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This work fundamentally investigates how the second harmonic generation (SHG) from commercial nonlinear crystals can be boosted by the addition of individual optical nanoantennas. Frequency conversion plays an important role in modern non-linear optics, and nonlinear crystals have become a widely used building block for non-linear processes. Still, SHG remains hampered by limited conversion efficiency. To strengthen SHG from the crystal surface, we investigate the interaction of LiNbO3 crystals with individual gold nanodiscs. The scattered intensities and resonance frequencies of the nanodiscs are analyzed by dark-field spectroscopy and simulations. Subsequently, the discs on LiNbO3 are excited by a pulsed femtosecond laser in a parabolic mirror setup. Comparing the SHG at the position of a single nanodisc at resonance on the crystal with that of the unstructured crystal and of gold nanodiscs on a reference substrate, local SHG enhancement of up to a factor of three was achieved in the focal volume through the presence of the antenna.

The integration of small wafer-based devices into flexible polymeric systems allows the fabrication of smart systems. Such systems are of high interest and are being developed in different fields. Active implants for biomedical applications promise new insights and therapy possibilities including the novel field of electroceuticals, which focuses on the treatment of systemic diseases by neuromodulation. For the fabrication of a new active flexible microelectrode array, we developed a process that allows the embedding of an array of small CMOS dies into a polymer foil. The process includes a transfer printing process based on adhesion, transferring the desired of the separated dies from UV-curable dicing tape to a substrate coated with sugar solution. The transfer printing process has shown to be highly reliable and selective, yielding a transfer success rate of 100% in most cases. The relative position of the transferred dies is conserved to less than $15~\mu \text{m}$ lateral displacement. To evaluate the process, the pull-off strength of the employed silicone stamps was measured. For stamps made of soft silicone, a pulling strength up to 83 kPa was obtained. In addition to this, a process for the embedding of the dies into a flexible foil system is presented. Using polydimethylsiloxane, the topography due to the dies’ height is reduced from more than $200~\mu \text{m}$ to approximately $10~\mu \text{m}$ , enabling the use of standard microelectromechanical fabrication processes on top.

We investigate mode conversion in 3D asymmetric nanocones using angle-dependent linear optical spectroscopy and second-harmonic generation microscopy supported by corresponding simulations. The results prove the efficient excitation of the plasmonic out-of-plane mode that enhances the electric near-field at the sharp tip. Furthermore, we introduce two advanced fabrication processes including either etch mask transfer by tilted etching into a metallic layer or tilted electron-beam lithography followed by tilted evaporation and lift-off. These processes enable the fabrication of tilted nanostructures which can be optimized for a given purpose. The combination of the optical properties and the introduced fabrication processes enables a new design of plasmonic nanostructures for ultra-compact sensors or photon sources.

Plasmonic nanostructures serve as optical antennas for concentrating the energy of incoming light in localized hotspots close to their surface. By positioning nanoemitters in the antenna hotspots, energy transfer is enabled, leading to novel hybrid antenna-emitter-systems, where the antenna can be used to manipulate the optical properties of the nano-objects. The challenge remains how to precisely position emitters within the hotspots. We report a self-aligned process based on dry laser ablation of a calixarene that enables the attachment of molecules within the electromagnetic hotspots at the tips of gold nanocones. Within the laser focus, the ablation threshold is exceeded in nanoscale volumes, leading to selective access of the hotspot areas. A first indication of the site-selective functionalization process is given by attaching fluorescently labelled proteins to the nanocones. In a second example, Raman-active molecules are selectively attached only to nanocones that were previously exposed in the laser focus, which is verified by surface enhanced Raman spectroscopy. Enabling selective functionalization is an important prerequisite e.g. for preparing single photon sources for quantum optical technologies, or multiplexed Raman sensing platforms.

Frequency conversion plays an important role in both fundamental and applied nano-optics. Doubling the frequency of light by second harmonic generation (SHG) is a vital process e.g. in laser optics or high-resolution microscopy. SHG can be created through symmetry breaking at plasmonic nanostructures, or the local high electric near-fields of plasmonic nanoantennas can be utilized to further enhance the SHG e.g. from nonlinear crystals. Examples of SHG microscopy using cylindrical vector beams in combination with tilted nanocones and radially symmetric oligomers are shown as well as enhancement studies of the SHG from nonlinear crystals decorated with polarization-matched nanostructures.

