Tip-Induced Nanopatterning of Ultrathin Polymer Brushes.

Patterned, ultra-thin surface layers can serve as templates for positioning nanoparticlesor targeted self-assembly of molecular structures, for example, block-copolymers. This work investigates the high-resolution, atomic force microscopebased patterning of 2 nm thick vinyl-terminated polystyrene brush layers and evaluates the line broadening due to tip degradation. This work compares the patterning properties with those of a silane-based fluorinated self-assembled monolayer (SAM), using molecular heteropatterns generated by modified polymer blend lithography (brush/SAM-PBL). Stable line widths of 20 nm (FWHM) over lengths of over 20000 µm indicate greatly reduced tip wear, compared to expectations on uncoated SiOx surfaces. The polymer brush acts as a molecularly thin lubricating layer, thus enabling a 5000 fold increase in tip lifetime, and the brush is bonded weakly enough that it can be removed with surgical accuracy. On traditionally used SAMs, either the tip wear is very high or the molecules are not completely removed. Polymer Phase Amplified Brush Editing is presented, which uses directed self-assembly to amplify the aspect ratio of the molecular structures by a factor of 4. The structures thus amplified allow transfer into silicon/metal heterostructures, fabricating 30 nm deep, all-silicon diffraction gratings that could withstand focused high-power 405 nm laser irradiation.

Air Retention under Water by the Floating Fern Salvinia: The Crucial Role of a Trapped Air Layer as a Pneumatic Spring.

The ability of floating ferns Salvinia to keep a permanent layer of air under water is of great interest, e.g., for drag-reducing ship coatings. The air-retaining hairs are superhydrophobic, but have hydrophilic tips at their ends, pinning the air-water interface. Here, experimental and theoretical approaches are used to examine the contribution of this pinning effect for air-layer stability under pressure changes. By applying the capillary adhesion technique, the adhesion forces of individual hairs to the water surface is determined to be about 20 µN per hair. Using confocal microscopy and fluorescence labeling, it is found that the leaves maintain a stable air layer up to an underpressure of 65 mbar. Combining both results, overall pinning forces are obtained, which account for only about 1% of the total air-retaining force. It is suggested that the restoring force of the entrapped air layer is responsible for the remaining 99%. This model of the entrapped air acting is verified as a pneumatic spring ("air-spring") by an experiment shortcircuiting the air layer, which results in immediate air loss. Thus, the plant enhances its air-layer stability against pressure fluctuations by a factor of 100 by utilizing the entrapped air volume as an elastic spring.

3D-Printed Scanning-Probe Microscopes with Integrated Optical Actuation and Read-Out.

Scanning-probe microscopy (SPM) is the method of choice for high-resolution imaging of surfaces in science and industry. However, SPM systems are still considered as rather complex and costly scientific instruments, realized by delicate combinations of microscopic cantilevers, nanoscopic tips, and macroscopic read-out units that require high-precision alignment prior to use. This study introduces a concept of ultra-compact SPM engines that combine cantilevers, tips, and a wide variety of actuator and read-out elements into one single monolithic structure. The devices are fabricated by multiphoton laser lithography as it is a particularly flexible and accurate additive nanofabrication technique. The resulting SPM engines are operated by optical actuation and read-out without manual alignment of individual components. The viability of the concept is demonstrated in a series of experiments that range from atomic-force microscopy engines offering atomic step height resolution, their operation in fluids, and to 3D printed scanning near-field optical microscopy. The presented approach is amenable to wafer-scale mass fabrication of SPM arrays and capable to unlock a wide range of novel applications that are inaccessible by current approaches to build SPMs.

Mechanically Induced Switching of Molecular Layers.

Within the field of switchable surfaces, azobenzenes are an extensively studied group of molecules, known for reversibly changing conformation upon illumination with light of different wavelengths. Relying on the ability of the molecules to change properties and structure as a response to external stimuli, they have been incorporated in various devices, such as molecular switches and motors. In contrast to the well-documented switching by light irradiation, we report the discovery of mechanically triggered switching of self-assembled azobenzene monolayers, resulting in changes of surface wettability, adhesion, and friction. This mechanically induced cis-trans isomerization is triggered either locally and selectively by AFM or macroscopically by particle impact. The process is optically reversible, enabling consecutive switching cycles. Collective switching behavior was also observed, propagating from the original point of impact in a domino-like manner. Finally, local force application facilitated nondestructive and erasable nanopatterning, the cis-trans nanolithography.

