Etching Pattern Research Articles

Plasmonic photoconductive terahertz focal-plane array with pixel super-resolution

AbstractImaging systems operating in the terahertz part of the electromagnetic spectrum are attractive due to their ability to penetrate many opaque materials and provide unique spectral signatures of various chemicals. However, the use of terahertz imagers in real-world applications has been limited by the slow speed, large size, high cost and complexity of present systems, largely due to the lack of suitable terahertz focal-plane array detectors. Here we report a terahertz focal-plane array that can directly provide the spatial amplitude and phase distributions, along with the ultrafast temporal and spectral information of an imaged object. It consists of a two-dimensional array of ~0.3 million plasmonic photoconductive nanoantennas optimized to rapidly detect broadband terahertz radiation with a high signal-to-noise ratio. We utilized the multispectral nature of the amplitude and phase data captured by these plasmonic nanoantennas to image different objects, including super-resolved etched patterns in a silicon substrate and defects in battery electrodes. By eliminating the need for raster scanning and spatial terahertz modulation, our terahertz focal-plane array offers more than a 1,000-fold increase in the imaging speed compared with the state of the art and potentially suits a broad range of applications in industrial inspection, security screening and medical diagnosis, among others.

Fabricating mesoscale polymer ribbons with tunable mechanical properties via evaporative deposition and dewetting.

Synthetic replication of the precise mesoscale control found in natural systems poses substantial experimental challenges due to the need for manipulation across multiple length scales (from nano- to millimeter). We address this challenge by using a 'flow coating' method to fabricate polymer ribbons with precisely tunable dimensions and mechanical properties. Overcoming barriers that previously limited the achievable range of properties with this method, we eliminate the need for substrate patterning and post-processing etching to facilitate the production of high aspect ratio, filament-like ribbons across a range of polymers-from glassy polystyrene to elastomeric poly(butadiene), as well as poly(butadiene-block-styrene). Our method uniquely enables the preservation of chemical fidelity, composition, and dimensions of these ribbons, leveraging polymers with elastic moduli from GPa to tens of MPa to achieve multi-scale features. We demonstrate the role of the elastocapillary length (γ/E) in determining morphological outcomes, revealing the increase in curvature with lower elastic modulus. This finding underscores the intricate relationship among surface tension, elastic modulus, and resultant structural form, enabling control over the morphology of mesoscale ribbons. The soft (MPa) polybutadiene-based ribbons exemplify our method's utility, offering structures with significant extensibility, resilience, and ease of handling, thus expanding the potential for future applications. This work advances our understanding of the fundamental principles governing mesoscale structure formation and unlocks new possibilities for designing soft materials with tailored properties, mirroring the complexity and functionality observed in nature.

Recent progress in plasma modification of 2D metal chalcogenides for electronic devices and optoelectronic devices.

Two-dimensional metal chalcogenides (2D MCs) present a great opportunity for overcoming the size limitation of traditional silicon-based complementary metal-oxide-semiconductor (CMOS) devices. Controllable modulation compatible with CMOS processes is essential for the improvement of performance and the large-scale applications of 2D MCs. In this review, we summarize the recent progress in plasma modification of 2D MCs, including substitutional doping, defect engineering, surface charge transfer, interlayer coupling modulation, thickness control, and nano-array pattern etching in the fields of electronic devices and optoelectronic devices. Finally, challenges and outlooks for plasma modulation of 2D MCs are presented to offer valuable references for future studies.

Improvement of AlGaN/GaN High-Electron-Mobility Transistor Radio Frequency Performance Using Ohmic Etching Patterns for Ka-Band Applications.

