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17 pages, 6224 KiB

Open AccessArticle

Electrodeposition of Bi-Te Thin Films on Silicon Wafer and Micro-Column Arrays on Microporous Glass Template

by Ning Su, Shuai Guo, Fu Li and Bo Li

Nanomaterials 2020, 10(3), 431; https://doi.org/10.3390/nano10030431 - 28 Feb 2020

Cited by 6 | Viewed by 3498

Abstract

Electrodeposition is an important method for preparing bismuth telluride (Bi₂Te₃)-based thermoelectric (TE) thin films and micro-column arrays. When the concentrations of Bi:Te in electrolytes were 3 mM:4 mM, the TE films satisfied the Bi₂Te₃ stoichiometry and [...] Read more.

Electrodeposition is an important method for preparing bismuth telluride (Bi₂Te₃)-based thermoelectric (TE) thin films and micro-column arrays. When the concentrations of Bi:Te in electrolytes were 3 mM:4 mM, the TE films satisfied the Bi₂Te₃ stoichiometry and had no dependence on deposition potential. With increasing over-potential, crystal grains changed from lamellar structures with uniform growth directions to large clusters with staggered dendrites, causing a decrease in the deposition density. Meanwhile, the preferred (110) orientation was diminished. The TE film deposited at −35 mV had an optimum conductivity of 2003.6 S/cm and a power factor of 2015.64 μW/mK² at room temperature due to the (110)-preferred orientation. The electrodeposition of TE micro-columns in the template was recently used to fabricate high-power micro-thermoelectric generators (micro-TEG). Here, microporous glass templates were excellent templates for micro-TEG fabrication because of their low thermal conductivity, high insulation, and easy processing. A three-step pulsed-voltage deposition method was used for the fabrication of micro-columns with large aspect ratios, high filling rates, and high density. The resistance of a single TE micro-column with a 60 μm diameter and a 200 μm height was 6.22 Ω. This work laid the foundation for micro-TEG fabrication and improved performance. Full article

(This article belongs to the Special Issue Novel Synthesis Strategies and Phenomena in Low-Dimensional Structures Like Nanowires and Thin Films)

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10 pages, 2344 KiB

Open AccessArticle

Direct Growth of Two Dimensional Molybdenum Disulfide on Flexible Ceramic Substrate

by Yixiong Zheng, Chunyan Yuan, Sichen Wei, Hyun Kim, Fei Yao and Jung-Hun Seo

Nanomaterials 2019, 9(10), 1456; https://doi.org/10.3390/nano9101456 - 14 Oct 2019

Cited by 8 | Viewed by 3485

Abstract

In this paper, we report the first successful demonstration of the direct growth of high-quality two-dimensional (2D) MoS₂ semiconductors on a flexible substrate using a 25-μm-thick Yttria-stabilized zirconia ceramic substrate. Few-layered MoS₂ crystals grown at 800 °C showed a uniform crystal [...] Read more.

In this paper, we report the first successful demonstration of the direct growth of high-quality two-dimensional (2D) MoS₂ semiconductors on a flexible substrate using a 25-μm-thick Yttria-stabilized zirconia ceramic substrate. Few-layered MoS₂ crystals grown at 800 °C showed a uniform crystal size of approximately 50 μm, which consisted of about 10 MoS₂ layers. MoS₂ crystals were characterized using energy-dispersive X-ray spectroscopy. Raman spectroscopy was performed to investigate the crystal quality under bending conditions. The Raman mapping revealed a good uniformity with a stable chemical composition of the MoS₂ crystals. Our approach offers a simple and effective route to realize various flexible electronics based on MoS₂. Our approach can be applied for MoS₂ growth and for other 2D materials. Therefore, it offers a new opportunity that allows us to demonstrate high-performance flexible electronic/optoelectronic applications in a less expensive, simpler, and faster manner without sacrificing the intrinsic performance of 2D materials. Full article

(This article belongs to the Special Issue Novel Synthesis Strategies and Phenomena in Low-Dimensional Structures Like Nanowires and Thin Films)

