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Inorganic Core-Shell Structures
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Inorganic Core-Shell Structures

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (31 August 2014) | Viewed by 58147

Special Issue Editor

Prof. Dr. A. Schmidt-Ott

E-Mail Website
Guest Editor
Materials for Energy Conversion and Storage, Faculty of Applied Sciences, Delft University of Technology, Julianalaan 136, NL-2628BL Delft, The Netherlands

Special Issue Information

Dear Colleagues,

A huge and growing number of articles referring to inorganic core-shell structures have been published during the last 10 years. These core-shell structures are probably the most prevalent class of structures in particle-based nanotechnology; their applications range from optoelectronics via catalysis to healthcare products. This present issue aims to provide a collection of selected core-shell structure synthesis methods, along with their links to applications or domains of application.

The collected articles will reflect the state-of-the-art in this exciting field and provide  perspective with respect to future opportunities. Any new developments in either the chemical or physical synthesis of core-shell structures are welcome; lithography-type approaches are not the focus here. While most of the present activities refer to methods based on the liquid phase, submission of papers involving the gas phase are particularly encouraged, as new approaches are found here that bear great potential with respect to versatility, process scalability, purity, and environmental friendliness.

On the other hand, liquid-based methods profit from a much longer history and offer a wealth of possibilities for controlling nanoparticle growth, including surfactant or solvent directed anisotropic growth and (organic) self-assembled structures that act as templates. While organics frequently play a crucial role in the synthesis procedure, the scope of this issue is restricted to inorganic products.

Prof. Dr. A. Schmidt-Ott
Guest Editor

Manuscript Submission Information

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Keywords

  • core-shell
  • nanoparticles
  • particle coating
  • heterostructures
  • surface passivation
  • surface state elimination
  • quantum dots
  • plasmonics
  • aggregation barrier
  • functional nanomaterials

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Published Papers (7 papers)

