Stress-Relief Engineering in a N-Doped C-Modified Hierarchical Nanoporous Si Anode with a Microcurved Pore Wall Structure for Enhanced Lithium Storage.

The commercialization of alloy-type anodes has been hindered by rapid capacity degradation due to volume fluctuations. To address this issue, stress-relief engineering is proposed for Si anodes that combines hierarchical nanoporous structures and modified layers, inspired by the phenomenon in which structures with continuous changes in curvature can reduce stress concentration. The N-doped C-modified hierarchical nanoporous Si anode with a microcurved pore wall (N-C@m-HNP Si) is prepared from inexpensive Mg-55Si alloys using a simple chemical etching and heat treatment process. When used as the anode for lithium-ion batteries, the N-C@m-HNP Si anode exhibits initial charge/discharge specific capacities of 1092.93 and 2636.32 mAh g-1 at 0.1 C (1 C = 3579 mA g-1), respectively, and a stable reversible specific capacity of 1071.84 mAh g-1 after 200 cycles. The synergy of the hierarchical porous structure with a microcurved pore wall and the N-doped C-modified layer effectively improves the electrochemical performance of N-C@m-HNP Si, and the effectiveness of stress-relief engineering is quantitatively analyzed through the theory of elastic bending of thin plates. Moreover, the formation process of Li15Si4 crystals, which causes substantial mechanical stress, is investigated using first-principles molecular dynamic simulations to reveal their tendency to occur at different scales. The results demonstrate that the hierarchical nanoporous structure helps to inhibit the transformation of amorphous LixSi into metastable Li15Si4 crystals during lithiation.

Chemically monodisperse tin nanoparticles on monolithic 3D nanoporous copper for lithium ion battery anodes with ultralong cycle life and stable lithium storage properties.

In this report, a simple and effective low-temperature synthesis route has been proposed to smoothly achieve monodisperse tin nanoparticles upon monolithic 3D nanoporous copper (3D-NPC@MTNPs) from chemical dealloying of as-cast Al-45 at% Cu alloy sheets in HCl solution; they exhibit superior Li storage properties and ultralong cycle life as the anode for lithium ion batteries (LIBs). The results show that the 3D-NPC@MTNPs composite can be fabricated on a large scale by electroless plating of Sn on a uniform NPC matrix with a pore size of ca. 200 nm in an acidic plating bath below room temperature. Compared to two dimensional copper foil supported tin thin films (2D-CF@TTFs), the 3D-NPC@MTNPs electrode displays a markedly higher first reversible capacity of 0.485 mA h cm-2 as well as superior cycling stability with 52.4% capacity retention and over 96.7% coulombic efficiency after 500 cycles. This can be largely ascribed to the synergistic effect between the favorable monodispersity of Sn nanoparticles with ultrafine particle size and single crystal nature and the unique 3D nanoporous electrode architecture with a large specific surface area and a good mass transfer channel, which facilitates the accommodation of mechanical strain, improvement of structural stability, enhancement of bonding force, and acceleration of mass transfer, which are indicative of a quite promising candidate as a high-performance anode for LIBs.

An Available Technique for Preparation of New Cast MnCuNiFeZnAl Alloy with Superior Damping Capacity and High Service Temperature.

Manganese (Mn)-copper (Cu)-based alloys have been found to have damping capacity and can be used to reduce harmful vibrations and noise effectively. M2052 (Mn-20Cu-5Ni-2Fe, at%) is an important branch of Mn-Cu-based alloys, which possesses both excellent damping capacity and processability. In recent decades, lots of studies have been carried out on the performance optimization of M2052, improving the damping capacity, mechanical properties, corrosion resistance, and service temperature, etc. The major methods of performance optimization are alloying, heat treatment, pretreatment, and different ways of molding etc., among which alloying, as well as adopting a reasonable heat treatment, is the simplest and most effective method to obtain perfect and comprehensive performance. To obtain the M2052 alloy with excellent performance for casting molding, we propose to add Zn and Al to the MnCuNiFe alloy matrix and use a variety of heat treatment methods for a comparison in the microstructure, damping capacity, and service temperature. Thus, a new type of cast-aged Mn-22.68Cu-1.89Ni-1.99Fe-1.70Zn-6.16Al (at.%) alloy with superior damping capacity and high service temperature is obtained by an optimized heat treatment method. Compared with the forging technique, cast molding is simpler and more efficient, and the damping capacity of this as-cast alloy is excellent. Therefore, there is a suitable reason to think that it is a good choice for engineering applications.