In this paper, AlGaN/GaN high-electron-mobility transistors (HEMTs) with ohmic etching patterns (OEPs) "fabricated to improve device radio frequency (RF) performance for Ka-band applications" are reported. The fabricated AlGaN/GaN HEMTs with OEP structures were used to reduce the source and drain resistances (Rs and Rd) for RF performance improvements. Within the proposed study using 1 μm hole, 3 μm hole, 1 μm line, and 3 μm line OEP HEMTs with 2 × 25 μm gate widths, the small signal performance, large signal performance, and minimum noise figure (NFmin) with optimized values were measured for 1 μm line OEP HEMTs. The cut-off frequency (fT) and maximum oscillation frequency (fmax) value of the 1 μm line OEP device exhibited optimized values of 36.4 GHz and 158.29 GHz, respectively. The load-pull results show that the 1 μm line OEP HEMTs exhibited an optimized maximum output power density (Pout, max) of 1.94 W/mm at 28 GHz. The 1 μm line OEP HEMTs also exhibited an optimized NFmin of 1.75 dB at 28 GHz. The increase in the contact area between the ohmic metal and the AlGaN barrier layer was used to reduce the contact resistance of the OEP HEMTs, and the results show that the 1 μm line OEP HEMT could be fabricated, producing the best improvement in RF performance for Ka-band applications.

A Cyclic Etching Process Using HFE-347mcc3 as a Lower-GWP Alternative to Perfluorocarbons for High-Aspect-Ratio SiO2 Features

As circuits continue to integrate at higher levels, the critical dimensions of DRAM and 3D-NAND are decreasing, leading to an increase in aspect ratios of various features such as contact holes and via holes in DRAM, and channel holes of stack layers in 3D-NAND. This trend has made the process of etching high-aspect-ratio SiO2 features more challenging. To achieve this, it is necessary to satisfy specific conditions including high selectivity to the mask or the underlayer film and the anisotropic etch profiles.Perfluorocarbons (PFCs) such as CF4 and c-C4F8 are commonly used for SiO2 etching. PFCs form a thicker steady-state fluorocarbon film on Si than SiO2, leading to high SiO2/Si selectivity. In addition, PFCs enable anisotropic etching since a passivation layer is formed on the sidewall, preventing lateral etching of the sidewall by chemical etchants.However, PFCs are a representative greenhouse gas with a high global warming potential (GWP) compared to CO2, causing significant adverse effects on global warming. Therefore, there have been efforts to reduce greenhouse gas emissions, such as setting goals for greenhouse gas reduction by each country through the Paris Agreement in 2015. Semiconductor manufacturers have also committed to reducing greenhouse gas emissions per silicon substrate area by 30% compared to 2010. In this regard, various studies are being conducted to develop a SiO2 etching process using alternative materials with lower GWP than PFCs. Fluorinated ethers and fluorinated alcohols are potential substitutes due to their low GWPs and short lifetimes. For example, heptafluoropropyl methyl ether (HFE-347mcc3) has a GWP of ~530 and an atmospheric lifetime of 5.2 years, significantly lower than those of PFCs.During etching of SiO2, the mask is susceptible to damage and corrosion by ions, resulting in various pattern deformations such as bowing, necking, and striation. These deformations adversely affect the miniaturization of the DRAM structure by reducing the process margin between holes and have a negative influence on the electrical characteristics of the device, such as contact resistance, line edge roughness, and line width roughness.To prevent these pattern deformations, the cyclic etching process that repeats the passivation layer deposition step and SiO2 pattern etching step was devised. A fluorocarbon film is deposited on the mask to protect it, then SiO2 is etched. The fluorocarbon film is deposited again to reinforce the mask and damaged fluorocarbon film during the etching process, and then SiO2 etching step is repeated to achieve the high-aspect-ratio SiO2 features.In this study, the cyclic etching process was conducted using HFE-347mcc3 as a lower-GWP alternative to PFCs to etch SiO2 contact holes. The effect of the duration of each step on the etch profile was investigated by adjusting the duration of the deposition and etching steps. This work demonstrated the feasibility of using HFE-347mcc3 as a lower-GWP alternative to PFCs for cyclic etching of SiO2 contact holes to obtain anisotropic etch profiles.

