Additional Etching Research Articles

Sampling Confined Fission Tracks for Constraining Geological Thermal Histories

Fission-track modeling rests on etching, counting and measuring the lattice damage trails from uranium fission. The tools for interpreting fission-track data are advanced but the results are never better than the data. Confined-track samples must be an adequate size for statistical analysis, representative of the track population and consistent with the model assumptions and with the calibration data. Geometrical and measurement biases are understood and can be dealt with up to a point. However, the interrelated issues of etching protocol and track selection are more difficult to untangle. Our investigation favors a two-step protocol. The duration of the first step is inversely proportional to the apatite etch rate so that different apatites etch to the same Dpar. A long immersion reveals many more confined tracks, terminated by basal and prism faces. This allows consistent length measurements and permits orienting each track relative to the c-axis. Long immersion times combined with deep ion irradiation reveal confined tracks deep inside the grains. Provided it is long enough, the precise immersion time is not important if the effective etch times of the selected tracks are calculated from their measured widths. Then, whether the sample is mono- or multi-compositional, we can, post hoc, select tracks with the desired properties. The second part of the protocol has to do with the fact that fossil tracks in geological samples appear to be under-etched compared to induced tracks etched under the same conditions. This should be assumed if the semi-axes of a fitted ellipse plot above the induced-track line. In that case, an additional etch can increase the track lengths to a point where they are consistent with the model based on lab-annealing of induced tracks, a condition for valid thermal histories. Here too, it is possible to select a subset of tracks with effective etch times consistent with the model if the widths of confined tracks are measured along with their lengths and orientations.

Cu gradient design to attain high efficient solution-processed CuIn(S,Se)2 solar cells

Solution-processed chalcopyrite solar cells are widely regarded as a promising alternative method in reducing the cost compared with vacuum-based techniques. It is noted that the absorber layer usually needs to be prepared under a high insert pressure (∼1.6 atm) to suppress element loss or under a mild pressure but additional surface etching is needed for fabricating high efficient solar cell. Herein, a copper gradient structured precursor is proposed to prepare CuIn(S,Se)2 (CISSe) film under a mild pressure (1.1 atm). The designed gradient Cu not only promotes crystal grain growth and tailors the defects, but also avoids the surface etching of the formed CISSe film for the fabrication of high efficient solar cells. Further, Cu gradient design decreases the conduction band offset of heterojunction, boosting the carriers transport across the p-n heterojunction. Accordingly, a 13.35% efficient CISSe solar cell, comparable to the high efficient CISSe solar cell prepared by this method under high pressure or with film surface etching, is fabricated. This work provides a facile pathway to fabricate high efficient solution-processed chalcopyrite solar cell, avoiding high selenization pressure and film etching, and shows huge potential for solution-processed copper-based solar cells.

Silane and acid etch cross contamination of dentin and composite reduced µ-tensile bond strength.

To investigate whether acid etch contamination of silane-treated composite influenced repair bond strength and whether silane contamination on dentin influenced composite bond strength to dentin. Forty composite blocks stored in water for 4 weeks were divided into four groups. Specimens in groups 1-3 were coated with Bis-Silane and contaminated with acid etch + water spray (group 1) or water spray (group 2). Group 3 was not contaminated. Group 4 was untreated. The occlusal third of 60 third molars was cut off, ground flat, and divided into three groups. After etching, the surfaces in groups A and B were contaminated with Bis-silane. The contaminated surfaces in group A were re-etched.Each composite repair group and composite-dentin group was divided into two subgroups receiving Adper Scotchbond 1 XT or Clearfil SE Bond 2 adhesives followed by a composite build up. After ageing for 3 months, specimens were sectioned into 1.1 mm × 1.1 mm rods for tensile testing and strength calculated at fracture. The fracture was examined using microscope. Bis-Silane surface treatment increased the repair bond strength. Contamination with acid reduced the strength of the repair bond. Similar results were obtained for both adhesives. Tooth surface contamination with silane reduced the bond strength between dentin and composite. Additional acid etching or water spray on silane contaminated dentin did not influence the weakened bond strength. Most fractures were adhesive type. Silane contamination on etched dentin and acid etch contamination on silanized composite surfaces significantly reduced tensile bond strength.

