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NEXAFS analysis of a plasma treated, partially crystalline poly(ehtylene terephtalate) surface
(1996)
Self-assembled octadecyltrichlorosilane (CH3(CH2)17SiCl3, OTS) films were deposited on an oxidized silicon wafer. They were carefully exposed to a low-pressure oxygen direct current (dc) plasma and/or Cr vapor. Subsequently, they were characterized by X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, and atomic force microscopy. Detailed information on the oxygen functionalization and the molecular conformation of the OTS films was obtained. The main result was that functionalization conditions can be found where the order of the film remains almost unaffected. Similarly, Cr evaporation of pure OTS films revealed only slight effects on the order in the film. Cr evaporation of an ordered but functionalized OTS film immediately changes its state toward a fully isotropic one. In the course of interaction, oxygen sites at the surface of the functionalized OTS film are reduced whereas Cr becomes oxidized. A redox reaction scheme is proposed for this interfacial reaction. Finally, it is concluded that the given study should be of importance for advanced plasma processing of polyolefins.
Barrier properties of plasma and chemically fluorinated polypropylene and polyethyleneterephthalate
(1995)
The functionalization, perfluorination or an coating of polypropylene (PP) and polyethyleneterephthalate (PET) surfaces in different plasma atmospheres and in an F[2] + N[2] gas mixture were investigated. The aim of this work was to form a barrier layer against solvent and fuel permeation. Typical test solvents were n-pentane, toluene, tetrachloroethylene and mixtures of n-pentane and methanol. The permeation was gravimetrically measured. The permeation of the solvent mixtures was analyzed by mass spectrometry and Fourier transform IR spectroscopy. The permeation of the solvent mixtures through the plasma-modified polymer samples was associated with increased absorption of polar solvent components in the polymer film. The thickness of the plasma-fluorinated PP surface layer was 10-100 nm and that of chemically fluorinated PP about 5000 nm. Nearly the same barrier efficiency was measured for both plasma- and chemically fluorinated samples.
Neues vom Urkilogramm
(1999)
Overlayers of SiO2 (nominally 4, 6 and 8 nm thick) on silicon, prepared by thermal oxidation, were investigated using x-ray photoelectron spectroscopy (XPS). The thickness of these overlayers was obtained from a measurement of the photoelectron intensities originating from the substrate and the oxide overlayer by applying an appropriate quantitative model. The uncertainty budget of that thickness measurement method is given. The relative combined standard uncertainty of the method was found to be 15%. The effective attenuation lengths or the corresponding electron inelastic mean free paths are of considerable importance for both the estimated values of overlayer thickness and combined standard uncertainties. The XPS results were compared with ellipsometry data.
Powder x-ray diffraction (XRD) defined -Al2O3 has been investigated by x-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XAES). The Au 4f7/2 orbital is used for static charge referencing. This feature originates from well-defined and chemically inert 20 nm highly dispersed gold particles deposited on the sample surface. The particles, with a narrow particle size distribution, were obtained from a highly purified colloidal solution (sodium concentration below 1 mg/l). This procedure allows a determination of gold-referenced XPS and XAES data sets. ©2001 American Vacuum Society.
Several approaches were investigated to produce monosort functionalized polymer surfaces with a high density and homogeneity of functional groups: (i) Plasma oxidation followed by wet-chemical reduction, (ii) formation of radicals and grafting on of functional group carrying molecules, (iii) plasma bromination followed by (iv) Williamson or Gabriel-like synthesis of spacer molecules, and (v) a pulsed plasma polymerization of functional groups bearing monomers or (vi) their copolymerisation with other comonomers. The formation of hydroxyl (OH), primary amino (NH2), and carboxyl (COOH) groups was studied in detail. The oxygen plasma treatment (i) in a low-pressure non-isothermal glow discharge results in the formation of a wide variety of O functional groups, polymer degradation and crosslinking. Low power densities and short exposure times (0.1 to 2 s) are required to functionalize a surface while preserving the original polymer structure. Carbonate, ester, and aromatic groups are rapidly degraded by an oxygen plasma treatment leading to scissions of polymer backbones and loss in molecular weight. Also the formation of macrocycles and C=C bonds was observed in a region of around 4 nm in depth. The investigated polymers could be classified by their degradation behaviour on exposure to the oxygen plasma.___TAGSTART___BR___TAGEND___ In order to maximize the process selectivity for OH groups, the variety of oxygen functionalities formed by the oxygen plasma was wet-chemically reduced by diborane, vitridetrade (Na complex), and LiAlH4. Typical yields were 9 to 14 OH groups per 100 carbon atoms.___TAGSTART___BR___TAGEND___ Plasma bromination (iii) (40 Br per 100 C atoms) of polymers, followed by grafting of spacer molecules (iv), has been proved to be a highly selective reaction.___TAGSTART___BR___TAGEND___ Another way to produce high densities of monosort functionalities was the pulsed plasma polymerization of functional group bearing monomers such as allylamine, allylalcohol or acrylic acid (v). The retention of chemical structure and functional groups during plasma polymerization was achieved by using low power densities and the pulsed plasma technique. The maximum yields were 30 OH, 18 NH2, and 24 COOH groups per 100 C atoms. To vary the density of functional groups a chemical copolymerization with ''chain-extending'' comonomers such as butadiene and ethylene was initiated in the pulsed plasma (vi). Additionally, the often-observed post-plasma oxidations of such layers initiated by reaction of trapped radicals with oxygen from the air were successfully suppressed by using NO gas as radical quencher.
