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Environmentally friendly approach to the synthesis of monodisperse and bright blue emitting Cd0.15Zn0.85S quantum dots
摘要： Nucleation and growth of quantum dots (QDs) in solution are mainly controlled by the kinetic and thermal modes of the reaction process. By influencing any of them, the properties of the final nanocrystals can be tuned. The influences of temperature and chemical nature of starting materials on nucleation and, as a consequence, on the structure and optical properties of Cd0.15Zn0.85S QDs have been systematically investigated by one-pot and hot-injection methods. All reactions were performed in organic disperse medium using N,N′-disubstituted and N,N′,N′-trisubstituted thioureas (TU) as a new sources of sulfur. In addition to environmental friendliness, each of them has a number of unique chemical properties. The effect of the substituents’ nature in thioureas on the morphology, size and optical properties of synthesized QDs has been studied. The strong correlation between the metal ratios taken to the reaction and elemental analysis (EDS) results for all obtained Cd0.15Zn0.85S QDs was found. However, prepared nanomaterials have different size (2.9 – 4.6 nm) and morphology. The optical features have also changed under the various thermal conditions. Especially, the changes in the photoluminescence spectra of QDs synthesized with different thioureas are noticeable. Highly photoluminescent (photoluminescence quantum yield PL QY up to 67 %), morphologically and structurally homogeneous blue-emitting Cd0.15Zn0.85S QDs were obtained.
关键词： semiconductors,quantum dots,substituted thioureas
更新于2025-09-11 14:15:04
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Reference Module in Materials Science and Materials Engineering || III-V and Group-IV-Based Ferromagnetic Semiconductors for Spintronics
摘要： From the first development of the transistor, the rapid growth of solid-state electronic circuits has been quite impressive. Innovations of semiconductor (SC) processing technologies have helped keep the pace of developing smaller electronic devices with higher performance. Operations of most electronic devices rely on the ability to control the flow of charges. However, when electronic devices reach the scale of 10 nm or even smaller, two big problems appear. First, many kinds of fluctuation make it difficult to control the flow of electron charges. For example, when the channel length of field effect transistors (FETs) reaches several nanometers, the transport of electrons cannot be described by the conventional diffusion equation. In nanoscale devices, even fluctuation of positions of doped atoms strongly affects the movement of electrons, making it difficult to predict and control the output current. This results in large fluctuation of device parameters. The second problem is the leak off-current that results in the large idling energy dissipation. When the channel length reaches sub-10 nm, the leak off-current appears due to the quantum tunneling effect. As the device size becomes smaller, a larger number of devices working at higher speed are integrated. Thus, larger idling energy is consumed. To overcome these problems, many emerging technologies are being explored and developed. One of the prospective technologies, called 'spintronics,' may help us to find solutions or a totally new framework of electronics.
关键词： Group-IV semiconductors,ferromagnetic semiconductors,Mn-doped,Fe-doped,electrical control of ferromagnetism,III-V semiconductors,tunneling magnetoresistance,spintronics
更新于2025-09-10 09:29:36
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Synthesis of Ge1?xSnx Alloy Thin Films by Rapid Thermal Annealing of Sputtered Ge/Sn/Ge Layers on Si Substrates
摘要： In this work, nanocrystalline Ge1?xSnx alloy formation from a rapid thermal annealed Ge/Sn/Ge multilayer has been presented. The multilayer was magnetron sputtered onto the Silicon substrate. This was followed by annealing the layers by rapid thermal annealing, at temperatures of 300 ?C, 350 ?C, 400 ?C, and 450 ?C, for 10 s. Then, the effect of thermal annealing on the morphological, structural, and optical characteristics of the synthesized Ge1?xSnx alloys were investigated. The nanocrystalline Ge1?xSnx formation was revealed by high-resolution X-ray diffraction (HR-XRD) measurements, which showed the orientation of (111). Raman results showed that phonon intensities of the Ge-Ge vibrations were improved with an increase in the annealing temperature. The results evidently showed that raising the annealing temperature led to improvements in the crystalline quality of the layers. It was demonstrated that Ge-Sn solid-phase mixing had occurred at a low temperature of 400 ?C, which led to the creation of a Ge1?xSnx alloy. In addition, spectral photo-responsivity of a fabricated Ge1?xSnx metal-semiconductor-metal (MSM) photodetector exhibited its extending wavelength into the near-infrared region (820 nm).
