Deposition of LaNiO3 thin films in an atomic layer epitaxy reactor Helene Seim,a† Heini Mo�lsa�,a Minna Nieminen,a Helmer Fjellva°g*b and Lauri Niinisto� a aHelsinki University of T echnology, L aboratory of Inorganic and Analytical Chemistry, FIN-02150 Espoo, Finland bUniversity of Oslo, Department of Chemistry, P.O. Box 1033 Blindern, N-0315 Oslo, Norway LaNiO3 thin films have been deposited in an atomic layer epitaxy (ALE) reactor, using La(thd)3, Ni(thd)2 and ozone as reactants, thereby proving the feasibility of the ALE technique to produce films of ternary oxides.Depositions were made on Corning glass in the temperature range 150–450 °C. The growth conditions were studied and the growth rate showed a linear dependence on the number of cycles. At 400 °C the growth rate was 0.24–0.26 A° per cycle.The growth rate of the LaNiO3 thin films was greatly influenced by the deposition temperature but in the temperature range 215–250 °C the growth saturated at 0.08 A° cycle-1 independent of the deposition temperature, thus indicating an ALE window. As-deposited thin films were amorphous but crystallized when heated at 600 °C. Simultaneously the colour of the films changed from yellow–brown to black.Possible reasons for the colour changes are discussed. Resistivity measurements showed that the crystalline thin films were metallic, r= (5–20)×10-6 V m. The amorphous thin films had resistivity values five orders of magnitude larger, r>3 V m. According to scanning electron microscopy (SEM) and atomic force microscopy (AFM), the films were homogeneous and dense.The surface roughness increased on crystallisation. X-Ray photoelectron spectroscopy (XPS) and magnetic susceptibility measurements were employed in order to further characterize the amorphous and crystalline thin films. Perovskite-type related oxides have found a variety of appli- In the case of laser deposition7,8 LaNiO3 was grown on LaAlO3, SrTiO3 and yttrium-stabilised zirconia (YSZ) sub- cations such as ferroelectrics, sensors, superconductors, electrodes and catalysts.1,2 Some of these oxides, e.g.PbTiO3 and strates. Depositions were carried out at substrate temperatures between 440 and 700 °C under an oxygen partial pressure of LaNiO3, are simple compounds from a chemical point of view, whereas the related high-temperature superconducting mate- (1.6–4.0)×10-4 bar.The method was successful in providing films with low resistivity, ca. 1.5×10-6 V m at 15 K. The films rials have a very complex chemistry with three or more different cations in the unit cell. Our interest is mainly focused obtained at 500 °C showed expected Pauli paramagnetic properties, whereas those obtained at 700°C showed a larger on LaNiO3, which is metallic, exhibits Pauli paramagnetic behaviour and has a slightly rhombohedrally distorted per- Curie–Weiss contribution to the magnetic susceptibility, thereby indicating the presence of local moments, probably ovskite-type structure. The metallic conductivity of LaNiO3 makes the material interesting for electrode applications.3,4 NiII species.8 In the spray-ICP technique at atmospheric pressure, the Quite often, metallic conductivity is first achieved for related oxides when turning to aliovalently substituted systems, such LaNiO3 films were deposited on MgO, sintered high-purity alumina, Si or sapphire substrates at temperatures between as e.g.La1-tSrtMnO35 and La1-tCatCrO3,6 where the chemical complexity is larger. 350 and 800 °C.9 (111)- and (100)-oriented LaNiO3 films were The metallic properties and a good lattice match with other obtainedon sapphire (001) and MgO(100) substrates,9 respectperovskite- type oxides like PbTiO3 and YBa2Cu3O7-d ively. The resistivity of films deposited above 600 °C was found (YBCO), make LaNiO3 a very interesting candidate for thin to be ca. 4×10-6 V m. LaNiO3 synthesized during such experi- film applications.Thin film depositions of LaNiO3 have been ments was found to have better characteristics as the bottom reported by various techniques including laser deposition, electrode for PbTiO3 ferroelectric films than the conventional spray combustion flame technique, rf magnetron sputtering, Pt electrodes. spray-ICP and spin coating followed by pyrolysis7–13 where Multilayer thin films of BaTiO3–LaNiO3 and PbTiO3– the motivation has been the use of LaNiO3 as an electrode, as LaNiO3 have been deposited on MgO substrates by using the a substrate for YBCO or