Decreasing Film Thickness Research Articles

Ultrathin film formation under combined effect of surface roughness and surface force for elastohydrodynamic lubrication of point contact problems

PurposeThe purpose of this study is to investigate the combined effect of surface force, solvation and Van der Waals forces and surface topography parameters of amplitude and wavelength on the formation of ultrathin films for elastohydrodynamic lubrication of point contact problems.Design/methodology/approachThe Newton–Raphson technique is used to simultaneously solve the Reynolds’ film thickness including surface roughness and elastic deformation, surface force of solvation and Van der Waals forces and load balance equations. Different values of surface amplitude and wavelength were simulated in addition to the load variation.FindingsThe simulation results revealed that roughness effects are important as the film thickness decreases. The oscillation in the pressure and film thickness is due to the combined action of the solvation force and surface topography parameters. The limiting values of the surface topography parameters of the amplitude and wavelength varied and depended on the load. For different values of wavelength and load, amplitude values up to 0.25 nm have no effect on ultrathin film formation.Originality/valueThe combined effect of the surface force and surface roughness on the formation of ultrathin films was evaluated for elastohydrodynamic lubrication of point contact problems under different operating conditions of load and surface topography parameters of amplitude and wavelength. The limited surface topography parameters of the amplitude and wavelength are shown and analyzed.

Optical and Chemical Investigations of PEO Thin Films Incorporated with Curcumin Nanoparticle: Effect of Film Thickness

Using the spin coating technique, polyethylene oxide (PEO)-Curcumin nanocomposite thin films have been deposited on a quartz substrate. The film thickness role on the optical properties was investigated. SEM investigated the morphology of the thin films and revealed that curcumin NPs have a spherical shape with an average size of less than 100 nm. FTIR bands observed at 1023 and 1120 cm–1 correspond to C–O stretching vibration. New bands observed for the thin films at 804, 1237, 1280, and 1340 cm–1 correspond to C–H, C–O, and O-H bending. The thin films’ optical properties with thickness 250, 500, and 750 nm were acquired from transmittance, reflectance, Tauc plot, extinction coefficient, and reflective index. The refractive index obtained from UV-Vis data falls between 1.5 and 2. Bandgap energy obtained for PEO thin film is 4.16 eV, while for both curcumin NPs and PEO-Curcumin nanocomposite thin films, the bandgap energy is 2.49 eV. Our results indicate that the optical absorption coefficient increases with decreasing film thickness. The obtained results are in good agreement with the existing reports.

Film thickness dependence of ferroelectric properties in polar-axis-oriented epitaxial tetragonal (Bi,K)TiO3 films prepared by hydrothermal method

Tetragonal (00l)-oriented epitaxial (Bi,K)TiO3 films were grown at 240 °C on (100)cSrRuO3//(100)SrTiO3 substrates by the hydrothermal method. KOH aqueous solutions and Bi(NO3)3 · 5H2O and TiO2 powders were used as the starting materials. Film thickness was controlled from 33 to 1200 nm by changing the deposition time, and the Bi/(Bi+K) ratio in the A-site of perovskite ABO3 was almost constant for all film thicknesses. Polar-axis (00l)-oriented epitaxial (Bi,K)TiO3 films were obtained without a secondary phase and/or other orientation for all thickness ranges. Large ferroelectricity with the remanent polarization (Pr) of about 84 µC/cm2, comparable to previously reported lead-based ferroelectric films, was observed for (Bi,K)TiO3 films down to 33 nm in thickness. On the other hand, Ec increased with decreasing film thickness, but did not show strong film thickness dependence like other perovskite ferroelectric films. These data are very useful for understanding the degradation mechanism of ferroelectric thin films.

Fatigue-free Cu films on wrinkled soft substrates

The fatigue behavior of nanocrystalline Cu films on polydimethylsiloxane (PDMS) substrates was studied. It is revealed that the Cu films on wrinkled PDMS substrates exhibit ultrahigh fatigue resistance without electrical failure. The electrical resistance either remains constant during cyclic loading or slightly increases and rapidly reaches saturation, which is attributed to the buffering effect of wrinkle structures on crack initiation and the suppression effect of surface undulations on crack propagation. The film thickness-dependence of fatigue resistance is sensitive to the amount of the strain amplitude. The fatigue resistance increases with decreasing film thickness at small strain amplitudes because of higher strength and smaller local strain concentration, while the fatigue resistance first increases and then decreases as the film thickness increases at large strain amplitudes, which is related to the extrinsic deformation capability of Cu films.

