Spatial Mapping of Sub-Bandgap States Induced by Local Nonstoichiometry in Individual Lead Sulfide Nanocrystals

Kislitsyn, Dmitry A.; Gervasi, Christian F.; Allen, Thomas L.; Palomaki, Peter K. B.; Hackley, Jason D.; Maruyama, Ryuichiro; Nazin, George V.

doi:10.1021/jz5019465

Cited by 14 publications

(18 citation statements)

References 45 publications

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“…It is also thought that excess passivation can delocalize charge too substantially and trap charge carriers, as the addition of excess ligands can sometimes reduce QY [15]. It may eventually be possible to image and monitor these mysterious defect states, as recent studies using scanning tunneling microscopy and spectroscopy show that the energy states of specific surface defects such as adatoms can be potentially spatially mapped to precise locations on QDs [108]. …”

Section: Optical Properties Dictated By the Surfacementioning

confidence: 99%

Quantum dot surface engineering: Toward inert fluorophores with compact size and bright, stable emission

Lim

Schleife

et al. 2016

Coordination Chemistry Reviews

109

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The surfaces of colloidal nanocrystals are complex interfaces between solid crystals, coordinating ligands, and liquid solutions. For fluorescent quantum dots, the properties of the surface vastly influence the efficiency of light emission, stability, and physical interactions, and thus determine their sensitivity and specificity when they are used to detect and image biological molecules. But after more than 30 years of study, the surfaces of quantum dots remain poorly understood and continue to be an important subject of both experimental and theoretical research. In this article, we review the physics and chemistry of quantum dot surfaces and describe approaches to engineer optimal fluorescent probes for applications in biomolecular imaging and sensing. We describe the structure and electronic properties of crystalline facets, the chemistry of ligand coordination, and the impact of ligands on optical properties. We further describe recent advances in compact coatings that have significantly improved their properties by providing small hydrodynamic size, high stability and fluorescence efficiency, and minimal nonspecific interactions with cells and biological molecules. While major progress has been made in both basic and applied research, many questions remain in the chemistry and physics of quantum dot surfaces that have hindered key breakthroughs to fully optimize their properties.

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Section: Optical Properties Dictated By the Surfacementioning

confidence: 99%

Quantum dot surface engineering: Toward inert fluorophores with compact size and bright, stable emission

Lim

Schleife

et al. 2016

Coordination Chemistry Reviews

109

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“…STS measurements in (b) and (c) were taken with a set-point of 1.9 V bias and 30 pA tunnelling current. Variations in the energies of electronic states across the NC roughly follow the NC topography, which is a result of the location-specific variation of the bias voltage drop inside the NC 56.…”

mentioning

confidence: 82%

“…A Au(111) substrate surface was prepared, under ultra-high vacuum conditions (∼10 −11 Torr), by several cycles of sputter-ing/annealing, using Ne gas, and annealed at ∼400 °C. Pentanethiol-terminated PbS NCs were synthesized as described previously, 56 suspended in pentane, and deposited onto the Au(111) surface using a solenoid pulse-valve. During deposition, the Au(111) substrate was held inside the load-lock section of the vacuum system, with the pressure not exceeding 10 −6 Torr during deposition.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…STS-based mapping of the local density of states (DOS) was recently used to study the spatial localization and spectral properties of sub-bandgap states in NCs arising due to local off-stoichiometry. 56 Here we apply this experimental approach to obtain atomic-scale DOS maps of individual ligand-free PbS NCs. Ligand-free NCs represent a well-defined model PbX system, unaffected by the uncontrolled variances of the ligand shell morphology, which makes this system more open to theoretical simulations.…”

