Showing papers on "Isotropic etching published in 2012"

Synthesis of Prussian Blue Nanoparticles with a Hollow Interior by Controlled Chemical Etching

Abstract: A facile route has been found to prepare Prussian blue (PB) hollow particles with a cubic shape (see picture). With PB mesocrystals used as a starting material, hollow interiors were created through controlled chemical etching in the presence of poly(vinylpyrrolidone). The hollow cavities and particle sizes could be tuned by changing the synthetic conditions, and the original PB crystallinity was preserved even after formation of interior hollows.

Metal assisted chemical etching for high aspect ratio nanostructures: A review of characteristics and applications in photovoltaics

Abstract: Metal assisted chemical etching (MacEtch) is a recently developed anisotropic wet etching method that is capable of producing high aspect ratio semiconductor nanostructures from patterned metal film. In this review article, we highlight the characteristics of MacEtch of silicon (Si) including controllability of the produced sidewall roughness, the inherent high aspect ratio, the weak crystal orientation dependence, impurity doping and solution concentration dependent porosity, as well as the applicability of MacEtch to non-Si based semiconductor materials including III–V compound semiconductors. Also reviewed are applications of MacEtch produced high aspect ratio Si nanostructures in photovoltaics, where the p–n junction can be in the planar Si tray, core–shell, or axial geometry, with nanowire, micropillar, or hole arrays serving as light trapping or carrier collection structures. The prospect of using MacEtch to improve the cost and efficiency of photovoltaic cells is discussed.

Development of a selective chemical etch to improve the conversion efficiency of Zn-rich Cu2ZnSnS4 solar cells.

Abstract: Improvement of the efficiency of Cu2ZnSnS4 (CZTS)-based solar cells requires the development of specific procedures to remove or avoid the formation of detrimental secondary phases. The presence of these phases is favored by the Zn-rich and Cu-poor conditions that are required to obtain device-grade layers. We have developed a selective chemical etching process based on the use of hydrochloric acid solutions to remove Zn-rich secondary phases from the CZTS film surface, which are partly responsible for the deterioration of the series resistance of the cells and, as a consequence, the conversion efficiency. Using this approach, we have obtained CZTS-based devices with 5.2% efficiency, which is nearly twice that of the devices we have prepared without this etching process.

Anisotropic Hydrogen Etching of Chemical Vapor Deposited Graphene

Abstract: We report a simple, clean, and highly anisotropic hydrogen etching method for chemical vapor deposited (CVD) graphene catalyzed by the copper substrate. By exposing CVD graphene on copper foil to hydrogen flow around 800 °C, we observed that the initially continuous graphene can be etched to have many hexagonal openings. In addition, we found that the etching is temperature dependent. Compared to other temperatures (700, 900, and 1000 °C), etching of graphene at 800 °C is most efficient and anisotropic. Of the angles of graphene edges after etching, 80% are 120°, indicating the etching is highly anisotropic. No increase of the D band along the etched edges indicates that the crystallographic orientation of etching is in the zigzag direction. Furthermore, we observed that copper played an important role in catalyzing the etching reaction, as no etching was observed for graphene transferred to Si/SiO(2) under similar conditions. This highly anisotropic hydrogen etching technology may work as a simple and convenient way to determine graphene crystal orientation and grain size and may enable the etching of graphene into nanoribbons for electronic applications.

Surface modification of Ti6Al4V open porous structures produced by additive manufacturing

Abstract: Additive manufacturing techniques can be used to produce micro-porous structures with global morphological properties that are highly controlled through robust computer design. Despite these advantages, most of these techniques still hold several functional constraints, resulting from present technical device limits and consequently the inability to control surface morphology at a microscale level. In this study, a novel protocol for surface modification of 3D titanium alloy-based open porous structures is developed, which applies a combination of chemical etching (CHE) and electrochemical polishing (ECP) using HF-based solutions. This protocol achieves significant and controllable roughness reduction of additive manufactured 3D Ti6Al4V open porous structures. Chemical etching mainly removes the attached powder grains, while ECP further decreases the roughness. In this way the heterogeneity of the strut surface roughness throughout the full 3D structure is effectively removed.

