Aerosol synthesis of germanium nanoparticles supported by external seeding: Theoretical and experimental analysis
Graphical abstract
Introduction
Semiconducting nanoparticles (NPs) out of silicon (Si) or germanium (Ge) have attracted attention in a wide field of applications over the last decades. The NPs are used as building blocks for the fabrication of functional devices e.g. thin film transistors (Meric et al., 2015), solar cells (Fan et al., 2010, Wang et al., 2013), lithium ion batteries (Duveau et al., 2015, Li et al., 2017), sensors (Chu et al., 2016), and thermoelectric generators (Basu et al., 2014). The properties of the functional devices can be tailored by particle properties like size, shape or composition. Contrary to Si, Ge has a 10–50 times larger absorption coefficient throughout the visible spectrum (Dash & Newman, 1955) and a 104 times higher electronic conductivity (Wang, Bao, Lou, Liang, & Zhou, 2016). Therefore, Ge is a promising material for NP based device fabrication. However, a well-controlled synthesis is essential to provide building blocks with defined size, shape and composition for thin-film formation.
The synthesis of Ge nanoparticles is achieved in the liquid phase by a variety of methods like colloidal synthesis in molten salts (Liu, Giordano, & Antonietti, 2012) or thermal reduction of GeO2 with magnesium (Wang et al., 2016). However, for a continuous and scalable production route with controllable product properties aerosol processes are more suited (Kruis, Fissan, & Peled, 1998). Synthesis strategies are well demonstrated in literature for non-thermal plasma (Ahadi et al., 2016, Holman and Kortshagen, 2011), laser ablation (Amoruso et al., 2004, Erogbogbo et al., 2011), and hot wall reactor processes (Onischuk et al., 2000, Wiggers et al., 2001).
In previous works we have shown the high versatility and scalability of hot wall reactors. Quite narrow particle size distribution of Si NPs can be obtained with tailor-made properties by low concentration and pressure to overcome broad distribution predicted by the self-preserving theory for coagulation (Dekkers and Friedlander, 2002, Körmer et al., 2012). Besides pure Si NPs also the formation of Si/Ge hybrid structures and alloys were demonstrated (Mehringer et al., 2014, Mehringer et al., 2015). It was shown that for the synthesis of well-defined Ge NPs the low concentration and pressure are not sufficient. Additional seed particles have to be added to suppress homogenous nucleation. Otherwise, very high nucleation rates occur which lead to high particle number concentrations. Due to the high number concentration agglomeration and sintering becomes relevant. Similar observations were made by Okuyama, Ushio, Kousaka, Flagan, and Seinfeld (1990) and Alam and Flagan (1986) who evaluated experimentally and theoretically the role of seed particles in the formation of TiO2 and Si. For Ge NP formation a detailed study and comparison of simulated and experimental data is not present. Therefore, in this work we introduce a hot wire generator (HWG) directly connected to the first stage as flexible and small external seeding unit. The HWG allows a stable and controllable production of ultrafine metal particles in high concentrations (Khan et al., 2014, Peineke et al., 2006) suitable for providing seed or catalyst particles (Nasibulin, Moisala, Brown, Jiang, & Kauppinen, 2005). The amount and size of the seed particles can be easily adjusted in the HWG which allows a detailed investigation of the effect of seed particles on particle formation. The experimental results are supported theoretically by a population balance model including global reaction kinetics, homogenous and heterogeneous nucleation and particle growth to describe the evolution of the particle size distribution.
