Fabrication Of Silicon Nanowire Arrays Research Articles

Solid-state dewetting of silver-thin films: self-assembled nano-geometries

The study presents the dynamics of solid-state dewetting of silver (Ag)-film annealed in N2 ambient, analyzed by atomic force microscopy and scanning electron microscopy. Varying the annealing parameters (i.e. temperature and time) and Ag-film thicknesses were taken into account, to determine their effect over the solid-state dewetting of Ag-films. Several morphological evolutions from nanohole to the presence of metastable nanorings were observed. It was determined that structures annealed at high temperature (≥900 °C) and/or time (≥2 h) results in formation of metastable nanorings and whose geometrical aspects and population grew with increasing film thickness. Possible applications of the structures for fabrication of silicon nanowire arrays and photo-emitters are briefly described.

Top-down fabrication of silicon-nanowire arrays for large-scale integration on a flexible substrate for achieving high-resolution neural microelectrodes

In order to implement a nanowire-integrated device, well-aligned arrays of a silicon nanowires are necessary for scalable and repeatable mass production. Especially for biomedical applications in neural engineering, device flexibility robust to mechanical bending, without compromising the electrical performance, is a key issue to be resolved. In this paper, a simple fabrication method and the large-scale integration of silicon-nanowire arrays is proposed by combining top---down fabrication with nanowire transfer on flexible substrate for applications in high-resolution neural stimulation microelectrodes. The arrayed silicon nanowires are fabricated on a p-type, (111)-oriented, single-crystalline-silicon substrate by a top-down process that includes silicon dry etching, silicon wet etching, and wet oxidation. After the fabrication of nanowire arrays, the device is transferred to flexible substrate using polyimide coating, electrode formation, and substrate removal. In order to verify the feasibility of the proposed method, a silicon-nanowire field-effect transistor (FET) switch is implemented and evaluated. The results of the proposed method show an excellent potential for high-resolution neural stimulation microelectrodes.

Fabrication of silicon nanowire arrays by near-field laser ablation and metal-assisted chemical etching

We present an elegant route for the fabrication of ordered arrays of vertically-aligned silicon nanowires with tunable geometry at controlled locations on a silicon wafer. A monolayer of transparent microspheres convectively assembled onto a gold-coated silicon wafer acts as a microlens array. Irradiation with a single nanosecond laser pulse removes the gold beneath each focusing microsphere, leaving behind a hexagonal pattern of holes in the gold layer. Owing to the near-field effects, the diameter of the holes can be at least five times smaller than the laser wavelength. The patterned gold layer is used as catalyst in a metal-assisted chemical etching to produce an array of vertically-aligned silicon nanowires. This approach combines the advantages of direct laser writing with the benefits of parallel laser processing, yielding nanowire arrays with controlled geometry at predefined locations on the silicon surface. The fabricated VA-SiNW arrays can effectively transfect human cells with a plasmid encoding for green fluorescent protein.

Fabrication of Silicon Nanowire Arrays by Macroscopic Galvanic Cell‐Driven Metal Catalyzed Electroless Etching in Aerated HF Solution

Macroscopic galvanic cell-driven metal catalyzed electroless etching (MCEE) of silicon in aqueous hydrofluoric acid (HF) solution is devised to fabricate silicon nanowire (SiNW) arrays with dissolved oxygen acting as the one and only oxidizing agent. The key aspect of this strategy is the use of a graphite or other noble metal electrode that is electrically coupled with silicon substrate.

The effects of substrate self-biasing on the growth of Sn-catalysed silicon nanowires grown at low pressure

We describe the fabrication of silicon nanowire arrays on silicon substrates using Sn as a catalyst metal and electron cyclotron resonance chemical vapour deposition as the growth method. This technique features low deposition pressures and long mean-free paths, allowing the ability to control the ion bombardment energies at the substrate with the application of RF power to the substrate. The applied RF signal generates a DC self-bias across the substrate. Wires have been grown under differing levels of DC self-bias from 0 to −100 V. The impact on wire density, morphology and catalyst stability is described.

Silicon Nanowire Resonators: Aerosol Nanoparticle Mass Sensing in the Workplace

In this article, We focus on silicon nanowire (SiNW)-based resonators that were fabricated and employed to sense aerosol nanoparticles (NPs) by measuring resonant frequency shifts induced by the mass of stuck NPs. The fabrication of SiNW arrays was performed using inductively coupled plasma (ICP) cryogenic dry etching and multiple thermal oxidations. The SiNWs were coated with gold (Au) for contacting to the homebuilt electrostatic NP sampler to collect the flowing NPs. A piezoelectric shear actuator mounted in the frequency measurement system was used to excite the SiNW sensors into resonance. Tested in a titanium dioxide (TiO2) aerosol sampling with a total concentration of ~8,500 NPs/cm3, the sensor displayed its feasibility as a nanobalance to detect aerosol NPs in the femtogram scale with a mass sensitivity of 7.1 Hz/fg and a mass resolution of 31.6 fg. To extend the operating life of the sensor, an ultrasonic removal method was used to detach the adhered NPs.

