Investigation of energy transfer by means of photobleaching

Photobleaching of organic laser dyes is used to investigate energy transfer in alcoholic solutions. By this means it becomes easy to indicate energy transfer, to estimate the influence of radiative transfer, and to calculate the number of transfered photons. Additional measurements are carried out on the donator decay time as a function of acceptor concentration. Rhodamine 6G-CV and rhodamine 6G-DTDC mixtures are investigated.     

Investigation of biopolymer networks by means of AFM

Natural hydrogel alginate was investigated by means of atomic force microscopy (AFM) to gain microscale information on the morphological and rheological properties of the biopolymer network cross-linked by various cations. Local rheological properties of the gels measured by force spectroscopy gave correlation between increasing ion selectivity and increasing polymer elasticity. Adhesive forces acting between the surface of the gel and the probe, and also the intrinsic rheological properties of bulk polymers affect the microscopical image formation.     

TEM study of the deformation structures around nano-scratches

An in-plane transmission electron microscopy (TEM) investigation carried out on nano-scratches made in a Ni₃Al foil revealed a high dislocation density within the scratch core, resulting in severe crystal rotations. The amount and sense of rotation were found to be asymmetrical about the longitudinal centre line of the scratch. Cross-sectional TEM analysis revealed that almost all the dislocations were confined within a semicircular zone having a radius similar to the calculated tip-sample contact size during scratching, in agreement with the in-plane TEM observations.     

Planarization of inhomogeneous structures by means of physical ion sputtering

The dynamics of ion-beam etching of test microstructures, simulating fragments of the surface structure of very large-scale modern integrated circuits, has been studied. Aluminum strip microstructures, 0.5 μm high and 1 μm wide deposited on the surface or embedded into SiO₂, were used as test samples. 1 keV Ar⁺ ion beam 1 with a current density 0.5 mA/cm₂, incident on the surface of a sample, rotating at a speed of 60 r/min, at an angle of 87°, has been used in the experiments. The surface morphology evolution was studied using atomic-force microscopy. The experiments demonstrate that physical ion sputtering at glancing incident angles can be used for the planarization of originally inhomogeneous structures. The achieved planarization degree allows one to use this method for defect detection in the metallization multilevel layers of very large-scale modern integrated circuits.     

Investigation of lattice dynamics by means of vibronic spectra

Electronic transitions at a foreign probe ion in a lattice exhibit vibrational sidebands. They may be used as a new tool to investigate lattice dynamics. To make this too effective the theory of vibronic spectra has been refined. The principal refinement is that of a partial Born-Oppenheimer approximation which establishes a rigid coupling of the electronic wavefunctions of the foreign ion to its own nucleus. The structural form of the one-phonon sideband is given as a projection of the classical Greens' function (imaginary part) onto single multipole-fields in lattice space. Employing a variety of electronic transitions and by careful group-theoretical analysis a complete irreducible sequence of projections can be extracted from the experiments. These functional forms depend sensibly on the eigenvectors of the lattice modes, whence they contain information, which cannot be received from neutron scattering. Moreover, the spectra related to the higher multipoles give insight into the disturbed (local) dynamics, whereas the lower type spectra concern the undisturbed (ideal) one. Systems, where the foreign probe ion has high symmetry, are most suitable for the new method. For systems of low local symmetry approximations are suggested by the low-frequency behaviour of the measured one-phonon band. Because of the high resolution of optical measurements, the information from vibronic spectra is comparable or even superior in detailed richness to neutron scattering data.     

Local chemical states and microstructure of photoluminescent porous silicon studied by means of EELS and TEM

Photoluminescent porous Si (PS) layers were formed on low resistivity p-type Si(100) wafers by anodization at a current density (Ia) of 100-350 mA cm(-2) at room temperature. The local chemical states and the microstructures of the PS layers were studied by means of electron energy loss spectroscopy (EELS) and transmission electron microscopy (TEM), and were correlated to the red photoluminescence (PL). The PS layer consists of sponge-like and tree-like structures. The tree-like structure becomes finer with increase of Ia. The fine tree-like structure is shown to be favorable for intensive PL. The EELS analysis reveals that the Si-4O structure, namely the basic structure of SiO2, and Si crystals coexist in the PS layers. The relative content of SiO2 to Si crystallites (R) increases with increase in Ia and decreases with the depth from the top surface of the PS layer. High R corresponds to intensive PL. These results suggest that PL may be connected with some kind of defects in SiO2 and/or defects in the boundary between Si crystallites and SiO2 structure in anodized PS layers, and that PL may be mainly emitted from the layer near the top surface of the PS layers.     

Non-destructive defect characterization of concrete structures reinforced by means of FRP

The aim of this work is to develop a reliable and precise non-destructive testing technique based on infrared thermography and post processing by means of neural networks. In particular, the experimental procedure to be implemented consists mainly in the “impulsive” heating of the structure and in the analysis of the superficial thermal response by means of a thermocamera. The procedure requires a detailed set-up, in order to assess its feasibility. In this work is presented the case study of a concrete structure strengthened by bonded FRP, with imposed well-known defects. The results obtained by means of infrared thermography were compared with results obtained by ultrasonic testing.     

