Structure and optical properties of AlxZn1−xO alloys by sol-gel technique

Al_xZn_1−xO (x = 0-0.5) thin films were prepared on quartz glass substrates by sol-gel technique. X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) were employed for microstructure characterization of these thin films. In films with up to 20 at.% Al incorporation, compound nano-crystal phase was observed while wurtzite structure disappeared. Zn3d electron binding energy and Zn LMM‘s chemical shift were both increased by more than 0.4 eV. Transmittance spectra revealed that these films possessed high transmittance in the visible region, and the end of UV absorption edge shifted to less than 300 nm when Al content exceeds 20 at.% due to quantum confinement effect.     

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.     

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.     

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.     

Mg-composition induced effects on the physical behavior of sprayed Zn1−xMgxO films

Thin films of Zn_1 − xMg_xO, with Mg compositions in the range, 0 < x < 0.4, have been deposited onto soda-lime glass substrates using chemical spray pyrolysis. The effects of altering the alloy composition on the chemical and physical properties of the layers were investigated using X-ray photoelectron spectroscopy, atomic force microscopy, Raman, optical and electrical measurements. The data shows systematic shifts in the properties of the layers with Mg-content. In particular, the optical absorption data showed that the influence of Mg-content on the energy gap of Zn_1 − xMg_xO films is significant. Layers with x = 0.24 had an optical energy band gap, E_g = 3.87 eV. The best layers produced had properties appropriate for application as Cd-free buffer layers in copper indium gallium selenide (CIGS) solar cells.     

Structural, optical, and magnetic properties of Fe-doped ZnO films prepared by spray pyrolysis method

Zn_1−xFe_xO thin films with different Fe content were deposited on glass substrates at 450 °C by spray pyrolysis technique. The effect of doping on the structural and optical properties of ZnO films was investigated. X-ray diffraction has shown that the films are polycrystalline and textured with the c-axis of the wurtzite structure along the growth direction. Scanning electron microscopy has shown that the surface of the films are homogeneous. The magnetic measurements performed at 5 K using a SQUID magnetometer showed the co-existence of paramagnetic, antiferromagnetic and ferromagnetic contributions.     

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.     

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.     

Characterization and ozone-induced coloration of ZnxNi1 − xO thin films prepared by sol-gel method

Zn_xNi_1 − xO thin films were prepared by sol-gel spin coating method onto glass substrates in combination with annealing process. Effect of zinc content on the structural, optical and ozone-induced coloration properties of as-prepared films was investigated by X-ray diffraction, field emission-scanning electron microscope, atomic force microscopy and UV-VIS spectrophotometer, respectively. X-ray diffraction results reveal that the structures of all films are still cubic NiO structure. Average grain size of Zn_xNi_1 − xO film increases with increasing annealing temperature and its crystallization is strongly affected by Zn content. Coloration of the films was obtained after UV/ozone exposure due to a presence of ozone-induced hydroxyl groups. Significant enhancement of coloration efficiency of the films is achieved as content of Zn increases.     

MgxZn1−xO (x = 0-1) films fabricated by sol-gel spin coating

Mg_xZn_1−xO films were deposited onto the glass substrate by a sol-gel spin coating method. The drying and annealing temperatures were 300 and 500 °C in air. As x varies from 0 to 1, it was observed that the crystal structure is changed from wurtzite ZnO to cubic MgO. The morphology characterizations of these films were observed by scanning electron microscope. The randomly oriented hexagonal nanorods were gown on the glass surface when x = 0 and 0.25, which became disappeared with increasing Mg contents. The optical properties of these films were investigated by room-temperature photoluminescence (PL) and UV-vis absorption spectra, which show that the optical band gap and photoluminescence in the visible and UV regions can be ideally tuned by varying the Mg contents in the Mg_xZn_1−xO alloy films.     

Structural characterization and optical properties of Cd(1−x)MnxSe thin films

Stoichiometric bulk ingot materials of the ternary mixture Cd_(1−x)Mn_xSe (0.05 ≤ x ≤ 0.9) were prepared by direct fusion of the constituent elements in vacuum sealed silica tubes. X-ray diffraction studies indicate that the investigated samples exhibited a hexagonal structure. The lattice parameters varied linearly with Mn content, following Vegard's law. Thin films were deposited by thermal evaporation from the pre-synthesized ingot material, onto glass substrates. X-ray and electron diffraction studies on the as-deposited and annealed films revealed an amorphous-to-crystalline phase transition at T_a ≈ 423 K. EDAX studies on the prepared films show that the as-deposited films are nearly stoichiometric. The transmittance and reflectance of the deposited Cd_(1−x)Mn_xSe films were measured at normal light incident in the wavelength spectral range 500-2500 nm. Analysis of the transmittance spectra in the entire wavelength range allowed the determination of the refractive index. The dispersion parameters have been calculated, from which the static refractive index as well as static dielecric constant were calculated. Analysis of the absorption coefficient of the investigated films revealed the existence of both the allowed direct and forbidden direct optical transition mechanisms. The corresponding energies were estimated.     