The fabrication and optical characterization of self-assembled arrangements of rough gold nanoparticles with a high area coverage and narrow gaps for surface-enhanced Raman spectroscopy (SERS) are reported. A combination of micellar nanolithography and electroless deposition (ED) enables the tuning of the spacing and size of the noble metal nanoparticles. Long-range ordered quasi-hexagonal arrays of gold nanoparticles on silicon substrates with a variation of the particle sizes from about 20 nm to 120 nm are demonstrated. By increasing the particle sizes for the homogeneously spaced particles, a large number of narrow gaps is created, which together with the rough surface of the particles induces a high density of intense hotspots. This makes the surfaces interesting for future applications in near-field-enhanced bio-analytics of molecules. SERS was demonstrated by measuring Raman spectra of 4-MBA on the gold nanoparticles. It was verified that a smaller inter-particle distance leads to an increased SERS signal.

We report on a compact and cost-effective integrated label-free biosensor configuration which is based on the refractive index sensitivity of the localized surface plasmon resonance (LSPR) of gold nanostructures. Aiming for compactification and miniaturization of the sensor, arrays of nanodiscs were fabricated on the planar surface of a gradient index (GRIN) lens, which acts as a substrate as well as an imaging objective for the light scattered by the gold structures. Integration of the lens into a microfluidic flow cell enabled the controlled exchange of liquid media at the sensor surface. The light scattered by the nanostructures was investigated spatially and spectrally resolved making use of the imaging properties of the GRIN lens. Dynamic spectral analysis during refractive index changes was conducted, revealing high sensitivities of up to 372 nm per refractive index unit for the shift of the LSPR. Biosensing capabilities were demonstrated by the detection of binding of an analyte by means of a testosterone-immunoassay.

International audience; Gold nanocones acting as optical antennas offer an excellent geometry for focusing light near the cone tip, acting as nano-light sources with spot sizes on the order of the tip radius. However only the vertical plasmon mode oscillating in the axial direction can effectively excite the tip, whereas lateral modes oscillating along the cone base create mostly unwanted background in applications. The present work investigates the three-dimensional plasmonic mode structure of nanocones both experimentally and numerically. By tuning the nanocone aspect ratio, the modes can be spectrally tuned relative to each other, making them coincide for maximum excitation, or tuning the base mode away from the vertical mode for effective background suppression.

Collective effects in assemblies of plasmonic nanostructures are attracting widespread interest. Such effects are governed by the interactions among the constituents of the overall structure, providing an alternative path to modify plasmon resonances [1]. A particularly interesting collective effect in these structures is the so-called dark plasmon mode, which has a net zero dipole moment and cannot be accessed using plane waves or linearly polarized light under normal incidence. An emerging way to excite collective dark modes in such structures is through the use of cylindrical vector beams (CVB) that exhibit inhomogeneous states of polarization such as azimuthal or radial polarizations [2,3]. The use of CVBs to excite collective nonlinear optical effects such as second-harmonic generation (SHG) in oligomers has started only recently [4]. Here, we demonstrate a similar possibility by tailoring SHG in plasmonic radial trimers using CVBs.

In second harmonic generation (SHG), the energy of two incoming photons, e.g., from a femtosecond laser, can be combined in one outgoing photon of twice the energy, e.g., by means of a nonlinear crystal. The SHG efficiency, however, is limited. In this work, the harvested signal is maximized by composing a hybrid system consisting of a nonlinear crystal with a dense coverage of plasmonic nanostructures separated by narrow gaps. The method of self-assembled diblock-copolymer-based micellar lithography with subsequent electroless deposition is employed to cover the whole surface of a lithium niobate (LiNbO3) crystal. The interaction of plasmonic nanostructures with light leads to a strong electric near-field in the adjacent crystal. This near-field is harnessed to enhance the near-surface SHG signal from the nonlinear crystal. At the plasmon resonance of the gold nanoparticles, a pronounced enhancement of about 60-fold SHG is observed compared to the bare crystal within the confocal volume of a laser spot.

