Reductive Deposition of Thin Cu Films Using Ballistic Hot Electrons as a Printing Beam

Nakamura

2019

Front. Chem.

Recent topics of application studies on porous silicon (PS) are reviewed here with a focus on the emissive properties of visible light, quasiballistic hot electrons, and acoustic wave. By exposing PS in solvents to pulse laser, size-controlled nc-Si dot colloids can be formed through fragmentation of the PS layer with a considerably higher yield than the conventional techniques such as laser ablation of bulk silicon and sol-gel precursor process. Fabricated colloidal samples show strong visible photoluminescence (~40% in quantum efficiency in the red band). This provides an energy- and cost-effective route for production of nc-Si quantum dots. A multiple-tunneling transport mode through nc-Si dot chain induces efficient quasiballistic hot electron emission from an nc-Si diode. Both the efficiency and the output electron energy dispersion are remarkably improved by using monolayer graphene as a surface electrode. Being a relatively low operating voltage device compatible with silicon planar fabrication process, the emitter is applicable to mask-less parallel lithography under an active matrix drive. It has been demonstrated that the integrated 100 × 100 emitter array is useful for multibeam lithography and that the selected emission pattern is delineated with little distortion. Highly reducing activity of emitted electrons is applicable to liquid-phase thin film deposition of metals (Cu) and semiconductors (Si, Ge, and SiGe). Due to an extremely low thermal conductivity and volumetric heat capacity of nc-Si layer, on the other hand, thermo-acoustic conversion is enhanced to a practical level. A temperature fluctuation produced at the surface of nc-Si layer is quickly transferred into air, and then an acoustic wave is emitted without any mechanical vibrations. The non-resonant and broad-band emissivity with low harmonic distortions makes it possible to use the emitter for generating audible sound under a full digital drive and reproducing complicated ultrasonic communication calls between mice.

Section: Emissive Properties and Applicationsmentioning

confidence: 99%

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

Nakamura

2019

Front. Chem.

“…(3) Reductive Deposition of Thin Films Highly reducing activity of emitted quasiballistic electrons is applicable to liquid-phase thin film deposition of metals and semiconductors under an incident mode [14,15]. Experimental configuration is shown in Fig.…”

Section: Ecs Transactions 86 (1) 39-45 (2018)mentioning

confidence: 99%

(Invited) Emerging Applications of Nanostructured Porous Silicon

2018

ECS Trans.

Electrochemical anodization of single-crystalline silicon (c-Si) renders it porous via a self-organized propagation of nano- to micro-scale pores. Porous silicon (PS) layer fabricated under the appropriate process parameters consists of highly packed quantum-size nanocrystalline silicon (nc-Si) dots. Current topics on its application studies are discussed here. It is shown that the use of luminescent self-standing PS layers as a starting material for fragmentation is very effective to improve the fabrication yield of colloidal nc-Si dots. The efficiency of quasiballistic electron emission from an nc-Si diode is remarkably enhanced by using monolayer graphene as a surface electrode. Mask-less parallel lithography under an active-matrix drive and reductive thin film deposition have been developed. The non-resonant, broad-band, and low-distortion sound emission based on thermos-acoustic effect in nc-Si can reproduce complicated ultrasound signals. This is applicable to compact ultrasound source for analyzing ultrasonic communication mechanism between mice.

“…[2][3][4][5] Though dots and nanowires of metals are directly formed, serious problems remain in EBID: both the purity and the uniformity of deposited thin films are insufficient because of incorporation of decomposed species into thin films and irradiation damages during the process. 4,5 We have reported application of quasiballistic hot electron emission from nanocrystalline silicon (nc-Si) diode 6,7 to reductive thin film deposition in dipping, [8][9][10][11] dripping, 12 and incidence 13,14 modes. In the incidence mode, salt solutions such as CuCl 2 , SiCl 4 , and GeCl 4 containing an objective ion are coated (∼100 nm in thickness) on a target substrate, and then irradiated with emitted quasiballistic electrons through a pressure-controlled gas space.…”

mentioning

confidence: 99%

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

Suda

Kojima

ECS J. Solid State Sci. Technol.

2018

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.