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LASER DIAGNOSTICS AND SPECTROSCOPY
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Raman scattering spectra in zinc oxide microstructures
placed in photon traps
I.A.Rakhmatullaev1, N.V.Tcherniega2, M.Kh.Davronov1, O.M.Tursunkulov1
1Center for Advanced Technologies under the Ministry of Innovative Development of the Republic of Uzbekistan, 3а,
Talabalar shaharchasi str., 100174, Tashkent 2Р.N. Lebedev Physical Institute of the Russian Academy of Sciences, Leninskii prospect, 53, 119991, Moscow
e-mail: ilyoss@rambler. ru
In recent years, interest in studying the structures of zinc oxide (ZnO) has increased significantly due to the high demand for this material [1,2]. In this work, the synthesis of ZnO microstructures was carried out by the method of microwave decomposition: 2 g of ZnO powder (Aldrich, 99% purity) and 1 ml of ethylene glycol solution were mixed and ground in an agate mortar for 20 min. Then, 2 g of the mixed powder was loaded into an alumina crucible and placed in the center of a microwave oven for 15 min at 180°C. As a result, samples in the form of extended rods were obtained. The surface morphology of ZnO microstructures was studied using a SEM-EVO MA10 scanning electron microscope (Carl Zeiss, Germany). The analysis showed (Fig. 1) that the samples are formations in the form of randomly oriented agglomerates with transverse dimensions up to 8 ^m. Raman spectra (RS) were recorded using a technique described in detail in [3,4]. RS were excited by the green line of a copper vapor laser (^=510.6 nm) [3,4].
"Fig. 1. SEM image of ZnO microstruc- "Fig. 2. Raman spectra of ZnO microstructures of various sizes when tures" they are excited by the green line of a copper vapor laser (Àex=510.6
nm): 1 - d =3 ^m; 2 - d =7 pm (I ~ 105 W/cm2)"
' av r ' av r v exc '
The main spectral change observed in the RS of the samples with different average dimension under study (Fig. 2) consists in a monotonic increase in the intensity of the E(LO) mode (580 cm-1) and the appearance of a shoulder in the region of 100-200 cm-1, similarly to the results obtained in [2]: the following modes were identified in the RS of ZnO powders: 1) the mode with a frequency of ~100 cm-1; 2) the mode at ~ 340 cm-1, which is attributed to the difference phonon Âh,gh - ÂI™ ; 3) at ~ 435 cm-1 ; 4) E(LO) at ~580 cm1 ; 5) a wide band between 1060 and 1190 cm1, which can be assigned to a combination of the A t and E2 modes. It was found that with a decrease in the size of the microstructures of the sample, an increase in the intensity of the RS signal is due to the fact that pores are formed between the faces of large particles, which contribute more to the scattered light than to the effective absorption of exciting radiation. This is also explained by the fact that when excitation radiation with a wavelength smaller than the size of microparticles enters such structures, radiation can be trapped as a result of multiple reflections from the walls of microresonator cuvettes (photon traps).
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[2] I.A. Averin, I.A. Pronin, N.D. Yakushova et al. Analiz strukturnoy evolyutsi poroshkov oksida tsinka, poluchennix metodom mexaicheskogo visokoenergeticheskogo razmola, J.Tex.fiz. vol.89, No. 9, pp.1406-1411 (2019).
[3] VS. Gorelik, I.A. Rakhmatullaev. Excitation of Raman optical processes in an ultradispersed medium by radiation from a pulsed-periodic laser, Technical Physics, vol. 50, No. 1, pp. 61-64 (2005).
[4] I.A. Rakhmatullaev, V.S. Gorelik, R.A. Muminov et al. Photoluminescence and Raman spectra of diamond micropowders placed
in photon traps, Scientific-technical journal, vol. 4, No. 1, 46-53 (2021).