Reactor wall effects in Si–Cl2–Ar atomic layer etching

This work complements our previous manuscript [J. Vac. Sci. Technol. A41, 062602 (2023)] where predictions from molecular dynamics (MD) simulations of silicon–chlorine–argon (Si–Cl2–Ar) atomic layer etching (ALE) are compared to experiments. When etch product distributions for atomic chlorine (Cl) and silicon chlorides were initially compared to optical emission spectroscopy (OES) signals, it appeared that there was a discrepancy between the MD predictions and experimental results at higher ion fluences. Experiments showed a relatively long period of nearly constant Cl-containing etch products released from the ion-bombarded surface (referred to as the “plateau”) but this effect was not observed in MD simulations. In this report, we demonstrate that the “plateau” observed in the OES signals is most likely due to the desorption of Cl-containing etch products from the walls of the reactor and subsequent adsorption on the Si substrate. Experiments varying the gas residence time in the chamber while keeping incoming gas concentrations and pressure constant support this interpretation. We also conducted experiments with an additional Ar-only flow in the chamber to reduce the concentration of Cl-containing species on the chamber walls. For both sets of flow modification experiments, we observe results consistent with the hypothesis that Cl-containing species desorbing from chamber walls are a significant cause of the observed discrepancy between MD predictions and experimental observations. If the measured OES signals are corrected for this “additional” source of Cl-containing species at the surface, the MD predictions and measured OES signals are in excellent agreement. This further supports the predictive capability of MD simulations to accurately capture the relevant physical and chemical processes in plasma-assisted ALE processes. We provide an order of magnitude estimate of the required density of Cl-containing species that would account for the additional etch products observed. Finally, we discuss the implications of this effect on ALE in plasma nanofabrication.

Polarization‐Enabled Tuning of Anapole Resonances in Vertically Stacked Elliptical Silicon Nanodisks

This work presents the polarization‐dependent behavior of the anapole state in stacked amorphous silicon (a‐Si) nanodisks with elliptical geometries. Using SiO2 as a spacer layer between the a‐Si disks, the high index contrast between these materials can be used to significantly reduce the fabrication complexity of the system compared to traditional methods that require additional etching of the spacers. A novel way of continuous tuning of the electric dipole anapole excitation within elliptical stacked a‐Si nanoresonators is demonstrated. By rotating the incident electric field's polarization angle, the anapole state can be selectively excited at two distinct wavelength positions separated by 80 nm. Experimental results show characteristic dips in the reflectance of the fabricated elliptical a‐Si stacks with wavelength positions between 1135 and 1217 nm depending on the polarization angle of the incident field which is corroborated by FDTD simulations. Through simulating the internal electric field in the resonators and using multipole decomposition, it is shown that the reflectance dips are due to anapole excitation in the individual disks. The capability to excite anapoles at two distinct wavelengths in the same structure has promising implications for the development of tunable sensors, frequency converters, and quantum memory applications.

A novel solution to improve static and dynamic retention characteristics by enhancing hydrogen passivation with in situ LD-TEOS/TEOS dual layer

We proposed a novel solution to improve both static and dynamic retention characteristics by additional etching of the thickness of Silicon Boron Nitride (SIBN), stopper when oxide etch, with in situ dual low deposition-tetraethyl orthosilicate (LD-TEOS)/TEOS Dual layer. As Dynamic Random Access Memory Cells shrink, it is difficult to obtain reliable retention properties, so it becomes more significant to reduce the number of interface trap (Nit) by hydrogen passivation. In this work, Nit decreased by reducing the thickness of SIBN, which has low hydrogen diffusion coefficients, improve the static and dynamic retention characteristics simultaneously through enhancing hydrogen passivation with in situ LD-TEOS Dual layer compensating for Metal contact to Other Bit line pad distance margin risk.

