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## Creator

[Ryo Matsumoto](https://orcid.org/0000-0001-6294-5403), Souma Kodani, Eiji Hitsuda, Yuki Nishimiya, [Yoshihiro Nemoto](https://orcid.org/0000-0001-8547-4990), [Yoshihiko Takano](https://orcid.org/0000-0002-1541-6928), Hiromi Tanaka

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This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Ryo Matsumoto, Souma Kodani, Eiji Hitsuda, Yuki Nishimiya, Yoshihiro Nemoto, Yoshihiko Takano, Hiromi Tanaka; Growth of Ruddlesden–Popper phase La4Ni3O10 thin film on LaAlO3 substrate via pulsed laser deposition method. J. Appl. Phys. 21 August 2026; 140 (7): 075301 and may be found at https://doi.org/10.1063/5.0338425.[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

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[Growth of Ruddlesden–Popper phase La4Ni3O10 thin film on LaAlO3 substrate via pulsed laser deposition method](https://mdr.nims.go.jp/datasets/8f40b89d-9747-4c42-9342-0357e0ced660)

## Fulltext

1 Growth of Ruddlesden-Popper phase La4Ni3O10 thin film on 1 LaAlO3 substrate via pulsed laser deposition method 2  3 *Ryo Matsumoto1, Souma Kodani3+, Eiji Hitsuda1,4, Yuki Nishimiya2, Yoshihiro Nemoto2,  4 Yoshihiko Takano1,4, Hiromi Tanaka3 5 *Corresponding author; Email: MATSUMOTO.Ryo@nims.go.jp 6  7 1International Center for Materials Nanoarchitectonics (MANA), 8 National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan 9 2Research Network and Facility Services Division, 10 National Institute for Materials Science, Tsukuba, Ibaraki 305-0047, Japan 11 3National Institute of Technology, Yonago College, Yonago, Tottori 683-8502, Japan 12 4Graduate School of Science and Technology, University of Tsukuba, 13 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8577, Japan 14 +Present address; Graduate School of Engineering, Tohoku University, Sendai, 980-0845, Japan 15  16 Abstract 17 Pulsed laser deposition (PLD) is a promising technique for thin-film growth from the perspectives of 18 both practical applications and the development of fundamental materials science. Recently, La3Ni2O7 19 thin films, belonging to the layered Ruddlesden–Popper (RP) nickelates Lan+1NinO3n+1, grown on 20 substrates inducing compressive strain due to lattice mismatch, have attracted considerable attention 21 as a new class of high transition-temperature superconductors at ambient pressure. Although the 22 emergence of superconductivity in the related RP-type nickelate La4Ni3O10 thin film is anticipated, 23 the growth of an oriented thin film along the c-axis with compressive strain has not been reported by 24 using the PLD process. In this study, we investigate the thin-film growth of La4Ni3O10 using the PLD 25 technique on a LaAlO3 substrate, which imposes a compressive strain. X-ray diffraction analysis and 26 transmission electron microscopy reveal that well-oriented La4Ni3O10 phases can be grown on the 27 LaAlO3 substrate. Although superconductivity is absent in the grown film, the phase formation of 28 La4Ni3O10 on the LaAlO3 substrate via the PLD process is the first step for the realization of ambient-29 pressure superconductivity in this system. 30  2 1. Introduction 31 The development of functional materials plays a central role in advancing modern technology and 32 improving the quality of life. Among various material forms, thin films are particularly important for 33 device applications because of their compatibility with integration and large-scale production. 34 Epitaxial thin films on single-crystalline substrates are typically grown by techniques such as chemical 35 vapor deposition (CVD), metal–organic decomposition (MOD), and molecular beam epitaxy (MBE), 36 depending on the target material1,2. Pulsed laser deposition (PLD) is another widely used method for 37 fabricating functional thin films, including semiconductors3, solid ionic conductors4, optoelectronic 38 materials5, and superconducting devices6. PLD offers several advantages, such as a relatively simple 39 process using a bulk target, high compositional homogeneity over large substrates, and flexibility of 40 the deposition environment7,8. In addition, epitaxial growth under lattice mismatch enables access to 41 metastable phases stabilized by substrate-induced strain, providing a powerful route to discovering 42 novel functional materials9. For these reasons, PLD has become a promising tool not only for device 43 applications but also for fundamental studies in condensed matter physics. 