Regular arrays of triangular‐microstructure formed on silicon (111) surface via ultrafast laser irradiation in KOH solution

The regular micrometer‐scale triangular arrays were formed using ultrafast femtosecond laser irradiation on (111) surface of silicon wafer immersed in KOH solution (0.1 g/ml). At low laser fluence, the resulting surface is covered by triangular pits microstructures, whereas at high laser fluence, the structures are transformed to multilayer‐triangular stacks‐microstructures. The number of triangular stacks layer increased as the laser fluence increased. The formation of triangle microstructure arrays depends on both silicon surface crystallographic orientation and the concentration of KOH solution. Either for lower KOH solution concentration (0.02 g/ml) or other silicon crystallographic orientation, triangle arrays cannot be obtained. We attribute the formation of triangular microstructure arrays to the laser‐assisted chemical etching process. Copyright © 2013 John Wiley & Sons, Ltd.     

High-performance silicon nanowire array photoelectrochemical solar cells through surface passivation and modification

Nanowire solar cells: Pt nanoparticle (PtNP) decorated C/Si core/shell nanowire photoelectrochemical solar cells show high conversion efficiency of 10.86 % and excellent stability in aggressive electrolytes under 1-sun AM 1.5 G illumination. Superior device performance is achieved by improved surface passivation of the nanowires by carbon coating and enhanced interfacial charge transfer by PtNPs.     

Mechanisms of surface processes in silicon etching

A unified view on the mechanism allowing one to explain the experimental features governing spontaneous silicon etching by atomic fluorine is presented. Analysis of the phenomenological equation of adsorption shows a significant difference between etching mechanisms at high and low heat of adsorption on the surface being etched. As follows from the parameter estimates, one or another case can be realized under different experimental conditions. At steady-state the etching is argued to be determined only by the processes taking place on the SiF. film surface. To describe the process, it is necessary to understand the mechanism of overcoming the surface barrier for fluorine penetration into the film. At low heat of fluorine adsorption the barrier is overcome by thermal activation. In the opposite case the etching mechanism includes electron tunneling from silicon to adatoms and creation of a surface electric field. The field lowers the high energetic barrier for fluorine penetration. Based on the kinetic equations describing the electronic and atomic processes on the surface, the equation of the field strength is obtained. This equation is analyzed in different limit cases. The observed features are shown to be reproduced at some conditions on the parameters. Definite predictions on the temperature dependence of the etch rate are made.     

Combined IR and XPS analysis of the native (1 0 0) surface of single‐crystalline silicon after HFaq etching

A combined analysis, based on angle‐resolved X‐ray photoelectron spectroscopy and multiple‐internal‐reflection infrared spectroscopy, of the (1 0 0) silicon surface after etching in dilute aqueous solution of HF is presented. The analysis shows that the surface is mainly formed by a heterogeneous distribution of SiH, SiH₂ and SiH₃ terminations, but contains (in addition to sub‐stoichiometric oxidized silicon) a form of reduced silicon, not consistent with the currently accepted picture of the native HF_aq‐etched surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Mass spectrometric analysis of low molecular mass polyesters by laser desorption/ionization on porous silicon

A low molecular mass polyester was analyzed by desorption/ionization on porous silicon (DIOS) mass spectrometry. The results were compared with those of matrix-assisted laser desorption ionization (MALDI) mass spectrometry using matrixes of alpha-cyano-4-hydroxycinnamic acid (CHCA) and 10,15,20-tetrakis(pentafluorophenyl)porphyrin (F20TPP). The CHCA matrix was not suitable for characterization of low molecular mass components of the polyester because the matrix-related ions interfered with the component ions. On the other hand, the F20TPP matrix showed no interference because no matrix-related ions appeared below m/z 822. However, the solvent selection for determining optimal conditions of sample preparation was limited, because F20TPP does not dissolve readily in any of the available organic solvents. In the DIOS spectra, the polymer ions were observed at high sensitivity without a contaminating ion. No matrix is needed for DIOS spectra of low molecular mass polyesters, facilitating sample preparation and selectivity of a precursor ion in post-source decay measurements.     

Ab initio potential energy surface and vibration‐rotation energy levels of silicon dicarbide,SiC2

The accurate ground‐state potential energy surface of silicon dicarbide, SiC₂, has been determined from ab initio calculations using the coupled‐cluster approach. Results obtained with the conventional and explicitly correlated coupled‐cluster methods were compared. The core‐electron correlation, higher‐order valence‐electron correlation, and scalar relativistic effects were taken into account. The potential energy barrier to the linear SiCC configuration was predicted to be 1782 cm^?1. The vibration‐rotation energy levels of the SiC₂, ²⁹SiC₂, ³⁰SiC₂, and SiC¹³C isotopologues were calculated using a variational method. The experimental vibration‐rotation energy levels of the main isotopologue were reproduced to high accuracy. In particular, the experimental energy levels of the highly anharmonic vibrational ν₃ mode of SiC₂ were reproduced to within 6.7 cm^?1, up to as high as the v₃ = 16 state.     

