Hydrophilic Silicon Research Articles

Comment on “Physicochemical controls on adsorbed water film thickness in unsaturated geological media” by Tetsu K. Tokunaga

Comment on “Physicochemical controls on adsorbed water film thickness in unsaturated geological media” by Tetsu K. Tokunaga

Role of Colloidal Silicon Dioxide in Eudragit<i> In-Situ </i>Forming Gel

Colloidal silicon dioxide (Aerosil) is fumed silica that has been used as gelling agents, thickening agents and filling agents. The objectives of this study were to characterize the effect of hydrophilic (aerosil 200) and hydrophobic (aerosil R972) colloidal silicon dioxide on physical properties of eudragit gels which N-methyl-pyrrolidone was employed as dispersing medium. The samples were investigated in terms of viscosity, rheology and syringeability. The results indicated that the aerosil 200 and aerosil R972 amount influenced the viscosity, rheology and syringeability of the prepared gels. Viscosity and syringeability of the systems were increased with an increased amount of both aerosils. However, the viscosity and syringeability of the prepared gels containing aerosil 200 were increased higher than that of systems containing aerosil R972. The rheological behaviors of all systems consisting aerosil 200 and R972 were non-Newtonian flow. These studies demonstrated that aerosil 200 and R972 could improve the physical properties of eudragit gels dispersed in N-methyl-pyrrolidone.

Effect of added salt on morphology of ultrathin polyelectrolyte films

Morphological evolution of polyelectrolyte ultrathin films as a function of externally added monovalent salt concentration and its correlation with the solution state morphology have been studied using dynamic light scattering (DLS) and tapping mode AFM. DLS data shows the presence of two different dynamical modes of relaxation in the solution state. Films are prepared from aqueous solution of poly(sodium-4-styrenesulfonate) (NaPSS) with different concentration of added NaCl on the hydrophilic silicon substrate using spin coating technique. Smooth and featureless surface morphology for salt free NaPSS films become rough with addition of salt and beyond a critical salt concentration DLA like fractal structures are formed on the films. Comparison of the surface morphology with slow mode dynamics in DLS establishes the presence of multichain polyelectrolyte clusters in the DLA pattern formed on the surface of the films. Compositional analysis of the films shows an accumulation of excess NaCl on the DLA structures with the increase of salt concentration. Our results show that the DLA patterns are primarily formed by the excess salt ions on their solidification during spin coating and multichain polyelectrolyte clusters nucleate on the preformed nuclei leading to the resultant surface morphology.

Functional Gold Nanorods: Functional Gold Nanorods: Synthesis, Self‐Assembly, and Sensing Applications (Adv. Mater. 36/2012)

The interior of the letters R-I-C-E on the back cover image contains a hydrophilic silicon oxide surface, whereas the background is coated with a hydrophobic film of a photoresist. Gold nanorods coated with a CTAB bilayer selectively accumulate in the hydrophilic letters when their aqueous solution is cast on the patterned substrate. The synthesis, self-assembly and sensing applications of functional gold nanorods are reviewed in detail by Eugene Zubarev and co-workers on p. 4811.

Modification of wetting properties of laser-textured surfaces by depositing triboelectrically charged Teflon particles

Hydrophilic laser-textured silicon wafers with natural oxide surfaces were rendered hydrophobic by depositing electrostatically charged submicrometer Teflon particles, a process termed as triboelectric Teflon adhesion. Silicon surfaces were micro-textured (∼5 μm) by laser ablation using a nanosecond pulsed UV laser. By varying laser fluence, micro-texture morphology of the wafers could be reproduced and well controlled. Wetting properties of the triboelectrically charged Teflon-deposited surfaces were studied by measuring apparent static water contact angles and water contact angle hysteresis as a function of substrate roughness and the amount of Teflon deposited. A similar study was also performed on various micro-textured silicon carbide surfaces (sandpapers). If the average substrate roughness is between 15 and 60 μm, superhydrophobic surfaces can be easily formed by Teflon deposition with water contact angle hysteresis less than 8°. This environmentally benign solvent-free process is a highly efficient, rapid, and inexpensive way to render contact-charged rough surfaces hydrophobic or superhydrophobic.

