Hydrofluoric Acid Solution Research Articles

Fabrication of nanoporous silver by de-alloying Cu-Zr-Ag amorphous alloys

Nanoporous silver (NPS) with a ligament size ranging from 15 to 40 nm was fabricated by de-alloying (Cu50Zr50)100-x Ag x (x = 10at%, 20at%, 30at%, and 40at%) amorphous ribbons in a mixed aqueous solution of hydrofluoric (HF) acid and nitric acid under free corrosion conditions. Nanoporous silver ligaments and pore sizes were able to be fine-tuned through tailoring the chemical composition, corrosion conditions, and de-alloying time. The ligament size increases with an increase in Ag content and de-alloying time, but decreases with an increase in HF concentration. This phenomenon may be attributed to the dissolution of Zr/Cu and the diffusion, aggregation, nucleation, and recrystallization of Ag, leading to an oriented attachment of adjacent nanocrystals as revealed by TEM analysis.

Electrodeposition of Copper on AZ91 Mg Alloy in Cyanide Solution

Copper electrodeposition on AZ91 Mg alloy was studied in views of preferential deposition on α- or β-phases and how to achieve uniform deposition over the entire surface on α- and β-phases in a cyanide solution. The inhomogeneous microstructure of AZ91 Mg alloy, particularly α- and β-phases, was found to result in non-uniform deposition of zincate layer, preferential deposition of zincate on β-phases, which leads to non-uniform growth of copper layer during the following electrodeposition process. The preferential depositions of zincate can be attributed to higher cathodic polarizations on the β-phases. Pin-hole defects in the copper electrodeposit were observed at the center of large size β-phase particles which is ascribed to gas bubbles formed at the β-phases. The activation of AZ91 Mg alloy in hydrofluoric acid solution was used to obtain uniform growth of zincate layer on both the α- and β-phases. By choosing an optimum activation time, a uniform zincate layer was obtained on the AZ91 Mg alloy surface and thereby uniform growth of copper was obtained in a cyanide copper electroplating solution.

Synthesis and white photoluminescence of porous polysilicon

Porous polysilicon is fabricated through hydrothermally etching polysilicon in the solution of hydrofluoric acid containing ferric nitrate, which is characterized by the pores with ~40nm and silicon nanocrystals (nc-Si) with an average size of ~4.1nm. Compared with the polysilicon, the reflectance of porous polysilicon is rather low. Using the Kubelka-Munk method, the band gap with ~3.35eV can be calculated. Under the excitation of 270nm, the white photoluminescence, which chromaticity coordinate, correlative color temperature and color rendering index are (0.36, 0.32), ~4185K and ~83.4, respectively, can be observed. Utilizing Gauss-Newton fitting method, white light can be decomposed into ultraviolet emission, blue emission and orange-red emission. Three peaks are attributed to the band gap emission of nc-Si, the luminescence centers formed in the silicon oxide layer and in the surface of nc-Si or in the silicon suboxidation layer encapsulating nc-Si, respectively. It is indicated that porous polysilicon might be a potential material in the white light emission field.

Synthesis of Nanoporous Metals, Oxides, Carbides, and Sulfides: Beyond Nanocasting