as the metallic part in SNS junctions.spray combustion flame technique.10 In similar studies LaNiO3 The crystal structure of the thin films of LaNiO3 is reported was deposited on sintered alumina, sapphire and MgO.11 The to be close to cubic,9–11 possibly corresponding to a high- lowest resistivity, 6×10-6 V m, was measured on a LaNiO3 temperature modification of LaNiO3, which is reported to film deposited on MgO at a temperature above 700°C.exist above 940 °C.14 This temperature is, however, above the As a bulk material, LaNiO3 can be synthesized in a rather thermal decomposition limit.15 Recent studies indicate that the straightforward way, provided that care is taken to avoid cubic modification occurs for stoichiometric samples and that decomposition owing to the reduction of NiIII at high temperaslight deviations in the oxygen content or the incorporation tures (above 800 °C in pure oxygen) and/or under low oxygen of alkali-metal impurities give a rhombohedral distortion.16 partial pressures. Decomposition will give phase mixtures consisting of La2Ni2O5, La4Ni3O10, La2NiO4 , LaNiO2, NiO, La2O3 and Ni depending on the conditions.14–16 The synthesis † Present address: University of Oslo, Department of Chemistry, P.O.Box 1033 Blindern, N-0315 Oslo, Norway. is best performed by using sol–gel precursors, e.g.citrate gels, 449 J. Mater. Chem., 1997, 7(3), 449–454450 or in basic carbonate melts. At low temperatures where struc- Characterization tural reconstructions are kinetically hindered, LaNiO3 can be Crystal structure data and crystallite orientation of the films reduced continuously in a topotactic reduction from LaNiO3 were determined by X-ray diffraction (XRD) measurements to LaNiO2.5=La2Ni2O5 .17 The latter type of reduction can with a Philips MPD 1880 powder diffractometer using Cu-Ka usually be performed for perovskite-type oxides with transition- radiation.The average thickness of a deposited thin film was metal cations in high oxidation states. During the reductions, estimated by measuring the thickness at three different points the properties of the materials may change dramatically, e.g.using a profilometer (Veeco Instruments Dektak 3030). The the conductivity may be changed by several orders of magni- steps were etched by 5 mol dm-3 hydrochloric acid. A four- tude. Hence, tuning the physical properties of the bulk and point probe method was used to measure the sheet resistances. presumably also thin films is partly possible via monitoring The measurements were performed in air at room temperature.the oxygen content of the material during thermal treatment. The resistances were measured at several places and an average The motivation for pursuing thin film deposition of LaNiO3 value was calculated. is manifold. Besides the applicational aspects of LaNiO3, it is A Seiko TG–DTA instrument of the SSC 5200 series was of fundamental interest prior to further studies of perovskite- used to study the thermal behaviour of the precursors, La(thd)3 type oxide thin films to demonstrate the feasibility of CVD and Ni(thd)2.TG and DTA curves were recorded simul- and ALE techniques for producing LaNiO3 thin films. Thin taneously in a nitrogen atmosphere under 7 mbar pressure.film growth of binary metal oxides by ALE has been demon- The sample masses were ca. 7 mg. strated for several compounds but the more complex ternary X-Ray photoelectron spectroscopy measurements were per- compounds have not yet been studied.18 The chemical com- formed with a Kratos Analytical Axis 165 instrument using plef LaNiO3 is fortunately considerably smaller than that monochromated Al-Ka radiation, 0.5 eV step and 80 eV ana- encountered, for example, in materials like La1-tSrtMnO3 and lyser pass energy.As many films were insulating, sample YBa2Cu3O7-d. Secondly, it is of interest to produce a LaNiO3 surfaces were flooded with slow electrons during the acqui- thin film for which the physical properties subsequently can sition.The deviation in the binding energies, due to the charge be adjusted by subjecting it to temperature/oxygen partial neutralisation, was corrected using the C 1s contamination pressure conditions which are selected independently on the peak referenced at 284.8 eV. A scanning electron microscope basis of studies of bulk samples. of type Philips XL30 was used to study the morphology and quality of the thin films.AFM measurements were made in a Nanoscope III