Z.W. Chen

Microstructure evolution and advanced performance of Mn3O4 nanomorphologies

Mn(3)O(4) morphologies with tetragonal single-crystal nanostructures including nanoparticles, nanorods and nanofractals were successfully prepared by a widely applicable chemical reaction route. The morphologies were synthesized using the reactants MnCl(2)·4H(2)O, H(2)O(2), and NaOH in a suitable surfactant and alkaline solution. The dripping speed of the NaOH solution plays an important role in the microstructure evolution of Mn(3)O(4) morphologies. The difference in the dripping speed of NaOH solutions leads to different Mn(3)O(4) nanomorphologies, which are called nanoparticles, nanorods and nanofractals. The average grain size of the Mn(3)O(4) nanoparticles ranged from a few to several tens of nanometers. The Mn(3)O(4) nanorods were smooth, straight, and the geometrical shape was structurally perfect. Their lengths ranged from several hundred nanometers to a few micrometers, and their diameters ranged from 10 nm to 30 nm. The fractal branches of the Mn(3)O(4) nanofractals were a few micrometers in length and several hundred nanometers in width. The catalytic properties of these Mn(3)O(4) nanomorphologies for the degradation of phenol were evaluated in detail. The results indicated that the Mn(3)O(4) nanofractals possess remarkable catalytic activity for the degradation of phenol in water treatment.

Facile strategy and mechanism for orthorhombic SnO2 thin films

Orthorhombic phase SnO2 is a material with unknown optical, electrical, and gas-sensing properties. It was found previously only at high pressures and temperatures. A facile strategy for the synthesis of orthorhombic SnO2 is of fundamental importance. Using pulsed-laser deposition, the authors report a kind of experimental realization of a pure orthorhombic SnO2 thin film under low pressure and temperature that are much lower than those of traditional methods. The optical properties of an orthorhombic SnO2 thin film were measured by spectrophotometric transmittance. The oxygen exchange reaction mechanism at the grain interfaces was proposed to explain the formation and optical properties of this orthorhombic phase.

Nucleation site and mechanism leading to growth of bulk-quantity Mn3O4 nanorods

We report a simple and effective method for the generation of bulk-quantity nanorods of manganese oxide, Mn3O4, under surroundings of a suitable surfactant and alkaline solution. It is found that the Mn3O4 nanorod is smooth, straight, and that the geometrical shape is structurally perfect, which is produced with lengths from several hundreds nanometers to a few micrometers, and diameters range from 10nmto30nm. We amazedly found that the dripping speed of the NaOH solution plays an important role in formation of bulk-quantity Mn3O4 nanorods. The difference of dripping speed of the NaOH solution leads to a large difference of Mn3O4 morphologies, which is observed in the transmission electron microscopy images. The growth of the Mn3O4 nanorods is suggested first to follow a self-catalyzed solution-liquid-solid mechanism.

Quantum dot formation and dynamic scaling behavior of SnO2 nanocrystals induced by pulsed delivery

Quantum dot formation and dynamic scaling behavior of SnO2 nanocrystals in coalescence regime for growth by pulsed-laser deposition is explored experimentally and theoretically, and the same is compared with that for continuous vapor deposition such as molecular-beam epitaxy. Using high-resolution transmission electron microscopy, unusual quantum dots of SnO2 nanocrystals are studied. We present kinetic Monte-Carlo simulations for pulsed-laser deposition in the submonolayer regime and give a description of the island distance versus pulse intensity. We found that the scaling exponent for pulsed-laser deposition is 1.28±0.03, which is significantly lower as compared to that for molecular-beam epitaxy (1.62±0.03). Theoretical simulations reveal that this attractive difference can be pursued to the large fraction of multiple droplet coalescence under pulsed vapor delivery.

Pulsed Laser Ablation for Tin Dioxide : Nucleation, Growth, and Microstructures

Pulsed-laser ablation approaches are being developed for the growth of oxide thin films as versatile platform for advanced applications. Semiconducting SnO 2 thin film is of fundamental importance in the advancement of microdevices. In this review, SnO 2 thin films of various microstructures have been made using the pulsed-laser deposition method. The microstructural aspects include tetragonal, porous, and orthorhombic structure characteristics. The quantum-dots and dynamic simulations of SnO 2 nanocrystals have blossomed into a submonolayer regime devoted to the nucleation and growth for these functional films. SnO 2 thin films with some of the microstructural features may have great implications for the development of novel prototype gas sensors and transparent conduction electrodes.

Evolution of electronic structure and spectral evaluation in single-crystal Mn3O4 nanorods.

