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| 3. |
- Tzalenchuk, Alexander, et al.
(author)
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Engineering and metrology of epitaxial graphene
- 2011
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In: Solid State Communications. - : Elsevier. - 0038-1098 .- 1879-2766. ; 151:16, s. 1094-1099
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Journal article (peer-reviewed)abstract
- ere we review the concepts and technologies, in particular photochemical gating, which contributed to the recent progress in quantum Hall resistance metrology based on large scale epitaxial graphene on silicon carbide.
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| 4. |
- Adamyan, Astghik, 1984, et al.
(author)
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Kinetic inductance as a microwave circuit design variable by multilayer fabrication
- 2015
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In: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 28:8
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Journal article (peer-reviewed)abstract
- We report on the development of a reliable NbN/Al/Nb/NbN multilayer fabrication technique for combining design elements with and without kinetic inductance in superconducting microwave circuits. As a proof-of-concept we demonstrate the application of the proposed technique to build a slow microwave propagation line matched to 50 Ω terminals. Fabrication details along with the design and measurements are discussed. At 8 GHz the presented device operates as a dc controllable full-turn phase shifter. We suggest that by exploiting the kinetic inductance as a design variable one can greatly improve operation parameters for a variety of standard microwave designs such as step-impedance filters and resonators.
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| 5. |
- Adamyan, Astghik, 1984, et al.
(author)
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Superconducting microwave parametric amplifier based on a quasi-fractal slow propagation line
- 2016
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In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 119:8
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Journal article (peer-reviewed)abstract
- Quantum limited amplifiers are sought after for a wide range of applications within quantum technologies and sensing. One promising candidate is the travelling wave parametric amplifier which exploits the non-linear kinetic inductance of a superconducting transmission line. This type of microwave amplifier promises to deliver a high gain, a quantum limited noise performance over several GHz bandwidth, and a high dynamic range. However, practical realizations of this type of device have so far been limited by fabrication defects, since the length of the superconducting transmission line required for achieving substantial parametric gain is on the order of similar to 1m. Here, we report on a design for a microwave traveling wave amplifier based on a slow propagation line comprising a central strip with high kinetic inductance and quasi-fractal line-to-ground capacitors. Due to an enhanced per unit length inductance (73 nH cm(-1)) and capacitance (15 pF cm(-1)), the line has a microwave propagation velocity as low as 9.8 x 10(8) cm s(-1). This translates into parametric gain up to 0.5 dB cm(-1) and a total gain of 6 dB for just a similar to 10 cm long transmission line. Moreover, the flexibility of the presented design allows balancing the line inductance and capacitance in order to keep the characteristic impedance close to 50 Omega and to suppress standing waves, both factors being essential in order to implement a practical parametric amplifier in the microwave domain.
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| 6. |
- Adamyan, Astghik, 1984, et al.
(author)
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Tunable superconducting microstrip resonators
- 2016
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 108:17
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Journal article (peer-reviewed)abstract
- We report on a simple yet versatile design for a tunable superconducting microstrip resonator. Niobium nitride is employed as the superconducting material and aluminum oxide, produced by atomic layer deposition, as the dielectric layer. We show that the high quality of the dielectric material allows to reach the internal quality factors in the order of Q(i) similar to 10(4) in the single photon regime. Q(i) rapidly increases with the number of photons in the resonator N and exceeds 10(5) for N similar to 10 - 50. A straightforward modification of the basic microstrip design allows to pass a current bias through the strip and to control its kinetic inductance. We achieve a frequency tuning delta f = 62 MHz around f(0) = 2.4 GHz for a fundamental mode and delta f = 164MHz for a third harmonic. This translates into a tuning parameter Q(i)delta f/f(0) = 150. The presented design can be incorporated into essentially any superconducting circuitry operating at temperatures below 2.5K.
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| 7. |
- Ahlers, F.J., et al.