AFM instrument. Magnetization measurements were carried out between 5 and 320 K in a magnetic field of Experimental 1 kOe with an MPMS system (Quantum Design). Film growth Films were grown in a flow-type ALE reactor which has been Results and Discussion described elsewhere.19 La(thd)3 and Ni(thd)2 (thd=2,2,6,6- tetramethylheptane-3,5-dionate), synthesized in Espoo, were Growth conditions for LaNiO3 films used as precursors and ozone as the oxidizer.Ozone was produced by feeding oxygen gas into the reactor through an A major motivation for this work was to demonstrate the feasibility of making LaNiO3 as a thin film in an ALE reactor. ozone generator (Fischer model 502). The concentration of ozone was ca. 10% (60 g m-3). The gas flow-rate during the Hence, the work was concentrated on studying the growth rate as a function of deposition temperature and number of pulse was ca. 60 cm3 min-1, measured for the oxygen gas. The reactant pulses were separated by nitrogen gas purging. After cycles, and to characterize the LaNiO3 thin films thereby obtained. Atomic layer epitaxy (ALE) is a technique used for lanthanum and nickel pulses the purging time was 2.5 s and after ozone it was 3 s.Typical reactant pulse durations were growing single crystals and thin films.20 In this method the reactants are alternately pulsed into the reactor chamber, 1.8 s for La(thd)3 and Ni(thd)2 and 1.0 s for ozone. Pulsing sequences used for obtaining various thin film thicknesses were where the substrates are located.Between the reactant pulses any excess of the reactants is purged out with an inert gas, chosen as amultiplet of a basic cycle consisting of 15 alternating cycles of La and O precursors followed by 15 cycles of Ni and leaving ideally one monolayer of the reactant chemisorbed on the substrate. In practice, however, the growth per cycle is a O precursors. The films were grown on Corning 7059 glass substrates fraction of a monolayer owing to steric and other effects.20–22 La–Ni–O thin films were deposited from La(thd)3 and under a pressure of 0.4–1 mbar (measured before the reaction chamber).The substrate size used was ca. 5×5 cm2. Ni(thd)2 using ozone as an oxygen source. By varying the source temperatures the optimum sublimation behaviour of Depositions were made in the temperature range 150–500 °C.The growth rate was studied, both as function of temperature the La and Ni precursors was found at source temperatures of 190 and 145 °C, respectively. The precursor materials were and by varying the number of cycles (30–272)×30 at a selected temperature, 400 °C. pulsed separately, since the difference in sublimation temperature is too large to mix the solid precursors before they are Several films were subsequently heated in a tube furnace in flowing oxygen at 600 °C for 12 h.Other thin films were heat- sublimed. The TG–DTG–DTA recordings of the precursor materials, La(thd)3 and Ni(thd)2, show almost complete subli- treated in a tube furnace which was connected to a gas mixing system and an oxygen sensor (yttrium-stabilised zirconia, mation.La(thd)3 sublimes at around 200 °C and Ni(thd)2 at around 150 °C, see Fig. 1. The pressure used in these thermo- Dansensor). Reduced oxygen partial pressure was obtained by using N2 [ p(O2)#3.8×10-4 bar] or a CO2–Ar mixture with analytical studies (7 mbar) is somewhat higher than the pressure in the reactor during the depositions (0.4–1 mbar). After 2% H2 [ p(O2)#10-24 bar].J .Mate r . Chem., 1997, 7(3), 449–454 451 Fig. 2 Dependence of LaNiO3 film thickness on the deposition temperature Fig. 3 Dependence of film thickness on the number of basic cycles Fig. 1 TG–DTG–DTA curves for the precursors recorded with a (deposition temperature 400°C) heating rate of 10 °C min-1 in flowing nitrogen at 7 mbar pressure: (a) La(thd)3 6.5 mg, (b) Ni(thd)2 7.1 mg basic cycle).This means that the thickness of the thin film can be controlled easily by the number of deposition cycles. depositions in the ALE reactor, however, there were residues in the source crucibles indicating partial decomposition during Characterization of as-deposited and annealed La–Ni–O films prolonged heating.The residue in the Ni(thd)2 crucible was partly white–grey, different from the pink source material. In The thin films deposited at temperatures below 450 °C are transparent and X-ray amorphous, as shown by X-ray diffrac- the case of La(thd)3, however, there were no visible changes