Quantitative X-ray Photoelectron Spectroscopy Research Articles

Quantitative Characterization of a Desalination Membrane Model System by X-ray Photoelectron Spectroscopy.

Aromatic polyamide films form the active layer in reverse osmosis desalination membranes. Despite widespread use of this technology, it suffers from low rejection rates for certain water contaminants and from membrane fouling. Through a better understanding of the fundamental surface chemical processes during reverse osmosis desalination, advances in membrane and material design are expected. The recent invention of a molecular layer-by-layer (mLbL) preparation technique [ Johnson , P. M. ; Molecular Layer-by-Layer Deposition of Highly Crosslinked Polyamide Films . J. Polym. Sci., Part B: Polym. Phys. 2012 , 50 ( 3 ), 168 - 173 ] yields films that are sufficiently smooth to warrant investigation with high-resolution microscopy and spectroscopy methods. We present high-resolution, quantitative X-ray photoelectron spectroscopy (XPS) data on the surface chemistry of ultrathin polyamide films that can serve as a model system for desalination membranes. We show that a quantitative analysis of the XPS spectra gives information about the functional groups of the film as well as other compounds present due to the synthesis under ambient conditions. Unpolymerized functional groups are identified and aid in understanding the degree of cross-linking. Investigation of polymers with synchrotron-based XPS requires taking beam-induced changes into account. We quantify X-ray beam damage and show that beam damage to the polyamide is limited, allowing long-term investigation of thin polyamide films. Characterizing mLbL-grown films via high-resolution XPS is the basis for a better understanding of the chemical interplay of polyamide surface functional groups with the major components of desalination systems.

The use of ionic liquids for the determination of the spectrometer transmission function in X-ray photoelectron spectroscopy (XPS)

The uncertainty of measurement in quantitative XPS analysis can be reduced by using a calibrated spectrometer transmission function T(E), which is usually determined by taking spectra from Au, Ag, Cu and Ge elemental reference materials. However, this approach is quite time-consuming due to required sample preparation steps like sputter cleaning etc., and the relatively big number of samples to be measured. This contribution proposes the use of the ionic liquids [C2C1im][NTf2] and [C3C1im][NTf2] as reference materials for a determination of T(E). These multi-elemental samples deliver five intensive photoemission peaks, F 1s, O 1s, N 1s, C 1s and S 2p, in an energy window from 160 eV to 700 eV which is of specific interest for applications of quantitative XPS for surface chemical analysis of soft matter, one of the major applications of XPS.

XPS analysis of the surface chemistry of sulfuric acid-treated kaolinite and diaspore minerals with flotation reagents

Kaolinite is one of the main associated minerals (gangue) in the processing of diasporic bauxites. Sulfuric acid pretreatment has been shown to have an improving effect on kaolinite-diaspore flotation separation, but the mechanism underpinning this effect is not well known. This study reports the surface chemistry of acid-treated kaolinite and diaspore in the presence of flotation reagents (sodium hexametaphosphate (SHMP) as a depressant and dodecylamine hydrochloride (DAH) as a collector) using X-ray photoelectron spectroscopy (XPS) analysis and zeta potential determinations. Quantitative XPS analysis revealed that the Al/Si atomic ratio on the kaolinite surface was reduced after the acid treatment. Compared with natural kaolinite, acid-treated kaolinite showed weakened adsorption properties for SHMP. Consequently, there was an enhanced DAH adsorption on the acid-treated kaolinite. High-resolution XPS analysis showed formations of “unsaturated Al” components on the diaspore surface after the acid treatment, which were ready to interact with phosphite groups of SHMP to depress diaspore in kaolinite flotation. Zeta potential studies also confirmed extended SHMP adsorption on acid-treated diaspore in comparison with the natural mineral. These findings form a firm knowledge for interpreting the application of kaolinite and diaspore in many adsorption studies, including the efficient separation between kaolinite and diaspore.

