The damage mechanism in copper studied using in situ TEM nanoindentation.

Copper (Cu) has a soft-plastic nature, which makes it susceptible to damages from scratching or abrasive machining, such as lapping and polishing. It is a challenge to control these damages as the damage mechanism is elusive. Nonetheless, controlling damages is essential, especially on the atomic surfaces of Cu. To interpret the damage mechanism, in situ transmission electron microscopy (TEM) nanoindentation was performed using a cube-corner indenter with a radius of 57 nm at a loading speed of 5 nm s-1. Experimental results showed that damages originate from dislocations, evolve to stack faults, and then form broken crystallites. When the indentation depth was 45 nm at a load of 20 µN, damages comprised dislocations and stacking faults. After increasing the depth to 67 nm and load to 30 µN, the formation of broken crystallites initiated; and the critical depth was 67 nm. To validate the damage mechanism, fixed-abrasive lapping, mechanical polishing, and chemical mechanical polishing (CMP) were conducted. Firstly, a novel green CMP slurry containing silica, hydrogen peroxide, and aspartic acid was developed. After CMP, a surface roughness Ra of 0.2 nm was achieved with a scanning area of 50 µm × 50 µm; and the thickness of the damaged layer was 3.1 nm, which included a few micro-stacking faults. Lapping and mechanical polishing were carried out using a silicon carbide plate and cerium slurry, with surface roughness Ra values of 16.42 and 1.74 nm, respectively. The damaged layer of the former with a thickness of 300 nm comprised broken crystallites, dislocations, and stacking faults and that of the latter with a thickness of 33 nm involved several stacking faults. This verifies that the damage mechanism derived from in situ TEM nanoindentation is in agreement with lapping and polishing. These outcomes propose new insights into understanding the origin of damages and controlling them, as well as obtaining atomic surfaces using a novel green CMP technique for soft-plastic metals.

Development of a Novel Water Jet Polisher Using Soft Abrasives for Small Complex-Structure Heat Pipes of Aluminum Alloy Produced Using Additive Manufacturing.

It is a challenge to polish the interior surface of a small bent pipe with complex structures and sizes less than 0.5 mm. This is because of the fact that traditional polishing methods could destroy, block, or break the small complex structures. For a small bent pipe made of aluminum alloy produced using additive manufacturing, the defects, such as adhered powders and spatters, are easy to jam the pipe without polishing, possibly resulting in catastrophic failure for aerospace applications. To overcome this challenge, a novel water jet polisher was developed using soft polymethyl methacrylate (PMMA) abrasives. After polishing a specific area, the adhered powders on the interior surface were reduced from over 140 to 2, 3, and 6 by the soft abrasives with mesh sizes of 200, 400, and 600, respectively. The surface roughness Sa was decreased from 3.41 to 0.92 µm after polishing using PMMA abrasives with a mesh size of 200. In comparison, silica abrasives were also employed to polish the small bent pipes, leading to the bent part of pipes breaking. However, this kind of failure was absent when using soft abrasives. Computational fluid dynamics calculations elucidate that a peak erosion rate of silica abrasives for a bent pipe with a turn angle of 30° is 2.18 kg/(m2·s), which is 17 times that of soft abrasives. This is why the small bent pipe was broken using silica abrasives, whereas it remained intact when polished with soft abrasives. In addition, water jet polishing has a lower erosion rate, a relatively smooth erosion curve, and less erosion energy, leaving the bent parts intact. The developed soft abrasive water jet polisher and the findings of this study suggest new possibilities for cleaning the adhered powders and spatters and polishing the interior surface of small bent pipes with complex structures.

Atomic surface of quartz glass induced by photocatalytic green chemical mechanical polishing using the developed SiO2@TiO2 core-shell slurry.

