Tracking Cation Exchange in Individual Nanowires Transistor Characterization.

Cation exchange is a versatile method for modifying the material composition and properties of nanostructures. However, control of the degree of exchange and material properties is difficult at the single-particle level. Successive cation exchange from CdSe to AgSe has been utilized here on the same individual nanowires to monitor the change of electronic properties in field-effect transistor devices.

Superionic phase transition in individual silver selenide nanowires.

Silver selenide (AgSe) is a promising material for applications as a solid-state electrolyte, with a superionic phase transition at 133 °C. Here, we studied the temperature dependent transport properties of single AgSe nanowires in a transistor geometry, which allowed us to determine charge carrier type, concentration, and mobility below and above the superionic phase transition temperature. We found the majority charge carriers to be n-type in the temperature range of 30-150 °C.

Stem cell autotomy and niche interaction in different systems.

The best known cases of cell autotomy are the formation of erythrocytes and thrombocytes (platelets) from progenitor cells that reside in special niches. Recently, autotomy of stem cells and its enigmatic interaction with the niche has been reported from male germline stem cells (GSCs) in several insect species. First described in lepidopterans, the silkmoth, followed by the gipsy moth and consecutively in hemipterans, foremost the milkweed bug.

The influence of a Te-depleted surface on the thermoelectric transport properties of Bi₂Te₃ nanowires.

We report on thermoelectric transport measurements along the basal plane of several individual, single-crystalline Bi₂Te₃ nanowires (NWs) with different cross-sectional areas, grown by a vapor-liquid-solid method. Lithographically defined microdevices allowed us to determine the Seebeck coefficient S, electrical conductivity σ, and thermal conductivity κ of individual NWs. The NWs studied show near intrinsic transport properties with low electrical conductivities of around σ = (3.

Thermoelectric characterization of bismuth telluride nanowires, synthesized via catalytic growth and post-annealing.

Bi(2) Te(3) nanowires are of significant interest for two fields: nanostructured thermoelectrics and topological insulators. The vapor-liquid-solid method is employed in combination with annealing in a Te atmosphere, to obtain single-crystalline Bi(2) Te(3) nanowires with reproducible electronic transport properties (electrical conductivity and Seebeck coefficient) that are close to those of intrinsic bulk Bi(2) Te(3) .

Imaging Schottky barriers and ohmic contacts in PbS quantum dot devices.

We fabricated planar PbS quantum dot devices with ohmic and Schottky type electrodes and characterized them using scanning photocurrent and photovoltage microscopies. The microscopy techniques used in this investigation allow for interrogation of the lateral depletion width and related photovoltaic properties in the planar Schottky type contacts. Titanium/QD contacts exhibited depletion widths that varied over a wide range as a function of bias voltage, while the gold/QD contacts showed ohmic behavior over the same voltage range.

Using nanowires to extract excitons from a nanocrystal solid.

Synthetic methods yielding highly uniform colloidal semiconductor nanocrystals with controlled shapes and sizes are now available for many materials. These methods have enabled geometrical control of optical properties, which are difficult or impossible to achieve in conventional bulk solids. However, incorporating nanocrystals efficiently into photodetectors remains challenging because of the low charge carrier mobilities typical of nanocrystal solids.

Color-selective photocurrent enhancement in coupled J-aggregate/nanowires formed in solution.

J-aggregates are ordered clusters of coherently coupled molecular dyes, (1) and they have been used as light sensitizers in film photography due to their intense absorptions. Hybrid structures containing J-aggregates may also have applications in devices that require spectral specificity, such as color imaging or optical signaling. (2) However the use of J-aggregates in optoelectronic devices has posed a long-standing challenge (3, 4) due to the difficulty of controlling aggregate formation and the low charge carrier mobility of many J-aggregates in solid state.

Structural characterization and primary in vitro cell culture of locust male germline stem cells and their niche.

The establishment of in vitro culture systems to expand stem cells and to elucidate the niche/stem cell interaction is among the most sought-after culture systems of our time. To further investigate niche/stem cell interactions, we evaluated in vitro cultures of isolated intact male germline-niche complexes (i.e.

In situ electrical monitoring of cation exchange in nanowires.

Controlling the extent of cation exchange reactions is a promising route for tuning the material composition and properties of nanostructures. Here we demonstrate how measuring the conductivity of nanowires during cation exchange can be used to monitor the transition from CdSe to Ag(2)Se, in situ. In addition, by imaging the same wire mat region before and after complete cation exchange, we find that the shape and morphology of the nanowires are completely preserved.

Quantitative DIC microscopy using an off-axis self-interference approach.

Traditional Normarski differential interference contrast (DIC) microscopy is a very powerful method for imaging nonstained biological samples. However, one of its major limitations is the nonquantitative nature of the imaging. To overcome this problem, we developed a quantitative DIC microscopy method based on off-axis sample self-interference.

Electrically Controlling and Monitoring InP Nanowire Growth from Solution.

Indium phosphide nanowires are of significant technological interest for applications ranging from single junction solar cells to high speed electronics. However, the efficient placement and integration of nanowires into devices remains a significant challenge. Here we extend the technique of electrically controlled solution-liquid-solid (EC-SLS) catalytic nanowire growth to indium phosphide.