Осаждение металлов в пористую структуру оксида алюминия

Introduction. Nanostructured porous anodic aluminum oxide is used as a matrix, where it is often necessary to introduce impurities of various metals into its structure. In this case, an effective solution is the electrochemical deposition of metals into the pores of anodic aluminum oxide. However, metals can be deposited on the cathode from aqueous solutions of salts in which the electrode potential is electronegative and less than the potential for hydrogen evolution in solutions. Materials and methods. The anodizing process takes place in two stages: preliminary anodizing and anodizing itself. Before preliminary anodization, experimental samples were coated with a chemically resistant varnish for separation between the electrolyte and air. Then the samples prepared in this way were dried for 4–6 hours, after which the second stage of anodization was carried out. Results. It has been revealed that substrate inhomogeneities can be reduced by slowing down the oxide growth process or by using pore blanks. Using similar methods, a highly ordered structure can be achieved. A more dense arrangement of pores can be achieved through the use of strong acids, forming a barrier layer of thinner thickness with more penetration paths. It is worth noting that when using such acids, the number of inhomogeneities becomes not such an important parameter. Discussion. Films were obtained with greater chemical strength and a thickness of 84-100 microns, a pore diameter of 0.15-0.3 microns. By carrying out additional etching, the pore diameter was increased to 0.6 µm. Etching of PHA can be carried out in an alkali solution in an anhydrous solution of ethyl alcohol. Also, pores can be dissolved by reanodizing in a solution of phosphoric acid. The barrier layer grows to 100 A, removal is carried out with dilute hydrofluoric acid. The resulting PHAs have a fairly porous, homogeneous structure with an average effective pore size of 0.45-0.65 μm. Conclusion. Conditions have been developed for the joint deposition of two metals from aqueous solutions at close values of their electrode potentials, such as iron and cobalt. The conditions for the deposition of copper from copper sulfate into the pores of porous aluminum oxide have been established at 25 – 70 t/l of sulfate and 7÷12% sulfuric acid. Resume. The research results can be useful in obtaining films of porous anodic aluminum oxide, which can be used as substrates for creating solar-electric energy converters based on materials with a perovskite structure. This is especially true for the Republic of North Ossetia-Alania and for the mountainous territories of the North Caucasus. The use of solar energy converters will make it possible to more efficiently electrify populated areas in mountainous areas.

Polymerization mechanisms of hexamethyldisiloxane in low-pressure plasmas involving complex geometries

Hexamethyldisiloxane (HMDSO) low-pressure plasmas are known for their versatility in the deposition of plasma polymer films (PPFs) with different properties and applications. Although they have been studied for decades, the reaction mechanisms of plasma polymer formation leave open questions, particularly when deposition on 3D materials with complex geometries such as cavities and undercuts is considered. In the present study, two configurations named “cavity” and “undercut” have been selected to study the influence of diffusion of film-forming species and surface reactivity in HMDSO plasmas without and with O2 admixture. A varying spatial chemical composition of the plasma polymer deposit along the penetration depth of the studied configurations indicates different sticking probabilities of the film-forming species. Furthermore, although ion-induced effects are usually only considered for direct plasma exposure, the obtained results and additional etching experiments reveal that the contribution of high-energy particles might still be considered underneath small openings. Finally, the relevance of oxidizing chemical reactions at the surface inside the configurations is clarified when O2 is added to the plasma.

Effects of Surface Treatment Method Forming New Nano/Micro Hierarchical Structures on Attachment and Proliferation of Osteoblast-like Cells.

Titanium (Ti) and Ti-based alloys are commonly used in dental implants, and surface modifications of dental implants are important for achieving osseointegration (i.e., direct connection between the implant surface and bone). This study investigated the effect of an eco-friendly etching solution-a hydrogen peroxide-sodium bicarbonate mixture-on the surface properties and contact angles of osteoblast adhesion and proliferation on Ti surfaces. Disk-shaped Ti specimens were prepared using different surface treatments (machining, sandblasting, and sandblasting/acid-etching), and they were immersed in the etching solution and ultrasonically cleaned. Surface characterization was performed using scanning electron microscopy, digital microscopy, contact angle analysis, and X-ray photoelectron spectroscopy. MG-63 osteoblasts were cultured on the specimens, and their adhesion to the specimen surface and proliferation were examined using staining and the MTT assay, respectively. Additional etching with the etching solution caused the formation of nano/micro hierarchical structures, increased surface roughness, and enhanced hydrophilicity. Osteoblast adhesion and proliferation were found to improve on the modified surfaces. The eco-friendly etching method has the potential to enhance the biological properties of Ti implant surfaces and thereby improve dental implant performance.

