X-ray Photoelectron Spectroscopy Binding Energy Research Articles

One-Step Synthesis and Operando Electrochemical Impedance Spectroscopic Characterization of Heterostructured MoP-Mo2N Electrocatalysts for Stable Hydrogen Evolution Reaction.

This study presents a novel synthesis of self-standing MoP and Mo2N heterostructured electrocatalysts with enhanced stability and catalytic performance. Facilitated by the controlled phase and interfacial microstructure, the seamless structures of these catalysts minimize internal resistivity and prevent local corrosion, contributing to increased stability. The chemical synthesis proceeds with an etching step to activate the surface, followed by phosphor-nitriding in a chemical vapor deposition chamber to produce MoP-Mo2N@Mo heterostructured electrocatalysts. X-ray diffraction analyses confirmed the presence of MoP, Mo2N, and Mo phases in the electrocatalyst. Morphology studies using scanning electron microscopy characterize the hierarchical growth of structures, indicating successful formation of the heterostructure. X-ray photoelectron spectroscopy (XPS) analyses of the as-synthesized and postcatalytic activity samples reveal the chemical shift in terms of the binding energy (BE) of the Mo 3d XPS peak, especially after catalytic activity. The XPS BE shifts are attributed to changes in the oxidation state, electron transfer, and surface reconstruction during catalysis. Electrochemical evaluation of the catalysts indicates the superior performance of the MoP-Mo2N@Mo heterostructured catalyst in hydrogen evolution reactions (HER), with lower overpotentials and enhanced Tafel slopes. The stability tests reveal changes in double layer capacitance over time, suggesting surface reconstruction and an increased active surface area during catalysis. Operando electrochemical impedance spectroscopy (EIS) further elucidates the dynamic changes in resistance and charge transfer during HER. Overall, a comprehensive understanding of the synthesis, characterization, and electrochemical behavior of the developed MoP-Mo2N@Mo heterostructured electrocatalyst, as presented in this work, highlights its potential utilization in sustainable energy applications.

Transition Metal β-Diketonate Adhesion Promoters in Epoxy-Anhydride Resin.

Epoxy to copper adhesion supports the reliability of numerous structures in electronic packaging. Compared to substrate pre-treatment, processing and cost considerations are in favor of adhesion promoters loaded in epoxy formulations. In this work, first row transition metal β-diketonates present such a compelling case when added in epoxy/anhydride resins: over 30% (before moisture aging) and 50% (after moisture aging) enhancement in lap shear strength are found using Co(II) and Ni(II) hexafluoroacetylacetonate. From extensive X-ray photoelectron spectroscopy (XPS) analyses on the adhesively failed sample surfaces, increased population of oxygen-containing functional groups, especially esters, is linked to the adhesion improvement. Assisted by XPS depth profile on the fractured epoxy side and in situ Fourier-transform infrared spectroscopy (FTIR), the previously discovered latent cure characteristics endowed by the metal chelates interacting with phosphine catalysts are regarded pivotal for pacing the anhydride consumption and allowing interfacial esterification reactions to occur. Further examinations on the XPS binding energy shifts and dielectric properties of the doped epoxy also reveal metal-polymer coordination that contribute to the adhesion and moisture resistance properties. These findings should stimulate future research of functional additives targeting at cure kinetics control and polar group coordination ideas for more robust epoxy-Cu joints.

Sol—gel approach to low-temperature synthesis of single-phase metastable La2Ga3O7.5 melilite with enhanced grain-boundary oxide ionic conductivity via a kinetically favorable mechanism

