Interplay between coordination sphere engineering and properties of nickel diketonate–diamine complexes as vapor phase precursors for the growth of NiO thin films

Abstract

NiO-based films and nanostructured materials have received an increasing attention for a variety of technological applications. Among the possible strategies for their fabrication, atomic layer deposition (ALD) and chemical vapor...

Growth of NiO Thin Films in the Presence of Water Vapor: Insights from Experiments and Theory

“…Correlation with XRD results indicate that, especially for the sample fabricated from Ni(thd) 2 TMEDA, this morphology can be associated with the occurrence of a (100) texturing (see the I (200) /I (111) values in Table 1). A comparison of the presently reported results with previous ones 37 clearly highlights that the introduction of water vapor in the reaction atmosphere plays an important role in the obtainment of thicker films, as observed in the CVD of Co 3 O 4 from analogous precursors. 34,35 From thickness data, the maximum growth rate (Table 1) was estimated to be ≈1.4 nm min −1 for deposits obtained under O 2 + H 2 O reaction atmospheres starting from Ni(tfa) 2 TMEDA and Ni(thd) 2 TMEDA.…”

“…In fact, upon utilizing Ni(tfa) 2 TMEDA, the film growth rate rises by ≈18 times under O 2 + H 2 O reaction atmospheres in comparison to the case of dry O 2 , whereas the growth rate increase is comparatively smaller for Ni(fod) 2 TMEDA (≈10 times) and Ni(thd) 2 TMEDA (≈5 times). 37 These data highlight that the highest growth rate increase occurs for the precursor capable of being involved in stronger hydrogen bonds with gas-phase water, i.e., Ni(tfa) 2 TMEDA. Because of the absence of bulky tert-butyl groups, Ni(tfa) 2 TMEDA presents the most sterically favorable environment for a prominent hydrogen bonding of water molecules with diketonate O atoms.…”

“…For all the other atoms the D95V(d) basis set was adopted . This level of theory was already used to predict properties of other β-diketonate–TMEDA compounds, ,, including the molecular structure of Ni(tfa) 2 TMEDA, Ni(fod) 2 TMEDA, and Ni(thd) 2 TMEDA in the absence of water molecules . Binding energies per water molecule ( W BE ) for the formation of hydrated precursors were calculated adopting the formula W BE = − E false( Ni false( normalL false) 2 TMEDA · n ( H 2 O ) false) − E false( Ni false( normalL false) 2 TMEDA false) − n · E false( normalH 2 normalO false) n with L = tfa, fod, and thd and n = number of water molecules.…”

“…Depositions were performed on pre-cleaned 38 1 × 1 cm 2 Si(100) substrates (MEMC Electronic Materials S.p.A, Merano (BZ), Italy). In each run the used Ni precursor, synthesized as previously reported, 37 was heated in an external glass vessel at a suitable vaporization temperature [75, 80, and 120 °C for Ni(tfa) 2 TMEDA, Ni(fod) 2 TMEDA, and Ni-(thd) 2 TMEDA, respectively], and its vapors were transported into the reaction chamber by electronic grade O 2 . An auxiliary O 2 flow was separately introduced into the reactor after passing through a water reservoir maintained at 35 °C.…”

“…32−36 Recently, we have reported on the preparation and chemicophysical characterization of three β-diketonate−diamine Ni(II) adducts, i.e., Ni(tfa) 2 TMEDA, Ni(fod) 2 TMEDA, and Ni-(thd) 2 TMEDA (Htfa = 1,1,1-trifluoro-2,4-pentanedione, Hfod = 2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione, Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione, TMEDA = N,N,N′,N′-tetramethylethylenediamine, Figure 1), featuring promising properties as molecular precursors for the vapor phase deposition of NiO thin films. 37 Preliminary CVD validation experiments under conventional dry O 2 atmospheres yielded very thin deposits, indicating a limited decomposition efficiency of the used precursors. This behavior was particularly evident for fluorinated compounds, i.e., Ni(tfa) 2 TMEDA and Ni(fod) 2 TMEDA, in spite of their better transport properties if compared to fluorine-free Ni(thd) 2 TMEDA.…”