Transition Metal-doped Semiconductors Research Articles

Adsorption and sensing performances of vacancy defects and Cu-embedded GaN/MoTe2 heterostructure for harmful gases: A DFT study

By utilizing density functional theory (DFT), we explore the adsorption and sensing performance of NO, NO2, SO2 and CO on intrinsic GaN/MoTe2 heterostructure, vacancy-defective GaN/MoTe2 heterostructures and Cu-embedded GaN/MoTe2 heterostructures, respectively. The results indicate that the VGa-GaN/MoTe2 heterostructure exhibits higher adsorption energy (yielding more negative values) for all four gases, demonstrating superior adsorption performance compared to the intrinsic system. Similarly, the Cu-GaN/MoTe2 heterostructure also improves the adsorption performance for nitrogen oxides. Meanwhile, the Cu-MoTe2/GaN heterostructure also significantly outperforms the intrinsic systems in terms of adsorption performance for the four harmful gases. Particularly, the Cu-MoTe2/GaN heterostructure has an adsorption energy of −2.22 eV for NO2 and a charge transfer amount of up to 0.72 e, indicating a strong chemical interaction between the adsorption system and gas molecules. Therefore, Cu-MoTe2/GaN is a potential ideal gas adsorption material. This work offers a theoretical foundation for transition metal-doped semiconductor heterostructures for future research.

Enhancing photoluminescence properties of Mn2+ doped CsPbCl3 nanocrystals via alkaline-earth Co-doping

Doping Mn2+ into CsPbCl3 nanocrystals (NCs) has garnered significant attention for its potential to create tailored optical properties in optoelectronic applications. However, this approach still faces challenges, including low photoluminescence quantum yield (PL QY), suboptimal Mn2+ doping efficiency, and inadequate stability. Herein, we delve into the specific realm of Mn2+ doping in CsPbCl3 NCs and delve into the effects of co-doping these NCs with alkaline earth (AE2+) metal ions. Through a comprehensive characterization of the co-doped NCs, we systematically unravel bonding characteristics, and luminescence behaviors induced by AE2+ co-doping. The outcomes underscore the notable enhancement in luminescence performance and stability achieved through AE2+ co-doping, particularly with Sr2+. The utilization of smaller AE2+ results in lattice contraction, leading to improved PL QY and heightened photostability. This work offers valuable insights into tailoring the performance of transition metal-doped semiconductor NCs for advanced optoelectronic devices, establishing a foundation for subsequent optimization and diverse applications.

Enhanced photo-Fenton catalytic activity over Cu-doped Bi12O17-xCl2 nanotube for tetracycline degradation: Oxygen vacancies-induced mixed valent Cu

Fenton photocatalyst constructed by transition metal-doped semiconductor material seems to be a promising alternative to classic Fenton catalysts. A series of Cu-doped tubular Bi12O17Cl2 with sufficient oxygen vacancies (ov) was successfully prepared through a hydrothermal method. The formation of ov in the Bi12 crystal lattice can favor the Fenton reaction not only by serving as a reaction site and increasing the charge density in the photocatalyst but also by partially reducing the dopant Cu2+ to Cu+, which consequently enhances the H2O2 activation to a significantly higher rate. Notably, Cu-doped Bi12O17Cl2 ov with an optimal dopant proportion of 4 % exhibited a preferable Fenton catalytic rate 4.5 times higher than pure photocatalytic degradation. This work investigates the mutual promotion of oxygen vacancies and dopant ions in the Fenton reaction and provides a novel development scheme for the advanced oxidation process.

Creation of Mo active sites on indium oxide microrods for photocatalytic amino acid production

As an n-type semiconductor, In2O3 is considered a promising photocatalyst for producing amino acids using biomass derivatives as precursors. However, similar to other intrinsic semiconductors, In2O3 suffers from poor charge dynamics. Herein, we show the synthesis of Mo-doped In2O3 (Mo-In2O3) with a porous rod-shaped structure through a one-step solvothermal reaction followed by calcination. Under visible-light irradiation, Mo-In2O3 achieves a high conversion rate of 81% for the reaction that transforms lactic acid into alanine with a selectivity of 91%. Spectroscopic techniques and density functional theory calculations reveal that Mo doping introduces defect states slightly below the conduction band of In2O3, which improves the separation of photogenerated electron-hole pairs. In addition, Mo atoms on the surface form extra adsorption and reaction centers that greatly enhance the reaction rate. This work provides insights into the development of transition metal-doped semiconductor photocatalysts to produce amino acids.