Starting with the stoichiometric and highly homogeneous gel-precursor, single-phase metastable melilite La2Ga3O7.5, as the end-member of solid solution La1+xSr1−xGa3O7+x/2 (0≼x≼1), has been synthesized by solid-state reaction at 700 °C for 2 h via a kinetically favorable mechanism and characterized by X-ray diffraction (XRD), Raman, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), AC impedance spectroscopy, etc. It has been revealed that the as-synthesized melilite La2Ga3O7.5 shows an orthorhombic symmetry with crystal cell parameters a = 11.4690(1) Å, b = 11.2825(4) Å, and c = 10.3735(4) Å, while has more Raman active modes than LaSrGa3O7 with a tetragonal structure, which was also synthesized under the same conditions for comparison, but tends to slowly decompose into perovskite LaGaO3 and Ga2O3 when annealed at 700 °C for over 20 h driven by its meta-stability. Moreover, the metastable La2Ga3O7.5 shows a higher XPS binding energy for the excess oxide ions in the crystal structure than those at normal lattice sites. Its intrinsic grain oxide ion conductivity can reach as high as 0.04 and 0.51 mS·cm−1 at 550 and 700 °C, respectively, characterized by a simple Arrhenius relationship ln(σT)—1/T with invariable activation energy, Ea = 1.22 eV, over the temperature range from 300 to 700 °C, along with an apparent grain boundary conductivity that is about double that from the grains thanks to the clean grain boundaries. This paper provides a new strategic approach to the synthesis of complex oxides that may be of high performance but are difficultly achieved by the conventional ceramic method at high temperatures.

Electron removal energies in noble-gas atoms up to 100 keV: Ab initio GW versus x-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) measures electron removal energies, providing direct access to core and valence electron binding energies, hence probing the electronic structure. In this Letter, we benchmark the ab initio many-body $GW$ approximation on the complete electron binding energies of noble-gas atoms (He-Rn), which span 100 keV. Our results demonstrate that $GW$ achieves an accuracy within 1.2% in XPS binding energies, by systematically restoring the underestimation from density-functional theory (error of 14%) or the overestimation from Hartree-Fock (error of 4.7%). Such results also imply the correlations of $d$ electrons are very well described by $GW$.

Ti(IV)-Exchanged Nano-ZIF-8 and Nano-ZIF-67 for Enhanced Photocatalytic Oxidation of Hydroquinone

The metal centres of nano-zeolitic imidazolate framework-8(Zinc) and 67(Cobalt) [nZIF-8(Zn) and nZIF-67(Co)] were partially exchanged with titanium (Ti) centres to form bimetallic nZIF-8(Zn/Ti) (52% Ti4+) and nZIF-67(Co/Ti) (38% Ti4+) respectively, for enhanced photocatalytic performance. A morphological and structural analysis by scanning electron microscopy, energy dispersive spectroscopy (EDS)-mapping and powder X-ray diffraction showed that the particle size, distribution, and the structural integrity of the Sodalite frameworks of the parent ZIFs were retained during the exchange process to form the new bimetallic Ti-ZIFs. Fourier transform infrared spectroscopy confirmed that no additional chemical bonds were formed during the process. X-ray photoelectron spectroscopy binding energies confirmed the preservation of the Zn(II), Co(II) and Ti(IV) oxidation states, as well as the Ti-content, consistent with inductively coupled plasma-optical emission spectrometry and EDS measurements. The Ti-exchanged ZIFs showed higher activity during the photocatalytic oxidation of hydroquinone in comparison with their parent ZIFs. Their kinetic rates were nearly five times faster than those of the parent ZIFs, with the first-order rate constants k = 0.189 min−1 for nZIF-8(Zn/Ti) and k = 0.139 min−1 for nZIF-67(Co/Ti). These catalysts are efficient, stable, and reusable for three photocatalytic cycles without a significant loss of catalytic activity.

An Efficient Cyan Emission from Copper (II) Complexes with Mixed Organic Conjugate Ligands.

Copper (II) complexes containing mixed ligands were synthesized in dimethyl formamide (DMF). The intense cyan emission at an ambient temperature is observed for solid copper (II) complexes with salicylic acid and a 12% quantum yield with a fluorescent lifetime of approximately 10 ms. Hence, copper (II) complexes with salicylic acid are excellent candidates for photoactive materials. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) reveal that the divalent copper metal centers coordinate with the nitrogen and oxygen lone pairs of conjugate ligands. XPS binding energy trends for core electrons in lower-lying orbitals are similar for all three copper (II) complexes: nitrogen 1s and oxygen 1s binding energies increase relative to those for undiluted ligands, and copper 2p3/2 binding energies decrease relative to that for CuCl2. The thermal behavior of these copper complexes reveals that the thermal stability is characterized by the following pattern: Cu(1,10-phenanthroline)(salicylic acid) > Cu(1,10-phenanthroline)(2,2’-bipyridine) > Cu(1,10-phenanthroline)(1-benzylimidazole)2.

