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Magnetism of the MoS2 semiconducting atomic layer was highlighted for its great potential in the applications of spintronics and valleytronics. In this study, we demonstrate an evolution of magneto-electrical properties of single layer MoS2 with the modulation of defect configurations and formation of a partial 1T phase. With Ar treatment, sulfur was depleted within the MoS2 flake leading to a 2H (low-spin) → partial 1T (high-spin) phase transition. The phase transition was accompanied by the development of a ferromagnetic phase. Alternatively, the phase transition could be driven by the desorption of S atoms at the edge of MoS2via O2 treatment while with a different ordering magnitude in magnetism. The edge-sensitive magnetism of the single-layer MoS2 was monitored by magnetic force microscopy and validated by a first-principle calculation with graded-Vs (sulfur vacancy) terminals set at the edge, where band-splitting appeared more prominent with increasing Vs. Treatment with Ar and O2 enabled a dual electrical characteristic of the field effect transistor (FET) that featured linear and saturated responses of different magnitudes in the Ids-Vds curves, whereas the pristine MoS2 FET displayed only a linear electrical dependency. The correlation and tuning of the Vs-1T phase transition would provide a playground for tailoring the phase-driven properties of MoS2 semiconducting atomic layers in spintronic applications.

Phase transformation and electric properties of lead-free piezoceramics (Bi 0.5 Na 0.5 ) 1− x Ba x TiO 3 with x =0.05, 0.06, and 0.07(BNB5T, BNB6T and BNB7T) were investigated using dielectric, piezoelectric and ferroelectric measurements. Electric field induced strain measurement shows “W” shape bipolar strain characteristics for BNB5T with typical ferroelectric P – E curve, while BNB6T and BNB7T, possessing pinch-off P – E , exhibit “V” shape field-induced strain. All the BNB x T specimens exhibit relaxor characteristic, identified by the Debye Law. Dielectric properties measured at elevated temperatures with the frequency variation (10–500 kHz) reveal frequency dispersion below the T d point, but no dispersion between T d and T m , which may be ascribed to an intermediate phase transition. By adding more Ba 2+ ions, the region of intermediate phase, distinguished by frequency dependence dielectric constant, expands to lower temperature. Moreover, the ferroelectric properties measured at elevated temperature were carried out below and at the depolarization temperature to well investigate the existence of this phase. Much less e – T profile dispersion were observed during the investigation of BNB6T and BNB7T, leading to possible existence of an intermediate phase in the investigated compositions. The results suggest that the linear field-induced-strain of (Bi 0.5 Na 0.5 ) 1− x Ba x TiO 3 are expected to be attributed to the intermediate phase.

We demonstrated the application of CoPd magnetic devices in single (H2) and dual (H2 and CO) gas detection by varying the thin-film structure. The anomalous Hall effect provided the read-out signal of the devices. The dual-gas sensor was particularly useful for examining whether methane reformation by steam was completed during H2 production where CO is a byproduct. Through in situ Fourier transform infrared and X-ray absorption spectroscopy, we discovered that H2 detection involved a charge-transfer effect between Co and Pd in addition to a surface-adsorption process, for both multilayer and alloy structures; however, CO detection was solely associated with a surface-adsorption process, which only occurred in the alloy structure. The proposed devices demonstrated performances exceeding those of current commercial models (solid-state based) regarding power consumption (

A relatively simple, and high-efficiency method is reported to synthesize AlN nanowires, using catalyst-assisted chemical vapor deposition. A thin film of 5 nm Ni layer was deposited on sapphire as catalyst. Structural property of as-grown nanowires was investigated in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) These large scale, high quality and uniform nanowires have smooth surface with diameter of 50 nm and length of 10–30 μ m, which are hexagonal single-crystalline with c = 0.497 nm, a = 0.272 nm and grow along [100] direction. Our results provide the first direct evidence of vapor-liquid-solid growth mechanism for AlN nanowires.

