Etching Mode Research Articles

Effect of Different Etching Modes on Shear Bond Strength of Universal Adhesives to Enamel

Aim: To evaluate the effect of different etching modes on the bonding efficacy of two universal adhesives to enamel.
 Materials and method: The study was performed in fifty five extracted human molar teeth. For shear bond strength testing, flat buccal surfaces were prepared. Teeth were randomly divided into five experimental groups according to two universal adhesives Single Bond Universal (3M ESPE, U.S.A) and Tetric N-Bond Universal (IvoclarVivadent) used in different etching modes i.e etch-and-rinse and self-etch mode and one control group of etch & rinse adhesive (Adper Single bond-2). Teeth were mounted in self-cure acrylic resin and composite restorations were placed in all the samples after application of adhesives according to the manufacturer’s instructions. Ten samples from each group were subjected to shear bond strength evaluation. Additionally one sample per group was subjected to scanning electron microscopic analysis for observing resin-enamel interfacial adaptation.
 Statistical analysis: Data collected was subjected to statistical analysis using one –way ANOVA and post-hoc tukey’s test at a significant level of p<0.05.
 Results: Enamel bond strength was significantly better in etch-and-rinse mode than the self etch mode for both Single Bond Universal (gp 2 & 3; p=0.017) and Tetric N-Bond Universal adhesives (gp 4 & 5; p=0.046) respectively.
 Conclusion: Phosphoric acid etching of enamel prior to the application of a mild universal adhesive is an advisable strategy for optimizing bonding.

The Method of Low-Temperature ICP Etching of InP/InGaAsP Heterostructures in Cl2-Based Plasma for Integrated Optics Applications.

Chlorine processes are widely used for the formation of waveguide structures in InP-based optoelectronics. Traditionally, ICP etching of InP in a Cl2-based plasma requires substrate temperatures in the range of 150–200 °C. This condition is mandatory, since during the etching process low-volatility InClx components are formed and at insufficient temperatures are deposited onto substrate, leading to the formation of defects and further impossibility of the formation of waveguide structures. The need to preheat the substrate limits the application of chlorine processes. This paper presents a method of ICP etching an InP/InGaAsP heterostructure in a Cl2/Ar/N2 gas mixture. A feature of the developed method is the cyclic etching of the heterostructure without preliminary heating. The etching process starts at room temperature. In the optimal etching mode, the angle of inclination of the sidewalls of the waveguides reached 88.8° at an etching depth of more than 4.5 μm. At the same time, the surface roughness did not exceed 30 nm. The selectivity of the etching process with respect to the SiNx mask was equal to 9. Using the developed etching method, test integrated waveguide elements were fabricated. The fabricated active integrated waveguide (p-InP epitaxial layers were not removed) with a width of 2 μm demonstrated an optical loss around 11 ± 1.5 dB/cm at 1550 nm. The insertion loss of the developed Y- and MMI-splitters did not exceed 0.8 dB.

Bonding Universal Dental Adhesive to Developmentally Hypomineralised Enamel.

To investigate the effect of pretreatment protocols involving Papacarie Duo gel and Scotchbond Universal (SU) on the microshear bond strength (µSBS) of resin composite (RC) to hypomineralised enamel (HE). Specimens of normal enamel (NE) and HE were derived from extracted hypomineralised first permanent molars (FPMs). Based on the colour of demarcated opacities, HE specimens were classified as creamy/white (CW) or yellow/brown (YB). The specimens were randomly allocated into eight groups (n = 20). Each group involved pretreatment with Papacarie Duo gel or no pretreatment, and SU applied in etch-and-rinse (E&R) or self-etch (SE) mode. All specimens were bonded with RC and subjected to µSBS testing. Failure modes were analysed using an optical microscope and SEM. Comparing NE with HE, the following factors were found to be significant (p < 0.001): type of enamel substrate, deproteinising pretreatment, and etching mode. Comparing CW HE with YB HE, a significant interaction between "deproteinising pretreatment" and "etching mode" was demonstrated (p = 0.028). When subjected to the concurrent use of Papacarie Duo gel and phosphoric acid etching, HE specimens showed a significant increase in µSBS (p < 0.001). Deproteinising pretreatment using Papacarie Duo gel followed by the application of SU in E&R mode led to increased µSBS of resin composite to HE.

