Assisted Etching Research Articles

Facile synthesis of uniform yolk–shell structured magnetic mesoporous silica as an advanced photo-Fenton-like catalyst for degrading rhodamine B

Uniform yolk–shell structured magnetic mesoporous silica nanosphere was fabricated via an ultrasound assisted etching method and demonstrated as an efficient photo-Fenton-like catalyst.

Luminescence evolution of porous GaN thin films prepared via UV-assisted electrochemical etching

Porous gallium nitride (GaN) thin films with different surface morphologies and free carriers properties were fabricated from Si-doped GaN thin films using ultra-violet assisted electrochemical etching approach under various etching voltages. Fluctuation of luminescence signals was observed in the photoluminescence spectra of porous GaN thin films. Taking advantage of the spectral sensitivity of infrared attenuated total reflection spectroscopy on semiconductor materials, roles of free carriers and porous structure in controlling luminescence properties of GaN were investigated thoroughly. The results revealed that enhancement in luminescence signal is not always attained upon porosification. Although porosification is correlated to the luminescence enhancement, however, free carrier is the primary factor to enhance luminescence intensity. Due to unavoidable significant reduction of free carriers from Si-doped GaN in the porosification process, control of etching depth (i.e., thickness of porous layer formed from the Si-doped layer) is critical in fabricating porous GaN thin film with enhanced luminescence response.

High density micro-pyramids with silicon nanowire array for photovoltaic applications

We use a metal assisted chemical etch process to fabricate silicon nanowire arrays (SiNWAs) onto a dense periodic array of pyramids that are formed using an alkaline etch masked with an oxide layer. The hybrid micro-nano structure acts as an anti-reflective coating with experimental reflectivity below 1% over the visible and near-infrared spectral regions. This represents an improvement of up to 11 and 14 times compared to the pyramid array and SiNWAs on bulk, respectively. In addition to the experimental work, we optically simulate the hybrid structure using a commercial finite difference time domain package. The results of the optical simulations support our experimental work, illustrating a reduced reflectivity in the hybrid structure. The nanowire array increases the absorbed carrier density within the pyramid by providing a guided transition of the refractive index along the light path from air into the silicon. Furthermore, electrical simulations which take into account surface and Auger recombination show an efficiency increase for the hybrid structure of 56% over bulk, 11% over pyramid array and 8.5% over SiNWAs.

Ionic liquid assisted chemical strategy to TiO2 hollow nanocube assemblies with surface-fluorination and nitridation and high energy crystal facet exposure for enhanced photocatalysis.

Realization of anionic nonmetal doping and high energy crystal facet exposure in TiO2 photocatalysts has been proven to be an effective approach for significantly improving their photocatalytic performance. A facile strategy of ionic liquid assisted etching chemistry by simply hydrothermally etching hollow TiO2 spheres composed of TiO2 nanoparticles with an ionic liquid of 1-butyl-3-methylimidazolium tetrafluoroborate without any other additives is developed to create highly active anatase TiO2 nanocubes and TiO2 nanocube assemblies. With this one-pot ionic liquid assisted etching process, the surface-fluorination and nitridation and high energy {001} crystal facets exposure can be readily realized simultaneously. Compared with the benchmark materials of P25 and TiO2 nanostructures with other hierarchical architectures of hollow spheres, flaky spheres, and spindles synthesized by hydrothermally etching hollow TiO2 spheres with nonionic liquid of NH4F, the TiO2 nanocubes and TiO2 nanocube assemblies used as efficient photocatalysts show super high photocatalytic activity for degradation of methylene blue, methyl orange, and rhodamine B, due to their surface-fluorination and nitridation and high energy crystal facet exposure. The ionic liquid assisted etching chemistry is facile and robust and may be a general strategy for synthesizing other metal oxides with high energy crystal facets and surface doping for improving photocatalytic activity.

Electric‐Driven Rotation of Silicon Nanowires and Silicon Nanowire Motors

In this work, the first highly controllable assembly and rotation of silicon nanowires and nanomotors in suspension are reported. Si and Si composite nanowires are fabricated with precisely controlled dimensions via colloidal assisted catalytic etching. The nanowires can be rotated with deterministic speed and chirality. The rotation speed and orientation not only depend on the applied AC electric frequency, but also on the electronic type, geometry, surface coating, as well as the electric conductance of suspension mediums. Theoretical analysis is used to understand the rotation of Si nanowires, and also the electric resistivity of Si nanowires is determined from their mechanical rotation. The Si nanowires are precisely assembled into nanomotors that can be rotated with controlled speeds and orientations at prescribed locations. This work provides a new paradigm for designing and actuating various Si‐based nanoelectromechanical system (NEMS) devices, which are relevant to man‐made nanomotors, nanorobots, and nanoengines.

Synthesis of porous ZnO nanospheres for gas sensor and photocatalysis

Monodispersed porous ZnO nanospheres with diameters about 400–600 nm were successfully fabricated by a facile and effective cationic surfactant assisted selective etching strategy. The as-synthesized ZnO materials were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope and N2 adsorption–desorption. These samples were used as the gas sensor, showing the high, stable and fast response to acetone, revealing the potential application as gas sensor to detect acetone. In addition, the photocatalytic degradation property of the porous ZnO nanospheres for methyl orange (MO) under UV irradiation was investigated. The degradation efficiency of MO reaches 96 % of the porous ZnO samples after 50 min of UV-light irradiation.

