Internal Atomic-Scale Structure Determination and Band Alignment of II-VI Quantum Dot Heterostructures

2019 ◽  
Author(s):  
Cecilia Gentle ◽  
Yuanheng Wang ◽  
Tyler N. Haddock ◽  
Conner P. Dykstra ◽  
Renske M. van der Veen
Keyword(s):  
Quantum Dots ◽  
Quantum Dot ◽  
Absorption Spectroscopy ◽  
Shell Structure ◽  
Electronic Band Structure ◽  
Band Alignment ◽  
Atomic Scale ◽  
Core Shell ◽  
Cdse Core ◽  
Electronic Band

<p>This work shows that ZnTe/CdSe core/shell quantum dots synthesized by standard literature procedures in actuality have an alloyed Cd<sup>­</sup><sub>x</sub>Zn<sub>1-x</sub>Te core. We employ X-ray absorption spectroscopy (XAS) at all four <i>K</i>-shell ionization edges (Zn, Te, Cd, Se) and perform a global fitting analysis in order to extract the first-shell bond distances. We combine our XAS results with transmission electron microscopy (TEM) sizing and elemental analyses, which allows us to propose models of the internal particle structure. Our multimodal characterization approach confirms <b>(1) </b>the presence of Cd-Te bonds, <b>(2) </b>cation<b> </b>alloying in the particle core (and the absence of anion alloying), and <b>(3) </b>a patchy pure-phase CdSe shell. We synthesize particles of different shell thicknesses and performed synthetic control studies that allowed us to discard a ZnTe/CdTe/CdSe core/shell/shell structure and confirm the alloyed core/shell structure. Our structural analysis is extended with electronic band structure calculations and UV/vis absorption spectroscopy, demonstrating that the alloyed Cd<sup>­</sup><sub>x</sub>Zn<sub>1-x</sub>Te/CdSe core/shell quantum dots exhibit a direct band gap, different from the predicted type-II band alignment of the intended ZnTe/CdSe core/shell quantum dots. This study highlights the challenges with synthesizing II-VI quantum dot heterostructures and the power of XAS for understanding the internal structure of heterogenous nanoparticles.</p>

Internal Atomic-Scale Structure Determination and Band Alignment of II-VI Quantum Dot Heterostructures

2019 ◽  
Author(s):  
Cecilia Gentle ◽  
Yuanheng Wang ◽  
Tyler N. Haddock ◽  
Conner P. Dykstra ◽  
Renske M. van der Veen
Keyword(s):  
Quantum Dots ◽  
Quantum Dot ◽  
Absorption Spectroscopy ◽  
Shell Structure ◽  
Electronic Band Structure ◽  
Band Alignment ◽  
Atomic Scale ◽  
Core Shell ◽  
Cdse Core ◽  
Electronic Band

<p>This work shows that ZnTe/CdSe core/shell quantum dots synthesized by standard literature procedures in actuality have an alloyed Cd<sup>­</sup><sub>x</sub>Zn<sub>1-x</sub>Te core. We employ X-ray absorption spectroscopy (XAS) at all four <i>K</i>-shell ionization edges (Zn, Te, Cd, Se) and perform a global fitting analysis in order to extract the first-shell bond distances. We combine our XAS results with transmission electron microscopy (TEM) sizing and elemental analyses, which allows us to propose models of the internal particle structure. Our multimodal characterization approach confirms <b>(1) </b>the presence of Cd-Te bonds, <b>(2) </b>cation<b> </b>alloying in the particle core (and the absence of anion alloying), and <b>(3) </b>a patchy pure-phase CdSe shell. We synthesize particles of different shell thicknesses and performed synthetic control studies that allowed us to discard a ZnTe/CdTe/CdSe core/shell/shell structure and confirm the alloyed core/shell structure. Our structural analysis is extended with electronic band structure calculations and UV/vis absorption spectroscopy, demonstrating that the alloyed Cd<sup>­</sup><sub>x</sub>Zn<sub>1-x</sub>Te/CdSe core/shell quantum dots exhibit a direct band gap, different from the predicted type-II band alignment of the intended ZnTe/CdSe core/shell quantum dots. This study highlights the challenges with synthesizing II-VI quantum dot heterostructures and the power of XAS for understanding the internal structure of heterogenous nanoparticles.</p>

