Hermetic Coatings Research Articles

Elucidating and Mitigating High‐Voltage Degradation Cascades in Cobalt‐Free LiNiO2 Lithium‐Ion Battery Cathodes (Adv. Mater. 3/2022)

Lithium-Ion Batteries In article number 2106402, Mark C. Hersam and co-workers show that lattice oxygen loss plays a critical role in the O3–O1 stacking transition in cobalt-free LiNiO2 lithium-ion battery cathodes, which subsequently induces Ni-ion migration and irreversible stacking faults, microscale electrochemical creep, cracking, and even bending of layers after high-voltage cycling. By suppressing oxygen evolution, hermetic graphene coatings arrest this degradation cascade, resulting in substantially improved high-voltage capacity retention.

Quo vadimus? Fundamental problems of developing hybrid prostheses of thoracic aorta

This article is a review briefly characterizing the state of the art of hybrid surgery of the thoracic aorta using the frozen elephant trunk technique worldwide and in Russia, also discussing unsolved problems of fundamental science, being key issues in creation of new models of hybrid prostheses of the thoracic aorta. The main attention is paid to the problem of radial stiffness of the stent-graft portion of the prosthesis. Performed is a detailed analysis of the factors influencing this characteristic of the sent graft: shape, size and number of cells of the stent element, thickness of the nitinol wire it is made of, method of edge connection, nitinol properties depending on the alloy grade and methods of thermoforming. It is shown that excessive stiffness leads to the development of d-SINE syndrome. This is followed by discussing the problem of optimal stiffness of stent grafts, based on the design of stent graft elements and elastic properties of the wall of the true channel of a dissecting aortic aneurysm. Also proposed is an approach to solving the problem of d-SINE, consisting in creation of conical stent grafts and/or a gradual decrease of radial stiffness of stent elements in the direction of the distal portion. Comprehensively addressed are disadvantages of the graft portion of the prosthesis, in 95% of items made of polyethylene terephthalate fiber: susceptibility to degradation associated with manufacturing defects and intraoperative microdamages, abrasive effect in the zone of contact with stent elements, partial postoperative hydrolysis and an inflammatory reaction to a foreign body, often being clinically pronounced. Also touched upon are certain aspects of creating hermetic coatings of the graft portion, with the use of vancomycin possessing low cytotoxicity as part of an antibacterial component being promising. As a whole, it is demonstrated that advances in creating a novel generation of hybrid prostheses should be associated with new approaches and materials, to be obtained at the junction of medicine and fundamental sciences.

CURRENT STATE OF METHODS AND MEANS OF REGISTRATION OF HIGH TEMPERATURES AND MECHANICAL STRESSES IN STRUCTURES

An analytical review of physically possible methods and available achievements in registering hydrostatic pressure or mechanical stresses using fiber optic fibers and sensors based on them based on published works that can be used in harsh environmental conditions is carried out. The results of the review show that fully distributed or quasidistributed fiber-optic systems for recording hydrostatic pressure or mechanical stress can be implemented on the following physical principles and apparatus with measures to compensate or suppress the influence of temperature: polarizing sensors on birefringent single- mode light guides and OTDR equipment; micro-flexible sensors with OTDR equipment on conventional multimode fibers; measuring systems on fiber Bragg gratings; on discrete sensors, in particular, on sealed fiber Fabry–Perot interferometers; Brillouin distributed sensors on single-mode fibers that are not sensitive to temperature changes. It is shown that single-mode birefringent fibers with hollow holes in the shell and fiber Bragg gratings written in the core have a good linear sensitivity to hydrostatic pressure and a weak dependence on temperature. Lattices in phosphorous-containing single-mode light guides have increased high-temperature properties up to ~500 C and higher. A number of discrete fiber sensors’ structures and pressure recorders are investigated. Various structures of sensitive elements of pressure sensors on sealed fiber Fabry–Perot interferometers and fiber gratings in spherical and cylindrical small-sized cases are investigated. Sensors based on Fabry–Perot fiber interferometers soldered into a glass capillary and protected from water by external high-temperature hermetic coatings showed good linearity in the pressure range of 0…540 ATM at temperatures up to ~200 C. The sensors are efficient at temperatures up to 600 °C and are promising for use in severe and special external conditions. The possibility of compensating the temperature sensitivity by selecting external coatings is shown. Pressure sensors were tested on local areas with microbends and it was shown that they can measure pressures up to ~24 МPа at temperatures up to ~450 C, but to compensate for the dependence of the readings on temperature, it must be measured by an independent sensor. The possibility of independent and simultaneous measurement of hydrostatic pressure and temperature along a single fiber using spontaneous Brillouin scattering is shown. Pressure is measured by the frequency shift of Brillouin scattering, and temperature by its intensity. The operation of the Brillouin recorder in the pressure range 0…34 MРа is demonstrated. The pressure resolution was ~0,2 МРа. New methods are proposed for detecting Brillouin scattering – a heterodyne signal with a high signal-to-noise ratio and based on frequency modulation of a semiconductor single-frequency distributed feedback laser. The measurement range has been increased by more than 10 km and the coordinate resolution has been increased. The Brillouin scattering method is promising for creating distributed systems for measuring hydrostatic pressure or mechanical stress for severe physical conditions, including temperatures of ≥3000 C.