Role of catalyst concentration on metal assisted chemical etching of silicon

A catalyst activates the etch solution in metal assisted chemical etching e.g. of crystalline silicon in aqueous etch solutions containing hydrofluoric acid and nitric acid. This work shows for the first time that the catalyst surface concentration determines the metal assisted etch process: The amount of electroless deposited palladium clusters on the silicon surface controls the etch rate, etch regime and resulting surface morphology independent of etch solution composition. Increasing palladium concentrations change the resulting surface morphology stepwise from macro-structured through macro- and nano-porous to polished, whereas catalyst-less etches result in polished surfaces. We adapt the well-known model of electro-chemical etching to explain the catalyst influence on silicon dissolution and show a clear analogy between catalyst concentration in metal assisted etching and current density in electrochemical etching.

Fabrication of Low-Adhesive Superhydrophobic Al Surfaces via Self-Assembled Primary Cell Assisted Etching

In this work, we present a novel etching method to fabricate the superhydrophobic Al surfaces in a salt solution. Hierarchical rough structures composed of micrometer-scale pits, protrusions, and rectangle plateaus and nanometer-scale step-like structures are formed on the Al surfaces by the self-assembled primary cell assisted etching and the preferential corrosion of grain boundaries and dislocations. After fluoroalkylsilane modification, the superhydrophobic Al surfaces with a 166.4° water contact angle and a 1° rolling angle are obtained. The developed method does not use any strong acids and has a smaller harm to the environment and operators.

Surface phonon polariton characteristic of honeycomb nanoporous GaN thin films

Nanoporous GaN thin films with honeycomb structure were fabricated via ultra-violet assisted electrochemical etching approach. Under different anodization voltages, two nanoporous samples with different porosity were fabricated. Porosity and surface phonon polariton (SPP) characteristics of the fabricated samples were investigated using polarized infrared attenuated total reflection technique. It was found that the porosity of nanoporous GaN has great influence on its SPP resonant frequency. It can modulate the resonance frequency towards lower value.

Characteristics of Nanostructure Silicon Photodiode using Laser Assisted Etching

Abstract We prepared nanostructures silicon photodiode (nPSi) by using laser assisted etching at fixed current density (30 mA/cm2) with different etching wavelengths of laser diode (532,650 and 810 nm), a (metal/nanostructure silicon/metal) photodiode has been fabricated from rapid thermal oxidation (RTO) and rapid thermal annealing (RTA) processes to improve the characterizations of PSi photodiode, A responsivity of (3A/w) was measured at (450 nm) with low value of dark current (1.33 μA/ cm) and higher value of photo current (610 μA/cm 2 ) at 5 volt reverse bias. The results show that the wavelength IR (810 nm) give us the best photodiode and electrical characteristics.

Influence of addifion of electronegative gases on the properties of capacitively coupled Ar plasmas

Investigation of electronegative plasmas has now been atrractive due to the advantages of negative-ion assisted etching and charge-free ion implantation in semiconductor manufacture. Langmuir electrostatic probe, as a simple, inexpensive and good spatial resolution diagnosic tool, is popularly used in investigating electronegative plasmas. In this paper, the Langmuir electrostatic probe is proposed to measure the capacitively coupled Ar plasmas with added electronegative gases, such as O2, Cl2 and SF6. The experimental results from the measurements of Ar plasmas with added electronegative gases driven by a 40.68 MHz field indicate that, with increasing flow rate of electronegative gas, high energy peak will occur in electron energy possibility function and shift towards higher energyside. The addition of electronegative gases reduces the electron density significantly as the electron temperature increases. We also calculate the electronegativity of Ar plasmas for the three kinds of electronegative gases. The preliminary interpretations of the above experimental phenomena are presented.

Creation and recovery of a W(111) single atom gas field ion source

Tungsten single atom tips have been prepared from a single crystal W(111) oriented wire using the chemical assisted field evaporation and etching method. Etching to a single atom tip occurs through a symmetric structure and leads to a predictable last atom unlike etching with polycrystalline tips. The single atom tip formation procedure is shown in an atom by atom removal process. Rebuilds of single atom tips occur on the same crystalline axis as the original tip such that ion emission emanates along a fixed direction for all tip rebuilds. This preparation method could be utilized and developed to prepare single atom tips for ion source development.

+0.4% Efficiency gain by novel texture for String Ribbon solar cells

This work introduces metal assisted etching for surface texturing of saw-damage free crystalline silicon independent from the crystallographic orientation. A noble metal serves as a catalyst for the chemical etching in an aqueous solution containing hydrofluoric acid and nitric acid. Metal assisted textured String Ribbon solar cells show a reduction ΔReff=−16%rel for the effective reflection Reff compared to untextured String Ribbon solar cells. This improvement results in an increase ΔJsc=+1.4mA/cm2 of the short circuit current density Jsc. Therefore, the median solar cell efficiency η increases by Δη=+0.4% from ηuntex=14.1% to ηtex=14.5%.

