[Show abstract][Hide abstract] ABSTRACT: Exchange bias effect with perpendicular anisotropy is of great interest for potential applications such as read heads in magnetic storage devices with high thermal stability and reduced dimension. Here we report a novel approach to achieving perpendicular exchange bias by orienting the ferromagnetic/antiferromagnetic coupling in the vertical geometry through a unique vertically aligned nanocomposite (VAN) design. Our results demonstrate robust perpendicular exchange bias phenomena in micrometer-thick films employing a prototype material system of antiferromagnetic BiFeO3 and ferromagnetic La0.7Sr0.3MnO3. The unique response of exchange bias to perpendicular magnetic field reveals the existence of exchange coupling along their vertical heterointerfaces, which exhibits strong dependence on their strain states. This VAN approach enables a large selection of material systems for achieving perpendicular exchange bias, which could lead to advanced spintronic devices.
[Show abstract][Hide abstract] ABSTRACT: Vertical interfaces in vertically aligned nanocomposite thin films have been approved to be an effective method to manipulate functionalities. However, several challenges with regard to the understanding on the physical process underlying the manipulation still remain. In this work, because of the ordered interfaces and large interfacial area, heteroepitaxial (BaTiO3)1-x:(Sm2O3)x thin films have been fabricated and used as a model system to investigate the relationship between vertical interfaces and dielectric properties. Due to a relatively large strain generated at the interfaces, vertical interfaces between BaTiO3 and Sm2O3 are revealed to become the sinks to attract oxygen vacancies. The movement of oxygen vacancies is confined at the interfaces and hampered by the misfit dislocations, which contributed to a relaxation behavior in (BaTiO3)1-x:(Sm2O3)x thin films. This work represents an approach to further understand that how interfaces influence on dielectric properties in oxide thin films.
[Show abstract][Hide abstract] ABSTRACT: Fast ion transport channels at interfaces in thin films have attracted great attention due to a range of potential applications for energy materials and devices, for, solid oxide fuel cells, sensors, and memories. Here, it is shown that in vertical nanocomposite heteroepitaxial films of SrZrO3–RE2O3 (RE = Sm, Eu, Gd, Dy, and Er) the ionic conductivity of the composite can be tuned and strongly enhanced using embedded, stiff, and vertical nanopillars of RE2O3. With increasing lattice constant of RE2O3 from Er2O3 to Sm2O3, it is found that the tensile strain in the SrZrO3 increases proportionately, and the ionic conductivity of the composite increases accordingly, by an order of magnitude. The results here conclusively show, for the first time, that strain in films can be effectively used to tune the ionic conductivity of the materials.
[Show abstract][Hide abstract] ABSTRACT: Addition of second-phase nanosize defects to YBa2Cu3O7-δ (YBCO) superconductor thin films is known to enhance flux pinning and increase current densities (Jc). The addition of Y2BaCuO5 (Y211) was previously studied in (Y211/ YBCO)N multilayer structures and in Y211 + YBCO films deposited from pie-shaped targets. This research systematically studies the effect of Y211 addition in thin films deposited by pulsed laser deposition from YBCO1-xY211x(x = 0-15 vol.%) single targets, at temperatures of 785°C-840°C. Interestingly, the resulting size of Y211 particles is 20-40 nm, in contrast to 10-15 nm in previous studies of Y211 and 5-10 nm for other second-phase defect additions, and the number density is reduced. A slight increase of Jc(H, T) was achieved, compared with previous optimization studies. Results and comparisons of flux pinning, intrinsic stresses imaged by TEM, current densities, critical temperatures, and microstructures will be presented. The overall low intrinsic stress on YBCO from Y211 lattice mismatch is smaller than previously studied second-phase defect additions known, which is hypothesized to be the driving force in achieving the unusually large second-phase nanoparticle size and volume fraction thus far in YBCO thin films.