In situ Y2Si2O7 coatings on SiC fibers: Thermodynamic analysis and processing

AbstractIt is shown using thermodynamic analysis and kinetic modeling that a processing window exists for the formation of Y2Si2O7 coatings on SiC. The proposed method is validated using an experimental procedure in which the in situ formation of Y2Si2O7 on a commercial SiC‐based fiber is demonstrated. The method involves the deposition of YPO4 on preoxidized fine diameter SiC‐based fibers, and heat treating the coated fibers within a calculated processing window of oxygen partial pressure, temperature, degree of preoxidation, and coating thickness. The results are promising for the development of environmentally resistant interfacial coatings for SiC‐fiber reinforced SiC‐based matrix composites. The proposed and validated approach allows a low‐cost method to obtain continuous hermetic coatings on SiC fibers with interfacial properties adequate for tough composite behavior that resists degradation under turbine engine conditions.

Fabrication of Hybrid Silicate Coatings by a Simple Vapor Deposition Method for Lithium Metal Anodes

AbstractLithium metal anodes are highly promising for next‐generation rechargeable batteries. However, implication of lithium metal anodes is hampered by the unstable electrochemical behavior. Herein, the fabrication of hermetic coatings of hybrid silicate on lithium metal surface using a simple vapor deposition technique under the ambient condition is reported. Such coatings consist of a “hard” inorganic moiety that helps to suppress lithium dendrites and a “soft” organic moiety that enhances the toughness. Lithium metal batteries, including Li–LiFePO4 and Li–S batteries, made with such coated anodes show significantly improved lifetime. This work provides a simple yet effective approach to stabilize lithium metal anodes for high‐performance lithium metal batteries.

Sensing carbon allotropes in protective coatings on optical fibers with far‐ and near‐field Raman spectroscopy and microscopy

Hermetic carbon coatings of different thicknesses ranging from 1 to 100 nm on a series of optical fibers are characterized with confocal Raman spectroscopy and atomic force microscopy. Standard far‐field Raman spectra in the region of 1,000–2,000 cm−1 were fitted and well reproduced using 5 individual components assigned to different species of graphite‐like and disordered phases. Based on the fitting, a new spectroscopic indicator was proposed: , where G* and D* and Δ are intensities at the maxima of the graphite‐like G peak and the disorder‐induced D peak and the dip between them, respectively. This indicator provides a measure of soot fraction in carbonaceous materials. A tip‐enhanced Raman scattering (TERS) technique confirmed the complex structure of the first‐order Raman D band assigned to disordered graphitic lattice vibrations. In addition, the TERS method provided convincing evidence for the formation of carbon allotropes, such as carbon nanotubes in the coatings. Possible effects of allotropes on hydrogen and water permeation through carbon coating are discussed in the view of the obtained results.

Probabilistic distributions of pinhole defects in atomic layer deposited films on polymeric substrates

Pinhole defects in atomic layer deposition (ALD) coatings were measured in an area of 30 cm2 in an ALD reactor, and these defects were represented by a probabilistic cluster model instead of a single defect density value with number of defects over area. With the probabilistic cluster model, the pinhole defects were simulated over a manufacturing scale surface area of ∼1 m2. Large-area pinhole defect simulations were used to develop an improved and enhanced design method for ALD-based devices. A flexible thermal ground plane (FTGP) device requiring ALD hermetic coatings was used as an example. Using a single defect density value, it was determined that for an application with operation temperatures higher than 60 °C, the FTGP device would not be possible. The new probabilistic cluster model shows that up to 40.3% of the FTGP would be acceptable. With this new approach the manufacturing yield of ALD-enabled or other thin film based devices with different design configurations can be determined. It is important to guide process optimization and control and design for manufacturability.

