No Arabic abstract
Bismaleimide (BMI) are thermosetting polymers mainly used in aerospace applications having properties of dimensional stability, low shrinkage, chemical resistance, fire resistance, good mechanical properties and high resistance against various solvents, acids, and water. BMI is commercially available as Homide 250. BMI coating has also been used for the corrosion protection. Metallization (AL) of BMI using vacuum evaporation was done which serves the purpose of prevention of space charge accumulation in aircraft bodies. Addition of inorganic materials like metal oxides can influence the properties of the polymer as an inorganic-organic composite. The organic-ionorganic composites have wide applications in electronics, optics, chemistry and medicine. Titanium dioxide (TiO2, Titania) has a wide range of applications starting from photocatalysis, dye-sensitized solar cells to optical coatings and electronics. A BMI-TiO2 composite was prepared by chemical route. Atmospheric Plasma Jet (APPJ) using Helium gas was also treated on BMI. XRD and FTIR studies of the composite system prepared at different temperatures showed its crystalline and structural configuration.
We present a methodology based on textit{ex-situ} (post-growth) electrochemistry to control the oxygen concentration in thin films of the superconducting oxide La$_2$CuO$_{4+y}$ grown epitaxially on substrates of isostructural LaSrAlO$_4$. The superconducting transition temperature, which depends on the oxygen concentration, can be tuned by adjusting the pH level of the base solution used for the electrochemical reaction. As our main finding, we demonstrate that the dopant oxygens can either occupy the interstitial layer in an orientationally disordered state or organize into a crystalline phase via a mechanism in which dopant oxygens are inserted into the substrate, changing the lattice symmetry of both the substrate and the epitaxial film. We discuss this mechanism, and describe the resulting methodology as a platform to be explored in thin films of other transition metal oxides.
Developments in optoelectronics and spin-optronics based on transition metal dichalcogenide monolayers (MLs) need materials with efficient optical emission and well-defined transition energies. In as-exfoliated MoS2 MLs the photoluminescence (PL) spectra even at low temperature consists typically of broad, overlapping contributions from neutral, charged excitons (trions) and localized states. Here we show that in superacid treated MoS2 MLs the PL intensity increases by up to 60 times at room temperature. The neutral and charged exciton transitions are spectrally well separated in PL and reflectivity at T=4 K, with linewidth for the neutral exciton of 15 meV, but with similar intensities compared to the ones in as-exfoliated MLs at the same temperature. Time resolved experiments uncover picoseconds recombination dynamics analyzed separately for charged and neutral exciton emission. Using the chiral interband selection rules, we demonstrate optically induced valley polarization for both complexes and valley coherence for only the neutral exciton.
Artificial atomic systems in solids are becoming increasingly important building blocks in quantum information processing and scalable quantum nanophotonic networks. Yet, synthesis of color centers that act as single photon emitters which are suitable for on-chip applications is still beyond reach. Here, we report a number of plasma and thermal annealing methods for the fabrication of emitters in tape-exfoliated hexagonal boron nitride (hBN) crystals. A two-step process comprised of Ar plasma etching and subsequent annealing in Ar is highly robust, and yields a seven-fold increase in the concentration of emitters in hBN. The initial plasma etching step generates emitters that suffer from blinking and bleaching, whereas the two-step process yields emitters that are photostable at room temperature and have an emission energy distribution that is red-shifted relative to that of pristine hBN. An analysis of emitters fabricated by a range of plasma and annealing treatments, combined with a theoretical investigation of point defects in hBN indicates that single photon emitters characterized by a high degree of photostability and emission wavelengths greater than ~700 nm are associated with defect complexes that contain oxygen. This is further confirmed by generating the emitters by annealing hBN in an oxidative atmosphere. Our findings advance present understanding of the structure of quantum emitter in hBN and enhance the nanofabrication toolkit that is needed to realize integrated quantum nanophotonics based on 2D materials.
Structural alterations in v-SiO2 induced by thermal poling, a treatment which makes the glass able to double the frequency of an impinging infrared light, are revealed by neutron diffraction as a breakdown of the macroscopic isotropy. This leads to concomitant changes in the vibrational density of states measured by inelastic neutron scattering. The observations are found to be consistent with the emergence of partial ordering within the glassy matrix along the direction of an electrostatic field applied during the poling treatment.
Microstructural analysis of a Mg-Zn alloy deformed at room temperature by high-pressure torsion (HPT) indicates that fine-scale precipitation occurs even without post-deformation heat treatment. Small-angle X-ray scattering detects precipitates with radii between 2.5-20 nm after one rotation, with little increase in particle size or volume fraction after 20 rotations. High resolution electron micrographs identify grain boundary precipitates of monoclinic Mg$_4$Zn$_7$ phase after three rotations and MgZn$_2$ after 20 rotations.