NIOBIUM (IV) β-DIKETONATES

Niobium tetrakis(2,2,6,6-tetramethylheptane-3,5-dionate)

Fig. TGA of Nb(thd)4

   Nb(THD) 4 : M= 826.00 (for Nb(C11H19O2)4 = C44H76NbO8], black powder , melting point 219-220°C, boiling point dec. 325°C [STREM Chemicals] .

   Nb(THD) 4 possessing relatively high melting point, was proposed as an alternative Nb MOCVD precursor, however its disadvantage is that it’s expensive and susceptible to oxidizing  hydrolysis, because of the low valence state of Nb.

The TGA of Nb(thd)4 [i] is presented on Fig.:

[i] S. Margueron, A. Bartasyte, V. Plausinaitiene, A. Abrutis, P. Boulet, V. Kubilius, Z. Saltyte, Proc. SPIE 8626, Oxide-based Materials and Devices IV, 862612 (18 March 2013); https://doi.org/10.1117/12.2010105

« Effect of deposition conditions on the stoichiometry and structural properties of LiNbO3 thin films deposited by MOCVD », https://www.spiedigitallibrary.org/conference-proceedings-of-spie/8626/862612/Effect-of-deposition-conditions-on-the-stoichiometry-and-structural-properties/10.1117/12.2010105.short?SSO=1

Nb(thd)4 surface decomposition chemistry study (by mass spectrometry during LiNbO3 growth by chemical beam epitaxy)

    Surface decomposition chemistry of Nb(thd)4 precursor during LiNbO3 film growth and its constituent metal oxides on sapphire and Si (0 0 1), as well as (for comparison) of other common CVD precursors for LiNbO3 growth by MOCVD ([Nb(OEt)5]2, Li(thd) , [Li(OBut)]6), was investigated by a combination of high vacuum (chemical beam) epitaxy and in situ mass spectrometry. The metal diketonates (including Nb(thd)4 ) was founfd to be instable are unstable at low pressures and temperatures, adversely impacting both storage and use; in contrast to metal alkoxides which have higher thermodynamic stability, but are prone to autocatalytic processes that can inhibit the film growth (as volatile metal-containing moieties are generated that subsequently desorb from the surface). Li/Nb precursor ratio strongly influenced growth rate of LiNbO3 films, suggesting a chemical interaction between the two precursors.[i]

[i] D. Saulys, V. Joshkin, M.Khoudiakov, T.F.Kuech, A.B.Ellis, S.R.Oktyabrsky, L. McCaughan, J. Crystal Growth, 2000, Vol. 217, Iss. 3, p.287-301, « An examination of the surface decomposition chemistry of lithium niobate precursors under high vacuum conditions », https://doi.org/10.1016/S0022-0248(00)00412-7https://www.sciencedirect.com/science/article/pii/S0022024800004127 

Nb(thd)4 for LiNbO3 by solid source MOCVD

     Niobium tetrakis(2,2,6,6-tetramethylheptane-3,5-dionate) Nb(thd)4 combined with Li(thd) was applied for the growth of c-axis LiNbO3 epitaxial films on c-plane sapphire substrates by solid source MOCVD, Li(thd)-rich source compositions were necessary to obtain stoichiometric LiNbO3 films. Rocking curve peak FWHMs were broader as films were grown at progressively lower substrate temperatures, the lowest FWHM 0.044° was achived for 710 °C growth temperature. Clearly visible optical waveguiding with optical attenuation values as low as 2 dB/cm was obtained for the best films in the single prism coupling experiments.[i]

     Accurately weighed mixtures of Nb(thd) 4 and Li(thd) (metal organic powders from Strem Chemicals, Inc.) were used MO precursors for the growth of epitaxial LiNbO3 thin films on c-plane sapphire substrates by the solid-source MOCVD in an inverted, vertical U-shaped quartz solid-source MOCVD reactor. Roughening and optical losses in lithium niobate films on sapphire increased with grain size and the depth of grooves between grains (for waveguiding applications, low optical propagation losses (< 2 dB/cm) are required - scattering from rough film surfaces is a major source of optical  attenuation.  Grain growth can be inhibited by increasing the nucleation density during the initial stage of growth , and thus surface roughness can be reduced even at high growth temperatures. A two-step growth process was developed , where nucleation and growth stages were controlled separately: (1 step) creation a high nucleation density by using low deposition temperature or high source partial pressure at early growth stages, and (2 step) growing main part of the layer with enhanced crystallinity at higher temperature or lower source partial pressure. LiNbO3 layer rms roughness < 2 nm was obtained, with crystalline quality reaching best films grown by the conventional one step growth method. Optical losses <1.8 dB/cm for the TEo mode at a wavelength of 632.8 nm were obtained.[ii]