INVESTIGATION ON STABILITY OF EXTRINSIC FABRY–PEROT INTERFEROMETRIC PRESSURE SENSORS FOR HIGH-TEMPERATURE/HIGH-PRESSURE UNDERGROUND APPLICATIONS

Long-term stability of extrinsic Fabry–Perot interferometric (EFPI) pressure sensors at high temperature/high pressure (HT/HP) liquid environments are discussed in this article. For HT/HP underground applications, a method of fabricating EFPI sensors with a high-energy CO2 pulse laser as heating source to thermally fuse tube and fiber is used. Through theoretical analysis and experiments, factors that influence stability of EFPI sensors at HT/HP liquid environments are reported. Based on theoretical analysis, numerical simulations, and experimental tests, methods and technologies that improve the stability of EFPI sensors at HT/HP liquid environments are proposed and demonstrated. First, a spindle-shaped diaphragm in the sensor head fabricated an optical route to improve energy distribution around tube. Second, placing EFPI sensors into a HT/HP environment to release residual stress left in the bonding points to eliminate drift when used in HT/HP environments. Third, carbon deposition of hermetic coatings was used to prevent liquid molecules from diffusing into the silica capillary tube. Finally, the long-term stability of EFPI pressure sensors at HT/HP liquid environments was tested through experiments. The results show that long-term drift of air gap of EFPI pressure sensors is less than 0.1% at 300 °C, and 30 MPa liquid environments is realized.

Hermetically Coated Nanosilver: No Ag+ Ion Leaching

ABSTRACTDry-coated nanosilver is a promising material for bio-applications. Its inert and non-porous nanothin SiO2 coating preserves the plasmonic properties of the nanosilver and cures its toxicity by (1) preventing direct cell to silver contact and (2) blocking the release of toxic silver ions. However, fully hermetic coatings have, to date, not been produced. During the coating process, a certain number of core particles are either coated only partially, or escape the coating process entirely. Here, a systematic parametric study was undertaken in order to optimize an aerosol reactor for the synthesis and dry-coating of nanosilver. The reactor was optimized with respect to coating injection height, jet number, mixing flow rate. By synthesizing xAg/SiO2 composite particles, small silver sizes (9-11 nm) with relatively high Ag ion release were obtained. This enabled the quantitative evaluation of the coatings by Ag ion release measurements.

Effects of deposition parameters on characteristics of carbon coatings on optical fibers prepared by thermal chemical vapor deposition

The effects of deposition parameters on characteristics of carbon coatings on optical fibers prepared by thermal chemical vapor deposition are investigated. The deposition parameters are selected as follows. The CH 4/(CH 4 + N 2) ratio is in the range between 20% and 100%; the temperature is set from 1173 to 1248 K; the working pressure is arranged between 50 and 100 kPa, and the residence time is ranging from 1.47 to 7.37 s. The deposition rate, microstructure, and electrical resistivity of carbon coatings are measured. The low-temperature surface morphology of carbon-coated optical fibers is elucidated. Experimental results indicate that the deposition rate increases with increasing the CH 4/(CH 4 + N 2) ratio, deposition temperature, working pressure, and residence time. The activation energy (= 456 kJ/mol) of carbon deposition from methane was shown to correlate to the activation energy of methane dissociation. The deposition rate is proportional to about first-order of partial pressure of methane, and thus, the deposition process is mainly controlled by the process to create mono-carbon species in the carbon film. As the deposition rate increases, the size and number of particles on the carbon coating surface and electrical resistivity of carbon coatings increase, while the ordered degree, nano-crystallite size, and sp 2 carbon atoms of the carbon coatings decrease. Additionally, the low-temperature surface morphology of carbon coatings shows that as the carbon coating thickness is large enough to sustain the thermal loading, decreasing the deposition rate is good for producing hermetic optical fiber coatings.

