Changes In Film Density Research Articles

The Influence of B4C Film Density on Damage Threshold Based on Monte Carlo Method for X-ray Mirror.

The uniformity and consistency of X-ray mirror film materials prepared by experimental methods are difficult to guarantee completely. These factors directly affect the service life of free electron laser devices in addition to its own optical properties. Therefore, the quality of the film material, especially the density, has a critical effect on its application. Boron carbide film and monocrystalline silicon substrate were suitable examples to explore their influence of density on the damage threshold based on Monte Carlo and heat-conduction methods. Through simulation results, it was found that the change in film density could affect the energy deposition depth and damage threshold. When the film density was 2.48 g/cm3, it had relatively high damage threshold in all energy ranges. And then the specific incident parameter for practical application was investigated. It was found that the damage mechanism of the B4C/Si was the melting of the interface. And the damage threshold was also higher with the film density of 2.48 g/cm3. Therefore, it was recommended to maintain the density at this value as far as possible when preparing the film, and to ensure the uniformity and consistency of the film material.

Band gap narrowing induced by oxygen vacancies in reactively sputtered TiO2 thin films

Amorphous TiO2-x thin films were deposited using direct current reactive magnetron sputtering. It was possible to tune the defect concentration by controlling the oxygen flow rate during the deposition process. The operating deposition regime has a significant influence on the properties of the TiO2-x film. The refractive index was found to decrease with increasing oxygen flow rate, which was essentially related to changes in film density. Besides this, increasing the oxygen vacancy defect concentration induced a slight decrease in the optical bandgap, as well as widening of the defect's Urbach band tails near the conduction band edge. For TiO2-x films deposited in oxygen-deficient conditions, the decrease in optical bandgap and widening of Urbach tails induced the shift of the Fermi level towards the conduction band, which enhanced the concentration of the charge carriers.

Thermo-optical properties and measurements of electronic polarizability coefficients of annealed tungsten bronzes without and within an oxygen plasma environment

WO3 thin films evaporated on unheated substrates were found to be substoichiometric and microcrystalline in nature as found by the ellipsometric studies, density, and porosity measurements. In this investigation, we measured the optical constants of WO3 thin films and of MxWO3 (M = H + , Li + , and Na + ) bronzes (with different concentrations, x) after being annealed at different temperatures over the range 298 to 453 K without and within an oxygen plasma environment using manual ellipsometry. It was found that the changes in film density and porosity of WO3 thin film when annealed at the temperature 413 K (without oxygen plasma) were not more than 3% and 12%, respectively, from the room temperature data. The thermo-optic coefficient (TOC) and electronic polarizability coefficient of WO3 thin film increased from 1.064 × 10 − 4 to 5.73 × 10 − 4 K − 1 and 0.1 × 10 − 26 to 0.3 × 10 − 26 cm3 K − 1, respectively, as a result of annealing the film at 413 K for 24 h. The samples HxWO3 (x = 0.172) and LixWO3 (x = 0.28, 0.332) upon annealing at 453 K (without and within oxygen plasma) over different annealing periods showed an increase in the TOC and in polarizability coefficients; as a result, the overall increase was from 0.15 × 10 − 4 to 8.7 × 10 − 4 K − 1 and 0.1 × 10 − 27 to 0.4 × 10 − 26 cm3 K − 1, respectively. By contrast, the samples H0.27WO3, Li0.125WO3, Na0.164WO3, and Na0.21WO3 attained negative TOCs after being annealed at 453 K over certain periods of time. In this case, the overall decrease in the TOC was from −0.9 × 10 − 4 to −6.7 × 10 − 3 K − 1, and the coefficient of temperature dependence of density decreased from −2.22 × 10 − 4 to −25.1 × 10 − 3 g cm − 3 K − 1. These new data were interpreted using different analytical models. Distinct annealing modes involve discrete chemical processes, and these processes were explained using separate chemical relations.

Retention of surface structure causes lower density in atomic layer deposition of amorphous titanium oxide thin films.