We have investigated growth conditions and structure of Wurzite AlN nanowires grown on sapphire (0002) substrates by chemical vapor deposition. The morphology, and structure were characterized by scanning electron microscopy, X-ray diffraction, and Raman analysis. Luminescence properties of AlN nanowires were studied by electron and photon excitation measurements, such as cathodoluminescence and photoluminescence. Band to band excitonic feature at 6.12 eV was first observed at room temperature in this study. Two typical defect band related transmissions around 3.0 eV and 4.85 eV were also observed, which are due to the radioactive recombination processes involving oxygen impurity and Al vacancies.

This paper reports on a magnetic device with a [Co40Pd60/Cu]10/Fe structure for use in the detection of H2. In a magneto-optical, transport, and gas-detection system, the proposed device presented sharp, reproducible H2-dependent magnetic/electrical properties. The device's saturation magnetization (induced resistance change) dropped (increased) by a factor of ∼5 when a H2 pressure of 75 kPa is given. Besides, the electrical signal-to-noise ratio of the device can be restored ∼50% by exposing it to a magnetic field of 1000 Oe, even when the sensitivity of the device dropped at a low H2 pressure (0.7 KPa). This demonstrates the applicability of the device for use as a low-pressure H2 detector. Operando x-ray spectroscopy revealed that changes in H2-induced magnetism arose from a Co-Pd charge transfer effect coupled to changes in the local-structure symmetry.

Using synchrotron x-ray techniques, we studied the Co2FeAl spin-polarization state that generates the half-metallicity of the compound during an A2 (low-spin) → B2 (high-spin) phase transition. Given the advantage of element specificity of x-ray techniques, we could fingerprint the structural and magnetic cross-reactions between Co and Fe within a complex Co2FeAl structure deposited on a MgO (0 0 1) substrate. X-ray diffraction and extended x-ray absorption fine structure investigations determined that the Co atoms preferably populate the (1/4,1/4,1/4) and (3/4,3/4,3/4) sites during the development of the B2 phase. X-ray magnetic spectroscopy showed that although the two magnetic elements were ferromagnetically coupled, they interacted in a competing manner via a charge-transfer effect, which enhanced Co spin polarization at the expense of Fe spin polarization during the phase transition. This means that the spin-polarization of Co2FeAl was electronically dominated by Fe in A2 whereas the charge transfer turned the dominance to Co upon B2 formation. Helicity-dependent x-ray absorption spectra also revealed that only the minority state of Co/Fe was involved in the charge-transfer effect whereas the majority state was independent of it. Despite an overall increase of Co2FeAl magnetization, the charge-transfer effect created an undesired trade-off during the Co–Fe exchange interactions, because of the presence of twice as many X sites (Co) as Y sites (Fe) in the Heusler X 2 YZ formula. This suggests that the spin-polarization of Co2FeAl is unfortunately regulated by compromising the enhanced X (Co) sites and the suppressed Y (Fe) sites, irrespective of the development of the previously known high-spin-polarization phase of B2. This finding provides a possible cause for the limited half-metallicity of Co2FeAl discovered recently. Electronic tuning between the X and Y sites is necessary to further increase the spin-polarization, and likely the half-metallicity as well, of the compound.

We have investigated the luminescence properties of single-chrystalline Wurtzite AlN nanowires by electron and photon excitation measurements, such as cathodoluminescence and photoluminescence. Band to band excitonic feature at 6.12eV was first observed at room temperature in this study. Two typical defect band related transmissions around 3.0eV and 4.85eV were also observed, which are due to the radioactive recombination processes involving oxygen impurity and Al vacancies. The Wurzite AlN nanowires were grown on sapphire (0002) substrates by catalyst-assisted chemical vapor deposition. The morphology and structure were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman analysis.

We report a simple synthesis of AlN nanowires via catalyst-assisted chemical vapor deposition method. These high quality and uniform nanowires have smooth surface with diameter of 50 nm and length of 10–30 µ m, which are hexagonal single-crystal with lattice parameters c = 0.497 nm, a = 0.272 nm and grow along [100] direction. The morphology and structure were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman analysis. Our results provide the first direct evidence of vapor-liquid-solid growth mechanism for the synthesis of AlN nanowires.