The role of water molecules on the adhesion property of cellulose/phenolic adhesive interface is investigated by molecular dynamics simulations. Cellulose is one of the most abundant substances in the world, and the major constituent in the wood structure. Phenolic adhesive is largely used in the wood manufacture for gluing the wood panels together. The cellulose/phenolic adhesive interface is a representative of the interface between the wood panels and adhesives in the wood products. As the wood panels and adhesive are sensitive to environmental humidity, the interfacial adhesion of such interface when subjected to a humid environment can be a major factor in the durability of final products. Here, the simulation results reveal that water molecules significantly reduce the adhesion energy between cellulose and phenolic adhesive of 86.5%. Meanwhile, it is demonstrated that the adhesion energy can be recovered after the interface experiences further dry conditioning. The hydrogen bonds between the cellulose and phenolic adhesive are found to account for the strong interfacial adhesion, which can be interrupted in the presence of water molecules and recovered after further dry conditioning. The durability of the wood products is mainly determined by water molecules absorbed at the bilayer interface, which should be considered in a wet condition.

A new strategy is proposed for protein crystallization methods in solution-growth or gel-growth by using different crystal growth devices applying electric (in the range of micro-Amperes) and magnetic fields (from 7 to 12 Tesla). The effect of combining both electric and magnetic fields is shown and is reviewed. Proteins with differing contents of a-helices and b-sheets, and crystallized in different crystallographic space groups are studied. The crystal quality is improved by using an electric field to electro-migrate ions to the ITO electrodes, and to orientate protein molecules by using a strong magnetic field in either solution or gel-growth to control the transport phenomena. Some advantages to increase the crystal quality for crystals from marginal conditions for X-ray diffraction are discussed. Finally, in order to separate the nucleation and the crystal growth processes (by using these electromagnetic fields), the obtainment of either large amount of small crystals for Powder X-ray Diffraction or big single crystals for the classic X-ray Crystallography (or Neutron Diffraction Crystallography) is also evaluated. Acknowledgements: The author (A.M.) gratefully acknowledges financial support from CONACYT-Mexico Project No. 175924.

Tunnel field effect transistors (TFETs) have generated much interest in the pursuit of energy-efficient electronics due to their potential to surpass the classical subthreshold-slope limit of 60 mV/decade, allowing them to switch at much lower voltages. Heterojunctions with a broken gap (type-III) or a small staggered gap (type-II) have become promising candidates for TFETs because they are predicted to provide steep subthreshold slopes limited only by the steepness of the band-edges of the material, while providing enough current for high speed operation. However, experimental results to date have not demonstrated subthreshold swings that are steeper than the classical limit. To solve this, it is necessary to understand how sharp the band-edges can be in such materials in the presence of realistic imperfections. We have studied this for some of the most commonly proposed materials systems: InAs/GaSb (type-III) and InGaAs/GaAsSb (type-II), which we have grown via MOCVD. Two-terminal measurements are used to reveal the steepness of the band-edges and to predict an ideal subthreshold slope that is intrinsic to the material interface. We find that these interfaces are prone to the formation of misfit dislocations due to strain buildup of intermixed compositions. I-V measurements show that these dislocations, along with point defects, result in less sharp band-edges and poorer predicted subthreshold swings. We propose that point-defects gettered by dislocations lead to defect states near the band edge that lower steepness, as well as strain fields and charge that cause band alignment to change across the interface. We have identified techniques to control these defect densities, including growing the III-Sb layer at the top to prevent As-Sb swap, purposely straining III-Sb layers, and lowering growth temperature near the interface to suppress intermixing. We have also employed annealing to allow lower and/or more uniform point defect concentrations and more uniform intermixing. We show that this can obtain considerably improved steepness. Low temperature measurements reveal that steepness is not a function of temperature, even in devices that show no observable defects in cross-section TEM, indicating that in all cases, the sharpness of tunneling is limited by materials defects and inhomogeneity. Furthermore, our temperature-independence in two-terminal measurements indicate that most published TFET devices, which show a strong temperature dependence of subthreshold slope, are likely overpowered by thermally-activated parasitic effects originating from the gate oxide and channel. Our results indicate that the design of TFETs need to be modified to mitigate such parasitic effects. Furthermore, even in the absence of such parasitics, the material quality likely limits the ultimate performance of band-edge switching in TFETs, and further control of materials or a change in design is required in order to perform better than the classical limit.

The prediction of structure and polymorphism in molecular crystals is a problem of importance in areas ranging from pharmaceuticals to industrial and high-energy materials. Because of the challenges associated with performing extensive, high-quality experiments on molecular crystals, theory and computation can play a significant role in this area provided the models and structure prediction algorithms are of sufficient accuracy and efficiency. In this talk, I will describe the efforts we are making to develop new free-energy based enhanced sampling computational strategies for predicting structure and polymorphism in molecular crystals and the mapping out the associated free energy landscapes. I will demonstrate the performance of the approach in a series of organic molecular crystals, several of which are blind predictions in which the crystal structures are not known a priori.

