High-Q, low-mode-volume and multiresonant plasmonic nanoslit cavities fabricated by helium ion milling.

Helium ion milling of chemically-synthesized micron-sized gold flakes is performed to fabricate ultra-narrow nanoslit cavities with a varying length and width down to 5 nm. Their plasmon resonances are characterized by one-photon photoluminescence spectroscopy. The combination of fabrication based on single-crystalline gold and resonant modes with low radiative losses leads to remarkably high quality factors of up to 24. Multiple Fabry-Pérot-type resonances in the visible/near infrared spectral range are observed due to the achieved narrow slit widths and the resulting short effective wavelengths of nanoslit plasmons. These features make nanoslit cavities attractive for a range of applications such as surface-enhanced spectroscopy, ultrafast nano-optics and strong light-matter coupling.

Colloidal Gold Nanoparticles Induce Changes in Cellular and Subcellular Morphology.

Exposure of cells to colloidal nanoparticles (NPs) can have concentration-dependent harmful effects. Mostly, such effects are monitored with biochemical assays or probes from molecular biology, i.e., viability assays, gene expression profiles, etc., neglecting that the presence of NPs can also drastically affect cellular morphology. In the case of polymer-coated Au NPs, we demonstrate that upon NP internalization, cells undergo lysosomal swelling, alterations in mitochondrial morphology, disturbances in actin and tubulin cytoskeleton and associated signaling, and reduction of focal adhesion contact area and number of filopodia. Appropriate imaging and data treatment techniques allow for quantitative analyses of these concentration-dependent changes. Abnormalities in morphology occur at similar (or even lower) NP concentrations as the onset of reduced cellular viability. Cellular morphology is thus an important quantitative indicator to verify harmful effects of NPs to cells, without requiring biochemical assays, but relying on appropriate staining and imaging techniques.

Efficient electron-induced removal of oxalate ions and formation of copper nanoparticles from copper(II) oxalate precursor layers.

Copper(II) oxalate grown on carboxy-terminated self-assembled monolayers (SAM) using a step-by-step approach was used as precursor for the electron-induced synthesis of surface-supported copper nanoparticles. The precursor material was deposited by dipping the surfaces alternately in ethanolic solutions of copper(II) acetate and oxalic acid with intermediate thorough rinsing steps. The deposition of copper(II) oxalate and the efficient electron-induced removal of the oxalate ions was monitored by reflection absorption infrared spectroscopy (RAIRS). Helium ion microscopy (HIM) reveals the formation of spherical nanoparticles with well-defined size and X-ray photoelectron spectroscopy (XPS) confirms their metallic nature. Continued irradiation after depletion of oxalate does not lead to further particle growth giving evidence that nanoparticle formation is primarily controlled by the available amount of precursor.

Investigating the Impact of a Genome-Wide Supported Bipolar Risk Variant of MAD1L1 on the Human Reward System.

Recent genome-wide association studies have identified MAD1L1 (mitotic arrest deficient-like 1) as a susceptibility gene for bipolar disorder and schizophrenia. The minor allele of the single-nucleotide polymorphism (SNP) rs11764590 in MAD1L1 was associated with bipolar disorder. Both diseases, bipolar disorder and schizophrenia, are linked to functional alterations in the reward system. We aimed at investigating possible effects of the MAD1L1 rs11764590 risk allele on reward systems functioning in healthy adults. A large homogenous sample of 224 young (aged 18-31 years) participants was genotyped and underwent functional magnetic resonance imaging (fMRI). All participants performed the 'Desire-Reason Dilemma' paradigm investigating the neural correlates that underlie reward processing and active reward dismissal in favor of a long-term goal. We found significant hypoactivations of the ventral tegmental area (VTA), the bilateral striatum and bilateral frontal and parietal cortices in response to conditioned reward stimuli in the risk allele carriers compared with major allele carriers. In the dilemma situation, functional connectivity between prefrontal brain regions and the ventral striatum was significantly diminished in the risk allele carriers. Healthy risk allele carriers showed a significant deficit of their bottom-up response to conditioned reward stimuli in the bilateral VTA and striatum. Furthermore, functional connectivity between the ventral striatum and prefrontal areas exerting top-down control on the mesolimbic reward system was reduced in this group. Similar alterations in reward processing and disturbances of prefrontal control mechanisms on mesolimbic brain circuits have also been reported in bipolar disorder and schizophrenia. Together, these findings suggest the existence of an intermediate phenotype associated with MAD1L1.

