MRC Laboratory of Molecular Biology
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Beneficial Effect of Li<inf>5</inf>FeO<inf>4</inf>Lithium Source for Li-Ion Batteries with a Layered NMC Cathode and Si Anode
No full textThe energy density of lithium-ion batteries can be increased by replacing the traditional graphite anode with a high capacity silicon anode. However, volume changes and interfacial instabilities cause a large irreversible capacity and a continual loss of lithium during cycling, which lead to rapid capacity loss. In this work, we add Li5FeO4 (LFO) to a LiNi0.5Mn0.3Co0.2O2 (NMC) cathode as a pre-lithiation additive, which increases the lithium inventory and extends the cycle life of Si-graphite/NMC full cells, and decreases the NMC particle degradation. LFO delivers a large 764 mAh g-1LFO capacity below 4.7 V vs Li/Li+. By tuning the LFO content in Si-graphite/LFO-NMC full cells, we show higher capacity, improved retention, lower impedance, and superior rate performance compared to full cells without LFO. Post-test characterizations demonstrate that LFO inclusion in the cathode matrix leads to less NMC secondary particle segregation/cracking and a thinner surface reduced layer on the NMC particles. The beneficial effects of LFO endure after the lithium reserve has been exhausted, highlighting a lasting synergy between the lithium source and electrode active materials. This study introduces a new approach to simultaneously increase lithium inventory and reduce cathode degradation, and makes critical advances toward enabling Si anodes for lithium-ion batteries
Wing-gust interactions: The effect of transverse velocity profile – invited –
No full textThe flow field and force produced during a wing-gust encounter have been compared between a top-hat and a sine-squared transverse gusts. Experiments are performed at Reynolds number between 20 000 and 30 000 in a water tow tank. Both gusts are generated by disturbing the flow in a section of the tank at different velocities, resulting in gust ratios, GR, equal to 0.5, 0.75, 1.0, and 1.5. Time-resolved force and flow field measurements are analysed and compared with linear theories. The force results show a smoother increase in lift for the sine-squared gust accompanied by a lower maximum lift. The specific range of GRs was selected to capture the non-linear behaviour of the top-hat gust on lift. However, for the same gust ratios, the sine-squared gusts remained in the linear regime. As a result, Küssner’s theory is found to accurately predict the loads resulting from the sine-squared gust for a larger range of gust ratios than the top-hat gust. The non-linear behaviour of the top-hat gust on the lift force is linked to higher levels of circulation shed from the wing edges and the development of non-planar wakes. It is concluded that the gust shape is a critical parameter determining the wing-gust encounter characteristics
Environmental evaluation of distributed versus centralized plastic waste recycling: Integrating life cycle assessment and agent-based modeling
No full textPlastic waste is internationally recognized as a problem, fueled by increased public awareness of environmental concerns and the steady increase in waste import bans. Modern sorting and recycling technologies are mature, but face implementation limitations in highly dense urbanized regions such as Singapore due to significant space constraints and expensive labor. Distributed plastic sorting and recycling facilities at small-scale closer to points of plastic waste generation offer the possibility of increasing the recovery of plastic waste streams in urbanized settings. To quantify the environmental performance of such systems, this study compares the life cycle greenhouse gas emissions of large-scale centralized facilities versus distributed small-scale facilities for sorting and recycling plastic bottles and takeaway containers generated in the central region of Singapore. An agent-based model is used to simulate different scenarios of plastic waste generation, collection routes, sorting, and recycling. The simulation results are used in a multi-level life cycle assessment to quantify the greenhouse gas emissions of the plastic sorting and recycling network as well as its individual entities. The results reveal that the life cycle greenhouse gas emissions of small-scale distributed plastic recycling compared to large-scale centralized systems are sensitive to the transport distance traveled and the type of trucks used
Observation of inter-layer charge transmission resonance at optically excited graphene-TMDC interfaces
No full textThe transfer of charge carriers across the optically excited hetero-interface of graphene and semiconducting transition metal dichalcogenides (TMDCs) is the key to convert light to electricity, although the intermediate steps from the creation of excitons in TMDC to the collection of free carriers in the graphene layer are not fully understood. Here, we investigate photo-induced charge transport across graphene-MoS2 and graphene-WSe2 hetero-interfaces using time-dependent photoresistance relaxation with varying temperature, wavelength, and gate voltage. In both types of heterostructures, we observe an unprecedented resonance in the inter-layer charge transfer rate as the Fermi energy (EF) of the graphene layer is tuned externally with a global back gate. We attribute this to a resonant quantum tunneling from the excitonic state of the TMDC to EF of the graphene layer and outline a new method to estimate the excitonic binding energies (Eb) in the TMDCs, which are found to be 400 meV and 460 meV in MoS2 and WSe2 layers, respectively. The gate tunability of the inter-layer charge transfer timescales may allow precise engineering and readout of the optically excited electronic states at graphene-TMDC interfaces
Interplay of charge transfer and disorder in optoelectronic response in Graphene/hBN/MoS<inf>2</inf> van der Waals heterostructures
