Substitution Of Zn Atoms Research Articles

Optical and electrical properties of individual p-type ZnO microbelts with Ag dopant

P-type ZnO microbelts were successfully synthesized by thermal diffusion of Ag in a step by step thermal annealing process. The effect of the annealing temperature on the room temperature photoluminescence (RT-PL) and current versus voltage (I–V) properties of Ag-doped ZnO microbelts were studied. With the increase of the annealing temperature, the deep-level emission (506 nm) decreased and the AgZn related violet emission peak at 405 nm was observed. The substitution of Zn atoms by Ag atoms is unstable at high temperature, which might be a limitation for Ag as the dopant of ZnO. In our experiment, the optimal annealing temperature is 250 °C, at which the strong neutral acceptor bound exciton (A0X) peak appeared in the low temperature-PL spectrum. Correspondingly, the conductivity type of the ZnO microbelt transformed from n to p. The symmetrical I–V curves exhibited slightly nonlinear behaviors. The result indicated the existence of Schottky barriers between the individual Ag-doped ZnO microbelt and the In electrodes.

Theoretical Investigation of Structural and Magnetic Properties of ZnnSen (n=6–13) Nanoclusters Doped with Manganese Atoms

With the generalized gradient approximation in first principle all‐electron calculations, the lowest energy structures of ZnnSen (n=6–13) nanoclusters were obtained as the pristine clusters. A number of configurations and structural isomers of ZnnSen (n=6–13) nanoclusters doped with single and two Mn atoms were used to investigate the structural and magnetic properties of manganese‐doped ZnnSen (n=6–13) nanoclusters. It arrives at a conclusion that Mn doping does not change the size‐dependent oscillating behavior in second‐order energy difference of ZnnSen (n=6–13) nanoclusters, but leads to the decrease of energy gap between lowest unoccupied molecular orbital and the highest occupied molecular orbital. Energy arguments indicate that Mn atoms prefer to substitute Zn atoms in Mn‐doped ZnnSen (n=6–13) nanoclusters. Owing the Mn–Mn short‐ranged superexchange mechanism, Mn atoms favor to locate at adjacent Zn atom sites in antiferromagnetic states of ZnnSen nanoclusters doped with two Mn atoms.

(Co, Zn)O compound obtained from ZnTe vapor deposition on Co/Si substrates

(Co, Zn)O compound has been obtained by a non-expensive synthesis route. ZnTe thin films were obtained by isothermal close space sublimation on the Co thin layer previously sputtered on silicon substrates. After the annealing process in humid ambient cobalt atoms diffusion and Zn oxidation were obtained besides partial Te evaporation. The detailed characterization of the samples by using XRD, RBS, AFM, XPS, VSM and MFM techniques point to the formation of room temperature ferromagnetic CoxZn(1−x)O phase (x<0.15). This ferromagnetic behavior is mainly attributed to Co atoms substituting Zn atoms in the ZnO network.

Effect of doping with Co and/or Cu on electronic structure and optical properties of ZnO

This paper reports on ab initio numerical simulations of the effect of Co and Cu dopings on the electronic structure and optical properties of ZnO, pursued to develop diluted magnetic semiconductors vitally needed for spintronic applications. The simulations are based upon the Perdew-Burke-Enzerh generalized gradient approximation on the density functional theory. It is revealed that the electrons with energies close to the Fermi level effectively transfer only between Cu and Co ions which substitute Zn atoms, and are located in the neighbor sites connected by an O ion. The simulation results are consistent with the experimental observations that addition of Cu helps achieve stable ferromagnetism of Co-doped ZnO. It is shown that simultaneous insertion of Co and Cu atoms leads to smaller energy band gap, redshift of the optical absorption edge, as well as significant changes in the reflectivity, dielectric function, refractive index, and electron energy loss function of ZnO as compared to the doping with either Co or Cu atoms. These highly unusual optical properties are explained in terms of the computed electronic structure and are promising for the development of the next-generation room-temperature ferromagnetic semiconductors for future spintronic devices on the existing semiconductor micromanufacturing platform.

