Characterization of surfaces of various polymers by electron spectroscopy

Cataloged from PDF version of article.X-ray induced photo and Auger electron spectroscopic techniques have been used to characterize the surface composition of biaxially oriented polypropylene sheets with and without corona discharge treatment. The surfaces of polypropylene sheets without corona treatment contain very small amounts of 0 and the C 1 s peak is narrow, consisting mainly of -CH groups and less than 5% -C-O groups. After corona treatment the intensity of the 01s peak increases by a factor of 8, the Cls peak broadens and -C-O intensity increases by a factor of 3. The surfaces of aluminized polypropylene contains both aluminium oxide and metallic aluminium. From the measured intensity ratio of the A13’/A10 peaks the thickness of the oxide layer is estimated to be smaller than 4 nm. Aging increases the carbon content of the surface without changing the aluminium oxide/ metal composition. 0 1997 Elsevier Science B.V

XPS investigation of Si-diode in operation

Cataloged from PDF version of article.X-ray photoelectron spectroscopy (XPS) is utilized to investigate a Si-diode during its operation under both forward and reverse bias. The technique traces chemical and location specified surface potential variations as shifts of the peak positions with respect to the magnitude as well as the polarity of the applied voltage bias, which enables one to separate the dopant dependent shifts from those of the chemical ones

Communication: Enhancement of dopant dependent x-ray photoelectron spectroscopy peak shifts of Si by surface photovoltage

Cataloged from PDF version of article.Binding energies measured by x-ray photoelectron spectroscopy (XPS) are influenced by doping, since electrons are transferred to (p-type) and from (n-type) samples when they are introduced into the spectrometer, or brought into contact with each other (p-n junction). We show that the barely measurable Si2p binding energy difference between moderately doped n- and p-Si samples can be enhanced by photoillumination, due to reduction in surface band-bending, which otherwise screens this difference. Similar effects are also measured for samples containing oxide layers, since the band-bending at the buried oxide-Si interfaces is manifest as photovoltage shifts, although XPS does not probe the interface directly. The corresponding shift for the oxide layer of the p-Si is almost twice that of without the oxide, whereas no measurable shifts are observable for the oxide of the n-Si. These results are all related to band-bending effects and are vital in design and performance of photovoltaics and other related systems. (C) 2011 American Institute of Physics

Probing Voltage Drop Variations in Graphene with Photoelectron Spectrosopy

Cataloged from PDF version of article.We use X-ray photoelectron spectroscopy (XPS) for characterization of voltage drop variations of large area single-layer graphene on quartz substrates, by application of a voltage bias across two gold electrodes deposited on top. By monitoring the spatial variation of the kinetic energies of emitted Cls photoelectrons, we extract voltage variations in the graphene layer in a chemically specific format. The potential drop is uniform across the entire layer in the pristine sample but is not uniform in the oxidized one, due to cracks and/or morphological defects created during the oxidation process. This new way of data gathering reintroduces XPS as a major analytical tool for extracting electrical as well as chemical information about surface and/or nanostructured materials

XPS for chemical- and charge-sensitive analyses

Cataloged from PDF version of article.By recording X-ray photoelectron spectroscopic binding energy shifts, while subjecting samples to a variety of optical and electrical stimuli, information about charge accumulation on materials or surface structures can be obtained. These stimuli included d.c. as well as a.c. electrical and/or optical pulses covering a wide frequency range (10−3 to 106 Hz) for probing charging and/or photovoltage shifts, stemming from impurities, dopants, defects, etc., whether created intentionally or not. The methodology is simple to implement and provides several new dimensions for thin films and materials analyses

Soft X-ray Photoemission Studies of the HfO2/SiO2/Si System

Cataloged from PDF version of article.Soft x-ray photoelectron spectroscopy with synchrotron radiation was employed to study the valence-band offsets for the HfO2/SiO2/Si and HfO2/SiOxNy/Si systems. We obtained a valence-band offset difference of -1.05+/-0.1 eV between HfO2 (in HfO2/15 Angstrom SiO2/Si) and SiO2 (in 15 Angstrom SiO2/Si). There is no measurable difference between the HfO2 valence-band maximum positions of the HfO2/10 Angstrom SiOxNy/Si and HfO2/15 Angstrom SiO2/Si systems. (C) 2002 American Institute of Physics