First-principles study of absolute XPS binding energy with PAW planewave pseudopotential method: application to tungsten disulfides

We propose an efficient theoretical method to take into account the core-hole spin density in the projector augmented wave method, combined with spin un-polarized pseudopotentials and the planewave basis set. We apply this method to the calculation of absolute core level X-ray photoelectron spectroscopy binding energies of WS2 and its related materials, and find the following points. First, inclusion of core-hole spin in the core-exited state is essential for accurate description of the binding energies, especially for light elements. Second, the calculated absolute binding energies show excellent agreement with experimental results. Finally, when oxygen atoms are incorporated in the basal plane of WS2 in the metallic phase, the O 1s binding energy is expected to appear at lower energy than the corresponding value in the semiconducting phase.

Metal-Ion Coupling in Metal-Organic Framework Materials Regulating the Output Performance of a Triboelectric Nanogenerator.

Metal-organic frameworks (MOFs) as friction nanopower generation materials have attracted more and more research and attention because of the inherent three-dimensional framework structure and large aperture. In this work, the ZUT-75(Mn) with a one-dimensional pore structure was synthesized by using electron-rich benzimidazole carboxylic acid ligands, and isomorphic offspring MOF materials were obtained by single crystal-single crystal solvent-assisted metal-ion exchange. The exchange process was monitored by liquid UV-vis spectroscopy, atomic absorption spectrometry, and energy-dispersive X-ray spectroscopy. The metal-oxygen coordination energy, X-ray photoelectron spectroscopy binding energy, and hard-soft acid-base principle verified the spontaneity of the central-metal-exchange reaction. The four materials were applied to a triboelectric nanogenerator (TENG), and the output performance law of ZUT-75 was Co-MT > Zn-MT > Cu-MT > Mn-MT. Among them, the charge and power densities of Co-MT were up to 127.05 μC m-2 and 3280.50 mW m-2. When the density functional theory calculation and variable-temperature magnetic susceptibility test results were combined, it was concluded that low metal-ion-coupling degree promoted the formation and transfer of contact electrifications, which greatly improved the output performance of the TENG. This work provided a new idea for improving the output performance of the TENG.

Benzobisthiazole-bridged white fluorescent emitting covalent organic framework for simultaneous mercury detection and removal

Mercury (Hg2+), a heavy metal ion, is considered one of the most toxic metals on earth and is widespread as an environmental pollutant. Various promising adsorbents have been developed with accessible chelating sites and high affinity for heavy metal ions. Herein, we utilized the advantages of covalent organic frameworks (COFs) and designed benzobisthiazole-bridged (BBT) fluorescent COFs (FCOFs) for Hg2+ sensing applications. The BBT-FCOF nanosheets has a π-π transition, effective electron transfer, and enhanced delocalization within the π orbitals of the BBT ring. It emits a white fluorescence enabling real-time detection of Hg2+ metal ions. The excellent sensing property of BBT-FCOF nanosheets was attributed to the high sensitivity towards Hg2+; this was confirmed by the x-ray photoelectron spectroscopy binding energy of sulfur and nitrogen atom in BBT-FCOF. The limit of detection of Hg2+ was 30 ppb, which is very low compared to other published methods. ICP-mass measurement also proved that BBT-FCOF nanosheets removed almost 99% of Hg and BBT-FCOF distribution coefficient (Kd) was calculated to be 5 × 105 g−1. The recyclability test proved that HCl effectively removed the adsorbed Hg2+ metal ions from BBT-FCOF nanosheets, making it a useful tool for real-time Hg2+ detection and removal from waste water.

