Blende ZnO Research Articles

Effect of Cu, Co, and Pb doping on physical properties of ZnO Zinc Blende and Hexagonal mixed phases thin films prepared by spray pyrolysis

Here we report the preparation of the Zinc Blende ZnO phase mixed with a small ratio of the Wurtzite phase. The spray pyrolysis technique has been employed for all films deposited onto amorphous glass substrates. The XRD results revealed the formation of mixed ZnO Zinc Blende (ZB) and Wurtzite (WU) phases with the ZB phase as the predominant phase. The crystallite size of both phases had estimated using Scherer’s equation and both phases were found to have the same crystallite size. The FE-SEM images show the formation of grain sizes bigger than those recorded from Scherer’s equation. XPS results confirm the existence of doped elements in the deposited films with different ratios. The optical band gap of the pure film was estimated and found to be 3.24 eV. Upon doping the band gap optical has been decreasing to 3.2 eV for Cu-doped ZnO and 3.22 and 3.24 eV for Pb and Co-doped films. The refractive index dispersion was found to change from normal to anomalous behavior for a pure film as the wavelength increases. Cu and Pb-doped films show dispersion relation and Co-doped film shows normal behavior. Also, the high-frequency dielectric constant has been determined and found to decrease upon all doping elements as compared to pure film.

Structural and optical properties of Zn-implanted silica: effect of fluence and annealing

The phase-structural composition of silica films grown on Si substrates implanted with different fluences of Zn ions has been studied using transmission electron microscopy (TEM) and electron diffraction. Small clusters (2–3 nm) and larger clusters (5–7 nm) were formed in the as-implanted silica films with Zn concentration of 6–8 at % and 16%–18%, respectively. Furnace annealing at 750 °С for two hours in air resulted in the formation of an orthorhombic Zn2SiO4 phase (space group R-3) in the case of low fluence (5 × 1016 cm−2) and in the formation of a zinc blended ZnO phase (space group F-43m) in the case of high fluence (1 × 1017 cm−2). Based on the Rutherford backscattering spectrometry (RBS) data, it has been shown that impurity losses during implantation and subsequent annealing increase with the fluence of the implanted ions. The photoluminescence data were consistent with the TEM and RBS.

Ab initio study of mechanical, phonon and electronic Properties of cubic zinc-blende structure of ZnO

The search for functional materials in opto-electronic devices is a major aspect of material research in contemporary times and a meta-stable structure of ZnO has been proposed as one such relevant materials. Herein the elastic constants, lattice dynamical and electronic properties of the cubic zinc-blende ZnO (ZB-ZnO) were studied at ambient pressure using the density functional theory method within the generalized gradient approximation. The result shows that ZB-ZnO is mechanically and dynamically stable, ductile and a direct band gap semiconductor and is very promising for opto-electronic applications. The results are in fair agreement with the available data in the literature.

Luminescence of ZnO nanocrystals in silica synthesized by dual (Zn, O) implantation and thermal annealing

Zinc blende ZnO nanocrystals (NCs) were synthesised in amorphous silica by high-fluence dual (Zn, O) ion implantation and subsequent thermal annealing in air. We observed the formation of core/shell nanoparticles at the depth of maximum Zn concentration as a result of an incomplete oxidation process. The silica matrix with ZnO NCs exhibits an intense white-greenish emission. Low-temperature photoluminescence spectroscopy revealed various radiative recombination mechanisms in the zinc blende ZnO NCs involving intrinsic defects that act as donors and acceptors.

Photocatalytic degradation of methylene blue using a ZnO/TiO2 heterojunction nanomesh electrode

In the present research, ZnO/TiO2 heterojunction nanomeshes (HNMs) were synthesized by anodizing and calcination. The structural study revealed the as-synthesized samples were composed of anatase TiO2, rutile TiO2,and zincblende-structured ZnO. TiO2 segments had a preferred orientation along the [110] direction, whereas ZnO nanoparticles were oriented along the [200] direction. In comparison to pure TiO2 nanomeshes, ZnO/TiO2 HNMs had higher methylene blue (MB) photodegradation capacity. Furthermore, the effects of different parameters, such as calcination temperature, initial pH, and mesh density, on MB photodegradation were investigated. The superior photocatalytic activity was achieved by the sample calcinated at 600°C due to the appearance of zinc-blende ZnO and the mixed crystal phases of anatase and rutile TiO2. A high degradation efficiency was obtained under alkaline conditions. When the mesh density was 200 per inch, the maximum photodegradation efficiency was achieved.

