Two-dimensional materials based on transition metal carbides have been intensively studied due to their unique properties including metallic conductivity, hydrophilicity and structural diversity and have shown a great potential in several applications, for example, energy storage, sensing and optoelectronics. While MXenes based on magnetic transition elements show interesting magnetic properties, not much is known about the magnetic properties of titanium-based MXenes. Here, we measured the magnetic properties of Ti3C2Tx MXenes synthesized by different chemical etching conditions such as etching temperature and time. Our magnetic measurements were performed in a superconducting quantum interference device (SQUID) vibrating sample. These data suggest that there is a paramagnetic-antiferromagnetic (PM-AFM) phase transition and the transition temperature depends on the synthesis procedure of MXenes. Our observation indicates that the magnetic properties of these MXenes can be tuned by the extent of chemical etching, which can be beneficial for the design of MXenes-based spintronic devices.
Band gap engineering of GaAsSbN nanowires (NWs) grown by Ga-assisted molecular beam epitaxy and demonstration of a Te-doped axial GaAsSbN NW-based Schottky barrier photodetector on p-Si (111) in the near-infrared region are reported. Stringent control on NW nucleation conditions, stem growth duration, and NW exposure to the N-plasma were found to be critical for the successful growth of high-quality dilute nitride quaternary GaAsSbN NWs in the axial configuration. Planar defect-free structures were realized with room temperature photoluminescence (PL) characteristics, revealing reduced N-induced point defects and nonradiative recombination centers. N incorporation in the dilute nitride NWs was ascertained from PL and Raman spectral mode shifts and shapes and weak temperature-dependent PL peak energy. The advantage of Te-doping in dilute nitride NWs using a GaTe captive source is the compensation of point defects, as evidenced by a significant improvement in PL characteristics, Raman mode shifts, and spectral shape, with improved photodetector device performance relative to intrinsic dilute nitride NWs. Te-doped GaAsSbN NW Schottky-based photodetectors have been demonstrated on both single and ensemble configurations with a resultant responsivity of 5 A/W at 860 nm and 3800 A/W at 1100, respectively. Detectivity of 3.2 × 10 10 Jones was achieved on the Te-doped ensemble NW device. The findings presented in this work showcase prospects for rich band gap engineering using doped GaAsSbN NWs for near-infrared region device applications.
Ga assisted GaAs/GaAsSb core-shell structured nanowires were successfully grown on chemically etched p-type Si(111) substrate by molecular beam epitaxy (MBE). The morphology, structural and optical properties of the nanowires are found to be strongly influenced by the shell growth temperature and Sb% in the nanowires. The nanowires exhibit planar defects like twins and stacking faults, with more stacking faults and micro-twins found at the top section. Optical characteristics of the nanowires as measured by 4K photoluminescence (PL) exhibit a red shift to 1.2 eV with increasing Sb incorporation up to 12%. The Raman spectra of reference GaAs nanowires show TO and LO modes representative of the zinc blende structure at 291 cm -1 and 267.8 cm -1 , respectively. Red shifts of both modes in conjunction with corresponding asymmetrical peak broadening observed in X-ray diffraction with increasing Sb incorporation are attributed to enhanced strain and disorder within the nanostructures. Nanowires of similar Sb composition but grown at different shell temperatures reveal straight nanowires with better microstructural and optical quality when grown at higher growth temperatures. The presence of GaAs passivation layer significantly enhanced the PL intensity such that PL was observed even at room temperature.
We report the growth of vertical, high-quality GaAs0.9Sb0.1 nanowires (NWs) with improved density on oxygen (O2) plasma-treated monolayer graphene/SiO2/p-Si(111) by self-catalyzed molecular beam epitaxy. An O2 plasma treatment of the graphene under mild conditions enabled modification of the surface functionalization and improved reactivity of the graphene surface to semiconductor adatoms. The rise in the disorder peak of the Raman mode, decreased surface conductivity, and creation of additional O2 groups of plasma-treated graphene compared to that of pristine graphene confirmed functionalization of the graphene. To enhance the nucleation centers further for the vertical yield of NWs on the graphene surface, NWs were grown on a higher Sb composition GaAs0.6Sb0.4 stem for surface engineering the graphene surface via the surfactant effect of Sb and for better lattice matching. The NWs grown under optimal conditions exhibited a zinc blende crystal structure with no discernible structural defects. The NWs with a GaAs-passivated shell exhibited photoluminescence emission at 1.35 eV at 4 K and 1.28 eV at room temperature. The ensemble device fabricated with a top segment of GaAsSb NW-doped n-type using a GaTe captive source exhibited an optical responsivity of 110 A/W with a detectivity of 1.1 × 1014 Jones. These results of hybrid GaAsSb NW heterostructure/graphene devices show significant potential toward the fabrication of flexible near-infrared photodetector device applications. Further, the simple and efficient O2 plasma treatment approach for surface engineering of graphene in conjunction with a high Sb compositional stem has shown to be a promising route that can be broadly applicable for the growth of other III–V ternary material systems for improving the vertical yield of NWs.
This study presents dual-responsive colloidal microgels to repair nonwoven fiber mats (NWFs) and recover their native morphological and functional properties. The formulation comprises poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAmco-AA) microgels loaded with iron oxide nanoparticles acting as magneto-responsive "bricks" and poly(N-isopropylacrylamide-co-N-4-benzoylphenyl acrylamide) (PNIPAm-co-BPAm) serving as photo-cross-linkable "mortar". The formulation is employed to repair small tears in meltblown polypropylene (PP) and polybutylene terephthalate (PBT) NWFs and recover the functional properties of the native membranes. Specifically, magnetically directed and UV-light-triggered repair recovers (i) the topological integrity, as shown by optical microscopy and image analysis of PP and PBT NWFs, (ii) the mechanical properties, as demonstrated by the values of tensile modulus of native, damaged, and repaired PP NWFs, and (iii) the permeability to sodium chloride of both PP and PBT NWFs. A comparative study of repair using magneto-responsive and photo-cross-linkable vs photocross-linkable-only formulations demonstrate that magnetic localization is vital to ensure rapid, spatially accurate, and effective recovery of the morphological and functional properties of damaged NWFs.
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