Nanomaterials

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3 pages, 187 KiB

Open AccessEditorial

Novel Research in Low-Dimensional Systems

by Orion Ciftja

Nanomaterials 2023, 13(2), 364; https://doi.org/10.3390/nano13020364 - 16 Jan 2023

Cited by 4 | Viewed by 984

Abstract

Low-dimensional systems exhibit unique properties that have attracted considerable attention during the last few decades [...] Full article

(This article belongs to the Special Issue Novel Research in Low-Dimensional Systems)

Research

Jump to: Editorial

18 pages, 2497 KiB

Open AccessArticle

Complex Phase-Fluctuation Effects Correlated with Granularity in Superconducting NbN Nanofilms

by Meenakshi Sharma, Manju Singh, Rajib K. Rakshit, Surinder P. Singh, Matteo Fretto, Natascia De Leo, Andrea Perali and Nicola Pinto

Nanomaterials 2022, 12(23), 4109; https://doi.org/10.3390/nano12234109 - 22 Nov 2022

Cited by 5 | Viewed by 1530

Abstract

Superconducting nanofilms are tunable systems that can host a 3D–2D dimensional crossover leading to the Berezinskii–Kosterlitz–Thouless (BKT) superconducting transition approaching the 2D regime. Reducing the dimensionality further, from 2D to quasi-1D superconducting nanostructures with disorder, can generate quantum and thermal phase slips (PS) [...] Read more.

Superconducting nanofilms are tunable systems that can host a 3D–2D dimensional crossover leading to the Berezinskii–Kosterlitz–Thouless (BKT) superconducting transition approaching the 2D regime. Reducing the dimensionality further, from 2D to quasi-1D superconducting nanostructures with disorder, can generate quantum and thermal phase slips (PS) of the order parameter. Both BKT and PS are complex phase-fluctuation phenomena of difficult experiments. We characterized superconducting NbN nanofilms thinner than 15 nm, on different substrates, by temperature-dependent resistivity and current–voltage (I-V) characteristics. Our measurements evidence clear features related to the emergence of BKT transition and PS events. The contemporary observation in the same system of BKT transition and PS events, and their tunable evolution in temperature and thickness was explained as due to the nano-conducting paths forming in a granular NbN system. In one of the investigated samples, we were able to trace and characterize the continuous evolution in temperature from quantum to thermal PS. Our analysis established that the detected complex phase phenomena are strongly related to the interplay between the typical size of the nano-conductive paths and the superconducting coherence length. Full article

(This article belongs to the Special Issue Novel Research in Low-Dimensional Systems)

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18 pages, 15281 KiB

Open AccessArticle

Causes and Consequences of Ordering and Dynamic Phases of Confined Vortex Rows in Superconducting Nanostripes

by Benjamin McNaughton, Nicola Pinto, Andrea Perali and Milorad V. Milošević

Nanomaterials 2022, 12(22), 4043; https://doi.org/10.3390/nano12224043 - 17 Nov 2022

Cited by 3 | Viewed by 1455

Abstract

Understanding the behaviour of vortices under nanoscale confinement in superconducting circuits is important for the development of superconducting electronics and quantum technologies. Using numerical simulations based on the Ginzburg–Landau theory for non-homogeneous superconductivity in the presence of magnetic fields, we detail how lateral [...] Read more.

Understanding the behaviour of vortices under nanoscale confinement in superconducting circuits is important for the development of superconducting electronics and quantum technologies. Using numerical simulations based on the Ginzburg–Landau theory for non-homogeneous superconductivity in the presence of magnetic fields, we detail how lateral confinement organises vortices in a long superconducting nanostripe, presenting a phase diagram of vortex configurations as a function of the stripe width and magnetic field. We discuss why the average vortex density is reduced and reveal that confinement influences vortex dynamics in the dissipative regime under sourced electrical current, mapping out transitions between asynchronous and synchronous vortex rows crossing the nanostripe as the current is varied. Synchronous crossings are of particular interest, since they cause single-mode modulations in the voltage drop along the stripe in a high (typically GHz to THz) frequency range. Full article

