Strong light scattering and broadband (UV to IR) photoabsorption in stretchable 3D hybrid architectures based on Aerographite decorated by ZnO nanocrystallites

Abstract

In present work, the nano- and microscale tetrapods from zinc oxide were integrated on the surface of Aerographite material (as backbone) in carbon-metal oxide hybrid hierarchical network via a simple and single step magnetron sputtering process. The fabricated hybrid networks are characterized for morphology, microstructural and optical properties. The cathodoluminescence investigations revealed interesting luminescence features related to carbon impurities and inherent host defects in zinc oxide. Because of the wide bandgap of zinc oxide and its intrinsic defects, the hybrid network absorbs light in the UV and visible regions, however, this broadband photoabsorption behavior extends to the infrared (IR) region due to the dependence of the optical properties of ZnO architectures upon size and shape of constituent nanostructures and their doping by carbon impurities. Such a phenomenon of broadband photoabsorption ranging from UV to IR for zinc oxide based hybrid materials is novel. Additionally, the fabricated network exhibits strong visible light scattering behavior. The developed Aerographite/nanocrystalline ZnO hybrid network materials, equipped with broadband photoabsorption and strong light scattering, are very promising candidates for optoelectronic technologies.

Figure 1

Aerographite (AG) nano- and microtubular hollow tetrapods (AGHT) as universal templates for growing hybrid 3D nanomaterials: (a) Fabrication concept for decorating the AGHT with ZnO nanotetrapods (ZnO-nT) using a single step sputtering process. By changing the deposition time, the morphology of loaded nanostructures can be tailored. (b–c) Typical SEM images demonstrating the morphologies of AGHT backbone before and after loading with ZnO nanostructures respectively.

Figure 2. SEM images demonstrating the morphologies of AGHT networks loaded with different types of ZnO nanostructures.

(a–c) SEM images at increasing magnifications (left to right corresponding to AG templates decorated with well separated ZnO nanodots. (d–f) Longer deposition time leads to complete coverage of AG tubes with ZnO nanocrystals as can be seen in zoomed series of SEM images (left to right). (g–i) Under appropriate deposition conditions, growth of ZnO nanotetrapods occurs which leads to the formation of hybrid material in form of self-assembled hierarchical networks of ZnO nanotetrapods on the AGHT architectures, the SEM morphologies at increasing magnifications (left to right) demonstrate such a hybrid network. The arm thickness of ZnO nT is ~100 nm.

Figure 3. Cathodoluminescence studies on ZnO-Aerographite hybrid networks.

With increase in deposition time, the growth behavior of ZnO structures varies from well separated ZnO nanodots to self-assembled hierarchal network of ZnO nanotetrapods. (a–c) SEM images for AG networks coated with ZnO at different deposition times (low to high) and corresponding μ-CL images (marked with arrow on right, see text for details). The CL spectra corresponding to Aerographite coated by ZnO nanodots, 150 nm ZnO @ AG, and 1 μm ZnO @ AG are shown in (d–f) respectively. The increase in intensity of UV exciton band emission peak for 1 μm ZnO film (f) is clear indication for the growth of crystalline ZnO nanostructures. The feature at ~1.6 eV in (e,f) is a second order grating artefact.

Figure 4. The scheme of defect levels responsible for CL bands.

Figure 5

(a) SEM image of a fragment of Aerographite covered by ZnO tetrapods (scale bar 1 μm), and color-composite μ-CL images: (525 + 675) nm (b), and (360 + 400 + 525) nm (c). (d) Illustrates the scattering behaviour of green light generated by a laser pointer.

Figure 6. Broadband photosensitivity of the ZnO-Aerographite hybrid nanomaterial in UV, visible and infrared regions of spectrum (see text for details).