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- 2012 (4) (entfernen)
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- XPS (2)
- Ageing process (1)
- Alcohol (1)
- Amine (1)
- Amine-SAM (1)
- Amino groups (1)
- Carbon nanotubes (1)
- Chemical derivatization (1)
- Derivatization (1)
- Graphite (1)
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.
Graphite and multiwall carbon nanotube surfaces were functionalized by vacuum-ultraviolet induced photochemistry in NH3 or O2, in order to introduce amino- (NH2) or hydroxyl (OH) functionalities, respectively. Modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), which showed significant incorporation of nitrogen (N) and oxygen (O) at the materials surface. While high-resolution XP spectra did not yield much specific information about the incorporated functional groups, chemical derivatization with 4-trifluoromethyl benzaldehyde and trifluoroacetic anhydride accompanied by XPS enabled quantification of NH2 and OH groups, respectively. Using near edge X-ray absorption fine structure spectroscopy, we assessed the conservation of the aromatic structure following functionalization treatments.
Functionalized organic layers prepared by plasma processes have complex surface chemistries. The problem of elucidating such chemistries is an extensively studied subject. One of the preponderant methods used to acquire information on specific functional groups is chemical derivatization XPS. In this communication, we focus on rather popular chemical derivatization XPS approaches, for instance, the quantification of amines with 4-trifluoromethyl benzaldehyde and of hydroxyl groups with trifluoroacetic anhydride. Although these procedures have been used for a long period by various laboratories, the use of varying protocols is obvious. Comparison of results is therefore difficult. We discuss steps toward a valid experimental procedure, in particular, the calculation of concentrations, the preparation of test samples, the pitfalls, and the shortcomings.
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.