Tuning protein GlnB-Hs surface interaction with silicon: FTIR-ATR, AFM and XPS study

Herbaspirillum seropedicae GlnB (GlnB-Hs) is a signal transduction protein involved in the control of nitrogen, carbon and energetic metabolism. The adsorption of GlnB-Hs deposited by spin coating on hydrophilic and hydrophobic silicon forms a thin layer that was characterized using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared attenuated total reflectance spectroscopy (FTIR-ATR). AFM allowed the identification of globular, face-up donut like array of protein on hydrophilic silicon substrate, favoring deprotonated residues to contact the silicon oxide surface. Over hydrophobic silicon, GlnB-Hs adopts a side-on conformation forming a filament network, avoiding the contact of protonated residues with silicon surface. XPS allowed us to determine the protonated and non-protonated states of nitrogen 1s (N 1s). The FTIR-ATR measurements provided information about protein secondary structure and its conservation, after surface adsorption.

FABRICATION AND OPTOELECTRONIC PROPERTIES OF MgxZn1-xO ULTRATHIN FILMS BY LANGMUIR–BLODGETT TECHNOLOGY

By transferring Mg x Zn 1-x O sol and stearic acid onto a hydrophilic silicon wafer or glass plate, the Langmuir–Blodgett (LB) multilayers of Mg x Zn 1-x O (x:0, 0.2, 0.4) were deposited. After calcinations at 350°C for 0.5 h and at 500°C for 3 h, Mg x Zn 1-x O ultrathin films were fabricated. The optimized parameters for monolayer formation and multilayer deposition were determined by the surface pressure-surface (Π-A) area and the transfer coefficient, respectively. The expended areas of stearic acid with Mg x Zn 1-x O sols under Π-A isotherms inferred the interaction of stearic acid with Mg x Zn 1-x O sols during the formation of monolayer at air–water interface. X-ray diffraction (XRD) was used to determine the crystal structures of Mg x Zn 1-x O nanoparticles and ultrathin films. The surface morphologies of Mg x Zn 1-x O ultrathin films were observed by scanning probe microscopy (AFM). And the optoelectronic properties of Mg x Zn 1-x O were detected and discussed based on photoluminescence (PL) spectra.

Electrodeposition of platinum and silver into chemically modified microporous silicon electrodes

Electrodeposition of platinum and silver into hydrophobic and hydrophilic microporous silicon layers was investigated using chemically modified microporous silicon electrodes. Hydrophobic microporous silicon enhanced the electrodeposition of platinum in the porous layer. Meanwhile, hydrophilic one showed that platinum was hardly deposited within the porous layer, and a film of platinum on the top of the porous layer was observed. On the other hand, the electrodeposition of silver showed similar deposition behavior between these two chemically modified electrodes. It was also found that the electrodeposition of silver started at the pore opening and grew toward the pore bottom, while a uniform deposition from the pore bottom was observed in platinum electrodeposition. These electrodeposition behaviors are explained on the basis of the both effects, the difference in overpotential for metal deposition on silicon and on the deposited metal, and displacement deposition rate of metal.

Scattering depth correction of evanescent waves in inelastic neutron scattering using a neutron prism

Grazing Incidence Neutron Spin Echo Spectroscopy (GINSES) has recently been applied to measure the dynamics of surfactant membranes close to a hydrophilic silicon wall. The scattering depth of the evanescent wave inside the microemulsion depends strongly on the angle of incidence and the wavelength. The inherently low scattering intensity of GINSES measurements, however, requires the integration over a rather broad wavelength band. In particular, at a pulsed source the instrument operates with a broad wavelength band covering all neutrons within one frame between two pulses. In order to yield viable counting statistics it is highly desirable to integrate data corresponding to significant fractions of the wavelength band. Therefore, in a normal reflectometry setup the penetration length would be smeared and blur the depth dependence of the experimental results. Here we describe a new method to strongly mitigate this effect and show its application in a GINSES experiment at the neutron spin echo instrument at the Spallation Neutron Source (SNS). A prism in front of the sample was introduced in order to adapt the angle of the incoming beam according to the wavelength by this optical component. As an example an experiment on a bicontinuous microemulsion using these neutron optics is presented.

