Characterization of Shell Material on Colloidal CdSe/ZnS Quantum Dots

2004 ◽  
Vol 818 ◽  
Author(s):  
Zhiheng Yu ◽  
Li Guo ◽  
Hui Du ◽  
Todd Krauss ◽  
John Silcox
Keyword(s):  
Quantum Dots ◽  
Surface Passivation ◽  
Core Shell ◽  
Shell Material ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Chemical Distribution ◽  
Electron Energy Loss

AbstractScanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) was used to determine the distribution of ZnS shell material on colloidal core-shell CdSe/ZnS quantum dots (QDs). A sub-nm electron probe was placed at various locations on core-shell QDs to ascertain the chemical distribution of the shell material. While a definite shell of ZnS was detected surrounding the CdSe core, the integrated EELS signals from positions around the QD suggest the distribution of the shell material may not be uniform. A non-uniform shell implies a reduced quality of the QD surface passivation.

scholarly journals Growth and characterization of CNT–TiO2 heterostructures

2014 ◽  
Vol 5 ◽  
pp. 946-955 ◽  
Author(s):  
Yucheng Zhang ◽  
Ivo Utke ◽  
Johann Michler ◽  
Gabriele Ilari ◽  
Marta D Rossell ◽  
...  
Keyword(s):  
Good Control ◽  
Atomic Layer ◽  
Oxide Material ◽  
Electronic Information ◽  
Transmission Electron ◽  
Layer Deposition ◽  
Metal Metal ◽  
Scanning Transmission ◽  
Electron Energy Loss

A thriving field in nanotechnology is to develop synergetic functions of nanomaterials by taking full advantages of unique properties of each component. In this context, combining TiO2 nanocrystals and carbon nanotubes (CNTs) offers enhanced photosensitivity and improved photocatalytic efficiency, which is key to achieving sustainable energy and preventing environmental pollution. Hence, it has aroused a tremendous research interest. This report surveys recent research on the topic of synthesis and characterization of the CNT–TiO2 interface. In particular, atomic layer deposition (ALD) offers a good control of the size, crystallinity and morphology of TiO2 on CNTs. Analytical transmission electron microscopy (TEM) techniques such as electron energy loss spectroscopy (EELS) in scanning transmission mode provides structural, chemical and electronic information with an unprecedented spatial resolution and increasingly superior energy resolution, and hence is a necessary tool to characterize the CNT–TiO2 interface, as well as other technologically relevant CNT–metal/metal oxide material systems.

Quantitative Measurement of Compositional Enrichment in Strained Alloy Quantum Dots

2001 ◽  
Vol 7 (S2) ◽  
pp. 218-219
Author(s):  
P.A. Crozier ◽  
M. Catalano
Keyword(s):  
Quantum Dots ◽  
Energy Loss ◽  
Electron Energy ◽  
Vision System ◽  
Wetting Layer ◽  
Spatially Resolved ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Alloy Quantum Dots ◽  
Electron Energy Loss

High spatial resolution information on the structure and composition of semiconductor quantum dots is necessary to relate microstructure to macroscopic electron-optical properties [1]. Scanning transmission electron microscopy (STEM) combined with electron energy-loss spectroscopy (EELS) can be used to determine the elemental composition of nanometer-sized particles. Applying these techniques to quantum dots is challenging because the dot nucleates on a very thin wetting layer of similar composition and is embedded in a matrix. Here we present a strategy to extract absolute compositional information on InGaAs dots. The method relies on modeling both the dot shape and the electron probe profile.Samples were prepared by depositing four monolayers of In0.5Ga0.5As onto a GaAs substrate giving a nominal wetting layer thickness of 1.2 nm [2]. STEM was performed on a Vacuum Generator's HB501 equipped with a GATAN parallel electron energy-loss spectrometer. An ES Vision system was used to acquire spatially resolved electron energy-loss spectra from the wetting layer and the quantum dots.

Synthesis and Optical Properties of CdSe and CdSe/ZnS Core/Shell Quantum Dots

2015 ◽  
Vol 1085 ◽  
pp. 176-181
Author(s):  
Puspendu Barik ◽  
Arup Ratan Mandal ◽  
Denis V. Kuznetsov ◽  
Anna Yu. Godymchuk
Keyword(s):  
Electron Microscopy ◽  
Quantum Dots ◽  
Excitation Wavelength ◽  
Core Shell ◽  
Shell Material ◽  
X Ray Diffraction ◽  
Chemical Route ◽  
X Ray ◽  
The Core ◽  
Transmission Electron

In this work, we have synthesized homogeneous, ordered CdSe and CdSe/ZnS core/shell quantum dots (QDs) by chemical route and characterized them using X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), and Photoluminescence (PL) spectroscopy. Coating with shell material was confirmed by red shift as well as enhancement in the PL peak compared to bare QDs. DLS data showed QDs and core/shell to be stable. PL spectra are red shifted relative to the excitation wavelength. Bare QDs and the core/shell material shows a Stoke-shift of 16 and 18 meV respectively.