Hydroxyapatite and lead-substituted hydroxyapatite near-surface structures: Novel modelling of photoemission lines from X-ray photoelectron spectra

X-ray photoelectron spectroscopy (XPS) is one of the main tools for hydroxyapatite (HA) surface characterization in developing materials for biomedical and heterogeneous catalysis. Despite the XPS technique's potential to correlate binding energies with existing photo-emitter sites on near-surfaces, few previous studies analyzed this aspect for HA and metal-substituted HA surfaces. In this work, we theoretically reconstructed the XPS spectra of stoichiometric HA and lead-substituted hydroxyapatite (PbCaHA, Ca10-xPbx(PO4)6(OH)2; x = 2, 10) using a first-principles linear combination of atomic orbitals embedded cluster approach and periodic supercell band structures within the framework of Density Functional Theory (DFT). We take into account photoemission lines contributions from Ca(1), Ca(2), Pb(1) and Pb(2) sites located on surface and near-surface depths (up to ∼15 Å) along the (001) and (100) surfaces. The calculated DFT spectra of HA and PbCaHA were compared with high-resolution XPS spectra previously characterized by synchrotron X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). A combined theoretical and experimental approach enables decoding of the complex structure of HA and PbCaHA in XPS spectra. It was found that XPS binding energies profiles depend significantly on photo-emitters from near-surface sites and surface crystallographic orientation. The main Ca 2p3/2 envelope peak in HA is predominantly from Ca(1) and Ca(2) sites (∼347.4 eV), while the weaker peak is due to the Ca(2) site only (∼345.0 eV). Variations on HA nanoparticle morphology could be a critical factor for changes in XPS binding energies' profile.

Boosting Efficient Ammonia Synthesis over Atomically Dispersed Co-Based Catalyst via the Modulation of Geometric and Electronic Structures

Boosting Efficient Ammonia Synthesis over Atomically Dispersed Co-Based Catalyst via the Modulation of Geometric and Electronic Structures

Polyvinylpyrrolidone-Stabilized Iridium Nanoparticles Catalyzed the Transfer Hydrogenation of Nitrobenzene Using Formic Acid as the Source of Hydrogen

Catalytic nitrobenzene reduction is crucial for the synthesis of 4,4-methylene diphenyl diisocyanate, which is used to produce polyurethane foams, thermoplastic elastomers, and adhesives. The stability and activity of nanoparticle catalysts are affected by surface ligands and stabilizers. We established the complete composition of 7.0 ± 1.1 nm iridium oxide nanoparticles that were stabilized by polyvinylpyrrolidone (PVP[Ir]). PVP[Ir] and its surface stabilizers were characterized using elemental analysis (EA), high-resolution X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD), FT-IR, and UV-vis spectroscopy. Notably, PVP[Ir] contained 33.8 ± 0.4% Ir. XPS binding energy analyses suggest that 7% of the Ir is Ir(0) and 93% is IrO2. Using formic acid as the source of hydrogen, PVP[Ir] catalyzed the selective hydrogenation of nitrobenzene to give aniline as the only product in 66% yield in 1 h at 160 °C in a high-pressure metal reactor. Less than 1% of the side products (azobenzene and azoxybenzene) were detected. In contrast, using alcohol as the hydrogen source led to a low yield and a poor selectivity for aniline.

Electrochemical Study of the Effect of Prussian Blue As a Mediator in a Solid-State Supercapacitor

In the present study, electrochemical, X-ray photoelectron spectroscopy (XPS), and In-situ X-ray absorption spectroscopy (XAS) measurements were performed to investigate the charge/discharge process in a solid-state mediator supercapacitor (SC) or redox electrolyte SC. Prussian blue (PB) was synthesized using a wet chemistry method. A solid-state asymmetrical supercapacitor was fabricated with the configuration of (active carbon) /polymer electrolyte membrane/ (active carbon + PB). A KCl saturated Ag/AgCl reference electrode was inserted in the cell to monitor the potentials of the positive and negative electrodes during the charge/discharge process. Both electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements indicated that the supercapacitor had a capacitor-like behavior. Upon negative polarization of the PB-containing electrode the specific capacitance of the SC was increased 80% while upon positive polarization, there was much less enhancement of the specific capacitance. The potentials of the two electrodes versus the reference electrode were displaced proportionally with increasing the voltage of the cell. The XPS results indicated that the potassium concentration in PB is 0.5 atomic % suggesting that iron ions had valence close to +3, which is consistent with the measured XPS binding energy of the Fe 2p3/2 line and the X-ray absorption Fe K-edge energy when compared with the appropriate reference compounds. This indicated that instead of a nominal chemical formula KFeFe(CN)6, the formula was actually closer to K0.07FeFe(CN)6. In-situ XAS results (Figure 1) confirmed that upon positive polarization of the PB-containing electrode there was only small degree of redox activity occurring. On the other hand, upon negative polarization of the PB-containing electrode there was significant redox activity occurring due to reduction of Fe3+ to Fe2+. The XAS results also confirmed that the redox activity is completely reversible between cycles 4 and 5. Figure 1