Functionalized mesoporous silicon for targeted-drug-delivery

The present work concerns a preliminary step in the production of anticancer drug loaded porous silicon (PSi) for targeted-drug-delivery applications. A successful procedure for the covalent attachment of folic acid, polyethylene glycol (PEG) and doxorubicin to hydrophilic mesoporous silicon layers is presented. A systematic approach has been followed to obtain the optimal composition of the N,N′-dicyclohexylcarbodiimide (DCC)/N-hydroxysuccimide (NHS) in dimethylsulfoxide (DMSO) solution for the surface activation process of the undecylenic acid (UD) grafted molecules to take place with minimal undesired byproduct formation. The effect of reactant concentration and kind of solvent (aqueous or DMSO) on the attachment of folic acid to the activated PSi layer has been investigated. The covalent attachment of the doxorubicin molecules to the PSi layer functionalized with folic acid and PEG is discussed. The drug release kinetics as a function of pH has been studied. The functionalized PSi particles show a high cytotoxicity compared to the equivalent amount of free drug. Cell toxicity tests show clearly that the incorporation of folate molecules increases substantially the toxicity of the loaded PSi particles. Accordingly this new functionalized PSi may be considered a proper candidate for targeted drug delivery.

Thin films of silica imbedded silicon and germanium quantum dots by solution processing

Hydrophilic silicon (0.9nm) and germanium (2.7nm) quantum dots (QDs), synthesized utilizing micelles to control particle size, were coated with silica using liquid phase deposition. The use of dodecyltrimethylammonium bromide as a surfactant yielded uniform spheres (Si@SiO2=57nm; Ge@SiO2=32nm), which could then be arrayed in three dimensions using a vertical deposition method on quartz plates. The silica coated QDs were characterized by UV–visible spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and transmission electron microscopy. The thin films were characterized by UV–visible spectroscopy, scanning electron microscopy, and the measurement of a photocurrent.

Non-Aqueous Virgin Coconut Oil Hair Gel

Virgin coconut oil (VCO) is gaining wide popularity in the scientic eld and among the public. The purpose of this research was to develop the non-aqueous hair gel by dispersing hydrophilic colloidal silicon dioxide (Aerosil 200) or hydrophobic colloidal silicon dioxide (Aerosil R 972) into virgin coconut oil and to determine the effect of Aerosil type on physical properties of prepared hair gel. Texture analysis and satisfied evaluation of prepared system were also conducted. At a suitable amount of Aerosil 200 and Aerosil R 972, the three-dimensional network led to the immobilization of a dispersing medium. The viscosity of the prepared gel was increased as the amount of Aerosil 200 or Aerosil R 972 was increased. However, the viscosity of gel containing Aerosil 200 was apparently higher than system prepared from Aerosil R 972. The rheological behavior of these gels depended on type and concentration of colloidal silicon dioxide. From texture analysis, the hardness and adhesion of systems comprising Aerosil 200 were higher than that containing Aerosil R 972 with concentration dependence. Satisfied evaluation by a panel consisting of human volunteers demonstrated that the developed non-aqueous virgin coconut oil gel could be used as the hair setting gel.

Scanning of Silicon Wafers in Contact with Aqueous CTAB Solutions below the CMC

Hydrophilic silicon wafers are studied against aqueous solutions of hexadecyl trimethyl ammonium bromide (CTAB) at concentrations between 0.05 mM up to 1 mM (CMC). AFM studies show that nanobubbles are formed at concentrations up to 0.4 mM. From 0.5 mM upward, no bubbles could be detected. This is interpreted as the formation of hydrophobic domains of surfactant aggregates, becoming hydrophilic at about 0.5 mM. The high contact angle of the nanobubbles (140-150° through water) indicates that the nanobubbles are located on the surfactant domains. A combined imaging and colloidal probe AFM study serves to highlight the surfactant patches adsorbed at the surface via nanobubbles. The nanobubbles have a diameter between 30 and 60 nm (after tip deconvolution), depending on the surfactant concentration. This corresponds to a Laplace pressure of about 30 atm. The presence of the nanobubbles is correlated with force measurements between a silica probe and a silicon wafer surface. The study is a contribution to the better understanding of the short-range attraction between hydrophilic surfaces exposed to a surfactant solution.

