Electrochemical Etching Of Silicon Research Articles

DFT Modeling of Chemical Reactions Occurring Under the Influence of Positive Ionic Complexes of Aqueous HF Solutions During Electrochemical Etching of Silicon

DFT Modeling of Chemical Reactions Occurring Under the Influence of Positive Ionic Complexes of Aqueous HF Solutions During Electrochemical Etching of Silicon

Energy Parameters of the Simplest Chemical Reactions Occurring at the First Stages of Silicon Electrochemical Etching – DFT-Modeling

Energy Parameters of the Simplest Chemical Reactions Occurring at the First Stages of Silicon Electrochemical Etching – DFT-Modeling

The effective of time etching and different acids on the morphological porous silicon

This paper study the characteristics of nano crystalline silicon prepared with the use of electrochemical etching with etching time (15,20) min for salt and Nitric acid (HNO3) and etching time (15,20) min for Ethanol and Hydrofluoric acid, and study the effect of this solutions on the characteristics of porous silicon (ps) will be produced by electrochemical etching by using electrochemical etching from p-type bulk silicon with resistivity (1-10 Ω.cm) with different time. after that, make a comparison for the morphological properties for porous silicon. Research employing X-ray diffraction and scanning electron microscopy instruments were also performed on the samples that were produced as a result. Micromachining etching uses electrochemical etching of silicon in HF solution. New wafer-etched structures are reported. Wall arrays, hole arrays, meander-shaped structures, spiral-like walls, microtubes, and more are produced. The electrochemical etch process and KOH etching time of the original pattern on final geometries are modelled.

Sorption Kinetics and Sequential Adsorption Analysis of Volatile Organic Compounds on Mesoporous Silica.

Adsorption-desorption behaviors of polar and nonpolar volatile organic compounds (VOCs), namely, isopropanol and nonane, on mesoporous silica were studied using optical reflectance spectroscopy. Mesoporous silica was fabricated via electrochemical etching of silicon and subsequent thermal oxidation, resulting in an average pore diameter of 11 nm and a surface area of approximately 493 m2/g. The optical thickness of the porous layer, which is proportional to the number of adsorbed molecules, was measured using visible light reflectance interferometry. In situ adsorption and desorption kinetics were obtained for various mesoporous silica temperatures ranging from 10 to 70 °C. Sorption as a function of temperature was acquired for isopropanol and nonane. Sequential adsorption measurements of isopropanol and nonane were performed and showed that, when one VOC is introduced immediately following another, the second VOC displaces the first one regardless of the VOC's polarity and the strength of its interaction with the silica surface.

Time-temperature indicator based on the variation of the optical response of photonic crystals upon polymer infiltration

Time-temperature indicators are used for sensing the thermal history of perishable products, like food and pharmaceutical goods. Their working principle is based on a temperature response that mimics the temperature dependence of the deterioration kinetics of a given product. For successful implementation, time-temperature indicators must be of minimum size, cost-effective, change-irreversible, and easy to read. This work presents a time-temperature sensor based on capillary imbibition of thermoplastic polymers into a mesoporous photonic crystal, which was tuned to reflect well-defined wavelengths of visible light. The photonic crystal was made by electrochemical etching of silicon, where a periodic structure was formed with microscale layers of alternating nanoscale porosity. Polymer infiltration induces an irreversible change of the effective refractive index of the crystal, leading to a progressive shift of the reflected light that can be seen by the naked eye. Importantly, the employed thermoplastic polymer (poly(ethylene vinyl-acetate)) presents a temperature-dependent viscosity that is well represented by the Arrhenius law, which is normally used to characterize the temperature-dependence of quality indexes. Therefore, each reflected color is associated to the time-temperature history of the system, representing the deterioration level of a monitored product.

Role of graphene on the optoelectrical stability of photodetectors based on porous silicon

In this research, the intrinsic instability of optical and electrical properties of porous silicon (PS) was minimized by deposition of reduced graphene oxide (rGO). The optoelectrical properties of the devices based on PS substrates showed a lack of stability under prolonged exposure to illumination. Therefore, despite many advantages of PS (e.g. high specific surface area), its application in electronic industries has been hindered. To resolve this problem, a thin layer of rGO was deposited on a bare PS substrate using electrophoretic deposition (EPD) technique. In order to obtain a high-quality porous substrate, the etching time was optimized in electrochemical etching of silicon. The most intense photoluminescence (PL) peak was reported for the sample etched for 20 min which could be due to its high absorption coefficient and large surface area. Moreover, a blue shift was observed in the PL peak position which can be assigned to quantum confinement effect reflecting the minimum crystallite size of this sample. The morphological study of the samples revealed complete coverage of the PS substrate by rGO. After graphene deposition, the PL quenching of PS samples was arrested even under prolonged exposure to laser illumination. For examining the electrical properties, metal-semiconductor-metal photodetectors were fabricated on bare PS and rGO/PS substrates. The results indicated that the photocurrent of the PS sample was diminished under 30-minute exposure to photons. However, the device based on rGO/PS illustrated higher photocurrent stability reflecting that the stability of optoelectrical properties of porous silicon could be enhanced by rGO deposition.

