Magnetic properties of Zn1−xCoxO bulks prepared by hot pressing

Zn_1−xCo_xO-diluted magnetic semiconductor bulks have been prepared by hot pressing. Mixed powders of pure ZnO and CoO were compacted under pressure of 10 MPa at the temperature of 1073 K. Then, the samples were annealed in vacuum at the temperature range from 673 K to 873 K for 10 h. The crystal structure and magnetic properties of Zn_1−xCo_xO bulks have been investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). X-ray photoelectron spectroscopy (XPS) and was used to study chemical valence of zinc and cobalt in the samples. The results showed that Zn_1−xCo_xO samples had c-axis-oriented wurtzite symmetry neither cobalt nor cobalt oxide phase was found in the samples if x was less than 0.15. Zn and Co were existed in Zn_0.9Fe_0.1O sample in Zn²⁺ and Co²⁺ states. The results of VSM experiment proved the room temperature ferromagnetic properties (RTFP) of Co-doped ZnO samples. The saturation magnetization and the coercivity of Zn_0.9Co_0.1O sample, observed in the M–H curve, were about 0.22 emu/g and 300 Oe, respectively.     

Regulate the content of magnesium in MgxZn1−xO films by vacuum anneal

Mg_xZn_1−xO thin films were grown on c-sapphire substrates by metal-organic chemical vapor deposition (MOCVD), followed by annealing in vacuum at different temperatures for 1 h. The UV emission peak was blue shifted in the photoluminescence (PL) spectra and a dramatic shift of (0 0 2) diffraction peak to higher angle was observed in X-ray diffraction (XRD) pattern with increasing anneal temperature. This suggested the band gap and the lattice parameter of Mg_xZn_1−xO had been affected by annealing in vacuum. Furthermore, the structure of the film became sparser due to annealing in vacuum. From the X-ray photoelectron spectroscopy (XPS) and ICP of the Mg_xZn_1−xO film, we can find that the anneal temperature have an effect on the content of each element in Mg_xZn_1−xO quantitatively. In addition, the value of x in Mg_xZn_1−xO varied slightly as the annealing temperature increased. The above phenomena indicated that annealing in vacuum could slightly adjust the percentage of Mg indirectly in Mg_xZn_1−xO film and offer a good idea in Mg_xZn_1−xO devices facture.     

Effect of crystallization quality on ferromagnetism in Zn1 − xCoxO nanopowders

In this paper, a series of Zn_1 − xCo_xO nanocrystals with different cobalt percentages were fabricated by a simple chemical method, which were intensively explored for spintronics applications. X-ray diffraction (XRD), ultraviolet-visible (UV-Vis) spectrophotometer, transmission electron microscope (TEM) and vibrating sample magnetometer (VSM) were used to characterize the structures and magnetic properties of prepared samples. It was concluded that Co²⁺ was well inserted into ZnO wurtzite structure. The ferromagnetism of Zn_1 − xCo_xO nanopowders was observed at room temperature. The relation between crystallization quality and magnetism of Zn_1 − xCo_xO nanopowders was discussed in detail. It was demonstrated the crystallization quality of Zn_1 − xCo_xO nanocrystals had a strong effect on the ferromagnetism.     

Preparation of PrxZn1 − xO nanopowder with UV-visible light response

We prepared Pr_xZn_1 − xO nanopowder using a combustion method. The sample was characterized by XRD, TEM, XPS, UV-visible and PL spectroscopy. The prepared Pr_xZn_1 − xO nanopowder had a good photon absorption performance in the range of 200-800 nm wavelength. Moreover, the 4f² electronic configuration of trivalent Pr³⁺ ions was revealed from the diffuse reflectance spectra. The single crystalline particle size was about 20-70 nm based on the TEM observation. A quantum size effect of the Pr_xZn_1 − xO nanopowder was also noted.     

The influence of ambient conditions on properties of MgxZn1−xO films by sputtering

The Mg_xZn_1−xO films were prepared in different Ar-O₂ mixture ambience by magnetron sputtering. According to the X-ray diffraction (XRD) patterns and the energy dispersive X-ray spectroscopy (EDS) results, it was found that the Mg contents in the films varied with the different ratios of O₂/O₂+Ar, and the crystal quality of the films improved with the increasing of Mg contents. Meanwhile, the ultraviolet and visible (UV-vis) absorption spectroscopy indicated that the band gap of the films also increased. Moreover, it could be seen that the photoluminescence (PL) spectrum was different from that of undoped Zinc oxide (ZnO) films or the results in other reports on the Mg_xZn_1−xO films: there was no blueshift effect happening for the near-band-edge (NBE) emission in Mg_xZn_1−xO films with different Mg contents.     