Size effects and structural modifications in amorphous TiO2 films deposited by atomic layer deposition (ALD) were investigated. As with the previously investigated ALD-deposited Al2O3 system we found that the film's structure and properties are strongly dependent on its thickness, but here, besides the significant change in the density of the films there is also a change in their chemical state. The thin near-surface layer contained a significantly larger amount of Ti+3 species and oxygen vacancies relative to the sample's bulk. We attribute this change in chemistry to the ALD specific deposition process wherein each different atomic species is deposited in turn, thereby forming a "corundum-like" structure of the near-surface layer resembling that found in the Al2O3 system. This, combined with the fact that each deposited layer starts out as a surface layer and maintains the surface structure over the next several following deposition cycles, is responsible for the overall decrease in the film density. This is the first time this effect has been shown in detail for TiO2, expending the previously discovered phenomenon to a new system and demonstrating that while similar effects occur, they can present in different ways for oxide systems with different structures and symmetries.

CO2/CH4 Pure- and Mixed-Gas Dilation and Sorption in Thin (∼500 nm) and Ultrathin (∼50 nm) Polymers of Intrinsic Microporosity

In this work, we present (i) the dilation and refractive index variation associated with changes in film density and (ii) gas uptake of pure CO2 and CH4, as well as their equimolar mixture in thin ...

Thermo optical properties and measurements of electronic polarizability coefficients of annealed tungsten bronzes without and within an oxygen plasma environment

WO3 thin films evaporated on unheated substrates were found to be substoichiometric and microcrystalline in nature as found by the ellipsometric studies, density, and porosity measurements. In this investigation, we measured the optical constants of WO3 thin films and of MxWO3 (M = H + , Li + , and Na + ) bronzes (with different concentrations, x) after being annealed at different temperatures over the range 298 to 453 K without and within an oxygen plasma environment using manual ellipsometry. It was found that the changes in film density and porosity of WO3 thin film when annealed at the temperature 413 K (without oxygen plasma) were not more than 3% and 12%, respectively, from the room temperature data. The thermo-optic coefficient (TOC) and electronic polarizability coefficient of WO3 thin film increased from 1.064 × 10 − 4 to 5.73 × 10 − 4 K − 1 and 0.1 × 10 − 26 to 0.3 × 10 − 26 cm3 K − 1, respectively, as a result of annealing the film at 413 K for 24 h. The samples HxWO3 (x = 0.172) and LixWO3 (x = 0.28, 0.332) upon annealing at 453 K (without and within oxygen plasma) over different annealing periods showed an increase in the TOC and in polarizability coefficients; as a result, the overall increase was from 0.15 × 10 − 4 to 8.7 × 10 − 4 K − 1 and 0.1 × 10 − 27 to 0.4 × 10 − 26 cm3 K − 1, respectively. By contrast, the samples H0.27WO3, Li0.125WO3, Na0.164WO3, and Na0.21WO3 attained negative TOCs after being annealed at 453 K over certain periods of time. In this case, the overall decrease in the TOC was from −0.9 × 10 − 4 to −6.7 × 10 − 3 K − 1, and the coefficient of temperature dependence of density decreased from −2.22 × 10 − 4 to −25.1 × 10 − 3 g cm − 3 K − 1. These new data were interpreted using different analytical models. Distinct annealing modes involve discrete chemical processes, and these processes were explained using separate chemical relations.

Combined in situ x-ray scattering and electrical measurements for characterizing phase transformations in nanometric functional films

This paper presents a combination of in situ synchrotron techniques (diffraction and reflectivity of x-rays) and sheet resistance measurements to study the phase transformations in functional thin films. The association of the three techniques enables simultaneously extracting structural and electrical characteristics of thin films during thermal annealing. For illustrating such combined experiments, two different examples are presented and discussed: the first one deals with solid phase reactions involved in the formation of Ni-based silicides with Pd alloy element, while the second one refers to amorphous-to-crystalline phase transition in chalcogenide materials. For the first case, it is shown that the combined experiments enable measuring the kinetics of Ni-silicide formation by detecting growing and consumed phases (crystallized or amorphous) exhibiting different electrical properties. In the second case, the correlated changes in film density, thickness and sheet resistance are evidenced upon Ge2Sb2Te5 (GST) thin film crystallization. A spread of transition temperature deduced from the different measured parameters is also demonstrated for the thinner GST films.

