Near-Field Radiative Heat Transfer Modulation with an Ultrahigh Dynamic Range through Mode Mismatching.

Modulating near-field radiative heat transfer (NFRHT) with a high dynamic range is challenging in nanoscale thermal science and engineering. Modulation depths [(maximum value - minimum value)/(maximum value + minimum value) × 100%] of ≈2% to ≈15.7% have been reported with matched modes, but breaking the constraint of mode matching theoretically allows for higher modulation depth. We demonstrate a modulation depth of ≈32.2% by a pair of graphene-covered SU8 heterostructures at a gap distance of ≈80 nm. Dissimilar Fermi levels tuned by bias voltages enable mismatched surface plasmon polaritons which improves the modulation. The modulation depth when switching from a matched mode to a mismatched mode is ≈4.4-fold compared to that when switching between matched modes. This work shows the importance of symmetry in polariton-mediated NFRHT and represents the largest modulation depth to date in a two-body system with fixed gap distance and temperature.

50-µm thick flexible dopant-free interdigitated-back-contact silicon heterojunction solar cells with front MoOx coatings for efficient antireflection and passivation.

We demonstrate experimentally a flexible crystalline silicon (c-Si) solar cell (SC) based on dopant-free interdigitated back contacts (IBCs) with thickness of merely 50 µm for, to the best of our knowledge, the first time. A MoOx thin film is proposed to cover the front surface and the power conversion efficiency (PCE) is boosted to over triple that of the uncoated SC. Compared with the four-time thicker SC, our thin SC is still over 77% efficient. Systematic studies show the front MoOx film functions for both antireflection and passivation, contributing to the excellent performance. A double-interlayer (instead of a previously-reported single interlayer) is identified at the MoOx/c-Si interface, leading to efficient chemical passivation. Meanwhile, due to the large workfunction difference, underneath the interface a strong built-in electric field is generated, which intensifies the electric field over the entire c-Si active layer, especially in the 50-µm thick layer. Photocarriers are expelled quickly to the back contacts with less recombined and more extracted. Besides, our thin IBC SC is highly flexible. When bent to a radius of 6 mm, its PCE is still 76.6% of that of the unbent cell. Fabricated with low-temperature and doping-free processes, our thin SCs are promising as cost-effective, light-weight and flexible power sources.

Near-infrared Hong-Ou-Mandel interference on a silicon quantum photonic chip.

Near-infrared Hong-Ou-Mandel quantum interference is observed in silicon nanophotonic directional couplers with raw visibilities on-chip at 90.5%. Spectrally-bright 1557-nm two-photon states are generated in a periodically-poled KTiOPO4 waveguide chip, serving as the entangled photon source and pumped with a self-injection locked laser, for the photon statistical measurements. Efficient four-port coupling in the communications C-band and in the high-index-contrast silicon photonics platform is demonstrated, with matching theoretical predictions of the quantum interference visibility. Constituents for the residual quantum visibility imperfection are examined, supported with theoretical analysis of the sequentially-triggered multipair biphoton, towards scalable high-bitrate quantum information processing and communications. The on-chip HOM interference is useful towards scalable high-bitrate quantum information processing and communications.

Greatly enhanced hole collection of MoO x with top sub-10 nm thick silver films for gridless and flexible crystalline silicon heterojunction solar cells.

Greatly enhanced hole collection of MoO x is demonstrated experimentally with a top sub-10 nm thick Ag film, allowing for an efficient dopant-free contacted crystalline silicon (c-Si) heterojunction solar cell without a front grid electrode. With the removal of shadows induced by the front grid electrode, the gridless solar cell with the MoO x /Ag hole-selective contact (HSC) shows an increment of ∼8% in its power conversion efficiency (PCE) due to the greatly improved short-circuit current density (J sc) as well as the almost undiminished fill factor (FF) and open-circuit voltage (V oc), while the gridless solar cells with the conventional MoO x /ITO and pure MoO x HSCs exhibit ∼20% and ∼43% degradations in PCE due to the overwhelming decrease in their FF and J sc, respectively. Through systematic characterizations and analyses, it is found that the ultrathin Ag film (more conductive than ITO) provides an additional channel for photogenerated holes to transport on MoO x , contributing to the great enhancement in the hole collection and the great suppression of the shunt loss in the gridless solar cells. A 50 µm thick gridless c-Si heterojunction solar cell with the MoO x /Ag HSC is 75% thinner but is 86% efficient compared to its 200 µm thick counterpart (while the 50 µm thick gridless solar cell with the MoO x /ITO HSC is much less efficient). It is over 82% efficient after being bent to a curvature radius as small as 4 mm, also showing superior mechanical flexibility to its counterpart with the MoO x /ITO HSC. Our MoO x /Ag double-layer HSC can be easily fabricated through thermal evaporation without breaking the vacuum, saving both the time and cost of the fabrication of the whole device. Therefore, this work provides a guide for the design of efficient HSCs for high-efficiency, low-cost, and flexible solar cells.

