Results 1 - 10 of 86107
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[en] Optical absorption and emission spectra are the important quantifiable properties for CuI as a promising optoelectronic material. Previous research on the sputter deposition of CuI focuses on room-temperature growth. Herein, the effect of growth temperature on the selected optical features of sputtered CuI thin films is investigated. An enhanced visible light transparency and a steeper absorption edge are achieved for CuI thin films by optimizing the growth temperature. The PL intensity ratio of free exciton to defect-related emission increases with increasing substrate temperature. These results suggest a strategy of growth temperature optimization for the enhanced absorption and emission of CuI for advanced optoelectronic applications. (© 2020 Wiley‐VCH GmbH)
[en] A nano-sized two-terminal memristor exhibiting volatile threshold switching (TS) is a promising candidate for the emulation of biological synaptic functions to realize efficient neuromorphic computing systems. The Ca dynamics play a vital role in generating a temporal response for neural functions by changing the synaptic weight of biological synapses. Herein, a thinnest synaptic device is fabricated demonstrating drift dynamics of Ag migration through the exfoliated h-BN sheets, which emulates neuromorphic computing operations. The TS characteristics with a large I up to ≈10 lead to bio-synaptic applications, including short-term and long-term memory. The experimental realization of the synaptic behavior is demonstrated with paired-pulse facilitation (PPF), spike-rate-dependent plasticity (SRDP), and transition from short-term plasticity (STP) to long-term plasticity (LTP). The transition from STP to LTP in this synaptic device verifies the Atkinson and Shiffrin psychological model of human brain learning experimentally. The input pulses with different spike-times are used to replicate the synaptic functionalities. The two-terminal diffusive memristors constructed with thin sheets of 2D-flexible h-BN resistive materials may lead to flexible neuromorphic devices for biological applications. (© 2020 Wiley‐VCH GmbH)
[en] The influence of N concentration on the crystallization kinetics, microstructural evolution, and composition of Ge-rich GeSbTe (GGST) alloys during thermal annealing, using X-ray diffraction and scanning and transmission electron microscopy is reported. It is shown that the incorporation of N in GGST tends to slow down the phase separation, crystallization, and growth processes during annealing. This can be attributed to the reduced diffusivity of Ge, which interacts and quickly bonds with N. Technological advantages of N doping are also discussed, considering the increased stability of the amorphous phase with respect to its parent crystalline phase, finer microstructure, flatness of the GeSbTe (GST) films after crystallization, and disappearance of the low-resistivity hexagonal phase at high temperature. (© 2020 Wiley‐VCH GmbH)
[en] We report the optical properties of thermally evaporated rare-earth (Dy) doped (GeS)(InS) thin film. Film of thickness 1100 nm has been deposited on a microscopic glass slide, and the as-prepared thin film has been characterized using X-ray diffraction, energy dispersive spectroscopy and UV–visible–near infrared spectroscopy. With annealing temperature, the refractive index is noticed to decrease from 2.51 to 2.27, while the optical bandgap is observed to increase from 2.03 to 2.29. The dispersion of the refractive index n for as prepared and annealed thin films have discussed using the single oscillator model proposed by the Wemple–Di Domenico relationship. The observed value of E (5.31–4.40 eV) and dispersion energy E (28.22–18.18 eV) are decreasing for as prepared and annealed thin films. The increase of bandgap has been explained in terms of the disorder in the system.