The behavior of Cr–Ni nanofilms on NiO(100) upon annealing and substrate-controlled oxidation studied by quantitative X-ray Photoelectron Spectroscopy

The interplay between metallic and oxidized phases of Cr, Ni nanodeposits has been investigated via a model system. The evolution upon annealing in ultra-high vacuum of metallic Cr ultra-thin or nanoparticulate films of less than 0.7 nm equivalent thickness on a NiO(100) single crystal substrate has been studied by means of X-ray Photoelectron Spectroscopy (XPS), angle resolved XPS and Low Energy Ion scattering. The NiO substrate provided oxygen in a highly controllable fashion, at first to the metallic Cr film, causing its fast oxidation at 550 K with parallel stoichiometric surface reduction of NiO to metallic Ni. The latter was subsequently subjected to slow re-oxidation by oxygen from the NiO bulk upon annealing up to 940 K, thus leading to complex interfaces that may include simultaneously metallic Cr, Ni and their respective oxides, all found together within a few atomic layers. The step-by-step monitoring of the evolution of the interfaces by XPS at various stages of annealing and the simulation of quantitative XPS data for alternative spatial distribution models of the co-existing phases yield structural information about the stacked layers produced by oxidation of Cr to Cr2O3 and metallic Ni, the re-oxidation of Ni0 via oxygen supplied by the NiO substrate and finally a mixing of the two oxides at 940 K with probable formation of a NiCr2O4 spinel.

Quantification of amine functional groups on silica nanoparticles: a multi-method approach.

Surface chemistry is an important factor for quality control during production of nanomaterials and for controlling their behavior in applications and when released into the environment. Here we report a comparison of four methods for quantifying amine functional groups on silica nanoparticles (NPs). Two colorimetric assays are examined, ninhydrin and 4-nitrobenzaldehyde, which are convenient for routine analysis and report on reagent accessible amines. Results from the study of a range of commercial NPs with different sizes and surface loadings show that the assays account for 50–100% of the total amine content, as determined by dissolution of NPs under basic conditions and quantification by solution-state 1H NMR. To validate the surface quantification by the colorimetric assays, the NPs are modified with a trifluoromethylated benzaldehyde probe to enhance sensitivity for quantitative 19F solid state NMR and X-ray photoelectron spectroscopy (XPS). Good agreement between the assays and the determination from solid-state NMR is reinforced by elemental ratios from XPS, which indicate that in most cases the difference between total and accessible amine content reflects amines that are outside the depth probed by XPS. Overall the combined results serve to validate the relatively simple colorimetric assays and indicate that the reactions are efficient at quantifying surface amines, by contrast to some other covalent modifications that have been employed for functional group quantification.

Reconfigurable Anticounterfeiting Coatings Enabled by Macroporous Shape Memory Polymers

Here, we report a new type of reconfigurable anticounterfeiting coating enabled by integrating the scientific principles of photonic crystal and shape memory polymer (SMP). The autonomous infusion of uncured oligomers in a polydimethylsiloxane (PDMS) stamp into a templated macroporous SMP photonic crystal coating, which was confirmed by quantitative X-ray photoelectron spectroscopy analysis, can program an iridescent pattern on the transparent SMP membrane with deformed macropores. By manipulation of the unconventional all-room-temperature shape memory effects exhibited by the shape memory copolymer comprising polyethylene glycol diacrylate and ethoxylated trimethylolpropane triacrylate, the iridescent pattern can be easily and instantaneously concealed and revealed by immersing in common household liquids (e.g., ethanol and water). Systematic experiments and theoretical simulations using scanning electron microscopy, atomic force microscopy, optical spectroscopy, scalar wave approximation modeling, and c...

Annealing process for recovery of carbonated (Mg,Ca)O protective layer for plasma discharge device

The carbonation behavior and decarbonation annealing of a protective (Mg,Ca)O layer for flat panel plasma discharge devices were investigated. Compared with a conventional MgO protective layer, the (Mg,Ca)O protective layer showed both high and low discharge voltages. Quantitative X-ray photoelectron spectroscopy analyses indicated that the high discharge voltages were caused by Ca carbonation. The progression of Ca carbonation was enhanced by exposure to air containing H2O but not by exposure to dry air. In addition, once (Mg,Ca)O is carbonated, it is impossible to decarbonate Ca by annealing in air at the temperature applied during the production process. We propose the use of annealing in vacuum as an effective method to promote the decarbonation of Ca and maintain a low discharge voltage for plasma discharge devices with (Mg,Ca)O protective layers.

