Study of Eutectic Etching Process for Defects Analysis in n type 4H SiC

Silicon Carbide (SiC) is a wide bandgap material with unique properties attractive for high power, high temperature applications. The presence of defects in the crystal is a major issue prior device fabrication. These defects affect the performance of the device. To delineate and identify the defects an easy and quick method is desirable. In this study defects delineation in n-type 4H-SiC has been carried out by KOH, KOH+NaOH and KOH+Na2O2 melts. Variation in etch pits size was found at various concentrations of the NaOH in KOH and for different total etching times in the KOH+Na2O2 melt. The eutectic solution etching technique is found to be more efficient to delineate defects and provides control on etching and surface roughness. The etching rates have been estimated under different experimental conditions. Detailed morphological investigations have been performed by wide field high resolution optical microscopy and scanning electron microscopy.

Comparative evaluation of adhesive performance to dentin: study in patients of different ages

The article describes in vitro evaluation of the micro-shear bond strength between composite resin and dentin specimens treated with self-etching, total-etching and universal dental adhesives for patients of different ages. The authors compared microstructure of resin-infiltrated zone for self-etching, total-etching and universal dental adhesive systems by means of scanning electron microscopy. These findings presented negatively effects of aging on the bond strength of dentinal surfaces and the advantages of adhesive protocol with universal adhesives for all ages.

Do total or partial etching procedures effect the rate of white spot lesion formation? A single-center, randomized, controlled clinical trial

ABSTRACT Objective: To determine whether total or partial etching procedures influence the appearance of white spot lesions (WSLs). Materials and Methods: This split-mouth, double-blind, controlled, randomized study included 20 patients (mean age 16.75 years), who had class I malocclusion, mild crowding, and satisfactory oral hygiene. A total of 40 maxillary quadrants were randomly allocated to be treated using a total etching (TE) or partial etching (PE) protocol. Quantitative light fluorescence images were captured at the beginning and at 3 (T1) and 6 (T2) months after beginning orthodontic treatmen, as well as when the debonding phase of orthodontic treatment was complete (T3). The presence of pre- and posttreatment WSLs was assessed with quantitative light fluorescence software and analyzed with Student's t-test. Results: The analyses showed that, at T2, the total etching group had significantly higher ΔQ and A scores than the partial etching group (P < .05). The ΔF scores increased significantly at all timepoints in the TE group, but only at T1 and T3 in the PE group. However, no differences were noted at T3 between the TE and PE groups (P > .05). The inclusion of only right-handed people may have limited the generalizability of the findings. The absence of analyses of the plaque and gingivitis scores of patients was another limitation of this study. Conclusions: WSL formation was observed mostly in maxillary lateral incisor teeth irrespective of the etching technique. Although PE seems to be more successful in the first 6 months, no difference was observed between PE and TE in the long term for WSL formation.

Nd:YAG laser influence on the hybridization quality, employing total-etching or self-etching adhesives: sem analysis

<p class="Traduc"><strong>Background:</strong> The application of Nd:YAG laser on dentin with the adhesive system non-polymerized can influenced the quality of hybrid layer formed. <strong>Objectives: </strong>The aim of this study is to assess through analysis by scanning electronic microscopy (SEM), the Nd:YAG laser influence on the hybridization quality, using conventional Adper Single Bond (SB) or self-etching Clearfil SE Bond-Kuraray (CSEB) adhesives.<strong> Methods: </strong>Nine bovine incisors were treated on their incisal with SB and with CSEB in their cervical portion. They were divided into 3 groups with 6 specimens in each and treated as follows; G1- adhesive system and polymerization; G2- adhesive system, laser (60mJ/pulse) and polymerization; G3- adhesive system, laser (140mJ/pulse) and polymerization. All samples were restored with composite resin (Filtek Z350-3M). The thickness, the presence of failures (gap/porosity) and tags/microtags in the hybrid layer were analyzed using the SEM. The data were submitted to ANOVA and Tukey statistical tests 5%. <strong>Results:</strong> The highest average of hybrid layer thickness (1.89±0.15) was observed for G3 and the smallest was observed for G1-CSEB (1.36±0.14). The multiple comparison of ratio test showed that the smallest prevalence of failures was for G3-CSEB and the best performance for the presence of tags/microtags was found for G2-SB.<strong> Conclusion: </strong>Independent of the adhesive system used, the Nd:YAG laser, according to the parameter applied, had a positive influence on the hybridization quality.</p>

The Control Method of Surface Morphology and Etch Rates for Silicon Etch Process With Extremely Deep and High Aspect Ratio

The manufacture method based on the silicon etching process is one of the most important methods to fabricate micro mechanical structure, e.g. micro-engine. In the processing, the high aspect ratio silicon etch process (HARSE process) is very important to improve the efficiency of structure. At the same time, the surface morphology should be controlled exactly to keep the performance of structure. In this paper, the feasibilities of controlling the surface morphology and Si etch rates were experimentally investigated. In the experiments, the width of structure changes from 15um to 1500um and the depth changes from 50um to 500um. The parameters of surface morphology including sidewall angle, surface roughness, and so on were measured and compared. The influence mechanisms of etching parameters were analyzed. The etching process were completed in a surface technology system (STS) multiplex advanced silicon etcher inductively coupled plasma (ICP) system with SF6/O2 plasma as etching plasma and C4F8 as passivation plasma. In the experiments, the etching experiments were conducted in a low pressure (5–50mTorr), high density, inductively coupled plasma etching reactor (ICP) with a planar coil. The Si etches rates and sidewall angle were investigated as a function of chamber pressure, cathode RF-power, and gas flow. The results indicated that the increasing of total etching time results in an acceleration in etch rate as well as the decrease in sidewall angle (the top width of trench is narrow than the bottom width). Meanwhile, the total passivation time has an opposite effect in the influence of etch rate and sidewall angle. All the experiments indicate that the quick shift between etch and passivation period leads to a smoother surface. An interesting phenomenon were discovered that the etch rate will not change with the changing of width parameter in most of the high aspect ratio silicon etch recipes when the width-depth ratio is upper than 0.34. An experiential function formula were fitted based on four parameters, including width and depth of the structure, and total etching and passivation time.