Ivana Aguiar

Nanoparticles for nucleation of heavy metal iodide films: Mercuric iodide and bismuth tri-iodide cases

Mercuric iodide and bismuth tri-iodide nanoparticles were synthesized by suspension in octadecene, from Hg(NO<inf>3</inf>)<inf>2</inf>. H<inf>2</inf>O and I<inf>2</inf>, and from Bi(NO<inf>3</inf>)<inf>3</inf>. 5H<inf>2</inf>O and I<inf>2</inf>, respectively. The best synthesis conditions were 2 hrs. at 60–70 ºC, followed by 10 min. at 95–110 ºC for mercuric iodide nanoparticles, and 4 hrs. at 80–110 ºC, followed by 10 min. at 180–210 ºC for bismuth tri-iodide ones. Nanoparticles were then washed and centrifugated with ether repeatedly. Compounds identity was confirmed by X-ray diffraction (XRD) and energy dispersive spectrometry (EDS). Nanoparticles were characterized by transmission (TEM) and scanning (SEM) electron microscopy. Disk-like and squared mercuric iodide nanostructures were obtained, 80–140 nm and 100–125 nm in size respectively. Rounded and rod-like bismuth tri-iodide nanoparticles, 30–500 nm in size were obtained. Acetonitrile and isopropanol suspensions of mercuric iodide nanoparticles, and acetonitrile suspension of bismuth tri-iodide nanoparticles exhibited peak maxima shifts in their UV-Vis spectra, as was reported for nanoparticles of other materials. It is the first time that mercuric iodide and bismuth tri-iodide nanoparticles are synthesized by the suspension method, although uniform shape and size distributions have not yet been obtained. They offer interesting perspectives for crystalline film nucleation, for improving current applications of these materials, as far as for opening new ones.

Influence of solvothermal synthesis conditions in BiSI nanostructures for application in ionizing radiation detectors

BiSI belongs to the A V B VI C VII chalcohalides group of compounds. These compounds show several interesting properties such as ferroelectricity, piezoelectricity along the c axis, and photoconductivity. Moreover, BiSI is a potential semiconductor material for room-temperature gamma and x-ray detection, given its band gap of 1.57 eV and its high density, 6.41 g cm−3. In this work we present BiSI nanostructures synthesized by the solvothermal method with the intention of using them for ionizing radiation detection. The solvent was varied to study its influence in morphology, particle size and size distribution. Three different conditions were tested, using either water, monoethylene glycol and a mixture of both solvents. Nanostructures were characterized by XRD to determine the phase obtained and reaction completeness; TEM was used to observe nanostructures morphology, size, size distribution and crystallinity; and finally FT-IR diffuse reflectance was used to study monoethylene glycol presence in the samples. Nanorods in the range of 100–200 nm width were obtained in all samples, but round nanoparticles of around 10 nm in diameter were also detected in samples synthesized only with monoethylene glycol. Samples synthesized in monoethylene glycol were used to fabricate pellets to construct detectors. The detectors responded to ionizing radiation and a resistivity in the order of 1013 Ω cm was estimated. This work proposes, to our knowledge, the first study of BiSI for its application in ionizing radiation detection.

HgI2 nanostructures obtained hydrothermally for application in ionizing radiation detection

The compound semiconductor HgI2 has been widely studied and employed as a material for ionizing radiation detection. Monocrystal growth is an intricate method for obtaining materials for this application. With the aim of finding a simpler and more effective way to develop ionizing radiation detectors, we employed HgI2 nanostructures subjected to a hydrothermal treatment and then pressed for this purpose. In the synthesis procedure, aqueous solutions of Hg(NO3)2 and NaI were mixed until their reaction completed and the suspension obtained was then placed in a homemade autoclave and heated at 120 °C for 2, 10 or 24 h. We confirmed the HgI2 tetragonal phase by powder XRD in all cases, independently of the synthesis conditions employed. Nanoparticles were characterized by their size and morphology by TEM. We used the HgI2 nanostructures to obtain a pellet by applying 0.7 GPa of pressure at room temperature. The pellet was then used to construct the detector, and we studied the electrical properties of the detector and its response to 241Am sources of different exposure rates. The resistivity and signal-to-noise ratio obtained are of the order of those reported for HgI2 detectors assembled with monocrystals. The results obtained in this work encourage us to work further on this topic, improving the method, scaling the detectors size and studying its spectrometric grade.

