Nanomaterials

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2 pages, 190 KiB

Open AccessEditorial

Superconducting- and Graphene-Based Devices

by Filippo Giubileo

Nanomaterials 2022, 12(12), 2055; https://0-doi-org.brum.beds.ac.uk/10.3390/nano12122055 - 15 Jun 2022

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Abstract

This Special Issue has been organized to collect new or improved ideas regarding the exploitation of superconducting materials, as well as graphene, aiming to develop innovative devices [...] Full article

(This article belongs to the Special Issue Superconducting- and Graphene-based Devices)

Research

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17 pages, 2904 KiB

Open AccessArticle

Lithium Diffusion in Silicon Encapsulated with Graphene

by Wei Qin, Wen-Cai Lu, Xu-Yan Xue, Kai-Ming Ho and Cai-Zhuang Wang

Nanomaterials 2021, 11(12), 3397; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11123397 - 15 Dec 2021

Cited by 3 | Viewed by 2054

Abstract

The model of a graphene (Gr) sheet putting on a silicon (Si) substrate is used to simulate the structures of Si microparticles wrapped up in a graphene cage, which may be the anode of lithium-ion batteries (LIBS) to improve the high-volume expansion of [...] Read more.

The model of a graphene (Gr) sheet putting on a silicon (Si) substrate is used to simulate the structures of Si microparticles wrapped up in a graphene cage, which may be the anode of lithium-ion batteries (LIBS) to improve the high-volume expansion of Si anode materials. The common low-energy defective graphene (d–Gr) structures of DV5–8–5, DV555–777 and SV are studied and compared with perfect graphene (p–Gr). First-principles calculations are performed to confirm the stable structures before and after Li penetrating through the Gr sheet or graphene/Si-substrate (Gr/Si) slab. The climbing image nudged elastic band (CI-NEB) method is performed to evaluate the diffusion barrier and seek the saddle point. The calculation results reveal that the d–Gr greatly reduces the energy barriers for Li diffusion in Gr or Gr/Si. The energy stability, structural configuration, bond length between the atoms and layer distances of these structures are also discussed in detail. Full article

(This article belongs to the Special Issue Superconducting- and Graphene-based Devices)

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18 pages, 8324 KiB

Open AccessArticle

Interface Kinetics Assisted Barrier Removal in Large Area 2D-WS₂ Growth to Facilitate Mass Scale Device Production

by Abid, Poonam Sehrawat, Christian M. Julien and Saikh S. Islam

Nanomaterials 2021, 11(1), 220; https://0-doi-org.brum.beds.ac.uk/10.3390/nano11010220 - 16 Jan 2021

Cited by 3 | Viewed by 2251

Abstract

Growth of monolayer WS₂ of domain size beyond few microns is a challenge even today; and it is still restricted to traditional exfoliation techniques, with no control over the dimension. Here, we present the synthesis of mono- to few layer WS₂ [...] Read more.

Growth of monolayer WS₂ of domain size beyond few microns is a challenge even today; and it is still restricted to traditional exfoliation techniques, with no control over the dimension. Here, we present the synthesis of mono- to few layer WS₂ film of centimeter² size on graphene-oxide (GO) coated Si/SiO₂ substrate using the chemical vapor deposition CVD technique. Although the individual size of WS₂ crystallites is found smaller, the joining of grain boundaries due to sp²-bonded carbon nanostructures (~3–6 nm) in GO to reduced graphene-oxide (RGO) transformed film, facilitates the expansion of domain size in continuous fashion resulting in full coverage of the substrate. Another factor, equally important for expanding the domain boundary, is surface roughness of RGO film. This is confirmed by conducting WS₂ growth on Si wafer marked with few scratches on polished surface. Interestingly, WS₂ growth was observed in and around the rough surface irrespective of whether polished or unpolished. More the roughness is, better the yield in crystalline WS₂ flakes. Raman mapping ascertains the uniform mono-to-few layer growth over the entire substrate, and it is reaffirmed by photoluminescence, AFM and HRTEM. This study may open up a new approach for growth of large area WS₂ film for device application. We have also demonstrated the potential of the developed film for photodetector application, where the cycling response of the detector is highly repetitive with negligible drift. Full article

(This article belongs to the Special Issue Superconducting- and Graphene-based Devices)

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16 pages, 2589 KiB

Open AccessArticle

Transport and Point Contact Measurements on Pr_1−xCe_xPt₄Ge₁₂ Superconducting Polycrystals

by Paola Romano, Francesco Avitabile, Angela Nigro, Gaia Grimaldi, Antonio Leo, Lei Shu, Jian Zhang, Antonio Di Bartolomeo and Filippo Giubileo

Nanomaterials 2020, 10(9), 1810; https://0-doi-org.brum.beds.ac.uk/10.3390/nano10091810 - 10 Sep 2020

Cited by 2 | Viewed by 2259

Abstract

We performed a detailed investigation of the superconducting properties of polycrystalline Pr_1−xCe_xPt₄Ge₁₂ pellets. We report the effect of Ce substitution, for x = 0.07, on magnetic field phase diagram H-T. We demonstrate that the upper critical [...] Read more.