High-precision and high-speed etching of diamond surfaces using Fe–Ni alloy catalyzed H–O plasma etching

Power devices with low losses are essential for achieving high-efficiency, low-cost, and miniaturized inverters and advance electronic technologies. Recently, diamond-based p-type groove semiconductor field-effect transistors have emerged as a hot research topic. Conventional method of fabricating surface grooves using inductively coupled plasma etching is costly and relatively slow. Here, we realized a novel diamond machining method using Fe–Ni alloy catalyzed H–O microwave plasma etching that can achieve high-rate and high-precision etching of diamond surfaces. Two major factors affecting the etching rate and pattern accuracy, wettability of diamond and carbon solubility with liquid metal, were identified. Oxygen added in H2 plasma allows the wetting increase, resulting in an improvement in uniformity of the etch area, while keeping the etch rate as high as 3 μm/min. The developed approached is promising for low-cost diamond patterning in electronic devices fabrication processes.

Development of Intentional Contamination in Iron by Bath for Silicon Wafers and Evaluation of VPD-Bulk and LPD-Bulk for Metallic Contaminants Analyses by ICPMS

This paper offers a preliminary study for the analysis of metallic contamination on front-end patterned wafers obtained by two different techniques based on the etching of the whole patterns, LPD-Bulk and VPD-Bulk coupled with an ICPMS. To elaborate the analysis of patterned wafers, methods were first verified and optimised on reference Si wafers. Both techniques are complementary methods for the etching of wafers. LPD-Bulk enables a fast etching of several micrometres of Si but with less precision than VPD-Bulk, which is more adapted for the etching of layers thinner than 1 micrometre. The intentional contamination in SC1 and H2O bath of monitoring wafers showed that contamination in H2O is better controlled due to the absence of chemical reactions, competition between oxidation and etching processes occurring during SC1. And diffusion of contaminants at the tested temperatures from 20°C to 80°C, does not occur. Heat treatment should be applied to allow the diffusion of metallic contaminants in the bulk of the wafers.

Process optimization for shallow trench isolation etch using computational models

The critical dimensions of advanced semiconductor manufacturing processes have decreased to a few tens of nanometers while the aspect ratios have increased beyond 100. The performance of plasma etch patterning processes as well as the cost and time of the development cycle are critical to the success of ramping a new technology node toward profitable high-volume manufacturing. In this paper, a computational patterning software, ProETCH®, has been developed with rigorous physics and advanced algorithms for modeling the etch patterning process, with the featured capabilities in calibrating the reaction mechanisms and optimizing the etch process. A shallow trench isolation etch process using self-aligned double patterning was investigated. A reaction mechanism of silicon etch by Ar/Cl2 plasma was developed to address the surface reactions, and a plasma hypermodel was introduced to correlate process operating conditions to plasma parameters at the wafer surface. The parameters of the reaction mechanism and the plasma hypermodel were calibrated with experimental data obtained from cross-sectional scanning electron microscope (XSEM) images. The calibrated model is used to identify the different fundamental pathways that contribute to the observed profile metrics in XSEMs. The model was then used for process development and optimization by solving the forward and inverse problems. In the forward problem, the model is used to predict the etching profile at different process conditions. Predictions for both interpolation conditions (process parameters within the range used for developing the model) and extrapolation conditions (process parameters outside of the range used for developing the model) agree well with the experimental data with the root mean square error less than 4 nm (1 nm resolution used for the mesh). In the inverse problem, the developed model is used to search for process conditions (e.g., values of bias power and pressure), which could result in desirable profiles. The solutions to the inverse problem demonstrate a degeneracy in process space of the etching process for a given target profile.

Silver diamine fluoride and resin-dentin bonding: Optimization of application protocols

