| 1. |
- Boschi, Alex, et al.
(författare)
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Mesoscopic 3D Charge Transport in Solution-Processed Graphene-Based Thin Films: A Multiscale Analysis
- 2023
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Ingår i: Small. - 1613-6810 .- 1613-6829. ; 19:42
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Tidskriftsartikel (refereegranskat)abstract
- Graphene and related 2D material (GRM) thin films consist of 3D assembly of billions of 2D nanosheets randomly distributed and interacting via van der Waals forces. Their complexity and the multiscale nature yield a wide variety of electrical characteristics ranging from doped semiconductor to glassy metals depending on the crystalline quality of the nanosheets, their specific structural organization ant the operating temperature. Here, the charge transport (CT) mechanisms are studied that are occurring in GRM thin films near the metal-insulator transition (MIT) highlighting the role of defect density and local arrangement of the nanosheets. Two prototypical nanosheet types are compared, i.e., 2D reduced graphene oxide and few-layer-thick electrochemically exfoliated graphene flakes, forming thin films with comparable composition, morphology and room temperature conductivity, but different defect density and crystallinity. By investigating their structure, morphology, and the dependence of their electrical conductivity on temperature, noise and magnetic-field, a general model is developed describing the multiscale nature of CT in GRM thin films in terms of hopping among mesoscopic bricks, i.e., grains. The results suggest a general approach to describe disordered van der Waals thin films.
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| 2. |
- Shetty, Naveen, 1988, et al.
(författare)
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Scalable Fabrication of Edge Contacts to 2D Materials : Implications for Quantum Resistance Metrology and 2D Electronics
- 2023
-
Ingår i: ACS Applied Nano Materials. - : American Chemical Society. - 2574-0970. ; 6:7, s. 6292-
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Tidskriftsartikel (refereegranskat)abstract
- We report a reliable and scalable fabrication method for producing electrical contacts to two-dimensional (2D) materials based on the tri-layer resist system. We demonstrate the applicability of this method in devices fabricated on epitaxial graphene on silicon carbide (epigraphene) used as a scalable 2D material platform. For epigraphene, data on nearly 70 contacts result in median values of the one-dimensional (1D) specific contact resistances ρc ∼ 67 Ω·μm and follow the Landauer quantum limit ρc ∼ n-1/2, consistently reaching values ρc < 50 Ω·μm at high carrier densityn. As a proof of concept, we apply the same fabrication method to the transition metal dichalcogenide (TMDC) molybdenum disulfide (MoS2). Our edge contacts enable MoS2 field-effect transistor (FET) behavior with an ON/OFF ratio of >106 at room temperature (>109 at cryogenic temperatures). The fabrication route demonstrated here allows for contact metallization using thermal evaporation and also by sputtering, giving an additional flexibility when designing electrical interfaces, which is key in practical devices and when exploring the electrical properties of emerging materials. © 2023 The Authors.
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| 3. |
- Charaev, Ilya, et al.
(författare)
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Single-photon detection using large-scale high-temperature MgB 2 sensors at 20 K
- 2024
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Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 15:1
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Tidskriftsartikel (refereegranskat)abstract
- Ultra-fast single-photon detectors with high current density and operating temperature can benefit space and ground applications, including quantum optical communication systems, lightweight cryogenics for space crafts, and medical use. Here we demonstrate magnesium diboride (MgB2) thin-film superconducting microwires capable of single-photon detection at 1.55 μm optical wavelength. We used helium ions to alter the properties of MgB2, resulting in microwire-based detectors exhibiting single-photon sensitivity across a broad temperature range of up to 20 K, and detection efficiency saturation for 1 μm wide microwires at 3.7 K. Linearity of detection rate vs incident power was preserved up to at least 100 Mcps. Despite the large active area of up to 400 × 400 μm2, the reset time was found to be as low as ~ 1 ns. Our research provides possibilities for breaking the operating temperature limit and maximum single-pixel count rate, expanding the detector area, and raises inquiries about the fundamental mechanisms of single-photon detection in high-critical-temperature superconductors.
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| 4. |
- Çlnar, Mustafa Neşet, et al.
