Showing papers on "Isotropic etching published in 2010"

Surface‐Protected Etching of Mesoporous Oxide Shells for the Stabilization of Metal Nanocatalysts

Abstract: Nanoparticles of transition metals, particularly noble metals, are widely used in catalysis. However, enhancing their stability during catalytic reactions has been a challenge that has limited the full use of the benefits associated with their small size. In this Feature Article, a general "encapsulation and etching" strategy for the fabrication of nanocatalyst systems is introduced in which catalyst nanoparticles are protected within porous shells. The novelty of this approach lies in the use of chemical etching to assist the creation of mesopores in a protective oxide shell to promote efficient mass transfer to encapsulated metal nanoparticles. The etching process allows for the direct transformation of dense silica coatings into porous shells so that chemical species can reach the catalyst surface to participate in reactions while the shells act as physical barriers against aggregation of the catalyst particles. By using the surface-protected etching process, both yolk-shell and core― satellite type nanoreactors are synthesized and their utilization in liquid- and gas-phase catalysis is demonstrated. The thermal and chemical stability ofthe metallic cores during catalytic reactions is also investigated, and further work is carried out to enhance recyclability via the introduction of superparamagnetic components into the nanoreactor framework.

Nonlithographic patterning and metal-assisted chemical etching for manufacturing of tunable light-emitting silicon nanowire arrays

Abstract: Semiconductor nanowires have potential applications in photovoltaics, batteries, and thermoelectrics We report a top-down fabrication method that involves the combination of superionic-solid-state-stamping (S4) patterning with metal-assisted-chemical-etching (MacEtch), to produce silicon nanowire arrays with defined geometry and optical properties in a manufacturable fashion Strong light emission in the entire visible and near infrared wavelength range at room temperature, tunable by etching condition, attributed to surface features, and enhanced by silver surface plasmon, is demonstrated

Oxidation Rate Effect on the Direction of Metal-Assisted Chemical and Electrochemical Etching of Silicon

Abstract: Assisted by noble metal particles, non-(100) Si substrates were etched in solutions with different oxidant concentrations at different temperatures. The etching directions of (110) and (111) Si substrates are found to be influenced by the concentration of oxidant in etching solutions. In solutions with low oxidant concentration, the etching proceeds along the crystallographically preferred ⟨100⟩ directions, whereas the etching occurs along the vertical direction relative to the surface of the substrate in solutions with high oxidant concentration. These phenomena are found for both n- and p-type substrates as well as in experiments with different oxidants. The experiments on metal-assisted chemical etching are complemented by additional experiments on metal-assisted electrochemical etching of (111) Si substrates with different current densities. As a function of current density, a change of etching directions is observed. This shows that the change of the etching directions is mainly driven by the oxidati...

Wafer-scale synthesis of single-crystal zigzag silicon nanowire arrays with controlled turning angles.

Abstract: Silicon nanowires (SiNWs) having curved structures may have unique advantages in device fabrication. However, no methods are available to prepare curved SiNWs controllably. In this work, we report the preparation of three types of single-crystal SiNWs with various turning angles via metal-assisted chemical etching using (111)-oriented silicon wafers near room temperature. The zigzag SiNWs are single crystals and can be p- or n-doped using corresponding Si wafer as substrate. The controlled growth direction is attributed to the preferred movement of Ag nanoparticles along ⟨001⟩ and other directions in Si wafer. Our results demonstrate that metal-assisted chemical etching may be a viable approach to fabricate SiNWs with desired turning angles by utilizing the various crystalline directions in a Si wafer.

Process for etching silicon with selectivity to silicon-germanium

Abstract: A method for performing a selective etching process is described The method includes preparing a substrate having a silicon layer (Si) and a silicon-germanium (SiGe x ) layer, and selectively etching the silicon layer relative to the silicon-germanium layer using a dry plasma etching process

Silicon Porosification: State of the Art

Abstract: This review is devoted to the analysis of the problems related to fabrication of the Si porous layers. The review was motivated by a great interest to Si-based porous materials from nano- to macro-scale for various applications in electronics, optoelectronics, photonics, chemical sensors, biosensors, etc. The peculiarities of the silicon porosification and the principles of preparing porous layers are considered in the present article. Various methods used for Si porosification such as chemical stain etching, chemical vapor etching, laser-induced etching, metal-assisted etching, spark processing and reactive ion (plasma) etching were analyzed. However, the main attention was focused on electrochemical porosification of Si. The review discusses in detail the influence of parameters such as electrolyte composition and pH, current density, etching time, temperature, wafer doping and orientation, lighting, magnetic field, and ultrasonic agitation on the process of Si porosification. It was shown that the stru...

