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As a promising novel route towards highly efficient optoelectronic devices, GaN based 3D core-shell light emitting diodes (LEDs) have attracted increased attention in recent years. In comparison to conventional 2D thin film LED, the 3D LED systems using a core-shell geometry with high aspect ratio are a breakthrough in technology with lots of advantages. In this paper, we review our developed growth strategies of these LED systems on Si and sapphire substrates. A catalyst free selective area growth of GaN 3D core-shell LED systems was realized using patterned substrates by metal organic vapor phase deposition in a convenient continuous-flux growth mode. We have recently suggested that the surface polarity plays a crucial role for the morphology of GaN 3D structure growth. In order to analyze the surface polarity of 3D submicron or micron structures, Kelvin probe force microscopy and selective etching techniques have been developed. During the growth of GaN submicron rods and micron columns on patterned SiO_x/sapphire templates, mixed polarity effects could be detected. A new "truncated pyramid + column" growth method was developed to effectively avoid the formation of mixed polarity and realize single N-polar GaN 3D devices. Transmission electron microscopy and spatially and spectrally resolved cathodoluminescence measurements evidently prove the core-shell structure of 3D LED systems.

The aim of this work is to provide an overview on the recent advances in the selective area growth (SAG) of (In)GaN nanostructures by plasma assisted molecular beam epitaxy, focusing on their potential as building blocks for next generation LEDs.

The first three sections deal with the basic growth mechanisms of GaN SAG and the emission control in the entire ultraviolet to infrared range, including approaches for white light emission, using InGaN disks and thick segments on axial nanocolumns. SAG of axial nanostructures is developed on both GaN/sapphire templates and GaN-buffered Si(111).

As an alternative to axial nanocolumns, section 4 reports on the growth and characterization of InGaN/GaN core-shell structures on an ordered array of top-down patterned GaN microrods. Finally, section 5 reports on the SAG of GaN, with and without InGaN insertion, on semi-polar (11-22) and non-polar (11-20) templates. Upon SAG the high defect density present in the templates is strongly reduced as indicated by a dramatic improvement of the optical properties. In the case of SAG on non-polar (11-22) templates, the formation of nanostructures with a low aspect ratio took place allowing for the fabrication of high-quality, non-polar GaN pseudo-templates by coalescence of these nanostructures.

Co-axial Zn_1−xMg_xO core, ZnO shell structures were grown using metal organic chemical vapor deposition (MOCVD), with Mg mole fractions of 2, 5 and 10%. The co-axial core shell structure, with the respective Mg concentration is verified using scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS). The response times (ṟise time and fall time) of the devices, after being exposed to methanol, varied with Mg mole fraction at the core, r-0.17s and, f-0.37s & f-0.48s for 2% Mg, r-0.81s and, f-5.98s & f-0.89s for 5% Mg and r-0.33s and f-0.13s for 10% Mg. The sensitivity of the devices at room temperature increased with the increment of Mg mole fraction at the core, 25%, 48% and 50% with Mg concentration of 0.02, 0.05 and 0.1, respectively, under high concentration of methanol. The estimated activation energy, corresponds to doubly charged oxygen vacancy (Vo²⁺).

Fe–6.5 wt.% Si powder coated with 10 wt.% MnZn(Fe₂O₄)₂ (MnZn ferrite) was successfully prepared by using dry-type stirring ball milling. The Fe–6.5 wt.% Si/MnZn(Fe₂O₄)₂ soft magnetic composites were prepared by subsequent spark plasma sintering. This paper aims at analyzing the microstructure and magnetic properties of Fe–6.5 wt.% Si/MnZn(Fe₂O₄)₂ soft magnetic composites (sintering temperature: 750${}^{\circ }$C, sintering pressure: 50 MPa, holding time: 8 min, heating rate: 60 K/min). Based on X-ray diffraction and scanning electron microscopy, microstructure and powder morphology were examined and magnetic measurements on bulk samples were conducted by vibrating sample magnetometer and impedance analyzer. According to the experiments results, Fe–6.5 wt.% Si/MnZn(Fe₂O₄)₂ composites displayed a core-shell structure, and ceramic phase was observed after sintering. The Fe–6.5 wt.% Si/MnZn(Fe₂O₄)₂ composites achieved high resistivity ($\rho :2.9$ m$\mathrm{\Omega }$/cm) while maintaining excellent magnetic properties ($M_s:174.00$ emu/g). Core losses especially at medium and high frequencies were significantly reduced.