Water-related energy is an inexhaustible and renewable energy resource in our environment, which has huge amount of energy and is not largely dictated by daytime and sunlight. The transparent characteristic plays a key role in practical applications for some devices designed for harvesting water-related energy. In this paper, a transparent triboelectric nanogenerator (T-TENG) was designed to harvest the electrostatic energy from flowing water for the first time. The output peak-to-peak open-circuit voltage and current density of the T-TENG could reach 10 V and 2 ?A/cm2, respectively, with the flow rate of the tap water of 93 ml/s. The instantaneous output power density of the T-TENG was 11.56 mW/m2 when connecting to a load resistor of 0.5 M?. Moreover, the transmittance of the as-prepared T-TENG was 87.41% with the organic film thickness of 1?m, larger than that of individual glass substrate of 83.41%, which was caused by the organic film acting as an antireflection coating. These results illustrated the potential applications of the T-TENG for harvesting wastewater energy in our living environment and on smart home system and smart car system.

The tremendous development of portable electronics makes it an urgent demand for sustainable energy sources. Recently, triboelectric nanogenerators (TENGs) have shown unique merits including large output power, high efficiency, and cost effective materials. Sliding-mode TENG structure based on in-plane charge separation are the most promising design, especially because grating structure can be integrated into it. Maximizing the energy output is always designers� only target. However, the inherent complexity in the physics of sliding-mode TENGs and their mismatch with other downstream energy storage and load components greatly limit their power output, which require thorough fundamental understanding and careful optimization of the TENG system. However, this system couples the complex effect of both electrostatics and circuit theory. There is neither previous theoretical understanding nor numerical models to deal with that. To address this issue, we proposed the first governing equation and equivalent circuit model for TENGs, leading to the demonstration of the first TENG simulation tool, in which the coupling simulation of both electrostatic and circuit part is realized for the first time. Utilizing this tool, we clearly uncover the output characteristics of sliding-mode TENGs to maximize their power output. Sliding-mode TENGs without grating structures are first studied to unveil their fundamental physics and verification of our method. We derive their first analytical model and resistive load characteristics. The �three-working-region� behavior is interpreted with the impedance match mechanism. A corresponding experiment is then performed as validation of theory, which shows good agreement with theoretical anticipation.[1] Next, we move to grating TENGs with multiple sliding units. To optimize the energy output, we perform an in-depth discussion on the influence of electrode structure, thickness of the dielectric layers, and number of grating units. As for the electrode structure, grating electrodes always lead to a better performance than plate electrodes. As for the dielectric thickness, the thickness of the dielectric of the longer plate should be much smaller than that of the shorter plate. As for the most important parameters of grating TENGs�the number of grating units, our calculation clearly indicates that increasing the number of grating units will generally improve the output performance. However, when the pitch is very fine, the edge effect begins to dominate, resulting in degradation of performance when the number of units continues to increase. Thus, there exists an optimum number of grating units and an optimum unit aspect ratio that mainly depends on the materials dielectric constant and the motion type. The optimization strategy provided here can serve as guidance of experiments towards practical application.[2] Reference 1. S. Niu, Z. L. Wang et al Adv. Mater. 25, 6184. 2. S. Niu, Z. L. Wang et al Energy Environ. Sci. 7, 2339.

The rapid depletion of natural Earth�s capital calls for scientists to get involved in the designing of functional materials, which should meet the need for rational preparation approaches, green chemistry principles and enhanced performances. 1,2 Semiconductor metal oxides (MOX) are flexible platforms suitable for different functional applications, such for instance solar energy conversion, photocatalysis, gas sensing. This lecture focuses on how a rational design and preparation of MOX nano- and micro-structures is actually critical in order to satisfy the need for enhanced functionality in the mentioned applications, especially photovoltaics, which might be critical for a �greener� vision of the future of our environment. Focus will be in particular given to: fabrication of hybrid photoanodes composed of TiO2 nanoparticles and multi wall carbon nanotubes (or graphene) below the percolation threshold able to boost dye sensitized solar cell (DSSC) functional performances; 2,3 integration of graphene in metal oxide-based DSSCs as transparent conductive material in front electrodes, as an alternative to more commonly applied materials, such as indium tin oxide and fluorine-doped tin oxide; 4 design and application of spray deposited ZnO optically transparent compact layer as blocking layer in ZnO-based DSSCs to boost device performances; 5,6 preparation of ZnO hierarchical structures to be applied as multifunctional active components in photoanodes for DSSCs, photocatalysis and gas sensing. Particular emphasis will be given to the exploitation of simple, cheap and low environmental impact techniques for advanced functional material preparation. 1.X. Peng, Nano Res., 2009, 2, 425-447 2.N. Armaroli, V. Balzani, Angew. Chem. Int. Ed., 2007, 46, 52 3.K. T. Dembele, G. S. Selopal, C. Soldano, R. Nechache, J. C. Rimada Herrera, I. Concina, G. Sberveglieri, F. Rosei, A. Vomiero, J. Phys. Chem. C., 2013, 117, 14510 4. J. Mater. Chem. A, DOI: 10.1039/c4ta04395b. 5. 6.S. Selopal, N. Memarian, R. Milan, I. Concina, G. Sberveglieri, A. Vomiero, ACS Appl. Mater. Interfaces, 2014, 6, 11236 G. N. Memarian, I. Concina, A. Braga, S.M. Rozati, A. Vomiero, G. Sberveglieri, Angew. Chem. Int. Ed., 2011, 50, 12321

