Nanomaterials

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8 pages, 1712 KiB

Open AccessArticle

Edge-Trimmed Nanogaps in 2D Materials for Robust, Scalable, and Tunable Lateral Tunnel Junctions

by Hai-Thai Nguyen, Yen Nguyen, Yen-Hsun Su, Ya-Ping Hsieh and Mario Hofmann

Nanomaterials 2021, 11(4), 981; https://doi.org/10.3390/nano11040981 - 10 Apr 2021

Cited by 3 | Viewed by 2608

Abstract

Lateral tunnel junctions are fundamental building blocks for molecular electronics and novel sensors, but current fabrication approaches achieve device yields below 10%, which limits their appeal for circuit integration and large-scale application. We here demonstrate a new approach to reliably form nanometer-sized gaps [...] Read more.

Lateral tunnel junctions are fundamental building blocks for molecular electronics and novel sensors, but current fabrication approaches achieve device yields below 10%, which limits their appeal for circuit integration and large-scale application. We here demonstrate a new approach to reliably form nanometer-sized gaps between electrodes with high precision and unprecedented control. This advance in nanogap production is enabled by the unique properties of 2D materials-based contacts. The large difference in reactivity of 2D materials’ edges compared to their basal plane results in a sequential removal of atoms from the contact perimeter. The resulting trimming of exposed graphene edges in a remote hydrogen plasma proceeds at speeds of less than 1 nm per minute, permitting accurate control of the nanogap dimension through the etching process. Carrier transport measurements reveal the high quality of the nanogap, thus-produced tunnel junctions with a 97% yield rate, which represents a tenfold increase in productivity compared to previous reports. Moreover, 70% of tunnel junctions fall within a nanogap range of only 0.5 nm, representing an unprecedented uniformity in dimension. The presented edge-trimming approach enables the conformal narrowing of gaps and produces novel one-dimensional nano-trench geometries that can sustain larger tunneling currents than conventional 0D nano-junctions. Finally, the potential of our approach for future electronics was demonstrated by the realization of an atom-based memory. Full article

(This article belongs to the Special Issue 2D Materials for Nanoelectronics)

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9 pages, 1968 KiB

Open AccessEditor’s ChoiceArticle

Electric Transport in Gold-Covered Sodium–Alginate Free-Standing Foils

by Carlo Barone, Monica Bertoldo, Raffaella Capelli, Franco Dinelli, Piera Maccagnani, Nadia Martucciello, Costantino Mauro and Sergio Pagano

Nanomaterials 2021, 11(3), 565; https://doi.org/10.3390/nano11030565 - 24 Feb 2021

Cited by 6 | Viewed by 2124

Abstract

The electric transport properties of flexible and transparent conducting bilayers, realized by sputtering ultrathin gold nanometric layers on sodium–alginate free-standing films, were studied. The reported results cover a range of temperatures from 3 to 300 K. In the case of gold layer thicknesses [...] Read more.

The electric transport properties of flexible and transparent conducting bilayers, realized by sputtering ultrathin gold nanometric layers on sodium–alginate free-standing films, were studied. The reported results cover a range of temperatures from 3 to 300 K. In the case of gold layer thicknesses larger than 5 nm, a typical metallic behavior was observed. Conversely, for a gold thickness of 4.5 nm, an unusual resistance temperature dependence was found. The dominant transport mechanism below 70 K was identified as a fluctuation-induced tunneling process. This indicates that the conductive region is not continuous but is formed by gold clusters embedded in the polymeric matrix. Above 70 K, instead, the data can be interpreted using a phenomenological model, which assumes an anomalous expansion of the conductive region upon decreasing the temperature, in the range from 300 to 200 K. The approach herein adopted, complemented with other characterizations, can provide useful information for the development of innovative and green optoelectronics. Full article

(This article belongs to the Special Issue 2D Materials for Nanoelectronics)

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11 pages, 8088 KiB

Open AccessArticle

Broadband Visible Nonlinear Absorption and Ultrafast Dynamics of the Ti₃C₂ Nanosheet

by Yabin Shao, Chen Chen, Qing He, Wenzhi Wu, Chensha Li and Yachen Gao

Nanomaterials 2020, 10(12), 2544; https://doi.org/10.3390/nano10122544 - 17 Dec 2020

Cited by 13 | Viewed by 2790

Abstract

The Ti₃C₂ nanosheet, as a new two-dimensional (2D) group, has been found to have attractive characteristics as material for electromagnetic shielding and energy storage. In this study, the nonlinear broadband absorption and ultrafast dynamics of the Ti₃C₂ [...] Read more.

