Zn-O Bond Length Research Articles

Efficient photocatalytic degradation of diclofenac drug using the Zn1-x-yPrxAlyO photocatalyst under UV light irradiation.

Herein, we report the efficient photocatalytic degradation of the diclofenac drug using the Zn1-x-yPrxAlyO photocatalyst [x, y] = (0.00, 0.00), (0.03, 0.01), (0.03,0.03) under UV light irradiation. The analysis of the structure reveals that the Pr3+ and Al3+ cations insertion into the ZnO lattice leads to a decrease in the lattice constant (a and c), Zn-O bond length, strain lattice, and crystallite size. These alterations are linked to the high degree of atomic disorder triggered by the dopants, which produce stress and strain in the ZnO structure. The Raman measurements confirmed the structural phase and showed changes in the position and intensity of the E2High mode, associated with oxygen vibrations and material crystallinity. The presence of the dopants reduces the concentration of VZn and VO++ type defects while increasing the levels of VO, VO+, and Oi defects, as observed from the fitting of the Photoluminescence spectra. Furthermore, it was noted that de Pr3+ and Al3+ cations insertion into ZnO increases the optical band gap, which is associated with the Moss-Burstein effect. The micrograph images show that dopants transform the morphology from quasi-spherical particles to irregular cluster structures. The textural analysis indicated that an increase in the concentration of Al3+ in the ZnO lattice led to a higher surface area, likely enhancing photocatalytic activity. The sample containing 3% Pr3+ and 3% Al3+ showed the highest photocatalytic activity and degraded up to 71.42% of diclofenac. In addition, experiments with scavengers revealed that hydroxyl radicals are the main species involved in the drug's photodegradation mechanism. Finally, the Zn1-x-yPrxAlyO compound is highly recyclable and stable.

Enhanced Photocatalytic and Photoluminescence Properties Resulting from Type-I Band Alignment in the Zn2GeO4/g-C3N4 Nanocomposites

Well-defined Zn2GeO4/g-C3N4 nanocomposites with a band alignment of type-I were prepared by the ultrasound-assisted solvent method, starting from g-C3N4 nanosheets and incorporating 0, 10, 20, and 40 wt% of Zn2GeO4. In this study, we have investigated in-depth the photoluminescence emission and photocatalytic activity of these nanocomposites. Our experimental results showed that an increased mass ratio of Zn2GeO4 to g-C3N4 can significantly improve their photoluminescence and photocatalytic responses. Additionally, we have noted that the broadband photoluminescence (PL) emission for these nanocomposites reveals three electronic transitions; the first two well-defined transitions (at ca. 450 nm and 488 nm) can be attributed to π*→ lone pair (LP) and π*→π transitions of g-C3N4, while the single shoulder at ca. 532 nm is due to the oxygen vacancy (Vo) as well as the hybridization of 4s and 4p orbital states in the Zn and Ge belonging to Zn2GeO4. These experimental findings are also supported by theoretical calculations performed under periodic conditions based on the density functional theory (DFT) fragment. The theoretical findings for these nanocomposites suggest a possible strain-induced increase in the Zn-O bond length, as well as a shortening of the Ge-O bond of both tetrahedral [ZnO4] and [GeO4] clusters, respectively. Thus, this disordered structure promotes local polarization and a charge gradient in the Zn2GeO4/g-C3N4 interface that enable an efficient separation and transfer of the photoexcited charges. Finally, theoretical results show a good correlation with our experimental data.

Structural, FTIR spectra and optical properties of pure and co-doped Zn1-x-y Fe x M y O ceramics with (M = Cu, Ni) for plastic deformation and optoelectronic applications.