Development of linear low‐density polyethylene nanocomposite films for storage of sugarcane juice

AbstractSugarcane juice is a cheap and popular product in the beverage industry, with colors varying from light gray to dark green containing abundant amounts of polyphenolic compounds, ascorbic acid, minerals, and pigments. With ample sucrose content, sugarcane juice has evolved as the primary raw material for manufacturing 70% of the world's sugar content. Despite having high nutritional value, the shelf life of juice is a severe concern owing to the onset of microbial activities, which speeds up the fermentation process immediately after the extraction, which calls for appropriate packaging for delaying the qualitative degradation. For this purpose, the physicochemical properties, microbial stability, and color properties of “Mandya” variety sugarcane juice was ascertained upon storage in developed nanocomposite films made of linear low‐density polyethylene (LLDPE) by varying the levels of compatibilizer, nanoclay, and thickness. Upon evaluating the results, it was observed that the critical physicochemical attributes, namely, total soluble solids (TSS), pH, total sugars, and overall acceptability, were found to decrease with an increase in the level of nanoclay and compatibilizer and decrease in film thickness. Zero plate counts were observed till day 15 of storage, and a gradual increase was noticed in the further days. Correspondingly, an increase in the overall color difference with the progression of storage also occurred. It was concluded from the analysis that film of 100 μm thickness prepared from a combination of 93% LLDPE, 5% compatibilizer, and 2% nanoclay gave superior shelf life, minimum change in quality parameters, and least microbial population in sugarcane juice.Practical ApplicationFruit juice industries are interested in using packaging films with high tensile strength and low permeability instead of expensive glass bottles. Nanocomposite technology could be an effective tool for developing high‐barrier packaging material. LLDPE has many applications for developing both rigid form and flexible films. Most research studies on sugarcane juice preservation are confined to bottling, and there is a scarcity of information on the storage of sugarcane juice in pouches. In this context, the goal of the present study is to develop a cost‐effective packaging technology for the storage of sugarcane juice.

Zinc water chemistry reduces dissolution of FeCrAl for nuclear fuel cladding

The use of accident tolerant fuels (ATF) will facilitate the continuing operation of light water reactors (LWR) by making them safer and more economical to operate. One of the ATF concepts is to use iron-chromium-aluminum (FeCrAl) alloys for the cladding of the fuel. These ferritic alloys were never used in power reactors before therefore their behavior needs to be characterized. Current results show a positive effect of zinc chemistry on the environmental degradation of ferritic FeCrAl. Autoclave tests at 288 °C show > 60% decrease in the dissolution rate of FeCrAl and 3–4 time decrease in the surface oxide film thickness.

Thickness-Dependent Polar Domain Evolution in Strained, Ultrathin PbTiO3 Films.

Ferroelectric ultrathin films have great potential in electronic devices and device miniaturization with the innovation of technology. In the process of product commercialization, understanding the domain evolution and topological properties of ferroelectrics is a prerequisite for high-density storage devices. In this work, a series of ultrathin PbTiO3 (PTO) films with varying thicknesses were deposited on cubic KTaO3 substrates by pulsed laser deposition and were researched by Cs-corrected scanning transmission electron microscopy (STEM), reciprocal space mapping (RSM), and piezoresponse force microscopy (PFM). RSM experiments indicate the existence of a/c domains and show that the lattice constant varies continuously, which is further confirmed by atomic-scale STEM imaging. Diffraction contrast analysis clarifies that with the decrease in PTO film thickness, the critical thickness for the formation of a/c domains could be missing. When the thickness of PTO films is less than 6 nm, the domain configurations in the ultrathin PTO films are the coexistence of a/c domains and bowl-like topological structures, where the latter ones were identified as convergent and divergent types of meron. In addition, abundant 90° charged domain walls in these ultrathin PTO films were identified. PFM studies reveal clear ferroelectric properties for these ultrathin PTO films. These results may shed light on further understanding the domain evolution and topological properties in ultrathin ferroelectric PTO films.

Size effects in the plastic deformation of NiAl thin films

Abstract This paper presents the first study of the plastic behavior of NiAl thin films with thicknesses in the micron and sub-micron range. The influence of geometrical and microstructural constraints was studied for different Al contents (45 to 50 at.% Al) and film thicknesses (0.2 to 3.1 μm) in the temperature range from 20 to 700 °C. The films were deposited on Si substrates and subjected to temperature changes resulting in thermal strains of up to 0.84%. The stress evolution in the films was measured by the substrate curvature method. The residual stress at room temperature of nearstoichiometric NiAl films significantly increased with decreasing film thickness indicating an increase of the film strength. At temperatures above 400 °C strong stress relaxation was found, which was more pronounced in thinner films suggesting the contribution of diffusional creep processes. The existence of a critical film thickness is suggested at which a transition from diffusion-controlled to dislocation-controlled plasticity occurs. The results have potential implications for the reliability of NiAl films as protective coatings in thermal engines.