44 Layered Ruddlesden–Popper (RP) nickelates, REn+1NinO3n+1 (RE = rare-earth element), have 45 long been investigated as functional materials, particularly for applications in solid oxide fuel cells10. 46 Recently, the n = 2 member, La3Ni2O7, has attracted considerable attention following the discovery of 47 superconductivity with a transition temperature (Tc) exceeding 80 K under high pressure11, above the 48 boiling point of liquid nitrogen. The orthorhombic structure of non-superconducting La3Ni2O7 49 undergoes to a superconducting tetragonal structure through a structural modification above 8 GPa12. 50 Many experimental and theoretical research have been conducted to investigate the superconducting 51 mechanism and possible enhancement of Tc13–21. In parallel, efforts have been directed toward 52 realizing superconductivity in La3Ni2O7 at ambient pressure for practical applications. Most recently, 53 superconducting La3Ni2O7 thin films with Tc above 40 K at ambient pressure were achieved by 54 epitaxial growth on SrLaAlO4 substrates using PLD22–24. In this case, lattice mismatch–induced strain 55 plays a role analogous to external pressure, stabilizing the superconducting phase. The realization of 56 superconductivity at ambient pressure in the RP nickelate thin film has opened new opportunities for 57 quantum device research using the PLD method. 58 Following the discovery of high-Tc superconductivity in compressed La3Ni2O7, pressure-59 induced superconductivity with Tc above 30 K has also been reported in the n = 3 RP nickelate 60 La4Ni3O10, again associated with a pressure-driven structural modification at around 20 GPa25–28. By 61 analogy with La3Ni2O7, the development of superconducting La4Ni3O10 thin films using PLD is highly 62 anticipated. However, the epitaxial growth of La4Ni3O10 thin films on a specific substrate with a 63 smaller in-plane lattice constant than that of La4Ni3O10 by PLD has not yet been systematically 64 investigated. In this work, we examine the growth conditions for La4Ni3O10 thin films with 00l 65 orientation on LaAlO3 (LAO) substrates, which induces a large lattice mismatch, using the PLD 66  3 method. X-ray diffraction (XRD) analysis reveals that the oriented film of La4Ni3O10 along the c-axis 67 is mainly grown on the LAO substrate. Local structural analysis indicates that the dominant region of 68 the film is the La4Ni3O10 phase, with minor contributions from the other phases and local defects. 69 films. By changing the parameters of the PLD process, a different layer number of La3Ni2O7 (n = 2) 70 was grown as a byproduct. Electrical transport measurements demonstrate a reduction of the band gap 71 with increasing layer number n. These findings provide important insights into the growth and 72 electronic structure of RP nickelate thin films and represent a key step toward the realization of 73 superconducting La4Ni3O10 thin films by PLD. 74  75 2. Expetimental procedures 76 La4Ni3O10 (n = 3) thin films were grown on 00l-oriented LaAlO3 substrates by the PLD using a 77 polycrystalline La4Ni3O10 target. The target was prepared by repeated solid-state reactions of La2O3 78 and NiO powders mixed in a molar ratio of 2:3. The mixed powders were calcined and sintered in air 79 at 1200°C for 24 h. Thin-film growth was carried out using a PLD system (PAC-LMBE, PASCAL 80 Co.) equipped with a Nd:YAG laser (λ = 1064 nm). During deposition, the laser repetition rate, 81 substrate temperature (Tsub), oxygen partial pressure (PO2), laser power, and distance between the 82 target and substrate (Dts) were varied to optimize growth conditions. The growth conditions in this 83 paper are summarized in Table S1. 