Atomic Layer Deposition of NiO Films on Si(100) Using Cyclopentadienyl-Type Compounds and Ozone as Precursors

Abstract

NiO films were grown on Si͑100͒ by atomic layer deposition using Ni͑Cp͒ 2 ͑Cp = cyclopentadienyl, C 5 H 5 ͒ or Ni͑EtCp͒ 2 ͓EtCp = ethylcyclopentadienyl, ͑C 2 H 5 ͒͑C 5 H 4 ͔͒ and ozone in the 150-300°C temperature range. The growth temperature dependence of structure, electronic density, and impurity levels for the prepared NiO films was studied using X-ray reflectivity, X-ray diffraction ͑XRD͒, Fourier transform infrared ͑FTIR͒ spectroscopy, time of flight-secondary ion mass spectroscopy ͑ToF-SIMS͒, and transmission electron microscopy. The behavior of films deposited using Ni͑Cp͒ 2 and Ni͑EtCp͒ 2 is compared and discussed. NiO films with good stoichiometry and low amounts of contaminants are obtained at a growth temperature ͑T g ͒ of 250°C or above. At a fixed T g , the growth rate for NiO films deposited using Ni͑Cp͒ 2 is higher than the one of films deposited using Ni͑EtCp͒ 2 . Furthermore, the growth rate for NiO deposited using Ni͑Cp͒ 2 at T g = 150°C is 0.32 nm/cycle and decreases substantially in films deposited at higher temperatures. The electronic density of NiO films deposited at 300°C is close to the one of bulk NiO ͑1.83 e − /Å 3 ͒. According to XRD and FTIR results, films deposited at T g ജ 200°C have a simple cubic polycrystalline structure. Impurities in NiO films decrease with increasing T g , as detected by ToF-SIMS.

Creating Highly Active Atomic Layer Deposited NiO Electrocatalysts for the Oxygen Evolution Reaction

“…Because of discrepancies in previous reports of this NiO ALD process, we performed a systematic characterization of the ALD deposition. [ 37,41,42 ] NiO was deposited at a stage temperature of 275 °C and a Ni(Cp) 2 bubbler temperature of 85-90 °C. Under these conditions, measurements of fi lm thickness after 75 cycles for different pulse lengths showed that saturation was achieved after ≈8 s for the Ni(Cp) 2 pulse and ≈3 s for the O 3 pulse as seen in Figure 1 a,b.…”

Stoichiometry of Nickel Oxide Films Prepared by ALD

“…This value corresponds to a growth rate of 0.92 Å per cycle and is within the (wide) range reported earlier for ALD-grown nickel oxide. [7] The XRR data attest the smoothness of the film, with an estimated root-50 mean-square roughness below 1 nm. A microscopic investigation indicates that despite the overall smoothness of the film, many pinholes are present (Figure 2b).…”

“…After cooling, the product contains 73% Ni by mass according to elemental analysis, which 115 corresponds to Ni 0.74 O. Thus, the ALD reaction between nickelocene and ozone at 230 °C yields, in contrast to what has been assumed in the literature to date, [7,8] a nickel-deficient oxide Ni 0.88 O that exhibits the crystal structure of NiO. Its stoichiometry can be 120 adjusted by annealing ( Figure 5).…”

“…[3] Metallocenes or their derivatives can be either hydrolyzed or oxidized in ALD mode (depending on their reactivity) to obtain various oxides MO or M 2 O 3 , M = Mg, Sr, Ba, Sc, Y, Zr, Fe, Ru, Co, Ni, Pt, Lu. [4][5][6][7] In the hydrolytic case 25 the electropositive element retains its initial oxidation state n from the Cp n M compound, whereas in an oxide obtained by oxidation of Cp n M the oxidation state of M may be higher than n. In the case of the ALD reaction between nickelocene and ozone (O 3 ), the stoichiometry of the product material has 30 not been investigated to date, under the assumption that nickel(II) oxide, NiO, should be formed. [7,8] This assumption is credible in NiO films formed from a hydrolysis reaction, [9] but much more questionable when the aggressive oxidant ozone is involved, especially since sub-stoichiometric oxides 35 are well documented.…”

“…[4][5][6][7] In the hydrolytic case 25 the electropositive element retains its initial oxidation state n from the Cp n M compound, whereas in an oxide obtained by oxidation of Cp n M the oxidation state of M may be higher than n. In the case of the ALD reaction between nickelocene and ozone (O 3 ), the stoichiometry of the product material has 30 not been investigated to date, under the assumption that nickel(II) oxide, NiO, should be formed. [7,8] This assumption is credible in NiO films formed from a hydrolysis reaction, [9] but much more questionable when the aggressive oxidant ozone is involved, especially since sub-stoichiometric oxides 35 are well documented. [10] Given the differences in physical and chemical properties between green NiO and the substoichiometric black solids Ni x O, x < 1, the stoichiometry of nickel oxide films deposited from the ALD reaction between nickelocene and ozone is worth an accurate investigation.…”