This paper reports the growth of bismuth tri-iodide thick films intended for direct and digital X-ray imaging. Films were grown by the vertical physical vapor deposition method, onto glass substrates 2"x 2" in size, with gold previously deposited as rear electrode. The film thickness was up to 33 µm (±5 %). Optical microscopy and SEM were performed on the films and grain size resulted to be up to 40 µm. A strong correlation was found between the microcrystals growth orientation and the growth temperature. At low temperatures, microcrystals grow with their c axis parallel to the substrate, whereas at higher temperatures, they grow with their c axis perpendicular to the substrate. The higher the growth temperature, the lower the dark current of the film, and the higher the resistivity, which was from 10 13 to 10 15 Ωcm. A sensitivity to X-rays of 6.9 nC/R.cm 2 was measured irradiating the films with X-rays from a mamographer. Film properties were correlated with the growth temperature, with previous results for bismuth tri-iodide films and monocrystals and with data for films of alternative materials such as lead and mercuric iodide.
Bismuth-based semiconductors are
promising candidates for applications
in photocatalysis, photodetection, solar cells, etc. BiSI in particular
is attracting attention. It has anisotropic optoelectronic properties
and comprises relatively abundant elements. However, the synthesis
of this ternary compound presents several challenges. Here, we delve
into the underlying chemical processes that lead to the crystal growth
of BiSI nanorods and optimize a solution-based synthesis. The mechanism
of formation of BiSI nanocrystals is the self-sacrifice of Bi2S3 nanostructures, which also act as templates.
The crystallographic similarities between the chalcogenide and the
chalcohalide allow for the solid state transformation from one to
the other. However, there is also a synergy with the I3
– species formed in the reaction media needed to
obtain BiSI. Our method makes use of a green solvent, avoids complicated
media, and drastically reduces the reaction time compared to other
methods. The obtained nanorods present a band gap of 1.6 eV, in accordance
with the reported values. This work presents insight into the chemistry
of bismuth-based semiconductors, while introducing an easy, green,
and scalable synthesis of a promising material, which could also be
applied to similar compounds and other chalcoiodides, such as SbSI.
In addition, the optical properties of the BiSI nanorods show their
potential in photovoltaic applications.
Bismuth sulpho iodide (BiSI) belongs to the family of chalcohalides, which present several attractive electro-optic properties. In particular, BiSI is a semiconductor which could be used in X and gamma ray detection due to a band gap of 1.6 eV, density of 6.4 g cm −3 , and absorption coefficient for 60 keV radiation of 5.6 cm 2 g −1 . This work presents a facile synthesis under solvothermal conditions of a nanocomposite consisting of BiSI nanorods and amorphous carbon structures. Furthermore, it studies its ionising radiation detection properties at room temperature, when prototype detectors were built from pellets. The construction conditions of pellets were also studied, varying the applied pressure and heat treatment to the nanocomposite. Dark current density and response to different exposure rates of a 241 Am source were measured for the prototype detectors built. It was found that heat treatment of pellets considerably improves detectors performance. Dark current density was one order of magnitude lower than for the pellets without heat treatment, and its response to the 241 Am source, linear, with a signal to noise ratio of 7 for 20 V. Finally, the resistivity for the heat treated detector was in the order of 10 11 Ω cm, comparable to other materials studied for this application.
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