[en] Deep ultraviolet (UV) photodetectors have wide applications both in civil and military fields. Many materials have been explored to realize deep UV photodetection. Amorphous gallium oxide (a-GaO), as a member of transparent amorphous oxide semiconductors (TAOSs), has attracted a great deal of attention due to its ultrawide bandgap and scalable synthesis at room temperature. Plenty of researches have been focused on this topic in recent years. Herein, the latest progresses in the preparation methods of a-GaO using radio-frequency sputtering, pulsed laser deposition, atomic layer deposition, and other deposition techniques are summarized. Dependence of the stoichiometry, crystallinity, optical, electrical, and morphological properties on different preparation parameters and doping/alloying elements is tentatively discussed, as well as those deep UV photodetectors based on a-GaO and related thin films. Finally, a short summary with further possible investigations is provided for a better understanding and development of a-GaO materials and photodetectors. (© 2020 Wiley‐VCH GmbH)
[en] A novel selective atomic layer deposition (ALD) process for depositing MoS using MoCl and HS precursors is proposed. On the surface of SiO, the prolonged introduction of MoCl vapor by increasing the MoCl pulsing time rapidly suppresses the subsequent MoS growth due to the intense self-etching effect of MoCl, that is, the detachment of weakly bonded surface adsorbates (MoCl*). In contrast, the surface of Al allows more facile adsorption of MoCl than in the case of the SiO surface, and thus effectively compensates for the reduced deposition rate. By optimizing the MoCl pulsing time, the self-aligned growth of MoS on predefined Al (5 nm) patterns (circular and letter patterns) on a SiO substrate with a negligible selectivity loss is demonstrated. (© 2021 Wiley‐VCH GmbH)
[en] Herein, eight uniform optical states (3 bit) are demonstrated by irradiating nanosecond laser pulses on thin InSbTe films having high stability (260 °C), revealing at least 1% reflectivity contrast between any two consecutive states with strikingly low noise variation of 0.18% at each level, which is almost a 50% lower value compared to GeSbTe and AgInSbTe materials, revealing the two times enhanced signal-to-noise ratio of the InSbTe material. Furthermore, a systematic structural evolution during multilevel switching is investigated using confocal Raman spectroscopic studies. The experimental findings demonstrate low-noise yet highly stable multilevel switching toward the development of reliable phase change photonic memory devices. (© 2020 Wiley‐VCH GmbH)
[en] The dielectric function of phase-change materials (PCMs) presents a tremendous difference for the amorphous and crystalline states. Therefore, the measurement of the mid-infrared transparency of thin films of PCMs will provide a cost-efficient method to reveal the dependence of amorphous-crystalline phase transition on their compositions. Although Sb-Te-Se system has shown the advantages of the high speed, low power consumption and long retention life, the information on the mid-infrared transparency of Sb-Te-Se thin films is still insufficient. In our investigation, combinatorial materials libraries of Sb-Te-Se thin films were synthesized. The composition and mid-infrared spectral transmittance of each pixel of Sb-Te-Se thin film in the library were characterized using the energy dispersive X-ray analysis (EDX) and Fourier-transform infrared (FTIR) spectrometer, respectively. The in-depth chemical composition for randomly selected pixels was identified using secondary ions mass spectroscopy (SIMS). The crystallographic structure of some pixels was also identified using micro-area X-ray diffraction (μ-XRD). It can be found that, with the change of composition in Sb-Te-Se thin films, their mid-infrared spectral transmittance can be organized into three distinctive groups, corresponding to amorphous Sb-Se, SbSe orthorhombic structure and SbTe rhombohedral structure, respectively. Therefore, the amorphous-crystalline phase transition and the phase-change from the orthorhombic structure of SbSe to the rhombohedral structure of SbTe can be completely reflected in the mid-infrared spectral transmittance of Sb-Te-Se thin films.
[en] In this study, doped thin cadmium peroxide films were prepared by pulsed laser deposition with different doping concentrations of aluminium of 0.0, 0.1, 0.3, and 0.5 wt.% for CdOAl and thicknesses in the range of 200 nm. XRD patterns suggest the presence of cubic CdO and the texture factor confirms that the (111) plane was the preferential growth plane, where the texture factor and the grain size decreased from 2.02 to 9.75 nm, respectively, in the pure sample to 1.88 and 5.65 nm, respectively, at a concentration of 0.5 wt%. For the predominant growth plane, the deviation of the diffraction angle Δθ and interplanar distance Δd from the standard magnitudes was 2.774° and 0.318 Å, respectively, for the pure sample decreased to − 2.633° and 0.301 Å for the largest doping concentration. The optical absorption was found to decrease with increasing doping concentration, where the changes in threshold wavelengths from the standard λ = 496 nm were blue shifted by Δλ = 142, 133, 128, and 152 nm, respectively, for the concentrations used. The occurrence of such blue shifts points to a widening of the band gap to Eg = 3.5, 3.4, 3.35, and 3.6 eV for concentrations of 0.0, 0.1, 0.3, and 0.5 wt%, respectively.
[en] Herein, undoped and antimony (Sb)-doped zinc oxide (ZnO) thin films are prepared by a sol-gel spin-coating method. The influence of different annealing atmospheres including nitrogen and argon on pertinent properties of the prepared films is scrutinized. Structural, optical, morphological, and electrical properties of all annealed films are investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL), ultraviolet-visible spectroscopy, and current-voltage measurement. The XRD results exhibit that the films possess ZnO hexagonal wurtzite without impurity. The deterioration in the crystallinity of the film is highly influenced by Sb dopant and annealing atmosphere exhibiting the decrease in nanoparticle size after annealing in nitrogen, argon atmosphere, and upon doping. XPS results confirm that Sb is well incorporated in ZnO lattice and the shift of XPS spectra in the films annealed in nitrogen atmosphere indicates nitrogen bonding with zinc. The PL spectra exhibit blueshift of near band edge emission due to the Sb dopant substituting in Zn site in ZnO lattice and red-infrared emission induced by Sb dopant. The decrease in electrical resistance of ZnO film can be obtained by Sb doping and annealing in nitrogen atmosphere. (© 2020 Wiley‐VCH GmbH)