Effect of Moisture on Dopant Segregation in Solid Hosts

Transition metal-doped semiconductor materials are extensively employed for light harvesting and photocatalytic applications owing to their increased light absorption and charge mobility. In this work, spatial tailoring of the Ni dopant in TiO2 nanostructures is performed by varying the secondary processing parameters to engineer the resulting optoelectronic properties for select applications. Specifically, the aging of the dried Ti sol and the resulting Ni segregation are observed to be moisture-driven phenomena based on the infrared and time-resolved UV–vis spectroscopy measurements. While X-ray diffraction and scanning transmission electron microscopy coupled with electron energy-loss spectroscopy characterizations show a clear difference in the crystal structures between pristine TiO2 powders and phase-segregated NiO–TiO2, the thermogravimetric measurements reveal substitution of the ethoxy group by ambient moisture, resulting in the ejection of hydroxylated Ni clusters. Furthermore, the doped system ...

Structural evolution and magnetic properties of anionic clusters Cr2Gen (n = 3–14): photoelectron spectroscopy and density functional theory computation

The structural, electronic and magnetic properties of dual Cr atoms doped germanium anionic clusters, (n = 3–14), have been investigated by using photoelectron spectroscopy in combination with density-functional theory calculations. The low-lying structures of are determined by DFT based genetic algorithm optimization. For with n ⩽ 8, the structures are bipyramid-based geometries, while cluster has an opening cage-like structure, and the half-encapsulated structure is gradually covered by the additional Ge atoms to form closed-cage configuration with one Cr atom interior for n = 10 to 14. Meanwhile, the two Cr atoms in clusters tend to form a Cr–Cr bond rather than be separated. Interestingly, the magnetic moment of all the anionic clusters considered is 1 μB. Almost all clusters exhibit antiferromagnetic Cr–Cr coupling, except for two clusters, and . To our knowledge, the cluster is the first kind of transition-metal doped semiconductor clusters that exhibit relatively stable antiferromagnetism within a wide size range. The experimental/theoretical results suggest high potential to modify the magnetic behavior of semiconductor clusters through introducing different transition-metal dopant atoms.

Recent Advances in Inorganic Nanoparticle-Based NIR Luminescence Imaging: Semiconductor Nanoparticles and Lanthanide Nanoparticles.

Several types of nanoparticle-based imaging probes have been developed to replace conventional luminescent probes. For luminescence imaging, near-infrared (NIR) probes are useful in that they allow deep tissue penetration and high spatial resolution as a result of reduced light absorption/scattering and negligible autofluorescence in biological media. They rely on either an anti-Stokes or a Stokes shift process to generate luminescence. For example, transition metal-doped semiconductor nanoparticles and lanthanide-doped inorganic nanoparticles have been demonstrated as anti-Stokes shift-based agents that absorb NIR light through two- or three-photon absorption process and upconversion process, respectively. On the other hand, quantum dots (QDs) and lanthanide-doped nanoparticles that emit in NIR-II range (∼1000 to ∼1350 nm) were suggested as promising Stokes shift-based imaging agents. In this topical review, we summarize and discuss the recent progress in the development of inorganic nanoparticle-based luminescence imaging probes working in NIR range.

The nature of structure and bonding between transition metal and mixed Si-Ge tetramers: A 20-electron superatom system.

A novel superatom species with 20-electron system, Six Gey M(+) (x + y = 4; M = Nb, Ta), was properly proposed. The trigonal bipyramid structures for the studied systems were identified as the putative global minimum by means of the density functional theory calculations. The high chemical stability can be explained by the strong p-d hybridization between transition metal and mixed Si-Ge tetramers, and closed-shell valence electron configuration [1S(2) 1P(6) 2S(2) 1D(10) ]. Meanwhile, the chemical bondings between metal atom and the tetramers can be recognized by three localized two-center two-electron (2c-2e) and delocalized 3c-2e σ-bonds. For all the doped structures studied here, it was found that the π- and σ-electrons satisfy the 2(N + 1)(2) counting rule, and thus these clusters possess spherically double (π and σ) aromaticity, which is also confirmed by the negative nucleus-independent chemical shifts values. Consequently, all the calculated results provide a further understanding for structural stabilities and electronic properties of transition metal-doped semiconductor clusters. © 2016 Wiley Periodicals, Inc.