We performed a detailed investigation of the superconducting properties of polycrystalline Pr_1−xCe_xPt₄Ge₁₂ pellets. We report the effect of Ce substitution, for x = 0.07, on magnetic field phase diagram H-T. We demonstrate that the upper critical field is well described by the Ginzburg–Landau model and that the irreversibility field line has a scaling behaviour similar to cuprates. We also show that for magnetic fields lower than 0.4 T, the activation energy follows a power law of the type ?^−1/2, suggesting a collective pinning regime with a quasi-2D character for the Ce-doped compound with x = 0.07. Furthermore, by means of a point contact Andreev reflection spectroscopy setup, we formed metal/superconductor nano-junctions as small as tens of nanometers on the PrPt₄Ge₁₂ parent compound (x = 0). Experimental results showed a wide variety of conductance features appearing in the dI/dV vs. V spectra, all explained in terms of a modified Blonder–Tinkham–Klapwijk model considering a superconducting order parameter with nodal directions as well as sign change in the momentum space for the sample with x = 0. The numerical simulations of the conductance spectra also demonstrate that s-wave pairing and anisotropic s-waves are unsuitable for reproducing experimental data obtained at low temperature on the un-doped compound. Interestingly, we show that the polycrystalline nature of the superconducting PrPt₄Ge₁₂ sample can favour the formation of an inter-grain Josephson junction in series with the point contact junction in this kind of experiments. Full article

(This article belongs to the Special Issue Superconducting- and Graphene-based Devices)

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12 pages, 4513 KiB

Open AccessFeature PaperArticle

Iron-Based Superconducting Nanowires: Electric Transport and Voltage-Noise Properties

by Sergio Pagano, Nadia Martucciello, Emanuele Enrico, Eugenio Monticone, Kazumasa Iida and Carlo Barone

Nanomaterials 2020, 10(5), 862; https://0-doi-org.brum.beds.ac.uk/10.3390/nano10050862 - 30 Apr 2020

Cited by 15 | Viewed by 2999

Abstract

The discovery of iron-based superconductors paved the way for advanced possible applications, mostly in high magnetic fields, but also in electronics. Among superconductive devices, nanowire detectors have raised a large interest in recent years, due to their ability to detect a single photon [...] Read more.

The discovery of iron-based superconductors paved the way for advanced possible applications, mostly in high magnetic fields, but also in electronics. Among superconductive devices, nanowire detectors have raised a large interest in recent years, due to their ability to detect a single photon in the visible and infrared (IR) spectral region. Although not yet optimal for single-photon detection, iron-based superconducting nanowire detectors would bring clear advantages due to their high operating temperature, also possibly profiting of other peculiar material properties. However, there are several challenges yet to be overcome, regarding mainly: fabrication of ultra-thin films, appropriate passivation techniques, optimization of nano-patterning, and high-quality electrical contacts. Test nanowire structures, made by ultra-thin films of Co-doped BaFe₂As₂, have been fabricated and characterized in their transport and intrinsic noise properties. The results on the realized nanostructures show good properties in terms of material resistivity and critical current. Details on the fabrication and low temperature characterization of the realized nanodevices are presented, together with a study of possible degradation phenomena induced by ageing effects. Full article

(This article belongs to the Special Issue Superconducting- and Graphene-based Devices)

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12 pages, 2423 KiB

Open AccessArticle

Current-Resistance Effects Inducing Nonlinear Fluctuation Mechanisms in Granular Aluminum Oxide Nanowires

by Carlo Barone, Hannes Rotzinger, Jan Nicolas Voss, Costantino Mauro, Yannick Schön, Alexey V. Ustinov and Sergio Pagano

Nanomaterials 2020, 10(3), 524; https://0-doi-org.brum.beds.ac.uk/10.3390/nano10030524 - 14 Mar 2020

Cited by 12 | Viewed by 2934

Abstract

The unusual superconducting properties of granular aluminum oxide have been recently investigated for application in quantum circuits. However, the intrinsic irregular structure of this material requires a good understanding of the transport mechanisms and, in particular, the effect of disorder, especially when patterned [...] Read more.