The dismutation of CCl2F2 was used to probe the effect of halogenation of chromia by Cl/F exchange reactions to find out the difference between the halogenated inactive and active catalysts. The heterogeneous reactions were performed in a continuous flow Ni reactor and also under simulated reaction conditions in a reactor where after the reaction X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectroscopy (XAES) analyses are possible without air exposure of the catalyst, i.e., under so-called "in situ" conditions. The Cr(III) 2p XP spectra, which revealed multiplet splitting features and satellite emission, were used for chemical analysis by using a simple evaluation procedure which neglects this inherent complexity. Chemical analysis was also applied by using chemical state plots for Cr 3s in order to cross-check Cr 2p related results. Both ex and in situ XPS show that as soon as Cr2O3 is exposed to CCl2F2 at 390°C fluorination as well as chlorination takes place at the catalyst surface. When the XPS surface composition reaches approximately 4 at. % fluorination and 6 at. % chlorination, maximum catalytic activity was obtained. Application of longer reaction times did not change significantly the obtained surface composition of the activated chromia. The fluorination and chlorination of chromia was further investigated by various HF and HCl treatments. The activated chromia samples and the Cr2O3, Cr(OH)3, CrF2OH, CrF3·H2O, α-CrF3, β-CrF3, and CrCl3 reference samples with well-known chemical structures were also characterized by X-ray absorption near edge structure (XANES), time-of-flight secondary ion mass spectroscopy (TOF-SIMS), pyridine-FTIR, wet chemical (F and Cl) analysis, X-ray powder diffraction (XRD), and surface area (BET) analysis. The results suggest that the formation of chromium oxide chloride fluoride species, e.g., chromium oxide halides, at the surface is sufficient to provide catalytic activity. The presence of any CrF3 and/or CrCl3 phases on the activated chromia samples was not found.
Plasma-deposited polymer films were prepared from organic molecules and investigated using near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectroscopy (XPS) for aging effects after exposure to air. Results from the investigation of homopolymers are summarized. Primarily the effect of the deposition parameters duty cycle and power are dealt with. The effect of the deposition parameter pressure is briefly discussed. An example to show the effect of feed gas composition on the aging of plasma polymerized ethylene/allyl alcohol and styrene/allyl alcohol copolymer is also given. In general, change in content of unsaturated or aromatic species, change in concentration of monomer functionality, and change in the oxygen content was observed in the plasma polymerized films on aging.
XPS and NEXAFS spectroscopy were used for the chemical characterization of pulsed plasma-deposited ethylene films before and after exposure to ambient air. The influence of external plasma parameters on the spectroscopic results was investigated. Information on the chemical character of the plasma-polymerized films, such as the regularity of the primary structure, the amount of long-living radicals, and branching or cross-linking or both was derived from this data. Irregularity and radical concentration for post-plasma reactions of the plasma-deposited films increased with the duty cycle or power. A decreased level of monomer fragmentation and, consequently, an increase in regularity is partially concluded from the experimental data when the monomer pressure is increased. The concentration of surface radicals available for post-plasma reactions also increased with monomer pressure. The correlation found between the degree of the post-plasma oxygen incorporation and the variation of the various external parameters agreed with earlier ToF-SSIMS findings.
The silicon based semiconductor structure Si/SiO2/Si3N4/LaF3/Pt can be used as a potentiometric oxygen sensor working at room temperature. A thermal re-activation can be applied to overcome the earlier disadvantage of an increase in response time with continuous use. Using the Pt gate electrode as a resistive heater, very short electrical high-power pulses can be applied. A heating time as short as 300 ns was sufficient for the re-activation of the sensor. This way, only the sensitive thin layer system LaF3/Pt was heated, and the whole sensor was at room temperature immediately after heating. Impedance spectroscopy, X-ray photoelectron spectroscopy (XPS) and quadruple mass spectrometric (QMS)thermogravimetry (TG) were used to investigate the mechanism of deterioration in dynamic sensor behaviour and re-activation. The formation of hydrated carbonate and the desorption of CO2 and H2O have been shown to be the causes.
CrN film coatings were prepared by magnetron sputter deposition at different nitrogen partial pressures. The film characterisation by XRD and DTG gives average bulk compositions of Cr2N and CrN for the coatings. Highly sensitive XPS investigations were performed and the chemical and phase compositions of a film surface range of about 10 nm thickness was estimated quantitatively from the deconvoluted peak intensities. It is demonstrated that the composition of the surface of chromium nitride thin films differs from the core and is more complex in constitution. Not only chromium nitrides (Cr2N and CrN) but also chromium oxynitrides and chromium oxides (CrOx and CrOxHy) were detected. Metallic chromium was also found in films prepared at higher nitrogen flow. The concentration of the estimated phases shows dependence on film preparation and additional heat treatment.
The formation of plasma-deposited materials made from organic molecules is a technologically attractive way to obtain films with unique properties, e.g. adhesion, wettability, conductivity or selected chemical functionalization. A detailed chemical characterization of these films is a great challenge for the analyst because of the co-existence of a large number of chemical species in plasma-deposited films. We investigated these types of organic films using photoelectron spectroscopy for chemical analysis (ESCA, XPS), near edge X-ray absorption fine structure (NEXAFS) spectroscopy at synchrotron radiation source BESSY II and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). A dedicated plasma preparation chamber was designed and added to the main analysis chamber of the respective spectrometers. This approach offers the possibility of studying plasma-deposited films without exposure to air before analysis (often called in-situ analysis) and the influence of post-plasma reactions, i.e. the ageing process. The present investigations are aimed at finding correlations between basic chemical properties of the deposited films and the plasma deposition parameters, e.g. duty cycle in pulsed plasmas and the power of discharge.
Plasma deposited allylamine films were studied by in situ ToF-SSIMS, XPS and NEXAFS Spectroscopy before exposure to ambient air. The influence of external plasma parameters such as duty cycle, plasma power, and monomer flow rate on (i) unsaturation, (ii) branching and cross-linking, (iii) nitrogen surface concentration and (iv) retention of amino groups was investigated. Harder plasma conditions, which can be obtained when high duty cycles, high plasma power, and low monomer flow rates are employed, increase the unsaturated, branched and cross-linked character of the plasma deposited films, while the surface concentration of N as well as the retention of the monomer's amino group decrease. As proven by NEXAFS findings and cross-checked by ToF-SSIMS results, the allylamine monomer's primary amino groups are partially transformed into other nitrogen functionalities during its plasma polymerization. Amongst them imines and nitriles are the conversion products with the highest probabilities of formation. Another conversion channel is the formation of nitrogen species not participating in the film growth. This is the reason for an increased N loss in plasma deposited allylamine films as observed independently by XPS and ToF-SSIMS when the plasma parameters are changed from mild to hard.