[i] Z. Lu, R. Hiskes, S.A. DiCarolis, R.K. Route, R.S. Feigelson, F. Leplingard and J.E. Fouquet, J. Mater. Research, 1994, Vol. 9, Iss. 9,  pp. 2258-2263, « Epitaxial LiNbO3 thin films on sapphire substrates grown by solid source MOCVD », https://doi.org/10.1557/JMR.1994.2258https://www.cambridge.org/core/journals/journal-of-materials-research/article/epitaxial-linbo3-thin-films-on-sapphire-substrates-grown-by-solid-source-mocvd/81116F2903DB2CDD527AFC09361A518D

[ii] S.Y. Lee, R.S. Feigelson, J. Cryst. Growth, 1998, vol. 186, Iss.4, p.594-606, « Reduced optical losses in MOCVD grown lithium niobate thin films on sapphire by controlling nucleation density », doi.org/10.1016/S0022-0248(97)00593-9, www.sciencedirect.com/science/article/pii/S0022024897005939 

Nb(thd)4 for LiNbO3 on LiTaO3, sapphire by solid source MOCVD

     Nb(thd)4 (combined with Li(thd)) was used as the Nb source for the deposition of Very high-quality single-phase, single-crystal LiNbO3 film on LiTaO3 and sapphire substrates by solid-source MOCVD for optical-waveguide applications. 2.4.  Deposition conditions … 3. Film composition Lu [67] found that a The stoichiometric mixture of Nb(THD)4 and Li(THD)  did not produce single-phase LiNbO3 films. The optimized growth parameters resulted in reproducible results (optiised film composition, crystallinity, and surface roughness). Different commercial sapphire substrates revealed variable quality, variation in heat-treatment procedure altered layer surface structure. Optical losses were low, but still significant compared to Ti-indiffused LiNbO3 waveguides.[i]

[i] RS Feigelson,  J. Cryst. Growth, 1996, vol.166, Iss.1–4, p.1-16, «  Epitaxial growth of lithium niobate thin films by the solid source MOCVD method », https://doi.org/10.1016/0022-0248(95)00570-6, https://www.sciencedirect.com/science/article/pii/0022024895005706

Nb(thd)4 for LiNbO3, LiNb3O8 and Li3NbO4 by liquid injection MOCVD and APMOCVD

    Mixtures of Nb(thd)4 and Li(thd), dissolved in 1,2-dimethoxyethane, were applied as precursors for the the growth of LiNbO3 films on sapphire by pulsed injection MOCVD and APMOCVD.  Phase composition of epitaxial/textured LiNbO3 films grown by both MOCVD methods, and for comparison by pulsed laser deposition, . was investigated by  XRD.  As a countercheck of the compositional analysis, Raman spectroscopy was used as method highly sensitive to the symmetry of materials. Raman spectra of synthesized powders were analysed for the identification of LiNb3O8 and Li3NbO4 phases using the wavenumbers of corresponding Raman modes. The observed asymmetry of XRD reflections profiles of LiNbO3 films may have different origins and may result in misleading conclusions about phase composition of textured LiNbO3 films.[i]

[i] Ausrine Bartasyte, V. Plausinaitiene, A. Abrutis, S. Stanionyte, S. Margueron, P. Boulet, T. Kobata, Y. Uesu,  J. Gleize, J. Phys.: Condensed Matter, 2013, Vol. 25,  No. 20, p. 205901 , « Identification of LiNbO3, LiNb3O8 and Li3NbO4 phases in thin films synthesized with different deposition techniques by means of XRD and Raman spectroscopy », https://iopscience.iop.org/article/10.1088/0953-8984/25/20/205901/meta https://www.researchgate.net/profile/Ausrine_Bartasyte2/publication/236580635_Identification_of_LiNbO_3_LiNb_3_O_8_and_Li_3_NbO_4_phases_in_thin_films_synthesized_with_different_deposition_techniques_by_means_of_XRD_and_Raman_spectroscopy/links/5449196f0cf2ea6541302301/Identification-of-LiNbO-3-LiNb-3-O-8-and-Li-3-NbO-4-phases-in-thin-films-synthesized-with-different-deposition-techniques-by-means-of-XRD-and-Raman-spectroscopy.pdf

Nb(thd)4 for (Na,K)NbO3 by MOCVD

     Tetramethylheptanedionate (THD) precursors including Nb(thd)4 (and Na(thd) )·H2O, K(thd)·H2O) were used as MO sources for the growth of ferroelectric (Na,K)NbO3 (NKN) thin films on Si substrates coated with amorphous insulating layers, by  horizontal hot-wall MOCVD. Both on SiO2/Si and SiNx/Si substrates, purely [001] oriented textured (Na,K)NbO3 layers with narrow mosaic broadening were obtained. Presence of Na, K, Nb, and O as the primary elements was detected by the ESCA analysis. Dielectric permittivity ε′ about 140 and loss tanδ less than 2% in the frequency range from 1 to 100 kHz was determined by the dielectric spectroscopy of NKN films on SiO2/Si substrates. Low current density of ∼10−8 A/cm2 at the field of 200 kV/cm was measured by the current–voltage (I–V) measurements of this layer.[i]