Nanoporous metal-based solids are of particular interest because they combine a large quantity of surface metal sites, interconnected porous networks, and nanosized crystalline walls, thus exhibiting unique physical and chemical properties compared to other nanostructures and bulk counterparts. Among all of the synthetic approaches, nanocasting has proven to be a highly effective method for the syntheses of metal oxides with three-dimensionally ordered porous structures and crystalline walls. A typical procedure involves a thermal annealing process of a porous silica template filled with an inorganic precursor (often a metal nitrate salt), which converts the precursor into a desired phase within the silica pores. The final step is the selective removal of the silica template in either a strong base or a hydrofluoric acid solution. In the past decade, nanocasting has become a popular synthetic approach and has enabled the syntheses of a variety of nanoporous metal oxides. However, there is still a lack of synthetic methods to fabricate nanoporous materials beyond simple metal oxides. Therefore, the development of new synthetic strategies beyond nanocasting has become an important direction. This Account describes new progress in the preparation of novel nanoporous metal-based solids for heterogeneous catalysis. The discussion begins with a method called dealloying, an effective method to synthesize nanoporous metals. The starting material is a metallic alloy containing two or more elements followed by a selective chemical or electrochemical leaching process that removes one of the preferential elements, resulting in a highly porous structure. Nanoporous metals, such as Cu, Ag, and CuTi, exhibit remarkable electrocatalytic properties in carbon dioxide reduction, oxygen reduction, and hydrogen evolution reactions. In addition, the syntheses of metal oxides with hierarchical porous structures are also discussed. On the basis of the choice of hard template, nanoporous metal oxides with bimodal pore size distributions can be obtained. Combining nanocasting with chemical etching, a cobalt oxide with a hierarchical porous structure was synthesized, which possessed a surface area up to 250 m(2) g(-1), representing the highest surface area reported to date for nanoporous cobalt oxides. Lastly, this Account also covers the syntheses of nanoporous metal carbides and sulfides. The combination of in situ carburization and nanocasting enabled the syntheses of two ordered nanoporous metal carbides, Mo2C and W2C. For nanoporous metal sulfides, an "oxide-to-sulfide" synthetic strategy was proposed to address the large volume change issue of converting metal nitrate precursors to metal sulfide products in nanocasting. The successful syntheses of ordered nanoporous FeS2, CoS2, and NiS2 demonstrated the feasibility of the "oxide-to-sulfide" method. Concluding remarks include a summary of recent advances in the syntheses of nanoporous metal-based solids and a brief discussion of future opportunities in the hope of stimulating new interests and ideas.

Local Transmittance Measurements As Advanced New Diagnostic Tool for the Optimization of Porous Si Foils for Li-Battery Anodes

The solar cell local characterization (CELLO) technique is a common tool for the characterization of solar cells and solar cell modules [1]. In this paper, we modify a standard CELLO measurement, the photocurrent measurement of a solar cell minimodule, in order to characterize porous silicon (PorSi) foils that were fabricated for the use as anodes in Li-Ion Batteries. In this modified set-up, the transmittance of various different laser wavelengths (401 nm, 650 nm, 830 nm, and 934 nm) of the PorSi-foil is measured and analyzed. From these measurements informations about the foil thickness and porosity can be extracted which are needed for the battery cycling and for the optimization of the PorSi formation. Compared to commercially available anode and cathode materials, silicon with its high gravimetrical capacity of 4200 mAh/g is the material of choice for high-capacity batteries. Due to the large volume expansion of over 400 %, the material has to be nano- or microstructured to avoid pulverization. Porous silicon foils benefit of their light weight and high amount of active material in a battery without increasing the weight of the battery itself. The porous silicon foils, presented in this paper, are fabricated in a “top-down” approach by large-scale (“in-line”) electrochemical etching process. The cost effective and fast production allows large-scale batteries for different kinds of applications. Furthermore, for this approach cost-effective solar Si material as anode material is used which is produced without curfloss, thus saving roughly 50% of classical wafering costs. The etching is performed in a two step-process: a) a low porous layer with pores of 50 - 150 nm width is etched; b) in a second step a highly-porous zip or releasing layer is etched in a 50 wt. % hydrofluoric acid solution. This zip or releasing layer is used in a layer-transfer process to separate the anode with the galvanically deposited Cu current collector from the p-doped silicon wafer (0.02 Ω*cm, (100)). In order to analyze the porous silicon foil with the CELLO technique, a PET tape with adhesive is used in a layer-transfer-process to separate the foil from the silicon wafer. The porous silicon foil anodes are tested in half-cells with metallic Lithium as counter and reference electrodes via cyclic voltammetry measurements and long-term cycling tests to guarantee a long-term stable anode. In order to cycle those anodes successfully, the thickness and porosity of such porous foils are crucial parameters. Due to the difficulties during the etching process and the problems of characterizing those films via standard characterization tools like SEM, AFM etc., this study focuses on the application of a new diagnostic tool (CELLO). For common CELLO measurements an intensity modulated laser beam is scanned with a piezoelectric mirror across a solar cell. The small signal response of the solar cell is mapped using a lock-in routine. For the characterization of the porous silicon films, the setup is slightly changed: a solar cell minimodule that is an encapsulated solar cell with front cover glass is used instead of a solar cell. This allows to place the transmittance sample, in our case a transparent PET-tape adhered to the porous silicon foil, directly on the mini-module glass. As reference for the calculation of a transmittance map, a photocurrent map with sample is recorded and subtracted from a photocurrent map without the sample, resulting in a transmittance map in ‰, shown in Figure 1 where different regions are highlighted and discussed in this paper. Figure 1 shows the transmittance map of the analyzed sample with different regions of interest I. areas with different porosities (tree rings, Fig. 1a), II. terraces (areas with different film thickness). Figure 1b shows first cycling experiments by galvanostatic/potentiostatic steps and a capacity limitation of 75 % of the maximum silicon capacity in order to reduce the volume expansion and stresses during cycling. It shows a stable capacity of over 600 mAh/g thus being a promising candidate for long time stable anodes. This study illustrates the promising new battery concept basing on a porous silicon film with a directly galvanically deposited Cu collector (Figure 1c) in order to reduce the lateral volume expansions of the anode and having a high amount of active material. Furthermore, this study emphasizes the need and development of a new diagnostic tool to extract film thicknesses and porosity out of the measurement data.