One-pot synthesis of luminescent hydrophilic silicon nanocrystals

A facile one-pot method of femtosecond laser ablation in solution to synthesize hydrophilic silicon nanocrystals is presented in this communication. These silicon nanoscrystals emit colorful photoluminescence when excited at different wavelengths. This simple method has potential applications in the preparation of luminescent silicon nanocrystals passivated with different organic molecules.

Study of Hydrophilic Si Direct Bonding with Ultraviolet Ozone Activation for 3D Integration

Wafer-level hydrophilic silicon direct bonding is demonstrated using ultraviolet ozone (UVO) activation. The activation is performed at room temperature in atmospheric ambient for 3, 6, 9, and 12 min under UVO exposure, respectively. The activation process helps to form a hydrophilic surface (contact angle < 10°) for hydrophilic bonding and to improve the surface roughness to <0.25 nm possibly by removing the surface hydrocarbon contaminants. After annealing at 200°C for 3 hr, excellent bonding strength is achieved. High bonding uniformity is obtained in the bonded wafers which are activated for 3 min exposure in UVO. Helium over-pressure in a bombing chamber and helium leak rate detection by a mass spectrometer are used for hermeticity measurement of Si cavities sealed and bonded after UVO activation. The detected helium leak rate indicates that the best hermeticity can be obtained with an activation time of 3 min. The C-V curves of the metal-oxide-semiconductor (MOS) capacitors which are fabricated using UVO clean on the Si surface prove that prolonged exposure to UVO can degrade the bonding quality.

Effect of organically modified layered silicates on the morphology of symmetrical blends of polystyrene and poly(methyl methacrylate)

The changes in morphology caused by the addition of organically modified layered silicate on equal volume fraction blends of polystyrene and poly(methyl methacrylate) are investigated. In thin films supported on silicon, without layered silicates, the PMMA forms a layer on the silicon, while the PS tend to minimize contact with both the hydrophilic silicon substrate and the PMMA phase, and tend to form discrete domains on top of the PMMA layer. With the introduction of layered silicates, the characteristic length scale of the structure decreases. On the other hand, in bulk samples, without the layered silicates, the equal volume fraction blend has the PS domains in a PMMA matrix. At 0.6 wt% of added silicate, in both thin film and bulk, the blend morphology converts from discrete to co-continuous. Electron micrographs reveal well dispersed silicate sheets locating at the interface between small PS domains in the PMMA phase. The change in morphology is conjectured to be the result of the interfacial location of the layered silicates rather than the change in viscosity ratio between the two phases.

Contrasting Micro/Nano Architecture on Termite Wings: Two Divergent Strategies for Optimising Success of Colonisation Flights

Many termite species typically fly during or shortly after rain periods. Local precipitation will ensure water will be present when establishing a new colony after the initial flight. Here we show how different species of termite utilise two distinct and contrasting strategies for optimising the success of the colonisation flight. Nasutitermes sp. and Microcerotermes sp. fly during rain periods and adopt hydrophobic structuring/‘technologies’ on their wings to contend with a moving canvas of droplets in daylight hours. Schedorhinotermes sp. fly after rain periods (typically at night) and thus do not come into contact with mobile droplets. These termites, in contrast, display hydrophilic structuring on their wings with a small scale roughness which is not dimensionally sufficient to introduce an increase in hydrophobicity. The lack of hydrophobicity allows the termite to be hydrophilicly captured at locations where water may be present in large quantities; sufficient for the initial colonization period. The high wettability of the termite cuticle (Schedorhinotermes sp.) indicates that the membrane has a high surface energy and thus will also have strong attractions with solid particles. To investigate this the termite wings were also interacted with both artificial and natural contaminants in the form of hydrophilic silicon beads of various sizes, 4 µm C18 beads and three differently structured pollens. These were compared to the superhydrophobic surface of the planthopper (Desudaba psittacus) and a native Si wafer surface. The termite cuticle demonstrated higher adhesive interactions with all particles in comparison to those measured on the plant hopper.