between the residue and the white La(thd)3 source material. tion patterns, see Fig. 4(a). They exhibit a range of colours, mostly from yellow to brown, but sometimes the leading edge The deposition temperature has a great influence on the film growth. The dependence of the film thickness on the growth of the substrate is almost black. The size of this black area tends to increase when the deposition temperature is lowered temperature for depositions consisting of 272 basic cycles (272×30 cycles) is shown in Fig. 2. The growth rate increases and thin films deposited at 150–215 °C are totally black–grey. The possible reasons for these colour variations are discussed as a function of temperature from 150°C to 215 °C. In the temperature region from 215 to 250°C the growth rate seems later. Some of the thin films deposited at 450 °C are partly crystalline and all the XRD peaks can be indexed as LaNiO3 to be constant at 0.08 A° cycle-1 (2.4 A° per basic cycle).This plateau shows saturation of the growth independent of the reflections. The crystalline LaNiO3 thin films are black and mirror-like. At higher reactor temperatures (500 °C) the films deposition temperature, which is an indication of a possible ALE window.21 At temperatures between 250 and 400°C the are black and much less mirror-like, and the XRD pattern indicates a phase mixture of La2NiO4 and NiO.This means growth rate increases again indicating another reaction mechanism. For thin films deposited above 400 °C the thicknesses that 450 °C is close to the upper temperature limit for successful deposition of LaNiO3. This temperature is far below the were not measured because of the poor film quality.The dependence of the film thickness on the number of observed decomposition temperature of polycrystalline LaNiO3 in an oxygen atmosphere.14,15 cycles was studied at 400°C, using the pulse durations described above. The growth rate shows an almost linear The amorphous films become crystalline when heated in flowing oxygen at 600 °C for 12 h either in the reactor or in a dependence on the number of cycles, see Fig. 3. The growth rate saturates to a value of 0.24–0.26 A° cycle-1 (7.2–7.8 A° per separate tube furnace. Some crystallinity develops also for thin452 Fig. 5 SEM picture of an LaNiO3 thin film deposited at 400 °C on Corning glass (pressure 0.4 mbar) and heated at 600 °C for 12 h in O2.Film thickness ca. 2000 A° . orientation and the intensities match well those of polycrystalline LaNiO3. Since Corning glass was used as the substrate, epitaxial or strongly textured films were not expected. The quality and morphology of the thin films were examined by scanning electron and atomic force microscopies. SEM pictures indicate that the thin films are dense and no phase inhomogenities are evident, but various amounts of depressions Fig. 4 Powder X-ray diffractogram (Cu-Ka radiation) of (a) an and other thickness variations in the thin films are seen in amorphous thin film, deposited at 400 °C, 0.4 mbar on Corning glass some samples. The surface of the LaNiO3 thin films obtained substrate, (b) an LaNiO3 thin film after annealing at 600 °C for 12 h in O2.Miller indices are given. Film thickness ca. 2000 A° . appears to be more smooth than that of LaNiO3 films deposited by other methods.9,11 Generally the SEM pictures are contourless. For some films, small amounts of spherical films heated at 500 °C in air for 12 h; however, when treated particles are observed, see Fig. 5. It was not possible to at 400 °C in air or oxygen they remain amorphous.distinguish between the composition of the thin film and the Simultaneously with the crystallization a colour change from particles. Similar particles have been reported for thin LaNiO3 yellow–brown to black occurs. The XRD patterns from the films made by spray combustion flame and spray-ICP tech- heated samples agree with that for LaNiO3, see Fig. 4(b). The niques.9,11 Such particles are observed for the crystalline as d-values obtained for a LaNiO3 film are listed in Table 1.well as for the amorphous thin films. No obvious relation Compared with the powder X-ray patterns of the polycrystal- between the number of particles and the deposition parameters line bulk materials, no splitting of reflections owing to a could be found. The SEM examinations show no significant rhombohedral distortion (aRH=5.395 A° and a=60.77° for difference between the amorphous, crystalline, yellow–brown