Direct Experimental Evidences Research Articles

Quantifying the interfacial triboelectricity in inorganic-organic composite mechanoluminescent materials

Mechanoluminescence (ML) sensing technologies open up new opportunities for intelligent sensors, self-powered displays and wearable devices. However, the emission efficiency of ML materials reported so far still fails to meet the growing application requirements due to the insufficiently understood mechano-to-photon conversion mechanism. Herein, we propose to quantify the ability of different phases to gain or lose electrons under friction (defined as triboelectric series), and reveal that the inorganic-organic interfacial triboelectricity is a key factor in determining the ML in inorganic-organic composites. A positive correlation between the difference in triboelectric series and the ML intensity is established in a series of composites, and a 20-fold increase in ML intensity is finally obtained by selecting an appropriate inorganic-organic combination. The interfacial triboelectricity-regulated ML is further demonstrated in multi-interface systems that include an inorganic phosphor-organic matrix and organic matrix-force applicator interfaces, and again confirmed by self-oxidization and reduction of emission centers under continuous mechanical stimulus. This work not only gives direct experimental evidences for the underlying mechanism of ML, but also provides guidelines for rationally designing high-efficiency ML materials.

Nitrogen transformation promotes the anaerobic degradation of PAHs in water level fluctuation zone of the Three Gorges Reservoir in Yangtze River, China: Evidences derived from in-situ experiment

Polycyclic aromatic hydrocarbons (PAHs) pose a great threat to human health and ecological system safety. The interception of nitrogen is common found in the riparian zone. However, there is no evidence on how nitrogen addition affects the anaerobic degradation of PAHs in soil of the water-level-fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) in Yangtze River, China. Here, we investigated the PAHs degradation rate, the variation of key functional genes and microbial communities after nitrogen addition in soil that experienced a flooding period of water-level-fluctuation. The results revealed that the ∑16PAHs were decreased 16.19 %–36.65 % and more 3–5-rings PAHs were biodegraded with nitrogen addition in WLFZ. The most genes involved in PAHs-anaerobic degradation and denitrification were up-regulated by nitrate addition, and phyla Firmicutes, Actinobacteria and Proteobacteria were more advantages in nitrogen addition groups. The Tax4Fun based genome function analysis revealed that the microbial activity of PAHs-degradation increased with nitrate addition. The co-occurrence network analysis indicated that nitrogen addition accelerated the metabolism of nitrogen and PAHs. It is the first time to provide the direct experimental evidences that nitrogen transformation in the WLFZ soil promotes anaerobic PAHs degradation. This work is of importance to understand the effect of nitrogen intercepted in the WLFZ soil of TGR in Yangtze River, China.

3D Extracellular Matrix Regulates the Activity of T Cells and Cancer Associated Fibroblasts in Breast Cancer.

BackgroundBreast cancer progression has been gradually recognized as a bidirectional interaction between cancer cells and tumor microenvironment including stroma cells, immune cells, and the dynamically altered ECM. However, there still lacks direct experimental evidences about how ECM properties modulate the activities of stroma and immune cells.MethodThe transcriptomic data and corresponding clinical information of breast cancer pawere obtained from TCGA. Patients were divided into ECM-high, ECM-median and ECM-low groups based on ssGSEA scores of C-ECM genes. The prognostic value of ECM was confirmed by univariate/multivariate Cox regression and survival analyses. GO and KEGG analyses were performed between ECM-high and -low groups. Then associations between ECM characteristics and clinical stages were verified by Masson’s trichrome and Sirius red/Fast Green staining of clinical breast cancer tissues. To evaluate the effects of ECM on CAF induction and T cell activation, the MRC-5, NIH/3T-3, primary T cells and Jurkat T cells were encapsulated in 3D collagen with different densities and organizations, and the expression levels of CAF biomarkers and secretion levels of IL-2 were assessed.ResultsECM scores showed broad variation across paracancerous and cancer samples as well as breast cancer molecular subtypes, and patients with different ECM groups showed distinct prognosis. Immunological activity and ECM associated biology processes were identified by GO and KEGG analyses across ECM-high and -low groups. According to MCP-counter algorithm, the infiltration of T cells was significantly lower in the ECM-high group, while CAF abundance was significantly higher. It is furtherly confirmed by clinical samples that collagen density and organization were associate with breast cancer progression. Finally, in vitro 3D-cultured fibroblasts and T cells validated that the density and organization of collagen showed significant effects on CAF induction and T cell activation.ConclusionOur study revealed a new mechanism of T cell immunosuppression and CAF induction, which could be of central importance for the breast cancer invasion and may constitute novel therapeutic targets to improve breast cancer outcomes.

