K. L. Tan

Plasma-induced immobilization of poly(ethylene glycol) onto poly(vinylidene fluoride) microporous membrane

Abstract Poly(vinylidene fluoride) (PVDF) microporous membranes with surface-immobilized poly(ethylene glycol) (PEG) were prepared by the argon plasma-induced grafting of PEG. The PEG was pre-coated on the membrane surface, including the pore surfaces, by dipping the membrane in a PEG/CHCl3 solution prior to the argon plasma exposure. The microstructure and composition of the PEG-grafted PVDF (PEG-g-PVDF) membranes were characterized by attenuated total reflectance (ATR) FT-IR, X-ray photoelectron spectroscopy (XPS), and thermogravimetric (TG) analysis. A moderate radio-frequency (RF) plasma power and plasma treatment time led to a high concentration of the grafted PEG polymer. The morphology of the modified membranes was studied by scanning electronic microscope (SEM). The pore size and water flux of the modified membranes were also characterized. The flux decreased with increasing surface concentration of the grafted PEG polymer, while the pore size remained almost unchanged. Protein adsorption experiments revealed that the PEG-g-PVDF membranes with a PEG graft concentration, defined as the [CO]/[CF2] ratio above 3.2 exhibited good anti-fouling property.

Surface modification of stainless steel by grafting of poly(ethylene glycol) for reduction in protein adsorption.

The surface of stainless steel was first modified by the silane coupling agent (SCA), (3-mercaptopropyl)trimethoxysilane. The silanized stainless-steel surface (SCA-SS surface) was subsequently activated by argon plasma and then subjected to UV-induced graft polymerization of poly(ethylene glycol)methacrylate (PEGMA). The chemical structures and composition of the pristine, silane-treated, plasma-treated and PEGMA graft-polymerized stainless-steel coupon surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. The graft polymerization of PEGMA onto the plasma-pretreated SCA-SS surface was studied with different argon plasma pretreatment time, macromonomer concentration, and UV graft polymerization time. In general, a brief plasma pretreatment, high PEGMA concentration, and long UV graft polymerization time readily resulted in a high graft concentration. The PEGMA graft-polymerized stainless-steel coupon (PEGMA-g-SCA-SS) with a high graft concentration, and thus a high PEG content, was found to be very effective in preventing bovine serum albumin and gamma-globulin adsorption.

Electrochemical impedance and X-ray photoelectron spectroscopic studies of the inhibition of mild steel corrosion in acids by cyclohexylamine

The inhibition of mild steel corrosion in 0.5 M H2SO4 by simple amines (cyclohexylamine, pyridine, triethylamine) was investigated by dc polarization, electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The results indicate a strong dependence of the inhibition performance on the nature of the metal surface, in addition to the structural effects of amines. Inhibition is accomplished by amine adsorption on the metal surface without detectable changes in the chemistry of corrosion. Adsorption is predominantly chemisorptive in the active region and by hydrogen bond formation in the passive region. Amine molecules with delocalized π electrons or high electron densities at their nitrogen atoms are effective inhibitors in the active region. The effectiveness for corrosion control in the passive region, however, is proportional to the number of NH linkages in the amine molecules.

Synthesis, characterization and anti-fouling properties of poly(ethylene glycol) grafted poly(vinylidene fluoride) copolymer membranes

Methoxypoly(ethylene glycol) monomethacrylate (PEGMA) graft-copolymerized poly(vinylidene fluoride) (PVDF) (the P(PEGMA)-graft-PVDF copolymer) was synthesized. The PVDF homopolymer in N-methyl-2-pyrrolidone (NMP) solution was first pretreated with ozone and the peroxide content of the ozone-treated PVDF was determined by assaying with 2,2-diphenyl-1-picrylhydrazyl (DPPH). The activated PVDF was then subjected to graft copolymerization with the PEGMA macromonomer in NMP. The microstructures and compositions of the P(PEGMA)-graft-PVDF copolymers were characterized by FT-IR, X-ray photoelectron spectroscopy (XPS), elemental analysis, differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. Ultra-filtration (UF) membranes were prepared from the P(PEGMA)-graft-PVDF copolymer by the phase-inversion method. The bulk and the surface compositions of the membranes were determined by elemental analysis and XPS, respectively. In general, the graft concentration increases with the PEGMA macromonomer concentration. Angle-resolved XPS analyses of the UF membranes prepared from the copolymer revealed a substantial surface enrichment of the hydrophilic PEGMA component. The morphology of the membranes was studied using scanning electron microscopy (SEM). The UF membrane prepared from the P(PEGMA)-graft-PVDF copolymer with a graft concentration ([PEGMA]/[CH 2 CF 2 ] ratio) above 0.06 was effective in preventing bovine serum albumin (BSA) adsorption.

Sulfur-Induced PtSi:C/Si:C Schottky Barrier Height Lowering for Realizing N-Channel FinFETs With Reduced External Resistance

In this letter, sulfur (S) segregation was exploited to attain a record-low electron barrier height (PhiB N) of 110 meV for platinum-based silicide contacts. Sulfur-incorporated PtSi:C/Si:C contacts were also demonstrated in strained FinFETs with Si:C source/drain stressors. Incorporation of sulfur at the PtSi:C/Si:C interface in the source/drain regions of FinFETs provides a 51% improvement in external resistances and a 45% enhancement in drive current as compared to devices without S segregation. The remarkable reduction in PhiB N is explained using charge transfer and dipole formation at the silicide/semiconductor interface with S segregation.

