Bulletin of the American Physical Society
74th Annual Gaseous Electronics Conference
Volume 66, Number 7
Monday–Friday, October 4–8, 2021;
Virtual: GEC Platform
Time Zone: Central Daylight Time, USA
Session MR14: Plasma Assisted Nano-structure Synthesis |
Hide Abstracts |
Chair: Shahid Rauf, Applied Materials Room: Virtual GEC platform |
Thursday, October 7, 2021 8:00AM - 8:15AM |
MR14.00001: Controlling the size of nanoparticles grown in low pressure plasmas using pulsed power Steven Lanham, Jordyn Polito, Zichang Xiong, Gunnar Nelson, Uwe R Kortshagen, Mark J Kushner Low temperature plasmas are a preferred method for synthesizing nanoparticles (NPs) in part due to their ability to produce particles with narrow size distributions. Particles in plasmas primarily charge negative thereby minimizing agglomeration by mutual repulsive forces. Current methods for growing NPs in plasmas are fine-tuned to carefully balance operating conditions to achieve control over particle size and composition. One method that has not been investigated is to use pulsed plasmas to control growth. During a power pulse, negatively charged NPs can be trapped in the positive plasma potential and grow to a desired size. In the pulse afterglow, the plasma potential dissipates, NPs discharge, are de-trapped and can flow out of the reactor. In this work, the impact of pulsing the power on NP growth was computationally investigated and corroborated through experiments. The growth and trajectories of particles were tracked using a 3D kinetic model (Dust Transport Simulator) under simulated pulsed plasma conditions from a 2D multi-fluid plasma model (Hybrid Plasma Equipment Model). Silicon NPs grown in Ar/SiH4 mixtures of a few Torr using inductive power were investigated. Experiments of pulsed plasmas under similar conditions confirm particle trapping. Results for particle growth rates, final particle sizes, and the viability of using pulsed plasmas to grow NPs will be discussed |
Thursday, October 7, 2021 8:15AM - 8:30AM |
MR14.00002: Predicting Plasma Conditions Necessary for Synthesis of γ-Al2O3 Nanocrystals AJ Cendejas, He Sun, Sophia E Hayes, Uwe R Kortshagen, Elijah J Thimsen Nonthermal plasma constitutes a unique synthesis environment which has proven capable of producing nanocrystals of several high melting point materials at relatively low gas temperatures over the last decade. Despite these efforts, the design of processes targeting new materials is almost entirely empirically driven. Here we present a simple particle heating model suitable for predicting plasma power necessary to crystallize Al2O3 nanoparticles. The model is used to calculate the temperature of particles suspended in the plasma as a function of applied power using only composition, pressure, background gas temperature and reactor geometry as inputs. Crystallization of the Al2O3 nanoparticle population was observed by X-ray diffraction and 27Al solid-state NMR when the predicted nanoparticle temperature was equal to the crystallization temperature of amorphous alumina. |
Thursday, October 7, 2021 8:30AM - 8:45AM |
MR14.00003: Plasma-synthesized Photoluminescent Gallium Nitride Nanocrystals for UV Light Dillon P Moher, Elijah J Thimsen Gallium nitride (GaN) is a semiconductor material of broad interest for its wide direct band gap, chemical stability, and non-toxicity. Thin-film methods of GaN synthesis are well studied, but synthesis strategies and studies related to spheroidal nanocrystals (NCs) of GaN are lacking. Colloidal or solution-based methods are limited by the synthesis temperature, typically required to be high due to the refractory nature of GaN. We have recently developed a gas-phase, plasma synthesis strategy for freestanding, pure, and size-controlled GaN NCs termed Nonequilibrium Plasma Aerotaxy. It feeds an aerosol of gallium metal carried by argon in addition to nitrogen into a flow-through, low pressure, capacitively-coupled tubular plasma generated by radiofrequency power. By controlling the residence time of the gas and the gallium mass concentration in the reactor, the size of the NCs and therefore their optoelectronic properties can be tuned. More recently, we have measured the photoluminescence quantum yield in the ultraviolet for these NCs and found it to be much higher than any previously reported values for freestanding GaN NCs. The required synthesis conditions, post-processing, and potential for solid-state ultraviolet lighting devices from these NCs will be discussed. |
Thursday, October 7, 2021 8:45AM - 9:00AM |
MR14.00004: Particle trapping of non-thermal plasmas for nanoparticle synthesis Zichang Xiong, Gunnar Nelson, Mohammadali Eslamisaray, Yaling Liu, Steven Lanham, Jordyn Polito, Mark J Kushner, Uwe R Kortshagen Low pressure nonthermal plasmas in cylindrical geometry with strong axial gas flow are widely used for nanoparticle synthesis. In these plasmas, large densities of nanoparticles and their small sizes result in the average nanoparticle charge often being less than one elementary charge. Therefore, the effect of nanoparticle trapping in these plasmas has not previously been considered. Here, we demonstrate the importance of particle trapping for various plasma configurations in argon:silane plasmas for silicon nanoparticle synthesis. The existence of trapped silicon particles is evidenced by turning off the silane precursor flow which stops the particle growth. Particles remain trapped in the argon plasma because the gas drag force acting on particles stopped in their growth is insufficient to overcome the electrostatic trapping force. Particles are only released once the plasma is turned off. The size distribution of trapped particles is compared to that of particles exiting the reactor in steady-state operation. The trapping position is determined from the known gas velocity and the measured time delay between turning off the plasma and collecting particles at the reactor exit. Particle trapping in an inductively coupled plasma configuration is compared with simulation results of a 2D multi-fluid plasma model coupled with a 3D kinetic model. Gas drag forces and electrostatic forces acting on particles are estimated to elucidate the trapping mechanism. |