Does a Self-adhesive Flowable Resin Composite Perform Similarly to Highly Filled and Conventional Flowable Resin Composites in Occlusal Cavities? A 2-year Follow-up Study.

The aim of this clinical trial was to compare a self-adhesive flowable resin composite, a highly filled flowable resin composite used in combination with a universal adhesive applied in self-etch mode, and a conventional flowable resin composite used in combination with a universal adhesive applied using two different application modes in occlusal cavities. Twenty-eight patients received 114 occlusal restorations. Cavities were divided into four groups: CS: a self-adhering flowable (Constic, DMG); GF: a highly filled flowable (G-ænial Universal Flo, GC) in combination with a universal adhesive applied in self-etch mode (G-Premio Bond, GC); TF-SE: a conventional flowable (Tetric N-Flow, Ivoclar Vivadent) in combination with a universal adhesive (Tetric N-Bond Universal, Ivoclar Vivadent) applied in self-etch mode; TF-ER: a conventional flowable (Tetric N-Flow, Ivoclar Vivadent) in combination with a universal adhesive (Tetric N-Bond Universal, Ivoclar Vivadent) applied in etch&rinse mode. Restorations were scored using modified USPHS criteria. Descriptive statistics were performed using chi-squared tests. At 24-month evaluations, none of the restorations were lost. The CS group showed significantly higher bravo scores for marginal adaptation than did the other experimental groups (p = 0.024). Significant changes were seen for CS and GF regarding marginal adaptation compared to baseline. Although the self-adhering flowable resin composite exhibited inferior marginal adaptation compared to the highly filled flowable and conventional flowable resin composites, the restored teeth demonstrated a clinically acceptable performance after 24 months.

Photovoltaic characteristics of structures with porous silicon obtained by various technological plans

In this work, the influence of technological parameters on the current-voltage characteristics of solar cells with porous silicon is investigated. It is shown that for photosensitive structures with a porous layer, the optimal mode is pore formation by electrochemical etching followed by diffusion. The effect of etching modes affects the character of the photosensitivity curve.

Dentin interaction with universal adhesive containing isopropanol solvent studied by solid-state NMR spectroscopy

ObjectiveThis study investigated the chemical and structural changes in the mineral phase and collagen of dentin during application of a mild universal adhesive. Particular attention was paid to the role of isopropanol and changes in water molecules. MethodsIn vitro application of the mild universal adhesive on dentin with two established etching modes (self-etch and etch-and-rinse) was studied using solid state nuclear magnetic resonance spectroscopy. ResultsIt was evidenced that the etch-and-rinse mode leads to a decrease of the inorganic apatite and a reorganization of the residual mineral phase with a low amount of adhesive phosphate monoesters calcium salt formed, compared to the self-etch mode. In contrast, the adhesive interacts very similarly to the level of dentin collagen in both protocols, with a strong decrease in the amount of the free water molecules induced by the presence of isopropanol as the adhesive solvent, but without significant changes in the initial collagen structure. For both modes, the adhesive acrylates monomers remain mobile and can infiltrate the collagen. SignificanceUnderstanding the molecular interactions between dentin and adhesive solutions is a major challenge for designing products that lead to the formation of ideal dentin resin hybrid layer. Notably, one point considered essential is the presence of unbound water which, over time, is associated with a hydrolytic degradation of the organic matrix. Isopropanol, as an adhesive solvent, leads to a decrease in the amount of the less stable water molecules while the water molecules strongly attached to the collagen are retained, thus preserving the collagen structure.

Influence of Different Application Methods on the Bonding Effectiveness of Universal Adhesives to Dentin in the Early Phase.

