Shuangfeng Jia

Symmetric and Asymmetric Au–AgCdSe Hybrid Nanorods

This paper describes a facile method for synthesis of Au-AgCdSe hybrid nanorods with controlled morphologies and spatial distributions. The synthesis involved deposition of Ag tips at the ends of Au nanorod seeds, followed by selenization of the Ag tips and overgrowth of CdSe on these sites. By simply manipulating the pH value of the system, the AgCdSe could selectively grow at one end, at both the ends or on the side surface of a Au nanorod, generating a mike-like, dumbbell-like, or toothbrush-like hybrid nanorod, respectively. These three types of Au-AgCdSe hybrid nanorods displayed distinct localized surface plasmon resonance and photoluminescence properties, demonstrating an effective pathway for maneuvering the optical properties of nanocrystals.

Epitaxial II–VI Tripod Nanocrystals: A Generalization of van der Waals Epitaxy for Nonplanar Polytypic Nanoarchitectures

We report for the first time the synthesis of nonplanar epitaxial tripod nanocrystals of II-VI compounds (ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe) on muscovite mica substrate. With CdS as a case study, we conclude via Raman spectroscopy and electron microscopy studies that the tripods, which are found to be polytypic, followed a seeded growth mechanism. The epitaxy, manifested by the in-plane alignment of the legs of the tripods within a substrate, is attributed to the van der Waals interaction between the tripod bases and the mica surface, instead of to the covalent chemical bond which would require lattice matching between the epilayer and the substrate. The results demonstrated herein could have widespread immediate implications, including the potential of van der Waals epitaxy to be applicable in producing ordered arrays of more complex nanoarchitectures from various classes of compounds toward a broad range of technological applications.

Asymmetric Supercapacitor Based on Porous N-doped Carbon Derived from Pomelo Peel and NiO Arrays

A three dimensional (3D) porous framework-like N-doped carbon (PFNC) with a high specific surface area was successfully fabricated through ammonia doping and graphitization based on pomelo peel. The obtained PFNC exhibits an enhanced specific capacitance (260 F g(-1) at 1 A g(-1)) and superior cycling performance (capacitance retention of 84.2% after 10000 cycles at 10 A g(-1)) on account of numerous voids and pores which supply sufficient pathways for ion diffusion during cycling. Furthermore, a fabricated asymmetric PFNC//PFN device based on PFNC and porous flake-like NiO (PFN) arrays achieves a specific capacitance of 88.8 F g(-1) at 0.4 A g(-1) and an energy density of 27.75 Wh kg(-1) at a power density of 300 W kg(-1) and still retains 44 F g(-1) at 10 A g(-1) and 13.75 Wh kg(-1) at power density of 7500 W kg(-1). It is important that the device is able to supply two light-emitting diodes for 25 min, which demonstrates great application potential.

Electron beam-assisted healing of nanopores in magnesium alloys

Nanopore-based sensing has emerged as a promising candidate for affordable and powerful DNA sequencing technologies. Herein, we demonstrate that nanopores can be successfully fabricated in Mg alloys via focused electron beam (e-beam) technology. Employing in situ high-resolution transmission electron microscopy techniques, we obtained unambiguous evidence that layer-by-layer growth of atomic planes at the nanopore periphery occurs when the e-beam is spread out, leading to the shrinkage and eventual disappearance of nanopores. The proposed healing process was attributed to the e-beam-induced anisotropic diffusion of Mg atoms in the vicinity of nanopore edges. A plausible diffusion mechanism that describes the observed phenomena is discussed. Our results constitute the first experimental investigation of nanopores in Mg alloys. Direct evidence of the healing process has advanced our fundamental understanding of surface science, which is of great practical importance for many technological applications, including thin film deposition and surface nanopatterning.

Self-assembly of KxWO3 nanowires into nanosheets by an oriented attachment mechanism.

The KxWO3 nanosheets consisting of superfine nanowires were successfully synthesized in ambient air. The detailed electron microscopy and X-ray diffraction investigations imply that the nanosheets were obtained by self-assembly of the ordered nanowires with exposed {0110}H facets. The sheet morphology is closely related with the growth conditions including temperature and time, etc. A possible mechanism based on the oriented attachment of neighboring nanowires for the formation of nanosheets is proposed. Our results shed light on the interfacial characteristics of self-assembled KxWO3 nanowires and can serve as guidance to the future design of relevant two-dimensional structures for various electrical and optical applications.