ZnO and Zn1−xCdxO nanocrystallites obtained by oxidation of precursor Langmuir-Blodgett multilayers

ZnO and Zn_1−xCd_xO nanocrystallites were prepared by oxidation of zinc arachidate-arachidic acid and zinc arachidate-cadmium arachidate-arachidic acid LB multilayers, respectively. The metal content of the multilayers was controlled by manipulation of subphase composition and pH. Precursor multilayers were oxidized in the temperature range of 400 °C-700 °C. The formation of ZnO and Zn_1−xCd_xO was confirmed by UV-Visible spectroscopy. Uniformly distributed, isolated and nearly mono-dispersed nanocrystallites of ZnO (11 ± 3 nm) and Zn_1−xCd_xO (18 ± 6 nm) were obtained.     

Characterization of Zn1 − xMgxO transparent conducting thin films fabricated by multi-cathode RF-magnetron sputtering

Transparent conducting thin films of Al-doped and Ga-doped Zn_1 − xMg_xO with arbitrary Mg content x were deposited on glass substrates by simultaneous RF-magnetron sputtering of doped ZnO and MgO targets, and their fundamental properties were characterized. MgO phase separation in Zn_1 − xMg_xO films was not detected by X-ray diffraction. The Zn_1 − xMg_xO films show high optical transparency in the visible region. Although the carrier density of the Zn_1 − xMg_xO films decreased with increasing x, the Zn_1 − xMg_xO films showed good electrical conductivity; electrical resistivity as low as 8 × 10^− 4 Ω ·cm was achieved for the Zn_0.9Mg_0.1O:Ga thin film.     

Synthesis of Zn1 − xCdxO bramble-like nanostructures

Ternary Zn_1 − xCd_xO bramble-like nanostructures with a Cd incorporation of about 6.7 at.% were produced onto Au-catalyzed Si substrate by thermal evaporation of Zn and Cd. The X-ray diffraction (XRD) analysis showed that the existence of lattice expansion in the c-axis orientation. The ultra-violet (UV) near-band-edge (NBE) emission of the Zn_1 − xCd_xO nanobrambles was red-shifted from 369 nm (3.37 eV) to 397 nm (3.13 eV) due to Cd substitution. The oxygen partial pressure was deemed as the critical experimental parameter for the formation of the bramble-like Zn_1 − xCd_xO nanostructures.     

Structural, electrical and optical properties of transparent Zn1 − xMgxO nanocomposite thin films

Zn_1 − xMg_xO thin films of various Mg compositions were deposited on quartz substrates using inexpensive ultrasonic spray pyrolysis technique. The influence of varying Mg composition and substrate temperature on structural, electrical and optical properties of Zn_1 − xMg_xO films were systematically investigated. The structural transition from hexagonal to cubic phase has been observed for Mg content greater than 70 mol%. AFM images of the Zn_1 − xMg_xO films (x = 0.3) deposited at optimized substrate temperature clearly reveals the formation of nanorods of hexagonal Zn_1 − xMg_xO. The variation of the cation-anion bond length to Mg content shows that the lattice constant of the hexagonal Zn_1 − xMg_xO decreases with corresponding increase in Mg content, which result in structure gradually deviating from wurtzite structure. The tuning of the band gap was obtained from 3.58 to 6.16 eV with corresponding increase in Mg content. The photoluminescence results also revealed the shift in ultraviolet peak position towards the higher energy side.     

Effects of ambient oxygen pressures and substrate temperatures in pulsed laser deposited Zn0.85Li0.15O thin films

Li doped zinc oxide Zn_1−xLi_xO (x = 0.15) thin films were grown by using the pulsed laser deposition method. The depositions were done onto Pt(111)/Ti/SiO₂/Si(100) substrate set at temperatures ranging from 300 °C to 700 °C, with varying the ambient O₂ pressure range of 3-20 mTorr. The effects of substrate temperatures and ambient O₂ pressures on the surface morphology and structural properties of the Zn_0.85Li_0.15O thin films were investigated by using the scanning probe microscopy and X-ray diffraction spectra, respectively. Also the chemical structures of the films were investigated by observing the X-ray photoelectron spectra of the core and shallower levels. We observed the deep blue PL emissions centered at about 390 nm (3.20 eV) from the Zn_0.85Li_0.15O thin films. It was investigated with respect to the ambient O₂ pressures during the deposition. It is considered that the deep blue PL emission in the Zn_0.85Li_0.15O thin film may be related to the incorporation of oxygen vacancies.     

