Research

15 pages, 1914 KiB

Open AccessArticle

Circumventing the Uncertainties of the Liquid Phase in the Compositional Control of VLS III–V Ternary Nanowires Based on Group V Intermix

by Vladimir G. Dubrovskii

Nanomaterials 2024, 14(2), 207; https://doi.org/10.3390/nano14020207 - 17 Jan 2024

Viewed by 609

Abstract

Control over the composition of III–V ternary nanowires grown by the vapor–liquid–solid (VLS) method is essential for bandgap engineering in such nanomaterials and for the fabrication of functional nanowire heterostructures for a variety of applications. From the fundamental viewpoint, III–V ternary nanowires based [...] Read more.

Control over the composition of III–V ternary nanowires grown by the vapor–liquid–solid (VLS) method is essential for bandgap engineering in such nanomaterials and for the fabrication of functional nanowire heterostructures for a variety of applications. From the fundamental viewpoint, III–V ternary nanowires based on group V intermix (InSb_xAs_1−x, InP_xAs_1−x, GaP_xAs_1−x and many others) present the most difficult case, because the concentrations of highly volatile group V atoms in a catalyst droplet are beyond the detection limit of any characterization technique and therefore principally unknown. Here, we present a model for the vapor–solid distribution of such nanowires, which fully circumvents the uncertainties that remained in the theory so far, and we link the nanowire composition to the well-controlled parameters of vapor. The unknown concentrations of group V atoms in the droplet do not enter the distribution, despite the fact that a growing solid is surrounded by the liquid phase. The model fits satisfactorily the available data on the vapor–solid distributions of VLS InSb_xAs_1−x, InP_xAs_1−x and GaP_xAs_1−x nanowires grown using different catalysts. Even more importantly, it provides a basis for the compositional control of III–V ternary nanowires based on group V intermix, and it can be extended over other material systems where two highly volatile elements enter a ternary solid alloy through a liquid phase. Full article

(This article belongs to the Special Issue Preparation and Application of Nanowires II)

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13 pages, 31318 KiB

Open AccessArticle

Influence of Different Carrier Gases, Temperature, and Partial Pressure on Growth Dynamics of Ge and Si Nanowires

by Nicolas Forrer, Arianna Nigro, Gerard Gadea and Ilaria Zardo

Nanomaterials 2023, 13(21), 2879; https://doi.org/10.3390/nano13212879 - 30 Oct 2023

Viewed by 909

Abstract

The broad and fascinating properties of nanowires and their synthesis have attracted great attention as building blocks for functional devices at the nanoscale. Silicon and germanium are highly interesting materials due to their compatibility with standard CMOS technology. Their combination provides optimal templates [...] Read more.

The broad and fascinating properties of nanowires and their synthesis have attracted great attention as building blocks for functional devices at the nanoscale. Silicon and germanium are highly interesting materials due to their compatibility with standard CMOS technology. Their combination provides optimal templates for quantum applications, for which nanowires need to be of high quality, with carefully designed dimensions, crystal phase, and orientation. In this work, we present a detailed study on the growth kinetics of silicon (length 0.1–1

μ

m, diameter 10–60 nm) and germanium (length 0.06–1

μ

m, diameter 10–500 nm) nanowires grown by chemical vapor deposition applying the vapour–liquid–solid growth method catalysed by gold. The effects of temperature, partial pressure of the precursor gas, and different carrier gases are analysed via scanning electron microscopy. Argon as carrier gas enhances the growth rate at higher temperatures (120 nm/min for Ar and 48 nm/min H

_{2}

), while hydrogen enhances it at lower temperatures (35 nm/min for H

_{2}

and 22 nm/min for Ar) due to lower heat capacity. Both materials exhibit two growth regimes as a function of the temperature. The tapering rate is about ten times lower for silicon nanowires than for germanium ones. Finally, we identify the optimal conditions for nucleation in the nanowire growth process. Full article

(This article belongs to the Special Issue Preparation and Application of Nanowires II)

