Tungsten disulfide thin films via electrodeposition from a single source precursor

Experimental Syntheses of precursors Syntheses were performed by using standard Schlenk and glove-box techniques under a dry N2 atmosphere. [NBu4]OH (40% aqueous solution), S(SiMe3)2, [Et4N]Cl, [NBu4]Cl, [Ph4P]Cl were obtained from Sigma Aldrich and [NH4]2[WS4] from Alfa Asear and were used as received. WSCl4 was made as described previously.1 Solvents were dried by distillation from CaH2 (CH2Cl2) or Na/benzophenone ketyl (n-hexane).


Electronic Supporting Information for
Tungsten disulfide thin films via electrodeposition from a single source precursor Shibin Thomas a 4 ] from Alfa Asear and were used as received. WSCl 4 was made as described previously. 1 Solvents were dried by distillation from CaH 2 (CH 2 Cl 2 ) or Na/benzophenone ketyl (n-hexane).
Infrared spectra were recorded on a Perkin-Elmer Spectrum 100 spectrometer in the range 4000-200 cm 1 , with samples prepared as Nujol mulls between CsI plates. 1 H NMR spectra were recorded using a Bruker AV 400 spectrometer and referenced to the residual protio-resonance of the solvent.

[PPh 4 ] 2 [WS 2 Cl 4 ]CHCl 3 :
A solution of tetraphenylphosphonium chloride (0.420 g, 1.12 mmol) in dichloromethane (5mL) was added to a solution of WSCl 4 (0.200 g, 0.56 mmol) in dichloromethane (5mL). turning green. The solution was allowed to stir for 30 minutes then a solution of hexamethyldisilathiane (0.100 g, 0.56 mmol) in dichloromethane (1 mL) was added, when the solution darkened and then turned a deep red. The solution was stirred for 30 mins. and concentrated under vacuum, after which the brown solid was precipitated out with n-hexane (10 mL), filtered and washed with chloroform (5 mL) before drying in vacuo. Yield: 0.50 g, 75%. Required for C 49 H 41 Cl 4 P 2 S 2 W

Attempted Preparation of [N n Bu 4 ] 2 [WS 2 Cl 4 ]:
A solution of tetrabutylammonium chloride (0.558 g, 2 mmol) in dichloromethane (5 mL) was added to a solution of WSCl 4 (0.400 g, 1 mmol) in dichloromethane (5 mL) which turned green. The solution was allowed to stir for 30 minutes then a solution of hexamethyldisilathiane (0.215 g, 1 mmol) in dichloromethane (2 mL) was added. The solution darkened and then turned a deep red. The solution was stirred for 30 min and concentrated under vacuum. The resulting sticky brown solid was precipitated out with diethyl ether (10 mL). IR spectrum (Nujol/ cm -1 ): 498s W=S, 295s, 235m W-Cl.

X-ray experimental
Data collections used a Rigaku AFC12 goniometer equipped with an enhanced sensitivity (HG) Saturn724+ detector mounted at the window of an FR-E+ SuperBright molybdenum (λ = 0.71073) rotating anode generator with VHF Varimax optics (70 micron focus) with the crystal held at 100 K (N 2 cryostream). Crystallographic parameters are presented in Table S1. Structure solution and refinement were performed using SHELX(T)-2018/2, SHELX-2018/3 through Olex2 3 and was mostly straightforward but showed significant residual electron peaks near to the tungsten, which are attributed to absorption correction problems. The CCDC reference number for the crystallographic information file in cif format is CCDC 2084213.

Film characterisation
A scanning electron microscope (SEM, Philips XL30 ESEM) was used to image the deposits after electrodeposition. The elemental composition was obtained by energy dispersive X-ray spectroscopy (EDX) coupled to SEM, using a Thermo Scientific NORAN System 7 X-ray Microanalysis System.
Wavelength dispersive X-ray spectroscopy (WDX) was employed for obtaining higher spectral resolution. The calibration of the EDX/WDX quantification was confirmed by comparison to a standard WS 2 single crystal sample (Ossila Technologies). Raman spectra were obtained using Renishaw Inc. spectrometer with 532 nm laser excitation. X-Ray diffraction (XRD) patterns were collected in grazing incidence mode (θ 1 = 1°) using a Rigaku SmartLab diffractometer (Cu-K α , λ = 1.5418 Å) with parallel Xray beam and a Hypix detector used in 1D mode.

Electrochemistry of [N n Bu 4 ] 2 [WS 4 ]
Our experiments showed that the simple ammonium salt, [NH 4 ] 2 [WS 4 ], is not sufficiently soluble in either CH 2 Cl 2 or MeCN and therefore it is not suitable as an electrolyte precursor to deposit WS 2 .
Several experiments were performed to electrodeposit WS 2 using the much more soluble

Calculation of Faradaic efficiency from EQCM
The faradaic efficiency of deposition is calculated using the Faraday equation; the mass of WS 2 deposited ( )   Where is the charge passed through the electrode in Coulomb, is the molecular weight of WS 2 (247.98 g/mol), is the Faraday constant (96485 C/ mol), and is the number of electrons transferred. The mass estimated from the EQCM measurements is compared with the theoretical mass (assuming all the charge passed is used for WS 2 deposition, i.e 100% current efficiency) to obtain the faradaic efficiency of deposition.