High-performance devices of quartz glass demand an atomic surface, which induces a challenge for chemical mechanical polishing (CMP) with a high material removal rate (MRR). Moreover, traditional CMP usually employs toxic and corrosive slurries, leading to the pollution of the environment. To overcome these challenges, a novel green photocatalytic CMP is proposed. In the CMP, SiO2@TiO2 core-shell abrasives were developed, and the CMP slurry included the developed abrasives, sodium carbonate, hydrogen peroxide and sorbitol. After photocatalytic CMP, the surface roughness Sa of quartz glass is 0.185 nm, with a scanning area of 50 × 50 µm2, and the MRR is 8.64 µm h-1. To the best of our knowledge, the MRR is the highest on such a big area of atomic surface for quartz glass. X-ray photoelectron spectroscopy reveals that SiO2@TiO2 core-shell abrasives were used as photocatalysts motivated by simulated solar light, generating electrons and holes and producing hydroxyl radicals through hydrogen peroxide. As a result, OH- could combine with Si atoms on the surface of quartz glass, forming Si-OH-Si bonds. Then the formed bonds were removed based on the balance between chemical and mechanical functions. The proposed CMP, developed SiO2@TiO2 abrasives and slurry provide new insights to achieve an atomic surface of quartz glass with a high MRR.

Atomic surface achieved through a novel cross-scale model from macroscale to nanoscale.

Chemical mechanical polishing (CMP) is widely used to achieve an atomic surface globally, yet its cross-scale polishing mechanisms are elusive. Moreover, traditional CMP normally employs toxic and corrosive slurries, resulting in potential pollution to the environment. To overcome these challenges, a novel cross-scale model from the millimeter to nanometer scale is proposed, which was confirmed by a newly developed green CMP process. The developed CMP slurry consisted of hydrogen peroxide, sodium carbonate, sodium hydroxycellulose, and silica. Prior to CMP, fused silica was polished by a ceria slurry. After CMP, the surface roughness (Sa) was 0.126 nm, the material-removal rate was 88.3 nm min-1, and the thickness of the damaged layer was 8.8 nm. The proposed model was built by fibers, through integrating Eulerian and Lagrangian models and reactive force field-molecular dynamics. The results predicted by the model were in good agreement with those of CMP experimentally. A model for large-sized fibers revealed that a direct contact area of 11.12% was obtained for a non-woven polishing pad during the CMP experiments. Another model constructed via combining Eulerian and Lagrangian functions showed that the stress at the intersections of the fibers varied mainly from 0.1 to 0.01 MPa and was higher than the stress at other parts. An increase in viscosity led to a decrease in the areas with low stress, demonstrating that viscosity enhanced the stress and facilitated the removal of material. At the microscale and nanoscale, the stress of the abrasive surface exposed to the workpiece changed from 2.21 to 6.43 GPa. Stress at the interface contributed to the formation of bridging bonds, further promoting the removal of material. With increasing the compressive stress, the material-removal form was transformed from a single atom to molecular chains. The proposed model and developed green CMP offer new insights to understand the cross-scale polishing mechanism, as well as for designing and manufacturing novel polishing slurries, pads, and setups.

A novel atomic removal model for chemical mechanical polishing using developed mesoporous shell/core abrasives based on molecular dynamics.

To improve polishing performance and reduce the environmental pollution of chemical mechanical polishing (CMP) tests, mesoporous shell/core silica abrasives were prepared, and a novel green CMP slurry was developed, including sorbitol, hydrogen peroxide and sodium carbonate. Prior to CMP, fused silica was roughly polished with ceria slurry. Using developed mesoporous abrasives, surface roughness Sa is reduced from 0.347 to 0.253 nm for a scanning area of 200 × 200 µm2, and the material removal rate (MRR) is increased from 70 to 127 nm min-1, compared with traditional solid abrasives. Based on molecular dynamics (MD) simulations, a novel atomic removal model is proposed for mesoporous abrasives through the immediate elastic recovery of atoms. MD simulations suggest that the formation of convex peaks and pits was inhibited by the mesoporous structure, promoting uniform distribution of surface atoms and atomic removal. This is different from a conventional simple increase of polishing times. In addition, more bridge bonds of Si-O-Si and a lower average Si-O bond order are produced in fused silica samples due to their mesoporous structure, contributing to a higher MRR.