A strategy for designing a concave Pt-Ni alloy through controllable chemical etching.

Abstract: This corrosion: Octahedral Pt-Ni alloy nanoparticles (NPs) are converted into concave Pt(3)Ni NPs by a coordination-assisted chemical-etching process. The corroded concave Pt-Ni NPs have a higher density of low-coordinate atoms in steps sites, a decisive property in heterogeneous catalysis.

Model for the Mass Transport during Metal-Assisted Chemical Etching with Contiguous Metal Films As Catalysts

Abstract: Metal-assisted chemical etching is a relatively new top-down approach allowing a highly controlled and precise fabrication of Si and Si/Ge superlattice nanowires. It is a simple method with the ability to tailor diverse nanowire parameters like diameter, length, density, orientation, doping level, doping type, and morphology. In a typical metal-assisted chemical etching procedure, a Si substrate is covered by a lithographic noble metal film and etched in a solution containing HF and an oxidant (typically H2O2). In general, the function of the metal is to catalyze the reduction of H2O2, which delivers electronic holes necessary for the oxidation and subsequent dissolution of the Si oxide by HF. However, the details of the etching process using contiguous metal thin films, especially the mass transport of reactants and byproducts are still not well understood. In this study, the etching mechanism was systematically investigated. Several models of metal-assisted chemical etching using a contiguous metal film...

Double patterning etching process

Abstract: A method of etching a substrate comprises forming on the substrate, a plurality of double patterning features composed of silicon oxide, silicon nitride, or silicon oxynitride The substrate having the double patterning features is provided to a process zone An etching gas comprising nitrogen tri-fluoride, ammonia and hydrogen is energized in a remote chamber The energized etching gas is introduced into the process zone to etch the double patterning features to form a solid residue on the substrate The solid residue is sublimated by heating the substrate to a temperature of at least about 100° C

Porosity control in metal-assisted chemical etching of degenerately doped silicon nanowires

Abstract: We report the fabrication of degenerately doped silicon (Si) nanowires of different aspect ratios using a simple, low-cost and effective technique that involves metal-assisted chemical etching (MacEtch) combined with soft lithography or thermal dewetting metal patterning. We demonstrate sub-micron diameter Si nanowire arrays with aspect ratios as high as 180:1, and present the challenges in producing solid nanowires using MacEtch as the doping level increases in both p- and n-type Si. We report a systematic reduction in the porosity of these nanowires by adjusting the etching solution composition and temperature. We found that the porosity decreases from top to bottom along the axial direction and increases with etching time. With a MacEtch solution that has a high [HF]:[H2O2] ratio and low temperature, it is possible to form completely solid nanowires with aspect ratios of less than approximately 10:1. However, further etching to produce longer wires renders the top portion of the nanowires porous. (Some figures may appear in colour only in the online journal)

Chemical-Assisted Thermal Disproportionation of Porous Silicon Monoxide into Silicon-Based Multicomponent Systems†

Abstract: Under the surface: Ag nanoparticles are deposited onto the surface of commercially available SiO particles, and subsequent chemical etching results in the formation of nanoporous SiO without changing the chemical and physical properties of the original SiO. Moreover, chemical-assisted thermal annealing produces a shape-preserving Si-based multicomponent system, which exhibits high-performance electrochemical properties.

Dry etching method for metal film

Abstract: A method for performing dry etching on a metal film containing Pt via a mask layer includes performing dry etching on the metal film by generating a plasma of an etching gas including a gaseous mixture of H 2 gas, CO 2 gas, methane gas and rare gas. With the dry etching method, it is possible to make a vertical sidewall of a hole or trench more vertical without using a halogen gas.

Chemical etching of zinc oxide for thin-film silicon solar cells.

