MRC Laboratory of Molecular Biology
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Surface electrical properties modulation by multimode polarizations inside hybrid perovskite films investigated through contact electrification effect
No full textSurface electrical properties is of great significance for developing high-performance organic-inorganic hybrid perovskite based electronic devices. The photovoltage-induced ions transport and redistribution at the surface region have been well studied, but their contributions to the surface electrical properties are still lack of experimental evidences. In this article, a self-powered polymer-based contact electrification probe (PCE-probe) is proposed to investigate the photovoltage- or applied bias-induced ion transport polarization (PI) and ferroelectric polarization (PF) inside the methylammonium lead iodide films (MAPI). Results show that both the PI- and PF-induced ion transport and redistribution create a similar local ion-doping region near the surface. Positive or negative ion-doping produces a n-type or p-type layer, which enhances the interficial junction inside MAPI-based solar cells and benefits the seperation and transfer of photogenerated carriers or excitons. The PI and PF effects can be added up or subtracted from each other depending on the polarization configuration. A qualitative relationship between the PCE-probe output and CE-effect, PI- and PF-induced transferred surface charges is investigated. These results can help to understand the polarization nature inside and the high power conversion efficiency of MAPI-based photovoltaic devices, and provide a feasible analysis method of PCE-probe for detecting surface electrical properties
Two-Colour Topology Finding of Quad-Mesh Patterns
No full textThe patterns of many structural systems must fulfil a property of two-colourability to partition their elements into two groups. Such examples include top versus bottom layers of continuous beams in elastic gridshells, corrugated versus non-corrugated directions in corrugated shells or warp versus weft threads in woven structures. Complying with such constraints does not depend on the geometry but on the topology of the structure, and, more specifically, on its singularities. This paper presents a search strategy to obtain patterns that fulfil this topological requirement, which represent only a fraction of the general design space. Based on an algebra for the exploration of the topology of quad meshes, including a grammar and a distance, a topology-finding algorithm is proposed to find the closest two-colour quad-mesh patterns from an input quad-mesh pattern. This approach is expressed as the projection to the two-colourable subspace of the design space. The distance underlying the definition of the projection measures the similarity between designs as the minimum number of topological grammar rules to apply to modify one design into another. A design application illustrates how two-colour topology finding can complement workflows for the exploration of structural patterns with singularities informed by the system's topological requirements
Low Resistance Soldering and Installation for a kA Level HTS Flux Pump
No full textThe HTS flux pump is a promising device which can charge the HTS magnet for various high field applications. In an HTS flux pump, the superconducting tapes are the circuit connections between the charging loop and the load circuit, and using soldering joints between the superconducting layers is a general method. For a large scale HTS flux pump, the joints should endure the electrical current over kA level, and with durable mechanical structures. In our kA level HTS flux pump, the HTS-copper joint was used to connect the charging loop, the HTS bridge and the potential HTS load. Three methods of HTS-copper soldering were tested and compared for a simple HTS-copper circuit: pure indium wire pre-tinning, IN52/SN48 ribbon direct soldering, and IN52/SN48 ribbon pre-tinning. Experiments show the soldering of IN52/SN48 ribbon pre-tinning archived the lowest joint resistance among these three methods, and the individual resistances were determined. This method was used to solder the joint for the kA level HTS flux pump, and acceptably low resistance was achieved
The mechanical and electrochemical properties of polyaniline-coated carbon nanotube mat
No full textThe measured capacitance, modulus and strength of carbon nanotube-polyaniline (CNT-PANI) composite electrodes render them promising candidates for structural energy storage devices. Here, CNT-PANI composite electrodes are manufactured with electrodeposition of PANI onto the bundle network of CNT mats produced via a floating catalyst chemical vapour deposition process. PANI comprises 0% to 30% by volume of the electrode. The composition, modulus, strength and capacitance of the electrodes is measured in the initial state, after the first charge, and after 1000 charge/discharge cycles. Electrode modulus and strength increase with increasing CNT volume fraction; in contrast, the capacitance increases with increasing PANI mass. Charging or cycling reduce the electrode modulus and strength due to a decrease in CNT bundle volume fraction caused by swelling; the electrode capacitance also decreases due to a reduction in PANI mass. A micromechanical model is able to predict the stress-strain response of pre-charged and cycled electrodes, based upon their measured composition after pre-charging and cycling. The electrodes possess up to 63% of their theoretical capacitance, and their tensile strengths are comparable to those of engineering alloys. Their capacitance and strength decrease by less than 15% after the application of 1000 charge/discharge cycles. These properties illustrate their potential as structural energy storage devices
Plasma-Enhanced Atomic Layer Deposition of Al<inf>2</inf>O<inf>3</inf> on Graphene Using Monolayer hBN as Interfacial Layer
No full textThe deposition of dielectric materials on graphene is one of the bottlenecks for unlocking the potential of graphene in electronic applications. The plasma enhanced atomic layer deposition of 10 nm thin high quality aluminum oxide (Al2O3) on graphene is demonstrated using a monolayer of hexagonal boron nitride (hBN) as protection layer. Raman spectroscopy is performed to analyze possible structural changes of the graphene lattice caused by the plasma deposition. The results show that a monolayer of hBN in combination with an optimized deposition process can effectively protect graphene from damage, while significant damage is observed without an hBN layer. Electrical characterization of double gated graphene field effect devices confirms that the graphene does not degrade during the plasma deposition of Al2O3. The leakage current densities are consistently below 1 pA µm−2 for electric fields across the insulators of up to 8 MV cm−1, with irreversible breakdown happening above. Such breakdown electric fields are typical for Al2O3 and can be seen as an indicator for high quality dielectric films