(This article belongs to the Special Issue Novel Research in Low-Dimensional Systems)

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20 pages, 3225 KiB

Open AccessArticle

Novel InGaSb/AlP Quantum Dots for Non-Volatile Memories

by Demid S. Abramkin and Victor V. Atuchin

Nanomaterials 2022, 12(21), 3794; https://doi.org/10.3390/nano12213794 - 27 Oct 2022

Cited by 11 | Viewed by 1498

Abstract

Non-volatile memories based on the flash architecture with self-assembled III–V quantum dots (SAQDs) used as a floating gate are one of the prospective directions for universal memories. The central goal of this field is the search for a novel SAQD with hole localization [...] Read more.

Non-volatile memories based on the flash architecture with self-assembled III–V quantum dots (SAQDs) used as a floating gate are one of the prospective directions for universal memories. The central goal of this field is the search for a novel SAQD with hole localization energy (E_loc) sufficient for a long charge storage (10 years). In the present work, the hole states’ energy spectrum in novel InGaSb/AlP SAQDs was analyzed theoretically with a focus on its possible application in non-volatile memories. Material intermixing and formation of strained SAQDs from a Ga_xAl_1−xSb_yP_1−y, In_xAl_1−xSb_yP_1−y or an In_xGa_1−xSb_yP_1−y alloy were taken into account. Critical sizes of SAQDs, with respect to the introduction of misfit dislocation as a function of alloy composition, were estimated using the force-balancing model. A variation in SAQDs’ composition together with dot sizes allowed us to find that the optimal configuration for the non-volatile memory application is GaSbP/AlP SAQDs with the 0.55–0.65 Sb fraction and a height of 4–4.5 nm, providing the E_loc value of 1.35–1.50 eV. Additionally, the hole energy spectra in unstrained InSb/AlP and GaSb/AlP SAQDs were calculated. E_loc values up to 1.65–1.70 eV were predicted, and that makes unstrained InGaSb/AlP SAQDs a prospective object for the non-volatile memory application. Full article

(This article belongs to the Special Issue Novel Research in Low-Dimensional Systems)

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12 pages, 2901 KiB

Open AccessArticle

Effect of TiO₂ Film Thickness on the Stability of Au₉ Clusters with a CrO_x Layer

by Abdulrahman S. Alotabi, Yanting Yin, Ahmad Redaa, Siriluck Tesana, Gregory F. Metha and Gunther G. Andersson

Nanomaterials 2022, 12(18), 3218; https://doi.org/10.3390/nano12183218 - 16 Sep 2022

Cited by 1 | Viewed by 1442

Abstract

Radio frequency (RF) magnetron sputtering allows the fabrication of TiO₂ films with high purity, reliable control of film thickness, and uniform morphology. In the present study, the change in surface roughness upon heating two different thicknesses of RF sputter-deposited TiO₂ films [...] Read more.

Radio frequency (RF) magnetron sputtering allows the fabrication of TiO₂ films with high purity, reliable control of film thickness, and uniform morphology. In the present study, the change in surface roughness upon heating two different thicknesses of RF sputter-deposited TiO₂ films was investigated. As a measure of the process of the change in surface morphology, chemically -synthesised phosphine-protected Au₉ clusters covered by a photodeposited CrO_x layer were used as a probe. Subsequent to the deposition of the Au₉ clusters and the CrO_x layer, samples were heated to 200 ℃ to remove the triphenylphosphine ligands from the Au₉ cluster. After heating, the thick TiO₂ film was found to be mobile, in contrast to the thin TiO₂ film. The influence of the mobility of the TiO₂ films on the Au₉ clusters was investigated with X-ray photoelectron spectroscopy. It was found that the high mobility of the thick TiO₂ film after heating leads to a significant agglomeration of the Au₉ clusters, even when protected by the CrO_x layer. The thin TiO₂ film has a much lower mobility when being heated, resulting in only minor agglomeration of the Au₉ clusters covered with the CrO_x layer. Full article

(This article belongs to the Special Issue Novel Research in Low-Dimensional Systems)