[Show abstract][Hide abstract] ABSTRACT: Auxetic-like strain states were generated in self-assembled nanocomposite
thin films of (Ba0.6Sr0.4TiO3)1−x
(BSTO − SmO). A switch from auxetic-like to elastic-like strain behavior was observed for x > 0.50, when the SmO switched from being nanopillars in the BSTO matrix to being the matrix with BSTO nanopillars embedded in it. A simple model was adopted to explain how in-plane strain varies with x. At high x (0.75), strongly enhanced ferroelectric properties were obtained compared to pure BSTO films. The nanocomposite method represents a powerful new way to tune the properties of a wide range of strongly correlated metal oxides whose properties are very sensitive to strain.
[Show abstract][Hide abstract] ABSTRACT: Iron-based superconductors have attracted great research interests from both the intriguing fundamental superconducting mechanism aspects and their potential applications in high fields owing to their high critical field Hc2 and low field anisotropy. However, one critical factor limiting the commercial applications of superconducting coated conductors is the significant manufacturing costs involved in the processing of the complex layered buffers and the subsequent epitaxial growth of superconducting coated conductors. Here we demonstrate a much simplified superconducting coated conductor design for Fe-based superconductor on glass and metallic substrates without bi-axial texturing buffers. Using this design, FeSe0.1Te0.9 thin films on glass show superconducting properties of critical temperatures Tczero of 10 K, and Tconset of 12.5 K, self-field critical current density (Jc) of 2.1×104 A/cm2 at 4 K, and upper critical field (Hc2) as high as 126 T. This work could lay a critical foundation toward future practical applications of Fe-based superconductor coated conductors.
Journal of Alloys and Compounds 06/2015; 647. DOI:10.1016/j.jallcom.2015.06.109 · 2.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Bi2FeMnO6 (BFMO) thin films with both conventional pseudo-cubic structure and novel supercell structure have been grown on SrTiO3 (001) substrates with different thicknesses of CeO2 buffer layers (ranging from 6.7 nm to 50.0 nm) using pulsed laser deposition. The correlation between the thickness of the CeO2 buffer layer and the structure of the BFMO films shows that the CeO2 buffer layer, as thin as 6.7 nm, is sufficient in triggering the novel BFMO supercell structure. This may be ascribed to the interfacial strain between the BFMO supercell structure and the CeO2 buffer layer which also serves as a seed layer. The buffer layer thickness is found to be critical to control the microstructure and magnetism of the formed BFMO supercell structures. Thin seed layers can produce a smoother interface between the BFMO film and the CeO2 buffer layer, and therefore better ferrimagnetic properties. Our results have demonstrated that strain and interface could be utilized to generate novel thin film structures and to tune the functionalities of the thin films.
[Show abstract][Hide abstract] ABSTRACT: Recent studies have shown that chemical immiscibility is important to achieve enhanced radiation tolerance in metallic multilayers as immiscible layer interfaces are more stable against radiation induced mixing than miscible interfaces. However, as most of these immiscible systems have incoherent interfaces, the influence of coherency on radiation resistance of immiscible systems remains poorly understood. Here, we report on radiation response of immiscible Cu/Fe multilayers, with individual layer thickness h varying from 0.75 to 100 nm, subjected to He ion irradiation. When interface is incoherent, the peak bubble density decreases with decreasing h and reaches a minimum when h is 5 nm. At even smaller h when interface is increasingly coherent, the peak bubble density increases again. However, void swelling in coherent multilayers with smaller h remains less than those in incoherent multilayers. Our study suggests that the coherent immiscible interface is also effective to alleviate radiation induced damage.
