Core-shell Rod Research Articles

Ultra-selective hydrogen sensors based on CuO - ZnO hetero-structures grown by surface conversion

Synergistic effects of mixed oxides have the potential to improve sensing performances of environmental, domestic and industrial monitoring devices. However, mixed oxides often come in the form of separate particles and are thus addressed separately by the environment, instead of capitalizing on the interface between the metal oxides. This paper describes a new core@shell gas sensing material of tetrapodal zinc oxide with a surface coating of crystalline copper oxide(t-ZnO@CuO). The special surface conversion strategy yields a unique, self-assembled and pinhole-free coating of CuO nanoplatelets. The morphologies, structural, chemical and gas sensing properties of the heterostructure were investigated. To evaluate the sensing properties of the heterostructure, t-ZnO@CuO was fabricated as nanosensors, consisting of one core-shell rod of CuO-coated crystalline ZnO. The single core@shell rod showed high selectivity towards hydrogen already at comparatively low operation temperatures of 150 °C. Computational calculations based on the density functional theory (DFT) have been carried out to understand the interaction of the H2 gas molecule with the surface of the CuO nanostructures. The surface conversion was done wet chemically and is a novel method for generating heterostructures that can be potentially transferred to heterojunctions with unique properties for chemosensors.

Micro-Nanoarchitectonics of Ga2O3/GaN Core-Shell Rod Arrays for High-Performance Broadband Ultraviolet Photodetection

This study presents broadband ultraviolet photodetectors (BUV PDs) based on Ga2O3/GaN core-shell micro-nanorod arrays with excellent performance. Micro-Nanoarchitectonics of Ga2O3/GaN core-shell rod arrays were fabricated with high-temperature oxidization of GaN micro-nanorod arrays. The PD based on the microrod arrays exhibited an ultrahigh responsivity of 2300 A/W for 280 nm at 7 V, the peak responsivity was approximately 400 times larger than those of the PD based on the planar Ga2O3/GaN film. The responsivity was over 1500 A/W for the 270–360 nm band at 7 V. The external quantum efficiency was up to 1.02 × 106% for 280 nm. Moreover, the responsivity was further increased to 2.65 × 104 A/W for 365 nm and over 1.5 × 104 A/W for 270–360 nm using the nanorod arrays. The physical mechanism may have been attributed to the large surface area of the micro-nanorods coupled with the Ga2O3/GaN heterostructure, which excited more photogenerated holes to be blocked at the Ga2O3 surface and Ga2O3/GaN interface, resulting in a larger internal gain. The overall high performance coupled with large-scale production makes it a promising candidate for practical BUV PD.

Preparation and black-white electrochromic performance of the non-contact ZnO@NiO core-shell rod array

In this paper, the non-contact ZnO@NiO core-shell rod array films with black-white electrochromic performance were designed and constructed by electrochemical deposition method. The blank porous NiO films were also prepared for comparison. The morphology, component and microstructure of the films were characterized using X-ray diffractometer (XRD), scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM). And their electrochromic (EC) performance was examined. The results show that the ZnO transition layer presents a hexagonal rod array nature, which is approximately perpendicular to the surface of substrate, thus, offered a three-dimensional frame for the growth of porous NiO. The ZnO@NiO film is composed of a large number of non-contact core-shell rods. The introduction of ZnO rod array transition layer not only led to the improvement of film/substrate connection but also resulted into the high EC performance including sharp black-white contrast, rapid switch speed and good stability. The heterojunction and P-N junction formed at the SnO2/ZnO/NiO interfaces might also play a role in the EC performance.

Dual Tumor Microenvironment Remodeling by Glucose-Contained Radical Copolymer for MRI-Guided Photoimmunotherapy.

