Control of lubricant transport by a CrN diffusion barrier layer during high-temperature sliding of a CrN-Ag composite coating

CrN-Ag composite coatings, 2 and 5 μm thick and containing 22 at.% Ag solid lubricant, were grown on Si(001) and 440C stainless steel substrates by reactive co-sputtering at T_s = 500 °C, and were covered with 200 nm thick pure CrN diffusion barrier cap layers. Annealing experiments at T_a = 625 °C, followed by quantitative scanning electron microscopy, energy dispersive x-ray spectroscopy, and Auger depth profile analyses indicate considerable Ag transport to the top surface for a barrier layer deposited at a substrate floating potential of −30 V, but negligible Ag diffusion when deposited with a substrate bias potential of −150 V. This is attributed to ion-irradiation induced densification which makes the cap layer an effective diffusion barrier. High temperature tribological sliding tests of this coating system against alumina balls at T_t = 550 °C indicate an initial friction coefficient μ = 0.43 ± 0.04 which decreases monotonically to 0.23 ± 0.03. This is attributed to the development of wear mediated openings in the barrier layer which allow Ag lubricant to diffuse to the sliding top surface. In contrast, pure CrN exhibits a constant μ = 0.41 ± 0.02 while CrN-Ag composite coatings without cap layer show a low transient μ = 0.16 ± 0.03, attributed to Ag transport to the surface, that however increases to μ = 0.39 ± 0.04 after ~ 6000 cycles as the Ag reservoir in the coating is depleted. That is, the dense CrN cap layer reduces the Ag lubricant flow rate and therefore prolongs the time when the coating provides effective lubrication. This results in a cumulative wear rate over 10,000 cycles of 3.1 × 10⁻⁶ mm³/Nm, which is 3.3 × lower than without diffusion barrier layer.     

Onset of thermal degradation in poly(p-phenylene vinylene) films deposited by chemical vapor deposition

We report on the thermal degradation characteristics of heat treated poly(p-phenylene vinylene) (PPV) films deposited using chemical vapor deposition. It was found that no decrease in the thickness of the films (110 nm) occurred after isothermal heat treatment in vacuum at 450 °C for up to 1 h, while films treated at 500 °C for 1 h decreased to 70% of their original thickness. In situ mass spectrometry during heat treatment of the film at 500 °C showed the release of significant amounts of material including toluene and xylene ion fragments. However, Fourier transform infrared spectroscopy shows no significant change in bond structure, indicating that the decrease in film thickness after heat treatment is due to release of material and densification, not crosslinking or bond breaking.     

Influence of growth temperature on the optical and structural properties of ultrathin ZnO films

This study investigates the effect of growth temperature on the optical and structural properties of ultrathin ZnO films on the polished Si substrate. Thickness of the ultrathin ZnO films deposited by atomic layer deposition (ALD) method was about 10 nm. Photoluminescence (PL), X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM) techniques were used to measure the properties of ultrathin ZnO films. Experimental results showed that the ultrathin ZnO film deposited at 200 °C had excellent ultraviolet emission intensity, and the average roughness of the film surface was about 0.26 nm.     

Investigation of the hydrogen gas sensing properties of nanoporous Pd alloy films based on AAO templates

In this study, the hydrogen sensing properties of nanoporous Pd-Ag and Pd-Cu alloy films based on anodic aluminum oxide (AAO) templates were investigated at various temperatures (25-100 °C) and hydrogen with concentrations in the range between 250 and 5000 ppm in high purity nitrogen to determine the temperature-sensitivity relationship. A hexagonally shaped AAO template of approximately 50 nm in diameter and 10 μm in length was fabricated as a substrate for supporting a nanoporous Pd alloy film with an approximate thickness of 80 nm. The morphologies of the AAO template and the Pd alloy films were studied by scanning electron microscopy (SEM). The hydrogen sensing properties of the nanoporous Pd-Ag and Pd-Cu alloy films were measured using a transient resistance method. The sensor responses of the nanoporous Pd-Ag and Pd-Cu films on the AAO template were better than the traditional Pd-Ag and Pd-Cu thin film sensors; the sensitivities of the sensors were approximately 1.6% and 1.2%, respectively, for 1000 ppm H₂, and the detection limit was 250 ppm at room temperature. The highest sensitivity was measured at room temperature for all alloy nanoporous sensors, and the sensitivity of the Pd-Ag nanoporous alloy was higher than that of the Pd-Cu nanoporous alloy.     

