Showing papers by "Tao Li published in 2018"

Large electrostrictive response in lead halide perovskites

Abstract: Lead halide perovskites have demonstrated outstanding performance in photovoltaics, photodetectors, radiation detectors and light-emitting diodes. However, the electromechanical properties, which are the main application of inorganic perovskites, have rarely been explored for lead halide perovskites. Here, we report the discovery of a large electrostrictive response in methylammonium lead triiodide (MAPbI3) single crystals. Under an electric field of 3.7 V µm−1, MAPbI3 shows a large compressive strain of 1%, corresponding to a mechanical energy density of 0.74 J cm−3, comparable to that of human muscles. The influences of piezoelectricity, thermal expansion, intrinsic electrostrictive effect, Maxwell stress, ferroelectricity, local polar fluctuation and methylammonium cation ordering on this electromechanical response are excluded. We speculate, using density functional theory, that electrostriction of MAPbI3 probably originates from lattice deformation due to formation of additional defects under applied bias. The discovery of large electrostriction in lead iodide perovskites may lead to new potential applications in actuators, sonar and micro-electromechanical systems and aid the understanding of other field-dependent material properties. The electromechanical properties of organic–inorganic hybrid perovskites are not well characterized. Here, a large electrostrictive strain of 1% is measured, suggesting both new electromechanical applications and implications for photovoltaics.

Internally extended growth of core–shell NH2-MIL-101(Al)@ZIF-8 nanoflowers for the simultaneous detection and removal of Cu(II)

Abstract: The excessive accumulation of toxic copper species makes it imperative to develop smart dual-functional materials for the simultaneous removal and detection of Cu(II) in drinking water. In this work, novel core–shell NH2-MIL-101(Al)@ZIF-8 nanoflowers were successfully fabricated via an internal extended growth mode under the regulation of polyvinylpyrrolidone (PVP) to achieve this goal. Benefiting from the specific affinity of imidazole nitrogen in ZIF-8 toward Cu(II), the resultant NH2-MIL-101(Al)@ZIF-8 shows high adsorption capacity (526.74 mg g−1). Moreover, the fluorescence of NH2-MIL-101(Al) shows a Cu(II)-dependent change, causing this composite to possess superior selective/sensitive detection with a broad linear range (1.5–625 μM) and a low detection limit (0.17 μM) for Cu(II). Specifically, the hybrid MOF@MOF structure provides greater sensitivity as compared to the individual constituent (pristine NH2-MIL-101(Al)) and the mixed state, which is ascribed to the rational optimization of the smart adsorbent based on the following two aspects. (i) The synergistic effect of the core–shell nanostructure improves the preconcentration ability at the interface between single MOFs. (ii) The existence of the three-dimensional hierarchical nanoflower architecture (structure optimization) accelerates the mass transport and sculpts the final composite with enhanced adsorption and detection ability. These indicate that the smart NH2-MIL-101(Al)@ZIF-8 nanoflower could be an excellent candidate for the synchronous remediation and selective detection of Cu(II) in aqueous systems, which could be potentially useful in wastewater treatment and water quality monitoring.

Optical control of polarization in ferroelectric heterostructures

Abstract: In the ferroelectric devices, polarization control is usually accomplished by application of an electric field. In this paper, we demonstrate optically induced polarization switching in BaTiO3-based ferroelectric heterostructures utilizing a two-dimensional narrow-gap semiconductor MoS2 as a top electrode. This effect is attributed to the redistribution of the photo-generated carriers and screening charges at the MoS2/BaTiO3 interface. Specifically, a two-step process, which involves formation of intra-layer excitons during light absorption followed by their decay into inter-layer excitons, results in the positive charge accumulation at the interface forcing the polarization reversal from the upward to the downward direction. Theoretical modeling of the MoS2 optical absorption spectra with and without the applied electric field provides quantitative support for the proposed mechanism. It is suggested that the discovered effect is of general nature and should be observable in any heterostructure comprising a ferroelectric and a narrow gap semiconductor.

Engineering Single-Atom Cobalt Catalysts toward Improved Electrocatalysis.