To investigate the changes in the dentin bond strengths of universal adhesives during the early phase and evaluate the effect of a double-layer adhesive application on the performance of the dentin bond. Three universal adhesives and a two-step self-etch adhesive were employed to ascertain the shear bond strengths (SBS) of specimens to bovine dentin with the use of the etch-and-rinse or self-etch mode. The specimens were further divided into two groups based on adhesive application in a single or a double layer. The bonded specimens were stored in distilled water at 37°C for 5 min or 1, 6, 12, or 24 h prior to SBS measurement and the adhesives' Knoop hardness number (KHN). All the adhesives showed increased SBS with prolonged storage periods regardless of the adhesive layer (single or double) or etching mode. Most universal adhesives in the double adhesive layer groups showed significantly higher SBS than single adhesive layer groups for the same storage period. All the adhesives also showed increased KHN with increased storage period. The SBS and KHN values of the adhesives increased with increasing storage duration over a 24-h period. Double adhesive layer application mediated increased dentin bond strength in the early phase.

Evaluation of developmentally hypomineralised enamel after surface pretreatment with Papacarie Duo gel and different etching modes: an in vitro SEM and AFM study.

This study aimed at investigating the surface morphology and nanotopography of normal enamel (NE) and developmentally hypomineralised enamel (HE) when subjected to various pretreatment protocols under scanning electron microscopy (SEM) and atomic force microscopy (AFM). Sixteen NE, 16 creamy/white (CW) HE and 16 yellow/brown (YB) HE specimens sectioned from extracted hypomineralised first permanent molars (FPMs) were included in this study. They were randomly distributed into 12 experimental groups (n = 4). Each group involved the following: (1) deproteinisation with Papacarie Duo® gel or no deproteinisation, and (2) the use of Scotchbond™ Universal Adhesive (Scotchbond) in self-etch (SE) mode or 37% phosphoric acid etchant. Subsequently, the surface morphology and nanotopography of pretreated enamel specimens were evaluated under SEM and AFM, respectively. SEM observation showed that deproteinisation with Papacarie Duo® gel before phosphoric acid etching led to favourable etching patterns. This was consistent across all groups irrespective of the type of enamel specimen and the severity of hypomineralisation. In contrast, AFM results identified three factors that influenced surface parameters: (1) type of enamel specimen, (2) severity of hypomineralisation and (3) etching mode. YB HE recorded higher surface roughness values than CW HE and NE when subjected to the same pretreatment protocol. Deproteinisation and the application of Scotchbond in SE mode led to minimal topographic changes; however, acid etching was associated with an increase in surface roughness. Deproteinisation with Papacarie Duo® gel followed by acid etching contributed to improved etching patterns on HE.

Effect of combination of etching modes on the design, structural and optical properties of the compliant substrates based on porous silicon

This study examines the effect of etching modes and their combination on the design, microstructure and optical properties of compliant substrates based on porous silicon. Data obtained from microstructural and spectroscopic methods of analysis showed that, under invariable parameters of the crystal lattice, the value of residual stresses, size of the crystallites, volume of crystalline fraction, and the reflectivity and energy of direct transitions in the porous layer of silicon all depend on the combination of the etching modes. However, they do not always correlate with the value of the layer porosity calculated from an analysis of SEM images. Competent selection of these parameters can provide additional advantages in case of monolithic integration of A III B V layers and the obtained compliant silicon substrate. Proper selection also ensures an efficient solution to problems concerning the control of deformation and residual stresses in the epitaxial layer. As an outcome, this will open up new methods of design and development for effective devices related to silicon-based electronics. • The effect of etching modes and their combination on the design, microstructure and optical properties of compliant substrate. • The residual stresses, size of the crystallites, volume of crystalline fraction depend on the etching modes combination. • The idea will open up new methods for the design of effective devices on the basis of silicon electronics.

