Abnormal Graphitization Behavior in Near-Surface/Interface Region of Polymer-Derived Ceramics.

The in situ free carbon generated in polymer-derived ceramics (PDCs) plays a crucial role in their unique microstructure and resultant properties. This study advances a new phenomenon of graphitization of PDCs. Specifically, whether in micro-/nanoscale films or millimeter-scale bulks, the surface/interface radically changes the fate of carbon and the evolution of PDC nanodomains, promotes the graphitization of carbon, and evolves a free carbon enriched layer in the near-surface/interface region. Affected by the enrichment behavior of free carbon in the near-surface/interface region, PDCs exhibit highly abnormal properties such as the skin behavior and edge effect of the current. The current intensity in the near-surface/interface region of PDCs is orders of magnitude higher than that in its interior. Ultrahigh conductivity of up to 14.47 S cm-1 is obtained under the action of the interface and surface, which is 5-8 orders of magnitude higher than that of the bulk prepared under the same conditions. Such surface/interface interactions are of interest for the regulation of free carbon and its resultant properties, which are the core of PDC applications. Finally, the first PDC thin-film strain gauge that can survive a butane flame with a high temperature of up to ≈1300 °C is fabricated.

Enhancing the Hydrophobicity and Antibacterial Properties of SiCN-Coated Surfaces with Quaternization to Address Peri-Implantitis.

Peri-implantitis is a major cause of dental implant failure. This disease is an inflammation of the tissues surrounding the implant, and, while the cause is multi-factorial, bacteria is the main culprit in initiating an inflammatory reaction. Dental implants with silicon carbonitride (SiCN) coatings have several potential advantages over traditional titanium implants, but their antibacterial efficiency has not yet been evaluated. The purpose of this study was to determine the anti-bacterial potential of SiCN by modifying the surface of SiCN-coated implants to have a positive charge on the nitrogen atoms through the quaternization of the surface atoms. The changes in surface chemistry were confirmed using contact angle measurement and XPS analysis. The modified SiCN surfaces were inoculated with Streptococcus mutans (S. mutans) and compared with a silicon control. The cultured bacterial colonies for the experimental group were 80% less than the control silicon surface. Fluorescent microscopy with live bacteria staining demonstrated significantly reduced bacterial coverage after 3 and 7 days of incubation. Scanning electron microscopy (SEM) was used to visualize the coated surfaces after bacterial inoculation, and the mechanism for the antibacterial properties of the quaternized SiCN was confirmed by observing ruptured bacteria membrane along the surface.

La(Ca)CrO3-Filled SiCN Precursor Thin Film Temperature Sensor Capable to Measure up to 1100 °C High Temperature.

Thin-film sensors are regarded as advanced technologies for in situ condition monitoring of components operating in harsh environments, such as aerospace engines. Nevertheless, these sensors encounter challenges due to the high-temperature oxidation of materials and intricate manufacturing processes. This paper presents a simple method to fabricate high temperature-resistant oxidized SiCN precursor and La(Ca)CrO3 composite thin film temperature sensors by screen printing and air annealing. The developed sensor demonstrates a broad temperature response ranging from 200 °C to 1100 °C with negative temperature coefficients (NTC). It exhibits exceptional resistance to high-temperature oxidation and maintains performance stability. Notably, the sensor's resistance changes by 3% after exposure to an 1100 °C air environment for 1 h. This oxidation resistance improvement surpasses the currently reported SiCN precursor thin-film sensors. Additionally, the sensor's temperature coefficient of resistance (TCR) can reach up to -7900 ppm/°C at 200 °C. This strategy is expected to be used for other high-temperature thin-film sensors such as strain gauges, heat flux sensors, and thermocouples. There is great potential for applications in high-temperature field monitoring.

Properties of SiCN Films Relevant to Dental Implant Applications.

