Emmanuel C. Onyiriuka

Surface Modification of Polystyrene by Gamma-Radiation

The effect of gamma-radiation on the surface chemical properties of polystyrene was studied by ESCA and FT-IR. Gamma-radiation produces surface >C=O and C-O containing functional groups only, and also causes oxidation to depths >10 nm as detected by ESCA. FT-IR spectra showed that below the top few molecular layers ester, acid, and carbonyl groups of various types were present. The α,β-unsaturated carbonyl/acid groups form a higher proportion of the total carbonyls with increasing depth. Surface oxidation follows pseudo-first-order kinetics; the extent of interior oxidation is linear with dose.

Solubilization of corona discharge- and plasma-treated polystyrene

Abstract Polystyrene tissue culture vessels are commercially treated by corona discharge or plasma surface oxidation to provide a hydrophilic surface, with 15–20% surface oxygen. ESCA and FTIR showed that oxidation forms hydroxyl, carbonyl, and carboxyl groups. We have discovered that water washing removes about half the oxidized species. It is believed that reaction with the vinyl polymer backbone to form carboxyl groups results in CC bond scission to form soluble fragments; addition and ring reactions would not yield soluble species. This functional group removal could affect the desired properties, such as the use of these groups as anchors in chemical coupling.

Electron beam surface modification of polystyrene used for cell cultures

The surface chemistry of polystyrene, used as tissue culture ware, subjected to electron beam irradiation was studied. Core-level and valence-band (VB) X-ray photoelectron spectroscopy (XPS) showed that electron beam (EB) treatment resulted in surface oxidation plus sterilization of the polymer material. The extent of oxidation by EB is linear with the dose and, as such, is analogous to gamma-radiation-induced oxidation. The data indicate that EB-radiation treatment alone provides a polystyrene surface analogous to that obtained by corona discharge or plasma plus low gamma sterilization.

Aluminum, Titanium Boride, and Nitride Films Sputter-Deposited from Multicomponent Alloy Targets Studied by XPS

X-ray photoelectron spectroscopy (XPS or ESCA), combined with argonion sputter depth profiling, has been employed for the characterization of aluminum, titanium boride, and nitride films deposited by dc-magnetron sputtering from multicomponent alloy targets. The XPS results show that metallic Al, TiB2, and TiN films are formed by this method. However, depth profile results indicated substantial oxide contamination as high as 30 atomic % throughout the bulk of the films. Given the gross oxide contamination, multicomponent alloy target materials appear to be unsuitable for producing high-quality metal/metallic films for applications where electrical conductivity is a critical requirement.

Amine-reactive surface chemistry of zinc phosphate glasses

Surface chemical studies on zinc phosphate glasses were carried out with an ammonia probe using FTIR and XPS. Low softening point zinc phosphate glasses can be co-extruded with high softening point polymers to form polymer filled blends. NH 3 reacts with P-OH groups (Br⊘nsted acid sites) to form bound NH 4 + and with the zinc ions (Lewis acid sites) to form coordinately bound NH 3 . Bulk nitridation reactions, forming various P-N bonds to >100 nm, occur concurrently. The glass surfaces were depleted in Zn compared to the batch compositions. Exposure to ambient water vapor removed Lewis acid bound ammonia; aqueous washing removed both types. Di- and tri-methyl amines also reacted with surface Br⊘nsted and Lewis acid sites. These amine reactions have the potential for binding polymer chains to the glass surface.

Modification of polystyrene cell culture surfaces by grafting a thin film of starch

A reactive form of a polymeric carbohydrate molecule, dialdehyde starch (DAS), physically adsorbed on polystyrene (PS) which acts as an alternative to chemical modification of the surface has been evaluated by XPS and IR. The DAS binding sites were assayed by chemical derivatization with the 2,4-dinitrophenylhydrazine (DNPH) probe molecule. The DNPH assay demonstrated that the DAS coating was effectively grafted onto the PS with suitable reactive sites available for chemical coupling to amine-containing molecules, such as the synthetic peptide GRGDSPK, which contains the RGD cell adhesion peptide. The effects of low gamma and electron-beam (E-beam) treatments used for sterilization purposes on the surface chemistry of the DAS coating were also studied. The integrity and the identity of the DAS coating on PS are maintained on exposure to either 1 Mrad gamma or E-beam radiation. However, at higher doses (2 Mrad), the aldehyde carbonyl group in the DAS coating is substantially transformed to the correspondin...

Adhesion and delamination of tantalum and chromium films on glass

The adhesion and delamination behavior of sputtered Ta and Cr films on barium boroaluminosilicate glass were investigated. The locus of delamination was determined by XPS analysis of peeled film strips to be at the film-glass interface. We found a strong correlation between the intensity and thickness of the metal suboxide interphase layer formed and resistance to film delamination. For Ta, we found that the presence of a sufficiently thick TaOx layer at the glass-film interface effectively prevented debonding of the film from the glass substrate. The role of oxygen in metal-glass bonding chemistry was explored by sputter deposition of metal films with in situ oxygen or air dosing. SIMS sputter-depth composition profiles confirmed the presence of a Ta-oxide phase (20-90 nm, depending on the dosing conditions) at the film-glass interface. We found that the delamination mechanism was prevented by in situ oxygen doping of the glass surface during film deposition. The cleanliness of the glass surface prior to...

Rapid Assay for Polystyrene Surface Oxidation

Polystyrene surfaces are often corona-discharge or plasma treated to oxidize the surface, which enhances the wettability. X-ray photoelectron spectroscopy (XPS), which requires time and an ultra-high vacuum, is generally used to measure this surface oxidation. A rapid, simple method for measuring polystyrene surface oxidation is described. The surface is soaked in a solution of Azure A dye, which adsorbs only to oxidized sites on the polystyrene. The excess dye is flushed away and the bound dye is desorbed with a detergent; an absorbance measurement at 635 nm is used to determine the quantity of desorbed dye. This value correlates with the polystyrene surface oxygen concentration and gives r2 = 0.93.

Refractive index measurement for planar photonic crystal using a microscopy-spectrometry method

We report a unique technique to measure the refractive index (n), extinction coefficient (k), and thickness of thin films based on either the reflection or transmission spectra. The method combines a spectrometer, an optical microscope and a video camera. It is inexpensive, versatile and fast (< a few sec). Using this technology, n&k of 1.68 and 0.376, respectively, at 1500 nm was measured on a planar photonic crystal. The photonic crystal with a dimension of 117 X 90 micrometers 2 mm has a periodic cermet structure on Si substrate made by Deutsch Telekom using the electron induced deposition.

Computer simulation of Nb2O5/SiO2 sputtering process for narrow-band optical filter

Sputter deposition process conditions for dielectric metal oxide films was simulated by SIMSPUDTM (Simulation of Sputtered Distributions). Collision cross-sections of Nb and Si were found to be 50 angstroms2 and 55 angstroms2 respectively by pinhole experiment and simulation. Film thickness distributions of Nb and Si films vs their oxide counterparts (Nb2O5 vs SiO2) showed that the deposition rate ratio of SiO2 to Si is 2.03 - 2.05:1 while Nb to Nb2O5 is 1.76 - 1.77:1. It was determined that the current density distribution and oxygen flow for reactive sputtering had great influence on film stoichiometry and thickness. It was also found that the ion source flattened the oxide film thickness. SIMSPUD was shown to be a desirable tool for new product development and as such could be beneficial in the design of the next generation PVD system.