The Ti₃C₂ nanosheet, as a new two-dimensional (2D) group, has been found to have attractive characteristics as material for electromagnetic shielding and energy storage. In this study, the nonlinear broadband absorption and ultrafast dynamics of the Ti₃C₂ nanosheet were investigated using nanosecond open-aperture Z-scan and transient absorption techniques. The mechanism of two-photon absorption (TPA) was revealed in the visible region (475–700 nm). At lower incident energies, nonlinear absorption could not happen. When the laser energy increased to 0.64 GW/cm², electrons in the valence band could absorb two photons and jump to the conduction band, with TPA occurring, which meant that the sample exhibited reverse saturable absorption (RSA). In addition, when transient absorption was used to investigate the ultrafast carrier dynamics of the sample, it demonstrated that the relaxation contains a fast decay component and a slow one, which are obtained from electron–phonon and phonon–phonon interactions, respectively. Moreover, with the increasing pump fluence, the fast decay lifetime τ₁ increased from 3.9 to 4.5 ps, and the slow one τ₂ increased from 11.1 to 13.2 ps. These results show that the Ti₃C₂ nanosheet has potential applications in broadband optical limiters. Full article

(This article belongs to the Special Issue 2D Materials for Nanoelectronics)

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9 pages, 1148 KiB

Open AccessArticle

Schottky Barrier Height and Image Force Lowering in Monolayer MoS₂ Field Effect Transistors

by Yonatan Vaknin, Ronen Dagan and Yossi Rosenwaks

Nanomaterials 2020, 10(12), 2346; https://doi.org/10.3390/nano10122346 - 26 Nov 2020

Cited by 20 | Viewed by 5922

Abstract

Understanding the nature of the barrier height in a two-dimensional semiconductor/metal interface is an important step for embedding layered materials in future electronic devices. We present direct measurement of the Schottky barrier height and its lowering in the transition metal dichalcogenide (TMD)/metal interface [...] Read more.

Understanding the nature of the barrier height in a two-dimensional semiconductor/metal interface is an important step for embedding layered materials in future electronic devices. We present direct measurement of the Schottky barrier height and its lowering in the transition metal dichalcogenide (TMD)/metal interface of a field effect transistor. It is found that the barrier height at the gold/ single-layer molybdenum disulfide (MoS₂) interfaces decreases with increasing drain voltage, and this lowering reaches 0.5–1 V We also show that increase of the gate voltage induces additional barrier lowering. Full article

(This article belongs to the Special Issue 2D Materials for Nanoelectronics)

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10 pages, 2245 KiB

Open AccessArticle

Benchmark Investigation of Band-Gap Tunability of Monolayer Semiconductors under Hydrostatic Pressure with Focus-On Antimony

by Xiangyu Dai, Zhengfang Qian, Qiaolu Lin, Le Chen, Renheng Wang and Yiling Sun

Nanomaterials 2020, 10(11), 2154; https://doi.org/10.3390/nano10112154 - 29 Oct 2020

Cited by 6 | Viewed by 2333

Abstract

In this paper, the band-gap tunability of three monolayer semiconductors under hydrostatic pressure was intensively investigated based on first-principle simulations with a focus on monolayer antimony (Sb) as a semiconductor nanomaterial. As the benchmark study, monolayer black phosphorus (BP) and monolayer molybdenum disulfide [...] Read more.

In this paper, the band-gap tunability of three monolayer semiconductors under hydrostatic pressure was intensively investigated based on first-principle simulations with a focus on monolayer antimony (Sb) as a semiconductor nanomaterial. As the benchmark study, monolayer black phosphorus (BP) and monolayer molybdenum disulfide (MoS₂) were also investigated for comparison. Our calculations showed that the band-gap tunability of the monolayer Sb was much more sensitive to hydrostatic pressure than that of the monolayer BP and MoS₂. Furthermore, the monolayer Sb was predicted to change from an indirect band-gap semiconductor to a conductor and to transform into a double-layer nanostructure above a critical pressure value ranging from 3 to 5 GPa. This finding opens an opportunity for nanoelectronic, flexible electronics and optoelectronic devices as well as sensors with the capabilities of deep band-gap tunability and semiconductor-to-metal transition by applying mechanical pressure. Full article

(This article belongs to the Special Issue 2D Materials for Nanoelectronics)

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12 pages, 2194 KiB

Open AccessArticle

Tunable Microwave Filters Using HfO₂-Based Ferroelectrics

by Martino Aldrigo, Mircea Dragoman, Sergiu Iordanescu, Florin Nastase and Silviu Vulpe

Nanomaterials 2020, 10(10), 2057; https://doi.org/10.3390/nano10102057 - 18 Oct 2020

Cited by 13 | Viewed by 2559

Abstract

In this paper, we present microwave filters that are based on 6-nm-thick ferroelectric thin films of hafnium oxide doped with zirconium (HfZrO), which are tunable continuously in targeted bands of interest within the frequency range 0.1–16 GHz, when the applied direct current (DC) [...] Read more.

