Mechanism of Liquid-Phase Reductive Thin-Film Deposition under Quasiballistic Electron Incidence

Abstract

Highly reducing activity of quasiballistic hot electrons emitted from a nanocrystalline silicon (nc-Si) diode is verified in terms of liquid-phase thin film deposition. Incident electrons reduce positive ions in salt solutions coated on a target substrate, and then result in deposition of thin metal (Cu) and semiconducting (Si, Ge, and SiGe) films. This mechanism is investigated here throughout the process from electron incidence to thin film deposition. Thermodynamic criterion deduced from classical nucleation theory suggests that the output electron energy of the nc-Si emitter is suitable for promoting preferential reduction of target ions in solutions leading to the nuclei formation. In accordance with mass-transport analyses on generated nanoclusters, the most primary factor of thin film growth is the dose of incident electron. The formulated deposition rate rapidly increases and reaches a stationary value within 0.1 s after electron incidence. The theoretical dependency of the thin film thickness on the electron incidence time is consistent with the experimental results. Specific features of this scheme as an alternative approach for thin film deposition are discussed in comparison with the conventional dry and wet processes.

(Invited) Evolutionary Applications of Functional Porous Silicon

“…This emitter operates not only in vacuum but also in atmospheric-pressure gases and even in solutions. The application studies have been carried out in vacuum (multibeam parallel lithography (10), high-sensitivity image sensor), in atmospheric pressure gases (negative ion generation, non-discharge VUV emission), and in solutions (H2 gas evolution, pH control, thin film deposition (11)).…”

Emerging Functions of Nanostructured Porous Silicon—With a Focus on the Emissive Properties of Photons, Electrons, and Ultrasound

“…Thermodynamic investigation supports that the incident electron energy meets the requirement for preferential nucleation of atoms rather than their out-diffusion (Suda et al, 2017). The theoretical analysis based on the reaction diffusion equation suggests that the deposition rate depends mainly on the incident electron current density J e , and that it reaches a stationary value within 0.1 s after electron incidence (Suda et al, 2018). At the typical condition of J e = 10–100 μA/cm 2 , the estimated stationary deposition rate of Cu, Si, and Ge films are around 0.2–2.0 nm/min.…”

Electron Field Emission from Multiply-Stacked Si Quantum Dots Structures with Graphene Top-Electrode

“…Electron field emission from Si nanocrystals has been intensively studied because its unique electron emission properties are expected to be suitable for various device applications such as electron microscope, electron lithography and field emission display (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). It is interesting to note that the liquid-phase depositions of Si and Ge films have been successfully demonstrated by using a hot electron emitter based on Si nanocrystals (11).…”