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812 results on '"Gessner, T."'

1. Nanomechanics of CNTs for Sensor Application

Author

Wagner, C., Hartmann, S., Wunderle, B., Schuster, J., Schulz, S. E., and Gessner, T.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

A nanoscopic simulation for an acceleration sensor is aimed based on the piezoresistive effect of carbon nanotubes (CNTs). Therefore, a compact model is built from density functional theory (DFT), compared with results of molecular dynamics (MD) that describes the mechanics of carbon nanotubes in a parameterized way. The results for the interesting kind of CNTs [(6,3) and (7,4)] within the two approaches agree in a satisfying way, when DFT-calculations are performed with atomic configurations obtained by MD geometry optimization. Geometry optimization yields the Poisson ratio for CNTs. Thus, values from MD and DFT are compared. The simulation finally aims the modeling of the conductive behavior of CNTs when strain is applied, but this needs further verification. Here, we present the prediction of the tight binding model for suitable CNTs., Comment: 5 pages, 4 figures, 2 tables

Published
2017
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2. Empirical transport model of strained CNT transistors used for sensor applications

Author

Wagner, C., Schuster, J., and Gessner, T.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We present an empirical model for the nearballistic transport in carbon nanotube (CNT) transistors used as strain sensors. This model describes the intrinsic effect of strain on the transport in CNTs by taking into account phonon scattering and thermally activated charge carriers. As this model relies on a semiempirical description of the electronic bands, different levels of electronic structure calculations can be used as input. The results show that the electronic structure of strained single-walled CNTs with a radius larger than 0.7nm can be described by a fully analytical model in the sensing regime. For CNTs with smaller diameter, parameterized data from electronic structure calculations can be used for the model. Depending on the type of CNTs, the conductance can vary by several orders of magnitude when strain is applied, which is consistent with the current literature. Further, we demonstrate the tuning of the sensor by an external gate which allows shifting the signal amplitude and the strain sensitivity. These parameters have to be balanced to get good sensing properties. Due to its basically analytical nature, the transport model can be formulated as a compact model for circuit simulations., Comment: 10 pages, 10 figures

Published
2017
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3. DFT investigations of the piezoresistive effect of carbon nanotubes for sensor application

Author

Wagner, C., Schuster, J., and Gessner, T.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We investigate the piezoresistive effect of carbon nanotubes (CNTs) within density functional theory (DFT) aiming at application-relevant CNTs. CNTs are excellent candidates for the usage in nano-electromechanical sensors (NEMS) due to their small band gap at zero strain leading to a finite resistivity at room temperature. The application of strain induces a band gap-opening leading to a tremendous change in the resistivity. DFT with the LDA approximation yields reasonable results for pure carbon systems like CNTs and is applied to calculate the electronic structure of experimentally relevant CNTs. For the transport part, a simple ballistic transport model based on the band gap is used. We compare our DFT results for the band gaps of strained CNTs to results of tight binding (TB) models. By introducing a scaling factor of $\sqrt{2}$, an excellent agreement of the the DFT data with TB model published by Yang et al. [1] is obtained., Comment: 4 pages, 5 figures

Published
2017
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5. Reactivity to combined experimental stress- and alcohol cue-exposure predicts real-life alcohol use and craving in individuals with alcohol use disorder

Author

Zaiser, J., primary, Hoffmann, S., additional, Zimmermann, S., additional, Gessner, T., additional, Bekier, N., additional, Abel, M., additional, Radler, P., additional, Langejürgen, J., additional, Vollstädt-Klein, S., additional, Stallkamp, J., additional, Kirschbaum, C., additional, Kiefer, F., additional, and Bach, P., additional

Published
2023
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34. A new technology platform for fully integrated polymer based micro optical fluidic systems

Author

Nestler, J., primary, Hiller, K., additional, Gessner, T., additional, Buergi, L., additional, Soechtig, J., additional, Stanley, R., additional, Voirin, G., additional, Bigot, S., additional, Gavillet, J., additional, Getin, S., additional, Fillon, B., additional, Ehrat, M., additional, Lieb, A., additional, Beckers, M.-C., additional, and Dresse, D., additional

Published
2006
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46. Effect of cleaning procedures on the electrical properties of carbon nanotube transistors—A statistical study.

Author

Tittmann-Otto, J., Hermann, S., Kalbacova, J., Hartmann, M., Toader, M., Rodriguez, R. D., Schulz, S. E., Zahn, D. R. T., and Gessner, T.

Subjects
ELECTRIC properties of carbon nanotubes, CARBON nanofibers, NANOSTRUCTURED materials synthesis, INTERFACES (Physical sciences), SURFACES (Physics), TRANSISTORS
Abstract

The interface between a carbon nanotube (CNT) and its environment can dramatically affect the electrical properties of CNT-based field-effect transistors (FETs). For such devices, the channel environment plays a significant role inducing doping or charge traps giving rise to hysteresis in the transistor characteristics. Thereby the fabrication process strongly determines the extent of those effects and the final device performance. In CNT-based devices obtained from dispersions, a proper individualization of the nanotubes is mandatory. This is generally realized by an ultrasonic treatment combined with surfactant molecules, which enwrap nanotubes forming micelle aggregates. To minimize impact on device performance, it is of vital importance to consider post-deposition treatments for removal of surfactant molecules and other impurities. In this context, we investigated the effect of several wet chemical cleaning and thermal post treatments on the electrical characteristics as well as physical properties of more than 600 devices fabricated only by wafer-level compatible technologies. We observed that nitric acid and water treatments improved the maximum-current of devices. Additionally, we found that the ethanol treatment successfully lowered hysteresis in the transfer characteristics. The effect of the chemical cleaning procedures was found to be more significant on CNT-metal contacts than for the FET channels. Moreover, we investigated the effect of an additional thermal cleaning step under vacuum after the chemical cleaning, which had an exceptional impact on the hysteresis behavior including hysteresis reversal. The presence of surfactant molecules on CNT was evidenced by X-ray photoelectron and Raman spectroscopies. By identifying the role of surfactant molecules and assessing the enhancement of device performance as a direct consequence of several cleaning procedures, these results are important for the development of CNT-based electronics at the wafer-level. [ABSTRACT FROM AUTHOR]

Published
2016
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