Matrix-free laser desorption/ionization mass spectrometry on silicon nanowire arrays prepared by chemical etching of crystalline silicon.

Abstract: This paper reports on the use of silicon nanowires (SiNWs), easily prepared in a single step by chemical etching of crystalline silicon in HF/AgNO3 aqueous solution, as a highly sensitive substrate for laser desorption/ionization mass spectrometry (LDI-MS) analysis. The SiNWs' diameter and length depend on the etchant concentration and dissolution time. Optimized LDI substrate consists of nanowires with an average diameter in the range of 20−100 nm and 2.5 μm in length. The optimized SiNWs' surface morphology coupled to a controlled surface chemistry allowed a significant LDI-MS performance through measurements of a broad range of analytes, including small molecules, peptides, and a bovine serum albumin (BSA) digest. A signal-to-noise ratio of 250 was ascertained for a 10 fmol bradykinin pick, in reflector mode acquisition. Likewise, the sutent, a small tyrosine kinase inhibitor, could be observed down to 10 fmol, as compared to 500 fmol limit detection using the classical matrix-assisted laser desorption...

Plasma etching method and apparatus thereof

Abstract: A method of etching a substrate includes positioning the substrate on a substrate support within a chamber, etching a formation in the substrate in the presence of plasma within the chamber, decreasing a positive charge within the formation, and further etching the formation in the substrate in the presence of plasma after decreasing the positive charge within the formation.

Realization of Vertical and Zigzag Single Crystalline Silicon Nanowire Architectures

Abstract: Silicon nanowire (SiNW) ensembles with vertical and zigzag architectures have been realized using wet chemical etching of bulk silicon wafers (p-Si(111) and p-Si(100)) with a mask of silver nanoparticles that are deposited by wet electroless deposition. The etching of SiNWs is based on subsequent treatments in chemical solutions such as 0.02 M aqueous solutions of silver nitrate (AgNO3) followed by 5 M hydrofluoric acid and 30% hydrogen peroxide (H2O2). The etching of the Si wafers is mediated by the reduction of silver on the silicon surface and in parallel by the oxidation of Si thereby forming SiO2 which is dissolved in the HF surroundings. The morphology of the starting silver (Ag) layer/Ag nanoparticles that form during processing on the Si wafer surfaces strongly influences the morphology of the SiNW ensembles and homogeneity of the etch profile. Our observations suggest that the Ag layer/Ag nanoparticles not only catalyze the wet chemical etching of silicon but also strongly catalyze the decomposit...

Superluminescent diodes by crystallographic etching

Abstract: An optoelectronic device, comprising an active region and a waveguide structure to provide optical confinement of light emitted from the active region; a pair of facets on opposite ends of the device, having opposite surface polarity; and one of the facets which has been roughened by a crystallographic chemical etching process, wherein the device is a nonpolar or semipolar (Ga,In,Al,B)N based device

Fabrication of Silicon Nanowires with Precise Diameter Control Using Metal Nanodot Arrays as a Hard Mask Blocking Material in Chemical Etching

Abstract: We report on a simple and cost-effective method to fabricate high density silicon nanowires (SiNWs) through catalytic chemical wet etching. Metallic chromium/gold (Cr/Au) nanodots were first deposited onto the silicon wafer using an anodic aluminum oxide (AAO) template. The AAO template was then removed before a thin blanket layer of gold catalyst was evaporated onto the sample surface. The gold-assisted chemical wet etching was carried out in a solution consisting of deionized water, hydrogen peroxide, and hydrofluoric acid to produce well-aligned silicon nanowires of uniform diameters. We demonstrate that the diameter of the silicon nanowires can be precisely controlled to a precision of 10 nm in the range of 40 to 80 nm through fine-tuning of the pore diameter of the AAO template. The reported fabrication procedure therefore gives a highly repeatable method to form well-aligned, uniform, and crystalline SiNWs of high density with controllable diameters below 100 nm. The use of Cr/Au as a hard mask bloc...