关键词： Raman spectroscopy,Ge-Sn,thin films,sputtering,semiconductors,nanocrystalline,X-ray diffraction,scanning electron microscopy
更新于2025-09-10 09:29:36
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Electronic exchange-correlation, many-body effect issues on first-principles calculations of bulk SiC polytypes
摘要： The first-principles Projector-Augmented Wave method (PAW) is used to investigate the electronic, phonon band structure and dielectric properties of four bulk silicon carbide (SiC) polytypes. We employ PAW pseudopotential density functional theory with Perdew, Burke and Ernzerhof (PBE) and hybrid HSE06 approximations of the exchange-correlation functional. Many-body effects are incorporated using the GW approximation of the self-interaction to study SiC properties. GW method in its single-shot variant, which is based on the many-body perturbation theory (MBPT), is used to calculate the quasi-particle (QP) energies of the band structure and the dielectric properties for different polytypes. The electronic band structure determination within GW method uses the Wannier procedure where a basis set of maximally localized Wannier function (MLWF) is constructed to interpolate the QP energies of few regular mesh k-points to the high-symmetry lines in Brillouin zone. As a consequence of QP correction to the Kohn–Sham energies, bandgap is increased by upto 3 eV in case of 4H–SiC, as compared to PBE bandgap. GW results are comparable to those of hybrid functionals and are in good agreement with the experimental results. The optical properties are then studied within PBE, HSE06 and include many-body effects. In addition, the phonon band structure has been investigated within HSE06 and compared to previous PBE results. We found good agreement with the previous theoretical results and the experimental available data.
关键词： silicon carbide,semiconductors,Density functional theory,power electronic device,polytypism
更新于2025-09-10 09:29:36
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Design for Highly Piezoelectric and Visible/Near-Infrared Photoresponsive Perovskite Oxides
摘要： Defect-engineered perovskite oxides that exhibit ferroelectric and photovoltaic properties are promising multifunctional materials. Though introducing gap states by transition metal doping on the perovskite B-site can obtain low bandgap (i.e., 1.1–3.8 eV), the electrically leaky perovskite oxides generally lose piezoelectricity mainly due to oxygen vacancies. Therefore, the development of highly piezoelectric ferroelectric semiconductor remains challenging. Here, inspired by point-defect-mediated large piezoelectricity in ferroelectrics especially at the morphotropic phase boundary (MPB) region, an efficient strategy is proposed by judiciously introducing the gap states at the MPB where defect-induced local polar heterogeneities are thermodynamically coupled with the host polarization to simultaneously achieve high piezoelectricity and low bandgap. A concrete example, Ni2+-mediated (1–x)Na0.5Bi0.5TiO3-xBa(Ti0.5Ni0.5)O3–δ (x = 0.02–0.08) composition is presented, which can show excellent piezoelectricity and unprecedented visible/near-infrared light absorption with a lowest ever bandgap ≈0.9 eV at room temperature. In particular, the MPB composition x = 0.05 shows the best ferroelectricity/piezoelectricity (d33 = 151 pC N–1, Pr = 31.2 μC cm–2) and a largely enhanced photocurrent density approximately two orders of magnitude higher compared with classic ferroelectric (Pb,La)(Zr,Ti)O3. This research provides a new paradigm for designing highly piezoelectric and visible/near-infrared photoresponsive perovskite oxides for solar energy conversion, near-infrared detection, and other multifunctional applications.
关键词： photovoltaics,ceramics,ferroelectrics,perovskite oxides,semiconductors
更新于2025-09-10 09:29:36
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Variation of the photoluminescence spectrum of InAs/GaAs heterostructures grown by ion-beam deposition
摘要： This work reports on an experimental investigation of the influence of vertical stacking of quantum dots, the thickness of GaAs potential barriers, and their isovalent doping with bismuth on the photoluminescence properties of InAs/GaAs heterostructures. The experimental samples were grown by ion-beam deposition. We showed that using three vertically stacked layers of InAs quantum dots separated by thin GaAs barrier layers was accompanied by a red-shift of the photoluminescence peak of InAs/GaAs heterostructures. An increase in the thickness of the GaAs barrier layers was accompanied by a blue shift of the photoluminescence peak. The effect of isovalent Bi doping of the GaAs barrier layers on the structural and optical properties of the InAs/GaAs heterostructures was investigated. It was found that the Bi content up to 4.96 atom % in GaAs decreases the density of InAs quantum dots from 1.53 × 1010 to 0.93 × 1010 cm?2. In addition, the average lateral size of the InAs quantum dots increased from 14 to 20 nm, due to an increase in the surface diffusion of In. It is shown that isovalent doping of GaAs potential barriers by bismuth was accompanied by a red-shift of the photoluminescence peak of InAs quantum dots of 121 meV.