L-doublet splittings in Δ vibrational state of 15N14N16O isotopomer

We report the direct experimental evidences of l-doublet fine splittings between the parity doublet e and f sub-states of β-site isotopomer of nitrous oxide (15N14N16O) in the (1220)←(0220) ro-vibrational transition for l = 2 (i.e. Δ state) vibrational state in the mid-IR 7.8 µm spectral region. Due to extremely small splittings it remains a challenge for recording the fine structure doubling features for l = 2 or higher states. The existence of l-type doubling was investigated by high-resolution and ultra-sensitive cavity ring-down spectroscopy coupled with an external-cavity quantum cascade laser. We determined several new spectroscopic parameters such as l-type doubling constants, Coriolis constants, band centres, rotational constants and centrifugal distortion constants for l = 2 state of β-site N2O isotopomer by probing the rotationally resolved spectral lines with higher J values in the P-branch. Subsequently, the pressure broadening effect on the l-doublets and the corresponding broadening coefficients for both e and f sub-states in Δ state of β-site N2O were explored. Our high-resolution spectroscopic measurements will be useful for better fundamental understanding of linear polyatomic molecules and their isotopomers.

Direct experimental evidences of the density variation of ultrathin polymer films with thickness

Beyond the peculiar glass transition temperature (Tg) studied extensively for over two decades, we have investigated in this work the variation of the mass density of polymer thin films, a key property barely put forward in the literature. We were able to directly measure the mass density of polystyrene (PS) and poly (methyl methacrylate) (PMMA) thin films as a function of their thickness from accurate Quartz Crystal Microbalance (QCM) dissolution experiments. Depending on the chemical nature of the polymers, the results showed an unambiguous variation of the mass density when the film thickness was reduced: an increase for PS and a decrease for PMMA films. In the last part, we measured the coefficient of thermal expansion (CTE) of both polymers to rationalize the apparent inconsistency of an increase/decrease in the mass density with the commonly observed depression/rise of the Tg of PS/PMMA films. Surprisingly, the coefficient of thermal expansion and the mass density showed a similar variation with thickness, pointing out a clear correlation between the glass transition temperature, the coefficient of thermal expansion and the free volume of the polymer.

Experimental Evidence of Chiral Symmetry Breaking in Kekulé-Ordered Graphene.

The low-energy excitations of graphene are relativistic massless Dirac fermions with opposite chiralities at valleys K and K^{'}. Breaking the chiral symmetry could lead to gap opening in analogy to dynamical mass generation in particle physics. Here we report direct experimental evidences of chiral symmetry breaking (CSB) from both microscopic and spectroscopic measurements in a Li-intercalated graphene. The CSB is evidenced by gap opening at the Dirac point, Kekulé-O type modulation, and chirality mixing near the gap edge. Our work opens up opportunities for investigating CSB related physics in a Kekulé-ordered graphene.

Caffeic Acid Phenyl Ester (CAPE) Protects against Iron-Mediated Cellular DNA Damage through Its Strong Iron-Binding Ability and High Lipophilicity.

