Black Silicon Substrate Research Articles

Novel synthesis of 1-D silicon nanowires grown on pyramidal black silicon substrates and intense visible emission

This work shows a new way to grow 1-D Silicon Nanowires (SiNWs) over pyramidal black silicon used as substrates. These nanostructures are grown by the plasma-assisted vapor–liquid-solid (VLS) as a bottom-up process, using tin thin films as a catalytic metal and dichlorosilane gas as a silicon precursor. SiNWs were obtained with diameters from 300-600 nm and 4–6 µm lengths on the black silicon surface. Due to the pyramid-shaped and porous nature of the black silicon surface, SiNWs form a complex mesh nanostructure. This network has a large surface area and exhibits intense and effective photoluminescence with a peak in the green spectrum, which is attributed to the quantum confinement effect that occurred in small nc-Si embedded inside SiNWs. These structural configurations hold significant promise for applications in optical biosensors, solar cells, and other prospective fields.

Two-dimensional metamaterials as meta-foams for optimized surface-enhanced solar steam generation

We report on a new class of metamaterials, which consists of meta-foams, optimized for high performance in enhanced solar steam generation. The design of these meta-foams involves precise dimensional control of a periodic two-dimensional micro-pore array. Proof-of-concept of meta-foams efficiency is demonstrated using two fabrication technologies. The first one involves microscale plasma etching onto a nanostructured black silicon substrate. As an alternative low-cost technique, we also use 3D printing of a graphene-containing polymer material. The experimental validation shows that the best evaporation rate reaches 1.34 kg/(h·m2) under 1 sun illumination, in open-air conditions under normal temperature and relative humidity conditions of 20 °C and 58%, an unmatched value so far under similar conditions, while the theoretical limit is estimated at 1.5 kg/(h·m2). This corresponding to a 89% conversion efficiency. Experimental data concur well with the predicted performance obtained by numerical simulations. The proposed model simultaneously accounts for both heat and mass transfer, including photothermal conversion and water phase change, to guide the optimization towards the maximization of the evaporation rate, an important figure of merit in many applications, including solar heat harvesting and solar water purification.

Titanium oxide antireflection thin film on metal-assisted chemical etching black silicon substrate by liquid-phase deposition

Titanium oxide antireflection thin film on metal-assisted chemical etching black silicon substrate by liquid-phase deposition

Ultralow Broadband Reflectivity in Black Silicon via Synergy between Hierarchical Texture and Specific‐Size Au Nanoparticles

AbstractAntireflectivity is one of the critical factors defining the performance of black silicon in optical, photothermal, photochemical, and optoelectronic applications. The photonic applications under visible light illumination are commonly tuned through surface texturing; however, their promising performance under longer wavelength (>1100 nm) requires either intrinsic lattice modifications or additional substance enhancement. Recent advances in microfabrication and material engineering have enabled in‐depth exploration into the synergy between surface texturing and material reinforcement. In this study, black silicon with novel chimney‐like hierarchical micro/nanostructures is fabricated via two‐step reactive ion etching, and subsequently gold nanoparticles (Au NPs) are loaded on the black silicon by magnetron sputtering deposition. The micro/nanostructures result in synergy effect with the Au NPs on suppression of light reflection. An ultralow broadband reflection (<1%, wavelength 220–2600 nm) is achieved from the Au‐loaded black silicon substrates. The impact of Au NPs and structural design such as size, spacing, shape, and etching duration on antireflectivity of black silicon is investigated. This study opens up new avenue for high‐efficiency applications of black silicon in the fields of sustainable energy and photonics/microelectronics.

Gold Nanoparticle-Assisted Black Silicon Substrates for Mass Spectrometry Imaging Applications.

Mass spectrometry imaging (MSI) based on matrix-assisted laser desorption ionization (MALDI) is widely used in proteomics. However, matrix-free technologies are gaining popularity for detecting low molecular mass compounds. Small molecules were analyzed with nanostructured materials as ionization promoters, which produce low-to-no background signal, and facilitate enhanced specificity and sensitivity through functionalization. We investigated the fabrication and the use of black silicon and gold-coated black silicon substrates for surface-assisted laser desorption/ionization mass spectrometry imaging (SALDI-MSI) of animal tissues and human fingerprints. Black silicon was created using dry etching, while gold nanoparticles were deposited by sputtering. Both methods are safe for the user. Physicochemical characterization and MSI measurements revealed the optimal properties of the substrates for SALDI applications. The gold-coated black silicon worked considerably better than black silicon as the LDI-MSI substrate. The substrate was also compatible with imprinting, as a sample-simplification method that allows efficient transference of metabolites from the tissues to the substrate surface, without compound delocalization. Moreover, by modifying the surface with hydrophilic and hydrophobic groups, specific interactions were stimulated between surface and sample, leading to a selective analysis of molecules. Thus, our substrate facilitates targeted and/or untargeted in situ metabolomics studies for various fields such as clinical, environmental, forensics, and pharmaceutical research.