Reduction of thermal conductivity in silicene nanomesh: insights from coherent and incoherent phonon transport.

Silicene nanomesh (SNM), a silicene sheet with periodically arranged nanoholes, has gained increasing interest due to its unique geometry and novel properties. In this paper, we have conducted molecular dynamics simulations to study the phonon transport properties of SNMs. The results demonstrate that the thermal conductivity of SNM, which is shown to be much lower than that of silicene, is little affected by temperature but can be effectively tuned by varying the porosity. To elucidate the underlying mechanisms for decreased thermal conductivity, we have investigated both coherent and incoherent phonon transport in SNMs. It is found that the phonon backscattering at the nanopore edges leads to extra thermal resistances. Additionally, the introduction of nanopores induces phonon localization and consequently hinders phonon transport in SNMs. The phonons of SNM exhibit coherent resonant behavior, which is believed to reduce the phonon group velocities and thus leads to a further reduction in thermal conductivity of SNMs. Our findings could be useful in the design of thermal properties of silicene for applications in thermoelectrics, thermal insulation and thermal protection.

Temperature-induced surface reconstruction and interface structure evolution on ligament of nanoporous copper.

Micromorphology and atomic arrangement on ligament surface of nanoporous metals play a vital role in maintaining the structural stability, adjusting the reaction interface and endowing the functionality. Here we offer an instructive scientific understanding for temperature-induced surface reconstruction and interface structure evolution on ligament of nanoporous copper (NPC) based on systematically experimental observations and theoretical calculations. The results show that with dealloying temperature increasing, ligament surface micromorphology of NPC evolves from smooth to irregularity and to uniformly compressed semisphere, and finally to dispersed single-crystal nanoparticles accompanying with significant changes of interface structure from coherence to semi-coherence and to noncoherence. It can guide us to impart multifunctionality and enhanced reaction activity to porous materials just through surface self-modification of homogeneous atoms rather than external invasion of heteroatoms that may bring about unexpected ill effects, such as shortened operation life owing to poisoning.

Shear deformation-induced anisotropic thermal conductivity of graphene.

Graphene-based materials exhibit intriguing phononic and thermal properties. In this paper, we have investigated the heat conductance in graphene sheets under shear-strain-induced wrinkling deformation, using equilibrium molecular dynamics simulations. A significant orientation dependence of the thermal conductivity of graphene wrinkles (GWs) is observed. The directional dependence of the thermal conductivity of GWs stems from the anisotropy of phonon group velocities as revealed by the G-band broadening of the phonon density of states (DOS), the anisotropy of thermal resistance as evidenced by the G-band peak mismatch of the phonon DOS, and the anisotropy of phonon relaxation times as a direct result of the double-exponential-fitting of the heat current autocorrelation function. By analyzing the relative contributions of different lattice vibrations to the heat flux, we have shown that the contributions of different lattice vibrations to the heat flux of GWs are sensitive to the heat flux direction, which further indicates the orientation-dependent thermal conductivity of GWs. Moreover, we have found that, in the strain range of 0-0.1, the anisotropy ratio of GWs increases monotonously with increasing shear strain. This is induced by the change in the number of wrinkles, which is more influential in the direction perpendicular to the wrinkle texture. The findings elucidated here emphasize the utility of wrinkle engineering for manipulation of nanoscale heat transport, which offers opportunities for the development of thermal channeling devices.

Adhesion contact deformation in nanobridge tests.

An accurate grasp of the mechanical properties, especially Young's moduli, of one dimensional nanomaterials plays a crucial role in the design and safe service of flexible electronic devices and implanted biomedical sensors. Nanobridge tests are widely used in the characterization of the mechanical properties of nanowires. In these tests, an atomic force microscope (AFM), functioning as a test machine, exerts a force to bend a nanowire suspended across a trench or a hole with the two ends fixed on a template or substrate. Adhesion contact deformation occurs inevitably during nanobridge testing between the AFM tip and the tested sample, thereby underestimating the Young's modulus of the tested nanowire and causing a pseudo-size effect in the determined Young's modulus. The present work systematically investigates the adhesion contact deformation in nanobridge tests and provides an analytical approach to evaluate the contact deformation and to determine the Young's modulus. To illustrate the developed methodology, AFM nanobridge tests were conducted on gold nanowires (180-340 nm wide, 3.6-5.1 µm long and 90 nm thick). The results indicate that when the contact deformation was taken into consideration, the average Young's modulus increased by 4.63%. Guidelines for minimizing the impact of contact deformation in practical experiments are presented. Furthermore, the results provide insight into the probable causes of the variation in experimentally obtained size-dependencies of Young's moduli of nanowires.

