Optical and dielectric properties of CuAl2O4 films synthesized by solid-phase epitaxy

The synthesis and properties of CuAl₂O₄ thin films have been examined. The CuAl₂O₄ films were deposited via reactive direct current magnetron sputter using a CuAl₂ target. As-deposited films were amorphous. Post-deposition annealing at high temperature in oxygen yielded solid-phase epitaxy on MgO. The film orientation was cube-on-cube epitaxy on (001) MgO single-crystal substrates. The films were transparent to visible light. The band gap of crystalline CuAl₂O₄ was determined to be ∼ 4 eV using a Tauc plot from the optical transmission spectrum. The dielectric constant of the amorphous films was determined to be ∼ 20-23 at 1-100 kHz.     

Highly efficient organic light-emitting diodes fabricated utilizing nickel-oxide buffer layers between the anodes and the hole transport layers

The electrical and the optical properties of organic light-emitting diodes (OLEDs) fabricated utilizing nickel-oxide (NiO) buffer layers between the anodes and the hole transport layers were investigated. The NiO layer was formed by using a thermally evaporated nickel thin film and a subsequent oxidation process. The tunneling holes in the OLED were increased due to the existence of the NiO layer between the anode and the hole transport layer, resulting in enhanced efficiency for the OLED. These results indicate that OLEDs with NiO buffer layers hold promise for potential applications in highly-efficient flat-panel displays.     

Ni-doped vertically aligned zinc oxide nanorods prepared by hybrid wet chemical route

Ni-doped zinc oxide (Ni:ZnO) nanorods were synthesized by incorporating nickel in vertically aligned ZnO nanorods. Ni was evaporated onto ZnO nanorods and the composite structure was subjected to rapid thermal annealing for dispersing Ni in ZnO nanorods. The optical band gap decreased with increasing amount of Ni incorporation. The origin of the photoluminescence peak at ∼ 400 nm was related to the defect levels introduced due to substitution of Ni²⁺ in the Zn²⁺ site with annealing. The Raman spectra indicated the presence of the characteristic peak at ∼ 436 cm^− 1 which was identified as high frequency branch of E₂ mode of ZnO. The Fourier Transformed Infrared spectra indicated the existence of the distinct characteristic absorption peak at 481 cm^− 1 for ZnO stretching modes. Current-voltage characteristics indicated that the current changed linearly with voltage for both the doped and undoped samples.     

Vertically aligned Mn-doped zinc oxide nanorods by hybrid wet chemical route

Mn-doped zinc oxide (Mn:ZnO) nanorods were synthesized by incorporating manganese in aligned ZnO nanorods. For this, Mn was evaporated onto ZnO nanorods and the composite structure was subjected to rapid thermal annealing. The nanorods were preferentially oriented in (0 0 2) direction as indicated by the XRD measurement. Optical band gap was seen to decrease with increasing amount of Mn incorporation. XPS studies indicated that incorporated Mn was in Mn²⁺ and Mn⁴⁺ states. Mn²⁺ atomic concentration was found to be larger than Mn⁴⁺ concentration in all the samples. The Raman spectra of the Mn:ZnO nanorods indicated the presence of the characteristic peak at ∼438 cm⁻¹ for high frequency branch of E₂ mode of ZnO. The PL peak at ∼376 nm (∼3.29 eV) was ascribed to the band edge luminescence while the peak at ∼394 nm (∼3.15 eV) was assigned to the donor bound exciton (D^oX) and free exciton transition related to Mn²⁺ states.     

Flower-like silicon dioxide/polymer composite particles synthesized by dispersion polymerization route

A vital issue for the manufacture of multifunctional thin films is to synthesize polymer/ceramic hybrid particles. Silicon dioxide (SiO₂)/polymer composite particles were synthesized through dispersion copolymerization of methyl methacrylate (MMA) in the presence of SiO₂ bullet-like particles, using a “grafting-through” approach. The SiO₂ particles were previously modified with the silane-coupling agent 3-(trimethoxysilyl)propyl methacrylate (MPTS). Scanning electron microscopy and transmission electron microscopy analyses confirmed the formation of particles with a rough surface and flower-like morphology. Fourier transform infrared spectroscopy, thermogravimetric analysis, and energy-dispersive X-ray investigations indicated that a nucleation and aggregation process of the growing copolymer MPTS/poly(methyl methacrylate) (PMMA) occurred on the surface of the modified SiO₂ particles. As a result, the SiO₂ core became embedded in a PMMA shell. The influence of MPTS and the concentration of polyvinylpyrrolidone as a steric stabilizer on the flower-like morphology was demonstrated. Dispersion polymerizations have been proven to be simple and effective ways to synthesize composite particles with a high surface area. By using homogeneous systems (i.e., the monomer was soluble in the reaction solvent), no emulsification process was required, and copious amounts of well-dispersed particles were produced. These characteristics open many application possibilities for the use of the synthesized particles in functional coatings and optical devices, for mechanical reinforcement in polymeric materials, and as biomaterials.     