Low Temperature Crystallization of Metastable Nickel Manganite Spinel Thin Films

Single‐phase metastable cubic spinel nickel manganite films, 0.5 ≤ Mn/(Mn+Ni) ≤ 0.8, were produced using chemical solution deposition. Of these, the sample with Mn/(Mn+Ni) = 0.80 showed the lowest electrical resistivity. Films annealed in Argon at 400°C for 5 h exhibit temperature coefficient of resistance values ranging from −3.81 to −3.93%/K and electrical resistivities of ~10 kΩ‐cm. It was found by transmission electron microscopy that the metastable spinel phase appeared in both pyrolyzed and post‐deposition annealed films. Spectroscopic ellipsometry measurements over the spectral range from 0.75 to 6.0 eV showed that the complex dielectric function spectra (ε = ε1 + iε2) varied as a function of the annealing conditions, due at least in part to changes in film density. Aging experiments have been used to identify variations in resistivity and temperature coefficient of resistance as functions of time to assess material stability. As a result, the aging coefficient was 6.5% for a film with Mn/(Ni+Mn) = 0.80 after aging at 150°C for 500 h.

Real‐Time Investigation of Crystallization and Phase‐Segregation Dynamics in P3HT:PCBM Solar Cells During Thermal Annealing

AbstractCrystallization and phase segregation during thermal annealing lead to the increase of power‐conversion efficiency in poly(3‐hexylthiophene) (P3HT):[6,6]‐phenyl C61‐butyric acid methyl ester (PCBM) bulk‐heterojunction solar cells. An understanding of the length and time scale on which crystallization and phase segregation occur is important to improve control of the nanomorphology. Crystallization is monitored by means of grazing incidence X‐ray diffraction in real time during thermal annealing. Furthermore, the change in film density is monitored by means of ellipsometry and the evolution of carrier mobilities by means of field effect transistors, both during annealing. From the combination of such measurements with those of device performance as a function of annealing time, it is concluded that the evolution of microstructure involves two important time windows: i) A first one of about 5 minutes duration wherein crystallization of the polymer correlates with a major increase of photocurrent; ii) a second window of about 30 minutes during which the aggregation of PCBM continues, accompanied by an increase in the fill factor.

Multilayers of Charged Polypeptides As Studied by in Situ Ellipsometry and Quartz Crystal Microbalance with Dissipation

The buildup of poly(L-glutamic acid) (PGA) and poly(L-lysine) (PLL) multilayers on silica and titanium surfaces, with and without an initial layer of polyethyleneimine (PEI), was investigated and characterized by means of in situ ellipsometry and quartz crystal microbalance with dissipation. A two-regime buildup was found in all systems, where the length of the first slow-growing regime is dependent on the structure of the initial layers. In the second fast-growing regime, the film thickness grows linearly while the mass increases more than linearly (close to exponentially) with the number of deposited layers. The film refractive indices as well as the water contents indicate that the film density changes as the multilayer film builds up. The change in film density was proposed to be due to polypeptides diffusing into the multilayer film as they attach. Furthermore, the use of PEI as the initial layer was found to induce a difference in the thickness increments for PGA and PLL.

Influence of plasma source frequency on composition and density of fluorinated amorphous carbon thin films

Different types of fluorinated amorphous carbon (a-C:H:F) thin films were grown from CH 4/CF 4/Ar mixtures using a 13.56 MHz radiofrequency and a 13.56 MHz radiofrequency–2.45 GHz microwave hybrid plasma source. Comparison of X-ray photoelectron spectroscopy (XPS) and X-ray reflectivity (XRR) allowed us to determine the film hydrogen concentration, which depends on the plasma source used, and showed that, independently of the plasma source employed, the fluorine incorporation occurs at the expenses of the hydrogen content. Moreover, films with lower fluorine content were deposited from the radiofrequency–microwave hybrid technique. XRR measurements suggested that with increasing fluorine content, the film density changes indicating a phase transition towards an open and less cross-linked structure. For a fixed gas mixture composition, the deposition of less dense films grown by radiofrequency–microwave hybrid plasma source is probably associated to a different plasma decomposition and lower energy of the bombarding species.