Abstract: A paradigm of coordination design and electronic engineering of single‐atom dispersed cobalt catalysts (SAC) is demonstrated, which leads to significantly enhanced electrocatalytic activities and selectivity, therefore presenting new oxygen electrocatalysis pathways via achieving the favored site–adsorbate interactions, and the illustration of the active sites in SAC indicates the metal‐natured catalytic sites and a media‐dependent catalytic pathway.

Black phosphorus quantum dots as dual-functional electron-selective materials for efficient plastic perovskite solar cells

Abstract: Organic–inorganic hybrid metal halide perovskite solar cells (PSCs) have attracted tremendous research interest due to their high power conversion efficiency and simple fabrication. However, the exploitation of new electron-selective materials which can simultaneously tailor the quality of metal halide perovskite film for low-temperature-produced plastic organic–inorganic halide perovskite solar cells (PSCs) is of key importance but remains a great challenge. Herein, facile solution-processed black phosphorus quantum dots (BPQDs) with ambipolar conductivity are developed as dual-functional electron-selective layer (ESL) in plastic PSCs. The BPQD ESL plays crucial roles in both forming a cascade energy level for fast electron extraction and guiding the crystallization behavior of the perovskite to yield compact perovskite films with less traps, good crystallization and ordered orientation. The perovskite films deposited on the BPQD ESL exhibit excellent optoelectronic properties, and the resulting plastic planar perovskite solar cells possess a reasonably high efficiency of 11.26%. The 3.15-fold enhancement in efficiency arises from both the efficient electron extraction and suppressed radiative and trap-assisted non-radiative recombination compared with the devices built on the bare ITO surface without an ESL. This work paves a promising way for developing novel electron-selective non-oxide materials for highly efficient solar cells.

Effects of graphene on the microstructures of SnO2@rGO nanocomposites and their formaldehyde-sensing performance

Abstract: Performance modulation of formaldehyde (HCHO) sensing active nanomaterials is of great significance in environmental monitoring and disease diagnosis. This paper reports a simple but robust solvothermal process to synthesize SnO2@rGO nanocomposites for HCHO sensors with rGO mass fractions of 0–2%. The phases, chemical compositions, microstructures and surface states of the as-obtained SnO2@rGO nanocomposites are well characterized. The results indicate that the addition of GO overcomes the agglomeration of SnO2 nanocrystals (3–5 nm) and highly enhances the specific surface area (SSA) of the SnO2@rGO nanocomposites, leading to higher response and lower operating temperature in the HCHO-sensing application. The SSA of SnO2@rGO is 133.1 m2/g, much larger than that (58.3 m2/g) of pure SnO2 nanocrystals. The SnO2@rGO nanocomposites exhibit highly selective and sensitive to HCHO vapors at a relatively low operating temperature range of 100–200 °C. The amount of GO added has a key effect on the HCHO-sensing performance, and the sample of SnO2@rGO-0.5% exhibits the highest response at 100 160 °C. Their recovery/response times are shorter than 20 s to HCHO vapors (less than 25 ppm). The enhanced HCHO-sensing performance is attributed to the formation of porous SnO2@rGO nanostructures with high SSAs and suitable electron transfer channels.

Expanding Interlayer Spacing of Hard Carbon by Natural K+ Doping to Boost Na-Ion Storage

Abstract: Heteroatom-doped carbon is an attractive material for anodes in lithium-/sodium-ion batteries as a replacement for traditional graphite anodes. However, the complex fabrication process and high cost limit practical applications of these carbon materials. Here, we report a low-cost, natural potassium-doped carbon material, which is directly carbonized from the coconut endocarp-a kind of high potassium-containing biomass material. The obtained carbon structure features an expanded d(002)-spacing (0.4 nm) originating from the superhigh potassium content (6654 mg kg-1). Because of the improvement on charge transfer kinetics and electrical properties, the potassium-doped carbon anode exhibits promising electrochemical performance in sodium-ion batteries, including high initial reversible capacity (314 mAh g-1) and good cycle stability (289 mAh g-1 after 200 cycles). Additionally, this work opens up a new approach for the design of heteroatom-doped carbon materials from the viewpoint of being naturally environmental friendly.

Enhanced Polymer Crystallinity in Mixed-Matrix Membranes Induced by Metal-Organic Framework Nanosheets for Efficient CO2 Capture.