Variation in structural,optical and magnetic properties of Zn1−xCrxO (x = 0.0, 0.10, 0.15, and 0.20) nanoparticles: Role of dopant concentration on non-saturation of magnetization

Cr-doped ZnO, i.e. Zn_1−xCr_xO (x = 0.00, 0.05, 0.10, 0.15 and 0.20) nanoparticles were synthesized by sol–gel route. The structural and morphological properties of these nanoparticles were investigated by high resolution transmission electron microscope (HRTEM). The average particle size of Zn_1−xCr_xO nanoparticles decreases from 75 to 40 nm with the increase in x from 0.00 to 0.20. The rings observed in selected area diffraction pattern revealed that up to x = 0.10 these nanoparticles have single phase ZnO. However, a secondary spinel phase of ZnCr₂O₄ was observed for higher Cr doping (x ≥ 0.15). The optical band gap calculated using UV–visible absorption was decreased from 3.27 to 2.27 eV with the increase in Cr-doping from 0.00 to 0.20 in ZnO nanoparticles. The undoped ZnO (Zn_1−xCr_xO; x = 0.00) nanoparticles did not show any hysteresis loop at room temperature, however, clear loops were obtained for x = 0.05–0.20. Additionally, magnetization (M) vs. applied magnetic field (H) loops for lower Cr-concentration (x = 0.05) saturate at 5 kOe, and while those with higher Cr concentration (x > 0.05) do not show saturation even at 10 kOe. This may be attributed to increase in the defects at higher Cr-doping into ZnO. The value of saturation magnetization was found to decrease from 4.24 emu g⁻¹ to 1.96 emu g⁻¹ with the increase in Cr doping from x = 0.05 to 0.20 in ZnO and may be due to the secondary ZnCr₂O₄ phase.     

The microwave-assisted synthesis and characterization of Zn1 − xCoxO nanopowders

In this paper, we present a simple microwave-assisted synthesis of Zn_1 − xCo_xO nanopowders. With the advantages of the microwave-assisted method, we have successfully synthesized good crystalline quality and good surface morphology Zn_1 − xCo_xO nanopowders. The nanopowders are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-VIS absorption, and micro-Raman spectroscopy. We found, in the synthesis process, the surfactant Triethanolamine (TEA) plays an important role on the morphology of Zn_1 − xCo_xO nanoparticles. The XRD study shows that for Co doping up to 5%, Co²⁺ ions are successfully incorporated into the ZnO host matrix. The absorption spectra of Zn_1 − xCo_xO (x = 1-5%) nanopowders show several peaks at 660, 611 and 565 nm, indicating the presence of Co²⁺ ions in the tetrahedral sites. The Raman study shows that the linewidth of E₂^low mode increases with Co concentration, which further indicates the incorporation of Co²⁺ ions into the ZnO host matrix.     

The properties of transparent semiconductor Zn1 − xTixO thin films prepared by the sol-gel method

Transparent semiconductor thin films of Zn_1 − xTi_xO (0 ≦ x ≦ 0.12) were deposited on alkali-free glass substrates by the sol-gel method. The effects of Ti addition on the crystallization, microstructure, optical properties and resistivity of ZnO thin films were investigated. The as-coated films were preheated at 300 °C, and then annealed at 500 °C in air ambiance. X-ray diffraction results showed all polycrystalline Zn_1 − xTi_xO thin films with preferred orientation along the (002) plane. Ti incorporated within the ZnO thin films not only decreased surface roughness but also increased optical transmittance and electrical resistivity. In the present study, the Zn_0.88Ti_0.12O film exhibited the best properties, namely an average transmittance of 91.0% (an increase of ~ 12% over the pure ZnO film) and an RMS roughness value of 1.04 nm.     

Structural and optical properties of rock-salt Cd1 − xZnxO thin films prepared by thermal decomposition of electrodeposited Cd1 − xZnxO2

Cd_1 − xZn_xO nanocrystalline thin films with rock-salt structure were obtained through thermal decomposition of Cd_1 − xZn_xO₂ (x = 0, 0.37, 0.57, 1) thin films which were electrodeposited from aqueous solution at room temperature. X-ray diffraction results showed that the Zn ions were incorporated into rock salt-structure of CdO and the crystal lattice parameters decreased with the increase of Zn contents. The bandgaps of the Cd_1 − xZn_xO thin films were obtained from optical transmission and were 2.40, 2.51, 2.63 and 3.25 eV, respectively.     