(författare)
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Toward Optimized Charge Transport in Multilayer Reduced Graphene Oxides
- 2022
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 22:6, s. 2202-2208
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Tidskriftsartikel (refereegranskat)abstract
- In the context of graphene-based composite applications, a complete understanding of charge conduction in multilayer reduced graphene oxides (rGO) is highly desirable. However, these rGO compounds are characterized by multiple and different sources of disorder depending on the chemical method used for their synthesis. Most importantly, the precise role of interlayer interaction in promoting or jeopardizing electronic flow remains unclear. Here, thanks to the development of a multiscale computational approach combining first-principles calculations with large-scale transport simulations, the transport scaling laws in multilayer rGO are unraveled, explaining why diffusion worsens with increasing film thickness. In contrast, contacted films are found to exhibit an opposite trend when the mean free path becomes shorter than the channel length, since conduction becomes predominantly driven by interlayer hopping. These predictions are favorably compared with experimental data and open a road toward the optimization of graphene-based composites with improved electrical conduction.
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| 5. |
- Fabbri, Filippo, et al.
(författare)
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Silicene nanosheets intercalated in slightly defective epitaxial graphene on a 4H-SiC(0001) substrate
- 2022
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Ingår i: Surfaces and Interfaces. - : Elsevier BV. - 2468-0230. ; 33
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Tidskriftsartikel (refereegranskat)abstract
- In the last years, epitaxial graphene (epi-Gr) demonstrated to be an excellent substrate for the synthesis of epitaxial or intercalated two dimensional (2D) materials. Among 2D materials, silicene has been for a long time a dream for the scientific community, for its importance both from the fundamental and the application point of view. Despite the theoretical prediction of silicene energetic viability, experimentally the substrate proved to play a fundamental role in the Si atom adsorption process leading, in case of metal substrates, to a mixed phase formation and, for van der Waals chemical inert substrates, to Si atom intercalation even at room temperature. Such an intercalation has been associated to the presence of surface defects. Very recently it has been shown that hundreds of nanometer area quasi-free standing silicene can be grown on top of an almost ideal epi-Gr layer synthesized on 6H-SiC substrate. In the present paper, using scanning tunneling microscopy and Raman analysis, we demonstrate that a non-ideal (slightly defective) epi-Gr network obtained by thermal decomposition of Si-terminated 4H-SiC(0001) enables the Si atom penetration forming intercalated silicene nanosheets at room temperature, thus opening a path towards controlled intercalation of silicon atoms through epi-Gr and formation of silicene nanosheets for future applications in nanotechnology.
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| 6. |
- Ghasemi, Shima, 1993, et al.
(författare)
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Exploring the impact of select anchor groups for norbornadiene/quadricyclane single-molecule switches
- 2023
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Ingår i: Journal of Materials Chemistry C. - 2050-7534 .- 2050-7526. ; 11:44, s. 15379-15776
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Tidskriftsartikel (refereegranskat)abstract
- To achieve the ultimate limit of device miniaturization, it is necessary to have a comprehensive understanding of the structure–property relationship in functional molecular systems used in single-molecule electronics. This study reports the synthesis and characterization of a novel series of norbornadiene derivatives capped with thioether and thioester anchor groups. Utilizing the mechanically controllable break junction technique, the impact of these capping groups on conductance across single-molecule junctions is investigated. Among the selection of anchor groups, norbornadiene capped with thioacetate and tert-butyl groups exhibits higher conductance (G ≈ 4 × 10−4 G0) compared to methyl thioether (G ≈ 2 × 10−4 G0). Electronic transmission through the considered set of single-molecule junctions has been simulated. The computational results for electron transport across these junctions align closely with the experimental findings, with the thioacetate- and tert-butyl-substituted systems outperforming the methyl thioether-capped derivative. In terms of junction stability, the methyl thioether-capped system is the most resilient, maintaining consistent conductance even after approximately 10 000 cycles. Meanwhile, the likelihood of observing molecular plateaus in both the thioacetate- and tert-butyl-substituted systems declines over time. These findings substantially advance both the design and understanding of functional molecular systems in the realm of single-molecule electronics, particularly in the context of molecular photoswitches.
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| 7. |
- He, Hans, et al.