Abstract: The design and fabrication of novel mixed-matrix membranes (MMMs) with simultaneously enhanced gas permeability and selectivity are highly sought for the industrial deployment of membrane technology for large-scale CO2 capture and storage. Conventional isotropic bulky particle fillers often exhibit limited interfacial compatibility that eventually leads to significant selectivity loss in MMMs. Here, we report the incorporation of chemically stable metal–organic framework (MOF) nanosheets into a highly permeable polymer matrix to prepare defect-free MMMs. MOF nanosheets are homogeneously dispersed within the polymer matrix, owing to their high aspect ratios that improve the polymer–filler integration. The strong hydrogen bonding and π–π interactions between the two components not only enhance the interfacial compatibility but also favor the efficient polymer chain packing along the surface of MOF nanosheets, leading to enhanced polymer crystallinity as well as size-sieving capability of the membranes. The ...

Effect of Cation-π Interaction on Macroionic Self-Assembly.

Abstract: A series of rod-shaped polyoxometalates (POMs) [Bu4 N]7 [Mo6 O18 NC(CH2 O)3 MnMo6 O18 (OCH2 )3 CNMo6 O18 ] and [Bu4 N]7 [ArNMo6 O17 NC(CH2 O)3 MnMo6 O18 (OCH2 )3 CNMo6 O17 NAr] (Ar=2,6-dimethylphenyl, naphthyl and 1-methylnaphthyl) were chosen to study the effects of cation-π interaction on macroionic self-assembly. Diffusion ordered spectroscopy (DOSY) and isothermal titration calorimetry (ITC) techniques show that the binding affinity between the POMs and Zn2+ ions is enhanced significantly after grafting aromatic groups onto the clusters, leading to the effective replacement of tetrabutylammonium counterions (TBAs) upon the addition of ZnCl2 . The incorporation of aromatic groups results in the significant contribution of cation-π interaction to the self-assembly, as confirmed by the opposite trend of assembly size vs. ionic strength when compared with those without aromatic groups. The small difference between two aromatic groups toward the Zn2+ ions is amplified after combining with the clusters, which consequently triggers the self-recognition behavior between two highly similar macroanions.

Heat treatment of electron beam melted (EBM) Ti-6Al-4V: microstructure to mechanical property correlations

Abstract: The paper presents a wide range of post processing heat treatment cycles performed to Electron Beam Melted (EBM) Ti6Al4V alloy and establishes correlations of heat treat process to microstructure and mechanical property (microhardness). The research also identifies the optimal heat treatment to obtain the best microstructure and mechanical properties (hardness and tensile).,Rectangular bars fabricated using EBM was used to study the different heat treatment cycles. A variety of heat treatments from sub s-transus, super s-transus, near s-transus and solution aircool plus ageing were designed. After the heat treatment process, the samples were analysed for, α lath width, prior s grain size, microhardness and nanohardness. Tensile tests were done for the heat treated samples showing most refined α lath structure with uniform globular grains.,A clear correlation was observed between α lath width and the microhardness values. The solution aircooled plus aged samples exhibited the best refinement in α-s morphology with uniform equiaxed grains. The tensile properties of the solution aircooled plus aged samples were comparable to that of the EBM printed samples and better than ASTMF1472 specifications.,There is hardly any prior work related to post processing heat treatment of EBM built Ti6Al4V other than HIP treatments. The variety of heat treatment cycles and its influence in microstructure and properties, studied in this research, gives a clear understanding on how to tailor final microstructures and select the optimal heat treatment process.

Epitaxial ferroelectric Hf0.5Zr0.5O2 thin film on a buffered YSZ substrate through interface reaction

Abstract: In this study, we used pulsed laser deposition to successfully grow epitaxial Hf0.5Zr0.5O2 (HZO) films on (001)-, (011)- and (111)-oriented yttria-stabilized zirconia (YSZ) substrates using TiN as the bottom electrode. It is found that the TiO2 buffer layer formed by the interface reaction is the key to epitaxial growth. The epitaxial HZO films (∼15 nm in thickness) exhibit ferroelectric behaviour with a remnant polarization of 7–30 μC cm−2 and a coercive field of 1.1–2.3 MV cm−1. Using piezoresponse force microscopy, polar domains can be written/read and reversibly switched with a phase change of 180° in all the films. X-ray diffraction and high-resolution transmission electron microscopy reveal the presence of nano domains, and a clear epitaxial relation among different layers whose interfaces are relaxed by reconstruction. X-ray absorption spectroscopy provides deep insight into the microstructural origin of ferroelectricity in HZO. A large interface strain stabilized ferroelectric state is observed which is manifested as the non-centrosymmetric Pca21 phase.

