Graphene-tuned EIT-like effect in photonic multilayers for actively controlled light absorption of topological insulators

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement As newly emerging nanomaterials, topological insulators with unique conducting surface states that are protected by time-reversal symmetry present excellent prospects in electronics and photonics. The active control of light absorption in topological insulators are essential for the achievement of novel optoelectronic devices. Herein, we investigate the controllable light absorption of topological insulators in Tamm plasmon multilayer systems composed of a Bi1.5Sb0.5Te1.8Se1.2 (BSTS) film and a dielectric Bragg mirror with a graphene-involved defect layer. The results show that an ultranarrow electromagnetically induced transparency (EIT)-like window can be generated in the broad absorption spectrum. Based on the EIT-like effect, the Tamm plasmon enhanced light absorption of topological insulators can be dynamically tuned by adjusting the gate voltage on graphene in the defect layer. These results will pave a new avenue for the realization of topological insulator-based active optoelectronic functionalities, for instance light modulation and switching

Topological insulator based Tamm plasmon polaritons

Topological insulators as relatively new quantum materials with the topologically protected conducting Dirac surface state reveal fantastic electronic and photonic characteristics. The photonic behaviors of topological insulators are particularly significant for exploring their optical phenomena and functional devices. Here, we present the generation of Tamm plasmon polaritons (TPPs) in a topological insulator multilayer structure consisting of a Bi 1.5 Sb 0.5 Te 1.8 Se 1.2 (BSTS) nanofilm and a one-dimensional photonic crystal (PC). The results illustrate that the TPP electric field can locally concentrate between the BSTS nanofilm and PC, contributing to the improved light-BSTS interaction with a 3-fold enhancement of light absorption. It is also found that the near-infrared TPP response can be dynamically tailored by adjusting the PC layer thickness, BSTS nanofilm thickness, and angle of incident light. The theoretical calculations are in excellent agreement with the numerical simulations. Additionally, the TPP field intensity and light-topological insulator interaction are capable of being further reinforced by introducing a dielectric spacer between the BSTS nanofilm and PC. Our results will enrich the optical characteristics and application potential of topological insulators

Bonding of graphite to Cu with metal multi-foils

Graphite/Cu bonding is essential for the fabrication of graphite-based plasma-facing parts and graphite-type commutators. Transient liquid phase bonding of graphite/Cu has been conducted separately with Ti/Cu/Ti and Ti/Cu/Ni/Ti multi-foils. The interfacial microstructure and mechanical properties of the bonded joints have been characterized. For the joint with Ti/Cu/Ti multi-foils, complete melting of the Ti/Cu/Ti multi-foils and interdiffusion between the molten zone and the Cu substrate occur during the bonding process, leading to formation of Ti–Cu intermetallics in the bonding area. The liquid phase flowing toward the sidewall of the Cu substrate gives rise to a thickness of the bonding area far less than those of the as-received multi-foils. For the joint with Ti/Cu/Ni/Ti multi-foils, the bonding area can be divided into three parts (areas I, II and III). The bonding areas I and III comprise Ti–Cu intermetallics and Ti(CuxNi1-x)2, while the bonding area II consists of an Ni layer and two thin TiNi3 reaction layers. The thickness of the whole bonding area is similar to those of the as-received multi-foils, indicating that addition of Ni foil can prevent the loss of liquid phase zone by inhibiting the excessive liquid phase formation. The addition of a Ni foil in bonding of the graphite/Cu may alleviate the joint residual stress by its intermediate coefficient of thermal expansion (CTE) to accommodate any thermal mismatch in the joint and by its superior ductility and plasticity, thus resulting in shear strength promotion of the joint with the Ti/Cu/Ni/Ti multi-foils by approximately 35% when compared to the Ti/Cu/Ti multi-foils

Aesthetic coatings for silver based alloys with improved protection efficiency

Ag-based alloy samples are submitted to innovative chemical and low pressure plasma treatments that lead to the deposition of aestheticcoatings with improved corrosion protection properties. The chemical treatments are carried out in alkaline dithionate solution in order to clean the surface and eventually remove the patina on aged samples, then the surface is protected by a Paraloid B72 coating containing different percentages of Al2O3 nanopigments. The plasma treatments are carried out by deposition of SiOx thin films in plasma fed with TEOS, Ar and O2. Before the PECVD deposition, a glow discharge in a low pressure hydrogen plasma eventually removes tarnishing, reducing the corrosion products layer back to silver. The coating protective effectiveness is assessed by means of electrochemical impedance spectroscopy and accelerated ageing tests. The corrosion mechanism of the coated samples is investigated by XRD analyses. Both the chemical and the plasma treatments show satisfactory results from an aesthetic point of view and good barrier effect against aggressive environmental agent

Magnetic characteristics of LaMnO3+δ thin films deposited by RF magnetron sputtering in an O2/Ar mixture gas