Thursday, October 7, 2021 9:00AM - 9:15AM |
MR14.00005: The Onset of Silicon Nanoparticle Nucleation in a Low Temperature Plasma Eric Husmann, Elijah J Thimsen, Jordyn Polito, Steven Lanham, Mark J Kushner Controlling the nucleation and growth of nanoparticles (NPs) in low temperature plasma systems is imperative for controlling the NP size distribution; and for some applications, such as chemical vapor deposition and polysilicon production, for preventing particle contamination. Although the mechanisms behind silicon NP nucleation and growth have been well studied, it is unclear how controllable system parameters, e.g., pressure and system geometry, affect the onset of NP nucleation. The diffusion of reactive silane species, particularly SiH2 and SiH3, is expected to significantly affect the feed concentration of silane required to nucleate silicon NPs (the nucleation onset concentration) due to losses at the reactor walls. Additionally, plasma parameters are expected to be significant as they are known to affect the size and structure of synthesized nanoparticles. In this work, the nucleation onset concentration was determined as a function of system pressure, applied plasma power, and reactor diameter for a tubular flow-through radiofrequency (RF) plasma generated using Ar/He/SiH4 gas mixtures. A quartz crystal microbalance (QCM) impactor was used to measure the total aerosol mass density after the plasma and thereby identify the nucleation onset. A comparison of the experimental results to a 2D multi-physics model will also be provided. |
Thursday, October 7, 2021 9:15AM - 9:30AM |
MR14.00006: Nucleation processes leading to Si nanoparticle growth in low temperature flowing plasmas Jordyn Polito, Steven Lanham, Eric Husmann, Elijah J Thimsen, Mark J Kushner Flowing low temperature plasmas (LTPs) are viable alternatives to traditional methods for synthesizing nanoparticles (a few to tens of nms in size) [1]. Nanoparticle (NP) size, composition, and structure are tunable by changing plasma operating parameters (gas composition, pressure, power, and reactor geometry). NPs in LTPs are synthesized in two stages: (1) nucleation - conception and growth of molecular clusters and (2) growth – agglomeration of clusters or surface deposition. The stages occur simultaneously, but initial nucleation is necessary. Nucleation in silane containing plasmas occurs by reactions between anion clusters and neutral or radical SinHm species. The conditions for the onset of nucleation are not well characterized. In this work we computationally investigate silicon NP nucleation and growth rates in a flowing LTP. The Hybrid Plasma Equipment Model (HPEM), a 2D reactor scale multi-physics model, was used to track NP formation processes in a Ar/He/SiH4 plasma. Results for trends in silicon NP nucleation and growth as functions of reactor tube diameter, inlet gas composition, pressure, and power are discussed, and compared to experiments for the threshold conditions that produce initial nucleation. |
Thursday, October 7, 2021 9:30AM - 9:45AM |
MR14.00007: Transport of Nanoparticles in Afterglow Region Using Multi-Hollow Discharge Plasma CVD Kazunori Koga, Sung Hwa Hwang, Pankaj Attri, Kunihiro Kamataki, Naho Itagaki, Masaharu Shiratani Plasma chemical vapor deposition (CVD) has attracted attention in nanoparticle synthesys because it is the dry process that can reduce impurity. It can control their coagulation by the charging of nanoparticles. So far, we have developed a multi-hollow discharge plasma CVD to produce size-controlled nanoparticles continuously using gas flow. Using the method, size-controlled Si and C nanoparticles were successfully produced [1-3]. Nanoparticles are nucleated and grow in the discharge region then transported toward the downstream region in which the substrates are set by gas flow. To realize bottom-up nanosystem fabrication, nanoparticle transport and deposition are important. Here, we have measured the amount of C nanoparticles (CNP) deposited on substrates as a parameter of the gap L between discharge and substrate to study the transport of CNP. The amount is proportional to the solid angle calculated from the L [3]. The result indicates the density of CNP is decreased as a function of L-2 by their diffusion to the sidewall. |
Thursday, October 7, 2021 9:45AM - 10:00AM |
MR14.00008: Plasma CVD Synthesis of graphene nanoribbon quantum dot devices with temperature-stable orbital-level spacing Naofumi Sato, Takahito Kitada, Mizuki Seo, Toshiro Kaneko, Tomohiro Otsuka, Toshiaki Kato We have demonstrated the scalable fabrication of graphene nanoribbon (GNR)-based quantum dot devices by advanced plasma CVD [1-4]. Systematic investigation revealed that fine structures are formed at the middle of the GNRs, resulting in the quantum-dot features of our GNRs. Detailed measurements at cryogenic temperatures revealed clear orbital-level spacings between the ground state and excited states in our GNR-based quantum-dot device. Furthermore, the orbital levels were found to be very stable even at high-temperature conditions (~20 K), which can be explained by the very fine structures formed in the middle of the GNR and relatively light effective mass of the GNR. More than 18% of devices fabricated within the same substrate showed orbital levels, indicating that integration of GNR-based quantum-dot devices is possible with our method. |
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