Gender Differences in Verbal and Visuospatial Working Memory Performance and Networks.

BACKGROUND: Working memory (WM) has been a matter of intensive basic and clinical research for some decades now. The investigation of WM function and dysfunction may facilitate the understanding of both physiological and pathological processes in the human brain. Though WM paradigms are widely used in neuroscientific and psychiatric research, conclusive knowledge about potential moderating variables such as gender is still missing. METHODS: We used functional magnetic resonance imaging to investigate the effects of gender on verbal and visuospatial WM maintenance tasks in a large and homogeneous sample of young healthy subjects. RESULTS: We found significant gender effects on both the behavioral and neurofunctional level. Females exhibited disadvantages with a small effect size in both WM domains accompanied by stronger activations in a set of brain regions (including bilateral substantia nigra/ventral tegmental area and right Broca's area) independent of WM modality. As load and task difficulty effects have been shown for some of these regions, the stronger activations may reflect a slightly lower capacity of both WM domains in females. Males showed stronger bilateral intraparietal activations next to the precuneus which were specific for the visuospatial WM task. Activity in this specific region may be associated with visuospatial short-term memory capacity. CONCLUSION: These findings provide evidence for a slightly lower capacity in both WM modalities in females.

CREB1 Genotype Modulates Adaptive Reward-Based Decisions in Humans.

Cyclic AMP response element-binding protein (CREB) contributes to adaptation of mesocorticolimbic networks by modulating activity-regulated transcription and plasticity in neurons. Activity or expression changes of CREB in the nucleus accumbens (NAc) and orbital frontal cortex (OFC) interact with behavioral changes during reward-motivated learning. However, these findings from animal models have not been evaluated in humans. We tested whether CREB1 genotypes affect reward-motivated decisions and related brain activation, using BOLD fMRI in 224 young and healthy participants. More specifically, participants needed to adapt their decision to either pursue or resist immediate rewards to optimize the reward outcome. We found significant CREB1 genotype effects on choices to pursue increases of the reward outcome and on BOLD signal in the NAc, OFC, insula cortex, cingulate gyrus, hippocampus, amygdala, and precuneus during these decisions in comparison with those decisions avoiding total reward loss. Our results suggest that CREB1 genotype effects in these regions could contribute to individual differences in reward- and associative memory-based decision-making.

Imaging of carbon nanomembranes with helium ion microscopy.

Carbon nanomembranes (CNMs) prepared from aromatic self-assembled monolayers constitute a recently developed class of 2D materials. They are made by a combination of self-assembly, radiation-induced cross-linking and the detachment of the cross-linked SAM from its substrate. CNMs can be deposited on arbitrary substrates, including holey and perforated ones, as well as on metallic (transmission electron microscopy) grids. Therewith, freestanding membranes with a thickness of 1 nm and macroscopic lateral dimensions can be prepared. Although free-standing CNMs cannot be imaged by light microscopy, charged particle techniques can visualize them. However, CNMs are electrically insulating, which makes them sensitive to charging. We demonstrate that the helium ion microscope (HIM) is a good candidate for imaging freestanding CNMs due to its efficient charge compensation tool. Scanning with a beam of helium ions while recording the emitted secondary electrons generates the HIM images. The advantages of HIM are high resolution, high surface sensitivity and large depth of field. The effects of sample charging, imaging of multilayer CNMs as well as imaging artefacts are discussed.

Passivation Dynamics in the Anisotropic Deposition and Stripping of Bulk Magnesium Electrodes During Electrochemical Cycling.