High Anodic-Voltage Focusing of Charge Carriers in Silicon Enables the Etching of Regularly-Arranged Submicrometer Pores at High Density and High Aspect-Ratio.

The anodic dissolution of silicon in acidic electrolytes is a well-known technology enabling the silicon machining to be accurately controlled down to the micrometer scale in low-doped n-type silicon electrodes. Attempts to scale down this technology to the submicrometer scale has shown to be challenging, though it premises to enable the fabrication of meso and nano structures/systems that would greatly impact the fields of biosensors and nanomedicine. In this work, we report on the electrochemical etching at high anodic voltages (up to 40 V) of two-dimensional regular arrays of millions pores per square centimeter (up to 30 × 106 cm−2) with sub-micrometric diameter (down to ~860 nm), high depth (up to ~40 μm), and high aspect-ratio (up to ~45) using low-doped n-type silicon electrodes (resistivity 3–8 Ω cm). The use of high anodic voltages, which are over one order of magnitude higher than that commonly used in electrochemical etching of silicon, tremendously improves hole focusing at the pore tips during the etching and enables, in turn, the control of electrochemical etching of submicrometer-sized pores when spatial period reduces below 2 μm. A theoretical model allows experimental results to be interpreted in terms of an electric-field-enhanced focusing of holes at the tip apex of the pores at high anodic voltages, with respect to the pore base, which leads to a smaller curvature radius of the tip apex and enables, in turn, the etching of pore tips to be preferentially sustained over time and space.

Hemispherical cavities on silicon substrates: an overview of micro fabrication techniques

Hemispherical photonic crystals found in species like Papilio blumei and Cicendella chinensis have inspired new applications like anti-counterfeiting devices and gas sensors. In this work, we investigate and compare four different ways to micro fabricate such hemispherical cavities: using colloids as template, by wet (HNA) or dry (XeF2) isotropic etching of silicon and by electrochemical etching of silicon. The shape and the roughness of the obtained cavities have been discussed and the pros/cons for each method are highlighted.

Modeling of the optical properties of porous silicon photonic crystals in the visible spectral range

Optical devices based on photonic crystals are of great interest because they can be efficiently used in laser physics and biosensing. Photonic crystals allow one to control the propagation of electromagnetic waves and to change the emission characteristics of luminophores embedded into photonic structures. One of the most interesting materials for developing one-dimensional photonic crystals is porous silicon. However, an important problem in application of this material is the control of the refractive index of layers by changing their porosity, as well as the refractive index dispersion. In addition, it is important to have the possibility of modeling the optical properties of structures to choose precisely select the fabrication parameters and produce one-dimensional photonic crystals with prescribed properties. In order to solve these problems, we used a mathematical model based on the transfer matrix method, using the Bruggeman model, and on the dispersion of silicon refractive index. We fabricated microcavities by electrochemical etching of silicon, with parameters determined by the proposed model, and measured their reflection spectra. The calculated results showed good agreement with experimental data. The model proposed allowed us to achieve a microcavity Q-factor of 160 in the visible region.

Influence of electro-chemical etching parameters on the reflectance spectra of porous silicon rugate filters

Today the porous silicon photonic crystals are widely used as components of the optical sensors. The structures with the resonance properties, e.g. a narrow reflection band, which provides high sensitivity of the device, generate considerable interest. One of the most interesting structures of this type are rugate filters. Rugate filter is a photonic crystal with a gradually varying under harmonic law index of refraction and narrow spectral reflection band. In this paper, we present our results of the optimization of silicon electrochemical etching parameters, in order to fabricate filters in a visible spectral range with reflection bandwidth of less than 30 nm and a reflectance higher than 80%.

In Situ Reductive Synthesis of Structural Supported Gold Nanorods in Porous Silicon Particles for Multifunctional Nanovectors.

