Nanomaterials

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19 pages, 945 KiB

Open AccessArticle

Shallow Donor Impurity States with Excitonic Contribution in GaAs/AlGaAs and CdTe/CdSe Truncated Conical Quantum Dots under Applied Magnetic Field

by Lorenz Pulgar-Velásquez, José Sierra-Ortega, Juan A. Vinasco, David Laroze, Adrian Radu, Esin Kasapoglu, Ricardo L. Restrepo, John A. Gil-Corrales, Alvaro L. Morales and Carlos A. Duque

Nanomaterials 2021, 11(11), 2832; https://doi.org/10.3390/nano11112832 - 25 Oct 2021

Cited by 8 | Viewed by 2340

Abstract

Using the effective mass approximation in a parabolic two-band model, we studied the effects of the geometrical parameters, on the electron and hole states, in two truncated conical quantum dots: (i) GaAs-(Ga,Al)As in the presence of a shallow donor impurity and under an [...] Read more.

Using the effective mass approximation in a parabolic two-band model, we studied the effects of the geometrical parameters, on the electron and hole states, in two truncated conical quantum dots: (i) GaAs-(Ga,Al)As in the presence of a shallow donor impurity and under an applied magnetic field and (ii) CdSe–CdTe core–shell type-II quantum dot. For the first system, the impurity position and the applied magnetic field direction were chosen to preserve the system’s azimuthal symmetry. The finite element method obtains the solution of the Schrödinger equations for electron or hole with or without impurity with an adaptive discretization of a triangular mesh. The interaction of the electron and hole states is calculated in a first-order perturbative approximation. This study shows that the magnetic field and donor impurities are relevant factors in the optoelectronic properties of conical quantum dots. Additionally, for the CdSe–CdTe quantum dot, where, again, the axial symmetry is preserved, a switch between direct and indirect exciton is possible to be controlled through geometry. Full article

(This article belongs to the Special Issue Electronics, Electromagnetism and Applications of Nanomaterials)

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9 pages, 3507 KiB

Open AccessArticle

Effects of Multi-Components on the Microwave Absorption and Dielectric Properties of Plasma-Sprayed Carbon Nanotube/Y₂O₃/ZrB₂ Ceramics

by Rong Li and Yuchang Qing

Nanomaterials 2021, 11(10), 2640; https://doi.org/10.3390/nano11102640 - 07 Oct 2021

Cited by 3 | Viewed by 1381

Abstract

Carbon nanotube (CNT)-reinforced Y₂O₃/ZrB₂ ceramics were fabricated via planetary ball milling and atmospheric-pressure plasma spraying for the first time. The phase composition, micromorphology, and electromagnetic (EM) wave absorption performance of the Y₂O₃/ZrB₂/CNT [...] Read more.

Carbon nanotube (CNT)-reinforced Y₂O₃/ZrB₂ ceramics were fabricated via planetary ball milling and atmospheric-pressure plasma spraying for the first time. The phase composition, micromorphology, and electromagnetic (EM) wave absorption performance of the Y₂O₃/ZrB₂/CNT hybrid was investigated from 8.2 to 12.4 GHz. Both the real and imaginary parts of the complex permittivity were enhanced as the ZrB₂ and CNT content increased. The Y₂O₃/ZrB₂/CNT hybrids corresponded to a ZrB₂ content of 15 wt.%, and the CNT content was 2 wt.% and showed an exceptional EM wave absorption capability, with a minimum reflection loss of −25.7 dB at 1.9 mm thickness, and the effective absorption band was in a full X-band. These results indicate that an appropriate CNT or ZrB₂ content can tune the complex permittivity and absorption performance of the Y₂O₃/ZrB₂/CNT ceramics. Full article

(This article belongs to the Special Issue Electronics, Electromagnetism and Applications of Nanomaterials)

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13 pages, 2783 KiB

Open AccessArticle

Substrate-Induced Strain Effect on Structural and Magnetic Properties of La_0.5Sr_0.5CoO₃ Films

by Miriam Sánchez-Pérez, Juan Pedro Andrés, Juan Antonio González, Ricardo López Antón, Marco Antonio López de la Torre and Oscar Juan Dura

Nanomaterials 2021, 11(3), 781; https://doi.org/10.3390/nano11030781 - 18 Mar 2021

Cited by 4 | Viewed by 2306

Abstract

We present a detailed study about the substrate-induced strain and thickness effects on the structure and magnetic properties of La_0.5Sr_0.5CoO₃ films. The in-plane tensile or compressive strain imposed by four different substrates configures an in-plane or out-of-plane easy [...] Read more.