Effect of Adhesive Application Method on the Enamel Bond Durability of a Two-Step Adhesive System Utilizing a Universal Adhesive-Derived Primer

This study aimed to evaluate the effect of the adhesive application method on the durability of the enamel bond and the thickness of the adhesive layer. A new-generation two-step universal adhesive system, G2-Bond Universal, and two conventional two-step adhesive systems were utilized. The shear bond strength to bovine enamel was measured after thermal cycling in both etch-and-rinse and self-etch modes. Fifteen specimens were divided into three groups as follows: Group I, wherein a strong air stream was applied over the bonding agent for 5 s; Group II, wherein a gentle air stream was applied over the bonding agent for 5 s; and Group III, which was prepared as in Group II, followed by the application of a second layer of the bonding agent and a gentle air stream for 5 s. The durability of the enamel bond and thickness of the tested adhesives were influenced by the application method in both etching modes. The application method used in Group II appeared to be most suitable in terms of the bonding of the adhesives to the enamel. The new-generation two-step self-etch adhesive, comprising a universal adhesive-derived primer and a hydrophobic bonding agent, showed superior bond performance to the conventional two-step adhesive systems.

Influence of Etching Mode and Composite Type on Bond Strength to Biodentine Using a “No-Wait” Universal Adhesive

The purpose of this study was to compare the shear bond strength (SBS) of four resin-based composite materials to a silicate-based cement using a “no-wait” universal bond with self-etch (SE) and etch-and-rinse (ER) modes. Acrylic blocks (n=80, 2mm depth, 5mm diameter central hole) were prepared. The holes were filled with BiodentineTM (BD) and divided into 4 main groups (n=20) according to the composite resin type used: Group FZ250: FiltekTM Z250 Universal Restorative (microhybrid), Group SDR: SDR Plus U Bulk Fill Flowable (low-viscosity bulk-fill), Group FBP: FiltekTM Bulk Fill Posterior (high-viscosity bulk-fill), Group EF: EsFlow™ Universal Flowable Composite (nanohybrid). A ‘no-wait’ universal bond (Clearfil Universal Bond Quick) was used for bonding application. Then each group was divided into 2 subgroups according to the etching mode applied (ER and SE). SBSs were measured and stereomicroscope was used to identify the failure modes. Selected samples of fracture surfaces were imaged by SEM. Tukey’s post-hoc and One-way ANOVA tests were used to analyze data. There were statistically significant differences among the composite groups (p&lt;0.05). When SDR showed the highest bond strength values in SE (17.13 ± 2.98 MPa) mode, FBP showed the lowest bond strength values in ER (8.89 ± 2.46 MPa) mode. The mean SBS was not different between the SE and ER modes (p&gt; 0.05). The SBS of BD to the resin composites depends on the composite type but application of the ‘no-wait’ universal bond in different etching modes is regardless of the SBS of BD to resin composites.

Update on Enamel Bonding Strategies

Optimal strategies for the application of an adhesive differ between enamel and dentin because of the differences in their composition. The development of adhesive systems has mainly focused on the bonding of dentin, rather than on the enamel, by etching with phosphoric acid (PA). Dental adhesive technologies continue to rapidly advance, and various adhesive systems have been developed since the study of Buonocore in 1955. He introduced the enamel acid-etch technique. Then, the etch-and-rinse (ER) system was developed, and subsequently, the self-etch (SE) system. Universal adhesives are a new generation of one-bottle SE adhesives that can be applied with either ER mode or SE mode, or a combined system involving selective enamel etching mode. Since the combination of PA etching and the SE system differs from conventional ER systems, the enamel bonding strategy should be carefully considered. This concise review of the literature on reliable enamel bonding strategies should prove helpful to clinicians to choose an appropriate adhesive system to achieve optimal clinical outcomes.

Thermodynamic Considerations in the Design of Electrochemical Atomic Layer Etching of Copper

Electrochemical atomic layer etching (e-ALE) is a unique approach for etching metals one atomic layer at a time. If practiced under optimal conditions, e-ALE ensures minimal evolution of surface roughness due to the atomic layer-by-layer etching characteristics. During e-ALE of copper (Cu), the crucial first step is the formation of a cuprous sulfide (Cu2S) monolayer via the surface-limited sulfidization reaction. In this paper, we investigate the surface coverage of this sulfide layer as a function of the sulfidization potential, and show that the equilibrium coverage attained can be modeled using the Frumkin adsorption isotherm. At a potential of –0.74 V vs SHE, sulfidization provides near-complete monolayer coverage of Cu by Cu2S, which then facilitates e-ALE in a layer-by-layer etching mode thereby maintaining a smooth post-etch surface. Operation at potentials negative with respect to –0.74 V provides sub-monolayer coverage, which manifests in roughness amplification during etching. This work provides a thermodynamics-guided foundation for the selection of operating conditions during Cu e-ALE.