As a multifunctional device for sensing experiments and fundamental research, tailor-made plasmonic nanostructures with continuously tunable resonances are created by preparing bow tie-shaped nanostructures on a flexible substrate. The bow ties are fabricated by electron beam lithography on a chromium sacrificial layer and transferred to a polydimethylsiloxane (PDMS) substrate. The structures on PDMS are analyzed by reflection dark-field spectroscopy and scanning electron microscopy. Dark-field spectra of individual nano-antennas are obtained while the substrate is relaxed, and while strain is applied and the substrate is elastically stretched. Depending on the alignment of the bow ties relative to the direction of the strain, the deformation of the substrates leads to an increase or decrease of the nanostructure gaps, and therefore to a fully reversible decrease or increase of the antenna coupling, respectively. The continuous change in coupling is visible as a blue-shift in the resonance of the coupling mode for increasing gap widths, and a red-shift for decreasing gap widths. This configuration offers interesting perspectives for molecular transport and sensing investigations under variable coupling conditions as well as for tunable SERS substrates and optical strain sensor applications. In particular, very narrow gaps are within reach in the transversal configuration.

We investigate collective effects in plasmonic oligomers of different symmetries using second-harmonic generation (SHG) microscopy with cylindrical vector beams (CVBs). The oligomers consist of gold nanorods that have a longitudinal plasmon resonance close to the fundamental wavelength that is used for SHG excitation and whose long axes are arranged locally such that they follow the distribution of the transverse component of the electric field of radially or azimuthally polarized CVBs in the focal plane. We observe that SHG from such rotationally symmetric oligomers is strongly modified by the interplay between the polarization properties of the CVB and interparticle coupling. We find that the oligomers with radially oriented nanorods exhibit small coupling effects. In contrast, we find that the oligomers with azimuthally oriented nanorods exhibit large coupling effects that lead to silencing of SHG from the whole structure. Our experimental results are in very good agreement with numerical calculations based on the boundary element method. The work describes a new route for studying coupling effects in complex arrangements of nano-objects and thereby for tailoring the efficiency of nonlinear optical effects in such structures. publishedVersion

We use cylindrical vector beams to investigate second-harmonic generation from rotationally symmetric arrangements of plasmonic nanoholes. The second-harmonic efficiency is shown to depend strongly on collective interactions between the nanoholes. acceptedVersion

Display Omitted The fabrication process of a gold nanocone on an atomic force microscopy cantilever is shown.The nanocone tip can be applied as a near-field scanning optical microscopy probe.The fabrication process was monitored step by step by scanning electron microscopy. A novel technique for the nanofabrication of gold nanocones on top of atomic force microscopy cantilever tips is demonstrated. The modified tips are intended as near-field scanning optical microscopy probes. The fabrication process is composed of cutting the probe apex with a focused gallium ion beam to create a platform for the nanocone fabrication. Three thin films are deposited on the cantilever, where gold as the active plasmonic material is sandwiched between a titanium adhesion layer and an Al2O3 thin film. At the top of the cantilever the deposited thin films are partially structured by a ring shaped focused ion beam pattern, leaving behind a cylindrical pillar. Finally, the gold nanocone is produced by argon ion etching with the top thin film on the pillar acting as a hard mask.

The interaction of metallic plasmonic nanostructures and organic semiconductor thin films plays a crucial role in engineering light harvesting and energy transfer processes, e.g., for optoelectronic applications. Plasmonic resonances of the metal structures can be used to increase the light emission or absorption of organic molecules. Here small molecules are employed since they can form organic layers with a defined crystalline order and orientation of the transition dipole. Extinction measurements combined with numerical simulations of a hybrid system consisting of a gold nanowire grating and a thin film of diindenoperylene (DIP) are reported. The experimental results are compared to the simulations and indicate an enhanced absorption in the wavelength region corresponding to the transition from the highest occupied molecular orbital to the lowest unoccupied molecular orbital of DIP. This enhancement is found to be related to the localized field enhancement near the individual nanostructures as well as to grating-induced effects. Notably, the hybrid system also exhibits parallel lattice resonances, which have recently been discussed for two-dimensional (2D) gold nanostructure arrays. In this study a hybrid plasmonic-organic small molecule system exhibiting these modes is investigated. The results for this model system show a way to modify the optical properties of plasmonic nanostructures by collective effects to achieve stronger light-matter interaction in a wide range of hybrid plasmonic systems.