The application of surface coatings is a popular technique to improve the performance of materials used for medical and dental implants. Ternary silicon carbon nitride (SiCN), obtained by introducing nitrogen into SiC, has attracted significant interest due to its potential advantages. This study investigated the properties of SiCN films deposited via PECVD for dental implant coatings. Chemical composition, optical, and tribological properties were analyzed by adjusting the gas flow rates of NH3, CH4, and SiH4. The results indicated that an increase in the NH3 flow rate led to higher deposition rates, scaling from 5.7 nm/min at an NH3 flow rate of 2 sccm to 7 nm/min at an NH3 flow rate of 8 sccm. Concurrently, the formation of N-Si bonds was observed. The films with a higher nitrogen content exhibited lower refractive indices, diminishing from 2.5 to 2.3 as the NH3 flow rate increased from 2 sccm to 8 sccm. The contact angle of SiCN films had minimal differences, while the corrosion rate was dependent on the pH of the environment. These findings contribute to a better understanding of the properties and potential applications of SiCN films for use in dental implants.

Studies on Oxygen Permeation Resistance of SiCN Thin Film and RRAM Applications.

In this study, a silicon carbon nitride (SiCN) thin film was grown with a thickness of 5~70 nm by the plasma-enhanced chemical vapor deposition (PECVD) method, and the oxygen permeation characteristics were analyzed according to the partial pressure ratio (PPR) of tetramethylsilane (4MS) to the total gas amount during the film deposition. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), and X-ray reflectivity (XRR) were used to investigate the composition and bonding structures of the SiCN film. An atomic force microscope (AFM) was used to examine the surface morphology of the SiCN films to see the porosity. The analysis indicated that Si-N bonds were dominant in the SiCN films, and a higher carbon concentration made the film more porous. To evaluate the oxygen permeation, a highly accelerated temperature and humidity stress test (HAST) evaluation was performed. The films grown at a high 4MS PPR were more susceptible to oxygen penetration, which changed Si-N bonds to Si-N-O bonds during the HAST. These results indicate that increasing the 4MS PPR made the SiCN film more porous and containable for oxygen. As an application, for the first time, SiCN dielectric film is suggested to be applied to resistive random access memory (RRAM) as an oxygen reservoir to store oxygen and prevent a reaction between metal electrodes and oxygen. The endurance characteristics of RRAM are found to be enhanced by applying the SiCN.

Electrochemical Performance of Carbon-Rich Silicon Carbonitride Ceramic as Support for Sulfur Cathode in Lithium Sulfur Battery.

As a promising matrix material for anchoring sulfur in the cathode for lithium-sulfur (Li-S) batteries, porous conducting supports have gained much attention. In this work, sulfur-containing C-rich SiCN composites are processed from silicon carbonitride (SiCN) ceramics, synthesized at temperatures from 800 to 1100 °C. To embed sulfur in the porous SiCN matrix, an easy and scalable procedure, denoted as melting-diffusion method, is applied. Accordingly, sulfur is infiltrated under solvothermal conditions at 155 °C into pores of carbon-rich silicon carbonitride (C-rich SiCN). The impact of the initial porosity and microstructure of the SiCN ceramics on the electrochemical performance of the synthesized SiCN-sulfur (SiCN-S) composites is analysed and discussed. A combination of the mesoporous character of SiCN and presence of a disordered free carbon phase makes the electrochemical performance of the SiCN matrix obtained at 900 °C superior to that of SiCN synthesized at lower and higher temperatures. A capacity value of more than 195 mAh/g over 50 cycles at a high sulfur content of 66 wt.% is achieved.

A SiCN Thin Film Thermistor Based on DVB Modified Polymer-Derived Ceramics.

Carbon-rich SiCN ceramics were prepared by divinylbenzene (DVB)-modified polysilazane (PSN2), and a high-conductivity SiCN thin film sensor suitable for medium-low temperature sensing was fabricated. The modified liquid precursors were patterned by direct ink writing to produce SiCN resistive grids with line widths of several hundreds of micrometers and thicknesses of several micrometers. The introduction of DVB not only increases the critical thickness of SiCN ceramics several times, but also significantly improves the conductivity of SiCN, making it meet the conductivity requirements of sensing applications in the mid-low temperature range. The electrical conductivity and microstructure of DVB-modified SiCN ceramics were studied in detail. In the temperature range of 30~400 °C, the temperature resistance performance of DVB modified SiCN resistance grid was measured. The SiCN ceramics with low DVB content not only have excellent electrical conductivity, but also have good oxidation resistance.

Design and Manufacturing of Si-Based Non-Oxide Cellular Ceramic Structures through Indirect 3D Printing.