Improved XPS analysis by visual inspection of the survey spectrum

In this paper, we have revisited a well‐known issue in quantitative X‐ray photoelectron spectroscopy (XPS) analysis: when quantitative XPS analysis is based solely on measured peak intensities, this can give rather confusing and misleading results. The problem is caused by peak intensity attenuation with photoelectron distance traveled in the sample and is an issue for samples where the atomic concentration varies substantially over the outermost ~5 nm. This is however the most significant depth range for many of the practical applications of nano‐structures which is today of increasing technological importance. We discuss 3 different methods to correct for the attenuation effect and their limitations. It is then pointed out how one can, by visually comparing observed peak shapes to a set of model spectra, often get a rough idea of the atom depth distribution in the surface region of the sample. This provides a practical tool to supplement the information obtained with XPS analysis based on peak intensities and chemical state information obtained from high‐resolution spectra.

Dynamic evolution of cathode electrolyte interphase (CEI) on high voltage LiCoO2 cathode and its interaction with Li anode

Realizing the charging of LiCoO2 to 4.6 V (vs. Li/Li+) reversibly has important value for achieving high volumetric and gravimetric energy density in rechargeable lithium batteries. However, the surface and interface instability of electrode at high voltage remains a primary problem. In this work, cathode electrolyte interphase (CEI) layer on LiCoO2 has been studied by X-ray photoelectron spectroscopy (XPS). In LiCoO2/Li battery, the dynamic evolution of CEI layer upon charging and discharging has been observed. Based on quantitative XPS analysis, a strong correlation on interface products between cathode and Li anode has been established. Such correlation mainly originates from the reversible formation and dissolution of the SEI layer on Li anode. The CEI layer evolution can be attributed to the sequential reactions through electrolyte and possibly physical migration of SEI fragments from Li anode. While in LiCoO2/graphite battery, the changes of the CEI on LiCoO2 becomes less significant due to the relative stable solid electrolyte interphase (SEI) layer forming on graphite anode, which further supports the strong correlation between CEI on cathode and solid electrolyte interphase (SEI) on Li anode. These results reveal the origin of the dynamical evolution of CEI on LiCoO2, and highlight that the impact of anode should be considered when interpreting the CEI on cathode, especially in rechargeable lithium batteries using lithium as anode.

Tunable superoleophobicity via harnessing the surface chemistry of UV responsive titania coatings.

Superoleophobic surfaces exhibiting tunable wettability are prepared by the combination of simple spray coating of Ultra Violet (UV) responsive titania nanoparticles and a low surface energy coating of a self-assembled monolayer (SAM) of 1H,1H,2H,2H-perflurodecyltrichlorosilane (PFDTS). Spray coating creates random micron-sized roughness with reentrant geometry, a necessary requirement for the superoleophobic surface, and a porous network at the nanometer size level, confirmed by the field emission scanning electron microscope (FE-SEM) images. By employing the rough surface and a low surface energy monolayer, the substrates possess superhydrophobicity with a water (γ = 72 mN m−1) contact angle of 163° and superoleophobicity with a decane (γ = 23 mN m−1) contact angle of 144°. Wettability of these surfaces is completely reversed to the superoleophilic state upon 6 h of UV irradiation. A quantitative X-ray photoelectron spectroscopy (XPS) analysis has confirmed the mechanism of decomposition of PFDTS molecules on the superoleophilic surfaces via interaction with the defect Ti3+ states of titania upon UV exposure. Furthermore, the superoleophobicity is restored to complete the transition cycle by changing the surface chemistry of the UV exposed surface via annealing and regrafting of the PFDTS monolayer.

