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Impact of transition metal ion doping on electron spin relaxation time in CdSe/ZnSe quantum dots
摘要： Theoretical calculations of spin relaxation time (SRT) of conduction electrons have been carried out considering the relaxation mediated by acoustic phonons using k.p perturbation theory and envelope function approximation in a transition metal doped II-VI semiconductor quantum dot under the strong con?nement regime. In this calculation, we are considering the transitions in the Zeeman sublevels arising due to magnetic impurity doping and applied magnetic ?eld in a Mn doped CdSe/ZnSe quantum dots. The occurrence of spin polarization switching at moderately low applied magnetic ?eld is established in Cd1(cid:1)xMnxSe/ZnSe quantum dots. The spin relaxation times have been found to be considerably longer with a higher dopant concentration in small magnetic ?elds (B < 2T) and at very low temperature (T < 50 K) regime. The results may help to demonstrate that, such small quantum dots can successfully be used as polarization switch in different spintronic nano-device.
关键词： Quantum dot,Electronic structure,Spin relaxation,Spintronics,Semiconductor
更新于2025-09-23 15:21:01
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A laser-ARPES study of LaNiO <sub/>3</sub> thin films grown by sputter deposition
摘要： Thin films of the correlated transition-metal oxide LaNiO3 undergo a metal–insulator transition when their thickness is reduced to a few unit cells. Here, we use angle-resolved photoemission spectroscopy to study the evolution of the electronic structure across this transition in a series of epitaxial LaNiO3 films of thicknesses ranging from 19 u.c. to 2 u.c. grown in situ by RF magnetron sputtering. Our data show a strong reduction in the electronic mean free path as the thickness is reduced below 5 u.c. This prevents the system from becoming electronically two-dimensional, as confirmed by the largely unchanged Fermi surface seen in our experiments. In the insulating state, we observe a strong suppression of the coherent quasiparticle peak, but no clear gap. These features resemble previous observations of the insulating state of NdNiO3.
关键词： LaNiO3,angle-resolved photoemission spectroscopy,electronic structure,metal–insulator transition,thin films
更新于2025-09-23 15:21:01
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On the role of magnesium in LiF:Mg,Ti thermoluminescent dosimeter
摘要： LiF doped with Mg and Ti is the most widely used thermoluminescent (TL) dosimeter for a large variety of applications. It has been argued that the Mg dopant is the most important defect in the TL process. Besides the common F-centre defects in LiF, optical absorption measurements have suggested the presence of Mg-related absorption bands at 380 nm (3.26 eV), and 310 nm (4.0 eV) when LiF:Mg is exposed to ionizing radiation, whose origin is not yet well understood. This work presents an investigation of the role of defects induced by Mg in LiF through electronic structure calculations. The calculations show that Mg interstitials induce a local lattice distortion characterized by the displacement of two opposite fluorine atoms, adjacent to the magnesium, away from their original sites by an average distance of 0.6 ? each, while the closest Li atoms are displaced by 0.1 ?. This defect introduces electronic states in the band-gap that can trap excess electrons produced during irradiation, thus enhancing the efficiency of the detector. Holes, on the other hand, are created and trapped in orbitals of mainly Mg-3s character. Additionally, the results suggest that irradiation can simultaneously remove a Li atom nearby a Mg interstitial; substitute a Li by a Mg atom or create a Li vacancy plus a Mg substitutional, giving rise to defects within the LiF gap that are more stable thermodynamically than the Mg interstitial itself.
关键词： magnesium dopant,LiF:Mg,Ti,thermoluminescent dosimeter,electronic structure calculations,defect states
更新于2025-09-23 15:21:01
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[NanoScience and Technology] Silicene (Prediction, Synthesis, Application) || Surface Functionalization of Silicene
摘要： For two-dimensional (2D) materials, an attractive feature is that all the atoms of the materials are exposed on the surface. Thus tuning the structure and properties by surface treatments becomes straightforward. Similar as graphene, the nearly zero-gap character of silicene hinders its applications in electronic and optoelectronic devices. In the case of graphene, functionalization through hydrogenation, halogenation, oxidation, have been widely explored in order to modify the electronic structure of graphene. However, the stable aromatic π-bond network of graphene makes it very inert and difficult to bond with foreign atoms. For example, hydrogen atoms on graphene usually form clusters instead of an ordered structure. In contrast, silicene possesses hybrid sp2-sp3 bonding, which is more readily to be modified or functionalized. Since the early stage of silicene research, theoretical investigations on the hydrogenation, halogenation, and oxidation of silicene have been widely reported in literature. Recently, increasing experimental successes have been achieved on functionalization of silicene. It is now imperative to review the progresses in the fast-growing field. In this chapter, we will discuss hydrogenation, halogenation oxidization individually. In each section, we first describe those theoretical predictions and then illustrate recent experimental successes. Finally, we will give some overview and outlook of this field.
