Anisotropic Etching

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Formation mechanism of SiGe nanorod arrays by combining nanosphere lithography and Au assisted chemical etching

Formation mechanism of SiGe nanorod arrays by combining nanosphere lithography and Au assisted chemical etching

principally an isotropic etching process. Therefore, as illustrated in Figure 4, there exist two etching mechan- isms competing for the formation of SiGe nanostruc- tures by Au-assisted chemical etching. As the etching temperature is low, both the corrosion reaction and Au- assisted etching process are kinetically impeded. Thus, necklike etched nanostructures with a limited height could be observed (Figure 4a). By increasing the etching temperature above 20°C, more temperature-sensitive Au-assisted anisotropic etching begins to dominate the whole etching process, and SiGe NRs form (Figure 4b). Nevertheless, isotropic corrosion reaction still proceeds in the meantime. Therefore, all SiGe NRs have a taper- like shape with a diameter less than that defined by the PS nanospheres (420 nm); that is also why all SiGe nanostructures in this study have a base horizontally lower than the surrounding Au film. It is also worth- while noting that if we increase the temperature above 40°C, only straight Si nanowire arrays would be obtained since the upper SiGe parts have been etched away (not shown here). This is because both the corrosion reaction and Au-assisted etching rates are significantly enhanced at such a high temperature.

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Triangle pore arrays fabricated on Si (111) substrate by sphere lithography combined with metal assisted chemical etching and anisotropic chemical etching

Triangle pore arrays fabricated on Si (111) substrate by sphere lithography combined with metal assisted chemical etching and anisotropic chemical etching

generated in the surrounding of the main large pores, as shown in Figure 3a. This result implies that small Au parti- cles were deposited on a silicon substrate through defects (e.g., cracks and voids) of the polystyrene mask. To obtain a cross-sectional image by SEM observation, a fracture sur- face was prepared by mechanical cleavage. From the cross section shown in Figure 3b, it was confirmed that the growth of the pores proceeded in the [111] crystallographic direction. A number of channels on the sidewalls of pores are thought to be reflected in the traces of Au nanoparticles divided from the circular thin film. The depth of the pores reached 6 μm after metal-assisted chemical etching for 1 min. In other words, the etching rate of 6 μm min −1 was obtained at room temperature using a metal catalyst. If a bare (111) silicon wafer is immersed in TMAH, which is a popular etchant for the anisotropic etching of silicon, etch- ing at the (111) surface hardly proceeds [16]. In brief, chemical etching in alkaline solution alone cannot form straight pores in the [111] direction. Of course, HF solution

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A comprehensive review on convex and concave corners in silicon bulk micromachining based on anisotropic wet chemical etching

A comprehensive review on convex and concave corners in silicon bulk micromachining based on anisotropic wet chemical etching

hydrofluoric acid (BHF) for a short time (about 20 sec) in order to remove any oxide layer formed over the nitride during the LOCOS process [177]. This step is attempted because the oxide etch rate in phosphoric acid is negligible in comparison to nitride etch rate. Subsequently, the buffered oxide is etched out in BHF. Now, the second step of silicon etching is employed. This step of silicon etching should be performed in TMAH as the oxide layer is being used as masking layer. The sidewalls of the currently etched cavities and of the grooves previously formed intersect each other in the shape of the convex corners, which are not etched back as they are passivated by the etch mask. Finally oxide layer is removed in BHF. As shown in SEM picture in Figure 50, the structure fabricated using this method comprise perfect convex corners. However, the process is illustrated for the fabrication of microfluidic channels with multiple reservoirs in Si{100} wafer, it can be utilized for other types of structures which contain convex corners such as proof mass for accelerometer [111]. Moreover this technique can be employed for Si{110} to form the microstructure with perfect convex corner as presented in Figure 52 [128]. Hence this is a generic process. In this method, the overlapped area between two mask is calculated using simple trigonometric relations. Accordingly the dimensions of masks are determined. It may me emphasize here that the dimensions of the mask for the fabrication of microstructure using wet anisotropic etching is determined considering the lateral undercutting and angles of etched sidewalls.