Aberrant glucose metabolism and immune evasion are recognized as two hallmarks of cancer, which contribute to poor treatment efficiency and tumor progression. Herein, a novel material system consisting of a glucose and TEMPO (2,2,6,6-tetramethylpiperidin-1-yl)oxyl) at the distal ends of PEO-b-PLLA block copolymer (glucose-PEO-b-PLLA-TEMPO), is designed to encapsulate clinical therapeutics CUDC101 and photosensitizer IR780. The specific core-shell rod structure formed by the designed copolymer renders TEMPO radicals excellent stability against reduction-induced magnetic resonance imaging (MRI) silence. Tumor-targeting moiety endowed by glucose provides the radical copolymer outstanding multimodal imaging capabilities, including MRI, photoacoustic imaging, and fluorescence imaging. Efficient delivery of CUDC101 and IR780 is achieved to synergize the antitumor immune activation through IR780-mediated photodynamic therapy (PDT) and CUDC101-triggered CD47 inhibition, showing M1 phenotype polarization of tumor-associated macrophages (TAMs). More intriguingly, this study demonstrates PDT-stimulated p53 can also re-educate TAMs, providing a combined strategy of using dual tumor microenvironment remodeling to achieve the synergistic effect in the transition from cold immunosuppressive to hot immunoresponsive tumor microenvironment.

Label-free and visible-light driven photoelectrochemical sensor with CuCo2O4@CoO Core-shell hybrid rod as photoanode for selective sensing diclofenac

Diclofenac (DCF), the non-steroidal anti-inflammatory drugs (NSAIDs), remaining in environment as a heavily pollutants, the development of rapid and accurate method for sensing trace level DCF is urgent. Herein, a novel photoelectrochemical (PEC) sensing platform with CuCo2O4@CoO core-shell hybrid rods as photoanode was developed for rapidly sensing DCF without any additional recognition units. The Cu-based composite show specific interaction with carboxyl and imino group, it could selective absorbing and sensing DCF from other coexisting NSAIDs such as ibuprofen (IB), ketoprofen (KP) and flurbiprofen (FP) based on chelating ability and electrochemical activity. The synergistic effect of the well design core-shell structure combining close-connected heterojunction could enhance the sensitivity of the PEC sensor. The PEC response of the sensor was found to be linearly proportional to the concentration of DCF in the range from 10 nmol L-1 to 500 μmol L-1. The detection limit (3S/N) is 6.5 nmol L-1. The application of PEC sensor was evaluated by the determination of DCF in environment water samples, the spiked recoveries are in the range from 86.0 to 115.8%. The relative standard deviation (RSD) value of reproducibility and repeatability are less than 4.3 and 3.9%, showing excellent sensitivity, good reproducibility, repeatability and high stability. This strategy opens up a new avenue for the constructed high sensitivity and high selectivity PEC sensor.

Fluorescence intermittency and spatial localization of core-shell quantum rod clusters in an inverse nematic gel

Formation of stable dispersions of CdSe/CdS core-shell quantum rods (CSQRs) in an inverse nematic gel (N-gel) is reported. The CSQRs distribute uniformly in the N-gel matrix and spontaneously form an ordered arrangement of bright clusters. Estimates show that \ensuremath{\sim}90% of CSQRs are homogeneously dispersed and \ensuremath{\sim}10% form clusters in the N-gel phase. Optical properties exhibited by individual CdSe/CdS CSQRs are retained in the dispersions, including a moderate polarization dependence. Extensive fluorescence confocal microscopy studies show evidence for suppressed fluorescence blinking of the clusters in the N-gel phase. The spatial constancy of such clusters is another attractive feature which makes them suitable as stable nanoemitters. The results are interpreted in terms of the unusual type of distribution of the helical gelator fibers in the N-gel phase which promotes self-assembly of the CSQRs and interactions within the clusters.

Microstructure and compressive properties of V–V8C7/Fe core-shell rod-reinforced iron-based composite fabricated via two-step in-situ reaction

To enhance the strength of iron-based alloys, a novel vanadium-vanadium carbide/iron (V–V8C7/Fe) core-shell rod-reinforced iron-based composite is designed and prepared via a two-step in-situ reaction at 1150 °C × 5 min +1100 °C × (4, 6, 8, 10 h). The V–V8C7/Fe core-shell rod consists of a ductile V-core and a gradient-structured V8C7/Fe-shell. The phases of the composite are V, V2C, V8C7, α-Fe, and P-rich phases. When the ratio (K) of the volume of V8C7/Fe-shell to the volume of the V-core is approximately 54, the comprehensive mechanical properties of the composite are optimal. The maximum hardness, maximum compressive strength and strain are about 1296 HV0.2, 1804 MPa and 13.9%, respectively. The high strength and high toughness of the composites are mainly attributed to the synergistic effect between the high toughness of the metal V-core and the gradient-distribution structure of the V8C7/Fe-shell layer.

