Novel organosiloxane vapor annealing process for improving properties of porous low-k films

A novel 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS)-vapor annealing method was developed for improving the mechanical strength of porous silica films with a low dielectric constant. TMCTS molecules react with Si-OH groups on the pore wall surfaces to form the polymer network which results in the high hydrophobicity and reinforcement of the silica wall. This method can be used to recover plasma damages induced by etching and ashing in fabricating Cu/low-k interconnects.     

Surface modified amorphous titanosilicate catalysts for liquid phase epoxidation

Titanium-containing mesoporous silica has been prepared by silylation of mixed oxides obtained via sol–gel method. These samples displayed enhanced activity in the epoxidation of styrene with Bu^tOOH in comparison to normal xerogels or other titanium-containing catalytic systems. The influence of the extension of the silylation reaction, as well as the use of different silylating agents, have been investigated. Samples were characterised by FTIR, XRF, ²⁹Si-MAS NMR, diffuse reflectance UV–Vis and N₂ adsorption–desorption isotherms, X-ray photoelectron spectroscopy (XPS) and FTIR of adsorbed deuteroacetonitrile. The improvement in the catalytic activity achieved has been related to the removal of OH groups by means of calcination or silylation treatments.     

Epoxidation of n-hexene and cyclohexene over titanium-containing catalysts

TS-1, Ti-beta and Ti-MCM-41 molecular sieves have been prepared by direct hydrothermal synthesis method and applied to the epoxidation of n-hexene and cyclohexene with H₂O₂ under mild conditions. Ti-beta with extremely low Al content was synthesized by using a seed method to suppress the formation of diol produced by Brønsted acid sites present in Ti-beta. It was also found that a large amount of by-products (1-ol and 1-one) formed over hydrophilic Ti-MCM-41. We further modified Ti-MCM-41 by silylation with bis(trimethylsilyl) trifluoroacetamide (BSTFA). Among these catalysts, the Ti-beta with low content of Al enhanced the yield of epoxide and suppressed the formation of diol markedly. The silylated Ti-MCM-41 reduced the formation of by-products and promoted the yields of epoxide significantly. Based on experimental results, a reaction mechanism with two parallel and competitive reactions was proposed.     

Effect of covalently bonded polysiloxane multilayers on the electrochemical behavior of graphite electrode in lithium ion batteries

Polysiloxane multilayers were covalently bonded to the surface of natural graphite particles via diazonium chemistry and silylation reaction. The as-prepared graphite exhibited excellent discharge–charge behavior as negative electrode materials in lithium ion batteries. The improvement in the electrochemical performance of the graphite electrodes was attributed to the formation of a stable and flexible passive film on their surfaces. It was also revealed that the chemical compositions of the multilayers exerted influence on the electrochemical behavior of the graphite electrodes. The result of this study presents a new strategy to the formation of elastic and strong passive film on the graphite electrode via molecular design. Owing to the diversity of polysilxoane multilayers, this method also enables researchers to control the surface chemistries of carbonaceous materials with flexibility.     

Determination of phenolic compounds in aromatic plants by RP-HPLC and GC-MS

It is well known that phenolic compounds are constituents of many plants and herbs, and they have attracted a great deal of public and scientific interest because of their health-promoting effects as antioxidants. Five plants, Vitex agnus-castus (Verbenaceae), Origanum dictamnus (Lamiaceae), Teucrium polium (Lamiaceae), Lavandula vera (Lamiaceae) and Lippia triphylla (Verbenaceae), were examined in order to determine their phenolic composition. Reversed phase high performance liquid chromatography was employed for the identification and quantification of phenolic compounds. Gas chromatography–mass spectometry(GC-MS) was also used for identification of phenolic compounds after silylation. Analysis of the non-volatile and thermolabile phenolic compounds by GC-MS presupposes their conversion into volatile and thermotolerant derivatives. The derivatization process was optimized against reagents, temperature and reaction time. A large excess of N,O-bis(trimethylsilyl)trifluoroacetamide containing trimethylchlorosilane proved to be the best derivatization reagent to convert analytes into volatile trimethylsilyl derivatives. The most abundant phenolic compounds detected were caffeic acid (0.12–0.93 mg 100 g⁻¹ dry sample), ferulic acid (0.34–1.52 mg 100 g⁻¹ dry sample), and (+)-catechin (0.22–0.43 mg 100 g⁻¹ dry sample).     

