ARXPS investigation of diffusion as a limiting process in the incorporation of adatoms into polystyrene surfaces treated by nitrogen plasmas

Polystyrene films were exposed to nitrogen plasmas for periods up to 4 min. ARXPS measurements revealed the presence of oxygen and nitrogen in the surface because of the plasma treatment. The depth profiles of these adatoms were determined by fitting a Thomas–Windle model profile to the data. As found previously, the best‐fit depth profiles resembled a step function, consistent with case II diffusion. However, the depth of penetration of the adatom species into the polymer surface was not found to vary with plasma duration, which is inconsistent with Case II diffusion, and provides evidence that diffusion processes do not limit the loading of adatom species into the surface during nitrogen plasma treatment. A possible reason for the generation of erroneous step function depth profiles is discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Study of the degradation of plasma‐oxidized polystyrene by time‐ and angle‐resolved x‐ray photoelectron spectroscopy

Angle‐resolved x‐ray photoelectron spectroscopy (ARXPS) measurements were made, in repeated sequences employing Al and Mg x‐ray sources alternately, on a polystyrene sample that had been exposed to an oxygen plasma. It was observed that oxygen was lost from the sample over a period of 5 h and 40 min. The ARXPS data sets were corrected for the time displacement between consecutive measurements at different photoemission angles and fitted with three simple models in order to extract oxygen concentration–depth profiles, consistent with the data, as a function of time. The oxygen depth profiles were found to evolve in a consistent manner, indicating both a loss of average oxygen content and thickness in the ‘oxidized polymer layer’. Copyright © 2003 John Wiley & Sons, Ltd.     

On the choice of the residual norm function in the interpretation of ARXPS data by regularized fitting

Angle‐resolved X‐ray photoelectron spectroscopy (ARXPS) data taken on a polystyrene film exposed to a nitrogen plasma are interpreted by the fitting of regularized depth profiles. Three ways of measuring the goodness of fit are compared—the χ² statistic with variances drawn from the raw spectra, the χ² statistic with variances drawn from the concentration figures obtained from the data analysis, and a simple sum of the squared differences (ssd) that does not require variances to be calculated. It is shown that for these data, the depth profiles obtained using an objective method for the choice of the regularization parameter are essentially identical irrespective of whether or how the variances are introduced into the calculation. Copyright © 2010 John Wiley & Sons, Ltd.     

ToF‐SIMS depth profiling of a complex polymeric coating employing a C60 sputter source

A complex poly(vinylidene difluoride) (PVdF)/poly(methyl methacrylate) (PMMA)‐based coil coating formulation has been investigated using time‐of‐flight SIMS (ToF‐SIMS). Employing a Bi₃⁺ analysis source and a Buckminsterfullerene (C₆₀) sputter source, depth profiles were obtained through the polymeric materials in the outer few nanometres of the PVdF topcoat. These investigations demonstrate that the PVdF coating's air/coating interface is composed principally of the flow agent included in the formulation. Elemental depth profiles obtained in the negative ion mode demonstrate variations in the carbon, oxygen and fluorine concentrations within the coating with respect to depth. All three elemental depth profiles suggest that the PVdF coating bulk possesses a constant material composition. The oxygen depth profile reveals the presence of a very thin oxygen‐rich sub‐surface layer in the PVdF coating, observed within the first second of the sputter/etch profile. Retrospectively, extracted mass spectra (from the elemental depth profile raw data set) of the PVdF coating sub‐surface and bulk layers indicates this oxygen‐rich sub‐surface layer results from segregation of the acrylic co‐polymers in the formulation towards the PVdF coating air/coating interface. Molecular depth profiles obtained in both the positive and negative secondary ion modes provide supporting evidence to that of the elemental depth profiles. The molecular depth profiles confirm the presence of a sub‐surface layer rich in the acrylic co‐polymers indicating segregation of the co‐polymers towards the PVdF topcoats air‐coating surface. The molecular depth profiles also confirm that the PVdF component of the topcoat is distributed throughout the coating but is present at a lower concentration at the air‐coating interface and in the sub‐surface regions of the coating, than in the coating bulk. Copyright © 2007 John Wiley & Sons, Ltd.     