Defects and Properties in Polymorph of ZnO

In this work, polymorphic models of the structures of ZnO is considered. We have studied the defects and defects behaviours in Wurtzite, zinc blende, and rocksalt ZnO by using first principles and quantum simulation methods. We used density functional theory (DFT) and molecular dynamics (MD) simulation methods to investigate the structural and electronic properties of defect ZnO. For DFT calculations, a computer code within QUANTUM-ESPRESSO is used. Calculations of energies versus lattice constants display the optimum values of the lattice constants for crystal systems. Results are reported using a step-by-step approach, starting from the primitive cell of bulk ZnO, going to a slab model by including a surface charge defects. Generally, the behaviour of intrinsic defects in ZnO, electronic properties, formation energies and workfunction of ZnO were investigated. The effect of different surface absorbents and surface defects on the workfunction of ZnO were studied using DFT calculations. Anisotropy and optical properties of defects have also been studied.

Luminescent Properties of (004) Highly Oriented Cubic Zinc Blende ZnO Thin Films.

Photoluminescence properties of cubic zinc blende ZnO thin films grown on glass substrates prepared by the spray pyrolysis method are discussed. X-ray diffraction spectra show the crystalline wurtzite with preferential growth in the (002) orientation and a metastable cubic zinc blende phase highly oriented in the (004) direction. Raman measurements support the ZnO cubic modification growth of the films. Photoluminescence (PL) spectra of zinc blende films are characterized by a new PL band centerd at 2.70 eV, the blue emission, in addition there are two principal bands that are also found in hexagonal ZnO films with the peak positions at 2.83 eV and 2.35 eV. The origin of the 2.70 eV band can be attributed to transitions from Zn-interstitial to Zn-vacancies. It is also important to mention that the PL intensity of the 2.35 eV band of the zinc blende thin films is relatively higher than in the band present in hexagonal ZnO films, which means that zinc blende films have more oxygen vacancies, as was corroborated by means of the energy dispersion spectroscopy (EDS) measurements. PL spectra at 77 °K were measured and the 2.70 eV band was confirmed for the zinc blende films. Some PL bands of cubic films also appeared for the hexagonal phase, which is due, to a certain extent, to the similar ions stacking of both wurtzite and zinc blende symmetries.

Structure, electrical properties and luminescence of ZnO nanocrystals deposited in SiO2/Si track templates

ZnO nanoclusters obtained by electrochemical deposition (ECD) of zinc in track template a-SiO2/Si-n have been studied. The structure SiO2/Si was irradiated at DC-60 cyclotron with 200 MeV Xe ions (Φ = 108 ions/cm2) with subsequent chemical etching in the diluted hydrofluoric acid (HF). Electrochemical deposition (ECD) of Zn in track template was carried out in the potentiostatic mode. The surface of samples was examined using a SEM JSM 7500F microscope. X-ray diffraction analysis was carried out using a D8 ADVANCE ECO X-ray diffractometer. According to XRD, the electrodeposition of zinc into the a-SiO2/Si-n track template resulted in a formation of zincblende (ZB) ZnO nanocrystals. Current-voltage characteristics and photoluminescence of SiO2/Si track template with ZnO ZB nanocrystals were investigated.

Atomistic Interface Dynamics in Sn-Catalyzed Growth of Wurtzite and Zinc-Blende ZnO Nanowires.

Unraveling the phase selection mechanisms of semiconductor nanowires (NWs) is critical for the applications in future advanced nanodevices. In this study, the atomistic vapor-solid-liquid growth processes of Sn-catalyzed wurtzite (WZ) and zinc blende (ZB) ZnO are directly revealed based on the in situ transmission electron microscopy. The growth kinetics of WZ and ZB crystal phases in ZnO appear markedly different in terms of the NW-droplet interface, whereas the nucleation site as determined by the contact angle ϕ between the seed particle and the NW is found to be crucial for tuning the NW structure through combined experimental and theoretical investigations. These results offer an atomic-scale view into the dynamic growth process of ZnO NW, which has implications for the phase-controllable synthesis of II-VI compounds and heterostructures with tunable band structures.

