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Atomic layer deposition (ALD) is a thin-film fabrication method that can be used to deposit films with precise thickness controllability and uniformity. The low deposition temperature of ALD, however, often interrupts the facile crystallization of films, resulting in inferior optical and electrical properties. In this study, the extremely localized crystallization of TiO2 thin films was demonstrated by per-cycle plasma treatment during the plasma-enhanced ALD process. By layering crystalline and amorphous films, a phase-gradient TiO2 film with precisely modulated optical and electrical properties was fabricated. Moreover, the ratio between the amorphous and crystalline layer thicknesses for a high dielectric constant and low leakage current density was optimized.

In this study, we demonstrated the seed layer mediated growth of high-quality BaTiO3 (BTO) thin films using a two-step radio frequency (RF) magnetron sputtering process. Since the as-grown BTO thin films obtained by RF magnetron sputtering at the deposition temperatures of 300–500 °C were amorphous with a low dielectric constant of 20, it is necessary to develop a fabrication process for obtaining crystalline high-k BTO thin films without sacrificing other film properties such as morphology and leakage current. First, it was revealed that ex-situ post-deposition annealing (PDA) at high temperatures in the 700–800 °C range led to the crystallization of BTO films and a high dielectric constant of 121. However, the film morphology deteriorated significantly during PDA, and consequently, a high leakage current was observed due to the rough and discontinuous surface containing voids and micro-cracks. To achieve an excellent leakage current characteristic as well as a high dielectric constant for a crystalline BTO thin film, in-situ crystallization was carried out through local epitaxial growth using a crystalline seed layer. The crystalline BTO seed layer was formed by annealing a 5-nm-thick amorphous BTO film at 700 °C on which the in-situ crystallized BTO main layer was deposited at 500 °C. The in-situ crystallization method resulted in a smooth and uniform surface and a high dielectric constant of 113. In addition, the in-situ crystallized BTO film exhibited a low leakage current density of 10−6 A/cm2 (at 0.8 V) displaying an improvement by a factor of 103 compared to the ex-situ crystallized BTO film.

Grain enlargement is a crucial requirement to synthesizing two-dimensional (2D) metal chalcogenides because it can minimize the effects of carrier scattering at the grain boundaries. To this end, r...

The continuous device scaling of dynamic random access memories has been increasing demands for the development of dielectric materials with high dielectric constants and low leakage currents. In this study, we developed MgO thin films through atomic layer deposition (ALD) using bis(ethylcyclopentadienyl)magnesium combined with two different reactants, H2O or O2 plasma, and compared the physical and chemical characteristics of MgO thin films produced by thermal ALD (Th-ALD) and plasma-enhanced ALD (PEALD). The films were deposited in a temperature range of 200–400 °C, and self-limited surface reactions were observed for both ALD processes. Th-ALD MgO films showed the oxygen deficient composition, while more stoichiometric MgO films were achieved by PEALD process. To evaluate the electrical characteristics of the MgO films, the metal–insulator–metal capacitors were fabricated. The electrical characteristics of the MgO film, such as the dielectric constant and leakage current, were compared according to the reactant type. The bulk-limited leakage current conduction mechanisms of the Th-ALD and PEALD MgO thin films were also investigated.

The synthesis of a continuous and high-quality large-area layer is a key research area in the field of two-dimensional (2D) metal chalcogenides. To date, several techniques, including chemical vapo...

In2O3 films were deposited by atomic layer deposition (ALD) using a newly synthesized heteroleptic In precursor, In(DMAMP)2(OiPr), and O3 at 150–300 °C. Self-limiting growth characteristics were exhibited for a wide ALD temperature range of 200–300 °C and growth rate of 0.029–0.033 nm/cycle. At a low temperature of 150 °C, the amorphous In2O3 film was deposited, while polycrystalline In2O3 films were achieved at 200–300 °C. The In2O3 films grown in this ALD temperature range had high densities of 7.0–7.2 g/cm3, which are comparable to those of bulk In2O3. At all growth temperatures (150–300 °C), no carbon or nitrogen impurities were detected, suggesting high reactivity of the In(DMAMP)2(OiPr) precursor. The ALD In2O3 films showed n-type electronic property with high electron concentrations of 1.6 × 1020–3.6 × 1020/cm3 and a Hall mobility of 31–39 cm2/V·s.