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11 pages, 5454 KiB

Open AccessArticle

The Stability of Metallic MoS₂ Nanosheets and Their Property Change by Annealing

by Li Li, Jiyang Chen, Keyue Wu, Chunbin Cao, Shiwei Shi and Jingbiao Cui

Nanomaterials 2019, 9(10), 1366; https://doi.org/10.3390/nano9101366 - 24 Sep 2019

Cited by 29 | Viewed by 4761

Abstract

Highly pure 1T MoS₂ nanosheets were grown at 200 °C by a hydrothermal process. The effects of mild annealing on the structural and physical properties of the MoS₂ were studied by heating the nanosheets in air and vacuum up to 350 [...] Read more.

Highly pure 1T MoS₂ nanosheets were grown at 200 °C by a hydrothermal process. The effects of mild annealing on the structural and physical properties of the MoS₂ were studied by heating the nanosheets in air and vacuum up to 350 °C. It was found that the annealing leads to an increase in resistivity for the nanosheets by 3 orders of magnitude, the appearance of two absorption bands in the visible range, and a hydrophilic to hydrophobic change in the surface wetting properties. Monitoring of the annealing process by Raman spectroscopy indicates that the material property changes are associated with a 1T to 2H MoS₂ phase transition, with activation energies of 517 meV in air and 260 meV in vacuum. This study provides another way to control the electrical, optical, and surface properties of MoS₂ nanosheets for fulfilling the needs of various applications. Full article

(This article belongs to the Special Issue Novel Synthesis Strategies and Phenomena in Low-Dimensional Structures Like Nanowires and Thin Films)

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11 pages, 2820 KiB

Open AccessArticle

Strain-Mediated Bending of InP Nanowires through the Growth of an Asymmetric InAs Shell

by Ya’akov Greenberg, Alexander Kelrich, Shimon Cohen, Sohini Kar-Narayan, Dan Ritter and Yonatan Calahorra

Nanomaterials 2019, 9(9), 1327; https://doi.org/10.3390/nano9091327 - 16 Sep 2019

Cited by 9 | Viewed by 3450

Abstract

Controlling nanomaterial shape beyond its basic dimensionality is a concurrent challenge tackled by several growth and processing avenues. One of these is strain engineering of nanowires, implemented through the growth of asymmetrical heterostructures. Here, we report metal–organic molecular beam epitaxy of bent InP/InAs [...] Read more.

Controlling nanomaterial shape beyond its basic dimensionality is a concurrent challenge tackled by several growth and processing avenues. One of these is strain engineering of nanowires, implemented through the growth of asymmetrical heterostructures. Here, we report metal–organic molecular beam epitaxy of bent InP/InAs core/shell nanowires brought by precursor flow directionality in the growth chamber. We observe the increase of bending with decreased core diameter. We further analyze the composition of a single nanowire and show through supporting finite element simulations that strain accommodation following the lattice mismatch between InP and InAs dominates nanowire bending. The simulations show the interplay between material composition, shell thickness, and tapering in determining the bending. The simulation results are in good agreement with the experimental bending curvature, reproducing the radius of 4.3 µm (±10%), for the 2.3 µm long nanowire. The InP core of the bent heterostructure was found to be compressed at about 2%. This report provides evidence of shape control and strain engineering in nanostructures, specifically through the exchange of group-V materials in III–V nanowire growth. Full article

(This article belongs to the Special Issue Novel Synthesis Strategies and Phenomena in Low-Dimensional Structures Like Nanowires and Thin Films)

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15 pages, 2247 KiB

Open AccessArticle

Structure and Electronic Properties of InSb Nanowires Grown in Flexible Polycarbonate Membranes

by Abhay Pratap Singh, Kevin Roccapriore, Zaina Algarni, Riyadh Salloom, Teresa D. Golden and U. Philipose

Nanomaterials 2019, 9(9), 1260; https://doi.org/10.3390/nano9091260 - 5 Sep 2019

Cited by 9 | Viewed by 3318

Abstract

A dense array of vertically aligned indium antimonide (InSb) nanowires with high aspect ratio (diameter 150 nm, length 20

μ

m) were grown in the pores of a track-etched polycarbonate membrane via a one-step electrochemical method. There are several reports on InSb nanowire [...] Read more.