Nanoparticle clusters light up in SERS.

Abstract: Seeing double: nanoparticle clusters (dimers, trimers, etc.) have long been pursued as enhancers in surface-enhanced Raman spectroscopy research. A recent report presents an elegant approach for the high-yielding fabrication of dimers of silver nanospheres from nanocubes by controlled chemical etching. These nanoparticle dimers are capable of strongly enhancing Raman signals of surface adsorbates.

Metal‐Catalyzed Etching of Vertically Aligned Polysilicon and Amorphous Silicon Nanowire Arrays by Etching Direction Confinement

Abstract: A systematic study of metal-catalyzed etching of (100), (110), and (111) silicon substrates using gold catalysts with three varying geometrical characteristics: isolated nanoparticles, metal meshes with small hole spacings, and metal meshes with large hole spacings is carried out. It is shown that for both isolated metal catalyst nanoparticles and meshes with small hole spacings, etching proceeds in the crystallographically preferred direction. However, the etching is confined to the single direction normal to the substrate surface when a catalyst meshes with large hole spacings is used. We have also demonstrated that the metal catalyzed etching method when used with metal mesh with large hole spacings can be extended to create arrays of polycrystalline and amorphous vertically aligned silicon nanowire by confining the etching to proceed in the normal direction to the substrate surface. The ability to pattern wires from polycrystalline and amorphous silicon thin films opens the possibility of making silicon nanowire array-based devices on a much wider range of substrates.

Method and apparatus for etching

Abstract: Embodiments of the invention relate to a substrate etching method and apparatus. In one embodiment, a method for etching a substrate in a plasma etch reactor is provided that include flowing a backside process gas between a substrate and a substrate support assembly, and cyclically etching a layer on the substrate.

Formation of AgPt alloy nanoislands via chemical etching with tunable optical and catalytic properties.

Abstract: An effective way is developed to fabricate AgPt alloy nanoislands on gold nanorods based on the galvanic replacement between Ag and PtCl42− in the presence of cetyltrimethylammonium bromide (CTAB). The optical and catalytic properties benefit from the porous structure composed of AgPt nanoislands. A large red shift (265 nm) after etching is observed for longitudinal surface plasmon resonance (SPR) in comparison with Au@Pt0.1@Ag. Alloy compositions in bulk miscibility gap can be obtained and finely tuned from Ag0.56Pt0.44 to Ag0.38Pt0.62. A unique composition dependence is found for both electrocatalytic oxidation of methanol and catalytic oxidation of o-phenylenediamine (OPD) by hydrogen peroxide. In both systems, the highest catalytic activity is achieved at the alloy composition of Pt0.62Ag0.38. Proper alloying with Ag not only improves the CO poisoning of Pt catalyst but also enhances the catalytic activity greatly.

Metal-Assisted Chemical Etching of Substrates

Abstract: Disclosed herein are various embodiments related to metal-assisted chemical etching of substrates on the micron, sub-micron and nano scales. In one embodiment, among others, a method for metal-assisted chemical etching includes providing a substrate; depositing a non-spherical metal catalyst on a surface of the substrate; etching the substrate by exposing the non-spherical metal catalyst and the substrate to an etchant solution including a composition of a fluoride etchant and an oxidizing agent; and removing the etched substrate from the etchant solution.

Si nanowire arrays as anodes in Li ion batteries

Abstract: Si nanowires can incorporate large amounts of Li without fracturing and are thus prime candidates for anodes in Li ion batteries. Anodes made from Si nanowires offer a specific capacity per gram more then 10 times larger than the present graphite standard. It is shown how optimized Si nanowire arrays embedded in Cu can be produced in a relatively simple way employing macropore etching in Si followed by chemical etching and Cu galvanic deposition. First tests of these arrays in half-cells and batteries demonstrated a substantially increased capacity, small irreversible losses and cycle stability. In particular more than 60 charge/discharge cycles could be realized without loss of capacity. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Semipolar GaN films on patterned r-plane sapphire obtained by wet chemical etching

Abstract: It is shown that (112¯2)-oriented GaN films can be achieved from r-sapphire patterned by chemical etching. Growth first occurs selectively from the inclined c-facet of sapphire, leading finally to a fully coalesced layer with (112¯2) orientation. The structural and optical quality of these layers was assessed by x-ray diffraction, cathodoluminescence and photoluminescence measurements. The results clearly show that the quality of (112¯2) GaN on patterned r-sapphire is markedly improved in comparison with (112¯2) GaN on m-sapphire.