We report here a considered novel study on the structural, FTIR spectra and optical properties of pure and co-doped Zn0.90-xFe0.1MxO with ((M = Cu, Ni and (x = 0.00, 0.10) and (0.00 < y < 0.20)) at different sintering temperatures Ts (Ts = 850 °C for series I and 1000 °C series II). Although the ZnO wurtzite structure is conformed for all samples, some secondary lines with little intensity are formed. But the number of these lines is higher for series I than for series II. The (c/a) value and U-parameter are almost constant for all samples, while Zn–O bond length L is slightly increased. The porosity and crystallite size are decreased by Fe, and also for (Fe + Cu) samples, and their values for series I are lower than for series II. The residual stress is tensile for most samples. Interestingly, the Young’s, rigid and bulk modulus, Poisson’s ratio and Debye temperature, obtained from FTIR analysis, are increased by Fe addition with a further increase for Fe + Ni) samples for both series. A ductile nature is obtained for pure, Fe and (Fe + Cu) samples; whereas a brittle nature is approved for (Fe + Ni) samples. On the other hand, the energy gap (Eg), residual lattice dielectric constant (εL) and carrier density N are increased by Fe addition, followed by a further increase for (Fe + Cu) samples, while the vice is versa for the inter-atomic distance R. For example, Eg was increased from 3.153 eV for pure ZnO to 3.974 eV for (Fe + Cu) samples (i.e., 0.821 eV more), while it was decreased to 2.851 eV for (Fe + Ni) samples (i.e., 0.302 eV less). A direct behavior is obtained between Eg and both elastic modulus (Y, β), lattice and micro strains (εL, εm), dislocation density (δ), residual stress (σ) and carrier density N, whereas a reverse behavior is obtained between Eg and both crystallite size (D), porosity (PS) and inter-atomic distance (R). These results are explained in terms of the generated blocked states of the conduction band as indicated by the Burstein Moss effect. These novel findings reveal that the co-doping has intense ZnO and moderate metal oxide modes in the ZnO matrix structure, which makes ZnO co-doped with (Fe + Cu) more suitable for gas sensors and optoelectronic devices. In contrast, ZnO co-doped with (Fe + Ni) samples is strongly recommended for altering plastic deformation. To our knowledge, the present investigation can be considered the first study and probably has never been discussed elsewhere, which highlights the present investigation.

Zinc isotope fractionation between Cr-spinel and olivine and its implications for chromite crystallization during magma differentiation

We report the first zinc isotope data (expressed as δ66Zn relative to the JMC-Lyon standard) for chromian spinels (Cr-spinels) and coexisting olivines in oceanic peridotites. All spinel-olivine pairs fall on the 1:1 fractionation line in the diagram of δ66Znspinel versus δ66Znolivine, suggesting equilibrium isotope fractionation. Cr-spinels are always isotopically lighter than coexisting olivines (Δ66Znspinel-olivine = δ66Znspinel − δ66Znolivine = −0.50‰ to −0.33‰; n = 13), which is opposite to the positive Zn isotope fractionation between Al-spinel and olivine observed in cratonic peridotites. The “inverse” Zn isotope fractionation between Cr-spinel and olivine is unlikely to have been caused by low-temperature alteration of the oceanic peridotites, given the lack of correlation between Δ66Znspinel-olivine values and chemical indices of serpentinization and weathering (e.g., LOIs, MgO/SiO2). Ionic model calculation indicates that even considering that Zn occurs at both tetrahedral and octahedral sites in the crystal lattice of spinel, the magnitude of equilibrium fractionation is still inconsistent with the observed Zn isotope fractionation between Cr-spinel and olivine. We suggest a “chemical effect” in which the ZnO bond length (tetrahedral site) in spinel increases when Cr substitutes Al in octahedral site, which is corroborated by the striking negative correlation of δ66Zn with Cr# [molar Cr3+/(Cr3+ + Al)] in natural spinels. Therefore, Zn isotopic compositions of natural spinels can be highly variable depending on their chemical compositions.During magma differentiation, zinc is moderately incompatible in silicate minerals (olivine and pyroxene) but highly compatible in Cr-spinels/chromites that have Zn contents tens of times higher than those of basaltic melts. Given its light Zn isotopic composition, chromite crystallization–if any–can evidently elevate δ66Zn and lower Zn contents of the residual melts. Lunar mare basalts are typically characterized by higher δ66Zn and lower Zn contents relative to terrestrial basalts, but modelling suggests that chromite crystallization during magmatic differentiation is unlikely to account for Zn isotopic and elemental data of lunar mare basalts. Global ocean island basalts (OIBs) and some intraplate alkali basalts have systematically higher δ66Zn and higher Zn contents than those of the normal mantle-derived melts (e.g., mid-ocean ridge basalts; MORBs), which contradicts with a chromite crystallization model. Instead, such signatures can reflect recycling of surface carbonates into the Earth’s deep mantle, reinforcing the application of zinc isotopes as a tracer of deep carbonate recycling.

