Film Depth Research Articles

Thermally-induced diffusion and structural phase transitions in Pt/Mn and Pt/Mn/Pt thin films

We demonstrate the possibility of diffusion formation of the chemically ordered L1 0-MnPt phase through the vacuum annealing of Pt(24 nm)/Mn(20 nm) and Pt(12 nm)/Mn(20 nm)/Pt(12 nm) layered stacks at 400 °C for 30 min. For the bi-layered stack annealed at 400 °C, the effect of Pt atoms segregation at the film/substrate interface was detected, which remained after annealing even at higher temperatures (500 °C and 600 °C) and prevented the whole homogenization of the chemical composition through the film depth. By contrast, for the tri-layered stack annealed at 400 °C, the presence of the additional Pt bottom layer enabled to change the rate and mechanism of reactive diffusion, leading to homogeneous distribution of components and enhanced crystallinity of the ordered L1 0-MnPt phase compared to the bi-layered sample. An explanation of the obtained experimental data is provided based on the fundamentals of mass transfer theory and its quantitative parameters (e.g. activation energy and diffusion coefficients).

Differential Hall Effect Metrology for Electrical Characterization of Advanced Semiconductor Layers

Semiconductor layers employed in fabricating advanced node devices are becoming thinner and their electrical properties are diverging from those established for highly crystalline standards. Since these properties also change as a function of depth within the film, accurate carrier profiling solutions are required. The Differential Hall Effect (DHE) technique has the unique capability of measuring mobility and carrier concentration (active carriers) through the depth of a semiconductor film. It comprises making successive sheet resistance and sheet Hall coefficient measurements as the thickness of the electrically active layer at a test region is reduced through successive material removal steps. Difference equations are then used to process the data and plot the desired depth profiles. The fundamentals of DHE were established in 1960s. Recently, the adaption of electrochemical processing for the material removal steps, and the integration of all other functionalities in a Differential Hall Effect Metrology (DHEM) tool, has made this technique more practical and accurate and improved its depth resolution to a sub-nm range. In this contribution, we review the development history of this important technique and present data from recent characterization work carried out on Si, Ge and SiGe layers.

Variations of the elemental composition distribution over the thickness of YBa2Cu3O7-δ thin films obtained by pulsed laser deposition from one target

Epitaxial YBa2Cu3O7‒δ (YBCO) films 150-200 and 300 nm thick, respectively, were deposited on SrTiO3 (100) substrates by pulsed laser deposition at different conditions: with and without using the velocity filtration technique. The films have T(R=0) in the range of 77.4 - 87 R(T) depending on the conditions of deposition from one target with YBa2Cu3O6.8 composition. The films contain Zn, Sr, Pd, Ag and Ti impurity elements obtained from the target (a total of no more than 2 at. % ). Data of the film resistance temperature dependences, X-ray phase analysis, analysis of X-ray fluorescence (XRF) spectra and study of the surface relief by SEM methods revealed the nonuniform distributions of impurity and matrix Y, Ba, Cu elements over the film depth. Impurity concentrations near the surface lead to the formation of faceted spiral pyramids on the surface, which probably evolve into large elongated particles according to the Ostwald mechanism. This knowledge is practically important for optimizing pulsed laser deposition technologies and creating 2D instruments and devices for studying physical phenomena.

Monte Carlo calculated absorbed-dose energy dependence of EBT3 and EBT4 films for 5-200 MeV electrons and 100 keV-15 MeV photons.