Biomedical application of single anatase phase TiO2 nanoparticles with addition of Rambutan (Nephelium lappaceum L.) fruit peel extract

Metal oxide nanoparticles are considered to be an important material due to their good mechanical stability, unique structure and catalytic properties. The hydrothermal method was followed along with rambutan (Nephelium lappaceum L.) fruit peel extract mixed with metal ions to prepare titanium dioxide (TiO2) nanorods. Though there are numerous similar works published in past decades, in comparison with those works, the novelty of this work is using rambutan fruit peel as a precipitation agent. The advantages of using such natural agents are that they are eco-friendly and economically feasible. The prepared TiO2 nanorods were co-cultured with human breast cancer cells (MDA-MB-231) and their cytotoxicity was evaluated. The morphology of the nanorods was analyzed through transmission electron microscopy. The average diameter of the TiO2 nanorods was found to be 70–90 nm. The anatase phase of the tetragonal structure was confirmed through X-ray diffraction analysis. The studies of the vibrational Raman active modes and optical properties confirmed the presence of TiO2. X-ray photoelectron spectroscopy binding energy of Ti2p3/2 determined as 460 eV and that of O1s determined as 532 eV confirmed the presence of TiO2. Cytotoxicity was analyzed using MDA-MB-231 and cell death was observed at 73.65 µg/ml.

Core-level shifts in x-ray photoelectron spectroscopy of arsenic defects in silicon crystal: A first-principles study

We systematically investigated the arsenic (As) 3d core-level x-ray photoelectron spectroscopy (XPS) binding energy and formation energy for As defects in silicon by first-principles calculation with a high accuracy of 0.1 eV by careful evaluation of the supercell size. For As, we adopt a pseudopotential with 3d states as the valence and the spherical hole approximation to ensure the convergence of self-consistent calculation for the XPS binding energy with large size systems. Some of the examined model defects have threefold coordinated As atoms. The XPS binding energies of these As atoms are distributed in the narrow region from −0.66 eV to −0.73 eV in neutral charge states. Such defects in negative charge states have a lower XPS binding energy by about 0.1 eV. From the XPS binding energy and electrical activity, negatively charged defects of a vacancy and two adjacent substitutional As atoms (As2V) are the most probable candidates for the experimentally observed peak at −0.8 eV called BEM from the reference substitutional As peak. Under the experimental condition, we find that As2V−,2− do not deeply trap electrons and are electrically inactive. We also demonstrate the surface effect that surface states near the bandgap decrease the XPS binding energy, which may generate defects with low binding energies similarly to the experimental peak at −1.2 eV called BEL.

An Introduction to Coding with Matlab: Simulation of X-ray Photoelectron Spectroscopy by Employing Slater’s Rules

Computational approaches toward simulating chemical systems and evaluating experimental data has gathered great momentum in recent years. The onset of more powerful computers and advanced software has been instrumental to this end. This manuscript presents a hands-on activity which trains students in basic coding skills within the Matlab framework. Moreover, students are able to simulate X-ray photoelectron spectroscopy (XPS) spectra of various elements using Slater’s rules, a cornerstone of computational chemistry and a key topic in many undergraduate courses. A semiworked cadmium XPS example is introduced herein from which the XPS binding energy of the 3d electron may be calculated. Results are then compared with experimental values. The close agreement (within 10%) offers a real sense of student satisfaction and an appreciation of the value of computational techniques. Further elements and electronic configurations are subsequently explored. In sum, this practical develops understanding in the areas of quantum chemistry, spectroscopy, and coding skills simultaneously.

