Nanostructured Ion-Selective MCM-48 Membranes

Templated MCM-48 silica was prepared using CTAB as surfactant. The MCM-48 powders and thin films were characterized by different techniques. MCM-48 layers were deposited on macroporous α-alumina supports and silicon nitride microsieves. The water permeability of MCM-48 was compared with the permeability of conventional mesoporous γ-alumina membranes. The applicability of MCM-48 as ion-selective electric field-driven switchable interconnect for microfluidic devices was demonstrated.     

Dendritic structures of poly(ethylene glycol) on silicon nitride and gold surfaces

A hydrophilic silicon nitride surface was grafted with poly(ethylene glycol) monomethyl ether (average formula weight of 5000 Da) in a one-step protocol. The domains of stable dendritic structures of self-assembled monolayer islands on a silicon nitride surface were observed with atomic force microscopy. The moduli of elasticity of these dendritic structures in air and in KCl aqueous solution were compared. The value of the Young's modulus of these structures is reduced by more than 3 orders of magnitude, from approximately 12 GPa measured in air to approximately 5 MPa in KCl solution. This dramatic reduction in elasticity was attributed to the swelling of the dendritic structures in aqueous solution, which was verified by the increased film thickness. These dendritic structures were not stable in the aqueous environment and could be removed by soaking in water for 22 h because of the hydrolysis of the silicate bonds. This fact was confirmed by the reduction of the C1s signal in the X-ray photoelectron spectroscopy experiments. These morphologies are not unique to silicon nitride substrate; similar features were also observed for thiolated poly(ethylene glycol) monomethyl ether molecules absorbed on a gold surface.     

Role of poly(diallyldimethylammonium chloride) in selective polishing of polysilicon over silicon dioxide and silicon nitride films

A cationic polymer, poly(diallyldimethylammonium chloride), or PDADMAC (MW ≈ 200,000), at a concentration of 250 ppm was used to enhance polysilicon removal rates (RRs) to ～600 nm/min while simultaneously suppressing both silicon dioxide and silicon nitride RRs to <1 nm/min, both in the absence or in the presence of ceria or silica abrasives during chemical mechanical polishing (CMP). These results suggest that aqueous abrasive-free solutions of PDADMAC are very attractive candidates for several front-end-of-line (FEOL) CMP processes. Possible mechanisms for the enhancement of poly-Si RR and the suppression of oxide and nitride RRs are proposed on the basis of the RRs, contact angle data on poly-Si films, zeta potentials of polishing pads, polysilicon films, silicon nitride particles, and silica and ceria abrasives, thermogravimetric analysis, and UV-vis spectroscopy data.     

Structure and protein binding capacity of a planar PAA brush

We performed neutron reflectometry (NR) and total internal reflection fluorescence (TIRF) spectroscopy to characterize the structure and the protein binding capacity of a planar poly(acrylic acid) (PAA) brush at different temperatures. A PAA brush was prepared by spin-coating planar quartz or silicon wafers with a thin film of poly(styrene). Then, the diblock copolymer poly(styrene)-poly(acrylic acid) was deposited on these modified wafers using the Langmuir-Sch?fer or Langmuir-Blodgett technique. PAA grafting densities of about 0.1 chains per nm2 were obtained. The NR experiments indicate a remarkable swelling of the PAA brush in contact with a buffer solution, when it is heated to 40 degrees C for several hours. The swollen brush structure remains upon cooling back to 20 degrees C suggesting a disentanglement of the initially formed PAA brush by the temporary heating. At pD = 6.7, the protein bovine serum albumin (BSA) with a negative net charge is strongly adsorbed to the swollen PAA brush. From the scattering length density profiles obtained from the NR curves, an almost homogeneous filling of the whole PAA brush space with BSA molecules can be deduced corresponding to an average BSA volume fraction of about 7-10% and an adsorbed protein mass of about 1.4 mg m-2. By analyzing the TIRF experiments, it is found that BSA adsorption is enhanced when increasing the temperature which represents an evidence for an entropic driving force for protein adsorption. However, the mechanism of BSA adsorption at a PAA brush appears to be different at 20 and 40 degrees C.     