(författare)
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Accurate graphene quantum Hall arrays for the new International System of Units
- 2022
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Ingår i: Nature Communications. - : Nature Research. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Graphene quantum Hall effect (QHE) resistance standards have the potential to provide superior realizations of three key units in the new International System of Units (SI): the ohm, the ampere, and the kilogram (Kibble Balance). However, these prospects require different resistance values than practically achievable in single graphene devices (~12.9 kΩ), and they need bias currents two orders of magnitude higher than typical breakdown currents IC ~ 100 μA. Here we present experiments on quantization accuracy of a 236-element quantum Hall array (QHA), demonstrating RK/236 ≈ 109 Ω with 0.2 part-per-billion (nΩ/Ω) accuracy with IC ≥ 5 mA (~1 nΩ/Ω accuracy for IC = 8.5 mA), using epitaxial graphene on silicon carbide (epigraphene). The array accuracy, comparable to the most precise universality tests of QHE, together with the scalability and reliability of this approach, pave the road for wider use of graphene in the new SI and beyond. © 2022, The Author(s).
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| 8. |
- He, Hans, et al.
(författare)
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Highly efficient UV detection in a metal-semiconductor-metal detector with epigraphene
- 2022
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Ingår i: Applied Physics Letters. - : American Institute of Physics Inc.. - 0003-6951 .- 1077-3118. ; 120:19
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Tidskriftsartikel (refereegranskat)abstract
- We show that epitaxial graphene on silicon carbide (epigraphene) grown at high temperatures (T >1850 °C) readily acts as material for implementing solar-blind ultraviolet (UV) detectors with outstanding performance. We present centimeter-sized epigraphene metal-semiconductor-metal (MSM) detectors with a peak external quantum efficiency of η ∼85% for wavelengths λ = 250-280 nm, corresponding to nearly 100% internal quantum efficiency when accounting for reflection losses. Zero bias operation is possible in asymmetric devices, with the responsivity to UV remaining as high as R = 134 mA/W, making this a self-powered detector. The low dark currents Io ∼50 fA translate into an estimated record high specific detectivity D = 3.5 × 1015 Jones. The performance that we demonstrate, together with material reproducibility, renders epigraphene technologically attractive to implement high-performance planar MSM devices with a low processing effort, including multi-pixel UV sensor arrays, suitable for a number of practical applications. © 2022 Author(s).
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| 9. |
- He, Hans, 1989, et al.
(författare)
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The performance limits of epigraphene Hall sensors doped across the Dirac point
- 2020
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 116:22
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial graphene on silicon carbide, or epigraphene, provides an excellent platform for Hall sensing devices in terms of both high electrical quality and scalability. However, the challenge in controlling its carrier density has thus far prevented systematic studies of epigraphene Hall sensor performance. In this work, we investigate epigraphene Hall sensors where epigraphene is doped across the Dirac point using molecular doping. Depending on the carrier density, molecular-doped epigraphene Hall sensors reach room temperature sensitivities of S-V=0.23V/(VT) and S-I=1440V/(AT), with magnetic field detection limits down to B-MIN=27 nT/root Hz at 20kHz. Thermally stabilized devices demonstrate operation up to 150 degrees C with S-V=0.12V/(VT), S-I=300V/(AT), and B-MIN similar to 100 nT/root Hz at 20kHz. Our work demonstrates that epigraphene doped close to the Dirac point could potentially outperform III-V Hall elements in the extended and military temperature ranges.
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| 10. |
- Hinrichs, Karsten, et al.