Effect of Ag nanoparticle size on the plasmonic photocatalytic properties of TiO2 thin films

Photocatalytic TiO₂ films combined with Ag nanoparticles (NPs) embedded-SiO₂ films were fabricated by means of a RF magnetron sputtering and subsequent rapid thermal annealing (RTA). X-ray diffraction results show that the TiO₂ films have anatase phase when annealed at 500 °C. The Ag NPs were formed by deposition and subsequent annealing at 600 °C. Scanning electron microscopy (SEM) results show that the density of the NPs decreases with increasing Ag film thickness. For example, the average NP diameter varies from ~ 19.3 to ~ 55.9 nm as the film thickness increases from 2 to 12 nm. Transmittance measurements show that as the Ag NP size decreases, the plasmonic peaks shift towards the shorter-wavelength region and become narrower. It is further shown that under UV-illumination (352 nm), all the TiO₂ films with the Ag NPs show higher methylene blue decomposition rates compared to the TiO₂ only films and the TiO₂ films with Ag NP (a 7 nm-thick Ag film) show the best decomposition rate among the samples possibly due to the combined effects of optimized localized field amplification and radiative efficiency.     

LiCoO2 cathode thin film fabricated by RF sputtering for lithium ion microbatteries

Thin films of lithium cobalt oxide were deposited on Pt or Pt/Ti/quartz glass substrates by radio frequency (RF) magnetron sputtering at the substrate temperatures from room temperature to 500 °C. As the substrate temperature increased, the film structure changed from amorphous structure to crystallinity with a strong (003) texture as characterized by X-ray diffraction. The surface morphology and cross-section were observed using scanning electron microscopy. It was found that the films tended to crack at a high substrate temperature. Charge-discharge tests of these films were conducted and compared. The different electrochemical characteristics of these films were attributed to the modified crystallography, morphology, and thermal stress. The LiCoO₂ film deposited at 400 °C showed a well-defined 4.0 V voltage plateau on charge and a 3.9 V plateau on discharge, and delivered 54.5 μAh/cm² μm at the first discharge capacity, with good cycling performance, giving evidence that such films could be used as the thin film cathodes for lithium microbatteries.     

Nano silicon top-layer for composite-induced multiphasic enhancement of thermal stability of hardness of diamond-like carbon nanofilm at 900 °C

The effect of 25-nm silicon top-layer on the hardness and thermal stability of 100-nm diamond-like carbon (DLC) film annealed at 750–900 °C has been investigated. The evolution of surface morphology, microstructure and reaction between C and Si was examined by high resolution scanning/transmission electron microscope, Raman and FTIR spectroscopy. The hardness of films was investigated using nano-indentation. After 750–900 °C annealing, the hardness of single carbon layer greatly decreased at 750 °C and then slightly increased at 900 °C due to the formation of SiC at the interface between the single C film and the Si substrate. In contrast, no significant variation occurred on the hardness of two-layer Si/C film under RTA at 750–900 °C. Although the higher annealing temperature resulted in higher sp²/sp³ bonding ratio as well as more sp² bonding formation in the carbon layer to soften the structure, the added Si top-layer can protect DLC from reaction with environmental oxygen and sustain the hardness of the composite film because of the multiphasic formation with extra SiC on the surface and at the interface between the C layer and Si substrate through great interdiffusion between Si and C for extending DLC high-temperature application.     

Temperature effect in the corrosion resistance of Ni-Fe-Cr alloy in chloride medium

The corrosion susceptibility of alloy 33 in 0.5 mol/L sodium sulphate solutions containing or not 0.1 mol/L sodium chloride was tested at three different temperatures: 22 °C, 40 °C and 60 °C. Electrochemical studies were performed using corrosion potential measurements (E_corr) as well as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Corrosion potential measurements showed that alloy 33 was passivated by a previously air formed film which was not destroyed during immersion in both solutions. No corrosion was observed during these tests although the temperature affected the film. Potentiodynamic polarization experiments showed that at high anodic potentials the previous film was broken up, and localized corrosion occurred in both solutions and at the three temperatures tested. Electrochemical impedance spectroscopy tests confirmed the presence of a stable passive film on the alloy surface at open circuit potential. Mott-Schottky analysis indicated that the passive film is an n-type semiconductor due to the presence of point defects of donor species, such as oxygen vacancies and interstitial metallic cations. As the potential increases the Cr(III) present in the barrier layer oxidizes producing Cr(VI) soluble species. The dissolution creates metallic cation vacancies that are acceptor species and the film changes from n-type to p-type semiconductor. The passive film rupture and the following localized attack are related to the drastic oxidative dissolution of the film at high anodic potentials, independent of its p-nature, chloride presence or increased temperature.     

