Formation of Pores in Thin Germanium Films under Implantation by Ge + Ions
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ion of Pores in Thin Germanium Films under Implantation by Ge+ Ions N. M. Lyadova*, T. P. Gavrilovaa, S. M. Khantimerova, V. V. Bazarova, N. M. Suleimanova, V. A. Shustova, V. I. Nuzhdina, I. V. Yanilkinb, A. I. Gumarovb, I. A. Faizrakhmanova, and L. R. Tagirova,b a
E. K. Zavoisky Kazan Physical Technical Institute, Kazan Research Center, Russian Academy of Sciences, Kazan, Tatarstan, 420029 Russia b Institute of Physics, Kazan Federal University, Kazan, Tatarstan, 420008 Russia *e-mail: [email protected] Received February 7, 2020; revised April 16, 2020; accepted April 16, 2020
Abstract—Results are presented of a study of the morphology of germanium films nanostructured by ion implantation. Film samples were grown by magnetron sputtering in an ultrahigh-vacuum installation and then irradiated with 40 keV Ge+ ions at fluences in the range of (1.8–8) × 1016 ions/cm2. Scanning electron microscopy demonstrated that vacancy complexes with diameters of ~50–150 nm are gradually formed in the bulk of implanted germanium with increasing implantation fluence. After a certain implantation fluence is reached, the complexes emerge on the surface, thereby forming a developed surface profile of the irradiated films. Keywords: nanostructured germanium, ion implantation, lithium-ion batteries. DOI: 10.1134/S1063785020070196
Recently, the possibility of using various highly dispersed systems (porous silicon, germanium) as anode materials for lithium-ion batteries (LIBs) has been extensively studied worldwide [1, 2]. Although germanium is more expensive than silicon, it has a substantially higher intrinsic electronic conductivity, as well as a high diffusion coefficient of lithium ions (at room temperature, the diffusion coefficient of a lithium ion in germanium is approximately two orders of magnitude higher than that in silicon). Fast transport of both electrons and Li ions will provide a higher charging/discharge rate of LIBs [3]. Several studies have already been reported in the literature aimed at developing germanium nanostructured electrodes [4– 6]. For example, nanoporous germanium (np-Ge) was first obtained in [5] by the chemical method, which enabled mass production of electrodes for LIBs. The nanoporous structure was stable against volume changes in the course of lithiation/delithiation and enabled fast charge/discharge processes. At the same time, ion implantation, as a productive and comparatively inexpensive method for modification of the surface properties of various materials [7–9], is widely used in microelectronics and serves to improve the surface-strength properties of various metallic articles. A porous layer appears in the near-surface layer of germanium in implantation of a wide variety of heavy ions with energy in the range from several to hundreds
of keV at a threshold implantation fluence of 1016 ions/cm2 [7]. In the present Letter, it is suggested to study a new material for LIB anodes, porous nanostructured films of amorphous germanium (α-Ge) produced by implantation of 40-keV Ge+ ions into amorphous ge
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