Analysis of deprotonated acids with silicon nanoparticle-assisted laser desorption/ ionization mass spectrometry

Chemically modified silicon nanoparticles were applied for the laser desorption/negative ionization of small acids. A series of substituted sulfonic acids and fatty acids was studied. Compared to desorption ionization on porous silicon (DIOS) and other matrix-less laser desorption/ionization techniques, silicon nanoparticle-assisted laser desorption/ionization (SPALDI) mass spectrometry allows for the analysis of acids in the negative ion mode without the observation of multimers or cation adducts. Using SPALDI, detection limits of many acids reached levels down to 50 pmol/μl. SPALDI of fatty acids with unmodified silicon nanoparticles was compared to SPALDI using the fluoroalkyl silylated silicon powder, with the unmodified particles showing better sensitivity for fatty acids, but with more low-mass background due to impurities and surfactants in the untreated silicon powder. The fatty acids exhibited a size-dependent response in both SPALDI and unmodified SPALDI, showing a signal intensity increase with the chain length of the fatty acids (C12-C18), leveling off at chain lengths of C18-C22. The size effect may be due to the crystallization of long chain fatty acids on the silicon. This hypothesis was further explored and supported by SPALDI of several, similar sized, unsaturated fatty acids with various crystallinities. Fatty acids in milk lipids and tick nymph samples were directly detected and their concentration ratios were determined by SPALDI mass spectrometry without complicated and time-consuming purification and esterification required in the traditional analysis of fatty acids by gas chromatography (GC). These results suggest that SPALDI mass spectrometry has the potential application in fast screening for small acids in crude samples with minimal sample preparation.     

Microstructure and surface roughness of graphite‐like carbon films deposited on silicon substrate by molecular dynamic simulation

Molecular dynamics simulations are performed on the atomic origin of the growth process of graphite‐like carbon film on silicon substrate. The microstructure, mass density, and internal stress of as‐deposited films are investigated systematically. A strong energy dependence of microstructure and stress is revealed by varying the impact energy of the incident atoms (in the range 1–120 eV). As the impact energy is increased, the film internal stress converts from tensile stress to compressive stress, which is in agreement with the experimental results, and the bonding of C‐Si in the film is also increased for more substrate atoms are sputtered into the grown film. At the incident energy 40 eV, a densification of the deposited material is observed and the properties such as density, sp³ fraction, and compressive stress all reach their maximums. In addition, the effect of impact energy on the surface roughness is also studied. The surface morphology of the film exhibits different characteristics with different incident energy. When the energy is low (<40 eV), the surface roughness is reduced with the increasing of incident energy, and it reaches the minimum at 50 eV. Copyright © 2012 John Wiley & Sons, Ltd.     

Enhancing the hydrophobicity of the mineral wool through surface modification with organo-silane

Mineral wool materials are consistently preferred material to be used for building thermal insulation because of their low heat conductivity, making energy-efficient structures impossible to construct without highly insulating thermal envelopes. A mineral wool with a hydrophobic external surface could be used for several applications where hydrophobicity would be helpful. Organo-silanes are one of the most promising materials to impart hydrophobic character to varied surfaces to achieve performance properties such as dust-resistant coatings on building glass, solar panels with self-cleaning surfaces, biofouling resistant paints, self-cleaning car windshields etc. In this study, mineral wool was treated with methyltrimethoxysilane (MTMS) to achieve hydrophobic surfaces.A Fourier Transform Infrared Spectrometer is used to confirm the successful deposition of organosilane/siloxane networks on glass wool fibre surfaces. The hydrophobicity of treated wool was assessed and quantified using a contact angle measurement. Contact angle measurement was used to quantify the hydrophobicity of treated wool. The thermal conductivity of treated mineral wool fiber was calculated using the portable Lee's disc method. To determine the thermal stability and crystallinity of the treated wool, X-ray diffraction spectroscopy and thermogravimetric analysis were used, respectively. The treated mineral wool exhibited excellent thermal stability up to 800 °C, and wettability tests proved the treated surface highly hydrophobic, allowing water droplets to roll off with contact angles up to 134.9°. Surface modification reduced thermal conductivity by 20%, showing good thermal resistance. Here, we show easy and sustainable methods of treating mineral wool surfaces, which can serve as a thermal insulation option under humid conditions.     