To use Monte Carlo simulations to study the absorbed-dose energy dependence of GAFChromic EBT3 and EBT4 films for 5-200MeV electron beams and 100keV-15MeV photon beams considering two film compositions: a previous EBT3 composition (Bekerat etal.) and the final composition of EBT3/current composition of EBT4 (Palmer etal.). A water phantom was simulated with films at 5-50mm depth in 5mm intervals. The water phantom was irradiated with flat, monoenergetic 5-200MeV electron beams and 100 and 150keV kilovoltage and 1-15MeV megavoltage photon beams and the dose to the active layer of the films was scored. Simulations were rerun with the films defined as water to compare the absorbed-dose response of film to water, . For electrons, the Bekerat etal. composition had variations in of up to from 5to200MeV. Similarly, the Palmer etal. composition had differences in up to from 5to200MeV. For photons, varied up to and from 100keV to 15MeV for the Bekerat etal. and Palmer etal. compositions, respectively. The depth of films did not appear to significantly affect for photons at any energy and for electrons at energies 50MeV. However, for 5 and 10MeV electrons, decreases of up to in were seen due to stacked films and increased beam attenuation in films compared to water. The up to and variations in for electrons and photons, respectively, across the energies considered in this study indicate the importance of calibrating films with the energy intended for measurement. Additionally, this work emphasizes potential issues with stacking films to measure depth dose curves, particularly for electron beams with energies 10MeV.

Porous-anodic-alumina-templated Ta-Nb-alloy/oxide coatings via the magnetron-sputtering/anodizing as novel 3D nanostructured electrodes for energy-storage applications

The Ta-52 at.%Nb thin alloy films were magnetron sputter-deposited over a low-aspect-ratio nanoporous anodic-alumina template formed in 0.05 M tartaric acid solution at 250 V and modified by the pore-widening technique to enlarge the pores up to ∼500 nm. The alloy coated the pores evenly, thus forming a 3D continuous conducting nanofilm on the template. Partially anodizing the templated alloy in a borate buffer solution of pH 7.5 generated a compact amorphous mixed-oxide anodic film thickening proportionally to the applied voltage. It was revealed that the oxide on the Ta-52 at.%Nb alloy grows with a slower migration of Ta5+ ions relative to Nb5+ ions, resulting in mixing Ta2O5 and Nb2O5 in the film depth and forming a few-nm-thick Nb2O5 outmost layer. The unique migration of Ta4+, Ta3+, Nb4+, and Nb3+ ions is assumed accountable for forming corresponding suboxides in the 3D anodic film in contrast to a flat Ta-52 at.%Nb alloy film used as a reference. The 3D anodic films behave as an n-type semiconductor with a low donor density Nd = ∼2 × 1018 cm−3, appropriate for dielectric applications. An unusual two-layered structure with a sharp electrical interface revealed in the 3D oxide films anodized to 30–130 V, comprising a low-resistivity layer superimposed on the high-resistivity layer, is explained by an immobile negative space charge in the outer film part. The air-annealing at moderate temperatures releases the space charge and transforms the two layers into a high-resistivity single layer having substantially improved dielectric properties and thermostable (up to 250 °C) capacitance of 1.2 μF cm−2 achieved for the film anodized to practical 50 V. The 3D films having up to 4.5 times enlarged effective surface area can be utilized as novel metal/oxide nanostructured electrodes for electrolytic microcapacitors suitable for classical electronic circuits and energy-storage applications.

Van der Waals epitaxial AlGaN/GaN growth on hexagonal BN via two-dimensional N-induced dislocation slip

We demonstrate the epitaxial growth of nitride heterojunction structures on two-dimensional materials. The growth behavior of Al atoms on hexagonal boron nitride (h-BN) involves preferential adsorption and diffusion along the N-top position, considerably improving AlN formation in the early stage of nucleation. Preferential N adsorption enables h-BN to provide a natural N surface for the substrate. Moreover, the natural N surface provided by h-BN can induce three-dimensional island-like order merging of the upper AlN layer, promoting dislocation slip annihilation. The dislocations annihilation depth of GaN films was shortened to 870 nm, resulting in an order of magnitude decrease in the density of screw dislocations to 5.50 × 107 cm−2 and considerable improvement in the performance of HEMT devices on SiC. Therefore, h-BN films can be used as two-dimensional insertion layers to obtain high-quality van der Waals epitaxial nitride films in GaN-based HEMT devices.

