Unravelling the Mechanisms of Gold-Silver Core-Shell Nanostructure Formation by in Situ TEM Using an Advanced Liquid Cell Design.

The growth of silver shells on gold nanorods is investigated by in situ liquid cell transmission electron microscopy using an advanced liquid cell architecture. The design is based on microwells in which the liquid is confined between a thin Si3N4 membrane on one side and a few-layer graphene cap on the other side. A well-defined specimen thickness and an ultraflat cell top allow for the application of high-resolution TEM and the application of analytical TEM techniques on the same sample. The combination of high-resolution data with chemical information is validated by radically new insights into the growth of silver shells on cetrimonium bromide stabilized gold nanorods. It is shown that silver bromide particles already formed in the stock solution play an important role in the exchange of silver ions. The Ag shell growth can be directly correlated with the layer-by-layer dissolution of AgBr nanocrystals, which can be controlled by the electron flux density via distinctly generated chemical species in the solvent. The derived model framework is confirmed by in situ UV-vis absorption spectroscopy evaluating the blue shift in the longitudinal surface plasmon resonance of anisotropic NRs in a complementary batch experiment.

Waveguide Bragg Gratings in Ormocer®s for Temperature Sensing.

Embedded channel waveguide Bragg gratings are fabricated in the Ormocer® hybrid polymers OrmoComp®, OrmoCore, and OrmoClad by employing a single writing step technique based on phase mask technology and KrF excimer laser irradiation. All waveguide Bragg gratings exhibit well-defined reflection peaks within the telecom wavelengths range with peak heights of up to 35 dB and -3 dB-bandwidths of down to 95 pm. Furthermore, the dependency of the fabricated embedded channel waveguide Bragg gratings on changes of the temperature and relative humidity are investigated. Here, we found that the Bragg grating in OrmoComp® is significantly influenced by humidity variations, while the Bragg gratings in OrmoCore and OrmoClad exhibit linear and considerably high temperature sensitivities of up to -250 pm/ ∘ C and a linear dependency on the relative humidity in the range of -9 pm/%.

Waveguide Bragg gratings in Ormocer hybrid polymers.

We report on the fabrication of Bragg gratings within rib-type waveguides of previously UV-cured inorganic-organic Ormocer hybrid polymers by applying the interferometric phase mask technique in conjunction with deep-UV laser radiation. The fabrication process as well as the influence of the applied laser fluence and the length of the Bragg grating on the characteristics of the Bragg grating's transmission and reflection spectra are discussed and compared to numerical simulations and calculations. Depending on the applied laser fluence and the chosen grating length, waveguide Bragg gratings with strong reflectivities of up to 98 % and narrow bandwidths of down to 120 pm have been achieved.

"Black" TiO2 Nanotubes Formed by High-Energy Proton Implantation Show Noble-Metal-co-Catalyst Free Photocatalytic H2-Evolution.

We apply high-energy proton ion-implantation to modify TiO2 nanotubes selectively at their tops. In the proton-implanted region, we observe the creation of intrinsic cocatalytic centers for photocatalytic H2-evolution. We find proton implantation to induce specific defects and a characteristic modification of the electronic properties not only in nanotubes but also on anatase single crystal (001) surfaces. Nevertheless, for TiO2 nanotubes a strong synergetic effect between implanted region (catalyst) and implant-free tube segment (absorber) can be obtained.

TiO2 Nanotubes: Nitrogen-Ion Implantation at Low Dose Provides Noble-Metal-Free Photocatalytic H2 -Evolution Activity.

Low-dose nitrogen implantation induces an ion and damage profile in TiO2 nanotubes that leads to "co-catalytic" activity for photocatalytic H2 -evolution (without the use of any noble metal). Ion implantation with adequate parameters creates this active zone limited to the top part of the tubes. The coupling of this top layer and the underlying non-implanted part of the nanotubes additionally contributes to an efficient carrier separation and thus to a significantly enhanced H2 generation.

Tunable conduction type of solution-processed germanium nanoparticle based field effect transistors and their inverter integration.

In this work we demonstrate the fabrication of germanium nanoparticle (NP) based electronics. The whole process chain from the nanoparticle production up to the point of inverter integration is covered. Ge NPs with a mean diameter of 33 nm and a geometric standard deviation of 1.19 are synthesized in the gas phase by thermal decomposition of GeH4 precursor in a seeded growth process. Dispersions of these particles in ethanol are employed to fabricate thin particulate films (60 to 120 nm in thickness) on substrates with a pre-patterned interdigitated aluminum electrode structure. The effect of temperature treatment, polymethyl methacrylate encapsulation and alumina coating by plasma-assisted atomic layer deposition (employing various temperatures) on the performance of these layers as thin film transistors (TFTs) is investigated. This coating combined with thermal annealing delivers ambipolar TFTs which show an Ion/Ioff ratio in the range of 10(2). We report fabrication of n-type, p-type or ambipolar Ge NP TFTs at maximum temperatures of 450 °C. For the first time, a circuit using two ambipolar TFTs is demonstrated to function as a NOT gate with an inverter gain of up to 4 which can be operated at room temperature in ambient air.