An in-house approach for fabrication of silicon nanowire arrays using electroless metal deposition and etching method

In this work, a simple and cost effective in-house process has been developed by combining the ultrasonication bath and electroless metal deposition and etching (EMDE) technique for the growth of vertically oriented, single-crystalline, silicon nanowire (SiNW) arrays with uniform coverage over the whole surface area of the wafer without using any template. The scanning electron microscopy (SEM) analysis shows the uniformity in distribution of SiNW arrays by the proposed method. The samples with as-grown SiNW arrays appear to be blackish in colour and provide a very low reflectance of less than 0.15% in the wavelength range of 300-900 nm. This implies that the as-grown SiNW arrays can be used as the antireflection coating-layer in SiNW-based solar cells and photodetector devices. The compatibility of these Si nanostructures with the well-matured Si-based CMOS technology also assure their application in the development of future generation nanoelectronic and nano-optoelectronic devices.

Wafer-scale fabrication of silicon nanowire arrays with controllable dimensions

A novel and facile method was successfully developed to fabricate wafer-scale Si nanowire arrays with well-controlled sizes through the in-situ porous anodic alumina (PAA) template-assisted wet-etching process. The diameter and filling ratio (inter-wire spacing) of the as-prepared Si nanowires are determined by the size and density of pores in the in-situ PAA templates, which can be tailored independently by adjusting the anodization voltages and the immersion time of PAA templates in phosphoric acid. The length of Si nanowires can be more than one hundred micrometers long, which is controlled by adjusting the wet-etching time. Moreover, this method is compatible with complex Si surface topology for creating desirable 3-dimensional hybrid micro/nano-structures. Such Si nanowire arrays exhibit ultralow reflectance and interesting wettability that are of great importance to photovoltaics and thermal management applications.

Roles of Ag in fabricating Si nanowires by the electroless chemical etching technique

Silicon wafers coated with a film of Ag pattern are used for investigating roles of Ag in the fabrication of silicon nanowire arrays (SiNWs) by the electroless chemical etching technique. The diameter of SiNWs grown in the mixed AgNO3/HF solution ranges from 20 to 250 nm. A growth mechanism for such obtained SiNWs is proposed and further experimentally verified. As a comparison as well as to better understand this chemical process, another popular topic on growing SiNWs in the H2O2/HF solution is also studied. Originating from different chemical reaction mechanisms, Ag film could protect the underneath Si in the AgNO3/HF solution and it could, on the contrary, accelerate etching of the underneath Si in the H2O2/HF solution.

Fabrication of silicon nanowire arrays based solar cell with improved performance

We report fabrication of solar cell (n +–p–p + structure) on black silicon substrates consisting of silicon nanowire (SiNW) arrays prepared by Ag induced wet chemical etching process in aqueous HF–AgNO 3 solution. SiNW arrays surface has low reflectivity (<5%) in the entire spectral range (400–1100 nm) of interest for solar cells. The solar cells were fabricated by conventional cell fabrication protocol. Performance of three types of cells, namely cell with SiNW over the entire front surface, cell with SiNW only in the active device area and control cell (on planar surface), has been compared. It was found that cell based on selectively grown shorter length SiNW arrays has the best cell performance.

Fabrication of Silicon Nanowire Arrays with Controlled Diameter, Length, and Density

A templated catalytic etching process has been developed to fabricate large-area arrays of silicon nanowires with controlled diameter, length, and density. The figure shows an example of an array constructed by this technique. Etched polystyrene spheres are used as templates to define the lateral dimensions of the array, whereas the length of the nanowires is defined by the duration of the etching process.

Silver catalysis in the fabrication of silicon nanowire arrays

A method involving dry deposition plus wet chemical etching was devised to fabricatesilicon nanowire (SiNW) arrays and to study silver catalysis during fabrication. Throughinvestigation of the track of catalyst particles, it was shown that Ag really catalyses theetching of silicon underneath Ag, which clarifies doubts about the formation of SiNWarrays during wet chemical etching. The intrinsic properties of Ag and the networkstructure of Ag clusters during etching facilitate the etching process. The etching product,i.e. vertical SiNW arrays containing an Ag nanocluster mesh, could be considered as aprototype secondary composite nanostructured catalyst with promise for futureapplications.