In this paper, we study the absorption efficiency spectra and electric field distribution of Ag nanoparticles enveloped with ${\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4$ nanoshell by applying the discrete dipole approximation theory. Three kinds of ${\mathrm{\text{Ag@Fe}}}_3{\mathrm{\text{O}}}_4$ core–shell nanoparticles (NPs) structural variables, including the same core with different shell thickness, the same outer shell with different core radius, and the same size of total radius have been discussed in detail. The simulated results show that the localized surface plasmon resonance (LSPR) peak wavelength of NPs is linearly proportional with the volume fraction of the shell, regardless of the outer shell material property and one structural variable. Compared to the plasmon resonance peak of the Ag nanoparticles, the LSPR shift of the NPs is dependent on both the total particles size and the outer ${\mathrm{\text{Fe}}}_3{\mathrm{\text{O}}}_4$ shell thickness. The electric field around the surface of NPs becomes weaker under the same damping when the core radius decreases. Based on the plasmonic characteristics revealed in this study, it is suggested that it would provide some key guidances for designing the future NPs structural variables for a broad range of plasmon applications.

Ag nanoparticles were synthesized by using thermal decomposition of Ag⁺–oleate complex. The mean size of Ag nanoparticle was confirmed as 10 nm with transmission electron microscopy (TEM). The crystal structure and optical property of Ag nanoparticles were studied with X-ray powder diffraction (XRD) and UV–vis spectroscopy, respectively. The Ag nanoparticles were used as seeds for Ag(core)/SiO₂(shell) nanocomposite particles. TEM images of Ag(core)/SiO₂(shell) nanocomposite particles showed that silver core was coated with 15 nm thickness of SiO₂ shell. The thickness of SiO₂ shells could be conveniently controlled by changing the concentration of sol–gel precursor or reaction time. The composition of Ag(core)/SiO₂(shell) nanocomposite particle was investigated with energy-dispersive X-ray (EDX) spectrometer.

The Ni-P/TiN coating was used as bipolar plate by electroless plating on Ti. Surface morphology and phase structure of the coatings were characterized by SEM and XRD, respectively. Corrosion resistance of Ni-P and Ni-P/TiN coating was measured in the simulated solution of Proton exchange membrane fuel cells (PEMFCs). The interfacial contact resistance (ICR) was conducted by applied different forces. SEM images indicated that the particles of core–shell structure were formed on the surface of coating on Ti substrate. The core–shell structure was composed of TiN core and Ni-P electroless plating shell. Compared with Ni-P coatings, the Ni-P/TiN coating showed better corrosion resistance behaviors and low ICR (below 10m$\mathrm{\Omega }$ cm${}^{-2}$ under pressure of 200 N/cm${}^2)$. TiN particles and distribution of core–shell were in favor of the formation of coating and compact surface morphology. The good conductivity was attributed to the compact surface morphology of coating. The Ni-P/TiN coating showed excellent interfacial conductivity and good corrosion resistance at applied high potential in simulated solution of PEMFCs.

Magnetite and biopolymer-magnetite nanoparticles coated with polyethylene glycol (PEG) and chitosan have been synthesized. The adsorption of the biopolymers on the magnetite nanoparticles is confirmed using Fourier Transform Infrared (FTIR) Spectroscopy. Atomic Force Microscopy (AFM) imaging revealed magnetite-biopolymer core–shell nanoparticles of typical size range 25–80 nm. We report a novel way of determining the thickness of the biopolymer coating using noncontact AFM imaging. AFM has been used to study the variation of the biopolymer coating thickness as a function of the magnetite core diameter, biopolymer type, and its concentration. The thickness of the chitosan coating varies in the range of 4–11 nm and increases linearly with increase in magnetite core size. PEG coating thickness has similar values as for the chitosan coating.

An update is presented on some recent syntheses of magnetic nanoparticles developed in our group for potential use in biomedical applications. Particular attention is paid to (i) the preparation of magnetic nanoparticles that are readily dispersed in aqueous solution (ii) the synthesis of alloy magnetic nanoparticles and (iii) novel synthesis methods used to control the physical properties of the nanoparticles.

In this paper, core–shell structured (ZnSe) is prepared bio synthesis by cold plasma technique under atmospheric pressure with an exposure time of 3min and a gas flow rate of 3L/min. Films’ structural characteristics and morphological characterization were investigated by X-ray diffractometer, atomic force microscopy (AFM) and scanning electron microscopy (FE-SEM). In addition, parameters like crystal size were calculated. Results showed XRD patterns exhibit structure of polycrystalline of preferential orientation (111) direction. SEM technique shows that the nanoparticles presented are spherical. AFM image verified film-formed spherical particles distribute uniformly. The antibacterial diffusion method property of these nanoparticles was performed against Gram-negative bacteria of Escherichia coli and Gram-positive bacteria of Staphylococcus aureus, showing good control of said bacteria. The maximum level of inhibition was found in coli form bacteria with an average inhibition zone diameter with S. aureus, implying an increasing trend with increasing/decreasing loading volume of NC volume. Therefore, these nanomaterials, which can be prepared in a simple and cost-effective way, may be suitable for new types of germicidal materials.

