Film Profile Research Articles

Synthesis of the Autocorrelation Function for Solving the Thin Film Reflectometry Inverse Problem

A method is proposed to estimate (using the autocorrelation function (ACF)) the thickness of layers determining the electron density profile of a thin film. The method does not require additional conditions and is applicable to an arbitrary reflectivity curve. It is based on the ACF synthesis by a superposition of Gaussians, whose parameters are related to the characteristics of the film layers and interfaces. The potential of this method is demonstrated by a number of model examples.

Surface Profile of Polystyrene Film on the QCM sensor Deposited by Ultrasonic Atomizer Spray Coating

A study of polystyrene polymer pattern onto the QCM produced using ultrasonic spray coating was presented. The patterned polymer coating was expected to be produced using the ultrasonic spray coating. The form of the 3D structure of the coating was observed using non-contact profilometer. The damping of the coating to the QCM sensor was measured through the minimum electrical impedance of the sensor. The impedance measurement performed on the specimens showed that some spray parameter gave a mechanical damping effect on the sensor. It was known that only the well-controlled operating conditions result in the formation of the pattern.

Clinical Evaluation of a Two-dimensional Liquid-Filled Ion chamber Detector Array for Verification of High Modulation Small Fields in Radiotherapy.

Introduction:Clinical evaluation of a two-dimensional (2D) liquid-filled ion chamber detector array used in the verification of highly modulated small beams of stereotactic body radiation therapy (SBRT) has been conducted.Materials and Methods:Measurements with the Octavius 1000 SRS (PTW, Freiburg, Germany) detector with 977 liquid-filled ion chambers were compared against EDR2 film and PTW Octavius Seven29. The performance of detector array has been evaluated on ten SBRT patient plans. Dose profiles of individual and composite fields' calculated using Pinnacle3 treatment planning system were compared against measurements with Octavius 1000 SRS detector array, EDR2 film, and Octavius Seven29 detector. Gamma index and profile comparison were used in the evaluation and assessment of the detector's performance.Results:The Gamma index measurements show agreement between Pinnacle3 computations and Octavius 1000 SRS array, PTW Octavius Seven29, and EDR2 film for >90% of the points using 2%, 2 mm tolerance criteria. Profiles obtained with the Octavius 1000 SRS were in agreement with the EDR2 film profiles, demonstrating the detector's superior sampling rate.Conclusions:The Octavius 1000 SRS is a dosimetrically accurate device to perform quality assurance checks in SBRT treatments. The broad range of measurements performed in this study quantified the dosimetric accuracy of Octavius 1000 SRS detector in the clinical setup of the small fields in radiotherapy.

A Spectral Finite Difference Method for Analysis of a Fluid-Lubricated Herringbone Grooves Journal Bearing under a Special Case at Rectangle Groove

A spectral difference method is applied to get numerical solutions for a fluid-lubricated herringbone grooved journal bearing with trapezoidal grooves by previous work of the authors. However, an inexpedience in which Fourier series of the film profile does not converge at jump points of groove start or groove end in the case of rectangle groove was still remained. In the paper, an inexpedience of numerical analysis under a special case at rectangle groove is challenged to solve. As a result, for compensation of which Fourier series does not converge at jump points in a special case of rectangle groove, Fourier coefficient of fluid film thickness is proposed as taking the limit of which in a case trapezoidal groove at trapezoidal angle approaches 0.

Dry etching of copper thin films in high density plasma of CH3COOH/Ar

Inductively coupled plasma reactive ion etching of copper thin films patterned with SiO2 masks was carried out using CH3COOH/Ar gas. The etch rate, etch selectivity to SiO2 mask, and the etch profiles of copper films were examined. The evolution study of the etch profile as a function of gas concentration and etch depth revealed the etch sequence and etch mechanism. In the optimized CH3COOH/Ar gas, the systematic approach on the etch characteristics of copper films was performed by changing the etch parameters including inductively coupled plasma (ICP) rf power, dc-bias voltage to substrate, and process pressure. As the ICP rf power and dc-bias voltage increased and the process pressure decreased, the etch rate increased and the etch profile improved. X-ray photoelectron spectroscopy was used to determine the etch mechanism in CH3COOH/Ar gas. Finally, the etching of copper films in the CH3COOH/Ar was achieved with good etch profile with a high degree of anisotropy.