Section: Introductionmentioning

confidence: 99%

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Diversity of sub-bandgap states in lead-sulfide nanocrystals: real-space spectroscopy and mapping at the atomic-scale

et al. 2015

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Colloidal semiconductor nanocrystals have emerged as a promising class of technological materials with optoelectronic properties controllable through quantum-confinement effects. Despite recent successes in this field, an important factor that remains difficult to control is the impact of the nanocrystal surface structure on the photophysics and electron transport in nanocrystal-based materials. In particular, the presence of surface defects and irregularities can result in the formation of localized sub-bandgap states that can dramatically affect the dynamics of charge carriers and electronic excitations. Here we use Scanning Tunneling Spectroscopy (STS) to investigate, in real space, sub-bandgap states in individual ligand-free PbS nanocrystals. In the majority of studied PbS nanocrystals, spatial mapping of electronic density of states with STS shows atomic-scale variations attributable to the presence of surface reconstructions. STS spectra show that the presence of surface reconstructions results in formation of surface-bound sub-bandgap electronic states. The nature of the surface reconstruction varies depending on the surface stoichiometry, with lead-rich surfaces producing unoccupied sub-bandgap states, and sulfur-rich areas producing occupied sub-bandgap states. Highly off-stoichiometric areas produce both occupied and unoccupied states showing dramatically reduced bandgaps. Different reconstruction patterns associated with specific crystallographic directions are also found for different nanocrystals. This study provides insight into the mechanisms of sub-bandgap state formation that, in a modified form, are likely to be applicable to ligand-passivated nanocrystal surfaces, where steric hindrance between ligands can result in under-coordination of surface atoms.

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“…Nazin and co-workers reported for the first time the connection between the atomic-scale nanocrystal surface morphology and atomic-scale variations in the electronic DOS. [126] Figure 10 exhibits the reported crystallographic directions and nanocrystal boundaries to identify via STS DOS mapping. The spatial mapping allows identifying the delocalized quantum-confined states and localized sub-bandgap states in PbS nanocrystals.…”

Section: (10 Of 21)mentioning

confidence: 99%

Quantum Dots Microstructural Metrology: From Time‐Resolved Spectroscopy to Spatially Resolved Electron Microscopy

Hasna

Hou

Welland

2020

Part & Part Syst Charact

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Quantum dots (QDs) have gained broad acceptance, applicability, and much interest in current semiconductor technology due to their unique optical and electrical properties. [1,2] QDs are semiconductors with size between 3 and 20 nm where electron and hole wave functions are highly confined. [3] The dimension should be comparable to the Bohr exciton radius of the material, and that leads to discrete energy levels in QD. QDs are attracted by their unique atomiclike narrow emission that can be tuned easily by controlling their size, structure, and composition. [4-6] The optical and electrical properties of QDs are better than organic fluorophores. For instance, QD has high quantum efficiency, excellent color gamut, narrow emission bandwidths, broad color tunability, high photostability, and high air stability. [7] These excellent properties make QD a potential candidate for applications in various fields such as optoelectronics, sensing, and imaging. [1,8-10] QDs are typically composed of group II-VI, III-V, and IV-VI compound semiconductors such as CdS, CdSe, PbS, ZnS, InAs, and ZnInS. [11-16] Because of minimal particle diameter, QDs have a high surface-to-volume ratio, and these surface trap states act as centers for nonradiative transitions that diminish the performance of QDs. This can be overcome by the growth of inorganic shells such as ZnS, CdTe, and CdSe. Various core-shell QDs such as CdSe/ZnS,

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Spatial Mapping of Sub-Bandgap States Induced by Local Nonstoichiometry in Individual Lead Sulfide Nanocrystals

Cited by 14 publications

References 45 publications

Quantum dot surface engineering: Toward inert fluorophores with compact size and bright, stable emission

Quantum dot surface engineering: Toward inert fluorophores with compact size and bright, stable emission

Diversity of sub-bandgap states in lead-sulfide nanocrystals: real-space spectroscopy and mapping at the atomic-scale

Quantum Dots Microstructural Metrology: From Time‐Resolved Spectroscopy to Spatially Resolved Electron Microscopy

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