Icosahedral quasicrystals (IQCs) are a form of matter that is ordered but not periodic in any direction. IQCs have the highest symmetry of all crystals and therefore exhibit orientationally highly uniform properties. This makes them candidates for materials with a complete photonic bandgap or as specialized alloys. All reported IQCs are intermetallic compounds and either of face-centered-icosahedral or primitive-icosahedral type, and the positions of their atoms have been resolved from diffraction data. However, unlike other quasicrystals, which have been observed experimentally in micellar or nanoparticle systems and suggested in bi-layer water, silicon, and mesoporous silica, IQCs have not been discussed in the context of non-intermetallic systems. In this contribution, we demonstrate the first self-assembly of an IQC by means of molecular dynamics simulations. The IQC self-assembles rapidly and reproducibly from a fluid phase in a one-component system of particles interacting via a tunable, isotropic pair potential extending only to the-third neighbor shell [1]. It is body-centered icosahedral, and in parameter space neighbors clathrates and other tetrahedrally bonded crystals. We provide a crystallographic structure model and show the presence of a diffusion mechanism not available in periodically ordered solids. Our finding is an important step towards addressing a central remaining question in the theory of crystal growth: How do atoms (or other elementary building blocks) arrange themselves rapidly, and with near structural perfection, into a long-range ordered configuration without the guidance of a unit cell? Finally, we suggest routes to search for the IQC and design it in soft matter and nanoscale systems. [1] M. Engel, P.F. Damasceno, P.L. Phillips, S.C. Glotzer, Nature Materials, in press (2014).

In the last two years methylammonium lead halide perovskite based solar cells have been characterized by a fast development, achieving power conversion efficiencies approaching 20% 1, 2. Impressively, most of the latest advancements have been the result of a higher control on the material processing and on the crystallization steps. On the other hand, the poor understanding of the relationship between structure and optoelectronic properties is still a limiting factor for a further improvement in the efficiency. Here, we demonstrate how the crystallization procedure as well as the nature of the precursors, i.e. the presence of chlorine, can affect the macroscopic structural and optical properties of CH3NH3PbI3 and the chlorine-doped CH3NH3PbI3 perovskite films. We investigate the optical and micro-structural properties of hybrid perovskite polycrystalline films deposited either on flat glass substrate or infiltrated into a mesoporous scaffold combining Raman spectroscopy 3 with X-Ray Diffraction measurements, High Resolution Scanning Electron Microscopy and Energy Dispersive X-ray spectroscopy 4. The specific organic-inorganic interactions are revealed by monitoring the Raman signal related to the Pb-I stretching modes and the CH3NH3+ rocking modes, as important markers of local distortion of the inorganic cage3. The experimental findings point to a clear trend, that is, an ordered arrangement of the organic cation in CH3NH3PbI3 crystallites grown on �flat� substrates with respect to a fully randomly orientation in the mesoporous scaffold. Interestingly, we observe that the displacement of the organic cations and their interaction with the inorganic cage result in a strain felt by the lattice that manifest as a band gap shrinking moving from meso to flat CH3NH3PbI3 film. On the other hand the presence of chlorine in the precursor to obtain the Chlorine-doped CH3NH3PbI3 also affects the crystal formation both at a molecular scale and at a mesoscopic level during crystal growth. In particular, the chlorine assists the crystallization favouring a preferential ordered arrangement of the organic cation in the unit cell even in the mesoporous scaffold, as revealed by XRD. We demonstrate that, although we do not find any chloride signature in the crystal unit cell, chlorine ions play an important role at a larger scale in driving the formation of crystals with a preferential order. We show that, when the crystallization is carried out on a flat substrate, most chlorine ions are segregated from the film in the forms of large perovskite crystals. When instead the perovskite film is crystallized in the presence of an oxide scaffold, these are retained at the mesoporous interface. References [1] Zhou, H. et al. Science. 345, 542�546 (2014). [2] Im, G. H. et al. Nat. Nanotechnol (2014). doi:10.1038/nnano.2014.181 [3] Grancini, G. et al. J. Phys. Chem. Lett. (2014). doi:10.1021/jz501877h [4] Quarti, C. et al. J. Phys. Chem. Lett. 5, 279?284 (2014)

The accumulation of biomass on marine structures (such as ship hulls) is a major problem for maritime operations as it is associated with increased fuel consumption, damage and corrosion as well as the spread of invasive species. With commonly applied biocidal antifouling coatings coming under more and more legislative pressure, viable alternatives are needed. Here we present an effective, non-toxic, slippery surface technology for marine fouling prevention applications, demonstrating promising performance in laboratory and field-based marine fouling studies.