Layer Thickness Effect on Lifetime of Copper Oxide Passivated Plasma Etched Copper Line

Cu is a widely used interconnect material in high density ICs, large area TFT LCDs, etc. Due to the difficulty in etching the Cu thin film using the conventional plasma etching method [1], the CMP method was developed to achieve this goal [2]. Kuo’s group developed a plasma-based Cu etch process that had a high rate even at the room temperature. [3,4]. This process has been applied to the fabrication of BiCMOS chips and TFTs [5,6]. Recently, the authors reported that CuOx could be an effective passivation material for Cu [7]. In this study, the CuOx passivation layer thickness effect on the reliability of the Cu line is studied using the electromigration (EM) method [8,9].The TiW/Cu stack was sputter deposited on the DHF cleaned Corning 1737 glass and etched into a 4-point test pattern. The Cu layer was etched by a 2-step plasma-based process [3,4]. The first step was to convert the patterned Cu film into a CuClx layer using the CF4/HCl (5/20 sccm) plasma at 70 mTorr and 600W in a parallel-plate reactor (PlasmaTherm 700C) operated at the RIE mode. The second step was to dissolve the CuClx layer in a dilute HCl solution (HCl:H2O=1:8 v/v). the TiW barrier film was etched in the CF4 (20 sccm) plasma at 60 mTorr and 600 W in the same RIE reactor. After stripping off the photoresist, a CuOx passivation layer was formed on the Cu surface by exposing the sample to the O2 plasma using the same reactor operated at the plasma etching (PE) mode. The EM stress was carried out under the constant current densities (J) condition at room temperature using the Agilent E3645A meter on a probe station (Signatone S-1160).Figure 1 shows the optical emission spectrum (OES) of the O2 plasma oxidation condition, i.e., 40 sccm, 200 mTorr, 300W at the PE mode. The two large peaks at 777 nm and 845 nm belong to the O radicals that are generated from the dissociative excitation. They correspond to transition states of 3p5P 3s5S and 3p3P 3s3S, respectively [10,11]. The O2 + vibrational state oxygens should show as peaks between 500 and 600 nm, which are very weak in Fig. 1. Therefore, the ion bombardment effect in this Cu oxidation process is much weaker than that of the oxygen radicals. Since the Cu layer was thin, the CuOx passivation layer was probably uniform over the Cu surface.Figure 2 shows the EM lifetimes of the TiW/Cu and TiW/Cu/CuOx lines with various CuOx passivation layer thicknesses. The general trend is that the lifetime is shortened with the increase of the current density. The breakage of the line can be contributed by the mechanism of voids formation and merging, which is accelerated by the increase of the current density [9]. In addition, the unpassivated line has a longer lifetime than the CuOx passivated line, i.e., red (12.5 nm thick CuOx layer) and blue (40 nm thick CuOx layer) lines. The thicker the passivation layer is, the shorter the EM lifetime is, which may be related to the heat dissipation effect. Since CuOx has a low thermal conductivity [12], the Cu line with a thick passivation layer is hotter than that with a thin passivation layer. The high temperature accelerates the voids formation and merging process [9].More detailed characterization of the CuOx passivation layer thickness effect will be presented and discussed.Authors acknowledge the financial support of this work through NSF CMMI project 1633580.1. H. Miyazaki, K. Takeda, N. Sakuma, S. Kondo, Y. Homma and K. Hinode., JVST B, 15(2), 237-240 (1997).2. J. Proost, T. Hirato, T. Furuhara, K. Maex and J.-P. Celis, JAP, 87(6), 2792-2802 (2000).3. Y. Kuo and S. Lee, JJAP, 39(3A), L188 (2000).4. S. Lee and Y. Kuo, JES, 148(9), G524-G529 (2001).5. Y. Kuo, H. Nominanda and G. Liu, JKPS, 48(91), S92-S97 (2006).6. J. Yang, Y. Ahn, J. Bang, W. Ryu, J. Kim, J. Kang, M. S. Yang, I. Kang, I. Cung, ECST, 16(9), 13 (2008).7. J. Q. Su and Y. Kuo, ECST, 98(3), 99-105 (2020).8. G. Liu and Y. Kuo, JES, 156(7), H579-H584 (2009).9. J. Q. Su, M. Li and Y. Kuo, ECS JSS, 9(10), 104009 (2020).10. U. Cvelbar, B. Markoli, I. Poberaj, A. Zalar, L. Kosec and S. Spaic, ASS, 253(4), 1861-1865 (2006).11. A. A. Kudryavtsev and L. D. Tsendin, Tech. Phys. Lett., 26(7), 582-587 (2000).12. M.-S. Liu, M. C.-C. Lin, I.-T. Huang and C.-C. Wang, ChET, 29(1), 72-77 (2006). Figure 1