Structure evolution from CdSSe alloy to CdS/CdSe core/shell for Cd(S, Se) composite quantum dots and its impact on the performance of sensitized solar cell

2021 ◽  
Author(s):  
Junfei Fang ◽  
Wenlei Lv ◽  
Yilong Lei ◽  
Jianping Deng ◽  
Pengchao Zhang ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Solar Cell ◽  
Quantum Dot ◽  
Structure Evolution ◽  
Core Shell ◽  
Cdse Core

CdSSe alloy and CdS/CdSe core/shell quantum dots (QDs) are widely studied in quantum dot solar cell (QDSSCs). However, up to date, there have been no detailed comparative investigations on the cell...

Investigation of the Electron Energy Spectrum in a Three Dimensional Regimented Tetragonal Quantum Dot Superlattice

2001 ◽  
Vol 677 ◽  
Author(s):  
Olga L. Lazarenkova ◽  
Alexander A. Balandin
Keyword(s):  
Quantum Dots ◽  
Energy Spectrum ◽  
Quantum Dot ◽  
Electron Energy ◽  
Electronic Band Structure ◽  
Three Dimensional ◽  
Electron Energy Spectrum ◽  
Real Crystal ◽  
Electronic Band ◽  
Gaas Quantum Dot

ABSTRACTWe analyze the electron energy spectrum in three-dimensional regimented arrays of semiconductor quantum dots. The coupling among quantum dots results in formation of three- dimensional electron mini-bands. Changing the size of quantum dots, inter-dot distance, barrier height and regimentation, one can control the electronic band structure of this quantum dot superlattice, which can also be referred to as quantum dot crystal due to its structure and energy spectrum that resemble those of a real crystal. Results of computer simulations carried out for a tetragonal InAs/GaAs quantum dot superlattice show that the electron density of states, effective mass tensor and other properties are different from those of bulk and conventional quantum well superlattices.

scholarly journals Conjugation ofE. coliO157:H7 Antibody to CdSe/ZnS Quantum Dots

2015 ◽  
Vol 2015 ◽  
pp. 1-7 ◽  
Author(s):  
N. T. Vo ◽  
H. D. Ngo ◽  
D. L. Vu ◽  
A. P. Duong ◽  
Q. V. Lam
Keyword(s):  
Quantum Dots ◽  
Shell Structure ◽  
Trioctylphosphine Oxide ◽  
Core Shell ◽  
Cdse Core ◽  
Green Method ◽  
Potential Measurement ◽  
E Coli ◽  
Luminescence Efficiency ◽  
Core Shell Structure

The conjugation of antibody to semiconductor quantum dots plays a very important role in many applications such as bioimaging, biomarking, and biosensing. In this research, we present some results of highly luminescent core/shell structure CdSe/ZnS on which theE. coliantibody was conjugated. The CdSe core was synthesized successfully with chemical “green” method. For biological applications, the capping surfactant, trioctylphosphine oxide, was substituted by a new one, mercaptopropionic acid (MPA), before the antibody attachment step. Finally, theE. coliantibody was attached to quantum dots CdSe/ZnS. Morphology, structure, and optical properties were investigated with PL, UV-Vis, TEM, and XRD methods. The successful ligand substitution and antibody attachment were confirmed by zeta potential measurement, FTIR spectroscopy, and TEM. The results showed quantum dots size of 2.3 nm, uniform distribution, and high luminescence. CdSe/ZnS core/shell structure had better stability and enhanced the luminescence efficiency up to threefold compared with the core CdSe. MPA ligand shifted the initial hydrophobic quantum dots to hydrophilic ones, which helped to dissolve them in organic solvents and attach the antibody.

