Formation of Heterostructured Silicon Thick Films in Atmospheric-Pressure Very High-Frequency Plasma Toward the Application to Lithium Ion Battery Anode

Formation of Heterostructured Silicon Thick Films in Atmospheric-Pressure Very High-Frequency Plasma Toward the Application to Lithium Ion Battery Anode | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Formation of Heterostructured Silicon Thick Films in Atmospheric-Pressure Very High-Frequency Plasma Toward the Application to Lithium Ion Battery Anode Afif Hamzens, Shota Mochizuki, Farrel Dzaudan Naufal, Koki Hiromoto, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5928700/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract The superiority of silicon (Si) film performance as anode material in the rechargeable battery technologies is tormented by the huge volume expansion during cycle. The combined structure of a microcrystalline Si with high porous/defect density and an isotropic amorphous Si has been proposed as a feasible solution. Our own deposition process using atmospheric-pressure (AP) plasma excited by very high-frequency (VHF) power has managed to create a non-composite Si film with gradient phase along thickness direction. This work investigates the formation of heterostructured Si thick film and its capability toward the application to the Lithium-ion Batteries (LIBs) anode. It is highly indicated that a slower gas flow rate and/or a larger power input cause the nanoparticle formation in the AP-VHF plasma to occur more actively, which significantly influenced the development of a crystalline layer with a high density of grain boundaries. The promising electrochemical performance imply a great potential of heterostructured Si as LIBs anode. PECVD atmospheric-pressure plasma silicon lithium-ion batteries Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Silicon (Si) has always become the most promising material for electronic devices and energy storage applications. The semiconductor properties of microcrystalline Si ( µc -Si) have made it popular for thin film transistors (TFTs) or solar cell applications[ 1 – 5 ], while its mechanical flexibility is sufficient for microelectromechanical system (MEMS) [ 6 – 8 ] and flexible electronic devices[ 9 – 11 ]. Recently, Si is frequently explored as the anode material of Lithium-Ion Batteries (LIBs). Si is potential as an enticing new material for anode since it offers much higher specific and volumetric capacity values than conventional graphite, and is able to operate under moderately low potential[ 12 – 19 ]. However, Si has a serious problem that it undergoes tremendous volume change (> 300%) during the lithiation/delithiation process[ 20 ]. Obrovac et al. have shown that the crack generation in Si anode due to the volume expansion makes it prone to be peeled off from the current collector during cycles[ 21 ]. Hence, research on Si anode have recently focused on the utilization of Si nanoparticles[ 22 – 24 ] and nanowires[ 25 – 27 ] as well as core-shell carbon-silicon (C/Si) structure[ 28 – 30 ] with conductive additives and binders to mitigate the volume expansion. However, the use of such composite-type anodes results in the decrease in the content of active Si material, which lowers the capacity and limits the energy density[ 31 ]. Non-composite-type Si anodes are still more favorable in battery industry from the viewpoint of achieving a cost-efficient manufacturing process while enhancing device performance[ 32 , 33 ]. The main challenge is to establish proper modifications on the non-composite-type Si anode to address the volume expansion issue. One of the ideas is to utilize high-density defects and/or porous microstructure. In this study, we propose the use of heterostructured Si films: a thick µc -Si top layer having high-density grain boundaries on a thinner amorphous Si ( a -Si) bottom layer. It can employ the best character from each phase while accommodating each other weaknesses[ 34 ]. A µc -Si is quite favorable due to its higher initial capacity[ 35 – 37 ], while the isotropic volume expansion on a -Si may provide better handling of volume expansion and lead to a good performance even after many cycles[ 38 , 39 ]. The higher-density grain boundaries in µc -Si may also serve in mitigating volume expansion without reducing Si content[ 32 , 40 ]. Our previous study has set precedence in producing heterostructured Si thin films using a simple plasma-enhanced chemical vapor deposition (PECVD) method with monosilane (SiH 4 ) and hydrogen (H 2 ) as the process gases [ 41 , 42 ], in which stable and homogeneous plasma excited by a very high-frequency (VHF) electric power under atmospheric-pressure (AP) is effectively used. In this study, we discuss both the deposition characteristics and electrochemical performance of thicker Si films prepared in AP-VHF plasma, aiming at developing the formation process of heterostructured Si thick films that can be applied to LIB anodes. Experimental methods The deposition of Si films was carried out using the specially designed AP-PECVD system. Figure 1a shows the side and the front views of the parallel-plate-type electrode system used for the plasma generation. The electrode was made of aluminum alloy and its surface (10 mm length and 105 mm width) was intentionally left uncoated from an insulating material in order to increase the electron density in the AP-VHF plasma more than using alumina-coated electrode that was adopted in our previous studies[41–44]. The electrode was connected to a 150-MHz VHF power source via an impedance matching unit. The electrode system could be moved horizontally in the direction of the gas flow, enabling the deposition of a Si film with uniform thickness in the area that the plasma passed over. This feature will be further discussed in the next section. Table 1 Experimental conditions He flow rate [slm] 25 H 2 flow rate [sccm] 500, 1250, 2500 SiH 4 flow rate [sccm] 50, 100 P VHF [W/cm 2 ] 40, 70, 90 Working pressure [Pa] 1 x 10 5 Substrate temperature [°C] 220 Deposition time [s] 20–240 Substrate Thermally oxidized Si wafer & 200 µm-thick Copper (Cu) foil The deposition process was conducted at a constant working pressure of 1 × 10 5 Pa. A gas mixture of helium (He), H 2 , and SiH 4 was used for each film deposition. The gas flow path was defined by quartz guide blocks around the electrode, ensuring a one-dimensional flow of the gas mixtures. We varied the flow rates of H 2 and SiH 4 , the input power density ( P VHF ) and deposition time as the principal parameters. The details of the experimental conditions are listed in Table 1. The film thickness profiles were measured by a step profiler (ACCRETECH Surfcom 590A), while the cross-sectional structure of the films was observed by using a scanning electron microscope (Hitachi S-4800) and a transmission electron microscope (JEOL JEM-2100). In order to analyze the microstructure of the films, Raman spectroscopy (Horiba Jobin Yvon LabRAM HR-800 & JASCO NRS-3100T) was used. The crystalline volume fraction ( %I C ) and grain boundary fraction ( %I GB ) were calculated from the integrated intensities of certain Raman peaks using the following equations: $$\:{\%I}_{\text{C}}=\frac{{I}_{\text{c}\text{-}\text{Si}}+{I}_{\text{gb}\text{-}\text{Si}}}{{I}_{\text{a-Si}}+{I}_{\text{c-Si}}+{I}_{\text{gb-Si}}}\:\times\:100\%$$ 1 $$\:{\%I}_{\text{GB}}=\frac{{I}_{\text{gb}\text{-}\text{Si}}}{{I}_{\text{gb-Si}}+{I}_{\text{c}\text{-}\text{Si}}}\:\times\:100\%$$ 2 where I c−Si , I gb−Si and I a−Si are the integrated intensities of the peaks related to microcrystalline Si (around 515–520 cm − 1 ), grain boundaries component (around 500–510 cm − 1 ), and amorphous Si (around 480 cm − 1 ) respectively[41, 45]. Electrochemical measurement of the Si thick film sample was performed using a Galvanostatic cycling of Si film – Li metal coin cell structure. A half-cell structure was used with Li metal as counter electrode, LiPF 6 + EC/DMC/EMC + FEC liquid as electrolyte, and a separator as shown in Fig. 1b. Results and discussion Si growth process in AP-VHF plasma Toward the formation of heterostructured Si thick films, we first review the growth process of Si films in AP-VHF plasma mainly based on our previous report on Si thin film formation[ 41 ]. Figure 2 shows the distribution of thickness and %I C of the Si films prepared without the electrode movement using the (a) 5 mm electrode ( P VHF = 30 W/cm 2 ) and (b) 16 mm electrode ( P VHF = 32 W/cm 2 ). The flow rates of He, H 2 , and SiH 4 were 50 slm, 500 sccm, and 50 sccm respectively, and the deposition time was 20 s. The horizontal axis is the position in the gas flow direction, and the zero position is defined at the front end of the electrode. The upper axis is converted to the average gas residence time in the plasma, calculated by dividing the electrode length by the average gas flow velocity. The deposition in the stationary condition resulted in the formation of Si films with inhomogeneous thickness and microstructure, as shown in Fig. 2 . A thick amorphous layer is created on the upstream