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12 pages, 3492 KiB

Open AccessArticle

Influence of Ink Properties on the Morphology of Long-Wave Infrared HgSe Quantum Dot Films

by Suhui Wang, Xu Zhang, Yi Wang, Tengxiao Guo and Shuya Cao

Nanomaterials 2022, 12(13), 2180; https://doi.org/10.3390/nano12132180 - 24 Jun 2022

Cited by 2 | Viewed by 1486

Abstract

As the core device of the miniature quantum dot (QD) spectrometer, the morphology control of the filter film array cannot be ignored. We eliminated strong interference from additives on the spectrum of a long-wave infrared (LWIR) QD filter film by selecting volatile additives. [...] Read more.

As the core device of the miniature quantum dot (QD) spectrometer, the morphology control of the filter film array cannot be ignored. We eliminated strong interference from additives on the spectrum of a long-wave infrared (LWIR) QD filter film by selecting volatile additives. This work is significant for detecting targets by spectroscopic methods. In this work, a filter film with characteristic spectral bands located in the LWIR was obtained by the natural evaporation of QD ink, which was prepared by mixing various volatile organic solvents with HgSe QD–toluene solution. The factors affecting the morphology of HgSe LWIR films, including ink surface tension, particle size, and solute volume fraction, were the main focus of the analysis. The experimental results suggested that the film slipped in the evaporation process, and the multilayer annular deposition formed when the surface tension of the ink was no more than 24.86 mN/m. The “coffee ring” and the multilayer annular deposition essentially disappeared when the solute particles were larger than 188.11 nm. QDs in the film were accumulated, and a “gully” morphology appeared when the solute volume fraction was greater than 0.1. In addition, both the increase rate of the film height and the decrease rate of the transmission slowed down. The relationship between film height and transmission was obtained by fitting, and the curve conformed to the Lambert–Beer law. Therefore, a uniform and flat film without “coffee rings” can be prepared by adjusting the surface tension, particle size, and volume fraction. This method could provide an empirical method for the preparation of LWIR QD filter film arrays. Full article

(This article belongs to the Special Issue Novel Research in Low-Dimensional Systems)

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12 pages, 2823 KiB

Open AccessArticle

Enhanced Stability and Mechanical Properties of a Graphene–Protein Nanocomposite Film by a Facile Non-Covalent Self-Assembly Approach

by Chunbao Du, Ting Du, Joey Tianyi Zhou, Yanan Zhu, Xingang Jia and Yuan Cheng

Nanomaterials 2022, 12(7), 1181; https://doi.org/10.3390/nano12071181 - 01 Apr 2022

Cited by 6 | Viewed by 1843

Abstract

Graphene-based nanocomposite films (NCFs) are in high demand due to their superior photoelectric and thermal properties, but their stability and mechanical properties form a bottleneck. Herein, a facile approach was used to prepare nacre-mimetic NCFs through the non-covalent self-assembly of graphene oxide (GO) [...] Read more.

Graphene-based nanocomposite films (NCFs) are in high demand due to their superior photoelectric and thermal properties, but their stability and mechanical properties form a bottleneck. Herein, a facile approach was used to prepare nacre-mimetic NCFs through the non-covalent self-assembly of graphene oxide (GO) and biocompatible proteins. Various characterization techniques were employed to characterize the as-prepared NCFs and to track the interactions between GO and proteins. The conformational changes of various proteins induced by GO determined the film-forming ability of NCFs, and the binding of bull serum albumin (BSA)/hemoglobin (HB) on GO’s surface was beneficial for improving the stability of as-prepared NCFs. Compared with the GO film without any additive, the indentation hardness and equivalent elastic modulus could be improved by 50.0% and 68.6% for GO–BSA NCF; and 100% and 87.5% for GO–HB NCF. Our strategy should be facile and effective for fabricating well-designed bio-nanocomposites for universal functional applications. Full article

(This article belongs to the Special Issue Novel Research in Low-Dimensional Systems)