Core-shell nanostructure in aGe0.9Mn0.1film observed via structural and magnetic measurements

We have characterized a film of Ge_0.9Mn_0.1 forming self-organized nanocolumns perpendicular to the Ge substrate with high resolution scanning transmission electron microscopy combined with electron energy loss spectroscopy, and bulk magnetization and positive muon spin rotation and relaxation (muSR) measurements. The Mn-rich nanocolumns form a triangular lattice with no detectable Mn atoms in the matrix. They consist of cores surrounded by shells. The combined analysis of bulk magnetization and muSR data enables us to characterize the electronic and magnetic properties of both the cores and shells. The discovered phase separation of the columns between a core and a shell is probably relevant for other transition-metal doped semiconductors.

Chloride ion sensors based on low-dimensional α-MnO2–Co3O4 nanoparticles fabricated glassy carbon electrodes by simple I–V technique

In this paper, we have synthesized codoped α-MnO2–Co3O4 nanoparticles (NPs) by a facile solvothermal technique using active reducing agents in alkaline reaction systems. The doped NPs are investigated using UV/vis, FT-IR spectroscopy, powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray energy dispersive spectroscopy (XEDS), and field-emission scanning electron microscopy (FESEM). α-MnO2–Co3O4 NPs are fabricated onto a flat-glassy carbon electrode (GCE, surface area, 0.0316cm2) to give a chemo-sensor with a fast response toward chloride ions (~10s) in liquid phase. The chemo-sensor also shows good sensitivity, long-term stability, reproducibility, and enhanced electrochemical responses. The calibration plot is linear (r2=0.9794) over the large chloride ions concentration (1.0–0.1μM) ranges. The sensitivity and detection limit is calculated as ~1.062μAcm−2mM−1 and ~0.35±0.05μM (signal-to-noise ratio, at a SNR of 3) respectively. We also discuss the possible future prospective uses of the transition-metal doped semiconductor nanomaterials in terms of chemical sensing.

Back Cover: Novel multifunctional materials based on oxide thin films and artificial heteroepitaxial multilayers (Phys. Status Solidi A 2/2011)

The combination of magnetic properties with dielectric, semiconducting, or ferroelectric materials in one and the same material [e.g. magnetic semiconductors (MS) or intrinsic multiferroics] – as well as in artificial heterostructures [e.g. ferromagnetic/dielectric heterostructures for magnetic tunnel junctions (MTJs) or artificial multiferroic heterostructures] allows for the design of materials with novel functionalities and provides the basis for various device applications. In their Feature Article on pp. 232–251, Opel et al. report on the combination of ferromagnetic, semiconducting, metallic, and dielectric materials properties in thin films and artificial heterostructures using laser molecular beam epitaxy. They discuss the fabrication and characterization of oxide-based ferromagnetic tunnel junctions, transition metal-doped semiconductors, intrinsic multiferroics, and artificial ferroelectric/ferromagetic heterostructures.

Wurtzite-Type CoO Nanocrystals in Ultrathin ZnCoO Films

Surface x-ray diffraction experiments reveal that, in cobalt-doped ZnO films two to five monolayers thick, Wurtzite-type CoO nanocrystals are coherently embedded within a hexagonal boron-nitride- (h-BN)-type ZnO matrix, supporting the model of a phase separation. First-principles calculations confirm that, in contrast with ZnO, the formation of h-BN-type CoO is unfavorable in the ultrathin film limit. Our results are important for understanding magnetic properties of transition metal-doped semiconductors in general.

Synthesis and Surface Characterization by Raman Spectroscopy of Water-Dispersible ZnS:Mn Nanocrystals Capped with Mercaptoacetic Acid