Graphical abstractDisplay Omitted Gold nanowire gratings for organic photovoltaic cells were fabricated on, within and below ITO electrodes.The nanogratings have been fabricated by e-beam lithography and nano imprint lithography.The gratings were analyzed by SEM, AFM and GISAXS measurements.The tuneability of the plasmon resonance has been shown by white light extinction spectroscopy. Organic photovoltaic devices are interesting alternatives to conventional silicon based photovoltaic cells, due to potentially lower material costs and energy consumption during the fabrication process. However, the energy conversion efficiency of organic photovoltaic cells may still be improved. One possible approach is a combination with metallic nanostructures to improve light absorption properties in the active layer. We report on the fabrication and characterization of metallic nanogratings integrated with an indium tin oxide (ITO) electrode to be combined with small-molecule organic photovoltaic cells. With respect to geometry and extinction properties gratings fabricated by two different fabrication methods, conventional electron beam lithography and nanoimprint lithography, are presented. Furthermore, gratings fabricated on top of ITO are compared to gratings integrated both below and within ITO electrodes. Fabricating structures below or within electrodes is advantageous for organic thin film techniques to avoid compromising the crystallinity of the organic thin film and short-circuiting across the thin layer.

It has been shown in the past that fractal geometries are beneficial for radio and communication antenna designs in terms of bandwidth and gain. Recently, this concept was extended to plasmonic nanoantennas. Here, we present a fabrication method based on electron beam lithography and focused helium ion beam milling to further miniaturize dimer nanoantennas of 0th, 1st and 2nd order Sierpiński fractals. With this state-of-the-art approach, it becomes feasible to experimentally move their resonance conditions into the sub-micron wavelength regime, while maintaining excellent pattern definition and achieving sub-10 nm gap sizes for high near-field enhancement. These highly sophisticated nanostructures are numerically simulated and analyzed by dark-field scattering spectroscopy to monitor the effects of the fractal structuring on the scattering spectra and near-field enhancement.

Milling with the focused helium ion beam of a helium ion microscope is one of the most accurate ways to produce nano-structures such as plasmonic nanoantennas. In addition to good and immediate control of the dimensions, features in the sub-10 nm regime are achievable. Especially small gaps and sharp tips in this regime may lead to very high field enhancement under excitation. However, the milling rate of 30 keV helium ions is rather low, making it time-consuming to cut nano-structures out of a gold film. We present two processes to work around the low milling rate to obtain arrays of nano-structures with maximum precision within a reasonable time. These strategies can both be adapted to either poly-crystalline gold films or single-crystalline gold flakes. Using single crystals from a fabrication point of view enables even higher precision due to constant etch rates over the whole crystal as well as straight edges and vertical side-walls due to the uniform crystalline structure.

Micro- and nanotopography as well as the surface chemistry of biomaterials affect cell adhesion, proliferation and cell differentiation. Furthermore, the organization and localization of intracellular adhesion components such as the actin cytoskeleton are also altered dependent on the material surface topography. However, the detailed influence of the material micro-structure on cellular mechanisms on the molecular level is still unknown. This study is intended to elucidate such effects using regular pillar structures to characterize the modulation of cell responses like the regulation of voltage-sensitive calcium channels as well as signaling molecules in human osteoblasts. To analyze cell behavior on defined biomaterial surfaces, human osteoblastic MG 63 cells were cultured on geometrically micro textured titanium coated silicon wafers, as opposed to planar titanium references. Samples were fabricated by a photolithographic process using the negative tone resist SU 8 and sputter-coated with 100 nm titanium. Immunofluorescence staining and flow cytometry are used to detect the expression levels and the function of T type calcium channels. Knowledge about the biocomplexity of cell behavior dependent on topographical characteristics is of clinical relevance for the development of implant designs in tissue engineering.

We prepare metal oligomers whose structure is matched to the local polarization of focused cylindrical vector beams. Significant collective second-harmonic signals prove the potential of such beams in engineering nonlinear effects on the nanoscale.

Graphical abstractDisplay Omitted Highlights? Development of processes to fabricate needle-type electrodes. ? Anisotropic dry-etching of cross-linked SU-8. ? Sidewalls of the needles are isolated. ? Active electrode is defined by maskless lithography. Arrays of needle-type electrodes are expected to surpass arrays of planar electrodes used for measuring neuronal activity or stimulation of neurons concerning properties like stimulation threshold, spatial resolution and signal-to-noise ratio. This work describes the fabrication of such needle-type electrodes. The three-dimensionally shaped electrodes are 50µm high. Typical values for the base diameter are 20µm and a few microns for the tip radius. The needles are fabricated from cross-linked SU-8 using dry etching. Gold and titanium are used as metallization and SiOxCy as insulator. The tips of the electrodes are covered with nano-columnar titanium nitride.