Atomic layer deposition (ALD) is an efficient technique that allows atomic-level surface control of metal catalysts for the design and development of electrocatalytic materials. Herein, we report a strategy for efficient catalyst design using a particle ALD method to enhance the electrocatalytic glycerol-oxidation-reaction (GOR) performance. Atomically controlled thin SnO2 layers were deposited on a carbon-supported Pt nanoparticle (Pt/C) surface using the ALD technique. The resulting SnO2 overcoated Pt/C (ALD(SnO2)–Pt/C) was then heat-treated at 400 °C under a N2 atmosphere. The onset potential as a kinetic parameter decreased with ALD (SnO2) coatings. The turnover frequency (TOF) for the GOR showed similar values for the tested samples (TOF of Pt/C: 74.86 h−1 and TOF of ALD(SnO2)–Pt/C: 91.29 h−1). Interestingly, interactions between the ALD SnO2 overcoating and Pt nanoparticles improved the catalytic stability for the GOR, preventing sintering of Pt nanoparticle catalysts. This demonstrates that an ALD SnO2 coating on defect sites of Pt can diminish Pt sintering for the GOR. From the GOR in an electrochemical batch reactor, the ALD(SnO2)–Pt/C catalyst also generated more glyceraldehyde (GAD) product than uncoated Pt/C at a similar glycerol conversion level. The density functional theory (DFT) calculations suggest that the binding energies of glycerol and reaction intermediates change at the interface of the SnO2-coated Pt surface compared to those at the Pt surface only, thus affecting the reaction chemistry for the electrocatalytic GOR. This work highlights how we can control reaction performance measures such as catalytic stability and product selectivity by using the particle ALD technique for electrocatalytic reactions such as glycerol oxidation.

Gas sensors for Internet of Things applications should meet two requisites – low power consumption and easy mounting universally. To satisfy the conditions, gas sensors need to operate at lower temperature and be flexible. In this study, we demonstrate a flexible gas sensor operating at room temperature using vertically aligned two-dimensional SnS2 nanomaterials. The atomic layer deposition (ALD) technique allows direct growth of SnS2 on a plastic substrate. The morphological structure of SnS2 is engineered by effecting changes in the growth temperature and substrate surface, which leads to the excellent sensing performance with respect to NO2 gas along with superior gas selectivity. The gas response is as high as 309 at 1 ppm of NO2 at room temperature, and a reliably high response is also observed even below 500 ppb of NO2. The fabricated flexible gas sensor exhibits comparable sensing performance and stability upon bending. Furthermore, the ALD achieves excellent uniformity in both the structural and electrical properties of SnS2 over a 4 in. wafer, which is essential for mass production. Therefore, we believe that this work would contribute to realizing the practical application of highly sensitive flexible gas sensors.

P-type tin monoxide (SnO) decorated TiO2 nanoparticles have been synthesized by the powder atomic layer deposition (p-ALD) method in a fluidized bed reactor at 150–250 °C. Successful deposition of SnO on a TiO2 surface was realized using a precursor combination of Sn(dmamp)2 and H2O as Sn source and reactant, respectively. Prepared SnO/TiO2 nanoparticles were characterized by XRF, XPS, XRD, and TEM-EDS. Formation of a p-SnO/n-TiO2 heterojunction resulted in improved photocatalytic methylene blue degradation performance compared to using a TiO2 photocatalyst, which might be attributed to facile separation of photo-induced electron-hole pairs as well as to increased UV/visible light absorption by adopting a narrow bandgap SnO.

