Substitutional Incorporation Research Articles

Investigation of in-situ co-doping by Sb and P of germanium films grown on Si(001) by molecular beam epitaxy

Heavily n-type doping of Germanium was the key parameter in recent breakthroughs of Si-compatible infrared emitting devices. We investigate an in-situ co-doping technique using Phosphorus (P) and Antimony (Sb) to fabricate smooth and heavily n-type doped Ge films epitaxially grown on Si(001) using molecular beam epitaxy. The role of the rapid thermal annealing process in the dopants activation and in the significant annihilation of the threading dislocations is presented. Hall effect measurements reveal a free electron concentration of 4.2 × 1019 cm−3 at room temperature. The accumulated strain in the Ge films is studied using X-ray diffraction (XRD) data for P, Sb and co-doping, before and after annealing. A correlation between XRD and Hall effect results revealed a synergistic mechanism associated with the presence of Sb that improves the substitutional incorporation of P atoms. Atom Probe Tomography was implemented to investigate the effect of annealing on the distribution and clustering of dopants. Clustering and inhomogeneity in the density of Sb atoms are observed before annealing, while the density of P atoms was found to be homogeneous. After annealing, the clustering of P becomes more prominent. We show that the clustering is a limiting factor for the activation efficiency of Phosphorus in heavily doped Germanium. The referenced publication has been retracted by the authors because of the use of unauthorized data represented by Figs. 8, 9, 10, 11, 12, 13, and 14. These figures were obtained with the help of other scientists in IM2NP Laboratory (Marseille, France) and have been only authorized for publication in the Ph.D. thesis of M. A. Zrir. The authors recognize that the publication of data that have been obtained with substantial help from other scientists can only be with their prior authorization. The authors sincerely apologize for this and recognize that the use of unauthorized data does not comply with the ethical standards of AIP Publishing and Journal of Applied Physics.

Optical properties of Cr-doped Zn1−xMnxTe semimagnetic nanocrystals

The effect of Cr co-doping on the optical properties of Mn-doped ZnTe nanocrystals (NCs) embedded in a glass matrix is studied in this paper. The substitutional incorporation of Cr2+ ions into these semiconducting NCs was strongly evidenced by optical absorption and crystal field theory analyses, which showed the characteristic transitions of Cr2+ and Cr3+ ions. Transmission electron microscopy images revealed the NC size and invariance lattice parameter, with the incorporation of Mn2+ and Cr2+ ions. PL spectra showed that co-doping with Cr favors a competition between Mn2+ and Cr2+ ions, resulting in a decrease in the rate of Mn2+ substitution, zinc vacancy filling (VZn) in Zn1−x−yMnxCryTe NCs, and the formation of interstitial Cr3+ ions in the host glass system.

Enhanced bolometric properties of nickel oxide thin films for infrared image sensor applications by substitutional incorporation of Li

This study aims to investigate the influence of substitutionally incorporated Li on sensing performance of nickel oxide films for bolometer applications by comparing Ni1-xO and (LiyNi1-y)1-xO films. From the results of structural analysis, it was confirmed that the film deposited from Li0.2Ni0.8O target contained Li which substitutionally occupies the Ni cation site while maintaining a cubic NiO structure. The substitutionally incorporated Li in nickel oxide can serve as an acceptor providing a hole carrier, like as a structural defect. However, in contrast to the structural defect, the substitutional incorporation of Li made it possible to increase the number of hole carriers in nickel oxide film while maintaining excellent film quality. In addition, the contact resistance with electrode was greatly reduced as a result of the substitutionally incorporated Li. These changes in structural and electrical properties lead to a significant reduction of 1/f noise arisen from the (LiyNi1-y)1-xO film. As a result, the sensing performance of the (LiyNi1-y)1-xO film as evaluated using the (αH/n)1/2/|β| value was nearly 10 times better than that of the Ni1-xO film. Consequently, it can be concluded that the substitutional incorporation of Li can significantly improve the sensing performance of nickel oxide films for bolometer applications.