In this paper, we present microwave filters that are based on 6-nm-thick ferroelectric thin films of hafnium oxide doped with zirconium (HfZrO), which are tunable continuously in targeted bands of interest within the frequency range 0.1–16 GHz, when the applied direct current (DC) voltage is swept between 0 V and 4 V. Here, we exploit the orthorhombic polar phase in HfO₂ through a careful doping using zirconium in an Atomic Layer Deposition (ALD) process, in order to guarantee phase stabilization at room temperature. Polarization versus voltage characterization has been carried out, showing a remanent polarization (P_r) of ~0.8 μC/cm² and the coercive voltage at ~2.6 V. The average roughness has been found to be 0.2 nm for HfZrO films with a thickness of 6 nm. The uniform topography, without holes, and the low surface roughness demonstrate that the composition and the structure of the film are relatively constant in volume. Three filter configurations (low-pass, high-pass, and band-pass) have been designed, modelled, fabricated, and fully characterized in microwaves, showing a frequency shift of the minimum of the reflection coefficient between 90 MHz and 4.4 GHz, with a minimum insertion loss of approximately 6.9 dB in high-pass configuration. Full article

(This article belongs to the Special Issue 2D Materials for Nanoelectronics)

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13 pages, 4145 KiB

Open AccessArticle

The Thermoelectric Properties of Monolayer MAs₂ (M = Ni, Pd and Pt) from First-Principles Calculations

by Qiang-Lin Wei, Heng-Yu Yang, Yi-Yuan Wu, Yi-Bao Liu and Yu-Hong Li

Nanomaterials 2020, 10(10), 2043; https://doi.org/10.3390/nano10102043 - 16 Oct 2020

Cited by 11 | Viewed by 2211

Abstract

The thermoelectric property of the monolayer MAs₂ (M = Ni, Pd and Pt) is predicted based on first principles calculations, while combining with the Boltzmann transport theory to confirm the influence of phonon and electricity transport property on the thermoelectric performance. More [...] Read more.

The thermoelectric property of the monolayer MAs₂ (M = Ni, Pd and Pt) is predicted based on first principles calculations, while combining with the Boltzmann transport theory to confirm the influence of phonon and electricity transport property on the thermoelectric performance. More specifically, on the basis of stable geometry structure, the lower lattice thermal conductivity of the monolayer NiAs₂, PdAs₂ and PtAs₂ is obtained corresponding to 5.9, 2.9 and 3.6 W/mK. Furthermore, the results indicate that the monolayer MAs₂ have moderate direct bang-gap, in which the monolayer PdAs₂ can reach 0.8 eV. The Seebeck coefficient, power factor and thermoelectric figure of merit (ZT) were calculated at 300, 500 and 700 K by performing the Boltzmann transport equation and the relaxation time approximation. Among them, we can affirm that the monolayer PdAs₂ possesses the maximum ZT of about 2.1, which is derived from a very large power factor of 3.9 × 10¹¹ W/K²ms and lower thermal conductivity of 1.4 W/mK at 700 K. The monolayer MAs₂ can be a promising candidate for application at thermoelectric materials. Full article

(This article belongs to the Special Issue 2D Materials for Nanoelectronics)

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9 pages, 1746 KiB

Open AccessArticle

Functionalization of Molybdenum Disulfide via Plasma Treatment and 3-Mercaptopropionic Acid for Gas Sensors

by Won Seok Seo, Dae Ki Kim, Ji-Hoon Han, Kang-Bak Park, Su Chak Ryu, Nam Ki Min and Joon Hyub Kim

Nanomaterials 2020, 10(9), 1860; https://doi.org/10.3390/nano10091860 - 17 Sep 2020

Cited by 8 | Viewed by 2551

Abstract

Monolayer and multilayer molybdenum disulfide (MoS₂) materials are semiconductors with direct/indirect bandgaps of 1.2–1.8 eV and are attractive due to their changes in response to electrical, physicochemical, biological, and mechanical factors. Since the desired electrical properties of MoS₂ are known, [...] Read more.

