Thin films of lead iodide (PbI2) produced by spray pyrolysis / Filmes finos de iodeto de chumbo (PbI2)produzidos por spray pyrolysis

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

Researchers in the whole world search alternative methods that minimize the time of deposition of thin films of promising semiconductor candidates for medical applications, such as X-rays detectors for digital radiography. Lead iodide (PbI2) has been among those as a good candidate for the fabrication of room temperature detectors. Other authors have fabricated prototype detectors using this material. Their experiments show high resolution and sensitivity for real time imaging, thus showing the material potentiality for medical applications in the future. Nevertheless, one of the drawbacks of their methods is the long deposition time needed for the fabrication of the thin films. In this work we present a new experimental methodology used for the deposition of thin films of lead iodide (PbI2). The alternative growth method is called spray pyrolysis. Note that an intrinsic advantage of the technique is the fact that it can be easily expanded for large area substrates as desired by the industrial fabrication line. Lead iodide powder was dissolved in deionized water at 100ºC (boiling water) where its solubility is higher than at room temperature. After the dissolution of the powder, the solution is cooled down to ambient temperature and filtered for the removal of the excess of formed crystals. The films were deposited from aqueous solutions on glass substrates sitting at different temperatures (from 150 to 270ºC). The total deposition time is about 2.5 hours leading to a film thickness of . In addition we also investigate the structural (X-ray diffraction and Raman scattering), electronic (dark conductivity as a function of temperature) and atomic force microscopy (AFM) properties of the obtained films. In order to induce crystalline grain growth after the deposition of the films, the original samples were also submitted to thermal treatment at 350ºC during 3 hours either in ambient or under controlled atmosphere (N2). The influence of oxygen doping was only observed in the first case. We analyze the variation of the size of the crystals (relative to the main peak - 001) and the activation energies for electric transport. The activation energy for films deposited at 200ºC is about 0.50 eV. For other deposition temperatures, varying from 150 to 250ºC, it was experimentally measured a minimum and maximum value of activation energy of 0.45 and 0.66 eV, respectively. In summary, the electronic and structural properties are correlated and discussed based on the deposition method, and thermal treatments. It is the present authors belief that thin films with interesting structural and electronic properties can be produced by spray pyrolysis with short deposition time.

ASSUNTO(S)

iodeto de chumbo digital medical image x-ray detector thin films spray pyrolysis pbi2 detector lead iodide radiografia digital

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