Surface Luminescence of Polycrystalline Zinc Oxide Excited by Hydrogen Atoms
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0957-K07-02
Surface Luminescence of Polycrystalline Zinc Oxide Excited by Hydrogen Atoms Michael Sushchikh1, Vladislav Styrov2,3, Vladimir Tyutunnikov2, and Nick Cordella1 1 Department of Chemical Engineering, University of California at Santa Barbara, Santa Barbara, CA, 93106-5080 2 Department of Physics, Azov State Technical University, Mariupol, Ukraine 3 School of Physics and Mathematics, Mariupol, Ukraine
ABSTRACT Excitation of a luminescence by highly exothermic chemical reaction on the surface of a luminophore provides a unique opportunity to separate surface luminescence from the bulk luminescence. This enables studies of the electronic properties of the semiconductor surfaces even if the surfaces are of complicate shapes. We have studied heterogeneous chemiluminescence (HCL) of ZnO powders. The luminescence was excited by a release of chemical energy, namely by catalytic recombination of hydrogen atoms. The HCL spectra were compared to the photoluminescence (PL) spectra. The HCL spectra were sensitive to the details of preparation and treatment whereas PL spectra almost did not change. HCL spectra of powder samples pretreated for enhancing “green” photoluminescence contain long wavelength tail (up to 800 nm) and their maximum is blue-shifted as compared with PL spectra. Different HCL bands at longer wavelengths were isolated by changing the temperature of the samples. Additional milling of ZnO led to amplification of the HCL-specific surface bands. “Special pure grade” ZnO showed neither PL nor HCL; however we were able to observe HCL surface bands with maxima at 610 nm and 730 nm after treatment of the sample in atomic hydrogen atmosphere at 573 K. Remarkably, such treatment did not cause appearance of the PL. The HCL in the presence of atomic hydrogen was steady in time and was caused by an abstraction of adsorbed hydrogen by incident hydrogen atoms, i.e. the reaction followed Eley-Rideal mechanism. The HCL can be utilized for in situ monitoring of the growth and evolution of ZnO in controlled atmosphere.
INTRODUCTION Zinc oxide found its applications in acousto- and optoelectronics, including laser technique and low-voltage cathodoluminescence. It is a well-known luminophore and is a subject of special interest recently because of its potential application as an emitter of shortwavelength light[1]. Suppressing its visible luminescence is essential for maximizing the yield in the UV region. High regularity crystal lattice is required and, hence, control of the crystal growth is essential[2]. We have studied surface luminescence of ZnO in a way where it is well separated from the bulk one. The surface luminescence was excited by catalytic recombination of hydrogen atoms on the ZnO surface which is known as heterogeneous chemiluminescence (HCL) [3]. The HCL spectra are compared to ones of photoluminescence (PL) originating from the bulk.
EXPERIMENT The high vacuum apparatus was described previously[4]. Here we provide important details. The experiments were conducted in a stainless steel chamber. The b
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