A dense array of vertically aligned indium antimonide (InSb) nanowires with high aspect ratio (diameter 150 nm, length 20

μ

m) were grown in the pores of a track-etched polycarbonate membrane via a one-step electrochemical method. There are several reports on InSb nanowire growth in the pores of a mechanically rigid, nano-channel alumina template (NCA), where nanowire growth occurs in the pores of the NCA. This work on InSb nanowire growth in pores of track-etched polycarbonate (PC) membrane sheds light on the various factors that affect nucleation and nanowire growth. The average length and diameter of the as-grown nanowires was about 10

μ

m and 150 nm, respectively. Two possible mechanisms accounting for two different morphologies of the as-grown nanowires are proposed. The polycrystallinity observed in some of the nanowires is explained using the 3D ‘nucleation-coalescence’ mechanism. On the other hand, single crystal nanowires with a high density of twin defects and stacking faults grow epitaxially by a two-dimensional (2D) nucleation/growth mechanism. To assess the electrical quality of the nanowires, two- and four-terminal devices were fabricated using a single InSb nanowire contacted by two Ni electrodes. It was found that, at low bias, the ohmic current is controlled by charge diffusion from the bulk contacts. On the other hand, at high bias, the effects of space charge limited current (SCLC) are evident in the current–voltage behavior, characteristic of transport through structures with reduced electrostatic screening. A cross-over from ohmic to SCLC occurs at about 0.14 V, yielding a free carrier concentration of the order of

10^{14}

cm

^{- 3}

. Full article

(This article belongs to the Special Issue Novel Synthesis Strategies and Phenomena in Low-Dimensional Structures Like Nanowires and Thin Films)

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10 pages, 2065 KiB

Open AccessArticle

Formation of Fe-Te Nanostructures during in Situ Fe Heavy Doping of Bi₂Te₃

by Jing Liang, Xiong Yao, Yu Jun Zhang, Fei Chen, Yuanzhen Chen and Iam Keong Sou

Nanomaterials 2019, 9(5), 782; https://doi.org/10.3390/nano9050782 - 22 May 2019

Cited by 4 | Viewed by 3903

Abstract

To study the in situ doping effect upon monotonically increasing dopant concentration, a Bi₂Te₃ layer doped with Fe up to ~6.9% along the growth direction was fabricated by the molecular beam epitaxy (MBE) technique. Its resistance versus temperature curve displays [...] Read more.

To study the in situ doping effect upon monotonically increasing dopant concentration, a Bi₂Te₃ layer doped with Fe up to ~6.9% along the growth direction was fabricated by the molecular beam epitaxy (MBE) technique. Its resistance versus temperature curve displays a superconductivity transition at about 12.3 K. Detailed structural and chemical analysis via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS) reveal that this layer consists of two types of unexpected Fe-Te nanostructures: one is FeTe thin layer formed near the surface, and the other is FeTe₂ nanorod embedded in the Bi₂Te₃ layer. Based on the results of further electrical and magnetotransport studies, it is likely that the observed superconductivity originates from the interface between the FeTe nanostructure and the neighboring Bi₂Te₃ layer. We have addressed the formation mechanisms of the observed nanostructures, which is attributed to the strong reaction between Fe and Te atoms during the growth process. The findings of this study also provide an unusual approach to synthesizing nanostructures via heavy doping if the dopant element is strongly reactive with an element in the host matrix. Full article

(This article belongs to the Special Issue Novel Synthesis Strategies and Phenomena in Low-Dimensional Structures Like Nanowires and Thin Films)