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9 pages, 1866 KiB

Open AccessArticle

Graphene Nanoribbon Gap Waveguides for Dispersionless and Low-Loss Propagation with Deep-Subwavelength Confinement

by Zhiyong Wu, Lei Zhang, Tingyin Ning, Hong Su, Irene Ling Li, Shuangchen Ruan, Yu-Jia Zeng and Huawei Liang

Nanomaterials 2021, 11(5), 1302; https://doi.org/10.3390/nano11051302 - 14 May 2021

Cited by 3 | Viewed by 2186

Abstract

Surface plasmon polaritons (SPPs) have been attracting considerable attention owing to their unique capabilities of manipulating light. However, the intractable dispersion and high loss are two major obstacles for attaining high-performance plasmonic devices. Here, a graphene nanoribbon gap waveguide (GNRGW) is proposed for [...] Read more.

Surface plasmon polaritons (SPPs) have been attracting considerable attention owing to their unique capabilities of manipulating light. However, the intractable dispersion and high loss are two major obstacles for attaining high-performance plasmonic devices. Here, a graphene nanoribbon gap waveguide (GNRGW) is proposed for guiding dispersionless gap SPPs (GSPPs) with deep-subwavelength confinement and low loss. An analytical model is developed to analyze the GSPPs, in which a reflection phase shift is employed to successfully deal with the influence caused by the boundaries of the graphene nanoribbon (GNR). It is demonstrated that a pulse with a 4 μm bandwidth and a 10 nm mode width can propagate in the linear passive system without waveform distortion, which is very robust against the shape change of the GNR. The decrease in the pulse amplitude is only 10% for a propagation distance of 1 μm. Furthermore, an array consisting of several GNRGWs is employed as a multichannel optical switch. When the separation is larger than 40 nm, each channel can be controlled independently by tuning the chemical potential of the corresponding GNR. The proposed GNRGW may raise great interest in studying dispersionless and low-loss nanophotonic devices, with potential applications in the distortionless transmission of nanoscale signals, electro-optic nanocircuits, and high-density on-chip communications. Full article

(This article belongs to the Special Issue Novel Research in Low-Dimensional Systems)

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11 pages, 277 KiB

Open AccessArticle

Energy Stored and Capacitance of a Circular Parallel Plate Nanocapacitor

by Orion Ciftja

Nanomaterials 2021, 11(5), 1255; https://doi.org/10.3390/nano11051255 - 11 May 2021

Cited by 7 | Viewed by 2076

Abstract

Nanocapacitors have received a great deal of attention in recent years due to the promises of high energy storage density as device scaling continues unabated in the nanoscale era. High energy storage capacity is a key ingredient for many nanoelectronic applications in which [...] Read more.

Nanocapacitors have received a great deal of attention in recent years due to the promises of high energy storage density as device scaling continues unabated in the nanoscale era. High energy storage capacity is a key ingredient for many nanoelectronic applications in which the significant consumption of energy is required. The electric properties of a nanocapacitor can be strongly modified from the expected bulk properties due to finite-size effects which means that there is an increased need for the accurate characterization of its properties. In this work, we considered a theoretical model for a circular parallel plate nanocapacitor and calculated exactly, in closed analytic form, the electrostatic energy stored in the nanocapacitor as a function of the size of the circular plates and inter-plate separation. The exact expression for the energy is used to derive an analytic formula for the geometric capacitance of this nanocapacitor. The results obtained can be readily amended to incorporate the effects of a dielectric thin film filling the space between the circular plates of the nanocapacitor. Full article

(This article belongs to the Special Issue Novel Research in Low-Dimensional Systems)

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19 pages, 1232 KiB

Open AccessArticle

Charge-Order on the Triangular Lattice: A Mean-Field Study for the Lattice S = 1/2 Fermionic Gas

by Konrad Jerzy Kapcia

Nanomaterials 2021, 11(5), 1181; https://doi.org/10.3390/nano11051181 - 30 Apr 2021

Cited by 3 | Viewed by 2760

Abstract

The adsorbed atoms exhibit tendency to occupy a triangular lattice formed by periodic potential of the underlying crystal surface. Such a lattice is formed by, e.g., a single layer of graphane or the graphite surfaces as well as (111) surface of face-cubic center [...] Read more.

