GADOLINIUM CYCLOPENTADIENYLS
Tris(cyclopentadienyl)gadolinium GdCp3
Fig. Molecular structure of GdCp3
Tris(cyclopentadienyl)gadolinium GdCp3 (M=352.53) has melting point 295°C (with decomposition). It was reported to be volatile and thus applicable
as CVD precursor. GdCp3 has ether solution exhibits green luminescence (λmax=523 nm, φ=0.2) (the suggestion is that the emission originates from a triplet of the Cp3 3− moiety.[i]
[i] A. Strasser, A. Vogler, Chem. Phys. Lett., 2003, Vol. 379, Iss. 3–4, p.287–290, “Optical properties of tris(cyclopentadienyl)gadolinium. Luminescence from an interligand triplet under ambient conditions”
GdCp3 for Gd-doped GaN films by MOCVD
GdCp3 was applied for the growth of Gd-doped GaN layers as precursor, which does not contain oxygen (and for comparison same layers were
grown with O-containing Gd(thd)3 precursor). The deposited GaN:Gd films were characterized by VSM, XRD, and EDS. The GaN:Gd layers grown with GdCp3 were practically oxygen-free, according to EDS (and had lower
magnetic moments/lower ferromagnetism by VSM), whereas those grown with Gd(thd)3 had some oxygen impurities and much higher magnetic moments/stronger ferromagnetic behaviour. This finding supports suggestion that the mechanism leading to RT ferromagnetism
in Gd-doped GaN is contributed by the oxygen impurities.[i] Co-doping with Si of the GdCp3-grown Ga1-xGdxN films resulted in conductive n-type layers, whereas compensated p-type films were obtained when co-doping with Mg. Room temperature ferromagnetism
was observed for the Si and Mg co-doped GaN films; the grown layers were incorporated into a RT spin-polarized LEDs, which demonstrated 14.6% at 5000 Gauss polarization degree of electroluminescence and retained
a degree of polarization of 9.3% after removal of the applied magnetic field.[ii]
[i]A.G. Melton, Zh.Q. Liu, B. Kucukgok, N. Lu, I. Ferguson, 2011 MRS Fall Meeting., MRS Proceedings 2012 1396 : mrsf11-1396-o04-06 (5 pages), DOI: http://dx.doi.org/10.1557/opl.2012.447, “Properties of MOCVD-Grown GaN:Gd Films for Spintronic Devices”
[ii] A. Melton, M. Kane, Zhiqiang Liu; Na Lu; I. Ferguson, High Capacity Optical Networks and Enabling Technologies (HONET), 2011, p.21 – 25, “Development of room temperature spin polarised emitters”
Tris(methylcyclopentadienyl)gadolinium Gd(MeCp)3
Fig. Molecular strucutre of Gd(MeCp)3
Tris(methylcyclopentadienyl)gadolinium Gd(MeCp)3 (M= 394.61) is light yellow crystalline powder. Gd(MeCp)3 volatile complex (was vaporized at 155-160°C temperature / 6mbar in CVD conditions) and was applied for the growth of Gd2O3 and GdN layers by ALD.
Gd(MeCp)3 for Gd2O3 films by ALD
Gd(MeCp)3 has been used as Gd source for the growth Gd2O3 thin films by ALD , using H2O as oxygen source (obtained layers properties were compared grown using Gd(thd)3/O3 ALD process). Gd(MeCp)3 precusor was vaporised
at 155-160°C/ 6mbar; the film growth mechanism was influenced by the partial decomposition of the precursor. Nevertheless, the uniform Gd2O3 films were obtained at 250 °C, with almost an ideal stoichiometry and low level of impurities (~0.5 at%
of C) as determined by TOF-ERDA. Gd2O3 films obtained using Gd(MeCp)3 were crystalline with cubic C-type structure even deposited at 150 °C, according to XRD; at ~200 °C growth temperature the strongest reflection changed from (4 0 0) to
(2 2 2); for comparison Gd(thd)3/O3 process produced oxygen-rich layers (amorphous if grown <250 °C but crystalline deposited >250°C (with (4 0 0) dominant reflection); at the optimized deposition temperatures grown layers were smooth with both
processes. Effective permittivity k~13 was reached for (CpCH3)3Gd/H2O-processed Gd2O3 layers. [i]
[i] J. Niinistö, N. Petrova, M. Putkonen, L. Niinistö, K. Arstila, T. Sajavaara, J. Cryst. Gr., 2005, Vol.285, Iss.1–2, p. 191-200, “ Gadolinium oxide thin films by atomic layer deposition Original Research Article”
Gd(MeCp)3 for GdN films by plasma enhanced ALD
Tris(methylcyclopentadienyl)gadolinium {Gd(MeCp)3} combined with N2 plasma, was applied as precursor for the growth of gadolinium nitride
(GdN) films on Si(100) by plasma-enhanced ALD (PEALD). GdN layers were grown at 150-300 °C temperatures and capped with TaN to prevent post-deposition oxidation. Initial determination of layer composition was performed by EDX; some samples were subsequently
depth profiled using AES or medium energy ion scattering (MEIS); Gd:N ratio close to 1:1 and a low incorporation of oxygen (∼5%) was achieved for the GdN layers grown at 200 °C. The deposited GdN films
were X-ray amorphous. Although partial thermal decomposition of the Gd(MeCp)3 influenced the growth, smooth GdN films (Ra.=∼0.7 nm) with good thickness uniformity (97%) were
obtained. The attempts to deposit GdN layer using thermal ALD with NH3 or mono-methyl-hydrazine (MeNH-NH2) were less successful.[i]
[i] Z. Fang, P.A. Williams, R. Odedra, H. Jeon, R.J. Potter, J. Cryst. Growth, 2012,Vol.338, Iss.1, p.111–117 , “Gadolinium nitride films deposited using a PEALD based process”
Gadolinium tris(ethylcyclopentadienyl) Gd(EtCp)3
Fig. Molecular structure of Gd(EtCp)3
Gadolinium tris(ethylcyclopentadienyl) Gd(EtCp)3 (C21H27Gd, M= 436.7) is light yellow crystalline powder, soluble in octane and other alkane solvents. (to at least 0.5M concentration). Gd(EtCp)3 is volatile – absence of residues in the vaporiser heated to temperatures 140-180° C was reported.