Effect of aircraft tire wear on water spray and water displacement drag

During an aircraft taxiing on a water-contaminated runway, the worn tires with shallower grooves will significantly deteriorate the safety of take-off and landing. The hydrodynamics generated by the tire-water-pavement interaction is numerically studied using the coupling method of Smoothed Particle Hydrodynamics and Finite Element Method. By comparing a completely worn tire with a new tire, the effects of tire wear on water spray and water displacement drag are analyzed. With the increasing tire speed and water film depth, the water spray composed of bow wave and side plume increases, and the water displacement drag decomposed of wave- and film-generated components also increases. The effects of tire wear depend on the relative height of tire grooves to the water film depth. For the shallow water film with a depth smaller than the grooves height, the water spray and water displacement drag of new tire is much smaller than those of worn tire, because the groove drainage effect can work very well. While for the deep water film that completely floods the grooves, the water spray and water displacement drag of new tire are similar with those of worn tires, because the groove drainage effect cannot be fully utilized.

A New Water Film Depth Prediction Model for Pavement Surface Drainage

The prediction of the water film depth (WFD) on the road surface can help with road skid resistance research and reduce the risk associated with driving on rainy days. At present, there are many empirical and analytical models based on drainage length, slope, rainfall intensity and other parameters. Considering the influence of road surface runoff and starting from the Reynolds number formula of road surface water flow, a new road surface WFD calculation formula that considers the movement state of laminar water flow is derived. The results show that the changing trends of various parameters in the prediction model (drainage length, rainfall intensity, road slope) affecting WFD are consistent with those of the existing model. It is also found that the initial water film depth, initial speed of rainwater, and rainfall angle have little impact on WFD. The predicted value of the model has a suitable matching degree compared with the classical empirical model, which provides a new approach to the prediction of road water film depth.

Transition of Cu film to Cu2O film through oxygen plasma treatment

Metal–oxide-semiconductor-based thin-film transistors have attracted increasing research attention owing to their wide bandgap and minimal leakage current. However, the prevalent n-type behavior of several oxide semiconductors prompted the exploration of p-type alternatives. Among these, Cu films are promising candidates for different fields. In this study, the effectiveness of oxygen plasma treatment for the transition of Cu films to their p-type oxide semiconductor phase, i.e., Cu2O, was demonstrated with a focus on low-temperature fabrication for future integration in flexible devices. We reported the adjustability of the oxidation depth of a Cu thin film and the effect of oxidation dynamics by controlling the bottom radio frequency power of a high-density plasma system. This novel approach enabled metal-to-semiconductor transitions and modulation of the physical properties of Cu2O thin films by inducing changes in their composition and microstrain. The oxidation dynamics, oxidation depth, crystallinity, and film surface were analyzed. Moreover, the changes in the optical bandgap were determined, with the transition of the Cu (111) phase to the Cu2O (111) phase confirmed as a function of the process time. As oxidation progressed, particles formed on the surface of the Cu2O thin film and the particle size increased. Further, the oxidized Cu thin film was determined to be Cu2O rather than CuO. Therefore, oxygen plasma treatment is expected to be a new approach to low-temperature oxidation.

Unprecedented Spatial Manipulation and Transformation of Dynamic Thermal Radiation Based on Vanadium Dioxide.

Reconfigurable infrared (IR) materials have widespread applications in thermal management and smart IR concealment. Although various reconfigurable IR materials can be customized by positive or negative differential VO2-based resonators, their insightful mechanism remains unknown. Here, we comprehensively investigate the fundamental design rule of reconfigurable thermal radiation between positive and negative differential thermal radiation properties for the first time. Importantly, the skin depth of VO2 film in the metal state is investigated to clarify the transformation from positive to negative differential thermal radiation properties, and the critical thickness is further derived, providing important guidance in designing the reconfigurable thermal radiation regulator. Furthermore, the reconfigurable multistate thermal images had been presented into one plate. The resulting emittance variation (△ε8-14μm) of the VO2-based resonator can change from 0.61 to -0.53, which consummates the ability for diverse demands such as infrared concealment, thermal illusion, and thermal management. This work constitutes a promising and universal route toward designing whole smart devices and may create new scientific and technological opportunities for platforms that can benefit from reconfigurable electromagnetic manipulation.