ObjectiveTo evaluate the effect of SDF-based treatments following delayed bonding and surface treatment approaches on resin-dentin bonding efficiency of a universal adhesive under different application modes. MethodsMid-coronal dentin surfaces from sound third molars were randomly treated with 38% silver diamine fluoride (SDF) and/or additionally with potassium iodide (SDF/KI). Untreated dentin served as control. SDF-treated teeth were assigned to groups according to surface treatment approaches (air-abrasion and water rinsing), the application mode of a mild universal adhesive (etch-and-rinse or self-etch) and delayed bonding (immediate, 7, 15 or 30 days). Microtensile bond strength (n = 5), SEM analyses of hybrid layer formation and dentin etching patterns and dentin permeability were evaluated. Data were analyzed with factorial ANOVA. ResultsSDF-based treatments affected dentin bonding depending on application mode and surface treatment approaches (p<0.001). Etch-and-rinse bonding was not affected by SDF-based treatments (p<0.05), producing more homogenous hybrid layers. While dentin etching patterns of etch-and-rinse application were not affected by SDF-based treatments, self-etching presented limitations. Bond strength reductions of self-etched dentin were restored by silver-removal strategies containing a water-rinsing step (p<0.05). Delayed bonding additionally reduced dentin permeability (p<0.05), further decreasing with longer periods (p<0.05). ConclusionAlthough the negative effect of SDF-based treatments on resin-dentin bonding can be avoided by strategies incorporating water-rinsing before hybridization, delayed bonding brings additional advantages due to higher mineral deposition. Clinical significanceWhile the etch-and-rinse technique avoids major bonding drawbacks to SDF-treated dentin, self-etch bonding requires removal of excess silver deposits before hybridization. Performing SDF-based treatments and dentin hybridization in separate sessions (>15 days apart) potentialize mineral deposition improving caries control and service life of composite restorations.

Etching mechanism of high-aspect-ratio array structure

Through-Silicon-Via (TSV) is an significant technology that is being widely employed in micro-electro-mechanical system (MEMS) manufactories. However, it is remain challenging to obtain a deep silicon etching with vertical-angle and smooth-sidewall characterizes by silicon-etching anisotropy through TSV technology. Herein, we use inductively coupled plasma (ICP) to obtain the deep silicon etching anisotropy. Chamber pressure, Bosch process cycles, bias powers, and the size of the etching pattern, which are the critical controllable process parameters, have been investigated to achieve the silicon-etching anisotropy. The results reveal that the sidewall angle of the array structure becomes increasingly slanted while raising chamber pressure from 2 to 15 Pa in the SF6 etching process of the first step of the cycle in the Bosch process. As the cycles increase from 60 to 240 cycles at the bias power of 100 w, the anisotropy decreases from 0.80 to 0.5. With RF bias powers rise from 200 to 400 w, the anisotropy enhances from 0.80 to 0.94. Due to the collision of active ions with each other, the sidewall angle and anisotropy of a high aspect-ratio array structure severely depend on the incidence angle of the active ions. The “Si etching balance model” has been established for the fabrication of TSV.

Deep neural network-based reduced-order modeling of ion–surface interactions combined with molecular dynamics simulation

With the advent of complex and sophisticated architectures in semiconductor device manufacturing, atomic-resolution accuracy and precision are commonly required for industrial plasma processing. This demands a comprehensive understanding of the plasma–material interactions—particularly for forming fine high-aspect ratio (HAR) feature patterns with sufficiently high yield in wafer-level processes. In particular, because the shape distortion in HAR pattern etching is attributed to the deviation of the energetic ion trajectory, the detailed ion–surface interactions need to be thoroughly investigated. In this study, molecular dynamics (MD) simulations were utilized to obtain a fundamental understanding of the collisional nature of accelerated Ar ions on the fluorinated Si surface that may appear on the sidewall of the HAR etched hole. High-fidelity data for ion–surface interaction features representing the energy and angle distributions (EADs) of sputtered atoms for varying degrees of surface F coverage and ion incident angles were obtained via extensive MD simulations. A deep learning-based reduced-order modeling (DL-ROM) framework was developed for efficiently predicting the characteristics of the ion–surface interactions. In the ROM framework, a conditional variational autoencoder (AE) was implemented to obtain regularized latent representations of the distributional data with the condition of the governing factors of the physical system. The proposed ROM framework accurately reproduced the MD simulation results and significantly outperformed various DL-ROMs, such as AE, sparse AE, contractive AE, denoising AE, and variational AE. From the inferred features of the sputtering yield and EADs of sputtered/scattered species, significant insights can be obtained regarding the ion interactions with the fluorinated surface. As the ion incident angle deviated from the glancing-angle range (incident angle >80°), diffuse reflection behavior was observed, which can substantially affect the ion transport in the HAR patterns. Moreover, it was hypothesized that a shift in sputtering characteristics occurs as the surface F coverage varies, based on the inferred EADs. This conjecture was confirmed through detailed MD simulations that demonstrated the fundamental relationship between surface atomic conformations and their sputtering behavior. Combined with additional atomistic-scale investigations, this framework can provide an efficient way to reveal various fundamental plasma–material interactions which are highly demanded for the future development of semiconductor device manufacturing.

