Monika Fleischer

Gold nanocone near-field scanning optical microscopy probes.

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.

Influence of temperature on HSQ electron-beam lithography

The authors present a study of the influence of temperature on hydrogen silsesquioxane (HSQ) e-beam lithography during drying, developing, and postdevelopment baking. In accordance with the observation that tempering at relatively low temperatures can already lead to noticeable cross-linking, comparable to the effect of e-beam exposure, the authors find that decreasing the prebake temperature below 90°C and drying the HSQ resist at room temperature in vacuum yields better resolution compared with resist that was dried in a furnace or on a hotplate at 90°C or above. Developing the exposed resist not at room temperature (23°C) but at 60°C results in significant contrast enhancement. Further solidification of the developed resist is obtained by baking the material above 300°C. Correlations between these findings and IR data are presented.

Three-dimensional optical antennas: Nanocones in an apertureless scanning near-field microscope

A sharp-tipped gold nanocone and the vertically aligned metallic tip of a near-field optical microscope together form a three-dimensional optical antenna with a highly controllable gap. Confocal measurements with different laser modes show the efficient axial excitation of the cones with a longitudinally polarized field. In the antenna configuration, extremely strong field enhancement up to a factor of 100 is obtained by tuning the gap between the two sharp tips down to few nanometers.

Effects of emotional stimuli on working memory processes in male criminal offenders with borderline and antisocial personality disorder

Abstract Objective. In the present study, we aimed to investigate the influence of concurrently presented emotional stimuli on cognitive task processing in violent criminal offenders primarily characterized by affective instability. Methods. Fifteen male criminal offenders with antisocial and borderline personality disorder (ASPD and BPD) and 17 healthy controls underwent functional magnetic resonance imaging (fMRI) while performing a working memory task with low and high working memory load. In a second experimental run, to investigate the interaction of emotion and cognition, we presented emotionally neutral, low, or high salient social scenes in the background of the task. Results. During the memory task without pictures, both groups did not differ in general task performance and neural representation of working memory processes. During the memory task with emotional background pictures, however, ASPD-BPD subjects compared to healthy controls showed delayed responses and enhanced activation of the left amygdala in the presence of emotionally high salient pictures independent of working memory load. Conclusions. These results illustrate an interaction of emotion and cognition in affective instable individuals with enhanced reactivity to emotionally salient stimuli which might be an important factor regarding the understanding of aggressive and violent behaviour in these individuals.

Facial Reactions during Emotion Recognition in Borderline Personality Disorder: A Facial Electromyography Study

Background: Previous studies have suggested increased sensitivity for emotional facial expressions and subtle impairments in emotion recognition from facial expressions in borderline personality disorder (BPD). It has been proposed that facial mimicry contributes to emotion recognition of and emotional response to facial expressions. This study investigated whether BPD patients differ in facial reactions, emotion recognition and their subjective emotional response to faces showing different emotional expressions. Method: Twenty-eight female BPD patients and 28 healthy controls underwent a facial recognition task with dynamic facial pictures while facial muscle activity (occipitofrontalis, corrugator supercilii, levator labii superioris, zygomaticus major and orbicularis oculi) was recorded. Furthermore, participants rated the emotional intensity of the presented faces and the intensity of their subjective feeling of this emotion. Results: Compared to controls, BPD patients showed enhanced responses of the corrugator supercilii muscle in response to angry, sad and disgusted facial expressions, and attenuated responses of the levator labii superioris in response to happy and surprised faces. There were no overall group differences regarding emotion recognition performance or intensity ratings. Conclusion: These results do not support the view that facial recognition in BPD is impaired or that there is a general hypersensitivity to the emotional state of others. Instead, they suggest a negativity bias in BPD, expressed by reduced facial responding to positive social signals and increased facial responding to negative social signals. This is a pattern of facial reactions that might contribute to the difficulties in social interactions frequently reported by patients with this disorder.

Tailoring gold nanostructures for near-field optical applications

A method of combined thin-film deposition, electron beam lithography, and ion milling is presented for the fabrication of gold and silver nanostructures. The flexibility of lithographical processes for the variation of geometric parameters is combined with three-dimensional control over the surface evolution. Depending on the etching angle, different shapes ranging from cones over rods to cups can be achieved. These size- and shape-tunable structures present a toolbox for nano-optical investigations. As an example, optical properties of systematically varying structures are examined in a parabolic mirror confocal microscope.