Electronic and Magnetic Properties of Ni-Doped Zinc-Blende ZnO: A First-Principles Study.

The electronic structure, band structure, density of state, and magnetic properties of Ni-doped zinc-blende (ZB) ZnO are studied by using the first-principles method based on the spin-polarized density-functional theory. The calculated results show that Ni atoms can induce a stable ferromagnetic (FM) ground state in Ni-doped ZB ZnO. The magnetic moments mainly originate from the unpaired Ni 3d orbitals, and the O 2p orbitals contribute a little to the magnetic moments. The magnetic moment of a supercell including a single Ni atom is 0.79 μB. The electronic structure shows that Ni-doped ZB ZnO is a half-metallic FM material. The strong spin-orbit coupling appears near the Fermi level and shows obvious asymmetry for spin-up and spin-down density of state, which indicates a significant hybrid effects from the Ni 3d and O 2p states. However, the coupling of the anti-ferromagnetic (AFM) state show metallic characteristic, the spin-up and spin-down energy levels pass through the Fermi surface. The magnetic moment of a single Ni atom is 0.74 μB. Moreover, the results show that the Ni 3d and O 2p states have a strong p-d hybridization effect near the Fermi level and obtain a high stability. The above theoretical results demonstrate that Ni-doped zinc blende ZnO can be considered as a potential half-metal FM material and dilute magnetic semiconductors.

Ab initio calculations of the magnetic properties of TM (Ti, V)-doped zinc-blende ZnO

In order to promote suitable material to be used in spintronics devices, this study purposes to evaluate the magnetic properties of the titanium and vanadium-doped zinc-blende ZnO from first-principles. The calculations of these properties are based on the Korringa–Kohn–Rostoker (KKR) method combined with the coherent potential approximation (CPA), using the local density approximation (LDA). We have calculated and discussed the density of states (DOSs) in the energy phase diagrams for different concentration values, of the dopants. We have also investigated the magnetic and half-metallic properties of this doped compound. Additionally, we showed the mechanism of the exchange coupling interaction. Finally, we estimated and studied the Curie temperature for different concentrations.

Magnetic properties of isolated Re ion and Re-Re complex in ZnO studied by GGA+U approach

Magnetic properties of Re substituting for the divalent Zn ions and impurity pairs in wurtzite and zinc blende ZnO are analyzed by employing the Generalized Gradient Approximation with the +U corrections. The +U term applied to d(Zn), p(O), and d(Re) orbitals stabilizes spin polarization of Re. Re impurity introduces a defect level located in the band gap, and Re2+ generates the local spin 5/2 in both wurtzite and zinc blende structures. Magnetic coupling of Re-Re pairs as a function of distance between the defects, their relative orientation, and the charge state was calculated. All magnetic coupling between impurities is antiferromagnetic and due to an intermediate O atom via strong d(Re)-p(O) hybridization between Re and O states. The defect states and magnetic moments come from d(Re) with a contribution of p(O) orbitals of the O nearest neighbors of Re. The results show that the Re-doped wurtzite ZnO may be a new type of magneto-optical materials with a great promise.

Room temperature sputter deposited catalyst-free nanowires with wurtzite/zinc blende ZnO superstructure and their application in electromechanical nanogenerators on polymer and paper substrates

Catalyst-free growth of ZnO nanowires using reactive magnetron sputtering at room temperature is reported. We discuss the growth of the nanowires using reactive magnetron sputtering as a function of argon and oxygen flow values changing at a set ratio of 10:2. A transition from nanostructured Zn to nanowire ZnO growth is observed at 20 sccm Ar and 4 sccm O2. Densification and improved alignment of the nanowires is visible for increasing flow values up to 50 sccm Ar and 10 sccm O2. Nanowires exhibit stacking fault regions of zinc blende ZnO in wurtzite ZnO. The regions encompass the whole width of the nanowires and their quantum well behavior is manifested in the photoluminescence spectra. The nanowires were subsequently deposited on paper and PET substrates and electromechanical nanogenerators were fabricated. Manual pressing and depressing of the devices induced voltages of 50 μV and 2 μV for the devices on PET and paper substrates, respectively.