Nanohardness measurement of carbon nitride thin films

AbstractA nanohardness measurement method using an atomic force microscope equipped with a diamond tip is described and applied to carbon nitride thin films. These films were prepared by radiofrequency magnetron sputtering at various substrate temperatures. Based on the general hardness definition, the hardness of thin films was determined directly from the indentation force and the (residual) indentation depth using fused silica as a standard reference. The hardnesses measured by this technique are quite reproducible. The hardnesses of the carbon nitride thin films with a thickness of ∼35 nm were in the range 31–35 GPa, increasing slightly with substrate temperature. This increase is in good correlation with the film density changes as measured by grazing‐incidence x‐ray reflectivity. Copyright © 2001 John Wiley & Sons, Ltd.

Low-temperature annealing effect on electron field emission of tetrahedral amorphous carbon films

The low-temperature annealing effect on electron field emission of tetrahedral amorphous carbon (ta-C) films was investigated. Ta-C films prepared by a filtered arc deposition technique were annealed at 400 °C for 60-120 min in a nitrogen atmosphere. The density and sp3 content in as-grown film were 3.3 g cm-3 and ~90%, respectively. After annealing, no obvious changes in film density or sp3 content were observed. The threshold electric field of electron emission of annealed ta-C films increased. Through annealing the clustering of sp2 bonded carbon would occur, resulting in bandgap reduction and the eventual increase of the emission barrier. After a given annealing period, the degree of clustering increased, and was responsible for the threshold electric field increasing further. The results implied that the control of the sp2 bonding configuration in addition to the sp3 bonding is important in obtaining good emission properties for ta-C films.

The Chemical Vapor Deposition of Zirconium Carbide onto Ceramic Substrates

AbstractZirconium carbide is an attractive ceramic material due to its unique properties such as high melting point, good thermal conductivity, and chemical resistance. The controlled preparation of zirconium carbide films of superstoichiometric, stoichiometric, and substoichiometric compositions has been achieved utilizing zirconium tetrachloride and methane precursor gases in an atmospheric pressure high temperature chemical vapor deposition system. Laminar and equiaxial microcrystalline morphologies were obtained for superstoichiometric and substoichiometric zirconium carbide; respectively, allowing cursory metallographic identification of composition. Observed reductions in film density associated with zirconium carbide films that contain additional free carbon or excess zirconium are reported. These changes in film density were found to be consistent with compositional changes. An apparently linear relationship (correlation of 0.99) between methane flow in this chemical vapor deposition system and zirconium carbide stoichiometry in the substoichiometric range deposited above ZrC0.61 has been observed.

Design Criteria for and Evaluation of Phantoms for Dental Radiography

Quality assurance (QA) of dental radiography should ensure high quality radiographs with minimum dose. Appropriate phantoms are needed to assess image quality, equipment performance and patient exposure. In order to visualise important image details or small differences in density of the oral tissues a high image contrast and spatial resolution is needed. The image quality phantom for intra-oral equipment may include teeth and contrast and spatial resolution test plate embedded in soft tissue substitute. Patient dose and some special technical factors of intra-oral X ray units can be checked by mailing a QA test packet to the user. This packet may contain TL dosemeters for dose measurements and individually packed X ray film for checking the diameter and collimation of primary beam and radiation quality. Important procedures in QA of the panoramic unit include the checking of beam alignment, the position of the patient positioning mechanism and lights, patient dose and image quality. A good quality periapical or whole status radiograph can be used as a reference film in constancy tests. It allows the dentist to compare recently processed radiographs for changes in film density, contrast, resolution, or other changes in image quality.