Regimes of optical mode coupling: from core-shell single particle to dimer

We study a transformation of a core-shell dielectric rod into a dimer by pulling the core rod out of the shell. We present simulated scattering spectra of two infinite dielectric rods with dipole Mie resonances tailored to the same frequency by choice of the refractive indices ratio. We identify a transition between weak and strong coupling regimes by examining the peak splitting of the dipole Mie resonance. We find that the splitting increases as the distance between the rod centres decreases. This behaviour is kept for all configurations: core-shell, eccentrically embedded rod and dimer.

Construction of core-shell structured WO3@SnS2 hetero-junction as a direct Z-scheme photo-catalyst

An ideal photocatalyst not only offers high photo-generated electron-hole pairs separation ability, but also has suitable redox potential. Here, a direct Z-scheme core-shell structured WO3@SnS2 hetero-junction photo-catalyst was prepared via two-step hydrothermal method, in which the core-shell structure, rod morphology and micro-composition of hetero-junction were confirmed through X-ray diffraction (XRD) patterns, Fourier transform infrared (FTIR) spectra, field emission scanning electron microscope (FE-SEM), transmission electron microscope (FEI-TEM) and X-ray photoelectron spectra (XPS). Their enhanced photo-catalytic abilities were evaluated by photo-degradation of Rhodamine (RhB), photo-reduction of dichromate (Cr6+) solution and photo-catalytic H2 production through comparing with pure WO3, SnS2 or the mixture of WO3 and SnS2 (WO3/SnS2). The absorption spectra and electrochemical properties were used to estimate the band gap of samples, the expanded spectral absorption capacity and improved electron-hole separation ability, which are important factors for enhanced photocatalytic performance. Furthermore, the direct Z-scheme charge transfer mechanism of WO3@SnS2 hetero-junction was determined through the combination of theoretical calculation and experimental characterizations, which played a decisive role for retaining excellent redox potential and increasing photo-catalytic ability of WO3 and SnS2.

Microstructure and mechanical property of Cf/SiC core/shell composite fabricated by direct ink writing

A novel approach for the fabrication of Short carbon fibers reinforced SiC ceramic composites filaments with core-shell microstructure by direct ink writing was firstly proposed. A novel core-shell feed rod for co-extrusion was designed. Fiber interface layer was prepared by precursor infiltration pyrolysis with polycarbosilane. The results indicated that the ratio (d/D) of carbon fiber (core) to SiC (shell) could be controlled effectively. The debonding and fracture of short fibers with high orientation might improve the fracture resistance of the Cf/SiC composite. The filament-based specimens with strength of ~123 MPa and porosity of ~31% (d/D = 0.6) were successfully fabricated.

Microstructure and impact properties of Ta-TaC core–shell rod-reinforced iron-based composite fabricated by in situ solid-phase diffusion

Tantalum-tantalum carbide (Ta-TaC) core–shell rod-reinforced iron-based composites were designed and fabricated by in situ solid-phase diffusion reaction at 1150 °C for 5, 10, 15, 20, and 80 min, respectively. Phase composition, microstructure, impact toughness, micro-hardness, and elastic modulus of the composite, morphologies and grain sizes of TaCs were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, impact test, and nano-indentation test. Furthermore, formation kinetics of TaC-Fe shell layer was analyzed by measuring the thickness of pure TaC layer as a function of heat treatment time and temperature. Results indicated the generation of dense and compact TaC layer around the Ta rod by in situ solid-phase diffusion reaction, and together they were designated as the Ta-TaC core–shell rod. Predominant features of the Ta-TaC core–shell rod included a gradient nanostructured TaC-Fe shell layer and a Ta core. Predominant phases of the Ta-TaC core–shell rod-reinforced iron-based composite were Ta, TaC, and α-Fe phases. Kinetic results of TaC-Fe shell layer exhibited parabolic relationship between the thickness of pure TaC layer and annealing time, and growth rate constant for pure TaC layer was estimated to be 6.25 × 10−8 cm2 s−1. TaC particles in TaC-Fe shell layer preferred a perfect cube morphology enclosed by {100} facets with minimized total surface free energy. Grain size of TaC increased gradually from about 150 to 500 nm with the increasing distance from the interface of Ta core/TaC-Fe shell layer to the substrate. The Ta-TaC core–shell rods play an important role in improving the mechanical properties of the composite. Micro-hardness of the TaC-Fe shell layer was in the range of 10.4–24.8 GPa, which is 3–8 times than that of the substrate due to the dense and compact TaC. Impact toughness of the composite was 100.6 J cm−2, which is markedly higher than that of the gray cast iron (7.8 J cm−2). Excellent impact toughness of the composite is mainly attributed to Ta core of Ta-TaC core–shell rod, which undergoes a large plastic deformation under external forces. Moreover, the compact TaC distributed around Ta rod reduced split action to the matrix, and the matrix absorbed large amount of crack propagation energy.