Simulation of Water Flow Path Length (WFPL) and Water Film Depth (WFD) for Wide Expressway Asphalt Pavement

This paper simulates actual rainfall conditions and raindrops flowing to form a water flow path (WFP) on the pavement surface of the wide expressway. Then, the different linear combination conditions, including longitudinal slope (LS), transverse slope (superelevation, TS), gradual change rate of TS, and pavement width (PW), were simulated and analyzed. The results show that (1) the influence of each linear index on the maximum water film path length (WFPLmax) and maximum water flow depth (WFDmax) differs (according to the absolute values of Beta, LS has the greatest influence on WFPLmax, and PW has the greatest influence on the WFDmax for both straight-line and circular-curve sections); (2) when the design value of LS is between 1.1% and 4%, the WFDmax can be effectively reduced by lowering the value of LS; (3) in the case of a high design value of LS, it can be considered to increase the TS of the pavement arch from 2% to 2.5% to effectively reduce the WFPLmax, and the wider PW, the better the reducing effect; (4) while widening the expressway, adjusting the TS from 2% to 2.5% can effectively offset the increasing effect of PW on the WFDmax. This research aims to fill the research gap in the simulation of runoff characteristics of wide expressway asphalt pavements and to improve the alignment design of expressways from the drainage perspective for the improvement of driving safety.

Prediction of water film depth on grooved airport runway induced by intense rainfall and wind

The runway water film depth (WFD) and its drainage have direct impact on hydroplaning risk and, consequently, aircraft operational safety. Understanding its relationship with weather and runway conditions can help manage such risk due to WFD. Thus, this study develops an empirical formula to correlate runway risk area with its influencing factors using a dataset generated by a comprehensive rainfall-runoff dynamic model. The model incorporates a wind speed induced stress and is validated with physical experiment collected data. The simulation and observation showed good agreement, verifying the model's capability to reasonably well simulate the WFD distribution on intricate grooved surfaces at the millimetre level, with the consideration of wind effects. Then, this study performs 456 numerical experiments at the lateral prototype scale considering various rainfall intensity, wind speed, runway deterioration area, and groove depth. The impact of these factors on the peak WFD and the runway risk area is quantitatively analysed. The proposed empirical formula and developed dynamic model enables accurate assessment and prediction of the runway risk area under extreme weather conditions for better management of potential hydroplaning.

The Mir-1 and Mir-2 Submersibles in Feature Films

Abstract This article considers the methods of capturing deep ocean images with deep manned submersibles Mir-1 and Mir-2 (6,000-m depth) for feature films. The filming of Titanic by IMAX (Stephen Low) and Lightstorm Entertainment (James Cameron) companies with the use of deep ocean technique was pioneering work. The problems, which were solved during filming, as well as the development of special equipment are discussed.

Study on tribology and cutting performance of boron doped diamond composite coated tool

Microcrystalline diamond (MCD), nanocrystalline diamond (NCD), boron doped microcrystalline diamond (BDMCD), and boron doped microcrystalline-nanocrystalline diamond (BDM-NCD) films were prepared by hot filament chemical vapor deposition (HFCVD) technique. Scanning electron microscopy (SEM), Raman spectroscopy and Rockwell indention testes were used to characterize the microstructure and properties of the coatings, and friction experiments were carried out to study the tribological properties of diamond films and GCr15 steel balls under different lubrication conditions. At the same time, the cutting performance of different diamond coated tools was studied by cutting 30% SiCp/Al composites. The results show that the residual compressive stress of the NCD film is the largest, which is −1.88 GPa. Due to the mitigation effect of the underlying BDMCD film, the BDM-NCD film has the smallest residual stress, which is −0.37 GPa. It can be seen from the friction test that the average coefficient of friction of NCD film is lower than that of MCD film due to the smooth surface. The average friction coefficient of BDM-NCD film is the lowest, which is 0.326. At the same time, the wear resistance of BDM-NCD film is the best, and the value is 0.53×10−6 mm3/Nmm. From the wear morphology, it can be seen that the amount of metastatic material adhered to the wear surface of the diamond films is less under water lubrication than under dry friction condition. Compared with dry friction, the wear scar depth of BDM-NCD film under water lubrication is smaller, showing the better tribological properties. Cutting experiments show that BDM-NCD film has the best wear resistance and the best cutting performance.

