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Eingeladener Vortrag
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The irradiation of single-crystalline indium phosphide (c-InP) by Ti:sapphire femtosecond laser pulses (130 fs, 800 nm) in air is studied by means of in-situ time resolved reflectivity measurements [fs-time-resolved microscopy (100 fs-10 ns) and point probing analysis (ns - µs)] and by complementary ex-situ surface analytical methods (Micro Raman Spectroscopy, Scanning Force, and Optical Microscopy). The dynamics of melting, ablation, and optical breakdown as well as structural changes resulting from rapid solidification are investigated in detail. Different laser-induced surface morphologies are characterized and discussed on the basis of recent ablation and optical breakdown models.
A stoichiometric amineepoxy formulation was cured in the presence of a thermoplastic, namely poly(vinylpyrrolidone) (PVP). The epoxy system consisted of the resin diglycidyl ether of bisphenol A (DGEBA) and the aromatic curing agent 4,4'-diaminodiphenylsulfone (DDS). As shown for this system in a former study by Oyama et al. [Oyama HT, Lesko JJ, Wightman JP. J Polym Sci B 1997;35:33146. [36]], preferential absorption of amine molecules by PVP can occur. In the present study, the focus is on the variations of local elastic properties within the epoxy interphase adjacent to the PVP layer. The curing was performed close to the glass transition temperature, Tα, of the PVP film, namely at 170 °C. Variations of the local amine concentration were tracked using energy-dispersive analysis of X-rays (EDX), by taking benefit of the sulfur contained in DDS. Using temperature-dependent dynamic mechanical analysis (DMA), a series of epoxy reference samples of different amineepoxy concentration ratios, r, was investigated in order to work out the relationship between r and the epoxy storage modulus at room temperature. In the excess-epoxy regime, r<1, the modulus is observed to increase with departure from the stoichiometric ratio, r=1. Considering the respective suppression of the ß-transition, the observed characteristic can be explained by an antiplasticisation effect. Depth-sensing indentation (DSI) experiments across the epoxy/PVP interphase provided evidence for strong modulus variations. In consistency with the EDX and the DMA data, in the vicinity of the PVP layer the local epoxy modulus is increased. The total change of the epoxy Young's modulus is ~1.1 GPa. However, the total width of the modulus decay of ~175 µm is ~2.5 times larger than the one of the DDS concentration gradient. This finding is discussed in terms of additional spatial variations of the DGEBA concentration as well as long-range diffusion currents of DDS induced by the interdiffusion processes and their effect on the final network of crosslinks.
A specially designed scanning force microscope (SFM, atomic force microscope – AFM) was incorporated into the chamber of a commercial scanning electron microscope (SEM) to investigate vibrating SFM cantilevers at their resonance. Inherently, the spatial resolution of electron microscopy is higher than that of optical methods. In this paper we present vibration modes (eigenmodes) of two different SFM cantilevers. Their nonlinear behavior is also explored in order to depict their 2nd harmonics (twice the fundamental frequency). Imaging of the local vibration is performed by measuring the frequency- and phase-selective responses of the SE signal at different X and Y positions of the scanned electron beam.
In this work, reactive magnetron-sputtered Pb(Zr,Ti)O3 thin films were used to fabricate well-ordered nanodot arrays by means of nanosphere lithography (NSL). NSL is based on a two-step etch process by means of, firstly adjusting the diameter of polystyrene spheres in the self-assembled polymeric nanosphere mask using reactive ion etching, and secondly transferring the mask to the substrate by ion milling with adjusted heights. Hence, structures with different aspect ratios can be fabricated.
Piezoresponse force microscopy was used as the inspection tool on both non-patterned and patterned films. Both the topography and polarization out of plane and in plane was deduced in this mode. Grains of nanodots with low aspect ratio form domain structures comparable to domains in non-patterned films. In contrast to that, nanodots with a higher aspect ratio form particular structures. The in-plane amplitude images show mostly a bisectioned domain assembly, while the out-of-plane amplitude images show in some cases more complex structures like 'c'-shaped domains or multi-domains around a center domain.
The patterning of the ferroelectric material was shown to affect the formation of ferroelectric domains. The initial polycrystalline, randomly-ordered films are re-oriented and show domain structures depending on nanodisc diameter and aspect ratio. This may enable tailoring of ferroelectric materials in their piezoelectric and pyroelectric properties by patterning.
We report surface plasmon resonance (spr) and confocal fluorescence results concerning the interaction of a gene-5-protein (g5p) with single-stranded DNA oligonucleotides (dT25) tethered to a gold surface. The spr data show that a highly stable g5pssDNA complex is readily formed on a gold surface with koff = 1.7 × 10-3 s-1. The extent of the complexion indicated involvement of the cooperative proteinprotein interactions within the binding to DNA. In the experiments where dT25 coexist with g5p in the solution, the fluorescence data show that g5p also mediates the binding between the non-complementary oligonucleotides in the solution and those immobilised on the surface.
Observation of nanoscale hot-spot generation on a 2, 4, 6-trinitrophenol (TNP) single crystal
(2011)
An energetic material (EM) creates a local thermal point when it accepts energy and the EM will explode due to thermal decomposition when the hot-spot temperature reaches the explosive temperature. The initial stage of the hot-spot formation on 2, 4, 6-trinitrophenol (TNP) single crystal has been observed at the nanometer scale using atomic force microscopy (AFM). The hot-spot generation has been directly initiated by means of an AFM tip. The phenomenon is accompanied by producing agglomerated spherical-like nanoparticles due to a low-temperature decomposition of TNP. It has been observed that the agglomerated particles are produced outside of the stimulated region. The observed decomposition process at the nanoscale doesn't lead to a self-sustaining shock as detonation or explosion. The results are of interest in relation to explore the origin of deformation-induced chemical decomposition or detonation of EM.