Silver nanowires and nanoparticles from a millifluidic reactor: application to metal assisted silicon etching

Silver nanowires and nanoparticles are synthesized by a polyol method in a millifluidic reactor. We have been able to optimize the flow chemistry reaction conditions to get a high yield of nanowires in a continuous flow. By changing reaction parameters we have demonstrated the synthesis of single crystalline silver nanoparticles in a rapid reaction time of only 3 minutes. All results are compared with standard batch and microwave reactions. An example of application is provided through the silver nanowire assisted etching of silicon wafers. This colloidal approach of metal assisted silicon etching allows transferring of the nanowire shape to silicon.

Enhanced Properties of Porous GaN Prepared by UV Assisted Electrochemical Etching

The structural and optical properties of porous GaN films on sapphire (0001) prepared by UV assisted electrochemical etching were reported in this study. SEM micrographs indicated that the shapes of the pores for both porous samples are nearly hexagonal. As compared to the as-grown GaN films, porous layers exhibit a substantial photoluminescence (PL) intensity enhancement with red-shifted band-edge PL peaks associated with the relaxation of compressive stress. The shift of E2(high) to the lower frequency in Raman spectra of the porous GaN films further confirms such a stress relaxation.

Nitrogen assisted etching of graphene layers in a scanning electron microscope

We describe the controlled patterning of nanopores in graphene layers by using the low-energy (<10 keV) focused electron beam in a scanning electron microscope. Regular nanometer-sized holes can be fabricated with the presence of nitrogen gas. The effect of the gas pressure, beam current, and energy on the etching process are investigated. Transmission electron microscopy, coupled with plasmon energy loss imaging, reveals the microstructure modification of the etched graphene. A nitrogen-ion assisted etching mechanism is proposed for the controlled patterning.

Deep ultraviolet diamond Raman laser

We present a synchronously pumped diamond Raman laser operating at 275.7 nm pumped by the 4th harmonic of a mode locked Nd:YVO4 laser. The laser had a threshold pump pulse energy of 5.8 nJ and generated up to 0.96 nJ pulses at 10.3% conversion efficiency. The results agree well with a numerical model that includes two-photon absorption of the pump and Stokes beams and uses a Raman gain coefficient of diamond of 100 cm/GW. We also report on the observation of nanometer scale two-photon assisted etching of the diamond crystal surfaces.

Fabrication of a nanoporous dual‐electrode system for electrochemical redox cycling

AbstractNanoporous electrodes are promising tools for highly sensitive electrochemical detection of molecules by redox cycling. In here, we report on a novel approach for the on‐chip fabrication of nanoporous dual‐electrode systems. The fabrication is based on template assisted dry etching into an electrode–insulator–electrode structure using a nanoporous alumina film as a mask. The mask itself is patterned by directly anodizing an aluminum layer on top of the chip. Homogeneous growth of the alumina nanopores on a wafer scale is achieved by adding a titanium intermediate film between the top electrode and the aluminum substrate as a stopping layer. The resulting electrodes are separated by approximately 100 nm and have pore diameters in the range of 30–50 nm. Thus they are ideally suited for redox cycling experiments based on fast diffusion of molecules between the electrodes. Integrating this process into microfabricated electrode structures promises to yield a stable and sensitive electrochemical sensor platform.magnified image Redox cycling scheme for a nanoporous dual‐electrode system. The close distance of anode and cathode provides a short diffusion path of oxidized and reduced molecules, as depicted by the arrows. The inlet shows a close‐up of the molecules within a pore. Different colours indicate different oxidation states.

Pd Assisted HF Etching of Si: Electrochemical Measurement

Metal-assisted HF etching of Si has attracted considerable attention as a new electroless method that can produce porous Si by immersing metal-modified Si in a HF solution without bias. Such etching generally uses not only metal-modified Si but also an oxidizing agent. Palladium exhibits high activity in assisted etching under dissolved-oxygen-free and dark conditions. In this study, we investigate the Pd assisted HF etching of n-Si by electrochemical measurements. The potential of Pd metal on Si is more negative than the potential of hydrogen evolution at open circuit conditions. Anodic current generation of Pd-modified Si electrodes at positive bias and the localization of etching under Pd films at low thickness indicate that Pd catalyzes the anodic dissolution of Si and the cathodic hydrogen evolution.

Controllable silicon nano-grass formation using a hydrogenation assisted deep reactive ion etching

Highly controllable silicon nano-grass formation is reported based on a hydrogen assisted reactive ion etching method in desirable shapes and locations. By controlling the etching parameters, one can achieve grass-free high aspect ratio vertical or three-dimensional structures on silicon substrates. On the other hand, one can program the etching procedure to arrive at grass-full surfaces and structures in pre-designed features and in desired places. The improved wetting properties of the grass-full surfaces have been investigated. In addition, the grass-full surface has been used to entrap kidney cells. Aspect ratios of the order of 40–50 and features of the size of 250 nm can be achieved.