Design Criteria for and Evaluation of Phantoms for Dental Radiography

Quality assurance (QA) of dental radiography should ensure high quality radiographs with minimum dose. Appropriate phantoms are needed to assess image quality, equipment performance and patient exposure. In order to visualise important image details or small differences in density of the oral tissues a high image contrast and spatial resolution is needed. The image quality phantom for intra-oral equipment may include teeth and contrast and spatial resolution test plate embedded in soft tissue substitute. Patient dose and some special technical factors of intra-oral X ray units can be checked by mailing a QA test packet to the user. This packet may contain TL dosemeters for dose measurements and individually packed X ray film for checking the diameter and collimation of primary beam and radiation quality. Important procedures in QA of the panoramic unit include the checking of beam alignment, the position of the patient positioning mechanism and lights, patient dose and image quality. A good quality periapical or whole status radiograph can be used as a reference film in constancy tests. It allows the dentist to compare recently processed radiographs for changes in film density, contrast, resolution, or other changes in image quality.

Sensitometric responses of selected medical radiographic films.

Radiographic films produce different densities and contrast when processor changes occur, and the magnitude and rate of change vary with film type. The ability to detect and interpret the clinical importance of film density changes may depend on the method of sensitometry used. The characteristics of several medical radiographic films and various sensitometers were examined under three sensitometric variations and five processing variations. Of all variations used, only exposure with a single-versus a double-sided sensitometer caused a film type to have a marked different response. The results indicate that mismatching the sensitometer spectral output with the spectral sensitivity of the film in most cases does not affect the density changes of the film. The fact that a few films may be sensitive to differences in spectral content of the exposing light and dual- versus single-sided exposure and that only a limited number of film types were tested, however, leads to the prudent conclusion that the exposure conditions for quality control purposes should match clinical exposure conditions as closely as possible.

Surface analysis of tested solar coatings

A variety of currently popular electroplated coatings have been exposed to 90°C, 95% RH and 90°C, 0% RH environments for times from 0 to 5000 h. The optical response was measured, and the samples subsequently investigated by surface analytical techniques. The types of coatings examined fall into four groups. Group 1 consists of black chrome coatings deposited on nickel substrates. Group 2 consists of black copper on a copper substrate. Group 3 consists of a black nickel on a nickel substrate. Group 4 consists of black paint with thickness sensitive absorber properties. Under the test conditions employed, only samples from group 1 and 2 were found to exhibit an optical change. Auger electron spectroscopy depth profiles of the chrome and oxygen in group 1 revealed only a slight change in the ratio of the area under the chrome profile to the area under the oxygen profile. Optical results show no difference in the high humidity samples, but a small change after dry exposure. Analysis of the chrome 2P binding energies obtained from X-ray photoelectron spectra indicate a mixture of Cr 6+, Cr 3+ and Cr in the samples showing no optical or morphological changes. The samples that did exhibit a degraded spectral response and changed morphology were found to contain only Cr 3+ and Cr. The lack of the Cr 6+ valence state in the degraded sample is believed to be responsible for the small changes in morphology and degraded spectral response. A simple reduction-oxidation model can provide the basis for a change in the observed valence states which is related to a change in film density which is manifested in the observed optical and morphological changes. The group 2 coating shows a simple increase in oxidation as revealed from integrated copper oxygen ratios obtained from AES depth profiles. The other coatings are believed to be stable due to the nature of the oxides and protective binder.

Estimation of density changes associated with growth in vacuum-deposited amorphous films of antimony

Amorphous antimony films consisting of separate islands were deposited onto SiO x and GeO x film substrates at room temperature in a vacuum of 10 -5 Torr. By comparison of the interferometrically determined thickness and the total mass of incident vapour determined with a quartz oscillator, it was found that a sudden change in film density occurs at a certain film thickness d 0. Another change in film density, which is gradual, occurs in the vicinity of a certain thickness d c (d c > d 0 ) . The change at d 0 is caused by the coalescence of neighbouring islands. The change at d c, at which the coalescence of amorphous islands is almost completed, is associated with crystallization.

Simple method for the generation of organ and vessel contours from roentgenographic or fluoroscopic images.

A simple method is described for outlining or contouring any area defined by a change in film density or fluoroscopic screen intensity. The entire process, except for the positioning of an electronic window, is accomplished using a small computer having appropriate software. The electronic window is operator positioned over the area to be processed. The only requirement is that the window be alrge enough to encompass the total area to be considered.