Pseudocapacitive Negative Electrodes Based on Mxene Ti2CT x for High-Power Li-Ion Batteries

Development of rapid charging systems in Li-ion batteries is one of the urgent tasks for the widespread use of environmental-friendly electric vehicles towards a sustainable and green society. However, in spite of numerous efforts devoted to realizing the high-power systems, their power density is not satisfactory, partly due to the poor rate capability of the negative electrodes. A novel family of layered compounds, MXene (M n +1X n T x : M = Ti, V, Nb, etc.; X = C, N; n = 1-3; T = surface termination groups) has attracted increasing attention as negative electrode material with high-rate capability for Li-ion batteries.[1] MXene is the derivative phase of ternary layered compounds, MAX phase (M n AX n : A = Al, Si, S, etc.), first synthesized with concentrated hydrofluoric acid (HF) solution to extract selectively the A element.[2] Due to the tunable compositions and structures in MXene, there are huge choices for the development of the high-power electrode materials. Gogotsi and colleagues have recently discovered that lithium fluoride (LiF) and hydrochloric acid (HCl) solution also selectively extracts the A element from MAX phase, and Ti3C2T x synthesized with the LiF and HCl solution exhibits higher performance as pseudocapactior in aqueous systems than HF-synthesized Ti3C2T x .[3]Therefore, the synthetic method for MXene is a key process to determine its electrochemical property. In this work, we have successfully synthesized Ti2CT x with the LiF and HCl solution. The charge-discharge measurement reveals that the Ti2CT x delivers large reversible capability of 260 mAh/g in 1M LiPF6/EC-DMC (1:1, v:v) electrolyte, which is larger than that of Ti2CT x prepared with concentrated HF solution (180 mAh/g).[4] Reaction mechanism was investigated with combined approach using XANES, XRD, and 7Li-MAS-NMR. We construct the prototype full cell with the Ti2CT x and LiNi1/3Co1/3Mn1/3O2 negative/positive electrodes, and demonstrate that the Ti2CT x is the promising electrode material for the high-power Li-ion batteries. [1] M. R. Lukatskaya, et al. and Y. Gogotsi, Science 341, 1502 (2013). [2] M. Naguib, et al. and M. W. Barsoum, Adv. Mater. 23, 4248 (2011). [3] M. Ghidiu, et al. and Y. Gogotsi, Nature 516, 78 (2014). [4] J. Come, et al. and P. Simon, J. Electrochem. Soc. 159, A1368 (2012). Figure 1. Charge-discharge profile of Ti2CT x in 1M LiPF6/EC-DMC (1:1, v:v) electrolyte and comparison in the rate capability synthesized with different solutions. Figure 1

Fluorinated graphene films with graphene quantum dots for electronic applications

This work analyzes carrier transport, the relaxation of non-equilibrium charge, and the electronic structure of fluorinated graphene (FG) films with graphene quantum dots (GQDs). The FG films with GQDs were fabricated by means of chemical functionalization in an aqueous solution of hydrofluoric acid. High fluctuations of potential relief inside the FG barriers have been detected in the range of up to 200 mV. A phenomenological expression that describes the dependence of the time of non-equilibrium charge emission from GQDs on quantum confinement levels and film thickness (potential barrier parameters between GQDs) is suggested. An increase in the degree of functionalization leads to a decrease in GQD size, the removal of the GQD effect on carrier transport, and the relaxation of non-equilibrium charge. The study of the electronic properties of FG films with GQDs has revealed a unipolar resistive switching effect in the films with a relatively high degree of fluorination and a high current modulation (up to ON/OFF ∼ 104–105) in transistor-like structures with a lower degree of fluorination. 2D films with GQDs are believed to have considerable potential for various electronic applications (nonvolatile memory, 2D connections with optical control and logic elements).

