Oxidation and wear behaviors of Ti-based thin films

The degradation of Ti-based coatings is known to be due to the formation of titanium oxide (TiO₂) at their surfaces. In this study, wear and thermal oxidation behaviors of various magnetron sputtered Ti-based thin films were studied after static oxidation and sliding wear. The oxidized surfaces after the static oxidation and the wear debris generated from pin-on-disc wear tests with alumina ball were characterized to identify the compounds, particularly titanium oxides, to gain a better understanding of the tribochemical reactions. The coatings that were examined include TiN, TiCN (N rich), TiCN (C rich), TiAlN, AlTiN, TiSiN, and TiCNO thin films. These coatings were characterized using Raman spectroscopy, scanning electron microscopy, and X-Ray diffractometer. The results show that TiSiN and AlTiN have the highest oxidation resistance, comparing with other coatings. As for the analyses of wear debris, all of the Ti-based coatings are worn by the mechanism of forming TiO₂, except AlTiN. AlTiN is worn by ploughing wear.     

Study of microstructure and magnetic properties of electrodeposited nanocrystalline CoFeNiCu thin films

In this study the nanocrystalline CoFeNiCu thin films were electrodeposited from baths containing sodium citrate as a complexing agent and pH of around 5. Electrodeposition conditions were changed in order to achieve optimum soft magnetic properties which are required for new generation magnetic head core. SEM, EDS, XRD and VSM were used for characterization of the deposited films. The SEM micrographs of the deposited films exhibited no micro-voids and more uniform surface morphology compared with films electroplated from conventional baths (with low pH and no additives). According to X-ray diffraction patterns, the films electroplated at current densities lower than 4 mA/cm² showed FCC (Cu) phase structure, and other films exhibited BCC (Fe) and/or FCC (Co) phases. Calculating grain size of the films by using Scherrer equation showed that all the coatings were nanocrystalline and double phase films had lower average grain size in comparison with single phase films. The VSM results demonstrated that the coercivity of the nanocrystalline films dramatically reduced with decreasing grain size and followed D⁶ law. However, grain size had no effect on the saturation magnetization, whereas the chemical composition significantly affected saturation magnetization of the films. The results also indicated that in order to obtain films with low coercivity and high saturation magnetization, the nickel and copper contents of the deposits must not exceed 12 and 5 at.%, respectively.     

Synthesis and characterization of sol-gel derived gallium-doped zinc oxide thin films

Gallium-doped ZnO (GZO) semiconductor thin films were prepared by a sol-gel spin coating process. The effects of Ga dopant concentrations on the microstructure, electrical resistivity, optical properties, and photoluminescence (PL) were studied. XRD results showed that all the as-prepared GZO films had a wurtzite phase and a preferred orientation along the [0 0 2] direction. ZnO thin films doped with Ga had lower electrical resistivity, lower RMS roughness, and improved optical transmittance in the visible region. The lowest average electrical resistivity value, 2.8 × 10² Ω cm, was achieved in the ZnO thin films doped with 2% Ga, which exhibited an average transmittance of 91.5%. This study also found that the optical band gap of Ga-doped films was 3.25 eV, slightly higher than that of undoped samples (3.23 eV), and the PL spectra of GZO films showed strong violet-light emission centers at about 2.86 eV (the corresponding wavelength of which is about 434 nm).     

Sensing properties of sprayed antimony doped tin oxide thin films: Solution molarity

Transparent conductive thin films of nanocrystalline Sb:SnO₂ have been deposited onto preheated glass substrates by using spray pyrolysis technique. The effect of the solution molarity on structural, morphological, optoelectronic properties of Sb:SnO₂ films has been investigated. XRD study reveals that films are polycrystalline with tetragonal crystal structure having average crystallite size about 20 nm. The compact and homogeneous grains are seen in FESEM images. The BEs of Sn 3d_5/2 for all samples show the Sn⁴⁺ bonding state for SnO₂. The BEs of Sb 3d_5/2 are in the range of 530.6-530.9 eV, indicating that all antimony detected is in a pentavalent state (Sb⁵⁺). Transparency of films in the visible region decreases with increase in precursor concentration. Photoluminescence study shows the strong violet and weak orange emission. The sensing properties of the Sb:SnO₂ films for acetone, ethanol and LPG with operating temperature and gas concentration have been investigated.     