Caffeic acid phenethyl ester (CAPE) and its structurally-related caffeic acid (CA), ferulic acid (FA) and ethyl ferulate (EF) are constituents of honeybee propolis that have important pharmacological activities. This study found that CAPE—but not CA, FA, and EF—could effectively prevent cellular DNA damage induced by overloaded iron through decreasing the labile iron pool (LIP) levels in HeLa cells. Interestingly, CAPE was found to be more effective than CA in protecting against plasmid DNA damage induced by Fe(II)–H2O2 or Fe(III)–citrate–ascorbate-H2O2 via the inhibition of hydroxyl radical (•OH) production. We further provided more direct and unequivocal experimental evidences for the formation of inactive CAPE/CA–iron complexes. CAPE was found to have a stronger iron-binding ability and a much higher lipophilicity than CA. Taken together, we propose that the esterification of the carboxylic moiety with phenethyl significantly enhanced the iron-binding ability and lipophilicity of CAPE, which is also responsible for its potent protection against iron-mediated cellular DNA damage. A study on the iron coordination mechanism of such natural polyphenol antioxidants will help to design more effective antioxidants for the treatment and prevention of diseases caused by metal-induced oxidative stress, as well as help to understand the structure–activity relationships of these compounds.

The multi-ferroelectricity in neodymium ferrite with perovskite structure

In this paper, single-phase orthoferrite NdFeO3 crystals with the space group of Pbnm were successful prepared via mild hydrothermal method. The NdFeO3 crystal performs a weak antiferromagnetic behavior by magnetic measurement. The Dzyaloshinskii Moriya interaction in NdFeO3 crystal causes an additional canting of the antiferromagnetically ordered spins which induce the ferroelectricity. The saturation electric polarization result is 0.0163 μC/cm2 with coercive field of 6.68 kV/cm, and the Curie temperature is 430 K. So we present the direct experimental evidences that the NdFeO3 sample simultaneously exists the ferroelectricity and weak antiferromagnetic at room temperature. This work can develop a route to obtain more species of multiferroic compounds with perovskite structure.

Direct experimental evidence for the non-linear elasticity of multi-functional alloy Ti2448

The ageing of human bone leads to bone diseases and the functional failure of joints. Joint replacement is effective in relieving paints and recovering functions. The mechanical properties of materials determine the performance of artificial replacements. The newly developed Ti2448 (Ti–24Nb–4Zr–8Sn-0.13O, wt.%) possesses excellent mechanical properties, especially its low modulus. Usually, metals show linear elasticity, complying with the Hooke's law. However, Ti2448 exhibits a special non-linear elastic deformation behavior, which is in contrast to most metals. While, deformation mechanisms underpinning this special non-linear elasticity is still unclear although extensive effort has been made in recent years. In this study, direct experimental evidences of stress-induced β→α″ martensitic transformation are obtained by employing in situ XRD and high-resolution transmission electron microscopy. It is found that martensitic transformation is the physical origin of the non-linear elasticity of Ti2448. The findings of this study shed light on understanding and further optimizing mechanical properties of Ti2448 and other multifunctional shape memory alloys.

Strain-Induced Metallization and Defect Suppression at Zipper-like Interdigitated Atomically Thin Interfaces Enabling High-Efficiency Halide Perovskite Solar Cells

Halide perovskite light absorbers have great advantages for photovoltaics such as efficient solar energy absorption, but charge accumulation and recombination at the interface with an electron transport layer (ETL) remain major challenges in realizing the absorbers' full potential. Here we report the experimental realization of a zipper-like interdigitated interface between a Pb-based halide perovskite light absorber and an oxide ETL by the PbO capping of the ETL surface, which produces an atomically thin two-dimensional metallic layer that can significantly enhance the perovskite/ETL charge extraction process. As the atomistic origin of the emergent two-dimensional interfacial metallicity, first-principles calculations performed on the representative MAPbI3/TiO2 interface identify the interfacial strain induced by the simultaneous formation of stretched I-substitutional Pb bonds (and thus Pb-I-Pb bonds bridging MAPbI3 and TiO2) and contracted substitutional Pb-O bonds. Direct and indirect experimental evidence for the presence of interfacial metallic states are provided, and a nonconventional defect-passivating nature of the strained interdigitated perovskite/ETL interface is emphasized. It is experimentally demonstrated that the PbO capping method is generally applicable to other ETL materials, including ZnO and SrTiO3, and that the zipper-like interdigitated metallic interface leads to about a 2-fold increase in the charge extraction rate. Finally, in terms of the photovoltaic efficiency, we observe a volcano-type behavior with the highest performance achieved at the monolayer-level PbO capping. This work establishes a general perovskite/ETL interface engineering approach to realize high-performance perovskite solar cells.