Optical properties of CdxZn(1−x)O films deposited by ultrasonic spray pyrolysis method

Cd_xZn_(1−x)O (x = 0, 0.59, 0.78 and 1) films have been produced by ultrasonic spray pyrolysis technique using aqueous solutions of CdCl₂ H₂O and ZnCl₂ on the microscope glass substrate between 325 and 400 °C. The Cd_xZn_(1−x)O samples have been crystallized both cubic and hexagonal structures. The optical properties of the samples were characterized by transmittance and absorption spectroscopy measurements. Transmissions of the samples have decreased with increasing x values. The optical band gap energies of the Cd_xZn_(1−x)O samples from the absorption spectra have been calculated between 2.48 and 3.23 eV by different Zn contents. The samples were annealed at 350 and 450 °C. The optical band gap energy has decreased at 350 °C whereas it increased at 450 °C.     

Ethanol-thermal synthesis of Cd1−xZnxS nanoparticles with enhanced photodegradation of 4-chlorophenol

Cd_1−xZn_xS nanoparticles were prepared by a one-pot solvothermal process from Zn(CH₃COO)₂, Cd(CH₃COO)₂ and NaS₂CNEt₂·3H₂O (sodium diethyldithiocarbamate, DDTC). The Cd_1−xZn_xS nanoparticles were characterized by X-ray powder diffraction, transmission electron microscope and high-resolution transmission electron microscope equipped with an energy-dispersive X-ray spectrometer. The absorption spectra of the Cd_1−xZn_xS nanoparticles can be tuned into visible region by modulating stoichiometric ratio between Zn and Cd. With the increase of Zn content, the Cd_1−xZn_xS nanoparticles showed an enhanced photocatalytic activity on degradation of 4-chlorophenol. The Cd_1−xZn_xS prepared under the optimal experimental condition (initial Zn/Cd = 3:1, 210 °C, 24 h, in ethanol) possessed the best photocatalytic activity. The conversion ratio could reach up to 84% after 12 h under irradiation of visible light for Cd_1−xZn_xS prepared in ethanol, which was obviously superior to those of products prepared in water. These results showed that both crystallinity and synthetic medium were responsible for the enhanced photocatalytic activity for 4-chlorophenol.     

Microstructure and optical properties of MgxZn1−xO thin films grown by means of pulsed laser deposition

The single-phase epitaxial Mg_xZn_1−xO (0.4 < x < 0.9) alloy films with wide band gap have been deposited on cubic LaAlO₃ (LAO) (100) substrates by pulsed laser deposition (PLD). X-ray diffraction measurement and TEM photograph indicate that the cubic phase could be stabilized up to Zn content about 0.6 without any phase separation. Films and substrates have a good heteroepitaxial relationship of (100) _MgxZn1−xO||(100)_LAO (out-of-plane) and (011)_MgxZn1−xO||(010)_LAO (in-plane)_. The lattice parameters a of Mg_xZn_1−xO films increase almost linearly with increasing ZnO composition, while the band gap energy of the materials increases from 5.17 to 5.27 eV by alloying with more MgO. The cross-section morphology reveals layer thickness of about 250-300 nm and AFM scan over a 30 μm × 30 μm area reveals a surface roughness R_a of about 100 nm.     

Structural and magnetic properties of transition metal doped ZnO films

Structural and magnetic properties have been studied for polycrystalline Zn_1 − xTM_xO films where transition metal (TM) = Fe, Cr. The Zn_1 − xTM_xO films were prepared by the radio frequency magnetron sputtering technique on Al₂O₃ (001) substrates. The microstructures of the films are characterized by X-ray diffraction and X-ray photoelectron spectroscopy. TM in the films exists mainly in the form of TM²⁺, and the TM²⁺ ions have substituted for the Zn²⁺ ions bonded in TM-O in the ZnO lattice and do not change the wurtzite structure of ZnO. The result of magnetic measurement shows that the Zn_1 − xTM_xO films are ferromagnetic at 5 K and 300 K respectively. Subsequently, we discuss the origin of the ferromagnetism in the films.     

Pulsed-laser deposition of heteroepitaxial corundum-type ZITO: cor-In2 − 2xZnxSnxO3

Thin films of corundum-type In_2 − 2xZn_xSn_xO₃ (cor-ZITO) were grown on lattice-matched substrates using pulsed laser deposition. The (001) of the corundum-type film grew heteroepitaxial to the (001) of a LiNbO₃ substrate with large grains along the in-plane and out-of-plane orientation characterized by glancing incidence X-ray diffraction and four-circle Φ-scans. A film with 34% In (metals basis) exhibited a wide optical gap of 3.9 eV and a modest conductivity of 134 S/cm, which suggests cor-ZITO is a potential low-cost transparent conducting oxide.     