On the electrografting of stainless steel from para-substituted aryldiazonium salts and the thermal stability of the grafted layer

In this study we explore the thermal stability of an organic layer electrografted onto stainless steel (ASTM 316) from four different aryldiazonium salts R-C₆H₄N₂⁺ (R = NO₂, F, H, or OCH₃). The coverage of the surfaces was analysed electrochemically by employing redox probes and cyclic voltammetry. The results obtained clearly show that the steel surface after grafting is electrochemically passivated by the presence of a surface coating. Polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS) was used to characterize the organic films on the surfaces and to monitor the thermal stability of these films from ambient temperature to 400 °C with 50 °C intervals. The PM-IRRAS spectra show a decrease in band intensities at 250 °C for nitrophenyl, independent of layer thickness and atmosphere (air or argon), 300 °C for methoxyphenyl, and 350 °C for phenyl and fluorophenyl films. All the characteristic IR bands were simultaneously and completely lost at 300, 350, 350, 400 and 400 °C for thin-layer nitrophenyl, thick-layer nitrophenyl, methoxyphenyl, fluorophenyl, and phenyl, respectively, which strongly indicates that the entire organic film is lost at these temperatures. The results show that it is mainly the substituent and the layer thickness that are responsible for the difference in thermal stability of the organic films and that all films withstood temperatures up to 200 °C.This study shows that electrochemical grafting from aryldiazonium salts is simple, fast, and has a low energy consumption which makes the procedure suitable for industrial applications.     

Preparations and characterizations of polycrystalline PbSe thin films by a thermal reduction method

Polycrystalline PbSe thin films were deposited on Si substrates by a thermal reduction method with the carbon as the reducing agent. The X-ray diffraction (XRD) spectra show that the deposited thin films predominately crystallize with the rock-salt structures above the evaporation temperature of 600 °C, and the PbSe thin film has the optimal crystal quality at 900 °C. The scanning electron microscopy (SEM) measurements reveal that the PbSe thin film with carbon addition has uniform crystal grain sizes and dense microstructure, while the thin film without carbon consists of loosely distributed and widely size-ranged crystal grains. The optical transmittance spectrum shows that the direct band gap of the PbSe film is about 0.256 eV. By the introduction of element S, PbSe_1−xS_x (0 ≤ x ≤ 1.0) thin films could be prepared, but excess amount of S additions (>20 at.%) would cause phase segregations between PbSe and PbS phases. The deposition method presented in this paper may be useful for mass-producing polycrystalline lead chalcogenide thin films in the future.     

High-efficiency red polymer light-emitting diodes based on optimizing blend polymer host

High efficiency stable red light-emitting diodes have been realized employing red copolymer (PFO-DHTBT15) from 9,9-dioctylfluorene (DOF) and 4,7-di(3-hexylthien-2-yl)-2,1,3-benzothiadiazole (DHTBT) blending into green copolymer (PFO-BT15) from 9,9-dioctylfluorene and 2,1,3-benzothiadiazole (BT) as a novel fluorescent emitting layer. The external quantum and luminous efficiency of device from blend film (PFO-DHTBT15:PFO-BT15 = 10:90) reached 5.2% and 3.16 cd/A at the current density of 35 mA/cm², respectively. The corresponding Commission Internationale de l’Eclairage coordinates is (0.64, 0.36). In comparison with the devices from phenyl-substituted poly [p-phenylene vinylene] derivative (P-PPV) as host of PFO-DHTBT15, the device from PFO-DHTBT15/PFO-BT15 blend film shows higher luminous efficiency and better stability under high current density at the same blend weight ratio. The improved device performance is mainly attributed to the effective energy transfer from PFO-BT15 copolymer to PFO-DHTBT15 copolymer and better carrier confinement.     