We present a detailed study about the substrate-induced strain and thickness effects on the structure and magnetic properties of La_0.5Sr_0.5CoO₃ films. The in-plane tensile or compressive strain imposed by four different substrates configures an in-plane or out-of-plane easy axis, respectively. The presence of a soft magnetic phase at the interface is also conditioned by the type of strain. The obtained results are discussed in terms of the different anisotropies that participate and control the final magnetic behavior. The relevance of these results lies in the feasibility of La_0.5Sr_0.5CoO₃ in memory applications and spintronic devices. Full article

(This article belongs to the Special Issue Electronics, Electromagnetism and Applications of Nanomaterials)

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23 pages, 8405 KiB

Open AccessArticle

Seawater Absorption and Adhesion Properties of Hydrophobic and Superhydrophobic Thermoset Epoxy Nanocomposite Coatings

by Ayman M. Atta, Mohamed H. El-Newehy, Meera Moydeen Abdulhameed, Mohamed H. Wahby and Ahmed I. Hashem

Nanomaterials 2021, 11(2), 272; https://doi.org/10.3390/nano11020272 - 21 Jan 2021

Cited by 9 | Viewed by 2275

Abstract

The enhancement of both thermal and mechanical properties of epoxy materials using nanomaterials becomes a target in coating of the steel to protect it from aggressive environmental conditions for a long time, with reducing the cost. In this respect, the adhesion properties of [...] Read more.

The enhancement of both thermal and mechanical properties of epoxy materials using nanomaterials becomes a target in coating of the steel to protect it from aggressive environmental conditions for a long time, with reducing the cost. In this respect, the adhesion properties of the epoxy with the steel surfaces, and its proper superhyrophobicity to repel the seawater humidity, can be optimized via addition of green nanoparticles (NPs). In-situ modification of silver (Ag) and calcium carbonate (CaCO₃) NPs with oleic acid (OA) was carried out during the formation of Ag−OA and CaCO₃−OA, respectively. The epoxide oleic acid (EOA) was also used as capping for Ca−O₃ NPs by in-situ method and epoxidation of Ag−OA NPs, too. The morphology, thermal stability, and the diameters of NPs, as well as their dispersion in organic solvent, were investigated. The effects of the prepared NPs on the exothermic curing of the epoxy resins in the presence of polyamines, flexibility or rigidity of epoxy coatings, wettability, and coatings durability in aggressive seawater environment were studied. The obtained results confirmed that the proper superhyrophobicity, coating adhesion, and thermal stability of the epoxy were improved after exposure to salt spray fog for 2000 h at 36 °C. Full article

(This article belongs to the Special Issue Electronics, Electromagnetism and Applications of Nanomaterials)

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9 pages, 1791 KiB

Open AccessArticle

Self-Rectifying Resistive Switching and Short-Term Memory Characteristics in Pt/HfO₂/TaO_x/TiN Artificial Synaptic Device

by Hojeong Ryu and Sungjun Kim

Nanomaterials 2020, 10(11), 2159; https://doi.org/10.3390/nano10112159 - 29 Oct 2020

Cited by 50 | Viewed by 3963

Abstract

Here, we propose a Pt/HfO₂/TaO_x/TiN artificial synaptic device that is an excellent candidate for artificial synapses. First, XPS analysis is conducted to provide the dielectric (HfO₂/TaO_x/TiN) information deposited by DC sputtering and atomic layer deposition [...] Read more.

Here, we propose a Pt/HfO₂/TaO_x/TiN artificial synaptic device that is an excellent candidate for artificial synapses. First, XPS analysis is conducted to provide the dielectric (HfO₂/TaO_x/TiN) information deposited by DC sputtering and atomic layer deposition (ALD). The self-rectifying resistive switching characteristics are achieved by the asymmetric device stack, which is an advantage of the current suppression in the crossbar array structure. The results show that the programmed data are lost over time and that the decay rate, which is verified from the retention test, can be adjusted by controlling the compliance current (CC). Based on these properties, we emulate bio-synaptic characteristics, such as short-term plasticity (STP), long-term plasticity (LTP), and paired-pulse facilitation (PPF), in the self-rectifying I–V characteristics of the Pt/HfO₂/TaO_x/TiN bilayer memristor device. The PPF characteristics are mimicked by replacing the bio-stimulation with the interval time of paired pulse inputs. The typical potentiation and depression are also implemented by optimizing the set and reset pulse. Finally, we demonstrate the natural depression by varying the interval time between pulse inputs. Full article

(This article belongs to the Special Issue Electronics, Electromagnetism and Applications of Nanomaterials)

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16 pages, 5698 KiB

Open AccessArticle

Investigating a Lock-In Thermal Imaging Setup for the Detection and Characterization of Magnetic Nanoparticles

by Lukas Steinmetz, Christoph Kirsch, Christoph Geers, Alke Petri-Fink and Mathias Bonmarin

Nanomaterials 2020, 10(9), 1665; https://doi.org/10.3390/nano10091665 - 25 Aug 2020

Cited by 6 | Viewed by 2556

Abstract

Magnetic hyperthermia treatments utilize the heat generated by magnetic nanoparticles stimulated by an alternating magnetic field. Therefore, analytical methods are required to precisely characterize the dissipated thermal energy and to evaluate potential amplifying or diminishing factors in order to ensure optimal treatment conditions. [...] Read more.

