Recently amorphous MoS2 thin film has attracted great attention as an emerging material for electrochemical hydrogen evolution reaction (HER) catalyst. Here we prepare the amorphous MoS2 catalyst on Au by atomic layer deposition (ALD) using molybdenum hexacarbonyl (Mo(CO)6) and dimethyl disulfide (CH3S2CH3) as Mo and S precursors, respectively. Each active site of the amorphous MoS2 film effectively catalyzes the HER with an excellent turnover frequency of 3 H2/s at 0.215 V versus the reversible hydrogen electrode (RHE). The Tafel slope (47 mV/dec) on the amorphous film suggests the Volmer-Heyrovsky mechanism as a major pathway for the HER in which a primary discharging step (Volmer reaction) for hydrogen adsorption is followed by the rate-determining electrochemical desorption of hydrogen gas (Heyrovsky reaction). In addition, the amorphous MoS2 thin film is electrically evaluated to be rather conductive (0.22 Ω(-1) cm(-1) at room temperature) with a low activation energy of 0.027 eV. It is one of origins for the high catalytic activity of the amorphous MoS2 catalyst.

Recently MoS₂ with a two-dimensional layered structure has attracted great attention as an emerging material for electronics and catalysis applications. Although atomic layer deposition (ALD) is well-known as a special modification of chemical vapor deposition in order to grow a thin film in a manner of layer-by-layer, there is little literature on ALD of MoS₂ due to a lack of suitable chemistry. Here we report MoS₂ growth by ALD using molybdenum hexacarbonyl and dimethyldisulfide as Mo and S precursors, respectively. MoS₂ can be directly grown on a SiO₂/Si substrate at 100 °C via the novel chemical route. Although the as-grown films are shown to be amorphous in X-ray diffraction analysis, they clearly show characteristic Raman modes (E(1)₂g and A₁g) of 2H-MoS₂ with a trigonal prismatic arrangement of S-Mo-S units. After annealing at 900 °C for 5 min under Ar atmosphere, the film is crystallized for MoS₂ layers to be aligned with its basal plane parallel to the substrate.

The ever-shrinking dimensions of dynamic random access memory (DRAM) require a high quality dielectric film for capacitors with a sufficiently high growth-per-cycle (GPC) by atomic layer deposition (ALD). SrTiO 3 (STO) films are considered to be the appropriate dielectric films for DRAMs with the design rule of ∼20 nm, and previous studies showed that STO films grown by ALD have promising electrical performance. However, the ALD of STO films still suffers from much too slow GPC to be used in mass-production. Here, we accomplished a mass-production compatible ALD process of STO films using Ti(O-i Pr) 2 -(tmhd) 2 as a Ti-precursor for TiO 2 layers and Sr( i Pr 3 Cp) 2 as a Sr-precursor for SrO layers. O 3 and H 2 O were used as the oxygen sources for the TiO 2 and SrO layers, respectively. A highly improved GPC of 0.107 nm/unit-cycle (0.428 nm/supercycle) for stoichiometric STO films was obtained at a deposition temperature of 370 °C, which is ∼7 times higher than previously reported. The origin of such high GPC values in this STO films could be explained by the partial decomposition of the precursors used and the strong tendency of water adsorption onto the SrO layer in comparison to the TiO 2 layer. The STO film grown in this study also showed an excellent step coverage (∼95%) when deposited inside a deep capacitor hole with an aspect ratio of 10. Owing to the high bulk dielectric constant (∼ 146) of the STO film, an equivalent oxide thickness of 0.57 nm was achieved with a STO film of 10 nm. In addition, the leakage current density was sufficiently low (3 Â 10 À8 Acm À2 at þ0.8 V). This process is extremely promising for fabrication of the next generation DRAMs.

Al 2 O 3 films were deposited by atomic layer deposition ͑ALD͒ using trimethylaluminum and O 3 as precursor and oxidant, respectively, at growth temperatures ranging from room temperature to 300°C on Si͑100͒ substrates. Growth rate and refractive index of the Al 2 O 3 films decreased from 0.20 to 0.08 nm/cycle and increased from 1.52 to 1.65, respectively, with increasing growth temperature. The dielectric constant slightly increased from 6.8 to 8 with increasing growth temperature in the same temperature range. Al 2 O 3 films grown using O 3 as oxidant show a smaller hysteresis, lower leakage current density, and higher breakdown field strength compared to those using H 2 O as oxidant at the same growth temperature. X-ray photoelectron spectroscopy showed that the films grown at lower temperatures have a smaller bandgap energy. The Al 2 O 3 films grown at a temperature as low as 100°C showed reasonable dielectric properties for dielectric film applications on flexible substrates.

Preferential growth of pure single-walled carbon nanotubes (SWNTs) over multi-walled carbon nanotubes (MWNTs) was demonstrated at low temperature by water plasma chemical vapor deposition. Water plasma lowered the growth temperature down to 450 degrees C, and the grown nanotubes were single-walled without carbonaceous impurities and MWNTs. The preferential growth of pure SWNTs over MWNTs was proven with micro-Raman spectroscopy, high-resolution transmission electron microscopy, and electrical characterization of the grown nanotube networks.

