C-axis Preferred Orientation Research Articles

Film thickness effect in c-axis oxygen vacancy-passivated ZnO prepared via atomic layer deposition by using H2O2

The presence of oxygen vacancies in zinc oxide is a long-standing problem preventing the fabrication of p-type ZnO materials; however, the use of H2O2 as the oxygen source for preparing ZnO films via atomic layer deposition can significantly suppress their formation. Thus, this paper presents the investigation of the film thickness effect on the properties of oxygen vacancy-passivated ZnO prepared using H2O2. Increasing the ZnO film thickness increased the crystallinity along the c-axis preferred growth orientation, the grain size, and the surface roughness but also reduced the c-axis tensile strain, oxygen vacancies, optical bandgap, and film transmittance. The oxygen vacancy decrease was due to the reduced grain boundaries and improved crystallinity resulting from the film thickness increase, consequently weakening the resistivity through a large decrease in carrier concentration and a small increase in carrier mobility.

Effect of sputtering power on the microstructure and photelectric properties of Al doped ZnO thin films

Investigation of the doped ZnO films deposited on different substrates plays a significant role in improving the optical properties of optical components. The Si wafer and glass were used as the substrates for comparison.The effect of sputtering power on the surface morphology, microstructure, optical and electrical properties of A1 doped ZnO (AZO for short) films were studied. The results show that the AZO films prepared on different substrates with various power all have a good c-axis preferred orientation; the surface particle size of the films increase gradually with the increasing sputtering power; the resistivity decreases first and increases when the the sputtering power reached 100 W. As for the films sputtered on glass, the result show that the visible light range has a high transmittance ( >80%), the absorption side wavelength is 350-400 nm.

Red luminescence and UV light generation of europium doped zinc oxide thin films for optoelectronic applications

In the present work, the Europium doped Zinc Oxide (ZnO: Eu) thin films were elaborated using spray pyrolysis technique. We are interested in investigating the structural properties, photoluminescence (PL) and third harmonic generation (THG) of the elaborated films. The structural properties of as-prepared thin films were characterized by X-ray diffraction (XRD). It confirms that all deposited thin films of Europium doped Zinc Oxide are crystallized in the hexagonal wurtzite structure. Both undoped and doped europium thin films show strong preferred c-axis orientation. Photoluminescence (PL) emission from Europium doped Zinc Oxide thin films, under excitation by 266 nm, shows characteristic transitions of Europium (5D0 → 7F0, 5D0 → 7F1, 5D0 → 7F2, etc.). It reveals the good incorporation of Eu3+ ions in the ZnO host. Additionally, the 5D0 → 7F2 is the most intense transition usually observed for Eu3+ embedded in materials of Zinc Oxide lattice. The dependence of third-order nonlinear susceptibility on doping rate was evaluated. The highest nonlinear susceptibility χ 3 is obtained for the 5% Europium doped ZnO sample.

Substrate temperature induced physical property variation of InxAl1-xN alloys prepared on Al2O3 by magnetron sputtering

In x Al 1-x N alloys were prepared on Al2O3 substrates using radio frequency magnetron sputtering. The physical properties of In x Al 1-x N alloys sputtered at different substrate temperatures were systematically studied. The results indicated that the sputtered In x Al 1-x N alloys had c-axis preferred orientation and exhibited phase separation under the substrate temperature over 450 °C. The In content was calculated about 0.62 according to the Vegard's law. It was found that the surface morphology of In0.62 Al0.38 N alloys showed a transition from nanodots to nanoclusters and disordered morphology as the substrate temperature was increased from 150 to 450 °C. This research will lay a good foundation for the application of InxAl1-x N-based optoelectronic devices.