Additive manufacturing of Polymer-Derived Ceramics (PDCs) is regarded as a disruptive fabrication process that includes several technologies such as light curing and ink writing. However, 3D printing based on material extrusion is still not fully explored. Here, an indirect 3D printing approach combining Fused Deposition Modeling (FDM) and replica process is demonstrated as a simple and low-cost approach to deliver complex near-net-shaped cellular Si-based non-oxide ceramic architectures while preserving the structure. 3D-Printed honeycomb polylactic acid (PLA) lattices were dip-coated with two preceramic polymers (polyvinylsilazane and allylhydridopolycarbosilane) and then converted by pyrolysis respectively into SiCN and SiC ceramics. All the steps of the process (printing resolution and surface finishing, cross-linking, dip-coating, drying and pyrolysis) were optimized and controlled. Despite some internal and surface defects observed by topography, 3D-printed materials exhibited a retention of the highly porous honeycomb shape after pyrolysis. Weight loss, volume shrinkage, roughness and microstructural evolution with high annealing temperatures are discussed. Our results show that the sacrificial mold-assisted 3D printing is a suitable rapid approach for producing customizable lightweight highly stable Si-based 3D non-oxide ceramics.

Fabrication of SiCN(O) Aerogel Composites with Low Thermal Conductivity by Wrapping Mesoporous Aerogel Structures over Mullite Fibers.

Silicon-based ceramic aerogels obtained by the polymer pyrolysis route possess excellent thermophysical properties, but their poor mechanical properties limit their broader applicability in thermal insulation materials. Herein, SiCN(O) ceramic aerogels were prepared under the toughening effect of a crosslinker (hexamethylene diisocyanate, HDI), which maintains the structural integrity of the aerogel during the wet gel-to-aerogel conversion. The aerogel maintained a high surface area (88.6 m2 g-1) and large pore volume (0.21 cm3 g-1) after pyrolysis. Based on this, mullite-fiber-reinforced SiCN(O) aerogels composites with outstanding thermal insulation properties and better mechanical performance were synthesized via ambient pressure impregnation. Furthermore, the effect of the impregnation concentration on the mechanical and insulation properties of the composites was investigated. The results revealed that the composite prepared with a solution ratio of 95 wt.% exhibited a low density (0.11 g cm-3) and a low thermal conductivity (0.035 W m-1 K-1), indicating an ~30% enhancement in its thermal insulation performance compared to the mullite fiber; the mesoporous aerogel structures wrapped on the mullite fibers inhibited the gas thermal conduction inside the composites.

Maximum Achievable N Content in Atom-by-Atom Growth of Amorphous Si-B-C-N Materials.

Amorphous Si-B-C-N alloys can combine exceptional oxidation resistance up to 1500 °C with high-temperature stability of superior functional properties. Because some of these characteristics require as high N content as possible, the maximum achievable N content in amorphous Si-B-C-N is examined by combining extensive ab initio molecular dynamics simulations with experimental data. The N content is limited by the formation of unbonded N2 molecules, which depends on the composition (most intensive in C rich materials, medium in B rich materials, least intensive in Si-rich materials) and on the density (increasing N2 formation with decreasing packing factor when the latter is below 0.28, at a higher slope of this increase at lower B content). The maximum content of N bonded in amorphous Si-B-C-N networks of lowest-energy densities is in the range from 34% to 57% (materials which can be grown without unbonded N2) or at most from 42% to 57% (at a cost of affecting materials characteristics by unbonded N2). The results are important for understanding the experimentally reported nitrogen contents, design of stable amorphous nitrides with optimized properties and pathways for their preparation, and identification of what is or is not possible to achieve in this field.

Characterization of thick and thin film SiCN for pressure sensing at high temperatures.