side, while a much thinner crystalline layer is created on the downstream side. The frequency of collision between particles in the gas phase is several orders of magnitude higher in AP plasma than common low-pressure plasma[ 41 ]. Hence, it is considered that the source SiH 4 gas is decomposed by the electron impact as soon as it enters the plasma zone to generate SiH x radicals, followed by the production of a variety of higher order radicals and even nanoparticles through the secondary reactions with various species[ 46 ]. The dissociation products diffuse to the substrate surface and are integrated into the developing film. The very rapid progress of both gas-phase and surface reactions lead to the growth of a -Si mainly from SiH x radicals in the upstream area[ 46 ]. In the downstream area, as a consequence of the SiH 4 gas consumption on the upstream side, the H 2 /SiH 4 ratio increases significantly from its initial value which generate abundant atomic hydrogen, promoting the crystallization of the growing Si film. Moreover, it is reasonable to note that the very rapid progress of the gas-phase reactions in the plasma readily cause the nucleation of clusters and their growth to nanoparticles both in amorphous and crystalline phase[ 46 – 48 ]. Thus, the contribution of crystalline nanoparticles can also be taken into account as an origin of the film crystallization. Crystalline phase thus becomes prominent in the downstream area. Although a µc -Si growth is not observed in the film deposited using the 5 mm electrode due to the short electrode length (Fig. 2 a), the film-forming reactions must have been the same as those for the 16 mm electrode since the deposition condition is almost the same. The use of a longer electrode leads to a larger deposition area due to the longer gas residence time (diffusion length of radicals) in the plasma. This also results in the increase in the volume of µc -Si and the better SiH 4 gas transforming efficiency[ 41 ]. The SiH 4 transforming efficiency, which is defined as the efficiency in transforming the source SiH 4 gas into useful Si film, is affected mainly by the diffusion length of radicals within the gas residence time in the plasma. It was calculated by integrating the thickness profiles of the Si films shown in Fig. 2 , assuming that the film density was the same as that of single crystalline Si (2.33 g/cm 3 ). Indeed, the efficiency of using the 5 mm electrode (3.0%) is lower than using the 16 mm electrode (6.3%). The longer electrode length is also likely to generate the larger amount of nanoparticles to contribute to the film deposition especially in the downstream area. Hence, a higher %I C value can be achieved in the film deposited using the 16 mm electrode than using the 5 mm electrode. As described above, the change in plasma chemistry occurs in a very short period of time (in the order of 0.1 ms) as the gas mixture flows in the AP-VHF plasma. Thus, the film formation with moving electrode produces a gradient microstructure in the direction of film thickness with uniform thickness obtained in the area that the plasma passes over[ 41 , 49 ]. Specifically, a -Si bottom and µc -Si top surfaces are formed by moving electrode toward the upstream side of the plasma (normal movement), while inverted layer structure is obtained by moving substrate inversely (inverse movement). From the TEM observations of Si film deposited with normal movement of the electrode shown in Fig. 3 , it has been confirmed that a thick a -Si layer is deposited on the substrate surface, while a much thinner µc -Si layer is formed on that. Judging from the thickness ratio, the µc -Si layer accounts for only about 20%. The formation of such an amorphous phase-dominated film can be predicted from the data taken without moving electrode in the same condition (Fig. 2 ), where the crystalline phase formation starts to occur after the maximal thickness position. Formation of heterostructured Si thick films From the viewpoint of mitigating the volume expansion during lithiation/delithiation and also of high initial capacity, we attempted to form a heterostructured Si thick film consisting of a thick µc -Si layer with a high density of grain boundaries and a thinner a -Si layer. As described in the previous section, significant generation of nanoparticles and their partial contribution to the growth of µc -Si films can be considered under condition that the gas residence time in the plasma is longer than ~ 0.5 ms. The greater the contribution of nanoparticles to the film growth, the more likely it is that the formation of Si-Si network structures in the growing Si film will be hindered and a high density of grain boundaries and /or voids will be introduced. An effective means for enhancing the contribution of Si nanoparticles is prolonging the gas residence time. Hence, we investigated the deposition conditions suitable for the formation of the heterostructured Si thick film by simultaneously decreasing the flow rate of the gas mixture in the plasma and increasing the input power density. Figure 4 shows the thickness profile and %I C of Si films deposited using a 10 mm-length electrode. The He flow rate decreased compared to the previous experiments (25 slm) with (a) H 2 /SiH 4 ratio of 10 (H 2 = 500 sccm, SiH 4 = 50 sccm) and (b) H 2 /SiH 4 ratio of 25 (H 2 = 1250 sccm, SiH 4 = 50 sccm). The input power density was adjusted in response to the increase in the H 2 flow rate. As seen in Fig. 4 a, a feature of the film formation that differs from the data shown in Fig. 2 is that the film thickness is significantly decreased despite being deposited under the same P VHF and duration. In addition, the crystalline phase is detected before the film reaches its maximum thickness. Another interesting feature is the small accumulation at the upstream area before the position of the maximal film thickness. Previous research on the deposition of Si oxide films using dielectric barrier discharge (DBD) system conducted by Martin et al. has shown a similar film-forming behavior[ 50 ]. The appearance of the two maxima suggests that there are two different deposition mechanism. Since the gas flow rate is halved, the formation of nanoparticles must have occurred much closer to the plasma entrance. The longer gas residence time also allows more nanoparticles to interact with atomic hydrogen and accumulate on the substrate surface, which explains the more rapid formation of crystalline phase. Figures 4 b shows the result of the attempt to enhance film crystallization and increase film thickness by increasing the H 2 /SiH 4 ratio and the deposition time. The step-profiler measurement results are smoothened to make the film thickness profile easier to observe. Since the deposition time is 20 times longer than that in Fig. 4 a, the value of the maximum thickness reaches 7.2 µ m with the average %I C of 74.5%. However, the film thickness profile shows a deposition characteristic similar to that in Fig. 4 a, indicating that the film-forming process is governed by the same deposition mechanisms. The improvement of film crystallinity and the shift of the second maximum to the upstream side might come from the impact of atomic hydrogen. Figure 4 c shows the time dependences of the maximal film thickness, which include the data shown in Figs. 4 a and 4 b. The thickness growths over deposition time under both conditions are almost linear, indicating that the film formation process is consistent irrespective of deposition time. These confirm that the AP-VHF plasma is clearly capable of depositing a thick Si film easily without significant change in deposition mechanism, only by increasing deposition time[ 45 , 51 , 52 ]. Notably, the thick film profile shown in Fig. 4 b has a sharp drop of thickness after the second maximum. In our experience, such a type of film thickness profile is quite new, since neither the film in Fig. 4 a nor other films obtained under conditions of lower P VHF and higher gas flow rate in our previous works ever show similar characteristics[ 41 , 44 ]. We consider that this reflects the considerably active formation of nanoparticles and their contribution to the film formation under the high P VHF input with the low gas flow rate. Based on the results shown in Fig. 4 , the deposition was conducted with the moving electrode in order to obtain Si films with uniform thickness. The electrode was moved in the opposite direction to the gas flow to create a heterostructured thick Si film with a crystalline bulk and an amorphous bottom layer. This film structure is believed to be suitable for LIBs anode since the initial interaction of µc -Si with Li + ion may boost the capacity, while the isotropic a -Si at the bottom can act as the mechanical support. Figure 5 a shows the SEM images of the Si film deposited with moving electrode at 0.02 mm/s. The deposition condition was the same as that in Fig. 4 b (H 2 = 1250 sccm, SiH 4 = 50 sccm and P VHF = 90 W/cm 2 ). From Fig. 5 a, the film thickness of only 1.3 µ m is observed despite a film thickness of at least 5 µ m can be predicted