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We demonstrate an efficient possibility to synthesize vertically aligned pure zinc oxide (ZnO) and Co-doped ZnO nanorods (NRs) using the low-temperature aqueous chemical synthesis (90°C). Two different mixing methods of the synthesis solutions were investigated for the Co-doped samples. The synthesized samples were compared to pure ZnO NRs regarding the Co incorporation and crystal quality. Electron paramagnetic resonance (EPR) measurements confirmed the substitution of Co2+ inside the ZnO NRs, giving a highly anisotropic magnetic Co2+ signal. The substitution of Zn2+ by Co2+ was observed to be combined with a drastic reduction in the core-defect (CD) signal (g ~ 1.956) which is seen in pure ZnO NRs. As revealed by the cathodoluminescence (CL), the incorporation of Co causes a slight red-shift of the UV peak position combined with an enhancement in the intensity of the defect-related yellow-orange emission compared to pure ZnO NRs. Furthermore, the EPR and the CL measurements allow a possible model of the defect configuration in the samples. It is proposed that the as-synthesized pure ZnO NRs likely contain Zn interstitial (Zni+) as CDs and oxygen vacancy (VO) or oxygen interstitial (Oi) as surface defects. As a result, Co was found to likely occupy the Zni+, leading to the observed CDs reduction and hence enhancing the crystal quality. These results open the possibility of synthesis of highly crystalline quality ZnO NRs-based diluted magnetic semiconductors using the low-temperature aqueous chemical method. [ABSTRACT FROM AUTHOR]

In this paper, we have synthesized Zn1-xAgxO (x = 0, 0.03, 0.06, and 0.09) nanorods (NRs) via the hydrothermal method at low temperature on silicon substrate. The characterization and comparison between the different Zn1-xAgxO samples, indicated that an increasing Ag concentration from x = 0 to a maximum of x = 0.09; All samples show a preferred orientation of (002) direction with no observable change of morphology. As the quantity of the Ag dopant was changed, the transmittances, as well as the optical band gap were decreased. X-ray photoelectron spectroscopy data clearly indicate the presence of Ag in ZnO crystal lattice. A nanoindentation-based technique was used to measure the effective piezo-response of different concentrations of Ag for both direct and converse effects. The value of the piezoelectric coefficient (d33) as well as the piezo potential generated from the ZnO NRs and Zn1-xAgxO NRs was found to decrease with the increase of Ag fraction. The finding in this investigation reveals that Ag doped ZnO is not suitable for piezoelectric energy harvesting devices. [ABSTRACT FROM AUTHOR]

Low temperature aqueous chemical synthesis (LT-ACS) of zinc oxide (ZnO) nanorods (NRs) has been attracting considerable research interest due to its great potential in the development of light-emitting diodes (LEDs). The influence of the molar ratio of the zinc acetate (ZnAc): KOH as a ZnO seed layer precursor on the density of interface defects and hence the presence of non-radiative recombination centers in LT-ACS of ZnO NRs/GaN LEDs has been systematically investigated. The material quality of the as-prepared seed layer as quantitatively deduced by the X-ray photoelectron spectroscopy is found to be influenced by the molar ratio. It is revealed by spatially resolved cathodoluminescence that the seed layer molar ratio plays a significant role in the formation and the density of defects at the n-ZnO NRs/p-GaN heterostructure interface. Consequently, LED devices processed using ZnO NRs synthesized with molar ratio of 1:5M exhibit stronger yellow emission (~575 nm) compared to those based on 1:1 and 1:3M ratios as measured by the electroluminescence. Furthermore, seed layer molar ratio shows a quantitative dependence of the non-radiative defect densities as deduced from light-output current characteristics analysis. These results have implications on the development of high-efficiency ZnO-based LEDs and may also be helpful in understanding the effects of the ZnO seed layer on defect-related non-radiative recombination. Published by AIP Publishing. [ABSTRACT FROM AUTHOR]

We present a study on n doping of C60 thin films by acridine orange base [3,6-bis(dimethylamino)acridine(AOB)] combining conductivity, field effect, and Seebeck measurements. An increase of more than six orders of magnitude in conductivity is observed for a doping ratio of 6 mol %, accompanied by a decrease in the activation energy from 0.64 to 0.15 eV compared to the undoped C60. We observe a clear doping effect immediately after sample preparation, but also a further activation by annealing or illumination. The field effect and Seebeck measurements confirm n-type conduction of C60 thin films and show that deep donor states are formed in AOB-doped C60 thin films. A field effect mobility of 0.2 cm2/V s is achieved for a doping level of 1.8 mol %. Near Infrared (NIR) and Fourier transform infrared (FTIR) spectra demonstrate electron transfer from the dopant to the matrix: For C60 doped with AOB, C60- is present in NIR absorption and FTIR spectra. On the other hand, a peak corresponding to acridine orange [3,6-bis(dimethylamino)acridinium chloride (AOBH+)] is also observed in the FTIR spectrum of C60:AOB, where AOBH+ corresponds to AOB with one additional proton attached. Electrochemical data of AOB and AOBH+ in acetontrile suggest that the AOB radical cation is not stable, but is rapidly transformed into a compound with similar properties to AOBH+. Conductivities of C60 thin films doped with bis(ethylenedithio)-tetrathiafulvalene were also investigated to confirm that the doping effect of AOB in C60 does not result from a simple electron transfer from AOB to C60. [ABSTRACT FROM AUTHOR]

Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 °C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (μ-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions. [ABSTRACT FROM AUTHOR]