Effects of oxygen partial pressure on the structural and electrical properties of Al and Sb co-doped p-type ZnO thin films grown by pulsed laser deposition

ZnO:Al0.01Sb0.02 thin films were grown on the c-plane sapphire via pulsed laser deposition at 500 °C under different oxygen partial pressures (0.13–66.66 Pa) and their structural and electrical properties were investigated. The thin films deposited under low oxygen partial pressures (0.13–7.99 Pa) grew with a c-axis preferred orientation and a 30° rotated one. At higher oxygen partial pressures (13.33–66.66 Pa), in addition to the main c-axis-oriented domains, partial domains with 32°- and 90°-tilted c-axes were observed. The ZnO:Al0.01Sb0.02 thin films deposited at low oxygen partial pressure and high oxygen partial pressure exhibited n-type and p-type conduction, respectively. The X-ray photoelectron spectroscopy analysis exhibited that the thin films contained more Sb5+ than Sb3+; therefore, the p-type conduction was owing to the Sb5+ ions, which formed the SbZn–2VZn complex.

Rapid thermal annealing induced the c-axis (00 l) preferred orientation and the p-type thermoelectric properties of Bi-Sb-Te thin films

Bi-Sb-Te thin films on SiO2/Si-wafer substrate were prepared by a magnetron co-sputtering process using Bi2Te3 (fixed: 50W) and Sb2Te3 (varied: 10, 15, 20 and 50W) targets. All as-deposited thin films were annealed by rapid thermal annealing (RTA) at 250°C under a vacuum state with a step of heating and holding each for 1 min. The effect of the RTA process onto thin film samples studied concerning the crystal structure, morphology, thickness, composition, and electrical and thermoelectric properties. The crystal structure of annealed samples showed the c-axis preferred orientation with the (00 l) plane (l = 15) and revealed a trend of p-type thermoelectricity behavior due to the RTA process. The annealed thin film compositions were BiTe, Bi0.92Sb0.08Te, Bi0.9Sb0.1Te, Bi0.88Sb0.12Te, and Sb2Te3. The Bi0.9Sb0.1Te thin film composition had the maximum power factor of 4.46 mW m–1 K–2 at a temperature of 100 °C.

Preparation of epitaxial La2-xGdxZr2O7 buffer layer for coated conductors using sol-gel method

La2-xGdxZr2O7 (LGZO) films were prepared on Ni-5at.%W rolling-assisted biaxially textured substrate (RABiTS-NiW) using sol-gel method. The lattice parameter of lanthanum zirconate was changed by gadolinium element doping, which reduced the lattice constant of lanthanum zirconate buffer layer to have a better match with the lattice of NiW substrate. In particular, the grain growth texture of the buffer layer film has been analyzed by X-ray diffraction, EBSD, SEM and TEM. The results show that the La1.25Gd0.75Zr2O7 film has the highest c-axis preferred orientation and dense microstructure. EBSD measurement reveals that the excellent grain-growth texture is formed within La1.25Gd0.75Zr2O7 film and the most misorientation angle is around 3°. Moreover, the epitaxial growth relationship of NiW(002)//La1.25Gd0.75Zr2O7(004) as well as NiW(200)//La1.25Gd0.75Zr2O7(440) is demonstrated by atomic resolution TEM observation. By means of suitable element substitution, the La1.25Gd0.75Zr2O7 is a quite promising candidate of single-phase buffer layer between YBa2Cu3O7-x and NiW substrate.

Optimizing the Structural, Electrical and Thermoelectric Properties of Antimony Telluride Thin Films Deposited on Aluminum Nitride-coated Stainless Steel Foil

In this study, we examined the thermoelectric (TE) properties of co-evaporated p-type antimony telluride (Sb2Te3) thin films on aluminum nitride (AlN)-coated stainless steel foil substrates. We investigated the influence of composition and substrate temperature on the thin-film microstructure and transport properties, by varying the tellurium (Te) concentration in the thin films as well as the substrate temperature during deposition (room temperature (RT) and 300 °C). Thin films prepared with an RT substrate were further annealed at 264 °C to obtain crystallized thin films with high phase purity. Columnar thin films with large grains and a standard multi-oriented crystal structure were obtained when thin films were deposited on substrates heated to 300 °C. Thin films deposited at RT and subsequently annealed at 264 °C had a dense, layered microstructure, with a preferential c-axis or (00 l) texture as the compositions approached phase stoichiometry. The temperature dependence of the thermoelectric properties was measured, and variations were interpreted in terms of the deviation from stoichiometry and the obtained microstructure. A maximum power factor (PF) of 0.87 mW/m ∙ K2 was obtained for off-stoichiometric 65.0 at% Te thin film, which was the highest among the samples deposited at high substrate temperatures. A higher PF of 1.0 mW/m ∙ K2 was found for off-stoichiometric thin films with 64.5 at% Te, which was deposited at RT and subsequently annealed. The improvement of thermoelectric power in films containing excess Te could be related to energy dependent carrier scattering at the Sb2Te3/Te interface.