Surface-tension- and injection-driven spreading of a thin viscous film

We consider the spreading of a thin viscous droplet, injected through a finite region of a substrate, under the influence of surface tension. We neglect gravity and assume that there is a precursor layer covering the whole substrate and that the rate of injection is constant. We analyse the evolution of the film profile for early and late time, and obtain power-law dependencies for the maximum film thickness at the centre of the injection region and the position of an apparent contact line, which compare well with numerical solutions of the full problem. We relax the conditions on the injection rate to consider more general time-dependent and spatially varying forms. In the case of power-law injection of the form$t^{k}$, we observe a switch in the behaviour of the evolution of the film thickness for late time from increasing to decreasing at a critical value of$k$. We show that point-source injection can be treated as a limiting case of a finite-injection slot and the solutions exhibit identical behaviours for late time. Finally, we formulate the problem with thickness-dependent injection rate, discuss the behaviour of the maximum film thickness and the position of the apparent contact line and give power-law dependencies for these.

Structural effects in partially-wetting thin evaporating liquid films near the contact line

Evaporating thin liquid films at triple-phase lines play important roles in phase-change processes. Many researchers have tried to model a steady one on an isothermal surface using continuum mathematical models. Usually they choose to solve the profile from a nanoscale position where the film thickness is slightly larger than the adsorbed film. This position is vaguely defined and due to the lack of experimental information, assumptions have to be made about the initial film profile especially the slope and curvature. In the present work, we apply the boundary conditions at the microscale and solve the film profile back through the nanoscale. The vagueness and assumptions are therefore avoided. To achieve comprehensive description for the very thin part near the adsorbed film, the structural force component and the short-range Born repulsion component are included in the disjoining pressure expression besides the dispersion component. We try out five different forms of dispersion components and five different forms of structural components. It is found that only when dispersion component, short-range Born repulsion component, and one specific form of structural component are working together, a complete film profile from microscale to nanoscale can be obtained including the thin film beyond the apparent contact line, and the obtained profile is qualitatively consistent with the most recent experimental report. The results indicate that an oscillatory structural force of exponential decay dominates when the film thickness is between 2 and 25 molecular diameters.

Concentric ripples of lubrication film in electrowetting

When a water drop approaches a solid surface in an ambient oil environment, a thin oil film will be formed between the drop and the solid surface. The lubrication film presents more complex behaviors when the external electrical field varies discretely, and in this work, concentric ripples are found in the thin film under a series of voltage steps, which is obviously different from the film profile when the applied voltage is continuously increased. According to the time evolution of the thin film, each voltage step adds a new concentric ripple outside the existing lubrication film. The radial wavelength and the maximum height of each ripple are revealed to have a linear relationship with the amplitude of the corresponding voltage step. The ripples finally break into microscopic oil droplets, and the size and the number of the droplets can be predicted with the diameter and the radial wavelength of each ripple.

A quantitative evaluation of inorganic boundary films formed in engine oils by TOF‐SIMS depth profiling with low energy Cs sputtering

Quantitative evaluation of lubrication boundary films was investigated by time‐of‐flight secondary ion mass spectrometry depth profiling with low energy Cs sputtering. Relative sensitivity correction coefficient (RSC) for calcium phosphate, calcium carbonate, or calcium sulfate was determined by measuring the pellets of the mixture of these compounds. The RSCs for the three calcium salts varied with measurement conditions such as sputter energy and primary ion species. By using the RSC determined in this investigation, the depth profiles of the boundary films formed in real engine oil were corrected to quantitative profiles. The difference of structures between two lubrication boundary films on the different substrate materials formed in the same engine oil was clarified.

Growth of epitaxial bismuth ruthenate pyrochlore films on yttria-stabilized zirconia (YSZ) and YSZ-buffered Si substrates by metal–organic chemical vapor deposition

Bismuth ruthenate (Bi2Ru2O7) thin films were deposited on (111) yttria-stabilized zirconia (YSZ) single crystals and (111)YSZ//(111)Si substrates by chemical vapor deposition using Bi(CH3)2[2-(CH3)2NCH2C6H4] and Ru(C7H11)(C7H9) as source materials and oxygen as a reactant gas. The film composition and X-ray diffraction ω-2θ scan profiles for thin films deposited using various source flow rate ratios revealed the existence of a process window to obtain stoichiometric Bi2Ru2O7. Within the process window, the kind of substrates did not strongly affect the deposition rates of Bi and Ru or the Bi/Ru ratio of the deposited films. It was also confirmed that the Bi2Ru2O7 thin films grew epitaxially on both substrates within the process window. In particular, epitaxial Bi2Ru2O7 thin films grew on the Si substrate with a YSZ buffer layer. Scanning electron microscopy revealed the formation of continuous dense Bi2Ru2O7 films without any cracks or voids, and a relatively smooth interface between Bi2Ru2O7 and the YSZ buffer layer on Si. The resistivity of the Bi2Ru2O7 films was almost constant (~550 and ~950 μΩcm for the films deposited on (111)YSZ single-crystal substrates and (111)YSZ//(111)Si substrates, respectively), even when the ratio of Bi and Ru source gas flow rates was changed in the process window. In addition, the resistivity of Bi2Ru2O7 films prepared on both kinds of substrates was almost independent of temperature from 10 to 300 K.