Ferroelectricity in Simple Binary ZrO2 and HfO2.

The transition metal oxides ZrO(2) and HfO(2) as well as their solid solution are widely researched and, like most binary oxides, are expected to exhibit centrosymmetric crystal structure and therewith linear dielectric characteristics. For this reason, those oxides, even though successfully introduced into microelectronics, were never considered to be more than simple dielectrics possessing limited functionality. Here we report the discovery of a field-driven ferroelectric phase transition in pure, sub 10 nm ZrO(2) thin films and a composition- and temperature-dependent transition to a stable ferroelectric phase in the HfO(2)-ZrO(2) mixed oxide. These unusual findings are attributed to a size-driven tetragonal to orthorhombic phase transition that in thin films, similar to the anticipated tetragonal to monoclinic transition, is lowered to room temperature. A structural investigation revealed the orthorhombic phase to be of space group Pbc2(1), whose noncentrosymmetric nature is deemed responsible for the spontaneous polarization in this novel, nanoscale ferroelectrics.

Nano- and Micro-Patterned S-, H-, and X-PDMS for Cell-Based Applications: Comparison of Wettability, Roughness, and Cell-Derived Parameters.

Polydimethylsiloxane (PDMS) is a promising biomaterial for generating artificial extracellular matrix (ECM) like patterned topographies, yet its hydrophobic nature limits its applicability to cell-based approaches. Although plasma treatment can enhance the wettability of PDMS, the surface is known to recover its hydrophobicity within a few hours after exposure to air. To investigate the capability of a novel PDMS-type (X-PDMS) for in vitro based assessment of physiological cell properties, we designed and fabricated plane as well as nano- and micrometer-scaled pillar-patterned growth substrates using the elastomer types S-, H- and X-PDMS, which were fabricated from commercially available components. Most importantly, we compared X-PDMS based growth substrates which have not yet been investigated in this context with H- as well as well-known S-PDMS based substrates. Due to its applicability to fabricating nanometer-sized topographic features with high accuracy and pattern fidelity, this material may be of high relevance for specific biomedical applications. To assess their applicability to cell-based approaches, we characterized the generated surfaces using water contact angle (WCA) measurement and atomic force microscopy (AFM) as indicators of wettability and roughness, respectively. We further assessed cell number, cell area and cellular elongation as indirect measures of cellular viability and adhesion by image cytometry and phenotypic profiling, respectively, using Calcein and Hoechst 33342 stained human foreskin fibroblasts as a model system. We show for the first time that different PDMS types are differently sensitive to plasma treatment. We further demonstrate that surface hydrophobicity changes along with changing height of the pillar-structures. Our data indicate that plane and structured X-PDMS shows cytocompatibility and adhesive properties comparable to the previously described elastomer types S- and H-PDMS. We conclude that nanometer-sized structuring of X-PDMS may serve as a powerful method for altering surface properties toward production of biomedical devices for cell-based applications.

Pulsed direct flame deposition and thermal annealing of transparent amorphous indium zinc oxide films as active layers in field effect transistors.

Indium-zinc oxide (IZO) films were deposited via flame spray pyrolysis (FSP) by pulsewise shooting a Si/SiO2 substrate directly into the combustion area of the flame. Based on UV-vis measurements of thin-films deposited on glass substrates, the optimal deposition parameters with respect to low haze values and film thicknesses of around 100 nm were determined. Thermal annealing of the deposited films at temperatures between 300 and 700 °C was carried out and staggered bottom gate thin-film transistors (TFT) were fabricated. The thin films were investigated by scanning electron microscopy, atomic force microscopy, X-ray diffraction, Fourier transformed infrared spectroscopy, and room-temperature photoluminescence measurements. The outcome of these investigations lead to two major requirements in order to implement a working TFT: (i) organic residues from the deposition process need to be removed and (ii) the net free charge carrier concentration has to be minimized by controlling the trap states in the semiconductor. The optimal annealing temperature was 300 °C as both requirements are fulfilled best in this case. This leads to field effect transistors with a low hysteresis, a saturation mobility of µSat = 0.1 cm(2)/(V s), a threshold voltage of Vth = -18.9 V, and an Ion/Ioff ratio on the order of 10(7). Depending on thermal treatment, the defect density changes significantly strongly influencing the transfer characteristics of the device.

Nanoscale characterization of TiO(2) films grown by atomic layer deposition on RuO(2) electrodes.

Topography and leakage current maps of TiO2 films grown by atomic layer deposition on RuO2 electrodes using either a TiCl4 or a Ti(O-i-C3H7)4 precursor were characterized at nanoscale by conductive atomic force microscopy (CAFM). For both films, the leakage current flows mainly through elevated grains and not along grain boundaries. The overall CAFM leakage current is larger and more localized for the TiCl4-based films (0.63 nm capacitance equivalent oxide thickness, CET) compared to the Ti(O-i-C3H7)4-based films (0.68 nm CET). Both films have a physical thickness of ∼20 nm. The nanoscale leakage currents are consistent with macroscopic leakage currents from capacitor structures and are correlated with grain characteristics observed by topography maps and transmission electron microscopy as well as with X-ray diffraction.