A facile one-pot oxidation-assisted dealloying protocol to massively synthesize monolithic core-shell architectured nanoporous copper@cuprous oxide nanonetworks for photodegradation of methyl orange.

In this report, a facile and effective one-pot oxidation-assisted dealloying protocol has been developed to massively synthesize monolithic core-shell architectured nanoporous copper@cuprous oxide nanonetworks (C-S NPC@Cu2O NNs) by chemical dealloying of melt-spun Al 37 at.% Cu alloy in an oxygen-rich alkaline solution at room temperature, which possesses superior photocatalytic activity towards photodegradation of methyl orange (MO). The experimental results show that the as-prepared nanocomposite exhibits an open, bicontinuous interpenetrating ligament-pore structure with length scales of 20 ± 5 nm, in which the ligaments comprising Cu and Cu2O are typical of core-shell architecture with uniform shell thickness of ca. 3.5 nm. The photodegradation experiments of C-S NPC@Cu2O NNs show their superior photocatalytic activities for the MO degradation under visible light irradiation with degradation rate as high as 6.67 mg min-1 gcat-1, which is a diffusion-controlled kinetic process in essence in light of the good linear correlation between photodegradation ratio and square root of irradiation time. The excellent photocatalytic activity can be ascribed to the synergistic effects between unique core-shell architecture and 3D nanoporous network with high specific surface area and fast mass transfer channel, indicating that the C-S NPC@Cu2O NNs will be a promising candidate for photocatalysts of MO degradation.

Laser acupuncture and prevention of bone loss in tail-suspended rats.

BACKGROUND: Skeletal unloading during spaceflight results in bone loss. This study investigated whether laser acupuncture could be an effective countermeasure to prevent unloading-induced bone loss in rats. METHODS: There were 18 rats that were randomly assigned into three groups: a control group, a tail-suspended group (TS), and a tail-suspended with laser acupuncture treatment group (TSA). The rats in the TSA group were treated with laser acupuncture at the KI1 (Yong Quan) and ST36 (Zu San Li) acupoints of the left leg for 3 min per day. Bone mineral density (BMD), biomechanical properties, and histomorphometry of both tibiae were determined after the animals were euthanized at the end of week 4. RESULTS: Compared with the control group, BMD in the TS group significantly decreased by 12.3% in cortical bone and 15.1% in cancellous bone, whereas BMD in the TSA group decreased by only 3.1% in cortical bone and 9.0% in cancellous bone. The hardness of cortical bone dropped 44.1% in the TS group and 22.3% in the TSA group compared with the control group. The histomorphometry data were in accordance with BMD measurements. Although acupuncture treatment was applied only to the left side, we observed similar changes between the measurements of both the left and right tibiae. CONCLUSION: Laser acupuncture on KI1 and ST36 can inhibit bone loss in rats subjected to unloading. The fact that similar changes between the right and left sides when only the left limbs were treated suggests that the preventive effect of laser acupuncture occurs via a systemic regulation.

Low intensity pulsed ultrasound increases the matrix hardness of the healing tissues at bone-tendon insertion-a partial patellectomy model in rabbits.