Transition metal based CuxNiyCoz-x-yO4 spinel composite solar selective absorber coatings for concentrated solar thermal applications

Solar selective absorber coatings, combining of nanostructured, ternary transition metal spinel structure and composite oxides were prepared by a series of transition metal (Co, Ni and Cu) based nitrate salts. A single-layered structure of crystalline phase spinel-type oxide AB2O4 in the framework of simple wet chemical route and dip coating method was prepared in the crystalline structure of CuxNiyCoz-x-yO4. The X-ray diffraction profile of the oxide film was found to coincide with that of crystalline [Cu2+0.31Co3+0.16Co2+0.53]A[Cu2+0.17Ni3+0.16Co3+1.67]BO4 in the ICDD database. Precursor salts were heated at a particular temperature to form hydroxy nitrate solution followed by suitable solvent with different binders to form adherent sol for dip coating technique. By optimizing sol concentration, withdrawal speed and annealing temperature, uniform absorber layer with solar absorptance of 0.91 and emittance of 0.14 were achieved in a single layer coating with a composite oxide formation. The optical, structural and morphological properties of the optimized coatings of single layer CuxNiyCoz-x-yO4 spinel and composite oxide have been characterized by UV–Vis–NIR spectrophotometer, emissometer, X-ray diffraction, field emission - scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy.

Investigation on the surface layer formed during electrochemical modification of pure iron

This paper presents an experimental and analytical investigation on electrochemical modification of pure iron, aiming to obtain a surface layer which has good machinability for further processing. The microstructures of the modified layer were compared from a relative low current density (10 A/cm2) to high current density (30 A/cm2) and characterized by various detection equipment. A detailed X-ray photoelectron spectroscopy (XPS) analysis was conducted to measure the composition profile of the black film on the modified layer. The results show that, during electrochemical modification, the subsurface formed a loose porous layer covered with a flimsy oxide. At low current density, uniform dissolution was obtained and the surface was not corroded off completely. However, at large current density, due to the strong electrochemical action and uneven flow field, the cross section of pure iron became waved and the surface shape deteriorated. The results of the water contact angle measurements show that the surface hydrophilicity was enhanced by electrochemical modification, which might improve the cooling effect of the machining region. The XPS analysis indicated a bi-layer structure of oxidation film on the modified layer and the outmost Fe3+ species layer was considered to be the oxidation of Fe2+ species from inner layer.

Design, fabrication, and validation of patient-specific electron tissue compensators for postmastectomy radiation therapy.

Background and purposePostmastectomy radiotherapy (PMRT) is complex to plan and deliver, but could be improved with 3D-printed, patient-specific electron tissue compensators. The purposes of this study were to develop an algorithm to design patient-specific compensators that achieve clinical goals, to 3D-print the planned compensators, and validate calculated dose distributions with film and thermoluminescent dosimeter (TLD) measurements in 3D-printed phantoms of PMRT patients.Materials and methodsAn iterative algorithm was developed to design compensators corresponding to single-field, single-energy electron plans for PMRT patients. The 3D-printable compensators were designed to fit into the electron aperture, with cerrobend poured around it. For a sample of eight patients, calculated dose distributions for compensator plans were compared with patients’ (multi-field, multi-energy) clinical treatment plans. For all patients, dosimetric parameters were compared including clinical target volume (CTV), lung, and heart metrics. For validation, compensators were fabricated and irradiated for a set of six 3D-printed patient-specific phantoms. Dose distributions in the phantoms were measured with TLD and film. These measurements were compared with the treatment planning system calculated dose distributions.ResultsThe compensator treatment plans achieved superior CTV coverage (97% vs 89% of the CTV receiving the prescription dose, p < 0.0025), and similar heart and lung doses (p > 0.35) to the conventional treatment plans. Average differences between calculated and measured TLD values were 2%, and average film profile differences were <2 mm.ConclusionsWe developed a new compensator based treatment methodology for PMRT and demonstrated its validity and superiority to conventional multi-field plans through end-to-end testing.