Highly enhanced mechanical stability of indium tin oxide film with a thin Al buffer layer deposited on plastic substrate

We here report that the mechanical stability of indium tin oxide (ITO) film deposited on the plastic substrate can be highly enhanced by a thin metal buffer layer with a minimized loss of transparency. Neither cracks nor fragmentation was observed for a 75 nm-thick ITO film with a 5 nm-Al layer even after severe bending to a radius of curvature of 1.25 mm, while a 160 nm-ITO film of similar surface resistance was cracked at 9 mm. The improved crack resistance is accounted for by the fact that the effective elastic mismatch between the film and the substrate can be alleviated with a ductile buffer layer, thus the crack propagation is suppressed.     

Influence of absorbed moisture on solubility of poly(vinyl alcohol) film during atmospheric pressure plasma jet treatment

Moisture in the hydrophilic material may potentially influence the plasma treatment effect. In order to understand how moisture absorbed into PVA affects the result of plasma treatment to the polymer, atactic poly(vinyl alcohol) (PVA) films with moisture regain (MR) of 2.5%, 9.3% and 78.3% corresponding to 10%, 65% and 98% relative humidity (RH), respectively were exposed to atmospheric pressure plasma jet. Another group was annealed at 140 °C for 20 min to discern the thermal effects from those due to plasma treatment. Scanning electron microscope (SEM) showed lamellae crystal structures were on the surface of the films with 65% and 98% RH, while some bubbles or salt grains appeared on the surface of film with 10% RH and the annealed film respectively. X-ray photoelectron spectroscopy (XPS) analysis indicated that oxygen concentration increased for plasma treated films with 65% and 98% RH and decreased for that with 10% RH. X-ray diffraction analysis (XRD) shows an increase in crystallinity in all the plasma treated films. It was found that the solubility of all the treated films was decreased, especially for the plasma treated film under 98% RH which is nearly insoluble in water at 50 °C for 20 min.     

Structural, morphological and electrical properties of spray deposited nano-crystalline CeO2 thin films

Nanocrystalline, uniform, dense, and adherent cerium oxide (CeO₂) thin films have been successfully deposited by a simple and cost effective spray pyrolysis technique. CeO₂ films were deposited at low substrate and annealing temperatures of 350 °C and 500 °C, respectively. Films were characterized by differential thermal analysis, X-ray diffraction, scanning electron microscopy, atomic force microscopy; two probe resistivity method and impedance spectroscopy. X-ray diffraction analysis revealed the formation of single phase, well crystalline thin films with cubic fluorite structure. Crystallite size was found to be in the range of 10-15 nm. AFM showed formation of smooth films with morphological grain size 27 nm. Films were found to be highly resistive with room temperature resistivity of the order of 10⁷ Ω cm. Activation energy was calculated and found to be 0.78 eV. The deposited film showed high oxygen ion conductivity of 5.94 × 10⁻³ S cm⁻¹ at 350 °C. Thus, the deposited material shows a potential application in intermediate temperature solid oxide fuel cells (IT-SOFC) and might be useful for μ-SOFC and industrial catalyst applications.     

Microstructure and electrical properties of Ti-Si-C-Ag nanocomposite thin films

Ti-Si-C-Ag nanocomposite coatings consisting of nanocrystalline TiC in an amorphous Si matrix with segregated Ag were deposited by dual magnetron sputtering from Ti₃SiC₂ and Ag targets. As evidenced by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy, for Ag contents below 10 at.%, the Ag forms ∼ 10 nm large crystallites that are homogeneously distributed in the films. For higher Ag contents, coalescence during growth results in the formation of > ∼ 100 nm Ag islands on the film surface. The electrical resistivity of the coatings was measured in a four-point-probe setup, and ranged from 340 μΩcm (for Ti-Si-C coatings without Ag) to 40 μΩcm (for high Ag content).     

Interficial stability of Cu/Cu(Ru)/Si contact system for barrier-free copper metallization

Films of Cu/Cu(Ru) and Cu(Ru) were deposited on Si substrates by magnetron sputtering. Samples were subsequently annealed and analyzed by four-point probe (FPP) measurement, X-ray diffraction (XRD), transmission electron microscopy (TEM) and Auger electron spectroscopy (AES). After annealing at 500 °C, resistivity values of both systems decrease, but the reduction is more significant for Cu(Ru). Moreover, the resistivity values of annealed Cu(Ru) film are still greater than those of annealed Cu/Cu(Ru) film. XRD data suggest that Cu/Cu(Ru) film has higher thermal stability and Cu silicide cannot be observed up to 500 °C. According to TEM results, after annealing at 500 °C, the grain size of the Cu(Ru) film is smaller than that of Cu/Cu(Ru) film. In conjunction with AES, XRD, TEM analyses and sheet resistance measurement, it indicates that Cu/Cu(Ru) seed layers are potentially good for advanced Cu interconnects from the views of interfacial stability and low resistivity.     