Ordered and twinned structure in hexagonal-based potassium tungsten bronze nanosheets

Non-stoichiometric hexagonal-based potassium tungsten bronze (KxWO3) nanosheets were synthesized by oxidizing tungsten foil in potassium hydroxide. The tungsten bronze nanosheets exhibited an ordered monoclinic superstructure as revealed by X-ray diffraction patterns. Further detailed structural investigation by employing electron microscopy techniques showed the coexistence of 120° rotation twinning variants in the superstructure phase, which may result from the rotation symmetry reduction induced by the ordered arrangements of K vacancies during crystal growth.

Twinning mediated growth of ZnSe tri- and bi-crystal nanobelts with single crystalline wurtzite nanobelts as building blocks

A variety of ZnSe nanostructures, including the single-, bi- and tri-crystal nanobelts, are successfully fabricated through the thermal evaporation method and comprehensively investigated by a combination of various transmission electron microscopy (TEM) techniques. All nanostructures are of metastable wurtzite phase and the bi- and tri-crystal nanobelts are both mediated by the {013} twinning, with the single crystal nanobelts as building blocks. Benefiting from the commonly observed morphological evolutions, not only the crystallographic relations for different variants in an individual bi- or tri-crystal nanobelt, but also the intrinsic connections between different morphologies are fully understood by selected area electron diffraction, convergent beam electron diffraction and high-resolution TEM techniques, which reveals that the accompanying formation of tri-crystal nanobelt, the {013} relationship, though maintained still, is not as strict as that in a bi-crystal nanobelt and holds a ∼0.75° deviation for a case study; the angles between adjacent twinning variants/planes are compressed from ∼125.0° in bi-crystal nanobelts to ∼120°, and finally form an asymmetric twinning plane distributions. The study helps deepen the understanding of tri-crystal and related complex semiconductor nanostructures.

Stepwise synthesis of cubic Au-AgCdS core-shell nanostructures with tunable plasmon resonances and fluorescence

Cubic Au-AgCdS core-shell nanostructures were synthesized through cation exchange method assisted by tributylphosphine (TBP) as a phase-transfer agent. Among intermediate products, Au-Ag core-shell nanocubes exhibited many high-order plasmon resonance modes related to the special cubic shape, and these plasmon bands red-shifted along with the increasing of particle size. The plasmon band of Au core first red-shifted and broadened at the step of Au-Ag₂S and then blue-shifted and narrowed at the step of Au-AgCdS. Since TBP was very crucial for the efficient conversion from Ag₂S to CdS, we found that both absorption and fluorescence of the final products could be controlled by TBP.

Orientation domains in vacancy-ordered titanium monoxide

This paper presents a study on orientation domains in the vacancy-ordered titanium monoxide TiO(x). Transmission electron microscopy analysis revealed the co-existence of 12 possible TiO(x) monoclinic domain variants, which are induced by the cubic-to-monoclinic phase transition attributed to the Ti and O vacancy ordering. These 12 monoclinic domain variants which are predicted by group theory might be randomly arranged. Furthermore, several hours of electron beam irradiation can lead to the vacancy ordering-disordering transition (i.e. monoclinic-to-cubic phase transformation) in TiO(x). Our results shed light on the structural characteristics in TiO(x) nanostructures and thus contribute to the fabrication and design of the related nanostructures.

Atomic-Scale Study of Cation Ordering in Potassium Tungsten Bronze Nanosheets

It has long been accepted that the formation of superlattices in hexagonal‐based potassium tungsten bronzes is attributed to K vacancies only, together with small displacements of W cations. Here, the superlattices within potassium tungsten bronze nanosheets both structurally and spectroscopically at atomic resolution using comprehensive transmission electron microscopy techniques are studied. The multidimensional chemical analyses are realized by energy‐dispersive X‐ray spectroscopy, electron energy‐loss spectroscopy, and X‐ray photoelectron spectroscopy, the atomic‐scale structures are characterized using aberration‐corrected scanning transmission electron microscopy with high‐angle annular‐dark‐field detector. The observed superstructures are mainly attributed to small amount of W vacancies within single atomic layer, which would recover to more uniform distributions of W vacancies with lower concentrations at higher temperature. The band regions of different orientation from the matrix tend to regulate the superstructures to be pinned along the same direction, forming domains of highly ordered structures. The characterization of cation ordering and recovery processes of nanostructures from chemical and structural point of view at atomic resolution enables rational design of optoelectronic devices with controlled physical properties.