Simultaneous Measurement of Isotope-Free Tracer Diffusion Coefficients and Interdiffusion Coefficients in the Cu-Ni System

A new formalism recently developed by Belova et al., based on linear response theory combined with the Boltzmann–Matano method, allows determination of tracer and interdiffusion coefficients simultaneously from a single, isotope-free, traditional diffusion couple experiment. An experimental methodology with an analytical approach based on the new formalism has been carried out using the model Cu-Ni system to effectively determine tracer diffusion coefficients from an isotope-free diffusion couple experiment. Cu thin films were deposited in between several binary diffusion couples with varying terminal alloy compositions (Cu-25Ni, Cu-50Ni, Cu-75Ni, Ni). Diffusion couples were annealed at 800, 900 and 1000 °C, and the superimposed concentration profiles of thin film and interdiffusion were analyzed for the simultaneous determination of tracer and interdiffusion coefficients. Processed concentration profiles obtained from the diffusion experiments were also fitted with simple Gaussian distribution function. Results were compared to existing literature data obtained independently by radiotracer experiments, and an excellent agreement has been observed.

Stability and collapse of holes in liquid layers

We investigate experimentally and theoretically the stability and collapse of holes in liquid layers on bounded substrates with various wettabilities. It is shown that for a liquid layer with a thickness of the order of the capillary length, a stable hole exists when the hole diameter is bigger than a critical value $d_{c}$. Consequently, a further increase of the liquid volume causes the hole to collapse. It is found that$d_{c}$increases with the size of the container, but its dependence on the contact angle is very weak. The experimental results are compared with theory, and good agreement is obtained. Moreover, we present investigations of the dynamics of the hole and the evolution of the liquid film profile after the collapse. The diameter of the hole during collapse and the minimum thickness of the liquid film shortly after the collapse obey different power laws with time. Simple theoretical models are developed which indicate that the collapse of the hole is triggered by surface tension and the subsequent closure process results from inertia, whereas the growth of the liquid column after hole closure results from the balance between the capillary force and inertia. Corresponding scaling coefficients are determined.

Surface and chemical characterization of ZnO:Eu3+/Yb3+ spin coated thin films using SEM-CL and TOF-SIMS

The morphological properties of sol-gel spin coated ZnO:Eu3+(1 mol%)/Yb3+(7 mol%) thin films grown on Si(100) substrates are reported. The surface composition analysis of the ZnO films were investigated by using field emission scanning electron microscopy and time-of-flight secondary ion mass spectroscopy (TOF-SIMS). TOF-SIMS was used to obtain depth profiles of the ZnO thin films at various features that formed on the surface during spin coating of the thin films. The films were also annealed at 1000 °C in order to determine if there was any inter-mixing of the Si substrate and the ZnO thin film when it was annealed. Two and three-dimensional (2D and 3D) depth profiles after annealing in both the positive and negative modes were measured. Analysis of the 3D images showed different features on the surface that appeared to be artificially embedded in the substrate, due to the experimental measuring setup of the TOF-SIMS. The details of these features are discussed. Inter-diffusion at the film/substrate was clear from the 3D profiles.

Study of the Effective Refractive Index Profile in Self-Assembling Nanostructured ITO Films

The optical characteristics and structural features of self-assembling nanostructured indium–tin oxide (ITO) films deposited onto substrates heated above 400°C are studied. Estimations of the distribution profiles of the material and effective refractive index in the films under study are obtained by computer simulation of a medium having spectral dependences of light transmission and reflection coefficients closest to those observed in the experiment. These results are in good agreement with scanning electron microscopy data for these films and make it possible to not only confirm the gradient character of such coatings but also restore some of its features. The further overgrowth of voids in self-assembling nanostructured films by means of the deposition of an additional material amount by magnetron sputtering at room temperature leads to a variation in the effective refractive index profile in them. Thus, it is possible to form transparent conductive films with an efficient refractive index profile adjusted for specific tasks. Adjustment of the refractive index profile in self-assembled ITO films acquires a special value for designing coatings with specified properties by virtue of a limited set of transparent conductive materials.

Kilovoltage transit and exit dosimetry for a small animal image-guided radiotherapy system using built-in EPID.