from the data in Fig. 4 b. In addition, the film crystallinity turns out to be lower (Fig. 5 c). One of the origins that may explain the surprising decrease in the film thickness is the very active etching effect of the growing Si film by atomic hydrogen occurring mainly in the downstream portion of the plasma zone[ 53 ]. Possibly, the Si layer formed by the large contribution of nanoparticles contains a high density of defects, which may lead to an extremely high etching rate by atomic hydrogen. Furthermore, the difference in diffusion characteristics between Si radicals and nanoparticles on the substrate surface must be considered. In the previous subsection, we have discussed how the nanoparticles dominantly contribute to film formation. Since Si nanoparticles have a weaker surface reaction to the substrate than radicals, the deposition rate tends to be lower. The plasma exposure time may also become limited during the electrode movement compared to the stationary conditions, which may further suppress the film formation. Investigating a significant number of depositions with moving electrode, we found that a slight modification of the deposition condition was enough to suppress the excessive etching effect by atomic hydrogen and to increase deposition rate. Figure 5 b shows the result obtained by increasing both the SiH 4 and H 2 gas flow rates (H 2 = 2500 sccm, SiH 4 = 100 sccm). A significant boost of film thickness is achieved while maintaining a reasonably high film crystallinity, as shown in Fig. 5 c. Electrochemical performance of the heterostructured Si thick film As discussed in the previous sections, a heterostructured Si thick film consisting of a crystalline bulk and an amorphous bottom layer has been successfully created through a moving electrode deposition process. To check whether or not the Si thick film can be applied to the anode of actual LIBs, a LIB half-cell was fabricated and its electrochemical characteristics were evaluated. A Si thick film was formed on a 200 µ m-thick Cu plate which was used as a current collector. The sample was then cut into pieces in the area of 1 cm × 1cm, and half-cells were assembled as shown in the schematic diagram of the LIB half-cell in Fig. 1 b. The Galvanostatic cycle measurements were carried out under a constant current of 0.9 mA in the potential range of 3.0 to 0 V vs. Li/Li + for both the charging and the discharging processes. Figure 6 shows the initial charge and discharge curve of the LIB half-cell. The capacity value of the initial charging and discharging process are 2838 mAhg − 1 and 2429 mAhg − 1 respectively, producing a Coulombic efficiency (CE) of 85.6%. The first slight bend on the charging potential curve detected at 0.80 V vs. Li/Li + implies the first moment of Li + ion insertion into the µc -Si surface layer. The alloying reaction of Li + ion with Si material proceeds further after reaching the potential plateau at 0.25 V vs. Li/Li + . An increase in voltage is observed after charging is stopped, which suggest the insufficient lithiation of the anode. In the discharging process, a sudden drop of potential is seen, which might be due to the presence of residual Li in the anode. Aside from those, there is no peculiarity of the potential curve’s pattern compared to that of LIB half-cells using Si anodes that have been reported in previous papers[ 52 , 54 , 55 ]. Researches are underway to clarify the details on the extent of lithiation and the structural changes of the anode. In future study, we will investigate the battery performance after many cycles and the effect of the formation of the solid electrolyte interface (SEI). Conclusions We have investigated the deposition characteristics of Si films in AP-VHF plasma and explored the basic performance of a LIB half-cell fabricated using the Si films as the anode. In the AP-VHF plasma, the chemistry occurring in the plasma changes very rapidly on a time scale of the order of 0.1 ms. As a result, the film thickness and microstructure under a stationary condition greatly varies along the gas flow direction, which causes the film growth with gradient microstructure in the thickness direction under deposition with moving electrode. It has strongly been suggested that the nanoparticle formation reaction in the AP-VHF plasma, particularly on the downstream side of the plasma zone, takes place more actively under conditions of a slower gas flow velocity and/or a higher power input. As a result, a heterostructured Si thick film with a µc -Si bulk and an a -Si bottom layer has been successfully formed. Note that the incorporation of nanoparticles into the resultant film plays a key role for the growth of a µc -Si layer having a high density of grain boundaries. The electrochemical performance examined on the LIB half-cell shows a promising capability of the heterostructured Si thick film toward the application to the anode of actual LIBs. Future study will focus not only on investigating the structural change during the lithiation/delithiation process but also on analyzing the battery performance after many cycles. Declarations Author contribution Afif Hamzens: Writing – original draft, Investigation, Formal analysis, Conceptualization, Data curation, Validation, Visualization. Shota Mochizuki: Investigation, Formal analysis, Conceptualization, Data curation. Farrel Dzaudan Naufal: Investigation, Data curation. Koki Hiromoto: Investigation, Data curation. Hiromasa Ohmi : Methodology, Supervision. Hiroaki Kakiuchi: Writing – review & editing, Methodology, Supervision, Project administration. Funding & Acknowledgement This research is partially supported by the Ministry of Education, Culture, Sports, Science, and Technology, Japan (MEXT) through scholarship funding. We express our sincere thanks to A. Takeuchi of Osaka University for his technical assistance. Data Availability The data of this study can be provided upon reasonable request. Competing interests: The authors declare no competing interests References Kim H-Y, Choi J-B, Lee J-Y (1999) Effects of silicon–hydrogen bond characteristics on the crystallization of hydrogenated amorphous silicon films prepared by plasma enhanced chemical vapor deposition. 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Journal of Power Sources 216:131–138. https://doi.org/10.1016/j.jpowsour.2012.04.105 Kulova TL, Skundin AM, Pleskov YuV, et al (2007) Lithium insertion into amorphous silicon thin-film electrodes. Journal of Electroanalytical Chemistry 600:217–225. https://doi.org/10.1016/j.jelechem.2006.07.002 Shi B, Zou Y, Xu G, et al (2023) Preparation of pure hydrogenated amorphous silicon film via PECVD method as anode materials for high-performance lithium-ion batteries. Solid State Ionics 402:116366. https://doi.org/10.1016/j.ssi.2023.116366 Domi Y, Usui H, Sugimoto K, Sakaguchi H (2019) Effect of Silicon Crystallite Size on Its Electrochemical Performance for Lithium‐Ion Batteries. Energy Technol 7:1800946. https://doi.org/10.1002/ente.201800946 Kakiuchi H, Ohmi H, Yasutake K (2018) Controllability of structural and electrical properties of silicon films grown in atmospheric-pressure very high-frequency plasma. J Phys D: Appl Phys 51:355203. https://doi.org/10.1088/1361-6463/aad47c Kakiuchi H, Ohmi H, Yamada T, et al (2015) Characterization of Si and SiO x films deposited in very high-frequency excited atmospheric-pressure plasma and their application to bottom-gate thin film transistors: Characterization of Si and SiO x films deposited. Phys Status Solidi A 212:1571–1577. https://doi.org/10.1002/pssa.201532328 Hamzens A, Kitamura K, Mochizuki S, et al (2023) Organosilicon-Based Thin Film Formation in Very High-Frequency Plasma Under Atmospheric Pressure. International Journal of Automation Technology 17:575–582. https://doi.org/10.20965/ijat.2023.p0575 Kakiuchi H, Ohmi H, Yasutake K (2020) Pulsed very high-frequency plasma-enhanced chemical vapor deposition of silicon films for low-temperature (120 °C) thin film transistors. J Phys D: Appl Phys 53:415201. https://doi.org/10.1088/1361-6463/ab9919 Elarbi N, Jemaï R, Outzourhit A, Khirouni K (2016) Amorphous/microcrystalline transition of thick silicon film deposited by PECVD. Appl Phys A 122:566. https://doi.org/10.1007/s00339-016-0103-y Kakiuchi H, Ohmi H, Yasutake K (2021) Gas-phase kinetics in atmospheric-pressure plasma-enhanced chemical vapor deposition of silicon films. Journal of Applied Physics 130:053307. https://doi.org/10.1063/5.0057951 Kawase MKM, Nakai TNT, Yamaguchi AYA, et al (1997) Numerical Simulation of Plasma Chemical Vapor Deposition from Silane: Effects of the Plasma-Substrate Distance and Hydrogen Dilution. Jpn J Appl Phys 36:3396. https://doi.org/10.1143/JJAP.36.3396 Sahu BB, Yin Y, Gauter S, et al (2016) Plasma engineering of silicon quantum dots and their properties through energy deposition and chemistry. Phys Chem Chem Phys 18:25837–25851. https://doi.org/10.1039/C6CP05647D Kakiuchi H, Ohmi H, Takeda S, Yasutake K (2022) Improvement of deposition characteristics of silicon oxide layers using argon-based atmospheric-pressure very