Sensing Enhancement of Electromagnetically Induced Transparency Effect in Terahertz Metamaterial by Substrate Etching

A broad range of terahertz (THz) metamaterials have been developed for refractive index sensing. However, most of these metamaterials barely make sufficient use of the excited electric field which is crucial to achieve high sensitivity. Here, we proposed a metamaterial sensor possessing electromagnetically induced transparency (EIT) resonance that is formed by the interference of dipole and quadrupole resonance. In particular, the strengthening of light-matter interaction is realized through substrate etching, leading to a remarkable improvement in sensitivity. Hence, three kinds of etching mode were presented to maximize the utilization of the electric field, and the corresponding highest sensitivity is enhanced by up to ~2.2-fold, from 0.260 to 0.826 THz/RIU. The proposed idea to etch substrate with a strong light-matter interaction can be extended to other metamaterial sensors and possesses potential applications in integrating metamaterial and microfluid for biosensing.

Clinical effects of different etching modes for universal adhesives: a systematic review and meta-analysis.

To evaluate the clinical performance of universal adhesives in etch-and-rinse or self-etch application modes through meta-analysis. A literature search was performed by two reviewers in the PubMed, Cochrane Library, and Embase databases (from January 2000 to March 2020). A total of 2,516 non-replicated records were identified and filtered. Studies that evaluated the clinical performance of universal adhesives using etch-and-rinse or self-etch mode were included. RevMan 5.3.5 (Cochrane, London, UK) was used to perform the meta-analysis. A total of 13 studies were included in the meta-analysis. The retention rates were higher in etch-and-rinse groups compared with self-etch groups [odds ratio (OR) =0.35, 95% confidence interval (CI): 0.18-0.71, P=0.003]. The etch-and-rinse approach also had better performance in marginal adaptation (OR =0.49, 95% CI: 0.36-0.67, P<0.001) and marginal staining (OR =0.49, 95% CI: 0.36-0.66, P<0.001). The current data showed a very low incidence rate of secondary caries or postoperative sensitivity, and there were no significant differences in the incidence rates between the etch-and-rinse groups and self-etch groups. The current evidence shows that, compared with self-etch approach, the etch-and-rinse approach for universal adhesives provides improved clinical outcomes in terms of retention rates, marginal adaptation, and marginal staining.

Influence of reduced application time on bonding durability of universal adhesives to demineralized enamel.

This study aimed to assess the effect of application time on the microshear bond strength (μSBS) of three universal adhesives in demineralized and sound enamel before and after aging. Bovine teeth (192) were prepared where buccal surfaces were ground and divided into two groups (sound enamel and demineralized enamel). The specimens in each group were divided into 12 subgroups by combining 3 adhesive agents (All-Bond Universal, Scotchbond Universal, and Tokuyama Universal Bond) × 4 adhesion strategy. Each adhesive was applied with either prolonged (PA) or reduced (RA) application time in etch-and-rinse or self-etch mode. Bonded composites were subjected to μSBS testing after 24-h or 2-year water storage. The results were evaluated using four-way ANOVA and Tukey's post-hoc test (α = 0.05). The μSBS of adhesives to sound enamel in both etching modes was mostly similar to demineralized enamel, regardless of application time and aging time. At 24-h, all adhesives with PA in self-etch mode showed higher μSBS when compared with RA, except Tokuyama Universal Bond, but after 2-year aging, no significant difference was found in μSBS between RA and PA. The μSBS of adhesives with PA in etch-and-rinse mode depended on used adhesive and enamel condition compared to RA, regardless of μSBS testing time. PA of adhesives did not reveal a significant difference in μSBS to enamel, regardless of substrate type and etching mode. After 2-year aging, the bond strength of universal adhesives presented no significant difference between PA and RA treatments.