关键词： electronic structure,silicene,functionalization,halogenation,2D materials,hydrogenation,oxidation
更新于2025-09-23 15:21:01
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First-principle study of g-AlxGa1-xN alloys: planar and buckled structures
摘要： The fundamental properties of g-AlxGa1-xN alloys with planar and buckled structures are investigated based on the first-principles. The results show that the band gaps of g-AlxGa1-xN alloys can be tuned, making them promising candidate materials for future light-emitting applications. For two-dimensional planar single layer structures, the band gap of g-AlxGa1-xN alloy increase monotonically with the increase of Al concentration. In contrast, for the buckled structures, as Al concentration increases, the band gap of the alloy structure first increase and then decrease, for the Al0.5Ga0.5N alloy, maximum band gap values can be achieved. The ε peaks and absorption coefficients of planar structures blue-shift, but those of the buckled structures red-shift. The absorption coefficients of the two type structures show two distinct absorption peaks in the deep ultraviolet, therefore deep ultraviolet emission is considered to be a remarkable feature of g-AlxGa1-xN alloys, indicating the potential use of g-AlxGa1-xN alloys for future UV luminescence applications.
关键词： g-AlxGa1-xN alloys,Electronic structure,Optical properties,Two-dimensional material,The first principles
更新于2025-09-23 15:19:57
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Selfa??Assembled Ruddlesdena??Popper/Perovskite Hybrid with Latticea??Oxygen Activation as a Superior Oxygen Evolution Electrocatalyst
摘要： The oxygen evolution reaction (OER) is pivotal in multiple gas-involved energy conversion technologies, such as water splitting, rechargeable metal–air batteries, and CO2/N2 electrolysis. Emerging anion-redox chemistry provides exciting opportunities for boosting catalytic activity, and thus mastering lattice-oxygen activation of metal oxides and identifying the origins are crucial for the development of advanced catalysts. Here, a strategy to activate surface lattice-oxygen sites for OER catalysis via constructing a Ruddlesden–Popper/perovskite hybrid, which is prepared by a facile one-pot self-assembly method, is developed. As a proof-of-concept, the unique hybrid catalyst (RP/P-LSCF) consists of a dominated Ruddlesden–Popper phase LaSr3Co1.5Fe1.5O10-δ (RP-LSCF) and second perovskite phase La0.25Sr0.75Co0.5Fe0.5O3-δ (P-LSCF), displaying exceptional OER activity. The RP/P-LSCF achieves 10 mA cm?2 at a low overpotential of only 324 mV in 0.1 m KOH, surpassing the benchmark RuO2 and various state-of-the-art metal oxides ever reported for OER, while showing significantly higher activity and stability than single RP-LSCF oxide. The high catalytic performance for RP/P-LSCF is attributed to the strong metal–oxygen covalency and high oxygen-ion diffusion rate resulting from the phase mixture, which likely triggers the surface lattice-oxygen activation to participate in OER. The success of Ruddlesden–Popper/perovskite hybrid construction creates a new direction to design advanced catalysts for various energy applications.
关键词： electronic structure,lattice-oxygen activation,hybrid construction,oxygen evolution reaction,synergistic effects
更新于2025-09-23 15:19:57
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Nonlinear optical rectification and electronic structure in asymmetric coupled quantum wires
摘要： Asymmetric coupled quantum wires provide the possibility for realizing obvious nonlinear optical rectification due to breaking the inversion symmetry. Here, we investigated nonlinear optical rectification (NOR) and electronic states in asymmetric coupled quantum wires (ACQWs). We find that the NOR max value of the ACQWs exhibits double peak structure with the increase of the geometrical asymmetry (i.e. the left wire radius deviating from the right wire radius), thus offering a direction for achieving remarkable NORS. In the double peak structure, the max value is one to two orders of magnitude larger than the min value. Furthermore, we find that the tunneling effect with respect to the ground state is reduced with the increase of the geometrical asymmetry, while the tunneling effect with respect to the first-excited state is firstly reduced, subsequently enhanced and then reduced with the increase of the geometrical asymmetry. Such coupling pictures elucidate the double peak structure in the NOR max value of the ACQWs. Our work enriches our understanding for the NOR and quantum states of the ACQWs, thereby laying the groundwork for the design and optimization of nonlinear nano-optical devices based on asymmetric coupled quantum wires such as THz radiation sources and infrared photo-detectors.