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11 pages, 3957 KiB

Open AccessArticle

Design and Regulation of Novel MnFe₂O₄@C Nanowires as High Performance Electrode for Supercapacitor

by Lei Geng, Fengfeng Yan, Chenhao Dong and Cuihua An

Nanomaterials 2019, 9(5), 777; https://doi.org/10.3390/nano9050777 - 21 May 2019

Cited by 43 | Viewed by 4337

Abstract

Bimetallic oxides have been considered as potential candidates for supercapacitors due to their relatively high electric conductivity, abundant redox reactions and cheapness. However, nanoparticle aggregation and huge volume variation during charging-discharging procedures make it hard for them to be applied widely. In this [...] Read more.

Bimetallic oxides have been considered as potential candidates for supercapacitors due to their relatively high electric conductivity, abundant redox reactions and cheapness. However, nanoparticle aggregation and huge volume variation during charging-discharging procedures make it hard for them to be applied widely. In this work, one-dimensional (1D) MnFe₂O₄@C nanowires were in-situ synthesized via a simply modified micro-emulsion technique, followed by thermal treatment. The novel 1D and core-shell architecture, and in-situ carbon coating promote its electric conductivity and porous feature. Due to these advantages, the MnFe₂O₄@C electrode exhibits a high specific capacitance of 824 F·g⁻¹ at 0.1 A·g⁻¹ and remains 476 F·g⁻¹ at 5 A·g⁻¹. After 10,000 cycles, the capacitance retention of the MnFe₂O₄@C electrode is up to 93.9%, suggesting its excellent long-term cycling stability. After assembling with activated carbon (AC) to form a MnFe₂O₄@C//AC device, the energy density of this MnFe₂O₄@C//AC device is 27 W·h·kg⁻¹ at a power density of 290 W·kg⁻¹, and remains at a 10 W·h·kg⁻¹ energy density at a high power density of 9300 W·kg⁻¹. Full article

(This article belongs to the Special Issue Novel Synthesis Strategies and Phenomena in Low-Dimensional Structures Like Nanowires and Thin Films)

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16 pages, 3110 KiB

Open AccessArticle

A Ferroelectric-Photovoltaic Effect in SbSI Nanowires

by Krystian Mistewicz, Marian Nowak and Danuta Stróż

Nanomaterials 2019, 9(4), 580; https://doi.org/10.3390/nano9040580 - 9 Apr 2019

Cited by 30 | Viewed by 6172

Abstract

A ferroelectric-photovoltaic effect in nanowires of antimony sulfoiodide (SbSI) is presented for the first time. Sonochemically prepared SbSI nanowires have been characterized using high-resolution transmission electron microscopy (HRTEM) and optical diffuse reflection spectroscopy (DRS). The temperature dependences of electrical properties of the fabricated [...] Read more.

A ferroelectric-photovoltaic effect in nanowires of antimony sulfoiodide (SbSI) is presented for the first time. Sonochemically prepared SbSI nanowires have been characterized using high-resolution transmission electron microscopy (HRTEM) and optical diffuse reflection spectroscopy (DRS). The temperature dependences of electrical properties of the fabricated SbSI nanowires have been investigated too. The indirect forbidden energy gap E_gIf = 1.862 (1) eV and Curie temperature T_C = 291 (2) K of SbSI nanowires have been determined. Aligned SbSI nanowires have been deposited in an electric field between Pt electrodes on alumina substrate. The photoelectrical response of such a prepared ferroelectric-photovoltaic (FE-PV) device can be switched using a poling electric field and depends on light intensity. The photovoltage, generated under λ = 488 nm illumination of P_opt = 127 mW/cm² optical power density, has reached U_OC = 0.119 (2) V. The presented SbSI FE-PV device is promising for solar energy harvesting as well as for application in non-volatile memories based on the photovoltaic effect. Full article

(This article belongs to the Special Issue Novel Synthesis Strategies and Phenomena in Low-Dimensional Structures Like Nanowires and Thin Films)