Influence of Mg substitution on structural, magnetic and dielectric properties of X-type barium[sbnd]zinc hexaferrites Ba2Zn2-xMgxFe28O46

Mg substituted X–type hexagonal ferrites with the chemical composition Ba2Zn2-xMgxFe28O46 (x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0) were successfully synthesised by a sol–gel auto–combustion technique, in order to investigate the effect of Mg substitution on structural, magnetic and dielectric properties. XRD analysis of prepared samples revealed the formation of pure X–type phase. The variations (decreasing trend) in lattice parameters with Mg substitution indicate the incorporation of Mg substitution into the crystal structure. The average crystallite size of heated powders was found to be in the range of 16–22 nm. For the first time, the RT hysteresis loops of Ba2Zn2Fe28O46 (Zn2X), Ba2Mg2Fe28O46 (Mg2X) and Ba2Zn2-xMgxFe28O46 (x = 0.0, 0.4, 0.8, 1.2, 1.6 and 2.0) were measured. The saturation magnetisation showed an initial decrease with x = 0.4 − 1.2, and then an increase with x > 1.2, to the largest final values of 63.29 A m2 kg−1 for the fully Mg–substituted x = 2.0. The value of coercivity lies in the range of 89.9–209.3 kA m−1 (1130–2630 Oe), and the magnetic results suggest that the compositions x = 0.0, 0.4 and 1.2 possess multi-domain microstructures, while x = 0.8, 1.6 and 2.0 possess single domain microstructures. The room temperature Mӧssbauer spectra were analysed with six sextets of five magnetic sublattices, and the results are presented as a function of Mg substitution. It was found that initial levels of Mg substitution reduce the Fe populations at a and b (spin up) sublattices, but that with x > 1.2 these become repopulated at fIV (spin down) site, resulting in an increase in magnetisation. Dielectric parameters such as dielectric constant and loss factor were studied as a function of frequency, and results show normal behaviour for ferrimagnetic materials. At low frequencies (100 Hz–2 MHz), relative permittivity was constant between 0.3 and 1.5 above 20 kHz, with the higher values belonging to the more dense samples. All Mg substituted samples had lower losses above 20 kHz than the pure Zn2X. In complex measurements at microwave frequencies (500 MHz–13.5 GHz), all samples had a real permittivity of around 7.5, except for the fully Mg–substituted sample (x = 2.0), which had a lower ε′ of 5.5. For two samples (x = 0.4 and 1.6) we observed dielectric resonances between 12.85 and 13.25 GHz. All showed a steady real permeability of around 1.2–1.5 over the whole 1–13 GHz range, and ferromagnetic resonance (FMR) between 1 and 5 GHz, and ∼12.5 GHz.

Air-annealed growth and characterization of Cd1-xZnxTe thin films grown from CdTe/ZnTe/CdTe multi-stacks

CdTe/ZnTe/CdTe thin film layers were vacuum-evaporated on glass-slides and annealed in box-furnace in the air. The samples were annealed at different temperatures of 350°C, 400°C and 450°C, respectively. At each temperature, three sets of samples were annealed for one, two and 3 h, respectively. The films showed good inter-diffusion and high crystallinity even at a lower temperature of 350°C. The 111(C) and 220(C) Cd1-xZnxTe planes showed an increasing left-hand shift in the 2θ axes, along with increasing annealing time and temperature. This trend is attributed to strain relaxation with increased annealing. Cd1-xZnxTe particle-size showed a sigmoid growth along with increasing temperature and time, while strain, dislocation-density, and the number of crystallites per unit area showed a sigmoid decay curve. At lower temperature, samples showed reduced bandgap due to charged defects and impurities like free Tellurium. At higher temperature bandgap increased, because of wire-like formation of TeO2 and their probable substitutional incorporation into Cd1-xZnxTe lattice sites. The TeO2 gradually formed into clusters. EDX results were finally co-related with the optical, structural and morphological results.