A corrosion study of nanocrystalline copper thin films

Thin nanocrystalline, compact films, based on the copper–nitrogen system, up to 2.5 μm thickness and 3.5% nitrogen, were deposited by magnetron sputtering at different partial pressure ratios of N₂ and Ar, without formation of Cu_xN compounds, the nitrogen concentration influencing grain size (down to 30 nm) and film homogeneity. Electrochemical corrosion properties were investigated using polarization curves and electrochemical impedance spectroscopy in 0.5 M NaCl aqueous solution, and compared with pure bulk copper; morphology was examined by scanning electron microscopy. Significant variations in corrosion currents between samples were attributed to grain size and structural defects on the grain boundaries.     

Physical properties of chemical vapour deposited nanostructured carbon thin films

A simple thermal chemical vapour deposition technique is employed for the deposition of carbon films by pyrolysing the natural precursor “turpentine oil” on to the stainless steel (SS) and FTO coated quartz substrates at higher temperatures (700-1100 °C). In this work, we have studied the influence of substrate and deposition temperature on the evolution of structural and morphological properties of nanostructured carbon films. The films were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), contact angle measurements, Fourier transform infrared (FTIR) and Raman spectroscopy techniques. XRD study reveals that the films are polycrystalline exhibiting hexagonal and face-centered cubic structures on SS and FTO coated glass substrates respectively. SEM images show the porous and agglomerated surface of the films. Deposited carbon films show the hydrophobic nature. FTIR study displays C-H and O-H stretching vibration modes in the films. Raman analysis shows that, high ID/IG for FTO substrate confirms the dominance of sp³ bonds with diamond phase and less for SS shows graphitization effect with dominant sp² bonds. It reveals the difference in local microstructure of carbon deposits leading to variation in contact angle and hardness, which is ascribed to difference in the packing density of carbon films, as observed also by Raman.     

Texture-dependent twin formation in nanocrystalline thin Pd films

Nanocrystalline Pd films were produced by electron-beam evaporation and sputter deposition. The electron-beam-evaporated films reveal randomly oriented nanograins with a relatively high density of growth twins, unexpected in view of the high stacking fault energy of Pd. In contrast, sputter-deposited films show a clear 〈1 1 1〉 crystallographic textured nanostructure without twins. These results provide insightful information to guide the generation of microstructures with enhanced strength/ductility balance in high stacking fault energy nanocrystalline metallic thin films.     

A study on crystallization, optical and electrical properties of the advanced ZITO thin films using co-sputtering system

Multi-functions (conductor, semiconductor and insulator) ZnInSnO (ZITO) transparent oxide thin films have been obtained by a co-sputtering system using ITO target and ZnO target with oxygen gas contents (0-8%). The ZITO film containing a small ITO content had the lowest resistivity (good electron mobility) and higher optical transmittance. In addition, the influences of thermal treatments (post-annealing and substrate temperature) on electrical properties and optical transmittance of ZITO films were studied. Photoluminescence (PL) of the ZITO film confirmed the contribution of ITO content and oxygen gas content on the photo-emission. The ZITO film with zinc atomic concentration of 58 at.% was a good candidate for TCO material (3.08 × 10⁻⁴ Ω cm). Under the substrate temperature of 100 °C or post-annealing temperature of 200 °C, the properties of ZITO film could be improved.     

Deposition of alpha-WC/a-C nanocomposite thin films by hot-filament CVD

Nanostructured tungsten carbide coatings containing amorphous carbon (a-C) phases are interesting composite materials. The incorporation of the a-C phase simultaneously improves the thermal stabilization of the carbide phase and the coatings' friction coefficient. Such nanocomposite coatings are also electrically conducting with resistivity values comparable to the transition metals, which make them useful for a number of electrochemical and electronic applications. Many deposition techniques have been used for the synthesis of these coatings. However, most of them lead to the formation of complex crystalline structures consisting of more than one carbide phase and varying amorphous contents.The novelty of this work is the formation of WC coatings with controllable film thickness and a-C content, almost fully composed by α-WC phase. Tungsten carbide coatings were deposited on silicon substrates using a hot filament chemical vapor deposition (HFCVD) equipment with hydrogen and methane as the deposition gasses. Two types of nanocomposite coatings were obtained with significant variations of the carbide phase and a-C contents.The results point to the W vaporization time as the main parameter influencing the film thickness. We also conclude that the formation of α-WC phase is the combining result of W filaments vaporization in vacuum and the carbon incorporation at low substrate temperature. The small crystallite size of the carbide grains (5-6 nm) could also explain the rapid diffusion of C through the tungsten-containing layer. Preliminary results show that the amount of a-C incorporated in the film is not only dependent on the CH₄/H₂ ratio but also on the substrate temperature.     