A new deposition technique is required to grow the active oxide semiconductor layer for emerging oxide electronics beyond the conventional sputtering technique. Atomic layer deposition (ALD) has the benefits of versatile composition control, low defect density in films, and conformal growth over a complex structure, which can hardly be obtained with sputtering. This study demonstrates the feasibility of growing amorphous In–Zn–Sn–O (a-IZTO) through ALD for oxide thin-film transistor (TFT) applications. In the ALD of the a-IZTO film, the growth behavior indicates that there exists a growth correlation between the precursor molecules and the film surface where the ALD reaction occurs. This provides a detailed understanding of the ALD process that is required for precise composition control. The a-IZTO film with In/Zn/Sn = 10:70:20 was chosen for high-performance TFTs, among other compositions, regarding the field-effect mobility (μFE), turn-on voltage (Von), and subthreshold swing (SS) voltage. The optimize...

Atomic layer deposition (ALD) of SnO and SnO 2 thin films was successfully demonstrated over a wide temperature range of 70–300 °C using a divalent Sn-precursor, bis( N- ethoxy-2,2-dimethyl propanamido)tin (Sn(edpa) 2 ). The regulated growth of the SnO 2 and SnO films was realized by employing O 2 -plasma and H 2 O, respectively. Pure SnO 2 and SnO films were deposited with negligible C and N contents at all the growth temperatures, and the films exhibited polycrystalline and amorphous structures, respectively. The SnO 2 films presented a high transmittance of > 85% in the wavelength range of 400–700 nm and an indirect band gap of 3.6–4.0 eV; meanwhile, the SnO films exhibited a lower transmittance of > 60% and an indirect band gap of 2.9–3.0 eV. The SnO 2 films exhibited n-type semiconducting characteristics with carrier concentrations of 8.5 × 10 16 –1.2 × 10 20 cm −3 and Hall mobilities of 2–26 cm 2 /V s. By employing an alternate ALD growth of SnO and SnO 2 films, SnO 2 /SnO multilayer structures were successfully fabricated at 120 °C. The in-situ quadrupole mass spectrometry analysis performed during ALD revealed that the oxidation of chemisorbed Sn-precursor occurs dominantly during the Sn(edpa) 2 /O 2 -plasma ALD process, resulting in the production of combustion by-products, whereas the Sn(edpa) 2 /H 2 O ALD process was governed by a ligand exchange reaction with the maintenance of the original oxidation state of Sn 2+ .

Herein, we performed a comparative study of plasma-enhanced atomic layer deposition (PEALD) of SnO2 films using Sn(dmamp)2 as the Sn source and either H2O plasma or O2 plasma as the oxygen source in a wide temperature range of 100&ndash, 300 &deg, C. Since the type of oxygen source employed in PEALD determines the growth behavior and resultant film properties, we investigated the growth feature of both SnO2 PEALD processes and the various chemical, structural, morphological, optical, and electrical properties of SnO2 films, depending on the oxygen source. SnO2 films from Sn(dmamp)2/H2O plasma (SH-SnO2) and Sn(dmamp)2/O2 plasma (SO-SnO2) showed self-limiting atomic layer deposition (ALD) growth behavior with growth rates of ~0.21 and 0.07&ndash, 0.13 nm/cycle, respectively. SO-SnO2 films showed relatively larger grain structures than SH-SnO2 films at all temperatures. Interestingly, SH-SnO2 films grown at high temperatures of 250 and 300 &deg, C presented porous rod-shaped surface morphology. SO-SnO2 films showed good electrical properties, such as high mobility up to 27 cm2 V&minus, 1&middot, s&minus, 1 and high carrier concentration of ~1019 cm&minus, 3, whereas SH-SnO2 films exhibited poor Hall mobility of 0.3&ndash, 1.4 cm2 V&minus, 1 and moderate carrier concentration of 1 &times, 1017&ndash, 30 &times, 1017 cm&minus, 3. This may be attributed to the significant grain boundary and hydrogen impurity scattering.

Steel corrosion is a key engineering issue in the development of advanced nuclear reactors using liquid metals. The present study demonstrates that the steel corrosion behaviors can be systematically understood and classified based on the types of valence electrons of liquid metals, namely, s-electron liquid metals (s-LMs), such as liquid Na and Li, and p-electron liquid metals (p-LMs), such as liquid lead-bismuth eutectic (LBE) and Pb, where the conduction band is composed of s and p valence electrons, respectively. Through a comparative analysis of the physiochemical states of 3d transition metal atoms dissolved in liquid Na and liquid LBE by means of first-principles molecular dynamics (FPMD), it is shown that the 3d and 4s orbitals of the transition metals hardly interact with the s band of s-LMs, while they strongly interact with the p band of p-LMs in a covalent manner. This fact is consistently seen in the electronic states and the atomic configuration and can be successfully used to explain the differences in the steel corrosion behaviors observed between the liquid metals by experiments. The present findings provide fundamental insights into the corrosion chemistry of liquid metals.