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Research

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2616 KiB  
Article
Gas-Phase Deposition of Ultrathin Aluminium Oxide Films on Nanoparticles at Ambient Conditions
by David Valdesueiro, Gabrie M. H. Meesters, Michiel T. Kreutzer and J. Ruud Van Ommen
Materials 2015, 8(3), 1249-1263; https://doi.org/10.3390/ma8031249 - 19 Mar 2015
Cited by 41 | Viewed by 8317
Abstract
We have deposited aluminium oxide films by atomic layer deposition on titanium oxide nanoparticles in a fluidized bed reactor at 27 ± 3 °C and atmospheric pressure. Working at room temperature allows coating heat-sensitive materials, while working at atmospheric pressure would simplify the [...] Read more.
We have deposited aluminium oxide films by atomic layer deposition on titanium oxide nanoparticles in a fluidized bed reactor at 27 ± 3 °C and atmospheric pressure. Working at room temperature allows coating heat-sensitive materials, while working at atmospheric pressure would simplify the scale-up of this process. We performed 4, 7 and 15 cycles by dosing a predefined amount of precursors, i.e., trimethyl aluminium and water. We obtained a growth per cycle of 0.14–0.15 nm determined by transmission electron microscopy (TEM), similar to atomic layer deposition (ALD) experiments at a few millibars and ~180 °C. We also increased the amount of precursors dosed by a factor of 2, 4 and 6 compared to the base case, maintaining the same purging time. The growth per cycle (GPC) increased, although not linearly, with the dosing time. In addition, we performed an experiment at 170 °C and 1 bar using the dosing times increased by factor 6, and obtained a growth per cycle of 0.16 nm. These results were verified with elemental analysis, which showed a good agreement with the results from TEM pictures. Thermal gravimetric analysis (TGA) showed a negligible amount of unreacted molecules inside the alumina films. Overall, the dosage of the precursors is crucial to control precisely the growth of the alumina films at atmospheric pressure and room temperature. Dosing excess of precursor provokes a chemical vapour deposition type of growth due to the physisorption of molecules on the particles, but this can be avoided by working at high temperatures. Full article
(This article belongs to the Special Issue Inorganic Core-Shell Structures)
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7795 KiB  
Article
Precursor-Less Coating of Nanoparticles in the Gas Phase
by Tobias V. Pfeiffer, Puneet Kedia, Maria E. Messing, Mario Valvo and Andreas Schmidt-Ott
Materials 2015, 8(3), 1027-1042; https://doi.org/10.3390/ma8031027 - 11 Mar 2015
Cited by 15 | Viewed by 7722
Abstract
This article introduces a continuous, gas-phase method for depositing thin metallic coatings onto (nano)particles using a type of physical vapor deposition (PVD) at ambient pressure and temperature. An aerosol of core particles is mixed with a metal vapor cloud formed by spark ablation [...] Read more.
This article introduces a continuous, gas-phase method for depositing thin metallic coatings onto (nano)particles using a type of physical vapor deposition (PVD) at ambient pressure and temperature. An aerosol of core particles is mixed with a metal vapor cloud formed by spark ablation by passing the aerosol through the spark zone using a hollow electrode configuration. The mixing process rapidly quenches the vapor, which condenses onto the core particles at a timescale of several tens of milliseconds in a manner that can be modeled as bimodal coagulation. Gold was deposited onto core nanoparticles consisting of silver or polystyrene latex, and silver was deposited onto gold nanoparticles. The coating morphology depends on the relative surface energies of the core and coating materials, similar to the growth mechanisms known for thin films: a coating made of a substance having a high surface energy typically results in a patchy coverage, while a coating material with a low surface energy will normally “wet” the surface of a core particle. The coated particles remain gas-borne, allowing further processing. Full article
(This article belongs to the Special Issue Inorganic Core-Shell Structures)
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1417 KiB  
Article
Film Growth Rates and Activation Energies for Core-Shell Nanoparticles Derived from a CVD Based Aerosol Process
by Frederik Weis, Martin Seipenbusch and Gerhard Kasper
Materials 2015, 8(3), 966-976; https://doi.org/10.3390/ma8030966 - 6 Mar 2015
Cited by 5 | Viewed by 7900
Abstract
Silica core-shell nanoparticles of about 60–120 nm with a closed outer layer of bismuth or molybdenum oxide of 1–10 nm were synthesized by an integrated chemical vapor synthesis/chemical vapor deposition process at atmospheric pressure. Film growth rates and activation energies were derived from [...] Read more.
Silica core-shell nanoparticles of about 60–120 nm with a closed outer layer of bismuth or molybdenum oxide of 1–10 nm were synthesized by an integrated chemical vapor synthesis/chemical vapor deposition process at atmospheric pressure. Film growth rates and activation energies were derived from transmission electron microscopy (TEM) images for a deposition process based on molybdenum hexacarbonyl and triphenyl bismuth as respective coating precursors. Respective activation energies of 123 ± 10 and 155 ± 10 kJ/mol are in good agreement with the literature and support a deposition mechanism based on surface-induced removal of the precursor ligands. Clean substrate surfaces are thus prerequisite for conformal coatings. Integrated aerosol processes are solvent-free and intrinsically clean. In contrast, commercial silica substrate particles were found to suffer from organic residues which hinder shell formation, and require an additional calcination step to clean the surface prior to coating. Dual layer core-shell structures with molybdenum oxide on bismuth oxide were synthesized with two coating reactors in series and showed similar film growth rates. Full article
(This article belongs to the Special Issue Inorganic Core-Shell Structures)
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854 KiB  
Article
Kinetic Study on the Formation of Bimetallic Core-Shell Nanoparticles via Microemulsions
by Concha Tojo and Nuria Vila-Romeu
Materials 2014, 7(11), 7513-7532; https://doi.org/10.3390/ma7117513 - 21 Nov 2014
Cited by 9 | Viewed by 5951
Abstract
Computer calculations were carried out to determine the reaction rates and the mean structure of bimetallic nanoparticles prepared via a microemulsion route. The rates of reaction of each metal were calculated for a particular microemulsion composition (fixed intermicellar exchange rate) and varying reduction [...] Read more.
Computer calculations were carried out to determine the reaction rates and the mean structure of bimetallic nanoparticles prepared via a microemulsion route. The rates of reaction of each metal were calculated for a particular microemulsion composition (fixed intermicellar exchange rate) and varying reduction rate ratios between both metal and metal salt concentration inside the micelles. Model predictions show that, even in the case of a very small difference in reduction potential of both metals, the formation of an external shell in a bimetallic nanoparticle is possible if a large reactant concentration is used. The modification of metal arrangement with concentration was analyzed from a mechanistic point of view, and proved to be due to the different impact of confinement on each metal: the reaction rate of the faster metal is only controlled by the intermicellar exchange rate but the slower metal is also affected by a cage-like effect. Full article
(This article belongs to the Special Issue Inorganic Core-Shell Structures)
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1253 KiB  
Article
Tunable Band Gap and Conductivity Type of ZnSe/Si Core-Shell Nanowire Heterostructures
by Yijie Zeng, Huaizhong Xing, Yanbian Fang, Yan Huang, Aijiang Lu and Xiaoshuang Chen
Materials 2014, 7(11), 7276-7288; https://doi.org/10.3390/ma7117276 - 31 Oct 2014
Cited by 2 | Viewed by 6842
Abstract
The electronic properties of zincblende ZnSe/Si core-shell nanowires (NWs) with a diameter of 1.1–2.8 nm are calculated by means of the first principle calculation. Band gaps of both ZnSe-core/Si-shell and Si-core/ZnSe-shell NWs are much smaller than those of pure ZnSe or Si NWs. [...] Read more.
The electronic properties of zincblende ZnSe/Si core-shell nanowires (NWs) with a diameter of 1.1–2.8 nm are calculated by means of the first principle calculation. Band gaps of both ZnSe-core/Si-shell and Si-core/ZnSe-shell NWs are much smaller than those of pure ZnSe or Si NWs. Band alignment analysis reveals that the small band gaps of ZnSe/Si core-shell NWs are caused by the interface state. Fixing the ZnSe core size and enlarging the Si shell would turn the NWs from intrinsic to p-type, then to metallic. However, Fixing the Si core and enlarging the ZnSe shell would not change the band gap significantly. The partial charge distribution diagram shows that the conduction band maximum (CBM) is confined in Si, while the valence band maximum (VBM) is mainly distributed around the interface. Our findings also show that the band gap and conductivity type of ZnSe/Si core-shell NWs can be tuned by the concentration and diameter of the core-shell material, respectively. Full article
(This article belongs to the Special Issue Inorganic Core-Shell Structures)
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Review

