| 1. |
- Drozdowska, Katarzyna, et al.
(författare)
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Optimum Choice of Randomly Oriented Carbon Nanotube Networks for UV-Assisted Gas Sensing Applications
- 2023
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Ingår i: ACS Sensors. - : American Chemical Society (ACS). - 2379-3694. ; 8:9, s. 3547-3554
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the noise and photoresponse characteristics of various optical transparencies of nanotube networks to identify an optimal randomly oriented network of carbon nanotube (CNT)-based devices for UV-assisted gas sensing applications. Our investigation reveals that all of the studied devices demonstrate negative photoconductivity upon exposure to UV light. Our studies confirm the effect of UV irradiation on the electrical properties of CNT networks and the increased photoresponse with decreasing UV light wavelength. We also extend our analysis to explore the low-frequency noise properties of different nanotube network transparencies. Our findings indicate that devices with higher nanotube network transparencies exhibit lower noise levels. We conduct additional measurements of noise and resistance in an ethanol and acetone gas environment, demonstrating the high sensitivity of higher-transparent (lower-density) nanotube networks. Overall, our results indicate that lower-density nanotube networks hold significant promise as a viable choice for UV-assisted gas sensing applications.
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| 2. |
- Dróżdż, Piotr A., et al.
(författare)
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A graphene/h-BN MEMS varactor for sub-THz and THz applications
- 2023
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 15:30, s. 12530-12539
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Tidskriftsartikel (refereegranskat)abstract
- Recent development of terahertz systems has created the need for new elements operating in this frequency band, i.e., fast tunable devices such as varactors. Here, we present the process flow and characterization of a novel electronic variable capacitor device that is made with the use of 2D metamaterials such as graphene (GR) or hexagonal boron nitride (h-BN). Comb-like structures are etched into a silicon/silicon nitride substrate and a metal electrode is deposited at the bottom. Next, a PMMA/GR/h-BN layer is placed on top of the sample. As voltage is applied between GR and metal, the PMMA/GR/h-BN layer bends towards the bottom electrode thus decreasing the distance between electrodes and changing the capacitance. The high tunability and complementary metal oxide semiconductor (CMOS)-compatible process flow of the platform for our device and its millimeter size make it promising for applications in future electronics and terahertz technologies. The goal of our research is to integrate our device with dielectric rod waveguides, thus making THz phase shifters.
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| 3. |
- Drozdz, Piotr A., et al.
(författare)
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Highly efficient absorption of THz radiation using waveguide-integrated carbon nanotube/cellulose aerogels
- 2022
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Ingår i: APPLIED MATERIALS TODAY. - : Elsevier BV. - 2352-9407. ; 29
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Tidskriftsartikel (refereegranskat)abstract
- This article presents the preparation, compositional and electromagnetic characterization of modified few-walled carbon nanotubes/nanofibrillar cellulose (FWCNT/NFC) aerogels integrated in a standard terahertz hollow waveguide and studies their operation as absorbers of electromagnetic waves in the WR-3.4 band (220-330 GHz). Hybrid aerogels consisting of different weight ratios of NFC and modified FWCNT are prepared by freezedrying and characterized through scanning electron microscopy and Raman spectroscopy, and then placed within waveguide cassettes in a simple, low-cost and efficient way that requires no special equipment. A broadband measurement setup is employed for examining the electromagnetic response of the materials. It is found that the materials are excellent absorbers with an average shielding efficiency of 66 dB in the best case and return loss above 10 dB across the band with a flat frequency response. FWCNT aerogels are assessed as a promising candidate for terahertz waveguide terminations.
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| 4. |
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| 5. |
- Przewłoka, Aleksandra, et al.
(författare)
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Characterization of Silver Nanowire Layers in the Terahertz Frequency Range
- 2021
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 14:23, s. 7399-
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Tidskriftsartikel (refereegranskat)abstract
- Thin layers of silver nanowires are commonly studied for transparent electronics. However, reports of their terahertz (THz) properties are scarce. Here, we present the electrical and optical properties of thin silver nanowire layers with increasing densities at THz frequencies. We demonstrate that the absorbance, transmittance and reflectance of the metal nanowire layers in the frequency range of 0.2 THz to 1.3 THz is non-monotonic and depends on the nanowire dimensions and filling factor. We also present and validate a theoretical approach describing well the experimental results and allowing the fitting of the THz response of the nanowire layers by a Drude–Smith model of conductivity. Our results pave the way toward the application of silver nanowires as a prospective material for transparent and conductive coatings, and printable antennas operating in the terahertz range—significant for future wireless communication devices.