Electrical response of Pt/Ru/PbZr0.52Ti0.48O3/Pt capacitor as function of lead precursor excess

We investigated the influence of the surface microstructure and chemistry of sol-gel grown PbZr0.52Ti0.48O3 (PZT) on the electrical performance of PZT-based metal-insulator-metal (MIM) capacitors as a function of Pb precursor excess. Using surface-sensitive, quantitative X-ray photoelectron spectroscopy and scanning electron microscopy, we confirm the presence of ZrOx surface phase. Low Pb excess gives rise to a discontinuous layer of ZrOx on a (100) textured PZT film with a wide band gap reducing the capacitance of PZT-based MIMs whereas the breakdown field is enhanced. At high Pb excess, the nanostructures disappear while the PZT grain size increases and the film texture becomes (111). Concomitantly, the capacitance density is enhanced by 8.7%, and both the loss tangent and breakdown field are reduced by 20 and 25%, respectively. The role of the low permittivity, dielectric interface layer on capacitance and breakdown is discussed.

An XPS Study with Depth Profiling for the Surface Oxide Layer Formed on Aluminides Produced on Superalloy 690 Substrates

Superalloy 690 substrates containing mainly Cr and Ni aluminides on the uppermost surface, formed by atmospheric plasma spraying and heat treatment, were oxidized at 1273 K in air for 2 h. Quantitative X-ray photoelectron spectroscopy (XPS) analyses indicated that the outermost surface layer formed on aluminides is composed of ~ 21.0 at.% Al+3 (as Al2O3), 17.0 at.% Al0 (elemental aluminium), 1.4 at.% Cr+3 (as Cr2O3) and 60.5 at.% O (in Al2O3 and Cr2O3 and also includes oxygen contaminant). Surface sputtering for 5 min exhibited splitting of Cr2p3/2 peak into a doublet comprising Cr+3 (0.9 at.%) and Cr0 (0.4 at.%) with the presence of 1.15 at.% Ni0 in the surface layer that mainly contained ~ 37.3 at.% Al+3, 7.3 at.% Al0 and 52.9 at.% O. Surface sputtering for 15 min indicated surface composition similar to surface sputtered for 5 min but with a marked reduction in ratio of Al+3/Al0 (32.2 at.% Al+3/11.90 at.% Al0) in the surface layer.

Surface Modifications of Na and K Metal Incorporated Cu(In,Ga)Se2 Absorbers Investigated by Synchrotron‐Based Spectroscopies

Na and K metals have been evaporated on a Cu(In,Ga)Se2 (CIGSe) thin film solar cell absorber at 400 °C in order to investigate the effect of alkali metal incorporation on the very near-surface (up to 5 nm) region of the CIGSe absorber using soft X-ray spectroscopy techniques, focusing on the main compositional and electronic modifications of the absorber surface. Quantitative X-ray photoelectron spectroscopy (XPS) showed Cu deficiency and Se enrichment on the CIGSe surface after alkali treatment which may play a role in assisting Na diffusion away from the surface, leaving behind a significantly higher K content than Na along the entire range of the CIGSe surface region probed, although nominally equal amounts of Na and K metal have been evaporated onto the CIGSe surface. A [K]/([K]+[Cu]) concentration ratio of 0.99 ± 0.01 at an information depth of ≈1.7 nm from the surface may indicate the formation of a wide band gap compound like KInSe2 (Eg ∼ 2.67 eV) on the CIGSe surface as a result of alkali metal deposition. Ultra-violet photoemission spectroscopy (UPS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) measurements further confirm a 1.09 eV surface band gap increase along with a type-inversion at the surface of the alkali metal-incorporated CIGSe as compared to the untreated CIGSe with a surface band gap of 1.3 ± 0.2 eV. These changes in the surface composition and electronic structure of the modified CIGSe surface as a result of the alkaline treatment could be attributed to the increase in alkali-treated CIGSe-based thin film solar cell efficiencies seen in recent years.