High-frequency magneto-electrical properties of Zn1 − x − yAlxCoyO thin films

The Al doping effects on high-frequency magneto-electric properties of Zn_{1 − x − y}Al_xCo_yO (x = 0-10.65 at.%) thin films were systematically studied. In the current work, the Zn_{1 − x − y}Al_xCo_yO thin films were deposited by magnetron co-sputtering onto quartz substrates. The magneto-impedance spectra of the thin films were measured by an impedance analyzer. Among all the doped films studied, the thin film with 6.03 at.% Al-doping showed the highest ac conductivity and relaxation frequency. To characterize the relaxation mechanism underlying the magneto-electric properties, a Cole-Cole impedance model was applied to analyze the impedance spectra. The analyzed result showed that the magneto-impedance of the Zn_{1 − x − y}Al_xCo_yO is contributed by multiple processes of magnetization dynamics and dielectric relaxation. The results imply that Zn_{1 − x − y}Al_xCo_yO may be applicable for high-frequency magneto-electric devices.     

Mixed cation effect in xR2O-(40 − x)Na2O-50B2O3-10Bi2O3 (R = Li, K) glasses

Mass density, glass transition temperature and ionic conductivity are measured in xLi₂O-(40 − x)Na₂O-50B₂O₃-10Bi₂O₃ and xK₂O-(40 − x)Na₂O-50B₂O₃-10Bi₂O₃ glass systems with 0 ≤ x ≤ 40 mol%. The strength of the mixed alkali effect in T_g, dc electrical conductivity and activation energy has been determined in each glass system. The magnitudes of the mixed alkali effect in T_g for the mixed Li/Na glass system are much smaller than those in the mixed K/Na glasses. The impact of mixed alkali effect on dc electrical conductivity in mixed Li/Na glass system is more pronounced than in the K/Na glass system. The results are explained based on dynamic structure model.     

Synthesis and electrical properties of ordered perovskite oxide Cd3−x−yCuxAyTeO6 (A = Li, Na; 0.00 ≤ x, y ≤ 0.15)

Polycrystalline Cd_3−x−yCu_xA_yTeO₆ (A = Li, Na) samples were prepared by solid-state reaction, and their crystal structure and electrical properties were investigated. In Cd_3−xCu_xTeO₆ and Cd_3−yA_yTeO₆ (A = Li, Na), the maxim solubility of x and y was 0.15 and 0.15 for A = Li, 0.05 for A = Na, respectively. For co-substituted samples Cd_2.9−yCu_0.1Li_yTeO₆ and Cd_2.9−yCu_0.1Na_yTeO₆, the maxim solubility of x was the same as single substitution above-mentioned. The alkali-metal substituted samples Cd_3−yA_yTeO₆ (A = Li, Na) showed a negative Seebeck coefficient, which indicates that the major conduction carriers are electron. On the other hand, the co-substituted samples Cd_2.9−yCu_0.1A_yTeO₆ (A = Li, Na) represented a positive Seebeck coefficient, and major conduction carriers were hole through substitution by copper ions.     

Influence of SnO2 addition on the thermoelectric properties of Zn1 − xSnxO (0.01 ≤ x ≤ 0.05)

The grain size and the density of the Zn_1 − xSn_xO (0 ≤ x ≤ 0.05) samples decreased with increasing SnO₂ content. The addition of a small amount of SnO₂ (x ≤ 0.01) to ZnO led to an increase in both the electrical conductivity and the absolute value of the Seebeck coefficient, resulting in a significant increase in the power factor. The thermoelectric power factor was maximized to a value of 1.25 × 10⁻³ Wm⁻¹ K⁻² at 1073 K for the Zn_0.99Sn_0.01O sample.     

Structural properties and morphology of Zn(1 − x)CdxO solid solution grown on ZnO and C-plane sapphire substrate

Zn_(1 − x)Cd_xO solid solutions with a composition ranging from pure ZnO up to x = 0.062 have been grown on ZnO and c-plane sapphire substrates by using metal organic chemical vapor deposition. The optical transmission spectra were used to estimate the cadmium mole fraction of the solid solutions. The lattice deformation and morphology of these films were examined in detail using high resolution X-ray diffraction and atomic force microscopy as Cd incorporation and used substrate. Our study reveals significant lattice deformation from x ≥ 0.7%. The atomic force microscopy images show facetted grains for films grown on ZnO substrate but rather round for c-plane sapphire substrate. The grain shape is controlled by the presence of the ionic charges on the polar surface of ZnO which is disturbed by cadmium incorporation and also the employed substrate material.