Flexible elemental thermoelectrics with ultra-high power density

Flexible thermoelectrics have attracted great attention due to their potential to convert waste heat to electricity to power wearable devices and IoT (Internet of things) sensors. Though organic thin-film thermoelectric materials are popular choice for preparing flexible thermoelectrics, they suffer from low thermoelectric performances due to the low figure of merit zT. In this work, we demonstrate a new strategy to design high-performance thermoelectrics by highlighting the influence of power factors instead of zT. To verify our claim, thermoelectric is prepared through sputtering high-power factor but low zT elemental thin films of Sb (p-type) and Ni (n-type) on a polyimide substrate. In this system, ascribed by the high-power factor (up to 7 mW/mK2), a high power density of up to 4.7 mW/cm2 at a temperature gradient of 50 K can be achieved, even with the low zT (<0.1). In addition, finite element method (FEM) analysis shows that the benefit of high-power factor increases with decreasing film thicknesses. Our results show that in the case of organics and inorganics thin films, maximizing power factor is more important than maximizing zT. This finding serves to guide the design paradigm of thermoelectrics for wearable devices and is useful for the broad organic electronics community.

Current-voltage-measurement temperature characteristics depending on the barrier-forming contact metal thickness in Au/Cu/n-Si/Au–Sb/Ni rectifying contacts

We experimentally have introduced the current–voltage-temperature (I–V-T) characteristics of the Au/n-type Si (D1), Au/Cu/n-Si (D2), Au/Cu(4 nm)/n-Si (D3) and Au/Cu(2 nm)/n-Si (D4) Schottky-barrier diodes (SBDs) in the temperature range of 40–320 K with the step of 10 K. The copper Schottky contact (SC) dots for the D2, D3 and D4 SBDs have the thickness of 100 nm, 4 nm and 2 nm, respectively. The top Au contact has been used as a shield to prevent oxidation of the copper SC metal. The Schottky barrier height (SBH) Φb0 values of 0.61 eV, 0.66 eV and 0.69 eV, and the ideality factor values of 1.04, 1.04 and 1.02 for the D2, D3 and D4 SBDs have been obtained at 300 K, respectively. The SBH value has increased with decreasing Cu thin film thickness. An average series resistance Rs value of 10.6 Ω has been obtained for the Au/Cu/n-Si diodes at 300 K. The obtained Rs and the ideality factor values are almost independent of the SC metal thickness. In the SBH vs temperature plots, the SBH value in the D3 and D4 diodes with 2 nm and 4 nm metal thickness almost remained unchanged from 320 K to 120 K, and in the D2 SBD from 320 K to 160 K. Therefore, it can be said from these results that the quality of the SBDs has increased with decrease in Cu Schottky film thickness.

Modeling the effects of solid thermal expansion and thermal stress on elastohydrodynamic lubrication

Temperature has a significant effect on the performance of elastohydrodynamic lubrication (EHL), and this topic has been extensively covered in many studies. These studies are focused on how temperature affects lubrication performance, without considering the effect of temperature on the deformation and the subsurface stress of the contact bodies. However, there will be a significant rise in temperature in the contact area under such conditions as high speeds, heavy loads, and high slide-roll ratios. This will generate significant thermal stress inside the solid, thus inhibiting the elastic deformation of the contact surface and impairing the lubrication performance in the contact area. In such cases, it is essential to consider the effects of solid thermal stress and thermal expansion on thermal elastohydrodynamic lubrication (TEHL). In this paper, a TEHL model that consider solid thermal expansion and thermal stress to solve point contact problems is developed. The effects of solid thermal expansion and thermal stress on pressure, film thickness, temperature, and subsurface stress are investigated. The results show that solid thermal expansion partially inhibits the elastic deformation of the contact surface, resulting in a decrease in film thickness and an increase in pressure. It is also found that solid thermal stress causes the subsurface von Mises stress of the upper contact body to increase and that of the lower contact body to decrease.