Although rechargeable magnesium (Mg) batteries show promise for use as a next generation technology for high-density energy storage, little is known about the Mg anode solid electrolyte interphase and its implications for the performance and durability of a Mg-based battery. We explore in this report passivation effects engendered during the electrochemical cycling of a bulk Mg anode, characterizing their influences during metal deposition and dissolution in a simple, nonaqueous, Grignard electrolyte solution (ethylmagnesium bromide, EtMgBr, in tetrahydrofuran). Scanning electron microscopy images of Mg foil working electrodes after electrochemical polarization to dissolution potentials show the formation of corrosion pits. The pit densities so evidenced are markedly potential-dependent. When the Mg working electrode is cycled both potentiostatically and galvanostatically in EtMgBr these pits, formed due to passive layer breakdown, act as the foci for subsequent electrochemical activity. Detailed microscopy, diffraction, and spectroscopic data show that further passivation and corrosion results in the anisotropic stripping of the Mg {0001} plane, leaving thin oxide-comprising passivated side wall structures that demark the {0001} fiber texture of the etched Mg grains. Upon long-term cycling, oxide side walls formed due to the pronounced crystallographic anisotropy of the anodic stripping processes, leading to complex overlay anisotropic, columnar structures, exceeding 50 µm in height. The passive responses mediating the growth of these structures appear to be an intrinsic feature of the electrochemical growth and dissolution of Mg using this electrolyte.

Hybrid van der Waals heterostructures of zero-dimensional and two-dimensional materials.

van der Waals heterostructures meet other low-dimensional materials. Stacking of about 1 nm thick nanosheets with out-of-plane anchor groups functionalized with fullerenes integrates this zero-dimensional material into layered heterostructures with a well-defined chemical composition and without degrading the mechanical properties. The developed modular and highly applicable approach enables the incorporation of other low-dimensional materials, e.g. nanoparticles or nanotubes, into heterostructures significantly extending the possible building blocks.

Preparation of conductive gold nanowires in confined environment of gold-filled polymer nanotubes.

Continuous conductive gold nanofibers are prepared via the "tubes by fiber templates" process. First, poly(l-lactide) (PLLA)-stabilized gold nanoparticles (AuNP) with over 60 wt% gold are synthesized and characterized, including gel permeation chromatography coupled with a diode array detector. Subsequent electrospinning of these AuNP with template PLLA results in composite nanofibers featuring a high gold content of 57 wt%. Highly homogeneous gold nanowires are obtained after chemical vapor deposition of 345 nm of poly(p-xylylene) (PPX) onto the composite fibers followed by pyrolysis of the polymers at 1050 °C. The corresponding heat-induced transition from continuous gold-loaded polymer tubes to smooth gold nanofibers is studied by transmission electron microscopy and helium ion microscopy using both secondary electrons and Rutherford backscattered ions.

Toward plasmonics with nanometer precision: nonlinear optics of helium-ion milled gold nanoantennas.

Plasmonic nanoantennas are versatile tools for coherently controlling and directing light on the nanoscale. For these antennas, current fabrication techniques such as electron beam lithography (EBL) or focused ion beam (FIB) milling with Ga(+)-ions routinely achieve feature sizes in the 10 nm range. However, they suffer increasingly from inherent limitations when a precision of single nanometers down to atomic length scales is required, where exciting quantum mechanical effects are expected to affect the nanoantenna optics. Here, we demonstrate that a combined approach of Ga(+)-FIB and milling-based He(+)-ion lithography (HIL) for the fabrication of nanoantennas offers to readily overcome some of these limitations. Gold bowtie antennas with 6 nm gap size were fabricated with single-nanometer accuracy and high reproducibility. Using third harmonic (TH) spectroscopy, we find a substantial enhancement of the nonlinear emission intensity of single HIL-antennas compared to those produced by state-of-the-art gallium-based milling. Moreover, HIL-antennas show a vastly improved polarization contrast. This superior nonlinear performance of HIL-derived plasmonic structures is an excellent testimonial to the application of He(+)-ion beam milling for ultrahigh precision nanofabrication, which in turn can be viewed as a stepping stone to mastering quantum optical investigations in the near-field.

Layer-by-layer assembled heteroatom-doped graphene films with ultrahigh volumetric capacitance and rate capability for micro-supercapacitors.

Highly uniform, ultrathin, layer-by-layer heteroatom (N, B) co-doped graphene films are fabricated for high-performance on-chip planar micro-supercapacitors with an ultrahigh volumetric capacitance of ∼488 F cm(-3) and excellent rate capability due to the synergistic effect of nitrogen and boron co-doping.

Fabrication of carbon nanomembranes by helium ion beam lithography.