Alkaline phosphatase labeled SERS active sandwich immunoassay for detection of Escherichia coli

In this study, a sandwich immunoassay method utilizing enzymatic activity of alkaline phosphatase (ALP) on 5-bromo-4-chloro-3-indolyl phosphate (BCIP) for Escherichia coli (E. coli) detection was developed using surface enhanced Raman spectroscopy (SERS). For this purpose, spherical magnetic gold coated core-shell nanoparticles (MNPs-Au) and rod shape gold nanoparticles (Au-NRs) were synthesized and modified for immunomagnetic separation (IMS) of E. coli from the solution. In order to specify the developed method to ALP activity, Au-NRs were labeled with this enzyme. After successful construction of the immunoassay, BCIP substrate was added to produce the SERS-active product; 5-bromo-4-chloro-3-indole (BCI). A good linearity (R2=0.992) was established between the specific SERS intensity of BCI at 600cm−1 and logarithmic E. coli concentration in the range of 1.7×101–1.7×106cfumL−1. LOD and LOQ values were also calculated and found to be 10cfumL−1 and 30cfumL−1, respectively.

Gain-modulated plasmonic Rabi oscillations of coupled nanocomplex

Strong coupling in nanostructures can bring intriguing optical phenomena such as ultrafast Rabi oscillation—periodical energy exchange phenomenon between two modes. Rabi splitting appears in the frequency-domain spectra for strong coupling system. However, in metallic nanosystems the time-domain Rabi oscillations are hard to be observed because the plasmon lifetime is limited by the heavy ohmic losses. Here we report a theoretical investigation of surface plasmon coupling behaviour of two gold nanorods with one being a core-shell rod filled with a gain material and find the periodic energy exchange phenomenon which recalls the concept of Rabi oscillation. The gain material-cored gold-shell structure dipolar mode hybridizes with the solid gold rod quadrupolar mode to form the Fano resonances. Energy exchange between the two rods happens through the near field coupling. Two approaches, to prolong plasmon lifetime by increasing the gain efficiency and to increase Rabi oscillation frequency by increasing the coupling strength, are suggested to increase the Rabi oscillation cycles. Our results offer a way to achieve unique control of light at the nanoscale and further to explore plasmonic Rabi oscillation phenomena in plasmonic nanosystems.

Presence of silver in the strengthening particles of an Al-Cu-Mg-Si-Zr-Ti-Ag alloy during severe overaging and creep

The results of a study aimed at investigating the presence of silver in the strengthening phases of age-hardenable AlCuMgSi alloys are presented. HR STEM observations were performed on Al-4Cu-0.55Mg-0.5Si--0.15Zr-0.1Ti-0.5Ag (wt%) alloy samples aged or crept at 200 °C to monitor the evolution of secondary phases over long times. Results showed that in the peak aged condition silver mostly segregated at the surface of some strengthening precipitates types. This occurred specifically at the particle/matrix interface of θ' phase while particles, matching the wide compositional range of the quaternary Q' phase were free from Ag. A third population of strengthening particles having the shape of a core-shell rod was also observed. They were characterized by a Mg- and Si-rich core and a Cu- and Ag-rich shell. The exposure at 200 °C for up to 570 h, caused an evident coarsening of Q' and θ' plate-like particles, and the Ag surface enrichment of the latter went progressively lost. On the contrary, silver concentrated inhomogeneously on the surface of the core-shell particles for which a relatively low coarsening rate was observed.