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| 6. |
- Przewłoka, Aleksandra, et al.
(författare)
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Single-walled carbon nanotube phase shifters for low THz frequencies
- 2021
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Ingår i: The 11th International Conference on Metamaterials, Photonic Crystals and Plasmonics, META 2021. - : META Conference. ; , s. 1058-1059
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Konferensbidrag (refereegranskat)abstract
- In this work single-walled carbon nanotube length dependence on phase tuning properties of dielectric rod waveguide is experimentally studied in ultra-wide frequency band of 0.1-0.5 THz.
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| 7. |
- Przewłoka, Aleksandra, et al.
(författare)
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Terahertz conductivity of silver nanowire networks
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Silver nanowires are an excellent candidate as highly conductive material for applications in flexible and transparent electronics such as solar cells, displays, and antennas. This paper reports on the electronic properties of thin silver nanowire networks with varying geometries and densities of the nanowires in the sub-terahertz range (0.2 THz to 1.2 THz) using time-domain and frequency-domain spectroscopies. The THz conductivity is extracted from transmission measurements and a modified Drude-Smith model is proposed to describe the conductivity of the networks. The low-density networks follow the Drude-Smith conductivity with the backscattering parameter close to -1, while the high-density networks form a semicontinuous metallic layer with a Drude-like response. The demonstrated approach is relevant for characterizing conductive nanomaterials in order to design novel THz optoelectronic devices.
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| 8. |
- Smirnov, Serguei, et al.
(författare)
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Sub‐THz Phase Shifters Enabled by Photoconductive Single‐Walled Carbon Nanotube Layers
- 2022
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Ingår i: Advanced Photonics Research. - : Wiley-VCH Verlagsgesellschaft. - 2699-9293 .- 2699-9293. ; , s. 2200042-2200042
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Tidskriftsartikel (refereegranskat)abstract
- Materials with tunable dielectric properties are highly relevant for terahertz (THz) applications. Herein, the tuning of the dielectric response of single-walled carbon nanotube layers by light illumination is studied for applications to THz phase shifters. The dependence of the length of individual nanotubes on the THz photoconductivity of the network is experimentally investigated in the frequency range of 0.2–1 THz by time-domain spectroscopy (TDS). The effective conductivity of the networks is described by a theoretical model that fits the measured dielectric function. Terahertz phase shifters are realized with the carbon nanotube layers as the optically tunable element deposited on the wall of rectangular dielectric waveguides. The phase of the electromagnetic wave propagating in the waveguide is shown to be tunable by illuminating the nanotubes. A linear phase shift with the frequency is measured between 75 and 500 GHz with a low change in amplitude due to the illumination.
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| 9. |
- Xenidis, Nikolaos, et al.
(författare)
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Dichroic absorption of aligned graphene-augmented inorganic nanofibers in the terahertz regime
- 2024
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Ingår i: Applied Materials Today. - : Elsevier BV. - 2352-9407. ; 39
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Tidskriftsartikel (refereegranskat)abstract
- This article investigates the dichroic properties of aligned γ-Al2O3 nanofibers coated with graphene in the terahertz (THz) regime, revealing significant variance in absorption based on the orientation of the electric field in relation to the nanofibers, arising from the anisotropic nature of the material. Samples are prepared in a hot-wall chemical vapor deposition reactor with varying growth times, resulting in 5 samples with increasing graphene content. Compositional characterization is carried out using scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The samples are characterized electromagnetically using two distinct measurement techniques. First, a novel waveguide measurement setup is deployed, wherein square waveguide cassettes are used to capture the anisotropic behavior of the material and equally measure both polarization states in 67–500 GHz. Then, the samples are characterized using terahertz time-domain spectroscopy up to 4 THz. Both techniques highlight absorption enhancement when the electric field is parallel to the fibers, opening new possibilities for THz devices using polarization filtering.
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| 10. |
- Xenidis, Nikolaos, et al.
(författare)
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Waveguide Measurements of Highly Anisotropic Graphene Augmented Inorganic Nanofibers
- 2023
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Ingår i: 2023 53rd European Microwave Conference, EuMC 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 576-579
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Konferensbidrag (refereegranskat)abstract
- This work presents the preparation and the frequency domain measurements of graphene augmented inorganic nanofibers oriented across the longitudinal axis of the fibers, embedded in a hollow WR-10 waveguide cassette. A simple measurement setup is employed, allowing for rapid, broadband characterization of the material under test. Due to the orientation of the fibers, highly anisotropic behavior is revealed.
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