The adsorbed atoms exhibit tendency to occupy a triangular lattice formed by periodic potential of the underlying crystal surface. Such a lattice is formed by, e.g., a single layer of graphane or the graphite surfaces as well as (111) surface of face-cubic center crystals. In the present work, an extension of the lattice gas model to

S = 1 / 2

fermionic particles on the two-dimensional triangular (hexagonal) lattice is analyzed. In such a model, each lattice site can be occupied not by only one particle, but by two particles, which interact with each other by onsite U and intersite

W_{1}

and

W_{2}

(nearest and next-nearest-neighbor, respectively) density-density interaction. The investigated hamiltonian has a form of the extended Hubbard model in the atomic limit (i.e., the zero-bandwidth limit). In the analysis of the phase diagrams and thermodynamic properties of this model with repulsive

W_{1} > 0

, the variational approach is used, which treats the onsite interaction term exactly and the intersite interactions within the mean-field approximation. The ground state (

T = 0

) diagram for

W_{2} \leq 0

as well as finite temperature (

T > 0

) phase diagrams for

W_{2} = 0

are presented. Two different types of charge order within

\sqrt{3} \times \sqrt{3}

unit cell can occur. At

T = 0

, for

W_{2} = 0

phase separated states are degenerated with homogeneous phases (but

T > 0

removes this degeneration), whereas attractive

W_{2} < 0

stabilizes phase separation at incommensurate fillings. For

U / W_{1} < 0

and

U / W_{1} > 1 / 2

only the phase with two different concentrations occurs (together with two different phase separated states occurring), whereas for small repulsive

0 < U / W_{1} < 1 / 2

the other ordered phase also appears (with tree different concentrations in sublattices). The qualitative differences with the model considered on hypercubic lattices are also discussed. Full article

(This article belongs to the Special Issue Novel Research in Low-Dimensional Systems)

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20 pages, 4715 KiB

Open AccessArticle

Scanning Thermal Microscopy of Ultrathin Films: Numerical Studies Regarding Cantilever Displacement, Thermal Contact Areas, Heat Fluxes, and Heat Distribution

by Christoph Metzke, Fabian Kühnel, Jonas Weber and Günther Benstetter

Nanomaterials 2021, 11(2), 491; https://doi.org/10.3390/nano11020491 - 16 Feb 2021

Cited by 4 | Viewed by 2481

Abstract

New micro- and nanoscale devices require electrically isolating materials with specific thermal properties. One option to characterize these thermal properties is the atomic force microscopy (AFM)-based scanning thermal microscopy (SThM) technique. It enables qualitative mapping of local thermal conductivities of ultrathin films. To [...] Read more.

New micro- and nanoscale devices require electrically isolating materials with specific thermal properties. One option to characterize these thermal properties is the atomic force microscopy (AFM)-based scanning thermal microscopy (SThM) technique. It enables qualitative mapping of local thermal conductivities of ultrathin films. To fully understand and correctly interpret the results of practical SThM measurements, it is essential to have detailed knowledge about the heat transfer process between the probe and the sample. However, little can be found in the literature so far. Therefore, this work focuses on theoretical SThM studies of ultrathin films with anisotropic thermal properties such as hexagonal boron nitride (h-BN) and compares the results with a bulk silicon (Si) sample. Energy fluxes from the probe to the sample between 0.6 µW and 126.8 µW are found for different cases with a tip radius of approximately 300 nm. A present thermal interface resistance (TIR) between bulk Si and ultrathin h-BN on top can fully suppress a further heat penetration. The time until heat propagation within the sample is stationary is found to be below 1 µs, which may justify higher tip velocities in practical SThM investigations of up to 20 µms⁻¹. It is also demonstrated that there is almost no influence of convection and radiation, whereas a possible TIR between probe and sample must be considered. Full article

(This article belongs to the Special Issue Novel Research in Low-Dimensional Systems)

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