We present a highly anisotropic dry etch process for bulk Titanium (Ti), based on a conventional parallel plate reactor system and the nontoxic feed gases SF"6, CHF"3 and O"2. This combination is commonly used for reactive ion etching of silicon, but to our knowledge has not yet been reported for etching bulk Ti. The influence of the process parameters total gas flow, gas composition, and process pressure on the Ti structures is discussed along with their optimization. With the optimized process we achieved an anisotropy of 0.9 with an etch rate of 40nm/min, and a resulting slope of the sidewalls of 85^o.

In tissue engineering, topographical modification of implants has been used as a powerful tool for the development of biorelevant implant designs. However, there is still a lack of knowledge about the fundamental principles of the cell–material interaction and quantitative correlations between cell biological parameters and physicochemical surface characteristics. The focus of our studies on cell architecture–cell function dependencies on regular micro-scaled surface structures was to investigate and further quantify the cell phenotype obtained from images of confocal microscopy and scanning electron microscopy. We used periodically structured titanium surfaces with regular cubic pillar geometry (dimension 3x3x5 µm and 5x5x5 µm) in comparison to planar samples. Confocal microscopy revealed a considerable rearrangement of the actin cytoskeleton on the top of the pillars with a reduced filament length. The quantification of different actin filament networks of cells grown on structured surfaces was carried out with a novel software for automatic filament recognition, covering the majority of filaments and their branching in noisy data. The quantitative analysis of cell phenotype changes on surfaces with regular geometry opens new possibilities for the data correlation cell vs. material.

In this article plasma enhanced growth of single vertical carbon nanotubes (CNTs) from individual nickel catalyst dots is studied, aiming at the fabrication of CNT field emitters. It is found that the growth of individual CNTs differs from that of CNT forests grown from unpatterned catalyst films, an effect that can be attributed to the difference in catalyst volumes. In the context of growth parameters the influence of temperature, growth time, catalyst volume, pressure and power is characterized. After determining the growth behavior, an individual CNT of desired geometry is fabricated on a conducting lead. The CNT is electrically characterized in terms of its field emission behavior and stable emission currents and its work function is determined to Φ = 5.4 ± 0.2 eV.

A versatile process for the fabrication of metallic nanocones is presented that is applicable to different surface topographies. The process is based on thin-film metallization, focused electron beam induced deposition of local etch masks, and argon ion milling. Nanocones can be crafted from different metals. Examples are shown for the optimization of the process for gold nanocones of different sizes. With this process, individual cones can be positioned on both planar and non-planar surfaces. It therefore enables integration of sharp-tipped nanocones into extreme topographies.

A microcolumn is presented containing a variable axis lens optimized for large scan fields and pixel numbers with minimal probe sizes for the deflected beam. At beam energy of 1 keV and a working distance of 38 mm the magnifying column can address scan fields of more than 7 x 7 mm(2) employing dynamic correction. Simulations of the design predict a probe diameter of 75 nm on axis up to similar to 1 mu m for a beam being deflected 5 mm of axis, assuming a field emission source. Within a scan field of 3 x 3 mm(2) this microcolumn could address over 1 gigapixels of less than 100 nm in size. Tests of the column, using the 135 nm probe of a SEM as the source, resulted in a beam size of similar to 720 nm on axis and up to 1.1 mu m for a beam deflected 5 mm off axis, consistent with simulations. (C) 2011 Elsevier B.V. All rights reserved.

Plasmonic near-fields can be structured with sub-optical wavelength resolution. This offers promising scenarios for trapping, guiding and manipulating cold atoms in plasmonically tailored dipole potentials, which could enable strong coupling between a single atom and a single plasmonic excitation. Here, we report on the interaction of Bose–Einstein condensates with the optical near-field above plasmonic micro- and submicrometre structures. At these structures, surface plasmon polaritons are excited by a laser in the Kretschmann configuration, giving rise to resonantly enhanced surface plasmons. We introduce a technique to measure the strength of optical near-fields by observing the reflection of cold atoms from the surface. In particular, the dependence of electromagnetic field enhancement on structure size is investigated. Furthermore, we show that the near-field induced potential landscape can be tailored to sub-micrometre dimensions by demonstrating matter–wave diffraction from a grating of plasmonic wires. Researchers have fired ultracold-atom Bose–Einstein condensates towards the submicrometre-featured potentials formed by the optical near-fields of surface plasmons. The strength and structural dependence of the optical near-fields were determined from the reflection of cold atoms. It is hoped that the work paves the way towards plasmonic guiding and the manipulation of cold atoms.