Effect of Nb,Ti, and W ion implantation on surface properties and cell compatibility of silicon carbide

Silicon carbide is considered as a bio-inert semiconductor material; consequently, it has been proposed for potential applications in human body implantation. In this study, we study the effect of implanting different metal ions on the surface properties of silicon carbide single crystal. The valence states of the elements and the surface roughness of implanted SiC were studied using X-ray photoelectron spectroscopy and atomic force microscope, respectively. Osteoblastic MG-63 cells were utilized to characterize the cytocompatibility of ion implanted SiC. The results show that after Nb ion implantation on the SiC surface, it mainly exists in the form of Nb–C bond, Nb–O bond, and a small amount of metallic niobium. The titanium implanted on SiC primarily forms Ti-C bond and Ti-O bond. The tungsten implanted on SiC mostly presents as metallic tungsten and W–O bond. The roughness of silicon carbide single crystal is improved by ion implantation of all three metal ions. Ion implantation of titanium and niobium can improve the cell compatibility and hydrophilicity of silicon carbide, whereas ion implantation of tungsten reduces the cell compatibility and hydrophilicity of silicon carbide.     

Porous silicon oxycarbide glasses from organically modified silica gels of high surface area

High surface area alkyl-substituted silica aerogels and xerogels were successfully prepared by sol-gel processing and supercritical drying. The gels were further heat treated in inert atmosphere to temperatures as high as 1000°C. Surface areas and pore structure of the gels and gels pyrolyzed at high temperatures were determined by multipoint BET surface area measurement. The aerogels and xerogels exhibited surface areas of about 1100 m²/g. No significant effect of pH was found on the surface areas of gels in the two step sol-gel process, but gels of low pH showed smaller pore diameter and higher density. Xerogels showed smaller surface area, pore size, and pore volume compared to aerogels. Upon pyrolyzing in inert atmosphere, the surface areas of all the gels decreased with temperature as a result of collapse of micropores and shrinkage of mesopores. Unlike pure silica gel, which loses almost all surface area and densifies at 1000°C, the advantage of the alkyl-substituted gels is that they maintained a high surface area of 400 m²/g at 1000°C.Also with the Department of Agronomy.     

Effective detection of peptides containing cysteine sulfonic acid using matrix-assisted laser desorption/ionization and laser desorption/ionization on porous silicon mass spectrometry

Cysteine sulfonic acid-containing peptides, being typical acidic peptides, exhibit low response in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. In this study, matrix conditions and the effect of diammonium hydrogencitrate (DAHC) as additive were investigated for ionization of cysteine sulfonic acid-containing peptides in MALDI. A matrix-free ionization method, desorption/ionization on porous silicon (DIOS), was also utilized to evaluate the effect of DAHC. When equimolar three-component mixtures of peptides carrying free cysteine, cysteine sulfonic acid, and carbamidomethyl cysteine were measured by MALDI using a common matrix, alpha-cyano-4-hydroxycinnamic acid (CHCA), no signal corresponding to cysteine sulfonic acid-containing peptide could be observed in the mass spectrum. However, by addition of DAHC to CHCA, the peaks of cysteine sulfonic acid-containing peptides were successfully observed, as well as when using 2,4,6-trihydroxyacetophenone (THAP) and 2,6-dihydroxyacetophenone with DAHC. In the DIOS mass spectra of these analytes, the use of DAHC also enhanced the peak intensity of the cysteine sulfonic acid-containing peptides. On the basis of studies with these model peptides, tryptic digests of oxidized peroxiredoxin 6 were examined as a complex peptide mixture by MALDI and DIOS. In MALDI, the peaks of cysteine sulfonic acid-containing peptides were observed when using THAP/DAHC as the matrix, but this was not so with CHCA. In DIOS, the signal from cysteine sulfonic acid-containing peptides was suppressed; however, the use of DAHC significantly enhanced the signal intensity with an increase in the number of observed peptides and increased signal-to-noise ratio in the DIOS spectra. The results show that DAHC in the matrix or on the DIOS chip decreases discrimination and suppression effects in addition to suppressing alkali-adduct ions, which leads to a beneficial effect on protonation of peptides containing cysteine sulfonic acid.     

The effect of vacuum-ultraviolet laser wavelengths on the surface treatment of polyolefinic polymers

The laser-induced modification of the surface morphology of poly(propylene) fibers and films was investigated. It is known that strongly absorbing fibers such as poly(ethylene terephthalate) and polyamide obtain characteristic surface morphologies after treatment with 193 or 248 nm laser irradiation. Polyolefinic material cannot be modified directly (i.e., without doping) by irradiation with these wavelengths. Therefore experiments were carried out using a 157 nm F₂-laser. After irradiation in a vacuum chamber at fluences in excess of 50 mJ/cm² poly(propylene) also reveals the well-known surface morphology. Compared with aromatic polymers a rather high number of pulses is needed to generate the effect. © 1993 John Wiley & Sons, Inc.     