Journal of Materials Research 05/2015; 30(09):1-10. DOI:10.1557/jmr.2015.24 · 1.82 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: NiO effectively promotes the sintering of highly refractory Y-doped BaZrO3 (BZY) through the formation of BaY2NiO5, providing a simple and cost-effective method for the fabrication of dense BZY electrolyte and Ni–BZY hydrogen separation membrane at ∼1400 oC. Unfortunately, insulating BaCO3 and Y2O3 phases formed on the surface of BZY and Ni–BZY prepared by solid state reaction method with NiO after annealing in wet CO2. Ni–BZY membranes prepared from different methods suffered different degree of performance loss in wet H2 at 900 °C. The chemical instability of Ni–BZY is attributed to the formation of a secondary phase (BaY2O4) generated from the reduction of BaY2NiO5 in H2 during the sintering process. Both BaY2O4 and BaY2NiO5 react with H2O, and CO2 at elevated temperatures, generating insulating Ba(OH)2 and BaCO3 phases, respectively. The less BaY2O4 is formed in the fabrication process, the better chemical stability the Ni–BZY membranes possess. Therefore, a new Ni–BZY membrane is prepared through a judicial combination of BZY powders prepared from combined EDTA-citric and solid state reaction methods, and demonstrates exceptional chemical stability in H2O and CO2, enabling stable and even improved hydrogen flux in wet 50% CO2 at 900 °C.
Journal of Power Sources 03/2015; 278. DOI:10.1016/j.jpowsour.2014.12.108 · 6.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: High energy particles can introduce severe radiation damage in metallic materials especially those with low stacking fault energy. Twin boundary (TB) has recently been shown to enable the reduction of defect density in heavy ion irradiated nanotwinned Ag. However, the defect-twin boundary interaction mechanisms in nanotwinned metals remain poorly understood. Here we report on the study of TB affected zone wherein time accumulative defect density and defect diffusivity are substantially different from those in twin interior. In situ studies also reveal surprising resilience of TBs in response to radiation: TBs continue to change their geometry to facilitate the capture, transportation and removal of defect clusters and can recover by absorbing opposite type of defects. This study provides further support for the implementation of TBs as effective defect sinks for the design of radiation tolerant nanostructured metallic materials.
[Show abstract][Hide abstract] ABSTRACT: Serum microRNAs (miRNAs) have been proposed as novel non‑invasive biomarkers for the early detection of cancer. Reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) is the most commonly used method for investigating miRNA expression levels, however, the interpretation of RT‑qPCR results depends largely on normalization to an appropriate endogenous control. The present study involved 129 patients with non‑muscle‑invasive bladder cancer (NMIBC), 121 patients with muscle‑invasive bladder cancer (MIBC) and 158 healthy controls. The aim of the present study was to determine the most stable reference genes for the investigations of serum miRNA in bladder cancer (BC). MiSeq sequencing was performed and the expression levels of 10 miRNAs and U6 were then measured using RT‑qPCR. Following RT‑qPCR, five genes (hsa‑miR‑193a‑5p, hsa‑miR‑16‑5p, U6, hsa‑miR‑191‑5p and hsa‑let‑7d‑3p) were selected for stability analysis using geNorm and NormFinder software. These algorithms identified hsa‑miR‑193a‑5p and hsa‑miR‑16‑5p as the most stably expressed reference genes. The availability of hsa‑miR‑193a‑5p and hsa‑miR‑16‑5p was confirmed in an additional cohort. One‑way analysis of variance indicated that no significant differences were present in the expression levels among the three groups. Furthermore, miR‑148b‑3p was selected as a target miRNA to determine the effect of hsa‑miR‑193a‑5p and hsa‑miR‑16‑5p on miRNA quantification. The combined use of hsa‑miR‑193a‑5p and hsa‑miR‑16‑5p enabled the detection of a significant upregulation of miR‑148b‑3p in the BC serum. The results of the present study demonstrated that normalization of miRNA data, using a combination of hsa‑miR‑193a‑5p and hsa‑miR‑16‑5p as reference genes, may produce reliable and accurate results for the detection of serum miRNAs in BC.