Elektrodepozisyon Yapılan ZnO İnce Filmlerinin Korozyon Davranışı

Electrochemical deposition method (ECD) has been widely used due to its advantages in stoichiometry control, large area growth, easy to form nano-structures, being low coast, possible formation of homogeneous thin films. In this study, nanostructured zinc oxide (ZnO) thin films were deposited on Indium tin oxide (ITO)-coated glass substrate using ECD. The effects of cathodic potential, time, temperature and pH on quality of the films were examined. ZnO thin films were achieved with in cathodic potential with -1.0 V and deposition time with 3600 seconds at temperature 130°C in dimethyl sulfoxide (DMSO). X-ray diffraction (XRD) analysis confirmed clearly that the ZnOthin films have sinle crystalline properties with a strong c-axis (0002) preferential orientation. According to the absorption measurements, the optical bandgap of the ZnOfilm was calculated as Eg 3.4 eV. ZnO thin films electrodeposited on ITO substrate were studied with Electrochemical Impedance Spectroscopy (EIS) and Tafel measurements. Nyquist, open circuit potential and Bode analysis were evaluated to find out the structural changing of ZnOand its corrosion behavior. With the help of these plots, solution resistance (Rs), polarization resistance (Rp), a constant phase element (CPE) and a CPE exponent (n) were calculated as 49.61 Ω, 4.97x106 Ω, 6.75x10-6 Ω-1.s.cm-2, 0.940, respectively. Also, we examined the ZnO thin films corrosion features with the help of tafel measurements. Considering all these measurement, the possible reason of increasing corrosion resistance can be interpreted as surface passivation depending on increasing defects caused by deposition.

A comparative analysis for effects of solvents on optical properties of Mg doped ZnO thin films for optoelectronic applications

Nanocrystalline Magnesium doped ZnO thin films (MgZnO) were synthesized on glass substrate using five different solvents i.e. 1-Propanol (1Pd), 2-Propanol (2Pd), Ethanol (Ed), Methanol (Md) and 2-Methoxyethanol (MEd) by sol-gel spin coating method. This study targeted the best solvent with MgZnO film for optoelectronic applications. The magnesium doping percentage was fixed at 5% for all samples to discover comparatively better doped results among different solvents. All the films synthesized by different solvents exhibited polycrystalline structure, particularly films with 1-Propanol and 2-Methoxyethanol showed preferred c-axis orientation at 180 °C pre-heating condition revealed by XRD pattern. Highest average crystallite size calculated by XRD study was for 2-Methoxyethanol solvent which possessed good crystalline quality. Crystalline quality was also confirmed by Raman analysis. FESEM images elucidated that all the films were crack free, had uniformly smooth grains and highest grain size for 2-Methoxyethanol solvent. EDS and FTIR spectra confirmed the magnesium presence in ZnO thin films for all solvents. The optical absorbance, transmittance and reflectance spectrum were analyzed by UV–vis spectroscopy. The highest transmittance (94 %), band gap value (3.36 eV) and better quality by PL analysis in comparison were found for 2-Methoxyethanol solvent. The data for optical constants were measured by spectroscopic ellipsometry. Furthermore real and imaginary parts of complex dielectric constant and energy loss functions were examined.