非平衡磁控溅射离子镀Cu-Nb纳米晶薄膜的微观结构及性能

研究了Nb含量对纳米晶Cu-Nb薄膜微观结构和性能的影响。使用非平衡磁控溅射离子镀技术,在具有(100)晶面的单晶Si基体和玻璃基体上制备不同Nb含量的Cu-Nb纳米晶薄膜,研究Nb含量对纳米晶Cu-Nb薄膜微观结构和性能的影响。将样品置于卧式真空退火炉中进行400 ℃退火,用配备了能量色散X射线光谱仪的场发射扫描电镜、原子力显微镜、X射线衍射仪、纳米压痕仪和四探针电阻率测试仪等分析了退火前后薄膜的微观结构、力学性能与电学性能。结果表明,沉积态Cu-Nb薄膜表面由致密的纳米晶组成,表面粗糙度最高仅为8.54 nm,且无明显的孔洞和裂纹等缺陷。随着Nb含量的增加,薄膜的平均晶粒尺寸下降5 nm,薄膜的硬度也因细晶强化而有所增加,在靶电流为1.3 A时达到最大值4.9 GPa。退火态样品在硬度、弹性模量、平均晶粒尺寸和表面粗糙度方面与沉积态薄膜相比有较小的变化,Cu-Nb薄膜表现出优良的热稳定性。Nb的加入可有效细化晶粒,达到细晶强化的效果,同时Cu-Nb不互溶的特性使得纳米晶薄膜在高温下也可保持较好的热稳定性。Nb靶溅射电流为0.5 A 时薄膜综合性能最佳,此时沉积态Cu-Nb薄膜的电阻率最低,为3.798×10^-7 Ω/m,硬度和弹性模量高达4.6 GPa和139.5 GPa,薄膜厚度为1050 nm,粗糙度R_a为4.70 nm。     

Synthesis and photovoltaic properties of two new unsymmetrical zinc-phthalocyanine dyes

Two new soluble unsymmetrical zinc-phthalocyanine derivatives (PC-HY1, PC-HY2) with D-π-A structure bearing three tert-butylphenyl or tert-butylthienyl groups and cyanoacrylic acid groups were synthesized through a low-cost “anhydride” method. The photophysical, electrochemical and photovoltaic properties of the phthalocyanine derivatives were studied. The two phthalocyanine derivatives showed strong and broad absorption in the UV and red/near-infrared (IR) region, especially for PC-HY2. The electrochemical properties indicated that the two phthalocyanine derivatives are latent materials for dye-sensitized solar cells. Under the illumination of AM 1.5, 100 mW cm⁻², dye-sensitized solar cells based on PC-HY1 and PC-HY2 showed power conversion efficiency (PCE) of 0.79% and 1.09%, respectively.     

Novel blue-violet photoluminescence from sputtered ZnO thin films

Although wurtzite ZnO has a simple crystal structure, the mechanism of its photoluminescence is still controversial and this topic has attracted numerous research efforts. The polycrystalline ZnO thin films studied here were deposited on Si (1 0 0) substrate by sputtering in pure Ar atmosphere, and then thermally annealed in air at various temperatures ranging from 300 °C to 1050 °C. The photoluminescence spectra of the as-synthesized ZnO thin films exhibited some interesting results: two novel and remarkable blue-violet emission peaks around 415 nm and 440 nm were discovered, while the usual strong green emission peak at 450-550 nm was absent. These two blue-violet peaks might originate from zinc interstitial and zinc vacancy point defects, which were introduced during sputtering in a non-oxygen atmosphere. Strong blue-violet emissions of ZnO are highly desirable and they have great potential in light emitting and biological fluorescence labeling applications.     

