Cobalt thin films were deposited by plasma-enhanced atomic layer deposition (PE-ALD) using CoCp 2 as a precursor and N 2 /H 2 plasma as a reactant. We systematically investigated the changes in Co film properties depending on N 2 /H 2 gas flow ratio to study the role of N during PE-ALD Co. With increasing N 2 flow ratio, the resistivity decreased reaching minimum value at f N2/H2 = 0.25 ∼ 0.33, which corresponds to the atomic ratio in NH 3 molecule, and then increased. With only N 2 or H 2 plasma, films with very high sheet resistance over 1 M/sq were deposited. The chemical compositions of Co films were analyzed by x-ray photoelectron spectroscopy (XPS) and thickness and conformality were determined by x-ray reflectometry (XRR) and field emission scanning electron microscopy (FE-SEM), respectively. Then, the silicidation of PE-ALD Co films producing epitaxial CoSi 2 were investigated by x-ray diffraction (XRD) and high-resolution cross-sectional transmission electron microscopy (HR-XTEM).

Layered Sn-based chalcogenides and heterostructures are widely used in batteries and photocatalysis, but its utilizations in a supercapacitor is limited by its structural instability and low conductivity. Here, SnS x thin films are directly and conformally deposited on a three-dimensional (3D) Ni-foam (NF) substrate by atomic layer deposition (ALD), using tetrakis(dimethylamino)tin [TDMASn, ((CH 3 ) 2 N) 4 Sn] and H 2 S that serves as an electrode for supercapacitor without any additional treatment. Two kinds of ALD-SnS x films grown at 160 °C and 180 °C are investigated systematically by X-ray diffractometry, Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy (TEM). All of the characterization results indicate that the films deposited at 160 °C and 180 °C predominantly consist of hexagonal structured-SnS 2 and orthorhombic-SnS phases, respectively. Moreover, the high-resolution TEM analyses (HRTEM) reveals the (001) oriented polycrystalline hexagonal-SnS 2 layered structure for the films grown at 160 °C. The double layer capacitance with the composite electrode of SnS x @NF grown at 160 °C is higher than that of SnS x @NF at 180 °C, while pseudocapacitive Faradaic reactions are evident for both SnS x @NF electrodes. The superior performance as an electrode is directly linked to the layered structure of SnS 2 . Further, the optimal thickness of ALD-SnS x thin film is found to be 60 nm for the composite electrode of SnS x @NF grown at 160 °C by controlling the number of ALD cycles. The optimized SnS x @NF electrode delivers an areal capacitance of 805.5 mF/cm 2 at a current density of 0.5 mA/cm 2 and excellent cyclic stability over 5000 charge/discharge cycles.

Future realization of a hydrogen-based economy requires a high-surface-area, low-cost, and robust electrocatalyst for the hydrogen evolution reaction (HER). In this study, the MoN x thin layer is synthesized on to a high-surface-area three-dimensional (3D) nickel foam (NF) substrate using atomic layer deposition (ALD) for HER catalysis. MoN x is grown on NF by the sequential exposure of Mo­(CO)6 and NH3 at 225 °C. The thickness of the thin film is controlled by varying the number of ALD cycles to maximize the HER performance of the MoN x /NF composite catalyst. The scanning electron microscopy and transmission electron microscopy (TEM) images of MoN x /NF highlight that ALD facilitates uniform and conformal coating. TEM analysis highlights that the MoN x film is predominantly amorphous with the nanocrystalline MoN grains (4 nm) dispersed throughout it. Moreover, the high-resolution (HR)-TEM analysis shows a rough surface of the MoN x film with an overall composition of Mo0.59N0.41. X-ray photoelectron spectroscopy depth-profile analysis reveals that oxygen contamination is concentrated at the surface because of surface oxidation of the MoN x film under ambient conditions. The HER activity of MoN x is evaluated under acidic (0.5 M H2SO4) and alkaline (0.1 M KOH) conditions. In an acidic electrolyte, the sample prepared with 700 ALD cycles exhibits significant HER activity and a low overpotential (η) of 148 mV at 10 mA cm–2. Under an alkaline condition, it achieves 10 mA cm–2 with η of 125 mV for MoN x /NF (700 cycles). In both electrolytes, the MoN x thin film exhibits enhanced activity and stability because of the uniform and conformal coating on NF. Thus, this study facilitates the development of a large-area 3D freestanding catalyst for efficient electrochemical water-splitting, which may have commercial applicability.