Effective attenuation lengths for photoelectrons in thin films of silicon oxynitride and hafnium oxynitride on silicon

We have used the National Institute of Standards and Technology Database for the Simulation of Electron Spectra for Surface Analysis (SESSA) to simulate photoelectron intensities for thin films of SiO_1.6N_0.4 and HfO_1.9N_0.1 on silicon with excitation by Al Kα X‐rays. We considered Si 2p_3/2 photoelectrons from SiO_1.6N_0.4 and the substrate and Hf 4f_7/2 photoelectrons from HfO_1.9N_0.1. The simulations were performed for ranges of film thicknesses and photoelectron emission angles and for two common configurations for X‐ray photoelectron spectroscopy (XPS), the sample‐tilting configuration and the Theta Probe configuration. We determined photoelectron effective attenuation lengths (EALs) by two methods, one by analyzing photoelectron intensities as a function of film thickness for each emission angle (Method 1) and the other by analyzing photoelectron intensities as a function of emission angle for each film thickness (Method 2). Our analyses were made with simple expressions that had been derived with the assumption that elastic‐scattering effects were negligible. We found that EALs from both methods were systematically larger for the Theta Probe configuration, by amounts varying between 1% and 5%, than those for the sample‐tilting configuration. These differences were attributed to anisotropy effects in the photoionization cross section that are expected to occur in the former configuration. Generally, similar EALs were found by each method for each film material although larger EALs were found from Method 2 for film thicknesses less than 1.5 nm. SESSA is a useful tool for showing how elastic scattering of photoelectrons modifies EALs for particular materials, film thicknesses, and XPS configurations. Copyright © 2012 John Wiley & Sons, Ltd.     

Interlaboratory study comparing analyses of simulated angle‐resolved X‐ray photoelectron spectroscopy data

An interlaboratory study has been conducted to determine the following: (i) the similarities and differences of film thicknesses and composition profiles obtained from analyses of simulated angle‐resolved X‐ray photoelectron spectroscopy (ARXPS) data by different analysts using different algorithms for data analysis, and (ii) the effects of two assumptions commonly made in data‐analysis algorithms for ARXPS on derived film thicknesses and composition profiles. The analyzed data were generated by the National Institute of Standards and Technology Database for the Simulation of Electron Spectra for Surface Analysis, (SESSA) which provides a simple way to study the influence of the aforementioned effects on compositional depth profile reconstruction. Sets of simulated ARXPS data were produced for thin films of SiO₂, SiON, HfO₂, and HfON of varying thicknesses on a Si substrate. For some HfON films, the N concentration varied with depth. Eleven groups participated in the round robin study. The majority (eight) employed a commercial ARXPS instrument in which the angular distribution is measured for a fixed sample geometry, in contrast to conventional ARXPS in which the sample is tilted for angular variation. The average deviations between the reported average depth, film thickness, and amount of material typically varied between 20% and 30% but were considerably larger, between 30% and 80%, for some cases. The average errors were generally larger for simulations that included elastic scattering and the finite analyzer‐acceptance angle (realistic conditions) than those for simulations that neglected elastic scattering and the finite analyzer‐acceptance angle (simplified conditions). The retrieved N depth profiles were quantitatively different from the true depth profiles and showed substantial variability among the group of members who used the same instrument and analysis software. Copyright © 2014 John Wiley & Sons, Ltd.     

Application of Cr Kα X‐ray photoelectron spectroscopy system to overlayer thickness determination

A laboratory hard X‐ray photoelectron spectroscopy (HXPS) system at 5.4‐keV excitation energy was used to measure the angle dependence of a silicon oxide overlayer on a Si(0 0 1) substrate with overlayer thickness ranging from 4 to 25 nm. The thickness values of the SiO₂ overlayers were determined by utilizing a focused monochromatized Cr Kα source and a high‐energy hemispherical analyzer with an angle‐resolved wide acceptance angle objective lens. The modulation of the photoemission intensity due to photoelectron diffraction, which deteriorates high‐precision thickness determination, was suppressed significantly by continuous sample rotation around the sample's normal during the measurements. The resultant thickness values very well agree with those determined by ellipsometry in the same sample set. To demonstrate merits of the large information depth measurements, profiling of a wedged SiO₂ layer buried in a gate stack model structure with Ir (8 nm) and HfO₂ (2 nm) overlayers was performed. Copyright © 2011 John Wiley & Sons, Ltd.     