(författare)
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Field Manipulation of Band Properties in Infrared Spectra of Thin Films
- 2023
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Ingår i: ADVANCED PHOTONICS RESEARCH. - 2699-9293. ; In Press
-
Tidskriftsartikel (refereegranskat)abstract
- This comprehensive optical study analyzes field manipulations of bands in infrared (IR) spectra of thin films and functional surfaces for varying measurement and sample conditions. Band variations related to the materials dielectric functions, the measurement geometry, the film thickness as well as the direction dependence of the probing electromagnetic fields are demonstrated. Examples are discussed for isotropic polymer films (approximate to 200 nm polymethylmethacrylate [PMMA]) on gold and silicon as well as an anisotropic hydrogen monolayer on a Si(111) surface, characterized by IR-attenuated total reflection, IR microscopy, and incidence-angle-dependent IR polarimetry. Even for fixed optical material properties, significant manipulations of band frequency and shape (shifts up to approximate to 14 cm-1 for PMMA, up to approximate to 3 cm-1 for H-Si) occur in not only polarization-dependent but also unpolarized spectra. The shown data underline that polarimetric measurements and optical analyses are essential for a detailed interpretation of band shapes. Field manipulations of bands in infrared spectra of thin films and functional surfaces are discussed. Examples are isotropic polymer films on gold and silicon as well as an anisotropic hydrogen monolayer on Si(111). Band variations relate to the materials dielectric functions, the measurement geometry, the film thickness as well as the polarization of the probing electromagnetic fields.image (c) 2023 WILEY-VCH GmbH
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| 11. |
- Iordanidou, Konstantina, 1989, et al.
(författare)
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Electric Field and Strain Tuning of 2D Semiconductor van der Waals Heterostructures for Tunnel Field-Effect Transistors
- 2023
-
Ingår i: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8252 .- 1944-8244. ; 15:1, s. 1762-1771
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Tidskriftsartikel (refereegranskat)abstract
- Heterostacks consisting of low-dimensional materials are attractive candidates for future electronic nanodevices in the post-silicon era. In this paper, using first-principles calculations based on density functional theory (DFT), we explore the structural and electronic properties of MoTe2/ZrS2 heterostructures with various stacking patterns and thicknesses. Our simulations show that the valence band (VB) edge of MoTe2 is almost aligned with the conduction band (CB) edge of ZrS2, and (MoTe2)m/(ZrS2)m (m = 1, 2) heterostructures exhibit the long-sought broken gap band alignment, which is pivotal for realizing tunneling transistors. Electrons are found to spontaneously flow from MoTe2 to ZrS2, and the system resembles an ultrascaled parallel plate capacitor with an intrinsic electric field pointed from MoTe2 to ZrS2. The effects of strain and external electric fields on the electronic properties are also investigated. For vertical compressive strains, the charge transfer increases due to the decreased coupling between the layers, whereas tensile strains lead to the opposite behavior. For negative electric fields a transition from the type-III to the type-II band alignment is induced. In contrast, by increasing the positive electric fields, a larger overlap between the valence and conduction bands is observed, leading to a larger band-to-band tunneling (BTBT) current. Low-strained heterostructures with various rotation angles between the constituent layers are also considered. We find only small variations in the energies of the VB and CB edges with respect to the Fermi level, for different rotation angles up to 30°. Overall, our simulations offer insights into the fundamental properties of low-dimensional heterostructures and pave the way for their future application in energy-efficient electronic nanodevices.
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| 12. |
- Karimi, Bayan, et al.
(författare)
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Electron-phonon coupling of epigraphene at millikelvin temperatures measured by quantum transport thermometry
- 2021
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 118:10
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the basic charge and heat transport properties of charge neutral epigraphene at sub-kelvin temperatures, demonstrating a nearly logarithmic dependence of electrical conductivity over more than two decades in temperature. Using graphene's sheet conductance as an in situ thermometer, we present a measurement of electron-phonon heat transport at mK temperatures and show that it obeys the T4 dependence characteristic for a clean two-dimensional conductor. Based on our measurement, we predict the noise-equivalent power of ∼ 10 - 22 W / Hz of the epigraphene bolometer at the low end of achievable temperatures.
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| 13. |
- Kim, Kyung Ho, 1984, et al.
(författare)
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Ambipolar charge transport in quasi-free-standing monolayer graphene on SiC obtained by gold intercalation
- 2020
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 102:16
-
Tidskriftsartikel (refereegranskat)abstract
- We present a study of quasi-free-standing monolayer graphene obtained by intercalation of Au atoms at the interface between the carbon buffer layer (Bu-L) and the silicon-terminated face (0001) of 4H-silicon carbide. Au intercalation is achieved by deposition of an atomically thin Au layer on the Bu-L followed by annealing at 850 °C in an argon atmosphere. We explore the intercalation of Au and decoupling of the Bu-L into quasi-free-standing monolayer graphene by surface science characterization and electron transport in top-gated electronic devices. By gate-dependent magnetotransport we find that the Au-intercalated buffer layer displays all properties of monolayer graphene, namely gate-tunable ambipolar transport across the Dirac point, but we find no observable enhancement of spin-orbit effects in the graphene layer, despite its proximity to the intercalated Au layer.
