H. R. Zhang

Strong photoluminescence of nanostructured crystalline tungsten oxide thin films

Strong photoluminescence (PL) is observed in nanostructured crystalline tungsten oxide thin films that are prepared by thermal evaporation. Two kinds of films are investigated—one made of nanoparticles and another of nanowires. At room temperature, strong PL emissions at ultraviolet-visible and blue regions are found in both of the films. Compared with the complete absence of emission of bulk phase tungsten oxide powder under the same excitation conditions, our results clearly demonstrate the quantum-confinement-effect-induced photoluminescence in nanostructured tungsten oxides.Strong photoluminescence (PL) is observed in nanostructured crystalline tungsten oxide thin films that are prepared by thermal evaporation. Two kinds of films are investigated—one made of nanoparticles and another of nanowires. At room temperature, strong PL emissions at ultraviolet-visible and blue regions are found in both of the films. Compared with the complete absence of emission of bulk phase tungsten oxide powder under the same excitation conditions, our results clearly demonstrate the quantum-confinement-effect-induced photoluminescence in nanostructured tungsten oxides.

Controlled self-assembled nanoaeroplanes, nanocombs, and tetrapod-like networks of zinc oxide

We report on the controlled growth of novel self-assembled nanostructures (nanoaeroplanes, nanocombs, and tetrapod-like networks of zinc oxide) by a simple thermal evaporation technique in a single-stage furnace. Scanning electron microscopy and transmission electron microscopy are used to investigate their morphologies and structures. Shapes are regular and unit sizes vary from 80 nm to 5 µm. The relationship between the preparation conditions and the nanomorphologies in the experiments is helpful for controlling the physical properties of the nanosystems and, hence, is described in some detail. A possible growth mechanism is discussed.

Oxygen vacancy formation, crystal structures, and magnetic properties of three SrMnO3−δ films

The crystal structures and magnetic properties of the 40 nm brownmillerite SrMnO2.5 film, perovskite SrMnO3-δ film, and mixed-phase film have been systematically investigated. The features of the oxygen vacancy ordering superstructure in the brownmillerite SrMnO2.5 film are observed from HRSTEM as follows: the dark stripes with a periodicity of four (110) planes of the cubic perovskite appearing at an angle of 45° with the substrate-film interface and extra reflection spots in fast Fourier transformation patterns along the (001) plane. When annealing the brownmillerite SrMnO2.5 film under higher oxygen pressure, the top portion undergoes structure transition into perovskite SrMnO3-δ as seen in the mixed-phase film consisting of the perovskite SrMnO3-δ phase dominating at the top part and the brownmillerite SrMnO2.5 phase dominating at the bottom part. The magnetic properties and Mn valences of the brownmillerite SrMnO2.5 film indicate that this film, similar to the bulk, is antiferromagnetic with TN at 37...

Facile synthesis of multifunctional Fe3O4@SiO2@Au magneto-plasmonic nanoparticles for MR/CT dual imaging and photothermal therapy

Magneto-plasmonic nanoparticles have exhibited great potential in cancer diagnosis and therapy because of their excellent magnetic and optically activable plasmonic properties. However, it is still a great challenge to combine these two components in one single-nanoparticle. In this work, we developed a facile method to synthesize monodispersed and uniform theranostic agents of Fe3O4@SiO2@GNSs–PEG (PMGNSs) nanoparticles. The as-synthesized PMGNSs composed of a superparamagnetic Fe3O4 inner core, silica as the midlayer and coated with gold nanoshells at the outside, with uniform size distribution of less than 100 nm. It has been demonstrated to be with excellent magnetic resonance (MR) and computed tomography (CT) imaging contrast abilities at different concentrations. Meanwhile, the as-synthesized PMGNSs exhibited high stability with no significant change of photothermal performance after five laser ON/OFF cycles, and high photothermal conversion ability with temperature increase of 40 °C under 808 nm laser irradiation at 2 W cm−2 for 10 min at the concentration of 160 μg ml−1. Furthermore, in vitro photothermal therapy ability has also been demonstrated on HePG2 cancer cells.

Correlation between magnetism and “dark stripes” in strained La1−xSrxCoO3 epitaxial films (0 ≤ x ≤ 0.1)

Using the technique of aberration-corrected scanning transmission electron microscopy, we performed a systematic analysis for the atomic lattice of the strained La1−xSrxCoO3 (0 ≤ x ≤ 0.1) epitaxial films, which have drawn a great attention in recent years because of their anomalous magnetism. Superstructures characterized by dark stripes are observed in the lattice image, evolving with combined Sr-doping and lattice strains. Fascinatingly, we found a close relation between the proportion of the Co ions in dark stripes and the saturation magnetization of the film: the latter grows linearly with the former. This result implies that the magnetism could be exclusively ascribed to the Co ions in dark stripes.