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Determination of precise crystallographic directions on Si{111} wafers using self-aligning pre-etched pattern

Determination of precise crystallographic directions on Si{111} wafers using self-aligning pre-etched pattern

mask patterns. Three {111} planes out of six are slanted at 70.5° with wafer surface, while other three make an angle of 109.5° to the wafer surface. Among three princi- ple orientations namely {100}, {110} and {111}, {100}-ori- ented wafers are most frequently used. Si{110} wafers are employed for specific applications such as microstruc- tures with vertical sidewalls. As the Si{111} planes have slowest etch rate in all kinds of wet anisotropic etchants, therefore Si{111} wafers are used for specific applications and to fabricate complicated structures using deep reac- tive ion etching (DRIE) assisted wet anisotropic etching [19–34]. In these structures, gap between freestanding structure and bottom surface can be controlled precisely.

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Highly-efficient low cost anisotropic wet etching of silicon wafers for solar cells application

Highly-efficient low cost anisotropic wet etching of silicon wafers for solar cells application

Chemical anisotropic etching is a promising approach toward the low-cost solar cells with pyrami- dal surface structure. Recent etching processes usually employ alkaline etchants i.e. aqueous solutions of Potassium hydroxide (KOH), 13 Sodium Hydroxide (NaOH) 14 and isopropyl alcohol (IPA) as a surface additive. 15 These solutions are mostly chosen due to their low cost and less time consump- tion. However, these etching processes have some drawbacks such as poor surface morphology and irregular pyramid size. 16 Nevertheless, more advanced and sophisticated techniques are being used which assures to have enhanced performance. Yet most of these techniques still have high cost and

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Etching characteristics of Si{110} in 20 wt% KOH with addition of hydroxylamine for the fabrication of bulk micromachined MEMS

Etching characteristics of Si{110} in 20 wt% KOH with addition of hydroxylamine for the fabrication of bulk micromachined MEMS

In all kinds of wet anisotropic etchants, Si{111} planes exhibit minimum etch rate. If the mask edges are aligned along the directions comprises {111} planes, wet aniso- tropic etching provides microstructures with smooth sidewalls due to the emergence of {111} planes at these directions. The angle between sidewall and wafer surface depends on the wafer orientation. Moreover, the number of directions along which {111} planes appear depend on the orientation of wafer surface. In the case of {100} wafer, four {111} planes making an angle of 54.7° with wafer surface expose at ⟨ 110 ⟩ directions. Hence {100} wafer is suitable to fabricate rectangular shaped cavities or suspended structures over rectangular shape cavity using wet anisotropic etching [3, 6, 12, 21]. In the case of the wafer with {110} surface, two slanted planes mak- ing an angle of 35.5° with wafer surface and four vertical planes with respect to wafer surface appear along ⟨ 110 ⟩ and ⟨ 112 ⟩ directions, respectively. Therefore, in order to fabricate microstructures with vertical sidewalls {110} wafer is a most appropriate choice [10, 28–34]. It can be used to fabricate deep channels/cavities with vertical sidewall.

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Metal assisted chemical etching of Ge(100) surfaces in water toward nanoscale patterning

Metal assisted chemical etching of Ge(100) surfaces in water toward nanoscale patterning

In our experiments, most etch pits were pyramidal, one of which is shown in Figure 1c. The outermost Ge atoms on the (111) and (100) faces have three and two backbonds, respectively. This probably induces a (100) facet to dissolve faster in water than a (111) facet, forming a pyramidal etch pit on the Ge(100) surface, as schematically shown in Figure 2b. This anisotropic etching is very unique, because it has not been observed on Si(100) surfaces with metallic particles immersed in HF solution with oxidants. It should be noted that Figure 1e exhibits some ‘rhomboid’ and ‘rectangular’ pits together with ‘square’ pits. We believe that the square

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Effect of Etching Time and Preparation on Push-Out Bond Strength of Composite to Intracanal Dentin of Primary Anterior Teeth

Effect of Etching Time and Preparation on Push-Out Bond Strength of Composite to Intracanal Dentin of Primary Anterior Teeth