Monolayer and multilayer molybdenum disulfide (MoS₂) materials are semiconductors with direct/indirect bandgaps of 1.2–1.8 eV and are attractive due to their changes in response to electrical, physicochemical, biological, and mechanical factors. Since the desired electrical properties of MoS₂ are known, research on its electrical properties has increased, with focus on the deposition and growth of large-area MoS₂ and its functionalization. While research on the large-scale production of MoS₂ is actively underway, there is a lack of studies on functionalization approaches, which are essential since functional groups can help to dissolve particles or provide adequate reactivity. Strategies for producing films of functionalized MoS₂ are rare, and what methods do exist are either complex or inefficient. This work introduces an efficient way to functionalize MoS₂. Functional groups are formed on the surface by exposing MoS₂ with surface sulfur vacancies generated by plasma treatment to 3-mercaptopropionic acid. This technique can create 1.8 times as many carboxyl groups on the MoS₂ surface compared with previously reported strategies. The MoS₂-based gas sensor fabricated using the proposed method shows a 2.6 times higher sensitivity and much lower detection limit than the untreated device. Full article

(This article belongs to the Special Issue 2D Materials for Nanoelectronics)

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13 pages, 3088 KiB

Open AccessArticle

Electromagnetic Analysis of Vertical Resistive Memory with a Sub-nm Thick Electrode

by Batyrbek Alimkhanuly, Sanghoek Kim, Lok-won Kim and Seunghyun Lee

Nanomaterials 2020, 10(9), 1634; https://doi.org/10.3390/nano10091634 - 20 Aug 2020

Cited by 4 | Viewed by 2786

Abstract

Resistive random access memories (RRAMs) are a type of resistive memory with two metal electrodes and a semi-insulating switching material in-between. As the persistent technology node downscaling continues in transistor technologies, RRAM designers also face similar device scaling challenges in simple cross-point arrays. [...] Read more.

Resistive random access memories (RRAMs) are a type of resistive memory with two metal electrodes and a semi-insulating switching material in-between. As the persistent technology node downscaling continues in transistor technologies, RRAM designers also face similar device scaling challenges in simple cross-point arrays. For this reason, a cost-effective 3D vertical RRAM (VRRAM) structure which requires a single pivotal lithography step is attracting significant attention from both the scientific community and the industry. Integrating an extremely thin plane electrode to such a structure is a difficult but necessary step to enable high memory density. In addition, experimentally verifying and modeling such devices is an important step to designing RRAM arrays with a high noise margin, low resistive-capacitive (RC) delays, and stable switching characteristics. In this work, we conducted an electromagnetic analysis on a 3D vertical RRAM with atomically thin graphene electrodes and compared it with the conventional metal electrode. Based on the experimental device measurement results, we derived a theoretical basis and models for each VRRAM design that can be further utilized in the estimation of graphene-based 3D memory at the circuit and architecture levels. We concluded that a 71% increase in electromagnetic field strength was observed in a 0.3 nm thick graphene electrode when compared to a 5 nm thick metal electrode. Such an increase in the field led to much lower energy consumption and fluctuation range during RRAM switching. Due to unique graphene properties resulting in improved programming behavior, the graphene-based VRRAM can be a strong candidate for stacked storage devices in new memory computing platforms. Full article

(This article belongs to the Special Issue 2D Materials for Nanoelectronics)

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Review

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15 pages, 4880 KiB

Open AccessReview

Perspectives on Atomic-Scale Switches for High-Frequency Applications Based on Nanomaterials

by Mircea Dragoman, Martino Aldrigo and Daniela Dragoman

Nanomaterials 2021, 11(3), 625; https://doi.org/10.3390/nano11030625 - 3 Mar 2021

Cited by 12 | Viewed by 2355

Abstract

Nanomaterials science is becoming the foundation stone of high-frequency applications. The downscaling of electronic devices and components allows shrinking chip’s dimensions at a more-than-Moore rate. Many theoretical limits and manufacturing constraints are yet to be taken into account. A promising path towards nanoelectronics [...] Read more.

Nanomaterials science is becoming the foundation stone of high-frequency applications. The downscaling of electronic devices and components allows shrinking chip’s dimensions at a more-than-Moore rate. Many theoretical limits and manufacturing constraints are yet to be taken into account. A promising path towards nanoelectronics is represented by atomic-scale materials. In this manuscript, we offer a perspective on a specific class of devices, namely switches designed and fabricated using two-dimensional or nanoscale materials, like graphene, molybdenum disulphide, hexagonal boron nitride and ultra-thin oxides for high-frequency applications. An overview is provided about three main types of microwave and millimeter-wave switch: filament memristors, nano-ionic memristors and ferroelectric junctions. The physical principles that govern each switch are presented, together with advantages and disadvantages. In the last part we focus on zirconium-doped hafnium oxide ferroelectrics (HfZrO) tunneling junctions (FTJ), which are likely to boost the research in the domain of atomic-scale materials applied in engineering sciences. Thanks to their Complementary Metal-Oxide Semiconductor (CMOS) compatibility and low-voltage tunability (among other unique physical properties), HfZrO compounds have the potential for large-scale applicability. As a practical case of study, we present a 10 GHz transceiver in which the switches are FTJs, which guarantee excellent isolation and ultra-fast switching time. Full article

(This article belongs to the Special Issue 2D Materials for Nanoelectronics)

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