ALKYLDITHIOCARBAMATE | mocvd-precursor-encyclopedia.de

RHODIUM DIALKYLDITHIOCARBAMATES

Fig. Rhodium dialkyldithiocarbamates

Rhodium bis(N,N-diethyldithiocarbamate) [Rh(S2C-NEt2)2] and several other Rh dialkyldithiocarbamates were synthesized, characterized and studied as potential precursors for the MOCVD deposition of Rh2S3 thin films. [[i]]

In another study mononuclear rhodium(II) dithiocarbamato complexes ‘Rh(S2CNR2)2(PPh3)’ and ‘Rh(S2CNR2)2’, (R=Me, Et) were shown to be actually mixtures of various rhodium(III) dithiocarbamato complexes.[[ii]]

Rhodium(III) NN'-dialkyldithiocarbamates (with alkyl = Et, n-Pr, benzyl) were shown to have non-equivalent α-methylene protons in the PMR spectra; it was explained by hindered rotation about the C---N bond.

[iii]

[i] N. M. Sosibo, Master Thesis, University of Zululand, 2004, « Synthesis and characterization of ruthenium and rhodium sulfide thin films and nanoparticles », URI: http://hdl.handle.net/10530/907, http://uzspace.uzulu.ac.za/bitstream/handle/10530/907/Synthesis%20and%20characterization%20of%20ruthenium%20and%20rhodium%20sulfide%20thin%20films%20and%20nanoparticles.%20Nda.pdf?sequence=1

[ii] G. Exarchos, S.D. Robinson, Polyhedron, 2000, Vol.19, Iss.1, p.123–124, « Observations concerning the constitution of some ‘rhodium(II) dithiocarbamato complexes’ », http://www.sciencedirect.com/science/article/pii/S0277538799003460

[iii] M.M. Dhingra, G. Govil, G., C.R. Kanekar, « Anomalous PMR spectra of cobalt(III) and rhodium(III) NN'-dialkyldithiocarbamates », Chem. Phys. Lett., 1971, 12 (2). pp.303-305, http://dx.doi.org/10.1016/0009-2614(71)85070-4, http://repository.ias.ac.in/15551/

Rhodium (I) (N,N-dimethyldithiocarbamate) bis(PPh3) adduct [Rh(S2CNMe2)](PPh3)2

Rhodium (I) (N,N-dimethyldithiocarbamate) (PPh3)( CO) adduct [Rh(S2CNMe2)] (PPh3)( CO)

Rhodium (III) tris(N,N-dimethyldithiocarbamate) [Rh(S2CNMe2)3] (PPh3) adduct

Rhodium (III) tris(N,N-dimethyldithiocarbamate) [Rh(S2CNMe2)3] (PPh3)(CO) adduct

New complexes RhI(S2CNMe2)(PPh3)2, RhI(S2CNMe2)(CO)PPh3, RhIII(S2CNMe2)3(PPh3), and RhIII(S2CNMe2)3(CO)PPh3 were obtained by the reaction of of Na(S2CNMe2) with acetone solutions of RhCl(PPh3)3 and trans-RhCl(CO)(PPh3)2. RhIII(S2CNMe2)3(PPh3), and RhIII(S2CNMe2)3(CO)PPh3 contain unidentate dithiocarbamate group, according to the IR and NMR sprectra.[i]

These complexes may be potentially used as Rh MOCVD precursors.

[i] Ch. O'Connor, J. D. Gilbert, G. Wilkinson, J. Chem. Soc. A, 1969, 84-87 « Unidentate dithiocarbamate complexes of rhodium and iron: dithiocarbamate and dithiocarbonate complexes of ruthenium », DOI: 10.1039/J19690000084, http://pubs.rsc.org/en/content/articlelanding/1969/j1/j19690000084#!divAbstract

Rhodium bis(diethyldithiocarbamate) [Rh(S2CNEt2)2]

Fig. TGA curve of Rh(S2C-NEt2)2

Synthesis and characterisation

Rhodium bis(N,N-diethyldithiocarbamate) [Rh(S2C-NEt2)2] was synthesized by metathesis reaction between rhodium chloride and sodium diethylditiocarbamate: RhCl3·xH2O (3.16 mmol) dissolved in MeOH solution was added at 0 °C to a MeOH solution of Na(S2CNEt2)2 (yellow reaction mixture) prepared in situ using NaOH (9.32 mmol), diethylamine (9.32 mmol) and CS2 (9.32 mmol, added drop wise at 0°C). The resultant orange precipitate was filtered, washed with MeOH and then hexane. (yield 30%)

[Rh(S2C-NEt2)2] was obtained in yields sufficient for its use as single source precursor for the deposition of the Rh2S3 thin films.

The TGA spectrum in Fig. shows the decomposition patterns of [Rh(S2C-NEt2)2]. Major decomposition started at 350°C and sharply continued until ~ 400 °C, exhibiting 65 % weight lossof the complex, proving its high volatility and the eligibility of this complex as a single source precursor in for MOCVD growth of Rh2S3 thin films. [i]

[Rh(S2CNEt2)2] for Rh2S3 thin films by AACVD

[Rh(S2CNEt2)2] was applied as a single molecule precursor for the deposition of Rh2S3 thin films on a glass substrates by AACVD. Following growth conditions were used: substrate glass temperature 350-450°C, concentration 0.20 g/ 20 mL Toluene, N2 carrier gas, flow rate 200 mL/min, duration 2 hours.

The black shiny thin films Rh2S3 thin films were characterised by XRD; they represented temperature dependent morphologies and consisted of orthorhombic Rh2S3 phase with characteristic (022), (411) and (611) lattice planes peaks. EDAX measurements ascertained the presence of rhodium (Rh) and sulphur (S). Adhesion of the film to the substrate is poor (may indicate the traces of organic matter on the film surface).

Surface morphological patterns of Rh2S3 layers grown at 350°C were investigated by SEM: surface consisted of grains with of ~0.3-0.6 µm, with large centres of growth sticking out on the surface, this non-uniform growth was attributed to the low energy on the substrate surface/thus growth diffusion being limited to only a few sites on the substrate surface (due to low growth temperatures). Surface morphology of layers grown at higher temperatures (450°C) was much better (much more uniform surface), consisting of randomly oriented grains that grew up into longer, more dense grains, with crystallites becoming more clearly defined and the surface smoother with rod-like growth features, indicating that the surface morphology is very sensitive to the substrate temperature.

Rh2S3 film thickness of 255.632 nm was obtained at 450°C temperature (corresponding to the growth rate of 2.13 nm/min).

Optical properties: the band gap energy for the chalcogenides of rhodium was reported to be lower than 1 eV, showing metallic to semiconducting behaviour. The band gap for the bulk Rh2S3 was reported to be 0.6 eV (deep in the infrared (IR) region), optical measurements showed no obvious absorption at the UV-Vis spectrum range (180-900 µm), indicating less importance in the mainstream semiconducting applications.[i]

[i] N.M. Sosibo, N. Revaprasadu, Mater. Science Eng.: B, 2008, Vol. 150, Iss. 2, p.111–115, « Synthesis and characterization of rhodium sulfide nanoparticles and thin films », http://www.sciencedirect.com/science/article/pii/S0921510707006563

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