Considering etching time and the differences in some micromechanical and histological properties of primary and permanent dentin [17], our alternative hypothesis was that applying shorter etching time for primary dentin than that recommended by the manufacturers for permanent dentin would yield higher bond strength values. This hypothesis has been approved in some previous studies [9- 11,13,17,19,20]. Evidence shows that decreasing the etching time of primary dentin increases the quality [14] and uniformity [10] of mechanical interlocking of resin tags between collagen fibrils in the hybrid layer. By decreasing the etching time, the morphology of the etched surface of primary dentin would be similar to that of permanent teeth after etching [13]. Application of shorter etching time prevents the formation of a layer with partially penetrated resin tags and denuded collagen fibrils beneath the hybrid layer [9,11], since this layer would be the weakest area at the dentin-adhesive interface [9]. However, the results of the current study did not reveal a significant difference in this regard and our alternative hypothesis was refuted. A previous study reported results similar to ours and did not find any significant difference in bond strength following seven and 15 seconds of etching [9]. But, it should be noted that in contrast to the current study, the afore-mentioned studies had been conducted on permanent dentin and used bond strength tests other than the push-out test. Such variability in methodologies as well as other factors such as the bonded surface area of dentin might have affected the results and may be responsible for the differences in the results of studies [13,14]. With regard to preparation of dentin surface, it should be noted that dentin has a tubular structure, and density and diameter of dentinal tubules closer to the pulp are greater than those in areas closer to the dentinoenamel junction. Dentinal tubules closer to the pulp have less calcified tissue. Thus, the bonding substrate is more abundant farther from the pulp and

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Effect Of Etching Time On Electrical Properties For Porous Silicon By Photo Electrochemical Etching

Effect Of Etching Time On Electrical Properties For Porous Silicon By Photo Electrochemical Etching

The built in potential of the porous silicon wafer was found as mentioned in the experimental work. Its value as shown in Figure 4, exhibits decrease with increasing etching time and this result agrees with capacitance value result and this is due to the decrease of the junction depiletion layer

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Multi Objective Optimization of Photochemical Machining for ASME 316 Steel Using Grey Relational Analysis

Multi Objective Optimization of Photochemical Machining for ASME 316 Steel Using Grey Relational Analysis

Fig.2 shows the main effect plot for grey relational grade. Here the uppermost values of parameters give best results of response variables. While the lower most values in the plot indicate the values of parameters for worst case results. According to the graph we can evidence that the response variables are optimum at Concentration 800 gram per litter, temperature 55°C and time 15 minute. The etching time has higher contribution to the variability of GRG over the selected range. and etching temperature has lower contribution. The most important factor observed from GRA is Etching time. The order of sequence as per importance is Etching time, etchant concentration and etchant temperature.

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Etching of enamel and dentin produces surface irregularities and helps forming microtags & macrotags which aids in micromechanical bonding to composite resins. Sazak et al., quoted many drawbacks of acid etching like damage to the tooth structure, multiple clinical steps making the procedure technique sensitive and time consuming and hybridization deficit [1]. As a possible alternative to acid conditioning the use of laser therapy has recently shown a promising front [2]. Er,Cr:YSGG(Erbium, Chromium : Ytrium Scandium Gallium Garnet) laser, a hydrokinetic laser system having a wavelength of 2780 nm was investigated by Usumez et al., and was found to have ablating effect on enamel and dentin [3].

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Anisotropic Picone identities and anisotropic Hardy inequalities

Anisotropic Picone identities and anisotropic Hardy inequalities

This paper is organized as follows: The proofs of Theorem . and a Sturmian com- parison principle to the anisotropic elliptic equation are given in Section ; Section  is devoted to the proof of Theorem . in which a key ingredient is to choose a suitable auxil- iary function (see (.) below) for the anisotropic case. Two corollaries are also furnished.

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Preparation of Porous Silicon by Electrochemical Etching Methods and its Morphological and Optical Properties

Preparation of Porous Silicon by Electrochemical Etching Methods and its Morphological and Optical Properties

In this work, porous silicon was prepared by electrochemical anodic etching with different fabrication parameters (etching time, current density, and solution composition). Then, the effects of different etching conditions on the morphology and the IR spectrum were analyzed. A crack formation model was established to analyze the formation mechanism of the porous silicon surface morphology. The experimental results indicate that the longitudinal etching depth increases with the etching time and that cracks and ridges are gradually formed. Both structures affect light trapping in the porous silicon. When the etching current density increases, the reflectance increases and electrochemical polishing causes the surface topography to become smoother. Two methods were used to prepare the composite structures. The composite structure prepared using a low concentration of HF has less pores, but the reflectance is significantly reduced. The composite structure prepared using H 2 O 2 has a more pores with

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Selective etching process

Selective etching process

A process for selectively etching silicon comprises preparing a solution of etchant which is a non-selective etch for at least silicon and aluminum. The prepared solution is preconditioned by adding atomic silicon to the solution and aging the solution after the addition of silicon for at least 30 minutes. Then, silicon substrates carrying aluminum are immersed in the preconditioned solution to etch the silicon while leaving the aluminum substantially unaffected.