Single-crystal Mn3O4 nanorods with tetragonal structure have been successfully prepared by a chemical reaction route. Transmission electron microscopy (TEM) and high-resolution TEM studies prove that the single-crystal Mn3O4 nanorod is smooth and straight, and that the geometrical shape is structurally perfect. We investigated the electronic characteristics of Mn3O4 nanorods by various spectral evaluations. The present study confirms that the hybridization between oxygen 2p and manganese 3d orbits plays an important role when considering electronic structures of Mn3O4 nanorods.

Insights from investigations of tin dioxide and its composites: electron-beam irradiation, fractal assessment, and mechanism

Tin dioxide (SnO2) is a unique strategic functional material with widespread technological applications, particularly in fields such as solar batteries, optoelectronic devices, and solid-state gas sensors owing to advances in its optical and electronic properties. In this review, we introduce the recent progress of tin dioxide and its composites, including the synthesis strategies, microstructural evolution, related formation mechanism, and performance evaluation of SnO2 quantum dots (QDs), thin films, and composites prepared by electron-beam irradiation, pulsed laser ablation, and SnO2 planted graphene strategies, highlighting contributions from our laboratory. First, we present the electron-beam irradiation strategies for the growth behavior of SnO2 nanocrystals. This method is a potentially powerful technique to achieve the nucleation and growth of SnO2 QDs. In addition, the fractal assessment strategies and gas sensing behavior of SnO2 thin films with interesting micro/nanostructures induced by pulsed delivery will be discussed experimentally and theoretically. Finally, we emphasize the fabrication process and formation mechanism of SnO2 QD planted graphene nanosheets. This review may provide a new insight that the versatile strategies for microstructural evolution and related performance of SnO2-based functional materials are of fundamental importance in the development of new materials.

Recent research situation in tin dioxide nanomaterials: synthesis, microstructures, and properties

This review article summarizes the new research in solid-state physical chemistry understanding of the microstructure characteristics of semiconductor tin oxide thin films made in the last years in our group. The work mainly focuses on the fabrication technology of semiconductor tin oxides thin films by using pulsed laser deposition (PLD) as well as the application of this technology on new micro- and nanostructured materials. It is an interdisciplinary work that integrates the areas of physics, chemistry and materials science.

Formation of orthorhombic SnO2 originated from lattice distortion by Mn-doped tetragonal SnO2

Tin dioxide (SnO2) is an n-type semiconductor material with a tetragonal rutile crystal structure under normal conditions and displays many interesting physical and chemical properties. Another form of SnO2 with an orthorhombic crystal structure is known to be stable only at high pressures and temperatures. However, there are limited reports on the effects of Mn-doped tetragonal phase SnO2 on micro/nanostructured characteristics. In this article, micro/nanostructures of Mn-doped tetragonal phase SnO2 have been successfully prepared by the chemical co-precipitation method. The micro/nanostructural evolution of Mn-doped tetragonal phase SnO2 under different heat treatment temperatures is evaluated by X-ray diffraction (XRD) and high-resolution transmission electron microscopy. It is surprisingly found that the orthorhombic phase SnO2 is formed in Mn-doped tetragonal phase SnO2. The obvious diffraction peaks and clear lattice fringes confirmed that the orthorhombic phase SnO2 nanocrystals exist in Mn-doped SnO2 samples. Experimental results indicated that the XRD peak intensities and crystal planes of the orthorhombic phase SnO2 decrease with increasing heat treatment temperatures. The formation of orthorhombic phase SnO2 is attributed to the lattice distortion of tetragonal phase SnO2 due to the Mn-doped tetragonal phase SnO2.

Facile fabrication and application of SnO2–ZnO nanocomposites: insight into chain-like frameworks, heterojunctions and quantum dots

Versatile strategies for the heterostructure and related performance of nanocomposites are of fundamental importance in the development of advanced functional materials. Semiconductor oxide materials, such as SnO2 and ZnO, have attracted great interest owing to their potential to combine desirable properties. In this work, a novel SnO2–ZnO heterostructured nanocomposite has been fabricated by a sol–gel method and supercritical fluid drying processes. Nanostructure analysis indicated that the SnO2–ZnO composites show chain-like frameworks with heterojunction features, which were embedded with SnO2 and ZnO quantum dots (QDs). The size distribution of SnO2 and ZnO QDs ranged from 3 to 7 nm, which were uniformly dispersed on SnO2–ZnO chain-like frameworks. The experimental results indicated that the calcination temperature could effectively affect the photocatalytic degradation of SnO2–ZnO nanocomposites. When the calcination temperature increased from 500 to 700 °C, the photocatalytic degradation rate increased as the reaction time increased from 30 to 150 min. The new insight obtained in this study will be beneficial for the practical applications of binary oxide semiconductor composites for the photocatalytic degradation of organic pollutants.