Single-walled carbon nanotubes (SWNTs) were successfully grown on SiO 2 /Si substrates at 450 °C by remote plasma enhanced chemical vapor deposition with a plasma power of 15 W. The ratio of D-band (disorder-induced mode) to G-band (tangential stretching mode) in the Raman spectra, an indicator of nanotube quality, is about 0.1 owing to their good quality. Even at 400 °C, SWNTs were also grown with low plasma power (<40 W), although the I D /I G ratios are higher than those at 450 °C. It is discussed that for low-temperature growth of SWNTs, the plasma power should be held at a low level to avoid the formation of disordered or amorphous carbons. The low-temperature growth of SWNTs may enable compatible integration of SWNTs with current complementary metal-oxide-silicon technology.

Amorphous molybdenum sulfide (MoSx) has been identified as an excellent catalyst for the hydrogen evolution reaction (HER). It is still a challenge to prepare amorphous MoSx as a more active and stable catalyst for the HER. Here the amorphous MoSx catalysts are prepared on carbon fiber paper (CFP) substrates at 200 °C by a simple hydrothermal method using molybdic acid and thioacetamide. Because the CFP is intrinsically hydrophobic due to its graphene-like carbon structure, two kinds of hydrophilic pretreatment methods [plasma pretreatment (PP) and electrochemical pretreatment (EP)] are investigated to convert the hydrophobic surface of the CFP to be hydrophilic prior to the hydrothermal growth of MoSx. In the HER catalysis, the MoSx catalysts grown on the pretreated CFPs reach a cathodic current density of 10 mA/cm(2) at a much lower overpotential of 231 mV on the MoSx/EP-CFP and 205 mV on the MoSx/PP-CFP, compared to a high overpotential of 290 mV on the MoSx of the nonpretreated CFP. Turnover frequency per site is also significantly improved when the MoSx are grown on the pretreated CFPs. However, the Tafel slopes of all amorphous MoSx catalysts are in the range of 46-50 mV/dec, suggesting the Volmer-Heyrovsky mechanism as a major pathway for the HER. In addition, regardless of the presence or absence of the pretreatment, the hydrothermally grown MoSx catalyst on CFP exhibits such excellent stability that the degradation of the cathodic current density is negligible after 1000 cycles in a stability test, possibly due to the relatively high growth temperature.

Since the discovery of carbon nanotubes (CNTs), [1] this new carbon allotrope has attracted a great deal of attention because of its nanoscale hollow tubular structure and potential applications. CNT arrays can be applied to various functional nanodevices, such as actuators, [2] nanotransistors, [3] field emitters, [4] and gas sensors. [5] Recently, syntheses of other inorganic nanotubes have mainly focused on compounds possessing graphite-analogue layered structures such as Group 6 chalcogenides (WS 2 , MoS 2 ) and boronitride (BN), [6] since high-temperature processes similar to the CNT synthesis method can be used to prepare their crystalline nanotubes. On the other hand, most oxide nanotubes, such as TiO 2 , SiO 2 , Al 2 O 3 , ZrO 2 , and V 2 O 5 , have been prepared using templating agents. [7] Recently, CNTs have been also used as a template to fabricate other nanoscale materials by filling, coating, confined reaction, and substitution reaction.[8]To our knowledge, no inorganic nanotubes or their arrays have been fabricated at temperatures below 400 C by chemical vapor deposition (CVD), which is more compatible with current device fabrication processes. Here we report the first successful fabrication of a hollow nanotube array of ruthenium oxide on a silicon wafer by atomic layer deposition (ALD), which is a special modification of CVD for self-limiting film growth.[9] In ALD, an appropriate precursor vapor and a reaction gas are alternately pulsed onto a substrate. The reaction chamber is purged with an inert gas between the pulses of the precursor vapor and the reaction gas. All the process steps are performed at low temperatures, normally lower than 400 C, to avoid thermal decomposition of the chemisorbed source molecules. The principle of the process is that film deposition occurs through the surface reaction between the reaction gas and the saturated surface monolayer of source molecules. Consequently, the thickness of the film can be accurately controlled by the number of process cycles, each of which consists of source gas pulse±purge±reaction gas pulse±purge. In this research, CNT arrays on porous anodic aluminum oxide (AAO) were used as a template to grow Ru thin films by ALD. The Ru-coated CNT arrays were then heated in an oxygen atmosphere to remove the CNT template. After ashing of the CNTs, ruthenium oxide nanotube arrays were obtained by the oxidation of ruthenium and the removal of CNTs.To prepare a removable template of CNT arrays, we used a procedure similar to that mentioned in a previous report.[ 10] Ordered hole arrays of AAO, of~35 nm pore diameter and 10 10 cm ±2 pore density, were fabricated by a two-step aluminum anodization. Scanning electron microscopy (SEM) and dynamic force microscopy (DFM) were used to image the ordered CNT arrays, showing that the exposed heights and the inner diameters of the CNTs are about 70±100 nm and 30±50 nm, respectively (Figs. 1a,d). As previously reported, [10] the CNTs are hollow, multi-walled, and highly defective, since they were obtained wit...