In this reaserch, we report the development of surfactant free-gold nanoparticle (AuNP)-DNA complexes that remained stable in solutions with extremely high ionic strength, using seawater as a model solution. Although the stability of AuNPs can be increased to a certain degree by functionalizing negatively charged DNA strands on their surface, they still have limited stability in highly concentrated salt solutions. However, we found that AuNPs functionalized with poly T (thymine) bases have exceptional stability in high ionic strength solutions. For example, AuNPs functionalized with a 5T spacer remained highly stable in seawater, with no color change and no red-shift in absorbance spectra for up to 9 days. Using this surprising property of poly T spacers, we prepared highly stable AuNP-DNA complexes containing random sequences by introducing 5T spacers on the random sequenced DNA strand. The random sequenced AuNP-DNA complexes remained stable in seawater, several molar concentrations of monovalent metal ion solutions (6.1 M Na+ or 4.8 M K+), and millimolar concentrations of diverse divalent metal ions. In addition, the highly stable AuNP-DNA complex maintained biological activity in seawater, which was demonstrated by complementary reaction and aptamer based biosensing. These results provide important insight into NP use for various applications under harsh biological and environmental conditions.

Stable cycling of lithium metal anode is challenging due to the dendritic lithium formation and high chemical reactivity of lithium with electrolyte and nearly all the materials. Here, we demonstrate a promising novel electrode design by growing two-dimensional (2D) atomic crystal layers including hexagonal boron nitride (h-BN) and graphene directly on Cu metal current collectors. Lithium ions were able to penetrate through the point and line defects of the 2D layers during the electrochemical deposition, leading to sandwiched lithium metal between ultrathin 2D layers and Cu. The 2D layers afford an excellent interfacial protection of Li metal due to their remarkable chemical stability as well as mechanical strength and flexibility, resulting from the strong intralayer bonds and ultrathin thickness. Smooth Li metal deposition without dendritic and mossy Li formation was realized. We showed stable cycling over 50 cycles with Coulombic efficiency ?97% in organic carbonate electrolyte with current density and areal capacity up to the practical value of 2.0 mA/cm2and 5.0 mAh/cm2, respectively, which is a significant improvement over the unprotected electrodes in the same electrolyte.

With rapid increase of efficiency from 3.8% to 17.9%, hybrid organic-inorganic perovskite solar cells have attracted much attention because of the excellent properties of organo-lead halide perovskite materials, which makes perovskite solar cells to be a promising candidate of next generation photovoltaic technology. However, the employment of organic hole transport materials and noble metal counter electrode increased its material cost and added the complexity of manufacture process, which has been regard as a potential hurdle for large-scale production and practical application. It is desirable to develop perovskite solar cells using low-cost materials with simple manufacturing process. Here, we reported perovskite heterojunction solar cells, fabricated with fully screen printing method in atmosphere environment using mesoporous TiO2 as electron transport layer, mesoporous ZrO2 as spacer layer and mesoporous NiO as active interfacial layer, respectively, whose pore was penetrated perovskite (CH3NH3PbI3) as light absorber, achieving a promising power conversion efficiency of 12.4% when measured under AM1.5G illumination. This fully printable device with all-inorganic materials offers a viable pathway to develop efficient low-cost solar cells with attractive properties for scale up and practical applications.

Adequate strength, tailored stiffness, and an interconnected porous architecture are crucial requirements for engineered bone tissue scaffolds; however high porosity reduces mechanical properties, making it difficult to fabricate scaffolds with the required mechanical properties (1). A potential solution to this on-going problem is the deposition of a stiff and strong polymer-nanocomposite coating onto a porous template using layer-by-layer (LbL) assembly. This technique involves the alternate deposition of oppositely charged electrolyte complexes (e.g. polymer and nanoparticles) onto a substrate resulting in the formation of multilayer films, and is one of the most versatile means to control film properties and molecular architecture at the nanoscale (2). The aim of this study was to adapt LbL assembly to fabricate nanocomposite coatings onto porous substrate, enabling customisation of mechanical properties and porosity to obtain materials suitable for bone tissue scaffold applications. LbL deposition was conducted using aqueous solutions of polyethyleneimine (PEI), polyacrylic acid (PAA) and nanoclay (MTM) (Sigma Aldrich), prepared as previously described (3). Open-cell polyurethane (PU) foam substrates (30 PPI, EasyFoam Ltd.) were alternately subjected to cationic (PEI), and anionic (PAA and MTM) solutions using a custom-built apparatus. The deposition of a single PEI/PAA/PEI/MTM multilayer was repeated in intervals of 5 multilayers to obtain the desired number. The coated samples were dried for 24 h after each interval and the total mass of the coating was determined before deposition of subsequent multilayers. The mechanical properties of coated foams were determined by quasi-static mechanical testing in compression. The physical properties of the multilayer film can be tailored by changing certain process parameters (4): pH of solutions, drying and deposition times, and salt concentration. These variables were systematically altered and the effect on deposition rate and mechanical properties were measured. The mass and thickness of the multilayer coating were found to correlate directly with the number of layers deposited. The elastic modulus of coated substrates increased by over an order of magnitude with the deposition of 60 multilayers. A micromechanical model for open-cell foams (5) was adapted to predict the porosity and mechanical properties of coated open-cell foams. It is expected that these results will serve as a guide to the design of scaffold materials with tailored stiffness and porosity within a suitable range for bone tissue scaffold materials. References 1. Hutmacher, D. (et al.), J Tissue Eng Regen M, 1: 245-60, 2007 2. Yoo, D. (et al), Nano Lett, 8: 1762-70, 2008 3. Ziminska, M. (et al.), Proceedings of the 26th ESB Conference, Liverpool, UK, 2014 4. Dubas, S. (et al.), Macromolecules, 32: 8153-60, 1999 5. Ashby, M. (et al.), Phil. Trans. R. Soc. A, 364: 15-30, 2006