Investigation of the key active intermediate for the synthesis of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane: Hydrolysis and nitrolysis of 1-acetoxymethyl-3,5,7-trinitro-1,3,5,7-tetraazacyclooctane

The problem whether 1-hydroxylmethyl-3,5,7-trinitro-1,3,5,7-tetraazacyclooctane is the key active intermediate for the synthesis of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) from urotropine or 3,7-dinitro-1,3,5,7-tetraazabicyclo[3.3.1]nonane (DPT) remains to be illuminated for decades. In this paper, the hydrolysis and nitrolysis of the esterified intermediate 1-acetoxymethyl-3,5,7-trinitro-1,3,5,7-tetraazacyclooctane (PHX) were studied to solve the long-standing puzzle. The 1H NMR spectrum and 13C NMR spectrum of the 1-hydroxymethyl-3,5,7-trinitro-1,3,5,7-tetraazacyclooctane were detected by tracking the hydrolysis of PHX, which provide direct experimental evidences for its existence. Meanwhile, it was found that 1-nitroso-3,5,7-trinitro-1,3,5,7-tetraazacyclooctane (MNX) is a stable intermediate in the nitrolysis of PHX to generate HMX, and the presence of small amounts of water in the nitrolysis of PHX not only stimulate the redox reaction between nitric acid and formaldehyde but also promote the reaction by hydrolyzing PHX to corresponding N-hydroxymethyl derivative, which verify that 1-hydroxymethyl-3,5,7-trinitro-1,3,5,7-tetraazacyclooctane is the key active intermediate in the synthesis of HMX.

On the fate of sinking diatoms: the transport of active buoyancy-regulating cells in the ocean.

Diatoms are one of the most abundant, diverse and ecologically relevant phytoplanktonic group, contributing enormously to global biogeochemical processes like the carbon and silica cycles. This large success has been partly attributed to the mechanical and optical properties of the silica shell (the frustule) that envelops their body. But since they lack motility it is difficult to conceive how they cope with the fast-fluctuating environment they live in and where distributions of resources are very heterogeneous and dynamical. This pinpoints an important but yet poorly understood feature of diatoms physiology: buoyancy regulation that helps them controlling their sinking speed and position in the water column. While buoyancy regulation by light and nutrients availability has been well studied, the effect of hydromechanical stress via fluid shear has been rather overlooked when considering diatoms dynamics. Here, we aim to start filling this gap by first presenting direct experimental evidences for buoyancy control in response to hydro-mechanical stress and then review recent theoretical models where simple couplings between local shear and buoyancy control always result in heterogeneous cell distributions, specific accumulation regions within complex flows and increased sedimentation times to the depths, features of direct ecological relevance. We conclude by suggesting future experiments aiming to unveil such coupling and therefore gain better understanding on the fate of these fascinating microorganisms in their natural habitat. This article is part of the theme issue 'Stokes at 200 (part 2)'.

Probing Orientation-Specific Charge-Dipole Interactions between Hexafluoroisopropanol and Halides: A Joint Photoelectron Spectroscopy and Theoretical Study.