Investigation of doping in Si crystals by means of electroreflectance

Summary In this work the importance of electroreflectance is evidenced in two specific applications concerning studies of semiconductor surfaces: i) determination of junction depths and carrier profiles, ii) mapping of inhomogeneity curves of the carrier distribution on Si surfaces. New information in both cases is obtained and briefly discussed. Work partially supported by Progetto Finalizzato Energetica (Sottoprogetto Energia Solare) of consiglio Nazionale delle Ricerche.     

Investigation of alumina lattice defects by means of thermoluminescence experiments

Summary Samples of α-alumina prepared at low temperature by means of a special procedure are investigated by recording their thermoluminescent emissionvs. temperature and wavelength. Taking into account the effect of thermal treatments, evidence is obtained for the presence of a distribution of electron traps of different depths. Arguments are advanced for characterizing the nature of the lattice defects originating these traps.     

Investigation of condensed matter by means of elastic thermal-neutron scattering

The application of elastic thermal-neutron scattering in investigations of condensed matter that were performed at the Institute for Theoretical and Experimental Physics is described. An account of diffraction studies with weakly absorbing crystals, including studies of the anomalous-absorption effect and coherent effects in diffuse scattering, is given. Particular attention is given to exposing the method of multiple small-angle neutron scattering (MSANS). It is shown how information about matter inhomogeneities can be obtained by this method on the basis of Molière’s theory. Prospects of the development of this method are outlined, and MSANS theory is formulated for a high concentration of matter inhomogeneities.     

Investigation of submicroscopic structures by very-slow-neutron transmission experiments

The transmission of very slow neutrons through a colloidal dispersion of silica particles was investigated at the FRM reactor, Munich. The experimental transmission shows a characteristic wavelength dependence which permits one to deduce several characteristic parameters of the scattering zones, in particular their size and number. The experimental results obtained are consistent with the known data for the substance chosen. This indicates that the simple method of very slow neutron transmission may be applied in certain cases as an alternative to the well-established techniques of X-ray or neutron small-angle scattering.Work supported by the Bundesministerium für Forschung und Technologie     

Amplitude modulation of the cw laser light in the TEM mn mode by means of a mechanical chopper

Amplitude modulation of the laser beam in a TEM _mn mode by means of a mechanical chopper is investigated on the basis of the chopping model represented by a moving system of infinitely long, parallel slots and mark spaces. The cases of rectangular and axial symmetry of the laser beam are both treated. The explicit expressions for the waveform of the modulated normalized transmitted laser power are deduced and their consequences investigated. It is found that in the case of rectangular symmetry, unlike the case of axial symmetry, the TEM _mn modes give, for a constant value of the mode numbern and for any value ofm, the same time dependence of the amplitude modulated laser power. The notion of the equivalent modulation widths is introduced and conditions for the efficient amplitude modulation are found.     

Investigation of KTiOPO4 nanocrystals by means of second-harmonic light emission

The finding of nonlinear nanometric-sized probes is of key importance for the development of nonlinear microscopy in physical as well as biological sciences. We isolate nonlinear KTiOPO4 nanocrystals and study them by second-harmonic generation microscopy （SHGM） and atomic force microscopy （AFM） independently. With both polarization analysis and defocused imaging of the emitted second harmonic field, we extract the Euler angles of the crystalline axes of a single nanocrystal. A balanced coherent optical homodyne detection shows the coherent nature of the nanocrystal nonlinear emission and allows a phase measurement of the emitted second-harmonic field. These features make the KTiOPO4 nanocrystal a good candidate for a vectorial probe of electromagnetic near fields.     

Investigation of clustering in light nuclei by means of relativistic-multifragmentation processes

New results concerning the topology of the fragmentation of relativistic nuclei ⁷Li and ¹⁰B are presented. A program is proposed for studying the cluster structure of stable and radioactive nuclei. The use of emulsions in the investigation of nuclear clustering in the fragmentation of light nuclei at energies are in excess of 1 GeV per nucleon is discussed.     

Investigation of magnetization reversal process in pinned CoFeB thin film by in-situ Lorentz TEM

Exchange bias effect has been widely employed for various magnetic devices.The experimentally reported magnitude of exchange bias field is often smaller than that predicted theoretically,which is considered to be due to the partly pinned spins of ferromagnetic layer by antiferromagnetic layer.However,mapping the distribution of pinned spins is challenging.In this work,we directly image the reverse domain nucleation and domain wall movement process in the exchange biased Co Fe B/Ir Mn bilayers by Lorentz transmission electron microscopy.From the in-situ experiments,we obtain the distribution mapping of the pinning strength,showing that only 1/6 of the ferromagnetic layer at the interface is strongly pinned by the antiferromagnetic layer.Our results prove the existence of an inhomogeneous pinning effect in exchange bias systems.