Nucleation of Threading Dislocations in 4H-SiC at Early Physical-Vapor-Transport Growth Stage

In this work, we identify the nucleation mechanism of threading dislocations (TDs) associated with stacking faults (SFs) and 15R-SiC at the early growth stage of 4H-SiC single crystals grown by the physical vapor transport (PVT) technology. By combining molten KOH etching and photochemical etching, we successfully reveal etch pits of TDs and linear etch patterns of SFs on the (112̅0) surface of 4H-SiC single crystals. Systematic investigations based on transmission electron microscopy (TEM) observations and Raman analysis indicate that the Si–C bilayer stacking sequence of SFs is (3, 2) in Zhdanov’s notation. The accumulation of SFs (3, 2) gives rise to the polymorph fluctuation and thus the formation of 15R-SiC at the early PVT growth stage of 4H-SiC single crystals. Quantitative stress analyses indicate that the strain field distributions along the SFs (3, 2) and the 15R-/4H-SiC interfaces are inhomogeneous, which give rise to the nucleation of TDs and low-angle grain boundaries (LAGBs), respectively. The nucleation of LAGBs releases the high stress at the 15R-/4H-SiC interface, which facilities the following 4H-SiC single-crystal growth. Our work indicates that the avoidance of polymorph fluctuation is important to the reduction of TDs at the early growth stage of PVT-grown 4H-SiC single crystals.

Assessing tolerances in direct write laser grayscale lithography and reactive ion etching pattern transfer for fabrication of 2.5D Si master molds

Assessing tolerances in direct write laser grayscale lithography and reactive ion etching pattern transfer for fabrication of 2.5D Si master molds

Systematic Study of the Multiple Variables Involved in V2AlC Acid-Based Etching Processes, a Key Step in MXene Synthesis.

The realization of the broad range of application of MXenes relies on the successful and reproducible synthesis of quality materials of tailored properties. To date, most MXenes have been produced making use of acid-based etching methods, yet an in-depth understanding of etching processes is lacking. Herein, we have engaged in a comprehensive study of the multiple variables involved in the synthesis of V2CTx with focus on the properties of etched materials. Two main sets of experiments were considered, each using a different V2AlC precursor and a range of synthesis variables including reaction time and temperature, mixing rate, and type of acid. Correlations of synthesis conditions-materials properties were investigated using a broad range of characterization techniques including analytical methods, scanning and transmission electron microscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Findings indicated the crucial relevance of properties of the MAX precursor such as elemental composition, particle size, and crystal structure on etching processes and properties of etched materials. Particularly, depending on the MAX precursor, two etching patterns were identified, core-shell and plate-by-plate, the latter describing a more efficient etching. Combined studies of elemental composition, crystal structure, and yield quantification allowed us to evaluate the effectiveness of etching processes. XRD studies revealed key crystal-structure-type of acid correlations showing advantages of using a HF/HCl mix over only HF. Analytical methods XRD and XPS delivered insights into undergoing chemical processes and their influence on bulk and surface chemistry of etched materials. The relevance for reaction kinetics of highly correlated variables such as reaction vessel dimensions, mixing efficiency, and reaction temperature was recognized. For the first time, a MXene synthesis has been investigated comprehensively highlighting its multivariable nature and the high variable intercorrelation, opening up venues for further investigation on MAX and MXene synthesis.