Unprecedented atomic surface of silicon induced by environmentally friendly chemical mechanical polishing.

Silicon (Si) dominates the integrated circuit (IC), semiconductor, and microelectronic industries. However, it is a challenge to achieve a sub-angstrom surface of Si. Chemical mechanical polishing (CMP) is widely used in the manufacturing of Si, while toxic and polluted slurries are usually employed in CMP, resulting in pollution to the environment. In this study, a novel environmentally friendly CMP was developed, in which a slurry is composed of ceria, hydrogen peroxide, sodium pyrophosphate, sodium carboxymethyl cellulose, sodium carbonate, and deionized water. After CMP, the surface roughness Sa was 0.067 nm with a measurement area of 50 × 50 µm2, and a sub-angstrom surface is achieved. To the best of our knowledge, it is the lowest surface roughness in such a large area. Transmission electron microscopy shows that the thickness of the damaged layer after CMP is 2.8 nm. X-ray photoelectron spectroscopy and infrared Fourier transformation reveal that during CMP, a redox reaction firstly took place between Ce3+ and Ce4+. Si and ceria are hydroxylated, forming Si-OH and Ce-OH, then dehydration and condensation occur, generating Si-O-Ce. These findings propose new insights to fabricate a sub-angstrom surface of Si for use in IC, semiconductor, and microelectronic industries.

Surface Modification of Hollow Structure TiO2 Nanospheres for Enhanced Photocatalytic Hydrogen Evolution.

Engineering the surface structure of semiconductor is one of the most promising strategies for improving the separation and transfer efficiency of charge, which is a key issue in photocatalysis. Here, we designed and fabricated the C decorated hollow TiO2 photocatalysts (C-TiO2), in which 3-aminophenol-formaldehyde resin (APF) spheres were used as template and carbon precursor. It was determined that the C content can be easily controlled by calcinating the APF spheres with different time. Moreover, the synergetic effort between the optimal C content and the formed Ti-O-C bonds in C-TiO2 were determined to increase the light absorption and greatly promote the separation and transfer of charge in the photocatalytic reaction, which is verified from UV-vis, PL, photocurrent, and EIS characterizations. Remarkably, the activity of the C-TiO2 is 5.5-fold higher than that of TiO2 in H2 evolution. A feasible strategy for rational design and construction of surface-engineered hollow photocatalysts to improve the photocatalytic performance was provided in this study.

Dispersion and Polishing Mechanism of a Novel CeO2-LaOF-Based Chemical Mechanical Polishing Slurry for Quartz Glass.

Quartz glass shows superior physicochemical properties and is used in modern high technology. Due to its hard and brittle characteristics, traditional polishing slurry mostly uses strong acid, strong alkali, and potent corrosive additives, which cause environmental pollution. Furthermore, the degree of damage reduces service performance of the parts due to the excessive corrosion. Therefore, a novel quartz glass green and efficient non-damaging chemical mechanical polishing slurry was developed, consisting of cerium oxide (CeO2), Lanthanum oxyfluoride (LaOF), potassium pyrophosphate (K4P2O7), sodium N-lauroyl sarcosinate (SNLS), and sodium polyacrylate (PAAS). Among them, LaOF abrasive showed hexahedral morphology, which increased the cutting sites and uniformed the load. The polishing slurry was maintained by two anionic dispersants, namely SNLS and PAAS, to maintain the suspension stability of the slurry, which makes the abrasive in the slurry have a more uniform particle size and a smoother sample surface after polishing. After the orthogonal test, a surface roughness (Sa) of 0.23 nm was obtained in the range of 50 × 50 µm2, which was lower than the current industry rating of 0.9 nm, and obtained a material removal rate (MRR) of 530.52 nm/min.