Near-field scanning optical microscopy enables the simultaneous topographical and subdiffraction limited optical imaging of surfaces. A process is presented for the implementation of single individually engineered gold cones at the tips of atomic force microscopy cantilevers. These cantilevers act as novel high-performance optical near-field probes. In the fabrication, thin-film metallization, electron beam induced deposition of etch masks, and Ar ion milling are combined. The cone constitutes a well-defined highly efficient optical antenna with a tip radius on the order of 10 nm and an adjustable plasmon resonance frequency. The sharp tip enables high resolution topographical imaging. By controllably varying the cone size, the resonance frequency can be adapted to the application of choice. Structural properties of these sharp-tipped probes are presented together with topographical images recorded with a cone probe. The antenna functionality is demonstrated by gathering the near-field enhanced Raman signature of individual carbon nanotubes with a gold cone scanning probe.

Knowledge about biocomplexity of cell behavior in dependence on topographical characteristics is of clinical relevance for the development of implant designs in tissue engineering. The aim of this study was to find out cell architecture–cell function dependencies of human MG-63 osteoblasts on titanium (Ti) arrays with regular geometry. We compared cubic pillar structures (SU-8, dimension 3 × 3 × 5 and 5 × 5 × 5 μm) with planar samples. Electrochemical surface characterization revealed a low amount of surface energy (including polar component) for the pillar-structured surfaces, which correlated with a reduced initial cell adhesion and spreading. Confocal microscopy of cell’s actin cytoskeleton revealed no stress fiber organization instead, the actin was concentrated in a surface geometry-dependent manner as local spots around the pillar edges. This altered cell architecture resulted in an impaired MG-63 cell function – the extracellular matrix proteins collagen-I and bone sialo protein (BSP-2) were synthesized at a significantly lower level on SU-8 pillar structures; this was accompanied by reduced β3-integrin expression. To find out physicochemical factors pertaining to geometrically microstructured surfaces and their influence on adjoining biosystems is important for the development of biorelevant implant surfaces.

In this work a biocompatible system of carbon nanotube electrodes that are fabricated from ferritin as the catalyst material is demonstrated. For this purpose, a layer of ferritin is patterned using negative resist and ion milling. Afterwards the amino acids around the ferritin cores are removed in oxygen plasma, and dense vertically aligned carbon nanotubes are grown from the well separated iron cores in a plasma enhanced chemical vapor deposition process. The application of low growth temperatures down to 450^oC allows for the use of flexible temperature sensitive substrates like artificial mica.

Mathematical modeling of the cell-material contact demands a thorough characterization of both the material surface and the cellular reaction. In earlier investigations we used stochastic material surfaces for this purpose. Also, other groups working on the same or similar subject used such stochastically structured material surfaces. In continuation of this work we now use fine-structured material surfaces with well-defined regular geometry because a stepwise and systematic variation of the structural parameters of geometrically defined surfaces makes it easier to find the characteristic parameters for modeling the cell-material interface. To begin with, we used grooves with rectangular profiles and cubic pillars. The grooves were etched in silicon by dry etching and then were sputter coated with 100 nm titanium. Arrays of cubic photo resist pillars with vertical side walls in different dimensions were obtained by a photolithographic process and were also sputter coated with 100 nm titanium. The samples were characterized by SEM and electrochemical methods. Human osteoblastic cells MG-63 (ATCC, LGC promochem, Manassas, USA) were cultured in Dulbecco's modified eagle medium with 10% fetal calf serum (FCS) at 37 °C and 5% CO 2 . MG-63 cells grown on microstructures within 24 h were visualized by SEM. We observed that cells on the grooved surfaces grew along the grooves mainly adhering to the horizontal edges of the material surface, whereas on the pillar structures the cells lie on the top of the pillars and are well spread. But the direction of spreading on the pillars is also determined by the horizontal and vertical edges of the surface structure.

A versatile and efficient tip-enhanced spectroscopic imaging technique based on a parabolic mirror (PM) assisted near-field optical microscope is demonstrated. The replacement of the conventional objective lens with a parabolic mirror allows the non-restricted investigation of sample materials regarding their opacity. In addition, an improved signal collection efficiency and effective excitation of the longitudinal plasmonic oscillation in the tip apex are obtained. The capabilities of PM-assisted tip-enhanced Raman (TER) and photoluminescence (PL) imaging in distinguishing the individual domains made of different chemical components in poly (3-hexythiophene)/[6, 6]-penyl-C61 butyric acid methyl ester (P3HT/PCBM) solar cell blend film and in the investigation of the plasmonic properties of geometrically well-defined Au cones are demonstrated. Copyright © 2009 John Wiley & Sons, Ltd.