关键词： photoluminescence,semiconductors,quantum dot,ion-beam deposition,nanoheterostructures,infrared photodetectors
更新于2025-09-10 09:29:36
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[Energy, Environment, and Sustainability] Nano-Energetic Materials || Nanomaterials for Hydrogen Production Through Photocatalysis
摘要： In the last few decades, nanostructured materials have been of great interest worldwide due to their unique characteristics and their sub-driven reactivity. Furthermore, the unlimited applications of such materials in different fields and their associated success had added extra value for their importance. The combination between nanomaterials and photocatalytic processes has been recently given a great attention in different applications. It may enhance the viability of the nanotechnology principles. One of these applications is the usage of nanophotocatalytic materials in hydrogen production via water-splitting reaction. This chapter will cover the main concepts of photocatalysis and its associated terms. The main features of efficient photocatalysts and the ways of measuring such properties are illustrated in this chapter. Also, a brief presentation for the current methods that are utilized in the preparation of these catalysts is provided. An overview of the different types of semiconductors that are employed in the domain of photo-based hydrogen generation via splitting of water is introduced through this chapter too. A new approach in the water-splitting process by introducing noble metals attached magnetic nanoparticle (core/shell structure) as promising photomaterials is also described in this chapter. However, these materials are used in different fields such as bio-medical processes, water treatment, and energy storage. They are expected to be of high significance in field of catalysis, since they can be easily separated and recovered, due to their magnetic character, reactions. Implementation of a suitable magnetic force can enhance the hydrogen productivity during the water-splitting process. These materials are possessing magnetic properties which could reveal a new approach to their photocatalytic activity via quenching the radiation scattering.
关键词： Water-splitting processes,Magnetic materials,Photocatalysis,Hydrogen energy,Semiconductors
更新于2025-09-10 09:29:36
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Excellent visible light photocatalytic H2 evolution activity of novel noble-metal-free Ni12P5/CdS composite
摘要： Novel noble-metal-free Ni12P5/CdS composite was designed and synthesized by a hydrothermal method. The photocatalytic H2 generation activity of the as-prepared Ni12P5/CdS is 1.93 fold of that of pure CdS under visible light (λ > 420 nm) irradiation. The enhanced activity of Ni12P5/CdS is ascribed to the improved separation e?ciency of photocarriers over a direct Z-scheme mechanism. It provides a potential strategy to improve the photocatalytic H2 evolution activity of CdS greatly by loading noble-metal-free Ni12P5 as electron co-catalyst via direct Z-scheme mechanism.
关键词： Water splitting,Photocatalysis,Semiconductors
更新于2025-09-10 09:29:36
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Amorphous InZnO:Li/ZnSnO:Li dual-active-layer thin film transistors
摘要： Amorphous Li-doped InZnO and ZnSnO (IZO:Li/ZTO:Li) dual-active-layer thin film transistors (TFTs) were fabricated by radio-frequency (RF) magnetron sputtering. The transmittance of the dual-stacked IZO:Li/ZTO:Li thin film was over 85% in the visible range. X-ray diffraction (XRD) result indicated that the thin film was amorphous. The influence of ZTO:Li layer thickness on the electrical characteristics and bias-stress stability of the dual-active-layer TFT was investigated. With the increasing thickness of ZTO:Li thin film, the saturation mobility (μSAT) increased firstly and then decreased, while the threshold voltage (VTH) shifted to the positive direction. The TFT with the optimized ZTO:Li thickness showed a superior performance with a μSAT of 33.2 cm2/V·s, a VTH of 3.2 V, a sub-threshold swing (SS) of 0.6 V/decade and a current on/off (ION/IOFF) up to 3.2 × 108.
关键词： B. Sputtering,A. Semiconductors,D. Electrical properties,A. Thin films,A. Amorphous materials
更新于2025-09-10 09:29:36
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Ferromagnetism induced by vacancies in (N, Al)-codoped 6H-SiC
摘要： The electronic structures and magnetic properties of 6H-SiC doped with N, C vacancies (VC), Si vacancies (VSi) and Al are studied by first principles calculations. The results indicate that the N substituting C in 6H-SiC cannot order magnetism but VSi can introduce magnetic moments effectively. Ferromagnetism coupling is obtained in (N, 2VSi)-codoped 6H-SiC. The ferromagnetism can be mainly attributed to the interactions between the 2p orbitals of C atoms around Si vacancies. More interestingly, substituting Si with Al can enhance the ferromagnetic states in 6H-SiC. We also studied the effect of charge on magnetic properties and provide an effective method of tuning magnetism in 6H-SiC.
关键词： First principles,Electronic structure,Dilute magnetic semiconductors,6H-SiC,Magnetic properties
更新于2025-09-10 09:29:36