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10 pages, 5195 KiB

Open AccessArticle

Applied Stress-Assisted Growth of Single Crystal γ-Fe₂O₃ Nanowires

by Lan Lu, Ligen Hong, Yi Chu, Huayong Pan, Shaoyun Huang, Yingjie Xing and Hongqi Xu

Nanomaterials 2018, 8(12), 1037; https://doi.org/10.3390/nano8121037 - 12 Dec 2018

Cited by 3 | Viewed by 2648

Abstract

It is difficult to obtain γ-Fe₂O₃ nanostructures by heating iron substrate in ambient conditions because γ-Fe₂O₃ is less thermodynamically stable than α-Fe₂O₃. In this work, we synthesize γ-Fe₂O₃ nanowires by [...] Read more.

It is difficult to obtain γ-Fe₂O₃ nanostructures by heating iron substrate in ambient conditions because γ-Fe₂O₃ is less thermodynamically stable than α-Fe₂O₃. In this work, we synthesize γ-Fe₂O₃ nanowires by heating iron particles under an external force. The stacking style of iron and oxygen ions under a strong shearing stress tends to adopt the γ-Fe₂O₃ structure regardless of the thermodynamic restriction. These γ-Fe₂O₃ nanowires exhibit a clear ferromagnetic property. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) measurements confirm that γ-phase structure appears only under the applied external force during the heating period. A window of the magnitude of the external force is found to help the nanowire growth on iron particles. The growth mechanism of γ-Fe₂O₃ nanowires other than α-Fe₂O₃ under the external force is discussed and an applied stress-assisted growth model is proposed. This work presents an easy approach to produce ferromagnetic iron oxide nanowires on a large scale. Full article

(This article belongs to the Special Issue Novel Synthesis Strategies and Phenomena in Low-Dimensional Structures Like Nanowires and Thin Films)

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14 pages, 7428 KiB

Open AccessArticle

Synthesis of Amorphous InSb Nanowires and a Study of the Effects of Laser Radiation and Thermal Annealing on Nanowire Crystallinity

by Zaina Algarni, Abhay Singh and Usha Philipose

Nanomaterials 2018, 8(8), 607; https://doi.org/10.3390/nano8080607 - 9 Aug 2018

Cited by 10 | Viewed by 4399

Abstract

Although various synthesis and characterization strategies have been employed for the synthesis of crystalline nanowires, there is very little work done on development of low-dimensional amorphous semiconductors. This paper presents a simple strategy to grow amorphous

I n S b

(a- [...] Read more.

Although various synthesis and characterization strategies have been employed for the synthesis of crystalline nanowires, there is very little work done on development of low-dimensional amorphous semiconductors. This paper presents a simple strategy to grow amorphous

I n S b

(a-

I n S b

) nanowires (NWs) in a chemical vapor deposition (CVD) system. The NWs were grown on

S i

substrate coated with indium film and the lack of crystallinity in the as-grown stoichiometric NWs was ascertained by Raman spectroscopy and electron transport measurements. A model proposed to explain the amorphous NW growth mechanism takes into account the fact that NW growth was carried out at the high temperature ramp-up rate of 75

^{\circ}

C/min. This high rate is believed to affect the growth kinematics and determine the arrangement of atoms in the growing NW. Raman spectrum of the as-grown sample shows a broad peak around 155 cm

^{- 1}

, indicative of the presence of high density of homopolar

S b

-

S b

bonds in the amorphous matrix. It was also found that high intensity laser light induces localized crystallization of the NW, most likely due to radiation-stimulated diffusion of defects in a-

I n S b

. The nonlinear trend of the current-voltage characteristics for individually contacted a-

I n S b

NWs was analyzed to prove that the non-linearity is not induced by Schottky contacts. At high bias fields, space charge limited conduction was the proposed electron transport mechanism. Post-growth annealing of the as-grown a-

I n S b

NWs was found to be very effective in causing the NWs to undergo a phase transition from amorphous to crystalline. Full article

(This article belongs to the Special Issue Novel Synthesis Strategies and Phenomena in Low-Dimensional Structures Like Nanowires and Thin Films)