Temperature gradient cooling technique: Boosting high power factor of Bi2S3+x thermoelectric material

Bi2S3 thermoelectric (TE) material has received extensive attention due to its earth-abundant and low-cost elements. This study has been successfully synthesized a series of Bi2S3+x bulks with a preferential c-axis orientation using temperature gradient cooling technique that is simple and high-yield, focusing on the effects of soaking temperature (TS) and the amount of excess S on their TE properties. We found that the electrical conductivity of TS = 1103 K sample was greatly enhanced due to the decreased Bi vacancy. Along with the moderated thermal conductivity, the highest ZT value was obtained almost in the whole temperature. Further adding excess S could effectively tailor carrier concentration and significantly enhance Seebeck coefficient, leading to a maximum power factor (PF) of 167 μW m−1 K−2 at 773 K for the Bi2S3.02 composition. TGCT prepared samples have a weak temperature dependence of PF and a high engineering power factor (PFeng). A maximum PFeng value of 50 mW m−1 K−1 was obtained at Thot = 773 K. Consequently, a peak ZT of 0.14 was achieved for Bi2S3.02 sample in despite of the slightly enhanced thermal conductivity, which is 133% higher than that (0.06) of pristine Bi2S3.

Investigation of physical properties of F-and-Ga co-doped ZnO thin films grown by RF magnetron sputtering for perovskite solar cells applications

F-and-Ga co-doped ZnO films were sputter-deposited on glass substrates by RF magnetron sputtering method. The fabricated films were characterized by different techniques. It was found that all the films were polycrystalline with a hexagonal wurtzite structure with a c-axis preferred orientation of growth. The effect of the substrate temperature on the surface morphology, electrical and optical properties of the films was also investigated. The optimal growth temperature was found to be 440 oC which led to the optimal film with the resistivity of 6.81 × 10−4 Ωcm, carrier concentration of 2.61 × 1020 cm−3, mobility of 35.1 cm2/V, over-90% transmittance in the region of 400–1200 nm and a wide optical bandgap of 3.49 eV. This optimal film was employed in as the front contact in perovskite solar cells and resulted in a high power-conversion efficiency of 15.32%. This indicates that such a film can be promisingly useful for high-performance thin-film solar cells.

Physical and biological changes associated with the doping of carbonated hydroxyapatite/polycaprolactone core-shell nanofibers dually, with rubidium and selenite

Electrospun selenium-containing carbonated hydroxyapatite/polycaprolactone (CHAP/PCL) core/shell nanofibers were synthesized at different contents of Rb+ as a dopant in the ceramic phase. Microstructural, morphological and mechanical properties of the nanofibers were analyzed as a function of the stoichiometric content of Rb+ ions defined by the parameter x in [RbxCa(10-0.5x)(PO4)5.8(SeO3)0.2(OH)2]/PCL (0 ≤ x ≤ 0.8). Rb+ ions were incorporated inside the CHAP crystal lattice, where they induced crystal growth in the preferred c-axis direction. They also induced internal disordering, leading to reduced crystallinity. High-resolution TEM imaging demonstrated that the fibers had the form of tubes internally filled with rod-shaped CHAP nanoparticles, whose size increased from 50 to 70 nm on average as the result of doping with Rb+. The nanoparticles without any Rb+, at x = 0, were aligned well with the fiber curvature, but this alignment diminished as the fibers became more oblique at higher contents of Rb+. The attachment of human fibroblasts on the nanofibers was slightly enhanced at higher Rb+ contents. This effect was tied to an increase in the surface roughness of the composite with the amount of Rb+ in the CHAP phase, conforming to the finding that nanoparticles accommodating more of the Rb+ dopant are prone to exhibit more surface defects due to the extension of the lattice distortions to the surface. Attributed to an increase in the amorphous character of CHAP at the higher contents of Rb+ and to the resulting degeneration of the reinforcement effect, most mechanical properties were compromised with the addition of Rb+.

