Multilayer Diffraction Reveals That Colloidal Superlattices Approach the Structural Perfection of Single Crystals

Toso, Stefano; Баранов, Д. А.; Altamura, Davide; Scattarella, Francesco; Dahl, Jakob; Wang, Xingzhi; Marras, Sergio; Alivisatos, A. Paul; Singer, Andrej; Giannini, Cinzia; Manna, Liberato

doi:10.26434/chemrxiv.13103507.v1

Cited by 10 publications

(29 citation statements)

References 21 publications

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“…As observed by Sandhyarani et al, the melting behavior of superlattices depends on these types of ordering interactions 12,31 . The use of GIWAXS to identify and evaluate this feature alongside SAXS, and grazing incidence small angle X-ray scattering (GISAXS) to characterize and analyze superlattices should yield further insight into the superlattice structures [13][14][15]43 . Altering the phase of the ligands could potentially manipulate the ligand ordering behavior to change distances between nanocrystals or modify superlattice assembly [43][44][45][46] .…”

Section: Resultsmentioning

confidence: 99%

“…The use of GIWAXS to identify and evaluate this feature alongside SAXS, and grazing incidence small angle X-ray scattering (GISAXS) to characterize and analyze superlattices should yield further insight into the superlattice structures [13][14][15]43 . Altering the phase of the ligands could potentially manipulate the ligand ordering behavior to change distances between nanocrystals or modify superlattice assembly [43][44][45][46] . We anticipate that these techniques can assist in optimizing future superlattices through employment of ligands with appropriate crystallization properties, and maintaining temperatures during superlattice formation that encourage certain ligand shell behavior.…”

Section: Resultsmentioning

confidence: 99%

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Observation of ordered organic capping ligands on semiconducting quantum dots via powder X-ray diffraction

et al. 2021

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Powder X-ray diffraction is one of the key techniques used to characterize the inorganic structure of colloidal nanocrystals. The comparatively low scattering factor of nuclei of the organic capping ligands and their propensity to be disordered has led investigators to typically consider them effectively invisible to this technique. In this report, we demonstrate that a commonly observed powder X-ray diffraction peak around $$q=1.4{\AA}^{-1}$$ q = 1.4 Å − 1 observed in many small, colloidal quantum dots can be assigned to well-ordered aliphatic ligands bound to and capping the nanocrystals. This conclusion differs from a variety of explanations ascribed by previous sources, the majority of which propose an excess of organic material. Additionally, we demonstrate that the observed ligand peak is a sensitive probe of ligand shell ordering. Changes as a function of ligand length, geometry, and temperature can all be readily observed by X-ray diffraction and manipulated to achieve desired outcomes for the final colloidal system.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Observation of ordered organic capping ligands on semiconducting quantum dots via powder X-ray diffraction

et al. 2021

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“…28,33−36 Our groups recently expanded the domain of application of Multilayer Diffraction to superlattices of colloidal semiconductor nanocrystals. 37,38 Briefly, these materials can be considered as multilayers where high-density inorganic domains (i.e., the nanocrystals) alternate with low-density organic layers (i.e., the ligands), whose scattering power can be neglected or approximated. Consequently, their diffractograms can be simulated by first computing the diffraction profile of the individual nanoparticles and then including the effects of the multilayer interference phenomena arising from the precise particle stacking.…”

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confidence: 99%

“…nanoplatelet structure, in contrast to the previous approximation of the nanocrystal as a stacking of scattering planes with no chemical identity. 38 This enabled us to refine the atomic structure of the constituent nanoplatelets, greatly increasing the potential of the method.…”

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confidence: 99%

“…Such a self-assembly process was exploited to create an extended periodicity along the thin direction of the nanoplatelets, producing a peculiar pattern of periodic peaks when the film is subject to a θ:2θ diffraction experiment. By applying the knowledge derived from our previous work on lead halide nanocrystal superlattices, 37,38 we developed an algorithm that enables the refinement of the nanoplatelets structure by means of a full-profile multiparametric fitting of their diffractogram. Despite relying only on a widely available lab-grade diffractometer, the amount of structural and compositional information that can be retrieved is noteworthy.…”