Structural, electrical and optical properties of ITO films with a thin TiO2 seed layer prepared by RF magnetron sputtering

Tin-doped indium oxide (ITO) films were deposited by RF magnetron sputtering on TiO₂-coated glass substrates (the TiO₂ layer is usually called seed layer). The properties of ITO films prepared at a substrate temperature of 300 °C on bare and TiO₂-coated glass substrates have been analyzed by using X-ray diffraction, atomic force microscope, optical and electrical measurements. Comparing with single layer ITO film, the ITO film with a TiO₂ seed layer of 2 nm has a remarkable 41.2% decrease in resistivity and similar optical transmittance. The glass/TiO₂ (2 nm)/ITO film achieved shows a resistivity of 3.37 × 10⁻⁴ Ω cm and an average transmittance of 93.1% in the visible range. The glass/TiO₂ may be a better substrate compared with bare glass for depositing high quality ITO films.     

Electric properties and surface characterization of transparent Al-doped ZnO thin films prepared by pulsed laser deposition

We grew 2 wt.% Al-doped ZnO (AZO) films on 5.08 cm-diameter polymer substrates at room temperature by the pulsed laser deposition (PLD) technique added the beam-rastering function. The structural properties, surface morphology, resistivity, mobility and chemical bonding states of AZO/polymer films were measured. The structuring of polymer surface by atmospheric plasma can occur at nm scales and can influence adhesion, optical and wettability properties of the materials. With increasing plasma treatment power, surface hydrophilicity and roughness for PET and PES polymer increased, respectively.     

Deposition of silicon oxynitride at room temperature by Inductively Coupled Plasma-CVD

Oxynitride thin films are used in important optical applications and as gate dielectric for MOS devices. Their traditional deposition processes have the drawbacks that high temperatures are needed, high mechanical stresses are induced and the deposition rate is low. Plasma assisted processes may alleviate these problems. In this study, oxynitride films were deposited at room temperature through the chemical reaction of silane, nitrogen and nitrous oxide (N₂O), in a conventional LPCVD furnace, which was modified into a high density Inductively Coupled Plasma (ICP) reactor. Deposition rates increased with applied coil power and were never lower than 10 nm/min, quite high for room temperature depositions. The films' refractive indexes and FTIR spectra indicate that for processes with low N₂O gas concentrations, when mixed together with N₂ and SiH₄, nitrogen was incorporated in the film. This incorporation increased the resistivity, which was up to 70 GΩ cm, increased the refractive index, from approximately 1.47 to approximately 1.50, and decreased the dielectric constant of these films, which varied in the 4-14 range. These characteristics are adequate for electric applications e.g. for TFT fabrication on glass or polymers which can not stand high temperature steps.     

Influence of DC magnetron sputtering parameters on the properties of amorphous indium zinc oxide thin film

Amorphous or crystalline indium zinc oxide (IZO) thin films, which are highly transparent and conducting, were deposited by DC magnetron sputtering. X-Ray diffraction technique was used for analyzing microstructures of the films, and also differential thermal analysis was performed for observing their crystallization behavior. The IZO thin films prepared were crystallized at much higher temperature than ITO films were. The crystallized samples showed (222) preferred orientations. By varying process parameters, the optimum conditions for the highest electrical conductivity and optical transmittance, and the lowest surface roughness were found. The resistivity of IZO films decreased as the deposition temperature increased until 250 °C, but sharp rise occurred at or above 300 °C. The extinction coefficients diminished in the films prepared with the conditions of higher deposition temperature, sputtering gas of light mass, and heat treatment. However, excessive amount of oxygen flow during deposition brought about the increase of the extinction coefficients. The variations of extinction coefficients mainly influenced the transmittance of the samples. On the basis of X-ray photoelectron spectroscopy analysis, atomic force microscopy measurement, spectroscopic ellipsometry and spectrophotometer measurement, several characteristics of IZO thin films were discussed comparing with those of ITO thin films. Very low surface roughness of IZO thin films could satisfy the requirement for organic light-emitting diode.     