Study on Photoluminescence Quenching of CdSe Core/Shell Quantum Dots with Organic Charge Transferring Material

2014 ◽  
Vol 981 ◽  
pp. 883-886
Author(s):  
Yu Qiu Qu ◽  
Liu Yang Zhang ◽  
Li Min An ◽  
Hong Wei ◽  
Gui Fan Li
Keyword(s):  
Quantum Dots ◽  
Fluorescence Quenching ◽  
Fluorescence Lifetime ◽  
Spectral Methods ◽  
Shell Structure ◽  
Core Shell ◽  
Cdse Core ◽  
Photoluminescence Quenching ◽  
Molecular Concentration ◽  
Pl Quenching

The effect of organic charge transferring material (CTM) on fluorescence of CdSe/ZnS and CdSe/CdS/ZnS core/shell quantum dots (QDs) are investigated by spectral methods. With the increase of organic molecular concentration, CTM can greatly quench the fluorescence of QDs and shorten the fluorescence lifetime of QDs. In the process of interacting with CTM, the efficiency of fluorescence quenching for CdSe/ZnS is significantly higher than that for CdSe/CdS/ZnS. The results of experiment show that the shell structure of QDs plays the major role in photoluminescence (PL) quenching. The mechanism of PL quenching of QDs is also analyzed.

High-Temperature Synthesis of CdSe-Based Core/Shell, Core/Shell/Shell, and Core/Graded-Shell Nanoplatelets for Stable and Efficient Narrowband Emitters

2019 ◽  
Author(s):  
Aurelio A. Rossinelli ◽  
Henar Rojo ◽  
Aniket S. Mule ◽  
Marianne Aellen ◽  
Ario Cocina ◽  
...  
Keyword(s):  
Quantum Dots ◽  
High Temperature ◽  
Equilibrium Shape ◽  
Size Variation ◽  
Crystal Defects ◽  
Atomic Scale ◽  
Quantum Yields ◽  
Core Shell ◽  
Compositional Gradient ◽  
High Quality

<div>Colloidal semiconductor nanoplatelets exhibit exceptionally narrow photoluminescence spectra. This occurs because samples can be synthesized in which all nanoplatelets share the same atomic-scale thickness. As this dimension sets the emission wavelength, inhomogeneous linewidth broadening due to size variation, which is always present in samples of quasi-spherical nanocrystals (quantum dots), is essentially eliminated. Nanoplatelets thus offer improved, spectrally pure emitters for various applications. Unfortunately, due to their non-equilibrium shape, nanoplatelets also suffer from low photo-, chemical, and thermal stability, which limits their use. Moreover, their poor stability hampers the development of efficient synthesis protocols for adding high-quality protective inorganic shells, which are well known to improve the performance of quantum dots. <br></div><div>Herein, we report a general synthesis approach to highly emissive and stable core/shell nanoplatelets with various shell compositions, including CdSe/ZnS, CdSe/CdS/ZnS, CdSe/Cd<sub>x</sub>Zn<sub>1–x</sub>S, and CdSe/ZnSe. Motivated by previous work on quantum dots, we find that slow, high-temperature growth of shells containing a compositional gradient reduces strain-induced crystal defects and minimizes the emission linewidth while maintaining good surface passivation and nanocrystal uniformity. Indeed, our best core/shell nanoplatelets (CdSe/Cd<sub>x</sub>Zn<sub>1–x</sub>S) show photoluminescence quantum yields of 90% with linewidths as low as 56 meV (19.5 nm at 655 nm). To confirm the high quality of our different core/shell nanoplatelets for a specific application, we demonstrate their use as gain media in low-threshold ring lasers. More generally, the ability of our synthesis protocol to engineer high-quality shells can help further improve nanoplatelets for optoelectronic devices.</div>

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