Mischa Nicklaus

Epitaxial Patterning of Bi2FeCrO6 Double Perovskite Nanostructures: Multiferroic at Room Temperature

There is an increasing interest in developing and characterizing multifunctional materials, as they exhibit rich physical and chemical properties and offer exciting opportunities, for example, to miniaturize integrated devices and extend the potential of establishing nanoarchitecture concepts. [ 1 , 2 ] In this context, multiferroic materials [ 3 ] which combine two or more ferroic functionalities are promising for applications in fi elds such as spintronics and non-volatile data storage. [ 4 ] As recently demonstrated [ 5 ] ferromagnetic–ferroelectric multiferroics can be advantageously used to encode the information in electric polarization and magnetization giving rise to a four logic state memory. The coupling between magnetic and electrical properties leads to additional versatility for related devices, such as electric fi eld-controlled magnetic data storage. [ 6 ] The recent emergence of Bi-based double perovskite thin fi lms, such as Bi 2 FeCrO 6 (BFCO) [ 7– 9 ] and Bi 2 CoMnO 6 , [ 10 ] with strong magnetic behavior at room temperature, create opportunities to practically apply multiferroics. In competition with rival technologies, downscaling the feature size of multifunctional materials is an important step to achieve very high-density memory devices. [ 11 , 12 ]

Imaging and modeling collagen architecture from the nano to micro scale

The collagen meshwork plays a central role in the functioning of a range of tissues including cartilage, tendon, arteries, skin, bone and ligament. Because of its importance in function, it is of considerable interest for studying development, disease and regeneration processes. Here, we have used second harmonic generation (SHG) to image human tissues on the hundreds of micron scale, and developed a numerical model to quantitatively interpret the images in terms of the underlying collagen structure on the tens to hundreds of nanometer scale. Focusing on osteoarthritic changes in cartilage, we have demonstrated that this combination of polarized SHG imaging and numerical modeling can estimate fibril diameter, filling fraction, orientation and bundling. This extends SHG microscopy from a qualitative to quantitative imaging technique, providing a label-free and non-destructive platform for characterizing the extracellular matrix that can expand our understanding of the structural mechanisms in disease.

Note: Tip enhanced Raman spectroscopy with objective scanner on opaque samples

We report on 14 nm lateral resolution in tip-enhanced Raman spectroscopy mapping of carbon nanotubes with an experimental setup that has been designed for the analysis of opaque samples in confocal side-access through a novel piezo-driven objective scanner. The objective scanner allows for fast and stable laser-to-tip alignment and for the adjustment of the focus position with sub-wavelength precision to optimize the excitation of surface plasmons. It also offers the additional benefit of imaging the near-field generated Raman scattering at the gap between tip and sample as direct control of the tip enhancement.

Photoluminescence mapping of oxygen-defect emission for nanoscale spatial characterization of fiber Bragg gratings

Confocal photoluminescence (PL) microscopy is used to gain insight into the inner structure of Ge-doped Fiber Bragg Gratings (FBGs). These measurements pinpoint room temperature PL emission from oxygen-related defects in the visible range, whose spatial distribution exhibits a periodicity associated with the spatial modulation of the refractive index printed inside the fiber core of the FBG. The period measured by PL mapping performed at submicrometric resolution matches the period of the refractive index variation determined from the optical transmission wavelength using the Bragg condition. Since the PL emission of oxygen-related defects can be used to probe local chemical changes inside fused silica, this novel and non-destructive experimental approach can be implemented for the direct characterization of FBGs, to study the effects of gas conditioning, ageing, and degradation under various environments.

Noncontact atomic force microscopy imaging of ferroelectric domains with functionalized tips

We report on an imaging method for ferroelectric domains by noncontact atomic force microscopy with dipole-molecule decorated tips. The Coulombic tip-sample interaction is revealing the domains monitored as an additional topography contribution. As proof of concept, we present agreement between numerical simulations and experiments on antiparallel out-of-plane domains on LiNbO3. This contact-free imaging technique promises substantially increased lifetime of read-heads for high-density ferroelectric data storages, and high resolution and improved image quality in scanning probe microscopy on systems with surface charge density variations.

EFFECT OF VERTICAL MECHANICAL COMPRESSION ON THE RESISTIVE SWITCHING CURRENTS OF TITANIUM DIOXIDE THIN FILMS

We report on a scanning probe investigation of the resistive switching behavior of TiO2 thin films as a function of an external bias voltage. Our initial conductive atomic force microscopy scans (c-AFM) on 30 nm thick films of sputtered TiO2 confirm the Ron–Roff ratio of approximately 4:1 reported in literature. After a tapping mode scan that compacts this layer by approximately 3%, a subsequent c-AFM scan reveals that the resistance in the compacted region has increased by a factor of 40 while the Ron–Roff ratio is only affected for small bias voltages.