Synthesis and properties of fluorine‐containing amphiphilic graft copolymer P(HFMA)‐g‐P(SPEG)

A series of amphiphilic graft copolymers P(HFMA)‐g‐P(SPEG) comprising poly(hexafluorobutyl methacrylate) (PHFMA) backbones and poly(ethylene glycol) (PEG) side chains were synthesized by copolymerization of HFMA and SPEG macromonomer with the p‐vinylbenzyl end group. The SPEG macromonomer was synthesized by reacting Methoxy poly(ethylene glycol) (MPEG) with p‐chloromethylstyrene in THF in the presence of NaH. The macromonomer and amphiphilic graft copolymer were characterized by FTIR, ¹H NMR, ¹⁹F NMR, and gel permeation chromatography (GPC). The critical micelle concentration (CMC) of the amphiphilic graft copolymer was measured by surface tension technique. The results showed that the CMC decreased with increasing HFMA contents in the graft copolymers. The interaction between P(HFMA)‐g‐P(SPEG) and bovine serum albumin (BSA) was studied by fluorescence spectroscopy, transmission electron microscopy (TEM), and photon correlation spectroscopy (PCS). The fluorescence spectrum showed that the fluorescence intensity of BSA increased with increasing content of HFMA in P(HFMA)‐g‐P(SPEG) and concentration of P(HFMA)‐g‐P(SPEG) in the P(HFMA)‐g‐P(SPEG)/BSA solution. TEM micrographs showed that P(HFMA)‐g‐P(SPEG) mainly formed core‐shell structure micelles. When BSA was added, the micelles changed from a core‐shell structure into a worm‐like, vesicle‐like and hollow‐like structure with different initial concentrations of the copolymer. The size distribution of the micelles increased proving that the copolymer micelles encapsulated the bovine serum albumin. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4895–4907, 2009     

Choose sides: differential polymer adhesion

AFM-based single molecule desorption measurements were performed on surface end-grafted poly(acrylic acid) monolayers as a function of the pH of the aqueous buffer to study the adhesion properties of polymers that bridge two surfaces. These properties were found to depend on the adhesion forces of both surfaces in a differential manner, which is explained with a simple model in analogy to the Bell-Evans formalism used in dynamic force spectroscopy. The measured interaction forces between the poly(acrylic acid) chains and silicon nitride AFM tips depend on the grafting density of the polymer monolayers as well as on the contour length of the polymer chains. This study demonstrates that the stability of polymer bridges is determined by the adhesion strengths on both surfaces, which can be tuned by using pH-dependent polyelectrolyte monolayers.     

化学转化-气相色谱法测定氮化硅中的游离硅

建立了用化学转化－气相色谱法测定氮化硅中游离硅的分析方法。游离硅和氮化硅与熔融的氢化钠反应,排出氢,氨和少量二氧化碳和水蒸汽。吸收除去氨、二氧化碳和水蒸汽后,用热导检测器检测氢。方法简便,准确,平均回收率为９６％,相对标准偏差〈５％。     

Oligonary Nitrides and Oxonitrides of Si,P, Al,and B in Combination with Rare Earth or Transition Metals as well as Molecular Precursor Compounds with Nitrido Bridges M‐N‐Si (M = Ti,Zr, Hf,W, Sn)

A novel synthetic approach is presented leading to hitherto unknown nitridosilicates, oxonitridosilicates, oxonitridoaluminosilicates, carbidonitridosilicates, as well as nitridoborates and oxonitridoborates of rare earth elements, alkali, and alkaline earth metals. Typically, the respective metals were reacted with silicon diimide, aluminum nitride, or poly(boron amide imide), respectively, under pure nitrogen atmosphere utilizing a radiofrequency furnace. Usually, the compounds are obtained within short reaction periods as coarsely crystalline products. Zink nitridophosphates of the sodalite structure type were obtained by the reaction of phosphorus nitride imide with zinc or zinc chalcogenides, respectively. Several molecular metal silylamides and imides containing nitridobridges between the metals and silicon were obtained by the reaction of differently chlorinated disilazanes with metal chlorides. During these investigations hitherto unknown bis(trimethylsilyl)ammonium salts have been discovered. Furthermore, we report about the synthesis of N‐silyl metal hydrazides.     