Photo‐stimulated “turn‐on/off” molecularly imprinted polymers based on magnetic mesoporous silicon surface for efficient detection of sulfamerazine

In this study, novel photo‐stimulated molecularly imprinted polymers based on magnetic mesoporous carrier surface were developed for selective identification and intelligent separation of sulfamerazine in complex samples. The photosensitive monomer of the molecularly imprinted polymers was azobenzene derivative 5‐[(4‐(methacryloyloxy)phenyl) diazenyl] isophthalic acid with stimulus reaction mechanisms, which has photoisomerization between trans and cis for N=N bonds. Further, the properties of the photo‐stimulated molecularly imprinted polymers were further evaluated through several sets of adsorption experiments. It illustrated that the maximum adsorption amount is 0.45 mmol/L. By ultraviolet spectrophotometry, the material reaches typical characteristic peaks of photo sensitivity, and the cycle time is 16 min. Three adsorption and desorption processes were repeated, the adsorption rate reached 34.4%. Overall, the photo‐stimulated molecularly imprinted polymers can enrich and separate determine sulfamerazine with high selectivity, which have good recovery for real samples.     

The effect of carbonaceous contamination on the investigation of the surface oxide on silicon by angle-resolved XPS

The carbon-contaminated native oxide layer on a standard silicon wafer was investigated by angle-resolved signal ratio X-ray photoelectron spectroscopy (AR/SR/XPS). The results, based on intensity measurements of C_1s , O_1s , Si _2p ⁴⁺ and Si^elemental _2p showed the carbon to be ingested into the oxide to a mean depth of 0.4 nm, and the oxide to consist of a fully oxidized layer ( 1 nm) on top, followed by a suboxidic layer (0.8 nm). The conclusions are that the depth location of the carbonaceous contamination is of cardinal importance for the correct interpretation of the oxidic data, and that for well studied systems routine measurements at two take-off angles suffice for quantitative results.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Enhancing the antifouling property of polyethersulfone ultrafiltration membranes through surface adsorption-crosslinking of poly(vinyl alcohol)

An adsorption-crosslinking process of poly(vinyl alcohol) (PVA) was introduced to modify the surface of polyethersulfone (PES) ultrafiltration membranes for enhancement of their antifouling property. XPS and water contact angle measurement confirmed the obvious enhancement of surface hydrophilicity. Ultrafiltration results showed that the spreading of PVA chains over the hydrophobic membrane surface caused substantial but acceptable decrease on membrane flux. The fouling type analysis indicated that PVA adsorption effectively improved the antifouling property of PES membranes. With a PVA concentration of 0.5 wt% and three cycles of alternative adsorption-crosslinking, the total and irreversible fouling ratio of modified membranes were 0.38 and 0.22, respectively, much lower than those of control PES membrane (0.61 and 0.47), and the flux recovery ratio was increased accordingly. The long-term ultrafiltration experiment demonstrated the improvement of recycling property and the reliability of adsorption-crosslinking process.     

Evolution of Etching Kinetics and Directional Transition of Nanowires Formed on Pyramidal Microtextures

Two‐scale roughened silicon (Si) textures are considered promising architectures for versatile applications because of their excellent self‐cleaning, light‐trapping, and biosensing capacities. In this study, we explore the directional control of nanowires formed on pyramidal microtextures through a single‐step metal‐assisted chemical etching (MACE). The measured current density of Si dissolution at catalytic etching enables quantitative monitoring of the etching kinetics of nanowire formation. The preferential orientation of fabricated nanowires on {111}‐plane pyramidal textures was found to positively correlate with the molar ratio of [AgNO₃] to ([AgNO₃]+[HF]), referred to as ρ. A distinct transition from <100> to <111> axial directions at ρ≥0.2 and ρ=0.07, respectively, was revealed. The <111>‐oriented nanowires on the pyramidal microtextures exhibited an excellent antireflection performance, with a reflectivity as low as 1.2 % at 600 nm. The results of this study may aid the design for the development of high‐performance Si‐based optoelectronic devices.     

Surface oxidation of high-surface-area silicon carbide: FT-IR studies

The surface of ultrafine silicon carbide powders, prepared by a laser-driven gas-phase reaction was studied as a self-supporting disk by FT infrared spectrometry. After evacuation silicon and carbon atoms located at the surface give rise tovSiH andvCH bands. When heating in oxygen, subtraction spectra showed features which could be strictly correlated with a progressive growth of a silica layer: SiH and CH bands were replaced by new bands characteristic of amorphous silica and the typical band of surface silanol groups on silica (3745 cm^–1) simultaneously increased.