Surface modification of polyester by oxygen‐ and nitrogen‐plasma treatment

In this paper, we present a study on the surface modification of polyethyleneterephthalate (PET) polymer by plasma treatment. The samples were treated by nitrogen and oxygen plasma for different time periods between 3 and 90 s. The plasma was created by a radio frequency (RF) generator. The gas pressure was fixed at 75 Pa and the discharge power was set to 200 W. The samples were treated in the glow region, where the electrons temperature was about 4 eV, the positive ions density was about 2 × 10¹⁵ m^?3, and the neutral atom density was about 4 × 10²¹ m^?3 for oxygen and 1 × 10²¹ m^?3 for nitrogen. The changes in surface morphology were observed by using atomic force microscopy (AFM). Surface wettability was determined by water contact angle measurements while the chemical composition of the surface was analyzed using XPS. The stability of functional groups on the polymer surface treated with plasma was monitored by XPS and wettability measurements in different time intervals. The oxygen‐plasma‐treated samples showed much more pronounced changes in the surface topography compared to those treated by nitrogen plasma. The contact angle of a water drop decreased from 75° for the untreated sample to 20° for oxygen and 25° for nitrogen‐plasma‐treated samples for 3 s. It kept decreasing with treatment time for both plasmas and reached about 10° for nitrogen plasma after 1 min of plasma treatment. For oxygen plasma, however, the contact angle kept decreasing even after a minute of plasma treatment and eventually fell below a few degrees. We found that the water contact angle increased linearly with the O/C ratio or N/C ratio in the case of oxygen or nitrogen plasma, respectively. Ageing effects of the plasma‐treated surface were more pronounced in the first 3 days; however, the surface hydrophilicity was rather stable later. Copyright © 2008 John Wiley & Sons, Ltd.     

Depth profiling of light elements in PAMBE‐grown GaN and helium‐implanted titanium with heavy ion time‐of‐flight elastic recoil detection

The heavy ion time‐of‐flight elastic recoil detection analysis (HI‐ERDA) technique was used to investigate the possibility of measuring near‐surface elemental depth profiles of light and mid‐Z elements in thin films of plasma‐assisted molecular beam epitaxy (PAMBE)‐grown GaN and helium‐implanted titanium. The great advantage of HI‐ERDA is the ability to measure mass‐separated elemental depth profiles simultaneously. However for some materials it is not certain whether HI‐ERDA can be used successfully because significant sputtering or other beam‐induced damage may occur. The damage to the surfaces by a 77 MeV iodine beam was assessed using RBS, AFM and profilometry. The results show that for thin PAMBE‐grown polycrystalline GaN films and for titanium that has been heavily implanted with helium a significant modification of the near‐surface region is caused by the probing heavy ion beam. For the PAMBE‐grown GaN films the most significant loss trend is observed for nitrogen. Surprisingly this was not accompanied by a change in surface topology. In contrast, an almost complete removal of the heavily helium‐implanted surface layer was measured for the titanium specimens. The investigation shows that reference measurements with additional techniques such as RBS, AFM and profilometry have to be performed to ascertain sample integrity before HI‐ERDA data can be used. Copyright © 2004 John Wiley & Sons, Ltd.     

Fick's law of diffusion depth profiles applied to the degradation of oxidized polystyrene during ARXPS analysis

Angle‐resolved x‐ray photoelectron spectroscopy (ARXPS) measurements were made, using Al Kα and Mg Kα radiation alternately, on a polystyrene sample that had been exposed to a helium plasma. It was observed that oxygen was introduced into the sample surface by the plasma treatment, and that some of it was lost over a period of 5 h under x‐ray irradiation in the vacuum of the spectrometer. Laplace transforms of Fick's law of diffusion profiles were derived and applied to the data. The ARXPS results obtained in this study are consistent with a sample history in which the oxidation of the polymer surface resulting from exposure to plasma is controlled by a diffusion process, whereas the loss of oxygen during exposure to x‐rays is principally controlled by a first‐order reaction such as the liberation of oxygen (presumably as CO₂) from carbon–oxygen groups by the action of radicals created by the ionizing radiation. Copyright © 2005 John Wiley & Sons, Ltd.     

XPS analysis of aluminum nitride films deposited by plasma source molecular beam epitaxy

Ten samples of crystalline aluminum nitride (AlN) film were deposited on sapphire and silicon substrates by a plasma source molecular beam method. The samples were analyzed using X‐ray photoelectron spectroscopy (XPS) depth profiling and high‐resolution X‐ray diffraction. Oxygen levels were observed to decrease exponentially from the surface into the bulk film. Aluminum, nitrogen and oxygen peaks were fitted with subpeaks in a consistent manner and the subpeaks were assigned to chemical states. AlN subpeaks were observed at 73.5 eV for Al2p and 396.4 eV for N1s. An N1s subpeak at 395.0 eV was assigned to N? N defects. No direct N? O bonds are assigned; rather it is proposed that an N? Al? O bond sequence is the source of higher binding energy N1s subpeaks. The observations in this study support a model in which oxygen is bound only to aluminum in the form of Al? O octahedral complexes dispersed or clustered throughout the main AlN matrix or as Al? O bonds on the crystal grain boundaries. The data also suggest that the AlN lattice parameters are related to oxygen content, since the c‐axis is observed to increase with increasing oxygen content. Copyright © 2008 John Wiley & Sons, Ltd.     