The interactions between hexafluoroisopropanol (HFIP) and halogen anions X- (F-, Cl-, Br-, and I-) have been investigated using negative ion photoelectron (NIPE) spectroscopy and ab initio calculations. The measured NIPE spectrum of each [HFIP·X]- (X = Cl, Br, and I) complex shows a pattern identical to the corresponding X- by shifting to the high electron binding energy side, indicative of the formation of the [HFIP···X-] structure in which X- interacts with HFIP via charge-dipole interactions. However, the spectrum of [HFIP·F]- appears completely different from that of F- and is more similar to the spectrum of the deprotonated HFIP anion (HFIP-H-). The geometry and electron density calculations indicate that a neutral HF molecule is formed upon HFIP interacting with F- via proton transfer, rendering a stable structure of [HFIP-H···HF]-. Two conformers of [HFIP-H·HF]- with HFIP being in synperiplanar and antiperiplanar configurations, respectively, are observed, providing direct experimental evidences to show the distinctly different and orientation-specific interactions between HFIP and halide anions.

Mechanical properties of cortical bones related to temperature and orientation of Haversian canals

The understanding of mechanical performances and microscopic failure mechanisms of cortical bones under service condition is necessary prerequisite of fracture prevention, which would support the development of bone tissue engineering and design of bionic bones. By using miniaturized horizontal in situ compression tester, the effects of both temperature and sampling orientations on the compressive strengths and fracture morphologies were investigated. The significant difference between fracture strengths and compressive strains at various temperatures indicated that the cortical bone was sensitive to temperature. Direct experimental evidences revealed the gradually fibrotic trend of fracture surfaces as a function of sampling orientation. Through the Haversian canals distribution analysis, the relationship between the distribution of Haversian canals and fracture path was established. Essentially, the competition between high density Haversian canals and stress concentration factor determines the initiation and propagation of cracks.

In situ investigations of interfacial degradation and ion migration at CH3NH3PbI3 perovskite/Ag interface

Interfacial properties between perovskite layers and metal electrodes play a crucial role in the device performance and the long-term stability of perovskite solar cells. Here, we report a comprehensive study of the interfacial degradation and ion migration at the interface between CH3NH3PbI3 perovskite layer and Ag electrode. Using in situ photoemission spectroscopy measurements, we found that the Ag electrode could induce the degradation of perovskite layers, leading to the formation of PbI2 and AgI species and the reduction of Pb2+ ions to metallic Pb species at the interface. The unconventional enhancement of the intensities of I 3d spectra provides direct experimental evidences for the migration of iodide ions from CH3NH3PbI3 subsurface to Ag electrode. Moreover, the contact of Ag electrode and perovskite layers induces an interfacial dipole of 0.3 eV at CH3NH3PbI3/Ag interfaces, which may further facilitate iodide ion diffusion, resulting in the decomposition of perovskite layers and the corrosion of Ag electrode.

Isotopic evidences of the preferential coordination between 12CO2 and urease enzyme

The active Ni(II) centre of metalloenzyme urease forms a coordination with substrate urea prior to the hydrolysis of urea. The present study provided the direct experimental evidences of isotope preferential coordination between Ni(II) metal centre of urease enzyme and substrate urea, which eventually alters the product yield. Furthermore, in-vitro experiments revealed that the specific 12CO2 isotopic species bridges between heavier isotope of substrate urea [13CO(NH2)2] and Ni(II) centre of urease for more effective coordination, which ultimately enhances the yield of the reaction. Finally, the in-vitro observations have been validated under in-vivo physiological conditions exploiting the urease activity of the gastric pathogen Helicobacter pylori present in human stomach. Hence, the present study paves the way for better understanding of the isotope-selective catalytic activity of urease enzyme and exemplifies the link between 12CO2 and urease enzyme.

Evidence of nanoscale Anderson localization induced by intrinsic compositional disorder in InGaN/GaN quantum wells by scanning tunneling luminescence spectroscopy

We present direct experimental evidences of Anderson localization induced by the intrinsic alloy compositional disorder of InGaN/GaN quantum wells. Our approach relies on the measurement of the luminescence spectrum under local injection of electrons from a scanning tunneling microscope tip into a near-surface single quantum well. Fluctuations in the emission line shape are observed on a few-nanometer scale. Narrow emission peaks characteristic of single localized states are resolved. Calculations in the framework of the localization landscape theory provide the effective confining potential map stemming from composition fluctuations. This theory explains well the observed nanometer scale carrier localization and the energies of these Anderson-type localized states. The energy spreading of the emission from localized states is consistent with the usually observed very broad photo- or electro-luminescence spectra of InGaN/GaN quantum well structures.