Polarization memory effect in the photoluminescence of nc-Si-SiOx light-emitting structures.

The polarization memory (PM) effect in the photoluminescence (PL) of the porous nc-Si−SiOx light-emitting structures, containing nanoparticles of silicon (nc-Si) in the oxide matrix and passivated in a solution of hydrofluoric acid (HF), has been investigated. The studied nc-Si−SiOx structures were produced by evaporation of Si monoxide (SiO) powder in vacuum and oblique deposition on Si wafer, and then the deposited silicon oxide (SiOx) films were annealed in the vacuum at 975 °C to grow nc-Si. It was found that the PM effect in the PL is observed only after passivation of nanostructures: during etching in HF solution, the initial symmetric nc-Si becomes asymmetric elongated. It was also found that in investigated nanostructures, there is a defined orientational dependence of the PL polarization degree (ρ) in the sample plane which correlates with the orientation of SiOx nanocolumns, forming the structure of the porous layer. The increase of the ρ values in the long-wavelength spectral range with time of HF treatment can be associated with increasing of the anisotropy of large Si nanoparticles. The PM effect for this spectral interval can be described by the dielectric model. In the short-wavelength spectral range, the dependence of the ρ values agrees qualitatively with the quantum confinement effect.

Tilted ion implantation as a cost-efficient sublithographic patterning technique

Tilted ion implantation (TII) is experimentally demonstrated to be a promising approach to pattern features smaller than pre-existing mask features on the surface of a wafer substrate. A key to this approach is a substantial change in the etch rate of a thin masking layer by TII. Fifteen degrees-tilted Ar+ implantation into a 10 nm-thick thermally grown silicon dioxide (SiO2) masking layer at a dose of 3 × 1014 cm−2 enhances its etch rate in dilute hydrofluoric acid solution by a factor of approximately 9. The features defined by TII are shown to be self-aligned to the pre-existing mask features and to have critical dimensions that can be adjusted by changing the implant tilt angle (θ) and/or geometrical dimensions of the pre-existing mask features. In this work, trenches of width as small as ∼9 nm and sub-20 nm holes are achieved by TII-enhanced patterning.

Removal of Fe, B and P impurities by enhanced separation technique from silicon-rich powder of the multi-wire sawing slurry

The silicon-rich powder, which was separated by tuning the particle surface potential combined with centrifugation, contains varied impurities like iron, boron and phosphorus. To remove these impurities, the process of pre-dispersion and magnetic separation was attempted. The aggregates in the silicon-rich powder were dispersed by surface potential tuning combined with microwave treatment. According to the DLVO theory and experimental results, the electrostatic repulsion of the particles was largest when the pH value of solution reached 13.0, and the fine silicon-rich particles can be kept sufficiently dispersed at this pH, which was good for the further separation by magnetic field with the 90% removal of iron impurity. The residual iron impurity can be further completely removed by the microwave acid leaching with the mixing acid solutions of hydrofluoric and hydrochloric acid. By combining these enhanced purification techniques, other bothersome impurities such as boron and phosphorus can also be reduced to the requirements of solar grade polysilicon. This work is good for the recycling of silicon scrap materials to the solar grade polysilicon.

Fluorinated graphene suspension for inkjet printed technologies

The possibility to control the size of the flakes of graphene suspension in the course of their fluorination in an aqueous hydrofluoric acid solution was demonstrated. The effect of the suspension composition, the fluorination time, temperature and thermal stress on the fragmentation process was investigated. The corrugation of suspension flakes, which occurs at fluorination due to a difference in the constants of graphene and fluorographene lattices, leads to the appearance of nonuniform mechanical stresses. The fact that the flake size after fragmentation is determined by the size of corrugation allows the assumption that the driving force of fragmentation is this mechanical stress. This assumption is confirmed by the break of the corrugated layers from flakes under thermal stress. Moreover, fluorination treatment at elevated temperatures (∼70 °C) significantly accelerates the fragmentation process. Suspensions of fluorinated graphene with nanometer size flakes are of interest for the development of 2D ink-jet printing technologies and production of thermally and chemically stable dielectric films for nanoelectronics. The printed fluorinated graphene films on silicon and flexible substrates have been demonstrated and the charges in metal–insulator–semiconductor structures have been estimated as the ultra low values of (0.5–2) × 1010 cm−2.