Investigation of structural network and mechanical properties of Titanium silicon nitride (TiSiN) thin films

Titanium silicon nitride (TiSiN) thin films were deposited on p-type c-Si (100) with different N2 flow rate by using chemical vapor deposition (CVD) technique. The microstructure, phonon modes, mechanical properties and compositional study of TiSiN thin films were characterised by scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy, nanoindentation and X-ray photoelectron spectroscopy (XPS),respectively. The SEM images show increases in surface roughness with increasing of N2 flow rate, however, improves the hardness and Young's modulus of TiSiN thin film. The XRD analysis reveals the presence of strain in TiSiN films. The estimated crystallites of TiSiN thin films was 7.51 and 7.39 nm for 40 and 100 sccm N2 flow rate. The XPS reveals the presence of 20 at. % Si content at 40 sccm N2 flow rate in the TiSiN film. To analyse the broad Raman spectra of TiSiN thin films, the peaks were convoluted into six individual Gaussian peaks. The quantitative and qualitative analysis XPS and Raman spectra of TiSiN thin films were carried out by using Origin 9.0 software.

From Flat Surfaces to Nanoparticles: In Situ Studies of the Reactivity of Model Catalysts

This perspective summarizes results of in situ adsorption and reaction experiments on graphene-supported nanoparticles: the particular aim is to point out similarities and differences between studies on “traditional” single crystal studies and the more complex, more realistic nanoparticles. It is shown that the use of quantitative X-ray photoelectron spectroscopy allows for gaining a detailed insight even into these complex systems, thereby facilitating a further step into bridging the materials gap from fundamental science to applied sciences. The use of graphene as a substrate gives intriguing new possibilities, as the template effect of graphene can lead to a very narrow size distribution of the clusters, while graphene itself is chemically innocent, thereby making side processes such as spill over and reverse spill over less likely. The systems discussed range from extremely well studied systems such as the adsorption and reaction of CO on a Pt(111) surface, to stepped surfaces and finally to nanocluster arrays supported on a graphene support. Also, the important chemistry of sulfur, being a strong catalyst poison, on such systems will be discussed. While the adsorption behavior on nanoclusters is strongly reminiscent of the adsorption on stepped surfaces, a strong increase in the reactivity of nanoparticles systems is found.

Drastic improvement of as-sputtered silicon nitride thin film quality at room temperature by ArF excimer-laser annealing method

Hydrogen-free silicon-nitride films have been deposited on 1200 Å-thick Si (100) wafers by using reactive sputtering at room temperature and annealed by ArF excimer-laser at room temperature. In-situ X-ray photoelectron spectroscopy (XPS) analyses showed that the 1200 Å-thick as-sputtered films were completely and uniformly annealed by ArF excimer-laser with the various energy densities leaving no unannealed portion in the depth direction. An as-sputtered film was also annealed in furnace at 1 000 °C for comparison. The influence of the energy density was further investigated by comparing the etch rate of the SiN film with the N/Si ratio adjusted by separating the unreacted-Si and N components from the SiN film. For the excimer-laser-annealed SiN films, the results of quantitative XPS analysis were in good agreement with the etching characteristics.The as-sputtered SiN film contained slightly higher Si than the stoichiometric ratio, with an adjusted-N/Si-ratio value 0.902, possibly due to sporadic presence unreacted-Si. At the laser energy densities ranging from 100 to 175 mJ/cm2, the excimer-laser-annealed SiN films displayed a much better film quality than the SiN film annealed at 1000 °C, due to a higher N/Si ratio.

Chemistry of surface nanostructures in lead precursor-rich PbZr0.52Ti0.48O3 sol–gel films

We present a study of the chemistry of the nanostructured phase at the surface of lead zirconium titanate PbZr0.52Ti0.48O3 (PZT) films synthesized by sol–gel method. In sol–gel synthesis, excess lead precursor is used to maintain the target stoichiometry. Surface nanostructures appear at 10% excess whereas 30% excess inhibits their formation. Using the surface-sensitive, quantitative X-ray photoelectron spectroscopy and glancing angle X-ray diffraction we have shown that the chemical composition of the nanostructures is ZrO1.82−1.89 rather than pyrochlore often described in the literature. The presence of a possibly discontinuous layer of wide band gap ZrO1.82−1.89 could be of importance in determining the electrical properties of PZT-based metal-insulator-metal heterostructures.