Transport properties around the metal-insulator transition for SrVO3 ultrathin films fabricated by electrochemical etching

By using electrochemical etching, we fabricated conductive ultrathin ${\mathrm{SrVO}}_{3}$ (SVO) films that exhibited metallic behavior down to 3 monolayers (ML). From an observed systematic change in transport properties with decreasing film thickness, it was found that the disorder in the films remained nearly unchanged during etching, and only the thickness was reduced. This is in contrast to the insulating behavior found for as-deposited SVO ultrathin films. For the etched films, the electron mobility at 200 K decreased with decreasing film thickness below 10 ML, originating from an increased scattering rate and electron effective mass near the metal-insulator transition. A slight upturn in the resistivity and a positive magnetoresistance at low temperatures were typically observed for the etched films down to 3 ML, which was explained by weak antilocalization of electrons in a weakly disordered metal.

Rapid growth of Cu2−xSe thin films on brass with mixed acid solutions stabilized by using sodium silicate as a sealant

Composite Cu2−xSe thin films can be rapidly prepared on brass by liquid chemical deposition in 1 min. With the addition of acetic acid in the oxidizing solution containing SeO2/H2SO4/ H2O2, the sizes of the selenide particles become smaller and thus much smoother films are obtained, while the films become thinner and denser as seen from their scanning electron microscopy and EDS results. X-ray diffraction and XPS results reveal that copper acetate is spontaneously formed with the acetate acid addition, and the existence of copper acetate hinders the growth of copper selenides, leading to the decrease in film thickness; during their mutual deposition, copper acetate probably fills the spaces among selenide particles, and thus improves the compactness and decrease the roughness of the composite film. The miniaturization of the selenide particles with the acetate acid addition results in a great improvement in both the hardness and wear resistance of the composite films. When the composite films are sealed by sodium silicate, a successive interlayer is formed on their outer surfaces that result in the further improvement in their corrosive resistance as reflected by the electrochemical test and thermal humidity test.

Anomalous Hall effect and anisotropic magnetoresistance of molecular beam epitaxy grown Cr2Te3 thin films

High-quality Cr2Te3 epitaxial thin films with thicknesses ranging from 2.5 to 30 nm have been epitaxially grown on SrTiO3(111) single-crystal substrates using molecular beam epitaxy. The optimal growth temperature of the films was found to be 275 °C. All Cr2Te3 films show semiconductor-to-metal transition which is coupled with the paramagnetic-to-ferromagnetic transition at TC = 175 K. Consequently, all Cr2Te3 films show negative magnetoresistance effect which is strongest near TC and can be understood within the framework of electronic phase separation scenario. Both anomalous Hall effect and out-of-plane magnetic hysteresis loops show that all Cr2Te3 films have perpendicular magnetic anisotropy with the easy magnetization axis along the c-axis of the films. With decreasing film thickness the coercivity increases and reaches 10 kOe for the thinnest 2.5-nm film. Magnetoresistance measurements at different angles between the direction of the magnetic field and the easy magnetization axis reveal that Cr2Te3 films show anisotropic magnetoresistance whose out-of-plane values are larger than those of in-plane ones.

Ferrimagnetic compensation and its thickness dependence in TbFeCo alloy thin films

Rare earth (RE)–transition metal (TM) ferrimagnetic thin films have attracted significant interest for their broad range of functionalities associated with the reduced net magnetization. Here, we study the magnetic properties of Tb-based RE–TM ferrimagnetic [Tbx(FeCo)1−x] thin films. We find that the Tb concentration at which the magnetic moments of the RE- and TM- sublattices compensate increases with decreasing film thickness when the films are grown on Pt underlayers. For the thinnest TbFeCo films (1.5 nm-thick), the magnetic compensation is not observed at room temperature, suggesting that the Tb atoms do not contribute to the magnetization. In these thin films, the perpendicular magnetic anisotropy (PMA) increases when a thin Co layer is inserted, while it drops to zero when a thin Tb layer is inserted. Such contrasting behavior reveals that the PMA originates from the Pt/Co interface. The Tb concentration at which magnetic compensation occurs decreases when the underlayer is changed from Pt to Ta. We infer that Tb becomes magnetically inactive due to intermixing with the Pt underlayer, causing the reduction in PMA.