Abstract: Chemical etching is widely applied to texture the surface of sputter-deposited zinc oxide for light scattering in thin-film silicon solar cells. Based on experimental findings from the literature and our own results we propose a model that explains the etching behavior of ZnO depending on the structural material properties and etching agent. All grain boundaries are prone to be etched to a certain threshold, that is defined by the deposition conditions and etching solution. Additionally, several approaches to modify the etching behavior through special preparation and etching steps are provided.

A chemical route to increase hot spots on silver nanowires for surface-enhanced Raman spectroscopy application.

Abstract: The effective number of surface-enhanced Raman spectroscopy (SERS) active hot spots on plasmonic nanostructures is the most crucial factor in ensuring high sensitivity in SERS sensing platform. Here we demonstrate a chemical etching method to increase the surface roughness of one-dimensional Ag nanowires, targeted at creating more SERS active hot spots along Ag nanowire’s longitudinal axis for increased SERS detection sensitivity. Silver nanowires were first synthesized by the conventional polyol method and then subjected to chemical etching by NH4OH and H2O2 mixture. The surfaces of silver nanowires were anisotropically etched off to create miniature “beads on a string” features with increased surface roughness while their crystallinity was preserved. Mapping of single-nanowire SERS measurements showed that the chemical etching method has overcome the limitation of conventional one-dimensional Ag nanowires with limited SERS active area at the tips to produce etched Ag nanowires with an increase in Raman ...

Corrodible downhole article and method of removing the article from downhole environment

Abstract: A method of removing a corrodible downhole article having a surface coating includes eroding the surface coating by physical abrasion, chemical etching, or a combination of physical abrasion and chemical etching, the surface coating comprising a metallic layer of a metal resistant to corrosion by a corrosive material.

Systematically controlling Kapitza conductance via chemical etching

Abstract: We measure the thermal interface conductance between thin aluminum films and silicon substrates via time-domain thermoreflectance from 100 to 300 K. The substrates are chemically etched prior to aluminum deposition, thereby offering a means of controlling interface roughness. We find that conductance can be systematically varied by manipulating roughness. In addition, transmission electron microscopy confirms the presence of a conformal oxide for all roughnesses, which is then taken into account via a thermal resistor network. This etching process provides a robust technique for tuning the efficiency of thermal transport while alleviating the need for laborious materials growth and/or processing.

Towards ultrathin copper indium gallium diselenide solar cells: proof of concept study by chemical etching and gold back contact engineering

Abstract: An innovative approach combining chemical etching and a "lift-off" process, which allows back contact processing after CIGSe deposition, permitted to use Au as a highly reflective back contact in ultrathin CIGSe solar cells. The Au back contact does not degrade the other parameters of the cell, as good ohmicity on CIGSe is achieved. An important photocurrent increase compared with regular Mo back contact solar cells is achieved by the enhanced light trapping effect due to the back reflector, leading to an absolute efficiency increase of +2.5% for a CIGSe thickness of 0.4 μm. This approach could be used for further investigations in improving the back side of ultrathin CIGSe solar cells.

Conjugated polymer–silicon nanowire array hybrid Schottky diode for solar cell application

Abstract: The hybrid Schottky diode based on silicon nanowire arrays (SiNWs) and poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) has been fabricated for high performance solar cells. The length of SiNWs on a silicon substrate, which is prepared by metal-assisted chemical etching, can be tuned by adjusting the length of the etching time. In addition, the average distances between the adjacent silicon nanowires can be controlled by changing the immersing time in a saturated PCl5 solution. The hybrid devices are made from the SiNWs with different wire lengths and various distances between adjacent wires by spin-casting PEDOT:PSS on the silicon substrates. It is found that the length and density play leading roles in the electric output characteristics. The device made from SiNWs with optimum morphology can achieve a power conversion efficiency of 7.3%, which is much improved in comparison with that of the planar one. The measurement of the transient photovoltage decay and the analysis of the current versus voltage curve indicate that the charge recombination process is a dominant factor on the device performance.