Cu-Ag core–shell nanoparticles with enhanced oxidation stability for printed electronics

In this work, we synthesized uniform Cu–Ag core–shell nanoparticles using a facile two-step process that consists of thermal decomposition and galvanic displacement methods. The core–shell structure of these nanoparticles was confirmed through characterization using transmission electron microscopy, energy-dispersive spectroscopy, and x-ray diffraction. Furthermore, we investigated the oxidation stability of the Cu–Ag core–shell nanoparticles in detail. Both qualitative and quantitative x-ray photoelectron spectroscopy analyses confirm that the Cu–Ag core–shell nanoparticles have considerably higher oxidation stability than Cu nanoparticles. Finally, we formulated a conductive ink using the synthesized nanoparticles and coated it onto glass substrates. Following the sintering process, we compared the resistivity of the Cu–Ag core–shell nanoparticles with that of the Cu nanoparticles. The results of this study clearly show that the Cu–Ag core–shell nanoparticles can potentially be used as an alternative to Ag nanoparticles because of their superior oxidation stability and electrical properties.

Energy Thresholds of DNA Damage Induced by UV Radiation: An XPS Study.

This work stresses on damage at the molecular level caused by ultraviolet radiation (UV) in the range from 3.5 to 8 eV, deoxyribonucleic acid (DNA) films observed by X-ray photoelectron spectroscopy (XPS). Detailed quantitative XPS analysis, in which all the amounts are relative to sodium-assumed not to be released from the samples, of the carbon, oxygen, and particularly, nitrogen components, reveals that irradiation leads to sugar degradation with CO-based compounds release for energies above 6.9 eV and decrease of nitrogen groups which are not involved in hydrogen bonding at energies above 4.2 eV. Also the phosphate groups are seen to decrease to energies above 4.2 eV. Analysis of XPS spectra allowed to conclude that the damage on bases peripheral nitrogen atoms are following the damage on phosphates. It suggests that very low kinetic energy photoelectrons are ejected from the DNA bases, as a result of UV light induced breaking of the phosphate ester groups which forms a transient anion with resonance formation and whereby most of the nitrogen DNA peripheral groups are removed. The degree of ionization of DNA was observed to increase with radiation energy, indicating that the ionized phosphate groups are kept unchanged. This result was interpreted by the shielding of phosphate groups caused by water molecules hydration near sodium atoms.

Surface modification of graphene and graphite by nitrogen plasma: Determination of chemical state alterations and assignments by quantitative X-ray photoelectron spectroscopy

Multilayer graphene (MLGR) and its bulk analog, highly oriented pyrolytic graphite (HOPG), were treated by radio frequency activated low pressure N2 gas plasma (at negative bias 0–200V, for 5–20min). Surface composition and chemical-state alterations were delineated by X-ray photoelectron spectroscopy (XPS). Covalently bonded nitrogen of 5–15at% incorporated into the surface. The higher N concentration in MLGR below 100V is attributed to the larger number of defects. The equal N content at 200V indicates intensive formation of reactive sites. In-depth distribution of N is restricted to 2–4 monolayers. Model calculation resulted in 23at% N (at 100V) in the top graphene layers of HOPG. Three different chemical states of nitrogen (pyridine-type at 398.3eV, pyrrole- and triazine-type at 399.7eV and N substituting C in graphite-like network at 400.9eV) were determined from high-resolution N1s spectral region for all samples. Pyridine and pyrrole–triazine components increase preferentially with increasing bias. Alterations of the C1s and O1s spectra are discussed in a critical approach. The amount of reacted carbon was consistent with that required for the three different nitrogen and oxygen states, thus validating the proposed assignments.