Section snippets
Theoretical approach for heterogeneous nucleation
The model for the particle synthesis of Ge NPs with seed particles applied in this work is based on the work of Körmer, Schmid, & Peukert (2010), who successfully implemented and validated an one-dimensional model of Artelt, Schmid, and Peukert (2003); Artelt, Schmid, and Peukert (2005) for the particle synthesis of Si in an aerosol reactor. Therefore, only the most important mechanisms and equations are briefly described in the next sections. Agglomeration and sintering are not considered in
Reactor setup
The reactor setup consists of two consecutive hot wall reactors (HWR I and HWR II) and is described in detail elsewhere (Mehringer et al., 2014). In this study, only the HWR I is used for particle synthesis. The standard operation pressure is 25 mbar. The metallic seed particles are produced by a hot wire generator by condensation from a supersaturated vapor (see Fig. 1). The vapor is generated by passing an electric current through a metallic wire, which is quenched by an inert gas to reach
Characterization of the seeding metal
In order to use the hot wire generator as an external seeding unit, a constant emission of seed particles with defined aerosol properties must be ensured during synthesis. One of the most critical properties is the particle concentration emitted into the hot wall reactor. The amount of particles depends on the material which evaporates over time and the resulting supersaturation around the wire (Peineke et al., 2006). Therefore, an essential parameter for the usability as seeding material is
Conclusion
We demonstrated the relevance and applicability of a hot wire generator as flexible seeding unit for synthesis of narrowly size distributed Ge NPs. The small particles from the HWG prevent the formation of small strongly agglomerated Ge NPs by suppressing the homogenous nucleation. We systematically investigated the influence of different process parameters on the seed particle production by the hot wire generator and the resulting Ge NPs morphology. To ensure exclusive heterogeneous nucleation
Acknowledgements
The authors acknowledge the funding of the Deutsche Forschungsgemeinschaft (DFG) through the Cluster of Excellence “Engineering of Advanced Materials” at the Friedrich-Alexander-Universität Erlangen-Nürnberg
References (48)
- et al.
On the relevance of accounting for the evolution of the fractal dimension in aerosol process simulations
Journal of Aerosol Science
(2003) - et al.
On the impact of accessible surface and surface energy on particle formation and growth from the vapour phase
Journal of Aerosol Science
(2005) - et al.
The self-preserving size distribution theory I. Effects of the knudsen number on aerosol agglomerate growth
Journal of Colloid and Interface Science
(2002) - et al.
High efficiency silicon-germanium thin film solar cells using graded absorber layer
Solar Energy Materials & Solar Cells
(2010) - et al.
Aerosol synthesis of silicon nanoparticles with narrow size distribution-Part 1: Experimental investigations
Journal of Aerosol Science
(2010) - et al.
Aerosol synthesis of silicon nanoparticles with narrow size distribution-Part 2: Theoretical analysis of the formation mechanism
Journal of Aerosol Science
(2010) - et al.
Synthesis of nanoparticles in the gas phase for electronic, optical and magnetic applications – a review
Jounal of Aerosol Science
(1998) - et al.
Homogeneous nucleation of silicon
Jounal of Aerosol Science
(1994) - et al.
Gas phase synthesis of anisotropic silicon germanium hybrid nanoparticles
Jounal of Aerosol Science
(2014) - et al.
A novel aerosol method for single walled carbon nanotube synthesis
Chemical Physics Letters
(2005)
Aggregate formation under homogeneous silane thermal decomposition
Journal of Aerosol Science
Modeling the synthesis of aluminum particles by evaporation-condensation in an aerosol flow reactor
Nanostructured Materials
Using a glowing wire generator for production of charged , uniformly sized nanoparticles at high concentrations
Journal of Aerosol Science
Why principal component analysis of STEM spectrum-images results in “abstract”, uninterpretable loadings?
Ultramicroscopy
Narrowing the size distribution of aerosol-made titania by surface growth and coagulation
Journal of Aerosol Science
Design, fabrication and analysis of germanium: Silicon solar cell in a multi-junction concentrator system
Solar Energy Materials and Solar Cells
Modeling and simulation of crystallization processes using parsival
Chemical Engineering & Technology
Controlled synthesis of germanium nanoparticles by nonthermal plasmas
Applied Physics Letters
Controlled nucleation aerosol reactors: Production of bulk silicon
Aerosol Science and Technology
Generation of silicon nanoparticles via femtosecond laser ablation in vacuum
Applied Physics Letters
Improved thermoelectric performance of hot pressed nanostructured n-type SiGe bulk alloys
Journal of Materials Chemistry A
Fluorescent and photostable silicon nanoparticles sensors for real-time and long-term intracellular pH measurement in live cells
Analytical Chemistry
Intrinsic optical absorption in single-crystal germanium and silicon at 77 °K and 300 °K
Physical Review A
Synergistic effects of Ge and Si on the performances and mechanism of the Ge x Si1– x electrodes for Li ion batteries
Chemistry of Materials
Cited by (9)
A constant number Monte Carlo approach to examine Non-Isothermal nucleation and growth in a limited vapor system
2024, Chemical Engineering JournalMobility analysis of nanocluster formation and growth from titanium tetraisopropoxide in a flow tube reactor
2022, Journal of Aerosol ScienceCitation Excerpt :The nucleation and growth of metal and metal oxide nanomaterials in the vapor phase in reactors including but not limited to flames (Meierhofer & Fritsching, 2021), flow tubes (Wergen et al., 2019), spark discharge systems (Meuller et al., 2012; Němec et al., 2020), non-thermal plasmas (Kortshagen et al., 2016; Mangolini, 2017) and laser vaporization sources (Kim et al., 2017) enables continuous, scalable material production, typically with high purity in comparison to liquid phase approaches (Swihart, 2003; Meierhofer & Fritsching, 2021; Schulz et al., 2019).