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1181 KiB  
Review
Core-Shell Structured Electro- and Magneto-Responsive Materials: Fabrication and Characteristics
by Hyoung Jin Choi, Wen Ling Zhang, Sehyun Kim and Yongsok Seo
Materials 2014, 7(11), 7460-7471; https://doi.org/10.3390/ma7117460 - 21 Nov 2014
Cited by 38 | Viewed by 7366
Abstract
Core-shell structured electrorheological (ER) and magnetorheological (MR) particles have attracted increasing interest owing to their outstanding field-responsive properties, including morphology, chemical and dispersion stability, and rheological characteristics of shear stress and yield stress. This study covers recent progress in the preparation of core-shell [...] Read more.
Core-shell structured electrorheological (ER) and magnetorheological (MR) particles have attracted increasing interest owing to their outstanding field-responsive properties, including morphology, chemical and dispersion stability, and rheological characteristics of shear stress and yield stress. This study covers recent progress in the preparation of core-shell structured materials as well as their critical characteristics and advantages. Broad emphasises from the synthetic strategy of various core-shell particles to their feature behaviours in the magnetic and electric fields have been elaborated. Full article
(This article belongs to the Special Issue Inorganic Core-Shell Structures)
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2069 KiB  
Review
PbSe-Based Colloidal Core/Shell Heterostructures for Optoelectronic Applications
by Gary Zaiats, Diana Yanover, Roman Vaxenburg, Jenya Tilchin, Aldona Sashchiuk and Efrat Lifshitz
Materials 2014, 7(11), 7243-7275; https://doi.org/10.3390/ma7117243 - 30 Oct 2014
Cited by 45 | Viewed by 13008
Abstract
Lead-based (IV–VI) colloidal quantum dots (QDs) are of widespread scientific and technological interest owing to their size-tunable band-gap energy in the near-infrared optical region. This article reviews the synthesis of PbSe-based heterostructures and their structural and optical investigations at various temperatures. The review [...] Read more.
Lead-based (IV–VI) colloidal quantum dots (QDs) are of widespread scientific and technological interest owing to their size-tunable band-gap energy in the near-infrared optical region. This article reviews the synthesis of PbSe-based heterostructures and their structural and optical investigations at various temperatures. The review focuses on the structures consisting of a PbSe core coated with a PbSexS1–x (0 ≤ x ≤ 1) or CdSe shell. The former-type shells were epitaxially grown on the PbSe core, while the latter-type shells were synthesized using partial cation-exchange. The influence of the QD composition and the ambient conditions, i.e., exposure to oxygen, on the QD optical properties, such as radiative lifetime, Stokes shift, and other temperature-dependent characteristics, was investigated. The study revealed unique properties of core/shell heterostructures of various compositions, which offer the opportunity of fine-tuning the QD electronic structure by changing their architecture. A theoretical model of the QD electronic band structure was developed and correlated with the results of the optical studies. The review also outlines the challenges related to potential applications of colloidal PbSe-based heterostructures. Full article
(This article belongs to the Special Issue Inorganic Core-Shell Structures)
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