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| 14. |
- Kim, Kyung Ho, 1984, et al.
(författare)
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Chemical Sensing with Atomically Thin Platinum Templated by a 2D Insulator
- 2020
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Ingår i: Advanced Materials Interfaces. - : Wiley. - 2196-7350. ; 7:12
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Tidskriftsartikel (refereegranskat)abstract
- Boosting the sensitivity of solid‐state gas sensors by incorporating nanostructured materials as the active sensing element can be complicated by interfacial effects. Interfaces at nanoparticles, grains, or contacts may result in nonlinear current–voltage response, high electrical resistance, and ultimately, electric noise that limits the sensor read‐out. This work reports the possibility to prepare nominally one atom thin, electrically continuous platinum layers by physical vapor deposition on the carbon zero layer (also known as the buffer layer) grown epitaxially on silicon carbide. With a 3–4 Å thin Pt layer, the electrical conductivity of the metal is strongly modulated when interacting with chemical analytes, due to charges being transferred to/from Pt. The strong interaction with chemical species, together with the scalability of the material, enables the fabrication of chemiresistor devices for electrical read‐out of chemical species with sub part‐per‐billion (ppb) detection limits. The 2D system formed by atomically thin Pt on the carbon zero layer on SiC opens up a route for resilient and high sensitivity chemical detection, and can be the path for designing new heterogenous catalysts with superior activity and selectivity.
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| 15. |
- Kovtun, Alessandro, et al.
(författare)
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Multiscale Charge Transport in van der Waals Thin Films: Reduced Graphene Oxide as a Case Study
- 2021
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 15:2, s. 2654-2667
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Tidskriftsartikel (refereegranskat)abstract
- Large area van der Waals (vdW) thin films are assembled materials consisting of a network of randomly stacked nanosheets. The multiscale structure and the two-dimensional (2D) nature of the building block mean that interfaces naturally play a crucial role in the charge transport of such thin films. While single or few stacked nanosheets (i.e., vdW heterostructures) have been the subject of intensive works, little is known about how charges travel through multilayered, more disordered networks. Here, we report a comprehensive study of a prototypical system given by networks of randomly stacked reduced graphene oxide 2D nanosheets, whose chemical and geometrical properties can be controlled independently, permitting to explore percolated networks ranging from a single nanosheet to some billions with room-temperature resistivity spanning from 10-5 to 10-1 ω·m. We systematically observe a clear transition between two different regimes at a critical temperature T*: Efros-Shklovskii variable-range hopping (ES-VRH) below T∗ and power law behavior above. First, we demonstrate that the two regimes are strongly correlated with each other, both depending on the charge localization length ζ, calculated by the ES-VRH model, which corresponds to the characteristic size of overlapping sp2 domains belonging to different nanosheets. Thus, we propose a microscopic model describing the charge transport as a geometrical phase transition, given by the metal-insulator transition associated with the percolation of quasi-one-dimensional nanofillers with length ζ, showing that the charge transport behavior of the networks is valid for all geometries and defects of the nanosheets, ultimately suggesting a generalized description on vdW and disordered thin films.
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| 16. |
- Md Hoque, Anamul, 1988, et al.
(författare)
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Spin-valley coupling and spin-relaxation anisotropy in all-CVD Graphene- MoS2 van der Waals heterostructure
- 2023
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Ingår i: Physical Review Materials. - 2475-9953. ; 7:4
-
Tidskriftsartikel (refereegranskat)abstract
- Two-dimensional (2D) van der Waals (vdW) heterostructures fabricated by combining 2D materials with unique properties into one ultimate unit can offer a plethora of fundamental phenomena and practical applications. Recently, proximity-induced quantum and spintronic effects have been realized in heterostructures of graphene (Gr) with 2D semiconductors and their twisted systems. However, these studies are so far limited to exfoliated flake-based devices, limiting their potential for scalable practical applications. Here, we report spin-valley coupling and spin-relaxation anisotropy in Gr-MoS2 heterostructure devices prepared from scalable chemical vapor-deposited (CVD) 2D materials. Spin precession and dynamics measurements reveal an enhanced spin-orbit coupling strength in the Gr-MoS2 heterostructure in comparison with pristine Gr at room temperature. Consequently, large spin-relaxation anisotropy is observed in the heterostructure, providing a method for spin filtering due to spin-valley coupling. These findings open a scalable platform for all-CVD 2D vdW heterostructures design and their device applications.