Quantitative analysis of angle‐resolved XPS spectra recorded in parallel data acquisition mode

The effects of anisotropy of the photoionization cross‐section and elastic scattering of photoelectrons in solids are investigated for angle‐resolved XPS spectra (ARXPS) recorded from α–Al₂O₃ substrate in parallel data acquisition mode. It is shown that for quantitative analysis of ARXPS spectra recorded in parallel data acquisition mode it is essential to account for the anisotropies of the photoionization cross‐sections of the detected photoelectrons for the concerned elements in the solid due to variation of the angle between the incident x‐rays and the detected photoelectrons. Neglecting the effect of elastic scattering only leads to minor errors in quantitative analysis of the ARXPS spectra. By adopting experimentally determined values for the relative sensitivity factors of the concerned photoelectrons in the solid as a function of the detection angle, cumbersome corrections for the effects of anisotropy of the photoionization cross‐section and elastic scattering can be avoided. Copyright © 2004 John Wiley & Sons, Ltd.     

Report on the 47th IUVSTA Workshop ‘Angle‐Resolved XPS: the current status and future prospects for angle‐resolved XPS of nano and subnano films’

A summary of the workshop entitled ‘Angle‐Resolved XPS: The Current Status and Future Prospects for Angle‐resolved XPS of Nano and Subnano Films’ is given, which was held at the Riviera Maya, Mexico, 26–30 March 2007, under the main sponsorship of the International Union for Vacuum Science, Technique and Applications (IUVSTA). Angle‐resolved X‐ray photoelectron spectroscopy (ARXPS) can provide detailed chemical as well as depth profile information about the near‐surface composition of materials and thin films. This workshop was held to review the present status and level of understanding of Angle‐resolved XPS, and to stimulate discussions leading to a deeper understanding of current problems and new solutions. The main goal of the workshop was to find better ways to perform experiments and, very importantly, better ways to extract information from the experimental data. This report contains summaries of presentations and discussions that were held in sessions entitled ‘Basics and Present Limits of ARXPS’, the Analysis of ARXPS Data, Applications of ARXPS, Equipment for ARXPS, and Future Developments in ARXPS'. There were 33 participants at the workshop. Copyright © 2009 John Wiley & Sons, Ltd.     

Combined IR and XPS analysis of the native (1 0 0) surface of single‐crystalline silicon after HFaq etching

A combined analysis, based on angle‐resolved X‐ray photoelectron spectroscopy and multiple‐internal‐reflection infrared spectroscopy, of the (1 0 0) silicon surface after etching in dilute aqueous solution of HF is presented. The analysis shows that the surface is mainly formed by a heterogeneous distribution of SiH, SiH₂ and SiH₃ terminations, but contains (in addition to sub‐stoichiometric oxidized silicon) a form of reduced silicon, not consistent with the currently accepted picture of the native HF_aq‐etched surface. Copyright © 2007 John Wiley & Sons, Ltd.     

X‐ray induced degradation of surface bound azido groups during XPS analysis

Mesoporous silica SBA‐15 was synthesized and silanized with azidopropyl triethoxysilane in order to design a clickable material. Fourier transform infrared analysis permitted to prove the attachment of the azidopropylene groups to SBA‐15 resulting in the reactive and functional material N₃‐SBA‐15. X‐ray photoelectron spectroscopy was used to determine the surface composition of SBA‐15. However, we unexpectedly found that the surface bound azido groups undergo X‐ray induced decomposition during the X‐ray photoelectron spectroscopy analysis resulting in the formation of nitrenes. These are very reactive groups able to intercalate C―C and C―H bonds of the propylene chains as judged from the N1s peak shape. Possible mechanisms of intercalation are suggested. C1s and N1s peaks were recorded at different exposure time. N/C, N⁺/N and N⁺/C undergo exponential decay. N⁺/N reaches the value of zero in less than 80 min of exposure to the X‐ray source. The N⁺/C decay plot was fitted with first‐order kinetics, and the decomposition kinetic constant (k_dec) was found to equal to 516.4 s^?1. This is a fast X‐ray induced degradation which must be considered with care when examining clickable materials with surface bound alkyl azido groups. Copyright © 2016 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.     