Modulating the Hysteresis of an Electronic Transition: Launching Alternative Transformation Pathways in the Metal–Insulator Transition of Vanadium(IV) Oxide

Materials exhibiting pronounced metal–insulator transitions such as VO2 have acquired great importance as potential computing vectors and electromagnetic cloaking elements given the large accompanying reversible modulation of properties such as electrical conductance and optical transmittance. As a first-order phase transition, considerable phase coexistence and hysteresis is typically observed between the heating insulator → metal and cooling metal → insulator transformations of VO2. Here, we illustrate that substitutional incorporation of tungsten greatly modifies the hysteresis of VO2, both increasing the hysteresis as well as introducing a distinctive kinetic asymmetry wherein the heating symmetry-raising transition is observed to happen much faster as compared to the cooling symmetry-lowering transition, which shows a pronounced rate dependence of the transition temperature. This observed kinetic asymmetry upon tungsten doping is attributed to the introduction of phase boundaries resulting from stabi...

Photovoltaic device performance of electron beam evaporated Glass/TCO/CdS/CdTe/Au heterostructure solar cells

Abstract We report on substrate temperature and Cu addition induced changes in the photovoltaic device performance of Glass/TCO/CdS/CdTe/Au heterostructures prepared by the electron beam evaporation technique. Prior to the photovoltaic study, the structural and optical properties of CdTe, CdTe:Cu and CdS/CdTe, CdS/CdTe:Cu layers were studied. X-ray diffraction (XRD) analysis showed that the deposited films belong to a zinc blende structure. The existence of the Te peak in the XRD pattern revealed the presence of excess Te in the deposited film structures, which confirmed the p-type conductive nature of the films. This was further substantiated by the electrical study. The low resistivity of 1 × 103 Ω cm was obtained for 4 wt.% of the Cu-doped CdTe film, which may be due to the substitutional incorporation of more efficient Cu2+ (Cd2+) into the CdTe lattice. The decrease in band gap with increasing Cu content may be attributed to the existence of shallow acceptor level formed by the incorporation of Cu into the CdTe lattice. The efficiency of the cell was increased with increasing Cu concentration and the cell prepared at room temperature with 4 wt.% of Cu addition possessed the maximum conversion efficiency of 1.68%. Further, a good photoresponse of the device is achieved as the Voc and Isc are increased with increase in the input power.

Annealing and Ni content effects on EPR and structural properties of Zn1–xNixO aerogel nanoparticles

AbstractZn1-xNixO aerogel nanopowders with nickel concentration in the range of 0.05 ≤ x ≤ 0.25, were synthesized by the sol-gel processing technique and post-annealed in air at 500 °C. Structural, vibrational, thermal and magnetic properties of the as-prepared and annealed Zn1-xNixO powdered samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman scattering, thermal gravimetric analysis (TGA) and electron paramagnetic resonance (EPR) spectroscopy. In addition to the ZnNiO phase, XRD analysis revealed the formation of a secondary NiO phase when the Ni content was greater than or equal to 10 %. The TEM images confirm that the particle size is in the range of 20 nm to 40 nm, in accordance with XRD results, and the particles are well dispersed. Raman scattering measurements confirm the wurtzite structure of the synthesized Zn1-xNixO nanopowders and show that intrinsic host-lattice defects are activated when Ni2+ions are substituted to the Zn sites. Room temperature ferromagnetic order was observed in all of the samples and was strongly dependent on the Ni content and thermal annealing. These results indicate that the observed room temperature ferromagnetism in ZnNiO may be attributed to the substitutional incorporation of Ni at Zn sites.

Synthesis of Ultrathin Composition Graded Doped Lateral WSe2/WS2 Heterostructures.