Structure and optical properties of Zr1−xSixN thin films on sapphire

A series of zirconium silicon nitride (Zr_1−xSi_xN) thin films were grown on r-plane sapphire substrates using reactive RF magnetron co-sputtering of Zr and Si targets in a N₂/Ar plasma. X-ray diffraction pole figure analysis, X-ray reflectivity, X-ray photoelectron spectroscopy (XPS), optical microscopy, and optical absorption spectroscopy were used to characterize the film stoichiometries and structures after growth at 200 °C and post-deposition annealing up to 1000 °C in ultra-high vacuum. The atomically clean r-plane sapphire substrates induce high quality (100) heteroepitaxy of ZrN films rather than the (111) orientation observed on steel and silicon substrates, but the addition of Si yields amorphous films at the 200 °C growth temperature. After the annealing treatment, films with Si content x < 0.15 have compressive stress and crystallize into a polycrystalline structure with (100) fiber texture. For x > 0.15, the films are amorphous and remain so even after ultra-high vacuum annealing at 1000 °C. XPS spectra indicate that the bonding changes from covalent to more ionic in character as Si―N bonds form instead of Zr―N bonds. X-ray reflectivity, atomic force microscopy (AFM) and optical microscopy data reveal that after post-deposition annealing the 100 nm thick films have an average roughness < 2 nm, except for Si content near x = 0.15 corresponding to where the film becomes amorphous rather than being polycrystalline. At this stoichiometry, evidence was found for regions of film delamination and hillock formation, which is presumably driven by strain at the interface between the film and sapphire substrate. UV-visible absorption spectra also were found to depend on the film stoichiometry. For the amorphous Si-rich films (x > 0.15), the optical band gap increases with Si content, whereas for Zr-rich films (x < 0.15), there is no band gap and the films are highly conductive.     

Effect of dopant concentration on the structural, electrical and optical properties of Mn-doped ZnO films

The Mn-doped ZnO (Zn_1 − xMn_xO) thin films with manganese compositions in the range of 0-8 at.% were deposited by radio-frequency (RF) magnetron sputtering on quartz glass substrates at room temperature (RT). The influence of Mn concentration on the structural, electrical and optical properties of Zn_1 − xMn_xO films has been investigated. X-ray diffraction (XRD) measurements reveal that all the films are single phase and have wurtzite structure with (002) c-axis orientation. The chemical states of Mn have been identified as the divalent state of Mn²⁺ ions in ZnO lattice. As the content of Mn increases, the c-lattice constant and the optical band gap of the films increase while the crystalline quality deteriorates gradually. Hall-effect measurements reveal that all the films are n-type and the conductivity of the films has a severe degradation with Mn content. It is also found that the intensity of RT photoluminescence spectra (PL) is suppressed and saturates with Mn doping.     

Enhanced ferromagnetic properties of multiferroic BiCoxFe1 − xO3 synthesized by hydrothermal method

The BiCo_xFe_1 − xO₃ samples have been successfully synthesized by hydrothermal process. The resulting products were characterized by X-ray powder diffraction (XRD), energy dispersive X-ray (EDS), differential thermal analysis (DTA), and physical property measurement system (PPMS).It was found that the magnetization of the obtained products was greatly enhanced by Co substituting for Fe ions. Furthermore, the value of magnetism of BiCo_xFe_1 − xO₃ samples can be adjusted by Fe doping concentration. DTA curve indicates the ferroelectric properties of the obtained BCFO samples are not affected by Co substitution. Therefore, it would be interesting to realize thin films with similar compositions and study their properties in the interest of device applications.     

Synthesis and characterization of Ni1−xZnxFe2O4 spinel ferrites from tailored layered double hydroxide precursors

In this paper, a series of pure Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrites have been synthesized successfully using a novel route through calcination of tailored hydrotalcite-like layered double hydroxide molecular precursors of the type [(Ni + Zn)_{1 − x − y}Fe_y²⁺Fe_x³⁺(OH)₂]^x+(SO₄²⁻)_x/2·mH₂O at 900 °C for 2 h, in which the molar ratio of (Ni²⁺ + Zn²⁺)/(Fe²⁺ + Fe³⁺) was adjusted to the same value as that in single spinel ferrite itself. The physico-chemical characteristics of the LDHs and their resulting calcined products were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy. The results indicate that calcination of the as-synthesized LDH precursor affords a pure single Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrite phase. Moreover, formation of pure ferrites starting from LDHs precursors requires a much lower temperature and shorter time, leading to a lower chance of side-reactions occurring, because all metal cations on the brucite-like layers of LDHs can be uniformly distributed at an atomic level.