Surface charge neutralization of insulating samples in x-ray photoemission spectroscopy

Larson, Paul E.; Kelly, Michael A.

doi:10.1116/1.581507

Cited by 93 publications

(28 citation statements)

References 3 publications

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“…XPS analyses were performed with a Quantum 2000 Scanning ESCA Microprobe (Physical Electronics, PHI, Eden Prairie, MN) equipped with a spherical capacitor energy analyzer used in the fixed analyzer transmission mode. The base pressure of the system was less than 10 Ϫ9 Torr, and spectra were typically acquired at a pressure below 5 ϫ 10 Ϫ9 Torr with a monochromatized Al K ␣ source operating at 100 W, with a beam diameter of 100 m. Sample charge-up was compensated for with a flux of low-energy electrons combined with a small current of low-energy positive ions (26). Under these conditions, the energy resolution for detailed scans [full width at half-maximum measured on silver Ag(3d 5/2 )] was 0.8 eV.…”

Section: X-ray Photoelectron Spectroscopy (Xps)mentioning

confidence: 99%

Monolayers of derivatized poly( l -lysine)-grafted poly(ethylene glycol) on metal oxides as a class of biomolecular interfaces

Ruiz-Taylor¹,

Martin²,

Zaugg³

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

158

114

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We report on the design and characterization of a class of biomolecular interfaces based on derivatized poly(L-lysine)-grafted poly-(ethylene glycol) copolymers adsorbed on negatively charged surfaces. As a model system, we synthesized biotin-derivatized poly(L-lysine)-grafted poly(ethylene glycol) copolymers, PLL-g-[(PEGm) (1؊x) (PEG-biotin)x], where x varies from 0 to 1. Monolayers were produced on titanium dioxide substrates and characterized by x-ray photoelectron spectroscopy. The specific biorecognition properties of these biotinylated surfaces were investigated with the use of radiolabeled streptavidin alone and within complex protein mixtures. The PLL-g-PEG-biotin monolayers specifically capture streptavidin, even from a complex protein mixture, while still preventing nonspecific adsorption of other proteins. This streptavidin layer can subsequently capture biotinylated proteins. Finally, with the use of microfluidic networks and protein arraying, we demonstrate the potential of this class of biomolecular interfaces for applications based on protein patterning. C ontrolling immobilization of biomolecules on surfaces, while preventing nonspecific adsorption of unwanted species, has become an important goal for monitoring specific biointeractions and binding of biomolecules or cells. Indeed, in diagnostic assays, biomaterial devices, and surface-related bioanalytical applications, nonspecific protein binding can often be the obstacle to higher sensitivity, reproducibility, or implant integration. Therefore, in past decades, many immobilization strategies have been established. These include physisorption to solid organic or inorganic supports (noncovalent coupling occurs by electrostatic and van der Waals forces), noncovalent chemisorption, and covalent immobilization on organic thin films of different molecular organization.Physisorption of biomolecules directly on the surface of inorganic substrate materials such as glass or organic coatings such as polymeric materials and adhesion layers (polylysine and nitrocellulose) probably constitutes the least technically challenging immobilization procedure. For instance, spotted microarrays of nucleic acids and, more recently, proteins are mostly based on physical adsorption (1). However, these methods suffer from some key limitations, such as their lack of control over the quantity and orientation of adsorbed biomolecules, and, hence, from lower reproducibility, lower interaction efficiencies, and high error rates. Moreover, additional passivation or blocking steps of the remaining sites are often required to limit the extent of nonspecific binding and protein denaturation. These are serious limitations for protein microarray applications.Attempts to control the biomolecular density and orientation of biomolecules at the solid-liquid interface to obtain better reproducibility have been undertaken through various strategies of covalent and site-specific immobilization. These include mostly immobilization via organic thin films such as selfassembled alkanethiol a...