Nanopores in track-etched polymer membranes characterized by small-angle x-ray scattering

Abstract: Nanochannels and nanowires with diameters ranging from 30 to 400 nm were produced by etching ion tracks in thin polyarylate and polycarbonate foils. The shape and the size distribution of dry and wet nanochannels, as well as of nanowires grown therein, were examined by small-angle x-ray scattering. The x-ray intensity as a function of the scattering vector exhibits pronounced oscillations showing that both the channels and the wires have a highly cylindrical geometry and a very narrow size distribution. UV exposure before chemical etching significantly improves the monodispersity of the nanopores. For fixed etching conditions, the scattering patterns provide evidence that the diameter of dry and water-filled channels as well as for embedded nanowires are identical, demonstrating that the pores in the polymer are completely filled.

Formation of Hexagonal Pyramids and Pits on V-/VI-Polar and III-/II-Polar GaN/ZnO Surfaces by Wet Etching

Abstract: The etching characteristics and evolution of the surface morphology of ZnO and GaN thin films during wet chemical etching were investigated. While the ZnO etch rates using acidic solutions were similar, regardless of etchant or polarity, the etch rate of the Ga-polar GaN surface was dependent on the etchant. N-polar GaN could be etched in alkali-based solutions such as KOH. The surface morphologies of etched ZnO were very similar to those of the GaN surface: hexagonal pyramids and stepped hexagonal pits formed during the etching of O-polar ZnO and N-polar GaN and of Zn-polar ZnO and Ga-polar GaN, respectively. The formation of a hexagonal etch pit on the etched Zn-polar and Ga-polar surfaces was enhanced by surface defects such as pits or threading dislocations. The etching of N-polar GaN by KOH proceeded through the evolutionary stages of hexagonal pyramids: formation, growth, dissociation, and isolation. Ga-polar GaN was etched through the formation, widening, and merging of hexagonal pits.

Selective silicon etch process

Abstract: A process for etching a silicon layer disposed on a substrate, including anisotropically etching a first trench in the silicon layer; selectively anisotropic wet etching silicon surfaces in the first trench, the wet etching comprising exposing the silicon surfaces to an aqueous composition including an aromatic tri(lower)alkyl quaternary onium hydroxide, and an unsymmetrical tetraalkyl quaternary phosphonium salt; in which the wet etching etches (110) and (100) planes of the silicon layer at about equal rates and preferentially to the (111) plane to form an enlarged trench having a sidewall in the (111) plane. A silicon alloy may be epitaxially deposited in the thus-produced trench as part of a process of introducing stress into at least a portion of the silicon layer.

Dielectric Breakdown of Thinned BaO–Al2O3–B2O3–SiO2 Glass

Abstract: The dielectric breakdown behavior of alkali-free glass was determined as a function of thickness and surface roughness. The thickness of commercially available glass (as-received thickness=50 μm) was reduced to a range of thicknesses between 47 and 5 μm by chemical etching. The RMS surface roughness of the as-received glass was in the range of 0.14–0.47 nm, and the surface roughness increased to up 10 nm after etching; it was also found that agitating the etching solution by ultrasound reduced the overall surface roughness. The evaluation of these samples revealed that the dielectric breakdown strength increased as the thickness decreased. However, the Weibull modulus representing the distribution of dielectric strengths showed a dependence on the surface roughness of the etched glass. A power law dependence, EB∝d−n, where d is the glass thickness and n=0.14 and 0.86, has been found to fit the data in the respective thickness ranges of 5–20 and 25–50 μm. Self-healing behavior, which allows the dielectric to continue to support a high electric field after breakdown, was found to be more likely as the dielectric layer thickness decreased. The susceptibility to self healing was correlated with the stored electrostatic energy and latent heat of vaporization for the gold electrode material.