Controlling intermetallic compound formation reaction between Sn and Ni–P by Zn addition

Effects of Zn addition on the interfacial reaction between Sn and Ni(P) were investigated by systematically varying the Zn concentration in the Sn solder. It was found that the typical Ni–Sn reaction product, Ni 3Sn 4 phase, was changed substantially by adding small amounts of Zn to the Sn. With the Zn addition, the ternary Ni 4(Sn 1− x ,Zn x ) phase formed at the interface during reflow and aging according to X-ray diffraction analysis. In the Ni 4(Sn 1− x ,Zn x ) phase, the lattice parameters contracted with increasing Zn content, in agreement with the Vegard's law. Since diffusions of the reactive species through the denser ternary intermetallic compound were more unlikely than through the binary Ni 3Sn 4, the Zn-containing solder showed a much slower electroless Ni–P consumption rate than Sn. The decrease in Ni consumption rate increased with the increasing Zn content in Sn. The reason for the decrease was that the growth rate of Ni 4(Sn 1− x ,Zn x ) phase was directly determined by substitution of Zn atoms into the Sn sublattice.

Photoluminescence properties of Co-doped ZnO nanorods array fabricated by the solution method

Highly ordered pure and Co-doped ZnO nanorod arrays were synthesized by a solution method at low temperature. The structures and morphology of the samples were studied by XRD, EDS and FESEM as well as Raman, which reveal that the samples are wurtzite structure; the Co atoms successfully substitute Zn atoms positions in nanocrystal. The PL properties of the as-prepared specimens were principally investigated using PL spectroscopy at room temperature and ultralow temperatures. The results strongly disclose that Co-doping can effectively adjust the energy level and abound the contents of surface states in ZnO nanorods, which lead to shift in the emission peak position in ultraviolet (UV) region and enhance the luminescence performance in visible (VL) light region of nanorod arrays. In addition, the slow vibration of phonons in nanocrystal lattice at ultralow temperature can also possibly contribute towards the novel emission performances of Co-doped arrays.

Ferromagnetic modification of ZnO film by Fe + ions implantation

The ZnO-based diluted magnetic semiconductors (DMSs) were achieved by ion implantation. Eighty kilo-electron-volt Fe + ions were implanted into n-type ZnO films at room temperature with doses ranging from 1 × 10 16 cm −2 to 8 × 10 16 cm −2 and subsequently annealed at 700 °C for 1 h in air ambient. PIXE was employed to determine the Fe-implanted content. The magnetic property was measured by the Quantum Design MPMS SQUID magnetometer. No secondary phases or clusters were detected within the sensitivity of XRD. Raman spectrum measurement showed that the Fe ions incorporated into the crystal lattice positions of ZnO through substitution of Zn atoms. Apparent ferromagnetic hysteresis loops measured at 10 K were presented. The relationships between the Fe-implanted content and the ferromagnetic property are discussed.

Effect of Mn doping on the electric and dielectric properties of ZnO epitaxial films

The Mn doping effects on the electric and dielectric properties of ZnO epitaxial films were studied. To optimize the stoichiometry of undoped ZnO film prepared by pulsed laser deposition, we evaluated the intensity ratio of the optical emission from excited oxygen atoms (O*) and excited zinc atoms (Zn*) generated by ablating a ZnO ceramic target in plume. The leakage current of undoped ZnO film decreased with an increase of the ratio I(O777*)∕I(Zn335*). Mn doping of ZnO was also effective in decreasing the leakage current. The ZnO:4at.% Mn had a very small leakage current, eight orders of magnitude less than that of undoped ZnO. With a Mn concentration above 4at.%, on the other hand, the leakage current was increased. The activation energy in ZnO:Mn obtained from the temperature dependence of the ac conductivity revealed that oxygen vacancy was responsible for the large current at the Mn concentration below 2at.%. For the sample with the Mn concentration of 2–3at.%, dominant conduction in ZnO:Mn epitaxial films originated from the interstitial Zn. When the Mn concentration was above 4at.%, the conduction was governed by the substitution of Zn atoms in the oxygen site. Impedance analysis revealed that the origin for large resistivity of ZnO:Mn films was not the ZnO/electrode interface but the bulky part of the films.

Dependence of Magnetism on Doping Concentration in V-Doped Bulk ZnO

Extensive calculations based on density functional theory have been carried out to understand the dependence of magnetic coupling on the concentration and distribution of V dopants in bulk ZnO. We considered three different doping concentration of V, namely 5.6%, 8.3% and 12.5%. At low doping concentration, ferromagnetic, anti-ferromagnetic and ferrimagnetic couplings are energetically nearly degenerate. Consequently, thermal fluctuation in samples may cause diverse magnetic behaviors. However, the ferromagnetic state becomes stable as the concentration of V increases to 12.5%. At low concentrations (5.6% and 8.3%) V atoms substitute Zn atoms uniformly in bulk ZnO, while they tend to cluster when their concentration reaches 12.5%. The present study provides an understanding of the conflicting experimental observations in V-doped bulk ZnO.