Porous silicon nanodisks (PSD) were fabricated by the combination of photolithography and electrochemical etching of silicon. By using PSD as a reducing agent, gold nanorods (AuNR) were in situ synthesized in the nanopores of PSD, forming PSD-supported-AuNR (PSD/AuNR) hybrid particles. The formation mechanism of AuNR in porous silicon (pSi) was revealed by exploring the role of pSi reducibility and each chemical in the reaction. With the PSD support, AuNR exhibited a stable morphology without toxic surface ligands (CTAB). The PSD/AuNR hybrid particles showed enhanced plasmonic property compared to free AuNR. Because high-density "hot spots" can be generated by controlling the distribution of AuNR supported in PSD, surface-enhanced raman scattering (SERS) using PSD/AuNR as particle substrates was demonstrated. A multifunctional vector, PSD/AuNR/DOX, composed of doxorubicin (DOX)-loaded PSD/AuNR capped with agarose (agar), was developed for highly efficient, combinatorial cancer treatment. Their therapeutic efficacy was examined using two pancreatic cancer cell lines, PANC-1 and MIA PaCa-2. PSD/AuNR/DOX (20 μg Au and 1.25 μg DOX/mL) effectively destroyed these cells under near-IR laser irradiation (810 nm, 15 J·cm(-2) power, 90 s). Overall, we envision that PSD/AuNR may be a promising injectable, multifunctional nanovector for biomedical application.

Electrochemical Fabrication of 3D Gradient Refractive Index Micro-Optics

Via electrochemical etching of silicon, followed by materials conversion, 3D gradient refractive index micro-optics were formed. Elements including flat lenses, Bragg mirrors, polarization sensitive optical splitters and structures with nearly arbitrary refractive index distributions were formed with a particular focus on micro-optics important for solar energy harvesting. The conversion from silicon to silica and titania enabled the optics to operate in the visible with minimal loss, something particularly important for solar energy harvesting applications.

Elimination of boundary effect in silicon electrochemical etching via mechanical stress

Elimination of boundary effect in silicon electrochemical etching via mechanical stress

Elimination of boundary effect in silicon electrochemical etching via mechanical stress

Application of thick macroporous silicon is always one of the hotspots in electrochemistry including micromachining and chemical sensing. One serious problem in macropore formation with high depth-width ratio is the boundary effect. In this work, we applied mechanical stress onto the boundary region of electrochemical etching, which helps to passivate the sidewall of macropore in boundary area, and therefore eliminate the boundary effect effectively. The CBM model was employed to explain the mechanism. Thick macroporous layers without boundary effect were successfully produced in both n-type and p-type silicon.

Porosity Control and Transfer in Silicon Nanostructures through Electrochemical & Chemical Etching

High surface area and controlled pore diameter silicon nanostructures were prepared using a two-step etching procedure. Firstly, the experimental conditions of silicon electrochemical etching leading to the formation of high surface area porous silicon thin films were described. Thereafter, the porous silicon layers were either lifted off the substrate to collect the porous particles or subjected to metal-assisted chemical etching (MaCE) in a hydrofluoric acid - silver nitrate solution to produce high aspect ratio porous silicon nanowires with controlled pore dimensions. The consecutive electrochemical and chemical (MaCE) silicon etching procedures enabled the synthesis of porous silicon nanowires with high specific surface area (up to 460 m²/g) along with low average pore diameter (below 6.5 nm).

The effect of the hydrofluoric acid etchant–silicon system anisotropy on the shape of pores formed upon electrochemical etching of silicon

The shape of nanopores formed in silicon upon electrochemical etching in hydrofluoric acid solutions has been explained by the effect of anisotropy of the components involved in etching. A semiempirical formula that allows one to characterize, with a certain accuracy, the degree of anisotropy of the etchant–silicon system and describe the shape of the resulting pores has been suggested.

Nanopore formation during electrolytic etching of silicon in hydrofluoric acid solutions

A stepwise scheme has been proposed for gaining insight into the nanopore formation process in silicon during electrolytic etching in hydrofluoric acid solutions. We have studied the influence of the concentration and nature of dopants (phosphorus, arsenic, and antimony) in silicon, current density, electric field strength, and etching time on the axial and radial pore sizes and the pore distribution density. The dopants have been shown to play a predominant role in the nanopore formation process. The shape and spatial orientation of nanopores in Si substrates with the (100) and (111) crystallographic orientations have been interpreted in terms of specific features of the electrochemical etching of silicon in hydrofluoric acid solutions, related to the action of the etching ion (HF2)−. The observed discrepancy between the experimentally determined and calculated radial nanopore sizes has been accounted for by the low probability ( 6.25%) of simultaneous interaction of the fluorine atoms of an (HF2)− ion with the corresponding silicon atoms located at vertices of a cube of the crystal lattice.

