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Molybdenum disulfide (MoS2), a semiconducting two-dimensional layered transition metal dichalcogenide (2D TMDC), with attractive properties enables the opening of a new electronics era beyond Si. However, the notoriously high contact resistance (RC) regardless of the electrode metal has been a major challenge in the practical applications of MoS2-based electronics. Moreover, it is difficult to lower RC because the conventional doping technique is unsuitable for MoS2 due to its ultrathin nature. Therefore, the metal–insulator–semiconductor (MIS) architecture has been proposed as a method to fabricate a reliable and stable contact with low RC. Herein, we introduce a strategy to fabricate MIS contact based on atomic layer deposition (ALD) to dramatically reduce the RC of single-layer MoS2 field effect transistors (FETs). We utilize ALD Al2O3 as an interlayer for the MIS contact of bottom-gated MoS2 FETs. Based on the Langmuir isotherm, the uniformity of ALD Al2O3 films on MoS2 can be increased by modulating the precursor injection pressures even at low temperatures of 150 °C. We discovered, for the first time, that film uniformity critically affects RC without altering the film thickness. Additionally, we can add functionality to the uniform interlayer by adopting isopropyl alcohol (IPA) as an oxidant. Tunneling resistance across the MIS contact is lowered by n-type doping of MoS2 induced by IPA as the oxidant in the ALD process. Through a highly uniform interlayer combined with strong doping, the contact resistance is improved by more than two orders of magnitude compared to that of other MoS2 FETs fabricated in this study. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) of multicomponent materials is challenging because the growth characteristics often deviate from what is expected due to the difference in surface characteristics of heterogeneous and single materials, resulting in undesired thickness or properties. For metal oxides, the growth characteristics highly rely on the surface hydroxyl groups, which play a role as the reactive site. Thus, studying the reaction mechanism of a precursor on hydroxyl-terminated heterogeneous surfaces is important for understanding the nonideal growth of ternary oxide. Here, we investigated the correlation between hydroxyl and the growth of ALD TiSiOx depending on temperature, analyzing infrared spectra, and chemical compositions. The results show that large amounts of hydroxyl are detected in TiSiOx deposited at 100 °C, where the adsorption of H2O on Ti–O–Si bonds is favorable. It leads to higher growth per cycle (GPC) than the estimated value. In contrast, the hydroxyl disappears at 200 °C due to dehydroxylation, resulting in lower GPC. Differences in hydroxyl also influence the film density as revealed in x-ray reflection spectra, which is related to the film qualities (e.g., elastic modulus and dry etch rates). This work provides insight into how to control hydroxyl in the ALD of ternary oxides, which is susceptible to hydroxyl incorporation, leading to undesired growth characteristics. [ABSTRACT FROM AUTHOR]

The effective production of hydrogen as an attractive alternative energy source requires efficient electrocatalysis of the oxygen evolution reaction (OER), the rate-determining step in water splitting. Ruthenium oxide has been investigated as a representative OER catalyst; however, additional research is required for practical applications because of its low stability and varied performance depending on the fabrication method. In this study, RuO 2 was prepared via atomic layer deposition (ALD). The crystallinity of the film was controlled by adjusting the ALD growth temperature, and its influence on the OER performance was examined. In addition, ALD cycles were controlled to study the influence of film thickness on the OER performance, allowing for a comparative analysis. The RuO 2 film was deposited onto carbon fiber paper (CFP) to enhance its active surface area for the OER. The as-obtained samples were analyzed using various techniques, including X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the crystalline RuO 2 grown at 400 °C performed better catalytic performance than amorphous RuO 2 grown at 350 °C, and adjusting the film thickness enhanced the electrochemical performance and stability of the catalyst film. • RuO 2 was synthesized using Ru(EtCp) 2 precursor via atomic layer deposition. • High-crystalline ruthenium oxide was obtained by changing growth temperature. • Crystalline RuO 2 exhibited enhanced catalytic properties for OER. • Catalytic activity of RuO 2 can be improved by controlling RuO 2 thickness. • Durability of the RuO 2 film can be improved by controlling RuO 2 thickness. [ABSTRACT FROM AUTHOR]