84 The crystal structure of the obtained films was characterized by X-ray diffraction (XRD) 85 using a SmartLab diffractometer (Rigaku) with monochromated Cu Kα1 radiation (λ = 1.5406 Å). The 86 temperature dependence of the electrical resistance was measured by a standard four-probe method 87 with a collinear geometry using Au wires attached with Ag paste in a physical property measurement 88 system (Quantum Design). Transmission electron microscopy (TEM) and atomic-resolution energy-89 dispersive X-ray spectroscopy (EDX) mapping were performed using a JEM-ARM200F microscope 90 (JEOL). Cross-sectional TEM specimens were prepared by focused ion beam (FIB) milling using a 91 JIB-4000 system (JEOL). 92  93 3. Results and discussion 94 Figure 1 shows an XRD pattern obtained by a θ–2θ scan of the La4Ni3O10 thin film on the LAO 95 substrate deposited under the conditions of Tsub = 690°C and PO2 = 20 Pa. The laser power and Dts 96 were set to 33 mJ and 30 mm, respectively. The film thickness of 93 nm was obtained with 6000 laser 97 pulses, estimated via TEM analysis as discussed later. The film clearly exhibits (00l) diffraction peaks 98 originating from the RP-type structure of La4Ni3O10, indicating that the film is highly oriented along 99 the c-axis. A peak position at around 47° with a square symbol among the tiny unknown peaks is near 100 that from (002) diffraction of LaNiO3. Other tiny and sharp unknown peaks possibly originate from 101 an extrinsic component, for example, Ag paste for the bond of the substrate to the sample holder of 102  4 PLD. The crystal structure of the LAO substrate is rhombohedral, and can be approximated as a 103 pseudo-cubic structure with aLAO = 3.787 Å29. On the other hand, bulk La4Ni3O10 has an orthorhombic 104 Amam structure with lattice parameters a = 5.415 Å, b = 5.465 Å, and c = 27.96 Å30. This structure 105 can be approximated by a pseudo-tetragonal unit cell with a4310 = b4310 = 3.847 Å and c4310 = 27.96 Å. 106 From this lattice mismatch, a compressive strain of −1.6% is expected to be applied to the La4Ni3O10 107 thin film grown on the LAO substrate. In the case of La3Ni2O7 films, the critical compressive strain 108 for the emergence of superconductivity at ambient pressure has been reported to be between −1.2% 109 and −2.1%23. The strain of −1.6% in the La4Ni3O10 film on the LAO substrate lies within this critical 110 range reported for La3Ni2O7 films, suggesting that epitaxial strain may significantly influence the 111 electronic states. Consistently, the out-of-plane lattice constant of the obtained film is estimated to be 112 c = 28.45 Å, which indicates the elongation of 1.8% compared with the bulk value due to the in-plane 113 compressive strain. Such an elongation of the c-axis is commonly observed in epitaxial thin films 114 under compressive strain and has also been reported in superconducting La3Ni2O7 films31. These 115 results indicate that the epitaxial strain imposed by the LAO substrate effectively modifies the lattice 116 structure of La4Ni3O10, which may provide a platform for tuning its electronic properties. 117 RP-type nickelates exhibit a complex phase diagram including n = 1, 2, 3, and ∞ within a 118 narrow growth window. During the modification of the growth conditions in the PLD process, the 119 La3Ni2O7 thin film is also obtained as the byproduct even with the same target composition as shown 120 in the bottom XRD pattern in Fig. 1. The film thickness is estimated to be approximately 50 nm, since 121 the number of laser pulses used for deposition was half that of the La4Ni3O10 film. The main difference 122 is a change in the value of PLD parameters, such as the Dts from 30 mm to 40 mm, the PO2 from 20 123 Pa to 35 Pa, and the Tsub from 690°C to 720°C. The n value of RP-type nickelates tends to decrease 124 with increasing Tsub and decreasing PO2 in the phase diagram32. Although the La4Ni3O10 phase seems 125 to be more stable under these conditions because the higher PO2 contributes to increase n value and 126 the difference in Tsub is slight, the La3Ni2O7 phase obviously appears. This result suggests that the 127 increase in Dts is considered to be the primary factor promoting the formation of the La3Ni2O7 phase. 