The first-principles study of electronic structures, magnetic and optical properties for Ce-doped ZnO

ABSTRACTElectronic structures, magnetic and optical properties of Ce-doped zinc-blende ZnO are studied by the first-principles of local spin density approximation based on the density function theory (DFT). Band structures, total density of states (TDOS), partial density of states (PDOS), ferromagnetic (FM), antiferromagnetic (AFM) and optical properties of Ce-doped ZnO are examined. The results show that the Fermi level move up to the conduction band and Ce-doped zinc-blende ZnO exhibits metallic, the band-gap become wider, and their conductivity are significantly improved in comparison to undoped system. All of these materials are direct transition semiconductor and shown metallic property. The conduction band and density of states have an obvious change. The Ce 4f orbital move into the conduction band, thus the bottom of conduction bands move to the low energy and show magnetism. The magnetic moments mainly arise from the Ce 4f orbitals. The absorption edge shift to the blue orientation and its intensity descend, which suggest the Ce-doped ZnO can be applied in magnetic system and photo-electronic sensor.

EPR detection of sphalerite ZnO in mechanically treated ZnO+0.1C nanosystem

The EPR spectrum of Mn2+ ions observed in nano-powders of wurtzite ZnO phase (ZnOWt) with 0.1wt% of carbon nanoparticles subjected to mechanical processing (MP) for tMP>90min where different than the well-known EPR spectrum of Mn2+ in ZnOWt. Such spectrum was observed earlier and it was attributed to either a new phase or a highly disordered nanocrystalline ZnOWt. Spin–Hamiltonian (S–H) parameters and line width (ΔB) have been determined by computer simulation of observed EPR spectrum of Mn2+: g=2.0010±0.0004, |A|=(73.6 ±0.3)·10−4cm−1, |D|=(102 ±30)·10−4cm−1, ΔB≈0.6mT. The comparison of S–H parameters of the EPR spectra of Mn2+ ions in a new formed phase and in ZnOWt indicates that the parameter A of the hyperfine structure in a new phase is slightly smaller and that the D parameter is more than two times lower than in ZnOWt. The content of the newly formed phase (~1% to 2%) is significantly higher than the content of external impurity states in the initial ZnO sample. The observed EPR spectrum is attributed to the Mn2+ ions in the zinc blende (sphalerite) ZnO phase (ZnOZB), created on the surface of ZnOwt nanoparticles during mechanical processing.

Catalytic potential of highly defective (211) surfaces of zinc blende ZnO.

Zinc blende (ZB) ZnO has gained increasing research interest due to its favorable properties and its stabilization on the nanoscale. While surface properties are important on the nanoscale, the studies on ZB ZnO surface properties are rare. Here we have performed first principles calculations of the energies and structures of ZB and wurtzite (WZ) ZnO surfaces. Our results indicate that, among the four surfaces parallel to the polar axes, such as (101̄0) and (112̄0) of the WZ phase and (110) and (211) of the ZB phase, the polar (211) surface has substantially lower surface vacancy formation energies than the others, which makes ZB ZnO promising for catalytic applications. Our results also imply that the stabilization of ZB ZnO on the nanoscale is due to some mechanisms other than surface energies.

Nanometric structures of highly oriented zinc blende ZnO thin films

Zinc oxide thin films in cubic zinc blende (ZB) crystalline phase on glass substrates by means of the spray pyrolysis technique were deposited. X-ray diffraction spectra revealed that the ZB–ZnO films grow highly oriented along the (004) crystalline direction with no epitaxial influence. Optical absorbance measurements indicated that the forbidden energy band gap is 3.18±0.02eV in accordance with reports on the experimental value of the band gap of ZB–ZnO structures. Atomic Force Microscopy images exhibit nanometric structures of the surface with the approximated aspect of circular nanodiscs. The thickness of the thin films is 350±20nm, which suggests a good stability of the films.