Gadolinium tris(ethylcyclopentadienyl) Gd(EtCp)3 was tested as Gd precursor for direct liquid injection ALD growth of Gd2O3 thin films.
Gd(EtCp)3 for Gd2O3 films by direct liquid injection ALD
Gadolinium tris(ethylcyclopentadienyl) Gd(EtCp)3 was proposed as potential precursor for direct liquid injection ALD growth of Gd2O3 thin films.
An example of Gd(EtCp)3 as precursor for ALD of Gd2O3 layers (combined with H2O vapor as oxygen source) was presented in [[i]]. Gd(EtCp)3 dissolved in n-octane or other alkane solvent in 0.01M to 0.5M concentration (preferably 0.05M), was vaporised
in a vaporizer temperature at 140-180° C temperatures (preferably 150-160° C) and applied for the Gd2O3 layer growth at deposition temperature 150-200° C (preferably 150° C, as at higher temperatures some CVD contribution to the growth was
observed). ALD growth occurred without unreacted Gd(EtCp)3 precursor or residue in the vaporizer; the growth process was highly self limited, without C impurity in the deposited Gd2O3 films.
[i] MA Ce, KC Kim, US Patent App. 12/465,094, 2009
Tris(isopropylcyclopentadienyl)gadolinium Gd(iPrCp)3
Fig. TGA-DSC curve of Gd(iPrCp)3
Tris(isopropylcyclopentadienyl)gadolinium Gd(iPrCp)3 (M =) is light yellow liquid, less viscous than La analog, having vapor pressure 0.01Torr/ 200 °C [i]
By other data, Gd(iPrCp)3 is yellow solid having melting point 47.7°C (according to TGA/DSC measurements, Fig.). Full vaporisation was achieved at ~300°C, with residual mass only 4%
Gd(iPrCp)3 was synthesized by metathesis reaction: GdCl3 + 3 Na(iPrCp) in THF as solvent at 60°C/ 3h and purified by vacuum distillation at 200°C/ 10-2 Torr pressure.
[i] Erbil, U.S. Pat. No. 4,882,206 (1989)
Gd(iPrCp)3 for Gd metal by CVD
Gd(iPrCp)3 was applied as precursor for deposition of Gd metal by CVD at 550°C growth temperature, ca. 1µm films were obtained. Other growth conditions were as follows: precursor
vaporisation temperature 140°C, reactor press. 5 Torr, Ar carrier gas flow 500sccm [i]
[i] United States Patent 4882206, 1989
Gd(iPrCp)3 for Gd2O3 films by plasma enhanced ALD
Gd(iPrCp)3 combined with O2 plasma was used as Gd precursor for the plasma enhanced
ALD growth of high-quality gadolinium oxide Gd2O3 thin films at 150-350 °C deposition temperatures. Relatively narrow window of temperature and precursor dose resulted in true layer-by-layer ALD growth of Gd2O3: at 250 °C, a saturated growth rate of
1.4 Å/cycle was observed, the refractive index was stable (∼1.80) and the dispersion characteristics were close to bulk Gd2O3, regardless of other deposition conditions; at 250 °C, the
O/Gd ratio was 1.3 (oxygen deficient, according to XPS) and films were very hygroscopic. At higher growth temperatures the optical properties of the grown Gd2O3 layers improved, but the growth mechanism was getting more CVD-like (indicating the onset of precursor
decomposition). The obtained Gd2O3 layers demonstrated a dielectric constant ~16, exhibited low C–V hysteresis, and 50 × reduction in gate leakage compared to SiO2 was achieved. However, formation of an ∼1.8 nm SiO2 interfacial layer and generation of a fixed charge of -1.21 × 1012 cm-2 was observed by the PE-ALD process , what may limit use of PE-ALD Gd2O3 as a gate dielectric. [i]
[i] S.A. Vitale, P.W. Wyatt , Ch. J. Hodson , Journal of Vacuum Science & Technology, (2012), A 30, 01A130; https://doi.org/10.1116/1.3664756 , “Plasma-enhanced atomic layer deposition and etching of high-k gadolinium oxide”, https://avs.scitation.org/doi/abs/10.1116/1.3664756
https://www.researchgate.net/profile/Steven_Vitale/publication/260507372_Plasma-enhanced_atomic_layer_deposition_and_etching_of_high-k_gadolinium_oxide/links/54c79d610cf22d626a36b868/Plasma-enhanced-atomic-layer-deposition-and-etching-of-high-k-gadolinium-oxide.pdf
Tris(tetramethylcyclopentadienyl) gadolinium(III) Gd(Me4Cp)3
Fig. Molecular structure of Gd(Me4Cp)3
Tris(tetramethylcyclopentadienyl) gadolinium(III) Gd(Me4Cp)3 (M=520.85) is potentially applicable as gadolinium ALD precursor. Gd(Me4Cp)3 has flash point 60 °C.
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