We investigated the potential use of the built-in electronic portal imaging device (EPID) in the small animal radiation research platform (SARRP) as a dosimeter in the kV energy range. To this end, we developed a method for converting portal images to a two-dimensional (2D) dose maps at the detector plane and object's exit surface and validated them against empirical dose measurements. We calibrated the SARRP's EPID to measure transit dose. The transit dose map was back-projected to calculate 2D dose distribution at the object's exit surface. The accuracy of transit and exit dose distributions was independently validated with a PinPoint ion chamber (IC) and Gafchromic EBT3 film measurements for a range of radiation dose rates (0.43-2.78 cGy/s), cone sizes (5-40 mm), in a homogeneous phantom of varying thickness (0-50 mm) and in an inhomogeneous phantom containing graphite, cork, air, and aluminum. In-air central axis (CAX) transit dose values measured with the EPID showed close agreement with film and IC measurements. The maximum differences in EPID in-air transit measurements with film or IC measurements were 1%. The EPID was capable of accurately measuring phantom transit dose independently of the attenuating phantom thickness, with average discrepancies of 0.5% and 2.9% with IC and film, respectively, where the maximum difference between the EPID and the IC was 1.8%. The results were slightly worse for film, with maximum differences in 4.9%. Output factor measurements using EPID were within 2.9% of both IC and film measurements. In addition, calculated exit doses agreed with film values within ≤3.1%, for attenuating phantom thicknesses ≥15 mm. The agreement became worse with decreasing phantom thickness; for thicknesses of 10 and 5 mm, agreements were ≤5.7% and ≤6.9%, respectively. Compared to film, transit and exit profiles measured with the EPID showed average differences <2% for both homogeneous and inhomogeneous materials. We developed and validated a novel 2D transit/exit dosimetry for a kV SA-IGRT system using an EPID. We verified the accuracy of our method to measure EPID transit and exit dose distributions for a range of dose rates, beam attenuation, and collimation. Our results indicate that the EPID can be used as a simple, convenient device for kV dose delivery verification in small animal radiotherapy.

Etch characteristics of copper thin films in high density plasma of CH4/O2/Ar gas mixture

Inductively coupled plasma reactive ion etching of copper thin films patterned with SiO2 masks was performed using CH4/O2/Ar gas mixture. The etch characteristics of copper films in CH4/Ar and O2/Ar gases were examined to determine the roles of CH4 and O2, respectively. The etch rates and etch profiles of copper films were investigated by varying the O2 concentration in CH4/O2/Ar gas mixture. In the optimized CH4/O2/Ar gas mixture, systematic etching of copper films was performed by changing the etch parameters, including ICP RF power, DC-bias voltage, and process pressure. As the ICP RF power and DC-bias voltage was increased and the process pressure was decreased, the etch rate increased and the etch profile improved. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy were used to determine the etch mechanism in the CH4/O2/Ar gas mixture. Finally, the etching of copper films in the optimized CH4/O2/Ar gas mixture was successfully achieved with good etch profile with a high degree of anisotropy.

Probing Boundary Conditions at Hydrophobic Solid-Water Interfaces by Dynamic Film Drainage Measurement.

A newly developed dynamic force apparatus was used to determine hydrodynamic boundary conditions of a liquid on a hydrophobic silica surface. For a given approach velocity of bubble to solid surfaces in an electrolyte solution, a reduced dimple formation and faster film drainage were observed by increasing the hydrophobicity of silica surfaces, indicating a significant change in hydrodynamic boundary conditions of water molecules from an immobile to a mobile water-hydrophobic silica interface. By comparing the measured film profiles with the predictions from the Stokes-Reynolds-Young-Laplace model, the slippage boundary condition of water on the hydrophobic silica surface of surface nanoroughness was quantified. Increasing the surface hydrophobicity was found to increase the mobility of water in the thin liquid film, promoting faster drainage of the liquid. For a given hydrophobicity of solids, the mobility of water occurred only above a critical bubble approach velocity and increased with increasing bubble approach velocity. In contrast, similar experiments with hydrophobized mica surfaces showed no-slip boundary condition of water at the molecularly smooth hydrophobic surface. The results collectively suggest that the observed mobility of water with more than 100 nm in thickness on the studied hydrophobic silica surfaces was due to the nanoroughness of hydrophobic surfaces. Such finding sheds light on one possible way of reducing the friction of water on hydrophobic solid surfaces by creating nanostructured surface of nanoroughness.