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| 17. |
- Polley, Craig Michael, 1984, et al.
(författare)
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Bottom-Up Growth of Monolayer Honeycomb SiC
- 2023
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 1079-7114 .- 0031-9007. ; 130:7
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Tidskriftsartikel (refereegranskat)abstract
- The long theorized two-dimensional allotrope of SiC has remained elusive amid the exploration of graphenelike honeycomb structured monolayers. It is anticipated to possess a large direct band gap (2.5 eV), ambient stability, and chemical versatility. While sp2 bonding between silicon and carbon is energetically favorable, only disordered nanoflakes have been reported to date. Here we demonstrate large-area, bottom-up synthesis of monocrystalline, epitaxial monolayer honeycomb SiC atop ultrathin transition metal carbide films on SiC substrates. We find the 2D phase of SiC to be almost planar and stable at high temperatures, up to 1200 °C in vacuum. Interactions between the 2D-SiC and the transition metal carbide surface result in a Dirac-like feature in the electronic band structure, which in the case of a TaC substrate is strongly spin-split. Our findings represent the first step towards routine and tailored synthesis of 2D-SiC monolayers, and this novel heteroepitaxial system may find diverse applications ranging from photovoltaics to topological superconductivity.
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| 18. |
- Shetty, Naveen, 1988, et al.
(författare)
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Long-term stability of molecular doped epigraphene quantum Hall standards: single elements and large arrays (R K/236 ≈ 109 Ω)
- 2023
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Ingår i: Metrologia. - : Institute of Physics. - 0026-1394 .- 1681-7575. ; 60:5
-
Tidskriftsartikel (refereegranskat)abstract
- In this work we investigate the long-term stability of epitaxial graphene (epigraphene) quantum Hall resistance standards, including single devices and an array device composed of 236 elements providing R K/236 ≈ 109 Ω, with R K the von Klitzing constant. All devices utilize the established technique of chemical doping via molecular dopants to achieve homogenous doping and control over carrier density. However, optimal storage conditions and the long-term stability of molecular dopants for metrological applications have not been widely studied. In this work we aim to identify simple storage techniques that use readily available and cost-effective materials which provide long-term stability for devices without the need for advanced laboratory equipment. The devices are stored in glass bottles with four different environments: ambient, oxygen absorber, silica gel desiccant, and oxygen absorber/desiccant mixture. We have tracked the carrier densities, mobilities, and quantization accuracies of eight different epigraphene quantum Hall chips for over two years. We observe the highest stability (i.e. lowest change in carrier density) for samples stored in oxygen absorber/desiccant mixture, with a relative change in carrier density below 0.01% per day and no discernable degradation of quantization accuracy at the part-per-billion level. This storage technique yields a comparable stability to the currently established best storage method of inert nitrogen atmosphere, but it is much easier to realize in practice. It is possible to further optimize the mixture of oxygen absorber/desiccant for even greater stability performance in the future. We foresee that this technique can allow for simple and stable long-term storage of polymer-encapsulated molecular doped epigraphene quantum Hall standards, removing another barrier for their wide-spread use in practical metrology.
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| 19. |
- Shetty, Naveen, 1988, et al.