128 Previous studies have reported that lighter elements tend to be scattered farther away from the target-129 to-substrate direction than heavier elements33. As a result, the concentration of lighter elements in 130 deposited films is reduced. Because this effect may become more pronounced with increasing Dts, the 131 formation of the Ni-deficient phase La3Ni2O7 is likely facilitated when Dts is increased from 30 mm 132 to 40 mm.  133  5  134 FIG. 1. XRD pattern using a θ–2θ scan of the La4Ni3O10 and La3Ni2O7 thin film on the LAO 135 substrate. The asterisks indicate diffraction peaks from the LAO substrate.  136  137 The local structure of the obtained La4Ni3O10 thin film was analyzed by TEM observation. A 138 tiny square region was picked up from the surface of the substrate and fabricated into an extremely 139 thin specimen using the FIB process to perform high-resolution TEM analysis, as shown in the 140 scanning ion microscope images in Fig. 2(a) and (b). The cross-section of the sample was analyzed 141 using a high-angle annular dark-field scanning TEM image, as shown in Fig. 2(c). The top region 142 corresponds to the surface of the film, and the bottom region corresponds to the boundary between the 143 grown film and the LAO substrate. The film thickness is 93 nm. Among the analyzed regions, the 144 crystal growth of La4Ni3O10 is observed as the main phase, which is consistent with the XRD 145 measurements. In addition, small regions of La2NiO4, La3Ni2O7, and amorphous-like distorted 146 structures are observed. For instance, the La3Ni2O7 phase is partially observed at around the boundary 147 between the deposited film and the LAO substrate, as shown in Fig. S1. The appearance of other RP-148 type nickelate phases strongly depends on the parameters of the PLD process, as discussed later. The 149 use of a lower laser repetition frequency may also enhance the quality of the grown crystal, although 150 it was limited in the present experiments due to problems with the PLD equipment. Figure 2(d) shows 151 an enlarged TEM image around the La4Ni3O10 region. The brightest atomic columns correspond to 152 lanthanum atoms, while the darker ones correspond to nickel atoms, which are identified by atomic-153 resolution EDX mapping, as shown in Fig. 2(e). In the EDX mapping, red and green indicate 154 lanthanum and nickel, respectively. Based on these TEM observations, the La4Ni3O10 thin film with 155 (00l) orientation is clearly grown on the LAO substrate using the PLD process. 156  6  157 FIG. 2. Scanning ion microscope images of the (a) analyzed region and (b) fabricated specimen 158 of La4Ni3O10 thin film on the LAO substrate for TEM observation. (c) High-angle annular dark-159 field scanning TEM images for the entire region from the substrate to the surface and (d) a 160 specific region containing La4Ni3O10. (e) Atomic-resolution EDX mapping image of the 161 La4Ni3O10 region. Red and Green colors indicate lanthanum and nickel atoms, respectively. 162  163 Figure 3(a) shows the temperature dependence of the electrical resistance for the La3Ni2O7 164 and La4Ni3O10 films. Both films exhibit an increasing trend in resistance with decreasing temperature, 165 namely semiconducting-like behavior without a superconducting transition. Because the thickness of 166 the deposited films was not accurately determined due to the existence of a minor phase as indicated 167 in the TEM observation, the electrical resistance is shown instead of resistivity. Although a direct 168 comparison of electrical resistivity is difficult, the measured resistance was analyzed using the 169 Arrhenius relationship, R=R0×exp(Ea/kBT), where R0 is the residual resistivity, Ea is the activation 170 energy, kB is the Boltzmann constant and T is the temperature, as shown in the Fig. 3 (b). The linear 171 fit around room temperature yields activation energies Ea of 38 meV and 18 meV for La3Ni2O7 and 172 