1,721,013 research outputs found
Comparison of bolometer type room temperature photodetectors, based on MWCNTs, combined with tobacco cells or embedded in a polymer matrix
No full textBolometer type photodetectors with a high sensitivity in a wide range of wavelengths, ranging from the ultraviolet throughout the visible and up to the near infrared, have been fabricated utilizing the same type of multi-walled carbon nanotubes, but different matrices: in the first case a biological matrix based on tobacco cells has been used and in the second case high density polyethylene, a conventional polymer. The two investigated nanocomposite materials showed very different temperature coefficients, but both a clear negative temperature coefficient type behavior. It has been found that, despite the very different sample conductivities, both nanocomposites can be operated as photodetectors at room temperature. For the polyethylene based nanocomposite device, random-telegraph-noise has been found to limit the bolometer operation. Instead, for the tobacco cell based nanocomposite bolometer, the high sensitivity of the dark current to ambient temperatures leads to baseline fluctuations, but the photocurrent amplitude remains almost unaffected and a good signal-to-noise ratio has been obtained also for low light intensities
Temperature dependent electrical properties and cycling stability of a highly loaded LDPE/MWCNT composite film with coplanar gold contacts
No full textA low density polyethylene based nanocomposite sample with a high concentration of multiwalled carbon nanotubes has been shown to have a rather high value of the electrical resistance temperature coefficient with a PTC type behavior over the whole investigated range between room temperature and 70°C. Due to a long-term drift of the electrical characteristics this type of nanocomposite cannot be used as stable temperature sensor but, after an initial burn-in procedure, a reliable operation as current limiting element has been demonstrated
Nanotechnologie und Nanoprozesse - Einführung und Bewertung
No full textDas Buch ist eine kompakt aufbereitete, didaktische Zusammenstellung der Nanotechnologie auf ihrem aktuellen Stand. Nach einem kurzen Abriss über die historische Entwicklung beschreibt das Werk die Verfahren zur Herstellung und Charakterisierung von wenige Nanometer großen Strukturen, leitet über zu deren (elektrischen) Anwendungen und den physikalischen Messmethoden zur Bestimmung der Eigenschaften von Nanodefekten, -schichten und -partikeln und erläutert schließlich alle wichtigen Präparationstechniken, die heute in der Nanotechnologie zur Verfügung stehen. Auf der Grundlage von gesicherten Fakten werden dabei eine Bewertung der Nanotechnologie, eine Abschätzung ihrer weiteren Entwicklung und ein Ausblick auf ihre Zukunftsaussichten gegeben.
In dieser zweiten Auflage wird gezeigt, wie sich die Herstellungsverfahren und die auf Nanotechniken beruhenden Bauelemente weiter entwickelt haben. Große Fortschritte sind in den Strukturierungsverfahren erzielt worden. Die apparative Weiterentwicklung der fokussierten Ionenstrahlen ermöglicht sowohl neuartige Bauelemente auf Feldeffektgrundlage als auch Anwendungen in der zerstörungsfreien Mikro- und Nanomikroskopie. Das Kapitel zum Nanoimprint wurde um die Diskussion der Softlithographie erweitert. Neben rein anorganischen Materialien wird der Blick auf Anwendungen mit organischen Werkstoffen gelenkt. Das Kapitel über die auf Nanostrukturen beruhenden innovativen elektronischen Bauelemente wurde wegen der Flut von neuen Entwicklungen neu geschrieben. Ausgewählte Schwerpunkte sind dabei Nanopartikel-Feldeffekttransistoren, Bauelemente auf der Basis von Nanoröhren und Solarzellen
The band bending effect of LiI/NaI treated TiO2photoanodes on the performance of dye-sensitized solar cells
No full textA new method has been developed for surface treatment of TiO2 photoanodes with LiI/NaI to enhance the photocurrent and, subsequently, the performance efficiency of the fabricated dye-sensitized solar cells (DSSCs). Three different concentrations (0.1, 0.25, and 0.5 mmol%) of LiI and NaI solutions were used to investigate the effect of this surface treatment on the device performance of DSSCs. A positive shift in the energy level of TiO2 has been experienced by surface treated devices, which is predominantly supported by the decrease in VOC. Furthermore, the introduction of LiI/NaI onto the TiO2 surface resulted in a reduction in the crystallite size, indicating an increase in the surface area which helps in more dye adsorption leading to higher JSC values of the devices. Besides, modification of the conduction band energy level, it also allows a fast electron injection process by shifting the density of states. Thus, this approach offers a simple but efficient route to enhance the photocurrent and efficiency of DSSCs