Design and development of novel piezoelectric nanogenerator based on pH dependent ZnO nanostructures

Piezoelectric nanogenerator (PENG) devices based on zinc oxide (ZnO) nanostructures of different pH (5, 9 and 12) encapsulated in polydimethylsiloxane (PDMS) have been fabricated and their morphology effect on the output performance has been analyzed. Electrical characterizations have been performed on the devices to examine their robustness, power generation ability, stability and durability. FTIR analysis has revealed the increase in Zn-O bond length with the increase in pH signifying the tensile strain built up within the crystallites. Hence, the PENG fabricated with pH 12 nanostructures has generated an open circuit voltage of ~34 V and a short circuit current of 6.9 nA. No significant change is observed in the output for 3 consecutive weeks. It is believed that the PENG developed by simple and cost-effective methods as reported can be utilized in low power consumption devices.

Band gap engineering, quantum confinement, defect mediated broadband visible photoluminescence and associated quantum States of size tuned zinc oxide nanostructures

A simple wet chemical method has been used to synthesize ZnO nanostructures. The ZnO nanocrystals exhibit hexagonal unit cell structure as revealed from the XRD pattern. The intensity difference of various diffraction peaks indicates that the growth of the ZnO nanostructure is anisotropic. Various lattice parameters, dislocation density, strain, particle size, and Zn-O bond length were also calculated. The band gap of the synthesized ZnO nanostructures was determined from the UV–vis absorption spectra using Tauc equation and the band gap of the synthesized ZnO varies from 3.34 eV to 3.57 eV by varying the growth duration. Crystallite sizes also decreased with increased growth duration. This variation of size leads to the change in band gap of the nanostructures. Thus, it is possible to tune the band gap of the nanostructures by varying the growth duration. The synthesized ZnO nanostructures exhibit visible photoluminescence due to deep level transitions. A simple weak quantum confinement model has been used to designate the observed photoluminescence emission peak associated with such transitions.

Structural and electrical properties of zno varistor with different particle size for initial oxides materials

&#x0D; &#x0D; &#x0D; We report here structural, electrical and dielectric properties of ZnO varistors prepared with two different particle sizes for initial starting oxides materials (5 µm and 200 nm). It is found that the particle size of ZnO does not influence the hexagonal wurtzite structure of ZnO, while the lattice parameters, crystalline diameter, grain size and Zn-O bond length are affected. The nonlinear coefficient, breakdown field and barrier height are decreased from 18.6, 1580 V/cm and 1.153 eV for ZnO micro to 410 V/cm, 7.26 and 0.692 eV for ZnO nano. While, residual voltage and electrical conductivity of upturn region are increased from 2.08 and 2.38x10-5 (Ω.cm)-1 to 4.55 and 3.03x10-5 (Ω.cm)-1. The electrical conductivity increases by increasing temperature for both varistors, and it is higher for ZnO nano than that of ZnO micro. The character of electrical conductivity against temperature is divided into three different regions over the temperature intervals as follows; (300 K ≤ T ≤ 420 K), (420 K ≤ T ≤ 580 K) and (580 K ≤ T ≤ 620 K), respectively. The activation energy is increased in the first region from 0.141 eV for ZnO micro to 0.183 eV for ZnO nano and it is kept nearly constant in the other two regions. On the other hand, the average conductivity deduced through dielectric measurements is increased from 2.54x10-7 (Ω.cm)-1 for ZnO micro to 49x10-7 (Ω.cm)-1. Similar behavior is obtained for the conductivities of grains and grain boundaries. The dielectric constant decreases as the frequency increases for both varistors, and it is higher for ZnO nano than that of ZnO micro. These results are discussed in terms of free excited energy and strength of link between grains of these varistors.&#x0D; &#x0D; &#x0D;