Pyrolytic carbon coated black silicon.

Carbon is the most well-known black material in the history of man. Throughout the centuries, carbon has been used as a black material for paintings, camouflage, and optics. Although, the techniques to make other black surfaces have evolved and become more sophisticated with time, carbon still remains one of the best black materials. Another well-known black surface is black silicon, reflecting less than 0.5% of incident light in visible spectral range but becomes a highly reflecting surface in wavelengths above 1000 nm. On the other hand, carbon absorbs at those and longer wavelengths. Thus, it is possible to combine black silicon with carbon to create an artificial material with very low reflectivity over a wide spectral range. Here we report our results on coating conformally black silicon substrate with amorphous pyrolytic carbon. We present a superior black surface with reflectance of light less than 0.5% in the spectral range of 350 nm to 2000 nm.

Application of Black Silicon for Nanostructure-Initiator Mass Spectrometry.

Nanostructure-initiator mass spectrometry (NIMS) is a matrix-free desorption/ionization technique with high sensitivity for small molecules. Surface preparation has relied on hydrofluoric acid (HF) electrochemical etching which is undesirable given the significant safety controls required in this specialized process. In this study, we examine a conventional and widely used process for producing black silicon based on sulfur hexafluoride/oxygen (SF6/O2) inductively coupled plasma (ICP) etching at cryogenic temperatures and we find it to be suitable for NIMS. A systematic study varying parameters in the plasma etching process was performed to understand the relationship of black silicon morphology and its sensitivity as a NIMS substrate. The results suggest that a combination of higher silicon temperature and oxygen flow rate gives rise to the formation of black silicon with fine pillar structures, whose aspect ratio are ∼ 8.7 and depth are <1 μm resulting in higher NIMS sensitivity which is attributed to surface restructuring caused by their low melting point upon laser irradiation. Interestingly, we find selectivity of these black silicon substrates to different analytes depending on the etching parameters. Though, the sensitivity of the dry etching process is lower than the traditional "wet" electrochemical etching process, it is suitable for many applications and is prepared using conventional equipment without the use of HF.

Silver hierarchical structures grown on microstructured silicon in chip for microfluidic integrated catalyst and SERS detector

In this Letter, silver (Ag) hierarchical nanostructures grown on black silicon (BS) are used as the catalyst and a surface-enhanced Raman scattering (SERS) detector integrated in a microfluid. The BS is fabricated via femtosecond laser ablation in an atmosphere of sulfur hexafluoride, and then hydrogenated with hydrofluoric acid. As formed, the BS substrate directly acts as a reducing template to grow silver hierarchical nano-structures. Particularly, Ag-BS composite micro/nano-structures can be in-situ constructed in silicon-based microchannels. These structures simultaneously serve as integrated catalytic reactors and a SERS substrate for sensing. The sensitivity is tested to be as low as 10-8 mol/L using Rhodamine 6G.

Improved SERS Intensity from Silver‐Coated Black Silicon by Tuning Surface Plasmons

An economical method of fabricating large‐area (up to a 100‐mm wafer) silver (Ag)‐coated black silicon (BS) substrates is demonstrated by cryogenic deep reactive ion etching with inductively coupled plasma. This method enables a simple adjustment of the spike structure (e.g., height, width, sidewall slope and density of the spikes) on the silicon substrate, which thus offers the advantages of accurate tuning the density and amplitude of the localized surface plasmons after Ag coating. Using this method, an enhancement factor of 109 is achieved for the probe molecule of rhodamine 6G (around two orders of magnitude higher than previous results based on Ag‐coated BS) in surface‐enhanced Raman scattering (SERS) measurement. The presented results pave the way to make Ag‐coated BS substrates as economic and large‐area platforms for diverse surface plasmon related applications (such as SERS and surface plasmon based biosensors).