Distributed Bragg reflector based on porous anodic alumina fabricated by pulse anodization

Abstract: In this paper, we demonstrate a distributed Bragg reflector (DBR) based on nanoporous anodic aluminum oxide (AAO) formed by pulse anodization. The AAO structure with alternating mild anodized (MA) and hard anodized (HA) layers having different porosities and thereby different refractive indices was fabricated in 0.3 M H₂SO₄ using potential pulses of 25 and 35 V. The effective refractive index of the HA layers can be tailored by changing the porosity of the HA layers. The porosity of the HA layers can be significantly increased by selective chemical etching of HA segments in 0.52 M H₃PO₄. Before etching, the porous AAO structure was supported by a polymer nanorod frame. On the selected surface area pores were infiltrated with polymers (polystyrene and PMMA). The designed AAO structure consists of alternating high and low refractive index layers and behaves as a distributed Bragg mirror reflecting light in two different ranges of wavelength. This behavior is extremely important in optical communication lines where two separate spectral bands of high reflectivity in the infrared region are desired.

Reuse of GaAs substrates for epitaxial lift-off by employing protection layers

Abstract: We demonstrate repeated use of GaAs wafers for multiple growths by employing lattice-matched epitaxial protection layers to preserve the wafer surface in its original condition following their etch removal after growth. The protection layers provide a regrowth surface that eliminates the need for repolishing prior to subsequent growth. Between growths, the protection layers are removed by wet chemical etching. The resulting surface quality is examined using atomic force microscope and energy dispersive spectrometry. We show that the surface roughness, chemical composition, morphology, and electronic properties of the GaAs surface after protection-layer removal are comparable to that of the original substrate surface. We show that p-n junction GaAs solar cells grown on original and reused wafers have nearly identical performance with power conversion efficiencies of ∼23%, under simulated 1 sun illumination, AM1.5 G. The high power conversion efficiency of GaAs solar cells combined with reduced costs associ...

Replacement/Etching Route to ZnSe Nanotube Arrays and Their Enhanced Photocatalytic Activities

Abstract: Well-aligned ZnSe nanotube arrays with diameters of 300–400 nm and wall thicknesses of 60–70 nm have been controllably prepared based on a replacement/etching method, with ZnO nanorod arrays on zinc substrate as sacrificial templates. An obvious difference of the solubility product (Ksp) between the ZnSe wall and ZnO core materials is crucial for the direct replacement of one type of anions by the other. Ammonia as the chemical etching agent is also important for dissolving ZnO nanorod core. The photocatalytic activities of the as-prepared ZnSe nanotube arrays have been studied for the degradation of methyl orange aqueous solution and compared with those of ZnO nanorod arrays and the intermediates including ZnO/ZnSe core/sheath nanorod arrays and partially dissolved ZnO core/ZnSe sheath nanorod arrays, respectively. The results indicate that ZnSe nanotube arrays exhibit superior photocatalytic performance to the other three nanostructured arrays, which can be mainly attributed to their full hollow interio...

Preparation of Various Prussian Blue Analogue Hollow Nanocubes with Single Crystalline Shells

Abstract: We report the preparation of monocrystalline Prussian blue (PB) analogue hollow nanocubes by applying a controlled chemical etching method with assistance of polyvinylpyrrolidone (PVP). The hollow particles obtained possess the original single-crystalline structures, with retention of the high surface areas. Our synthetic route based on chemical etching is quite simple, and it can be scaled up for mass production.

Plasma etching method and semiconductor device manufacturing method

Abstract: A plasma etching method is provided for etching a substrate corresponding to an etching object within an etching apparatus that includes a supply condition adjustment unit for adjusting a supply condition for supplying etching gas to the substrate, a temperature adjustment unit for adjusting a temperature of the substrate placed on a stage along a radial direction, and a plasma generating unit for generating plasma within a space between the supply condition adjustment unit and the stage. The plasma etching method includes a control step in which the temperature adjustment unit controls the temperature of the substrate to be uniform within a substrate plane of the substrate, and an adjustment step in which the supply condition adjustment unit adjusts a concentration distribution of active species contained in the plasma generated by the plasma generation unit within the space above the substrate.