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14 pages, 1986 KiB

Open AccessArticle

Composition of Vapor–Liquid–Solid III–V Ternary Nanowires Based on Group-III Intermix

by Vladimir G. Dubrovskii

Nanomaterials 2023, 13(18), 2532; https://doi.org/10.3390/nano13182532 - 11 Sep 2023

Cited by 1 | Viewed by 665

Abstract

Compositional control in III–V ternary nanowires grown by the vapor–liquid–solid method is essential for bandgap engineering and the design of functional nanowire nano-heterostructures. Herein, we present rather general theoretical considerations and derive explicit forms of the stationary vapor–solid and liquid–solid distributions of vapor–liquid–solid [...] Read more.

Compositional control in III–V ternary nanowires grown by the vapor–liquid–solid method is essential for bandgap engineering and the design of functional nanowire nano-heterostructures. Herein, we present rather general theoretical considerations and derive explicit forms of the stationary vapor–solid and liquid–solid distributions of vapor–liquid–solid III–V ternary nanowires based on group-III intermix. It is shown that the vapor–solid distribution of such nanowires is kinetically controlled, while the liquid–solid distribution is in equilibrium or nucleation-limited. For a more technologically important vapor-solid distribution connecting nanowire composition with vapor composition, the kinetic suppression of miscibility gaps at a growth temperature is possible, while miscibility gaps (and generally strong non-linearity of the compositional curves) always remain in the equilibrium liquid–solid distribution. We analyze the available experimental data on the compositions of the vapor–liquid–solid Al_xGa_1−xAs, In_xGa_1−xAs, In_xGa_1−xP, and In_xGa_1−xN nanowires, which are very well described within the model. Overall, the developed approach circumvents uncertainty in choosing the relevant compositional model (close-to-equilibrium or kinetic), eliminates unknown parameters in the vapor–solid distribution of vapor–liquid–solid nanowires based on group-III intermix, and should be useful for the precise compositional tuning of such nanowires. Full article

(This article belongs to the Special Issue Preparation and Application of Nanowires II)

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10 pages, 4858 KiB

Open AccessArticle

Improved Through-Plane Thermal Conductivity of Poly(dimethylsiloxane)Composites through the Formation of 3D Filler Foam Using Freeze-Casting and Annealing Processes

by Jooyoung Lee, Wonyoung Yang, Geunhyeong Lee, Youngsung Cho and Jooheon Kim

Nanomaterials 2023, 13(15), 2154; https://doi.org/10.3390/nano13152154 - 25 Jul 2023

Viewed by 955

Abstract

The configuration of a continuous and oriented thermal pathway is essential for efficient heat dissipation in the oriented direction. Three-dimensional (3D) conductive filler structures provide a suitable approach for constructing continuous thermal pathways in polymer-based composites. The aluminum nitride/reduced graphene oxide/poly(dimethylsiloxane) (AlN/rGO/PDMS) composite [...] Read more.

The configuration of a continuous and oriented thermal pathway is essential for efficient heat dissipation in the oriented direction. Three-dimensional (3D) conductive filler structures provide a suitable approach for constructing continuous thermal pathways in polymer-based composites. The aluminum nitride/reduced graphene oxide/poly(dimethylsiloxane) (AlN/rGO/PDMS) composite material is made with a 3D foam structure and focuses on reducing GO and forming foam via polyvinyl alcohol (PVA). We analyze the successful fabrication of hybrid fillers and composites using various methods. The fabricated composite with a 3D network filler foam achieves a through-plane thermal conductivity of 1.43 W/mK and achieves 752% higher thermal conductivity compared to pure PDMS, which is superior to composites without 3D foam. The continuous 3D filler structure via freeze-drying and annealing processes provides efficient thermal dissipation in the through-plane direction pathway, which is critical for enhancing thermal conductivity. Therefore, this work produces a polymer composite material with improved thermal conductivity through various processes. Full article

(This article belongs to the Special Issue Preparation and Application of Nanowires II)