(author)
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The EMRP project GraphOhm- Towards quantum resistance metrology based on graphene
- 2014
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In: CPEM Digest (Conference on Precision Electromagnetic Measurements). - 0589-1485. - 9781479952052 ; , s. 548-549, s. 548-549
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Conference paper (peer-reviewed)abstract
- A new joint research project (JRP) integrating metrology institutes and universities from nine countries is aimed at realization of a new generation of standards for quantum resistance metrology. The project exploits graphene's properties to simplify operation of standards without compromising the unprecedented precision delivered by semiconductor quantum Hall devices. Higher operating temperatures (above 4.2 K, and up to 8 K) and together with lower magnetic fields (below 5 T, and potentially down to 2 T) will lead to a significantly improved and cost-saving dissemination of intrinsically referenced resistance standards to all end-users relying on electrical measurements.
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| 8. |
- Alexander-Webber, J. A., et al.
(author)
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Giant quantum Hall plateaus generated by charge transfer in epitaxial graphene
- 2016
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 6
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Journal article (peer-reviewed)abstract
- Epitaxial graphene has proven itself to be the best candidate for quantum electrical resistance standards due to its wide quantum Hall plateaus with exceptionally high breakdown currents. However one key underlying mechanism, a magnetic field dependent charge transfer process, is yet to be fully understood. Here we report measurements of the quantum Hall effect in epitaxial graphene showing the widest quantum Hall plateau observed to date extending over 50 T, attributed to an almost linear increase in carrier density with magnetic field. This behaviour is strong evidence for field dependent charge transfer from charge reservoirs with exceptionally high densities of states in close proximity to the graphene. Using a realistic framework of broadened Landau levels we model the densities of donor states and predict the field dependence of charge transfer in excellent agreement with experimental results, thus providing a guide towards engineering epitaxial graphene for applications such as quantum metrology.
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| 9. |
- Alexander-Webber, J. A., et al.
(author)
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Phase Space for the Breakdown of the Quantum Hall Effect in Epitaxial Graphene
- 2013
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In: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 111:9, s. e096601-
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Journal article (peer-reviewed)abstract
- We report the phase space defined by the quantum Hall effect breakdown in polymer gated epitaxial graphene on SiC (SiC/G) as a function of temperature, current, carrier density, and magnetic fields up to 30 T. At 2 K, breakdown currents (Ic) almost 2 orders of magnitude greater than in GaAs devices are observed. The phase boundary of the dissipationless state (ρxx=0) shows a [1-(T/Tc)2] dependence and persists up to Tc>45 K at 29 T. With magnetic field Ic was found to increase ∝B3/2 and Tc∝B2. As the Fermi energy approaches the Dirac point, the ν=2 quantized Hall plateau appears continuously from fields as low as 1 T up to at least 19 T due to a strong magnetic field dependence of the carrier density.
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| 10. |
- Andzane, J., et al.
(author)
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Application of Tuning Fork Sensors for In-situ Studies of Dynamic Force Interactions Inside Scanning and Transmission Electron Microscopes
- 2012
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In: Medziagotyra. - : Kaunas University of Technology (KTU). - 1392-1320. ; 18:2, s. 197-201
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Journal article (peer-reviewed)abstract
- Mechanical properties of nanoscale contacts have been probed in-situ by specially developed force sensor based on a quartz tuning fork resonator (TF). Additional control is provided by observation of process in scanning electron microscope (SEM) and transmission electron microscope (TEM). A piezoelectric manipulator allows precise positioning of atomic force microscope (AFM) probe in contact with another electrode and recording of the IF oscillation amplitude and phase while simultaneously visualizing the contact area in electron microscope. Electrostatic control of interaction between the electrodes is demonstrated during observation of the experiment in SEM. In the TEM system the TF sensor operated in shear force mode: Use of TEM allowed for direct control of separation between electrodes. New opportunities for in situ studies of nanomechanical systems using these instruments are discussed.
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