Features of the two-stage formation of macroporous and mesoporous silicon structuresя

The aim of this work was the formation of multilayer structures of macroporous silicon and the study of their structural, morphological, and optical properties in comparison with the properties of multilayer structures of mesoporous silicon. The paper presents the results of the development of techniques for the formation of multilayer structures of porous silicon por-Si by stepwise change in the current with two-stage modes of electrochemical etching.The data on the morphology, composition, and porosity of macroporous and mesoporous silicon samples were obtained using scanning electron microscopy, IR spectroscopy, and X-ray reflectivity. It was shown that with the two-stage growth of porous silicon layers, the depth of the boundary between the layers of the structure was determined by the primary mode of electrochemical etching, while the total layer thickness increased with an increase in the current density of electrochemical etching.A comparative analysis of the relative intensity and fine structure of vibrational modes of IR spectra indicated a significantly more developed specific pore surface and greater sorption capacity of mesoporous silicon as compared to macroporous silicon.&#x0D; &#x0D; &#x0D; REFERENCES&#x0D; 1. Pacholski C. Photonic crystal sensors based on porous silicon. Sensors. 2013;13(4): 4694–4713. https://doi.org/10.3390/s130404694 2. Harraz F. A. Porous silicon chemical sensors and biosensors: A review. Sensors and Actuators B: Chemical. 2014;202: 897–912. https://doi.org/10.1016/j.snb.2014.06.0483. Qian M., Bao X. Q., Wang L. W., Lu X., Shao J., Chen X. S. Structural tailoring of multilayer porous silicon for photonic crystal application. Journal of Crystal Growth. 2006;292(2): 347–350. https://doi.org/10.1016/j.jcrysgro.2006.04.0334. Len’shin A. S., Kashkarov V. M., Turishchev S. Yu., Smirnov M. S., Domashevskaya E. P. Effect of natural aging on photoluminescence of porous silicon. Technical Physics Letters. 2011;37(9): 789–792. https://doi.org/10.1134/S10637850110901245. Kheifets L. I., Neimark A. B. Multiphase processes in porous media. Moscow: Khimiya Publ.; 1982. 320 p. (In Russ.)6. Canham L. Handbook of porous silicon. Switzerland: Springer International Publishing; 2014. 733 p.7. Zimin S. P. Porous silicon – material with new properties. Soros Educational Journal. 2004;8(1): 101–107. Available at: http://window.edu.ru/resource/217/21217/files/0401_101.pdf (In Russ., abstract in Eng.) 8. Seredin P. V., Lenshin A. S., Goloshchapov D. L., Lukin A. N., Arsentyev I. N., Bondarev A. D., Tarasov I. S. Investigations of nanodimensional Al2O3films deposited by ion-plasma sputtering onto porous silicon. Semiconductors. 2015;49(7): 915–920. https://doi.org/10.1134/S10637826150702109. Seredin P. V., Lenshin A. S., Mizerov A. M., Leiste H., Rinke M. Structural, optical and morphological properties of hybrid heterostructures on the basis of GaN grown on compliant substrate por-Si(111). Applied Surface Science. 2019;476: 1049–1060. https://doi.org/10.1016/j.apsusc.2019.01.23910. Seredin P. V., Leiste H., Lenshin A. S., Mizerov A. M. Effect of the transition porous silicon layer on the properties of hybrid GaN/SiC/por-Si/Si(111) heterostructures. Applied Surface Science. 2020;508(145267): 1–14. https://doi.org/10.1016/j.apsusc.2020.14526711. Lenshin A. S., Barkov K. A., Skopintseva N. G., Agapov B. L., Domashevskaya E. P. Influence of electrochemical etching modes under one stage and two Stage formation of porous silicon on the degree of oxidation of its surface layer under natural conditions. Kondensirovannye sredy i mezhfaznye granitsy = Condensed Matter and Interphases. 2019;21(4): 534–543. https://doi.org/10.17308/kcmf.2019.21/2364 (In Russ., abstract in Eng.) 12. Buttard D., Dolino G., Bellet D., Baumbach T., Rieutord F. X-ray reflectivity investigation of thin p-type porous silicon layers. Solid State Communications. 1998;109(1): 1–5. https://doi.org/10.1016/S0038-1098(98)00531-613. Lenshin A. S., Seredin P. V., Agapov B. L., Minakov D. A., Kashkarov V. M. Preparation and degradation of the optical properties of nano-, meso‑,and macroporous silicon. Materials Science in Semiconductor Processing. 2015;30: 25–30. https://doi.org/10.1016/j.mssp.2014.09.04014. Ksenofontova O. I., Vasin A. V., Egorov V. V., Bobyl’ A. V., Soldatenkov F. Yu., Terukov E. I., Ulin V. P., Ulin N. V., Kiselev O. I. Porous silicon and its applications in biology and medicine. Technical Physics. 2014;59(1): 66–77. https://doi.org/10.1134/S1063784214010083