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16 pages, 5252 KiB

Open AccessArticle

Evolution of Cu-In Catalyst Nanoparticles under Hydrogen Plasma Treatment and Silicon Nanowire Growth Conditions

by Weixi Wang, Éric Ngo, Pavel Bulkin, Zhengyu Zhang, Martin Foldyna, Pere Roca i Cabarrocas, Erik V. Johnson and Jean-Luc Maurice

Nanomaterials 2023, 13(14), 2061; https://doi.org/10.3390/nano13142061 - 12 Jul 2023

Viewed by 1102

Abstract

We report silicon nanowire (SiNW) growth with a novel Cu-In bimetallic catalyst using a plasma-enhanced chemical vapor deposition (PECVD) method. We study the structure of the catalyst nanoparticles (NPs) throughout a two-step process that includes a hydrogen plasma pre-treatment at 200 °C and [...] Read more.

We report silicon nanowire (SiNW) growth with a novel Cu-In bimetallic catalyst using a plasma-enhanced chemical vapor deposition (PECVD) method. We study the structure of the catalyst nanoparticles (NPs) throughout a two-step process that includes a hydrogen plasma pre-treatment at 200 °C and the SiNW growth itself in a hydrogen-silane plasma at 420 °C. We show that the H₂-plasma induces a coalescence of the Cu-rich cores of as-deposited thermally evaporated NPs that does not occur when the same annealing is applied without plasma. The SiNW growth process at 420 °C induces a phase transformation of the catalyst cores to Cu₇In₃; while a hydrogen plasma treatment at 420 °C without silane can lead to the formation of the Cu₁₁In₉ phase. In situ transmission electron microscopy experiments show that the SiNWs synthesis with Cu-In bimetallic catalyst NPs follows an essentially vapor-solid–solid process. By adjusting the catalyst composition, we manage to obtain small-diameter SiNWs—below 10 nm—among which we observe the metastable hexagonal diamond phase of Si, which is predicted to have a direct bandgap. Full article

(This article belongs to the Special Issue Preparation and Application of Nanowires II)

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15 pages, 10174 KiB

Open AccessArticle

Construction of Ag/Ag₂S/CdS Heterostructures through a Facile Two-Step Wet Chemical Process for Efficient Photocatalytic Hydrogen Production

by Yu-Cheng Chang and Ying-Ru Lin

Nanomaterials 2023, 13(12), 1815; https://doi.org/10.3390/nano13121815 - 07 Jun 2023

Cited by 1 | Viewed by 1292

Abstract

We have demonstrated a two-step wet chemical approach for synthesizing ternary Ag/Ag₂S/CdS heterostructures for efficient photocatalytic hydrogen evolution. The CdS precursor concentrations and reaction temperatures are crucial in determining the efficiency of photocatalytic water splitting under visible light excitation. In addition, [...] Read more.

We have demonstrated a two-step wet chemical approach for synthesizing ternary Ag/Ag₂S/CdS heterostructures for efficient photocatalytic hydrogen evolution. The CdS precursor concentrations and reaction temperatures are crucial in determining the efficiency of photocatalytic water splitting under visible light excitation. In addition, the effect of operational parameters (such as the pH value, sacrificial reagents, reusability, water bases, and light sources) on the photocatalytic hydrogen production of Ag/Ag₂S/CdS heterostructures was investigated. As a result, Ag/Ag₂S/CdS heterostructures exhibited a 3.1-fold enhancement in photocatalytic activities compared to bare CdS nanoparticles. Furthermore, the combination of Ag, Ag₂S, and CdS can significantly enhance light absorption and facilitate the separation and transport of photogenerated carriers through the surface plasma resonance (SPR) effect. Furthermore, the Ag/Ag₂S/CdS heterostructures in seawater exhibited a pH value approximately 2.09 times higher than in de-ionized water without an adjusted pH value under visible light excitation. The ternary Ag/Ag₂S/CdS heterostructures provide new potential for designing efficient and stable photocatalysts for photocatalytic hydrogen evolution. Full article