On the correlation between electrical, optical and magnetic properties of Zn1−xPrxO nanoparticles

We report here the structure, electrical, optical and magnetic properties of Zn1−xPrxO nanoparticles with various x values (0.00 ≤ x ≤ 0.50). X-ray diffraction pattern revealed wurtzite structure for all samples with an additional unknown peak formed at 2Ɵ = 28° for Pr = 0.00, 0.05, 0.10 samples. The cell parameters and dislocation density are increased with increasing Pr up to 0.30, followed by a decrease at Pr = 0.50. While a little bit decrease in the average grain size and an increase in the ZnO bond length are obtained. The nonlinear coefficient β, breakdown field EB and barrier voltage Vab are gradually shifted to lower values as Pr increases. They are decreased from 31.3, 2333 V cm−1 and 0.005 V for ZnO to 8.9, 750 V cm−1 and 0.001 V for 0.50 of Pr. The electrical conductivity versus temperature shows two conduction mechanisms and it is generally increased by increasing Pr and temperature. The conduction mechanisms are obtained at a temperatures width of (300–540 K) and (540–620 K), respectively. The activation energy Ea is decreased from 0.42 eV to 0.13 eV by 0.50 of Pr in the first region, while it is increased from 0.42 eV to 0.93 eV in the second region. The optical band gap Eg and exaction photon energy Eex are decreased by increasing Pr up to 0.50. They are decreased from 3.1 eV and 3.4 eV for ZnO to 1.62 eV and 2.79 eV by 0.50 of Pr, while Urbach energy Eu increased from 0.32 eV to 1.13 eV. Magnetization curves revealed room temperature ferromagnetism (RTFM) as Pr increases. The coercivity of the field Hc, saturated and remnant magnetization, magnetic moment are also increased by Pr up to 0.50. Our results are discussed in terms of oxygen vacancies, the density of states and local spin-polarized electrons exhibited by Pr as a dopant to ZnO.

Zinc Isotope Fractionation during Sorption onto Al Oxides: Atomic Level Understanding from EXAFS

Interactions between aqueous Zn and mineral surfaces can lead to notable Zn isotope fractionation that affects Zn source fingerprinting, which needs an atomic-level understanding. In this study, we demonstrate that Zn isotope fractionation (Δ66Znsorbed-aqueous) during Zn sorption onto γ-Al2O3 depends on both pH and Zn concentration and ultimately correlates to surface coverage (Γ). At pH values of 6.0-6.5 and/or Zn concentrations of 0.1-0.2 mM, where Γ < 0.8 μmol m-2, Δ66Znsorbed-solution is 0.47 ± 0.03‰, whereas Δ66Znsorbed-aqueous decreases to 0.02 ± 0.07‰ at pH values of 7.0-8.0 and Zn concentrations of 0.4-0.8 mM, with a high Γ ranging from 1.5 to 3.2 μmol m-2. Using extended X-ray absorption fine structure (EXAFS) spectroscopy, we elucidated that a Zn-Al layered double hydroxide (LDH) with a Zn-O bond length of 2.06 Å forms at high surface coverage (1.5 < Γ < 3.2 μmol m-2). In contrast, at low surface coverage (Γ < 0.8 μmol m-2), the sorbed Zn occurs as a tetrahedrally coordinated inner-sphere surface complex with an average Zn-O interatomic distance of 1.98 Å. Such contrasts lead to an atomic level understanding of the strong links between isotope fractionation, local bonding structures (i.e., coordination and bond distances), and solution chemistry, which is crucial for more effective applications of stable metal isotopes as environmental tracers.