Interface characterization of a metal‐oxide‐semiconductor structure by biased X‐ray photoelectron spectroscopy

X‐ray photoelectron spectroscopy (XPS) measurements of a Pt/HfO₂(SiO₂)/Si metal‐oxide‐semiconductor (MOS) structure under a bias voltage applied between the gate metal and the silicon substrate were studied. The binding energy shifts of Pt 4f, Hf 4f, O 1s and Si 2p according to the applied voltage were investigated using the MOS structure. After the influence of measurements on the results was carefully examined under various conditions, the amount of the shifts was analyzed from a viewpoint of band alignment. Based on the experimental results, a new way of interpreting the deviation of the electric properties from the ideal ones in a band diagram was proposed. It was demonstrated that the biased XPS is a very powerful method to understand the origin of the electric properties of MOS. Copyright © 2010 John Wiley & Sons, Ltd.     

X‐ray photoelectron and carbon Kα emission measurements and calculations of O‐, CO‐, N‐, and S‐containing substances

X‐ray fluorescence measurements for O‐containing [polyethylene oxide, polyvinyl alcohol, polyvinyl methyl ether], CO‐containing [polyvinyl methyl ketone, polyethylene terephthalate], N‐containing [poly‐4‐vinylpyridine (P4VP), polyaniline oligomer (PAO)], and S‐containing [polyphenylene sulfide] substances are presented. Carbon Kα X‐ray emission spectra (XES) and X‐ray photoelectron spectra (XPS) are compared with our DFT calculations performed with the Amsterdam density functional (ADF) program. The combined analysis of valence XPS and carbon Kα XES allows us to determine the individual contributions from pσ‐ and pπ‐bonding molecular orbitals of the polymers. The ΔSCF calculations yield the accurate C1s core‐electron binding energies (CEBEs) for all carbon sites of the organic compound. We calculate all CEBEs of the model molecules using the ΔE _KS approach. Our simulated C1s photoelectron and C Kα emission spectra are in good agreement with our measurements. We also obtain WD (work function and the other energies) values for the polymers and PAO from the difference between calculated (gas‐phase) and measured (solid) CEBE values. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 162–172, 2007     

Online wide‐angle X‐ray diffraction/small‐angle X‐ray scattering measurements for the CO2‐laser‐heated drawing of poly(ethylene terephthalate) fiber

Fiber‐structure‐development in the poly(ethylene terephthalate) fiber drawing process was investigated with online measurements of wide‐angle and small‐angle X‐ray scattering with both a high‐luminance X‐ray source and a CO₂‐laser‐heated drawing system. The intensity profile of the transmitted X‐ray confirmed the location of the neck‐drawing point. The diffraction images had a time resolution of several milliseconds, and this still left much room for improvement. Crystal diffraction appeared in the wide‐angle X‐ray images almost instantaneously about 20 ms after necking, whereas a four‐point small‐angle X‐ray scattering pattern appeared immediately after necking. With the elapse of time after necking, the four‐point scattering pattern changed into a meridional two‐point shape. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1090–1099, 2005     

Quantitative analysis of styrene‐pentafluorostyrene random copolymers by ToF‐SIMS and XPS

Poly(styrene) (PS), poly(2,3,4,5,6‐pentafluorostyrene) (5FPS) and their random copolymers were prepared by bulk radical polymerization. The spin‐cast polymer films of these polymers were analyzed using X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The surface and bulk compositions of these copolymers were found to be same, implying that surface segregation did not occur. The detailed analysis of ToF‐SIMS spectra indicated that the ion fragmentation mechanism is similar for both PS and 5FPS. ToF‐SIMS quantitative analysis using absolute peak intensity showed that the SIMS intensities of positive styrene fragments, particularly C₇H₇⁺, in the copolymers are higher than the intensities expected from a linear combination of PS and 5FPS, while the SIMS intensities of positive pentafluorostyrene fragments are smaller than expected. These results indicated the presence of matrix effects in ion formation process. However, the quantitative approach using relative peak intensity showed that ion intensity ratios are linearly proportional to the copolymer mole ratio when the characteristic ions of PS and 5FPS are selected. This suggests that quantitative analysis is still possible in this copolymer system. Copyright © 2005 John Wiley & Sons, Ltd.     