Scandium doped Ge2Sb2Te5 for high-speed and low-power-consumption phase change memory

Abstract: To bridge the gap of access time between memories and storage systems, the concept of storage class memory has been put forward based on emerging nonvolatile memory technologies. For all the nonvolatile memory candidates, the unpleasant tradeoff between operation speed and retention seems to be inevitable. To promote both the write speed and the retention of phase change memory (PCM), Sc doped Ge2Sb2Te5 (SGST) has been proposed as the storage medium. Octahedral Sc-Te motifs, acting as crystallization precursors to shorten the nucleation incubation period, are the possible reason for the high write speed of 6 ns in PCM cells, five-times faster than that of Ge2Sb2Te5 (GST) cells. Meanwhile, an enhanced 10-year data retention of 119 °C has been achieved. Benefiting from both the increased crystalline resistance and the inhibited formation of the hexagonal phase, the SGST cell has a 77% reduction in power consumption compared to the GST cell. Adhesion of the SGST/SiO2 interface has been strengthened, attribut...

Multilevel Manipulation of Supramolecular Structures of Giant Molecules via Macromolecular Composition and Sequence

Abstract: We have successfully synthesized a series of monodispersed chain-like giant molecules with precisely controlled macromolecular composition and sequence based on polyhedral oligomeric silsesquioxane (POSS) nanoparticles using an orthogonal “click” strategy. Their nonspherical supramolecular structures, such as lamellae, double gyroids, and hexagonal packed cylinders, are mainly determined by the composition (namely, the number of incorporated amphiphilic nanoparticles). In addition, by precisely alternating the sequence of arranged nanoparticles in the giant molecules with identical chemical compositions, the domain sizes of their supramolecular structures could be fine-tuned. This is attributed to the macromolecular conformational differences caused by collective hydrogen bonding interactions in each set of sequence isomeric giant molecules. This work has demonstrated multilevel manipulation of supramolecular structures of giant molecules: coarse tuning by composition and fine-tuning by sequence.

The insight-HXMT mission and its recent progresses

Abstract: The Hard X-ray Modulation Telescope (HXMT or also dubbed as Insight-HXMT) is China’s first astronomical satellite. It was launched on 15th June 2017 in JiuQuan, China and is currently in service smoothly. It was designed to perform pointing, scanning and gamma-ray burst (GRB) observations and, based on the Direct Demodulation Method (DDM), the image of the scanned sky region can be reconstructed. Here we introduce the mission and its progresses in aspects of payload, core sciences, ground calibration/facility, ground segment, data archive, software, in-orbit performance, calibration, background model, observations and preliminary results.

Resin from Liaohe Heavy Oil: Molecular Structure, Aggregation Behavior, and Effect on Oil Viscosity

Abstract: Resin accounts for over 30% of the composition of Liaohe heavy crude oil and can result in severe difficulties in oil recovery and transportation. To determine the structure of the resin extracted from Liaohe heavy oil, matrix-assisted laser desorption ionization time-of-flight mass spectrometry, elemental analysis, Fourier-transform IR spectroscopy, and NMR spectroscopy were employed to determine the chemical structure of the resin. The results showed that the resin molecule is composed of anthracene, two cycloalkanes, and six alkyl chains grafted on the cyclic-structure core. UV–visible spectroscopy, turbidity measurements, dynamic light scattering, optical microscopy, and scanning electron microscopy were used to observe the resin aggregation behavior upon addition of a poor solvent. The effect of the resin on the rheology of model oils was investigated systematically. The π–π interactions among resin molecules impose a critical impact on the assembly of the resins. The quantum mechanics calculations r...

