skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Single Entity Behavior of CdSe Quantum Dot Aggregates During Photoelectrochemical Detection
We demonstrate that colloidal quantum dots of CdSe and CdSe/ZnS are detected during the photooxidation of MeOH, under broad spectrum illumination (250 mW/cm 2 ). The stepwise photocurrent vs. time response corresponds to single entities adsorbing to the Pt electrode surface irreversibly. The adsorption/desorption of the QDs and the nature of the single entities is discussed. In suspensions, the QDs behave differently depending on the solvent used to suspend the materials. For MeOH, CdSe is not as stable as CdSe/ZnS under constant illumination. The photocurrent expected for single QDs is discussed. The value of the observed photocurrents, > 1 pA is due to the formation of agglomerates consistent with the collision frequency and suspension stability. The observed frequency of collisions for the stepwise photocurrents is smaller than the diffusion-limited cases expected for single QDs colliding with the electrode surface. Dynamic light scattering and scanning electron microscopy studies support the detection of aggregates. The results indicate that the ZnS layer on the CdSe/ZnS material facilitates the detection of single entities by increasing the stability of the nanomaterial. The rate of hole transfer from the QD aggregates to MeOH outcompetes the dissolution of the CdSe core under certain conditions of electron injection to the Pt electrode and in colloidal suspensions of CdSe/ZnS.  more » « less
Award ID(s):
1905312 1726897
PAR ID:
10381244
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
Frontiers in Chemistry
Volume:
9
ISSN:
2296-2646
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; (, Journal of the American Chemical Society)
    We designed a novel multicoordinating ligand based on the N-heterocyclic carbene (NHC) anchoring molecules and applied them for stabilizing luminescent quantum dots in aqueous media. The ligand is synthesized via nucleophilic addition reaction between amine-appended imidazole/poly(ethylene glycol) compounds and poly(isobutylene-alt-maleic anhydride) (PIMA), followed by carbene generation. We find that these NHC-based polymers exhibit fast and robust coordinating affinity to CdSe QDs overcoated with ZnS shells. The removal of hydrophobic coating and the generation of carbene are demonstrated by 1H NMR spectroscopy. 13C NMR spectroscopy confirms the existence of carbene-Zn complexes which is crucial for binding transition-metals on QD surfaces. These QDs exhibit absorption and emission features with little to no change before and after cap exchange, and their PL intensity is increased under light exposure. Excellent colloidal stability of these QD samples is observed in a wide range of competitive conditions over long period of time. Agarose gel electrophoresis indicates that the polymer coating imparts QDs with good compatibility in different aqueous buffers, and it prevents protein adsorption. 
    more » « less
  2. ; ; ; ; ; (, ChemPhotoChem)
    Abstract The photoluminescence (PL) saturation of CdSe/ZnS core/shell inorganic semiconductor quantum dots (QDs) and its utility as a probe for saturated excitation (SAX) microscopy are reported. Under saturating excitation power densities, the PL signal was demodulated and recorded at harmonics of the fundamental frequency. For commercially available Qdot® 655 ITK™ QDs, the power density required to achieve saturation was dependent upon the local environment of the QDs. For QDs deposited and dried on a glass substrate, the excitation power density required for PL saturation was less than 1 kW/cm2. Compared to this, saturation of PL for QDs dispersed in water required an excitation power density greater than 200 kW/cm2. This observation is manifested as a limitation in the imaging of hydrated samples, as demonstrated for HeLa cells labelled with biotinylated‐phalloidin followed by labelling with streptavidin‐coated QDs. As saturation affects the obtained spatial resolution in several imaging formats, including confocal imaging, the provided data will aid in obtaining the optimal spatial resolution when using QD probes to image biological samples. 
