10:30 AM - 10:45 AM
△ [6a-C21-6] Modeling of reductive thin-film deposition process promoted by ballistic electron incidence
Keywords:Nanocrystalline silicon diode, Ballistic hot electron, Printing deposition
When energetic electrons emitted from nanocrystalline silicon (nc-Si) ballistic electron emitter are irradiated to a target substrate coated with a metal or semiconductor salt solution, positive ions in the solution are reduced followed by thin film deposition on the target substrate. As previously reported, it has been confirmed that thin metal or semiconductor films were deposited on various target substrates including insulating substrates under this printing scheme. To clarify the deposition process of this electron incidence mode, analyses of the reduction, nucleation, and the subsequent deposition are reported here. The result of modeling is discussed in relation to the experimental observations.
Based on past experimental results, the following thin film deposition model was provided. Ballistic electron incidence induce reductive reaction at electron penetration depth followed by nanocluster formation. Then, the generated nanoclusters diffuse toward the target substrate and deposit thereon. We analyzed the free energy for cluster formation under ballistic electron incidence and the diffusion process of the generated nanocluster using thermodynamic nucleation theory and reaction-diffusion law, respectively.
The thermodynamic analysis shows that the output electrons emitted from the nc-Si emitter have sufficient energy to reduce positive ions in the solution. This means that ballistic electron incidence instantly induce reductive reaction at electron penetration depth followed by nanocluster formation. Then, calculation of the cluster concentration in the solution based on the reaction-diffusion law reveals that the generated nanocluster diffuses a distance that is about the thickness of the coated solution (~ 100 nm) in a short time. In addition, the relationship between the calculated film deposition rates of each material and the electron irradiation time shows that the deposition rate sharply increases from the start of ballistic electron irradiation and saturates at about 0.1 s. The saturated value is consistent with the thin film deposition rate obtained from Faraday's law. It has been shown that the most important determining factor of this deposition mode is the dose of ballistic electrons rather than nucleation or diffusion process. Since this printing scheme can form various metals and semiconductors on varied substrates at room temperature, it is potentially useful for fabrication of thin film devices.
Based on past experimental results, the following thin film deposition model was provided. Ballistic electron incidence induce reductive reaction at electron penetration depth followed by nanocluster formation. Then, the generated nanoclusters diffuse toward the target substrate and deposit thereon. We analyzed the free energy for cluster formation under ballistic electron incidence and the diffusion process of the generated nanocluster using thermodynamic nucleation theory and reaction-diffusion law, respectively.
The thermodynamic analysis shows that the output electrons emitted from the nc-Si emitter have sufficient energy to reduce positive ions in the solution. This means that ballistic electron incidence instantly induce reductive reaction at electron penetration depth followed by nanocluster formation. Then, calculation of the cluster concentration in the solution based on the reaction-diffusion law reveals that the generated nanocluster diffuses a distance that is about the thickness of the coated solution (~ 100 nm) in a short time. In addition, the relationship between the calculated film deposition rates of each material and the electron irradiation time shows that the deposition rate sharply increases from the start of ballistic electron irradiation and saturates at about 0.1 s. The saturated value is consistent with the thin film deposition rate obtained from Faraday's law. It has been shown that the most important determining factor of this deposition mode is the dose of ballistic electrons rather than nucleation or diffusion process. Since this printing scheme can form various metals and semiconductors on varied substrates at room temperature, it is potentially useful for fabrication of thin film devices.