The crystal race; engaging children in the crystal world

The United Nations Educational, Scientific and Cultural Organization (UNESCO) in association with the International Union of Crystallography (IUCr) declared 2014 as the International Year of Crystallography. One of the main activities, around the world, was providing students from all levels with crystallography demonstrations specially selected for their ages. In Uruguay most of the activities celebrated that year were carried out by a group of professors and students from Facultad de Química, Universidad de la República (1). In order to show how science and technology make a huge impact in our everyday lives and make for interesting and exciting career options, we designed and performed “The Crystal Race”. For the first time, this activity was performed during the ”Semana de la Ciencia y la Tecnología (SCyT)” (Science and Technology Week) in 2014, promoted by the “Dirección de Innovación, Ciencia y Tecnología para el Desarrollo” (DICyT, Innovation, Science and Technology Administration for the Development) and the Ministerio de Educación y Cultura (MEC, Ministry of Education and Culture). The competition consists in a typical race like “Ludo” and Trivial Pursuit, where participants race through a board by rolling a die, to get to the center and win. Seven teams are formed, and each is assigned a crystalline system name (cubic, hexagonal, orthorhombic, monoclinic, triclinic, tetragonal and rhombohedric trigonal-), a number, and a pawn. The number indicates the order of play and the pawn corresponds to the crystalline name. The gameplay consists of each team answering questions about crystals and their properties. The activity was designed for school aged children (especially in the age range between 9-12 years old) and also seeks to maintain the attention of children during it. We performed the race in state and private schools with different social and economic backgrounds (more than 10). With this activity we have improved the children ́s knowledge about crystallography, crystals properties and their application in their daily lives. Also, we have encouraged the interest of young students on science.

National crystal growing competition in Uruguay: three years of success

During the IYCr-2014 Uruguay held its First National Crystal Growing Competition (CNCC – Concurso Nacional de Crecimiento de Cristales). The competition was organized by an interdisciplinary group within the Facultad de Química, Universidad de la República (School of Chemistry, University of Uruguay) which continued the work throughout 2015 and 2016. The contest ́s main objective, aligned with that of the International Crystal Growing Competition, is to reach-out to the community, increasing public awareness of science in general and crystallography in particular, and encouraging young people to participate in scientific activities. Participation of young students from primary and secondary level education and social institutions was especially encouraged. Growing a crystal garden (for ages 6 to 12) or single crystals (for ages 13 to 18) within a 5-week time frame, with the guidance of a trained tutor, were the main rules imposed to participants. For the first two years tutors participated in hands-on training workshops dictated by the organizing group in over 30 different locations across the country, whereas in 2016 we were able to produce audiovisual material available on-line [1] and distributed an Spanishtranslation of chapters 7 and 8 of the book “Cristalografía: La vissione a raggi X” [2] to replace face-to-face workshops. Participants sent their crystals/gardens to Facultad de Química for evaluation by a panel of experts (including a former Dean and retired Prof. of Crystallography). In 2015 and 2016 the crystal/garden was accompanied by a 3-minutes video record of the process. This video was expected to be suitable to be sent to the International Crystal Growing Competition organized by the IUCr where one mention (2014) and two prizes (2015) were obtained [3]. Winning teams received a variety of prizes and mentions ranging from tablets for secondary school students to crystal growing kits for primary schools. For high school participants the first prize is a hands-on activity named “Chemist for one day”, where they are introduced to organic and inorganic synthesis and characterization techniques including single crystal and powder X-ray diffraction. During the three years the competition we reached more than 2000 participants and over 100 institutions, including schools, high-schools, social aid and pleasure clubs and a youth detention center. Every year the finalists with their tutors got together on a closing ceremony where they shared their experience with the organizers, their families and close friends. The three editions of the CNCC obtained funding from local agencies and institutions ANII (PR_PCTI_2014_14131), PEDECIBA (2014-2015), CSEAM-UdelaR (2014-2016) and Facultad de Química (2014-2016) and donations from Droguería Uruguay S.A. (2014) and PERRIN S.A. (2014-2016). The availability of funding has been irregular and the difficulties to fund the 2016 edition took a toll in the number of participants (~60 groups) that decreased significantly from 2014 and 2015 editions (~200 groups each year). Even though this has been honorary work and there are difficulties to sort-out, so far the experience has been a very positive success and we plan on continuing it in 2017 and beyond.