Comparative study for seed layer solvent effects on structural and optical properties of MgZnO thin films deposited by chemical bath deposition technique

C-axis oriented Magnesium doped Zinc Oxide (MgZnO) thin films are promising candidates for variety of applications especially optoelectronic devices. In this work, the effects of seeding solvents on structural and optical properties of MgZnO films were analyzed. The comparison was performed by varying the seed layer solvent i.e. 2-Methoxyethanol, 2-Propanol, Ethanol and Methanol. MgZnO thin films were synthesized on different seed layered glass substrates using Chemical Bath Deposition (CBD) method. The XRD results revealed the hexagonal wurtzite structure for all samples. However, the film with seed layer 2-Methoxyethanol solvent had preferred c-axis orientation and better crystallanity. For 2-Methoxyethanol solvent based seed layer: the morphological study showed wrinkled free, unfractured and highly aligned MgZnO nanorods grown perpendicular to the substrate. Energy dispersive x-ray (EDS) spectroscopy confirmed the presence of magnesium in ZnO film. Highest average transmittance of and band gap value of was recorded through UV–vis spectroscopy. The optical constants (refractive index and extinction coefficient) were determined by reflectance and absorbance data. Furthermore complex dielectric constant and energy loss functions were estimated.

Fabrication of -oriented apatite ceramics using a non-topochemical reactive α-tristrontium phosphate template

ABSTRACTTextured ceramics are generally fabricated by reactive-templated grain growth using a template material with a suitable anisotropy and topochemical relationship to the target ceramics. We have previously synthesized hexagonal plate-like α-tristrontium phosphate (α-Sr3(PO4)2; α-TSP) single crystals with no topochemical relationship to the apatite system. In the present study, we focused on using the facets of α-TSP particles as nucleation sites for textured apatite, and fabricated <001>-oriented strontium fluoroapatite (Sr10(PO4)6F2; SrFAp) through a reaction between aligned α-TSP platelets and SrF2. The SrFAp phase was formed with a preferred c-axis orientation at 900°C. Sintering in an F-containing atmosphere led, moreover, to fabrication of textured SrFAp ceramics with a high ratio of conversion into apatite. In this way, textured polycrystalline ceramics with no topochemical relationship to the template material can be fabricated through reactive-templated grain growth using the facets of the template particles as nucleation sites.

Structural and physical parameters of sol-gel spin coated ZnO thin films: Effect of sol concentration

Zinc oxide thin films are deposited by sol–gel spin coating on glass substrates for varying sol concentrations and the effect is studied on a range of structural and physical parameters which are determined by X-ray diffraction and X-ray peak profile analysis. The diffraction peaks confirms the formation of ZnO with hexagonal wurtzite phase. The film with highest sol concentration shows preferred c-axis orientation. The crystallinity of the films increases with increase in concentration of the sol. The X-ray peak broadening analysis was employed to estimate the physical parameters such as strain, stress and energy density corresponding to major diffraction peaks by the Williamson-Hall (W-H) method with three different models namely uniform deformation model, uniform stress deformation model and uniform deformation energy density model. To the best of our knowledge studies of ZnO thin films deposited with various sol concentrations using these models have not been reported. The deposited ZnO thin films may be used in solar cells to enhance their efficiency.

Effect of additives in precursor solution on ZnO thin-film deposition by sol–gel dip-coating method

ZnO films consisting of nanoparticles were obtained by the sol–gel dip-coating method using citric acid and ethylenediaminetetraacetic acid (EDTA) as additives. The size of the nanoparticles was decreased by using the additives, and continuous ZnO films were formed when citric acid was added to a precursor solution. The crystallinity of the ZnO films depended on the additives and pre-annealing temperature to dry the precursor solution. When the pre-annealing temperature was at 260 °C, ZnO films with preferred c-axis orientation were obtained regardless of the additives. At the pre-annealing temperature of 120 °C, the additives prevented the crystallization of ZnO. The ZnO film pre-annealed at 120 °C was directly patterned by light irradiation from a high-pressure mercury lamp during pre-annealing. EDTA in the precursor solution improved the patterning selectivity.

Anisotropic Epitaxial Behavior in the Amorphous Phase-Mediated Hydroxyapatite Crystallization Process: A New Understanding of Orientation Control.