Atmospheric pressure Micro-jet plasma technique is used in this study to create Ag–ZnO core/shell nanoparticles. Several different methods, including X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray dispersive spectroscopy (EDS), transmission electron microscopy (TEM) and ultraviolet-visible spectroscopy (UV–Vis), confirmed the characterization of the synthesized Ag–ZnO core/shell nanoparticles. The pureness of these nanoparticles was validated by XRD analysis, which showed no peaks associated with secondary phases for Ag–ZnO. The synthesis of very pure Ag–ZnO core/shell nanoparticles was also verified by EDX analysis. To understand the high agglomeration rate, the surface morphology was studied by FE-SEM. The Ag–ZnO core/shell nanoparticles were measured to be between 20 and 60nm in size by transmission electron microscopy. Ag–ZnO core/shell nanoparticles showed energy band gaps of 3.22eV. After that, the antibacterial activity of the prepared nanoparticles was tested against two different types of Gram-positive bacteria $($Staphylococcus. epidermidis and Staphylococcus aureus$)$ and two different types of Gram-negative bacteria $($Klebsiella. pneumonia and Escherichia coli$)$ that were isolated from the oral cavity. Additionally, the antifungal activity of the prepared nanoparticles was tested against two different types of yeast $($Candida$)$. Antimicrobial activity was shown by the Ag–ZnO nanoparticles produced using the micro-jet plasma method, and the findings suggested that these nanoparticles may be used to eliminate dangerous and harmful bacteria and fungi.

In this short review, we report the facile fabrication of various interesting multi-component nanostructures including arrays of core-shell nanowires, multiwall nanotubes, segmented nanowires and multilayer stacked nanodisks, using anodized alumina membrane (AAM). We demonstrate that metallic (Cu, Ni and Au) and polymeric (PPV and PPy) one-dimensional (1D) arrays can be readily prepared by electrochemical deposition into the AAM. By optimizing the experimental design and conditions, we developed techniques to produce various multi-component nanostructures such as polymer/metal or metal/metal core-shell nanowires as well as nanotubes, with reasonably good control over both the length and the shell thickness of the nanostructures. Furthermore, we extend this method to make segmented nanowires as well as multilayer stacked nanodisks. Selective functionalization of the segmented nanowires resulted in end-on or side-on adhesion of nanowires during assembly. We illustrate the possibility of utilizing these 1D arrays to present patterns with luminescent and/or magnetic properties at this length scale.

The composite supercapacitor electrodes were rationally fabricated by facile electrochemical deposition of polypyrrole (PPy) on NiCo₂O₄ nanowire arrays which were grown radially on carbon fiber (CF). When used as electrodes in supercapacitors, the composite nanostructures demonstrated prominent electrochemical performances with a high areal capacitance (1.44F/cm² at a current density of 2mA/cm²), a good rate capability (80.5% when the current density increases from 2mA/cm² to 20mA/cm²), and a good cycling ability (85% of the initial specific capacitance remained after 5000 cycles at a high current density of 10mA/cm²). The excellent electrochemical performance of NiCo₂O₄@PPy nanostructures can be mainly ascribed to the good electrical conductivity of PPy, the enhanced adherent force between electrode materials and CF to hold the electrode fragments together by means of NiCo₂O₄ nanowires, the short ion diffusion pathway in ordered porous NiCo₂O₄ nanowires and the three-dimensional nanostructures.

New types of core–shell nanoparticles are reported: Pb@GaS fullerene-like and nanotubular structures, achieved via the continuously high reactor temperatures and ultra-hot strong-gradient annealing environments created by highly concentrated sunlight. Structural and chemical characterizations suggest a formation mechanism where vaporized Pb condenses into nanoparticles that are stabilized as they become covered by molten GaS, the ensuing crystallization of which creates the outer layers. Hollow-core GaS fullerene-like nanoparticles and nanotubes were also observed among the products, demonstrating that a single solar procedure can generate a variety of core–shell and hollow nanostructures. The proposed formation mechanisms can account for their relative abundance and the characterization data.

Electrodes of rationally designed composite nanostructures can offer many opportunities for the enhanced performance in electrochemical energy storage. This paper attempts to illustrate the design and production of NiMoO₄/polypyrrole core–shell nanostructures on nickel foam to be used in supercapacitor via a facile hydrothermal and electrodeposition process. It has been verified that this novel nanoscale morphology has outstanding capacitive performances. While employed as electrodes in supercapacitors, the composite nanostructures showed remarkable electrochemical performances with a great areal capacitance (3.2F/cm² at a current density of 5mA/cm²), and a significant cycle stability (80% capacitance retention after 1000 cycles). The above results reveal that the composite nanostructures may be a likely electrode material for high-performance electrochemical capacitors.