Photoluminescence Study of Deep Level Defects in ZnO Thin Films

In the present work, zinc oxide (ZnO) thin films were prepared by heating, at 500 ∘C, metallic Zn films deposited onto Si (100) substrates by RF magnetron sputtering. According to the x-rays diffraction patterns, the polycrystalline hexagonal ZnO phase (wurtzite) was obtained with a preferential orientation along the (101) planes. The increase of both the crystallites size and the Zn-O bond length, as a function of the heating time, reflect the improvement of the crystalline quality of the investigated films. The investigated films emitted in ultraviolet, visible and infrared regions. The ultraviolet emission was linked to the crystalline quality of the films. All the visible emission related defects were identified. Their concentrations vary differently as a function of the heating time. The infrared emission originated from the oxygen anti-sites (OZn). The correlation between the decrease of the electrical resistivity and the increase of both 2 + charged oxygen vacancies ( $V_{O}^{++})$ and hydrogen impurities (H-I) defects suggested that the unintentional n-type conductivity in ZnO came from the collective contribution of $V_{O}^{++}$ and H-I defects.

Sonochemically synthesized ZnO nanosheets and nanorods: Annealing temperature effects on the structure, and optical properties

ZnO nanopowders were successfully synthesized by the ice-bath assisted sonochemical method. The nanopowders were annealed in air for 3h at different annealing temperatures (Ta) ranging from 300 to 700°C. The effect of Ta on the structural and morphological properties was investigated by the x-ray diffraction (XRD) and the transmission electron microscopy (TEM). The optical properties were studied by recording the optical absorption and photoluminescence (PL) spectra. The XRD analysis showed that the thermal annealing leads to an improvement in the crystallinity associated with an increase in the crystallite size as well as an increase in both the Zn-O bond length and unit cell volume. Also, it was found that the increase of Ta results in a shift in the diffraction angle toward lower values associated with a decrease in the micro-strain. The morphological study confirms that the samples are mixtures of nanosheets and nanorods. In addition, the length and diameter of the nanorods increase as the annealing temperature increases. The optical absorption spectra show that the exciton peak of the as-prepared sample is red shifted from 370 to 378nm by thermal annealing, and the optical band gap decreases from 3.45 to 3.36eV. The photoluminescence spectra were reordered at an excitation wavelength of 325nm, and the deconvolution of the spectra reveals four emission bands where the main UV band (at λ=397nm) can be attributed to exciton recombination related to near-band-edge. Furthermore, the thermal annealing results in a reduction of the PL intensity of the annealed samples.

Seed-layer-free hydrothermal growth of zinc oxide nanorods on porous silicon

Zinc oxide (ZnO) nanorods were grown on porous silicon (PS) using hydrothermal synthesis without a metal catalyst or a seed layer. Scanning electron microscopy, x-ray diffraction, and temperature-dependent photoluminescence (PL) were carried out to investigate the structural and optical properties of the ZnO-PS sample. Most of the nanorods had an average diameter about of 120 nm and an average length of 5 µm, and were assembled into flower-like clusters where several nanorods were joined at a central point. In some cases, ZnO nanorods were merged in parallel bundles. The ZnO nanorods exhibited an overall compressive residual stress. The Zn-O bond length was 1.953 A. ZnO-PS exhibited one PL peak in the ultraviolet (UV) range, and two peaks in the visible range. The UV and green emission peak were generated from the ZnO nanorods, while the red emission peak was attributed to the PS. The fitting parameters for Varshni’s empirical equation were α = 8 × 10−4 eV/K, β = 186 K, and Eg(0) = 3.375 eV, and the thermal activation energy was about 32 meV.

Structural and vibrational properties of ZnO nanoparticles synthesized by the chemical precipitation method

In this article we study the structural and vibrational properties of ZnO nanoparticles. The details of process and mechanism responsible for the synthesis of nanoparticles by a high yield yet facile chemical precipitation method are explained. The prepared nanomaterial was subjected to various characterizations. Elemental composition of ~30nm average size nanoparticles was evident through transmission electron microscope (TEM) and energy dispersive X-ray spectroscopy (EDS). Identification of hexagonal wurtzite phase and determination of lattice parameters, crystallite size, strain, crystallinity index, ZnO bond length, Young's modulus, specific surface area, and dislocation density of prepared ZnO nanocrystallites were revealed through extensive X-ray diffraction (XRD) analysis. Vibrational properties of prepared nanoparticles are determined through micro-Raman (μR) and Fourier transform infrared (FTIR) spectroscopies. The FTIR and micro-Raman investigations of Infrared and Raman active vibrational modes of ZnO nanoparticles are not only mutually supportive but more significantly, the vibrational properties thus determined are highly correlated with the structural properties determined through TEM, EDS and XRD investigations.