Agglomeration in Porous Silicon Prepared from Si-Nanowires Structures

Silicon nanowires (SiNW’s) arrays prepared by electroless etching method are attractive due to their significant light absorption properties across the visible spectrum [1]. Typical silicon nanowires grown by electroless etching is shown in Figure 1a. Following this preparation of silicon nanowires, these samples are etched in an electrolytic HF and ethanol solution to produce porous silicon quantum confined structures. Mechanical behavior of materials at nanoscale is different due to their quantum confinement effect. When porous silicon nano-structures are prepared from SiNWs obtained through electroless process, they may have a tendency to become thin. Ultimately these nano-structures may collapse and form bunches on the surface [2], as shown in Figure 1b. However, bunched silicon nanowires structures may be desirable in some applications but may not be for some others. In order to avoid bunching of SiNWs, it may be necessary to reduce the surface tension during the growth of nanowires [3]. (a) (b) Fig 1. Cross-section images of silicon nanowires (a) grown by electroless etching, (b) Porous silicon structures prepared from SiNWs. SiNW’s were grown by eletroless etching in a solution of hydrofluoric acid (HF) and silver nitrate (AgNO3) at room temperature [4]. The prepared nanowires were then etched in an electrolytic solution containing HF and ethanol to make porous Si quantum confined structures. Reflectance and photoluminescence studies are performed on this structures Figure 1

New transition metal oxide fluorides with ReO3-type structure

Abstract The new niobium oxide fluorides MNbO2F4 [M = (Cr, Fe)], CrNb2O4F5, and Fe2Nb3O6F9 were prepared by treatment of chromium or iron nitrate with Nb-containing hydrofluoric acid solutions. Crystal structures were investigated by means of X-ray powder diffraction. All new compounds can be structurally refined in the cubic ReO3-type. The iron niobium oxide fluorides are reddish orange, and chromium containing phases exhibit a light green color. The niobium atoms are in the highest formal oxidation state.

Recovery of Vanadium from H2SO4-HF Acidic Leaching Solution of Black Shale by Solvent Extraction and Precipitation

The recovery of vanadium from sulfuric and hydrofluoric mixed acid solutions generated by the direct leaching of black shale was investigated using solvent extraction and precipitation methods. The process consisted of reduction, solvent extraction, and stripping, followed by precipitation and calcination to yield vanadium pentoxide. The influence of various operating parameters on the extraction and recovery of vanadium was studied. Vanadium (IV) was selectively extracted using a mixture of 10% (v/v) di(2-ethylhexyl)phosphoric acid and 5% (v/v) tri-n-butylphosphate in sulfonated kerosene. Using six extraction and five stripping stages, the extraction efficiency for vanadium was 96.7% and the stripping efficiency was 99.7%. V2O5 with a purity of 99.52% was obtained by oxidation of the loaded strip solution and precipitation of ammonium polyvanadate at pH 1.8 to 2.2, followed by calcination of the dried precipitate at 550 °C for 2 h. It was concluded that the combination of solvent extraction and precipitation is an efficient method for the recovery of vanadium from a multi-element leach solution generated from black shale.

Texturing a pyramid-like structure on a silicon surface via the synergetic effect of copper and Fe(III) in hydrofluoric acid solution

An innovative approach is proposed to texture a pyramid structure on a silicon surface via Cu-catalyzed chemical etching in the HF/FeCl3 system. The surface and cross-section morphologies of the formed pyramid structure were examined by scanning electron microscopy and atomic force microscopy. The results revealed that numerous silicon pyramid-like structures with hemlines of 0.1∼3μm and height of 0.1∼2μm are close together, and the top angle of the pyramid structure is 90°. Additionally, the systematic study of the effects of the etching time and the concentration of FeCl3 on the pyramid-like structures by the atom configuration model of silicon crystal faces demonstrated that the etching proceeds preferentially along the <100> directions of silicon. A formation mechanism of the pyramid-like structure is proposed. The results imply that the synergetic effect of Cu nanoparticles and Fe(III) could conveniently generate a pyramid-like architecture on the surface of silicon in hydrofluoric acid solution.