Semiconductor nanocrystals have been extensively studied due to their size-dependent optical properties and wide applications. Many efforts have been made to develop nanoparticles with superior optical characteristics, e.g., higher quantum yields, more accessible absorption wavelengths, and wider absorption and narrower emission bands. The incorporation of transition metal ions into semiconductor nanocrystals induces radiative recombination of excited electron-hole pair at doping ion sites rather than at surfaces, which shifts photoluminescence wavelength and increases quantum efficiency. Therefore, transition metal-doped semiconductor nanocrystals have great potential applications as a novel material for display and light-emitting devices. The functionalization of surfaces is another important aspect of nanoparticle fabrication. In particular, it is important to make nanoparticles water-dispersible for many biological applications. Surfactants play important roles in the control of dispersed particle sizes, optical properties, and solubility by passivating nanocrystal surfaces. Here, we report on the synthesis and properties of water-dispersible Mn-doped ZnS nanoparticles stabilized by mercaptoacetic acid (ZnS:Mn-MAA). MAA is widely used as a capping agent in the synthesis of nanoparticles. MAA is also the simplest molecule that has two terminal functional groups, a thiol and a carboxylic acid, which can be deprotonated, allowing it to bind to the surfaces of nanoparticles. In this respect, it would be interesting to determine the nature of surface-bound MAA and, in particular, to determine which functional group is involved in this binding. Here, we present the Raman spectra of MAA adsorbed on the surfaces of ZnS:Mn nanocrystals and propose a structure for surfacebound MAA based on spectral analyses and density functional theory (DFT) calculations.

Half‐Metallic Ferromagnetism and Stability of Transition Metal Pnictides and Chalcogenides

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Tight-binding study of the magnetic properties of Mn-doped Ge

A generalized tight-binding bond Stoner model satisfying charge self-consistence is used to study Mn-doped Ge. We fit the tight-binding parameters to first-principles nonmagnetic band structures of zinc blende MnGe, and then calculate the ferromagnetic and antiferromagnetic band structures with the local stoner model. The predicted band structures match the first-principles ferromagnetic and antiferromagnetic calculations of the MnGe well and reveal that the MnGe is a half-metallic ferromagnet with integer magnetic moment in Bohr magneton. Applied to low concentrations of Mn doping, this model produces good magnetic moments, spin-dependent density of states, and energetics for Mn doping concentrations down to 0.03125. These results are in agreement with corresponding first-principles calculations. This method can be applied to other transition-metal doped semiconductors.

Intralayer and interlayer energy transfer from excitonic states into the Mn3d5shell in diluted magnetic semiconductor structures

We show that the Dexter-F\"orster-like radiationless resonance energy-transfer process from excitonic states into the Mn ${3d}^{5}$ shell in wide-gap (II,Mn)VI semiconductors is strongly enhanced if the total spin of the overall process is conserved. This requirement cannot be fulfilled in processes involving a bright exciton, i.e., other excitonic complexes or processes need to be involved. Of these we discuss dark excitons, donor-bound excitons ${D}^{0}X,$ negatively charged excitons ${X}^{\ensuremath{-}},$ and an Auger-like process. A careful analysis of the magnetic field and time dependence of the excitonic and Mn luminescence in the (Zn,Cd,Mn)Se samples under study gives evidence that the ${D}^{0}X$ complex plays a dominant role in the intralayer energy transfer. In asymmetric double quantum well (ADQW) structures consisting of a (Zn,Cd)Se well and a (Zn,Cd,Mn)Se well embedded in ZnSe barriers, there is a competition between the intralayer and interlayer energy-transfer processes from excitonic states into the Mn system. These interlayer processes take place between the Mn ions situated in the (Zn,Cd,Mn)Se well and spatially indirect excitons [where the hole is confined in the (Zn,Cd,Mn)Se and the electron confined in the (Zn,Cd)Se] as well as spatially direct excitons of the (Zn,Cd)Se well. The continuous magnetic-field tuning demonstrates convincingly the subtle interplay of excitonic band structure of the ADQW and spin effects in the energy-transfer processes. A spin-dependent energy transfer should be a general feature of rare-earth or transition-metal doped semiconductors such as II-VI or III-V semiconductors or even Er-doped Si or ${\mathrm{SiO}}_{2}.$

Calculation of carrier equilibrium effects in transition-metal doped semiconductors with application to Cr-doped GaAs

A diagram useful for representing the electronic levels arising from transition-metal impurities in tetrahedral semiconductors is proposed. Computer calculations of carrier equilibrium effects are described, highlighting the problems of including all relevant physical effects. The calculations are believed to be amongst the most complete attempted to date. Semi-insulating behaviour, conduction activation energy, relative occupations of Cr valence states, and compensation dependence of Cr solubility in Cr-doped GaAs are elucidated. The calculations suggest that the Cr levels tend to follow the valence band edge, rather than the conduction band, as temperature varies, and that the saturated solubility of the neutral species CrIII at the melting point is about 1017 cm-3. The calculated variation of electrical resistivity with compensation shows a structured 'resistivity edge', in the region of which the Fermi potential, fractional occupations of Cr oxidation states, and the apparent conduction activation energy all vary rapidly.