high-frequency plasma. Journal of Applied Physics 132:103302. https://doi.org/10.1063/5.0101596 Martin S, Massines F, Gherardi N, Jimenez C (2004) Atmospheric pressure PE-CVD of silicon based coatings using a glow dielectric barrier discharge. Surface and Coatings Technology 177–178:693–698. https://doi.org/10.1016/j.surfcoat.2003.08.008 Chen B, Tay FEH, Iliescu C (2008) Development of thick film PECVD amorphous silicon with low stress for MEMS applications. In: Micro- and Nanotechnology: Materials, Processes, Packaging, and Systems IV. SPIE, pp 130–140 Han J, Tang D-M, Kong D, et al (2020) A thick yet dense silicon anode with enhanced interface stability in lithium storage evidenced by in situ TEM observations. Science Bulletin 65:1563–1569. https://doi.org/10.1016/j.scib.2020.05.018 Ohmi H, Kimoto K, Nomura T, et al (2021) Study on silicon removal property and surface smoothing phenomenon by moderate-pressure microwave hydrogen plasma. Materials Science in Semiconductor Processing 129:105780. https://doi.org/10.1016/j.mssp.2021.105780 Yu Z, Zhou L, Tong J, et al (2022) Improving Electrochemical Performance of Thick Silicon Film Anodes with Implanted Solid Lithium Source Electrolyte. J Phys Chem Lett 13:8725–8732. https://doi.org/10.1021/acs.jpclett.2c02090 Uehara M, Suzuki J, Tamura K, et al (2005) Thick vacuum deposited silicon films suitable for the anode of Li-ion battery. Journal of Power Sources 146:441–444. https://doi.org/10.1016/j.jpowsour.2005.03.097 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 20 Mar, 2025 Reviews received at journal 14 Mar, 2025 Reviews received at journal 04 Mar, 2025 Reviewers agreed at journal 20 Feb, 2025 Reviewers agreed at journal 20 Feb, 2025 Reviewers invited by journal 20 Feb, 2025 Editor assigned by journal 31 Jan, 2025 Submission checks completed at journal 31 Jan, 2025 First submitted to journal 30 Jan, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5928700","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":409501790,"identity":"58c11982-06b3-4bf6-8432-eee52d6cfe61","order_by":0,"name":"Afif Hamzens","email":"data:image/png;base64,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","orcid":"","institution":"Osaka University","correspondingAuthor":true,"prefix":"","firstName":"Afif","middleName":"","lastName":"Hamzens","suffix":""},{"id":409501791,"identity":"4480e0b5-819a-4d7a-8288-ce599feb8c55","order_by":1,"name":"Shota Mochizuki","email":"","orcid":"","institution":"Osaka University","correspondingAuthor":false,"prefix":"","firstName":"Shota","middleName":"","lastName":"Mochizuki","suffix":""},{"id":409501792,"identity":"77f36857-5447-4a4e-b3ea-f65ee80dbe5c","order_by":2,"name":"Farrel Dzaudan Naufal","email":"","orcid":"","institution":"Osaka University","correspondingAuthor":false,"prefix":"","firstName":"Farrel","middleName":"Dzaudan","lastName":"Naufal","suffix":""},{"id":409501793,"identity":"6dd35151-0bbd-4796-9754-a8c92b4eed46","order_by":3,"name":"Koki Hiromoto","email":"","orcid":"","institution":"Osaka University","correspondingAuthor":false,"prefix":"","firstName":"Koki","middleName":"","lastName":"Hiromoto","suffix":""},{"id":409501794,"identity":"7cf99ac0-b70d-4684-bb70-96db10cb7772","order_by":4,"name":"Hiromasa Ohmi","email":"","orcid":"","institution":"Osaka University","correspondingAuthor":false,"prefix":"","firstName":"Hiromasa","middleName":"","lastName":"Ohmi","suffix":""},{"id":409501795,"identity":"9c248ee5-218a-4b22-88ff-1e05bfa71601","order_by":5,"name":"Hiroaki Kakiuchi","email":"","orcid":"","institution":"Osaka University","correspondingAuthor":false,"prefix":"","firstName":"Hiroaki","middleName":"","lastName":"Kakiuchi","suffix":""}],"badges":[],"createdAt":"2025-01-30 08:38:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5928700/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5928700/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":75311592,"identity":"a94cfd7b-8c0e-4ab1-8fbd-219c2ae726ba","added_by":"auto","created_at":"2025-02-03 09:09:31","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":143575,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic illustration of \u003cstrong\u003e(a)\u003c/strong\u003ethe experimental setup, and \u003cstrong\u003e(b)\u003c/strong\u003e the half-cell battery structure\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-5928700/v1/d112999b173e7091fc647b10.png"},{"id":75311594,"identity":"ab237a01-5065-45b5-84a3-4ce9545f7191","added_by":"auto","created_at":"2025-02-03 09:09:31","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":102255,"visible":true,"origin":"","legend":"\u003cp\u003eVariations of thickness and \u003cem\u003e%I\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e of the Si films deposited with \u003cstrong\u003e(a)\u003c/strong\u003e \u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e = 30 W/cm\u003csup\u003e2\u003c/sup\u003e using the 5 mm-length electrode, and \u003cstrong\u003e(b)\u003c/strong\u003e \u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e = 32 W/cm\u003csup\u003e2\u003c/sup\u003e using the 16 mm-length electrode[41]\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-5928700/v1/af58392f7ffbbaa4d6a81d04.png"},{"id":75311596,"identity":"7ca690cb-5ca3-4f55-aaa5-7d0444ed9612","added_by":"auto","created_at":"2025-02-03 09:09:31","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":93193,"visible":true,"origin":"","legend":"\u003cp\u003eCross-sectional TEM image of Si films deposited with moving electrode at 0.5 mm/s using the 5 mm-length electrode. The film was deposited with H\u003csub\u003e2\u003c/sub\u003e/SiH\u003csub\u003e4\u003c/sub\u003e = 10 (H\u003csub\u003e2\u003c/sub\u003e = 500 sccm, SiH\u003csub\u003e4\u003c/sub\u003e = 50 sccm) and \u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e = 30 W/cm\u003csup\u003e2\u003c/sup\u003e[41]\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-5928700/v1/24a9e13374c2cd1974fef498.png"},{"id":75311610,"identity":"99617962-1100-43f5-8ee6-308ce8b42b27","added_by":"auto","created_at":"2025-02-03 09:09:32","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":189365,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e and \u003cstrong\u003e(b)\u003c/strong\u003e Variations of thickness and \u003cem\u003e%I\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e of the Si films deposited using the 10 mm-length electrode. The films were prepared with \u003cstrong\u003e(a)\u003c/strong\u003e \u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e = 40 W/cm\u003csup\u003e2\u003c/sup\u003e, H\u003csub\u003e2\u003c/sub\u003e/SiH\u003csub\u003e4\u003c/sub\u003e = 10, and deposition time = 20 s, and \u003cstrong\u003e(b)\u003c/strong\u003e \u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e = 90 W/cm\u003csup\u003e2\u003c/sup\u003e, H\u003csub\u003e2\u003c/sub\u003e/SiH\u003csub\u003e4\u003c/sub\u003e = 25, and deposition time = 240 s. \u003cstrong\u003e(c)\u003c/strong\u003e Time dependences of the maximal thickness of the Si film deposited under the same conditions as those in \u003cstrong\u003e(a)\u003c/strong\u003e and \u003cstrong\u003e(b)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-5928700/v1/793d006e48668710a7a57ac4.png"},{"id":75311625,"identity":"342c2047-5650-4c0b-a0ed-202ff4336dc9","added_by":"auto","created_at":"2025-02-03 09:09:33","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":345587,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e and \u003cstrong\u003e(b)\u003c/strong\u003e Cross-sectional SEM images of the Si thick film deposited with \u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e = 90 W/cm\u003csup\u003e2\u003c/sup\u003e and H\u003csub\u003e2\u003c/sub\u003e/SiH\u003csub\u003e4\u003c/sub\u003e = 25. The SiH\u003csub\u003e4\u003c/sub\u003e flow rate was \u003cstrong\u003e(a)\u003c/strong\u003e 50 sccm and \u003cstrong\u003e(b) \u003c/strong\u003e100 sccm. Both thick films were prepared with moving electrode at 0.02 mm/s. \u003cstrong\u003e(c)\u003c/strong\u003e Crystalline volume fractions and \u003cstrong\u003e(d)\u003c/strong\u003e grain boundary fractions of the Si thick films\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-5928700/v1/2dcef13cd8347f361e1ab2b5.png"},{"id":75312774,"identity":"3bd95f33-03ff-4e89-8f09-e2b8e9cda407","added_by":"auto","created_at":"2025-02-03 09:17:32","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":156589,"visible":true,"origin":"","legend":"\u003cp\u003ePotential to capacity curves of the initial charge (lithiation) and discharge (delithiation) process of heterostructured Si thick film deposited with \u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e = 90 W/cm\u003csup\u003e2\u003c/sup\u003e, H\u003csub\u003e2\u003c/sub\u003e/SiH\u003csub\u003e4\u003c/sub\u003e = 25 (SiH\u003csub\u003e4\u003c/sub\u003e = 100 sccm), and electrode moving speed = 0.02mm/s\u0026nbsp;\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-5928700/v1/ebb7384da4a497b32a4d1bd4.png"},{"id":75313822,"identity":"74805e23-cfdd-475d-97eb-b2ed83e89bd9","added_by":"auto","created_at":"2025-02-03 09:25:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1662832,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5928700/v1/fdeab9c4-54c0-48de-8598-01e1c270c320.