Dynamic XPS measurements of ultrathin polyelectrolyte films containing antibacterial Ag–Cu nanoparticles

Cataloged from PDF version of article.Ultrathin films consisting of polyelectrolyte layers prepared by layer-by-layer deposition technique and containing also Ag and Cu nanoparticles exhibit superior antibacterial activity toward Escherichia coli. These films have been investigated with XPS measurements under square wave excitation at two different frequencies, in order to further our understanding about the chemical/physical nature of the nanoparticles. Dubbed as dynamical XPS, such measurements bring out similarities and differences among the surface structures by correlating the binding energy shifts of the corresponding XPS peaks. Accordingly, it is observed that the Cu2p, Ag3d of the metal nanoparticles, and S2p of cysteine, the stabilizer and the capping agent, exhibit similar shifts. On the other hand, the C1s, N1s, and S2p peaks of the polyelectrolyte layers shift differently. This finding leads us the claim that the Ag and Cu atoms are in a nanoalloy structure, capped with cystein, as opposed to phase separated entities. VC 2014 American Vacuum Society

Electrooxidation of methanol on doped polypyrrole films in acidic media

Cataloged from PDF version of article.Electrooxidation of methanol was realised on platinum and perchlorate anion doped polypyrrole film electrodes in acidic media. A systematic kinetic investigation was performed and optimum experimental conditions for the preparation of the electrocatalytic system were determined. The presence of ClO4- anions was confirmed by XPS analysis of the doped polymer matrix. (C) 2001 Elsevier Science B.V. All rights reserved

Impedance-type measurements using XPS

Cataloged from PDF version of article.An impedance type of measurement using X-ray photoelectron spectroscopy is applied for probing charging/discharging dynamics of a sample containing Rb deposited on a SiO(2)/Si substrate containing an octadecyltrichlorosilane (OTS) bilayer coating. The OTS bilayer coatings have possible use as anti-relaxation wall coatings for alkali atom vapor cells in miniaturized instruments such as chip-scale atomic clocks, and/or magnetometers. The measurement consists of the application of bipolar square wave pulses of +/- 10.0 V amplitude to the sample with varying frequencies in the range of 10(-2) to 10(2) Hz while recording X-ray photoemission data. For a conducting sample this type of measurement twins all the photoemission peaks at -10.0 and +10.0 eV positions at all frequencies with exactly 20.0 eV difference between them. However, for samples amenable to charging, the difference between the twinned peaks is less than 20.0 eV, and gradually decreases at correspondingly lower frequencies. For the sample under consideration here at 0.01 Hz, the twinned O1s and Si2p peaks, representing the SiO(2) substrate, are separated by 18.2 eV, displaying a 1.8 eV charging shift. These positions differ from those of the C1s (18.0 eV) representing the OTS bilayer and the Rb3d peaks (18.1 eV). These results reveal that the Rb is electrically (perhaps also chemically) isolated from the OTS bilayer, which may be correlated with the improved performance of the OTS bilayers as anti-relaxation coatings in these alkali atom magnetometer cells. (C) 2009 Elsevier B. V. All rights reserved

XPS and in-situ IR investigation of Ru/Si02 catalyst

Cataloged from PDF version of article.Ru(NO)(N0&/Si02 catalyst precursors were characterized via XPS and in-situ reflectance IR spectroscopy before, during and after reduction by hydrogen over the temperature range 300-800 K. IR results indicated that the catalyst precursor lost NO3 groups first, with subsequent loss of NO both in a reducing atmosphere and during thermal annealing. XPS was used to derive information on the oxidation state of Ru in the various steps of the annealing and/or reduction processes. 0 1997 Elsevier Science B.V