In this work, LaMnO _3+ _δ thin films have been successfully fabricated by RF magnetron sputtering using different O _2 /Ar flux ratios. The crystal structures, morphologies, stoichiometry, surface chemical states and magnetic properties of films are thoroughly characterized by x-ray powder diffraction (XRD), Raman spectrometer, scanning electron microscopy (SEM), x-ray photoelectron spectroscopy (XPS) and superconducting quantum interference device (SQUID). The magnetic characteristics of LaMnO _3+ _δ films are systematically studied with the transformation from Mn ^3+ to Mn ^4+ , which is strongly controlled by the deposited O _2 /Ar flux ratios. We demonstrate that LaMnO _3+ _δ films undergo an antiferromagnet, the coexistence of ferromagnetism and antiferromagnetism and a robust ferromagnetism ordering by the variation of Mn ^3+ /Mn ^4+ ratios. The LMO film deposited in pure argon atmosphere shows negligible FM signal and an inconspicuous T _C . With the increase of deposited O _2 /Ar flux ratios, the Curie temperature of LMO films increases from 100 K to 224 K and then decreases to 140 K and meanwhile the irreversibility temperature fluctuates between 24 K and 100 K. The appearance of cluster glass state and the unexpected exchange bias phenomenon where the film deposited at highest O _2 /Ar flux ratio has a H _EB  ∼ 115 Oe is observed. All these evolutions of magnetization characteristics are discussed in terms of the strength of ferromagnetic interactions and the degree of competition between ferromagnetic and antiferromagnetic interactions in LaMnO _3+ _δ films. Our work serves as prerequisites for LaMnO _3 -based magnetic heterostructures grown by RF magnetron sputtering

Non-invasive assessment of the corrosion behaviour of metallic ar-tefacts displayed in museum showcases

Paper 932

An impedance spectroscopy system for the in-situ assessment of the conservation state of archaeological bronzes

paper 9626 - The protective effectiveness of bronze patinas can be evaluated using electrochemical impedance spectroscopy (EIS). However, EIS, a well-established method to investigate metal coatings for general purposes, requires to perform the measurement in an electrolytic solution that may alter the surface of an artefact of archaeological or artistic interest, furthermore the need of evaluating and monitoring the conservation state of irremovable artefacts, is not satisfied by the widely employed EIS laboratory instruments. In this work, a portable impedance spectroscopy analyzer equipped with a specially designed dry- probe, that avoids the use of the electrolyte, is proposed for the evaluation of the protective effectiveness of surface layers of metallic cultural heritage artefacts. The overall system has been tested on different kinds of patinas, synthetized from sulphate and nitrate solutions on a Cu-Sn alloy, with the ultimate goal of establishing a procedure for the in situ assessment of bronzes of archaeological and artistic interest. The protective effectiveness of bronze patinas can be evaluated using electrochemical impedance spectroscopy (EIS). However, EIS, a well-established method to investigate metal coatings for general purposes, requires to perform the measurement in an electrolytic solution that may alter the surface of an artefact of archaeological or artistic interest, furthermore the need of evaluating and monitoring the conservation state of irremovable artefacts, is not satisfied by the widely employed EIS laboratory instruments. In this work, a portable impedance spectroscopy analyzer equipped with a specially designed dry- probe, that avoids the use of the electrolyte, is proposed for the evaluation of the protective effectiveness of surface layers of metallic cultural heritage artefacts. The overall system has been tested on different kinds of patinas, synthetized from sulphate and nitrate solutions on a Cu-Sn alloy, with the ultimate goal of establishing a procedure for the in situ assessment of bronzes of archaeological and artistic interes

Microstructural and Mechanical Characterizations of Mo/W and Mo/Graphite Joints with BNi2 Paste

Brazing of Mo to W and to graphite is achieved using BNi2 paste (containing Ni, Cr, Si, and B). For the Mo/W or Mo/graphite joint, the joining area consists of a diffusion area and a brazing area. The diffusion area is composed of MoNi and Mo, which is formed by diffusion of the Mo substrate into the braze during brazing. The brazing area of the Mo/W joint contains Ni(ss) (solid solution), Cr(ss), Ni3B, CrB, and Ni4W, while the brazing area of the Mo/graphite joint mainly comprises Ni(ss), MoNi, Ni3B, and CrB. A continuous chromium carbide layer is formed at the brazing area/graphite interface in the Mo/graphite joint due to the reaction of Cr in the BNi2 braze with the graphite. Nanoindentation measurements of the joints show that the diffusion area exhibits the highest hardness and elastic modulus in the joints. The shear strengths of the Mo/W and Mo/graphite joints are 58.1 ± 16.0 and 13.0 ± 4.0 MPa, respectively. The Mo/W and Mo/graphite joints fracture after the shear tests in the W and graphite sides, respectively, near the joining area, indicating that both fractures are caused by the stress concentration in the corresponding areas