Tuning the Wettability of a Thin Polymer Film by Gradually Changing the Geometry of Nanoscale Pore Edges.

Controlling wetting of solids by liquids attracts attention because of its scientific and technological importance. In this paper, the wettability of a highly uniform porous poly(methyl methacrylate) film on a silicon substrate containing a high density of randomly distributed self-similar pores was gradually tuned by changing the shape of nanometric crownlike structures around the pores. Fine-tuning the topography of these thin films was performed by isothermal annealing. The equilibrium contact angle of a water droplet placed on the surface of the films could be varied from 72 to 102°. The contact angle changes were assumed to be a consequence of changes in surface topography in the nanoscale. A simple method of a quantitative description of the change of the topography of these films was developed. Critical dimensions of these films were determined in horizontal and vertical directions relative to the surface plane. The slope coefficient (SC) describing how sharp the structures are, is defined as the ratio between the critical dimensions: the root-mean-square roughness σ and the autocorrelation length ξ. For SC > 0.08, the contact angle increased proportionally to the value of SC, whereas for SC < 0.08, the contact angle proportionally decreased. At the highest SC values, the contact angles were 6-10% higher than those predicted for flat porous surfaces using the Cassie-Baxter equation. We suggest that this discrepancy is due to the capillary tension caused by the submicron-scale undulation of the triple line, which was found to be proportional to the height of the crownlike pore edges and the value of SC. The same effect is responsible for the linear dependence of the contact angle on the SC value.

[Polymicrobial liver abscesses and pleural empyema in a 40-year-old male after tooth extraction and closed periodontal treatment: A case report]. / Polymikrobielle Leberabszesse und Pleuraempyem bei einem 40-jährigen Mann nach Zahnextraktion und geschlossener Parodontitis-Behandlung: Ein Fallbericht.

We report on a 40-year-old patient who presented with fever, right upper abdominal pain, right-sided chest pain and acute dyspnea. Imaging revealed several liver abscesses, as well as extensive right pleural empyema. Sixteen weeks previously, the patient underwent tooth extraction of the third molars (18, 28, 38, 48) and a first molar (46), and systematic closed periodontitis treatment. Four different species of the physiological microbiota of the oral cavity were detected in the pleura or liver abscess punctate (Streptococcus anginosus, Streptococcus constellatus, Actinomyces odontolyticus, Prevotella denticola). An underlying immune defect was ruled out. Ultrasound-guided drainage of liver abscesses and surgical treatment of pleural empyema by video-assisted thoracoscopy (VATS) and insertion of thoracic suction drains was performed, accompanied by targeted antibiotic therapy. Over a course of 6 weeks, the patient recovered completely. The case report illustrates severe infectious side effects of major dental interventions, and it critically summarizes current dental guideline recommendations on peri-interventional antimicrobial therapy. Therefore, a good clinical follow up after major tooth extractions is imperative.

Macro-mechanics controls quantum mechanics: mechanically controllable quantum conductance switching of an electrochemically fabricated atomic-scale point contact.

Here, we present a silver atomic-scale device fabricated and operated by a combined technique of electrochemical control (EC) and mechanically controllable break junction (MCBJ). With this EC-MCBJ technique, we can perform mechanically controllable bistable quantum conductance switching of a silver quantum point contact (QPC) in an electrochemical environment at room temperature. Furthermore, the silver QPC of the device can be controlled both mechanically and electrochemically, and the operating mode can be changed from 'electrochemical' to 'mechanical', which expands the operating mode for controlling QPCs. These experimental results offer the perspective that a silver QPC may be used as a contact for a nanoelectromechanical relay.

Atomic Scale Plasmonic Switch.

The atom sets an ultimate scaling limit to Moore's law in the electronics industry. While electronics research already explores atomic scales devices, photonics research still deals with devices at the micrometer scale. Here we demonstrate that photonic scaling, similar to electronics, is only limited by the atom. More precisely, we introduce an electrically controlled plasmonic switch operating at the atomic scale. The switch allows for fast and reproducible switching by means of the relocation of an individual or, at most, a few atoms in a plasmonic cavity. Depending on the location of the atom either of two distinct plasmonic cavity resonance states are supported. Experimental results show reversible digital optical switching with an extinction ratio of 9.2 dB and operation at room temperature up to MHz with femtojoule (fJ) power consumption for a single switch operation. This demonstration of an integrated quantum device allowing to control photons at the atomic level opens intriguing perspectives for a fully integrated and highly scalable chip platform, a platform where optics, electronics, and memory may be controlled at the single-atom level.