Chemical properties of plasma-polymerized styrene films can be effectively controlled by the appropriate choice of external plasma parameters, such as duty cycle, power and monomer pressure. Chemical properties here are the regularity of the primary structure, the amount of long living radicals and branching or cross-linking or both in plasma polymerized styrene films, which can be indirectly monitored by X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Principally, XPS and NEXAFS spectra of plasma-polymerized styrene show all the spectroscopic fingerprints characteristic of atactic polystyrene indicating an inherent similarity of the respective primary chemical structures. There is an increase in irregularity and radical concentration for the plasma deposited films with increasing duty cycle or power. With an increase in monomer pressure, a decreased level of monomer fragmentation and, consequently, an increase in regularity must be concluded from the experimental data. The applied power regulates the fragmentation of the monomers as monitored by spectroscopic signals correlated to the aromatic rings. A trend in the extent of the post-plasma oxygen incorporation according to the variation of the various external plasma parameters was deduced, which agrees with earlier ToF-SIMS findings
Selected FTIR, XPS and NEXAFS spectroscopy results obtained with films deposited with different plasma polymerization processes and different monomers (styrene, acetylene, ethylene and butadiene) are presented. In detail FTIR spectra, XPS surveys, XPS valence bands and core level signals including shake-up features as well as carbon K-edge absorption spectra are qualitatively and, in some cases, semi-quantitatively considered. Information on the film formation, the chemistry of the films and the film stability against air exposure are derived from spectroscopic features. With styrene chemically rather well defined plasma polymer layers can be formed with rather high deposition rates applying a pulse plasma process. Using ethylene, acetylene or butadiene as a monomer in the plasma deposition process the deposition rates are smaller. Using these monomers plasma polymer films can be obtained with a primary chemical structure which is similar to each other but more or less different from those of the respective conventional polymers. The main difference between these samples is their individual concentration of unsaturated carbon species. Finally, a technologically relevant example, i.e. a plasma deposited polymer barrier layer deposited on the inner wall of a poly(ethylene) vessel is briefly considered.
First results of an inter-laboratory comparison (27 participants in Europe, Japan and USA) of XPS data obtained with non-conducting samples are presented. Binding energies of Al 2s for alumina, N 1s and imide C 1s for Kapton and Sr 3p3/2 for a strontium titanate film on glass were obtained after static charge referencing with the help of 15 nm gold particles deposited at the surface of the test samples. For the alumina sample C 1s static charge referenced data are also presented. Repeat standard deviations (sr), between standard deviations (sb), reproducibility standard deviations (sR) and total means are evaluated from the experimental data. It can be stated that although the repeat standard deviation is as small as 0.05 eV in the best case, the standard deviation characterizing the reproducibility of the method is obviously not better than 0.15 eV in the best case at the present time. The knowledge of these standard deviations is important for metrology, validations of analytical procedures relying on qualitative photoelectron spectroscopy and XPS databanking.
Several possibilities exist to produce a modified polymer surface with a high density of only one sort of functional group such as: (i) the plasma grafting of unfragmented monomer molecules and their polymerization forms OH, NH2, COOH groups, etc. in concentrations of approximately 25 groups per 100 C atoms; (ii) selective plasma bromination provides 1025 CBr groups; (iii) the plasma oxidation of polymer surfaces in an O2 plasma followed by the chemical reduction of all O-containing groups to OH groups by diborane, vitride (Na complex) or LiAlH4 yields 914 OH groups per 100 carbon atoms; and (iv) the grafting of spacers with different endgroups onto OH or CBr groups produces 710 spacer molecules/100 C. This work was focused on the formation of thin plasma deposited polymer layers with a maximum of (homo)functional groups and with a minimum of chemical irregularities using the pulsed plasma technique. The monomers were allylalcohol, allylamine, acrylonitrile and acrylic acid. The further intent was to study the interactions of functional groups (OH, COOH, NH2) and deposited metals (Cr, Al, Ti). It was expected that more basic (NH2), weakly basic or neutral (OH) or more acidic (COOH) groups would show different interactions and chemical reactions with metal atoms.
The retention of chemical structure and functional groups during plasma polymerization was investigated. Usually plasma polymer layers, prepared by a continuous wave radio-frequency plasma, are often chemically irregular in their structure and composition. To minimize these irregularities low wattages and the pulsed plasma technique were applied to avoid fragmentations. The first goal was to produce plasma polymers comprising double or triple bonds as precursors for electrically conducting polymers. Acetylene, ethylene, butadiene and polystyrene were used as monomers and deposited as thin polymer films by pulsed plasmas of low wattages. Styrene polymerization was strongly enhanced in the dark phase (plasma off) of a pulsed r.f. plasma caused by the reactivity of the vinyl-type double bond. This could be confirmed by a verification of a rather high chemical regularity of the film sample. The oxygen content of this film measured by X-ray photoelectron spectrometry (XPS) was in situ 0% and after 24 h exposure to air lower than 1%. Additionally, post-plasma oxidations of trapped radicals with air could be suppressed using NO gas as radical quencher. Such quenched plasma polymer layers were completely stable against oxidation for a number of weeks. During the low-wattage pulse plasma polymerization metal atoms were simultaneously or layer by layer evaporated into the growing layer and in situ measured by XPS. These metal atoms are acting as dopants. Here, Li, K, Mg and Cr were used at different concentrations providing electrical conductivity and magnetic properties for the film.
Eine neue Generation von alterungsbeständigen Plasmapolymeren mit definierter chemischer Struktur
(2000)
Polymeroberflächenfunktionalisierungen im gepulsten Plasma mit nachfolgender chemischer Behandlung
(2000)
The chemical and morphological stabilities of polymer segments in the near-surface layer were investigated by spectroscopic methods such as X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. Model studies were undertaken with LangmuirBlodgett films, self-assembled monolayers and oligomer films. For thin polymer layers (30 to 500 nm), the changes in molecular-weight distributions of some polymers were investigated systematically by size exclusion chromatography, matrix-assisted laser desorption/ionizationtime-of-flight mass spectrometry and thermal-field flow fractionation for oxygen- and helium-plasma exposures. The polymer surfaces were found to be relatively stable at exposure to an oxygen low-pressure plasma up to ca. 2 s. This is important information to get maximum adhesion to metals in composites. In correlation to their redox potentials, potassium, aluminium and chromium react with oxygen functional groups at the polymer/metal interface. In a dedicated study, chromium was found to attack aromatic rings and form different reaction products.
