| 11. |
- Persson, Axel R., et al.
(author)
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Electron Tomography Reveals the Droplet Covered Surface Structure of Nanowires Grown by Aerotaxy
- 2018
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In: Small. - : Wiley. - 1613-6810. ; 14:33
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Journal article (peer-reviewed)abstract
- For the purpose of functionalizing III-V semiconductor nanowires using n-doping, Sn-doped GaAs zincblende nanowires are produced, using the growth method of Aerotaxy. The growth conditions used are such that Ga droplets, formed on the nanowire surface, increase in number and concentrations when the Sn-precursor concentration is increased. Droplet-covered wires grown with varying Sn concentrations are analyzed by transmission electron microscopy and electron tomography, which together establish the positioning of the droplets to be preferentially on {−111}B facets. These facets have the same polarity as the main wire growth direction, [−1−1−1]B. This means that the generated Ga particles can form nucleation sites for possible nanowire branch growth. The concept of azimuthal mapping is introduced as a useful tool for nanowire surface visualization and evaluation. It is demonstrated here that electron tomography is useful in revealing both the surface and internal morphologies of the nanowires, opening up for applications in the analysis of more structurally complicated systems like radially asymmetrical nanowires. The analysis also gives a further understanding of the limits of the dopants which can be used for Aerotaxy nanowires.
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| 12. |
- Sivakumar, Sudhakar, et al.
(author)
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Aerotaxy : gas-phase epitaxy of quasi 1D nanostructures
- 2021
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In: Nanotechnology. - : IOP Publishing. - 0957-4484 .- 1361-6528. ; 32:2, s. 25605-25605
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Journal article (peer-reviewed)abstract
- Cost- and resource-efficient growth is necessary for many applications of semiconductor nanowires. We here present the design, operational details and theory behind Aerotaxy, a scalable alternative technology for producing quality crystalline nanowires at a remarkably high growth rate and throughput. Using size-controlled Au seed particles and organometallic precursors, Aerotaxy can produce nanowires with perfect crystallinity and controllable dimensions, and the method is suitable to meet industrial production requirements. In this report, we explain why Aerotaxy is an efficient method for fabricating semiconductor nanowires and explain the technical aspects of our custom-built Aerotaxy system. Investigations using SEM (scanning electron microscope), TEM (transmission electron microscope) and other characterization methods are used to support the claim that Aerotaxy is indeed a scalable method capable of producing nanowires with reproducible properties. We have investigated both binary and ternary III-V semiconductor material systems like GaAs and GaAsP. In addition, common aspects of Aerotaxy nanowires deduced from experimental observations are used to validate the Aerotaxy growth model, based on a computational flow dynamics (CFD) approach. We compare the experimental results with the model behaviour to better understand Aerotaxy growth.
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| 13. |
- Sivakumar, Sudhakar, et al.
(author)
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Doping of GaAsP nanowires grown by aerotaxy
- 2019
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Conference paper (peer-reviewed)abstract
- Nanowire (NW) Photovoltaics are a promising route for low-cost multi-bandgap tandem cells, which is taxing in terms of processing and lattice matching in traditional planar geometries.[1] III-V nanowires are more suitable for monolithic integration as they can assimilate the lattice mismatch to a larger extent.[2] GaAsP is a material that offers a wide tunability of the band gap from near infrared (Eg = 1.42 eV) to visible regions (Eg = 2.3 eV) and is one of the best-suited materials for growth on silicon.[3]Controlled synthesis of GaAs(1-x)P(x) NWs with a bandgap ranging from 1.42 to 1.90 eV (at 300K) through the scalable Aerotaxy [4] technique has already been reported.[5]The present work concerns doping of GaAsP NWs by controlling precursor (DEZn) flows during growth by Aerotaxy. Here we present structural, optical and electrical studies of doped GaAs(1-x)P(x) NWs by high-resolution TEM, Photoluminescence, 4-point probe and Hall measurements.
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| 14. |
- Sivakumar, Sudhakar
(author)
-
Understanding and Optimization of III-V nanowire growth in Aerotaxy
- 2021
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Doctoral thesis (other academic/artistic)abstract
- III-V semiconductor nanowires are high aspect ratio nanostructures with superior properties that can potentially enhance the functionality of next-generation opto-electronic devices. At present, the most reliable method for fabricating III-V semiconductor nanowires is the particle-assisted vapor-liquid-solid growth using a substrate-based growth process. However, a substrate-based process limits the number of nanowires that can be produced per cycle and is an obstacle to the industrial production of III-V nanowires. A viable alternative technology for the high-throughput synthesis of III-V nanowires is vital to exploit the true potential of III-V semiconductor nanowires. Aerotaxy is a gas-phase vapor-liquid-solid growth technology that can mass-produce III-V semiconductor nanowires without a substrate. It reduces the cost of production by eliminating the need for a crystalline substrate and can produce nanowires at a phenomenal rate.This thesis explores the fundamental limits of the Aerotaxy technology in producing III-V nanowires. GaAs and GaAsP material systems were adopted to explore the fundamentals of Aerotaxy nanowire growth. Growth experiments were designed to probe the growth parameter dependence of nanowire properties like morphology, crystal structure and composition. In addition to that, the efficiency of in situ doping (p- and n- type) in Aerotaxy was evaluated using optical and electrical characterization techniques. The growth parameter space was explored to demonstrate the reproducibility and efficiency of Aerotaxy nanowire growth. To better understand the growth, a pseudo-particle continuum model for Aerotaxy growth was developed. The results from the model shows good agreement with experimental quantitative and qualitative observations.The studies presented in the thesis also explores the fabrication of complex nanostructures like branched GaAsP nanowires. By tuning the diameter of the initial catalytic particle, we were able to induce branching in GaAsP nanowires. Apart from that, GaAs nanowires grown from alternative metal particles like Ga, AuAg and Ag in Aerotaxy shows promising initial results. Mass-producing III-V nanowires using alternative seed metals that are compatible with Si could bring novel functionalities while reducing production costs. The importance nano-safety is also highlighted in the context of a high-throughput production environment.
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| 15. |
- Valderas Gutiérrez, Julia, et al.
(author)
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Enhanced Optical Biosensing by Aerotaxy Ga(As)P Nanowire Platforms Suitable for Scalable Production
- 2022
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In: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 5:7, s. 9063-9071
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Journal article (peer-reviewed)abstract
- Sensitive detection of low-abundance biomolecules is central for diagnostic applications. Semiconductor nanowires can be designed to enhance the fluorescence signal from surface-bound molecules, prospectively improving the limit of optical detection. However, to achieve the desired control of physical dimensions and material properties, one currently uses relatively expensive substrates and slow epitaxy techniques. An alternative approach is aerotaxy, a high-throughput and substrate-free production technique for high-quality semiconductor nanowires. Here, we compare the optical sensing performance of custom-grown aerotaxyproduced Ga(As)P nanowires vertically aligned on a polymer substrate to GaP nanowires batch-produced by epitaxy on GaP substrates. We find that signal enhancement by individual aerotaxy nanowires is comparable to that from epitaxy nanowires and present evidence of single-molecule detection. Platforms based on both types of nanowires show substantially higher normalized-to-blank signal intensity than planar glass surfaces, with the epitaxy platforms performing somewhat better, owing to a higher density of nanowires. With further optimization, aerotaxy nanowires thus offer a pathway to scalable, low-cost production of highly sensitive nanowire-based platforms for optical biosensing applications.
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