Kinetics and mechanism of oxidation of silicon nitride bonded silicon carbide ceramic

Thermogravimetry (TG) has been used to study the oxidation of a commercial silicon nitride bonded silicon carbide (SNBSC) ceramic. The oxidation was studied in air and carbon dioxide atmospheres between 800 and 1300°C. TG/mass spectrometry (MS) shows that the silicon nitride bonding phase oxidises first. The kinetics follow a multi-stage mechanism with diffusion control. Carbon dioxide was found to be a more powerful oxidant than air at temperatures above 1050°C.     

AFM study of forces between silica, silicon nitride and polyurethane pads

Interaction of silica and silicon nitride with polyurethane surfaces is rather poorly studied despite being of great interest for modern semiconductor industry, e.g., for chemical-mechanical planarization (CMP) processes. Here we show the results from the application of the atomic force microscopy (AFM) technique to study the forces between silica or silicon nitride (AFM tips) and polyurethane surfaces in aqueous solutions of different acidity. The polyurethane surface potentials are derived from the measured AFM data. The obtained potentials are in rather good agreement with measurements of zeta-potentials using the streaming-potentials method. Another important parameter, adhesion, is also measured. While the surface potentials of silica are well known, there are ambiguous results on the potentials of silicon nitride that is naturally oxidized. Deriving the surface potential of the naturally oxidized silicon nitride from our measurements, we show that it is not oxidized to silica despite some earlier published expectations.     

Temperature-dependent intermolecular force measurement of poly(N-isopropylacrylamide) grafted surface with protein

We have investigated the temperature dependence of the intermolecular force between poly(N-isopropylacrylamide) (PNiPAM) grafted surface and bovine serum albumin (BSA) in phosphate buffer (pH 7.4) using atomic force microscopy at the nanonewton scale. These observations show that the interaction force is nearly zero below the phase transition temperature of PNiPAM and that it increases steeply during the phase transition. Since the PNiPAM chains are grafted onto the aminosilane (gamma-aminopropyltriethoxysilane)-treated silicon wafer, we measured the force-distance curve of BSA-immobilized tips for the bare and the aminosilane-treated silicon wafer. These surfaces show no temperature dependence and their values are different from those of the PNiPAM-grafted surfaces at 30 degrees C. The results indicate that the measured adhesion force is between the PNiPAM-grafted surface and the BSA-immobilized tip. Our studies on the intermolecular force between other surfaces (CH(3)- and COOH-terminated self-assembled monolayers) and the BSA-immobilized tip indicate that the variation in the intermolecular force between the PNiPAM surface and BSA with temperature can be attributed to the changes in the properties of the PNiPAM chains. From consideration of the PNiPAM phase transition mechanism, it is speculated that the intermolecular force between the PNiPAM-grafted surface and BSA would be affected by changes in the arrangement of the bound water molecules around the PNiPAM chain and by changes in the conformation (i.e., in the chain mobility) of the PNiPAM chain during the phase transition.     

Influence of Pressure on SiNx:H Film by LF-PECVD

Hydrogenated silicon nitride films as an effective antireflection and passivation coating of silicon solar cell were prepared on p-type polished silicon substrate (1.0 Ωcm) by direct LF-PECVD (low frequency plasma enhanced chemical vapor deposition) of Centrotherm. The preferable passivation effect was obtained and the refractive index was in the range of 2.017-2.082. The refractive index of the hydrogenated silicon nitride films became larger with the increase of the pressure. Fourier transform infrared spectroscopy was used to study the pressure influence on the film structural properties. The results highlighted highhydrogen bond and high Si-N bonds density in the film, which were greatly influenced by the pressure. The passivation effect of the films was influenced by the Si dangling bonds density. Finally the effective minority liftetime degradation with time was shown and discussed by considering the relationship between the structural properties and passivation.     