(This article belongs to the Special Issue Preparation and Application of Nanowires II)

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23 pages, 3828 KiB

Open AccessArticle

Modeling Catalyst-Free Growth of III-V Nanowires: Empirical and Rigorous Approaches

by Vladimir G. Dubrovskii

Nanomaterials 2023, 13(7), 1253; https://doi.org/10.3390/nano13071253 - 01 Apr 2023

Cited by 2 | Viewed by 827

Abstract

Catalyst-free growth of III-V and III-nitride nanowires (NWs) by the self-induced nucleation mechanism or selective area growth (SAG) on different substrates, including Si, show great promise for monolithic integration of III-V optoelectronics with Si electronic platform. The morphological design of NW ensembles requires [...] Read more.

Catalyst-free growth of III-V and III-nitride nanowires (NWs) by the self-induced nucleation mechanism or selective area growth (SAG) on different substrates, including Si, show great promise for monolithic integration of III-V optoelectronics with Si electronic platform. The morphological design of NW ensembles requires advanced growth modeling, which is much less developed for catalyst-free NWs compared to vapor–liquid–solid (VLS) NWs of the same materials. Herein, we present an empirical approach for modeling simultaneous axial and radial growths of untapered catalyst-free III-V NWs and compare it to the rigorous approach based on the stationary diffusion equations for different populations of group III adatoms. We study in detail the step flow occurring simultaneously on the NW sidewalls and top and derive the general laws governing the evolution of NW length and radius versus the growth parameters. The rigorous approach is reduced to the empirical equations in particular cases. A good correlation of the model with the data on the growth kinetics of SAG GaAs NWs and self-induced GaN NWs obtained by different epitaxy techniques is demonstrated. Overall, the developed theory provides a basis for the growth modeling of catalyst-free NWs and can be further extended to more complex NW morphologies. Full article

(This article belongs to the Special Issue Preparation and Application of Nanowires II)

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17 pages, 6715 KiB

Open AccessArticle

Additive Manufacturing of Co₃Fe Nano-Probes for Magnetic Force Microscopy

by Robert Winkler, Michele Brugger-Hatzl, Lukas Matthias Seewald, David Kuhness, Sven Barth, Thomas Mairhofer, Gerald Kothleitner and Harald Plank

Nanomaterials 2023, 13(7), 1217; https://doi.org/10.3390/nano13071217 - 29 Mar 2023

Cited by 6 | Viewed by 2114

Abstract

Magnetic force microscopy (MFM) is a powerful extension of atomic force microscopy (AFM), which mostly uses nano-probes with functional coatings for studying magnetic surface features. Although well established, additional layers inherently increase apex radii, which reduce lateral resolution and also contain the risk [...] Read more.

Magnetic force microscopy (MFM) is a powerful extension of atomic force microscopy (AFM), which mostly uses nano-probes with functional coatings for studying magnetic surface features. Although well established, additional layers inherently increase apex radii, which reduce lateral resolution and also contain the risk of delamination, rendering such nano-probes doubtful or even useless. To overcome these limitations, we now introduce the additive direct-write fabrication of magnetic nano-cones via focused electron beam-induced deposition (FEBID) using an HCo₃Fe(CO)₁₂ precursor. The study first identifies a proper 3D design, confines the most relevant process parameters by means of primary electron energy and beam currents, and evaluates post-growth procedures as well. That way, highly crystalline nano-tips with minimal surface contamination and apex radii in the sub-15 nm regime are fabricated and benchmarked against commercial products. The results not only reveal a very high performance during MFM operation but in particular demonstrate virtually loss-free behavior after almost 8 h of continuous operation, thanks to the all-metal character. Even after more than 12 months of storage in ambient conditions, no performance loss is observed, which underlines the high overall performance of the here-introduced FEBID-based Co₃Fe MFM nano-probes. Full article

(This article belongs to the Special Issue Preparation and Application of Nanowires II)

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