Fabrication and Optical Properties of Large-Scale ZnO Nanotube Bundles via a Simple Solution Route

Abstract

Large-scale ZnO nanotube bundles were successfully synthesized by a single solution method at lower temperature. Every ZnO nanotube bundle is composed of closely packed nanotubes, with inner diameters of ∼350 nm and wall thicknesses of ∼60 nm, and forms radiating structures. The influence of the reaction time on the size and shapes of the ZnO samples was studied in detail, and the results revealed that the reaction time plays an important role in determining final morphologies of the samples. The formation of the tubular structure may be due to the selective dissolution of the metastable Zn-rich (0001) polar surfaces, and a possible growth model was proposed. Optical properties of the ZnO nanotube bundles were also investigated by photoluminescence (PL) spectroscopy. It was found that the UV emission peak of the nanotube bundles did not change its position, while the visible emission band showed an obvious red shift when the nanotube bundles were annealed in ambient oxygen. Moreover, the UV emission was further identified to originate from the radiative free exciton recombination by the temperature-dependent PL.

Indirect optical transition due to surface band bending in ZnO nanotubes

“…1 It is obvious that 1D nanostructures of ZnO with a wide band gap ͑E g = 3.37 eV͒ and a large exciton binding energy ͑60 meV͒ have become important nanomaterials owing to their special properties and potential applications in nanoscale electric and optoelectronic devices. [1][2][3][4][5][6][7] During the past decade, different 1D ZnO nanostructures such as nanotubes, [8][9][10][11][12][13][14][15] nanowires, 1 nanorods, 16 nanobelts, 17,18 tetrapods, 19 and nanoribbons 20 have been successfully fabricated by different methods. Among these 1D structures, the tubular structures of ZnO become particularly important since numerous applications, such as dye-sensitized photovoltaic cells 21 and bio/ gas sensors, 22,23 are required their high porosity and large surface area to fulfill the demand for high efficiency and activity.…”

“…Although the synthesis of ZnO nanotubes ͑ZNTs͒ have been successfully realized by a few groups, the systematical investigations on their optical properties, especially temperature-dependent photoluminescence ͑PL͒ and timeresolved PL ͑TRPL͒, are still limited. [13][14][15] It is well known that both temperature-dependent PL and TRPL are very sensitive tools for characterizing the radiative and nonradiative recombination process in the materials, which are very helpful in understanding the optical performance and mechanism of the materials. Therefore, the investigation on the temperature-dependent PL and TRPL properties of ZNTs are necessary and urgent to be done for prompting their applications.…”

“…To date, ZnO nantubes has been synthesized by electrochemical method, [10][11][12] low temperature solution method, 8,9,13,14 vapor phase growth 15 and so on. As a common knowledge, the reproducibility and control of growth in synthesis of ZnO nanostructures are a major issue.…”

Fabrication, Structural Characterization and Optical Properties of the Flower-Like ZnO Nanowires

“…Then the ZnO nanowires sprouted from these nuclei surfaces and grew along the [0001] direction because the surface energy of the (0002) facet is the lowest. According to the ZnO crystal growth mode, the growth rate along the [0001] direction is faster than along any other directions [39]. So, the growth along the [0001] direction is a dominating growth facet compared to other growth facets.…”

Synthesis of Inorganic Nanotubes

“…13). [108] In this method, an aqueous solution of Zn(NO 3 ) 2 and hexamethylenetetramine is stirred over long periods and heated at 90 8C. This method yields nanotubes with an inner diameter of $350 nm and a wall thickness of $60 nm, and forms radiating structures.…”