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Formation of Heterostructured Silicon Thick Films in Atmospheric-Pressure Very High-Frequency Plasma Toward the Application to Lithium Ion Battery Anode","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSilicon (Si) has always become the most promising material for electronic devices and energy storage applications. The semiconductor properties of microcrystalline Si (\u003cem\u003e\u0026micro;c\u003c/em\u003e-Si) have made it popular for thin film transistors (TFTs) or solar cell applications[\u003cspan additionalcitationids=\"CR2 CR3 CR4\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e], while its mechanical flexibility is sufficient for microelectromechanical system (MEMS) [\u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] and flexible electronic devices[\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Recently, Si is frequently explored as the anode material of Lithium-Ion Batteries (LIBs). Si is potential as an enticing new material for anode since it offers much higher specific and volumetric capacity values than conventional graphite, and is able to operate under moderately low potential[\u003cspan additionalcitationids=\"CR13 CR14 CR15 CR16 CR17 CR18\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHowever, Si has a serious problem that it undergoes tremendous volume change (\u0026gt;\u0026thinsp;300%) during the lithiation/delithiation process[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Obrovac et al. have shown that the crack generation in Si anode due to the volume expansion makes it prone to be peeled off from the current collector during cycles[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Hence, research on Si anode have recently focused on the utilization of Si nanoparticles[\u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e] and nanowires[\u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] as well as core-shell carbon-silicon (C/Si) structure[\u003cspan additionalcitationids=\"CR29\" citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] with conductive additives and binders to mitigate the volume expansion. However, the use of such composite-type anodes results in the decrease in the content of active Si material, which lowers the capacity and limits the energy density[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eNon-composite-type Si anodes are still more favorable in battery industry from the viewpoint of achieving a cost-efficient manufacturing process while enhancing device performance[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The main challenge is to establish proper modifications on the non-composite-type Si anode to address the volume expansion issue. One of the ideas is to utilize high-density defects and/or porous microstructure. In this study, we propose the use of heterostructured Si films: a thick \u003cem\u003e\u0026micro;c\u003c/em\u003e-Si top layer having high-density grain boundaries on a thinner amorphous Si (\u003cem\u003ea\u003c/em\u003e-Si) bottom layer. It can employ the best character from each phase while accommodating each other weaknesses[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. A \u003cem\u003e\u0026micro;c\u003c/em\u003e-Si is quite favorable due to its higher initial capacity[\u003cspan additionalcitationids=\"CR36\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], while the isotropic volume expansion on \u003cem\u003ea\u003c/em\u003e-Si may provide better handling of volume expansion and lead to a good performance even after many cycles[\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. The higher-density grain boundaries in \u003cem\u003e\u0026micro;c\u003c/em\u003e-Si may also serve in mitigating volume expansion without reducing Si content[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOur previous study has set precedence in producing heterostructured Si thin films using a simple plasma-enhanced chemical vapor deposition (PECVD) method with monosilane (SiH\u003csub\u003e4\u003c/sub\u003e) and hydrogen (H\u003csub\u003e2\u003c/sub\u003e) as the process gases [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e], in which stable and homogeneous plasma excited by a very high-frequency (VHF) electric power under atmospheric-pressure (AP) is effectively used. In this study, we discuss both the deposition characteristics and electrochemical performance of thicker Si films prepared in AP-VHF plasma, aiming at developing the formation process of heterostructured Si thick films that can be applied to LIB anodes.\u003c/p\u003e"},{"header":"Experimental methods","content":"\u003cp\u003eThe deposition of Si films was carried out using the specially designed AP-PECVD system. Figure\u0026nbsp;1a shows the side and the front views of the parallel-plate-type electrode system used for the plasma generation. The electrode was made of aluminum alloy and its surface (10 mm length and 105 mm width) was intentionally left uncoated from an insulating material in order to increase the electron density in the AP-VHF plasma more than using alumina-coated electrode that was adopted in our previous studies[41–44]. The electrode was connected to a 150-MHz VHF power source via an impedance matching unit. The electrode system could be moved horizontally in the direction of the gas flow, enabling the deposition of a Si film with uniform thickness in the area that the plasma passed over. This feature will be further discussed in the next section.\u003c/p\u003e\n\u003cdiv\u003e\n \u003cdiv align=\"left\"\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e Experimental conditions\u003c/div\u003e\n \u003ctable id=\"Taba\" border=\"1\"\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eHe flow rate [slm]\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eH\u003csub\u003e2\u003c/sub\u003e flow rate [sccm]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e500, 1250, 2500\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSiH\u003csub\u003e4\u003c/sub\u003e flow rate [sccm]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50, 100\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e [W/cm\u003csup\u003e2\u003c/sup\u003e]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e40, 70, 90\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWorking pressure [Pa]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1 x 10\u003csup\u003e5\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSubstrate temperature [°C]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e220\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eDeposition time [s]\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e20–240\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSubstrate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eThermally oxidized Si wafer \u0026amp; 200 µm-thick Copper (Cu) foil\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eThe deposition process was conducted at a constant working pressure of 1 × 10\u003csup\u003e5\u003c/sup\u003e Pa. A gas mixture of helium (He), H\u003csub\u003e2\u003c/sub\u003e, and SiH\u003csub\u003e4\u003c/sub\u003e was used for each film deposition. The gas flow path was defined by quartz guide blocks around the electrode, ensuring a one-dimensional flow of the gas mixtures. We varied the flow rates of H\u003csub\u003e2\u003c/sub\u003e and SiH\u003csub\u003e4\u003c/sub\u003e, the input power density (\u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e) and deposition time as the principal parameters. The details of the experimental conditions are listed in Table 1.\u003c/p\u003e\n\u003cp\u003eThe film thickness profiles were measured by a step profiler (ACCRETECH Surfcom 590A), while the cross-sectional structure of the films was observed by using a scanning electron microscope (Hitachi S-4800) and a transmission electron microscope (JEOL JEM-2100). In order to analyze the microstructure of the films, Raman spectroscopy (Horiba Jobin Yvon LabRAM HR-800 \u0026amp; JASCO NRS-3100T) was used. The crystalline volume fraction (\u003cem\u003e%I\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e) and grain boundary fraction (\u003cem\u003e%I\u003c/em\u003e\u003csub\u003eGB\u003c/sub\u003e) were calculated from the integrated intensities of certain Raman peaks using the following equations:\u003c/p\u003e\n\u003cdiv id=\"Equ1\"\u003e\n \u003cdiv id=\"FileID_Equ1\" name=\"EquationSource\"\u003e$$\\:{\\%I}_{\\text{C}}=\\frac{{I}_{\\text{c}\\text{-}\\text{Si}}+{I}_{\\text{gb}\\text{-}\\text{Si}}}{{I}_{\\text{a-Si}}+{I}_{\\text{c-Si}}+{I}_{\\text{gb-Si}}}\\:\\times\\:100\\%$$\u003c/div\u003e\n \u003cdiv\u003e1\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Equ2\"\u003e\n \u003cdiv id=\"FileID_Equ2\" name=\"EquationSource\"\u003e$$\\:{\\%I}_{\\text{GB}}=\\frac{{I}_{\\text{gb}\\text{-}\\text{Si}}}{{I}_{\\text{gb-Si}}+{I}_{\\text{c}\\text{-}\\text{Si}}}\\:\\times\\:100\\%$$\u003c/div\u003e\n \u003cdiv\u003e2\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003ewhere \u003cem\u003eI\u003c/em\u003e\u003csub\u003ec−Si\u003c/sub\u003e, \u003cem\u003eI\u003c/em\u003e\u003csub\u003egb−Si\u003c/sub\u003e and \u003cem\u003eI\u003c/em\u003e\u003csub\u003ea−Si\u003c/sub\u003e are the integrated intensities of the peaks related to microcrystalline Si (around 515–520 cm\u003csup\u003e− 1\u003c/sup\u003e), grain boundaries component (around 500–510 cm\u003csup\u003e− 1\u003c/sup\u003e), and amorphous Si (around 480 cm\u003csup\u003e− 1\u003c/sup\u003e) respectively[41, 45]. Electrochemical measurement of the Si thick film sample was performed using a Galvanostatic cycling of Si film – Li metal coin cell structure. A half-cell structure was used with Li metal as counter electrode, LiPF\u003csub\u003e6\u003c/sub\u003e + EC/DMC/EMC + FEC liquid as electrolyte, and a separator as shown in Fig.