Fluorine plasma treatment is applied to cross-link a novolak based negative tone optical resist (maN-2400) to achieve increased dry etching selectivity. Furthermore, fluorine plasma treatment is used to strengthen the same resist to keep it in place during a second lithography step on top of the first one. Using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, cross-linking and passivation of the resist during plasma treatment is demonstrated. In contrast to the application of a baking process after resist development, AFM images show that fluorine plasma treatment preserves the intrinsic structure of the resist.

For gas-flow aligned growth of carbon nanotubes (CNTs), it is important to minimize interaction of the growing CNTs with the substrate. The authors present a method to fabricate thin catalyst films on top of protruding hydrogen silsesquioxane (HSQ) patterns. Self-alignment of the catalyst film with the HSQ pattern is achieved by exposing two layers of resist, polymethyl methacrylate (PMMA) on top of HSQ, simultaneously. By selecting appropriate development parameters for PMMA and HSQ, a common exposure dose can be applied. After a standard lift-off process HSQ is developed and CNTs are grown on the protruding HSQ patterns resulting in gas-flow aligned CNTs that can be further processed, e.g., for the fabrication of CNT based transistors.

One of the challenges in biological applications of nanotechnology is the manipulation of micro and nanoparticles in microfluidic systems. In one approach, the short-range forces exerted on particles by electric fields, e.g. via dielectrophoresis, can be utilized for this purpose. By a combination of dielectrophoresis and electroosmosis it is possible to act on particles in larger volumes. In this work a new method for examining particle distributions in microfluidic devices is presented together with results of experiments in which the method was used to investigate the combination of dielectrophoresis and electroosmosis.

In this work we perform a feasibility study of electron beam size determination based on the measurement of the beam current using a structured substrate, which is moved via a stage underneath the beam. This method is suitable for low energy electrons and does not require beam movement or the knowledge of exact lateral beam or substrate positions to obtain the beam size. In addition, the device can be extended to acquire beam shape information.

The possibility of controlled gripping during micromanipulation procedures is widely desired in the fields of microbiology and microassembly. For achieving it, measurement or calculation of the forces exerted by the end segment of the manipulator are required. This work presents a method for detecting the gripping moment for a mechanically actuated silicon microgripper. A procedure that combines measurements with simulation results was developed for calculating the forces exerted by the tips of the gripper.

We present a process for fabricating small catalyst particles for carbon nanotube growth on insulating substrates. For this purpose we define hydrogen silsesquioxane (HSQ) resist structures on top of conducting and grounded metallic catalyst layers and a sacrificial chromium layer, using e-beam lithography. The developed resist structures act as an etch mask in the subsequent ion milling step, by which the surrounding metal layers are removed. Having wet etched the Cr mask and HSQ resist, metal structures remain which serve as catalyst in a chemical vapour deposition (CVD) process resulting in single wall carbon nanotubes with a diameter range of 0.8-2.0nm on insulating substrates.

The manipulation of micro- and nano-particles in fluids is one of the challenges for biological applications of microfluidic systems. In this work a method is developed for the local immobilization of particles collected from relatively large volumes. Micro- or nano-particles suspended in a liquid in microfluidic channels can be manipulated both by electro-osmosis (EO) and by dielectrophoresis (DEP) via the use of metallic electrodes. A positive dielectrophoretic force pulls the particles towards the edges of the electrodes. However, dielectrophoresis is a short-range interaction, hence only the particles in the immediate vicinity can be influenced and fixed. In contrast, electro-osmosis can be used to induce a circulation in the channel and thus exert a long-range interaction. In this approach, electro-osmosis and dielectrophoresis are combined for the manipulation of particles in a fluid cell to immobilize most of the particles distributed in the cell on a test-device. To this effect the fluid is locally circulated in the channel by an electro-osmotic flow which is induced by a voltage applied to a set of electrodes (EO-electrodes). Particles that come close to a second set of electrodes (DEP-electrodes) to which appropriate voltages are applied are influenced by the short-range interaction of the dielectrophoresis, whereby they are captured at these electrodes.

High resolution metallic nanostructures with well-defined geometry, such as antennae, cones and rods, are essential for nanophotonics and plasmonics. In order to fabricate such structures, we use the negative electron beam resist hydrogen silsesquioxane (HSQ) as an etch mask for an underlying metal stack. By exposing the resist and developing it in tetramethyl ammonium hydroxide (TMAH), structures with dimensions of few tens of nanometers can be fabricated. Afterwards the surrounding metal is removed by ion milling. Finally, the HSQ is lifted off via a sacrificial chromium layer. The process was used to fabricate arrays of cones and antennae of different sizes, either resonant for optical or for infrared wavelengths. Furthermore simulations of the electric field in the vicinity of the metal nanostructures were performed using the finite element method.