Material Deposition into Porous Silicon Template

Porous silicon (PSi) is often fabricated by the electrochemical etching of silicon in a fluoride-based solution [1-4]. One of the unique properties of PSi layer is the ability to precisely tune the pore size and morphology through the variation of the silicon dopant type and level and controlling the applied anodic current and etching time. The compatibility of PSi with existing silicon processing technology adds another advantage. A wide range of materials including metals, conducting polymers, oxides, magnetic alloys and semiconductors can be deposited inside the pores of PSi templates by different techniques including; the electrochemical deposition, immersion plating and electroless deposition, sol-gel and chemical vapor deposition. Such deposition strategies would lead to various surface morphologies such as nanowires or nanorods, nanotubes, nanorings, nanodots and heterogeneous nano-macrostructures. The dimensions of as-formed hybrid structures can be controlled by regulating the shape and pore size of PSi template as well as the deposition conditions. In this work, we used PSi as a template-directing synthesis of various metallic and polymeric nano-macrostructures. Firstly, preparation of various shapes and morphologies of PSi templates are given. Examples of chemical and electrochemical deposition of metals and conducting polymers are provided. We then focus on understanding of the mechanism of Cu deposition by the immersion plating method using the XPS sputter depth profiling into PSi template as a case study and discuss the processing issues associated with its deposition inside the nanoscale pores under the open-circuit condition. Various pore diameters ranging from < 5 nm up to > 1 µm are accessible in PSi layers. Typical examples of SEM images of PSi templates, mainly ordered 5 µm macropores, 120 nm medium-sized pores and 20 nm mesopores are presented in Fig.1 [5]. Results of the synthesis and characterization of the obtained PSi-deposited materials will be presented and thoroughly discussed during the conference. Keywords: Porous silicon; electrochemical deposition; immersion plating; Cu deposition; conducting polymer References F.A. Harraz, J. Sasano, T. Sakka, Y.H. Ogata, J. Electrochem. Soc., 149 (2002) C456.F. A. Harraz, A. M. Salem, B. A. Mohamed, A. Kandil, I. A. Ibrahim. Appl. Surf. Sci., 264, (2013) 391.F. A. Harraz. Appl. Sur. Sci., 287, (2013) 203.F. A. Harraz, S. M. El-Sheikh, T. Sakka, Y. H. Ogata, Electrochim. Acta, 53, (2008) 6444.K. Fukami, F. A. Harraz, T. Yamauchi, T. Sakka, Y. H. Ogata. Electrochem. Commun., 10, (2008) 56. Figure 1

Macroporous silicon for high-capacitance devices using metal electrodes.

In this paper, high-capacity energy storage devices based on macroporous silicon are demonstrated. Small footprint devices with large specific capacitances up to 100 nF/mm2, and an absolute capacitance above 15 μF, have been successfully fabricated using standard microelectronics and MEMS techniques. The fabricated devices are suitable for high-density system integration. The use of 3-D silicon structures allows achieving a large surface to volume ratio. The macroporous silicon structures are fabricated by electrochemical etching of silicon. This technique allows creating large structures of tubes with either straight or modulated radial profiles in depth. Furthermore, a very large aspect ratio is possible with this fabrication method. Macroporous silicon grown this way permits well-controlled structure definition with excellent repeatability and surface quality. Additionally, structure geometry can be accurately controlled to meet designer specifications. Macroporous silicon is used as one of the electrodes over which a silicon dioxide insulating layer is grown. Several insulator thicknesses have been tested. The second capacitor electrode is a solid nickel filling of the pores prepared by electroplating in a low-temperature industry standard process. The use of high-conductivity materials allows reaching small equivalent series resistance near 1 Ω. Thanks to these improvements, the presented devices are capable of operating up to 10 kHz.PACS84.32.Tt; 81.15.Pq; 81.05.Rm

Graphene masks as passivation layers in the electrochemical etching of silicon

Site-specific masking with graphene films has the potential to facilitate low-cost, high-throughput micro-patterns on silicon substrates over large areas. Here, a facile approach to using graphene as a masking agent on silicon wafers for site-specific patterning is demonstrated. Graphene sheets were deposited via a sealing-tape-exfoliation method onto hydride-terminated (Si–H) silicon substrates. Raman confocal mapping showed inhibition of oxidation of the Si wafer underlying the graphene, indicating that the graphene restricts the diffusion of oxygen onto the Si surface. The graphene coated Si substrates were then electrochemically etched in an aqueous HF/ethanol (3:1 (v/v)) anodization solution. Scanning electron microscopy showed that the graphene layer successfully restricted the etching of the Si surface, however, near the edge sites of the graphene deep etching occurred.