\u0026nbsp;1b.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003eSi growth process in AP-VHF plasma\u003c/h2\u003e \u003cp\u003eToward the formation of heterostructured Si thick films, we first review the growth process of Si films in AP-VHF plasma mainly based on our previous report on Si thin film formation[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the distribution of thickness and \u003cem\u003e%I\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e of the Si films prepared without the electrode movement using the (a) 5 mm electrode (\u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e = 30 W/cm\u003csup\u003e2\u003c/sup\u003e) and (b) 16 mm electrode (\u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e = 32 W/cm\u003csup\u003e2\u003c/sup\u003e). The flow rates of He, H\u003csub\u003e2\u003c/sub\u003e, and SiH\u003csub\u003e4\u003c/sub\u003e were 50 slm, 500 sccm, and 50 sccm respectively, and the deposition time was 20 s. The horizontal axis is the position in the gas flow direction, and the zero position is defined at the front end of the electrode. The upper axis is converted to the average gas residence time in the plasma, calculated by dividing the electrode length by the average gas flow velocity. The deposition in the stationary condition resulted in the formation of Si films with inhomogeneous thickness and microstructure, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. A thick amorphous layer is created on the upstream side, while a much thinner crystalline layer is created on the downstream side.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe frequency of collision between particles in the gas phase is several orders of magnitude higher in AP plasma than common low-pressure plasma[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. Hence, it is considered that the source SiH\u003csub\u003e4\u003c/sub\u003e gas is decomposed by the electron impact as soon as it enters the plasma zone to generate SiH\u003csub\u003ex\u003c/sub\u003e radicals, followed by the production of a variety of higher order radicals and even nanoparticles through the secondary reactions with various species[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. The dissociation products diffuse to the substrate surface and are integrated into the developing film. The very rapid progress of both gas-phase and surface reactions lead to the growth of \u003cem\u003ea\u003c/em\u003e-Si mainly from SiH\u003csub\u003ex\u003c/sub\u003e radicals in the upstream area[\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn the downstream area, as a consequence of the SiH\u003csub\u003e4\u003c/sub\u003e gas consumption on the upstream side, the H\u003csub\u003e2\u003c/sub\u003e/SiH\u003csub\u003e4\u003c/sub\u003e ratio increases significantly from its initial value which generate abundant atomic hydrogen, promoting the crystallization of the growing Si film. Moreover, it is reasonable to note that the very rapid progress of the gas-phase reactions in the plasma readily cause the nucleation of clusters and their growth to nanoparticles both in amorphous and crystalline phase[\u003cspan additionalcitationids=\"CR47\" citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. Thus, the contribution of crystalline nanoparticles can also be taken into account as an origin of the film crystallization. Crystalline phase thus becomes prominent in the downstream area. Although a \u003cem\u003e\u0026micro;c\u003c/em\u003e-Si growth is not observed in the film deposited using the 5 mm electrode due to the short electrode length (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea), the film-forming reactions must have been the same as those for the 16 mm electrode since the deposition condition is almost the same.\u003c/p\u003e \u003cp\u003eThe use of a longer electrode leads to a larger deposition area due to the longer gas residence time (diffusion length of radicals) in the plasma. This also results in the increase in the volume of \u003cem\u003e\u0026micro;c\u003c/em\u003e-Si and the better SiH\u003csub\u003e4\u003c/sub\u003e gas transforming efficiency[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. The SiH\u003csub\u003e4\u003c/sub\u003e transforming efficiency, which is defined as the efficiency in transforming the source SiH\u003csub\u003e4\u003c/sub\u003e gas into useful Si film, is affected mainly by the diffusion length of radicals within the gas residence time in the plasma. It was calculated by integrating the thickness profiles of the Si films shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, assuming that the film density was the same as that of single crystalline Si (2.33 g/cm\u003csup\u003e3\u003c/sup\u003e). Indeed, the efficiency of using the 5 mm electrode (3.0%) is lower than using the 16 mm electrode (6.3%). The longer electrode length is also likely to generate the larger amount of nanoparticles to contribute to the film deposition especially in the downstream area. Hence, a higher \u003cem\u003e%I\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e value can be achieved in the film deposited using the 16 mm electrode than using the 5 mm electrode.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs described above, the change in plasma chemistry occurs in a very short period of time (in the order of 0.1 ms) as the gas mixture flows in the AP-VHF plasma. Thus, the film formation with moving electrode produces a gradient microstructure in the direction of film thickness with uniform thickness obtained in the area that the plasma passes over[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]. Specifically, \u003cem\u003ea\u003c/em\u003e-Si bottom and \u003cem\u003e\u0026micro;c\u003c/em\u003e-Si top surfaces are formed by moving electrode toward the upstream side of the plasma (normal movement), while inverted layer structure is obtained by moving substrate inversely (inverse movement). From the TEM observations of Si film deposited with normal movement of the electrode shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, it has been confirmed that a thick \u003cem\u003ea\u003c/em\u003e-Si layer is deposited on the substrate surface, while a much thinner \u003cem\u003e\u0026micro;c\u003c/em\u003e-Si layer is formed on that. Judging from the thickness ratio, the \u003cem\u003e\u0026micro;c\u003c/em\u003e-Si layer accounts for only about 20%. The formation of such an amorphous phase-dominated film can be predicted from the data taken without moving electrode in the same condition (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), where the crystalline phase formation starts to occur after the maximal thickness position.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eFormation of heterostructured Si thick films\u003c/h3\u003e\n\u003cp\u003eFrom the viewpoint of mitigating the volume expansion during lithiation/delithiation and also of high initial capacity, we attempted to form a heterostructured Si thick film consisting of a thick \u003cem\u003e\u0026micro;c\u003c/em\u003e-Si layer with a high density of grain boundaries and a thinner \u003cem\u003ea\u003c/em\u003e-Si layer. As described in the previous section, significant generation of nanoparticles and their partial contribution to the growth of \u003cem\u003e\u0026micro;c\u003c/em\u003e-Si films can be considered under condition that the gas residence time in the plasma is longer than ~\u0026thinsp;0.5 ms. The greater the contribution of nanoparticles to the film growth, the more likely it is that the formation of Si-Si network structures in the growing Si film will be hindered and a high density of grain boundaries and /or voids will be introduced. An effective means for enhancing the contribution of Si nanoparticles is prolonging the gas residence time. Hence, we investigated the deposition conditions suitable for the formation of the heterostructured Si thick film by simultaneously decreasing the flow rate of the gas mixture in the plasma and increasing the input power density.