First-principles calculation of X-ray photoelectron spectroscopy binding energy shift for nitrogen and phosphorus defects in 3C-silicon carbide

We systematically investigated the formation energies and the core-level X-ray photoelectron spectroscopy binding energy (XPSBE) shifts of nitrogen (N) 1s and phosphorus (P) 2p for defects including N and P in 3C-SiC by a first-principles calculation using the generalized gradient approximation, whose reliability for n-type defects was confirmed by some tests using the HSE06 hybrid functional. XPSBEs were separated into the local potential average around the impurity and the relaxation energy of the wave function to analyze the relationship between the XPSBE shift and the defect structures. It is difficult to understand the relaxation energy intuitively. The electrons localized around the impurity atom, which have energy levels in energy gaps, make a large contribution to the relaxation energies. Considering the formation energies, we predicted some XPS peaks expected to be found.

Formation and characterization of embedded Fe3Si binary structures in Si

Chemical and electronic properties of ion beam synthesized Fe-Si binary structures are studied using X-ray photoelectron spectroscopy binding energy analysis. Ferromagnetic Fe-Si (Fe3Si) binary structure formation is enhanced in the ion-beam synthesis process by applying an in situ external magnetic field parallel to the Si substrate during the Fe implantation. Core-level analysis shows features corresponding to chemical environments of different Fe-Si phases. Fe 2p3/2 and Fe 3s peaks were analyzed, considering peak position, symmetry, and splitting. The ferromagnetic Fe3Si phase shows a highly asymmetric 2p3/2 peak at 706.6 eV and peak splitting in the 3s peak due to the exchange interaction with unfilled 3d electrons in the valance band. In contrast, the Si core-level did not show any significant features leading to the identification of Fe-Si binary compounds. The Si 2p peak showed a constant 0.2 eV peak shift toward the high-energy side compared to the elemental Si. Further valance band spectra reveal distinct features to help identify the Fe3Si phase. In general, core and valance band features of Fe-Si binary compounds provided definitive information about Fe3Si phase identification and its electronic structure with direct evidence of the exchange interaction, which occurs between core levels, valance band, and the unfilled 3d shell.

First-principles X-ray photoelectron spectroscopy binding energy shift calculation for boron and aluminum defects in 3C-silicon carbide

We systematically investigated the core-level X-ray photoelectron spectroscopy (XPS) binding energy shifts of B 1s and Al 2p and formation energies for defects including boron and aluminum in 3C-silicon carbide (SiC) by first-principles calculation. We analyzed the relation between the XPS binding energy shift and defect states and found that the defects with localized electrons in the band gap or energy gap in the valence band have larger XPS relaxation energies (XPSREs) than those without localized electrons. In contrast, spread electrons and electrons localized away from the core hole hardly affect the XPSREs. Further, we analyzed the dependence on crystal matrices, that is, elemental and compound semiconductors, on XPS spectra by comparing the XPS spectra of Si and 3C-SiC. Although the variation of the local potential in 3C-SiC is larger than that in Si, the variations of their relaxation energies are comparable.

Initial stages in functionalization of polystyrene upon treatment with oxygen plasma late flowing afterglow

A remote microwave discharge was applied as a source of oxygen (O) atoms for treatment of polystyrene in the preparation chamber of an x-ray photoelectron spectroscopy (XPS) instrument. The density of O atoms as measured with a calibrated catalytic probe was 2 × 1018 m−3. Such a small O atom density allowed for investigating the initial stages of polymer functionalization. The samples were subjected to various fluences of O atoms from approximately 2 × 1021 to 3 × 1023 m−2, and the functional groups were determined by XPS without breaking vacuum conditions. The results showed rapid destruction of the aromatic rings even at low O atom fluences. The initial functionalization caused the formation of hydroxyl groups followed by carbonyl groups, but the measurable amount of the carboxyl or ester groups, let alone carbonate, appeared only after the fluence of approximately 1 × 1022 m−2. The concentration of functional groups of the high XPS binding energy shift increased at elevated fluences until it became comparable with those of the low energy shift at the largest fluence used in this investigation, i.e. 3 × 1023 m−2. The O concentration on the polymer surface as determined from XPS survey spectra was first rapidly increasing up to the fluence of a few 1022 m−2 and then continue increasing slowly with the increasing fluence even beyond 1 × 1023 m−2. This investigation, which was performed in situ, gives us new knowledge for understanding the initial steps of polymer functionalization.