Silicon Dioxide Coating of Titanium Dioxide Nanoparticles from Dielectric Barrier Discharge in a Gaseous Mixture of Silane and Nitrogen

The coating of titanium dioxide nanoparticles with silicon dioxide has been carried out by dielectric barrier discharge (DBD) plasma treatments to enhance the thermostability of Titania for applications at high temperature processes. During the first coating processing step, a closed film of silicon nitride was produced via plasma treatment in a gaseous mixture of silane and nitrogen, while atmospheric surface contaminations got mainly removed. In the second processing step, the DBD plasma treatment in oxygen or air was used to convert the silicon nitride mainly into silicon dioxide. Remaining carbon impurities at the interfaces between titanium dioxide and silicon nitride after the nitrogen/silane plasma treatment were subsequently removed simultaneously. Atomic force microscopy and X-ray photoelectron spectroscopy were employed to study the DBD plasma treatments of the TiO₂ nanoparticles.     

Grafting BSA onto poly[(L-lactide)-co-carbonate] microspheres by click chemistry

Model protein bovine serum albumin (BSA) was covalently grafted onto poly[(L-lactide)-co-carbonate] microsphere surfaces by "click chemistry." The grafting was confirmed by confocal laser scanning microscopy and X-ray photoelectron spectroscopy. The maximum amount of surface-grafted BSA was 45 mg x g(-1). The secondary structure of the grafted BSA was analyzed by FTIR and the results demonstrated that the grafting did not affect protein structure. This strategy can also be used on microspheres prepared from poly(L-lactide)/poly[(L-lactide)-co-carbonate] blend materials.     

High density cationic polymer brushes from combined “click chemistry” and RAFT‐mediated polymerization

A simple method for preparing cationic poly[(ar‐vinylbenzyl)trimethylammonium chloride)] [poly(VBTAC)] brushes was used by combined technology of “click chemistry” and reversible addition‐fragmentation chain transfer (RAFT) polymerization. Initially, silicon surfaces were modified with RAFT chain transfer agent by using a click reaction involving an azide‐modified silicon wafer and alkyne‐terminated 4‐cyanopentanoic acid dithiobenzoate (CPAD). A series of poly(VBTAC) brushes on silicon surface with different molecular weights, thicknesses, and grafting densities were then synthesized by RAFT‐mediated polymerization from the surface immobilized CPAD. The immobilization of CPAD on the silicon wafer and the subsequent polymer formation were characterized by X‐ray photoelectron spectroscopy, water contact angle measurements, grazing angle‐Fourier transform infrared spectroscopy, atomic force microscopy, and ellipsometry analysis. The addition of free CPAD was required for the formation of well‐defined polymer brushes, which subsequently resulted in the presence of free polymer chains in solution. The free polymer chains were isolated and used to estimate the molecular weights and polydispersity index of chains attached to the surface. In addition, by varying the polymerization time, we were able to obtain poly(VBTAC) brushes with grafting density up to 0.78 chains/nm² with homogeneous distributions of apparent needle‐like structures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Preparation of SiBN films deposited by MOCVD

SiBN films were prepared by the MOCVD method using triethylsilane and triethylboron as source materials. The SiBN films were a mixture of boron nitride and silicon nitride determined by IR spectra. The relationship between the ratio of mixture and the preparation condition is clarified. The ratio of silicon nitride to boron nitride in the films was proportional to the ratio of triethylsilane to triethylboron under a large excess of ammonia flow condition. The reaction temperature also influenced the ratio of boron nitride and silicon nitride in the films. The deposition rate of the film increased up to 800°C with a maximum at 1000°C, and decreased up to 1300°C with small value. The crystallinity of SiBN films was very poor because the crystal growth was obstructed.     

Determination of sulfonamides in bovine milk with column-switching high performance liquid chromatography using surface imprinted silica with hydrophilic external layer as restricted access and selective extraction material