Reactions and Intermediates at the Metal-Polymer Interface - Detected by XPS and NEXAFS Spectroscopy
(1998)
Modelling plasma-induced reactions on polymer surfaces using aliphatic self-assembling and LB layers
(1998)
Different types of plasma, irradiative and chemical activation were compared in terms of surface functionalization. Corona and spark jet plasmas are characterized by low gas temperatures and high rates in surface modification. UV irradiation in the presence of ozone does not involve any particle bombardment and acts only by enhanced photooxidative processes. Although ion implantation can be avoided, this method is not free of radiative damage in both the surface-near region and the bulk of polymers. Furthermore, its functionalization rate is low. In relation to low-pressure O2 plasma modification, all treatments mentioned here have a low efficiency in adhesion promotion due to oxidative degradation of macromolecules and formation of molecular debris known as the ''weak boundary layer''.
Plasma polymerised films of acrylic acid, allyl alcohol and allyl amine were prepared and studied by XPS (X-ray photoelectron spectroscopy) and XAS (X-ray absorption spectroscopy). The influence of external plasma parameters on certain chemical aspects of the films was investigated. The use of XPS and NEXAFS (near edge X-ray absorption fine structure) as complimentary tools in the surface characterisation of thin films has been highlighted. Certain chemical aspects of the plasma polymerised films such as presence of ROCdouble bond; length as m-dashO in the case of plasma polymerised acrylic acid films, presence of RCdouble bond; length as m-dashO and RCOR bonds in case of plasma polymerised allyl alcohol films and presence of RCdouble bond; length as m-dashN and C?N in case of plasma polymerised allyl amine films were studied. The concentration of ROCdouble bond; length as m-dashO species was found to decrease with increase in r.f. duty cycle in the case of plasma polymerised acrylic acid films. In case of plasma polymerised allyl alcohol films there is a decrease in the concentration of RCdouble bond; length as m-dashO species and increase in the concentration of RCOR species at higher pressures, while in the case of plasma polymerised allyl amine films the concentration of RCdouble bond; length as m-dashN and C?N increases at higher powers, with an increase in C?N more pronounced at higher powers.
Br bonding on plasma brominated graphite surfaces has been studied by using Near Edge X-ray Absorption Fine Structure (NEXAFS) and X-ray Photoelectron Spectroscopy (XPS). Br2 and bromoform were used as plasma gases in an r.f. cw low pressure plasma process. Kr plasma had been used to study separately the physical and chemical plasma etching effects. At early steps of plasma bromination which lead to only small XPS Br surface concentration values a quick decay of aromaticity has been observed. At low Br surface concentration radical or even electrophilic addition of bromine onto sp2 carbon atoms is discussed as the dominating reaction pathway. At higher Br surface concentrations the inherent formation of sp3 defects in the graphene network by chemical etching processes promotes nucleophilic substitution of bromine at sp3 carbons as a competing reaction pathway. Both reaction pathways lead to CBr species characterized by the same Br 3d XPS binding energy. However more than one Br 3d component in XP spectra has been found at lower Br2 plasma induced Br surface concentrations and complexation of bromine at HOPG is assumed as a third way of interaction with Br2 plasma.
A combined XPS, NEXAFS, and ToF-SIMS chemical surface characterization of carbohydrate-functionalized gold and glass surfaces is presented. Spot shape and chemical composition across a spot surface are provided by surface-sensitive methods as ToF-SIMS and XPS, used in their imaging modes. Moreover, the feasibility of this multimethod approach to control relevant production steps of a carbohydrate microarray prototype is demonstrated.
We present a new synchrotron X-ray photoelectron spectroscopy strategy for surface chemical analysis of materials. Our approach is based on the acquisition of photoelectron spectra at constant kinetic energies with the help of a tunable synchrotron X-radiation source. This ensures both constant and tunable information depth for all elements in a very thin organic layer. Many of the problems known to XPS depth profiling using laboratory equipment are thereby avoided. Using our methodology, the 95% information depth, z95%, can be tuned down to about 0.7 nm in organic materials. The upper limit in our study at the HE-SGM monochromator dipole magnet beamline at the synchrotron radiation source BESSY II is about 4.3 nm. Elemental quantification is achieved through relative sensitivity factors (RSF) specific to the measurement conditions, determined either with the help of calculated photoionization cross sections and inelastic mean free paths or experimentally. The potential of the technique is demonstrated for the in-depth analysis of plasma deposited nitrogen-rich organic thin films used in biomedical applications.
Experimental N K-edge NEXAFS data of surface immobilized azide, 1,2,3-triazole and terpyridyl groups are interpreted with the help of DFT spectrum simulations. Assignments of π* resonances in experimental N K-edge NEXAFS spectra to nitrogen atoms within these functional groups have been made. The azide was immobilized on gold as the head group of a thiol SAM, 1,2,3-triazole was formed on this SAM by click reaction and terpyridyl groups were introduced as substituents of the acetylene used for the click reaction. For azide-terminated molecules, DFT spectrum simulations are found to be useful to find measurement conditions delivering experimental N K-edge NEXAFS data with negligible X-ray damage. The 1,2,3-triazole group is found to be rather stable under X-ray irradiation.
Low- and atmospheric-pressure plasma co-polymerisations of binary gas mixtures of C2H4 and NH3 or N2, respectively, were investigated for depositing N-rich plasma polymer coatings for biomedical applications. Deposition kinetics and relevant surface characteristics of resulting plasma polymerised ethylene enriched with nitrogen, PPE:N, coatings were investigated as a function of the gas mixture ratio, X = NH3(N2)/C2H4. Physico-chemical properties of the coatings were determined using a combination of complementary surface-sensitive techniques: for example, total nitrogen concentrations, [N], up to 40 at.% were measured by X-ray Photoelectron Spectroscopy, XPS, while those of primary amines, [NH2], were determined by performing chemical derivatisation followed by XPS analyses. PPE:N films were further characterised by UVVIS Ellipsometry, Near Edge X-ray Absorption Fine Structure Spectroscopy, IR Spectroscopy and by Contact Angle Goniometry measurements. The stability of the coatings was tested, both in terms of water solubility and of ageing in ambient atmosphere. For the latter, selected samples were stored in the laboratory for different durations, in order to assess possible changes in their chemical structures.