Effects of different acetylene/nitrogen ratios on characteristics of carbon coatings on optical fibers prepared by thermal chemical vapor deposition

The effects of C 2H 2/(C 2H 2 + N 2) ratios on the characteristics of carbon coatings on optical fibers prepared by thermal chemical vapor deposition are investigated. The C 2H 2/(C 2H 2 + N 2) ratios are set to 60, 70, 80, 90, and 100%. Additionally, the deposition temperature, working pressure, and mass flow rate are 1003 K, 133 kPa, and 40 sccm, respectively. The deposition rate, microstructure, and electrical resistivity of carbon coatings are measured. The low-temperature surface morphology of carbon-coated optical fibers is elucidated. Experimental results indicate that the deposition rate increases with increasing the C 2H 2/(C 2H 2 + N 2) ratio, and the deposition process is located at a surface controlled regime. As the deposition rate increases, the electrical resistivity of carbon coatings increases, while the ordered degree, nano-crystallite size, and sp 2 carbon atoms of the carbon coatings decrease. Additionally, the low-temperature surface morphology of the carbon coatings shows that if the carbon coating thickness is not smaller than 289 nm, decreasing the deposition rate is good for producing hermetic optical fiber coatings.

Robust and Hermetic Borosilicate Glass Coatings by E-Beam Evaporation

The use of a plasma-assisted e-beam evaporation process enables a cost-efficient exploitation of the outstanding material properties of borosilicate glass – a chemically very inert material with minimal moisture absorption, excellent optical properties and excellent time and temperature stability. This paper gives further insight on the deposition and structuring of borosilicate glass films and the achievable film properties as well as feasible applications.

Ultrananocrystalline diamond film as an optimal cell interface for biomedical applications

Surfaces of materials that promote cell adhesion, proliferation, and growth are critical for new generation of implantable biomedical devices. These films should be able to coat complex geometrical shapes very conformally, with smooth surfaces to produce hermetic bioinert protective coatings, or to provide surfaces for cell grafting through appropriate functionalization. Upon performing a survey of desirable properties such as chemical inertness, low friction coefficient, high wear resistance, and a high Young's modulus, diamond films emerge as very attractive candidates for coatings for biomedical devices. A promising novel material is ultrananocrystalline diamond (UNCD) in thin film form, since UNCD possesses the desirable properties of diamond and can be deposited as a very smooth, conformal coating using chemical vapor deposition. In this paper, we compared cell adhesion, proliferation, and growth on UNCD films, silicon, and platinum films substrates using different cell lines. Our results showed that UNCD films exhibited superior characteristics including cell number, total cell area, and cell spreading. The results could be attributed to the nanostructured nature or a combination of nanostructure/surface chemistry of UNCD, which provides a high surface energy, hence promoting adhesion between the receptors on the cell surface and the UNCD films.

Channel cracks in a hermetic coating consisting of organic and inorganic layers

Flexible electronic devices often require hermetic coatings that can withstand applied strains. This letter calculates the critical strains for various configurations of channel cracks in a coating consisting of organic and inorganic layers. The authors show that the coating can sustain the largest strain when the organic layer is of some intermediate thicknesses.

PECVD Silicon Carbide as a Thin Film Packaging Material for Microfabricated Neural Electrodes

AbstractThis paper reports our effort to develop amorphous silicon carbide (a-SiC) films for use as hermetic thin film coatings for mechanically-flexible neural electrodes. In our work, the a-SiC films were deposited by plasma enhanced chemical vapor deposition (PECVD) using two distinct methods, namely a single precursor approach using trimethylsilane, and a dual precursor approach using methane (CH4) and silane (SiH4). The mechanical properties of films deposited on Si substrates were characterized using the wafer curvature and load-deflection methods. The effectiveness of the films as moisture barriers for polyimide substrates was characterized by measuring the leakage currents of SiC-coated interdigitated electrode structures soaked in PBS. A microfabricated prototype of the flat interface nerve electrode (FINE) based on a flexible polyimide substrate and a PECVD SiC capping layer was fabricated using a monolithic process based on conventional micromachining techniques. To facilitate this approach, a reactive ion etching process was developed that exhibited high etch rates and high selectively to the SiC films.