Repeated Etching Cycles of Resin Infiltration up to Nine Cycles on Demineralized Enamel: Surface Roughness and Esthetic Outcomes-In Vitro Study.

Resin infiltration (RI) is used to mask enamel opacities. There are three recommended etching cycles. However, anecdotal evidence suggests that favorable esthetics outcomes can be obtained by increasing the etching cycles. This study aimed to evaluate the effects of repeated etching cycles during RI application on esthetic changes and surface roughness of demineralized enamel at multiple treatment stages. Artificial demineralization was prepared on the buccal surface of ninety sound extracted premolars. The teeth were divided into nine groups (n = 10); with each consecutive group having one additional etching cycle up to nine etching cycles. Resin infiltrant was performed twice, first for 3 min (Resin 1) and again for 1 min (Resin 2). Surface roughness and esthetic changes were assessed using a profilometer (Ambios XP-200) and Minolta spectrophotometer, respectively, at baseline (sound enamel), etching, resin 1, resin 2, 7 days, and 28 days post resin applications. Data were analyzed with two-way ANOVA (p < 0.05). There was a significant interaction between the different stages and various groups of etching cycles on surface roughness, F(48, 126) = 3.48, p < 0.001. There was a significant interaction between the different stages and various groups of etching cycles on color changes, F(4, 126) = 1.177, p = 0.045. The surface roughness of demineralized enamel infiltrated with RI was less than that of sound enamel (baseline). There is a significant difference in color changes between resin 1 and resin 2 (p < 0.05). After five etching cycles, RI improved the esthetic of the color of teeth similar to the baseline. Surface roughness and color changes remained constant for 28 days. RI can be considered an effective and predictable treatment option for the restoration of early enamel lesions owing to its better surface characteristics and reliable masking effects. The color stability and surface roughness stay unaltered for up to 28 days.

Real-time 3D plane-wave imaging using annular capacitive micromachined ultrasonic transducer array

Imaging methods and 2D sparse arrays have been extensively researched to realize real-time 3D volumetric imaging with higher frame rates. In this study, we developed a 3D plane-wave imaging method using an annular capacitive micromachined ultrasonic transducer (CMUT) array as a breakthrough technique for realizing 3D imaging with a limited number of elements. We adopted the double oxidation and wafer bonding processes for creating the cavity of a CMUT with a 2 µm silicon membrane. To ensure surface uniformity before the bonding process, we implemented an additional reactive ion etching process after the second oxidation. The characterization results showed that the resonant frequency of the proposed device was 6.2 MHz with 65 V collapse voltage. The demonstration of real-time 3D volumetric imaging was conducted in oil using a Vantage 64 ultrasound research system. A plane-wave imaging scheme was used to detect wire phantoms immersed in the oil, with 289 plane waves transmitted over a range of 20° from the center of the annular array. The reconstructed data were used to create three orthogonal cross sections of the target region. The − 6 dB lateral and axial resolutions were 0.56 mm and 0.35 mm for the wires positioned at 18 mm from the proposed device, which were narrow enough to detect a wire phantom of 380 µm diameter. The normalized frame rate was calculated and compared with that in a previous study. We verified that plane-wave imaging has advantages in real-time imaging when compared with the classic phased array and synthetic phased array. Thus, the annular CMUT array is a promising mechanism for real-time 3D imaging with higher frame rate than that possible with previous methods.