(författare)
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Ultralow 1/f noise in epigraphene devices
- 2024
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 124:9
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Tidskriftsartikel (refereegranskat)abstract
- We report the lowest recorded levels of 1/ f noise for graphene-based devices, at the level of S V / V 2 = S I / I 2 = 4.4 × 10 − 16 (1/Hz), measured at f = 10 Hz ( S V / V 2 = S I / I 2 < 10 − 16 1/Hz for f > 100 Hz) in large-area epitaxial graphene on silicon carbide (epigraphene) Hall sensors. This performance is made possible through the combination of high material quality, low contact resistance achieved by edge contact fabrication process, homogeneous doping, and stable passivation of the graphene layer. Our study explores the nature of 1/ f noise as a function of carrier density and device geometry and includes data from Hall sensors with device area range spanning over six orders of magnitude, with characteristic device length ranging from L = 1 μm to 1 mm. In optimized graphene Hall sensors, we demonstrate arrays to be a viable route to improve further the magnetic field detection: a simple parallel connection of two devices displays record-high magnetic field sensitivity at room temperature, with minimum detectable magnetic field levels down to B min = 9.5 nT/√Hz. The remarkable low levels of 1/ f noise observed in epigraphene devices hold immense capacity for the design and fabrication of scalable epigraphene-based sensors with exceptional performance.
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| 20. |
- Shetty, Naveen, 1988, et al.
(författare)
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Ultralow 1/f noise in epigraphene devices
- 2024
-
Ingår i: Applied Physics Letters. - : American Institute of Physics Inc.. - 0003-6951 .- 1077-3118. ; 124:9
-
Tidskriftsartikel (refereegranskat)abstract
- We report the lowest recorded levels of 1/ f noise for graphene-based devices, at the level of S V / V 2 = S I / I 2 = 4.4 × 10 − 16 (1/Hz), measured at f = 10 Hz ( S V / V 2 = S I / I 2 < 10 − 16 1/Hz for f > 100 Hz) in large-area epitaxial graphene on silicon carbide (epigraphene) Hall sensors. This performance is made possible through the combination of high material quality, low contact resistance achieved by edge contact fabrication process, homogeneous doping, and stable passivation of the graphene layer. Our study explores the nature of 1/ f noise as a function of carrier density and device geometry and includes data from Hall sensors with device area range spanning over six orders of magnitude, with characteristic device length ranging from L = 1 μm to 1 mm. In optimized graphene Hall sensors, we demonstrate arrays to be a viable route to improve further the magnetic field detection: a simple parallel connection of two devices displays record-high magnetic field sensitivity at room temperature, with minimum detectable magnetic field levels down to B min = 9.5 nT/√Hz. The remarkable low levels of 1/ f noise observed in epigraphene devices hold immense capacity for the design and fabrication of scalable epigraphene-based sensors with exceptional performance. © 2024 Author(s).
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| 21. |
- Shtepliuk, Ivan, et al.
(författare)
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Clustering and Morphology Evolution of Gold on Nanostructured Surfaces of Silicon Carbide: Implications for Catalysis and Sensing
- 2021
-
Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 4:2, s. 1282-1293
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Tidskriftsartikel (refereegranskat)abstract
- A fundamental understanding of the behavior of gold (Au) nanostructures deposited on functional surfaces is imperative to discover and leverage interface-related phenomena that can boost the efficiency of existing electronic devices in sensorics, catalysis, and spintronics. In the present work, Au layers with nominal thickness of 2 nm were sputter-deposited on graphenized SiC substrates represented by buffer layer (BuL)/4H-SiC and monolayer epitaxial graphene (MLG)/4H-SiC. Morphometric analysis by means of scanning electron microscopy shows that Au on BuL self-assembles in nearly round-shaped plasmonically active islands, while on MLG, a fractal growth of considerably larger and ramified islands is observed. To correlate the experimentally established differences in surface morphology on the two types of graphenized substrates with energetics and kinetics of Au nanostructure growth, the deposit-substrate interaction strength was studied using density functional theory (DFT) calculations, molecular dynamics simulations, and optical measurements. The theoretical considerations involve participation of Au clusters with different sizes and energetics at the initial stages of the metal nanostructure formation. The results indicate that gold exhibits a considerably stronger interaction with BuL than with MLG, which can be considered as a key aspect for explaining the experimentally observed morphological differences. From the statistical analysis of Raman spectra, indications of Au intercalation of MLG are discussed. The current research shows that, due to its unique surface chemistry, buffer layer has peculiar affinity to gold when compared to other atomically flat surfaces, which is beneficial for boosting high-performance catalytic and sensing technologies based on low-dimensional materials.
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