Monday, Dec 10th

Norberto Masciocchi opened the School giving a very educational Introduction to Single Crystal and Powder Diffraction techniques and their applications to Structural Analysis of crystalline phases. Several methods for indexing, volume prediction, and structure determination were presented. The influence of instrumental effects and many tips for identifying and correcting them were discussed. During his lectures, he also highlighted the importance of using synchrotron sources, especially in the case of moderately complex materials (as better figures of merit and more accurate structural models can be obtained – at the expenses of much longer beam-access times).

Matteo Leoni illustrated the fundamental physics behind diffraction and reviewed the “crystallographic” phase problem. He also brilliantly presented powerful computational tools for Microstructural Analysis of many classes of materials (metals, intermetallics, oxides, and clays) developed in Trento, Italy, jointly with Paolo Scardi (Scardi et al., Reference Scardi and Leoni2002; Leoni et al., Reference Leoni, Confente and Scardi2006; Scardi and Leoni, Reference Scardi and Leoni2006).

Finally, remote and local Software Installation sessions were gently organized by all teachers of the School, even by extending installation late in the night to overcome some technical problems offered by the variety of operating systems. Wi-fi-driven TOPAS-6 licenses were provided to all participants for the hands-on sessions.

Tuesday, Dec 11th

Before the Hands-on Session on Structure Solution, Norberto Masciocchi illustrated very important crystallographic concepts behind all the computational procedures presented in the following hours using the TOPAS-6 program. Starting from a simple inorganic structure (CaSiF₆·2H₂O), and ending with organics ones (salicylic acid, triphenylphosphine, and a widely marketed antismoke drug), an extensive tutorial session provided hints on how to solve the indexing step, the space-group selection, the Le-Bail/Pawley refinement, and the structure solution processes (by real space modeling and global optimization procedures). Some relevant information, such as fast estimates of crystal densities, unit cell rational transformations, and rigid body formalisms, were presented. Data which could not be analyzed locally were supplied to all participants for further use. A glance on the Fundamental Parameters Approach and to Rietveld-based Quantitative Phase Analysis terminated the session.

In the afternoon, before entering the hands-on session, Matteo Leoni highlighted the philosophy of the Whole Pattern Powder Modeling, starting from a historical context and the meaning of the very popular (seldom misused) equations (Scherrer, Williamson–Hall). The use of phenomenological peak profile functions (Gaussian, Lorentzian, or mixture thereof), widely used in a number of programs, was criticized, in favor of a physically-based approach, like the one implemented in WPPM to describe shapes and widths of the Bragg peaks. Hands-on tutorials were initially based on a simple X-ray diffraction pattern of defective nanocrystalline ceria, used to show evidence all different contributions (including instrumental ones) to peak broadening to extract the shape and size distribution of the domains and the content of dislocation and faults. The case was proposed in a very didactic manner, by including a step-by-step procedure to embrace several microstructural parameters. Subsequently, all attendees were asked to perform on their laptops the full analysis of diffraction data from a ball-milled Fe-Mo alloy. Using PM2K, under the continuous supervision by Matteo, participants learned about the difficult steps which are inherent in such an intricate modeling, particularly if a conventional lab source is employed. This was significantly illustrated by the difficult modeling on a simple NIST standard, such as LaB₆.

Wednesday, Dec 12th

After 2 days of activities stressing the importance of using diffraction data from synchrotron sources to perform high level analyses of defective and nanomaterials, Alexandre M.G. Carvalho (beamline scientist at XRD1 of LNLS/CNPEM) delivered a very informative lecture, entitled “LNLS/Sirius Past and Future of the Brazilian Light Sources”. Beyond summarizing the status of the actual XRD beamlines of LNLS (UVX machine), he also presented the features of the new hard X-rays beamlines present at Sirius, the recently inaugurated Synchrotron in the Campinas Area (first photons delivered in November 2018), where faster and more flexible experiments can be planned. Details on the HARPIA (High angular resolution powder X-ray diffraction), PAINEIRA (Powder Diffraction), HERA, and EMA (Extreme condition X-ray Methods of Analysis) beamlines were provided. Participants of To.Sca.Lat.-1.0 also learned about the opportunities to apply for beamtime, and how to participate in CNPEM Summer Schools, PhD, and Post-doctoral Programs.

In the following presentation, Antonella Guagliardi introduced Total Scattering methods, comparing them with conventional Rietveld analyses. The main focus of her presentation was the Debye Scattering Equation analysis for nanomaterials, a topic mastered also in the form of computational tools developed by her Group (specifically, the DebUsSy suite, Cervellino et al., Reference Cervellino, Giannini and Guagliardi2010, Reference Cervellino, Frison, Bertolotti and Guagliardi2015). By treating Bragg and non-Bragg (diffuse) scattering on the same footing and including inelastic Compton effects, DebUsSy uses a physically-based modeling to retrieve important structural and microstructural information of nanosized materials, ranging from lattice relaxation and sample stoichiometry, to size and shape (and their distribution) of nanocrystals and, finally, to more complex defectiveness in the core (stacking faults, localized strain) and on the surface (e.g. in homo- or hetero-core-shell systems).

The Atomic Pair Distribution Function method was later introduced by Federica Bertolotti, who brilliantly showed the main differences between the conventional approaches that assume an ideal infinite crystal periodicity. Federica showed that the quality of a meaningful PDF, particularly targeted toward defective or nanosized materials, depends on experimental parameters (Q _max> 20 Å⁻¹) and on data reduction and modeling processing (following the so-called small or large box modeling approaches). Some frontier applications of the method were finally presented (e.g. PDF computed tomography and in-situ studies of nanoparticles growth).

