Manipulating Electronic Structure from the Bottom-Up: Colloidal Nanocrystal-Based Semiconductors

Volk, Sebastian; Yazdani, Nasser; Wood, Vanessa

doi:10.1021/acs.jpclett.0c01417

Cited by 11 publications

(19 citation statements)

References 131 publications

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“…The NC surface and its ligands thus have a significant effect on how NCs are processed (e.g., their solvation, stability in solution, and assembly from colloidal form into solids) , and on their functionality (e.g., their catalytic, electronic, optical, phononic, and thermal performance). − For example, for NCs used in catalysis, the surface ligands can impact the catalyst energy efficiency and selectivity. − In the case of (opto)electronics, the type of ligand as well as its orientation determines the surface electrical dipole of individual NCs. This tunes the energy position of the electronic states of individual NCs as well as their assemblies and thus optical absorption and emission. , Furthermore, the electronic transport properties of NC solids depend on the electronic wave function confinement of individual NCs as well as the NC packing in the NC solid (facet-to-facet alignment and spacing), all of which are determined by the ligands. , Mechanical, phononic, and thermal conductivity of solids assembled from NCs are governed by the number of ligand interconnections, their orientation, and the elasticity. − These examples illustrate the importance of ligands in optimizing the performance of NCs and NC thin films for different applications.…”

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confidence: 99%

Ligand Dynamics in Nanocrystal Solids Studied with Quasi-Elastic Neutron Scattering

et al. 2021

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Nanocrystal surfaces are commonly populated by organic ligands, which play a determining role in the optical, electronic, thermal, and catalytic properties of the individual nanocrystals and their assemblies. Understanding the bonding of ligands to nanocrystal surfaces and their dynamics is therefore important for the optimization of nanocrystals for different applications. In this study, we use temperature-dependent, quasi-elastic neutron scattering (QENS) to investigate the dynamics of different surface bound alkanethiols in lead sulfide nanocrystal solids. We select alkanethiols with mono- and dithiol terminations, as well as different backbone types and lengths. QENS spectra are collected both on a time-of-flight spectrometer and on a backscattering spectrometer, allowing us to investigate ligand dynamics in a time range from a few picoseconds to nanoseconds. Through model-based analysis of the QENS data, we find that ligands can either (1) precess around a central axis, while simultaneously rotating around their own molecular axis, or (2) only undergo uniaxial rotation with no precession. We establish the percentage of ligands undergoing each type of motion, the average relaxation times, and activation energies for these motions. We determine, for example, that dithiols which link facets of neighboring nanocrystals only exhibit uniaxial rotation and that longer ligands have higher activation energies and show smaller opening angles of precession due to stronger ligand–ligand interactions. Generally, this work provides insight into the arrangement and dynamics of ligands in nanocrystal solids, which is key to understanding their mechanical and thermal properties, and, more generally, highlights the potential of QENS for studying ligand behavior.

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Ligand Dynamics in Nanocrystal Solids Studied with Quasi-Elastic Neutron Scattering

et al. 2021

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“…This means that analysis of the electrical properties of nanocrystal crystal thin films requires careful modeling [47] and often a multi-pronged approach. [135,138] For example, Volk et al [139] used a combination of measurements to show midgap electronic states of nanocrystals solids stemming from nanocrystal dimerization [140] and charging of doped nanocrystals. [47] In particular, the time aspects associated with charge localization in the film must be kept in mind when designing the measurement protocols.…”

Section: Packing and Ordering Of Nanocrystals Within Thin Filmsmentioning

confidence: 99%

Nanocrystal Quantum Dot Devices: How the Lead Sulfide (PbS) System Teaches Us the Importance of Surfaces

