707 ISSN 1063-7850, Technical Physics Letters, 2020, Vol. 46, No. 7, pp. 707–709. © Pleiades Publishing, Ltd., 2020. Russian Text © The Author(s), 2020, published in Pis’ma v Zhurnal Tekhnicheskoi Fiziki, 2020, Vol. 46, No. 14, pp. 33–35. Formation of Pores in Thin Germanium Films under Implantation by Ge + Ions N. M. Lyadov a *, T. P. Gavrilova a , S. M. Khantimerov a , V. V. Bazarov a , N. M. Suleimanov a , V. A. Shustov a , V. I. Nuzhdin a , I. V. Yanilkin b , A. I. Gumarov b , I. A. Faizrakhmanov a , and L. R. Tagirov a,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: nik061287@mail.ru 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) × 10 16 ions/cm 2 . 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 dis- persed systems (porous silicon, germanium) as anode materials for lithium-ion batteries (LIBs) has been extensively studied worldwide [1, 2]. Although germa- nium is more expensive than silicon, it has a substan- tially 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 magni- tude 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 compara- tively inexpensive method for modification of the sur- face 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 ger- manium 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 10 16 ions/cm 2 [7]. In the present Letter, it is suggested to study a new material for LIB anodes, porous nano- structured films of amorphous germanium (α-Ge) produced by implantation of 40-keV Ge + ions into amorphous germanium, and examine how the mor- phology of the near-surface layer of the resulting films depends on the implantation fluence in the range of (1.8–8) × 10 16 ions/cm 2 . Starting α-Ge films with the thicknesses of ~600 nm were produced by magnetron sputtering of a germa- nium target (purity 99.95%, GIRMET LLC, Russia) in an ultra-high-vacuum setup (SPECS/BESTEC, Germany) at room temperature in an argon atmo- sphere. Single-crystal (012) Al 2 O 3 sapphire plates served as substrates. The substrates were cleaned in several stages: first, ultrasonically with chemical sol- vents, and, in the final stage, in a vacuum chamber (immediately before the sputtering) by the ion milling method. The base pressure in the magnetron chamber did not exceed 5 × 10 –9 mbar, and the working argon pressure was 6 × 10 –3 mbar. The magnetron sputtering power was 50 W. The germanium deposition rate was 8.33 nm/min, as indicated by a quartz thickness gauge. The film thickness was measured with a BRUKER Dektak XT stylus nanoprofilometer.