Si nanowires organic semiconductor hybrid heterojunction solar cells toward 10% efficiency.

Abstract: High-efficiency hybrid solar cells are fabricated using a simple approach of spin coating a transparent hole transporting organic small molecule, 2,2′,7,7′-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (Spiro-OMeTAD) on silicon nanowires (SiNWs) arrays prepared by electroless chemical etching. The characteristics of the hybrid cells are investigated as a function of SiNWs length from 0.15 to 5 μm. A maximum average power conversion efficiency of 9.92% has been achieved from 0.35 μm length SiNWs cells, despite a 12% shadowing loss and the absence of antireflective coating and back surface field enhancement. It is found that enhanced aggregations in longer SiNWs limit the cell performance due to increased series resistance and higher carrier recombination in the shorter wavelength region. The effects of the Si substrate doping concentrations on the performance of the cells are also investigated. Cells with higher substrate doping concentration exhibit a significant drop in the incident photons...

Fabrication and photocatalytic properties of silicon nanowires by metal-assisted chemical etching: effect of H2O2 concentration

Abstract: In the current study, monocrystalline silicon nanowire arrays (SiNWs) were prepared through a metal-assisted chemical etching method of silicon wafers in an etching solution composed of HF and H2O2. Photoelectric properties of the monocrystalline SiNWs are improved greatly with the formation of the nanostructure on the silicon wafers. By controlling the hydrogen peroxide concentration in the etching solution, SiNWs with different morphologies and surface characteristics are obtained. A reasonable mechanism of the etching process was proposed. Photocatalytic experiment shows that SiNWs prepared by 20% H2O2 etching solution exhibit the best activity in the decomposition of the target organic pollutant, Rhodamine B (RhB), under Xe arc lamp irradiation for its appropriate Si nanowire density with the effect of Si content and contact area of photocatalyst and RhB optimized.

Vertical etching with isolated catalysts in metal-assisted chemical etching of silicon

Abstract: Metal assisted chemical etching with interconnected catalyst structures has been used to create a wide array of organized nanostructures. However, when patterned catalysts are not interconnected, but are isolated instead, vertical etching to form controlled features is difficult. A systematic study of the mechanism and catalyst stability of metal assisted chemical etching (MACE) of Si in HF and H2O2 using Au catalysts has been carried out. The effects of the etchants on the stability of Au catalysts were examined in detail. The role of excess electronic holes as a result of MACE was investigated via pit formation as a function of catalyst proximity and H2O2 concentration. We show that a suppression of excess holes can be achieved by either adding NaCl to or increasing the HF concentration of the etching solution. We demonstrate that an electric field can direct most of the excess holes to the back of the Si wafer and thus reduce pit formation at the surface of Si between the Au catalysts. The effect of hydrogen bubbles, generated as a consequence of MACE, on the stability of Au catalysts has also been investigated. We define a regime of etch chemistry and catalyst spacing for which catalyst stability and vertical etching can be achieved.

Catalytic activity of noble metals for metal-assisted chemical etching of silicon

Abstract: Metal-assisted chemical etching of silicon is an electroless method that can produce porous silicon by immersing metal-modified silicon in a hydrofluoric acid solution without electrical bias. We have been studying the metal-assisted hydrofluoric acid etching of silicon using dissolved oxygen as an oxidizing agent. Three major factors control the etching reaction and the porous silicon structure: photoillumination during etching, oxidizing agents, and metal particles. In this study, the influence of noble metal particles, silver, gold, platinum, and rhodium, on this etching is investigated under dark conditions: the absence of photogenerated charges in the silicon. The silicon dissolution is localized under the particles, and nanopores are formed whose diameters resemble the size of the metal nanoparticles. The etching rate of the silicon and the catalytic activity of the metals for the cathodic reduction of oxygen in the hydrofluoric acid solution increase in the order of silver, gold, platinum, and rhodium.