Recent Notable Approaches to Study Self‐Assembly of Nanoparticles with X‐Ray Scattering and Electron Microscopy

Abstract

several issues far from being resolved: for many systems long-range periodic order is not routinely achieved, reproducibility is often not optimal and truly emergent and new properties arising from the supercrystal formation could be demonstrated for just a few systems. [3][4][5][6][7] From the materials science perspective there is no established figure of merit or common set of parameters allowing to quantify "quality" of NP superlattices and supercrystals. In lieu of such standard procedures, terms as well-ordered, crystalline order, quasicrystalline, etc., are usually used in literature. However, there exist no commonly accepted definitions of what qualifies, e.g., as "well-ordered."In this review, we want to highlight some recent experimental developments and new approaches to study self-assembly of NPs or structure formation of NP supercrystals and their final structure. We focus on NP, the broad field of photonic materials prepared by self-assembly of larger colloidal particles is not covered herein. [8][9][10] The introduction of the basic concepts of NP self-assembly will be kept short and should be considered as an overview, for more background and details excellent comprehensive reviews are available. [2,11] We will then briefly address and discuss the expectations associated with self-assembled materials, especially the proposed emergence of new properties directly related to order. In the second part of the review, we will present recent innovative approaches for the investigation of self-assembly and self-assembled structures that go beyond the standard characterization. We focus mainly on structure and structure formation and less on properties, so most of the studies are based on scattering and electron microscopy. Figure 1 provides an overview roughly following this outline. Self-Assembly of NanoparticlesSelf-assembly is a broad term and occurs on all scales from atoms, ions, and molecules to galaxies, as pointed out by Whitesides and Grzybowski. [12] It can be defined as the autonomous organization of multiple discrete components into ordered structures, driven by energetics or entropy or both. [2,13] In nature, countless examples of highly complex and functional structures resulting from self-assembly can be found, Self-assembly of nanoparticles (NPs) has evolved into a powerful tool for the synthesis of superstructures with tailored properties. The quality, diversity, and complexity of synthesized structures are continuously improving and fascinating new collective properties are demonstrated. At the same time, the rapid development of electron microscopy and synchrotron sources for X-rays has enabled new exciting experimental approaches to study structure and structure formation in the context of NP self-assembly. In this review, some recent studies and what can be learned from them are highlighted and discussed. It is started with a general introduction covering important concepts, experimental approaches, commonly obtained structures, the ideas of artificial atoms, and emerging properties a...

Real-Time X-ray Scattering Discovers Rich Phase Behavior in PbS Nanocrystal Superlattices during In Situ Assembly

“…The origin of a certain superlattice configuration for the case of PbS NCs is still a subject of ongoing research because, even at seemingly similar conditions, different self-assembled superlattice structures have been observed. , The recently emerged in situ X-ray scattering methods of the self-assembly characterization represent a promising route for providing insights into the assembly mechanism and uncover the time-resolved superlattice transitions. − However, the discussion and determination of the ligand grafting density are often absent in the literature, which complicates comparison between experimental results obtained for similar systems in independent investigations and hinder the development of theoretical models that would help to navigate the assembly pathway to produce the targeted superlattices.…”

Importance of Monitoring the Synthesis of Light‐Interacting Nanoparticles – A Review on In Situ, Ex Situ, and Online Time‐Resolved Studies

“…[ 100 ] In particular, the solvent needs to have a very low vapor pressure to be compatible with the ultrahigh vacuum required by the microscope. [ 103 ] Some approaches use a sample cell with an electron‐transparent window enclosing a liquid film with a thickness <1 µm. [ 104 ] State‐of‐the‐art liquid cells are equipped with temperature control and can include electrodes, using modern microfabrication techniques.…”

“…[252] The use of LP-TEM monitoring during in situ batch kinetic studies is also challenging, requiring the solvent to be compatible with the ultrahigh vacuum present in the instrument. [103] In some approaches, a sample cell with an electron-transparent window is used, enclosing the liquid to a thickness <1 µm. [104] The liquid cell can support temperature control and even include electrodes, using modern microfabrication techniques.…”

“…[ 175 ] As a result, nanoparticle synthesis methods are still under substantial development, with emphasis on not only improving kinetic control [ 23,26,62,176,177 ] but also reducing production cost, [ 46,178–180 ] and expanding the properties/applications of the nanomaterials. [ 103,181–184 ]…”

“…[175] As a result, nanoparticle synthesis methods are still under substantial development, with emphasis on not only improving kinetic control [23,26,62,176,177] but also reducing production cost, [46,[178][179][180] and expanding the properties/applications of the nanomaterials. [103,[181][182][183][184] In this section, we focus on the kinetic and mechanistic information obtained during the synthesis of plasmonic and optoelectronic nanomaterials in batch reactors with the aim of i) surveying time-resolved data with ex situ/in situ capabilities, ii) discussing selected studies to highlight the importance and differences between in situ and ex situ characterization, and iii) detailing the limitations of batch reactors in terms of reproducibility and time resolution.…”