BACKGROUND: This study evaluated the low intensity pulsed ultrasound enhancement on matrix hardness of the healing tissues at the bone-tendon junction. METHODS: Sixteen 18 week-old mature female rabbits were used. An established transverse partial patellectomy was performed at the distal one-third of the patella. Animals were then divided according to their body weight into ultrasound group (n = 8) with daily treatment of low intensity pulsed ultrasound and control group (n = 8) without ultrasound treatment. Animals were euthanized at week 8 and 16 postoperatively to evaluate the radiographic new bone formation and the Vickers hardness of the matrix of the healing tissues at the bone-tendon junction. FINDINGS: (1) Comparing with the control group, the anterior-posterior area of the new bone in the ultrasound treated group was found on average to be 3.0 and 3.1 times greater at week 8 and 16, respectively (P < 0.01). (2) The Vickers hardness of the new bone in ultrasound group was 11.3% (P < 0.05) significantly lower at week 8 but 20.0% (P < 0.05) significantly higher at week 16 as compared with that of the control group. (3) The Vickers hardness of the newly regenerated fibrocartilage zone, healing tendon, and cartilaginous metaplasia in ultrasound group was found higher than the control group at both week 8 and 16, but the difference was significant at week 16 only, being 44.1% (P < 0.05), 20.1% (P < 0.01), and 46.4% (P < 0.01) higher, respectively. INTERPRETATION: The preliminary findings suggested for the first time that low intensity pulsed ultrasound treatment resulted in the enhancement of the matrix hardness in new bone, fibrocartilage, cartilaginous metaplasia, and healing tendon at the healing bone-tendon junction. These findings can be extrapolated into clinical practice, i.e. the more rapid healing induced by low intensity pulsed ultrasound, the earlier mobilization of the affected joint. The beneficial effects on prevention of the musculoskeletal deterioration resulting from the prolonged immobilization would be therefore expected.

Regional variations in microstructural properties of vertebral trabeculae with structural groups.

STUDY DESIGN: Micro-computed tomography (CT) scanning to investigate three-dimensional microstructural properties of L4 vertebral bodies. OBJECTIVE: To identify the regional variations in the three-dimensional microstructural properties of vertebral cancellous bones with respect to structural types for the prediction of related regional fracture risks. SUMMARY OF BACKGROUND DATA: The literature contains no reports on regional variations in morphologic properties of vertebral trabeculae with microstructural types, which may shed light on the patterns of osteoporotic fractures. METHODS: Ninety cubic cancellous specimens were obtained from 6 normal L4 vertebral bodies of 6 male donors 62 to 70 years of age and were scanned using a high-resolution micro-CT system. These specimens were further divided into two groups according to the average structure model index (SMI) of the 15 trabecular specimens in each vertebral body. Adjustment for age differences was done for the microstructural parameters, i.e.-, bone volume fraction, trabecular number, trabecular thickness, structure model index, degree of architectural anisotropy, and connectivity density, to allow investigation on the regional variations in different transverse layers and vertical columns independent of age. RESULTS: Trabecular specimens with lower mass were liable to form high-SMI group and the differences in all parameters reached significance level either between columns or between layers from two groups. CONCLUSIONS: The anterior column in the high-SMI group is more susceptible to vertebral body wedge fracture; and in the low-SMI group, off-axis bone damage is most harmful to the central column of vertebral trabeculae. The data obtained may help to identify the most critical locations of fracture risks at an early stage and provide a microstructural basis for the repair and clinical treatment of vertebral fractures.

Effect of surface roughness on dip-pen nanolithography.

In the present work, five gold thin films with various surface roughnesses were prepared by sputtering and the influence of the surface roughness of gold substrate on dip-pen nanolithography (DPN) was studied using 1-octadecanethiol (ODT) and poly(vinylidene fluoride-trifluorethylene) [P(VDFTrFE)] as inks. It was shown that surface roughness influences both the contrast in lateral force microscopy (LFM) images and the transport rate of ink. Surfaces with less roughness give good contrast in LFM images, while rough surfaces give poor contrast. The transport rate of ink increases as the roughness decreases; however, the extent of the influence is strongly ink-dependent.

Nanofabrication with atomic force microscopy.

Atomic force microscopy (AFM) was developed in 1986. It is an important and versatile surface technique, and is used in many research fields. In this review, we have summarized the methods and applications of AFM, with emphasis on nanofabrication. AFM is capable of visualizing surface properties at high spatial resolution and determining biomolecular interaction as well as fabricating nanostructures. Recently, AFM-based nanotechnologies such as nanomanipulation, force lithography, nanografting, nanooxidation and dip-pen nanolithography were developed rapidly. AFM tip (typical radius ranged from several nanometers to tens of nanometers) is used to modify the sample surface, either physically or chemically, at nanometer scale. Nanopatterns composed of semiconductors, metal, biomolecules, polymers, etc., were constructed with various AFM-based nanotechnologies, thus making AFM a promising technique for nanofabrication. AFM-based nanotechnologies have potential applications in nanoelectronics, bioanalysis, biosensors, actuators and high-density data storage devices.