Carbon nanofibers (CNFs) are used as active materials for electrodes in various energy devices, such as lithium ion secondary batteries, supercapacitors, and fuel cells. Recent studies have shown that nanoscale coatings on carbon nanotubes increase the output and lifespan of these devices owing to the improvement of their mechanical and chemical properties. Among various coating methods, atomic layer deposition (ALD) can adjust the thickness of the coating layer conformally without any directional growth. Therefore, ALD can coat particles with high aspect ratios, such as CNFs, even at nanometer levels of thickness. In this work, we grew two different morphologies of a SnO2 layer on CNF. We used two types of ALD equipment: flow-type ALD (static ALD), and fluidized bed reactor-type ALD (dynamic ALD). Static ALD could form a discontinuous SnO2, while a uniform SnO2 layer was formed by pre-inserting a layer of Al2O3. On the other hand, dynamic ALD formed a uniform SnO2 layer without pre-insertion of an Al2O3 layer. X-ray photoelectron spectroscopy analysis revealed that both Sn4+ and Sn2+ were present in SnO2 on the CNF deposited by static ALD, probably due to the formation of an interfacial layer between the SnO2 and CNF. When the dynamic ALD method was used, only Sn4+ was present in the SnO2 on CNF. Cyclic voltammetry analysis was performed to characterize the electrochemical properties of the SnO2-coated CNF as an electrode on a direct methanol fuel cell. It was revealed that the discontinuous SnO2 on CNF deposited by static ALD showed the highest current efficiency as well as enhanced electrocatalytic stability.

In this study, atomic layer deposition (ALD) of Cu2S was explored using bis(dimethylamino-2-methyl-2-butoxy)copper(II) and 5% H2S combination as Cu and S sources, respectively. The reaction resulted in a high growth rate of ∼0.22–0.24 nm/cycle at 150–200 °C owing to the high reactivity of the Cu precursor. At all investigated temperatures, Cu2S films with Cu oxidation state of +1 were obtained with negligible impurity levels. It was revealed that stoichiometric Cu2S films could be deposited at 120–150 °C, while sulfur deficient films was formed at 200 °C. Cu2S ALD process at low temperatures of 100–120 °C resulted in continuous film formation while the higher deposition temperatures of >150 °C led to island formation. Cu2S films showed p-type electrical characteristic with high hole concentrations of 4 × 1019–1021 cm−3 and Hall mobility of 2 cm2/vs. Lastly, the as-deposited Cu2S films exhibited an optical band gap of 1.2 eV which widened upon prolonged surface oxidation and in addition displayed NIR intra-band absorption.