Band alignment of semiconductors from density-functional theory and many-body perturbation theory

The band lineup, or alignment, of semiconductors is investigated via first-principles calculations based on density functional theory (DFT) and many-body perturbation theory (MBPT). Twenty-one semiconductors including C, Si, and Ge in the diamond structure, BN, AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe, CdS, CdSe, and CdTe in the zinc-blende structure, and GaN and ZnO in the wurtzite structure are considered in view of their fundamental and technological importance. Band alignments are determined using the valence and conduction band offsets from heterointerface calculations, the ionization potential (IP) and electron affinity (EA) from surface calculations, and the valence band maximum and conduction band minimum relative to the branch point energy, or charge neutrality level, from bulk calculations. The performance of various approximations to DFT and MBPT, namely the Perdew-Burke-Ernzerhof (PBE) semilocal functional, the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional, and the $GW$ approximation with and without vertex corrections in the screened Coulomb interaction, is assessed using the $GW{\ensuremath{\Gamma}}^{1}$ approximation as a reference, where first-order vertex corrections are included in the self-energy. The experimental IPs, EAs, and band offsets are well reproduced by $GW{\ensuremath{\Gamma}}^{1}$ for most of the semiconductor surfaces and heterointerfaces considered in this study. The PBE and HSE functionals show sizable errors in the IPs and EAs, in particular for group II-VI semiconductors with wide band gaps, but are much better in the prediction of relative band positions or band offsets due to error cancellation. The performance of the $GW$ approximation is almost on par with $GW{\ensuremath{\Gamma}}^{1}$ as far as relative band positions are concerned. The band alignments based on average interfacial band offsets for all pairs of 17 semiconductors and branch point energies agree with explicitly calculated interfacial band offsets with small mean absolute errors of both $\ensuremath{\sim}0.1\text{eV}$, indicating a good overall transitivity of the band offsets. The alignment based on IPs from selected nonpolar surfaces performs comparably well in the prediction of band offsets at most of the considered interfaces. The maximum errors are, however, as large as 0.3, 0.4, and 0.7 eV for the alignments based on the average band offsets, branch point energies, and IPs, respectively. This margin of error should be taken into account when performing materials screening using these alignments.

Stable zinc-blende ZnO thin films: formation and physical properties

The development of technologically important material zinc-blende ZnO has been hindered due to the difficulties inherent in obtaining a stable zinc-blende phase. In this paper, we fabricate the stable zinc-blende ZnO on Pt/Ti/SiO2/Si substrate through phase transformation from the originally wurtzite to the zinc-blende phase. X-ray diffraction data in combination with high-resolution TEM measurements provide the direct evidence on the formation of the well-defined zinc-blende structure with predominated (202) orientation. According to the experimental results and first principles calculations, the incorporation of titanium dopants into ZnO system favors the formation of the zinc-blende structure. The platinum (Pt) surface stabilizes the ZnO zinc-blende structure at the interface (thin film) due to its low ZnO/Pt interface energy, preventing the decomposition in ZnO wurtzite and Zn2TiO4. Additionally, magnetic and optical properties of the ZnO zinc-blende thin films are investigated. Unexpectedly, the film is found to exhibit magnetization of ~75 emu/cm3, while its ZnO wurtzite counterpart is non-ferromagnetic.

First-principles investigations of Mn doped zinc-blende ZnO based magnetic semiconductors: Materials for spintronic applications

ZnO based magnetic semiconductors are intensively investigated because of showing strong potential as base materials for spintronic devices. In this study, full potential linearized augmented plane-wave plus local orbitals FP-L(APW+lo) scheme of computation is used to explore the structural, electronic and magnetic properties of Manganese-doped ZnO based magnetic semiconductors in zinc-blende (ZB) phase. For comprehensive understanding of Mn-doping effect on ZnO, several compositions of Mn:ZnO for 12.5%, 25%, 37.5%, 50%, 62.5%, 75% and 87.5% of Mn concentration are investigated. Our obtained results show a successful induction of the magnetic moment (MM) by Mn-doping into the ZnO matrix, without any geometrical deformation. However a marginal increase in the value of lattice constants is found up to 25% concentration of Mn for this system and for above compositions, it tends to decrease revealing the formation of secondary phases. It is also found that Mn:ZnO system favors ferromagnetic coupling for 12.5% and 25% of Mn contents that has been switched to anti-ferromagnetic coupling for higher Mn contents. The spin polarized electronic structure of Mn:ZnO system was calculated within the generalized gradient approximation (GGA). In addition, the Hubbard parameter was also employed to improve the electronic band structure calculations. The calculations performed at GGA+U level related to electronic band structures show zero energy gap for majority spin carriers, whereas a considerable energy gap is noted for minority spin carriers. This distinguished response of Mn:ZnO system to majority and minority spin carriers, in terms of resistivity and conductivity, highlights its importance for diverse applications as based material in spintronic devices like spin dependent transports, currents and other spin based electronic applications.