A series of hamburger-like Ag@ZnO/C core–shell plasmonic photocatalysts have been synthesized via a simple solvothermal method for degradation of tetracycline (TC) under visible light irradiation, possessing high photocatalytic activity and good stability. The presence of localized surface plasmon resonance (LSPR) in the Ag core has increased the photocatalytic activity over an extended wavelength range. The plasmon-induced resonant energy transfer (PIRET) and direct electron transfer (DET) have facilitated the excitation and separation of photogenerated $e^{-}/h^{+}$ pairs, which has been further confirmed by electrochemical investigations. The presences of hydroxyl radicals ($\cdot \mathrm{\text{OH}}$), superoxide radicals ($\cdot {\mathrm{\text{O}}}_2^{-})$ and singlet oxygen (¹O${}_2)$ in the photocatalytic reaction system of Ag@ZnO/C photocatalyst have been demonstrated by electron spin resonance (ESR) measurements. All of the experiment results indicate that the ternary structure of Ag@ZnO/C can effectively enhance the photocatalytic activity. Furthermore, the effects of introduced Ag contents and carbon source dosage were researched by comparative photocatalytic experiments, and the potential structures of photodegradation products were studied by HPLC-MS.

The development of heterojunction composites with core–shell structure could effectively facilitate the separation of carriers. In this work, a novel In₂O₃-SnS₂ (IOS) core–shell heterojunction photocatalyst was successfully synthesized for the efficient photocatalytic reduction of hexavalent chromium (Cr(VI)), namely, the In₂O₃ nanorods were obtained through successive hydrothermal and carbonization process using urea and glucose as template. Then, SnS₂ nanosheets were successfully in situ coated onto In₂O₃ nanorods. The spectroscopic characterization and photo-electrochemistry test indicated that the IOS core–shell heterojunction could effectively accelerate the separation and transport of carriers and suppress the recombination of carriers. The photocatalytic performance of IOS was evaluated by photocatalytic reduction Cr(VI). The results showed that IOS-4 samples almost completely removed Cr(VI) (20 mg/L), within 90 min under visible light, which was superior to pure In₂O₃ and SnS₂. Furthermore, IOS samples also possess excellent stability, the removal efficiency was still maintained at 90% after five cycles. This work provided a reliable method for designing core–shell heterojunctions for the photocatalytic removal of Cr(VI) under visible light.

Bifunctional nanospheres of silica encapsulating Fe₃O₄ and LaF₃:Eu nanoparticles were synthesized in a reverse microemulsion solution. The nanospheres were perfectly monodispersed with a small diameter of 20 nm. The composition of the bifunctional nanospheres was confirmed by powder X-ray diffraction. Their magnetic and luminescent properties were measured at room temperature. The relaxation efficiency and T₂-weighted images showed the high-performance for the product as a resonance imaging contrast agent. In addition, a qualitative cell uptake in human cervical cancer HeLa cells demonstrated that the SFLE nanospheres were efficiently up-taken into cytosol. Taken together, these findings suggest that the SiO₂/Fe₃O₄-LaF₃:Eu³⁺ nanospheres are good luminescence probes for bio-imaging.

The core–shell structure composite magnetic nanoparticles (NPs), Fe₃O₄@chitosan@nimodipine (Fe₃O₄@CS@NMDP), were successfully synthesized by a chemical cross-linking method in this paper. NMDP is widely used for cardiovascular and cerebrovascular disease prevention and treatment, while CS is of biocompatibility. The composite particles were characterized by an X-ray diffractometer (XRD), a Fourier transform infrared spectroscopy (FT-IR), a transmission electron microscopy (TEM), a vibrating sample magnetometers (VSM) and a high performance liquid chromatography (HPLC). The results show that the size of the core–shell structure composite particles is ranging from 12nm to 20nm and the coating thickness of NMDP is about 2nm. The saturation magnetization of core–shell composite NPs is 46.7emu/g, which indicates a good potential application for treating cancer by magnetic target delivery. The release percentage of the NMDP can reach 57.6% in a short time of 20min in the PBS, and to 100% in a time of 60min, which indicates the availability of Fe₃O₄@CS@NMDP composite NPs for targeting delivery treatment.

A highly efficient and convenient strategy is developed for the one-step in-situ synthesis of carbon encapsulated Cr₂O₃ nanocrystals with core-shell structure (Cr₂O₃@C). The explosive reaction of chromocene with ammonium persulfate in an autoclave at 200${}^{\circ }$C is crucial for the formation of this nanostructure. The Cr₂O₃ nanocrystals have a diameter of 5 to 20nm, which are entirely encapsulated by the amorphous carbon shell. The Cr₂O₃@C anode can retain a stable reversible capacity of 397mAhg${}^{-1}$ after 50 cycles at a current density of 119mA g${}^{-1}$.