Inhomogeneous superconductivity in rare-earth (RE)-doped CaFe2As2 (Ca122) compounds leads to a novel state of matter in which the superconducting and magnetic states can be simultaneously controlled by using an electric current (I). Both La- and Ce-doped Ca122 single crystals show a very broad superconducting transition width (ΔTc) due to their non-bulk nature. Surprisingly, ΔTc becomes sharper or broader after an electric current larger than a threshold value (It) is applied, with a concomitant change in the normal-state magnetism. The sharpened (broadened) ΔTc is accompanied by a decrease (an increase) in the amplitude of the ferromagnetic signals. The sensitive changes in the superconductivity and magnetism that occur when an external current is applied are related to the inhomogeneous electronic states that originate from the Fe magnetic state and/or self-organized superconducting/magnetic composites in Ca122 compounds. These discoveries shed new light on the role of Fe in Fe-based superconductors and will provide new ideas for the design of novel superconducting devices. Clues to the superconducting behavior of a complex, iron-based substance can be revealed with a technique based on electric current. When rare-earth atoms are incorporated into calcium–iron–arsenic (CaFe2As2) crystals, simultaneous magnetic and superconductive properties emerge after cooling below 50 K. Soon-Gil Jung and Tuson Park from South Korea’s Sungkyunkwan University, Suwon, and colleagues report that passing milliamp-level electric currents through rare-earth-doped CaFe2As2 causes unexpected shifts in superconducting transition temperatures and magnetic field responses. In some samples, a sharpening of the superconductivity onset point was accompanied by a loss of magnetic signals, while in others magnetism improved at the expense of well-defined superconducting temperatures. The researchers conclude that these changes arise from inhomogeneities within doped CaFe2As2, possibly from iron magnetic states or tiny self-assembled nanocomposites that become unstable past a current threshold. Large inhomogeneous electronic states in rare-earth-doped CaFe2As2 produce striking results of manipulating the superconducting phases via current-driven magnetic state. Magnetization hysteresis loops at superconducting state (2 K) and normal state (50 K) for La-doped CaFe2As2 are largely changed by the electric current because their high-Tc regions are localized. Current path between high-Tc regions is considered as a long wire, thus current-induced large magnetic field around the path can modulate the magnetic state in normal/weak superconducting regions. These observations provide new insights into the role of Fe in the Fe-based superconductors and ideas for the design of new superconducting devices.

High-quality SnO2 films with excellent crystallinities, purities, and high densities grown at low deposition temperatures (

The fabrication of high-k BaTiO3 (BTO) films for applications such as multilayer ceramic capacitors or dynamic random access memory has been achieved via the ex-situ crystallization of amorphous BTO into perovskite structure through post-deposition annealing (PDA). However, high-temperature PDA at temperatures exceeding 700 °C results in the severe degradation of BTO properties. In other words, ex-situ crystallization via PDA results in an increased dielectric constant but is accompanied by inferior leakage current characteristics caused by rough surface morphologies and defects such as voids and cracks. In this study, we demonstrate the in-situ crystallization of BTO films by introducing a high-quality SrRuO3 (SRO) film as a seed layer. The SRO film is deposited using rf magnetron sputtering at 270 °C–500 °C, and stoichiometric SRO films are obtained on SiO2, Al2O3, and TiN substrates by controlling the growth temperature; subsequently, rapid thermal annealing at 700 °C is conducted to crystallize the SRO film. The polycrystalline SRO film on the TiN substrate exhibits excellent morphology with uniform grains as well as a continuous and smooth surface, whereas the SRO films on the SiO2 and Al2O3 substrates exhibit rough and discontinuous surfaces. The SRO seed layer on TiN permits the in-situ growth of crystalline BTO films at a relatively low temperature of 500 °C featuring a high dielectric constant of 160 and a low leakage current density of 9.5 × 10-7 A/cm2 at 0.8 V, which are 2.2 and 3.3 × 107 times improved compared with those of the ex-situ crystallized BTO film on bare TiN, respectively.

Research on two-dimensional (2D) metal dichalcogenides is rapidly expanding owing to their unique characteristics that do not exist in bulk materials. The industrially compatible development of these emerging materials is indispensable to facilitate the transition of 2D metal dichalcogenides from the research stage to the practical industrial application stage. However, an industrially relevant method, i.e., the low-temperature synthesis of wafer-scale, continuous, and orientation-controlled 2D metal dichalcogenides, still remains a significant challenge. Here, we report the low-temperature (≤350 °C) synthesis of uniform and continuous n-type SnS2 thin films via the combination of atomic layer deposition (ALD) of tin oxides and subsequent sulfurization. Well-crystallized and aligned SnS2 layers parallel to the substrate are demonstrated through the phase engineering of the ALD-grown tin oxide and the substrate surface. The additional H2S plasma treatment at 300 °C leads to the formation of stoichiometric SnS2. The formation of conformal SnS2 layers over a three-dimensional undulating hole structure is confirmed, which reveals the potential for applications beyond the planar structured architecture. The present results could be a step toward the realization of 2D metal dichalcogenides in industry.