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Structure and Surface Passivation of Ultrathin Cesium Lead Halide Nanoplatelets Revealed by Multilayer Diffraction

et al. 2021

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The research on two-dimensional colloidal semiconductors has received a boost from the emergence of ultrathin lead halide perovskite nanoplatelets. While the optical properties of these materials have been widely investigated, their accurate structural and compositional characterization is still challenging. Here, we exploited the natural tendency of the platelets to stack into highly ordered films, which can be treated as single crystals made of alternating layers of organic ligands and inorganic nanoplatelets, to investigate their structure by multilayer diffraction. Using X-ray diffraction alone, this method allowed us to reveal the structure of ∼12 Å thick Cs–Pb–Br perovskite and ∼25 Å thick Cs–Pb–I–Cl Ruddlesden–Popper nanoplatelets by precisely measuring their thickness, stoichiometry, surface passivation type and coverage, as well as deviations from the crystal structures of the corresponding bulk materials. It is noteworthy that a single, readily available experimental technique, coupled with proper modeling, provides access to such detailed structural and compositional information.

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Collective Diffraction Effects in Perovskite Nanocrystal Superlattices

et al. 2022

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Conspectus For almost a decade now, lead halide perovskite nanocrystals have been the subject of a steadily growing number of publications, most of them regarding CsPbBr3 nanocubes. Many of these works report X-ray diffraction patterns where the first Bragg peak has an unusual shape, as if it was composed of two or more overlapping peaks. However, these peaks are too narrow to stem from a nanoparticle, and the perovskite crystal structure does not account for their formation. What is the origin of such an unusual profile, and why has it been overlooked so far? Our attempts to answer these questions led us to revisit an intriguing collective diffraction phenomenon, known for multilayer epitaxial thin films but not reported for colloidal nanocrystals before. By analogy, we call it the multilayer diffraction effect. Multilayer diffraction can be observed when a diffraction experiment is performed on nanocrystals packed with a periodic arrangement. Owing to the periodicity of the packing, the X-rays scattered by each particle interfere with those diffracted by its neighbors, creating fringes of constructive interference. Since the interfering radiation comes from nanoparticles, fringes are visible only where the particles themselves produce a signal in their diffraction pattern: for nanocrystals, this means at their Bragg peaks. Being a collective interference phenomenon, multilayer diffraction is strongly affected by the degree of order in the nanocrystal aggregate. For it to be observed, the majority of nanocrystals within the sample must abide to the stacking periodicity with minimal misplacements, a condition that is typically satisfied in self-assembled nanocrystal superlattices or stacks of colloidal nanoplatelets. A qualitative understanding of multilayer diffraction might explain why the first Bragg peak of CsPbBr3 nanocubes sometimes appears split, but leaves many other questions unanswered. For example, why is the split observed only at the first Bragg peak but not at the second? Why is it observed routinely in a variety of CsPbBr3 nanocrystals samples and not just in highly ordered superlattices? How does the morphology of particles (i.e., nanocrystals vs nanoplatelets) affect the appearance of multilayer diffraction effects? Finally, why is multilayer diffraction not observed in other popular nanocrystals such as Au and CdSe, despite the extensive investigations of their superlattices? Answering these questions requires a deeper understanding of multilayer diffraction. In what follows, we summarize our progress in rationalizing the origin of this phenomenon, at first through empirical observation and then by adapting the diffraction theory developed in the past for multilayer thin films, until we achieved a quantitative fitting of experimental diffraction patterns over extended angular ranges. By introducing the reader to the key advancements in our research, we provide answers to the questions above, we discuss what information can be extracted from patterns exhibiting collective interference effects, an...

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Multilayer Diffraction Reveals That Colloidal Superlattices Approach the Structural Perfection of Single Crystals

Cited by 10 publications

References 21 publications

Observation of ordered organic capping ligands on semiconducting quantum dots via powder X-ray diffraction

Observation of ordered organic capping ligands on semiconducting quantum dots via powder X-ray diffraction

Structure and Surface Passivation of Ultrathin Cesium Lead Halide Nanoplatelets Revealed by Multilayer Diffraction

Collective Diffraction Effects in Perovskite Nanocrystal Superlattices

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