The irradiation-induced cross-linking of aromatic self-assembled monolayers (SAMs) is a universal method for the fabrication of ultrathin carbon nanomembranes (CNMs). Here we demonstrate the cross-linking of aromatic SAMs due to exposure to helium ions. The distinction of cross-linked from non-cross-linked regions in the SAM was facilitated by transferring the irradiated SAM to a new substrate, which allowed for an ex situ observation of the cross-linking process by helium ion microscopy (HIM). In this way, three growth regimes of cross-linked areas were identified: formation of nuclei, one-dimensional (1D) and two-dimensional (2D) growth. The evaluation of the corresponding HIM images revealed the dose-dependent coverage, i.e., the relative monolayer area, whose density of cross-links surpassed a certain threshold value, as a function of the exposure dose. A complete cross-linking of aromatic SAMs by He(+) ion irradiation requires an exposure dose of about 850 µC/cm(2), which is roughly 60 times smaller than the corresponding electron irradiation dose. Most likely, this is due to the energy distribution of secondary electrons shifted to lower energies, which results in a more efficient dissociative electron attachment (DEA) process.

Carbon nanomembranes (CNMs) supported by polymer: mechanics and gas permeation.

Gas permeation characteristics of carbon nanomembranes (CNMs) from self-assembled monolayers are reported for the first time. The assembly of CNMs onto polydimethylsiloxane (PDMS) support membranes allows mechanical measurements under compression as well as determination of gas permeation characteristics. The results suggest that molecular-sized channels in CNMs dominate the permeation properties of the 1 nm thin CNMs.

Development of schizoaffective psychosis in the course of a long-term occupation as spiritual healer: coincidence or causality?

Psychotic reactions in the context of meditation and esoteric practices have been described in the psychiatric literature. In most cases, these psychotic conditions are transient and do not lead to functional impairment. The authors present the case of a 46-year-old woman who had worked as a spiritual healer for several years and, in the course of this occupation, increasingly developed a highly specific configuration of psychotic symptoms (all of which could be convincingly traced back to the formerly used spiritual techniques) along with depressive symptoms and severe functional impairment. The differential diagnosis was initially complicated by the relative conformity of the patient's psychotic symptoms with her occupational practices and the absence of other, more typical, symptoms of schizophrenia. Only a thorough anamnesis with another spiritual healer and precise identification of psychopathology helped to disentangle the merely uncommon from the pathologic features of this case. Possible mechanisms of psychotogenesis are discussed in light of the literature and the specific features of the presented case. Although a single case report cannot prove a causal link between spiritual healing and development of psychosis, the patient's specific psychopathology, with preeminently disturbed self-experience, and its consistency with the patient's spiritual practices suggest at least a contributory role in this case.

Enhanced infrared LSPR sensitivity of cap-shaped gold nanoparticles coupled to a metallic film.

We report on optical properties of gold deposited on SiO2 nanospheres randomly adsorbed on a thin gold layer. Extinction peaks with optical density of more than 2 are observed in the visible as well as near-IR regimes. The peak wavelength of the latter was affected exquisitely by the thickness of the top layer. A helium ion microscope (HIM) was used for careful observation of morphological transformation accompanying the change in the deposition thickness. Growth of grain structures into a capped-dimer structure was accompanied by slight blue-shift of the visible peak and significantly greater red-shift of the near-IR peak. Our finite-difference time-domain (FDTD) calculations show that these peaks in the visible and near-IR can be respectively attributed to dipole modes associated with transverse and longitudinal oscillations of free electrons in the gold-capped dimer. To investigate the refractive index sensitivity of these peaks, we used two approaches: immersion in solutions of varying refractive index and coating with an organic layer. With the first approach that characterizes the bulk sensitivity, the visible peak shows sensitivity of 122 nm/RIU, while the near-IR peak shifts at the rate of 506 nm/RIU. With the second approach that reflects the local sensitivity, the surface was saturated with alkaline phosphatase (ALP), whose subsequent reaction led to formation of a thin insoluble organic layer, causing a relatively small blue-shift, under 7 nm, of the visible peak and much larger red-shift, over 50 nm, of the near-IR peak when measured in buffer. When the same reaction was measured at end points in the air, the shift was as large as 444 nm for the near-IR peak.

Imaging nanocarbon materials: soot particles in flames are not structurally homogeneous.