In‐depth diffusion of oxygen into LDPE exposed to an Ar–O2 atmospheric post‐discharge: a complementary approach between AR‐XPS and Tof‐SIMS techniques

The in‐depth oxygen diffusion into a low density polyethylene film is performed in the post‐discharge of an atmospheric plasma torch, supplied in argon as carrier gas and with or without oxygen as reactive gas. The chemical and structural properties of the polymer surface and bulk are studied in terms of plasma parameters (treatment time, power, and reactive gas flow rate). A good correlation between XPS and Fourier transform infrared spectroscopy analyses is demonstrated. The penetration depth of oxygen into the bulk of the polymer is investigated by angle resolved‐XPS and time‐of‐flight SIMS. It is shown that, depending on the plasma conditions, oxygen could penetrate up to 20–40 nm into the low density polyethylene during the atmospheric plasma treatment. Copyright © 2014 John Wiley & Sons, Ltd.     

Analysis of functional groups on the surface of plasma-treated carbon nanofibers

Plasma chemically modified carbon nanofibers were characterized by X-ray photoelectron spectroscopy with regard to the content of carbon, oxygen, and nitrogen and the contribution of carboxylic groups or ester, carbonyl and hydroxylic groups or ether on the surface. Unfortunately, X-ray photoelectron spectroscopy only provides an average value of the first 10 to 15 molecular layers. For comparison, depth profiles were measured and wet chemical methods were applied to estimate the thickness of the functionalized layer and the distribution of oxygen-containing functional groups within the near-surface layers. The results indicate that the fiber surface is covered by a monomolecular oxygen-containing layer and that plasma treatment allows a complete oxygen functionalization of the uppermost surface layer. The best conditions for plasma treatment found within the set of parameters applied to generate complete functionalization are: plasma gas O(2)/Ar ratio 1:1, gas pressure 1-1.5 hPa, plasma power 80 W, treatment time >or= 5 min. Additionally, three quick and easy methods are presented to estimate the efficiency of plasma treatment with regard to surface functionalization: pyrolysis, contact angle measurements, and light permeability measurements of aqueous carbon nanofiber suspensions.     

Toward accurate characterization of nitrogen depth profiles in ultrathin oxynitride films

Good accuracy in depth profile analyses of nitrogen in ultrathin oxynitride films is desirable for process development and routine process monitoring. Low energy SIMS is one of the techniques that has found success in the accurate characterization of thin oxynitride films. This work investigated the artifacts in a typical depth profile analysis of nitrogen with the current SIMS technique and the ways to improve the accuracy by selecting optimal analytical conditions. It was demonstrated that surface roughness developed rapidly in a SiO₂/Si stack when it was bombarded with an O₂⁺ beam at 250 eV and angle of incidence from 70 to 79° . The roughness caused distortion in the measured depth profiles of nitrogen and the major component elements. However, the above roughness and the distortion in the depth profiles can be eliminated by using a 250 eV O₂⁺ beam at an angle of incidence above 80° . Depth profile analyses with a 250 eV 83° O₂⁺ beam exhibited minimal surface roughening and insignificant variation in the secondary ion yield of SiN^? from SiO₂ bulk to the SiO₂/Si interface, facilitating an accurate analysis of nitrogen distribution in a SiO₂/Si stack. In addition, depth profiles of the major component elements such as ¹⁸O^? and ²⁸Si^? delivered clear information on the location of the SiO₂/Si interface. Using the new approach, we compared nitrogen distribution in thin SiNO films with the decoupled‐plasma nitridation (DPN) at various powers. Copyright © 2008 John Wiley & Sons, Ltd.     