Crystallization and chain conformation of semicrystalline and amorphous polymer blends studied by wide‐angle and small‐angle scattering

We examine the crystallization and chain conformation behavior of semicrystalline poly(ethylene oxide) (PEO) and amorphous poly(vinyl acetate) (PVAc) mixtures with wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and small‐angle neutron scattering (SANS) experiments. For blends with PEO weight fractions (wt_PEO) greater than or equal to 0.3, below the melting point of PEO, the WAXD patterns reveal that crystalline PEO belongs to the monoclinic system. The unit‐cell parameters are independent of wt_PEO. However, the bulk crystallinity determined from WAXD decreases as wt_PEO decreases. The scattered intensities from SAXS experiments show that the systems form an ordered crystalline/amorphous lamellar structure. In a combination of WAXD and SAXS analysis, the related morphological parameters are assigned correctly. With the addition of amorphous PVAc, both the average amorphous layer thickness and long spacing increase, whereas the average crystalline layer thickness decreases. We find that a two‐phase analysis of the correlation function from SAXS, in which the scattering invariant is linearly proportional to the volume fraction of lamellar stacks, describes quantitatively the crystallization behavior of PEO in the presence of PVAc. When wt_PEO is close to 1, the samples are fully spaced‐filled with lamellar stacks. As wt_PEO decreases from 1.0 to 0.3, more PVAc chains are excluded from the interlamellar region into the interfibrillar region. The fraction outside the lamellar stacks, which is completely occupied with PVAc chains, increases from 0 to 58%. Because the radius of gyration of PVAc with a random‐coil configuration determined from SANS is smaller than the average amorphous layer thickness from SAXS, we believe that the amorphous PVAc chains still persist with a random‐coil configuration even when the blends form an ordered structure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2705–2715, 2001     

Summary of ISO/TC 201 Standard: ISO 16129‐:2012 – Surface chemical analysis — Procedures to assess the day‐to‐day performance of an X‐ray photoelectron spectrometer

This International Standard is designed to allow the user to simply assess, on a routine basis, several key parameters of an X‐ray photoelectron spectrometer. It is not intended to provide an exhaustive performance check but instead provides a rapid set of tests that may be conducted frequently. Aspects of instrument behaviour covered by this document include the vacuum, measurements of spectra of conductive or non‐conductive samples and the current state of the X‐ray source. Other important aspects of the instrument performance (e.g. lateral resolution) fall outside the scope of this standard. The standard is intended for use with commercial X‐ray photoelectron spectrometers equipped with a monochromated Al Kα X‐ray source or with a unmonochromated Al or Mg Kα X‐ray source. Copyright © 2012 John Wiley & Sons, Ltd.     

A two‐stage surface treatment for the long‐term stability of hydrophilic SU‐8

The use of SU‐8 photoresist as a structuring material for portable capillary‐flow cytometry devices has been restricted by the near‐hydrophobic nature of the SU‐8 surface. In this work, we evaluate the use of chemical and plasma treatments to render the SU‐8 surface hydrophilic and characterise the resulting surface utilising a combination of techniques including contact angle goniometry, atomic force microscopy and X‐ray photoelectron spectroscopy. In particular, for low‐power plasma treatments, we find that the chemistry of the plasma used to modify the SU‐8 surface and the incorporation of O₂ on that modified surface are paramount for improved surface wettability, whilst plasma‐induced surface roughness is not a necessary requirement. We demonstrate a technique to obtain a hydrophilic SU‐8 surface with contact angle as low as 7° whilst controlling and significantly reducing the level of surface roughness generated via the applied plasma. An additional chemical treatment step is found to be essential to stabilise the activated SU‐8 surface, and incubation of the samples with ethanolamine is demonstrated as an effective second‐stage treatment. Application of the optimised two‐stage surface treatment to cross‐linked SU‐8 is shown to result in a smooth hydrophilic surface that remains stable for over 3 months. Copyright © 2015 The Authors Surface and Interface Analysis Published by John Wiley & Sons Ltd.     