Parallel Fabrication of Plasmonic Nanocone Sensing Arrays

A fully parallel approach for the fabrication of arrays of metallic nanocones and triangular nanopyramids is presented. Different processes utilizing nanosphere lithography for the creation of etch masks are developed. Monolayers of spheres are reduced in size and directly used as masks, or mono- and double layers are employed as templates for the deposition of aluminum oxide masks. The masks are transferred into an underlying gold or silver layer by argon ion milling, which leads to nanocones or nanopyramids with very sharp tips. Near the tips the enhancement of an external electromagnetic field is particularly strong. This fact is confirmed by numerical simulations and by luminescence imaging in a confocal microscope. Such localized strong fields can amongst others be utilized for high-resolution, high-sensitivity spectroscopy and sensing of molecules near the tip. Arrays of such plasmonic nanostructures thus constitute controllable platforms for surface-enhanced Raman spectroscopy. A thin film of pentacene molecules is evaporated onto both nanocone and nanopyramid substrates, and the observed Raman enhancement is evaluated.

Nonlinear optical point light sources through field enhancement at metallic nanocones

A stable nonlinear optical point light source is investigated, based on field enhancement at individual, pointed gold nanocones with sub-wavelength dimensions. Exciting these cones with near-infrared, focused radially polarized femtosecond beams allows for tip-emission at the second harmonic wavelength (second harmonic generation, SHG) in the visible range. In fact, gold nanocones with ultra-sharp tips possess interesting nonlinear optical (NLO) properties for SHG and two-photon photoluminescence (TPPL) emission, due to the enhanced electric field confinement at the tip apex combined with centrosymmetry breaking. Using two complementary optical setups for bottom or top illumination a sharp tip SHG emission is discriminated from the broad TPPL background continuum. Moreover, comparing the experiments with theoretical calculations manifests that these NLO signatures originate either from the tip apex or the base edge of the nanocones, clearly depending on the cone size, the surrounding medium, and illumination conditions. Finally, it is demonstrated that the tip-emitted signal vanishes when switching from radial to azimuthal polarization.

Roadmap on biosensing and photonics with advanced nano-optical methods

This roadmap, through the contributions of ten groups worldwide, contains different techniques, methods and materials devoted to sensing in nanomedicine. Optics is used in different ways in the detection schemes. Raman, fluorescence and infrared spectroscopies, plasmonics, second harmonic generation and optical tweezers are all used in applications from single molecule detection (both in highly diluted and in highly concentrated solutions) to single cell manipulation. In general, each optical scheme, through device miniaturization and electromagnetic field localization, exploits an intrinsic optical enhancement mechanism in order to increase the sensitivity and selectivity of the device with respect to the complex molecular construct. The materials used for detection include nanoparticles and nanostructures fabricated with different 2D and 3D lithographic methods. It is shown that sensitivity to a single molecule is already accessible whether the system under study is a single cell or a multitude of cells in a molecular mixture. Throughout the roadm

Neural correlates of risk taking in violent criminal offenders characterized by emotional hypo- and hyper-reactivity

Recent approaches suggest that emotional reactivity can be used to differentiate between subgroups of individuals who are at risk for showing elevated levels of aggression and violence. In this study, we examined how emotion governs decision making within two subgroups of antisocial criminal offenders with either emotional hypo- or hyper-reactivity compared with healthy, noncriminal controls. Offenders were recruited from high-security forensic treatment facilities and penal institutions and underwent functional magnetic resonance imaging during a financial decision-making task. In this task, participants were required to choose between low-risk (bonds) and high-risk alternatives (stocks). Bonds were always the safe choice; stocks could win or lose, with a varying degree of uncertainty. We found that emotionally hypo-reactive offenders differed most from healthy controls by showing diminished neural activation in the rostral anterior cingulate cortex in response to uncertainty as well as decreased activity in the prefrontal cortex when trying to regulate their behavior accordingly (i.e., when consistently choosing “safe alternatives”). Hence, the data indicate that emotionally hypo-reactive offenders (with psychopathic traits) constitute a special subgroup within antisocial offenders characterized in particular by a limited capacity to emotionally represent uncertainty and to anticipate punishment.