Pressure measurement in high temperature environments is important in many applications to provide valuable information for performance studies. Information on pressure patterns is highly desirable for improving performance, condition monitoring and accurate prediction of the remaining life of systems that operate in extremely high temperature environments, such as gas turbine engines. A number of technologies have been recently investigated, however these technologies target specific applications and they are limited by the maximum operating temperature. Thick and thin films of SiCN can withstand high temperatures. SiCN is a polymer-derived ceramic with liquid phase polymer as its starting material. This provides the advantage that it can be molded to any shape. CERASET™ also yields itself for photolithography, with the addition of photo initiator 2, 2-Dimethoxy-2-phenyl-acetophenone (DMPA), thereby enabling photolithographical patterning of the pre-ceramic polymer using UV lithography. SiCN fabrication includes thermosetting, crosslinking and pyrolysis. The technology is still under investigation for stability and improved performance. This work presents the preparation of SiCN films to be used as the body of a sensor for pressure measurements in high temperature environments. The sensor employs the phenomenon of drag effect. The pressure sensor consists of a slender sensitive element and a thick blocking element. The dimensions and thickness of the films depend on the intended application of the sensors. Fabrication methods of SiCN ceramics both as thin (about 40-60 µm) and thick (about 2-3 mm) films for high temperature applications are discussed. In addition, the influence of thermosetting and annealing processes on mechanical properties is investigated.

Effects of Si/C Ratio on the Phase Composition of Si-C-N Powders Synthesized by Carbonitriding.

Si-C-N based materials possess interesting properties such as high hardness and oxidation resistance. The compacts of silicon and cornstarch with different Si/C ratios were subjected to carbonitriding at 1350-1550 °C. Reaction products were characterized by X-ray powder diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscope (TEM). The effects of Si/C ratio on the phase composition of Si-C-N powders were investigated. The results revealed that the Si/C ratio played a crucial role on the formation of crystalline silicon carbonitride (SiCN) and the phase composition of Si-C-N powders. It was demonstrated that liquid silicon is an important medium and reaction site for the introduction of nitrogen, so the Si content in reactants has affected the N content in the product. On the other hand, carbon participates in the carbonization of Si3N4 and the formation of SiC. The contents of C-N bond and SiCN in the products are carbon content-dependent. Combining the above two aspects, the maximum yield of SiCN can be achieved with the Si/C ratio of 1:1 to 1:1.5.

Nanochannel Diffusion-Controlled Nitridation of Polycarbosilanes for Diversified SiCN Fibers with Interfacial Gradient-SiC xN y Phase and Enhanced High-Temperature Stability.

Diversified SiCN fibers with gradient-SiC xN y phase in the interfacial regions between the major phases of carbon-rich SiC phase and Si3N4 phase were prepared via nanochannel diffusion-controlled nitridation of polycarbosilane fibers under different NH3 flow rates. The obtained fibers with excellent mechanical properties showed a different nanostructure and improved high-temperature behavior compared with polysilazane- and polysilylcarbodiimide-derived SiCN ceramics. The enhanced high-temperature properties could be contributed to the inhibition of carbothermal reduction of the Si3N4 phase by the gradient-SiC xN y phase in the interfacial region between the Si3N4 phase and carbon-rich SiC phase. Meanwhile, a suitable amount of interfacial SiC xN y phase as well as the fine distributed microstructure can be helpful to inhibit the high-temperature crystallization of both the SiC phase and Si3N4 phase. Additionally, a nanostructural model has been proposed to understand the effect of interfacial gradient-SiC xN y phase and compositional-dependent high-temperature behavior of obtained SiCN fibers. Our findings provide a novel strategy to prepare SiCN-based ceramic materials with excellent high-temperature stabilities, which we expect to possess great potential in structural and (multi)functional applications at high temperatures and under harsh environments.

Continuous SiCN Fibers with Interfacial SiC xN y Phase as Structural Materials for Electromagnetic Absorbing Applications.

SiCN ceramics are one of the most important electromagnetic wave (EMW) absorbing materials for application in harsh environments, but research studies on optimizing phase distribution in SiCN ceramics for excellent EMW absorbing properties are still lacking. Herein, continuous SiCN fibers with an interfacial SiC xN y phase were prepared through nanochannel diffusion-controlled nitridation of polycarbosilane fibers with an NH3 gas flow. The existence of the interfacial SiC xN y phase distributed between the carbon-rich SiC phase and Si3N4 phase can improve the impedance matching and efficiently promote the production of macroscopic dipole moments in the heterointerfaces of SiC xN y-SiC and SiC xN y-Si3N4 for an enhanced multifarious polarization relaxation loss. The EMW absorption properties can be further improved by optimizing the microstructure with a continuous carbon-rich SiC phase for possessing an excellent conductive loss by converting the EMW energy into current flow. Finally, under the synergy of the interfacial SiC xN y phase and the continuous carbon-rich SiC phase, SiCN fibers can present excellent EMW absorption properties with extremely strong absorption ability (reflection loss of -63.7 dB), ultrathin thickness (1.78 mm), and wide effective absorption bandwidth (4.20 GHz). These obtained SiCN fibers also possess excellent mechanical properties with the tensile strength higher than 2.0 GPa and excellent high-temperature stability up to 1500 °C. This work provides a strategic method for optimizing the microstructure of SiCN ceramics for admirable EMW absorption properties, and the obtained SiCN fibers can be used as reinforcements of ceramic matrix composites for stealth applications under harsh environments.

