The Core/Shell Structure of CdSe/ZnS Quantum Dots Characterized by X‐Ray Absorption Fine Spectroscopy

Wei, Huijing; Zhou, Jing; Zhang, Linjuan; Wang, Fang; Wang, Jianqiang; Jin, Chan

doi:10.1155/2015/764712

Cited by 12 publications

(10 citation statements)

References 46 publications

(57 reference statements)

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“…In this contribution, we make use of X-ray absorption spectroscopy (XAS) in the construction of atomic-scale structural models of CSQDs. XAS is ideally suited for probing the internal structure of multicomponent materials because of its elemental specificity and sensitivity to the local structure surrounding the absorbing atom. − In particular, the extended X-ray absorption fine structure (EXAFS) region of the XAS spectrum can ascertain coordination numbers, distinguish between types of scattering atoms, calculate bond lengths, and determine bond angles in the local (∼6 Å) environment of the absorbing atom in the nanoparticle.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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This work shows that ZnTe/CdSe core/shell quantum dots synthesized by a standard literature procedure in actuality have an alloyed Cd x Zn 1−x Te core. We employ Xray absorption spectroscopy (XAS) at all four K-shell ionization edges (Zn, Te, Cd, and Se) and perform global fitting analysis 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 (1) the presence of Cd−Te bonds, (2) cation alloying in the particle core (and the absence of anion alloying), and (3) 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 x Zn 1−x 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 heterogeneous nanoparticles.

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Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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“…An analysis of the nearest coordination shells around a photoabsorber can be performed using conventional methods of analysis to determine the local structure parameters and degree of disorder. The combination of XANES and EXAFS analyses has proved to be a robust methodology for the characterisation of complex systems [ 164 , 165 ], even when only EXAFS measurements are obtained and XANES spectra are used only for comparison purposes [ 166 , 167 ]. This approach can provide both local symmetry information (through XANES), as well as structural and stoichiometry information (through EXAFS), which can be used as an input for the subsequent analysis of scattering data and computer modelling [ 165 ] or as a support to density functional theoretical (DFT) calculations [ 168 ].…”

Section: Surface Chemistry Of Qdsmentioning

confidence: 99%

Semiconductor Quantum Dots as Target Analytes: Properties, Surface Chemistry and Detection

et al. 2022

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Since the discovery of Quantum Dots (QDs) by Alexey I. Ekimov in 1981, the interest of researchers in that particular type of nanomaterials (NMs) with unique optical and electrical properties has been increasing year by year. Thus, since 2009, the number of scientific articles published on this topic has not been less than a thousand a year. The increasing use of QDs due to their biomedical, pharmaceutical, biological, photovoltaics or computing applications, as well as many other high-tech uses such as for displays and solid-state lighting (SSL), has given rise to a considerable number of studies about its potential toxicity. However, there are a really low number of reported studies on the detection and quantification of QDs, and these include ICP–MS and electrochemical analysis, which are the most common quantification techniques employed for this purpose. The knowledge of chemical phenomena occurring on the surface of QDs is crucial for understanding the interactions of QDs with species dissolved in the dispersion medium, while it paves the way for a widespread use of chemosensors to facilitate its detection. Keeping in mind both human health and environmental risks of QDs as well as the scarcity of analytical techniques and methodological approaches for their detection, the adaptation of existing techniques and methods used with other NMs appears necessary. In order to provide a multidisciplinary perspective on QD detection, this review focused on three interrelated key aspects of QDs: properties, surface chemistry and detection.

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“…14 XAS studies with CdSe/ZnS QDs have included ligand exchange chemistry 15 , exciton binding energy measurements, 16 and CdSe/ZnS electronic structure studies with elucidation of the ZnS shell oxidation states. 17 Magnetic Fe/Fe2O3 nanoparticles (NPs) examined with XAS revealed the iron and iron oxide bonding environment while also detecting trace boron and nickel used during the synthetic protocol. 18 An investigation of Fe/Ag and Ag/Fe core-shell NPs produced by a sodium borohydride reduction of Ag and Fe salts with XAS was able to discern subtle FeB and Fe2B surface bonding environments.…”

Section: Introductionmentioning

confidence: 99%

Chemical insights into silica growth on nanoscale diamond using multimodal characterization and simulation

Sandoval

Lopez

Arreola

et al. 2023

Preprint

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Surface chemistry of materials that host quantum bits such as diamond are an important avenue of exploration as quantum computation and quantum sensing platforms mature. Interfacing diamond in general, and nanoscale diamond (ND) in particular with silica is a potential route to integrate the quantum bit into a photonic device, fiber optic, cells or tissues with flexible functionalization chemistry. While silica growth on ND cores has been used successfully for quantum sensing and biolabeling, the surface mechanism to initiate growth was unknown. This report describes the surface chemistry responsible for silica bond formation on diamond and uses X-ray absorption spectroscopy (XAS) to probe the diamond surface chemistry and its electronic structure with increasing silica thickness. A modified Stöber (Cigler) method was used to synthesize 2–35 nm thick shells of SiO2 onto carboxylic acid rich ND cores and the diamond features and surface structure were characterized by overlapping techniques including electron microscopy. Importantly, we discovered that SiO2 growth on carboxylated NDs eliminates the presence of carboxylic acids and that basic ethanolic solutions converts the ND surface to an alcohol-rich surface prior to silica growth. The data supports a mechanism that alcohols on the ND surface generate silyl-ether (ND-O-Si-(OH)3) bonds due to rehydroxylation by ammonium hydroxide in ethanol. Additionally, resonant inelastic X-ray scattering (RIXS) maps produced by the transition edge sensor supports the chemical analysis provided by XAS. The suppression of the diamond electronic structure as a function of SiO2 thickness was observed, and the Auger electron escape depth was modeled using the NIST database for the Simulation of Electron Spectra for Surface Analysis (SESSA) to support our experimental results. Researchers using high-pressure high temperature (HPHT) NDs or any alcohol-terminated material (metal oxides, oxidized silicon carbide or cubic-boron nitride) for quantum sensing applications may exploit these results to design new core-shell quantum sensors with base-catalyzed reactions and metal oxide precursors.

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The Core/Shell Structure of CdSe/ZnS Quantum Dots Characterized by X‐Ray Absorption Fine Spectroscopy

Cited by 12 publications

References 46 publications

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

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

Semiconductor Quantum Dots as Target Analytes: Properties, Surface Chemistry and Detection

Chemical insights into silica growth on nanoscale diamond using multimodal characterization and simulation

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