Quantum Hall coherent perfect absorption in graphene.

[Formula: see text] absorption in a two-dimensional electron gas (2DEG) with Dirac spectrum is demonstrated to be obtained by controlling the interference of multiple incident radiations, referred to as coherent perfect absorption (CPA). However, when a 2DEG such as graphene is exposed to a magnetostatic bias, it resonantly could absorb electromagnetic radiation by transitions of its Dirac electrons between non-equidistant and nonlinear Landau levels. Here, the magneto-optical terahertz (THz) CPA in graphene under the quantum Hall effect (QHE) regime at both strong and subtesla magnetostatic bias fields is addressed. Our findings show that an effective magneto-optical surface conductivity corresponding to right- and left-handed circular (RHC- and LHC) polarizations could model a magneto-tunable CPA in graphene in THz range. Significantly, graphene under QHE regime reveals different tunable CPA properties for each circularly polarized beams by the intensity of the applied magnetic bias. Moreover, it is observed that different phase modulations at CPA frequencies are achieved for RHC and LHC polarizations. Considering the maximum efficiency for a 2D absorber, our results demonstrate the magnetostatic tuning of CPA in 2D Dirac materials for long-wavelength sensing applications and signal processing.

Crystallization Retardation and Synergistic Trap Passivation in Perovskite Solar Cells Incorporated with Magnesium-Decorated Graphene Quantum Dots.

One of the encouraging strategies for enhancing the efficiency of perovskite solar cells (PSCs) is to reduce defects, trap states of pinholes, and charge recombination rate in the light absorber layer of perovskite, which can be addressed by increasing the perovskite grain size. The utilization of Mg-decorated graphene quantum dots (MGQD) or graphene quantum dots (GQDs) into a perovskite precursor solution for further crystal modification is introduced in this study. Studies on the crystalline structure and morphology of MGQD generated from GQDs demonstrate that MGQD has a greater crystal size than GQD. Therefore, higher light absorption in the whole UV-vis spectrum and a larger grain size for the perovskite/MGQD layer compared to the perovskite/GQD sample are achieved. Moreover, more photoluminescence peak quenching of perovskite/MGQD and extended carrier recombination lifetime (from 3 to 40 ns) verify the surface and grain boundary trap passivation compared to pristine perovskite. Consequently, PSCs in an n-i-p configuration containing perovskite/MGQD show a higher performance of 10.2% in comparison to the pristine perovskite at 7.2%, attributed to the enhanced JSC from 13.2 to 19.1 mA cm-2. Thus, incorporating MGQDs into the perovskite layer is a hopeful approach for obtaining a superior perovskite film with impressive charge extraction and decreased nonradiative charge recombination.

Correction to "Engineering Water and Solute Dynamics and Maximal Use of CNT Surface Area for Efficient Water Desalination".

[This corrects the article DOI: 10.1021/acsomega.9b00188.].

Encapsulation Strategies for Highly Stable Perovskite Solar Cells under Severe Stress Testing: Damp Heat, Freezing, and Outdoor Illumination Conditions.

A key direction toward managing extrinsic instabilities in perovskite solar cells (PSCs) is encapsulation. Thus, a suitable sealing layer is required for an efficient device encapsulation, preventing moisture and oxygen ingression into the perovskite layer. In this work, a solution-based, low-cost, and commercially available bilayer structure of poly(methyl methacrylate)/styrene-butadiene (PMMA/SB) is investigated for PSCs encapsulation. Encapsulated devices retained 80% of the initial power conversion efficiency (PCE) at 85 °C temperature and 85% relative humidity after 100 h, while reference devices without SB (only PMMA) suffer from rapid and intense degradation after only 2 h, under the same condition. In addition, encapsulated devices retained 95% of the initial PCE under -15 °C freezing temperature after 6 h and retained ∼80% of the initial PCE after immersion in HCl (37%) for 90 min. Moreover, applying an additional aluminum metal sheet on the PMMA/SB protective bilayer leads to the improvement of device stability up to 500 h under outdoor illumination, retaining almost 90% of the initial PCE. Considering the urge to develop reliable, scalable, and simple encapsulation for future large-area PSCs, this work establishes solution-based bilayer encapsulation, which is applicable for flexible solar modules as well as other optoelectronic devices such as light-emitting devices and photodetectors.improvement of device stability up to 500 h under outdoor illumination, retaining almost 90% of the initial PCE. Considering the urge to develop reliable, scalable, and simple encapsulation for future large-area PSCs, this work establishes solution-based bilayer encapsulation, which is applicable for flexible solar modules as well as other optoelectronic devices such as light-emitting devices and photodetectors.

Interfacial Linkage and Carbon Encapsulation Enable Full Solution-Printed Perovskite Photovoltaics with Prolonged Lifespan.

