ions in a short period of time. At this higher concentrations, precipitation of Zn 2+ ions occurs at faster rate than required for HMT-assisted oriented growth of ZnO nanostructures, [ 14,15 ] resulting in growth of nonpolar planes of ZnO along with polar (0001) plane forming parallelogram-shaped 2D ZnO nanofl akes.Figure 1 a,b shows the SEM pictures of the ZnO nanofl ake growth on Si substrate at 30 s and 1 min. 2D ZnO nanofl akes grow from sheet structures to hexagonal crystal structure, Semiconductor nanostructures have attracted considerable research i...

Perforated ZnO nanoflakes as a new feature of ZnO achieved by the hydrothermal-assisted sol–gel technique

“…This feature is due to the inherent structure of wurtzite. In addition, the thickness of the particles was \50 nm; therefore, these particles could be considered nanoflakes, which are similar to the other researchers' results [9,20]. This irregularity is related to the crystal growth along c orientation.…”

“…The hexagonal flake-like particles are observed with approximately Ø = 1 lm and oriented in \ 0001 [ direction [20]. This feature is due to the inherent structure of wurtzite.…”

Sonochemistry: Science and Engineering

“…The change in precursor concentration, as a result, affects morphology of nanoparticle during growth [21][52] [70]. In a typical case of ZnO synthesis, the shape of ZnO changed from 1D nanorods and nanowires to 2D nanosheets, nanocups, nanoflakes etc.…”

“…The effect of time of experiment and number of cycle induces morphological variation in nanomaterials formation [21][77][78] [79]. With increasing time and cycle of sonication, formation of new structures is made easier by the primary growth that serve as seed.…”

“…Evidence of nuclear fusion during cavitation, though a disputed concept, epitomizes the effect of ultrasound and presents a simple, viable tool to study nuclear reactions [15]. Such conditions can induce abnormal physical and chemical changes and facilitate the very basic reaction between atoms and molecules to produce extraordinary class of materials [16] [17] [18] [19][20] [21]. However, the utility of sonochemistry lies in the fact that the ions and radicals inside the bubble comes from the chemical solution; therefore, choosing appropriate chemicals based on their vapor pressure can help customize the overall process.…”