Controlling the Growth and Luminescence Properties of Well-Faceted ZnO Nanorods

Abstract

In this work, we synthesized ZnO nanorods by a wet chemical process. By varying different parameters of the synthesis process like precursor concentration, solvent used, surfactant, temperature, and reaction time, we were able to control the aspect ratio (l/d) and sharpness factor (S f ) h/b) of the rods. Rods with an aspect ratio of ∼20 and a sharpness factor of 10 were repeatedly obtained and characterized from scanning electron microscopy. High-resolution transmission electron microscopy and dark field analysis revealed that nanorods grow as a single crystal along the c axis [0001]. UV and visible emission was obtained in both flat-and sharp-terminated rods. According to the XPS analysis, rods present an excess of Zn 2+ of ∼4% that is responsible for the strong yellow emission band. Such defects were removed by annealing of the sample at 200 °C for 2 h. Possible mechanisms of changes in the morphology produced by changes in the synthesis process are also discussed.

Origin of the surface recombination centers in ZnO nanorods arrays by X-ray photoelectron spectroscopy

“…We also found in Figure 4(a) and 4(b) that the component O3 ascribed to chemisorbed oxygen can not be removed by annealing even at temperatures as high as 500 o C. As mentioned before, O3 is usually ascribed to the specific chemisorbed oxygen, such as -CO 3 , adsorbed O 2 or adsorbed H 2 O [26][27][28][29][30][31][32][33][34][35]. In Figure 4 it can be observed that the binding energy of the O3 peak shifts from 532.87±0.3 eV to 532.28 ±0.3 eV and the FWHM also decreased from 2.01 eV to 1.60 eV after annealing.…”

“…The peak position of O3 can vary depending on adsorbant, e.g. from 532.25 eV [29] to 533.21 eV [35], and the exact energy position depended on the relative ratio between the different components involved in O3 peak due to the growth process [26][27][28][29][30][31][32][33][34][35].…”

“…Although some groups have reported the possible functional groups attached in the surface of the ZnO [25][26][27][28][29][30][31][32][33][34][35], so far, there are no investigations which try to build the relationship between the chemical origin and surface recombination centers. On the basis of the discussion in the first paragraph, we believe that the investigation on identifying the chemical origin of surface recombination center is rather important than just revealing the existence of surface recombination in the emission process, because it will open to an effective way to control the surface recombination，utilize the surface states for sensor application and efficiently enhance the properties of optoelectronic devices based on ZnO nanostructures.…”

Effect of Heat Treatment Method on Properties of ZnO Thin Films Deposited by RF Magnetron Sputtering

“…The Zn-O bonds of the ZnO thin film annealed by furnace show stronger than that of the other samples. Also, the XPS spectra of O 1s exhibit component located at about 528.85 eV, which is related to O 2− ion in ZnO thin films surrounded by Zn atoms with full complement [12]. The O-Zn bonds in the ZnO thin film annealed by furnace show stronger than that of the other sample, same like the Zn 2p 3/2 .…”

Toward the Optimization of Low-temperature Solution-based Synthesis of ZnO Nanostructures for Device Applications

“…The room-temperature luminescence of ZnO NSs is usually distinguished by a sharp UV emission peak centered at ~ 380 nm and attributed to a near-band-edge emission (NBE), and a broad emission peak covers the entire visible region extending between 400 -750 nm as shown in Figure 2.3. [40][41][42][43][44] However, the source of these deep level emissions (DLEs) in the ZnO is highly controversial, and possibly these DLE peaks are composed of multiple sub-bands e.g., green, yellow and orange-red bands. The green emission band centered at ~ 500 -550 nm, is usually ascribed to oxygen vacancy (VO) or zinc vacancy (VZn).…”