Improvement of brightness with Al2O3 passivation layers on the surface of InGaN/GaN-based light-emitting diode chips

In this study, sputtered 50, 70 and 90 nm thick Al₂O₃ thin films were evaluated as a passivation layer in the process of InGaN-based blue as LEDs (Light-Emitting Diodes) in order to improve the brightness of LED lamps. For packaged LED lamps, lamps with Al₂O₃ passivation layer had higher brightness than ones with SiO₂ passivation layer, and LED lamps with 90-nm Al₂O₃ passivation layer were the brightest among four kinds of lamps. Although lamps with Al₂O₃ passivation layer had a bias voltage 0.25 V at 20 mA forward current higher the lamps built with SiO₂ passivation layer, their brightness was improved about 13.6% higher than the conventional LEDs with no change in emitting wavelength.     

Plasma influence on the properties and structure of indium tin oxide films produced by reactive middle frequency pulsed magnetron sputtering

Reactive pulsed magnetron sputtering was used to produce conductive and transparent tin-doped indium oxide (ITO) films with low thickness inhomogeneity. Due to the parallel operation of two magnetrons, the deposition system allows in situ investigations of the plasma influence on the film properties. The distribution of the film resistivity, refractive index, structure and stoichiometry along the substrate are presented and related to the spatial distribution of the plasma flow escaping the magnetrons, and the substrate temperature. A higher plasma flow likely causes a localized relaxation of the distorted In-O bonds in amorphous phase which prevails in ITO films prepared at unheated substrates. This leads to a decrease of the film resistivity due to free electrons density and mobility enhancement. The free electron density increase is caused likely by generation of oxygen vacancies. Deposition on a heated substrate (T_s / T_m = 0.3) leads to a change of the film growth mode due to enhanced surface diffusion of the adatoms which results in a textured low resistivity film. This also causes significant improvements of the homogeneity of the film properties that is important for ITO applications.     

High conductivity and transparent ZnO:Al films prepared at low temperature by DC and MF magnetron sputtering

Aluminum-doped zinc oxide thin films have been deposited by DC and MF magnetron sputtering from a ceramic oxide target in argon atmosphere without direct heating of the substrates. The samples were prepared at different predetermined conditions of input power or discharge voltage and the influence upon electronic, optical, and microstructural properties has been investigated. The as-deposited layers show low resistivity, such as 9 × 10^− 4 Ω cm minimum for DC excitation and 1.2 × 10^− 3 Ω cm for MF mode, with growth rates up to 130 nm/min, and resulting substrate temperatures always below 200 °C. Low resistivity of the films is combined with high transmission, 85-90% in the visible wavelength range (400-800 nm). A strong (002) texture perpendicular to the substrate has been found, with lower strain for DC than for MF sputtering.     

Studies on the structural and optical properties of zinc oxide nanobushes and Co-doped ZnO self-aggregated nanorods synthesized by simple thermal decomposition route

Pure and Co-doped zinc oxide nanomaterials were prepared by a simple low temperature synthesis and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution-transmission electron microscopy (HR-TEM), diffused reflectance spectroscopy (DRS) and electron paramagnetic resonance (EPR) techniques. The results showed the formation of nanobushes that consists of several nanowires for pure ZnO and the nanorods formed by self-aggregation for Co-doped ZnO. The presence of Co²⁺ ions replacing some of the Zn²⁺ in the ZnO lattice was confirmed by EPR and DRS studies. The mechanism for the formation of self-aggregated and self-aligned ZnO rods after the incorporation of cobalt in the lattice by the building block units is discussed in this study. Morphological studies were carried out using SEM and HR-TEM, which supports the validity of the proposed mechanism for the formation of ZnO nanobushes and Co-doped ZnO nanorods. The synthesized nanomaterials were found to have good optoelectronic properties.     

Experimental study of the organic light emitting diode with a p-type silicon anode

We have fabricated and studied an organic light emitting diode (OLED) with a p-type silicon anode and a SiO₂ buffer layer between the anode and the organic layers which emits light from a semitransparent top Yb/Au cathode. The luminance of the OLED is up to 5600 cd/m² at 17 V and 1800 mA/cm², the current efficiency is 0.31 cd/A. Both its luminance and current efficiency are much higher than those of the OLEDs with silicon as the anodes reported previously. The enhancement of the luminance and efficiency can be attributed to an improved balance between the hole- and electron-injection through two efficient ways: 1) restraining the hole-injection by inserting an ultra-thin SiO₂ buffer layer between the Si anode and the organic layers; and 2) enhancing the electron-injection by using a low work function, low optical reflectance and absorption semitransparent Yb/Au cathode.     