Formation of highly vertical trenches with rounded corners via inductively coupled plasma reactive ion etching for vertical GaN power devices

A trench-gate metal-oxide-semiconductor field-effect transistor (T-MOSFET) has great potential for use in gallium nitride (GaN)-based vertical power switching devices owing to its high blocking voltage and high current capability. To form an optimal trench shape that has highly vertical sidewalls and rounded corners, we developed a dry-etching technique using inductively coupled plasma reactive ion etching (ICP-RIE). A highly vertical trench was obtained by including SiCl4 reactive gas mixed with Cl2 gas in the ICP-RIE process, where Si-related byproducts suppressed the etching of the sidewall and allowed selective etching in the vertical direction. We found that the optimization of the bias power was a key to suppress the formation of subtrenches and to avoid an isotropic etching mode. The optimal etching condition leads to natural formation of rounded corners at the trench bottom. In addition, a multistep-bias etching technique was applied to reduce etching-induced damage. Cross-sectional transmission electron microscopy images revealed that lattice distortion on the sidewall surface was eliminated by multistep-bias etching. Based on the rectification properties of the Schottky barrier diodes formed on the trench sidewalls, the Schottky barrier height was comparable to the not-etched surfaces. This indicates that the gap states caused by etching-induced damage can almost be eliminated in the multistep-bias process. The proposed technique is suitable for GaN-based vertical T-MOSFETs.

Degree of conversion and dentin bond strength of light-cured multi-mode adhesives pretreated or mixed with sulfinate agents.

The influence of sulfinate agents applied as a dentin pretreatment or a mixture with multi-mode one-step self-etch adhesives (1-SEAs) on the degree of conversion (DC) and micro-tensile bond strength (μTBS) of light-cured 1-SEAs was investigated. 1-SEAs Clearfil Universal Bond Quick (UBQ) or Scotchbond Universal Adhesive (SBU) were applied to dentin in etch&rinse or self-etch mode using various application strategies: 1) no pretreatment, 2) pretreatment with 90 wt% ethanol, 3) pretreatment with a sulfinate agent Clearfil DC Activator (UDC) or Scotchbond Universal DCA (SDC), or 4) a mixture of UBQ+UDC or SBU+SDC. μTBS was measured after 24 h. Additionally, DC was measured using attenuated total reflectance Fourier-transform infrared spectroscopy. Pretreatment with sulfinate agents resulted in the highest μTBS and DC, significantly improving them especially in etch&rinse mode. The mixture of sulfinate agents with 1-SEAs was less effective. Pretreatment with ethanol significantly improved μTBS in etch&rinse mode but compromised μTBS in self-etch mode.