World Journal of Condensed Matter Physics, 2011, 1, 130-136 doi:10.4236/wjcmp.2011.14019 Published Online November 2011 (http://www.SciRP.org/journal/wjcmp) Copyright © 2011 SciRes. WJCMP Hydrogen Incorporation in Undoped ZnO Nanoparticles Suhendro Purbo Prakoso, Rosari Saleh * Jurusan Fisika, Fakultas MIPA-Universitas Indonesia, Depok, Indonesia. Email: * rosari.saleh@ui.ac.id Received May 27 th , 2011; revised June 10 th , 2011; accepted June 20 th , 2011. ABSTRACT Zinc Oxide nanoparticles in the size range of ~18 - 23 nm are prepared using wet chemical method. Hydrogen concen- tration in the samples was obtained by drying the precipitate at various temperatures. XRD pattern showed a single phase wurzite structure for ZnO nanoparticles. Average crystallite sizes and lattice parameters determined from XRD pattern showed a gradual increase with increasing dry temperature, while the lattice strain showed the opposite direc- tion. Optical studies revealed the optical gap ranging from 3.05 - 3.24 eV. Hydrogen incorporation in the specimen was studied using infrared absorption measurement. Infrared absorption measurements revealed six hydrogen-related local vibrational modes in the wave number range from 2800 to 3600 cm –1 . To remove hydrogen, some samples were an- nealed up to 800˚C. Infrared absorption measurements showed that the local vibational modes disappeared. This shows that the observed local vibrational modes are due to the presence of hydrogen. The results of XRD and optical studies will be correlated with the results obtained from infrared absorption measurements. Keywords: ZnO Nanoparticles, Structural and Optical Properties, H Bonding 1. Introduction Recently, a wide-band gap semiconductor has been re- ceiving much attention due to its electronic, optical and piezoelectric properties at the nanoscale, leading to a wide range of optoelectronic applications [1-4]. The ac- tivity has intensified more recently because of the possi- bility that a wide-band gap semiconductor might be use- ful for spintronics or spin-base quantum computation [5,6]. ZnO nanoparticles are among one of wide-band gap semiconductor that possess extraordinary electronic and optical properties useful for optoelectronic devices and UV lasers [7-8]. The structure of ZnO nanoparticles is pivotal to the above potential applications. For exam- ple, it has been reported that the ZnO properties are heavily dependent on the size and morphology tailored by preparation conditions [9-12]. Most of ZnO nanopar- ticles were prepared by several high temperature methods such as vapor-phase transport, vapor-liquid-solid growth, vapor-phase epitaxy and template-assisted techniques along with some low-temperature routes such as wet chemical reactions and electrochemical techniques [13]. As grown, ZnO is almost always exhibits n type con- ductivity, with electrons in the conduction band as the charge carriers. The origin of this conductivity has been discussed for years and is still controversial. Tradition- ally, the nature of this conductivity has been attributed to native defects. However, Van de Walle [14] in his first- principles investigation, based on density functional the- ory suggested that the presence of hydrogen atom in ZnO can act as a shallow donor. This behavior is unexpected and very different from hydrogen’s role in other semi- conductors, in which it acts only as a compensating cen- ter counteracting the prevailing conductivity. The pres- ence of hydrogen in the crystal-growth is not surprising and it is very difficult to avoid its incorporation into the sample during the process of the crystal-growth. How- ever, almost all optoelectronic applications require the control of the conductivity from n-type to p-type. There- fore, we believe that understanding hydrogen properties in ZnO is necessary not only for the academic point of view but also for semiconductor applications. In this paper we present information on hydrogen bonding and hydrogen concentrations in ZnO nanoparti- cles synthesized using wet chemical method. To obtain various concentration of hydrogen in the nanoparticles the mixture was dried at various temperatures. The in- fluence of dry temperature on hydrogen bonding, struc- tural properties and optical properties are investigated