Simplified perovskite solar cells (PSCs) were fabricated with the perovskite layer sandwiched and encapsulated between carbon-based electron transport layer (ETL) and counter electrode (CE) by a fully blade-coated process. A self-assembled monolayer of amphiphilic silane (AS) molecules on transparent conducting oxide (TCO) substrate appeals to the fullerene ETL deposition and preserves its integrity against the solvent damage. The AS serves as a "molecular glue" to strengthen the adhesion toughness at the TCO/ETL interface via robust chemical interaction and bonding, facilitating the interfacial charge extraction, increasing PCEs by 77 % and reducing hysteresis. A PCE of 18.64 % was achieved for the fully printed devices, one of the highest reported for carbon-based PSCs. AS-assisted interfacial linkage and carbon-material-assisted self-encapsulation enhance the stability of the PSCs, which did not experience performance degradation when stored at ambient conditions for over 3000 h.

Photoelectrochemical Water-Splitting Using CuO-Based Electrodes for Hydrogen Production: A Review.

The cost-effective, robust, and efficient electrocatalysts for photoelectrochemical (PEC) water-splitting has been extensively studied over the past decade to address a solution for the energy crisis. The interesting physicochemical properties of CuO have introduced this promising photocathodic material among the few photocatalysts with a narrow bandgap. This photocatalyst has a high activity for the PEC hydrogen evolution reaction (HER) under simulated sunlight irradiation. Here, the recent advancements of CuO-based photoelectrodes, including undoped CuO, doped CuO, and CuO composites, in the PEC water-splitting field, are comprehensively studied. Moreover, the synthesis methods, characterization, and fundamental factors of each classification are discussed in detail. Apart from the exclusive characteristics of CuO-based photoelectrodes, the PEC properties of CuO/2D materials, as groups of the growing nanocomposites in photocurrent-generating devices, are discussed in separate sections. Regarding the particular attention paid to the CuO heterostructure photocathodes, the PEC water splitting application is reviewed and the properties of each group such as electronic structures, defects, bandgap, and hierarchical structures are critically assessed.

Chemical Vapor Deposition of Two-Dimensional Boron Sheets by Thermal Decomposition of Diborane.

Two-dimensional (2D) boron sheets (borophenes) are promising materials for the next generation of electronic devices because of their metallic conductivity. Molecular beam epitaxy has remained the main approach for the growth of borophene, which considerably restricts large-scale production of 2D boron sheets. The high melting point of boron and the growth of borophenes at moderate temperatures posed a significant challenge for the synthesis of borophenes. Employing diborane (B2H6) pyrolysis as a pure boron source, we report, for the first time, the growth of atomic-thickness borophene sheets by chemical vapor deposition (CVD). A methodical study on the effect of temperature, deposition rate, and pressure on the growth of 2D boron sheets is provided and detailed analyses about the morphology and crystalline phase of borophene sheets are presented. The CVD-borophene layers display an average thickness of 4.2 Å, χ3 crystalline structure, and metallic conductivity. We also present experimental evidence supporting the formation of stacked bilayer and trilayer borophene sheets. Our method paves the way for empirical investigations on borophenes.

Nanofibrous Scaffolds Containing Hydroxyapatite and Microfluidic-Prepared Polyamidoamin/BMP-2 Plasmid Dendriplexes for Bone Tissue Engineering Applications.

OBJECTIVE: The aim of this study is to fabricate functional scaffolds to gene delivery bone morphogenetic protein-2 (BMP-2) plasmid for bone formation in bone tissue engineering. METHODS: Dendriplexes (DPs) of generation 4 polyamidoamin (G4-PAMAM)/BMP-2 plasmid were prepared through microfluidic (MF) platform. The physiochemical properties and toxicity of DPs were evaluated by DLS, AFM, FESEM and MTT assay. In order to create a suitable environment for stem cell growth and differentiation, poly-l-lactic acid (PLLA) and poly-l-lactic acid/poly (ethylene oxide) (PLLA/PEO) scaffolds containing hydroxyapatite nanoparticles (HA) and DPs were fabricated by the electrospinning method. The osteogenic potency of the scaffolds on human adipose tissue-derived mesenchymal stem cells (hASCs) was investigated. RESULTS: The results revealed that tuning the physical properties of DPs by adjusting flow parameters in microfluidic platform can easily improve the cell viability compared to conventional bulk mixing method. Also, the result showed that the presence of HA and DPs in PLLA/PEO scaffold enhanced alkaline phosphatase (ALP) activity and increased the amount of deposited Ca, as well as, related to osteogenesis gen markers. CONCLUSION: This study indicated that on using the MF platform in preparation of DPs and loading them along with HA in PLLA/PEO scaffold, the osteogenic differentiation of hASCs could be tuned.

Engineering Water and Solute Dynamics and Maximal Use of CNT Surface Area for Efficient Water Desalination.

