LASER SHOCK IMPRINTING OF METALLIC NANOSTRUCTURES AND SHOCK PROCESSING OF LOW-DIMENSIONAL MATERIALS

Laser shock imprinting (LSI) is proposed and developed as a novel ultrafast room-temperature top-down technique for fabricating and tuning of plasmonic nanostructures, and processing of one-dimensional semiconductor nanowires and two-dimensional crystals. The technique utilizes a shock pressure generated by laser ablation of sacrificial materials. Compared with conventional technologies, LSI features ambient condition, good scalability, low cost and high efficiency

Social complexification and pig (Sus scrofa) husbandry in ancient China : a combined geometric morphometric and isotopic approach

Funding: This work was supported by the CNRSCASS program for the training of Chinese PhD students.Peer reviewedPublisher PD

Laser Shock Tuning Dynamic Interlayer Coupling in Graphene–Boron Nitride Moiré Superlattices

In the emergence of graphene and many two-dimensional (2D) materials, the most exciting applications come from stacking them into 3D devices, promising many excellent possibilities for neoteric electronics and optoelectronics. Layers of semiconductors, insulators, and conductors can be stacked to form van der Waals heterostructures, after the weak bonds formed between the layers. However, the interlayer coupling in these heterostructures is usually hard to modulate, resulting in difficulty to realize their emerging optical or electronic properties. Especially, the relationship between interlayer distance and interlayer coupling remains to be investigated, due to the lack of effective technology. In this work, we have used laser shocking to controllably tune the interlayer distance between graphene (Gr) and boron nitride (BN) in the Gr/BN/Gr heterostructures and the strains in the 2D heterolayers, providing a simple and effective way to modify their optic and electronic properties. After lase shocking, the reduction of interlayer distance is calculated by molecular dynamics (MD) simulation. Some atoms in Gr or BN are out-of-plane as well. In Raman measurements, the G peak in the heterostructure shows a red-shifted trend after laser shocking, indicating the strong phonon coupling in the interlayer. Moreover, the larger transparency after laser shocking also verifies the stronger photon coupling in the heterostructure. To investigate the effects of the interlayer coupling of heterostructure on its out-of-plane electronic behavior, we have investigated the electronic tunneling behavior. The heterostructure after laser shock reveals a lager tunneling current and lower tunneling threshold, proving an unexpected better electrical property. From DFT calculations, laser shocking can modulate the band gap structure of graphene in Gr/BN/Gr heterostructures; therefore, the heterostructures can be implemented as a unique photonic platform to modulate the emission characters of the anchored CdSe/ZnS core–shell quantum dots. Remarkably, the effective laser shocking method is also applicable to various otherwise noninteracting 2D materials, resulting in many new phenomena, which will lead science and technology to unexplored territories

Molecular engineering tuning optoelectronic properties of thieno[3,2-b]thiophenes-based electrochromic polymers

Thieno[3,2-b]thiophene (TT) monomers end-capped with 3,4-ethylenedioxythiophene (EDOT) moieties are electropolymerized to form pi-conjugated polymers with distinct electrochromic (EC) properties. Steric and electronic factors (electron donor and acceptor substituents) in the side groups of the TT core, as well as the structure of the polymer backbone strongly affect the electrochemical and optical properties of the polymers and their electrochromic characteristics. The studied polymers show low oxidation potentials, tunable from-0.78 to +0.30 V (vs. Fc/Fc(+)) and the band gaps from 1.46 to 1.92 eV and demonstrate wide variety of color palettes in polymer films in different states, finely tunable by structural variations in the polymer backbone and the side chains. EC materials of different colors in their doped/dedoped states have been developed (violet, deep blue, light blue, green, brown, purple-red, pinkish-red, orange-red, light gray, cyan and colorless transparent). High optical contrast (up to 79%), short response time (0.57-0.80 s), good cycling stability (up to 91% at 2000 cycles) and high coloration efficiency (up to 234.6 cm(2) C-1) have been demonstrated and the influence of different factors on the above parameters of EC polymers have been discussed.Shenzhen Key Laboratory of Organic Optoelectromagnetic Functional Materials of Shenzhen Science and Technology Plan [ZDSYS20140509094114164]; Shenzhen Peacock Program [KQTD2014062714543296]; Shenzhen Science and Technology Research Grant [JCYJ20140509093817690]; Nanshan Innovation Agency Grant [KC2015ZDYF0016A]; Guangdong Key Research Project [2014B090914003, 2015B090914002]; Guangdong Talents Project; National Basic Research Program of China [2015CB856505]; National Natural Science Foundation of China [51373075]; Guangdong Academician Workstation [2013B090400016]; Natural Science Foundation of Guangdong Province [2014A030313800]; Santander Universities Research Mobility AwardSCI(E)中国科学引文数据库(CSCD)ARTICLE163-766