We report the permeation barrier properties of Al2O3/ZrO2 multi-layers deposited by remote plasma atomic layer deposition. Electrical Ca degradation tests were performed to derive the water vapor transmission rate (WVTR) of Al2O3, ZrO2 and Al2O3/ZrO2 multi-layers at 50 °C and 50% relative humidity (RH). Al2O3/ZrO2 multi-layers exhibit better barrier properties than Al2O3 and ZrO2 layers, and when more individual layers were deposited in the same total thickness, the WVTR value was reduced further, indicating a better barrier property. The WVTR of the Al2O3 and ZrO2 layers were 9.5 × 10−3 and 1.6 × 10−2 g/m2 day, respectively, but when deposited alternatively with 1 cycle of each layer, the WVTR decreased to 9.9 × 10−4 g/m2 day. X-ray diffraction results indicated that ZrO2 has a monoclinic structure but Al2O3 and Al2O3/ZrO2 multi-layers show an amorphous structure. Cross sectional Al2O3/ZrO2 multi-layer structures and the formation of a ZrAl x O y phase are observed by transmission electron microscopy (TEM). X-ray photoelectron spectrometry (XPS) results indicate that Al2O3 and ZrO2 contain 33.7% and 37.8%, respectively, Al–OH and Zr–OH bonding. However, the ZrAl x O y phase contained 30.5% Al–OH and Zr–OH bonding. The results of transmittance measurement indicate that overall, Al2O3, ZrO2 and Al2O3/ZrO2 multi-layers show high transmittance greater than 80% in the visible region. [ABSTRACT FROM AUTHOR]

The wettability of metal oxides, which is directly related to the surface free energy (SFE), is used in a wide range of robust functional coatings, from hydrophilic to hydrophobic. Because wettability is significantly affected by solid surface properties, several studies on the determinant factors and their correlations have been conducted through the thin-film coating of metal oxides. Herein, we found that HfO 2 thin films deposited via atomic layer deposition (ALD) are intrinsically hydrophilic. Simultaneously, a thickness-dependent wettability change is observed. These observations were investigated by measuring water contact angles (WCAs), film surface compositions, roughness, morphologies, and microcrystalline structures of the ALD-grown HfO 2 thin films. It was deduced that the surface oxygen species significantly affected the intrinsic hydrophilicity of HfO 2 thin films. In addition, the crystalline orientations evolved with film thickness, and thermal annealing was used to determine the thickness-dependent WCA trend. In particular, the transformation of the preferred m(-111) crystal orientation with a low SFE had a dominant impact on the SFE change in the HfO 2 thin films. Considering the lack of fundamental studies on the SFE of ALD-grown HfO 2 thin films, we believe that this study will help understand the wettability of HfO 2 and its overall surface science. • Hydrophilicity and surface free energy (SFE) properties of ALD-grown HfO 2 thin films were studied. • In contrast to most previous literatures, our ALD-grown HfO 2 showed hydrophilic nature. • Surface non-lattice oxygen species could result in hydrophilicity of HfO 2 thin films. • Additionally, thickness-dependent phase transformation induced surface energy changes. • The preferred and low-SFE m(-111) orientations dominantly determines the overall SFE of ALD-grown HfO 2 thin films. [ABSTRACT FROM AUTHOR]