Single-atom Co-N4 catalytic sites anchored on N-doped ordered mesoporous carbon for excellent Zn-air batteries

• Co-SA/N-C 900 was synthesized via in-situ pyrolysis of co-precursors containing sucrose, dicyandiamide, and Co salt without additional acid etching and pyrolysis activation. • The large specific surface area and an ordered mesoporous structure endow the accessibility of active sites. • Atomic Co-N 4 catalytic sites with adjacent graphitic N dopants can boost the intrinsic activity of the obtained catalyst. • Co-SA/N-C 900 exhibits an onset potential of 0.96 V and a half-wave potential of 0.87 V, outperforming commercial Pt/C. Developing efficient transition metal-nitrogen-carbon (TM-N-C) catalysts with abundant accessible active sites has been in the limelight in recent years due to their exceptional application potential in Zn-air batteries (ZABs). Herein, we report the simple and environmentally-friendly fabrication of a single-atom Co electrocatalyst, Co-SA/N-C 900 , via in-suit pyrolysis of the co-precursor containing sucrose, dicyandiamide, and Co salts. The Co single atoms coordinated with adjacent N atoms are anchored on the doped ordered mesoporous carbon, generating the atomic Co-N 4 moiety. Co-SA/N-C 900 displays high oxygen reduction reaction (ORR) activity with an onset potential of 0.96 V and a half-wave potential of 0.87 V. Notably, the liquid ZAB with Co-SA/N-C 900 catalyst exhibits exceptional discharge specific capacity of 706.38 mAh g –1 , peak power density of 191.11 mW cm –2 , and excellent stability at high current densities up to 100 mA cm –2 , surpassing commercial Pt/C. According to the density functional theory (DFT) study, the Co-N 4 moiety with graphitic N dopants can decrease the rate-determining step (RDS) energy barrier and thus accelerate the ORR process. This study offers experimental and theoretical guidelines for the rational design of TM-N-C catalysts for practical implementation with notable ORR activity for application in ZABs. Co-SA/N-C 900 possesses atomic Co-N 4 moiety with graphitic N dopants, a large specific surface area, and an ordered mesoporous structure simultaneously, which is conducive to the accessibility of reactant molecules towards the active sites for more efficient mass transfer during the electrocatalytic process, exhibiting efficient ORR activity and Zn-air battery performance.

Evaluation of Self-Adhering Flowable Composites on Repeated Bracket Bonding Process: An In Vitro Study

Duration of orthodontic treatment becomes major concern. The present study compared shear bond strength (SBS) and adhesive remnant index (ARI) values of different adhesive systems with different application methods on rebonding process of retrieved orthodontic brackets. Eighty premolar teeth were equally divided into five groups. Transbond XT (TXT) which belongs to total-etch system was used in Group 1 as the control group. Nova Compo-SF (NC) and Vertise Flow (VF) (Kerr Dental, Italy) which are self-adhering flowable composites were used in Group 2 (NC+etch) and Group 3 (VF+etch) respectively with additional etching before application. Group 4 (NC) and Group 5 (VF) were used by following instructions of each brand. The brackets were debonded with a bracket removing plier and rebonded with the same procedures after sandblasting of the bracket and surface cleaning of the enamel. SBS and ARI were measured for each sample. Comparison between all groups was performed by Kruskal-Wallis test and chisquare test. The highest SBS was observed in NC+etch (median = 11.44, mean = 13.49±9.42), followed by NC (median = 10.17, mean = 11.35±6.55), TXT (median = 6.36, mean = 8.06±6.33), VF+etch (median = 5.68, mean = 6.75±4.58), and VF (median = 2.62, mean = 2.92±2.57), respectively. ARI 1 was observed in 81.3% of TXT whereas 62.5% of NC+etch. ARI 1, 2, and 3 were equally distributed in VF+etch group (31.3%). ARI 5 was observed in 37.5% of NC and 62.5% of VF. Analyses referred to statistically significant differences between five groups regarding both SBS and ARI (p &lt; 0.001). As NC showed the highest SBS on rebonding process, it can be a promising alternative to TXT which is the gold standard.