Design of Photonic Crystal Triplexer with Core-Shell Rod Defects

We investigate an optical compact triplexer based on two photonic crystal waveguides and resonant cavities. For performing wavelength selection, we use three core-shell rods as the resonant cavities. The core rods are created by introducing air holes in the center of the silicon rods. By varying the radii of the air holes, three specific wavelengths 1.31, 1.49 and 1.55 μm can be obtained. This structure is designed and its performance is verified by the finite-difference time-domain method, which is highly suitable for photonic integrated circuits (PICs). The average output transmission efficiency and quality factor are more than 98.85% and 560, respectively. The mean value of the crosstalk between output channels is about −36.49 dB. The present device is extremely compact with total size 96.24 μm2, which is suitable for PICs and can be utilized in the fiber-to-the-home system.

Band Engineered Epitaxial 3D GaN-InGaN Core–Shell Rod Arrays as an Advanced Photoanode for Visible-Light-Driven Water Splitting

3D single-crystalline, well-aligned GaN-InGaN rod arrays are fabricated by selective area growth (SAG) metal-organic vapor phase epitaxy (MOVPE) for visible-light water splitting. Epitaxial InGaN layer grows successfully on 3D GaN rods to minimize defects within the GaN-InGaN heterojunctions. The indium concentration (In ∼ 0.30 ± 0.04) is rather homogeneous in InGaN shells along the radial and longitudinal directions. The growing strategy allows us to tune the band gap of the InGaN layer in order to match the visible absorption with the solar spectrum as well as to align the semiconductor bands close to the water redox potentials to achieve high efficiency. The relation between structure, surface, and photoelectrochemical property of GaN-InGaN is explored by transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), Auger electron spectroscopy (AES), current-voltage, and open circuit potential (OCP) measurements. The epitaxial GaN-InGaN interface, pseudomorphic InGaN thin films, homogeneous and suitable indium concentration and defined surface orientation are properties demanded for systematic study and efficient photoanodes based on III-nitride heterojunctions.

Blood Clot Mechanical Properties measured with Arrays of Magnetically Actuated Core-Shell Microrods

Understanding blood clot formation and mechanical properties is vital, as clotting or bleeding disorders are a leading cause of morbidity and mortality in the world. One in four trauma patients admitted to the emergency room has an acute traumatic coagulopathy, requiring blood products and/or the management of specific clotting or fibrinolytic disorders. Such patients would be better served at or near the site of injury with a point-of-care diagnostic device capable of immediate coagulopathy detection and early diagnostic indications. We have developed arrays of magnetically actuated core-shell microrods able to assess the time evolution of fluid properties at the microscale. Here we describe their application to assessing the mechanical properties of a developing blood clot. Our core-shell post structures, 25 microns tall and 2.5 microns in diameter, consist of flexible poly(dimethylsiloxane) (PDMS) cores surrounded by 100 nm nickel shells. Packaged in a microfluidic channel, our arrays measure changes in fluid properties with less than 15 microliters of fluid and have the potential to become point-of-care devices. We present the use of these core-shell rod arrays as an assay for clot development, capable of producing clinically relevant clotting time measurements in animal plasmas, and will report on progress made in whole blood samples.

Analysis of photonic band gaps in a two-dimensional photonic crystal with centrifugal core-shell rods

The absolute photonic band gap (PBG) in two-dimensional (2D) photonic crystal with excentric core-shell rods is studied in this paper. The core rod shifts away from the core-shell rod center, and its position is decided by two new introduced parameters — the shift angle θ and the offset ρ. We use the FDTD algorithm to calculate the photonic bands of the photonic crystal, and analyze how the offset and shift angle affect the photonic bang gap of excentric core-shell photonic crystal for different core rod size. It has been shown that the variation of the photonic band gap is quite peculiar.

Competition between liquid crystallinity and block copolymerself-assembly in core-shell rod-coil block copolymers.

Core-shell type of architecture revealed the subtle competition between liquid-crystalline ordering and block copolymer (BCP) self-assembly in a rod-coil BCP system.

Impact of surface bond-order loss on phonon dispersion relations and thermal conductivity of cylindrical Si nanowires

The effect of bond-order loss of atoms in the surface skin on the thermal conductivity in cylindrical silicon nanowires has been investigated based on the isotropic elastic continuum model. The frequency change of torsional, longitudinal, and flexural modes of phonon vibration have been examined with a core-shell cylindrical rod structure. Results suggest that the thermal conductivity of the wire increases significantly due to the effect of surface bond-order loss that modifies the Young's modulus in the surface atomic shells, yet atoms in the core region remain as they are in the bulk.