Plasma deposited styrene/allyl alcohol and ethylene/allyl alcohol copolymer films were prepared and characterized using XPS, NEXAFS and ToF-SIMS. The relative partial flow rates of the co-monomers are used as deposition process parameters to vary and all other process parameters were constrained to conditions optimized for retention of functional groups. By doing this it is possible to control certain chemical properties of the copolymer films such as unsaturation, oxygen and hydroxyl group relative surface contents. The aging behavior of the plasma copolymer films on air was studied, too. Non-linear variations of relative oxygen contents, contents of C—OR species and contents of carbonyl species are obtained vs. variation of feed gas composition for both monomer combinations. The chemical character of the plasma copolymer films varies between the limits given by the respective plasma homopolymers. The observed non-linear correlations are discussed in terms of approaches developed for classic radical copolymerization. The aging behavior of the different plasma copolymers films depends on the feed gas composition. Principally these aging phenomena known from plasma polymer aging studies of that respective monomer which dominates the character of the plasma copolymer are observed.
Plasma deposited ethylene/allylamine and styrene/allylamine copolymer films were prepared and analyzed using XPS, NEXAFS and ToF-SIMS. The relative partial flow rate of the each monomer was used as the variable deposition parameter, while the other deposition parameters were kept constant at optimized values for the retention of functional groups. The effect of the variation in the relative partial flow rates of co-monomers on various chemical aspects of the films like unsaturation, nitrogen retention and branching was investigated revealing several non-linear correlations. This observation is taken as an indication for chemical copolymerization processes during film deposition. An attempt is made to compare these non-linear correlations with approaches which have been developed for classic radical copolymerization processes. The aging behavior of these plasma copolymer films was also studied; the results indicated a stabilization against oxidation in comparison to the aging of allylamine plasma homopolymers.
It is known that aminosilanized Si wafers may be used as microarray platforms. Results of an XPS study of a cleaning applied to Si wafers prior to aminosilanization are presented and discussed. Furthermore, the results of an aminosilanization protocol optimized in terms of nitrogen chemistry are described. After optimization of the protocol a free amine content of 94% was reached. The surface chemistry was investigated in this study by using XPS, time of flight (ToF)-SIMS and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Reference to aminosilanization protocols reported in the literature has been made.
A toluene solution of 4,4´-methylenebis(2,6-diethylaniline) was spin coated on Si wafers. The samples were derivatized with pentafluorobenzaldehyde (PFB) in order to determine the primary amino groups on the surface. XPS C 1s and N 1s and C and N K-edge NEXAFS of underivatized and derivatized films were carefully analyzed. The result was that after 10 min of exposure the gas-surface reaction was already completed. A reasonable derivatization reaction yield in the order of 90% is derived from the experiments. This number correlates well to a reaction yield obtained by a wet chemical approach.
Ageing studies of plasma deposited organic films by surface chemical analysis (ESCA, ToF-SIMS, XAS)
(2007)
We have used an atmospheric pressure DBD apparatus to deposit novel families of N-rich plasma polymers (PP:N), using mixtures of three different hydrocarbon precursors in nitrogen at varying respective gas flow ratios. This research focuses on the overall chemical characterisation of those materials, with specific attention to (semi)-quantitative analysis of functional groups. Well-established and some lesser-known analytical techniques have been combined to provide the best possible chemical and structural characterisations of these three families of PP:N thin films, namely XPS, NEXAFS and FT-IR spectroscopy.
Die Akkreditierung für Prüfverfahren in der Oberflächenanalytik wird gemeinhin als sehr schwierig angesehen. Durch das unlängst eingeführte flexible Konzept der Akkreditierung, auch Prüfartenakkreditierung genannt, eröffnen sich nunmehr neue Möglichkeiten. Aus dem Bereich des Normenwesens in der Oberflächenanalytik erhalten die Prüflaboratorien zusätzliche Unterstützung. Die Validierung von ESCA-Prüfverfahren und ein wohldokumentiertes Prüfmittelmanagement sind weitere Bausteine auf dem Weg zur erfolgreichen Akkreditierung. Oberflächenanalyseverfahren sind akkreditierfähig.
Carbohydrate films on gold based on dimannoside thiols (DMT) were prepared, and a complementary surface chemical analysis was performed in detail by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), near-edge X-ray absorption fine structure (NEXAFS), FT-IR, and contact angle measurements in order to verify formation of ω-carbohydrate-functionalized alkylthiol films. XPS (C 1s, O 1s, and S 2p) reveals information on carbohydrate specific alkoxy (C–O) and acetal moieties (O–C–O) as well as thiolate species attached to gold. Angle-resolved synchrotron XPS was used for chemical speciation at ultimate surface sensitivity. Angle-resolved XPS analysis suggests the presence of an excess top layer composed of unbound sulfur components combined with alkyl moieties. Further support for DMT attachment on Au is given by ToF-SIMS and FT-IR analysis. Carbon and oxygen K-edge NEXAFS spectra were interpreted by applying the building block model supported by comparison to data of 1-undecanethiol, poly(vinyl alcohol), and polyoxymethylene. No linear dichroism effect was observed in the angle-resolved C K-edge NEXAFS.
The determination of amino groups on surfaces capable of binding biomolecules is important for the understanding and optimization of technologically relevant coupling processes. In this study, three different types of amino-functionalized model surfaces, amino thiolate on Au, amino siloxane on Si, and polyethylene (PE) foils and films reacted with 1,2-diaminoethane (DAE) were derivatized with 3,5-bis(trifluoromethyl)phenyl isothiocyanate. Subsequently, these samples were analyzed by chemical derivatization X-ray photoelectron spectroscopy (CD-XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). The determination of amino groups by this analytical approach allows gaining insight into the availability of groups on surfaces that can actually serve as attachment sites for biomolecules in technical applications. In the case of the amino thiolate on Au, almost 90% of the expected amino groups were detected by CD-XPS. Investigation of the amino siloxane films revealed lower yields for the derivatization reaction in the order of 30%. The lowered reaction yields are thought to be due to interactions between the amino siloxane`s amino and silanol groups or the underlying substrate, making them inaccessible to the derivatization agent. The aminated PE samples are characterized by a complex surface chemistry and structure, and reaction yields of the derivatization reaction cannot be unequivocally derived. However, 1-3% of the total carbon atoms in the surface layer were found to be bound to amino groups accessible to the derivatization agent. It can be concluded that, depending on the detailed character of the investigated amino-terminated surface, the amount of amino groups accessible to CD-XPS can be substantially lower than the total amount of amino groups present at the surface.