Gas-Phase Synthesis and Structure of Monomeric ZnOH: A Model Species for Metalloenzymes and Catalytic Surfaces

Monomeric ZnOH has been studied for the first time using millimeter and microwave gas-phase spectroscopy. ZnOH is important in surface processes and at the active site of the enzyme carbonic anhydrase. In the millimeter-wave direct-absorption experiments, ZnOH was synthesized by reacting zinc vapor, produced in a Broida-type oven, with water. In the Fourier-transform microwave measurements, ZnOH was produced in a supersonic jet expansion of CH(3)OH and zinc vapor, created by laser ablation. Multiple rotational transitions of six ZnOH isotopologues in their X(2)A' ground states were measured over the frequency range of 22-482 GHz, and splittings due to fine and hyperfine structure were resolved. An asymmetric top pattern was observed in the spectra, showing that ZnOH is bent, indicative of covalent bonding. From these data, spectroscopic constants and an accurate structure were determined. The Zn-O bond length was found to be similar to that in carbonic anhydrase and other model enzyme systems.

Zn-O tetrahedral bond length variations in normal spinel oxides

Six synthetic single crystals of spinel phases with different compositions along the ZnAl 2 O 4 -ZnCr 2 O 4 solid solution were structurally and chemically characterized by X-ray diffraction and electron microprobe techniques. As predicted, unit-cell parameters and octahedral bond lengths (M-O) increase with increasing replacement of Al 3+ by Cr 3+ . Despite the constant occupancy of the T site by Zn, also the tetrahedral bond length T Zn-O shows significant variations along this binary. These variations are positively correlated with variations in M-O bond lengths. The present data in conjunction with data from literature provide a basis for quantitative analyses of the variation in T Zn-O in normal spinel structures. A negative correlation between T Zn-O and the ionic potential at M ( M IP ) suggests that increasing M IP is related to a stronger electrostatic cation-cation repulsion across the shared octahedral edge M (O-O) shared of the structure. An observed negative correlation between M IP and M (O-O) shared suggests that a decrease of M (O-O) shared provides a more efficient shielding effect to reduce the octahedral cation interactions. In normal Zn B 2 O 4 spinels (where B = Al 3+ , Cr 3+ , Ga 3+ , V 3+ , Fe 3+ , and Mn 3+ ) cations with a smaller size provides a higher charge density. Increasing charge density at the M site causes shortening of M (O-O) shared , which in turn results in shorter T Zn-O bond length. In general, variations in T Zn-O are required by the structure to better provide an oxygen shielding effect to the octahedral cation-cation repulsion.

Structural and optical analysis of ZnBeMgO powder and thin films

We here report the structural and optical studies of Zn 1− x− y Be x Mg y O (0 ≤ x ≤ 0.15; 0 ≤ y ≤ 0.20) powders and thin films. From the Rietveld refinement of the powder X-ray diffraction (XRD) patterns it was revealed that the value of ‘ a’ lattice parameter remains almost unchanged whereas ‘ c’ parameter reduces with Be and Mg co-doping in ZnO. The Zn-O bond length also decreases in co-doped samples. Raman studies of the pure ZnO powder showed all the characteristic peaks of the wurtzite hexagonal structure and with (Be, Mg) co-doping new modes appeared which can be attributed to arise as a result of substitution. The XRD of the films prepared from the powders using pulsed laser deposition (PLD) technique exhibited the preferential orientation and with increase in co-doping the (0 0 0 2) peak also shifts to higher 2 θ values suggesting the incorporation of Be/Mg at the Zn-site. From the UV–visible optical transmittance measurement it was noticed that the band gap of the pristine ZnO film is 3.3 eV which enhanced up to 4.51 eV for Zn 0.7Be 0.1Mg 0.2O film which lies in the solar blind region and is very useful in the realization of deep UV detectors.

