Preparation of ZnO Nanorod/Graphene/ZnO Nanorod Epitaxial Double Heterostructure for Piezoelectrical Nanogenerator by Using Preheating Hydrothermal

Summary

One-step fabrication method for obtaining freestanding epitaxial double heterostructure is presented. This approach could achieve ZnO coverage with a higher number density than that of the epitaxial single heterostructure, leading to a piezoelectric nanogenerator with an increased output electrical performance.

Abstract

Well-aligned ZnO nanostructures have been intensively studied over the last decade for remarkable physical properties and enormous applications. Here, we describe a one-step fabrication technique to synthesis freestanding ZnO nanorod/graphene/ZnO nanorod double heterostructure. The preparation of the double heterostructure is performed by using thermal chemical vapor deposition (CVD) and preheating hydrothermal technique. In addition, the morphological properties were characterized by using the scanning electron microscopy (SEM). The utility of freestanding double heterostructure is demonstrated by fabricating the piezoelectric nanogenerator. The electrical output is improved up to 200% compared to that of a single heterostructure owing to the coupling effect of the piezoelectricity between the arrays of ZnO nanorods on the top and bottom of graphene. This unique double heterostructure have a tremendous potential for applications of electrical and optoelectrical devices where the high number density and specific surface area of nanorod are needed, such as pressure sensor, immuno-biosensor and dye-sensitized solar cells.

Introduction

Recently, the portable and wearable electronics devices became an essential element for a comfortable life owing to the nanotechnology development, which results in the tremendous demands for a power source in the range of microwatt to milliwatt. Considerable approaches for the power source of portable and wearable devices have been achieved by the renewable energy, including solar energy ^1,2, thermal ^3,4 and mechanical source ^5,6. Piezoelectric nanogenerator have been intensively studied as one of possible candidate for energy harvesting device from environments, such as rustling the leaf ⁷, sound wave ⁸ and move....

Protocol

1. Chemical Vapor Deposition (CVD) Growth of Single Layered Graphene

Note: The graphene used in this study was grown on copper (Cu) foil using the thermal chemical vapor deposition (CVD) technique (Figure 1A). Growth is uniform over an area of 2 cm x 10 cm for this system.

1. Wash the Cu foil (2 cm x 10 cm) with mild flow of acetone, isopropyl alcohol (IPA) and distilled water, respectively.
2. Place the cleaned Cu foil in a 2 in. quartz tube (Figure 1B), and then purge the chamber with vacuum (approximately 1 mTorr) for 10 min by using rotary pump.
3. Configure the temperature of dig....

Results

The scanning electron microscopy (SEM) images shown in Figure 6 present the morphologies of hydrothermally grown ZnO nanorods. The preheating hydrothermal technique can result in two different nanostructures depending on the growth time. Figure 6A shows a typical image of ZnO nanorod on graphene/PET substrate at the growth time of 5 hr. In contrast, the image shown in Figure 6B indicates that the growth of ZnO nanorod at the growth time o.......

Discussion

Please note that the high quality (>99.8%, annealed) of Cu foil should be considered as a substrate for successful growth of single layer graphene. Otherwise, the single layer graphene is not uniformly grown over the Cu foil, leading to dramatically decrease in conductivity of graphene. A 1 hr annealing at high temperature would help the improvement of the Cu foil crystallinity as well as removal of any contaminants from the Cu foil.

The growth of ZnO nanorod depends on the conditions for .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Cu foil	Alfa Aesar	13382
poly(methyl methacrylate) (PMMA)	Aldrich	182230
zinc nitrate hexahydrate	Sigma-Aldrich	228732
hexamethylenetetramine (HMT)	Sigma-Aldrich	398160
polyethylenimine (PEI)	Sigma-Aldrich	408719
indium tin oxide (ITO) coated PET	Aldrich	639303
Silicone Elastomer Kit	Dow Corning	Sylgard 184 a, b
Nickel Etchant Type1	Transene Company	41212