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295 results on '"Kolahdouz, Mohammadreza"'

12. Effect of electrolyte concentration and symmetry on the heterogeneous surface charge in an electrically gated nanochannel

Author

Kateb, Movaffaq, Fathipour, Morteza, and Kolahdouz, Mohammadreza

Subjects
Physics - Applied Physics, Physics - Computational Physics, Physics - Fluid Dynamics
Abstract

The present study aims to investigate utilizing field-effect for inducing heterogeneous surface charge and consequently changing the fluid flow in a solid-state nanochannel with converging-diverging periodicity. It is shown that the combination of geometry and applied gate voltage (V_{G}) would generate heterogeneous surface charge at the channel walls which can be modulated by V_{G}, i.e. a moderate V_{G} (0.7-0.9 V) causes charge inversion in diverging sections of the channel while V_{G} > 0.9 enables charge inversion in the entire channel but it is still non-uniform in each section. The results show that zeta ({\zeta}) potential is a function of V_{G} which shows a linear to non-linear transition due to dilution of electrolyte in agreement with density functional theory and Monte Carlo simulations. In contrast, electrolyte symmetry has a minor effect on the variation of {\zeta} potential. It is also shown that the difference in {\zeta} potential across the channel ({\Delta}{\zeta}) increases by dilution of electrolyte and utilizing a more symmetric electrolyte with lower valances. For the first time, it is shown that {\Delta}{\zeta} presents a maximum with the V_{G}. The V_{G} corresponding to the maximum {\Delta}{\zeta} decreases with both dilution of electrolyte and higher anion valance. This is of practical importance to overcome leakage current problem of field-effect fluidic devices. It is also shown that the velocity field can be altered by changing both electrolyte concentration and symmetry. However, applying VG was found to be a more efficient way than electrolyte modifications. This includes generating circulation inside the channel which is of prime importance for applications such as mixing or separation/trapping., Comment: 8 pages, 6 figures. arXiv admin note: text overlap with arXiv:2002.07058

Published
2020

14. Modulation of heterogeneous surface charge and flow pattern in electrically gated converging-diverging nanochannel

Author

Kateb, Movaffaq, Kolahdouz, Mohammadreza, and Fathipour, Morteza

Subjects
Physics - Applied Physics, Physics - Biological Physics, Physics - Chemical Physics, Physics - Fluid Dynamics
Abstract

The present study aims at utilizing field effect phenomenon to induce heterogeneous surface charge and consequently changing the fluid flow in a solid state nanochannel with converging-diverging periodicity. It is shown that the proposed geometry causes non-uniform radial field adjacent to channel walls which is stronger around the diverging section and weaker next to the converging part of the wall. The later generates heterogeneous surface charge at channel walls depending on the applied gate potential i.e. applying low gate potential enables effective modulation of surface charge with the same polarity of the intrinsic charge at channel walls, while moderate gate potential causes charge inversion in diverging sections of the channel and generates reverse flow and thus results in fluid flow circulation. The potential application of flow circulation for trapping and rejection of particles is also demonstrated., Comment: 6 pages, 8 figures

Published
2019
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26. Reducing parasitic capacitance of strained Si nano p-MOSFET by control of virtual substrate doping

Author

Khatami, Mohammad Mahdi, Shalchian, Majid, and Kolahdouz, Mohammadreza

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Biaxially strained Si channel p-MOSFETs on virtual SiGe substrates suffer from a parasitic parallel channel in virtual substrate. This channel participates in current passing through the devices and increases parasitic capacitors which degrades the high frequency response. In this paper a new approach has been introduced to eliminate the channel which in turn reduces parasitic capacitors of the MOSFET. It is illustrated that, increasing virtual substrate doping, can reduce and finally eliminate this unintentional channel. In this work 2D simulation has been used to investigate the impact of the proposed method., Comment: 5th International Congress on Nanoscience & Nanotechnology (ICNN2014)

Published
2015

36. Characterization and Predictive Modeling of Epitaxial Silicon-Germanium Thermistor Layers

Author

Malm, B. Gunnar, Kolahdouz, Mohammadreza, Forsberg, Fredrik, and Niklaus, Frank

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics, Quantum Physics
Abstract

The thermal coefficient of resistance (TCR) for epitaxial silicon-germanium (SiGe) layers has been analyzed by experiment and simulation. Predictive simulation using drift-diffusion formalism and self-consistent quantum-mechanical solutions yielded similar results, TCR around 2%/K at 300 K. This modeling approach can be used for different, graded and constant, SiGe profiles,. It is also capable of predicting the influence of background auto-doping on the TCR of the detectors

Published
2011

50. Highly Efficient DFB Laser-Assisted Grating As2S3 Chalcogenide for Integrated Photonics

Author

Mafakheri, Afshin, Parsanasab, Gholam-Mohammad, Sorayaie, Parvin, Mostajeran, Samaneh, Akbari, Ladan, and Kolahdouz, Mohammadreza

Abstract

Chalcogenide (As2S3) is a material with promising applications in integrated photonics. This material has the potential for low-threshold, compact, and high-coherence light sources. Our team has developed a chalcogenide-based distributed feedback (DFB) laser using a ridge polymer waveguide structure, incorporating a 500 nm As2S3 grating as the wavelength selective element. With precise engineering of the DFB laser structure, we have achieved single-mode lasing with an 18 nJ lasing threshold and a side mode suppression ratio (SMSR) of 28 dB. Additionally, we have found that the single-mode lasing persists over a wide range of pump power energy. To validate our experimental results, we performed a numerical simulation of the proposed structure, which confirmed experimental results.

Published
2024
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