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Gold etching for microfabrication

Gold etching for microfabrication

Significant progress in the development of wet etchants for gold has also been made. Traditionally, iodine- and cyanide- based etch processes have been used, but due to toxicity of the latter, it is only used in a few niche applications. The dominant gold etchant is iodine-iodide, and while it is satisfactory for most applications, it has some process issues and is particu- larly prone to undercutting arising from galvanic effects. The introduction of microcontact printing using self-assembled monolayers as etch masks had also led to the development of various new gold etches which are compatible with these materials. The use of electrochemical etching has also been explored, and for applications such as gold seed layer removal, it has some advantages over con- ventional wet etching. Finally, in the last decade there has been considerable work on the development of various non-aqueous etchants, and once issues relating to chemical handling, disposal and costs have been addressed, these etchants may become viable alternatives to aqueous etchants.

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Portable etching machine

Portable etching machine

Other than that, this machine will operates by using motor that can spin the PCB for etching process. It will supply by 12V input and the speed of motor can be control and can spin by forward and reverse. Then, the motor will stop automatically because of it is sets with a timer so that within the time setting the operation will end. In the duration of the time limit if the unwanted copper of the PCB still there, the process will be repeated.

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LENGTH OF RESIN TAGS IN SELF ETCHING SEALANT WITH AND WITHOUT PRE ETCHING WITH PHOSPHORIC ACID. AN INVITRO COMPARATIVE STUDY

LENGTH OF RESIN TAGS IN SELF ETCHING SEALANT WITH AND WITHOUT PRE ETCHING WITH PHOSPHORIC ACID. AN INVITRO COMPARATIVE STUDY

Similar to the results from previous studies, which have demonstrated the beneficial effects of enamel etching with phosphoric acid. [20,21] Present study results also found significantly improved enamel bonding for surfaces pre-etched with phosphoric acid. For Group A mean resin tag length of 18.98 microns was found. It could be due to greater depth of demineralization with increased penetration of resin, resulting in longer tags. Phosphoric acid pre- etching removes the outermost enamel and creates micro irregularities, with adherent surface, resulting in higher bond strength values. [22,23]

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Fabrication and Optical Characterization of Silicon Nanostructure Arrays by Laser Interference Lithography and Metal-Assisted Chemical Etching

Fabrication and Optical Characterization of Silicon Nanostructure Arrays by Laser Interference Lithography and Metal-Assisted Chemical Etching

After developing, a thick layer of silver (varying between 15and 30 nm) was deposited on the samples surface using a thermal evaporation system following by the lift- off technique. The deposition rate was kept at 1 Å/s for all thicknesses. The resist layer was then lifted using acetone in an ultrasonic bath. Subsequently, the samples were immersed in etching solution containing 0.4M H 2 O 2 and 4.8M HF. After the

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Metal electrode integration on macroporous silicon: pore distribution and morphology

Metal electrode integration on macroporous silicon: pore distribution and morphology

Using as-prepared solutions as well as 20-day-old solu- tions, the pore distribution was affected by the presence of the Ti/Au mask. More specifically, the pores tend to grow in proximity of the metal edges. As a consequence, the pores grow with a random distribution in the direction parallel to the metal strips, and they grow with a regular spacing in the transverse direction. In the case of geome- tries with 2-μm pitches, a silicon wall in the middle of the unmasked area is formed. The depth and the high rough- ness of the top surface of this wall are due to the nucleation phase in which the initiation of the pore growth follows an almost-uniform etching of the surface. The dimension of this wall, as well as the pore diameter, depends on the

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The clinical effects of laser preparation of tooth surfaces for fissure sealants placement: a systematic review and meta-analysis

The clinical effects of laser preparation of tooth surfaces for fissure sealants placement: a systematic review and meta-analysis

The present systematic review included randomized clinical trials to evaluate retention rates, secondary car- ies, clinical times and the effect on patient psychology when lasers were used in preparation for sealant place- ment. A total of five studies were included in the sys- tematic review and three of them were quantitatively analyzed. The assessment of quality exhibited overall high risk, indicating an under-grading of the quality of the existing evidence. In terms of retention rates, the available evidence suggested that laser preparation was not significantly different than acid-etching. Meta-ana- lysis showed similar outcomes of laser and acid prepar- ation after three, six, and 12 months. The incidence of secondary caries between laser preparation and acid preparation was similar. Furthermore, it was of highly accepted by patients and did not provoke dental anxiety.

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