Indium oxide (In 2 O 3 ) thin films were deposited by atomic layer deposition using dimethyl( N -ethoxy-2,2-dimethylcarboxylicpropanamide)indium (Me 2 In(EDPA)) and H 2 O as the In-precursor and reactant, respectively. The In 2 O 3 films exhibited a saturated growth rate of 0.083 nm/cycle at a deposition temperature of 300 °C. Porous and amorphous films were grown at 150 °C, whereas dense polycrystalline films were deposited at higher deposition temperatures of 200–300 °C. XPS analysis revealed negligible carbon and nitrogen impurities incorporation within the films. The estimated bandgap of the In 2 O 3 films by spectroscopic ellipsometry and UV–vis spectroscopy was about 3.7 eV and the increase in refractive index with deposition temperature from 150 to 300 °C indicated that dense films were grown at higher temperatures. The high transmittance (>94% in visible light) and good electrical properties (resistivity ∼1.2–7 mΩ cm, Hall mobility ∼28–66 cm 2 /V s) of the In 2 O 3 films make them a viable option for optoelectronic applications.

Two-dimensional (2-D) metal chalcogenides have received great attention because of their unique properties, which are different from bulk materials. A challenge in implementing 2-D metal chalcogenides in emerging devices is to prepare a well-crystallized layer over large areas at temperatures compatible with current fabrication processes. Tin monosulfide, a p-type layered semiconductor with a high hole mobility, is a promising candidate for realizing large-area growth at low temperatures because of its low melting point. However, tin sulfides exist in two notable crystalline phases, SnS and SnS2. Therefore, it is imperative to control the oxidation state of Sn to achieve a pure SnS film. Here, the synthesis of SnS thin films by atomic-layer-deposition (ALD) is demonstrated using bis(1-dimethylamino-2-methyl-2-propoxy)tin(II) and H2S as Sn and S sources, respectively, over a wide temperature window (90–240 °C). Impurities such as carbon, oxygen, and nitrogen were negligibly detected. The morphological evol...

Aluminum oxide (AlO x ) thin films were synthesized by mist-chemical vapor deposition (mist-CVD) using aluminum acetylacetonate (Al(acac) 3 ) dissolved in an aqueous solvent mixture of acetone and water. Nitrogen gas was used to purge the precursor solution and growth rates between 7.5–13.3 nm/min were achieved at substrate temperatures of 250–350 °C. The AlO x layers deposited at temperatures below 350 °C exhibit 3–5 at% residual carbon levels, however those grown at 350 °C exhibit only 1–2 at% carbon impurity. Reasonable dielectric properties were obtained in the latter, with a dielectric constant (κ) of ~ 7.0, breakdown field of ~ 9 MV/cm and relatively low leakage current density of ~ 8.3×10 −10 A/cm 2 .

A new series of ruthenocene complexes were prepared from RuCl3·xH2O and 6,6-dimethylfulvene as potential precursors for thin-film deposition. The formation of these complexes was the result of an unforeseen nucleophilic attack of the solvent molecules (alcohols/amines) on the 6,6-dimethylfulvene ligand during the reaction. Complexes [RuII(C5H4C(CH3)2OCH3)2] (1), [RuII(C5H4C(CH3)2OC2H5)2] (2), [RuII(C5H4C(CH3)2N(CH3)2)2] (3), and [RuII(C5H4C(CH3)2N(CH2CH3)2)2] (4) were isolated in pure form and characterized by Fourier transform (FT) infrared and FT nuclear magnetic resonance spectroscopy as well as elemental and thermogravimetric (TG) analyses. Crystallographic studies of complexes 1–3 revealed a monomeric ruthenocene structure for all complexes and showed that the deprotonated alkylalkoxide or dialkylamide of the solvent molecule was attached to the exocyclic carbon of the fulvene ligand. Although the complexes were formed as ruthenocenes instead of the expected ruthenium fulvene complexes, they all disp...

