ZnO nanorod bunches formation by Electrophoresis Deposition Technique: influence of the conductivity of the substrate

Abstract

A novel and simple self-assembled direct formation of ZnO nanorod (NR) bunches on boron (p-type)-doped crystalline Si (100) substrates has been achieved by the EPD technique. All the nanostructures were formed from a colloidal dispersion of ZnO NPs in 2-propanol, at room temperature, and without the use of sacrificial templates or pre-deposited Au nanoclusters on Si substrates.ZnO nanoparticle (NPs) colloidal dispersions were prepared based on a modification of the precipitation method reported by Bahnemann et al. [1]. ZnO NPs sizes were estimated from the absorbance spectra of NPs colloidal dispersions and compared to measurements obtained by TEM, which yielded an average diameter of 5 nm with a narrow size distribution, between 4 and 7 nm.The morphology of ZnO NR bunches is affected by the p-type Si substrate wholeconductivity (i.e., B dopant concentration). The nanorod diameters and lengths, as well as thebunch diameters, are larger for substrates with lower conductivity. A ZnO nanoporous film isobtained on non-conductive (nominally undoped) Si substrates without any one-dimensionalformation. XRD patterns indicated that ZnO NRs were preferentially formed in (002) directioncorresponding to c-axis orientation in the wurtzite structure.Photoluminescence (PL) spectra from NR bunches show a low UV excitonic emissionpeak and a broad visible emission peak. The light emission properties of nanostructures arestrongly determined by the properties of NPs used for the EPD deposition and not by thenanostructure morphology. The incorporation of NaOH during ZnO NP synthesis is useful tocomplete reactions of all the available Zn2+ to form dispersions with a higher ZnO NPsconcentration. Therefore, as virtually all the Zn is consumed, PL spectra do not exhibit Zn-typedefects compared to previous work [2].The easy obtaining of different morphologies of ZnO nanostructures depending on the Sisubstrate conductivity is desirable for their use as functional materials in technological devices.The results presented in this work expand the EPD technique applications to form nanorodnanostructures in a single step, representing a high technological potential for nanoscale device applications [3].