While polymer-based membranes and the consistent plants and elements have long been considered and optimized, there are only few studies on optimization of the new generation of carbon-based porous membranes for water desalination. By modeling the elements and their corresponding parameters in a vertical configuration via COMSOL Multiphysics software, an experimental setup was modified that contained various bare and carbon nanotube (CNT)-covered microprocessed porous membranes in parallel and in series. Several design parameters such as inlet pressure, length of outlet, vertical distance of the parallel membranes, and horizontal distances of the series membranes were optimized. Taking advantage of the uttermost surface area of CNTs and the engineered particle trajectory, almost 90% NaCl rejection and 97% Allura red rejection were obtained with very high permeation values. Considering microsized outlets, the results of particle rejections are outstanding owing to the smart design of the setup. The results of this work can be extended to larger and smaller scales up to the point where the governing equations still hold.

Water Softening Using a Light-Responsive, Spiropyran-Modified Nanofiltration Membrane.

A novel technique for the covalent attachment of a light-responsive spiropyran onto polyamide thin film composite nanofiltration (NF) membranes in a one-step reaction using low-energy electron beam technology is described. The effect of illumination of the immobilized spiropyran was studied, as well as the resulting membrane properties with respect to MgSO4 retention, water permeability rate, and chlorine resistance. Electron beam irradiation showed a direct effect on the transformation of the rough PA NF membrane surface into a ridge-and-valley structure. Upon UV light irradiation, the spiropyran transformed into zwitterionic merocyanine, which had shown MgSO4 removal of >95% with water permeation rates of 6.5 L/(m²·h·bar). Alternatively, visible light was used to convert merocyanine to spiropyran, which achieved >95% of MgSO4 retention with a water flux of around 5.25 L/(m²·h·bar). The modified NF membranes showed higher chlorine resistance as well as a higher normalized water flux as compared to the reference membrane, without a loss of ion retention. All the NF membranes were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. This study demonstrates a simple and inexpensive method for the immobilization of molecules onto polymeric membranes, which may be applied in water softening.

A graphene/Si Schottky diode for the highly sensitive detection of protein.

Herein, a graphene/Si-based device was introduced for bovine serum albumin (BSA) sensing. In this study, it is shown that the Schottky junction at the interface of graphene/Si is highly sensitive to BSA under UV light exposure. The reverse bias current of the junction, which is sensitive to UV light, changes under exposure to BSA at different concentrations. By UV light absorption, we showed that the addition of the BSA solution to the junction affected the output characteristic of the fabricated device. Moreover, the output characteristic of the device shows that the device can be considered as a self-powered detector that would reduce the need for batteries. The results obtained in this study would open up a way towards the fabrication of an on-chip biosensor for the sensing of biological agents such as BSA.

Electron Transport in Quasi-Two-Dimensional Porous Network of Titania Nanoparticles, Incorporating Electrical and Optical Advantages in Dye-Sensitized Solar Cells.

The integration of fast electron transport and large effective surface area is critical to attaining higher gains in the nanostructured photovoltaic devices. Here, we report facilitated electron transport in the quasi-two-dimensional (Q2D) porous TiO2 . Liquid electrolyte dye-sensitized solar cells were prepared by utilizing photoanodes based on the Q2D porous substructures. Due to electron confinement in a microscale porous medium, directional diffusion toward collecting electrode is induced into the electron transport. Our measurements based on the photocurrent and photovoltage time-of-flight transients show that at higher Fermi levels, the electron diffusion coefficient in the Q2D porous TiO2 is about one order of magnitude higher when compared with the conventional layer of porous TiO2 . The results show that microstructuring of the porous TiO2 leads to an approximately threefold improvement in the electron diffusion length. Such a modification may considerably affects the electrical functionality of moderate or low performance dye-sensitized solar cells for which the internal gain or collection efficiency is typically low.

Variable electron beam diameter achieved by a titanium oxide/carbon nanotube hetero-structure suitable for nanolithography.

We report the fabrication of a titanium oxide/carbon nanotube based field emission device suitable for nanolithography and fabrication of transistors. The growth of carbon nanotubes (CNTs) is performed on silicon substrates using a plasma-enhanced chemical vapor deposition method. The vertically grown CNTs are encapsulated by titanium oxide (TiO(2)) using an atmospheric pressure chemical vapor deposition system. Field emission from the CNTs is realized by mechanical polishing of the prepared structure. Possible applications of such nanostructures as a lithography tool with variable electron beam diameter has been investigated. The obtained results show that a spot size of less than 30 nm can be obtained by applying the proper voltage on TiO(2) surrounding gate. Electrical measurements of the fabricated device confirm the capability of the structure for fabrication of field emission based field effect transistors. By a voltage applied between the gate and the cathode electrode, the emission current from CNTs shows a significant drop, indicating proper control of the gate on the emission current.