Novel indium complexes [(CH3)2In(OR)]2 (1–7) were synthesized using a series of donor-functionalized alkoxide ligands as potential precursors for thin-film applications. These complexes showed dimeric configurations with two μ2-O bridging between the metal centers. Moreover, the indium metal centers in these complexes exhibited pentacoordinated states with distorted trigonal-bipyramidal geometry. The complexes were characterized by Fourier transform (FT)-infrared, and FT-nuclear magnetic resonance spectroscopies, elemental analyses, and thermogravimetric analyses (TGA). The TGA curves of complexes 4 and 7 exhibited a single-step mass loss at 100–275 °C, indicating good volatility and thermal stability.

Two-dimensional (2D) metal dichalcogenides have drawn considerable interest because they offer possibilities for the implementation of emerging electronics. The emerging electronics are moving toward two major directions: vertical expansion of device space and flexibility. However, the development of a synthesis method for 2D metal dichalcogenides that meets all the requirements remains a significant challenge. Here, we propose a promising method for wafer-scale, conformal, and low-temperature (≤240 °C) synthesis of single-phase SnS2 via the atomic layer deposition technique. There is a trade-off relationship between the crystallinity and orientation preference of SnS2, which is efficiently eliminated by the two-step growth occurring at different temperatures. Consequently, the van der Waals layers of the highly crystalline SnS2 are parallel to the substrate. Thin-film transistors (TFTs) comprising the SnS2 layer show reasonable electrical performances (field-effect mobility: ∼0.8 cm2 V-1 s-1 and on/off ratio: ∼106), which are comparable to that of a single-crystal SnS2 flake. Moreover, we demonstrate nonplanar and flexible TFTs to identify the feasibility of the implementation of future electronics. Both the diagonal-structured TFT and flexible TFT fabricated without a transfer process show electrical performances comparable to those of rigid and planar TFTs. Particularly, the flexible TFT does not exhibit substantial degradation even after 2000 bending cycles. Our work would provide decisive opportunities for the implementation of future electronic devices utilizing 2D metal chalcogenides.

A sneak path current—a current passing through a neighboring memory cell—is an inherent and inevitable problem in a crossbar array consisting of memristor memory cells. This serious problem can be alleviated by serially connecting the selector device to each memristor cell. Among the various types of selector device concepts, the diffusive selector has garnered considerable attention because of its excellent performance. This selector features volatile threshold switching (TS) using the dynamics of active metals such as Ag or Cu, which act as an electrode or dopant in the solid electrolyte. In this study, a diffusive selector based on Ag-doped HfOx is fabricated using a co-sputtering system. As the Ag concentration in the HfOx layer varies, different electrical properties and thereby TS characteristics are observed. The necessity of the electroforming (EF) process for the TS characteristic is determined by the proper Ag concentration in the HfOx layer. This difference in the EF process can significantly affect the parameters of the TS characteristics. Therefore, an optimized doping condition is required for a diffusive selector to attain excellent selector device behavior and avoid an EF process that can eventually degrade device performance.

Atomic layer deposition of SnO was explored using a novel Sn complex, bis(dimethylamino-2methyl-2butoxy)tin(II) [Sn(dmamb)2], and H2O as the Sn precursor and reactant, respectively. Sn(dmamb)2 showed a facile ligand exchange reaction with H2O at temperatures of 100–200 °C, which resulted in the fabrication of pure SnO thin films. Amorphous SnO films were obtained at all the investigated temperatures, but the pure Sn2+–O2− phase was observed only in the films produced at 100 and 150 °C. The amorphous SnO was crystallized by a rapid thermal annealing post-process in N2 ambient at 450 °C. A bottom-gate thin film transistor was fabricated using a crystallized SnO channel layer, and excellent drain current modulation and p-type behavior were obtained, with an on/off ratio of ~7 × 104 and a saturation field effect mobility of 0.5 cm2/V·s.

In this study, we investigated the effects of SnO artificial layer on the solid electrolyte interphase (SEI) in SiO anodes by varying the layer thickness via the atomic layer deposition technique. Two major SEI components, namely LiF and Li2CO3, were obtained from the electrolyte decomposition, which appeared on the anode surface depending on the artificial SnO–layer thickness. Experimental results revealed that the excellent interfacial kinetics of the SnO-100 sample originated from the multi-component SEI suppressing the electrolyte decomposition. The thickness of the SnO artificial layer was optimized based on the electrochemical performance. Therefore, it can be inferred that artificial layer on anodes provides an efficient way to control the SEI composition and improves the electrochemical activities of the anode materials.

