Thickness dependent electrical properties of CdO thin films prepared by spray pyrolysis method

A large number of thin films of cadmium oxide have been prepared on glass substrates by spray pyrolysis method. The prepared films have uniform thickness varying from 200–600 nm and good adherence to the glass substrate. A systematic study has been made on the influence of thickness on resistivity, sheet resistance, carrier concentration and mobility of the films. The resistivity, sheet resistance, carrier concentration and mobility values varied from 1·56–5·72×10⁻³ Ω-cm, 128–189 Ω/□, 1·6–3·9×10²¹ cm⁻³ and 0·3–3 cm²/Vs, respectively for varying film thicknesses. A systematic increase in mobility with grain size clearly indicates the reduction of overall scattering of charge carriers at the grain boundaries. The large concentration of charge carriers and low mobility values have been attributed to the presence of Cd as an impurity in CdO microcrystallites. Using the optical transmission data, the band gap was estimated and found to vary from 2·20–2·42 eV. These films have transmittance around 77% and average reflectance is below 2·6% in the spectral range 350–850 nm. The films aren-type and polycrystalline in nature. SEM micrographs of the CdO films were taken and the films exhibit clear grains and grain boundary formation at a substrate temperature as low as 523 K.     

高性能导电薄膜的制备

采用磁控溅射法在玻璃基底上制备了Cr-Cu-Al-Cr薄膜,用焊接法测试薄膜附着性能,用x射线衍射仪（XRD）、原子力显微镜（AFM）和台阶仪对薄膜进行表征,研究溅射过程中以及在高温大气环境下薄膜的防氧化方法,分析薄膜晶粒大小与电性能关系,制备出性能较好的导电膜。     

Thickness dependent structural, magnetic and transport properties of nanostructured cobalt thin films

This paper presents structural, magnetic, and transport properties measurements carried out on Co thin film as a function of thickness. The structure of the Co thin film changes from amorphous to nano-crystalline with the increase in film thickness. The corresponding magnetic and transport measurements show drastic changes in coercivity, saturation field and resistivity value as a function of Co film thickness. Observed magnetization and resistivity behaviour is mainly attributed to the (i) Change in crystal structure, (ii) stress relaxation, (iii) grain growth as revealed by X-ray diffraction (XRD), and atomic force microscopy (AFM) measurements.     

Thickness dependent magnetic properties of BiFeO3 thin films prepared by pulsed laser deposition

BiFe_1 ? xMn_xO₃ thin films having thickness 65 and 130 nm was fabricated on LAO substrates using pulsed laser deposition technique and its structural and magnetic properties were examined. Atomic force microscopy images confirmed that, as the thickness of the films increases the particles size also increases resulting in the decrease of magnetization. The possible cause for the lowering of magnetization with film thickness was discussed. Increase of spontaneous magnetization in BiFeO₃ at room temperature was observed with Mn substitution for Fe. The blocking temperature was found to decrease with increasing film thickness.     

Thickness dependent properties of nickel oxide thin films deposited by dc reactive magnetron sputtering

Nickel oxide thin films of various thicknesses were grown on glass substrates by dc reactive magnetron sputtering technique in a pure oxygen atmosphere with sputtering power of 150 W and substrate temperature of 523 K. Crystalline properties of NiO films as a function of film thickness were investigated using X-ray diffraction. XRD analysis revealed that (200) is the preferred orientation and the orientation of the films changed from (200) to (220) at film thickness of 350 nm. The maximum optical transmittance of 60% and band gap of 3.82 eV was observed at the film thickness of 350 nm. The lowest electrical resistivity of 5.1 Ω cm was observed at a film thickness of 350 nm, thereafter resistivity increases with film thickness.     

MOCVD of highly conductive CdO thin films

Thin films of cadmium oxide have been deposited onto alumino–silicate glass substrates by atmospheric pressure metal organic chemical vapor deposition using DMCd and n-butanol, a novel oxygen source. Studies were conducted to evaluate how different conditions such as temperature and precursor concentration influenced the film growth. Film characterization showed that at an optimum temperature range of 270–290 °C, CdO exhibits low spreading resistance of 17.1 per square, for a 400 nm film, compared with 10 per square for 1.1 m indium tin oxide film, and high transmittance, between 600 and 900 nm, up to 90% with a band gap of 2.4 eV. Within this optimum temperature range, the grain size and surface roughness are shown to be a minimum.     

Analysis of thermal effect on transparent conductive oxide thin films ablated by UV laser

Transparent conductive oxide thin films are applied to many computer, communication and consumer electronics products including thin film transistor liquid crystal displays, organic light emitting diodes, solar cells, mobile phones, and digital cameras. The laser direct write patterning of the indium tin oxide (ITO) thin film processing technique produces a heat affected zone that has an enormous effect on the electro-optical efficiency of transparent conductive oxide films. This is because direct laser writing patterning in thermal machining process can create debris and micro-cracks in the substrate. Therefore, this study establishes the ultraviolet (UV) laser ablation of temperature model on the polycarbonate and soda-lime glass substrates using the finite element analysis software ANSYS, and measures the temperature field based on the laser micro-patterning process. The meshing model determines the structure of the pre-processors and parameters were set with ANSYS parameter design language. This study also simulates the Gaussian distribution laser irradiation on the pre-processor structure. A UV laser processing system made micro-patterning on ITO thin films to analyze which conditions damaged the substrates. Comparing the simulation and experiment results reveals the minimum laser ablation threshold of the ITO thin films with the melting and vaporization temperatures. Simulation results show that the temperature distribution on PC and soda-lime glass substrates after laser irradiation of 1.05 μs with a laser output power of 0.07 W produces temperatures of approximately 52 °C, 54 °C and 345°Cand 205 °C at the laser output power of 0.46 W. The experiment results show that the patterning region is similar to the simulation results, and the lower laser power does not damage the substrates.     