Magnetic hyperthermia treatments utilize the heat generated by magnetic nanoparticles stimulated by an alternating magnetic field. Therefore, analytical methods are required to precisely characterize the dissipated thermal energy and to evaluate potential amplifying or diminishing factors in order to ensure optimal treatment conditions. Here, we present a lock-in thermal imaging setup specifically designed to thermally measure magnetic nanoparticles and we investigate theoretically how the various experimental parameters may influence the measurement. We compare two detection methods and highlight how an affordable microbolometer can achieve identical sensitivity with respect to a thermal camera-based system by adapting the measurement time. Furthermore, a numerical model is used to demonstrate the optimal stimulation frequency, the degree of nanomaterial heating power, preferential sample holder dimensions and the extent of heat losses to the environment. Using this model, we also revisit some technical assumptions and experimental results that previous studies have stated and suggest an optimal experimental configuration. Full article

(This article belongs to the Special Issue Electronics, Electromagnetism and Applications of Nanomaterials)

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16 pages, 6318 KiB

Open AccessArticle

Molecular Adsorption of NH₃ and NO₂ on Zr and Hf Dichalcogenides (S, Se, Te) Monolayers: A Density Functional Theory Study

by Shimeles Shumi Raya, Abu Saad Ansari and Bonggeun Shong

Nanomaterials 2020, 10(6), 1215; https://doi.org/10.3390/nano10061215 - 22 Jun 2020

Cited by 16 | Viewed by 3326

Abstract

Due to their atomic thicknesses and semiconducting properties, two-dimensional transition metal dichalcogenides (TMDCs) are gaining increasing research interest. Among them, Hf- and Zr-based TMDCs demonstrate the unique advantage that their oxides (HfO₂ and ZrO₂) are excellent dielectric materials. One possible [...] Read more.

Due to their atomic thicknesses and semiconducting properties, two-dimensional transition metal dichalcogenides (TMDCs) are gaining increasing research interest. Among them, Hf- and Zr-based TMDCs demonstrate the unique advantage that their oxides (HfO₂ and ZrO₂) are excellent dielectric materials. One possible method to precisely tune the material properties of two-dimensional atomically thin nanomaterials is to adsorb molecules on their surfaces as non-bonded dopants. In the present work, the molecular adsorption of NO₂ and NH₃ on the two-dimensional trigonal prismatic (1H) and octahedral (1T) phases of Hf and Zr dichalcogenides (S, Se, Te) is studied using dispersion-corrected periodic density functional theory (DFT) calculations. The adsorption configuration, energy, and charge-transfer properties during molecular adsorption are investigated. In addition, the effects of the molecular dopants (NH₃ and NO₂) on the electronic structure of the materials are studied. It was observed that the adsorbed NH₃ donates electrons to the conduction band of the Hf (Zr) dichalcogenides, while NO₂ receives electrons from the valance band. Furthermore, the NO₂ dopant affects than NH₃ significantly. The resulting band structure of the molecularly doped Zr and Hf dichalcogenides are modulated by the molecular adsorbates. This study explores, not only the properties of the two-dimensional 1H and 1T phases of Hf and Zr dichalcogenides (S, Se, Te), but also tunes their electronic properties by adsorbing non-bonded dopants. Full article

(This article belongs to the Special Issue Electronics, Electromagnetism and Applications of Nanomaterials)

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11 pages, 2013 KiB

Open AccessArticle

Design and Simulation of a Multi-Sheet Beam Terahertz Radiation Source Based on Carbon-Nanotube Cold Cathode

by Yifan Zu, Xuesong Yuan, Xiaotao Xu, Matthew T. Cole, Yu Zhang, Hailong Li, Yong Yin, Bin Wang and Yang Yan

Nanomaterials 2019, 9(12), 1768; https://doi.org/10.3390/nano9121768 - 12 Dec 2019

Cited by 8 | Viewed by 3203

Abstract

Carbon nanotube (CNT) cold cathodes are proving to be compelling candidates for miniaturized terahertz (THz) vacuum electronic devices (VEDs) owning to their superior field-emission (FE) characteristics. Here, we report on the development of a multi-sheet beam CNT cold cathode electron optical system with [...] Read more.

Carbon nanotube (CNT) cold cathodes are proving to be compelling candidates for miniaturized terahertz (THz) vacuum electronic devices (VEDs) owning to their superior field-emission (FE) characteristics. Here, we report on the development of a multi-sheet beam CNT cold cathode electron optical system with concurrently high beam current and high current density. The microscopic FE characteristics of the CNT film emitter is captured through the development of an empirically derived macroscopic simulation model which is used to provide representative emission performance. Through parametrically optimized macroscale simulations, a five-sheet-beam triode electron gun has been designed, and has been shown to emit up to 95 mA at 3.2 kV. Through careful engineering of the electron gun geometric parameters, a low-voltage compact THz radiation source operating in high-order

{TM}_{5, 1}

mode is investigated to improve output power and suppress mode competition. Particle in cell (PIC) simulations show the average output power is 33 W at 0.1 THz, and the beam–wave interaction efficiency is approximately 10%. Full article

(This article belongs to the Special Issue Electronics, Electromagnetism and Applications of Nanomaterials)

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