Iron Single Atoms Anchored on Nitrogen-Doped Carbon Matrix/Nanotube Hybrid Supports for Excellent Oxygen Reduction Properties.

Single-atom non-precious metal oxygen reduction reaction (ORR) catalysts have attracted much attention due to their low cost, high selectivity, and high activity. Herein, we successfully prepared iron single atoms anchored on nitrogen-doped carbon matrix/nanotube hybrid supports (FeSA-NC/CNTs) by the pyrolysis of Fe-doped zeolitic imidazolate frameworks. The nitrogen-doped carbon matrix/carbon nanotube hybrid supports exhibit a specific surface area of 1626.814 m2 g-1, which may facilitate electron transfer and oxygen mass transport within the catalyst and be beneficial to ORR performance. Further electrochemical results revealed that our FeSA-NC/CNTs catalyst exhibited excellent ORR activity (half-wave potential: 0.86 V; kinetic current density: 39.3 mA cm-2 at 0.8 V), superior to that of commercial Pt/C catalyst (half-wave potential: 0.846 V; kinetic current density: 14.4 mA cm-2 at 0.8 V). It also has a great stability, which makes it possible to be a valuable non-noble metal electrode material that may replace the latest commercial Pt/C catalyst in the future.

An X-state solid-liquid mixture with unusual mechanical properties formed by water and coordination polymer nanosheet nanoarchitectonics.

Removal of water from a mixture of water and inorganic solids usually leads to a drastic change in the mechanical properties from liquid-like to brittle solid type. Here, we demonstrate that there is an unusual state, the X state, formed by naturally drying up a dough which is composed of Ni(H2O)2[(Ni(CN)4]·H2O nanosheets and water. This X-state mixture shows mechanical characteristics different from both pure liquids and brittle solids. The deformation curve of the X-state mixture contains three linear parts. However, the deformation is recoverable because the deformation curve can be repeated as long as fracture does not occur. The ice-like water formed among the nanosheets is believed to be an important reason for generating this X-state mixture. The unique properties of the X-state mixture may find applications, such as impact absorbents, which require materials with considerable strength, modulus and toughness.

Metformin Alleviates Hepatic Steatosis and Insulin Resistance in a Mouse Model of High-Fat Diet-Induced Nonalcoholic Fatty Liver Disease by Promoting Transcription Factor EB-Dependent Autophagy.

Nonalcoholic fatty liver disease (NAFLD) results from an abnormal accumulation of lipids within hepatocytes, and is commonly associated with obesity, insulin resistance, and hyperlipidemia. Metformin is commonly used to treat type 2 diabetes mellitus and, in recent years, it was found to play a potential role in the amelioration of NAFLD. However, the mechanisms underlying the protective effect of metformin against NAFLD remain largely unknown. Transcription factor EB (TFEB) is a master transcriptional regulator of lysosomal biogenesis and autophagy and, when activated, is effective against disorders of lipid metabolism. However, the role of TFEB in hepatic steatosis is not well understood. In this report, we demonstrate that the activity of TFEB is reduced in the liver of mice fed a high-fat diet. Metformin treatment significantly reverses the activity of TFEB, and the protective effect of metformin against hepatic steatosis and insulin resistance is dependent on TFEB. We show that metformin-induced autophagy is regulated by TFEB, and our findings reveal that TFEB acts as a mediator, linking metformin with autophagy to reverse NAFLD, and highlight that TFEB may be a promising molecular target for the treatment of NAFLD.

Precisely Engineering Architectures of Co/C Sub-Microreactors for Selective Syngas Conversion.