New Insights into Understanding Irreversible and Reversible Lithium Storage within SiOC and SiCN Ceramics.

Within this work we define structural properties of the silicon carbonitride (SiCN) and silicon oxycarbide (SiOC) ceramics which determine the reversible and irreversible lithium storage capacities, long cycling stability and define the major differences in the lithium storage in SiCN and SiOC. For both ceramics, we correlate the first cycle lithiation or delithiation capacity and cycling stability with the amount of SiCN/SiOC matrix or free carbon phase, respectively. The first cycle lithiation and delithiation capacities of SiOC materials do not depend on the amount of free carbon, while for SiCN the capacity increases with the amount of carbon to reach a threshold value at ~50% of carbon phase. Replacing oxygen with nitrogen renders the mixed bond Si-tetrahedra unable to sequester lithium. Lithium is more attracted by oxygen in the SiOC network due to the more ionic character of Si-O bonds. This brings about very high initial lithiation capacities, even at low carbon content. If oxygen is replaced by nitrogen, the ceramic network becomes less attractive for lithium ions due to the more covalent character of Si-N bonds and lower electron density on the nitrogen atom. This explains the significant difference in electrochemical behavior which is observed for carbon-poor SiCN and SiOC materials.

Meso-Structuring of SiCN Ceramics by Polystyrene Templates.

A simple one-pot synthesis of well-defined PS-silazane nano-composites (polystyrene, PS) is described. In contrast to the, thus far, used two-step procedure ((1) assembly of a PS template bed and (2) careful filling of the voids between the PS spheres), which is restricted to macro structuring, we are able to simply mix the PS template and a commercially available silazane precursor HTT-1800 in toluene. The key is the alteration of the zeta potential of the PS template leading to a homogeneous dispersion in the silazane-toluene mixture. Removal of solvent gives rise to a highly ordered PS-silazane nano-composites and subsequent pyrolysis leads to mesoporous silicon carbonitride (SiCN) materials. The one-pot procedure has two advantages: easy upscaling and the use of PS spheres smaller than 100 nm in diameter, here 60 nm. The PS template was characterized by photon correlation spectroscopy, zeta potential measurements, scanning electron microscopy (SEM), and thermal gravimetric analysis (TGA). The resulting mesoporous SiCN materials were analyzed by SEM, transmission electron microscopy (TEM), nitrogen sorption analysis, and Fourier transform infrared measurements (FT-IR).

A Study of Trimethylsilane (3MS) and Tetramethylsilane (4MS) Based α-SiCN:H/α-SiCO:H Diffusion Barrier Films.

Amorphous nitrogen-doped silicon carbide (α-SiCN:H) films have been used as a Cu penetration diffusion barrier and interconnect etch stop layer in the below 90-nanometer ultra-large scale integration (ULSI) manufacturing technology. In this study, the etching stop layers were deposited by using trimethylsilane (3MS) or tetramethylsilane (4MS) with ammonia by plasma-enhanced chemical vapor deposition (PECVD) followed by a procedure for tetra-ethoxyl silane (TEOS) oxide. The depth profile of Cu distribution examined by second ion mass spectroscopy (SIMs) showed that 3MS α-SiCN:H exhibited a better barrier performance than the 4MS film, which was revealed by the Cu signal. The FTIR spectra also showed the intensity of Si-CH3 stretch mode in the α-SiCN:H film deposited by 3MS was higher than that deposited by 4MS. A novel multi structure of oxygen-doped silicon carbide (SiC:O) substituted TEOS oxide capped on 4MS α-SiC:N film was also examined. In addition to this, the new multi etch stop layers can be deposited together with the same tool which can thus eliminate the effect of the vacuum break and accompanying environmental contamination.