The Story Behind the Link between Molecular Chirality and Crystal Shape

AbstractHere we describe the story behind the link between molecular chirality and macroscopic phenomena, the latter being a probe for the direct assignment of absolute configuration of chiral molecules. First, a brief tour of the history of molecular stereochemistry, starting with the classic experiment reported byPasteurin 1848 on the separation of enantiomorphous crystals of a salt of tartaric acid, and his conclusion that the molecules of life are chiral of single‐handedness. With time, this study raised, inter alia, two fundamental questions: the absolute configuration of chiral molecules and how a molecule of given configuration shapes the enantiomorphous morphology of its crystal. As for the first question, following the beginning of crystal structure determination by X‐ray diffraction in 1912, it took almost 40 years beforeBijvoetassigned molecular chirality through the esoteric method involving anomalous X‐ray scattering. We have been able to address and link both questions through ‘everyday concepts of left and right’ (in the words ofJack Dunitz) by the use of ‘tailor‐made’ auxiliaries. By such means, it proved possible to reveal, through morphology, etch patterns, epitaxy and symmetry reduction of both chiral and, paradoxically, centrosymmetric crystals, the basic chiral symmetry of the molecules of life, the α‐amino acids and sugars.

Double-Band Metasurface Infrared Optics for Integrated Multichannel Spectral Sensors

Simultaneously identifying the composition of mixtures and determining their concentration levels has aroused much attentions recent years to meet the large demands of compact and low-cost infrared spectral sensors to replace their conventional bulky counterparts with costly separated infrared components. In this work, we propose a design method for multi-channel metasurface infrared array optics covering two bands (MWIR/LWIR) for construction of integrated infrared gas sensors. The use of metasurface microstructures with same height realizes the effective filtering and focusing of electromagnetic waves at multiple wavelengths in the both infrared bands, which is beneficial to decrease the manufacturing costs. Four-channel metasurface lens arrays and filter arrays with operating wavelengths of 3.5 μm, 9.7 μm, 10.6 μm and 3.9 μm corresponding to the infrared absorption peaks of three gases of ethanol, ammonia, ethylene and one reference wavelength respectively, were designed and produced by photolithographic patterning and dry etching processes on silicon substrates. The multi-channel metasurface infrared optics have the advantages of easy fabrication and integration with wide-band infrared detector array to form a compact infrared spectral detector, which meets the requirements of small volume and low cost to advanced infrared spectral sensors for applications in portable smart sensing systems and internet of things.

Fabrication of Black Silicon Microneedle Arrays for High Drug Loading.

Silicon microneedle (Si-MN) systems are a promising strategy for transdermal drug delivery due to their minimal invasiveness and ease of processing and application. Traditional Si-MN arrays are usually fabricated by using micro-electro-mechanical system (MEMS) processes, which are expensive and not suitable for large-scale manufacturing and applications. In addition, Si-MNs have a smooth surface, making it difficult for them to achieve high-dose drug delivery. Herein, we demonstrate a solid strategy to prepare a novel black silicon microneedle (BSi-MN) patch with ultra-hydrophilic surfaces for high drug loading. The proposed strategy consists of a simple fabrication of plain Si-MNs and a subsequent fabrication of black silicon nanowires. First, plain Si-MNs were prepared via a simple method consisting of laser patterning and alkaline etching. The nanowire structures were then prepared on the surfaces of the plain Si-MNs to form the BSi-MNs through Ag-catalyzed chemical etching. The effects of preparation parameters, including Ag+ and HF concentrations during Ag nanoparticle deposition and [HF/(HF + H2O2)] ratio during Ag-catalyzed chemical etching, on the morphology and properties of the BSi-MNs were investigated in detail. The results show that the final prepared BSi-MN patches exhibit an excellent drug loading capability, more than twice that of plain Si-MN patches with the same area, while maintaining comparable mechanical properties for practical skin piercing applications. Moreover, the BSi-MNs exhibit a certain antimicrobial activity that is expected to prevent bacterial growth and disinfect the affected area when applied to the skin.

Effect of different adhesive systems on dental defects and sensitivity to teeth in composite resin restoration: a systematic review and meta-analysis.