Hydrogen-free carbon thin films prepared by new type surface-wave-sustained plasma (SWP)

In this paper is described the simple structure of a new type surface-wave-sustained plasma (SWP) source without a magnetic field surrounding the chamber wall. In the source, the plasma is excited and sustained by 2.45 GHz microwaves, and the plasma density is measured by a single Langmuir probe in the target direction. The results indicate that the electron density obtained in this system is as high as 9 × 10¹¹ cm^− 3 even at a low pressure of 2.8 Pa. A graphite target (99.998%) and argon (99.999%) are used for depositing hydrogen-free amorphous carbon films by the new SWP source. The Raman spectra of the carbon films were obtained, and the results denote that the structure of the carbon films prepared by SWP is typical of diamond-like carbon; the Raman intensity ratio I_D/I_G is 2.97. The surface morphology was investigated by using an atomic force microscope (AFM). The images demonstrate that the hydrogen-free carbon films deposited by SWP have a very smooth surface, with a grain size of about 20 nm and surface roughness R_a of about 0.778 nm.     

On plastic strain recovery in freestanding nanocrystalline metal thin films

In a recent article [J. Rajagopalan, J.H. Han, M.T.A. Saif, Science 315 (2007) 1831–1834], we have reported substantial (50–100%) plastic strain recovery in freestanding nanocrystalline metal films (grain size 50–65 nm) after unloading. The strain recovery was time dependent and thermally activated. Here we model the time evolution of this strain recovery in terms of a thermally activated dislocation propagation mechanism. The model predicts an activation volume of ≈42b³ for the strain recovery process in aluminum.     

Growth of CdS thin films and nanowires for flexible photoelectrochemical cells

In this study, cadmium sulfide (CdS) nanocrystal thin films and nanowires have been deposited onto mechanically flexible substrates via dc-electrodeposition, which is a very suitable technique for large area manufacturing. For the first time with this study, flexible CdS nanocrystal thin films were integrated into photoelectrochemical (PEC) cells and their performances were compared with CdS nanowires. It has been demonstrated that PEC performance of both nanocrystal thin films and nanowires were a strong function of production conditions such as deposition time and voltage. The maximum power conversion efficiency of the CdS nanocrystal thin films obtained in this study was 0.3%. On the other hand, higher efficiencies (about 1.4%) were observed for the CdS nanowires. UV-vis analysis confirmed that both transmittance and band gap energies of the CdS nanowires were lower than that of CdS nanocrystal thin films. X-ray diffraction analysis revealed that both nanocrystal thin films and nanowires have a preferred orientation at 26° (2θ), which can be attributed to the CdS (0 0 2) structure.     

Amorphous and nanocrystalline sputtered Mg–Cu thin films

Binary Mg–Cu amorphous alloys were first fabricated in 1980s via liquid quenching. In this study, the Mg_1−xCu_x (x varying from 38 at.% to 82 at.%) partially amorphous thin films are prepared via co-sputtering. Upon thermal annealing, the Mg₂Cu or MgCu₂ nanocrystalline phases are induced in the Mg-rich or Cu-rich thin films, respectively. Due to the presence of fine nanocrystalline Mg₂Cu or MgCu₂ particles in the Mg–Cu amorphous matrix, the as-sputtered thin films show satisfactory Young's modulus 100 GPa and hardness 4 GPa.     

Characterization of cobalt oxide thin films prepared by a facile spray pyrolysis technique using perfume atomizer

Cobalt oxide (Co₃O₄) thin films were prepared by a facile spray pyrolysis technique using perfume atomizer from aqueous solution of hydrated cobalt chloride salt (CoCl₂·6H₂O) as source of cobalt. The films were deposited onto the amorphous glass substrates kept at different temperatures (300-500 °C). The influences of molar concentration of the starting solution and substrate temperature on the structural, morphological and optical properties of (Co₃O₄) thin films were studied. It was found from X-ray diffraction (XRD) analysis that the films prepared with molar concentration greater than 0.025 M/L were polycrystalline spinel type cubic structure. The preferred orientation of the crystallites of these films changes gradually from (6 2 2) to (1 1 1) when the substrate temperature increases. By Raman spectroscopy, five Raman active modes characteristic of Co₃O₄ spinel type cubic structure were found and identified at 194, 484, 522, 620 and 691 cm⁻¹. The scanning electron microscopy (SEM) images showed micro porous structure with very fine grains less than 50 nm in diameter. These films exhibited also a transmittance value of about 70% in the visible and infra red range.