Authors: Seiichi Sato | Shuhei Tsubota | Takahisa Ichinohe
Source: ECS Meeting Abstracts (article, 2024-11-22)
Field: Materials Science — Materials Chemistry

Significant Changes in Electrical Resistance of Conductive Porous Silicon Films Produced from Thiol-Modified Silicon Nanoparticle Inks Materials that reversibly modify their electrical resistance in response to external stimuli have attracted the interest of many researchers due to their potential applications in low-energy consumption memories and memristive devices for constructing electrical neural networks. For example, various chalcogenide glasses, such as Ge 2 Sb 2 Te 5 [1] and Ag- or In-incorporated Sb 2 Te [2], can change resistances by 3–6 orders of magnitude, originating from the phase changes between amorphous (high resistance) and crystal (low resistance) states due to rapid and gradual Joule heating. Similar dynamic ranges of resistance changes have been observed in metal-doped glasses [3], such as Ta:Ta 2 O 5 , Cu:Ta 2 O 5 , Ag:SiO 2 , Ni:NiO, and nanocomposite Sb-SiO 2 , using the conductive filament growth/rupture in glasses. Furthermore, devices containing ferroelectric materials, such as Pt/BaTiO 3 /Nb:SrTiO 3 tunnel junctions and Sc-doped AlN/MoS 2 ferroelectric field-effect transistors, exhibit similar dynamic ranges by ferroelectric polarization switching. Among these, nanometer-sized Si is a unique material whose resistance can be controlled by near-infrared optical and electrical stimulations [4]. This is the advantage of incorporating resistance change materials into optical communication systems, resulting in the construction of optoelectronic neural networks. However, the following shortcomings of nanometer-sized Si hinder its applications: (1) serious conductivity degradation that proceeds in air and (2) insufficient dynamic ranges of the resistance changes. Recently, we produced sulfur (S)-terminated Si nanoparticles, whose surface is difficult to oxidize even in the air [5]. Because S atoms, which are known to act as donors in Si, are located at the outermost surface of nanoparticles, the electron doping from S atoms can be considerably influenced by the surface-adsorbed molecules. Considering the large surface-to-volume ratio in nanoparticles, the electrical resistances of Si nanoparticle films can potentially be largely changeable through adsorption/desorption of electron-withdrawing molecules, such as O 2 and halogens. In this study, we demonstrated that surface S termination considerably reduces resistances in Si nanoparticles, and that S-terminated nanoparticles can reversibly change resistances similar to hitherto reported resistance change materials. Figure 1 shows current–voltage characteristics of the S-terminated Si nanoparticles measured under N 2 and O 2 atmospheres. As shown in the figure, changing the atmospheric gas significantly altered the current. For example, by changing the atmospheric gas from N 2 to O 2 , the resistance at 2 V changed from 5×10 6 Ω to greater than 10 12 Ω and vice versa. This reversible resistance change is due to O 2 adsorption/desorption on the film surface. The electron-withdrawing nature of O 2 may induce band bending at the nanoparticle surface as depicted in the figure, and the induced energy barrier may prevent the interparticle transport of electrons, which agrees with the small energy barrier found in our conductive atomic force microscopy measurements. The dynamic range of the resistance change was remarkably comparable to the ranges of the conventional phase change materials, indicating that by terminating the surface with S atoms, Si nanomaterials can be used not only in sensors but also photo-stimulated synaptic devices by controlling the amount of the adsorbed O 2 , for example, through light irradiation [4]. References [1] Z. Song, R. Wang, Y. Xue, S. Song, Nano Res. 15 , 765–772 (2022). [2] K. D. Shukla, N. Saxena, S. Durai, A. Manivannan, Sci. Rep. 6 , 37868 [7 pages] (2016). [3] S. Gao, G. Liu, Q. Chen, W. Xue, H. Yang, J. Shang, B. Chen, F. Zeng, C. Song, F. Pan, R.-W. Li, ACS Appl. Mater. Interfaces 10 , 6453–6462 (2018). [4] L. Yin. C. Han, Q. Zhang, Z. Ni, S. Zhao, K. Wang, D. Li, M. Xu, H. Wu, X. Pi, D. Yang, Nano Energy 63 , 103859 [11 pages] (2019). [5] S. Sato, T. Dobashi, S. Matsuda, Chem. Eng. J. 268 , 356–361 (2015). Figure 1 Silicon ; Porous silicon ; Materials science ; Electrical conductor ; Nanoparticle ; Electrical resistance and conductance ; Porosity ; Nanotechnology ; Thiol ; Chemical engineering ; Composite material ; Optoelectronics ; Chemistry ; Engineering ; Organic chemistry Silicon Nanostructures and Photoluminescence ; Nanowire Synthesis and Applications ; Anodic Oxide Films and Nanostructures