Microanalysis of Soot Particulates using Stem

1997 ◽  
Vol 502 ◽  
Author(s):  
David C. Bell ◽  
Lenore C. Rainey ◽  
ÁrpÁd B. Palotás ◽  
John B. Vandersande
Keyword(s):  
Energy Loss ◽  
Combustion Process ◽  
Operating Conditions ◽  
Engine Exhaust ◽  
Transmission Electron ◽  
Exhaust Duct ◽  
Scanning Transmission ◽  
Combustion Processes ◽  
Electron Energy Loss

ABSTRACTScanning transmission electron microscopy (STEM) coupled with energy dispersive x-ray analysis (EDX) and electron energy-loss spectroscopy (EELS) has been used to characterize the elemental composition and oxidation conditions of various soot samples. The STEM employed in this investigation was the Vacuum Generators HB603, with a microanalytical resolution approaching 1 rnm, that allowed the analysis of individual soot particles and aggregates. The aim of this research is quantification of the EDX spectra which is possible after background and absorption corrections. This information can then be used for comparative studies of different fuels and combustion processes. EELS has been employed to determine the amount of graphitic carbon in a soot particulate, and the detection of trace elements of low atomic number. It has been shown in soot that for Carbon the energy-loss of the p shell electrons increases with the amount of oxidation at high temperatures. Analysis and characterization of gas turbine soot, collected from an engine exhaust duct of a 737-300 aircraft showed an abundance of different elements. Some of these elements originated from the fuel and combustion processes, while other elements were components of the engine itself that combined with the soot particulates during the combustion process. The study showed that soot impurities were found in all discrete sections of aggregates, and that only one or two small soot particulates were necessary to obtain a chemical fingerprint. Other investigations include; coal soot, diesel soot at different engine operating conditions and soot produced from wood burning. The richness of the spectra obtained and the ability to quantify results represents an opportunity to accomplish source identification in a novel, powerful way.

Structural and Chemical Characterization of Al(Ga)N/GaN Quantum Well Structures Grown by Plasma Assisted Molecular Beam Epitaxy

2012 ◽  
Vol 186 ◽  
pp. 70-73 ◽  
Author(s):  
Jolanta Borysiuk ◽  
Piotr Dłużewski ◽  
Zbigniew Zytkiewicz ◽  
Marta Sobańska ◽  
Kamil Kłosek ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Molecular Beam Epitaxy ◽  
Scanning Transmission Electron Microscopy ◽  
Molecular Beam ◽  
Chemical Characterization ◽  
Quantum Well Structures ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Electron Energy Loss

Growth of high quality GaN/AlN heterostructures by plasma assisted molecular beam epitaxy (PAMBE) is possible with excess of Ga on the surface. During growth of AlN this additional Ga acts as surfactant and improves mobility of the Al adatoms on the growing surface, at the possible cost of Ga segregation and creation of mixed AlGaN interlayer. Scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) were used to determine chemical composition of high crystallographic quality GaN-AlN multilayer structure. It was shown that segregation occurs at AlN-GaN heterointerfaces, while GaN-AlN interfaces have abrupt stepwise change of the chemical composition. HRTEM results show creation of trench defects at the periphery of growing AlN islands in the case of nonoptimized growth.

scholarly journals Hydrogenation of terminal and internal olefins using a biowaste-derived heterogeneous cobalt catalyst

2018 ◽  
Vol 4 (9) ◽  
pp. eaau1248 ◽  
Author(s):  
Florian Korbinian Scharnagl ◽  
Maximilian Franz Hertrich ◽  
Francesco Ferretti ◽  
Carsten Kreyenschulte ◽  
Henrik Lund ◽  
...  
Keyword(s):  
Magnetic Behavior ◽  
Magnetic Composite ◽  
Metal Composite ◽  
X Ray Diffraction ◽  
Transmission Electron ◽  
Water As Solvent ◽  
Scanning Transmission ◽  
Product Separation ◽  
Electron Energy Loss

Hydrogenation of olefins is achieved using biowaste-derived cobalt chitosan catalysts. Characterization of the optimal Co@Chitosan-700 by STEM (scanning transmission electron microscopy), EELS (electron energy loss spectroscopy), PXRD (powder x-ray diffraction), and elemental analysis revealed the formation of a distinctive magnetic composite material with high metallic Co content. The general performance of this catalyst is demonstrated in the hydrogenation of 50 olefins including terminal, internal, and functionalized derivatives, as well as renewables. Using this nonnoble metal composite, hydrogenation of terminal C==C double bonds occurs under very mild and benign conditions (water or methanol, 40° to 60°C). The utility of Co@Chitosan-700 is showcased for efficient hydrogenation of the industrially relevant examples diisobutene, fatty acids, and their triglycerides. Because of the magnetic behavior of this material and water as solvent, product separation and recycling of the catalyst are straightforward.

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