Self-assembled monolayers of aromatic omega-aminothiols on gold: surface chemistry and reactivity
(2010)
Amino-terminated self-assembled monolayers on gold substrates were studied by X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure (NEXAFS) measurements, and atomic force microscopy (AFM). Two different ω-amino-4,4'-terphenyl substituted alkanethiols of the general structure H2N-(C6H4)3-(CH2)n-SH (ATPn) were used: 2-(4''-amino-1,1':4',1''-terphenyl-4-yl)ethane-1-thiol (n = 2, ATP2) and 3-(4''-amino-1,1':4',1''-terphenyl-4-yl)propane-1-thiol (n = 3, ATP3). Moreover, the addressability of amino groups within the films was investigated by chemical derivatization of ATPn SAMs with 3,5-bis(trifluoromethyl)phenyl isothiocyanate (ITC) forming fluorinated thiourea ATPn-F films. Evaluation of high-resolution C 1s and N 1s XPS data revealed successful derivatization of at least 50% of surface amino species. Furthermore, it could be demonstrated by angle-resolved NEXAFS spectroscopy that chemical derivatization with ITC has no noticeable influence on the preferential upright orientation of the molecules in the SAMs.
We investigated the ageing of amine-terminated
self-assembled monolayers (amine-SAMs) on different silica
substrates due to exposure to different ambient gases,
pressures, and/or temperatures using time-of-flight secondary
ion mass spectrometry (ToF-SIMS) with principal component
analysis and complementary methods of surface
analysis as X-ray photoelectron spectroscopy (XPS) and
near edge X-ray absorption fine structure (NEXAFS). The
goal of this study is to examine the durability of primary
amine groups of amine-SAMs stored in a user laboratory
prior to being used as supports for biomolecule immobilization
and other applications. We prepared amine-SAMs on
the native oxides of silicon wafers and glass slides using 3-
aminopropyl triethoxysilane, by using optimized conditions
such as anhydrous organic solvent and reaction time scale of
hours to avoid multilayer growth. Selected commercial
amine-SAM slides have been investigated, too. When the
amine-SAMs are exposed to air, oxygen incorporation
occurs, followed by formation of amide groups. The formation
of oxygen species due to ageing was proved by ToFSIMS,
XPS, and NEXAFS findings such as CNO- secondary
ion emission at m/z 42, observation of the N 1s HNC=O
component peak at 400.2400.3 eV in XPS, and, last but not
least, by formation of a π*(HNC=O) resonance at 401 eV in
the N K-edge X-ray absorption spectrum. It is concluded
that the used multi-method approach comprising complementary
ToF-SIMS, XPS, and NEXAFS analyses is well
suited for a thorough study of chemical aspects of ageing
phenomena of amine-SAM surfaces.
Research on carbohydrate based interactions with proteins, nucleic acids or antibodies has gained increased interest in the last years especially in clinical diagnosis or drug development. The efficiency of diagnostic interfaces depends upon the number of probe molecules, e.g. carbohydrates. The control of surface parameters as density and distribution of immobilized carbohydrates is essential for a reliable interaction with protein analytes. A controlled production of biomolecular interfaces can be reached by a stepwise quality control during buildup of these biointerfaces.
Here, ß-amino-cyclodextrin molecules were attached to amine-reactive silicon oxide surfaces via click chemistry to construct a model biosensor surface. The amount of surface bound carbohydrates was determined indirectly after chemical derivatization with 4-(trifluoromethyl)-benzylamine (TFMBA). Moreover, these surfaces were used to form host-guest complexes of ferrocene (guest) and β-cyclodextrin (host) moieties to mimic the target binding (sensing) of the model biosensor. Surface chemical analysis of all steps during biosensor construction was performed using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure spectroscopy (NEXAFS). Our approach widens the possibilities to generate switchable surfaces based on ß-Cyclodextrin surfaces for biosensor applications.
In Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopy X-Ray photons are used to excite tightly bound core electrons to low-lying unoccupied orbitals of the system. This technique offers insight into the electronic structure of the system as well as useful structural information. In this work, we apply NEXAFS to two kinds of imidazolium based ionic liquids ([CnC₁im]⁺[NTf₂]⁻ and [C₄C₁im]⁺[I]⁻). A combination of measurements and quantum chemical calculations of C K and N K NEXAFS resonances is presented. The simulations, based on the transition potential density functional theory method (TP-DFT), reproduce all characteristic features observed by the experiment. Furthermore, a detailed assignment of resonance features to excitation centers (carbon or nitrogen atoms) leads to a consistent interpretation of the spectra.
In this study, a new direct functionalization method of silicon nitride (Si3N4) using azidation and click chemistry is presented. First, amino groups (NHx) were created on a Si3N4 substrate by fluoride etching. These NHx-terminated Si3N4 surfaces were analyzed by chemical derivatization X-ray photoelectron spectroscopy (CD-XPS) with 4-trifluoromethylbenzaldehyde (TFBA) and a derivatization yield of 20% was concluded. In the second step freshly prepared NHx surfaces were transformed into azides which were used immediately in a click reaction with halogenated alkynes. The presented combination of amination, azidation and click reaction is a promising alternative for common silane-based Si3N4 functionalization methods.
We report a surface analytical study of poly(methyl methacrylate) (PMMA) microparticles (beads) with a grafted shell of poly(acrylic acid) (PAA) with thicknesses up to 4 nm using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy. These polymer microparticles were analyzed before and after reaction of the surface carboxyl (CO2H) groups with 2,2,2-trifluoroethylamine (TFEA) to gain a better understanding of methods with use of covalently bound probe molecules for surface group analysis. The results obtained with chemical derivatization XPS using TFEA are discussed in terms of surface quantification of reactive CO2H groups on these PAA-coated microparticles. A labeling yield of about 50% was found for TFEA-derivatized particles with amounts of surface-grafted CO2H groups of 99 µmol/g or more, which is consistent with predicted reaction yields for homogeneously dispersed PAA hydrogels.