Thickness dependence of breakdown field in thin films

Studies of the thickness dependence of dielectric breakdown in thin films are of fundamental importance for the development of devices. Here a systematic study of the d.c. breakdown in “built-up” ionic films of barium stearate is reported in the thickness range (25–2000 Å). These films are ideally suited for such studies because of their perfect reproducibility and control of their thicknesses which are uniform and very accurately known. The breakdown strength is found to be a power dependent function of thickness as predicted by Forlani and Minnaja's theory based on an electron ionization avalanche mechanism. The films studied have recently been found to be promising for making devices.     

Carbon nanotube based transparent conductive thin films

Carbon nanotube (CNT) based optically transparent and electrically conductive thin films are fabricated on plastic substrates in this study. Single-walled carbon nanotubes (SWNTs) are chemically treated with a mixture of concentrated sulfuric acid and nitric acid before being dispersed in aqueous surfactant-contained solutions. SWNT thin films are prepared from the stable SWNT solutions using wet coating techniques. The 100 nm thick SWNT thin film exhibits a surface resistivity of 6 kohms/square nanometer with an average transmittance of 88% on the visible light range, which is three times better than the films prepared from the high purity as-received SWNTs.     

Preparation of highly transparent conductive Al-doped ZnO thin films and annealing effects on properties

Aluminum-doped ZnO (ZAO) thin films were deposited on fused quartz substrates by radio frequency sputtering in pure argon ambient at 450 °C. Effects of in situ annealing temperature and annealing atmosphere on microstructure, electrical and optical properties of ZAO films have been investigated. Results showed that as-grown film without annealing treatments attained lowest resistivity of 1.1 × 10⁻⁴Ω cm. And all films performed high average transmittance greater than 90% in visible region. X-Ray diffraction (XRD), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS) were utilized to characterize the microstructure properties of films. XRD results indicated that as-grown film had higher crystalline quality and larger grain size than annealed films. Al atoms replaced Zn efficiently to provide electrons stable in all samples. PL spectra revealed that high annealing temperature and oxygen atmosphere would generate more Zn vacancy (V_Zn) and oxide antisite defect (O_Zn), respectively and composition content results from XPS provided supports to this.     

Transparent amorphous conductive Cd-In-Sb-O thin films for flexible devices

Transparent conductive amorphous Cd-In-Sb-O thin films were deposited on a flexible polyethylene naphthalate film by rf magnetron sputtering at room temperature. The large Hall mobility of ∼26 cm² V⁻¹ s⁻¹ was observed on the films with carrier density >10²⁰ cm⁻³. The carrier density varied from the order of 10²⁰ to 10¹⁷ cm⁻³ with increasing the oxygen partial pressure. The Hall mobility reached up to ∼17 cm² V⁻¹ s⁻¹, even at carrier density of ∼10¹⁷ cm⁻³. Flexible transparent filed-effect transistor was also fabricated using the Cd-In-Sb-O thin films as a channel layer and the device performance was investigated. The device exhibited a field-effect mobility of ∼0.45 cm² V⁻¹ s⁻¹ and an on-off ratio of ∼10² at room temperature.     

Nanostructuring thin Au films on transparent conductive oxide substrates

Fabrication processes of Au nanostructures on indium-tin-oxide (ITO) surface by simple, versatile, and low-cost bottom-up methodologies are investigated in this work. A first methodology exploits the patterning effects induced by nanosecond laser irradiations on thin Au films deposited on ITO surface. We show that after the laser irradiations, the Au film break-up into nanoclusters whose mean size and surface density are tunable by the laser fluence. A second methodology exploits, instead, the patterning effects of standard furnace thermal processes on the Au film deposited on the ITO. We observe, in this case, a peculiar shape evolution from pre-formed nanoclusters during the Au deposition stage on the ITO, to holed nanostructures (i.e. nanorings), during the furnace annealing processes. The nanorings depth, height, width, and surface density are shown to be tunable by annealing temperature and time.     

Picosecond thermal pulses in thin gold films

In this paper it has been shown that, with the advent of lasers with a very short pulse duration, the effect of thermal wave propagation becomes important. To consider this effect, hyperbolic heat conduction in thin gold films was studied. It was shown that for heat fluxes of the order 10⁸ W·cm^–2, a thermal wave is generated in thin gold films. The consideration of the hyperbolicity of heat transfer enables one to describe the temperature profile with one value of fluence.     

Segregation effects in thin films

Atomic segregation and second-phase precipitation at surfaces and interfaces have a strong influence on many properties of bulk materials. Because these regions are different in chemistry and sometimes in lattice structure from the bulk, they can exert a pronounced influence on thin film properties, more so than in bulk materials owing to the large extent of the segregated and/or precipitated zones compared with the film thickness. Some of the similarities and the contrasting features of the segregation phenomena observed between thin films and bulk materials are noted. The thermodynamic aspects and diffusion kinetics which control segregation, the surface reactions and the formation of surface compounds in thin films are discussed. The influence of segregation and interfacial reactions on thin film properties and common experimental methods of studying segregation are briefly reviewed with selected examples.