Enhanced antibacterial activity of silver-decorated sandwich-like mesoporous silica/reduced graphene oxide nanosheets through photothermal effect

Drug resistance of bacteria has become a global health problem, as it makes conventional antibiotics less efficient. It is urgently needed to explore novel antibacterial materials and develop effective treatment strategies to overcome the drug resistance of antibiotics. Herein, we successfully synthesized silver decorated sandwich-like mesoporous silica/reduced graphene oxide nanosheets (rGO/MSN/Ag) as a novel antibacterial material through facile method. The rGO and Ag nanoparticles can be reduced in the reaction system without adding any other reductants. In addition, the rGO/MSN/Ag showed higher photothermal conversion capacity due to the modification of silver nanoparticles and exhibited excellent antibacterial activities against Pseudomonas putida, Escherichia coli and Rhodococcus at relatively low dosages, which was confirmed by the minimum inhibitory concentration (MIC) test. Meanwhile, the E. coli with a high concentration was selected for exposure using an 808 nm laser, and the antibacterial effect was obviously enhanced by the near-infrared irradiation induced photothermal effect. Moreover, the hepatocyte LO2 were used for the cytotoxicity evaluation, and the rGO/MSN/Ag showed low toxicity and were without detectable cytotoxicity at the antimicrobial dose. As the prepared rGO/MSN/Ag nanosheets have the advantages of low-cost and high antibacterial activity, they might be of promising and useful antibacterial agents for different applications.

Negative thermal expansion and magnetocaloric effect in Mn-Co-Ge-In thin films

MnCoGe-based alloys with magnetostructural transition show giant negative thermal expansion (NTE) behavior and magnetocaloric effects (MCEs) and thus have attracted a lot of attention. However, the drawback of bad mechanical behavior in these alloys obstructs their practical applications. Here, we report the growth of Mn-Co-Ge-In films with thickness of about 45 nm on (001)-LaAlO3, (001)-SrTiO3, and (001)-Al2O3 substrates. The films grown completely overcome the breakable nature of the alloy and promote its multifunctional applications. The deposited films have a textured structure and retain first-order magnetostructural transition. NTE and MCE behaviors associated with the magnetostructural transition have been studied. The films exhibit a completely repeatable NTE around room temperature. NTE coefficient α can be continuously tuned from the ultra-low expansion (α ∼ −2.0 × 10−7/K) to α ∼ −6.56 × 10−6/K, depending on the growth and particle size of the films on different substrates. Moreover, the films e...

One dimensional electron gas at the LaAlO3/SrTiO3 interface and its transport properties

Quasi-one-dimensional electron gases (q1DEGs) have been obtained by fabricating LaAlO3 nanowires, using the technique of electrostatic spinning plus post annealing, above TiO2-terminated SrTiO3 substrate. The q1DEG exhibits an electronic transport behavior of variable range hopping with the one dimension characteristic. Visible light illumination produces a strong effect on transport process, depressing the resistance of the q1DEG by a factor up to 8. As expected, gating effect is weak at relative high temperatures, ∼3.2% at 150 K and 1.5% at 300 K under a back gate of 200 V. Aided by light illumination, however, the gating effect is 35-fold amplified, and the resistance increases under not only negative gates but also positive gates, different from the normal gating effect without illumination. Possible explanations for these phenomena are given.

A conductive scanning study of La0.67Sr0.33MnO3/Nb:SrTiO3 hetero-junction

Basing on conductive atomic force microscopy, we presented a direct conductance mapping for the interface of the La0.67Sr0.33MnO3/Nb:SrTiO3 hetero-junction. The most remarkable observation is the presence of an interfacial layer in Nb:SrTiO3 adjacent to the manganite film. Within this layer, the AFM tip/Nb:SrTiO3 contact shows a current-voltage dependence that strongly deviates from Shockley equation, unlike a Schottky diode. Spatial extension of this layer is explored and possible transport mechanism in or outside this interfacial layer is discussed. The present work gives a direct intuitional image on the interface of manganite junction. The principle proven here can be extended to other complex oxide interfaces.

Single orthorhombic b axis orientation and antiferromagnetic ordering type in multiferroic CaMnO3 thin film with La0.67Ca0.33MnO3 buffer layer

The detailed crystal structure and antiferromagnetic properties of a 42 nm thick CaMnO3 film grown on a LaAlO3 substrate with a 9 nm La0.67Ca0.33MnO3 buffer layer have been investigated. Compared with a CaMnO3 film directly grown on a LaAlO3 substrate, only one kind of orthorhombic b axis orientation along the [100] axis of the substrate is observed in the CaMnO3 film with a La0.67Ca0.33MnO3 buffer layer. To determine the antiferromagnetic ordering type of our CaMnO3 film with a buffer layer, the first-principles calculations were carried out with the results, indicating that the CaMnO3 film, even under a tensile strain of 1.9%, is still a compensated G-type antiferromagnetic order, the same as the bulk. Moreover, the exchange bias effect is observed at the interface of the CaMnO3/La0.67Ca0.33MnO3 film, further confirming the antiferromagnetic ordering of the CaMnO3 film with a buffer layer. In addition, it is concluded that the exchange bias effect originates from the spin glass state at the La0.67Ca0.33...