Plasma-chemical bromination applied to graphitic materials, in particular to highly ordered pyrolytic graphite is reviewed. The resulting bromination efficiency of the plasma-chemical treatment was subject of systematic process optimization. The plasma of elemental bromine vapour produced bromine concentrations on graphene surfaces of more than 30 % Br/C using either inductively or capacitively coupled low-pressure radio-frequency plasmas. Plasma brominated graphite surfaces have been studied by Near Edge X-ray Absorption Fine Structure, X-ray Photoelectron Spectroscopy, Atomic Force Microscopy and Scanning Electron Microscopy. The introduction of bromine into graphene-like graphite layers and its binding situation were investigated. To study the physical effect of the plasma bromination process, Kr plasma was also used because of its chemical inertness but similar atomic mass. Covering the samples with a Faraday cage or with a LiF window should help to differentiate between physical, chemical and radiation effects of the plasma. Bromination was assigned to radical or electrophilic addition of bromine onto fully substituted aromatic double bonds (sp² C) with exothermal reaction enthalpy. Low bromination shows a strong decay of aromatic double bonds, higher bromination percentage let disappear all aromatic rings. The formed C–Br bonds were well suited for efficient grafting of organic molecules by post-plasma wet-chemical nucleophilic substitution. This grafting onto the graphene surface was demonstrated using aminosilane and different diamines. The bromination of double bonds changes the hybridization of carbon atoms from plane sp² to tetrahedral sp³ hybridization. Thus, the plane topography of graphene is destroyed and the conductivity is lost.
In order to investigate molecular recognition on surfaces, an azide-functionalized monolayer was deposited on gold. The monolayer was characterized by X-ray photoelectron spectroscopy (XPS) and angle-resolved near-edge X-ray absorption fine structure (NEXAFS) experiments and the decomposition of the azide upon irradiation with X-ray beams was investigated. Subsequently, various alkyne-functionalized host and guest molecules were attached to the azide by 1,3-dipolar cycloaddition. These modified surfaces and their host–guest chemistry were analysed by XPS and angle-resolved NEXAFS. The reversibility of guest binding was shown for one example as a proof of principle.
In this study, epoxy-terminated silicon oxide surfaces were chemically derivatized with trifluoroacetic anhydride (TFAA) and 4-(trifluoromethyl)-benzylamine (TFMBA) and analyzed by X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy and water contact angle measurements. TFAA was used for quantitative derivatization to determine the amount of reactive epoxy groups on these surfaces. Furthermore, epoxy-terminated surfaces were derivatized with TFMBA (a model compound for biomolecules with an amino linker) yielding secondary amines because of formation of covalent C–N bonds between TFMBA and the epoxy films. Fluorine being part of TFAA and TFMBA composition was used to follow the progress of the chemical derivatization reaction. Both derivatization agents – TFAA and TFMBA – gave comparable reaction yields of ~60% on epoxy silicon surfaces, whereas on epoxy glass slides, the derivatization yields were considerably lower (30–40%).The protocol for attachment of TFMBA (model compound) on epoxy-modified surfaces was adapted to (bio)molecules with an amino linker, e.g. carbohydrates to prepare carbohydrate-functionalized biointerfaces.
The chemical constitution of functionalized supports is an important parameter that determines their performance in a broad range of applications, e.g. for immobilization of biomolecules. Supports with amino functionalized surfaces are also often used for DNA microarray experiments. However, spectral data which have been reported for surfaces with amino functionalities suffer from some inconsistencies. In this article a detailed XPS (X-ray photoelectron spectroscopy) and NEXAFS (Near edge X-ray absorption fine structure) database for amino functionalized surfaces is presented. Amino-terminated surfaces prepared from aliphatic and aromatic aminosilanes or aminothiols and a field sample are considered. Effects of aging in air and damage by radiation are addressed as well.
Functionalised surfaces are of interest in many fields, e.g. in biomedicine, materials science and molecular electronics. In this study a series of self-assembled aliphatic and aromatic monolayers on gold substrates with terminal amino groups was investigated. Four different thiol molecules were used: aliphatic 11-aminoundecane-1-thiol (AUDT), aromatic 4-aminobenzenethiol (ABT) and aromatic ω-amino thiols with an alkyl spacer as 4-aminophenylbutane-1-thiol (APBT) and 3-(4''-amino-1,1':4',1''-terphenyl-4-yl)propane-1-thiol (ATPT). Evaluation of N 1s XPS data revealed that on the aromatic self-assembled monolayers (SAMs) amino groups exist preferentially as primary amines, whereas on the aliphatic SAM protonated and/or hydrogen-bonded amines are the major species. This result is crosschecked by N K edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy and can be rationalised by the different basicity of aliphatic and aromatic amines.
The photoinduced pseudorotaxane formation between a photoresponsive axle and a tetralactam macrocycle was investigated in solution and on glass surfaces with immobilized multilayers of macrocycles. In the course of this reaction, a novel photoswitchable binding station with azobenzene as the photoswitchable unit and diketopiperazine as the binding station was synthesized and studied by NMR and UV/Vis spectroscopy. Glass surfaces have been functionalized with pyridine-terminated SAMs and subsequently withmultilayers of macrocycles through layer-by-layer self assembly.
A preferred orientation of the macrocycles could be confirmed by NEXAFS spectroscopy. The photocontrolled Deposition of the axle into the surface-bound macrocycle-multilayers was monitored by UV/Vis spectroscopy and led to an increase of the molecular order, as indicated by more substantial linear dichroism effects in angle-resolved NEXAFS spectra.
Organosilanes are used routinely to functionalize various support materials for further modifications. Nevertheless, reliable quantitative information about surface functional group densities after layer formation is rarely available. Here, we present the analysis of thin organic nanolayers made from nitrogen containing silane molecules on naturally oxidized silicon wafers with reference-free total reflection X-ray fluorescence (TXRF) and X-ray photoelectron spectroscopy (XPS). An areic density of 2−4 silane molecules per nm2 was calculated from the layer’s nitrogen mass deposition per area unit obtained by reference-free TXRF. Complementary energy and angle-resolved XPS (ER/ARXPS) in the Si 2p core-level region was used to analyze the outermost surface region of the organic (silane layer)−inorganic (silicon wafer) interface. Different coexisting silicon species as silicon, native silicon oxide, and silane were identified and quantified. As a result of the presented proof-of-concept, absolute and traceable values for the areic density of silanes containing nitrogen as intrinsic marker are obtained by calibration of the XPS methods with reference-free TXRF. Furthermore, ER/AR-XPS is shown to facilitate the determination of areic densities in (mono)layers made from silanes having no heteroatomic marker other than silicon. After calibration with reference-free TXRF, these areic densities of silane molecules can be determined when using the XPS component intensity of the silane’s silicon atom.