Tuning the Performance of Single-Atom Electrocatalysts: Support-Induced Structural Reconstruction

Abstract: Creating active and stable electrocatalysts remains a highly desirable and critical goal in the fields of catalysis and clean energy conversion. Single-atom catalyst (SAC), as a new research frontier in heterogeneous catalysis, has demonstrated emerging prospects for many electrocatalytic reactions. Support-assisted pyrolysis approaches are widely used in the synthesis of single-atom electrocatalysts. While extensive efforts have been devoted to increase the loading of the atomically dispersed metal sites, the role of the support in creating these active metal sites remains largely unexplored. Herein, we compare catalysts created by support-free and support-assisted pyrolysis of vitamin B12 and cobalt tetramethoxyphenylporphyrin, respectively, and demonstrate an important effect of support-induced structural reconstruction that directly controls the activation of SAC. Electrochemical studies show support-free catalysts are inactive for oxygen reduction reaction whereas the support-assisted pyrolysis yield...

Tuning of Polyoxopalladate Macroanionic Hydration Shell via Countercation Interaction.

Abstract: Three types of macroanion-countercation interactions in dilute solution, decided by the strength of electrostatic attraction and the change of hydration shells are reported: minor interaction between macroanions [MO8 Pd12 (SeO3 )8 ]6- (M=Zn2+ or Ni2+ ) and monovalent cations (Na+ , K+ , Rb+ , Cs+ ), leaving their hydration shells intact (solvent-separated ion-pairs); strong binding between macroanions and divalent cations (Sr2+ , Ba2+ ) to form solvent-shared ion-pairs with partial dehydration; very strong electrostatic attraction between macroanions and Y3+ ion with contact ion-pairs formation by severely breaking their original hydration shells and forming new ones. In addition, divalent cations can help the macroanions self-assemble into hollow spherical blackberry structures through counterion-mediated attraction, whereas macroanions with mono- or trivalent cations only stay as discrete ions due to either weak interaction or a small number of bound countercations.

Probing of Local Multifield Coupling Phenomena of Advanced Materials by Scanning Probe Microscopy Techniques.

Abstract: The characterization of the local multifield coupling phenomenon (MCP) in various functional/structural materials by using scanning probe microscopy (SPM)-based techniques is comprehensively reviewed. Understanding MCP has great scientific and engineering significance in materials science and engineering, as in many practical applications, materials and devices are operated under a combination of multiple physical fields, such as electric, magnetic, optical, chemical and force fields, and working environments, such as different atmospheres, large temperature fluctuations, humidity, or acidic space. The materials' responses to the synergetic effects of the multifield (physical and environmental) determine the functionalities, performance, lifetime of the materials, and even the devices' manufacturing. SPM techniques are effective and powerful tools to characterize the local effects of MCP. Here, an introduction of the local MCP, the descriptions of several important SPM techniques, especially the electrical, mechanical, chemical, and optical related techniques, and the applications of SPM techniques to investigate the local phenomena and mechanisms in oxide materials, energy materials, biomaterials, and supramolecular materials are covered. Finally, an outlook of the MCP and SPM techniques in materials research is discussed.

Scandium doping brings speed improvement in Sb 2 Te alloy for phase change random access memory application

Abstract: Phase change random access memory (PCRAM) has gained much attention as a candidate for nonvolatile memory application. To develop PCRAM materials with better properties, especially to draw closer to dynamic random access memory (DRAM), the key challenge is to research new high-speed phase change materials. Here, Scandium (Sc) has been found it is helpful to get high-speed and good stability after doping in Sb2Te alloy. Sc0.1Sb2Te based PCRAM cell can achieve reversible switching by applying even 6 ns voltage pulse experimentally. And, Sc doping not only promotes amorphous stability but also improves the endurance ability comparing with pure Sb2Te alloy. Moreover, according to DFT calculations, strong Sc-Te bonds lead to the rigidity of Sc centered octahedrons, which may act as crystallization precursors in recrystallization process to boost the set speed.

Effect of Aromatic and Aliphatic Pendants in Poly(maleic acid amide-co-vinyl acetate) on Asphaltene Precipitation in Heavy Oil

Abstract: Asphaltene precipitation often brings difficulties to the recovery and transportation of heavy crude oil. Poly(maleic acid amide-co-vinyl acetate) copolymers with various aromatic (phenyl, naphthyl, and benzimidazole) pendants and/or aliphatic (octyl, tetradecyl, and octadecyl) grafts were synthesized and found to be capable of dispersing asphaltenes effectively. To study the influence of aromatic and aliphatic pendants in copolymers on asphaltene precipitation behaviors, the initial precipitation point, turbidity, and size of asphaltene precipitates from model heavy oils in the presence and absence of copolymers were determined by UV–vis spectroscopy, turbidity meter, and dynamic light scattering, respectively. The effect of copolymers on the viscosity of Tahe heavy oil with high asphaltene content was investigated by the rheological approach. The results revealed that the copolymers with both aromatic and aliphatic pendants dispersed asphaltene, reduced its precipitates, and thus improved the flowabilit...

