Manipulations of nanocrystal (NC) surfaces have propelled the applications of colloidal NCs across various fields such as bioimaging, catalysis, electronics, and sensing applications. In this Feature Article, we discuss the surface chemistry of colloidal NCs, with an emphasis on semiconductor quantum dots, and the binding motifs for various ligands that coordinate NC surfaces. We present isothermal titration calorimetry (ITC) as a viable technique for studying the thermodynamics of the ligand association and exchange at NC surfaces by discussing its principles of operation and highlighting results obtained to date. We give an in-depth description of various thermodynamic models that can be used to interpret NC–ligand interactions as measured not only by ITC, but also by NMR, fluorescence quenching, and fluorescence anisotropy techniques. Understanding the complexity of NC surface–ligand interactions can provide a wide range of avenues to tune their properties for desired applications.
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This content will become publicly available on September 5, 2024
Stimuli-Responsive Surface Ligands for Direct Lithography of Functional Inorganic Nanomaterials
Colloidal nanocrystals (NCs) have emerged as a diverse class of materials with tunable composition, size, shape, and surface chemistry. From their facile syntheses to unique optoelectronic properties, these solution-processed nanomaterials are a promising alternative to materials grown as bulk crystals or by vapor-phase methods. However, the integration of colloidal nanomaterials in real-world devices is held back by challenges in making patterned NC films with the resolution, throughput, and cost demanded by device components and applications. Therefore, suitable approaches to pattern NCs need to be established to aid the transition from individual proof-of-concept NC devices to integrated and multiplexed technological systems.
In this Account, we discuss the development of stimuli-sensitive surface ligands that enable NCs to be patterned directly with good pattern fidelity while retaining desirable properties. We focus on rationally selected ligands that enable changes in the NC dispersibility by responding to light, electron beam, and/or heat. First, we summarize the fundamental forces between colloidal NCs and discuss the principles behind NC stabilization/destabilization. These principles are applied to understanding the mechanisms of the NC dispersibility change upon stimuli-induced ligand modifications. Six ligand-based patterning mechanisms are introduced: ligand cross-linking, ligand decomposition, ligand desorption, in situ ligand exchange, ion/ligand binding, and ligand-aided increase of ionic strength. We discuss examples of stimuli-sensitive ligands that fall under each mechanism, including their chemical transformations, and address how these ligands are used to pattern either sterically or electrostatically stabilized colloidal NCs. Following that, we explain the rationale behind the exploration of different types of stimuli, as well as the advantages and disadvantages of each stimulus.
We then discuss relevant figures-of-merit that should be considered when choosing a particular ligand chemistry or stimulus for patterning NCs. These figures-of-merit pertain to either the pattern quality (e.g., resolution, edge and surface roughness, layer thickness), or to the NC material quality (e.g., photo/electro-luminescence, electrical conductivity, inorganic fraction). We outline the importance of these properties and provide insights on optimizing them. Both the pattern quality and NC quality impact the performance of patterned NC devices such as field-effect transistors, light-emitting diodes, color-conversion pixels, photodetectors, and diffractive optical elements. We also give examples of proof-of-concept patterned NC devices and evaluate their performance. Finally, we provide an outlook on further expanding the chemistry of stimuli-sensitive ligands, improving the NC pattern quality, progress toward 3D printing, and other potential research directions. Ultimately, we hope that the development of a patterning toolbox for NCs will expedite their implementation in a broad range of applications.
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- Award ID(s):
- 1905290
- NSF-PAR ID:
- 10478895
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Accounts of Chemical Research
- Volume:
- 56
- Issue:
- 17
- ISSN:
- 0001-4842
- Page Range / eLocation ID:
- 2286 to 2297
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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