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Träfflista för sökning "WFRF:(Lisauskas Alvydas) "

Sökning: WFRF:(Lisauskas Alvydas)

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1.
  • Bauer, Maris, et al. (författare)
  • Terahertz detection with graphene field-effect transistors
  • 2015
  • Ingår i: Graphene Week 2015.
  • Konferensbidrag (refereegranskat)abstract
    • Detectors for quasi-optical and guide THz waves are key elements of any THz technology. In recent years, there has been much progress in their development. Notably, field-effect transistors (FETs) have been shown to be well suited for detector implementation at room temperature exploiting (self-)mixing effects in their channels [1]. They reach a typical noise-equivalent power (NEP) of several tens of pW/Hz^1/2 at 0.6 THz in CMOS and other technologies. First focal-plane arrays and cameras have been implemented. Frequency coverage to at least 5 THz has been demonstrated. Recently, this type of detection concept has been extended successfully to graphene-based FETs [2] opening the way to freely positionable THz detectors on a wide variety of substrates (also flexible plastics). We have improved the technology (see Fig. 1) [3] and reach, for GFETs on Si, an optical NEP of 150 pW/Hz^1/2 at 0.3 THz, with considerable room for improvement. An unusually strong thermoelectric contribution has been identified [2, 3] which may help to engineer enhanced detector performance.
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2.
  • Bauer, Maris, et al. (författare)
  • The potential for sensitivity enhancement by the thermoelectric effect in carbon-nanotube and graphene Tera-FETs
  • 2015
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 647:1, s. UNSP 012004-
  • Konferensbidrag (refereegranskat)abstract
    • We report on terahertz (THz) measurements with graphene field-effect transistors with integrated antennas (Tera-FETs) lay special emphasis on thermoelectric contributions to the detected THz photoresponse. Graphene Tera-FETs with integrated broad-band bow-tie antennas were fabricated in a CVD-based growth process and were successfully applied for detection at 600 GHz with optical NEPs down to 515 pW/Hz^1/2. While rectification of THz radiation by (distributed) resistive mixing of charge-density waves induced in the gated transistor channel region is well known, significant additional contributions to the detected signal have experimentally been observed and hot-carrier thermoelectric effects have been identified as a possible origin of these signals. We also observe similar signal contributions in carbonnanotube transistors.
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3.
  • Koh, J. H., et al. (författare)
  • Dielectric relaxation behavior of Ag(Ta,Nb)O-3 interdigital capacitors on oxide substrates
  • 2004
  • Ingår i: Japanese Journal of Applied Physics. - : IOP Publishing. - 0021-4922 .- 1347-4065. ; 43:4A, s. 1434-1437
  • Tidskriftsartikel (refereegranskat)abstract
    • The time-dependent dielectric relaxation behavior of Ag(Ta,Nb)O-3 interdigital capacitors was investigated for tunable device applications. Ag(Ta,Nb)03 thin films, which have high k-factor (tunability/ loss tangent), were deposited on the oxide substrates by pulsed laser deposition technique. Ag(Ta,Nb)03 thin film on the LaAlO3 substrate has an epitaxial relationship with the substrate. The observed tunabilities and K-factors of Ag(Ta,Nb)O-3/LaAlO3 and Ag(Ta,Nb)O-3/AI(2)O(3) interdigital capacitors were 5.9% and 17.8 and 3.8% and 9.9, respectively, at 40 V (maximum electric field of 100 kV/cm), 300 K, and 1 MHz. Capacitance relaxation follows the power law C(t) = C-infinity + C-0(t/ls)-(beta) with a very small exponent negligibly fitted in the time domain. Due to this small exponent, the capacitance was changed by less than 0.05% in 2V in 71 s. Time-dependent leakage current was measured by employing the Ag(Ta,Nb)O-3(0.4mum)/Al2O3 interdigital capacitor. The time-dependent relaxation current follows the power law j(t) = j(leak) +j(0)(t/ls)-(alpha) with an exponent alpha = 0-98, j(leak) = 1.14 x 10(-14), and j(0) = 11.42s.
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7.
  • Przewłoka, Aleksandra, et al. (författare)
  • Characterization of Silver Nanowire Layers in the Terahertz Frequency Range
  • 2021
  • Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 14:23, s. 7399-
  • 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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8.
  • Przewłoka, Aleksandra, et al. (författare)
  • Terahertz conductivity of silver nanowire networks
  • 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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9.
  • Zak, Audrey, 1990, et al. (författare)
  • 20 μm gate width CVD graphene FETs for 0.6 THz detection
  • 2014
  • Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - 2162-2027 .- 2162-2035. ; , s. Art. no. 6956250-
  • Konferensbidrag (refereegranskat)abstract
    • We have fabricated 20 μm gate width graphene field effect transistors (GFETs) based on graphene grown by chemical vapor deposition (CVD). These GFETs are integrated with split bow-tie antennae for room temperature, direct detection of a 0.6 THz signal. Our detectors reach a maximum optical responsivity of 3.0 V/W and a minimum noise-equivalent power (NEP) of 700 pW/Hz^0.5. The successful demonstration of THz detection using CVD graphene introduces the possibility for scalable detector production.
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10.
  • Zak, Audrey, 1990, et al. (författare)
  • Antenna-integrated 0.6 THz FET direct detectors based on CVD graphene
  • 2014
  • Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 14:10, s. 5834-5838
  • Tidskriftsartikel (refereegranskat)abstract
    • We present terahertz (THz) detectors based on top-gated graphene field effect transistors (GFETs) with integrated split-bow-tie antennas. The GFETs were fabricated using graphene grown by chemical vapor deposition (CVD). The THz detectors are capable of room-temperature rectification of a 0.6 THz signal and achieve a maximum optical responsivity better than 14 V/W and minimum optical noise-equivalent power (NEP) of 515 pW/Hz^0.5. Our results are a significant improvement over previous work on graphene direct detectors and are comparable to other established direct detector technologies. This is the first time room-temperature direct detection has been demonstrated using CVD graphene, which introduces the potential for scalable, wafer-level production of graphene detectors.
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