Ligand induced ferromagnetism in ZnO nanostructures

Complementary to the experimental finding that ZnO nanoparticles become ferromagnetic when coated with N and S containing ligands such as dodecylamine and dodecanethiol [Garcia et al., Nano Lett. 7, 1489 (2007)], we provide the first theoretical understanding of the origin of magnetism in ligated ZnO nanoparticles as well as the structural properties of the ligated systems by using density functional theory and generalized gradient approximation for exchange and correlation, and a cluster model for the nanoparticles. We show that N or S atoms of the ligand bind to the Zn sites. The accompanying changes in the Zn-O bond length, hybridization between Zn 4s orbitals with N 2p or S 3p orbitals, and consequently the redistribution of charges between Zn and O atoms result in a magnetic system where the 2p electrons in O and N, and 3p electrons in S sites are spin polarized. Furthermore, the sites nearest to the Zn atom attached to the ligand carry bulk of the magnetic moment. Studies, as a function of cluster size, also illustrate that magnetism resides only on the surface. Our results confirm that the use of ligands can pave a new way for introducing magnetism in ZnO nanostructures, which can be used to develop magnetic sensors to detect N and S containing molecules.

Investigating the interaction mechanism between zinc and Saccharomyces cerevisiae using combined SEM-EDX and XAFS

The interaction mechanism between zinc and the intact yeast cells of Saccharomyces cerevisiae was investigated by using the scanning electron microscopy with energy-dispersive X-ray analysis, as well as X-ray absorption fine structure spectroscopy (XAFS). Displacement of H+, K+, Mg2+, and Na+ during zinc uptake confirmed the existence of both covalent interactions and ionic interactions between Zn2+ and the microbe. Ion exchange mechanism played a role in zinc uptake. The local environment of Zn accumulated in the intact yeast cells was determined by XAFS, which suggests that the nearest neighboring atom of the bound zinc ion on the biomass is oxygen atom. The adsorbed zinc ion on the intact cells of S. cerevisiae is a tetrahedron structure, with the Zn-O bond length of 1.97 A, and the coordination number is only 3.2 of Zn-O structure in the first shell.

Observation of Depolarized ZnO(0001) Monolayers: Formation of Unreconstructed Planar Sheets

A novel nonpolar structure of 2 monolayer (ML) thick ZnO(0001) films grown on Ag(111) has been revealed, using surface x-ray diffraction and scanning tunneling microscopy. Zn and O atoms are arranged in planar sheets like in the hexagonal boron-nitride prototype structure. The observed depolarization is accompanied by a significant lateral 1.6% expansion of the lattice parameter and a 3% reduced Zn-O bond length within the sheets. The nonpolar structure stabilizes an atomically flat surface morphology unseen for ZnO surfaces thus far. The transition to the bulk wurtzite structure occurs in the 3-4 ML coverage range, connected to considerable roughening.

Infrared Lattice Vibrations of Nitrogen-doped ZnO Thin Films

AbstractNitrogen (N) is the most promising p-type dopant for zinc oxide (ZnO), and its bonding state must be governed by the substitution of N atoms into anion sites. We have synthesized un-doped ZnO and N-doped ZnO thin films by utilizing a pulsed laser deposition (PLD) method. The N-doped ZnO thin film possessed shorter c-axis length than the un-doped ZnO thin film. This fact seems to be owing to that Zn-N bond length is shorter than Zn-O bond length in wurtzite structure. Besides, from the result of Fourier transform infrared (FT-IR) measurement, the absorption peak of the N-doped ZnO thin film emerged at 406 cm−1, and was attributed to transverse optical (TO) phonon of E1 mode. The infrared lattice vibrations of the N-doped ZnO thin films can be induced by the complex factors consisting of not only the decreases in reduced mass and interionic distance, but also the increase in covalency.