Molecular Medicine Reports 03/2015; 12(1). DOI:10.3892/mmr.2015.3428 · 1.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: MicroRNA-214 (miR-214) has been reported to be dysregulated in human bladder cancer tissues. We aimed to investigate the clinical correlation, biological significance and molecular network of miR-214 in bladder cancer. Our results showed miR-214 was down-regulated in bladder cancer tissues and significantly associated with tumor stage, lymph node status, grade, multifocality, history of non-muscle-invasive bladder cancer (NMIBC). Moreover, miR-214 could serve as an independent factor of recurrence-free survival (RFS) and overall survival (OS) for patients with muscle-invasive bladder cancer (MIBC). Restoration of miR-214 expression in bladder cancer cell lines inhibited cell proliferation, migration, invasion and markedly promoted apoptosis. Dual-luciferase reporter assay recognized PDRG1 as direct downstream target gene of miR-214. PDRG1 was significantly increased in tumors low of miR-214 and knockdown of PDRG1 mimicked the effects of miR-214 overexpression. Our findings manifest that miR-214 could exert tumor-suppressive effects in bladder cancer by directly down-regulating oncogene PDRG1 and suggest an appealing novel indicator for prognostic and therapeutic intervention of bladder cancer.
PLoS ONE 02/2015; 10(2):e0118086. DOI:10.1371/journal.pone.0118086 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The impedance spectroscopy of Z-type hexaferrite Sr3Co2Fe24O41 (SCFO) has been investigated as a function of temperature from 303 to 503 K. The frequency dependent impedance (
) and modulus (
) spectra show that for the air annealed SCFO, the electrical responses of SCFO are thermal activated and there is a distribution of relaxation times. The scaling behaviors of
spectra further suggest that the distribution of relaxation times is temperature independent. The Cole-Cole plots in impedance formalism show that the electrical response of SCFO originates from both the grain and the grain-boundaries. The activation energies for grain and grain boundary are 0.66 eV and 0.67 eV, respectively. The frequency dependent conductivity (
) spectra follow the universal power law. The fitting results of
spectra show that the small polaron
hopping is the most probable conduction mechanism for SCFO. Moreover, the scaling behavior of
spectra further confirms that the distribution of local electrical response times is temperature independent. The air plus O2 annealed SCFO shows thermally activated electrical responses and scaling behaviors as well. The above results show that although the electrical responses of SCFO are temperature dependent, the relaxation mechanism in SCFO is temperature independent.
[Show abstract][Hide abstract] ABSTRACT: Li2MnO3 is an attractive cathode material due to its low cost, non-toxicity and potentially high capacity. However, its electrochemical inactivity, poor electronic conductivity and uncertainty about underlying mechanism have limited its development. In this work, an in-situ technique for extraction of Li and O during deposition of the thin film cathode is developed to investigate structural and electrochemical effects in a controlled fashion. MnO2 has been observed in samples with severe O and Li deficiency (capacity of 115 mAh g-1), while Li2MnO3 cathodes with slightly excess O and Li (capacity of 225 mAh g-1) can be synthesized by tuning growth conditions appropriately. Formation of MnO2 phase, especially in Li and O deficient structures, could be a possible reason for irreversible capacity loss in Li2MnO3 related materials. Further investigation into stoichiometric and microstructure variations enabled by this technique allows rapid investigation of Li2MnO3 as well as other Li-rich composites.