Stability and structures in atmospheric pressure DC non-transferred arc plasma jets of argon, nitrogen, and air

The stability of dc non-transferred arc plasma jets and their internal structures is investigated through fast photography, emission spectroscopy, and arc dynamics under different operating conditions. A novel method to explore structures inside extremely intense hot plasma jet is conceived and applied for the first time to investigate arc plasma jets. The study revealed distinct interesting structures and their evolution inside the plasma jet, apparently not reported earlier. The associated fundamental mechanisms are identified from direct experimental evidences. Respective steady state jet characteristics with and without air entrainment are obtained from computational fluid dynamic simulation. Arc root motion, air entrainment, and interaction between electromagnetic and fluid dynamic body forces are found to result in a variety of interesting dynamics and structures inside the plasma jet under different operating conditions. Observed behaviors are notably different in argon, nitrogen, and air plasma. While no unusual structures are found over a range of lower flow rates, interesting structures evolve at higher flow rates. Statistical behavior of these structures is found to have a significant dependence on the gas flow rate and torch power. Apart from air entrainment in the downstream, observed isolated temperature islands inside the jet in the upstream have potential to affect particle trajectory, physical processes, and process chemistry in a significant manner.

One Second Formation of Large Area Graphene on a Conical Tip Surface via Direct Transformation of Surface Carbide.

Graphene functionalized nanotips are expected to possess promising potential for various applications based on the outstanding electrical and mechanical properties of graphene. However, current methods, usually requiring a high growth temperature and identical crystal surface to match graphene lattice, are suitable for graphene formation on a flat surface. It remains a big challenge to grow graphene on a nanosized convex surface and fabricate functionalized nanotips with high quality graphene at the apex. In this work, a novel ultrafast annealing method is developed for growing large area graphene on Ni nanotips within 1-2 s. Few layered or multiple layered graphene is presented on the apex or sidewall of the conical tip surface. Direct experimental evidences support that thus-produced graphene is formed via the direct conversion of nickel carbide at the outer surface under the instantaneous high temperature, which is different from the conventional segregation mechanism. This newly developed ultrafast method provides a new route to produce graphene efficiently and economically, promising for both convex surfaces and flat substrates. Moreover, the graphene functionalized nanotips exhibit a great potential for nanoelectrical measurements and conductive scanning probe microscopy (SPM) applications.

Characterization of bulk traps and interface states in AlGaN/GaN heterostructure under proton irradiation

This paper provides a systematic study on the bulk traps and interface states in a typical AlGaN/GaN Schottky structure under proton irradiation. After 3 MeV proton irradiation with a dose of 5 × 1014 H+/cm2, a positive flat band voltage shift of 0.3 V is observed according to the capacitance-voltage (C-V) measurements. Based on this, the distribution of electrons across AlGaN and GaN layers is extracted. Associated with the numerical calculation, direct experimental evidences demonstrate that the bulk traps within the AlGaN layer dominate the carrier removal effect under proton irradiation. Furthermore, the effects of proton irradiation on AlGaN/GaN interface states were investigated by utilizing the frequency dependent conductance technique. The time constants are extracted, which increase from 1.10–2.53 μs to 3.46–37 μs after irradiation. Meanwhile, it shows that the density of interface states increases from 9.45 × 1011–1.70 × 1013 cm−2·eV−1 to 1.8 × 1012–1.8 × 1013 cm−2·eV−1 with an increase in trap activation energy from 0.34 eV–0.32 eV to 0.41 eV–0.35 eV after irradiation. The Coulomb scattering effect of electron trapping at interface states with deeper energy levels is utilized to explain the mobility degradation in this paper.