关键词： Asymmetric coupled quantum wires,Electronic structure,Nonlinear optical rectification
更新于2025-09-23 15:19:57
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Theoretical and experimental study on the electronic and optical properties of K <sub/>0.5</sub> Rb <sub/>0.5</sub> Pb <sub/>2</sub> Br <sub/>5</sub> : a promising laser host material
摘要： The data on the electronic structure and optical properties of bromide K0.5Rb0.5Pb2Br5 achieved by first-principle calculations and verified by X-ray spectroscopy measurements are reported. The kinetic energy, the Coulomb potential induced by the exchange hole, spin-orbital effects, and Coulomb repulsion were taken into account by applying the Tran and Blaha modified Becke–Johnson function (TB-mBJ), Hubbard U parameter, and spin-orbital coupling effect (SOC) in the TB-mBJ + U + SOC technique. The band gap was for the first time defined to be 3.23 eV. The partial density of state (PDOS) curves of K0.5Rb0.5Pb2Br5 agree well with XES K Ll and Br Kb2, and XPS spectra. The valence band (VB) is characterized by the Pb-5d3/2 and Pb-5d5/2 sub-states locating in the vicinities of ~20 eV and ~18 eV, respectively. The VB middle part is mainly formed by K-3p, Rb-4p and Br-4s states, in which the separation of Rb-4p3/2 and Rb-4p1/2 was also observed. The strong hybridization of Br-p and Pb-s/p states near ~6.5 eV reveals a major covalent part in the Br–Pb bonding. With a large band gap of 3.23 eV, and the remarkably high possibility of inter-band transition in energy ranges of 4–7 eV, and 10–12 eV, the bromide K0.5Rb0.5Pb2Br5 is expected to be a very promising active host material for core valence luminescence and mid-infrared rare-earth doped laser materials. The anisotropy of optical properties in K0.5Rb0.5Pb2Br5 is not significant, and it occurs at the extrema in the optical spectra. The absorption coefficient a(u) is in the order of magnitude of 106 cm?1 for an energy range of 5–25 eV.
关键词： electronic structure,X-ray spectroscopy,optical properties,laser host material,first-principle calculations,K0.5Rb0.5Pb2Br5
更新于2025-09-23 15:19:57
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Understanding the effect of the carbon on the photovoltaic properties of the Cu2ZnSnS4
摘要： In this work, crystalline structure, formation energy, electronic, optical and current-voltage properties of Cu2ZnSnS4 (CZTS) with the presence of carbon (C) impurity at various sites is studied using the first-principles density functional theory (DFT) based on the generalized gradient approximation (GGA). Here, we considered possible four substitutional configurations of carbon doped CZTS supercells: Cu by C (Ccu), Cu by Zn (Czn), Sn by C (Csn) and S by C (CS). It was found that the presence of C leads to the formation of localized polarons which have dual functionality; (i) cause an increase in the scattering-limited mobility which reduces the transport efficiency, (ii) create deep acceptor level which acts as a recombination center allowing the scattering of the generated charges carriers. An enhancement in the photo-absorption is observed due to an increase in the density of states at the valence bands after the incorporation of C. This results in the efficiency enhancement by 8%. In addition, the presence of C reduces the transport efficiency and improves the photogeneration efficiency of CZTS in solar cell applications.
关键词： Carbon doped CZTS,Localized polaron,DFT,Optical properties,Solar cell,Electronic structure
更新于2025-09-23 15:19:57
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Electronic structure and stability of anionic AuGen (n?=?1–20) clusters and assemblies: a density functional modeling
摘要： In the present study electronic structure and stabilities of cationic gold-doped germanium clusters, AuGen (n = 1 to 20), and their assemblies have been investigated by density functional theory (DFT) modeling. Computational results show a good relationship between the thermodynamic parameters, average binding energy, embedding energy, fragmentation energy, etc., with the percentage hybridization between different Ge 4s, Ge 4p, and Au 5d atomic orbitals, which plays a dominating role in the stabilization of anionic AuGe7, AuGe10, Au(Ge7)2, Au(Ge9)2, and Au(Ge10)2 clusters. Other thermodynamic and chemical parameters are also found consistent with the observed thermodynamic stabilities of the nanoclusters. In smaller size range (n < 11), Au atom always absorbs on the surface or vertex of pure Ge cluster. From n = 11, endohedral doping starts. In the assembled clusters, Au atom play the role as a bridging atom in Au(Ge7)2, Au(Ge9)2, and Au(Ge10)2 clusters. Stability of the AuGe7, AuGe10, Au(Ge7)2, Au(Ge9)2, and Au(Ge10)2 are explained using magic number in shell-filled model and mixed (π-σ) aromatic rule. As per the symmetry and structure of AuGe12 cluster, it is comparable to a nido-cluster, and hence, its stability is explained using Wade-Mingos rule. Calculated VDE, ADE, HOMO-LUMO gap, and VIP have very close agreement with the experimental results. IR and Raman frequencies show that the vibration nature of the clusters could produce electromagnetic radiation in the far infrared region which is useful for medical applications.
关键词： ADE and VDE,Electronic structure,Cluster and cluster assembly,IR and Raman,DOS,Density functional theory
更新于2025-09-23 15:19:57