Lateral transition-metal dichalcogenide and their heterostructures have attracted substantial attention, but there lacks a simple approach to produce large-scaled optoelectronic devices with graded composition. In particular, the incorporation of substitution and doping into heterostructure formation is rarely reported. Here, we demonstrate growth of a composition graded doped lateral WSe2/WS2 heterostructure by ambient pressure chemical vapor deposition in a single heat cycle. Through Raman and photoluminescence spectroscopy, we demonstrate that the monolayer heterostructure exhibits a clear interface between two domains and a graded composition distribution in each domain. The coexistence of two distinct doping modes, i.e., interstitial and substitutional doping, was verified experimentally. A distinct three-stage growth mechanism consisting of nucleation, epitaxial growth, and substitution was proposed. Electrical transport measurements reveal that this lateral heterostructure has representative characteristics of a photodiodes. The optoelectronic device based on the lateral WSe2/WS2 heterostructure shows improved photodetection performance in terms of a reasonable responsivity and a large photoactive area.

Boron-Incorporating Silicon Nanocrystals Embedded in SiO2: Absence of Free Carriers vs. B-Induced Defects

Boron (B) doping of silicon nanocrystals requires the incorporation of a B-atom on a lattice site of the quantum dot and its ionization at room temperature. In case of successful B-doping the majority carriers (holes) should quench the photoluminescence of Si nanocrystals via non-radiative Auger recombination. In addition, the holes should allow for a non-transient electrical current. However, on the bottom end of the nanoscale, both substitutional incorporation and ionization are subject to significant increase in their respective energies due to confinement and size effects. Nevertheless, successful B-doping of Si nanocrystals was reported for certain structural conditions. Here, we investigate B-doping for small, well-dispersed Si nanocrystals with low and moderate B-concentrations. While small amounts of B-atoms are incorporated into these nanocrystals, they hardly affect their optical or electrical properties. If the B-concentration exceeds ~1 at%, the luminescence quantum yield is significantly quenched, whereas electrical measurements do not reveal free carriers. This observation suggests a photoluminescence quenching mechanism based on B-induced defect states. By means of density functional theory calculations, we prove that B creates multiple states in the bandgap of Si and SiO2. We conclude that non-percolated ultra-small Si nanocrystals cannot be efficiently B-doped.

Postsynthetic Route for Modifying the Metal—Insulator Transition of VO2 by Interstitial Dopant Incorporation

The thermally driven orders-of-magnitude modulation of resistance and optical transmittance observed in VO2 makes it an archetypal first-order phase transition material and underpins functional applications in logic and memory circuitry, electromagnetic cloaking, ballistic modulation, and thermochromic glazing to provide just a few representative examples. VO2 can be reversibly switched from an insulating to a metallic state at an equilibrium transition temperature of 67 °C. Tuning the phase diagram of VO2 to bring the transition temperature closer to room temperature has been a longstanding objective and one that has tremendous practical relevance. Substitutional incorporation of dopants has been the most common strategy for modulating the metal—insulator transition temperature but requires that the dopants be incorporated during synthesis. Here we demonstrate a novel postsynthetic diffusive annealing approach for incorporating interstitial B dopants within VO2. The postsynthetic method allows for the tr...

Strontium-doped calcium silicate bioceramic with enhanced in vitro osteogenic properties

Gehlenite (GLN, Ca2SiAl2O7) is a bioceramic that has been recently shown to possess excellent mechanical strength and in vitro osteogenic properties for bone regeneration. Substitutional incorporation of strontium in place of calcium is an effective way to further enhance biological properties of calcium-based bioceramics and glasses. However, such strategy has the potential to affect other important physicochemical parameters such as strength and degradation due to differences in the ionic radius of strontium and calcium. This study is the first to investigate the effect of a range of concentrations of strontium substitution of calcium at 1, 2, 5, 10 mol% (S1-GLN, S2-GLN, S5-GLN and S10-GLN) on the physicochemical and biological properties of GLN. We showed that up to 2 mol% strontium ion substitution retains the monophasic GLN structure when sintered at 1450 °C, whereas higher concentrations resulted in presence of calcium silicate impurities. Increased strontium incorporation resulted in changes in grain morphology and reduced densification when the ceramics were sintered at 1450 °C. Porous GLN, S1-GLN and S2-GLN scaffolds (∼80% porosity) showed compressive strengths of 2.05 ± 0.46 MPa, 1.76 ± 0.79 MPa and 1.57 ± 0.52 MPa respectively. S1-GLN and S2-GLN immersed in simulated body fluid showed increased strontium ion release but reduced calcium and silicon ion release compared to GLN without affecting overall weight loss and pH over a 21 d period. The bioactivity of the S2-GLN ceramics was significantly improved as reflected in the significant upregulation of HOB proliferation and differentiation compared to GLN. Overall, these results suggest that increased incorporation of strontium presents a trade-off between bioactivity and mechanical strength for GLN bioceramics. This is an important consideration in the development of strontium-doped bioceramics.