A layer-wise topographic study of a polymeric light-emitting diode: indium-tin oxide/poly (2,3-diphenyl-p-phenylene vinylene) / Ag

Scanning tunneling microscopy was used to characterize surface topographies relevant to polymeric light-emitting diodes (LEDs) whose active medium is a thin film of poly(2,3-diphenyl-p-phenylene vinylene) (DP-PPV). We performed a sequence of topographic studies on an indium-tin oxide (ITO) substrate, a DP-PPV film deposited on the ITO substrate, and a Ag layer of thickness of about 100 Å as evaporated on the DP-PPV film. ITO showed a granular structure, DP-PPV exhibited a fibrous-like bundled structure, and the Ag layer formed clusters whose surface roughness was comparable to the layer thickness. The different surface topographies were quantified by using the scaling of the height-height correlation functions.     

Kinetics and driving forces of abnormal grain growth in thin Cu films

The abnormal growth of individual (1 0 0) oriented grains is monitored by the in situ electron backscatter diffraction technique for more than 24 h at three different annealing temperatures (90 °C, 104 °C and 118 °C) in 1-5 μm thick Cu films on polyimide substrates. The (1 0 0) grain growth velocity increases with higher film thickness and annealing temperature, as suggested by an earlier model by Thompson and Carel. As a result, the final (1 0 0) texture fraction becomes more dominant for higher annealing temperatures and larger film thicknesses. The Thompson-Carel model, however, predicts that the (1 1 1) grains will preferably grow at temperatures up to 118 °C. Our calculations of the driving forces revealed that in addition to minimization of the strain energy (due to the thermal mismatch between film and substrate) and of the surface energy, the energy stored in the dislocations plays a decisive role in grain growth. Our observations can be understood by the notion that initially available (1 0 0) grain nuclei start to grow very rapidly, due to dislocation annihilation, and thus “overrun” the (1 1 1) grains in size.     

Supercapacitor behavior of CuO-PAA hybrid films: Effect of PAA concentration

The Cu-poly(acrylic) acid (PAA) thin films were deposited at room temperature by a simple and cost effective polymer assisted deposition (PAD) method. The solution containing Cu salt and PAA was spin coated to yield the thin films with desired properties. The Cu-PAA films were annealed at 400 °C in ambient air for 4 h to obtain CuO-PAA phase. The effect of PAA concentration on the film properties is studied and characterized by employing various techniques. The structural and surface morphological studies are carried out using X-ray diffraction (XRD) and scanning electron microscope (SEM) respectively. Fourier transform infrared spectroscopy (FT-IR) and FT-Raman spectroscopy are employed to investigate the hybrid film formation. Wetting behavior is studied by measuring the contact angle of water on the film surface. Cyclic voltammetry (CV) studies were carried out to investigate the specific capacitance of CuO-PAA films in aqueous 1 M H₂SO₄ electrolyte. Hybrid films deposited with 2 mM PAA exhibits highest specific capacitance of 65 F g⁻¹.     

Preparation and characterization of polyindole nanofibers by electrospinning method

Polyindole nanofibers with diameter ranging from 770 nm to 250 nm were firstly fabricated by an electrospinning method. Chemically synthesized polyindole was dissolved in acetonitrile to make polymer solution under ultrasonification. Electrospinning of polyindole was then carried out under electrical field strength of 1.0 kV/cm. The electrospun polyindole nanofibers exhibited smooth surface and the diameter of the fibers was ranged from 768 nm to 255 nm. The specific surface areas of polyindole nanofibers were ranged from 32 to 65 m²/g, which is significantly higher than that of the powder with same volume. The electrical conductivity of the polyindole nanofibers can reach 0.24 S/cm, which is much higher than that of the polyindole film. The polyindole nanofibers showed high thermal stability with glass transition temperature (T_g) around 132 °C and melting point (T_m) around 239 °C. The crystallinity of polyindole nanofibers was higher than that of polyindole film due to the formation of ordered molecule chains during the electrospinning. Cyclic voltammetry test results revealed that the doping and de-doping processes of BF₄⁻ ions were reversible and polyindole nanofibers had high electronically activity in the electrolytic solution containing LiBF₄.