Patterning of organic layers using negative and positive working Top-CARL process

The Top-CARL process is a technique for patterning organic materials some tens of microns thick by top-resist silylation and pattern transfer via oxygen reactive ion etching. The influence of exposure dose, temperature and top-resist layer thickness on the silylation process is studied. A dyed version of the resist is examined. Its polarity can be changed from negative to positive working by addition of a small amount of a photo base.     

Silylation of hyaluronan to improve hydrophobicity and reactivity for improved processing and derivatization

A novel hyaluronan (HA) derivative was synthesized through silylation reaction to improve the hydrophobicity of HA, to enhance its solubility in common organic solvents, and to make it more reactive for further derivatizations (e.g. esterification). While HA can not be silylated directly, its ion-paired complex with a long aliphatic chain quaternary ammonium salt (HA-CTA) was an effective starting material for the silylation reaction. The degree of silylation (DS) was controlled by changing the reaction parameters such as temperature, time and amount of silylation reagent. Silylated HA-CTA with a high DS (>3.2) was soluble in xylenes and hexane, while that with a low DS (3.2>DS>2.5) was only soluble in acetone, THF and 1,2-dichloroethane. The silyl groups and ammonium cations were also easily removed through hydrolysis to regenerate the native HA.     

Repair of plasma-damaged p-SiOCH dielectric films in supercritical CO2

The silylation of plasma-damaged p-SiOCH low-k dielectric films was investigated with trimethychlorosilane (TMCS), hexamethyldisilazane (HMDS) and dimethyldichlorosilane (DMDCS) dissolved in supercritical CO₂ (scCO₂) and the effect of thermal pre-treatment on the repair performance was also studied. The surface hydrophobicity was rapidly recovered by silylation and the order of recovery efficiency was HMDS (85.4°) > DMDCS (83.4°) > TMCS (75.0°). The FTIR analyses revealed that the restoration to the original state was not achieved over various reaction conditions (up to 31 MPa, 85 °C, and 3 h reaction time). After pre-treatment in a vacuum cell at 250 °C, the Si-O-Si peak intensity increased slightly, and the surface hydrophobicity was partially recovered to 54.4° due to the removal of physically adsorbed H₂O molecules as well as some extent of dehydration of neighboring surface silanol groups. The hydrophobicity increased to 84.4° after subsequent treatment with HMDS in scCO₂. From DSIMS, the carbon concentration did not increase in bulk region after silylation of thermally pre-treated low-k films.     

Fabrication of hydrophobic surface with hierarchical structure on Mg alloy and its corrosion resistance

A hydrotalcite/hydromagnesite conversion coating with hierarchical structure has been fabricated on a Mg alloy substrate by in situ hydrothermal crystallization method. A MgO layer existing between the hydrotalcite/hydromagnesite film and the substrate was formed prior to the hydrotalcite/hydromagnesite film during the crystallization process. After surface treatment with silane coupling agent, the surface of conversion coating changes from hydrophilic to hydrophobic. Scanning electron microscopy (SEM) revealed that the silylated conversion coating with hierarchical structure maintains the original rough surface of which was composed of numerous micro-scale flakes and beautiful flower-like protrusions. Polarization measurements have shown that the hydrophobic conversion coating exhibited a low corrosion current density value of 0.432 μA/cm², which means that the hydrophobic conversion coating can effectively protect Mg alloy from corrosion. Electrochemical impedance spectroscopy (EIS) showed that the impedance of the hydrophobic conversion coating was 9000 Ω. It means that the coating served as a passive layer with high charge transfer resistance.     

Controlled silylation of montmorillonite and its polyethylene nanocomposites

An alkylammonium modified montmorillonite, Cloisite 20A, was reacted with trimethylchlorosilane in order to replace the edge hydroxyl groups of the clay. Since the reaction will liberate HCl, reactions were performed both in the presence and absence of sodium hydrogencarbonate. Without sodium hydrogencarbonate, the proton, which was generated in situ, could replace a portion of the alkylammonium ions and further react with trimethylchlorosilane. The product, TMS-20H, has a smaller basal spacing than Cloisite 20A itself. If the proton was trapped by the hydrogencarbonate ions, only the edge silanol groups react with trimethylchlorosilane. The product, TMS-20A, maintained the same basal spacing as the precursor. The presence of the edge trimethylsilyl groups were confirmed by thermogravimetric analysis and infrared spectroscopy. Intercalated polyethylene nanocomposite could be fabricated by melt blending polyethylene with TMS-20A, while only microcomposites could be formed using TMS-20H. The structure of the hybrid was characterized by X-ray diffraction and transmission electron microscopy.