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the thickness profile and \u003cem\u003e%I\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e of Si films deposited using a 10 mm-length electrode. The He flow rate decreased compared to the previous experiments (25 slm) with (a) H\u003csub\u003e2\u003c/sub\u003e/SiH\u003csub\u003e4\u003c/sub\u003e ratio of 10 (H\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;500 sccm, SiH\u003csub\u003e4\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;50 sccm) and (b) H\u003csub\u003e2\u003c/sub\u003e/SiH\u003csub\u003e4\u003c/sub\u003e ratio of 25 (H\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1250 sccm, SiH\u003csub\u003e4\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;50 sccm). The input power density was adjusted in response to the increase in the H\u003csub\u003e2\u003c/sub\u003e flow rate. As seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, a feature of the film formation that differs from the data shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e is that the film thickness is significantly decreased despite being deposited under the same \u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e and duration. In addition, the crystalline phase is detected before the film reaches its maximum thickness.\u003c/p\u003e \u003cp\u003eAnother interesting feature is the small accumulation at the upstream area before the position of the maximal film thickness. Previous research on the deposition of Si oxide films using dielectric barrier discharge (DBD) system conducted by Martin et al. has shown a similar film-forming behavior[\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. The appearance of the two maxima suggests that there are two different deposition mechanism. Since the gas flow rate is halved, the formation of nanoparticles must have occurred much closer to the plasma entrance. The longer gas residence time also allows more nanoparticles to interact with atomic hydrogen and accumulate on the substrate surface, which explains the more rapid formation of crystalline phase.\u003c/p\u003e \u003cp\u003eFigures \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb shows the result of the attempt to enhance film crystallization and increase film thickness by increasing the H\u003csub\u003e2\u003c/sub\u003e/SiH\u003csub\u003e4\u003c/sub\u003e ratio and the deposition time. The step-profiler measurement results are smoothened to make the film thickness profile easier to observe. Since the deposition time is 20 times longer than that in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, the value of the maximum thickness reaches 7.2 \u003cem\u003e\u0026micro;\u003c/em\u003em with the average \u003cem\u003e%I\u003c/em\u003e\u003csub\u003eC\u003c/sub\u003e of 74.5%. However, the film thickness profile shows a deposition characteristic similar to that in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, indicating that the film-forming process is governed by the same deposition mechanisms. The improvement of film crystallinity and the shift of the second maximum to the upstream side might come from the impact of atomic hydrogen.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec shows the time dependences of the maximal film thickness, which include the data shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb. The thickness growths over deposition time under both conditions are almost linear, indicating that the film formation process is consistent irrespective of deposition time. These confirm that the AP-VHF plasma is clearly capable of depositing a thick Si film easily without significant change in deposition mechanism, only by increasing deposition time[\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eNotably, the thick film profile shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb has a sharp drop of thickness after the second maximum. In our experience, such a type of film thickness profile is quite new, since neither the film in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea nor other films obtained under conditions of lower \u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e and higher gas flow rate in our previous works ever show similar characteristics[\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. We consider that this reflects the considerably active formation of nanoparticles and their contribution to the film formation under the high \u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e input with the low gas flow rate.\u003c/p\u003e \u003cp\u003eBased on the results shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the deposition was conducted with the moving electrode in order to obtain Si films with uniform thickness. The electrode was moved in the opposite direction to the gas flow to create a heterostructured thick Si film with a crystalline bulk and an amorphous bottom layer. This film structure is believed to be suitable for LIBs anode since the initial interaction of \u003cem\u003e\u0026micro;c\u003c/em\u003e-Si with Li\u003csup\u003e+\u003c/sup\u003e ion may boost the capacity, while the isotropic \u003cem\u003ea\u003c/em\u003e-Si at the bottom can act as the mechanical support.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea shows the SEM images of the Si film deposited with moving electrode at 0.02 mm/s. The deposition condition was the same as that in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb (H\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;1250 sccm, SiH\u003csub\u003e4\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;50 sccm and \u003cem\u003eP\u003c/em\u003e\u003csub\u003eVHF\u003c/sub\u003e = 90 W/cm\u003csup\u003e2\u003c/sup\u003e). From Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea, the film thickness of only 1.3 \u003cem\u003e\u0026micro;\u003c/em\u003em is observed despite a film thickness of at least 5 \u003cem\u003e\u0026micro;\u003c/em\u003em can be predicted from the data in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb. In addition, the film crystallinity turns out to be lower (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec).\u003c/p\u003e \u003cp\u003eOne of the origins that may explain the surprising decrease in the film thickness is the very active etching effect of the growing Si film by atomic hydrogen occurring mainly in the downstream portion of the plasma zone[\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. Possibly, the Si layer formed by the large contribution of nanoparticles contains a high density of defects, which may lead to an extremely high etching rate by atomic hydrogen. Furthermore, the difference in diffusion characteristics between Si radicals and nanoparticles on the substrate surface must be considered. In the previous subsection, we have discussed how the nanoparticles dominantly contribute to film formation. Since Si nanoparticles have a weaker surface reaction to the substrate than radicals, the deposition rate tends to be lower. The plasma exposure time may also become limited during the electrode movement compared to the stationary conditions, which may further suppress the film formation.\u003c/p\u003e \u003cp\u003e Investigating a significant number of depositions with moving electrode, we found that a slight modification of the deposition condition was enough to suppress the excessive etching effect by atomic hydrogen and to increase deposition rate. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb shows the result obtained by increasing both the SiH\u003csub\u003e4\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003e gas flow rates (H\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;2500 sccm, SiH\u003csub\u003e4\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;100 sccm). A significant boost of film thickness is achieved while maintaining a reasonably high film crystallinity, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eElectrochemical performance of the heterostructured Si thick film\u003c/h3\u003e\n\u003cp\u003eAs discussed in the previous sections, a heterostructured Si thick film consisting of a crystalline bulk and an amorphous bottom layer has been successfully created through a moving electrode deposition process. To check whether or not the Si thick film can be applied to the anode of actual LIBs, a LIB half-cell was fabricated and its electrochemical characteristics were evaluated. A Si thick film was formed on a 200 \u003cem\u003e\u0026micro;\u003c/em\u003em-thick Cu plate which was used as a current collector. The sample was then cut into pieces in the area of 1 cm \u0026times; 1cm, and half-cells were assembled as shown in the schematic diagram of the LIB half-cell in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb. The Galvanostatic cycle measurements were carried out under a constant current of 0.9 mA in the potential range of 3.0 to 0 V vs. Li/Li\u003csup\u003e+\u003c/sup\u003e for both the charging and the discharging processes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the initial charge and discharge curve of the LIB half-cell. The capacity value of the initial charging and discharging process are 2838 mAhg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 2429 mAhg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e respectively, producing a Coulombic efficiency (CE) of 85.6%. The first slight bend on the charging potential curve detected at 0.80 V vs. Li/Li\u003csup\u003e+\u003c/sup\u003e implies the first moment of Li\u003csup\u003e+\u003c/sup\u003e ion insertion into the \u003cem\u003e\u0026micro;c\u003c/em\u003e-Si surface layer. The alloying reaction of Li\u003csup\u003e+\u003c/sup\u003e ion with Si material proceeds further after reaching the potential plateau at 0.25 V vs. Li/Li\u003csup\u003e+\u003c/sup\u003e. An increase in voltage is observed after charging is stopped, which suggest the insufficient lithiation of the anode. In the discharging process, a sudden drop of potential is seen, which might be due to the presence of residual Li in the anode. Aside from those, there is no peculiarity of the potential curve\u0026rsquo;s pattern compared to that of LIB half-cells using Si anodes that have been reported in previous papers[\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e, \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e, \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e]. Researches are underway to clarify the details on the extent of lithiation and the structural changes of the anode. In future study, we will investigate the battery performance after many cycles and the effect of the formation of the solid electrolyte interface (SEI).