Embelin Restores Carbapenem Efficacy against NDM-1-Positive Pathogens.

Abstract: The emergence and spread of carbapenemase in Gram-negative pathogens poses an enormous threat to global public health. New Delhi metallo-β-lactamase-1 (NDM-1) inactivates nearly every class of β-lactam antibiotics, including carbapenem; however, there is no clinically useful NDM-1 inhibitor. Embelin, an important ingredient in traditional herbal medicine, has anti-tumor effects. The current study is the first to discover and examine the inhibitory activity of embelin against β-lactamase NDM-1. The IC50 of embelin was 2.1 ± 0.2 μM when tested against NDM-1 carbapenemase. Most regions of the embelin molecule were buried within NDM-1's active site, and the hydroxyl group of embelin interacted directly with the metal ion Zn2+, as shown by molecular dynamic simulation. Systematic analysis of the antibacterial activities of embelin and antibiotics demonstrated that embelin restored meropenem activity against a panel of NDM-positive pathogens, such as Escherichia coli, Klebsiella pneumoniae, and Acinetobacter baumannii. Based on these results, embelin could be a promising carbapenem adjuvant candidate against NDM-1-producing bacterial strains.

Pressure Effect on the Rheological Behavior of Waxy Crude Oil with Comb-Type Copolymers Bearing Azobenzene Pendant

Abstract: In this work, a pressure responsive poly(α-octadecene-co-maleic acid azobenzene amide) (Azo-MAC) was synthesized and able to enhance the flowability of waxy crude oil with asphaltenes significantly under high pressure. High-pressure UV–vis spectrometer was used to characterize its pressure response under pressures. The onset temperature and enthalpy during wax crystallization of Liaohe waxy crude oil under various pressures were determined by using high-pressure differential scanning calorimeter. The viscosity and yield stress were measured by high-pressure rheometer. On the basis of our experimental data, a mechanism was propounded that the conformation transformation from cis to trans of azobenzene groups in Azo-MAC at enhanced pressure may destroy the assembly of asphaltenes, disturb the crystallization of paraffins and thus improve the flowability of oils. Azo-MAC should be an ideal additive for exploitation and transportation of oils under high pressure.

Hydrogen bonding directed co-assembly of polyoxometalates and polymers to core–shell nanoparticles

Abstract: A general strategy has been developed here to co-assemble polyoxometalates (POMs) and polymers into core–shell hybrid nanoparticles via hydrogen bonding interaction Due to the hydrogen bonds between the pyridine groups of poly(4-vinyl pyridine) (P4VP) and the hydrogen bonding donor groups on the POM surface, P4VP is stabilized by the POMs and dispersed as discrete hybrid core–shell nanoparticles in aqueous solution For these thermodynamically stable nanoparticles, the P4VP cores are covered with hexagonal close-packed POMs The size of the core–shell particles is controlled by the electrostatic repulsive interaction among the POMs The introduction of extra salts screens the repulsive force among the POMs, thus increasing the size of the core–shell structures

Nicotine-enhanced stemness and epithelial-mesenchymal transition of human umbilical cord mesenchymal stem cells promote tumor formation and growth in nude mice.