LaNiO317) is observed.The crystalline film is therefore cubic. and black films. This is consistent with earlier reports on LaNiO3 thin films AFM measurements (Fig. 6) show that the as-deposited deposited by other techniques.9–11 For the LaNiO3 film heated/ amorphous thin films contain small crystallites.The rough- crystallized in oxygen at 600 °C [Fig. 4(b)], the unit-cell param- nesses of the as-deposited films are the same or even less than eter a=3.804 A° was calculated. As seen from the Miller indices the roughness of the substrate, which is a sign of smooth in Fig. 4(b) for LaNiO3, there is no indication of a preferred growth of the amorphous thin film. No variations in microstructure due to thickness variations or different deposition Table 1 Positions of Bragg reflections given as d-values for LaNiO3 temperatures were found.However, owing to annealing the thin film crystallized at 600 °C; data from refs. 11 and 23 are included crystallite size and the roughness of the films increases, see for comparison Fig. 6. hkl d/A° a d/A°b d/A° c Crystallinity, colour and physical properties 100 3.809 3.816 3.850 110 2.690 2.692 2.730 The La–Ni–O films show a large range of characteristics, from 111 2.187 2.192 2.229 amorphous to crystalline, from yellow via brown to black, and 200 1.905 1.907 1.932 a five orders of magnitude variation in resistivity. In order to 210 1.703 1.708 1.728 understand the cause of these variations a number of annealing 211 1.548 1.578 experiments, XPS, magnetic susceptibility and resistivity stud- 220 1.345 1.348 1.365 ies were undertaken.First the colour will be considered. The thin films annealed aThis study. bRef. 11. cRef. 23.J . Mate r . Chem., 1997, 7(3), 449–454 453 described for deposition of the mixed oxide.The number of cycles used was 5000. Depositions of the Ni–O thin films were made at 250, 350 and 400 °C. XRD measurements show that the as-deposited Ni–O thin films were crystalline. The XRD patterns for films grown at 250°C (1 mbar) and 350 °C (0.8 mbar) were indexed as NiO. At 400 °C (1 mbar) the thin film consisted of a mixture of NiO and Ni. The La–O thin film growth was studied in the temperature range 200–450 °C, depositions being made every 50°C.XRD measurements show that the as-deposited thin films were crystalline when grown at temperatures between 350 and 450°C.24 In order to study further the possible reasons for the changes in colour, some annealing experiments were carried out under a reducing atmosphere. In a very reducing atmosphere [CO2–N2–2% H2 ; p(O2)=10-24 bar, T=600 °C], complete decomposition occurs for both amorphous and crystalline La–Ni–O films, giving in both cases dark brown films containing crystalline Ni+La2O2CO3 (type I or IA).Under modestly reducing conditions [N2; p(O2)=10-4 bar], the yellow and brown amorphous films turn black. However, they still remain X-ray amorphous. These experiments show that the atmosphere is of great importance for obtaining a crystalline LaNiO3 thin film, and further that the colour is not connected directly with the crystallinity. For La–Ni–O films converted to crystalline LaNiO3 by heat treatment in oxygen, exposure to N2 does not change the colour or the diffraction pattern. The latter experiments were conducted under normal atmospheric conditions, under which the thin film may reoxidize from a reduced state, see below.If the amorphous phase is less stable than the crystalline LaNiO3 under an N2 atmosphere, the observed changes in colour may possibly be due to decomposition of Fig. 6 Atomic force microscopy (AFM) pictures of LaNiO3 thin films the amorphous LaNiO3 phase into X-ray amorphous forms of deposited on Corning glass at 250°C (film thickness ca. 670 A° ). (a) Asdeposited, (b) after annealing at 600 °C for 12 h in O2 . one or more of the phases La2Ni2O5, La4Ni3O10, La2NiO4, LaNiO2, NiO, La2O3 and Ni. The range of oxygen non-stoichiometry in LaNiO3 is large in O2 at 600 °C contain LaNiO3 . They are black, independent at low temperatures where topotactic reduction will remove of the state of the intermediate amorphous film.The reason oxygen from alternating sheets in the crystal structure, resulting for the yellow–brown–black colouring of the amorphous films in La2Ni2O5 with octahedral and square-planar coordinated appears unclear. The colour variations may have different nickel.25 At higher temperatures than, say, 500 °C, such causes: (i) film thickness; (ii) carbon impurities introduced reduction is no longer possible, the kinetically stable perovsk- from decomposed precursor; (iii) degree of crystallinity; ite-related structure is broken up and the thermodynamically (iv) multiphase nature of the thin films; or (v) oxygen non- stable two-phase mixture is obtained.For topotactically stoichiometry. The first possibility can be excluded since the reduced bulk specimens, complete reoxidation occurs at room colour variations are found over films where the measured temperature.It is therefore not very probable that the thin thickness is constant. Furthermore, some of the blackest films film should contain regions with significantly different oxygen are actually very thin. Possibility (ii) is also unlikely, since non-stoichiometries.enhanced carbon formation owing to thermal decomposition As regards the electrical resistivity, it was found to vary of La(thd)3 and Ni(thd)2 precursors is expected at the higher from 3.2 V m for an amorphous as-deposited film to deposition temperatures. This is not the case since films 1.8×10-5 V m for the same LaNiO3 film after annealing and deposited at 400 °C still have colour variations, whereas some crystallization. The lowest resistivity observed was films deposited at 200 °C are virtually black.All films deposited 5.4×10-6 V m. The latter value is slightly larger than found at temperatures below 450°C are X-ray amorphous and turn for spray-ICP deposited films9 and for laser deposited LaNiO3 crystalline only after thermal treatment. Hence, the colour films,8 but probably equal within reasonable uncertainty limits.differences are not just connected with the X-ray crystallinity On the other hand, the resistivity is significantly lower and the of the films; however, they may still be connected with micro- minimum is obtained at lower temperature than for LaNiO3 crystallinity. prepared by pyrolysis of spin-coated organometallic films.13 The colour variations in the amorphous thin films could There is no difference in resistivity between the yellow, brown possibly be caused by a multiphase situation (iv), being due to and black amorphous films.either a mixture of La2O3 and NiO or other La–Ni–O phases. In order to evaluate this possibility, films of the single oxides Characterization by XPS and magnetic susceptibility La2O3 and NiO were deposited, using La(thd)3 and Ni(thd)2 measurements as precursors and the same pulsing and purging times as Characterization of the electronic state of nickel in La–Ni–O films was attempted via XPS and magnetic susceptibility454 studies.The surface chemistry of two films with and without annealing was studied with XPS. The films were deposited at 250 and 400 °C and the annealing was carried out in O2 at 600 °C for 12 h.As the samples were measured without any in situ cleaning in UHV, both carbon and oxygen contamination species were present on the surface. No other impurities were detected from the spectra. The surface concentration of nickel in the nonannealed specimen was roughly three times that of lanthanum whereas for annealed samples the amounts of lanthanum and nickel at the surface were nearly equal.As the last sequence in the growth of the films was 15 cycles of nickel and ozone precursors, the XPS results indicate that the outermost layers reacted only during the annealing when the films also changed from amorphous to crystalline. The O 1s line shape changed markedly upon annealing (Fig. 7). The as-deposited films had two resolvable components. The broad high binding energy component at 531.3±0.1 eV probably originates from the chemisorbed O- and OH- groups and the nickel-bound oxygen.26–28 The low energy component at 528.7 eV was assigned to the La2O3 component.29 However, the annealed films were composed of three resolvable peaks. The positions of the low and high binding energy components Fig. 8 XP spectra of the Ni LMM Auger level of (a) an NiO reference film grown at 250 °C; (b) as-deposited and (c) annealed LaNiO3 films remained nearly unchanged (at 531.6 and 528.7 eV). The grown at 400 °C on a Corning glass substrate additional component at 530.0±0.1 eV is in good accordance with the reported values for LaNiO3.27,28 ted by the deposition temperature and annealing.Nickel Since the La 3d3/2 emission interferes severely with the Ni 2p interferes with the La 3d3/2 signal, but a subtle change in the emission, both