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eWe have investigated the deposition characteristics of Si films in AP-VHF plasma and explored the basic performance of a LIB half-cell fabricated using the Si films as the anode. In the AP-VHF plasma, the chemistry occurring in the plasma changes very rapidly on a time scale of the order of 0.1 ms. As a result, the film thickness and microstructure under a stationary condition greatly varies along the gas flow direction, which causes the film growth with gradient microstructure in the thickness direction under deposition with moving electrode. It has strongly been suggested that the nanoparticle formation reaction in the AP-VHF plasma, particularly on the downstream side of the plasma zone, takes place more actively under conditions of a slower gas flow velocity and/or a higher power input. As a result, a heterostructured Si thick film with a \u003cem\u003e\u0026micro;c\u003c/em\u003e-Si bulk and an \u003cem\u003ea\u003c/em\u003e-Si bottom layer has been successfully formed. Note that the incorporation of nanoparticles into the resultant film plays a key role for the growth of a \u003cem\u003e\u0026micro;c\u003c/em\u003e-Si layer having a high density of grain boundaries. The electrochemical performance examined on the LIB half-cell shows a promising capability of the heterostructured Si thick film toward the application to the anode of actual LIBs. Future study will focus not only on investigating the structural change during the lithiation/delithiation process but also on analyzing the battery performance after many cycles.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAuthor contribution\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAfif Hamzens:\u003c/strong\u003e Writing \u0026ndash; original draft, Investigation, Formal analysis, Conceptualization, Data curation, Validation, Visualization. \u003cstrong\u003eShota Mochizuki:\u003c/strong\u003e Investigation, Formal analysis, Conceptualization, Data curation. \u003cstrong\u003eFarrel Dzaudan Naufal:\u003c/strong\u003e Investigation, Data curation. \u003cstrong\u003eKoki Hiromoto:\u003c/strong\u003e Investigation, Data curation. \u003cstrong\u003eHiromasa Ohmi\u003c/strong\u003e: Methodology, Supervision. \u003cstrong\u003eHiroaki Kakiuchi:\u003c/strong\u003e Writing \u0026ndash; review \u0026amp; editing, Methodology, Supervision, Project administration.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFunding \u0026amp; Acknowledgement\u003c/p\u003e\n\u003cp\u003eThis research is partially supported by the Ministry of Education, Culture, Sports, Science, and Technology, Japan (MEXT) through scholarship funding. We express our sincere thanks to A. Takeuchi of Osaka University for his technical assistance.\u003c/p\u003e\n\u003cp\u003eData Availability\u003c/p\u003e\n\u003cp\u003eThe data of this study can be provided upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests:\u003c/strong\u003e The authors declare no competing interests\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eKim H-Y, Choi J-B, Lee J-Y (1999) Effects of silicon\u0026ndash;hydrogen bond characteristics on the crystallization of hydrogenated amorphous silicon films prepared by plasma enhanced chemical vapor deposition. 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Science Bulletin 65:1563\u0026ndash;1569. https://doi.org/10.1016/j.scib.2020.05.018\u003c/li\u003e\n\u003cli\u003eOhmi H, Kimoto K, Nomura T, et al (2021) Study on silicon removal property and surface smoothing phenomenon by moderate-pressure microwave hydrogen plasma. Materials Science in Semiconductor Processing 129:105780. https://doi.org/10.1016/j.mssp.2021.105780\u003c/li\u003e\n\u003cli\u003eYu Z, Zhou L, Tong J, et al (2022) Improving Electrochemical Performance of Thick Silicon Film Anodes with Implanted Solid Lithium Source Electrolyte. J Phys Chem Lett 13:8725\u0026ndash;8732. https://doi.org/10.1021/acs.jpclett.2c02090\u003c/li\u003e\n\u003cli\u003eUehara M, Suzuki J, Tamura K, et al (2005) Thick vacuum deposited silicon films suitable for the anode of Li-ion battery. Journal of Power Sources 146:441\u0026ndash;444. https://doi.org/10.1016/j.jpowsour.2005.03.097\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"plasma-chemistry-and-plasma-processing","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Plasma Chemistry and Plasma Processing](https://www.springer.com/journal/11090 ","snPcode":"11090","submissionUrl":"https://mc.manuscriptcentral.com/pcpp","title":"Plasma Chemistry and Plasma Processing","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"PECVD, atmospheric-pressure plasma, silicon, lithium-ion batteries","lastPublishedDoi":"10.21203/rs.3.rs-5928700/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5928700/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe superiority of silicon (Si) film performance as anode material in the rechargeable battery technologies is tormented by the huge volume expansion during cycle. The combined structure of a microcrystalline Si with high porous/defect density and an isotropic amorphous Si has been proposed as a feasible solution. Our own deposition process using atmospheric-pressure (AP) plasma excited by very high-frequency (VHF) power has managed to create a non-composite Si film with gradient phase along thickness direction. This work investigates the formation of heterostructured Si thick film and its capability toward the application to the Lithium-ion Batteries (LIBs) anode. It is highly indicated that a slower gas flow rate and/or a larger power input cause the nanoparticle formation in the AP-VHF plasma to occur more actively, which significantly influenced the development of a crystalline layer with a high density of grain boundaries. The promising electrochemical performance imply a great potential of heterostructured Si as LIBs anode.\u003c/p\u003e","manuscriptTitle":"Formation of Heterostructured Silicon Thick Films in Atmospheric-Pressure Very High-Frequency Plasma Toward the Application to Lithium Ion Battery Anode","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-02-03 09:09:23","doi":"10.21203/rs.3.rs-5928700/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-03-20T11:45:57+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-03-14T16:29:32+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-03-04T22:16:15+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"128418001588375636106109370112919907583","date":"2025-02-20T20:47:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"272302298294190576870499825941026736125","date":"2025-02-20T14:49:57+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-02-20T12:45:00+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-01-31T10:39:02+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-01-31T10:37:40+00:00","index":"","fulltext":""},{"type":"submitted","content":"Plasma Chemistry and Plasma Processing","date":"2025-01-30T08:23:52+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"plasma-chemistry-and-plasma-processing","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":" Learn more about [Plasma Chemistry and Plasma Processing](https://www.springer.com/journal/11090 ","snPcode":"11090","submissionUrl":"https://mc.manuscriptcentral.com/pcpp","title":"Plasma Chemistry and Plasma Processing","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"044cb6e1-0b78-4584-8e03-af1caa7fcf9e","owner":[],"postedDate":"February 3rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-05-10T05:53:28+00:00","versionOfRecord":[],"versionCreatedAt":"2025-02-03 09:09:23","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5928700","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5928700","identity":"rs-5928700","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}