A novel restricted access-molecularly imprinted material (RA-MIP) with selectivity for sulfonamides was synthesized using initiator-transfer agent-terminator (iniferter) method, a "living"/controlled radical polymerization technique. The material was prepared by grafting two layers with different functions on the silica support. To perform a "grafting from" polymerization, iniferter was immobilized on the surface of silica. The internal sulfamethazine imprinted polymer and the external poly(glycidyl methacrylate) [poly(GMA)] were then grafted successively. The hydrophilic structures were formed on the external layer of the material by the hydrolysis of the linear poly(GMA) for protein removal. The result has shown that this restricted access-MIP grafted silica (RA-MIP-SG) not only has the selectivity for the template and its analog, but also has the ability of exclusion for bovine serum albumin (BSA). It indicated that the material possesses both properties of molecularly imprinted polymer (MIP) and restricted access material (RAM). Using RA-MIP-SG as pre-column, a column-switching HPLC method was established for the determination of sulfonamides in bovine milk. Direct sample injection was performed in the analysis, which provides a convenient analytical procedure. Good linearity in the range of 2-400 ng mL(-1) (R>0.998) has been obtained for seven sulfonamides in the study. The recoveries of all the analytes at three concentration levels are between 93% and 107% with the RSD<8.0%. The limits of quantification and limits of detection are less than or equal to 2.7 ng mL(-1) and 0.8 ng mL(-1) respectively. It demonstrated this RA-MIP-SG can be applied in sample extraction and clean-up for the determination of sulfonamides in bovine milk by direct injection and column-switching HPLC with good efficiency and reliability.     

Multilayers and poly(allylamine hydrochloride)-graft-poly(ethylene glycol) modified bovine serum albumin nanoparticles: Improved stability and pH-responsive drug delivery

To improve the colloidal stability of bovine serum albumin(BSA) nanoparticles(NPs) in diverse mediums, poly(allylamine hydrochloride)(PAH)/sodium poly(4-styrene sulfonate)(PSS) multilayers and poly(allylamine hydrochloride)-graft-poly(ethylene glycol)(PAH-g-PEG) coating were coated on the surface of BSA NPs.Stabilities of the BSA NPs in diverse mediums with different surfaces were detected by dynamic light scattering(DLS).Multilayers and PAH-g-PEG coated BSA NPs can be well dispersed in various mediums with a narrow polydispersity index(PDI).The BSA NPs with the highest surface density of PEG show the best stability.The multilayers and PAH-g-PEG coating do not deter the pH-dependent loading and release property of BSA NPs.At pH 9,the encapsulation efficiency of doxorubicin reaches almost 99%,and the release rate at pH 5.5 is significantly higher than that at pH 7.4.     

High-Performance Gel-Permeation Chromatography of Bovine Skim Milk Proteins

Abstract

The separation of bovine skim milk proteins by gel-permeation high performance liquid chromatography was examined. Toya-Soda TSK-GEL (Type SW) columns were used with an eluent of .05 M phosphate buffer (pH 6.80) containing .1 M sodium sulfate at .5 ml/min. Bovine whole milk was centrifuged to remove lipids, and the resultant skim milk directly injected. A 2000SW column yielded three protein peaks: 1 = casein, IgG and BSA; 2 = 6-lactoglobulins and BSA; and 3 = α-lactalbumin and BSA. A 3000SW plus 2000SW column system with a 30 μl injection volume yielded four protein peaks: 1 = minor amounts of α - and β-casein; 2 = casein, BSA and IgG; 3 = β-lactoglobulins; and 4 = α¹-lactalbumin. A 3000SW plus 2000SW column system with a 10 μl injection volume yielded five protein peaks: 1 = casein; 2 = IgG; 3 = BSA; 4 = β-lactoglobulins; and 5 = α-lactalbumin. Both the single column and dual column applications yielded three nonprotein peaks, which were dialyzed from solution. Thus, a high speed analytical separation of milk proteins was achieved according to molecular size, but this application is highly dependent on sample size.     

Room-temperature ferromagnetism in silicon oxide/silicon nitride composite films

Room-temperature ferromagnetism has been observed in silicon oxide/silicon nitride composite films formed on Si substrates at different substrate temperatures, and the ferromagnetic properties of the samples have been found to depend on the silicon nitride content of the films. It is proposed that the ferromagnetism is related to the interface states between the silicon oxide particles and silicon nitride particles. The saturation magnetization (M_S) reached its maximum value in the film produced at a substrate temperature of 400 °C. A further study on the magnetic properties of the film has been carried out using first-principles calculations based on the density functional theory. The calculations suggest that the magnetic moments of the film originate from N 2p and Si 2p states in the vicinity of the hetoro-interface.