the weak Ni 3p and Ni LMM Auger emissions splitting ratio of the La 3d5/2 component was detected after were also studied. In all films analysed the Ni 2p peak was annealing the films. This could indicate changes in the conduc- very similar in shape and position to the reference spectrum tion band electron configuration which could be due to changes of NiO film, verifying that no Ni2O3 was present on the surface.However, in the Ni LMM Auger signal of the annealed in the La coordination number before and after annealing, as films (Fig. 8) a slight change in the peak shape was observed.discussed by Burroughs et al.30 This could be related to structural changes in the matrix. Metallic LaNiO3 is reported to be Pauli paramagnetic.8 Any The La 3d5/2 core-level spectra show split lines with maxima presence of reduced NiII species will add an additional Curie– at 834.1±0.3 and 838.1±0.3 in agreement with the literature Weiss contribution to the susceptibility.Sagoi et al.8 reported, values for LaNiO3.26 The positions of the lines remain unaffec- for LaNiO3 deposited at 700 °C, the presence of 16% NiII, whereas in the low-resistivity films they observed no Curie– Weiss contribution from NiII. The present susceptibility measurements were performed on small pieces of the substrate coated with the La–Ni–O film. Two approaches were used: Fig. 7 XP spectra of the O 1s level of (a) as-deposited and (b) annealed LaNiO3 films grown at 400°C on a Corning glass substrateJ . Mate r . Chem., 1997, 7(3), 449–454 455 the first involved measurement of the substrate plus film, then measurements and aiding their interpretation as well as Mr. Mikko Utriainen, MSc, for the AFM measurements. removal of film by treatment with hydrochloric acid and subtraction of the measured signal for the pure substrate; the second method was a simple comparison between as-measured References susceptibilities without subtraction of the contribution from the glass substrate.The magnetic susceptibility curves for the 1 N. Q. Minh, J. Am. Ceram. Soc., 1993, 76, 563. 2 Properties and Applications of Perovskite-type Oxides, ed.as-deposited film at 400 °C are very similar to those observed L. G. Tejuca and J. L. G. Fierro, Marcel Dekker, New York, for a film annealed subsequently at 600°C in O2 . All curves 1992, ch. 10–17. show a small Curie–Weiss contribution. This indicates that the 3 U.Ko� nig, O. Blum, R. Christ and I. Reeh, J. Phys. Chem., 1993, as-deposited films contain the same amount of reduced nickel 97, 488.species. For all samples a more or less clear cusp appear in 4 R. N. Singh, L. Bahadur, J. P. Pandey and S. P. Singh, J. Appl. Electrochem., 1994, 24, 149. x(T ) around 50 K. It is possible that a similar, but less 5 A. Mackor, T. P. M. Koster, J. G. Kraaijkamp, J. Gerretsen and pronounced, peak is also present in the data of Xu et al.31 In J. P. G. M. van Eijk, Proc. 2nd Int. Symp. Solid Oxide Fuel Cells, the study by Sreedhar et al.32 it is not possible to observe this The Electrochemical Society, Pennington, NJ, 1991, p. 463. peak, but the reason for this might be few measuring points 6 J. Mizusaki, S. Yamauchi, K. Fueki and A. Ishikawa, Solid State in the relevant temperature range. The feature is hardly present Ionics, 1984, 12, 119. in the as-deposited La–Ni–O at 400 °C, however, becoming 7 K.M. Satyalakshmi, R. M. Mallya, K. V. Ramanathan, X. D. Wu, B. Brainard, D. C. Gautier, N. Y. Vasanthacharya and very pronounced after crystallization and oxidation. It is M. S. Hedge, Appl. Phys. L ett., 1993, 62, 1233. believed that the feature is due to adsorbed oxygen.33 8 M. Sagoi, T. Kinno, T. Hushimoto, J. Yoshida and K.Mizushima, Appl. Phys. L ett., 1993, 62, 1833. 9 H. Ichinose, M. Nagano, H. Katsuki and H. J. Takagi, J. Mater. Conclusions Sci., 1994, 29, 5115. 10 H. Ichinose, Y. Shiwa and M. Nagano, Jpn. J. Appl. Phys., 1994, Thin film growth of LaNiO3 by an ALE process has been 33, 5903. demonstrated from b-diketonate type precursors and ozone. 11 H. Ichinose, Y. Shiwa and M. Nagano, Jpn.J. Appl. Phys., 1994, 33, 5907. Even a very low deposition temperature of 250 °C can be used 12 C. C. Yang, M. S. Chen, T. J. Hong, C. M. Wu and J. M. Wu, Appl. but crystallization requires annealing at 600 °C. The annealed Phys. L ett., 1995, 66, 2643. films show metallic behaviour and are black, in contrast to 13 A. Li, C. Ge and P. Lu�, Appl. Phys. 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