Group VI transition metal dichalcogenides monolayers MX2 (MoS2, MoSe2, WS2,and WSe2) feature a spin splitting with opposite sign in the two degenerate but inequivalent valleys located at corners of 1st Brillouin zone. This spin-valley coupling, particularly pronounced in tungsten dichalcogenides, along with nonzero but contrasting Berry curvatures at K valleys can benefit potential spintronics and valleytronics with the important consequences of spin-valley interplay and the suppression of spin and valley relaxations. In this talk we address the spin-valley coupling in 2D WS2 with optical spectroscopy and photocurrent spectroscopy. This giant spin-valley coupling, together with the valley dependent Berry curvature, may lead to rich possibilities for manipulating spin and valley degrees of freedom in these 2D semiconductors.

Ion-induced reduction of metal oxides is a widely reported phenomenon. Previous studies have used surfaces-sensitive techniques such as x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) to link the phenomenon to the energy of formation of an oxide, preferential sputtering and bombardment-induced segregation of different elements. This study investigates the effective depth of ion-induced reduction on representative iron oxides (hematite Fe2O3, goethite FeOOH and magnetite Fe3O4) using synchrotron radiation. By varying the incident photon energies, oxidation states at different depths can be probed with consistent charge compensation. The spectra are resolved on energy sensitive Tougaard�s background, in comparison to a more convenient Shirley�s one. Complementary information is also obtained using x-ray absorption of near-edge structure (XANES). The study aims to establish a correlation between ion doses and the extent of reduction induced by them. This understandings may lead to a novel way to include a structurally integrated metallic state in a surface thin film of oxides.

Silicon industry has been doing very successfully in the last decades mainly by scaling down the silicon devices. InAs nanowires (NWs) are competitive candidates for high performance n-type devices owing mainly to their high electron mobility. However, the ability to improve the performance of InAs NW field effect transistors (FETs) through scaling down has not been studied a lot. To make things complicated, InAs NWs may have zinc blend (ZB) or wurtzite (WZ) phases, or even mixture of ZB and WZ phases when their diameters are different. Our previous studies demonstrate excellent off characteristics and enhancement-mode in FETs based on ultrathin (with sub-10 nm diameter) InAs NWs having pure WZ structure.[1, 2] High Ion/Ioff ratio up to 108, and subthreshold swing of 120 mV/decade have been observed. Diameter-dependent property changes have been studied and quantum confinement effects have been considered. Here, we study the effect of shortening the channel length of the InAs NWs FETs. FETs with the channel length down to tens of nanometers are fabricated and studied. Ballistic transport is observed in short channel devices. The effects of different phases are also studied. Reference: [1] Mengqi Fu, Dong Pan, Yingjun Yang, Tuanwei Shi, Zhiyong Zhang, Jianhua Zhao, H. Q. Xu and Qing Chen*, Appl. Phys. Lett. 105 (2014) 143101. [2] D. Pan, M. Q. Fu, X. Z. Yu, X. L. Wang, L. J. Zhu, S. H. Nie, S. L. Wang, Q. Chen, P. Xiong, S. von Moln�r, J. H. Zhao, Nano Lett., 14(2014), 1214.

