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This article takes an effort to establish the potential of atomic layer deposition (ALD) technique toward the field of supercapacitors by preparing molybdenum disulfide (MoS) as its electrode. While molybdenum hexacarbonyl [Mo(CO)] serves as a novel precursor toward the low-temperature synthesis of ALD-grown MoS, HS plasma helps to deposit its polycrystalline phase at 200 °C. Several ex situ characterizations such as X-ray diffractometry (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and so forth are performed in detail to study the as-grown MoS film on a Si/SiO substrate. While stoichiometric MoS with very negligible amount of C and O impurities was evident from XPS, the XRD and high-resolution transmission electron microscopy analyses confirmed the (002)-oriented polycrystalline h-MoS phase of the as-grown film. A comparative study of ALD-grown MoS as a supercapacitor electrode on 2-dimensional stainless steel and on 3-dimensional (3D) Ni-foam substrates clearly reflects the advantage and the potential of ALD for growing a uniform and conformal electrode material on a 3D-scaffold layer. Cyclic voltammetry measurements showed both double-layer capacitance and capacitance contributed by the faradic reaction at the MoS electrode surface. The optimum number of ALD cycles was also found out for achieving maximum capacitance for such a MoS@3D-Ni-foam electrode. A record high areal capacitance of 3400 mF/cm was achieved for MoS@3D-Ni-foam grown by 400 ALD cycles at a current density of 3 mA/cm. Moreover, the ALD-grown MoS@3D-Ni-foam composite also retains high areal capacitance, even up to a high current density of 50 mA/cm. Finally, this directly grown MoS electrode on 3D-Ni-foam by ALD shows high cyclic stability (>80%) over 4500 charge-discharge cycles which must invoke the research community to further explore the potential of ALD for such applications.

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Ruthenium (Ru) thin films were grown on thermally-grown SiO2 substrate using atomic layer deposition (ALD) by a sequential supply of a zero-valent metallorganic precursor, (ethylbenzyl) (1-ethyl-1,4-cyclohexadienyl)Ru(0) (EBECHRu, C16H22Ru), and molecular oxygen (O2) between 140 and 350°C while the typical temperature was 225°C. A self-limiting film growth was confirmed at the deposition temperature of 225°C and the growth rate was ∼0.042 nm/cycle on the SiO2 substrate with a negligible number of incubation cycles (approximately 3 cycles). Plan-view transmission electron microscopy analysis showed that nucleation was started after only 3 ALD cycles and the maximum nuclei density of 1.67 × 1012/cm2 was obtained after 7 ALD cycles. A continuous Ru film with a thickness of ∼2.3 nm was formed after 60 ALD cycles. The film resistivity was decreased with increasing deposition temperature, which was closely related to its crystallinity and microstructure, and the minimum resistivity of ∼14 μΩ-cm was obtained at the deposition temperature of 350°C. The step coverage of the film deposited between 225 and 270°C was approximately 100% over the contact holes (bottom diameter: 0.065 μm) with a high aspect ratio (32:1). Finally, the ALD-Ru film was successfully evaluated in terms of its performance as a seed layer for Cu electroplating and as a bottom electrode for a metal-insulator-metal capacitor using an ALD-TiO2 single layer or an ALD HfO2/La2O3/HfO2 multilayer as a dielectric.

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This study evaluated a simple and novel route to fabricate single-phase SnS thin films, consisting of the growth of smooth amorphous SnS2 films by atomic layer deposition at very low temperature using tetrakis(dimethylamino)tin {TDMASn, [(CH3)2N]4Sn} and hydrogen sulfide followed by H2 annealing at controlled higher temperatures. The properties of the SnS films fabricated by subjecting the amorphous as-grown SnS2 films deposited at 100 °C to post-H2 annealing at 360 °C were superior to those of the as-grown SnS films deposited at 200 °C in terms of their phase purity, optical band gap, adhesion, and surface roughness. Raman spectroscopy, x-ray diffraction, x-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and atomic force microscopy consistently showed that single-phase, stoichiometric crystalline (orthorhombic structure) SnS films (Sn/S ratio: ∼1), without any incorporated sulfur-rich tin sulfides, could be fabricated with a very low surface roughness [root mean square (RMS) roughness: ∼7 nm] using the proposed scheme. On the other hand, the as-grown SnS film at 200 °C still contained a small amount of SnS2 phase and its RMS surface roughness was as high as 16 nm. The optical band gap of the as-grown SnS film was 1.85 eV, whereas that of the annealed SnS film was ∼1.2 eV, confirming the latter's improved phase purity. The SnS film fabricated by H2 annealing was a p-type semiconductor with a carrier concentration of ∼2.3 × 1016/cm3 and a hole mobility of ∼15 cm2/V s. The present scheme to prepare high-quality SnS films might be useful for fabricating photovoltaic or solar conversion devices.