The last lecture of the day was delivered by Matteo Leoni who introduced a probabilistic, physically-based formulation to interpret general stacking defects in a variety of materials, including intermetallics, clays and, of course, nanostructured species. A demonstration of the power of the DIFFaX+ code for the refinement of faulted and <3D periodic structures was also presented.

Thursday, Dec 13th

The hands-on session using DebUsSy started from a general overview of the philosophy of the database construction (as integrated within DebUsSy) from available structural information (loading CIF files or manually introduced by the user). At this point, simulation of XRPD patterns from selected clusters (e.g. with different sizes) was performed and used to visually compare the effects of the physical parameters used to build the database. The second part of the tutorial session on DebUsSy was performed jointly with all participants using scattering data from nanometric magnetite and TiO₂, the last sample containing two polymorphic phases and data from synchrotron and lab sources, respectively. Step-by-step settings of all parameters were presented by Antonella, who also taught the participants how to interpret the results given by the refinement using DebUsSy. A nice discussion followed, focused on the meaning of the mass and number distribution and on their validity when compared by imaging analysis.

In the afternoon, a hands-on session with PDFGui (Farrow et al., Reference Farrow, Juhás, Liu, Bryndin, Božin, Bloch, Proffen and Billinge2007) was organized by Federica Bertolotti, who showed how to calibrate the instrumental parameters from the analysis of PDF data of a standard material (here, microcrystalline nickel powder). One case of a PDF analysis of a biphasic sample was presented and generated a deep discussion on the data reduction procedure (which assumes the a-priori knowledge of the sample stoichiometry when averaging atomic scattering factors of each element in the scaling procedure). Finally, the correct relation between the PDF-derived scale factors and the phase composition was analytically derived. All the experimental data and input files for the PDFGui tutorial were kindly provided by Prof. Simon J.L. Billinge (Columbia University).

At the end of this day, all participants were encouraged to explore the neighborhood of the location where the To.Sca.Lat.-1.0 was held. In the natural preservation area next to beautiful Armação beach and Peri lagoon, teachers and attendees shared sport activities such as football, tracking, swimming, and contemplating nature.

Friday, Dec 14th

In the final day, a scientific presentation titled “An Overview of Total Scattering Analysis for NanoScience” was delivered by Antonella Guagliardi, who illustrated forefront examples of the Debye scattering equation applied to explore the structural defectiveness of nanomaterials and, particularly, quantum dots. These included the case of crystal symmetry breaking and vacancies in colloidal lead chalcogenides quantum dots (Bertolotti et al., Reference Bertolotti, Dirin, Ibáñez, Krumeich, Cervellino, Frison, Voznyy, Sargent, Kovalenko, Guagliardi and Masciocchi2016a), stacking faults modeling in zincblende cadmium selenide nanocrystals (Moscheni et al., Reference Moscheni, Bertolotti, Piveteau, Protesescu, Dirin, Kovalenko, Cervellino, Pedersen, Masciocchi and Guagliardi2018), twin boundaries in fully inorganic lead halide perovskite nanocrystals (Bertolotti et al., Reference Bertolotti, Protesescu, Kovalenko, Yakunin, Cervellino, Billinge, Terban, Pedersen, Masciocchi and Guagliardi2017), and strain in metals and alloys (Bertolotti et al., Reference Bertolotti, Moscheni, Migliori, Zacchini, Cervellino, Guagliardi and Masciocchi2016b; Ulbrich et al., Reference Ulbrich, Bertolotti, Masciocchi, Cervellino, Guagliardi and Campos2018).

To.Sca.Lat.-1.0 participants were invited to present their scientific projects during the School. A total of 10 oral communications were presented by young students, most of them supported by grants generously offered by ICDD, AIC, and Bruker.

During the Closing Session all teachers, attendees, and organization members were warmly acknowledged by Prof. Campos, the local Chairman of To.Sca.Lat.-1.0. Prof. Leopoldo Suescun (Uruguay), one of the most active Latin America crystallographers, encouraged to start thinking about a second edition of the school and the proposal was greatly embraced by the attendees. Future locations (and local Chairmen) for a potential second edition of To.Sca.Lat. were also proposed: Costa Rica (Prof. José Javier Saavedra Arias) or Uruguay (Prof. Leopoldo Suescun) are awaiting you!

Of course, this event could not have existed without the help of several public bodies and private companies, here collectively gathered in a non-ordered list: Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES grant PAEP no. 88881.192068/2018-01), To.Sca.Lab. (University of Insubria & IC-CNR), the Italian Crystallographic Association, the University of Trento and, as generous commercial sponsor, Bruker (who also provided a shared wi-fi access to the TOPAS-6 license). The International Center for Diffraction Data (ICDD) generously sponsored the attendance of a few participants, by assigning them a special award (see Figure 3). We are heartily indebted to all of them for their financial support.

Figure 3. (Colour online) Four attendees receiving the ICDD prize from School Director Carlos Eduardo Maduro de Campos. Left to right: Wilson Daniel Calcedo Chacón (Colombia), Igon Antunes Vogel Maldonado (Brazil), Carla Yelpo Galán (Uruguay), Prof. Carlos Eduardo Maduro de Campos (School Director, Brazil), Harol Santiago Álvarez Pérez (Peru).