The precise control of crystallization is a key in the construction and engineering of crystalline materials, especially in biomineralization. Although it is generally accepted that biomineral crystals have evolved from their amorphous precursors, there are intense debates about crystallographic orientation control. By using in situ high-resolution transmission electron microscopy, we herein reveal that hydroxyapatite (HAP) is produced through its epitaxial growth from amorphous calcium phosphate with a preferential c-axis orientation. Abnormally but interestingly, this anisotropic epitaxial crystallization priority along the c-axis is not affected by the existing HAP crystalline substrate, which is exactly the same on either {002} or {100} facets. Molecular dynamics simulations suggest this preference is correlated with the interfacial energetic controls at the amorphous-crystalline transition frontier. The orientation control of biominerals here shows the key role of the interface energy, rather that the organic molecules or matrices, which provides a complementary understanding of the general c-axis orientation control of HAP in various biomineralization cases and aids in the development of an alternative strategy for crystallization control of functional materials.

Effect of substrate temperature on F and Al co-doped ZnO films deposited by radio frequency magnetron sputtering

In this study, F and Al co-doped ZnO (FAZO) films were fabricated by radio frequency (RF) magnetron sputtering technique using an AlF3-doped ZnO ceramic target. The effect of substrate temperature (Ts) on the structural, morphological, elemental, chemical states, electrical and optical properties of the FAZO films were systematically studied by X-ray diffraction, scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectrometry, and ultraviolet–visible–near infrared spectrophotometry. The results show that the doping F and Al did not change the structure of the ZnO, and all films show a typical wurtzite structure with c-axis preferred orientation. As the Ts value increases, the surface morphology of the film changed from “pyramid” shape to “crater” shape and to smooth and dense. The doping effect of F and Al gradually appeared with the increase in Ts. The FAZO film exhibited good performance with mobility of 29.92 cm2/Vs, carrier concentration of 2.84 × 1020 cm−3, resistivity of 7.35 × 10−4 Ω cm, and average transmittance of nearly 90% in the optical spectral range of 400–1400 nm at Ts = 440 °C. When the FAZO films were used as front electrode material for perovskite thin film solar cells, a higher conversion efficiency was obtained compared with that of the AZO film used as reference.

Alcoholic Solvent Influence on ZnO Synthesis: A Joint Experimental and Theoretical Study

Zinc oxide nanoparticles were prepared by a solvothermal synthesis using various alcoholic reaction solvents including ethanol, 1-propanol, 1-butanol, 1-pentanol, and 1-octanol, at 170 °C. The nucleation and growth processes of the ZnO nanoparticles were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) characterization, and they were corroborated by means of quantum chemical calculations at the density functional theory level (DFT). On the basis of the results of joint microstructural and theoretical study, the nucleation and preferential growth mechanism of ZnO nanoparticles is proposed. The effect of various alcoholic solvent on the overall shape and growth rate along the preferential c-axis of ZnO nanoparticles were corroborated by means of theoretical simulations of interface-solvent interaction by using nanoclusters (ZnO)n (n = 12 and 36). The (ZnO)36–CH3(CH2)nOH (n ≤ 7) interaction has been found to be spontaneous exergonic process only in the presence of 1-butanol as reaction medium with ΔG*INT = −4.95 kcal mol–1, whereas endergonic in the presence of all remaining alcohols used (ΔG*INT > 0). The results of X-ray diffraction size-strain analysis reveal that solely the use of 1-butanol as solvent leads to rather isotropic crystallite shape (Dv⊥c-ax ∼12 nm, Dv∥c-ax ∼12 nm), whereas in the presence of all remaining alcohols used ZnO nanoparticles grew prevailing in the c-direction to form nanorods. The alcohols of different size and polarity acts as a solvent and reactant as well as controlling agents for crystal growth, providing different binding interactions involved in both the nucleation processes and preferential growth of ZnO nanoparticles. The calculated values of EO···H and EZn–O of (ZnO)36–CH3(CH2)7OH (1-octanol) interaction indicate a weaker interaction of the nonpolar 1-octanol and polar a little positively charged Zn surface of ZnO crystal as well as a higher preferential growth rate along the c-axis in comparison to polar alcoholic media.