Single-molecule force spectroscopy of membrane proteins from membranes freely spanning across nanoscopic pores.

Single-molecule force spectroscopy (SMFS) provides detailed insight into the mechanical (un)folding pathways and structural stability of membrane proteins. So far, SMFS could only be applied to membrane proteins embedded in native or synthetic membranes adsorbed to solid supports. This adsorption causes experimental limitations and raises the question to what extent the support influences the results obtained by SMFS. Therefore, we introduce here SMFS from native purple membrane freely spanning across nanopores. We show that correct analysis of the SMFS data requires extending the worm-like chain model, which describes the mechanical stretching of a polypeptide, by the cubic extension model, which describes the bending of a purple membrane exposed to mechanical stress. This new experimental and theoretical approach allows to characterize the stepwise (un)folding of the membrane protein bacteriorhodopsin and to assign the stability of single and grouped secondary structures. The (un)folding and stability of bacteriorhodopsin shows no significant difference between freely spanning and directly supported purple membranes. Importantly, the novel experimental SMFS setup opens an avenue to characterize any protein from freely spanning cellular or synthetic membranes.

Electrochromic switching of monolithic Prussian blue thin film devices.

Monolithic, crystalline and highly oriented coordination network compound (CNC) Prussian blue (PB) thin films have been deposited though different routes on conductive substrates. Characterization of the monolithic thin films reveals a long-term stability, even after many redox cycles the crystallinity as well as the high orientation remain intact during the electrochromic switching process.

A photolithographic approach to spatially resolved cross-linked nanolayers.

The preparation of cross-linked nanosheets with 1-2 nm thickness and predefined shape was achieved by lithographic immobilization of trimethacryloyl thioalkanoates onto the surface of Si wafers, which were functionalized with 2-(phenacylthio)acetamido groups via a photoinduced reaction. Subsequent cross-linking via free radical polymerization as well as a phototriggered Diels-Alder reaction under mild conditions on the surface led to the desired nanosheets. Electrospray ionization mass spectrometry (ESI-MS), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), as well as infrared reflection-absorption spectroscopy (IRRAS) confirmed the success of individual surface-modification and cross-linking reactions. The thickness and lateral size of the cross-linked structures were determined by atomic force microscopy (AFM) for samples prepared on Si wafers functionalized with a self-assembled monolayer of 1H,1H,2H,2H-perfluorodecyl groups bearing circular pores obtained via a polymer blend lithographic approach, which led to the cross-linking reactions occurring in circular nanoareas (diameter of 50-640 nm) yielding an average thickness of 1.2 nm (radical cross-linking), 1.8 nm (radical cross-linking in the presence of 2,2,2-trifluoroethyl methacrylate as a comonomer), and 1.1 nm (photochemical cross-linking) of the nanosheets.

Ultra-large scale AFM of lipid droplet arrays: investigating the ink transfer volume in dip pen nanolithography.

There are only few quantitative studies commenting on the writing process in dip-pen nanolithography with lipids. Lipids are important carrier ink molecules for the delivery of bio-functional patters in bio-nanotechnology. In order to better understand and control the writing process, more information on the transfer of lipid material from the tip to the substrate is needed. The dependence of the transferred ink volume on the dwell time of the tip on the substrate was investigated by topography measurements with an atomic force microscope (AFM) that is characterized by an ultra-large scan range of 800 × 800 µm(2). For this purpose arrays of dots of the phospholipid1,2-dioleoyl-sn-glycero-3-phosphocholine were written onto planar glass substrates and the resulting pattern was imaged by large scan area AFM. Two writing regimes were identified, characterized of either a steady decline or a constant ink volume transfer per dot feature. For the steady state ink transfer, a linear relationship between the dwell time and the dot volume was determined, which is characterized by a flow rate of about 16 femtoliters per second. A dependence of the ink transport from the length of pauses before and in between writing the structures was observed and should be taken into account during pattern design when aiming at best writing homogeneity. The ultra-large scan range of the utilized AFM allowed for a simultaneous study of the entire preparation area of almost 1 mm(2), yielding good statistic results.

Titania-mediated stabilization of fluorescent dye encapsulation in mesoporous silica nanoparticles.