La4Ni3O10, respectively. These results indicate that the Ea tends to decrease with increasing n in RP-173 type nickelates. In the case of La3Ni2O7 thin films, the bandgap drastically decreases by tuning the 174 carrier concentration through the O3 annealing process, and metallic superconducting phases appear 175 under very narrow optimal conditions22–24. Following the La3Ni2O7 case, carrier tuning by O3 176 annealing may also be effective for inducing superconductivity in La4Ni3O10 thin films. Although the 177 O3 annealing around 300°C inside the PLD chamber contributes to the reduction of the resistance, as 178 shown in Fig. 3(c), no superconducting transition is observed in the La4Ni3O10 thin film. The reduction 179  7 in resistance induced by O3 annealing gradually recovers over a period of two months, as shown in 180 Fig. S2. This aging effect is consistent with previous reports on superconducting La3Ni2O7 thin films 181 and suggests that the resistance reduction originates from carrier doping rather than the presence of 182 metallic impurity phases such as LaNiO3. As a future investigation, exploring the optimal conditions 183 of O3 annealing to tune the carrier concentration in La4Ni3O10 thin films may open the possibility of 184 achieving superconductivity without external pressure. 185  186 FIG. 3. (a) Temperature dependence of electrical resistance for the obtained films with the main 187 phase La3Ni2O7 and La4Ni3O10. (b) The Arrhenius relationship at around room temperature. (c) 188 Temperature dependence of the sheet resistance of the as-grown La4Ni3O10 film and the O3-189 annealed one. 190  191 4. Conclusion 192 The thin-film growth of RP-type La4Ni3O10 on an LAO substrate is investigated using the PLD method. 193 XRD analysis reveals that an oriented La4Ni3O10 film along the c-axis is grown on the LAO substrate 194 as the main phase. The elongation of the c-axis provides possible evidence of compressive strain 195 induced between the deposited film and the substrate. The local structure of the film is analyzed by 196 TEM, where the crystal growth of La4Ni3O10 is confirmed by atomic-resolution column imaging and 197 EDX mapping. Minor phases of other RP-type nickelates, La2NiO4 and La3Ni2O7, are also observed. 198 By using different PLD conditions, La3Ni2O7 film with the c-axis orientation on LAO substrate was 199 obtained as a byproduct. Although the grown films exhibit semiconducting behavior without 200 superconducting transitions, carrier tuning via O3 annealing may provide an effective route to induce 201 superconductivity in La4Ni3O10 films, representing a promising direction for future study. 202  203 Supplementary Material 204 The detailed parameters of PLD growth, the TEM image with EDX mapping near the boundary 205 between the deposited film and the substrate in the La4Ni3O10 film, and the gradually increasing 206  8 resistance behavior of the La4Ni3O10 film after O3 annealing are shown in the SM. 207  208 Acknowledgement 209 This work was partly supported by JSPS KAKENHI Grant Number 23H01835, 23K13549, 23KK0088, 210 25K01508, and JST K Program Grant Number JPMJKP25Z2. The TEM observation was carried out 211 with the support of "Advanced Research Infrastructure for Materials and Nanotechnology in Japan 212 (ARIM)" of the Ministry of Education, Culture, Sports, Science and Technology (MEXT) with 213 Proposal Number JPMXP1225NM5218. The XRD analysis was supported by Dr. T. Hiroto in 214 Materials Fabrication and Analysis Platform of NIMS. This work was supported by NIMS Joint 215 Research Hub Program and the World Premier International Research Center Initiative (WPI), MEXT, 216 Japan.  217  218 Data Availability 219 The data that supports the findings of this study are available from the corresponding author upon 220 reasonable request. 221  222 References 223 1 S.A. Chambers, “Epitaxial Growth and Properties of Doped Transition Metal and Complex Oxide Films,” 224 Advanced Materials 22(2), 219–248 (2010). 225 2 J.V. Mantese, A.L. Micheli, A.H. Hamdi, and R.W. 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