Phase transition of two-dimensional ferroelectric and paraelectric Ga2 O3 monolayers: A density functional theory and machine learning study
No full textGa2O3 is a wide-band-gap semiconductor of great interest for applications in electronics and optoelectronics. Two-dimensional (2D) Ga2O3 synthesized from top-down or bottom-up processes can reveal new heterogeneous structures and promising applications. In this paper, we study phase transitions among three low-energy stable Ga2O3 monolayer configurations using density functional theory and a machine learning Gaussian approximation potential, together with solid-state nudged elastic band calculations. Kinetic minimum energy paths involving direct atomic jump as well as concerted layer motion are investigated. The low phase transition barriers indicate feasible tunability of the phase transition and orientation via strain engineering and external electric fields. Large-scale calculations using the trained machine learning potential on the thermally activated single-atom jumps reveal the clear nucleation and growth processes of different domains. The results provide useful insights into future experimental synthesis and characterization of 2D Ga2O3 monolayers
Build Charging Database of Linear-Motor Type Flux Pump and Analyze the Influence of DC-Bias Field Using Fixed Step Size Search Algorithm
No full textThe linear-motor type flux pump is a wireless DC power source for high-Temperature superconducting coils, which is compact in size, efficient in energy use, fast in output control, etc. It consists of three major parts: DC windings, phase windings and iron circuit, which generates a DC-bias AC travelling wave in its airgap. In theory, there are three controllable parameters such as DC-bias field, amplitude of the AC travelling wave, and the field frequency (travelling speed). By changing those parameters, we change the applied fields and its DC output current into superconducting coils. For studying the impact of those parameters on its DC output, this paper uses a fixed step algorithm to collect the current charging data, by automatically controlling the flux pump device, and then establishes an output database. By using this algorithm, we have searched out the maximum pumped current and analyzed the impact of the three parameters. We have also found out that, in order to get maximum current output, the value of the DC-bias field should be close to the amplitude of AC magnetic field
Online Morphological Adaptation for Tactile Sensing Augmentation
No full textSensor morphology and structure has the ability to significantly aid and improve tactile sensing capabilities, through mechanisms such as improved sensitivity or morphological computation. However, different tactile tasks require different morphologies posing a challenge as to how to best design sensors, and also how to enable sensor morphology to be varied. We introduce a jamming filter which, when placed over a tactile sensor, allows the filter to be shaped and molded online, thus varying the sensor structure. We demonstrate how this is beneficial for sensory tasks analyzing how the change in sensor structure varies the information that is gained using the sensor. Moreover, we show that appropriate morphology can significantly influence discrimination, and observe how the selection of an appropriate filter can increase the object classification accuracy when using standard classifiers by up to 28%
Millimeter-wave-to-terahertz superconducting plasmonic waveguides for integrated nanophotonics at cryogenic temperatures
No full textPlasmonics, as a rapidly growing research field, provides new pathways to guide and modulate highly confined light in the microwave-to-optical range of frequencies. We demonstrated a plasmonic slot waveguide, at the nanometer scale, based on the high-transition-temperature (Tc) superconductor Bi2Sr2CaCu2O8+δ (BSCCO), to facilitate the manifestation of chip-scale millimeter wave (mm-wave)-to-terahertz (THz) integrated circuitry operating at cryogenic temperatures. We investigated the effect of geometrical parameters on the modal characteristics of the BSCCO plasmonic slot waveguide between 100 and 800 GHz. In addition, we investigated the thermal sensing of the modal characteristics of the nanoscale superconducting slot waveguide and showed that, at a lower frequency, the fundamental mode of the waveguide had a larger propagation length, a lower effective refractive index, and a strongly localized modal energy. Moreover, we found that our device offered a larger SPP propagation length and higher field confinement than the gold plasmonic waveguides at broad temperature ranges below BSCCO’s Tc. The proposed device can provide a new route toward realizing cryogenic low-loss photonic integrated circuitry at the nanoscale
Customer entrepreneurship on digital platforms: Challenges and solutions for platform business models
No full textDrawing on the mixed methods of qualitative research and agent-based simulation, this study examines: (a) how end-users use digital platforms to become customer–entrepreneurs undertaking commercial activities on platforms; and (b) how platform providers can convert this customer entrepreneurship into a revenue stream. Considering that end-users have traditionally been defined as passive and uncharged actors in platform business models, an in-depth understanding of their commercial activities and the viable revenue model to monetize this emerging customer practice is warranted. Our qualitative study reveals that customer–entrepreneurs make substantial use of platform offerings to advertise their products; communicate with end-consumers; and accept payments. These commercial activities are largely exercised for free on platforms, even though they could otherwise serve as a source of revenue. On this point, our simulation results identify two pricing models achieving the generation of nearly identical revenues over time. First, platform providers may charge both advertising and transaction fees, which maximize the survival of professional customer–entrepreneurs. Second, platform businesses may levy advertising fees only, which maximizes the survival of informal customer–entrepreneurs operating on a micro-scale and part-time basis. This study offers theoretical, methodological, and managerial implications for platform studies