The surfaces of polymeric dialyzer membranes consisting of polysulfone and polyvinylpyrrolidone were investigated regarding the lateral distribution and quantitative surface composition using time-of-flight secondary-ion-mass-spectrometry and x-ray photoelectron spectroscopy. Knowledge of the distribution and composition on the outer surface region is of utmost importance for understanding the biocompatibility of such dialyzer membranes. Both flat membranes and hollow fiber membranes were studied.
Solgel prepared ternary FeF3–MgF2 materials have become promising heterogeneous catalysts due to their porosity and surface Lewis/Brønsted acidity (bi-acidity). Despite the good catalytic performance, nanoscopic characterisations of this type of material are still missing and the key factors controlling the surface properties have not yet been identified, impeding both a better understanding and further development of ternary fluoride catalysts. In this study, we characterised the interaction between the bi-acidic component (FeF3) and the matrix (MgF2) on the nano-scale. For the first time, the formation pathway of FeF3–MgF2 was profiled and the template effect of MgF2 during the synthesis process was discovered. Based on these new insights two novel materials, FeF3–CaF2 and FeF3–SrF2, were established, revealing that with decreasing the atomic numbers (from Sr to Mg), the ternary fluorides exhibited increasing surface acidity and surface area but decreasing pore size. These systematic changes gave rise to a panel of catalysts with tuneable surface and bulk properties either by changing the matrix alkaline earth metal fluoride or by adjusting their ratios to Fe or both. The template effect of the alkaline earth metal fluoride matrix was identified as the most probable key factor determining the surface properties and further influencing the catalytic performance in ternary fluoride based catalysts, and paves the way to targeted design of next-generation catalysts with tunable properties.
A novel photoswitchable rotaxane was synthesised and its switching behaviour in solution was analysed with NMR and UV-Vis. A monolayer of rotaxanes was deposited on glass surfaces and the on-surface photoswitching was investigated. Angle-resolved NEXAFS spectra revealed a preferential orientation that reversibly changes upon switching.
In this work, fullerene has been functionalized with cyanuric Chloride at room temperature by a nitrene mediated [2 + 1] cycloaddition reaction. The adduct after functionalization is inherently in the form of azafulleroid and shows broad UV absorption in the wavelength range of 200–800 nm, as well as photothermal conversion and fluorescence with a high quantum yield.
Modification of polyethylene and polypropylene surfaces by atmospheric-pressure plasmas using mixtures of nitrogen and hydrogen was studied using Fouriertransform infrared spectroscopy in the attenuated total reflection mode (FTIR-ATR) and by near-edge x-ray absorption fine structure spectroscopy (NEXAFS) in order to shed some light on the chemical nature of nitrogen-containing functional Groups on the polymer surface. Using FTIR-ATR spectroscopy combined with hydrogendeuterium isotope exchange of active hydrogen atoms, it was shown that the direct treatment of PE foils by dielectric barrier discharges (DBDs) in N2/H2 mixtures and a subsequent exposure of the samples to the ambient air results in the formation of –NH2 moieties of primary amides on the polymer surface. Corresponding in situ experiments with streaming N2/H2 DBD post-discharges virtually free of H2O and O2, on the other hand, showing the absence of –NH2, proving that no primary amines or amides are formed by this treatment although substantial amounts of nitrogen are incorporated. Moreover, directly N2/H2-plasma-treated polymer surfaces, similar to afterglow-treated low-density polyethylene (LDPE), show amphiphilic character as to be seen by chemical derivatization with nucleophilic reagents 4-(trifluoromethyl) phenylhydrazine and 4-(trifluoromethyl)benzylamine, in addition to electrophilic aromatic aldehydes normally
used to derivatize such surfaces.
The presence of imines or other functional groups with CN moieties which may be invoked to explain the dual (amphiphilic) reactivity is proven by NEXAFS studies on ultrathin plasma-treated PE films, confirming significant amounts of nitrogen in CN bonds and carbon in CC bonds.
Graphene and its derivatives have recently attracted much attention for sensing and deactivating pathogens. However, the mechanism of multivalent interactions at the graphene–pathogen interface is not fully understood. Since different physicochemical parameters of graphene play a role at this interface, control over graphene’s structure is necessary to study the mechanism of these interactions. In this work, different graphene derivatives and also zwitterionic graphene nanomaterials (ZGNMs) were synthesized with defined exposure, in terms of polymer coverage and functionality, and isoelectric points. Then, the switchable interactions of these nanomaterials with E. coli and Bacillus cereus were investigated to study the validity of the generally proposed “trapping” and “nano-knives” mechanisms for inactivating bacteria by graphene derivatives. It was found that the antibacterial activity of graphene derivatives strongly depends on the accessible area, i.e. edges and basal plane of sheets and tightness of their agglomerations. Our data clearly confirm the authenticity of “trapping” and “nano-knives” mechanisms for the antibacterial activity of graphene sheets.
Low biodegradability of graphene derivatives and related health risks are the main limiting factors for their in vivo biomedical applications. Here, we present the synthesis of enzyme-functionalized graphene sheets with self-degrading properties under physiological conditions and their applications in Tumor therapy. The synergistic enzyme cascade glucose oxidase and myeloperoxidase are covalently conjugated to the surface of graphene sheets and two-dimensional (2D) platforms are obtained that can produce sodium hypochlorite from glucose. The enzyme-functionalized graphene sheets with up to 289 nm average size are degraded into small pieces (≤40 nm) by incubation under physiological conditions for 24 h. Biodegradable graphene sheets are further loaded with doxorubicin and their ability for Tumor therapy is evaluated in vitro and in vivo. The laser-triggered release of doxorubicin in combination with the enzymatic activity of the functionalized graphene sheets results in a synergistic antitumor activity.
Taking advantage of their neutrophil-like activity, fast biodegradability, high photo- and chemotherapeutic effects, the novel two-dimensional nanoplatforms can be used for tumor therapeutic applications.