The unusual superconducting properties of granular aluminum oxide have been recently investigated for application in quantum circuits. However, the intrinsic irregular structure of this material requires a good understanding of the transport mechanisms and, in particular, the effect of disorder, especially when patterned at the nanoscale level. In view of these aspects, electric transport and voltage fluctuations have been investigated on thin-film based granular aluminum oxide nanowires, in the normal state and at temperatures between 8 and 300 K. The nonlinear resistivity and two-level tunneling fluctuators have been observed. Regarding the nature of the noise processes, the experimental findings give a clear indication in favor of a dynamic random resistor network model, rather than the possible existence of a local ordering of magnetic origin. The identification of the charge carrier fluctuations in the normal state of granular aluminum oxide nanowires is very useful for improving the fabrication process and, therefore, reducing the possible sources of decoherence in the superconducting state, where quantum technologies that are based on these nanostructures should work. Full article

(This article belongs to the Special Issue Superconducting- and Graphene-based Devices)

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20 pages, 626 KiB

Open AccessArticle

Calculations of Some Doping Nanostructurations and Patterns Improving the Functionality of High-Temperature Superconductors for Bolometer Device Applications

by Jose C. Verde, Alberto S. Viz, Martín M. Botana, Carlos Montero-Orille and Manuel V. Ramallo

Nanomaterials 2020, 10(1), 97; https://0-doi-org.brum.beds.ac.uk/10.3390/nano10010097 - 03 Jan 2020

Cited by 1 | Viewed by 2477

Abstract

We calculate the effects of doping nanostructuration and the patterning of thin films of high-temperature superconductors (HTS) with the aim of optimizing their functionality as sensing materials for resistive transition-edge bolometer devices (TES). We focus, in particular, on spatial variations of the carrier [...] Read more.

We calculate the effects of doping nanostructuration and the patterning of thin films of high-temperature superconductors (HTS) with the aim of optimizing their functionality as sensing materials for resistive transition-edge bolometer devices (TES). We focus, in particular, on spatial variations of the carrier doping into the CuO

_{2}

layers due to oxygen off-stoichiometry, (that induce, in turn, critical temperature variations) and explore following two major cases of such structurations: First, the random nanoscale disorder intrinsically associated to doping levels that do not maximize the superconducting critical temperature; our studies suggest that this first simple structuration already improves some of the bolometric operational parameters with respect to the conventional, nonstructured HTS materials used until now. Secondly, we consider the imposition of regular arrangements of zones with different nominal doping levels (patterning); we find that such regular patterns may improve the bolometer performance even further. We find one design that improves, with respect to nonstructured HTS materials, both the saturation power and the operating temperature width by more than one order of magnitude. It also almost doubles the response of the sensor to radiation. Full article

(This article belongs to the Special Issue Superconducting- and Graphene-based Devices)

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12 pages, 530 KiB

Open AccessArticle

GFET Asymmetric Transfer Response Analysis through Access Region Resistances

by Alejandro Toral-Lopez, Enrique G. Marin, Francisco Pasadas, Jose Maria Gonzalez-Medina, Francisco G. Ruiz, David Jiménez and Andres Godoy

Nanomaterials 2019, 9(7), 1027; https://0-doi-org.brum.beds.ac.uk/10.3390/nano9071027 - 18 Jul 2019

Cited by 9 | Viewed by 2870

Abstract

Graphene-based devices are planned to augment the functionality of Si and III-V based technology in radio-frequency (RF) electronics. The expectations in designing graphene field-effect transistors (GFETs) with enhanced RF performance have attracted significant experimental efforts, mainly concentrated on achieving high mobility samples. However, [...] Read more.

Graphene-based devices are planned to augment the functionality of Si and III-V based technology in radio-frequency (RF) electronics. The expectations in designing graphene field-effect transistors (GFETs) with enhanced RF performance have attracted significant experimental efforts, mainly concentrated on achieving high mobility samples. However, little attention has been paid, so far, to the role of the access regions in these devices. Here, we analyse in detail, via numerical simulations, how the GFET transfer response is severely impacted by these regions, showing that they play a significant role in the asymmetric saturated behaviour commonly observed in GFETs. We also investigate how the modulation of the access region conductivity (i.e., by the influence of a back gate) and the presence of imperfections in the graphene layer (e.g., charge puddles) affects the transfer response. The analysis is extended to assess the application of GFETs for RF applications, by evaluating their cut-off frequency. Full article

(This article belongs to the Special Issue Superconducting- and Graphene-based Devices)

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