Fischer-Tropsch synthesis (FTS) is an effective route to produce olefins, gasoline, diesel, and oxygenates from syngas (CO + H2 ). However, it still remains a challenge for regulating the product distribution of FTS. Here, a series of Co/C sub-microreactors with precise designed nanoarchitectures are synthesized for selective syngas conversion. Through a combination of surface protection-assisted etching and following carbonization process, Co/C sub-microreactors with solid cube, double-shelled hollow box, and hollow box architectures, namely, Co/C-Cube, Co/C-DBox, Co/C-Box can be obtained. In FTS, comparing with solid Co/C-Cube, double-shelled hollow structured Co/C-DBox is inclined to grow long-chain hydrocarbon products, whereas hollow structured Co/C-Box avails the formation of short-chain hydrocarbon chemicals. Therefore, shape selective catalysis and controlled product distribution of FTS are realized by tuning the architectures of Co/C sub-microreactors. It is expected to fundamentally unravel the heterogeneous catalytic process via upfront designing and precisely regulating the architectures of micro/nanoreactors.

Modular Construction of Prussian Blue Analog and TiO2 Dual-Compartment Janus Nanoreactor for Efficient Photocatalytic Water Splitting.

Janus structures that include different functional compartments have attracted significant attention due to their specific properties in a diverse range of applications. However, it remains challenge to develop an effective strategy for achieving strong interfacial interaction. Herein, a Janus nanoreactor consisting of TiO2 2D nanocrystals integrated with Prussian blue analog (PBA) single crystals is proposed and synthesized by mimicking the planting process. In situ etching of PBA particles induces nucleation and growth of TiO2 nanoflakes onto the concave surface of PBA particles, and thus enhances the interlayer interaction. The anisotropic PBA-TiO2 Janus nanoreactor demonstrates enhanced photocatalytic activities for both water reduction and oxidation reactions compared with TiO2 and PBA alone. As far as it is known, this is the first PBA-based composite that serves as a bifunctional photocatalyst for solar water splitting. The interfacial structure between two materials is vital for charge separation and transfer based on the spectroscopic studies. These results shed light on the elaborate construction of Janus nanoreactor, highlighting the important role of interfacial design at the microscale level.

Single-Crystal Lattice Filling in Connected Spaces inside 3D Networks.

Connected vessel effects have been widely utilized from ancient times. It is quite interesting to know whether there are any special effects when single-crystal lattices fill the connected spaces inside 3D networks. In some single-crystal and 3D network pairs, there seems to exist a specific rule: when single-crystal lattices fill the connected spaces inside 3D networks, the front of the lattice in each channel is determined by the symmetrical center of the lattice structure. However, this needs to be validated by using various single-crystal lattice to fill the 3D networks with different compositions. Here we report a method to establish a gradient environment which can favor the formation of a micrometer-sized single crystal lattice across various 3D networks. The fronts of the filled lattices form the shapes which are the equilibrium shapes of the single crystals no matter what the single crystals or the 3D networks are, indicating the specific rule while the single-crystal lattices fill the 3D networks. The single crystals filled in the connected spaces inside 3D networks, which are functional materials, and had alternating properties, such as 4-fold higher electronic conductivity, which improve their performance in applications.

Fenofibrate Improves Insulin Resistance and Hepatic Steatosis and Regulates the Let-7/SERCA2b Axis in High-Fat Diet-Induced Non-Alcoholic Fatty Liver Disease Mice.

Fenofibrate is widely used in clinical therapy to effectively ameliorate the development of non-alcoholic fatty liver disease (NAFLD); however, its specific molecular mechanism of action remains largely unknown. MicroRNAs (miRNAs) are key mediators in regulating endoplasmic reticulum (ER) stress during NAFLD, and the deregulation of miRNAs has been demonstrated in NAFLD pathophysiology. The present study aimed to identify whether fenofibrate could influence miRNA expression in NAFLD and investigate the specific mechanism of action of fenofibrate in lipid metabolism disorder-associated diseases. We found that fenofibrate alleviated ER stress and increased the levels of SERCA2b, which serves as a regulator of ER stress. Additionally, the levels of let-7 miRNA were regulated by fenofibrate; let-7 was found to target the 3' untranslated region of SERCA2b. The present data suggest that the protective effects of fenofibrate against insulin resistance and its suppressive activity against excessive hepatic lipid accumulation may be related to the alteration of the let-7/SERCA2b axis and alleviation of ER stress.