[Show abstract][Hide abstract] ABSTRACT: Bone morphogenetic proteins (BMPs) are members of the TGF-β superfamily signaling factors. Expression of several BMPs (BMP2, BMP4 and BMP7) is correlated to poor prognosis in gastric cancer patients. The function of BMP9, the latest discovered and most powerful osteogenetic factor, in gastric cancer is relatively unclear. In this report, we investigated the expression, function and underlying molecular mechanisms of BMP9 in gastric cancer. The results show that BMP9 expression was markedly decreased in gastric cancer tissues and cell lines. Enforced BMP9 expression in the gastric cancer cell lines SGC-7901 and MNK-45 increased apoptosis and reduced viability and migration. The in vivo function of BMP9 was evaluated in a xenograft mouse model. Tumors derived from SGC-7901 cells with enforced BMP9 expression (SGC-7901/BMP9) showed significantly reduced size and weight compared to that from control cells. Enforced BMP9 expression resulted in decreased Akt activity shown as lower levels of phosphorylation at Ser473 and Thr308 in Akt. The PI3K/Akt inhibitor LY294002 potentiated BMP9's viability and migration suppression, and apoptosis induction, which was associated with reduced expression of snail and VEGF and increased expression of E-cadherin. In addition, tumors derived from SGC-7901/BMP9 showed reduced Akt activity and VEGF expression, and increased E-cadherin expression. Therefore, our studies reveal for the first time that inhibition of the PI3K-Akt pathway is involved in the tumor suppressor effects of BMP9 in gastric cancer. This article is protected by copyright. All rights reserved
Journal of Cellular Biochemistry 01/2015; DOI:10.1002/jcb.25063 · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Functional ferromagnetic (Fe2O3)x:(CeO2)1-x vertically aligned nanocomposite (VAN) layers were deposited as either buffer or cap layers for YBa2Cu3O7-δ (YBCO) thin films. The composition of Fe2O3 dopants in the VAN nanolayers is controlled at 10%, 30% and 50% in order to create different arrangements of Fe2O3 and CeO2 nanopillars and therefore to tune the flux pining landscapes. The composition variation provides tunable and ordered arrangements of magnetic nanodopants and interfacial defects as pinning centers in the YBCO thin films. The superconducting property measurements show that most doped samples obtain a Tc above 90 K and the Jcsf measured at 75K and 65K maximized at 3.07MA/cm2 and 9.2 MA/cm2 for 30% Fe2O3 VAN doped sample. As the temperature decreased to 5 K, the sample with 50% Fe2O3 VAN doped sample show the best pinning effect due to pronounced magnetic pinning effects. This work demonstrates the tunable density of magnetic pinning centers can be achieved by VAN to meet the specific pinning requirement.
Physica C Superconductivity 12/2014; 510. DOI:10.1016/j.physc.2014.12.004 · 1.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Human astroviruses (HAstVs) are one of the leading viral agents of acute gastroenteritis. However, there is limited information on HAstVs in China. Here, we describe the molecular characterization of HAstVs in Shandong, China via sewage surveillance. A total of 23 sewage samples were collected from sewage treatment plants in the cities of Jinan and Linyi in 2013. After concentration via adsorption-elution method, 9 samples (39.1%) were positive by reverse transcription PCR (RT-PCR) for the presence of the 719-nt HAstV nucleotide sequence. Genetic cloning and sequencing were performed on positive PCR products, and 26 HAstV sequences were obtained. Phylogenetic analysis on these sequences revealed 4 genotypes (HAstV-1, -2, -4 and -5), with HAstV-1 and -5 as the most common genotypes in Jinan and Linyi, respectively. Homologous comparison revealed Shandong sequences had relatively less genetic divergence among themselves than with foreign sequences. This study represents the first effort to investigate the genotypes and molecular epidemiology of HAstVs via sewage surveillance in China. The high detection rate in this study reflects that HAstVs circulated at a relatively high frequency in the local population, and demonstrates that environmental surveillance is an effective method in investigating circulating HAstVs.
[Show abstract][Hide abstract] ABSTRACT: Making silicon an efficient light-emitting material is an important goal of silicon photonics. Here we report the observation of broadband sub-bandgap photoluminescence in silicon nanowires with a high density of stacking faults. The photoluminescence becomes stronger and exhibits a blue shift under higher laser powers. The super-linear dependence on excitation intensity indicates a strong competition between radiative and defect-related non-radiative channels, and the spectral blue shift is ascribed to the band filling effect in the heterostructures of wurtzite silicon and cubic silicon created by stacking faults.