Direct visualization of electric current induced dipoles of atomic impurities

Learning the electron scattering around atomic impurities is a fundamental step to fully understand the basic electronic transport properties of realistic conducting materials. Although many efforts have been made in this field for several decades, atomic scale transport around single point-like impurities has yet been achieved. Here, we report the direct visualization of the electric current induced dipoles around single atomic impurities in epitaxial bilayer graphene by multi-probe low temperature scanning tunneling potentiometry as the local current density is raised up to around 25 A/m, which is considerably higher than that in previous studies. We find the directions of these dipoles which are parallel or anti-parallel to local current are determined by the charge polarity of the impurities, revealing the direct evidence for the existence of the carrier density modulation effect proposed by Landauer in 1976. Furthermore, by $in$ $situ$ tuning local current direction with contact probes, these dipoles are redirected correspondingly. Our work paves the way to explore the electronic quantum transport phenomena at single atomic impurity level and the potential future electronics toward or beyond the end of Moore's Law

A grazing Gomphotherium in Middle Miocene Central Asia, 10 million years prior to the origin of the Elephantidae

Feeding preference of fossil herbivorous mammals, concerning the coevolution of mammalian and floral ecosystems, has become of key research interest. In this paper, phytoliths in dental calculus from two gomphotheriid proboscideans of the middle Miocene Junggar Basin, Central Asia, have been identified, suggesting that Gomphotherium connexum was a mixed feeder, while the phytoliths from G. steinheimense indicates grazing preference. This is the earliest-known proboscidean with a predominantly grazing habit. These results are further confirmed by microwear and isotope analyses. Pollen record reveals an open steppic environment with few trees, indicating an early aridity phase in the Asian interior during the Mid-Miocene Climate Optimum, which might urge a diet remodeling of G. steinheimense. Morphological and cladistic analyses show that G. steinheimense comprises the sister taxon of tetralophodont gomphotheres, which were believed to be the general ancestral stock of derived “true elephantids”; whereas G. connexum represents a more conservative lineage in both feeding behavior and tooth morphology, which subsequently became completely extinct. Therefore, grazing by G. steinheimense may have acted as a behavior preadaptive for aridity, and allowing its lineage evolving new morphological features for surviving later in time. This study displays an interesting example of behavioral adaptation prior to morphological modification

Physics-Informed Machine Learning for Accurate Prediction of Temperature and Melt Pool Dimension in Metal Additive Manufacturing

The temperature distribution and melt pool size have a great influence on the microstructure and mechanical behavior of metal additive manufacturing process. The numerical method can give relatively accurate results but is time-consuming and, therefore, unsuitable for in-process prediction. Owing to its remarkable capabilities, machine learning methods have been applied to predict melt pool size and temperature distribution. However, the success of traditional data-driven machine learning methods is highly dependent on the amount and quality of the training data, which is not always convenient to access. This article proposes a physics-informed machine learning (PIML) method, which integrates data and physics laws in the training parts, overcoming the problems of low speed and data availability. An artificial neural network constrained by the heat transfer equation and a small amount of labeled data is developed to predict the melt pool size and temperature distribution. Besides, the locally adaptive activation function is utilized to improve the prediction performance. The result shows that the developed PIML model can accurately predict the temperature and melt pool dimension under different scanning speeds with a small amount of labeled data, which shows significant potential in practical application

Laser shock peening enables 3D gradient metal structures:A case study on manufacturing self-armored hydrophobic surfaces

Gradient heterostructures typically exhibit excellent mechanical properties. The traditional laser shock method can produce only 1D or 2D gradient structures along the thickness of a material. In this study, we propose a technique called 3D gradient laser shock peening without coating (3LSPwoC) for manufacturing 3D gradient metal structures. An excellent application of this method is the manufacture of multi-scale hydrophobic surfaces with integrated enhanced armor (IE-armor) in a flexible, large-scale and low-cost manner. Hydrophobic surfaces of metals are of great importance, but are typically mechanically fragile and degrade quickly, as the surface nanostructures tend to break under mechanical forces. Current approaches either expose the functional large-aspect-ratio nanostructures directly to external forces or have unbalanced strength-ductility synergy for dynamic loads, resulting in degradation of the properties. A self-armored hydrophobic surface structure was obtained by a combination of laser shock and low surface energy treatment. An IE-armor structure with a well-designed strength-ductility synergy was considered to protect the rich nano-hydrophobic structures. The arrayed micro-pits and abundant micro-nano structures in the pits realized a stable Cassie-Baxter state, resulting in a superhydrophobic surface. The alternating regular distribution of hard and sub-hard domains on the metal surface, together with the soft domain in the core, formed a 3D gradient structure, which achieved excellent synergistic plastic deformation and provided superior mechanical robustness. The 3D gradient metal structure manufactured using the 3LSPwoC process is expected to play a crucial role in highly reliable functional surfaces in aerospace, locomotive manufacturing, and ocean engineering