ABSTRACT

1. Centro de Física Aplicada y Tecnología Avanzada UNAM-Querétaro ABSTRACT RESULTS AND DISCUSSION Nanodiamond thin films were deposited onto Si (100) substrates using Tequila as precursor by Pulsed Liquid Injection Chemical Vapor Deposition (PLICVD) at 850 °C. Some samples were exposed to beta particle irradiation in the dose range from 100 to 1600 Gy, and it was found that the thermo luminescence response is a linear function of dose. The glow curve displays two maxima centered at 170 and 350 °C, which does not shift when dose changes, indicating that first order kinetics processes are involved. From the results, we conclude that the new nanodiamond films are promising high dose thermoluminescence dosimeters. INTRODUCTION Figure 3. Micro-Raman spectrum of a nano-diamond film obtained using the PLICVD technique and tequila as precursor. The sharp band displayed is characteristic of good quality diamond structure. Figure 2. Atomic force microscopy image of a tequila-derived PLICVD synthesized diamond film surface.. Some phosphor materials, when previously exposed to radiation, have the property of emitting light when heated. This phenomenon, called thermally stimulated luminescence or thermoluminescence (TL), is used to measure the amount of radiation (dose) to which a material has been exposed, if the amount of light emitted (thermoluminescent emission) is proportional to the exposure dose. Dosimetry refers to the measurement of radiation dose, and the phenomenom of TL is the basis of the TL dosimetry, which since it was proposed by Farrington Daniels in the 1950s remained as the most widely used dosimetric technique [1, 2]. EXPERIMENTAL A Risø TL/OSL model TL/OSL-DA-20 unit equipped with a 90Sr beta radiation source was used to perform beta irradiations and the TL measurements. All irradiations were accomplished using a 5 Gy/min dose rate at room temperature ( 295 K (22 °C)). The TL readouts were carried out under N2 atmosphere using a heating rate of 5 K/s. Figure 1 show a simplified diagram and a picture of the TL measurement system. To characterize the structure, Raman spectroscopy was carried out using a Dilor micro-Raman spectrometer with a 20 mW, 632 nm He-Ne laser equipped with a confocal microscope. The PLICVD system use small micro-doses of liquid precursors the precise micro-doses of such solution are injected through a computer-driven system into the evaporation zone, where they instantly evaporate (flash evaporation), so there is no time for chemical changes of the precursor. Figure 4. Characteristic glow curves of nano-diamond films growth using the PLICVD technique and tequila as precursor, and after being exposed to beta particle irradiation in the dose range from 100 up to 1,600 Gy. Figure 5. Integrated TL as a function of irradiation dose, as obtained from nano diamond films subjected to beta particle irradiation. CONCLUSIONS We conclude that nanodiamond films growth from tequila using the PLICVD technique are promising for the development of high dose detectors and dosimeters. The technique assures good reproducibility of samples synthesis. The characteristic glow curves display emission in the interval from 200 to 250 °C, which is considered very suitable to guarantee both, thermal stability to avoid TL fading under storage, and non interference of the TL signal and the black body radiation. • References • 1.- S. W. S. McKeever, Thermoluminescence of Solids (Cambridge University Press Cambridge 1985). • 2.- R. Chen, S. W. S. McKeever, Theory of Thermoluminescence and Related Phenomena (World Scientific Singapore 1997). • 3.- J. W. Munford, L. M. Apatiga, J. I. Golzarri, V. M. Castaño, Mater. Lett. 37, 330 (1998). • 4.- M. Zhang, Y. Xia, L. Wang, B. Gu, Int. J. Mod. Phys. B 37, 3198 (2004). • 5.- S. Preciado-Flores, M. Schreck, R. Meléndrez, V. Chernov, R. Bernal, C. Cruz-Vázquez, F. Brown, M. 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Barboza-Flores, Phys. Stat. Sol. (a) 202, 2154 (2005). • 14.- Pham V. Huong, Diamond Relat. Mater. 1, 33 (1991). • K. Kobashi, K. Nishimura, Y. Kawate, T. Horiuchi, Phys. Rev. B 38, 4067 (1988). Figure 1. Simplified diagram and a TL measurement picture. Acknowledgments This work was partially supported by Universidad Nacional Autónoma de México through Oficina de Colaboración Insterinstitucional. Diamond samples were prepared in the laboratory under Dr. Miguel Apátiga assistence, to whom the authors are indebted. The authors also thank Dr. J. G. Bañuelos, Dr. J. Ocotlán, and Dr. J. Saniger for the AFM images, to Dr. R. Sato, Dr. S. Jiménez and Ing. F. Melgarejo for the Raman facilities, as well as to Mr. A. Loeza for technical support.