Designing FeCr0.7NiCu0.5Ti0.5 high-entropy alloy doped with rare earth yttrium: Effects on microstructure and passive film

After constant potential passivation (CPP), the effect of rare earth yttrium (Y) on the corrosion resistance of the passive film on the surface of FeCr0.7NiCu0.5Ti0.5 alloy in H2SO4 was investigated. The results manifested that when Y content exceeded 0.04, the microstructure of Ni3Ti transformed into Cu5Y phase, and gradually expanded with the addition of Y. XPS etching analysis of passive film composition with changing etching depth and cyclic polarization analysis of passive film pitting corrosion sensitivity are two methods used to assess the corrosion resistance of alloy. Compared with FeCr0.7NiCu0.5Ti0.5 alloy and FeCr0.7NiCu0.5Ti0.5Y0.06 alloy, the passivation current density after CPP reduced from 5.682 × 10−3 to 4.630 × 10−4 A/cm2. With the addition of Y, the protection and density of the passive film was enhanced, resulting in an improvement in the corrosion resistance of the alloy. The pitting corrosion behavior was related to the changes in inclusion content and morphology caused by Y, and rare earth was advantageous to boost the passivation capability of FeCr0.7NiCu0.5Ti0.5 series alloy.

Self-assembly behavior of fluorinated amphiphilic copolymer in aqueous solution and its properties in the solid film state

Owing to the high electronegativity of fluorine atoms, incorporation of fluorinated moieties in a polymer can confer unique properties such as low surface energy and self-assembling ability in solution. In this study, a series of amphiphilic copolymers were prepared by radical polymerization using three monomers: 2-((2,3,3,3- tetrafluoro- 2- (1,1,2,3,3,3- hexafluoro −2- (perfluoroethoxy) propoxy) propanoyl)oxy) ethyl acrylate (FHEMA), maleic anhydride (MAH), and acrylic acid (AA). The PFHEMA block provided low surface tension, and the MAH and AA blocks (containing carboxyl) increased solubility. The properties of the polymer (PFHEMA-co-PMAH-co-PAA) can be regulated by changing the PFHEMA length. Characterization by Fourier-transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC) indicated successful polymerization (FHA01 and FHA02). When the FHEMA/MAH/AA molar ratio was 3:8:9 (FAA02), the surface tension of the hydrolyzed amphiphilic copolymers FAA02 at 300 mg·mL−1 in aqueous solution was 15.76 mN·m−1, the lowest value due to a higher fluorine content than FAA01. FAA02 self-assembled in water to form pH-sensitive micelles with diameters greater than 140 nm. For the FAA02 film, both the F/C ratio and arrangement of fluorine-containing side chains decreased with increasing film depth. Thus, this type of fluorine-containing low surface free energy material can be developed into a high performance coating material.

Hydrophobic-Hydrophilic Block Copolymer Mediated Tuning of Halide Perovskite Photosensitive Device Stability and Efficiency.