Low-pressure flame synthesis of carbon-stabilized TiO<inf>2</inf>-II (srilankite) nanoparticles
2021, Journal of Aerosol ScienceCitation Excerpt :The synthesis flame structure and the resulting materials are influenced by parameters such as fuel-to-oxidizer ratio, thermodynamic pressure, fuel and oxidizer composition, inert gas presence, and burner-exit gas velocity. Various low-pressure synthesis methods have been studied for metal-oxide nanoparticles, including non-thermal or microwave-supported plasma (Mangolini., Thimsen, & Kortshagen, 2005; Rosenberger, Münzer, Kiesler, Wiggers, & Kruis, 2018), laser ablation (Seto, 2006), and hot-wall reactor processes (Körmer, Jank, Ryssel, Schmid, & Peukert, 2010; Wergen et al., 2019). Each of these low-pressure synthesis methods were conducted at pressures between 18 torr and 130 torr.
Silica nanocluster binding rate coefficients from molecular dynamics trajectory calculations
2020, Journal of Aerosol ScienceCitation Excerpt :High temperature and non-equilibrium aerosol reactors, including flame (Koirala, Pratsinis, & Baiker, 2016; Li, Ren, Biswas, & Tse, 2016; Wang, 2011), furnace (Körmer, Jank, Ryssel, Schmid, & Peukert, 2010; Wergen et al., 2019), spark (Meuller et al., 2012; Tabrizi, Ullmann, Vons, Lafont, & Schmidt-Ott, 2008), and plasma systems (Chen et al., 2018, 2019), are tractable routes to scalable metal and ceramic nanoparticle production from vapor phase precursors.
Analysis of ultrafine metal oxide particles in aerosols using mobility-resolved time-of-flight mass spectrometry
2019, Journal of Aerosol ScienceCitation Excerpt :Glowing-wire evaporation (GWE) is a suitable alternative as this evaporation-recondensation method operates under low voltage which requires nearly no insulation and furthermore, intrinsically produces high amounts of charged species through thermionic emission and UV ionization (Peineke & Schmidt-Ott, 2008; Schmidt-Ott, Schurtenberger, & Siegmann, 1980). GWE can produce aerosols from a wide range of precursor metals (Peineke, Attoui, & Schmidt-Ott, 2006) and typical setups can be kept quite compact in size which is favorable for the connection to a DMA-TOF-MS. Furthermore, GWE already proved to be valuable for designing complex aerosol processes as it can provide seed particles in high concentrations for heterogeneous nucleation (Wergen et al., 2019). Although this process was investigated in the past by mass spectrometry, the information that could be extracted from the spectra was limited to compositional information for a smaller part of the detected species (Kangasluoma et al., 2015).
Single-step aerosol synthesis of oxygen-deficient blue titania
2019, Chemical Engineering ScienceCitation Excerpt :Gas phase processes are favorable for industrial application because of their scalability and continuous operation. They enable high mass output at constant quality (Domaschke et al., 2018; Kruis et al., 1998; Wergen et al., 2019) and are generally well understood as shown by available models for structure formation (Artelt et al., 2006). Pure aerosol routes for TiO2−x production were reported harnessing flame aerosol synthesis: Both vapor-fed (Dhumal et al., 2009) and liquid-fed (Teleki and Pratsinis, 2009) routes can lead to powders containing significant amounts of Magnéli phases.