For the first time, nascent soot particles are probed by using helium-ion microscopy (HIM). HIM is a technique that is similar to scanning electron microscopy (SEM) but it can achieve higher contrast and improved surface sensitivity, especially for carbonaceous materials. The HIM microscope yields images with a high contrast, which allows for the unambiguous recognition of smaller nascent soot particles than those observed in previous transmission electron microscopy studies. The results indicate that HIM is ideal for rapid and reliable probing of the morphology of nascent soot, with surface details visible down to approximately 5 nm, and particles as small as 2 nm are detectable. The results also show that nascent soot is structurally and chemically inhomogeneous, and even the smallest particles can have shapes that deviate from a perfect sphere.

A universal scheme to convert aromatic molecular monolayers into functional carbon nanomembranes.

Free-standing nanomembranes with molecular or atomic thickness are currently explored for separation technologies, electronics, and sensing. Their engineering with well-defined structural and functional properties is a challenge for materials research. Here we present a broadly applicable scheme to create mechanically stable carbon nanomembranes (CNMs) with a thickness of ~0.5 to ~3 nm. Monolayers of polyaromatic molecules (oligophenyls, hexaphenylbenzene, and polycyclic aromatic hydrocarbons) were assembled and exposed to electrons that cross-link them into CNMs; subsequent pyrolysis converts the CNMs into graphene sheets. In this transformation the thickness, porosity, and surface functionality of the nanomembranes are determined by the monolayers, and structural and functional features are passed on from the molecules through their monolayers to the CNMs and finally on to the graphene. Our procedure is scalable to large areas and allows the engineering of ultrathin nanomembranes by controlling the composition and structure of precursor molecules and their monolayers.

Cooperative self-assembly of discoid dimers: hierarchical formation of nanostructures with a pH switch.

Derivatives of the self-complementary 2-guanidiniocarbonyl pyrrole 5-carboxylate zwitterion (1) (previously reported by us to dimerize to 1•1 with an aggregation constant of ca. >10(10) M(-l) in DMSO) aggregate in a diverse manner depending on, e.g., variation of concentration or its protonation state. The mode of aggregation was analyzed by spectroscopic (NMR, UV) and microscopic (AFM, SEM, HIM, and TEM) methods. Aggregation of dimers of these zwitterions to higher supramolecular structures was achieved by introduction of sec-amide substituents at the 3-position, i.e., at the rearward periphery of the parent binding motif. A butyl amide substituent as in 2b enables the discoid dimers to further aggregate into one-dimensional (rod-like) stacks. Quantitative UV dilution studies showed that this aggregation is strongly cooperative following a nucleation elongation mechanism. The amide hydrogen seems to be essential for this rod-like aggregation, as neither 1 nor a corresponding tert-amide congener 2a form comparable structures. Therefore, a hydrogen bond-assisted π-π-interaction of the dimeric zwitterions is suggested to promote this aggregation mode, which is further affected by the nature of the amide substituent (e.g., steric demand), enabling the formation of bundles of strands or even two-dimensional sheets. By exploiting the zwitterionic nature of the aggregating discoid dimers, a reversible pH switch was realized: dimerization of all compounds is suppressed by protonation of the carboxylate moiety, converting the zwitterions into typical cationic amphiphiles. Accordingly, typical nanostructures like vesicles, tubes, and flat sheets are formed reversibly under acidic conditions, which reassemble into the original rod-like aggregates upon readjustment to neutral pH.

Video-based and interference-free axial force detection and analysis for optical tweezers.

For measuring the minute forces exerted on single molecules during controlled translocation through nanopores with sub-piconewton precision, we have developed a video-based axial force detection and analysis system for optical tweezers. Since our detection system is equipped with a standard and versatile CCD video camera with a limited bandwidth offering operation at moderate light illumination with minimal sample heating, we integrated Allan variance analysis for trap stiffness calibration. Upon manipulating a microbead in the vicinity of a weakly reflecting surface with simultaneous axial force detection, interference effects have to be considered and minimized. We measured and analyzed the backscattering light properties of polystyrene and silica microbeads with different diameters and propose distinct and optimized experimental configurations (microbead material and diameter) for minimal light backscattering and virtually interference-free microbead position detection. As a proof of principle, we investigated the nanopore threading forces of a single dsDNA strand attached to a microbead with an overall force resolution of ±0.5 pN at a sample rate of 123 Hz.