This meta-analysis aimed to elucidate the effects of various acid etching patterns on the sensitivity of teeth and their clinical effectiveness following composite resin repair. PubMed, Cochrane Library, Web of Science, and Embase databases were searched for relevant studies on the postoperative sensitivity (POS) of composite resin restorations after using different bonding systems. The retrieval was from the inception of the databases to August 13, 2022, with no filter of written language. Literature screening was conducted by two independent researchers. The Cochrane risk-of-bias assessment tool was adopted for quality evaluation, and Stata 15.0 for analysis. Twenty-five randomized controlled trials were included in the present study. Following resin composite restoration, 1309 restorations were bonded by self-etching (SE) adhesives, whereas 1271 restorations were bonded by total-etching (TE) adhesives. The meta-analyses showed that there is no evidence to prove the SE and TE will affect POS at present when measured using the modified United States Public Health Service (USPHS) criteria [RR = 1.00 (95% CI: 0.96, 1.04)], the World Dental Federation (FDI) [RR = 1.06 (95% CI: 0.98, 1.15)], or the visual analog scale (VAS) [SMD = 0.02 (95% CI: -0.15, 0.20)] scales. At a certain follow-up time, TE adhesives provide better outcomes in terms of color match, marginal staining, and marginal adaptation. In other words, TE adhesives have better esthetic results. The type of bonding technique (ER and SE) does not affect the risk and degree of POS in class I/II and class V restorations. Further research is required to verify whether these findings apply to different forms of composite resin restorations. Besides the fact that TE barely increase postoperative sensitivity, it also yields superior cosmetic results.

Resin Cement/Enamel Interface: A Morphological Evaluation of the Acid-Base Resistant Zone, Enamel Etching Pattern, and Effect of Thermocycling on the Microshear Bond Strength.

To evaluate the effects of etching mode (self-etch and etch-and-rinse) on acid-base resistant zone (ABRZ) formation at the resin cement/enamel interface and enamel etching pattern, as well as the effects of thermocycling (0, 5000, and 10,000 cycles) on the enamel microshear bond strength (μSBS) mediated by dual-cure resin cements (DCRC). Two DCRC were used in 4 groups: Panavia V5 in self-etch (V5NE) and etch-and-rinse mode (V5E); and Estecem II in self-etch (ENE) and etch-and-rinse mode (EE). For ABRZ observation, the bonded interface was subjected to a demineralizing solution. The morphological attributes of the interface and etching patterns were observed using FE-SEM. For μ-SBS, cylinders with a 0.79-mm internal diameter and 0.5-mm height were made with DCRC and tested in shear after 0, 5000, and 10,000 thermal cycles (TC) (5°C and 55°C) (n = 10). The formation of an enamel ABRZ was observed in all groups with different morphological features between self-etch and etch-and-rinse groups. A funnel-shaped erosion beneath the interface was present using V5NE and ENE modes where enamel was dissolved, while ABRZ formation was confirmed and no funnel-shaped erosion was noticed using V5E and EE. No significant differences in μSBS were observed between resin cements. However, significantly lower µSBSs were recorded when the self-etching mode was used. Thermocycling resulted in a significant reduction in µSBS for all groups. Selective enamel etching should be recommended to improve the interfacial quality when dual-cure resin luting cements are used.

High quality factor silicon nitride nanomechanical resonators fabricated by maskless femtosecond laser micromachining

Freestanding silicon nitride (SiN) devices are central to the field of nanomechanical resonators and other technology applications such as transmission electron imaging and nanopore bioassays. Nanofabrication techniques used for fabricating these devices often lack flexibility. While photolithography requires printing of an expensive photomask for each new design iteration, electron beam lithography is slow and commands high equipment cost. Here, we demonstrate maskless rapid prototyping of freestanding SiN nanomechanical resonators fabricated by femtosecond laser ablation of a plain SiN membrane in ambient air. We fabricate microbeams with different widths from 7 to 100 μm, and we characterize their resonance frequency and mechanical quality (Q) factors. We find that membrane cracking can be avoided during fabrication by carefully engineering the etch pattern, and that laser etching has a negligible effect on built-in tensile stress. For each beam, Q-factors are measured for several eigenmodes and are found to remain high after laser etching. All beams show quality factors greater than 105, while unetched plain membranes have Q &amp;gt; 106. Possible causes for Q-factor reduction are identified, along with future process improvement directions.