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Review

Jump to: Research

13 pages, 2049 KiB

Open AccessReview

Synthesis of Vertical Carbon Nanotube Interconnect Structures Using CMOS-Compatible Catalysts

by Zichao Ma, Shaolin Zhou, Changjian Zhou, Ying Xiao, Suwen Li and Mansun Chan

Nanomaterials 2020, 10(10), 1918; https://doi.org/10.3390/nano10101918 - 25 Sep 2020

Cited by 8 | Viewed by 3140

Abstract

Synthesis of the vertically aligned carbon nanotubes (CNTs) using complementary metal-oxide-semiconductor (CMOS)-compatible methods is essential to integrate the CNT contact and interconnect to nanoscale devices and ultra-dense integrated nanoelectronics. However, the synthesis of high-density CNT array at low-temperature remains a challenging task. The [...] Read more.

Synthesis of the vertically aligned carbon nanotubes (CNTs) using complementary metal-oxide-semiconductor (CMOS)-compatible methods is essential to integrate the CNT contact and interconnect to nanoscale devices and ultra-dense integrated nanoelectronics. However, the synthesis of high-density CNT array at low-temperature remains a challenging task. The advances in the low-temperature synthesis of high-density vertical CNT structures using CMOS-compatible methods are reviewed. Primarily, recent works on theoretical simulations and experimental characterizations of CNT growth emphasized the critical roles of catalyst design in reducing synthesis temperature and increasing CNT density. In particular, the approach of using multilayer catalyst film to generate the alloyed catalyst nanoparticle was found competent to improve the active catalyst nanoparticle formation and reduce the CNT growth temperature. With the multilayer catalyst, CNT arrays were directly grown on metals, oxides, and 2D materials. Moreover, the relations among the catalyst film thickness, CNT diameter, and wall number were surveyed, which provided potential strategies to control the tube density and the wall density of synthesized CNT array. Full article

(This article belongs to the Special Issue Novel Synthesis Strategies and Phenomena in Low-Dimensional Structures Like Nanowires and Thin Films)

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19 pages, 4723 KiB

Open AccessReview

Review on Quasi One-Dimensional CdSe Nanomaterials: Synthesis and Application in Photodetectors

by Weifeng Jin and Luodan Hu

Nanomaterials 2019, 9(10), 1359; https://doi.org/10.3390/nano9101359 - 23 Sep 2019

Cited by 25 | Viewed by 4133

Abstract

During the past 15 years, quasi one-dimensional (1D) Cadmium Selenide (CdSe) nanomaterials have been widely investigated for high-performance electronic and optoelectronic devices, due to the unique geometrical and physical properties. In this review, recent advancements on diverse synthesis methods of 1D CdSe nanomaterials [...] Read more.

During the past 15 years, quasi one-dimensional (1D) Cadmium Selenide (CdSe) nanomaterials have been widely investigated for high-performance electronic and optoelectronic devices, due to the unique geometrical and physical properties. In this review, recent advancements on diverse synthesis methods of 1D CdSe nanomaterials and the application in photodetectors have been illustrated in detail. First, several bottom-up synthesis methods of 1D CdSe nanomaterials have been introduced, including the vapor-liquid-solid method, the solution-liquid-solid method, and electrochemical deposition, etc. Second, the discussion on photodetectors based on 1D CdSe nanomaterials has been divided into three parts, including photodiodes, photoconductors, and phototransistors. Besides, some new mechanisms (such as enhancement effect of localized surface plasmon, optical quenching effect of photoconductivity, and piezo-phototronic effect), which can be utilized to enhance the performance of photodetectors, have also been elaborated. Finally, some major challenges and opportunities towards the practical integration and application of 1D CdSe nanomaterials in photodetectors have been discussed, which need to be further investigated in the future. Full article

(This article belongs to the Special Issue Novel Synthesis Strategies and Phenomena in Low-Dimensional Structures Like Nanowires and Thin Films)

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