Optical, electrical and ferromagnetic studies of ZnO:Fe diluted magnetic semiconductor nanoparticles for spintronic applications

In the present investigation, diluted magnetic semiconductor (Zn1−xFexO) nanoparticles with different doping concentrations (x=0, 0.02, 0.04, 0.06, and 0.08) were successfully synthesized by sol-gel auto-combustion method. The crystal structure, morphology, optical, electrical and magnetic properties of the prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis using x-rays (EDAX), ultraviolet–visible spectrophotometer, fluorescence spectroscope (FS), vibrating sample magnetometer (VSM) and broad band dielectric spectrometer (BDS). XRD results reveal that all the samples possess hexagonal wurtzite crystal structure with good crystalline quality. The absence of impurity phases divulge that Fe ions are well incorporated into the ZnO crystal lattice. The substitutional incorporation of Fe3+ at Zn sites is reflected in optical absorption spectra of the samples. Flouorescence spectra of the samples show a strong near-band edge related UV emission as well as defect related visible emissions. The semiconducting behavior of the samples has been confirmed through electrical conductivity measurements. Magnetic measurements indicated that all the samples possess ferromagnetism at room temperature.

Retraction Note to: Investigation of Co-Doped ZnO Nanowires by X-ray Absorption Spectroscopy and Ab Initio Simulation

The local structure of single room- and high-temperature Co-implanted ZnO nanowires with subsequent thermal annealing has been studied using hard-x-ray techniques in combination with ab initio Zn K-edge x-ray absorption near-edge structure (XANES) simulations. X-ray fluorescence data reveal a homogeneous distribution of Co atoms/ions with concentration of about 0.1 at.% to 0.3 at.% in the nanowires. XANES data indicate substitutional incorporation of Co2+ ions at Zn sites in both types of nanowire. Improved structural order around Co atoms is obtained in nanowires with high-temperature ion implantation followed by thermal annealing. The ab initio Zn K-edge simulations not only confirm recovery of implantation-induced damage in the ZnO host lattice by the thermal annealing process, but also assist in studying the effect of oxygen vacancies in the Zn K-edge XANES spectra. Microphotoluminescence data certify that high-temperature ion implantation with subsequent thermal annealing is an effective approach to achieve the strongest optical activation of Co ions and good energy transfer to Co ions from the ZnO host matrix.

Comparison of chemical bath-deposited ZnO films doped with Al, Ga and In

A comparative study is presented on chemical bath-deposited ZnO films, doped with the group-13 metals Al, Ga and In. The study reveals marked differences in dopant incorporation in the films, which increases in the order: In, Al and Ga. The presence of dopant in the solution induces significant modifications in the deposition rate, which varies between 110 and 40 nm min−1. All films are (002)-textured, whereas the lattice stress evolution with the dopant type and concentration suggests that Ga has the highest degree of substitutional incorporation in Zn sites. The average visible transmittance is higher than 80%, while the infrared reflectivity depends on the free carrier density in the films, which is the lowest for undoped ZnO and increases in the order: In-, Al- and Ga-doped ZnO. Optical measurements also yield an inverse correlation between carrier density and mobility. Doping enlarges the bandgap, as well as the Urbach energy that is related to the films’ disorder. The lowest electrical resistivity, measured by four-point probe, is 1.7 × 10−2 Ω cm and is obtained for In-doped films after being exposed to ultraviolet light. Ga-doped films are found to exhibit the highest stability of the conductivity upon ultraviolet exposure.