Cathodoluminescence and photoluminescence of swift ion irradiation modified zinc oxide-porous silicon nanocomposite

We report the room temperature cathodoluminescence and photoluminescence of swift ion irradiated (130 MeV Nickel ion) porous silicon zinc oxide nanocomposites. The evolution of a broad and flat emission band from 1.5 to 3.5 eV is demonstrated. Annealing effect of irradiation is found to result in a relative increase in the band edge emission. Emission wavelength can be tuned in the complete visible range by changing the substrate characteristics.     

Carbon additive effects on the nanostructure and magnetic property of the Co-Fe-Zr-B-C films

In this study, the carbon additive Co-Fe-Zr-B alloy films were prepared by dual-gun co-sputtering. The effects of the carbon addition and heat treatment on the nanostructure and magnetic properties of the Co-Fe-Zr-B-C alloy films are reported. The experimental results show that a crystalline (Co, Fe) phase formed after heat treatment at 400 in the Co-Fe-Zr-B-C films with low carbon additive level. Carbon atoms inhibited the crystallization of the as-deposited Co-Fe-Zr-B-C films. From the TEM observation, the nanostructures, such as the atomic structure and grain sizes, showed a strong carbon content dependence. The coercivities of the Co-Fe-Zr-B-C films annealed at 400 varied from 18 to 0.3 Oe with the increasing carbon addition. However, the films annealed at higher temperature exhibited a dramatic increase in the coercivities, which correlated to the formation of the crystalline (Co, Fe) phase. The resistivities of the Co-Fe-Zr-B-C films relied on the carbon contents rather than on annealing temperatures.     

Self-assembled microspheres of glucose-containing polyaniline by alkali-guided method

Glucose-containing polyaniline (PANI) microspheres were prepared via a self-assembly process which started in alkaline solution by the oxidative polymerization of N-glucosylaniline (G-An). The products were characterized by SEM, TEM, FT-IR, UV-Vis, ¹H NMR and GPC measurements. It was found that the polymerization of G-An by alkali-guided method gave complicated structures and both the pH value and the dose of oxidant could affect the morphology of the product.     

Study on the Hall-effect and photoluminescence of N-doped p-type ZnO thin films

N-doped, p-type ZnO thin films have been grown by plasma-assisted metal-organic chemical vapor deposition method. The results under optimized growth conditions included a resistivity of 1.72 Ω cm, a Hall mobility of 1.59 cm²/V s, and a hole concentration of 2.29 × 10¹⁸ cm^− 3, and were consistently reproducible. A N-related free-to-neutral-acceptor emission and an associated phonon replica were evident in room temperature photoluminescence spectra, from which the N acceptor energy level in ZnO was estimated to be 180 meV above the valence band maximum.     

Effects of phosphorus doping source temperatures on fabrication and properties of p-type ZnO thin films

Phosphorus-doped p-type ZnO thin films have been deposited by metalorganic chemical vapor deposition using P₂O₅ as the dopant source. The conductivity types of the as-grown thin films were strongly temperature-dependent. When the substrate temperature maintains at the optimal one of 420 °C, the evaporating temperature of the phosphorus source plays significant roles in controlling the phosphorus content doping into films, then influences the films' performance. Optimizing the growth parameters, the optimal results were obtained with a resistivity of 6.49 Ω cm, a Hall mobility of 0.40 cm²/V s and a hole concentration of 2.42 × 10¹⁸ cm^− 3. The optical property of the optimal film was characterized by PL measurements, which indicated the film is of high optical quality.     

Hexagonal nanoplatelets of CuSe synthesized through facile solution phase reaction

A novel solution-phase synthetic route for obtaining hexagonal nanoplatelets of copper selenide is presented. Chemical reaction involved in the synthesis is the reduction of copper selenite with hydrazine hydrate. The reaction is performed in various solvents and in the presence of different capping agents. The structure, composition and properties of the nanomaterials obtained were studied with various techniques. The reduction reaction carried out in ethylene glycol even in the absence of any capping agents gave the best results. The relatively low temperature of reaction, usage of single precursor and the surfactant-free growth of nanomaterials make this synthetic route a promising one in perspectives of material science.