Adsorption Behavior of Hydrophobin and Hydrophobin/Surfactant Mixtures at the Solid–Solution Interface

The adsorption of surface-active protein hydrophobin, HFBII, and HFBII/surfactant mixtures at the solid-solution interface has been studied by neutron reflectivity, NR. At the hydrophilic silicon surface, HFBII adsorbs reversibly in the form of a bilayer at the interface. HFBII adsorption dominates the coadsorption of HFBII with cationic and anionic surfactants hexadecyltrimethyl ammonium bromide, CTAB, and sodium dodecyl sulfate, SDS, at concentrations below the critical micellar concentration, cmc, of conventional cosurfactants. For surfactant concentrations above the cmc, HFBII/surfactant solution complex formation dominates and there is little HFBII adsorption. Above the cmc, CTAB replaces HFBII at the interface, but for SDS, there is no affinity for the anionic silicon surface hence there is no resultant adsorption. HFBII adsorbs onto a hydrophobic surface (established by an octadecyl trimethyl silane, OTS, layer on silicon) irreversibly as a monolayer, similar to what is observed at the air-water interface but with a different orientation at the interface. Below the cmc, SDS and CTAB have little impact upon the adsorbed layer of HFBII. For concentrations above the cmc, conventional surfactants (CTAB and SDS) displace most of the HFBII at the interface. For nonionic surfactant C(12)E(6), the pattern of adsorption is slightly different, and although some coadsorption at the interface takes place, C(12)E(6) has little impact on the HFBII adsorption.

In Vitro Dissolution Methods for Hydrophilic and Hydrophobic Porous Silicon Microparticles

Porous silicon (PSi) is an innovative inorganic material that has been recently developed for various drug delivery systems. For example, hydrophilic and hydrophobic PSi microparticles have been utilized to improve the dissolution rate of poorly soluble drugs and to sustain peptide delivery. Previously, the well-plate method has been demonstrated to be a suitable in vitro dissolution method for hydrophilic PSi particles but it was not applicable to poorly wetting hydrophobic thermally hydrocarbonized PSi (THCPSi) particles. In this work, three different in vitro dissolution techniques, namely centrifuge, USP Apparatus 1 (basket) and well-plate methods were compared by using hydrophilic thermally carbonized PSi (TCPSi) microparticles loaded with poorly soluble ibuprofen or freely soluble antipyrine. All the methods showed a fast and complete or nearly complete release of both model compounds from the TCPSi microparticles indicating that all methods described in vitro dissolution equally. Based on these results, the centrifuge method was chosen to study the release of a peptide (ghrelin antagonist) from the THCPSi microparticles since it requires small sample amounts and achieves good particle suspendability. Sustained peptide release from the THCPSi microparticles was observed, which is in agreement with an earlier in vivo study. In conclusion, the centrifuge method was demonstrated to be a suitable tool for the evaluation of drug release from hydrophobic THCPSi particles, and the sustained peptide release from THCPSi microparticles was detected.

Fabrication of highly ordered nanoscale poly (lactic acid) surface based on self-assembled silica microspheres

A simple process was developed to fabricate poly (lactic acid) (PLA) film possessing a highly ordered nanoscale surface. For the first step, an array of silica microspheres was prepared by self-assembly on a completely hydrophilic silicon wafer. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) images showed that a highly ordered array was formed, and then this array was used as the template for fabricating polymer film with highly ordered nanoscale surface. Next, a PLA solution was spin coated on the template. After solidifying, silica microspheres were embedded in the thin layer of PLA, maintaining their highly organized structures. Finally, silica microspheres were etched away by hydrofluoric acid, and only the PLA film with a close-packed hexagonally pattern structure was left on the silicon wafer substrate.