No full textStrong optoelectronic response in the binary van der Waals heterostructures of graphene and transition metal dichalcogenides (TMDCs) is an emerging route towards high-sensitivity light sensing. While the high sensitivity is an effect of photogating of graphene due to inter-layer transfer of photo-excited carriers, the impact of intrinisic defects, such as traps and mid-gap states in the chalcogen layer remain largely unexplored. Here we employ graphene/hBN (hexagonal boron nitride)/MoS2 (molybdenum disulphide) trilayer heterostructures to explore the photogating mechanism, where the hBN layer acts as interfacial barrier to tune the charge transfer timescale. We find two new features in the photoresponse: First, an unexpected positive component in photoconductance upon illumination at short times that preceeds the conventional negative photoconductance due to charge transfer, and second, a strong negative photoresponse at infrared wavelengths (up to 1720 nm) well-below the band gap of single layer MoS2. Detailed time and gate voltage-dependence of the photoconductance indicates optically-driven charging of trap states as possible origin of these observations. The responsivity of the trilayer structure in the infrared regime was found to be extremely large (> 108 A/W at 1550 nm using 20 mV source drain bias at 180 K temperature and ≈ - 30 V back gate voltage). Our experiment demonstrates that interface engineering in the optically sensitive van der Waals heterostructures may cast crucial insight onto both inter- and intra-layer charge reorganization processes in graphene/TMDC heterostructures
Stable Spatially Localized Configurations in a Simple Structure—A Global Symmetry-Breaking Approach
No full textWe revisit the classic stability problem of the buckling of an inextensible, axially compressed beam on a nonlinear elastic foundation with a semi-analytical approach to understand how spatially localized deformation solutions emerge in many applications in mechanics. Instead of a numerical search for such solutions using arbitrary imperfections, we propose a systematic search using branch-following and bifurcation techniques along with group-theoretic methods to find all the bifurcated solution orbits (primary, secondary, etc.) of the system and to examine their stability and hence their observability. Unlike previously proposed methods that use multi-scale perturbation techniques near the critical load, we show that to obtain a spatially localized deformation equilibrium path for the perfect structure, one has to consider the secondary bifurcating path with the longest wavelength and follow it far away from the critical load. The novel use of group-theoretic methods here illustrates a general methodology for the systematic analysis of structures with a high degree of symmetry
Magnifying viewer using poly-si thin-film phototransistor and liquid-crystal micro-lens array
No full textWe have confirmed fundamental functions of a flatpanel imager using a poly-Si thin-film phototransistor and liquid-crystal micro-lens array. It is found that the electric current measured in the pixel on the white area is definitely larger than that on the black area. Particularly in this paper, it is clarified that the current difference for the lens-on state is more obvious than that for the lens-off state, and that for the polarizer-on state is also more obvious than that for the polarizer-off state. The experimental results are the same as what we expect and indicate the excellent effect of the liquid-crystal micro-lens array on the flatpanel imager using a poly-Si thin-film phototransistor. The magnifying viewer can be high-resolutional by the flatpanel imager using the poly-Si thin-film phototransistor and liquid-crystal micro-lens array
Guiding of terahertz photons in superconducting nano-circuits
No full textThe field of plasmonics, as one of the fascinating areas of photonics, has received great attention for its capability of deep subwavelength confinement. We present a nanoscale plasmonic slot waveguide based on high transition temperature (T{c}) superconductor Bi{2}Sr{2}CaCu{2}{O}{8+\delta},(BSCCO). The effect of geometrical parameters on the modal properties of the BSCCO plasmonic slot waveguide and the thermal tuning of the modal properties of the waveguide are explored. It is shown that the rising of temperature results in increasing the mode effective refractive index in exchange for decreasing the propagation length of surface plasmon polaritons (SPPs). Our proposed plasmonic waveguide paves the way for the development of the BSCCO based THz photonic integrated circuity at the nanoscale
Nano-second timescale drain voltage induced electrical instabilities in hydrogenated amorphous silicon thin film transistors
No full textIn this work, we study the device degradation of a-Si:H thin film transistors upon application of high frequency nano-second timescale pulse stress on the drain contact. Degradation mechanisms at different field stress levels have been investigated using real-time current-voltage, capacitance-voltage and Raman spectroscopy measurements. A positive V T shift under moderate electric field stress followed by a V T recovery (negative shift) at high drain fields has been observed. Spatial variance in the degradation has been studied. A variance in the degradation mechanism from the hot to cold contact is observed. No material changes are observed, confirmed through Raman spectroscopy as the field stress is applied. The role of self-heating in degradation is studied by varying the pulse width of the field stress in nano-seconds range. Finally, the impact of thermal and gate bias anneal on V T shift has been investigated through electrical measurements in a recursive stress-anneal cycle
Spin filtering by proximity effects at hybridized interfaces in spin-valves with 2D graphene barriers
No full textWe report on spin transport in state-of-the-art epitaxial monolayer graphene based 2D-magnetic tunnel junctions (2D-MTJs). In our measurements, supported by ab-initio calculations, the strength of interaction between ferromagnetic electrodes and graphene monolayers is shown to fundamentally control the resulting spin signal. In particular, by switching the graphene/ferromagnet interaction, spin transport reveals magneto-resistance signal MR > 80% in junctions with low resistance × area products. Descriptions based only on a simple K-point filtering picture (i.e. MR increase with the number of layers) are not sufficient to predict the behavior of our devices. We emphasize that hybridization effects need to be taken into account to fully grasp the spin properties (such as spin dependent density of states) when 2D materials are used as ultimately thin interfaces. While this is only a first demonstration, we thus introduce the fruitful potential of spin manipulation by proximity effect at the hybridized 2D material / ferromagnet interface for 2D-MTJs