Degenerative and regenerative processes involved in midgut pseudotumor formation in the stick insect (Carausius morosus).

Spontaneous and experimentally induced pseudotumor formation in Carausius morosus impairs the midgut tissue homeostasis. Spontaneous pseudotumor formation begins by the break down of a single or a small group of columnar cells (CCs) and is followed by the degeneration of neighboring CCs. There are not only marked similarities but also decisive differences between normal dying CCs in healthy specimens and the degeneration of CCs leading to pseudotumors: in both cases, the apical cell parts with the nucleus are extruded into the midgut lumen, but only during of pseudotumor formation an "amorphous substance" originates from the basal parts of the CCs.

Quantitative phase contrast imaging of THz electric fields in a dielectric waveguide.

We apply phase contrast imaging to enable, sharply focused visualization of terahertz waves in electro-optic media. The approach allows quantitative characterization of THz waves in the 60 GHz - 4.5 THz frequency range in a thin dielectric slab and in-focus observation of THz waves in polaritonic structures.

Midgut pseudotumors and the maintenance of tissue homeostasis: studies on aging and manipulated stick insects.

Stick insects (Carausius morosus) develop pseudotumors in aging adults. Pseudotumor formation starts at the M2 midgut region where an accumulation of stomatogastric nerve terminals is observed. Pseudotumors arise from dying columnar cells whose basal parts form an "amorphous substance" at the basement membrane whereas the apical parts, including the nucleus, are expelled into the gut lumen.

Electroluminescence from nanocrystals in an electromigrated gap composed of two different metals.

We present a technique for making nanoscale gaps with work function offsets based on electromigrating leads composed of two different metals. Electroluminescence spectra from plain metal gaps with and without CdSe/ZnS (core/shell) nanocrystals are qualitatively very similar and exhibit features that are much broader than the photoluminescence spectra obtained from the same nanocrystals. These observations can be explained by inelastic scattering of conduction electrons in the metal leads or by electroluminescence from small metallic clusters that can form during the fabrication process.

Structural polarity and dynamics of male germline stem cells in an insect (milkweed bug Oncopeltus fasciatus).

Knowing the structure opens a door for a better understanding of function because there is no function without structure. Male germline stem cells (GSCs) of the milkweed bug (Oncopeltus fasciatus) exhibit a very extraordinary structure and a very special relationship with their niche, the apical cells. This structural relationship is strikingly different from that known in the fruit fly (Drosophila melanogaster) -- the most successful model system, which allowed deep insights into the signaling interactions between GSCs and niche.

Bias-induced photoluminescence quenching of single colloidal quantum dots embedded in organic semiconductors.

We demonstrate reversible quenching of the photoluminescence from single CdSe/ZnS colloidal quantum dots embedded in thin films of the molecular organic semiconductor N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD) in a layered device structure. Our analysis, based on current and charge carrier density, points toward field ionization as the dominant photoluminescence quenching mechanism. Blinking traces from individual quantum dots reveal that the photoluminescence amplitude decreases continuously as a function of increasing forward bias even at the single quantum dot level.

Apoptosis of male germ-line stem cells after laser ablation of their niche.

Male germ-line stem cells (GSCs) and their niche-the apical cells or hub cells-display a unique feature at the apices of insect testicular follicles. In the locust, Locusta migratoria, the niche consists of only one large apical cell surrounded by about 60 GSCs. The apical cell can be readily identified in the intact follicle.

Tumor cell specific toxicity of Inula helenium extracts.

The aim of the research program was to identify botanical extracts with antineoplastic activity. In this respect extracts prepared from Inula helenium roots showed a remarkable activity. As evidenced by the MTT assay, the Inula helenium extract revealed a highly selective toxicity toward four different tumor cell lines (HT-29, MCF-7, Capan-2 and G1), but a much lower toxicity against healthy human peripheral blood lymphocytes (PBLs) from two donors.

No evidence of androgenic hormone from the testes of the glowworm, Lampyris noctiluca.

The widely accepted concept, stating that insects have no true sex hormones, and that primary as well as secondary sex characteristics are controlled by the genetic inventory of each single cell, is challenged by the report of Naisse, J. [1966a. Contrôle endocrinien de la différenciation sexuelle chez l'Insecte Lampyris noctiluca (Coléoptère Malacoderme Lampyride).

Structural polarity and dynamics of male germline stem cells in the milkweed bug (Oncopeltus fasciatus).

The male germline stem cells (GSCs) of the milkweed bug present an extraordinary structural polarity that is, to our knowledge, unequalled by any other type of stem cells. They consist of a perikaryon and numerous projections arising from the cell pole directed toward the apical cells, the proposed niche of the GSCs. The projections can traverse a considerable distance until their terminals touch the apical cells.

Case of unilateral wing formation in the female of the glowworm Lampyris noctiluca.

On July 27, 1999, the first author found a unilaterally winged adult glowworm in a park in the city of Mainz. Except for the wings on the left side, the specimen exhibited female characteristics that extended to external sexual appendages, the lantern and the gonads. The internal organization showed some remarkable differences between right (wingless) and left (winged) side.

Embryonic integument and "molts" in Manduca sexta (Insecta, Lepidoptera).

In Manduca sexta the germ band is formed 12 h post-oviposition (p.o.) (=10% development completed) and is located above the yolk at the egg surface.