Mesoporous silica nanoparticles hosting guest molecules are a versatile tool with applications in various fields such as life and environmental sciences. Current commonly applied pore blocking strategies are not universally applicable and are often not robust enough to withstand harsh ambient conditions (e.g. geothermal). In this work, a titania layer is utilized as a robust pore blocker, with a test-case where it is used for the encapsulation of fluorescent dyes. The layer is formed by a hydrolysis process of a titania precursor in an adapted microemulsion system and demonstrates effective protection of both the dye payload and the silica core from disintegration under otherwise damaging external conditions. The produced dye-MSN@TiO2 particles are characterized by means of electron microscopy, elemental mapping, ζ-potential, X-ray diffraction (XRD), nitrogen adsorption, Thermogravimetric analysis (TGA), fluorescence and absorbance spectroscopy and Fourier Transform Infrared Spectroscopy - Total Attenuated Reflectance (FT-IR ATR). Finally, the performance of the titania-encapsulated MSNs is demonstrated in long-term aqueous stability and in flow-through experiments, where owing to improved dispersion encapsulated dye results in improved flow properties compared to free dye properties. This behavior exemplifies the potential advantage of carrier-borne marker molecules over free dye molecules in applications where accessibility or targeting are a factor, thus this encapsulation method increases the variety of fields of application.

Gold mesoflower arrays with sub-10 nm intraparticle gaps for highly sensitive and repeatable surface enhanced Raman spectroscopy.

Self-assembling Au mesoflower arrays are prepared using a polymethylmethacrylate (PMMA) template on an iron substrate via a combined top-down/bottom-up nanofabrication strategy. The PMMA template with the holes around 300-500 nm in diameter is first fabricated by using polymer blend lithography on iron substrates, and the highly homogeneous Au mesoflower arrays with less than 10 nm intraparticle gaps are subsequently obtained by an in situ galvanic reaction between HAuCl4 solution and the iron substrate under optimal stirring of the solution as well as reaction time. Owing to the unique mesostructures and uniformity, Raman measurements show that the gold mesoflower arrays obtained demonstrated a strong and reproducible surface enhanced Raman scattering (SERS) enhancement on the order of ∼10(7)-10(8). The development of a SERS substrate based on the Au mesoflowers with high spatial density of hot spots, relatively low cost and facial synthesis provides a novel strategy for applications in chemical and biomolecular sensing.

Dry under water: air retaining properties of large-scale elastomer foils covered with mushroom-shaped surface microstructures.

Superhydrophobic surfaces are well known for most different functions in plants, animals, and thus for biomimetic technical applications. Beside the Lotus Effect, one of their features with great technical, economic and ecologic potential is the Salvinia Effect, the capability to keep a stable air layer when submerged under water. Such air layers are of great importance, e.g., for drag reduction (passive air lubrication), antifouling, sensor applications or oil-water separation. Some biological models, e.g., the floating fern Salvinia or the backswimmer Notonecta, show long term stable air retention even under hydrodynamic conditions. Therefore, they are ideal models for the development of technical biomimetic air retaining surfaces. Up to now, several prototypes of such surfaces have been developed, but none provides both, stable air retention and cost effective large scale production. Meanwhile, a novel biomimetic surface is commercially available and produced on a large scale: an adhesive elastomeric film with mushroom-shaped surface microstructures that mimic the adhesion system of animals. In this study, we show that these films, which have been initially developed for a different purpose, due to their specific geometry at the microscale, are capable of stable air retention under water. We present first results concerning the capabilities of mushroom-shaped surface microstructures and show that this elastomer foil is able to stabilize a permanent air layer under water for more than two weeks. Further, the stability of the air layer under pressure was investigated and these results are compared with the predicted theoretical values for air retention of microstructured surfaces. Here, we could show that they fit to the theoretical predictions and that the biomimetic elastomer foil is a promising base for the development of an economically and efficient biomimetic air retaining surface for a broad range of technical applications.

High aspect ratio constructive nanolithography with a photo-dimerizable molecule.

A major challenge in constructive nanolithography is the preservation of the lateral resolution of a monolayer-thick template pattern while amplifying it to a structure with a thickness above 10 nm. So far, the most successful approach to achieve this is surface-initiated polymerization (SIP) from e-beam structured monolayer templates in a multistep process. However, spreading of the polymer on the substrate leads to a rapid line-widening. Therefore, structures with lateral resolutions well below 100 nm and thicknesses above 10 nm (aspect ratio: 0.1) were not reported yet. Our approach of photoinduced, constructive, reversible nanolithography, is based on nanografting within a coumarin-derivative thiol (CDT) solution using the tip of an atomic force microscope (AFM). By photodimerization and the formation of disulfide bonds, the CDT polymerizes in a single-step process. We demonstrate the highest lateral resolution in constructive nanolithography at thicknesses above 10 nm (40 nm lateral resolution at 12 nm thickness, aspect ratio: 0.3).