We investigated the moisture barrier properties of SiO 2 layers deposited via plasma-enhanced atomic layer deposition (PE-ALD) for encapsulation of an organic light-emitting diode (OLED). First, the growth characteristics and film properties of PE-ALD SiO 2 using diisopropylamino silane (DIPAS) and O 2 plasma were investigated. The film properties were significantly improved by applying proper O 2 plasma treatment. The O 2 plasma treatment increased the adsorption of the metal precursor by creating sufficient hydroxyl groups on the substrate. We not only increased the adhesion between the thin film and the polymeric substrate through O 2 plasma treatment before the deposition process but also formed a high-density thin film, resulting in excellent moisture barrier properties. Consequently, the water vapor transmission rate (WVTR) was significantly reduced to 7.73 × 10−3 g/m2∙day, which was 10 times lower than that of a control sample. These newly developed methods can be applied to other metal oxides, such as Al 2 O 3 and ZrO 2 , for OLED encapsulation with a low WVTR. [ABSTRACT FROM AUTHOR]

Abstract Tin oxide (SnO x) is a promising oxide semiconductor due to the distinct properties of n-type SnO 2 and p-type SnO based on its stoichiometry. However, the stoichiometry control of SnO x remains challenging due to the thermodynamic instability of SnO. In the study, we focus on establishing the controllable stoichiometry of SnO x via atomic layer deposition (ALD) and subsequent treatment. The controllable synthesis of SnO 2 and SnO is investigated by multiple analyses involving the chemical composition, crystal structure, and band structure. The ALD SnO x is composed mostly of Sn4+ O bonds with intrinsic oxygen vacancies and is transformed into crystalline SnO 2 phase via post-annealing. The refractive index (~1.8) and optical bandgap energy (~3.6 eV) of ALD SnO x correspond to those of SnO 2. Post-deposition treatment with H 2 plasma enables the effective transformation of SnO 2 into SnO due to the easy penetration of H+ ion into the film and de-bonding of Sn O via ion bombardment. The transformed SnO exhibits a significant amount of Sn2+ O bonds with a refractive index of 2.8 and optical bandgap energy of ~2.9 eV. Specifically, the transformed SnO exhibits promise as an oxide semiconductor because it exhibits excellent stability with respect to re-oxidation into SnO 2 or further reduction into Sn metal. The present study advances practical applications that require a stable p-n junction through n-type SnO 2 and p-type SnO in various forms of device architectures. Highlights • Formation of SnO 2 and SnO was controlled by atomic layer deposition and post-process. • Chemical composition, crystal structure, and band structure of SnO x were analyzed. • As-deposited SnO x exhibits typical characteristics of SnO 2. • Post-deposition treatment with H 2 plasma effectively transforms SnO 2 into SnO. • Transformed SnO is stable against re-oxidation or reduction during post-process. [ABSTRACT FROM AUTHOR]

The effects of the ligand of precursor on the growth characteristics and electrical properties of W films prepared by ALD were systematically investigated using two newly synthesized precursors, WCl 5 and HEtCpW(CO) 3. [Display omitted] • Newly synthesized precursors for atomic layer deposition (ALD) of tungsten thin films. • Comparison of WCl 5 and HEtCpW(CO) 3 with theoretical calculation and film properties. • Quantum chemical calculations of the precursor adsorption on the substrate surface. We compared the growth characteristics and film properties of tungsten (W) thin films prepared by atomic layer deposition (ALD) using two newly synthesized precursors, tungsten pentachloride (WCl 5) and ethylcyclopentadienyltungsten(V) tricarbonyl hydride (HEtCpW(CO) 3), with Ar/H 2 plasma as the reactant. The purpose of this study was to evaluate the suitability of these precursors for W thin films used in interconnect technology. The growth characteristics and film properties were significantly affected by the ligands of the precursors. The chemical compositional analysis results showed that high-purity thin films were obtained using the WCl 5 precursor, compared to the films obtained using the HEtCpW(CO) 3 precursor, which were relatively high in carbon content and oxygen impurities. The W thin films obtained from the WCl 5 precursor showed superior electrical properties compared to those of the HEtCpW(CO) 3 precursor, which were related to the crystallinity and film density in addition to the impurities. These results provide profitable information regarding the selection of a pertinent precursor for the device fabrication. [ABSTRACT FROM AUTHOR]