Microstructural evolution underlying the ternary stages of the elastic behaviors for poly(ether‐b‐amide) copolymer elastomers

Three stages of elastic behavior were observed during cyclic deformations for poly(ether‐b‐amide) (PEBA) segmented copolymers based on crystalline hard segments of polyamide 12 (PA12) and amorphous soft segments of poly(tetramethylene oxide) (PTMO). The underlying microstructural evolution was characterized by a combination of in situ Fourier transform infrared spectroscopy (FTIR), wide‐angle X‐ray diffraction (WAXD), and small‐angle X‐ray scattering (SAXS) technologies. The γ–α″ phase transition of crystalline PA12 occurred upon stretching, and the orientation of the α″ phase was less reversible under larger strains. PTMO chain orientation cannot be restored to the initial state, contributing to plastic deformation. Driven by the entropy effect, the strain‐induced crystallization of PTMO can fuse during sample retarding, exerting little influence on the residual strain. For PEBA with a shore D hardness of 35 D, the long period (L) can be restored to the initial L after the sample was unloaded until system fibrillation. The tie molecules between adjacent oriented lamellae can be by drawn out high stress in a PEBA material with a shore D hardness of 40 D, and the relaxation led to a second long period. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 855–864     

Observation of surface contamination layer by X‐ray reflectometry (XRR) analyses

Ultra‐thin HfO₂ films of 3.5, 5.0, and 8.0 nm nominal thicknesses were prepared, respectively, on silicon substrates by using atomic layer deposition method. Through the analyses of X‐ray reflectometry (XRR), X‐ray photoelectron spectroscopy, and transmission electron microscopy for HfO₂ films with and without sample cleaning, the effects of surface contamination on XRR curve and film thickness were investigated, and contamination layer was observed and the thickness of the layer was determined. X‐ray photoelectron spectroscopy results indicated that the amount of surface contamination varied considerably because of the surface cleaning. XRR curve shapes and the positions of thickness fringes changed and the thickness from Fourier analyses of the curves were different for the same sample due to the different surface contamination. Contamination layer of about 1 nm thickness was observed by Fourier analysis of XRR curve. Simulation for XRR curve showed the best fit to data when contamination layer of about 1 nm thickness was considered, and the result was consistent with that of the Fourier analysis. Copyright © 2016 John Wiley & Sons, Ltd.     

Application of the Fe3O4@1,10‐phenanthroline‐5,6‐diol@Mn nano‐catalyst for the green synthesis of tetrazoles and its biological performance

The Fe₃O₄ magnetic particles were modified with 1,10‐phenanthroline‐5,6‐diol (Phen) and the related Mn complex (Fe₃O₄@Phen@Mn) synthesized as a heterogeneous catalyst to be used for the one‐pot three‐component synthesis of various tetrazoles. The catalysts were characterized by several methods, such as the elemental analysis, FT‐IR, X‐ray powder diffraction, dispersive X‐ray spectroscopy, scanning electron microscopy, transmission electron microscopy, dynamic light scattering, thermogravimetric‐differential thermal analysis, vibrating sample magnetometer and X‐ray photoelectron spectroscopy. In addition, the antioxidant and antibacterial activities of the catalyst and its Phen ligand were in vitro screened with 2,2‐diphenyl‐1‐picrylhydrazyl by free radical scavenging methods. Results showed that the synthesized compounds possess strong antioxidant activity (IC50; 0.172  ±  0.005 mg ml^?1) as well as a good antibacterial potential in comparison to standards.     

Thickness and coverage determination of multilayer with an island‐like overlayer by hard X‐ray photoelectron spectroscopy at multiple photon energies

To obtain depth profiles of the elemental composition of materials, we propose the use of hard X‐ray photoelectron spectroscopy (HAXPES) over a range of incident photon energies (PEs). Photoelectron intensities are measured as a function of PE and take‐off angle (TOA) from a multilayer sample (Au/SiO₂/Si). The top layer of the sample (Au) formed an island‐like structure, which we modeled as bumps and dips (surface roughness). The PE dependence, measured at angles close to the surface normal, is consistent with the theoretical results, in contrast to the TOA dependence. The Au coverage and layer thicknesses are calculated by curve fitting using experimental and theoretical results. Copyright © 2014 John Wiley & Sons, Ltd.     

Characterization of proton‐conducting organic–inorganic polymeric materials by ASAXS

The distribution of ZrO₂ and phosphotungstic acid (PTA) in a matrix of sulfonated polyether ketone was investigated by anomalous small‐angle X‐ray scattering (ASAXS). Scattering curves were obtained using X‐ray energies near the Zr and W absorption edges, allowing the independent analysis of the distribution of ZrO₂ and PTA in the sample. The interaction between both inorganic components improved their dispersion considerably when compared with films containing just one of the additives. The synergism was correlated to previous investigations concerning proton conductivity and permeability of the membranes developed for direct methanol fuel cell. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2981–2992, 2005