Resistive temperature sensor based on a syndiotactic polystyrene/MWCNT composite material as sensitive NIR bolometer
No full textA syndiotactic polystyrene/multi-walled carbon nanotube composite based electrical heater and temperature sensor has been investigated regarding its room-temperature bolometer functionality in the near-infrared wavelength range. With the appropriate electrical contact material, a perfectly linear current-voltage characteristics and very good room-temperature conductivity stability has been obtained after a prior Joule heating burn-in procedure. Using LEDs at 780 nm and 1300 nm for excitation a linear, with respect to the light intensity, bolometer operation with good long-term stability and a very good signal-to-noise ratio has been achieved
Transport and noise spectroscopy of MWCNT/HDPE composites with different nanotube concentrations
No full textElectrical current transport and low-frequency noise spectra of multiwall carbon nanotubes in high-density polyethylene matrix have been measured in a temperature range between 10 and 300 K. The dc electrical investigations suggest that these composites can be regarded as a random resistor network, where the resistors are formed by tunnel junctions between carbon nanotubes. A crossover of the conduction from a low-field to a high-field regime is found in current-voltage characteristics. In particular, the high-field regime has a strong dependence on carbon nanotube concentration. Noise measurements reveal a standard 1/f behavior due to resistance fluctuations. However, in samples with different concentration of nanotubes, an unusual temperature dependence of the noise is observed. The samples with higher percentage of nanotubes seem to be the most promising ones for devices application, since their noise level is lower in the whole investigated temperature range
Effect of concentration on low-frequency noise of multiwall carbon nanotubes in high-density polyethylene matrix
No full textTransport and noise measurements of multiwall carbon nanotubes in high-density polyethylene matrix are reported. In these composites current transport occurs through a random tunnel junctions network, formed by adjacent carbon nanotubes. Low-frequency noise investigations reveal a 1/f
behavior induced by resistance fluctuations. An unusual temperature dependence in samples with different nanotube concentration is found. This can be explained by a transition from a fluctuation-induced tunneling mechanism to a thermally activated regime, occurring at increasing nanotube concentration and resulting in a decrease in the overall noise
Measurement Setup for In-Situ Quantum Yield Characterization of Solar Cells during High Energy Particle Irradiation
No full textAn extremely simple on-line quantum yield measurement tool was developed, that permits to measure the photocurrent spectra of solar cells under harsh measurement conditions without the need of optical windows or moving parts. The small photocurrent, induced by the sequential illumination by a series of LEDs with different emission wavelengths, distributed within the responsivity range of the tested solar cell, is converted to a proportional frequency and then monitored using the audio-card of a personal computer and an appropriate Labview-based Software. Subsequently the quantum yield measurements were performed in-situ during the irradiation of a conventional crystalline Silicon solar cell with 1.7 MeV protons in the spectral range between 400 nm and 880 nm. In this case the complete photocurrent spectrum can been monitored continuously with good temporal resolution
Investigation of the solvent influence on polymer–fullerene solar cells by low frequency noise spectroscopy
No full textThe electron density of states and recombination kinetics of bulk heterojunction solar cells have been determined by means of low-frequency noise spectroscopy at room temperature and in dark conditions. The observed differences in the disorder parameter and electron lifetime are attributed to a different film ordering of the active layer because of the influence of a solvent additive. Blends prepared with the reference solvent resulted in the lowest electron lifetime and density of states population, while blends prepared with the addition of a high boiling point solvent resulted in a more efficient charge carrier separation and a higher electron lifetime
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