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Dynamic Plowing Lithography is employed to carve holes in a PMMA surface by indenting the sample during Tapping Mode imaging. The dependence of the dimensions of the holes on the tip shape, on the modulation voltage amplitude, and on the number of contacts between the tip and sample is studied. The results give some insights in the physico-chemical mechanisms accompanying such rapid modifications. Two-dimensional arrays of holes have also been carved, in order to study the result of the superposition of single holes.
Two different methods of nanolithography, namely dynamic plowing lithography (DPL) and indentation by means of force-displacement curves (FDI), have been compared by performing them on two different polymers, poly (methylmethacrylate) and polystyrene. No fundamental differences can be found out in the efficiency of the two methods, i.e., in the depth of the lithographed structure as a function of the scanning parameters. The main drawback of FDI is that it is much more time consuming than DPL. On the other hand, when the sample is lithographed with DPL, the border walls that surround the lithographed structure are very much bigger than the border walls created through FDI. The physicochemical properties of the border walls created through DPL have been investigated. Several experimental data reveal that such border walls are very much softer and looser than unmodified polymers and suggest that during DPL the fast oscillating tip is able to break polymer chains. This does not happen with FDI, where border walls are simply made up of the material carved out by the tip. A method to eliminate these undesirable border walls is suggested.
Poly(methyl methacrylate) (PMMA) surfaces have been modified by dynamic plowing lithography. The resulting modified structures, presenting regions of different densities and stiffnesses, have been studied by forcedisplacement curves. The elasto-plastic response, the stiffness, and the adhesion of the modified samples have been characterized. Forcedisplacement curves are able to distinguish between unmodified PMMA and two different structures resulting from the lithography, i.e. compressed PMMA and low density PMMA. In particular, the low density regions are made up of cluster-like globular particles, whose elasto-plastic response and adhesion are measured and whose contribution to the total elasto-plastic response and to the adhesion has been studied in detail.
The adhesion of poly(methyl methacrylate) (PMMA) and polystyrene (PS) films, whose surface has been previously structured by dynamic plowing lithography (DPL), has been measured by means of forcedisplacement curves. The different adhesion of modified and unmodified PS leads to the assumption that polymer chains are broken during DPL. After measuring the energy dissipated by the tip during DPL, in order to check that the transferred energy is sufficient to break covalent bonds, the polymer chain scission caused by the lithographic process has been definitely confirmed by size exclusion chromatography measurements of the lithographed films.
Laser ablation of single-crystalline indium phosphide (InP) was performed in air by means of linearly polarized Ti:sapphire femtosecond-pulses (800 nm, 130 fs, 10 Hz). As a result of the first laser pulses, several morphological changes (crater formation, rim formation, ripple structures and cones) were observed. These effects were explored using force modulation microscopy (FMM), a technique based on scanning force microscopy (SFM), allowing the simultaneous imaging of both topography and local stiffness at a high lateral resolution. The first laser pulse induces the formation of a protruding rim (height <20 nm, width ~300 nm) bordering the ablated crater. A Fourier-analysis of the multi-pulse generated topographies reveals the formation of wavelength-sized periodic ripples (modulation depth <100 nm) with an orientation perpendicular to that of the electric field vector of the laser radiation. Besides these morphological alterations, also material modifications were observed in the irradiated regions by means of the FFM technique. Within the ablated craters, local stiffness variations were found revealing an inhomogeneous material composition/structure as a consequence of the femtosecond pulse laser treatment.
Laser ablation of single-crystalline indium phosphide (InP) was performed in air by means of linearly polarized Ti : sapphire femtosecond pulses (800 nm, 130 fs, 10 Hz). As a result of the irradiation with a variable number of laser pulses per spot (N /spl les/ 5), several morphological changes (crater formation, rim formation, ripple structures, and cones) were observed. These effects were explored using force modulation microscopy (FMM), a technique based on scanning force microscopy, allowing the simultaneous imaging of both topography and local stiffness at a high lateral resolution. The first laser pulse induces the formation of a protruding rim (height < 20 nm, width /spl ap/ 300 nm) bordering the ablated crater. A Fourier analysis of the multipulse generated topographies reveals the formation of wavelength-sized periodic ripples (modulation depth < 100 nm) with an orientation perpendicular to that of the electric field vector of the laser radiation. Besides these morphological alterations, material modifications were also observed in the irradiated regions by means of the FMM technique. Within the ablated craters, local stiffness variations were found revealing an inhomogeneous material composition/structure as a consequence of the femtosecond pulse laser treatment.
Bulk samples and thin films of polyamides (PA6 and PA12) were exposed to fluorine (1 - 10 vol.-% F2 in N2) and analysed with photoelectron (XPS) and infrared spectroscopy. Fluorination affects both, the amide and the hydrocarbon parts of the polymers. However, only the carbon atom next to the carbonyl is readily fluorinated. Chemical modification of the amide group is apparent in a large binding energy shift (+5 eV) of the N1s level and the appearance of a CO band at 1734 cm-1. It is concluded that the amide C-N bond is cleaved in the fluorination process and that COOH and NF2 end groups are formed. This conclusion is corroborated by the appearance of ester oxygen in the XPS and by the 19F NMR spectra of the volatile products that show fluorine signals chemically shifted about 200 ppm towards lower field as compared with the CHF environment.
After a delamination process in a C-fiber reinforced polymer composite, the identification of the polymer residue of poly-(phenylene sulphide) on carbon fiber surfaces gives important information on the composite failure mechanism. Using scanning force microscopy (SFM) in its lateral force imaging mode or with the stiffness imaging mode, it is almost impossible to distinguish the two composite components owing to a very low material-based contrast of the local friction and compliance. The new technique using contrast based on a local AC current measurement allows a clear identification of the conducting carbon fiber and the non-conducting polymer coverage.