Zn(O,S) Buffer Layer Deposited by High Vapor Transport Deposition for Controlling Band Alignment of Cu2ZnSn(SxSe1−x)4 Thin‐Film Solar Cell Heterojunction

The replacement of the CdS buffer layer is desirable for the development of nontoxic and environmentally friendly kesterite thin‐film solar cells. Band alignment is critical to the energy conversion of solar cells and achieving optimum design of the layers requires high control of the process. Herein, the band alignment dependence of the CZTSSe/Zn(O,S) interface using different oxygen concentrations is reported, which results in a high controllability process for the energy levels of the buffer layers, which is desirable to achieve higher solar cell efficiencies. It is also demonstrated that a Zn(O,S) thin‐film layer can be deposited using a novel process: high vapor transport deposition. The main advantages observed are as follows: 1) absorber and buffer layers can be deposited in the same vacuum reactor, thus avoiding atmospheric contamination; 2) no additional etching or annealing process is needed; and 3) the process conditions have accuracy control of gas injection, which allows precise tuning of the oxygen content in the film. Optimal oxygen concentration is determined to avoid spike‐like CBO, achieving a conversion efficiency level of 6.87% for kesterite‐based thin‐film solar cells with a Cd‐free buffer layer.

Using a Au/pitted a-plane GaN substrate to aggregate polar molecules for highly efficient surface-enhanced Raman scattering.

Searching for efficient surface-enhanced Raman scattering (SERS) substrates remains a challenge. In this study, we used metal-organic chemical vapor deposition to directly grow a pitted a-plane GaN thin film, subsequently covered by a thin Au layer (∼25nm), for use as a SERS substrate, without the need for any additional etching or lithography process. The SERS substrate containing these micrometer-sized pits provided a low limit of detection (∼10-9 M) for Rhodamine 6G (R6G), with a high enhancement factor (4.27 × 108) relative to normal Raman spectroscopy. Furthermore, Raman spectral mapping indicated that most of the R6G molecules were concentrated in the pits, enhancing the localization of the probe molecules for further analysis. The same molecular localization phenomenon was also effective for polar methylene blue but not for nonpolar paraffin. The molecular aggregation became more ambiguous upon increasing the thickness of the Au layer, suggesting that the polarity of the Ga and N atoms in the pits was responsible for the efficient aggregation of the polar R6G molecules, which could be potentially beneficial for biomedical detection.

Transparency and icephobicity of moth eye-inspired tailored omniphobic surface

ABSTRACT In this work, we presented a facile method to introduce a transparent and anti-icing omniphobic surface fabricated on the glass substrate. The uniform moth eye-inspired structure was generated by the Deep Reactive Ion Etching method and followed by an additional wet etching step to enhance the sharpness of the nanostructure. A hydrophobe compound was assembled on the rough substrate by chemical vapor coating to achieve remarkable liquid-repellent properties. The tensile strength test was conducted using a designed apparatus to evaluate the anti-icing performance of functional surfaces compared to the as-received one. In addition, the optical performance in terms of transmittance and reflectance also was tested and revealed significant optical enhancement owing to the unique design of nanoarrays. The results demonstrated the great potential and proposed design for multifunctional surfaces.

The Effect of Dental Adhesive Composition and Etching Mode on Microleakage of Bonding Agents in Primary Molar Teeth.

The dilemma of microleakage at the composite-tooth interface is still a major challenge in operative dental practice. This study aimed to compare the microleakage of universal adhesive with self-etch and total-etch bonding strategies for restoration of class-II primary molar cavities. This in vitro, experimental study was conducted on 75 extracted primary molars. Class-II cavities were prepared in mesial or distal surfaces. The teeth were randomly divided into five groups of Adper Single Bond 2 (3M ESPE; St Paul, MN, USA), Clearfil SE Bond (Kuraray Noritake, Osaka, Japan), G-Bond (GC Corp., Tokyo, Japan), G-Premio Bond (GC Corp., Tokyo, Japan) with total-etch mode and G-Premio Bond with self-etch mode. Cavities were also restored with Nano-hybrid resin composite (Grandio, VOCO, Cuxhaven, Germany) and incubated for 24 hours, followed by thermocycling at 1500× between 5-55°C within a dwell time of 20 seconds. Later, the cavities were placed in 1M silver nitrate solution and evaluated under a stereomicroscope. Finally, microleakage was assessed quantitatively and qualitatively. One tooth in each group was prepared and evaluated under a scanning electron microscope (SEM). Data were analyzed using One-way ANOVA, Tukey's post hoc test and Chi-square test (p< 0.05). The microleakage values were significantly different in the study groups (p&lt; 0.05). The highest level of microleakage was noted in G-Bond and the lowest in G-Premio Bond with total etching. There was a significant correlation between the qualitative and quantitative measurements of microleakage. The G-Premio Bond yielded acceptable results in terms of microleakage in total-etch and self-etch modes. However, additional etching is recommended to improve the quality of bonding.