Photoluminescent Properties of (Ca,Zn)TiO3:Pr,B Particles Synthesized by the Peroxide‐Based Route Method

(Ca1−x,Znx)TiO3:Pr, B red phosphor particles were prepared using the peroxide‐based route and their photoluminescent (PL) properties were investigated by changing the sintering temperature, the concentration of the activator, the ratio of Ca to Zn, and the amount of H3BO3 flux. For the CaTiO3:Pr phosphor, a pure perovksite‐type CaTiO3 phase was formed when the sintering temperature was 700°–800°C. It was found that the substitution of Zn atoms instead of Ca considerably enhanced the 614‐nm red emissions. The PL intensity of (Ca1−x,Znx)TiO3:Pr phosphor was also additionally improved by adding an H3BO3 flux. Finally, the optimized phosphor Ca0.85Zn0.15TiO3:0.001Pr,0.1B showed the highest PL intensity.

Structural, electrical and optical properties of zirconium-doped zinc oxide films prepared by radio frequency magnetron sputtering

Transparent and conducting zirconium-doped zinc oxide films have been prepared by radio frequency magnetron sputtering at room temperature. The ZrO 2 content in the target is varied from 0 to 10 wt.%. The films are polycrystalline with a hexagonal structure and a preferred orientation along the c axis. As the ZrO 2 content increases, the crystallinity and conductivity of the film are initially improved and then both show deterioration. Zr atoms mainly substitute Zn atoms when the ZrO 2 content are 3 and 5 wt.%, but tend to cluster into grain boundaries at higher contents. The lowest resistivity achieved is 2.07 × 10 − 3 Ω cm with the ZrO 2 content of 5 wt.% with a Hall mobility of 16 cm 2 V − 1 s − 1 and a carrier concentration of 1.95 × 10 20 cm − 3 . All the films present a high transmittance of above 90% in the visible range. The optical band gap depends on the carrier concentration, and the value is larger at higher carrier concentration.

Modification of the Oxidative Power of ZnO(101̄0) Surface by Substituting Some Surface Zn Atoms with Other Metals

We use oxygen vacancy formation energy (OVFE) as a measure of how easily lattice oxygen may participate in the Mars and Van Krevelen mechanism for oxidation reactions. We calculate with density functional theory how OVFE is affected when some of Zn atoms in ZnO(1010) surface layer are substituted by other metal dopants. We find that Li, Na, K, Rb, Cs, Os, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, and Cd decrease OVFE and prefer to be located at the surface of ZnO rather than in the bulk. Mg, Ca, Sr, Ba, Sc, Y, La, Ti, Zr, Hf, Ce, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Al, Ga, Sn, and Pb increase OVFE. Most of the dopants that increase OVFE prefer to substitute Zn atoms in the bulk, except for Ca, Sr, Ba, La, Ce, Re, Fe, Ru, Co, Sn, and Pb, which prefer to substitute a Zn atom at the surface. These calculations lead us to conclude that doping an oxide is an efficient method of modifying its oxidative power.

Phase evolution of Zn 1− xMn xO system synthesized via oxalate precursors

Polycrystalline samples with nominal composition Zn 1− x Mn x O have been prepared by a co-precipitation technique in which kinetics of high temperature reactions are favoured by the use of highly reactive particles. Structural and compositional analysis reveal that following the decomposition of the oxalate precursor a secondary ZnMnO 3 phase is formed already at 400 °C. By means of XRD and HRTEM, a defect spinel-type structure is presumed for this Zn–Mn–O compound. A diluted magnetic semiconductor in which Mn atoms are homogeneously substituting Zn atoms in the semiconductor matrix is not obtained in the whole temperature range by this synthesis method. The microstructural situation is then far from that theoretically predicted for spintronic systems.

Preparation and characterization of zinc-doped gallophosphate molecular sieve

The effect of Zn doping on crystallization of gallophosphate molecular sieve, cloverite, synthesized hydrothermally at 170 °C, using starting gels with ZnO, was investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), and molecular dynamics (MD) simulation, etc. The SEM observations and crystallinities estimated from XRD data revealed that Zn-doped cloverite with very good crystallinity was successfully prepared, and the addition of ZnO to the starting gel was effective in promoting the crystallization process in a short reaction time. The results of chemical analyses, estimated unit cell dimensions, and MD simulations suggested the substitution of Zn atoms for Ga atoms in the framework of Zn-doped cloverite.