Covalent immobilization of invertase onto the surface-modified polyaniline from graft copolymerization with acrylic acid

Abstract Invertase was covalently immobilized on the emeraldine (EM) base form of polyaniline (PAN) films and powders with surface-grafted acrylic acid (AAc) polymer. The immobilization proceeded via the amide linkage formation between the amino groups of invertase and the carboxyl groups of the grafted AAc polymer chains on EM in the presence of a water-soluble carbodiimide. The surface structure and composition of the grafted–modified and enzyme-functionalized EM base were characterized by X-ray photoelectron spectroscopy (XPS). It was found that the amount of immobilized invertase increased linearly with the concentration of surface-grafted AAc polymer chains. EM powders could be graft-modified and enzyme-functionalized more effectively than EM films. The decrease in activity of the immobilized invertase was considered to be due to, among other factors, the reduced accessibility of substrate molecules to the active sites of the enzyme and the conformational change of the invertase molecules as a result of the covalent immobilization. However, the immobilized enzyme was less sensitive to temperature deactivation below the optimum temperature as compared to that of the free form. The optimum pH value of invertase was not affected by the immobilization reaction, but the pH stability range was broadened. The immobilized invertase also exhibited a significantly improved stability during storage in buffer solution over that of the free enzyme.

The chemical nature of the nitrogens in polypyrrole and polyaniline: A comparative study by x‐ray photoelectron spectroscopy

The chemical nature of the nitrogens corresponding to various intrinsic redox states of polypyrrole (PPY) and polyaniline (PAN) has been critically compared using x‐ray photoelectron spectroscopy (XPS) as a primary tool. Proton modifications of nitrogens in PPY give rise to a number of intrinsic redox states analogous to those observed in PAN. The behavior of the corresponding oxidation states in both polymers towards oxidation/reduction, deprotonation/reprotonation, or charge–transfer interactions with electron acceptors are grossly similar. However, the nitrogens of the two oxidized polymer complexes do differ in their thermal degradation behavior which suggests that the oxidized pyrrolylium nitrogens are more susceptible to deprotonation than their oxidized counterparts.

Preparation of polyanilines doped in mixed protonic acids: Their characterization by X-ray photoelectron spectroscopy and thermogravimetry

Abstract A comparative study of polyaniline chemically prepared and simultaneously doped in protonic acid mixtures is presented. As the resultant polyaniline salts (PANI salts) are insoluble, solid-state techniques such as X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG), derivative thermogravimetry (DTG) and elemental analysis have been applied to study the dopant environment as well as the electronic and chemical structure of the polymers. Both XPS and TG/DTG indicate that in the presence of competing acids, the stronger acid component is preferentially incorporated over the others. No advantage can be gained by the use of mixed-acid systems. XPS confirms that ring substitution by the dopant and the degree of protonation can be accurately measured based on the percentage of charged nitrogen in the N 1s envelope. Previous methods based on the total halogen content can lead to serious errors. TG results suggest an upper application temperature limit of about 150°C, at which point elimination of dopant occurs with loss of conductivity.

Modification of Si(100) surface by the grafting of poly(ethylene glycol) for reduction in protein adsorption and platelet adhesion

The modification of argon plasma-pretreated single-crystal Si(100) wafer surfaces via the UV-induced graft polymerization of poly(ethylene glycol) methacrylate (PEGMA) macromonomer (molecular weight approximately 340) for biomaterials applications was explored. The modified Si(100) surfaces were characterized by X-ray photoelectron spectroscopy and atomic force microscopy. Surface peroxide concentrations resulting from the argon plasma treatment and subsequent atmospheric exposure were determined by a coupling reaction with diphenylpicrylhydrazyl. The results suggested that a short plasma treatment time of 10 s and brief air exposure were sufficient for generating an optimum amount of peroxides and hydroperoxides for the subsequent UV-induced graft polymerization. The graft concentration of the PEGMA polymer increased with increasing PEGMA macromonomer concentration for the graft polymerization and with increasing UV graft polymerization time. The PEGMA graft-polymerized silicon surface with a high poly(ethylene glycol) graft concentration was very effective in preventing protein adsorption and platelet adhesion. The grafted PEGMA polymer layer on the Si(100) surface exhibited fairly good stability during storage in a buffer solution.

Strained N-Channel FinFETs with 25 nm Gate Length and Silicon-Carbon Source/Drain Regions for Performance Enhancement

We report the demonstration of 25 nm gate length L_G tri-gate FinFETs with Si_0.99C_0.01 source and drain (S/D) regions. The strain-induced mobility enhancement due to the Si_0.99C_0.01 S/D leads to a drive current I_Dsat improvement of 20% at a fixed off-state current I_off of 1times10^-7 A/mum. With additional channel strain engineering, FinFETs incorporating Si_0.99C_0.01 S/D and a tensile-stress silicon nitride (SiN) capping etch-stop layer (ESL) achieve an I_Dsat enhancement of 56%