ISSN 10628738, Bulletin of the Russian Academy of Sciences. Physics, 2011, Vol. 75, No. 11, pp. 1480–1481. © Allerton Press, Inc., 2011. Original Russian Text © R.G. Valeev, E.A. Romanov, S.V. Khokhryakov, 2011, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2011, Vol. 75, No. 11, pp. 1573–1574.
Luminescence of ZnS and ZnSe Nanostructures in Anodic Aluminum Oxide Porous Matrices R. G. Valeeva, b, E. A. Romanovb, S. V. Khokhryakovb a
Physicotechnical Institute, Ural Branch, Russian Academy of Sciences, Izhevsk, 426000 Russia b Udmurt State University, Izhevsk, 426034 Russia mail:
[email protected]
Abstract—Investigations of the luminescent characteristics of ZnSe and ZnS nanostructures obtained by thermal deposition on porous anodic aluminum oxide films are presented. Luminescence associated with the interaction of semiconductors with the matrix material was detected. DOI: 10.3103/S1062873811110268
INTRODUCTION Zinc chalcogenides possess a unique combination of mechanical, electrical, and luminescent properties. Among materials of this kind, zinc selenide and sulfide are considered today to be an alternative to CdS in optoelectronic devices due to their wide energy gaps (2.77 and 3.7 eV, respectively), low specific resistance, and high photosensitivity [1]. A special place is given to various nanostructures of zinc selenide and sulfide, from quantum dots to nano sized objects with a complex spatial structure, includ ing tetrapods [2–4]. Furthermore, arrays of ordered nanostructures of zinc selenide and sulfide, insulated from each other by dielectric layers, attract special interest, since they are promising building blocks for quantum logic devices and quantum computers, high efficiency elements for information display systems, solar cells, and visible light sources [5]. Porous anodic aluminum oxide (AAO), the struc ture of which can be considered as hexagonally packed cylindrical pores strictly perpendicular to the film plane, is a promising template material for creating highlyordered semiconductor nanostructures [6]. Researchers have suggested numerous methods for filling the pores with material, e.g., electrochemical deposition, molecular beam epitaxy, and gasphase deposition [7]. In this work, a simple method of ther mal spraying was used to obtain ZnS and ZnSe nano structures in an AAO matrix [8]. The structure and luminescent properties of the derived materials were studied by means of scanning electron microscopy and UV spectroscopy. EXPERIMENTAL Aluminum oxide films with highlyordered porous structure were synthesized via the anodic oxidation of aluminum [9]. Aluminum plate with a thickness of 0.5 mm (Goodfellow, 99.999%) was used as the initial
material. We had annealed the plates beforehand in a muffle kiln at 500°С for 10 h, and then buffed them in order to increase the size of aluminum crystallites and to achieve better pore ordering. The anodic oxidation of aluminum was performed in a twoelectrode elec trochemical cell using a B550 source of constant cur rent (V = 0–299 V, I = 0–299 mA). Platinum wire served as the auxiliary electrode. A potential difference of 70 V was applied to the electrodes. Electrolyte, the temperature of which was kept near 0°С, was pumped through the cell by a peristaltic pump during the anod izing process. The Al was then selectively dissolved in a 10% solu tion of Br2 in CH3OH in order to strip the oxide film from its surface. The obtained films were washed with methanol and dried in air. The barrier layer was removed by etching the film in a 5% solution of H3PO4 at 60°С for 5 minutes. Zinc selenide was sprayed onto the porous surface of AAO via discrete thermal evaporation of the poly crystalline material under high vacuum (10–5 Pa) [10]. For further SEM investigations, the aluminum oxide matrix was etched in a 5% solution of H3PO4; we used the original samples for UV spectroscopy measure ments. SEM images of the sample surfaces synthesized by spraying onto the AAO matrix were obtained on a Supra 50 VP (LEO) electron microscope, equipped with the Oxford INCA Energy+ Xray microanalysis system. RESULTS AND DISCUSSION Fig. 1 shows the SEM image of an array of zinc selenide nanostructures grown by spraying onto AAO matrices with a pore diameter of 50 nm. We can see that individual nanostructures with diameters of about 50 nm are hexagonally ordered with a spatial periodicity of about 100 nm. Their heights are almost
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Intensity, rel. units
LUMINESCENCE OF ZnS AND ZnSe NANOSTRUCTURES
Fig. 1. SEM image of the array of zinc selenide nanostruc tures.
identical. The arrangement and diameter of the nano structures are analogous to those of the channels in the AAO films, attesting to the replication of the template structure by zinc selenide. As regards zinc sulfide, a similar pattern would be observed due to the total identity of the synthesis method with our way of obtaining ZnSe nanostructures. Luminescence spectra of the zinc selenide and sul fide nanostructures obtained by spraying onto AAO matrices with a pore diameter of 50 nm are pre sented in Fig. 2. Three main peaks are seen in the spectra at 415, 445, and 515 nm, along with a shoulder with a wavelength of 490 nm (in the ZnS spectrum) and a plateau between 530–560 nm (in the ZnSe spectrum). It is known from the literature that ZnS luminesces in the green–blue spectral range (510–480 nm), while ZnSe luminesces in the yellow–red range (575–620) [11]. We may therefore assign the shoulder with the wavelength of 490 nm to the luminescence of ZnS; the corresponding range for ZnSe should then be the pla teau at 530–560 nm. The most intense maxima are probably associated with luminescence due to interac tion between the semiconductors and the matrix material. ACKNOWLEDGMENTS Authors are grateful to A.A. Eliseev and K.S. Napol’skikh (Faculty of Materials Science, Mos cow State University,) for their help in carrying out the SEM and UV spectroscopic measurements. This work was supported by the Basic Research Program of the Presidium of the Russian Academy of Sciences, projects no. 20 (09P21016) and 27; RF Presidential Grant no. 02.120.11.369MK; and
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Fig. 2. Luminescence spectra of ZnS (black line) and ZnSe (gray line) nanostructures, obtained by excitation using radiation with a wavelength of 244 nm.
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BULLETIN OF THE RUSSIAN ACADEMY OF SCIENCES. PHYSICS
Vol. 75
No. 11
2011