Quantitative Analysis of Thin Aluminium-Oxynitride Films by EPMA

 Thin films of aluminium oxynitride with diverse composition were prepared by dc-magnetron sputtering of aluminium, utilising sputtering power as well as argon, oxygen and nitrogen gas flows to vary the composition. Since film properties depend mainly on the content of incorporated oxygen and nitrogen, a method for quantitative analysis of the main constituents based on electron probe micro analysis with energy dispersive detection was developed. The excellent precision of the quantitative results for aluminium as well as oxygen and nitrogen are shown. Furthermore, a film layer analysis program was applied for the quantification of several films deposited under the same deposition parameters on silicon wafers, from 520 nm down to 40 nm thickness, showing that electron probe micro analysis with energy dispersive detection is a reliable method for quantitative compositional analysis of thin aluminium oxynitride films down to approximately 20 nm thickness. Since this method of analysis provides only bulk information, expected inhomogeneities of the depth distribution of the film components were checked by secondary ion mass spectrometry depth profiles of two thin films and correlated to the EPMA results. The thickness of the films was determined by ellipsometry. Received September 1, 1998     

Ultrashallow depth profiling using SIMS and ion scattering spectroscopy

The accuracy of ultrashallow depth profiling was studied by secondary ion mass spectrometry (SIMS) and high‐resolution Rutherford backscattering spectroscopy (HRBS) to obtain reliable depth profiles of ultrathin gate dielectrics and ultrashallow dopant profiles, and to provide important information for the modeling and process control of advanced complimentary metal‐oxide semiconductor (CMOS) design. An ultrathin Si₃N₄/SiO₂ stacked layer (2.5 nm) and ultrashallow arsenic implantation distributions (3 keV, 1 × 10¹⁵ cm^?2) were used to explore the accuracy of near‐surface depth profiles measured by low‐energy O₂⁺ and Cs⁺ bombardment (0.25 and 0.5 keV) at oblique incidence. The SIMS depth profiles were compared with those by HRBS. Comparison between HRBS and SIMS nitrogen profiles in the stacked layer suggested that SIMS depth profiling with O₂⁺ at low energy (0.25 keV) and an impact angle of 78° provides accurate profiles. For the As⁺‐implanted Si, the HRBS depth profiles clearly showed redistribution in the near‐surface region. In contrast, those by the conventional SIMS measurement using Cs⁺ primary ions at oblique incidence were distorted at depths less than 5 nm. The distortion resulted from a long transient caused by the native oxide. To reduce the transient behavior and to obtain more accurate depth profiles in the near‐surface region, the use of O₂⁺ primary ions was found to be effective, and 0.25 keV O₂⁺ at normal incidence provided a more reliable result than Cs⁺ in the near‐surface region. Copyright © 2007 John Wiley & Sons, Ltd.     

Removal of Ar+ beam‐induced damaged layers from polyimide surfaces with argon gas cluster ion beams

An Ar Gas Cluster Ion Beam (GCIB) has been shown to remove previous Ar⁺ ion beam‐induced surface damage to a bulk polyimide (PI) film. After removal of the damaged layer with a GCIB sputter source, XPS measurements show minor changes to the carbon, nitrogen and oxygen atomic concentrations relative to the original elemental bulk concentrations. The GCIB sputter depth profiles showed that there is a linear relationship between the Ar⁺ ion beam voltage within the range from 0.5 to 4.0 keV and the dose of argon cluster ions required to remove the damaged layer. The rate of recovery of the original PI atomic composition as a function of GCIB sputtering is similar for carbon, nitrogen and oxygen, indicating that there was no preferential sputtering for these elements. The XPS chemical state analysis of the N 1s spectra after GCIB sputtering revealed a 17% damage ratio of altered nitrogen chemical state species. Further optimization of the GCIB sputtering conditions should lead to lower nitrogen damage ratios with the elemental concentrations closer to those of bulk PI. Copyright © 2010 John Wiley & Sons, Ltd.     

Heavy‐ion elastic recoil detection analysis as a useful tool for tracking experimental modifications in bulk calcium silicates

Chemical modifications carried out on unique amorphous nano‐structured calcium silicate have been traced by time‐of‐flight heavy‐ion elastic recoil detection analysis (HERDA). It could be shown that this ion‐beam analysis method allows not only surface but also depth analysis of the silicate samples and the modifications effected upon it. While providing a challenge for standard analysis methods, the highly porous, low‐density nature of the calcium silicate proved to be an asset for the ion‐beam analysis technique chosen. Presented are depth profiles giving elemental compositions and providing the bases for representative chemical formula for the silicates studied. It was proven that a study of the surface composition of this nano‐structured silicate is sufficient for indicating the bulk composition of a sample of this material. Copyright © 2005 John Wiley & Sons, Ltd.     