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Section: X-ray Photoelectron Spectroscopy (Xps)mentioning

confidence: 99%

Monolayers of derivatized poly( l -lysine)-grafted poly(ethylene glycol) on metal oxides as a class of biomolecular interfaces

Ruiz-Taylor¹,

Martin²,

Zaugg³

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

158

114

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“…Charge neutralization was employed by compensating the sample surface with both low-energy electrons and low-energy ions during data collection. This procedure reduced the charging effects generally observed in insulating samples and improved energy resolution of the respective peaks [25].…”

Section: Surface Chemical Composition Analyzed By Xpsmentioning

confidence: 98%

Impact of Ethylene Oxide Butylene Oxide Copolymers on the Composition and Friction of Silicone Hydrogel Surfaces

et al. 2012

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The surface chemical compositions of three types of silicone hydrogel contact lenses, PureVision Ò (balafilcon A), ACUVUE Ò OASYS Ò (senofilcon A), and O 2 OPTIX Ò (lotrafilcon B), were analyzed using X-ray photoelectron spectroscopy prior to and following treatment in a test solution of diblock copolymer of poly (ethylene oxide) and poly(butylene oxide) (EO-BO). Prior to treatment, differences in surface elemental compositions of the lenses were found to reflect known bulk compositions and/or respective surface treatments. Following solution treatment, surface chemical modifications were apparent in balafilcon A and lotrafilcon B, especially in the distribution of chemical functionalities present at the surface. Only modest changes in surface composition were observed for the senofilcon A material. Atomic force microscopy (AFM) was employed to evaluate the surface topography and frictional properties of the lenses prior to and following similar solution treatments. AFM measurements in saline revealed large disparities between the coefficients of friction of the three lenses, with balafilcon A and lotrafilcon B exhibiting coefficients of friction approximately five times greater than that of senofilcon A. Lens surface treatment with the diblock copolymer test solution produced a significant reduction in the coefficients of friction of the two lenses exhibiting higher friction, yet only a small reduction in friction was observed for senofilcon A lens. Together, these results depict a strong correlation between the surface chemistry and frictional response of the lens systems as they relate to solution treatment with this specific diblock copolymer.

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“…This is necessary especially when using monochromatized X-ray radiation. (140) This approach also minimizes the shift observed when using nonmonochromatic radiation. Another method is to use a metallic grid (e.g.…”

Section: Insulatorsmentioning

confidence: 99%

X‐Ray Photoelectron Spectroscopy in Analysis of SurfacesUpdate based on the original article by Steffen Oswald,Encyclopedia of Analytical Chemistry, © 2000, John Wiley & Sons, Ltd.

Oswald

2013

Encyclopedia of Analytical Chemistry

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X‐ray photoelectron spectroscopy (XPS) is an analytical technique that uses photoelectrons excited by X‐ray radiation (usually Mg Kα or Al Kα) for the characterization of surfaces to a depth of 2–5 nm. Elemental identification and information on chemical bonding are derived from the measured electron energy and energy shifts, respectively. The use of ultrahigh vacuum (UHV) during analysis requires special sample handling. Depth profiling is possible using ion sputtering. In contrast to the most popular surface analytical technique, Auger electron spectroscopy (AES), nonconducting material can be investigated, weak material damage occurs, and the chemical shifts are easier to interpret. However, the lateral resolution of the complementary AES technique (typically down to 20 nm) is much better than for XPS (50 µm for standard equipment, down to lower than 3 µm for dedicated instruments). The detection limit (of about 0.1 at%) is not as low as for mass spectroscopic techniques, but the quantification from XPS peak area measurements is more reliable, even disclaiming standard sample measurements. This article briefly discusses the principles of the technique, sample requirements, and the typical measuring strategy. Possible information sources (elements, chemical bonding, depth and lateral distributions) are described and their quantification principles are summarized. The main part deals with typical applications relating to several material classes (metals, semiconductors, insulators, and polymers) to give an impression of the capabilities of the method over a wide range of research and technological problems. A comparison with further complementary analytical techniques is given as a summary. Technological developments in electronics, nanotechnology, polymers, biotechnology, and medicine are all concerned with surface‐related phenomena, suggesting sustained interest in XPS in the foreseeable future.

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Surface charge neutralization of insulating samples in x-ray photoemission spectroscopy

Cited by 93 publications

References 3 publications

Monolayers of derivatized poly( l -lysine)-grafted poly(ethylene glycol) on metal oxides as a class of biomolecular interfaces

Monolayers of derivatized poly( l -lysine)-grafted poly(ethylene glycol) on metal oxides as a class of biomolecular interfaces

Impact of Ethylene Oxide Butylene Oxide Copolymers on the Composition and Friction of Silicone Hydrogel Surfaces

X‐Ray Photoelectron Spectroscopy in Analysis of SurfacesUpdate based on the original article by Steffen Oswald,Encyclopedia of Analytical Chemistry, © 2000, John Wiley & Sons, Ltd.

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