Controlling the flow of electric charges enables nanoelectronics and modernizes the information technology. The spin degree of freedom of electrons embraces emerging spintronics, important to solid-state computing. The atomic membrane of transition metal dichalcogenides (TMDs) possesses a nonequivalent carrier distribution in crystal momentum space. The protection from its broken inversion symmetry makes the valley index of charge carriers a new degree of freedom for information processing. A variety of valleytronic devices such as valley filters, valves, and thermoelectric valley current have been proposed. Optical control and detection of valley polarization has been reported in monolayer TMDs due to the valley optical selection rules. However, electrical generation and control of valley-polarized carriers that is the key to the utilization of the valley degree of freedom in nanoelectronics, yet remains a formidable challenge. Here we experimentally demonstrate valley-polarized light emission by electrical spin-polarized carriers injection into monolayer WS2 using the ferromagnetic semiconductor, (Ga, Mn)As, as a spin aligner. The valley polarization is electrically generated due to the unique spin-valley locking, i.e., valley polarization is achieved through spin polarization of the charge carriers. Our valley polarization heterojunction becomes a circularly polarized light source due to the direct band gap and valley degree of freedom of monolayer WS2. The unique correlation between spin and valley indices of electric carriers opens the new dimension in utilizing both spin and valley for next-generation electronics and computing.

ZnO nanostructures have attracted tremendous attention in the field of ultraviolet (UV) optoelectronic devices for their wide band gap and large exciton binding energy. Various methods have been applied to gain high quality ZnO nanorods (NRs) array. However, these methods usually require complex set-up and the product yield is low. Besides growth, intentionally incorporating dopant to manipulate the electrical performance of the UV devices based on ZnO NRs is of great significance. Nevertheless, the dopants introduce structural defects in the core of NRS, impairing the UV emission. To address above noted challenges, we propose a two-step methodology of growing Ga doped core-shell ZnO NRs with enhanced optical property. Firstly, undoped ZnO NRs array is grown on p-GaN wafer by low-cost hydrothermal method in our experiments. Successively, the NRs array is annealed and serves as template to be coated with gallium doped zinc oxide (GZO) thin film by pulsed laser deposition. The structure is designed to show two advantages. On the one hand, the Ga doped shell builds up high concentration electron layer to prevent the holes from diffusing to the surface and suppresses their recombination with deep energy levels. On the other hand, surface doping could enhance the n-type conductivity and circumvent the doping deficiency of hydrothermal method. Scanning Electron Microscopy shows that samples are well aligned and free of entanglement. High resolution transmission electron microscopy images clearly resolve the core-shell structure of the NRs and the thickness of the shell is measured. Temperature dependent photoluminescence are studied. In near band edge region, defect-related shoulder near 3.33 eV (10 K) is largely suppressed in the core-shell NRs. Two electron satellite of donor bound exciton peak emerge in the spectrum of the coated sample, from which the dopant ionization energy is calculated to be 56 meV, fairly close to the 54.5 meV ionization energy of Ga. As for deep level emission (DLE), an asymmetric broad peak dominates the visible region from 10K up to room temperature. The relative intensity of DLE (DLE/NBE) reduces by 57% after 5 nm GZO coating, indicating the improvement of the optical property. Furthermore, the broad DLE peak is decomposed to two components by Gaussian fitting. In contrast to the red-shift in the control sample, both the green component (c.a. 2.44 eV) and the orange-red peak (c.a. 2.12 eV) shift to higher energy due to Burstein Moss effect (BM) in the core-shell rod between 200 and 300 K, implying additional donors (e.g. Ga) are incorporated into the sample. X-ray photoelectron spectroscopy is conducted and further confirms the existence of Ga. A detailed study on the components of the element oxygen is implemented. The high energy component of O 1S reflects the amount of surface absorbed O. This component is largely reduced in the core-shell samples, indicating the decrease of surface depletion.

The demand of low cost materials has become one of the major challenges scientists face to address critical contemporary issues such as sustainable energy sources. For instance, one of the promising alternatives for the transition of fossil fuel-based energy to a clean and renewable technology relies on the widespread implementation of solar-related energy systems, however, the high cost of energy production poses an intrinsic limitation. In this context, low cost materials development is required to balance the necessary increase in power generation and conversion efficiency and the costs of implementation and operation. Furthermore, a better comprehensive understanding of materials growth and properties relationships using quantum confinement and nanoscale strategies to raise the theoretical limits by changing the fundamental physics and chemistry is the key to success. Such ideas were demonstrated by the thermodynamic modeling and low-cost design of crystalline arrays of quantum rods- and dots-based oxides with controlled orientation, size, and shape onto various substrates at nano-, meso-, and micro-scale by aqueous chemical growth at low-temperature. Tailored dimensionality effects on their surface chemistry, electronic structure, and energetics for a low cost and sustainable generation of hydrogen from the two most abundant and geographically-balanced free resources available on this planet, that is the sun and seawater were also presented.