The polymer additive strategy provides a facile and cost-effective way for passivating defects and trap sites at the grain boundaries and interfaces and acting as a barrier against the external degradation factors in perovskite-based devices. However, limited literature exists discussing the integration of hydrophobic and hydrophilic polymer additives in the form of a copolymer within the perovskite films. The inherent difference in the chemical structure of these polymers and their interaction with perovskite components and the environment leads to critical differences in the respective polymer-perovskite films. The current work utilizes both homopolymer and copolymer strategies to understand the effect of polystyrene (PS) and polyethylene glycol (PEG), two common commodity polymers, over the physicochemical and electro-optical properties of the as-fabricated devices and the distribution of polymer chains across the depth of perovskite films. The hydrophobic PS integrated perovskite devices PS-MAPbI3, 36 PS-b-1.4-PEG-MAPbI3, and 21.5 PS-b-20-PEG-MAPbI3 outperform hydrophilic PEG-MAPbI3 and pristine MAPbI3 devices and exhibit higher photocurrent, lower dark currents, and greater stability. A critical difference is also observed in the stability of devices, where rapid decay of performance is observed in the pristine MAPbI3 films. The deterioration in performance is highly limited for hydrophobic polymer-MAPbI3 films as they maintain 80% of their initial performance.

An integrated analytical model for friction characteristics of aircraft tire on wet runway pavement

The challenging issues of tire-water-pavement interaction are to determine the deformed tire profile and the effective tire-pavement contact length due to water intrusion. This study aims to develop an integrated analytical model to analyze friction characteristics of an aircraft tire on wet runway pavement. The tire-water-pavement interaction model consists of the Brush model for tire-pavement contact and the flexible ring model for tire deformation with consideration of hydrodynamic force. The feasible contact footprint and the deformed tire profile are solved using an interactive process between two models. The model shows the ability to predict friction coefficients at various tire loading, velocity, slip ratio, and water conditions. The thicker water film depth causes the reduction of tire-pavement contact length and the increases of hydrodynamic force, resulting in poor skid resistance of pavement. The calculated friction coefficients at different velocities are further used to predict hydroplaning speed and calculate braking distance of aircraft tire. The results demonstrate the significant effect of water depth on the risk of aircraft hydroplaning and overrun on runway pavement.

Oxide Film Formation on Stainless Steel 304L by Anodizing Method with Different Power Sources

In order to generate a nanoporous oxide film, stainless steel 304L is anodized using an alternating current (AC) and direct current (DC) source in an ethylene glycol solution containing ammonium fluoride, NH4F, and water, H2O. This study focuses on the differences between AC and DC anodizing in terms of current density versus time response, thickness, and depth of the oxide film formed on the anodized specimens, surface roughness, and element composition of the specimens because there is limited study on AC anodizing of stainless steel. In 0.5% 0.3M NH4F and 3% H2O in a glycol solution, the AC and DC anodizing is conducted for 30 minutes at voltages ranging from 30 V to 50 V and 21.2 V to 35.4 V, respectively. The current density versus time response revealed that AC anodizing produced more current density than DC anodizing. As for the thickness and depth of the generated oxide films, only the specimens that had been anodized in AC indicated an increase in these films, whereas specimens that had been anodized in DC showed the metal dissolving as the specimens degraded. The surface roughness of AC anodized specimens reduced with increasing anodizing voltage, whereas DC anodized specimens increased with increasing anodizing voltage. The element composition of the anodized specimens revealed that the mass percentage of oxygen, O element is higher for AC anodized specimens compared to DC specimens. This suggests that AC anodizing on stainless steel might offer important advantages and should be further researched.

Dynamic Propagation Depth in Substrate-Supported Polymer Films: A Molecular Dynamics Simulation

The properties of substrate-supported polymer films are strongly related to the properties of the substrate. This work studies the dynamic propagation depth of the substrate effect in polymer films using molecular dynamics simulations. From the layer-resolved diffusion of polymer chains, the dynamic propagation depth of the substrate effect into nonadsorbed chains λdyn is estimated to be about 2.3Rg (Rg is the radius of gyration of polymers in the bulk) and 3.5Rg for the weakly and strongly attractive substrates, respectively, much larger than the thickness of the adsorbed layer hads ≈ 1.2Rg. The dynamics of adsorbed and nonadsorbed polymers located below λdyn strongly depend on the substrate attraction strength. Our results reveal that the influence of substrate on the nonadsorbed polymer chains comes mainly from the tails of adsorbed chains and provides new insights into the molecular mechanism of the propagation of the substrate effect in polymer films.