Universal Correlation of Nitrogen 1s and Oxygen 1s Photoelectron Binding Energies with Chemical Composition in Nitrogen-Containing Plasma Polymers

The incorporation of oxygen into nitrogen-containing plasma deposited polymers was studied by X-ray Photoelectron Spectroscopy (XPS). As the oxygen content of the plasma polymer increased, the binding energy of the N 1s photoelectrons increased. Conversely, the binding energy of the O 1s photoelectrons was inversely proportional to the nitrogen content of the plasma polymer. The data from a large number of samples all obeyed the same universal correlations of photoelectron binding energy versus chemical composition. The data were described by the same curve regardless of whether the oxygen was incorporated rapidly into the thin film during plasma deposition or whether the oxygen was added slowly during spontaneous oxidation of the film in air. This implies that the same thermodynamic principles of radical reactions governed the addition of oxygen to the plasma polymer. The shift in the O 1s and N 1s photoelectron binding energies as a function of chemical composition was used to monitor the proximity of nitrogen and oxygen. By contrasting the experimental data with a simple binomial model which described the random addition of oxygen to a lattice containing carbon and nitrogen, we were able to show that oxygen was preferentially added near nitrogen-containing groups in plasma polymers.     

Inter‐laboratory comparison of elemental analysis and gas chromatography/combustion/isotope ratio mass spectrometry. II. δ15N measurements of selected compounds for the development of an isotopic Grob test

An inter‐laboratory exercise was carried out by a consortium of five European laboratories to establish a set of compounds, suitable for calibrating gas chromatography/combustion/isotope ratio mass spectrometry (GC‐C‐IRMS) devices, to be used as isotopic reference materials for hydrogen, carbon, nitrogen and oxygen stable isotope measurements. The set of compounds was chosen with the aim of developing a mixture of reference materials to be used in analytical protocols to check for food and beverage authentication. The exercise was organized in several steps to achieve the certification level: the first step consisted of the a priori selection of chemical compounds on the basis of the scientific literature and successive GC tests to set the analytical conditions for each single compound and the mixture. After elimination of the compounds that turned out to be unsuitable in a multi‐compound mixture, some additional oxygen‐ and nitrogen‐containing substances were added to complete the range of calibration isotopes. The results of δ¹³C determinations for the entire set of reference compounds have previously been published, while the δD and δ¹⁸O determinations were unsuccessful and after statistical analysis of the data the results did not reach the level required for certification. In the present paper we present the results of an inter‐laboratory exercise to identify and test the set of nitrogen‐containing compounds present in the mixture developed for use as reference materials for the validation of GC‐C‐IRMS analyses in individual laboratories. Copyright © 2009 John Wiley & Sons, Ltd.     

Depth characterization by confocal raman microscopy of oxygen inhibition in free radical photopolymerization of acrylates: Contribution of the thiol chemistry

The oxygen inhibition of acrylate photopolymerization using visible light was depth characterized by confocal Raman microscopy. The sample thickness was found to influence the depth conversion profile. With increasing sample thickness, the conversion at the surface was increased and the oxygen‐affected layer (OAL) decreased, up to a limit where the profiles became independent of the thickness. The addition of a thiol in the acrylate mixture reduced the OAL and the conversion in this region increased. This effect was noticeable even at low concentration of thiol. Real‐time infrared spectroscopy (RT‐FTIR) experiments pointed out that for low thiol content, this beneficial effect is not only attributable to the thiol–ene process—oxygen insensitive—but also to the homopolymerization of acrylates which is enhanced. Homopolymerization and thiyl radical addition were found to have the same impact on the overall mechanism. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Novel use of glow discharge optical emission spectroscopy (GDOES) to study corrosion of AA2024‐T3 in the presence and absence of inhibitors – part 3: investigating the effects of various proportions of inhibitor in the coating matrix or in nanocontainers

Elemental depth profiling by glow discharge optical emission spectroscopy has been used to characterize the corrosion products on AA2024‐T3. In previous work, the aluminium, oxygen and copper depth profiles were shown to provide information regarding surface roughening, the thickness of corroded layers and extent of copper de‐alloying/relocation. Nitrogen, sulfur, phosphorus and chromium depth profiles were examined in the hope of detecting inhibitor species within the corroded/altered layers after 5 h of exposure to a corrosive solution. In the present work, the study is extended to longer exposure time. The work presents a further study of the leaching of benzotriazole from the coating matrix or from nanocontainers during various times of exposure to a corrosive environment. Copyright © 2016 John Wiley & Sons, Ltd.