Quantitative and nondestructive determination of residual stress for SiO2 thin film by laser-generated surface acoustic wave technique

The laser-generated surface acoustic wave (SAW) technique is a promising method to measure the mechanical properties of thin films quickly and nondestructively. Residual stress is inevitable during the processing and manufacturing of integrated circuits, which will have a major impact on the physical and mechanical properties of the thin film materials and cause deterioration to the structural strength. In this study, the SAW technique based method is proposed for quantitative and nondestructive measuring the residual stress in the nanostructured films. The method is verified by the experiment measuring the SiO2 films in the thickness range of 100–2000 nm. The experimental procedures, including signal excitation, reception and processing, are described in detail. By matching the SAW experimental dispersion curve with the calculated theoretical dispersion curve containing the residual stress, the residual stress of the SiO2 films along [110] and [100] crystallographic orientation of the Si wafer is successfully quantified. The determination results are ranged from −65.5 to 421.1 MPa and the stress value increases as the film thickness decreases, revealing the residual stress of the SiO2 film is compressive. Meanwhile, the conventional substrate curvature method as a comparison is used to verify the correctness and superiority of the proposed SAW method for the residual stress determination.

Magnetron sputtered yttria stabilized zirconia doped with Mn

8 at. % yttria stabilized zirconia (8YSZ), doped with 0.25 at. % Mn, was deposited on a Si (100) substrate using radio frequency magnetron sputtering. The film was characterized by scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction (XRD). They were used in order to obtain information regarding the composition and uniformity of the samples, determine their crystal structure, and measure the film thicknesses, respectively. In addition, the kinetics of the YSZ phase growth was investigated. Several samples were heat treated for 1 h in air at various temperatures in the range of 750–900 °C, which made it possible to estimate the apparent activation energy of the process. The activation energies were determined by intensity change and thickness variation with temperature. A decrease in film thickness was observed, and the growth of the YSZ phase showed low activation energies of 0.61 and 0.51 eV by thickness and intensity measurements, respectively. As expected, the composition complies with the composition of 8YSZ since the sputtering target was 8YSZ. No XRD shift of peaks was observed relative to undoped 8YSZ, apparently because the concentration of Mn was low.

Analysis and Evaluation of Paint Film Thickness Variation due to Solvent Volatilization Based on Drying Rate Curves

During the drying process of paints, the solvent contained in the paint volatilizes and the film thickness decreases. Since this property is highly dependent on the drying temperature and can affect the quality of the paint, appropriate temperature conditions and film thickness control are required. In this study, a model based on mass transfer theory was developed to calculate the paint film thickness at an arbitrary elapsed time. As a validation test, wet film thickness was measured by a non-contact film thickness gauge and compared with the analytical results. As a result, accurate paint film thickness prediction was achieved by setting appropriate parameters for different drying conditions.

Dependence of reflectance on angular deposition and film thickness of ZnS/Ag nanolayers

This paper presents the spectral reflectance of thermally evaporated ZnS/Ag nanostructures. The coating of ZnS/Ag nanostructures was performed in two steps while varying the film thickness and deposition angle. Silver metal wire (99.99% purity) was heated under vacuum at a pressure of \(2.5 \times 10^{-5}\) mBars and deposited on glass slide substrates in the diffusion pump microprocessor vacuum coater (Edwards AUTO 306). Pieces of zinc sulphide (99.99% purity) were heated and deposited to the glass slides previously coated with silver to form the ZnS/Ag/glass composite. The optical reflectance of the samples was studied by the UV/Vis/NIR spectrometer (Perkin Elmer Lambda 19) with UV-WinLab software. The reflectance was measured at angles of incidence between \(15^o\) and \(75^o\). Spectrophotometric studies showed that reflectance decreased with decrease in film thickness and decreased with increase in deposition angle of silver nanoparticles. The reflectance of ZnS/Ag nanostructures decreased with increase in deposition angle of zinc sulphide.

MAX-Phase Films Overcome Scaling Limitations to the Resistivity of Metal Thin Films

Metal thin films have been widely used as conductors in semiconductor devices for several decades. However, the resistivity of metal thin films such as Cu and TiN increases substantially (>1000%) as they become thinner (<10 nm) when using high-density integration to improve device performance. In this study, the resistivities of MAX-phase V2AlC films grown on sapphire substrates exhibited a significantly weaker dependence on the film thickness than conventional metal films that resulted in a resistivity increase of only 30%, as the V2AlC film thickness decreased from approximately 45 to 5 nm. The resistivity was almost identical for film thicknesses of 10-50 nm. The small change in the resistivity of V2AlC films with decreasing film thickness originated from the highly ordered crystalline quality and a small electron mean free path (11-13.6 nm). Thus, MAX-phase thin films have great potential for advanced metal technology applications to overcome the current scaling limitations of semiconductor devices.