Distribution of heavy metals and metalloids in bulk and particle size fractions of soils from coal-mine brownfield and implications on human health.

Heavy metals (HMs) and metalloids migrate into their surroundings, thus increasing environmental risks and threatening human health. Current studies on coal-mine brownfields, however, have not thoroughly investigated soil-associated HMs and metalloids produced by coal mining. Therefore, this study explored the spatial and particle fraction distribution and human health implications of HMs and metalloids. The soil-associated HMs and metalloids are Arsenic (As), Cadmium (Cd), Chromium (Cr), Copper (Cu), Mercury (Hg), Manganese (Mn), Nickel (Ni), Lead (Pb), Scandium (Sc), Titanium (Ti) and Zinc (Zn). Results showed that Cd, Cu, Pb, and Ni were enriched in bulk soils. Cadmium, Cu and Pb from anthropogenic source were mainly found at entrance roadsides and in sites closest to coal mines. HMs and metalloids primarily accumulated in fine fractions (<1, 1-5, and 5-10 µm). Moreover, HM and metalloid loadings substantially accumulated in the 75-250 µm and 250-1000 µm fractions. Most fine soil fractions showed moderate to strong potential ecological risks, whereas all the coarse particle fractions (50-75, 75-250, and 250-1000 µm) presented slight potential ecological risk. Exposure to soil-associated HMs and metalloids mainly occurred via ingestion. The total non-carcinogenic risks to children and adults fell below the safe level of 1, whereas the total carcinogenic risks to these individuals were higher than that of the maximum acceptable level set by the United States Environmental Protection Agency (USEPA, 1 × 10 -4). The total carcinogenic risk was mainly contributed by Cd and Ni through ingestion and dermal access. Therefore, hygiene and food security in areas should be emphasized.

Over-expression of heat shock protein 70 protects mice against lung ischemia/reperfusion injury through SIRT1/AMPK/eNOS pathway.

Lung ischemia/reperfusion injury (LIRI) usually occurs during in lung transplantation and extracorporeal circulation operation and may develop into pulmonary infections, acute rejection and bronchiolitis obliterans syndrome. Recent studies have discovered the protective effect of heat shock protein 70 (HSP70) on various types of injuries. In the present study, we firstly explore the role of over-expressed HSP70 on the protection against LIRI. Lung Wet/Dry (W/D) ratio, biomarkers in the bronchoalveolar lavage fluid (BALF), lung histological changes and apoptosis markers, oxidative products and proinflammatory cytokines in the lung tissues were analyzed. Next, the expression of eNOS, SIRT1 and AMPK were measured. Finally, the changes of the lung W/D ratio and biomarkers in the BALF using the inhibitors of SIRT1/AMPK/eNOS pathway were evaluated. Mice exposed to LIRI procedure had significant increases in lung W/D ratio and biomarkers (protein level, LDH level, leukocytes and total cells) in BALF. LIRI also caused histological injury, demonstrated by hemorrhage, alveolar septal thickening and fibrin deposition. Apoptosis, oxidative products and proinflammatory cytokines in lung tissue were also induced by LIRI. The over-expression of HSP70 antagonized the impacts of LIRI by attenuating these parameters. It significantly increased the expression of eNOS, SIRT1 and AMPK, while the inhibition of SIRT1 and AMPK deactivated the eNOS expression. The lung W/D ratio and biomarkers in BALF were increased while mice were given inhibitors of eNOS, SIRT1 and AMPK. We concluded that over-expression of HSP70 had protective effect on LIRI and HSP70 might be involved in the protection through a SIRT1/AMPK/eNOS pathway.