Hydrothermal formation and up‐conversion luminescence of Er3+‐doped GdNbO4

AbstractThe effect of concentration of Er3+ on the up‐conversion and photoluminescence properties of Gd1.00−xErxNbO4, x=0‐0.50 which has monoclinic fergusonite‐type structure as a main phase has been investigated, using a processing technique based on hydrothermal method. Under weakly basic hydrothermal condition at 240°C for 5 hours, a single phase of fergusonite‐type Gd1.00−xErxNbO4 solid solution was directly formed as nanocrystals by the substitutional incorporation of Er3+ into GdNbO4 because of the gradual and linear decrease in the lattice parameters of the monoclinic phase corresponding to the Vegard's Law. The gadolinium niobate doped with 2 mol% Er3+, Gd0.98Er0.02NbO4 after heating at 1300°C for 1 hour, which has nanocrystalline structure whose crystallite size is around 29 nm, exhibits the highest photoluminescence intensity in the green spectral region, 515‐560 nm under excitation at wavelength of 254 nm. On the other hand, the up‐converted luminescence intensity of the niobate nanocrystals becomes the maximum at the concentration of 20 mol% Er3+, Gd0.80Er0.20NbO4 under excitation at 980 nm. These results demonstrate that the material, Er3+‐doped GdNbO4 nanocrystals prepared through hydrothermal route and postheating has potential for up‐converting phosphor.

Concentration dependence of luminescence properties of GdNbO 4 :Er 3+ /Yb 3+ synthesized through hydrothermal route

Abstract To investigate the concentration dependence of the optical, up-conversion, and photoluminescence properties of phosphors based on GdNbO 4 co-doped with Er 3+ and Yb 3+ an approach through hydrothermal synthesis route including subsequent heating in air was adopted. A single phase of monoclinic fergusonite-type Gd 1.00-(x+y) Er x Yb y NbO 4 solid solution (x = 0–0.50, y = 0–0.30) was directly formed as nanocrystals by the substitutional incorporation of 0–50 mol% Er 3+ and 0–30 mol% Yb 3+ under hydrothermal condition at 240 °C for 5 h. The nanocrystalline GdNbO 4 :Er 3+ /Yb 3+ whose crystallite sizes are around 18–38 nm showed the up-converted emission in the green spectral region, 515–565 nm under excitation at wavelengths of 980 nm in addition to the photoluminescence under excitation both at 259 nm and at 377 nm. At the concentration of 20 mol% Er 3+ (x = 0.20), the up-converted emission intensity of the Gd 1.00-(x+y) Er x Yb y NbO 4 solid solution became the highest by the incorporation of 20 mol% Yb 3+ (y = 0.20). Although the emission intensity of samples changed depending on their concentrations, x and y, the nanocrystalline GdNbO 4 co-doped with 5 mol% Er 3+ and 20 mol% Yb 3+ presented the strongest up-converted emission.

Absence of an N-Linked Glycosylation Motif in the Glycoprotein of the Live-Attenuated Argentine Hemorrhagic Fever Vaccine, Candid #1, Results in Its Improper Processing, and Reduced Surface Expression