[i] Ch.-R. Cho, Mater. Lett., 2002, vol. 57, Iss. 4, p.781-786, « c-Axis oriented (Na, K) NbO3 thin films on Si substrates using metalorganic chemical vapor deposition », https://doi.org/10.1016/S0167-577X(02)00872-8, https://www.sciencedirect.com/science/article/abs/pii/S0167577X02008728

Nb(thd)4 for SrxBa1-xNb2O6 by solid source MOCVD

     Accurately weighed mixtures of  tetramethylheptanedionate (thd) sources  (Nb(thd)4 combined with Sr(thd)2 and Ba(thd)2) were applied as MO precursors for the growth of 200 – 300 nm thick single phase SrxBa1−xNb2O6 (SBN) films on MgO(100) substrates by solid source MOCVD. The deposited films were completely (001) oriented, according to XRD 2θ scans. However, according to Φ scans, the layers contained four in-plane grain orientations; altering the Sr/(Sr+Ba) and Nb/(Sr+Ba) ratios could control volume fractions of these orientations; the fractions did not change with the cooling rate or deposition rate. Films with composition Sr0 58Ba0.42Nb1.94O6 demonstrated mainly two in-plane orientations and refractive indices no= 2.20 and ne = 2.13 (compared to no = 2.31 and ne = 2.27 for bulk SBN60); optical waveguiding behavior was demonstrated in these films.[i]

[i] Z Lu, RS Feigelson, RK Route, R Hiskes, S. A. Dicarolis , MRS Proceedings, Volume 335 (Symposium Y – Metal-Organic Chemical Vapor Deposition of Electronic Ceramics), 1993, 59 , « Growth of (001)-oriented SBN thin films by solid source MOCVD », https://doi.org/10.1557/PROC-335-59https://www.cambridge.org/core/journals/mrs-online-proceedings-library-archive/article/growth-of-001oriented-sbn-thin-films-by-solid-source-mocvd/D3815A0D819F82FB1A1C891F586C36A2

Nb(thd)4 for SrxBa1-xNb2O6 on MgO(110), MgO(001), Sr0.75Ba0.25Nb2O6 (001) by solid source MOCVD

    Powder of Nb(thd)4 combined Sr(thd)2, Ba(thd)2 was applied as MO source for the growth of epitaxial SrxBa1−xNb2O6 thin films on MgO(110), MgO(001), Sr0.75Ba0.25Nb2O6 (001) substrates by solid source MOCVD. Varying source compositions was controlling film compositions. Decreasing growth rate improved the crystallinity of the layers. When the substrate temperature was <535°C, amorphous layers were grown. On Sr0.75Ba0.25Nb2O6 (001) substrates single crystalline SrxBa1−xNb2O6 films were obtained, whereas layers deposited on MgO(001) and MgO(110) substrates revealed four in-plane orientations. Layers grown on MgO(001) substrates demonstrated waveguiding behavior both for TE and TM modes; the measured refractive indices were similar to those of bulk crystal.[i]

[i] M Lee, RS Feigelson , J. Cryst. Growth, 1997, Vol. 180, Iss. 2, p.220-228, « Growth of epitaxial strontium barium niobate thin films by solid source metal-organic chemical vapor deposition », https://www.sciencedirect.com/science/article/pii/S0022024897002315

Nb(thd)4 for Pb(Mg1/3Nb2/3)O3 by MOCVD

    Nb(thd)4 in combination with Pb, Mg, and Ti tetramethylheptanedionates was used as precursor for the growth of thin epitaxial films of Pb(Mg0.33Nb0.67)O3 (PMN) and Pb(Mg0.33Nb0.67)O3–PbTiO3 (PMN–PT) on (001) SrTiO3 and SrRuO3/SrTiO3 single crystal substrates at 700°C by the solid-source MOCVD.  Pure PMN films were prepared using pre-mixed source material (5.5 eq. of Pb(thd)4, 1 eq. of Mg(thd)2 and 2 eq. of Nb(thd)4). Films were single phase perovskite according to XRD. Pb/Mg/Nb/O was 18% /7% /13% /62% by RBS. Films of PMN–10%PT and PMN–20%PT films had dielectric constants 1200–1500 and 600–700, respectively.[i]

[i] S.Y Lee, M.C.C. Custodio, H.-J. Lim, R.S Feigelson, J.-P. Maria, S. Trolier-McKinstry, J. Cryst. Growth, 2001, vol.226, Iss.2–3, p.247-253, « Growth and characterization of Pb(Mg1/3Nb2/3)O3 and Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films using solid source MOCVD techniques », https://doi.org/10.1016/S0022-0248(01)00796-5, https://www.sciencedirect.com/science/article/pii/S0022024801007965

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