We review the discovery of localized surface plasmon resonances (LSPRs) in doped semiconductor quantum dots (QDs), an advance that has extended nanoplasmonics to materials beyond the classic gamut of noble metals. The initial demonstrations of near‐infrared LSPRs in QDs of heavily self‐doped copper chalcogenides and conducting metal oxides are setting the broad stage for this new field. We describe the key properties of QD LSPRs. Although the essential physics of plasmon resonances are similar to that in metal nanoparticles, the attributes of QD LSPRs represent a paradigm shift from metal nanoplasmonics. Carrier doping of quantum dots allows access to tunable LSPRs in the wide frequency range from the THz to the near‐infrared. Such composition or carrier density tunability is unique to semiconductor quantum dots and not achievable in metal nanoparticles. Most strikingly, semiconductor quantum dots allow plasmon resonances to be dynamically tuned or switched by active control of carriers. Semiconducting quantum dots thus represent the ideal building blocks for active plasmonics. A number of potential applications are discussed, including the use of plasmonic quantum dots as ultrasmall labels for biomedicine and electrochromic materials, the utility of LSPRs for probing nanoscale charge dynamics in semiconductors, and the exploitation of strong coupling between photons and excitons. Further advances in this field necessitate efforts toward generalizing plasmonic phenomena to a wider range of semiconductors, developing strategies for achieving controlled levels of doping and stabilizing them, investigating the spectroscopy of these systems on a fundamental level, and exploring their integration into optoelectronic devices.

Whereas pathways of chemical reactions involving small molecules are well-understood, the dynamics of reactions in extended solids remain difficult to elucidate. Frequently, kinetic studies on bulk materials provide a picture averaged over multiple domains or grains, smearing out interesting dynamics such as critical nucleation phenomena or sharp phase transitions occurring within individual, often nanoscale, grains, or domains. By optically monitoring a solid-state reaction with single nanocrystal resolution, we directly identified a unique, previously unknown, reaction pathway. Reaction trajectories of single cadmium selenide nanocrystals undergoing ion exchange with silver reveal that each individual nanocrystal waits a unique amount of time before making an abrupt switch to the silver selenide phase on a few hundred millisecond time scale. The gradual reaction progress of ensemble-scale cation exchange is actually comprised of these sharp single-nanocrystal switching events. Statistical distributions of waiting times suggest that the reaction is a cooperative transition rather than a diffusion-limited cation-by-cation exchange, which is confirmed by a stochastic reaction model. Such insight, achievable from single nanocrystal reaction studies, furthers mechanistic understanding of heterogeneous reactions, solid-state catalysis, bottom-up nanostructure growth, and materials' transformations and degradation in reactive environments.

This article reviews the state-of-the art status of thermal atomic layer etching of various materials such as metals, metal oxides, metal nitrides, semiconductors, and their oxides. We outline basic thermodynamic principles and reaction kinetics as they apply to these reactions and draw parallels to thermal etching. Furthermore, a list of all known publications is given organized by the material etched and correlated with the required reactant for each etch process. A model is introduced that describes why in the nonsaturation mode etch anisotropies may occur that can lead to unwanted performance variations in high aspect ratio semiconductor devices due to topological constraints imposed on the delivery of reactants and removal of reactant by-products.

Luminescence blinking is an inherent feature of optical emission from individual fluorescent molecules and quantum dots. There have been intense efforts, although not with complete resolution, toward the understanding of the mechanistic origin of blinking and also its mitigation in quantum dots. As an advance in our microscopic view of blinking, we show that the luminescence blinking of a quantum dot becomes unusually heavy in the temporal vicinity of a reactive transformation. This stage of heavy blinking is a result of defects/dopants formed within the quantum dot on its path to conversion. The evolution of blinking behavior along the reaction path allows us to measure the lifetime of the critical dopant-related intermediate in the reaction. This work establishes luminescence blinking as a single-nanocrystal level probe of catalytic, photocatalytic, and electrochemical events occurring in the solid-state or on semiconductor surfaces.

High aspect ratio (HAR) ONON channel hole patterning in 3D NAND flash presents grand challenges. This report summarizes some of the recent progresses in patterning from a HAR etch and Deposition-Etch-Co-Optimization (DECO) perspective. HAR etch mechanisms will be discussed focusing on how to reduce aspect ratio dependent etching (ARDE) effect. Highlights of the new low temperature etch process will be presented where significant improvement on ARDE is observed. New simulation results from a Monte Carlo feature scale model provide insights in ion scattering and mask interactions on channel hole profile control. Deposition and etch co-optimization (DECO) is a new frontier to enable better channel hole shape control at HAR. Film tier optimization and carbon liner insertion results show improvement in channel hole profile control.