A snapback-free and fast-switching planar-gate SOI LIGBT with three electron extracting channels

In this paper, a snapback-free and fast-switching SOI LIGBT with three electron extracting channels (TEC) is proposed and investigated. Compared with SBM LIGBT, the trench gate of n-MOS is changed to a planar gate, and a P- region is added to prevent N+ short circuit while providing electron extracting channel. Simulation results show that TEC decreases EOFF by 15% at VON=1.8V relative to SBM when all three channels are open, while TEC still decreases EOFF by 10% at VON =1.55V relative to SBM when only two channels are available. The device achieves the same breakdown voltage level of 603V as SBM without additional trench etch process required.

One-step in-situ low damage etching of SiC/SiC composites by high-temperature chemical-assisted laser processing

SiC/SiC composites have a promising application prospect in the fields of aero-engine turbine blades and other hot-end components due to their excellent properties. It is difficult to machine SiC/SiC composites by traditional mechanical processing because of the ultra-high hardness and anisotropic character. The routinely laser direct processing in the air produce thermal effect damage, resulting in heat-affected zones and microcracks. Here high-temperature chemical-assisted nanosecond laser processing was investigated to realize one-step in-situ fast etching without causing damage to the structure of SiC/SiC composites. Firstly, the chemical wet etching only occurred in the laser-induced local high-temperature region. There was no additional etching damage to the substrate material in the region where the temperature was relatively low. Secondly, chemical liquid served as a transparent constraint layer, the ablation pressure on the material increased in a liquid confined environment. In comparison with laser direct etching in the air, the exposed fiber was not a needle-like structure and tubular structure but turned into a thin and flat tongue-like structure. The etching behavior of 0° fiber layer, 90° fiber layer, and crossing regions of fibers of different directions at low and high laser intensities were studied. Further, the hardness and friction coefficient of SiC/SiC composites after laser direct etching in the air and high-temperature chemical-assisted laser etching were compared. The chemical elementary composition before and after etching was measured to reveal the oxidized and carbonized characteristics. It was concluded that the action mechanism was the combined result of high-temperature decomposition, laser-induced ablation pressure in the liquid confined region, and local chemical wet etching. The results demonstrate that high-temperature chemical-assisted laser etching has some advantages over traditional laser beam machining and is a potential processing method for SiC/SiC composites.

A comprehensive in vitro study on the performance of two different strategies to simplify adhesive bonding

ObjectiveThe purpose of this study is to compare the bonding performance and mechanical properties of two different resin composite cements using simplified adhesive bonding strategies.Materials and methodsShear bond strength of two resin composite cements (an adhesive cement: Panavia V5 [PV5] and a self‐adhesive cement: RelyX Universal [RUV]) to human enamel, dentin, and a variety of restorative materials (microfilled composite, composite, polymer‐infiltrated ceramic, feldspar ceramic, lithium disilicate and zirconia) was measured. Thermocycle aging was performed with selected material combinations.ResultsFor both cements, the highest shear bond strength to dentin was achieved when using a primer (PV5: 18.0 ± 4.2 MPa, RUV: 18.2 ± 3.3 MPa). Additional etching of dentin reduced bond strength for RUV (12.5 ± 4.9 MPa). On enamel, PV5 achieved the highest bond strength when the primer was used (18.0 ± 3.1 MPa), while for RUV etching of enamel and priming provided best results (21.2 ± 6.6 MPa). Shear bond strength of RUV to restorative materials was superior to PV5. Bonding to resin‐based materials was predominantly observed for RUV.ConclusionsWhile use of RUV with the selective‐etch technique is slightly more labor intensive than PV5, RUV (with its universal primer) displayed a high‐bonding potential to all tested restorative materials, especially to resin.Clinical significanceFor a strong adhesion to the tooth substrate, PV5 (with its tooth primer) is to be preferred because etching with phosphoric acid is not required. However, when using a wide range of varying restorative materials, RUV with its universal primer seems to be an adequate option.