Templated self-assembly of ZnO films on monolayer patterns with nanoscale resolution.

Lithographically defined self-growing ZnO films were prepared by a bioinspired chemical bath deposition technique (CBD). We observed a high selectivity of ZnO deposition: Teflon-like per-fluoro-decyl-trichlorosilane (FDTS) monolayers repelled ZnO primary particles, whereas amino-functionalized areas of the substrate were selectively covered by a highly anisotropic, oriented, and compact ZnO film with a thickness of 50 nm. The size of the primary particles in our methanol-based solution was approximately 2.5 nm. On the amino substrate they formed agglomerates not larger than 30 nm. Monolayer patterns made by polymer blend lithography were templated with an edge resolution of 30 nm. By using a specialized derivative of microcontact printing, we prepared layout-defined silane templates, which reliably determined the growth of a layout-defined, patterned oxide film with submicrometer lateral resolution.

Design of chemically activated polymer microwells by one-step UV-lithography for stem cell adhesion.

A novel method to produce sub-microwalled chemically activated polymer microwells by one-step UV-lithography under ambient conditions which are selectively coated with gelatin is introduced. The dimensions as well as the shape of the resulting polystyrene structures are both tunable merely by the irradiation time through one and the same mask. It is shown that the UV-irradiation initiates three effects at those surface areas which are not covered by the mask: (i) oxidation, (ii) cross-linking, and (iii) degradation of polystyrene. The superposition of those effects results in the formation of microscaled, oxidized polymer wells separated by polymer walls, whereas the polymer walls are formed below the mask structures. Topographical changes induced by the UV-irradiation are investigated by atomic force microscopy after different irradiation times. It is shown by X-ray photoelectron spectroscopy and ellipsometric investigations that the chemical composition of the irradiated areas and the degradation of polystyrene reach an equilibrium state after an irradiation time of 10 min. The lateral distribution of the cross-linked and oxidized and of the nonmodified polystyrene after irradiation was determined by fluorescence microscopy and time-of-flight secondary ion mass spectrometry. After the irradiated samples were treated with gelatin solution, it was found that stem cells selectively attach to the irradiated areas. This is due to the selective immobilization of the gelatin on the irradiated polymer areas, which was proved by X-ray photoelectron spectroscopy experiments.

Periodical nanostructured multiline copper films self-organized by electrodeposition: structure and properties.

Nanoscale patterned electrodeposition of metals on flat substrates has become a topic of great interest both scientifically and technologically in recent years. Here, we demonstrate the self-organized growth of extended arrays of parallel nanoscale copper wires on flat glass chips from an ultrathin aqueous electrolyte layer. Regular, periodic patterns of copper nanowires with diameters in the range of 40 nm-400 nm were grown, forming parallel arrays of alternating lines of copper and cuprous oxide at periodicities down to approx. 80 nm, depending on the deposition parameters such as voltage and pH. The resulting multiline films are investigated with respect to their structure and electrical properties using Electrical Force Microscopy, Scanning Electron Microscopy and Scanning Auger Electron Spectroscopy. The results of the experiments show a strongly anisotropic behavior of the electrical properties of multiline nanostructures corresponding to their strongly anisotropic geometry.

Development of thermo-reporting nanoparticles for accurate sensing of geothermal reservoir conditions.

The inaccessibility of geological reservoirs, both for oil and gas production or geothermal usage, makes detection of reservoir properties and conditions a key problem in the field of reservoir engineering, including for the development of geothermal power plants. Herein, an approach is presented for the development of messenger nanoparticles for the determination of reservoir conditions, with a proof of concept example of temperature detection under controlled laboratory conditions. Silica particles are synthesized with a two-layer architecture, an inner enclosed core and an outer porous shell, each doped with a different fluorescent dye to create a dual emission system. Temperature detection happens by a threshold temperature-triggered irreversible release of the outer dye, thus changing the fluorescence signal of the particles. The reported particle system consequently enables a direct, reliable and fast way to determine reservoir temperature. It also displays a sharp threshold for accurate sensing and allows detection at concentration ranges as low as few nanograms of nanoparticles per milliliter.