Biosorption of Pb2+ and Zn2+ by Ca-alginate immobilized and free extracellular polysaccharides produced by Leuconostoc citreum B-2.

AIMS: Heavy metal pollution seriously threatens human health and ecological environment. Due to high efficiency and excellent development prospect, adsorption technology has attracted worldwide attention. It is significant to develop renewable adsorbents with excellent adsorption performance. SCOPE: In this study, the Pb2+ and Zn2+ adsorption capacity of Ca-alginate immobilized and free (without immobilization) Leu. citreum B-2 extracellular polysaccharides (EPS) was investigated. Isotherm and kinetic models were used to evaluate the adsorption performance. The adsorbents were characterized by SEM, FT-IR and XPS spectroscopy. CONCLUSIONS: The maximum biosorption of Pb2+ 269.54 and Zn2+ 49.88 mg/g was achieved with immobilized EPS. Thermodynamic studies showed that the adsorption of Pb2+ and Zn2+ on EPS was a spontaneous and feasible process, and the adsorption properties of EPS were exothermic for lead and endothermic for zinc. All the adsorption processes conformed to the pseudo-second-order model and Langmuir adsorption isotherm model, indicating that the adsorption was mainly chemisorption taken placed on single adsorption surface. SEM results showed that the surface of EPS become denser after adsorption. FTIR and XPS analysis indicated that the adsorption mechanism mainly involved the complexation reaction and ion exchange of functional groups such as CO, O-C-O, -COOH and C-OH.

Optimized Colossal Near-Field Thermal Radiation Enabled by Manipulating Coupled Plasmon Polariton Geometry.

Collective optoelectronic phenomena such as plasmons and phonon polaritons can drive processes in many branches of nanoscale science. Classical physics predicts that a perfect thermal emitter operates at the black body limit. Numerous experiments have shown that surface phonon polaritons allow emission two orders of magnitude above the limit at a gap distance of ≈50 nm. This work shows that a supported multilayer graphene structure improves the state of the art by around one order of magnitude with a ≈1129-fold-enhancement at a gap distance of ≈55 nm. Coupled surface plasmon polaritons at mid- and far-infrared frequencies allow for near-unity photon tunneling across a broad swath of k-space enabling the improved result. Electric tuning of the Fermi-level allows for the detailed characterization and optimization of the colossal nanoscale heat transfer.

Unidirectional Enhanced Emission from 2D Monolayer Suspended by Dielectric Pillar Array.

Monolayers of transition metal dichalcogenides show great promise for optoelectronic devices as atomically thin semiconductors. Although dielectric or metal nanostructures have been extensively studied for tailoring and enhancing emission from monolayers, their applications are limited because of the mode concentrating inside the dielectric or the high optical losses in metals, together with the low quantum yield in monolayers. Here, we demonstrate that a metal-backed dielectric pillar array can suspend monolayers to increase the radiative recombination, and simultaneously, create strongly confined band-edge modes on surface directly accessible to monolayers. We observe unidirectional enhanced emission from WSe2 monolayers on polymer pillar array.

Strongly coupled slow-light polaritons in one-dimensional disordered localized states.

Cavity quantum electrodynamics advances the coherent control of a single quantum emitter with a quantized radiation field mode, typically piecewise engineered for the highest finesse and confinement in the cavity field. This enables the possibility of strong coupling for chip-scale quantum processing, but till now is limited to few research groups that can achieve the precision and deterministic requirements for these polariton states. Here we observe for the first time coherent polariton states of strong coupled single quantum dot excitons in inherently disordered one-dimensional localized modes in slow-light photonic crystals. Large vacuum Rabi splittings up to 311 µeV are observed, one of the largest avoided crossings in the solid-state. Our tight-binding models with quantum impurities detail these strong localized polaritons, spanning different disorder strengths, complementary to model-extracted pure dephasing and incoherent pumping rates. Such disorder-induced slow-light polaritons provide a platform towards coherent control, collective interactions, and quantum information processing.