The Design of Hermetically Double-Coated Optical Fibers to Minimize Hydrostatic Pressure–Induced Stresses

The design of hermetically double-coated optical fibers to minimize hydrostatic pressure–induced stresses is investigated. Several stresses are important in the hermetically double-coated optical fibers, and they would produce the excess bending losses or the failure of hermetic coatings. These stresses can be minimized by appropriately selecting material's properties of hermetic coatings and their thicknesses. The hydrostatic pressure–induced stresses in optical fibers with some selected metallic coatings are also considered. The results show that chromium has the best performance in the minimization of hydrostatic pressure–induced stresses. However, lead and indium are poor materials.

Thermal Radiative Properties of a Semitransparent Fiber Coated With a Thin Absorbing Film

This study presents the hemispherical model to predict the hemispherical total thermal radiative properties of a fiber coated with a thin film. The fiber is composed of semi-transparent media, such as fused silica. The film is made of strong absorbing media with thickness on the order of tens of nanometers. The film is assumed to be “locally flat” at the point of incidence for radiative transfer analysis because the thickness of the film is much less than the fiber radius. Wave optics is employed to calculate the reflectance and transmittance of the thin film while the ray tracing method is used for radiative transport analysis of the fiber. Effects of film and fiber substrate optical properties, film thickness and temperature on predicted thermal radiative properties are investigated. One of the applications of the proposed model is for studying the chemical vapor deposition of hermetic coatings on optical fibers, in which the thermal radiative properties of the fiber–film system heavily influence the fiber surface temperature and chemical reaction rate.

In vitro and in vivo evaluation of ultrananocrystalline diamond for coating of implantable retinal microchips

In this work, ultrananocrystalline diamond (UNCD) thin films were evaluated for use as hermetic and bioinert coatings for a retinal microchip. These films were deposited on highly conductive Si substrates at different temperatures (from 400 to 800 degrees C), using microwave plasma enhanced chemical vapor deposition with argon-rich Ar/CH4 gas mixtures and different relative amounts of hydrogen (0-20%). Scanning electron microscopy studies showed that all the films are dense and continuous. Results of cyclic voltammetry test revealed that when there was <2% of hydrogen in the plasma, the film obtained renders the surface electrochemically inactive, with very low leakage currents ( approximately 4 x 10(-7) A/cm2 at +/-5 V). In addition, in vivo tests of the UNCD-coated Si samples were performed by implanting them in the eyes of rabbits for 4-6 months within the eye physiological environment. According to all these results, it was concluded that UNCD is a promising candidate for use as the encapsulating coatings for implantable retinal microelectronic devices.

Characterization of CVD carbon films for hermetic optical fiber coatings

Thin carbon films are being studied as hermetic coatings for optical fibers used in harsh environment applications. This work details an experimental study of pyrolytic carbon films grown in a cold walled chemical vapor deposition (CVD) reactor. The films are grown from methane, acetylene, propane and butane precursors on stationary 3-mm quartz rods. Results are presented at 15 and 600 torr, total pressure for substrate temperatures between 1050 and 1750 K. Hydrocarbon precursor gas concentrations are varied between 10 and 100% in N 2 dilutant. Auger electron spectroscopy (AES) shows mostly carbon composition, with trace levels of Cr and O 2 impurities. X-Ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) reveal small amounts of SiC at the carbon–glass interface, but could not resolve a continuous transition layer. The thickness, microstructure and surface roughness are analyzed using environmental scanning electron microscopy (ESEM). ESEM reveals an increase in deposition rate with temperature and concentration for all hydrocarbon species and a noticeable change in surface morphology with deposition temperature and hydrocarbon species. Raman spectroscopy is used to relate film microstructure to deposition conditions, providing non-intrusive evaluation of crystalline size and hermetic properties.

Critical issues In The Mechanical Reliability of Lightguide Fibers

AbstractIn order to guarantee a minimum initial strength, lightguide fibers are proof-tested. However, the strength of these fibers is known to depend on time (due to fatigue and aging) and this time-dependence must be taken into account in the calculation of fiber lifetimes. While hermetic coatings can be applied to eliminate strength degradation with time, they are rarely used. It is thus necessary to understand the time-dependent behavior well enough to ensure a desired lifetime (without an excessive and costly safety factor), or alternatively, it is necessary to validate a fundamental strength limit. This paper discusses the progress that has been made on issues related to such fiber lifetime predictions. In particular, it is pointed out that the possible variations in flaw character and coating chemistry make simple generalizations difficult and require that fundamental understandings be developed.