    more » « less
  3. (, The European Physical Journal Applied Physics)
    Understanding the rate processes controlling the growth of semiconductor nanocrystals in liquid solutions is of great importance in tailoring the sizes of semiconductor nanocrystals for the applications in optoelectronics, bioimaging and biosensing. In this work, we establish a simple relationship between the photoluminescence (PL) peak wavelength and the growth time of semiconductor nanocrystals under the condition that the contribution of electrostatic interaction to the quantum confinement is negligible. Using this relationship and the data available in the literature for CdSe and CdSe/ZnS nanocrystals, we demonstrate the feasibility of using the PL peak wavelength to analyze the growth behavior of the CdSe and CdSe/ZnS nanocrystals in liquid solutions. The results reveal that the diffusion of monomers in the liquid solution is the dominant rate process for the growth of CdSe/ZnS nanocrystals, and the activation energy for the growth of CdSe nanocrystals in the liquid solution is ∼9 kJ/mol. The feasibility to use this approach in the analysis of the thickness growth of core–shell nanocrystals with and without mechanical stress is also discussed. Such an approach opens a new avenue to in-situ monitor/examine the growth of semiconductor nanocrystals in liquid solutions. 
    more » « less
  4. ; ; ; ; ; ; (, Chemical Science)
    Indium phosphide quantum dots (InP QDs) are nontoxic nanomaterials with potential applications in photocatalytic and optoelectronic fields. Post-synthetic treatments of InP QDs are known to be essential for improving their photoluminescence quantum efficiencies (PLQEs) and device performances, but the mechanisms remain poorly understood. Herein, by applying ultrafast transient absorption and photoluminescence spectroscopies, we systematically investigate the dynamics of photogenerated carriers in InP QDs and how they are affected by two common passivation methods: HF treatment and the growth of a heterostructure shell (ZnS in this study). The HF treatment is found to improve the PLQE up to 16–20% by removing an intrinsic fast hole trapping channel ( τ h,non = 3.4 ± 1 ns) in the untreated InP QDs while having little effect on the band-edge electron decay dynamics ( τ e = 26–32 ns). The growth of the ZnS shell, on the other hand, is shown to improve the PLQE up to 35–40% by passivating both electron and hole traps in InP QDs, resulting in both a long-lived band-edge electron ( τ e > 120 ns) and slower hole trapping lifetime ( τ h,non > 45 ns). Furthermore, both the untreated and the HF-treated InP QDs have short biexciton lifetimes ( τ xx ∼ 1.2 ± 0.2 ps). The growth of an ultra-thin ZnS shell (∼0.2 nm), on the other hand, can significantly extend the biexciton lifetime of InP QDs to 20 ± 2 ps, making it a passivation scheme that can improve both the single and multiple exciton lifetimes. Based on these results, we discuss the possible trap-assisted Auger processes in InP QDs, highlighting the particular importance of trap passivation for reducing the Auger recombination loss in InP QDs. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; (, Small)
    Abstract Vapor‐based deposition techniques are emerging approaches for the design of carbon‐supported metal powder electrocatalysts with tailored catalyst entities, sizes, and dispersions. Herein, a pulsed CVD (Pt‐pCVD) approach is employed to deposit different Pt entities on mesoporous N‐doped carbon (MPNC) nanospheres to design high‐performance hydrogen evolution reaction (HER) electrocatalysts. The influence of consecutive precursor pulse number (50‐250) and deposition temperature (225–300 °C) are investigated. The Pt‐pCVD process results in highly dispersed ultrasmall Pt clusters (≈1 nm in size) and Pt single atoms, while under certain conditions few larger Pt nanoparticles are formed. The best MPNC‐Pt‐pCVD electrocatalyst prepared in this work (250 pulses, 250 °C) reveals a Pt HER mass activity of 22.2 ± 1.2 A mg−1Ptat ‐50 mV versus the reversible hydrogen electrode (RHE), thereby outperforming a commercially available Pt/C electrocatalyst by 40% as a result of the increased Pt utilization. Remarkably, after optimization of the Pt electrode loading, an ultrahigh Pt mass activity of 56 ± 2 A mg−1Ptat ‐50 mV versus RHE is found, which is among the highest Pt mass activities of Pt single atom and cluster‐based electrocatalysts reported so far. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email