Junin virus (JUNV), a highly pathogenic New World arenavirus, is the causative agent of Argentine hemorrhagic fever (AHF). The live-attenuated Candid #1 (Can) strain currently serves as a vaccine for at-risk populations. We have previously shown that the Can glycoprotein (GPC) gene is the primary gene responsible for attenuation in a guinea pig model of AHF. However, the mechanisms through which the GPC contributes to the attenuation of the Can strain remain unknown. A more complete understanding of the mechanisms underlying the attenuation and immunogenicity of the Can strain will potentially allow for the rational design of additional safe and novel vaccines. Here, we provide a detailed comparison of both RNA and protein expression profiles between both inter- and intra-segment chimeric JUNV recombinant clones expressing combinations of genes from the Can strain and the pathogenic Romero (Rom) strain. The recombinant viruses that express Can GPC, which were shown to be attenuated in guinea pigs, displayed different RNA levels and GPC processing patterns as determined by Northern and Western blot analyses, respectively. Analysis of recombinant viruses containing amino acid substitutions selected at different mouse brain passages during the generation of Can revealed that altered Can GPC processing was primarily due to the T168A substitution within G1, which eliminates an N-linked glycosylation motif. Incorporation of the T168A substitution in the Rom GPC resulted in a Can-like processing pattern of Rom GPC. In addition, JUNV GPCs containing T168A substitution were retained within the endoplasmic reticulum (ER) and displayed significantly lower cell surface expression than wild-type Rom GPC. Interestingly, the reversion A168T in Can GPC significantly increased GPC expression at the cell surface. Our results demonstrate that recombinant JUNV (rJUNV) expressing Can GPC display markedly different protein expression and elevated genomic RNA expression when compared to viruses expressing Rom GPC. Additionally, our findings indicate that the N-linked glycosylation motif at amino acid positions 166–168 is important for trafficking of JUNV GPC to the cell surface, and the elimination of this motif interferes with the GPC release from the ER.

RETRACTED ARTICLE: Investigation of Co-Doped ZnO Nanowires by X-ray Absorption Spectroscopy and Ab Initio Simulation

The local structure of single room- and high-temperature Co-implanted ZnO nanowires with subsequent thermal annealing has been studied using hard-x-ray techniques in combination with ab initio Zn K-edge x-ray absorption near-edge structure (XANES) simulations. X-ray fluorescence data reveal a homogeneous distribution of Co atoms/ions with concentration of about 0.1 at.% to 0.3 at.% in the nanowires. XANES data indicate substitutional incorporation of Co2+ ions at Zn sites in both types of nanowire. Improved structural order around Co atoms is obtained in nanowires with high-temperature ion implantation followed by thermal annealing. The ab initio Zn K-edge simulations not only confirm recovery of implantation-induced damage in the ZnO host lattice by the thermal annealing process, but also assist in studying the effect of oxygen vacancies in the Zn K-edge XANES spectra. Microphotoluminescence data certify that high-temperature ion implantation with subsequent thermal annealing is an effective approach to achieve the strongest optical activation of Co ions and good energy transfer to Co ions from the ZnO host matrix.

Rock Salt Ni/Co Oxides with Unusual Nanoscale‐Stabilized Composition as Water Splitting Electrocatalysts

The influence of nanoscale on the formation of metastable phases is an important aspect of nanostructuring that can lead to the discovery of unusual material compositions. Here, the synthesis, structural characterization, and electrochemical performance of Ni/Co mixed oxide nanocrystals in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is reported and the influence of nanoscaling on their composition and solubility range is investigated. Using a solvothermal synthesis in tert‐butanol ultrasmall crystalline and highly dispersible Ni x Co1− x O nanoparticles with rock salt type structure are obtained. The mixed oxides feature non‐equilibrium phases with unusual miscibility in the whole composition range, which is attributed to a stabilizing effect of the nanoscale combined with kinetic control of particle formation. Substitutional incorporation of Co and Ni atoms into the rock salt lattice has a remarkable effect on the formal potentials of NiO oxidation that shift continuously to lower values with increasing Co content. This can be related to a monotonic reduction of the work function of (001) and (111)‐oriented surfaces with an increase in Co content, as obtained from density functional theory (DFT+U) calculations. Furthermore, the electrocatalytic performance of the Ni x Co1− x O nanoparticles in water splitting changes significantly. OER activity continuously increases with increasing Ni contents, while HER activity shows an opposite trend, increasing for higher Co contents. The high electrocatalytic activity and tunable performance of the nonequilibrium Ni x Co1− x O nanoparticles in HER and OER demonstrate great potential in the design of electrocatalysts for overall water splitting.