Abstract: Cigarette smoking is a well-known risk factor in the development and progression of malignant diseases. Nicotine, the major constituent in cigarette smoke, has also shown negative effects on stem cells. Mesenchymal stem cells (MSCs) have been widely demonstrated to migrate into tumors and play key roles in cancer progression. However, the mechanisms by which nicotine impacts MSCs and tumorigenesis of lung cancer are still undetermined. In this study we investigated the effects of nicotine on human umbilical cord mesenchymal stem cells (hUC-MSCs) and the impacts of nicotine-treated hUC-MSCs on tumor formation and progression. We found that nicotine has a toxic effect on hUC-MSCs and changes the morphology, inhibits proliferation and promotes apoptosis of hUC-MSCs in a dose-dependent manner. Nicotine-treated hUC-MSCs produce higher level of IL-6. Moreover, nicotine promotes migration, stemness and epithelial-mesenchymal transition (EMT) of hUC-MSCs by inhibiting E-cadherin expression and upregulating mesenchymal markers such as N-cadherin and Vimentin, leading to the induction of stem cell markers Sox2, Nanog, Sall4, Oct4 and CD44. Migration and proliferation of non-small cell lung cancer A549 cells and breast cancer MCF-7 cells are promoted after their coculture with nicotine-treated hUC-MSCs in a cell-cell contact-independent manner. Furthermore, nicotine-treated hUC-MSCs promote tumor formation and growth of A549 cells in nude mice. These studies demonstrated that the enhanced stemness and EMT of hUC-MSCs induced by nicotine are critical for the development of tobacco-related cancers.

Tailoring nanopore formation in atomic layer deposited ultrathin films

Abstract: Selectivity is a critical attribute of catalysts used in manufacturing of essential and fine chemicals. An excellent way to induce selectivity in catalysts is by using ultrathin films with tailored nanoporosity. For instance, nanopores can be created in atomic layer deposition (ALD) ultrathin over-coatings on supported metal nanoparticles by subjecting the coatings to high temperature annealing. These nanopores expose the active surface of the underlying metal nanoparticles. The dimensions of these nanopores can be tuned to impart shape selectivity: only reactants or products with a specific size or shape can fit inside the pore. In this work, the authors explore the underlying mechanism driving nanopore formation in ALD films. Ultrathin films of ALD TiO2 (∼2.5 nm thick) and ALD Al2O3 (∼4.9 nm thick) were deposited on nonporous γ-Al2O3 nanoparticles. The pore formation and evolution were monitored in situ during thermal annealing using small-angle x-ray scattering (SAXS), and the crystallinity was monitor...

Atomic scale insight into the effects of Aluminum doped Sb 2 Te for phase change memory application

Abstract: To date, the unpleasant trade-off between crystallization speed and thermal stability for most phase change materials is detrimental to achieve phase change memory (PCM) with both features of high-speed and good-retention. However, it is proved that Al doping in Sb2Te, served as storage media in PCM, favors both a high writing speed (6 ns) and a good retention (103 °C), as well as a low power consumption. Judging by experimental and theoretical investigations, doped Al atoms prefer to replace Sb in Sb2Te lattice, strongly bonded with 6 Te atoms, to form a homogeneous phase. While in amorphous Al doped Sb2Te (AST), Al atoms are in tetrahedral environment, firmly bonded with four Sb/Te atoms. The strong bonding in Al centered tetrahedron in amorphous AST can obstruct the collective motion of Sb atoms near the matrix boundary, leading to the improvement in thermal stability and the confinement in grain size.

Structure-Function Correlative Microscopy of Peritubular and Intertubular Dentine

Abstract: Peritubular dentine (PTD) and intertubular dentine (ITD) were investigated by 3D correlative Focused Ion Beam (FIB)-Scanning Electron Microscopy (SEM)-Energy Dispersive Spectroscopy (EDS) tomography, tapping mode Atomic Force Microscopy (AFM) and scattering-type Scanning Near-Field Optical Microscopy (s-SNOM) mapping. The brighter appearance of PTD in 3D SEM-Backscattered-Electron (BSE) imaging mode and the corresponding higher grey value indicate a greater mineral concentration in PTD (~160) compared to ITD (~152). However, the 3D FIB-SEM-EDS reconstruction and high resolution, quantitative 2D map of the Ca/P ratio (~1.8) fail to distinguish between PTD and ITD. This has been further confirmed using nanoscale 2D AFM map, which clearly visualised biopolymers and hydroxyapatite (HAp) crystallites with larger mean crystallite size in ITD (32 ± 8 nm) than that in PTD (22 ± 3 nm). Correlative microscopy reveals that the principal difference between PTD and ITD arises primarily from the nanoscale packing density of the crystallites bonded together by thin biopolymer, with moderate contribution from the chemical composition difference. The structural difference results in the mechanical properties variation that is described by the parabolic stiffness-volume fraction correlation function introduced here. The obtained results benefit a microstructure-based mechano-chemical model to simulate the chemical etching process that can occur in human dental caries and some of its treatments.