Black silicon SERS substrate: Effect of surface morphology on SERS detection and application of single algal cell analysis

In this study, we have investigated the effect of the surface morphology of the black silicon substrate on surface enhanced Raman spectroscopy (SERS) and explored its application of single algal cell detection. By adjusting the O2 and SF6 flow rates in the cryogenic plasma etching process, different surface morphologies of the black silicon substrate was produced without performing the lithographic process. It was found the Raman signals were better enhanced as the tip density of the black silicon substrate increased. In addition, as the thickness of the deposited gold layer increased, the SERS effect increased as well, which could be owing to the generation of more hot spots by bridging individual silicon tips through deposition of gold layer. For the black silicon substrate with tip density of 30tips/μm2 and covered by 400nm deposited gold layer, the detection limit of 10fM R6G solution concentration with uniform SERS effect across the substrate was achieved. Furthermore, detection of individual algal cell (Chlorella vulgaris) was performed at the SERS substrate as fabricated and the Raman signals of carotenoid and lipid were substantially enhanced.

Improvement of Ge-on-Si photodiodes by black silicon light trapping

A light-trapping scheme for normal incidence Ge-on-Si photodiodes, utilizing needle-like black silicon nanostructures is presented. Simulations reveal that light absorption in thin rear Ge films can be enhanced several times due to both the antireflection and the scattering effect of the nanostructure. It is shown that especially films with thicknesses ≤100 nm benefit from the black silicon nanostructure, e.g., resulting in a 5 to 10 times higher absorptance at 1500 nm for a 100 nm thick film. Theoretical predictions are experimentally proved by reflectance-transmittance measurements of crystalline Ge films sputtered on black silicon substrates.

Separation followed by direct SERS detection of explosives on a novel black silicon multifunctional nanostructured surface prepared in a microfluidic channel

The article describes the multifunctionality of a novel black silicon (BS) nanostructured surface covered with a thin layer of noble metal prepared in the a microfluidic channel. It is focused on the separation properties of the BS substrate with direct detection of the separated analytes utilizing surface enhanced Raman spectroscopy. The same BS substrate is providing the stationary phase and a surface enhancement of the Raman signal that has been measured previously to be around 10. As tested molecules, the common components of explosives 1,3 dinitrobenzene and 2,4 dinitrotoluene were used. The separation of selected molecules was achieved with the dried toluene as a mobile phase in a 25 micrometers deep, 5 mm wide, and 4 cm long microfluidic channel during the 2 min. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Structural and optical property tailoring of black silicon with fs-laser pulses

ABSTRACTIrradiating a planar silicon surface with femtosecond laser pulses under a sulfuric atmosphere creates first a structured surface featuring cones of up to 20 microns in height, and second a 0.1 – 1 μ m thick layer of multi-crystalline silicon on theses cones containing up to 1 at.% sulfur acting as n-type dopant. Further, the sulfur establishes energy states within the band gap of silicon allowing for the absorption of infrared (IR) light with energies below the band gap energy of silicon. This black silicon process is distinguished by the fact that only one single laser process is required to tailor three material characteristics in on step: the surface structure, the doping and the light absorption. In this work we study structural and optical material characteristics of black silicon. For the first time this work presents properties of black silicon processed with shaped femtosecond laser pulses. Finally, black silicon substrate is used as substrate for manufacturing a black silicon solar cell with a femtosecond laser pulse formed sulfur emitter. For such a black silicon solar cell we achieved a record efficiency of η =4.5%

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.

The role of heat transfer during reactive-ion etching of polymer films

A study of the kinetics of O2 and Ar reactive-ion etching (RIE) of organic polymer films and an analysis of substrate heat transfer was carried out. Radiative heat transfer played a significant role in determining the substrate temperature profile during RIE. At the relatively low pressure of 5 mTorr, where anisotropic etch profiles are typically achieved, radiative heat transfer accounted for nearly 85% of the total energy (heat) flux away from the substrate. RIE processing time (substrate temperature) drastically affected the RIE rate of chain-scissioning polymers, which included poly(methyl methacrylate) and poly(α-methylstyrene), while processing time had absolutely no effect on etch rates of cross-linking polymers. To confirm the role of radiative heat transfer during RIE, the underside of a silicon wafer was painted black, which increased the total radiative surface emittance and lowered the steady-state substrate temperature for a given set of RIE conditions. Ultimate etch rates of poly(methyl methacrylate) were measurably lower for films on the black-silicon substrates. Thermal bonding alleviated substrate heating and greatly improved etch rate control.