Coupling a single quantum emitter, such as a fluorescent molecule or a quantum dot (QD), to a plasmonic nanostructure is an important issue in nano-optics and nano-spectroscopy, relevant for a wide range of applications, including tip-enhanced near-field optical microscopy, plasmon enhanced molecular sensing and spectroscopy, and nanophotonic amplifiers or nanolasers, to mention only a few. While the field enhancement of a sharp nanoantenna increasing the excitation rate of a very closely positioned single molecule or QD has been well investigated, the detailed physical mechanisms involved in the emission of a photon from such a system are, by far, less investigated. In one of our ongoing research projects, we try to address these issues by constructing and spectroscopically analysing geometrically simple hybrid heterostructures consisting of sharp gold cones with single quantum dots attached to the very tip apex. An important goal of this work is to tune the longitudinal plasmon resonance by adjusting the cones' geometry to the emission maximum of the core–shell CdSe/ZnS QDs at nominally 650 nm. Luminescence spectra of the bare cones, pure QDs and hybrid systems were distinguished successfully. In the next steps we will further investigate, experimentally and theoretically, the optical properties of the coupled systems in more detail, such as the fluorescence spectra, blinking statistics, and the current results on the fluorescence lifetimes, and compare them with uncoupled QDs to obtain a clearer picture of the radiative and non-radiative processes.

Graphene was discovered more than a decade ago and proved the existence of a two-dimensional system of carbon. It became clear very quickly that this exceptional material has truly outstanding electronic, mechanical, thermal and optical properties. Consequently a broad range of applications appeared, as graphene science speedily moved forward. Since then, a lot of effort has been devoted not only to the study of graphene, but also to its fabrication. Graphene grown by chemical vapour deposition (CVD) on structured substrates is a promising route for the future.

Localized surface plasmon resonances of metallic nanoparticles can be used for biosensing because of their sensitive dependence on the refractive index of the surrounding medium. The binding of molecules to the particles causes a change of the effective refractive index in their close vicinity, which leads to a reversible shift of the resonance. We present simulations and sensing experiments of a plasmon resonance based biosensor that makes use of the narrow antisymmetric resonance in coupled plasmonic vertical dimers. The sensitivity of the antisymmetric resonance is compared with that of a surface lattice resonance for refractive index sensing of bulk and of thin layers of molecules. The functionality of such a sensor surface is demonstrated via a testosterone immunoassay for detection of antibody from a solution by binding to surface-immobilized antigen in a fluidic channel.

In the context of quantum computing in silicon using spin states the quantum Hall effect offers an opportunity to perform transport measurements with spin-polarized electrons in individual edge states at low filling factors. Suitable Hall bar devices consisting of MOS field effect transistors with embedded split-gates under the top gate have been fabricated. When characterizing the devices at 1.5K and magnetic fields up to 8T Shubnikov-de Haas measurements indicate, that filling factors as low as 1/2 corresponding to a single filled edge state can be realized. Transport through constrictions induced by the split-gates shows fluctuations which can be interpreted as the effect of transmission resonances in a one-dimensional channel such that the peaks at the lowest top gate voltage correspond to single mode states in the channel.

Dielectrophoresis is a convenient method for manipulation of dielectric substances in liquid. However, for substances at the nanoscale, the turbulence due to electro-osmosis flow will strongly disturb the movement of the substances. In this work, devices based on dielectrophoresis using nanoelectrode arrays have been investigated to reduce the electro-osmosis flow. Nanoscaled organic substances and biomolecules in aqueous solution, for example, polystyrene beads, bovine serum albumin and antibody molecules, were successfully trapped between the nanoelectrodes. Furthermore, the results demonstrate that the required applied voltage can be reduced by a factor of five in comparison with those using microelectrodes.

The characterization of micrometer and submicrometer particles requires in some cases their individual handling and manipulation. Electrical fields and potential differences may cause problems when biological structures are investigated in a life sustaining, thus electrically conductive environment. Therefore mechanical manipulation is preferable. We present a mechanically actuated microgripper fabricated in silicon by means of e-beam lithography, optical lithography and five deep etch processing steps.