The role of the etchant ion in the formation and growth of pores in silicon during its etching in hydrofluoric acid solutions

The role of the etchant ion (HF2)– in the formation of pores in silicon during its etching in hydrofluoric acid solutions has been elucidated. The pore shape, size, and orientation in (100) and (111) silicon substrates have been explained by specific features of the etchant ion (HF2)–.

Electrochemical oxidation of graphite in aqueous hydrofluoric acid solution at high current densities

Abstract Electrochemical oxidation of graphite was performed at high current densities in 47% HF aqueous solution. Cyclic voltammetry indicated that covalent C F bonding formed above 2.4 V vs Pb/PbF2. The sample obtained at higher current densities than 200 mA cm−2 was stage 1 type material with an interlayer spacing of 0.55 nm and it contained a considerable amount of oxygen, together with the covalently bonded fluorine. The discharge profile of this sample as a cathode of lithium primary battery was similar to that of C2.5F prepared under F2 gas atmosphere and the capacity reached 550 mAh g−1. This strongly indicated that not only fluorine but also oxygen in this sample was utilized.

MgF2-coated porous magnesium/alumina scaffolds with improved strength, corrosion resistance, and biological performance for biomedical applications

Porous magnesium (Mg) has recently emerged as a promising biodegradable alternative to biometal for bone ingrowth; however, its low mechanical properties and high corrosion rate in biological environments remain problematic. In this study, porous magnesium was implemented in a scaffold that closely mimics the mechanical properties of human bones with a controlled degradation rate and shows good biocompatibility to match the regeneration rate of bone tissue at the affected site. The alumina-reinforced Mg scaffold was produced by spark plasma sintering and coated with magnesium fluoride (MgF2) using a hydrofluoric acid solution to regulate the corrosion rate under physiological conditions. Sodium chloride granules (NaCl), acting as space holders, were leached out to achieve porous samples (60%) presenting an average pore size of 240μm with complete pore interconnectivity. When the alumina content increased from 0 to 5vol%, compressive strength and stiffness rose considerably from 9.5 to 13.8MPa and from 0.24 to 0.40GPa, respectively. Moreover, the biological response evaluated by in vitro cell test and blood test of the MgF2-coated porous Mg composite was enhanced with better corrosion resistance compared with that of uncoated counterparts. Consequently, MgF2-coated porous Mg/alumina composites may be applied in load-bearing biodegradable implants.

Two-Layer Microstructures Fabricated by One-Step Anisotropic Wet Etching of Si in KOH Solution.

Anisotropic etching of silicon in potassium hydroxide (KOH) is an important technology in micromachining. The residue deposition from KOH etching of Si is typically regarded as a disadvantage of this technology. In this report, we make use of this residue as a second masking layer to fabricate two-layer complex structures. Square patterns with size in the range of 15–150 μm and gap distance of 5 μm have been designed and tested. The residue masking layer appears when the substrate is over-etched in hydrofluoric acid (HF) solution over a threshold. The two-layer structures of micropyramids surrounded by wall-like structures are obtained according to the two different masking layers of SiO2 and residue. The residue masking layer is stable and can survive over KOH etching for long time to achieve deep Si etching. The process parameters of etchant concentration, temperature, etching time and pattern size have been investigated. With well-controlled two-layer structures, useful structures could be designed for applications in plasmonic and microfluidic devices in the future.

Size Control of Porous Silicon-Based Nanoparticles via Pore-Wall Thinning.

Photoluminescent silicon nanocrystals are very attractive for biomedical and electronic applications. Here a new process is presented to synthesize photoluminescent silicon nanocrystals with diameters smaller than 6 nm from a porous silicon template. These nanoparticles are formed using a pore-wall thinning approach, where the as-etched porous silicon layer is partially oxidized to silica, which is dissolved by a hydrofluoric acid solution, decreasing the pore-wall thickness. This decrease in pore-wall thickness leads to a corresponding decrease in the size of the nanocrystals that make up the pore walls, resulting in the formation of smaller nanoparticles during sonication of the porous silicon. Particle diameters were measured using dynamic light scattering, and these values were compared with the nanocrystallite size within the pore wall as determined from X-ray diffraction. Additionally, an increase in the quantum confinement effect is observed for these particles through an increase in the photoluminescence intensity of the nanoparticles compared with the as-etched nanoparticles, without the need for a further activation step by oxidation after synthesis.