Lin

Yarema

Liu

et al. 2021

Chimia

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Semiconducting thin films made from nanocrystals hold potential as composite hybrid materials with new functionalities. With nanocrystal syntheses, composition can be controlled at the sub-nanometer level, and, by tuning size, shape, and surface termination of the nanocrystals as well as their packing, it is possible to select the electronic, phononic, and photonic properties of the resulting thin films. While the ability to tune the properties of a semiconductor from the atomistic- to macro-scale using solution-based techniques presents unique opportunities, it also introduces challenges for process control and reproducibility. In this review, we use the example of well-studied lead sulfide (PbS) nanocrystals and describe the key advances in nanocrystal synthesis and thin-film fabrication that have enabled improvement in performance of photovoltaic devices. While research moves forward with novel nanocrystal materials, it is important to consider what decades of work on PbS nanocrystals has taught us and how we can apply these learnings to realize the full potential of nanocrystal solids as highly flexible materials systems for functional semiconductor thin-film devices. One key lesson is the importance of controlling and manipulating surfaces.

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“…q e m e j,(n∈j),λ, q p nλ A qλ exp(i q • r n ), (8) corresponds to the interaction of light with excitations of the electric charge distribution.…”

Section: Quantum Microscopic Plasmon-polariton Modelmentioning

confidence: 99%

“…2 Supercrystals are tailored through particle-particle interaction and the choice of their building blocks. Initially, the discussion focused on collective vibrational and electronic modes of supercrystals made from semiconducting nanoparticles, 8 but interest recently turned to collective optical excitations, 9 especially, when using metallic nanoparticles as the supercrystal building blocks. 6,7,[10][11][12] The optical properties of metallic nanoparticle supercrystals are dominated by the response of their free electrons.…”

Section: Introductionmentioning

confidence: 99%

“…18 Supercrystal plasmon polaritons differ greatly in their properties from the excitations of the individual nanoparticles, they determine the optical response of metallic supercrystals, and open new pathways for scientific discoveries and technological development. 6,8,19,20 Recently, we showed that plasmonic supercrystals can be used to explore phenomena in the ultrastrong regime of light-matter coupling (USC). 6,10,21 In this regime the coupling strength is a considerable fraction of the bare frequency of the system, which leads to peculiar properties of the polariton states.…”

Section: Introductionmentioning

confidence: 99%

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Plasmon-Polaritons in Nanoparticle Supercrystals: Microscopic Quantum Theory Beyond the Dipole Approximation

Barros,

Vieira,

Mueller

et al. 2021

Preprint

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Crystals of plasmonic metal nanoparticles have intriguing optical properties. They reach the regimes of ultrastrong and deep strong light-matter coupling, where the photonic states need to be included in the simulation of material properties. We propose a quantum description of the plasmon polaritons in supercrystals that starts from the dipole and quadrupole excitations of the nanoparticle building blocks and their coupling to photons. Our model excellently reproduces results of finite difference time domain simulations. It provides detailed insight into the emergence of the polariton states. Using the example of a face centered cubic crystals we show that the dipole and quadrupole states mix in many high symmetry directions of the Brilouin zone. A proper description of the plasmon and plasmon-polariton band structure is only possible when including the quadrupole-derived states. Our model leads to an expression of the reduced coupling strength in nanoparticle supercrystals that we show to enter the deep strong coupling regime for metal fill fractions above 0.8. In addition to the plasmon-polariton energies we analyse the relative contributions of the dipole, quadrupole, and photonic states to their eigenfunctions and are able to demonstrate the decoupling of light in the deep strong coupling regime. Our results pave the way for a better understanding of the quantum properties of metallic nanoparticle supercrystals in the ultrastrong and deep-strong coupling regime.

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Manipulating Electronic Structure from the Bottom-Up: Colloidal Nanocrystal-Based Semiconductors

Cited by 11 publications

References 131 publications

Ligand Dynamics in Nanocrystal Solids Studied with Quasi-Elastic Neutron Scattering

Ligand Dynamics in Nanocrystal Solids Studied with Quasi-Elastic Neutron Scattering

Nanocrystal Quantum Dot Devices: How the Lead Sulfide (PbS) System Teaches Us the Importance of Surfaces

Plasmon-Polaritons in Nanoparticle Supercrystals: Microscopic Quantum Theory Beyond the Dipole Approximation

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