Here, we demonstrate high-performance p-type thin film transistors (TFTs) with a SnO channel layer grown by atomic layer deposition (ALD). The performance of the SnO TFTs relies on hole carriers and defects in SnO and near the back-channel surface of SnO as well as the quality of the gate dielectric/SnO interface. The growth of SnO films at a high temperature of 210 °C effectively suppresses the hole carrier concentration, leading to a high on-current/off-current (Ion/Ioff) ratio. In addition, the SnO films grown at 210 °C achieve high field effect mobility (μFE) compared with the SnO films grown at lower temperatures because of their large grain size and lower impurity contents. However, the SnO films grown at 210 °C still contain defects and hole carriers, especially near the back-channel surface. The post-deposition process – back-channel surface passivation with ALD-grown Al2O3 followed by post-deposition annealing at 250 °C – considerably alleviates the defects and hole carriers, resulting in superior TFT performance (Ion/Ioff: 2 × 106, subthreshold swing: 1.8 V dec−1, μFE: ∼1 cm2 V−1 s−1). We expect that the SnO ALD and subsequent process will provide a new opportunity for producing high-performance p-type oxide TFTs.

Steels are easily corroded in a liquid lead-bismuth eutectic (LBE) because their components, such as Fe, Cr and Ni, exhibit a high solubility in the liquid LBE. To understand the reason for such a high solubility of these 3d transition metals, we have performed first-principles molecular dynamics calculations and analyzed the pair-correlation functions, electronic densities of states, and Bader charges and volumes of the 3d transition metals dissolved in the liquid LBE as impurities. The calculations show that the 4s and 3d orbitals of the 3d impurity atoms largely interact with the 6p band of the LBE, which generates bonding orbitals. We suggest that the high stability of 3d metals in the liquid LBE is caused by the interactions of the 4s and 3d orbitals with the 6p band. Spin polarization is induced by V, Cr, Mn, Fe and Co impurity atoms in a similar manner to the Slater-Pauling curve of solid transition metals, which exhibits a downward shift in the atomic number by approximately two. Based on the degree of spin polarization and the shifted trend of the Slater-Pauling curve, we suggest that Ni exhibits a higher solubility than Cr and Fe because of the differences in their interaction strengths between their 3d orbitals and the 6p band. In addition, the 4s and 3d orbitals of the 3d impurity atoms were found to interact more favorably with the Bi 6p band than the Pb 6p band, which is consistent with the fact that liquid Bi is more corrosive to steels than is liquid Pb.

A new series of germanium (1-5) and tin (6-10) complexes were successfully synthesized by employing N-alkoxy functionalized carboxylamide as the stabilizing ligands and these complexes could potentially serve as precursors for thin film applications. All complexes were characterized by Fourier transform (FT) infrared, and nuclear magnetic resonance spectroscopies as well as elemental and thermogravimetric (TG) analyses. The single crystal X-ray study of complexes 5 and 10 revealed that they crystalized in the monoclinic space group (P2(1)/c) as monomers. The metal centers in these complexes are coordinated to four oxygen atoms and display a distorted trigonal-bipyramidal geometry. Thermogravimetric analysis and volatility study of complexes demonstrated good volatility and stability for the compounds 2-4 and 6-9. Among these complexes, Ge(mdpa)2 (3) and Sn(edpa)2 (9) exhibited excellent physcio-chemical properties with clean single step curves and low residual mass in their TG analyses.

In 2 O 3 thin films were grown from a newly developed, liquid, homoleptic, In-based complex, tris(1-dimethylamino-2-methyl-2-propoxy)indium [In(dmamp) 3 ], and O 3 by atomic layer deposition (ALD) at growth temperatures of 150–200 °C. In(dmamp) 3 exhibited single-step evaporation with negligible residue and excellent thermal stability between 30 and 250 °C. The self-limiting surface reaction of In 2 O 3 during ALD was demonstrated by varying the In(dmamp) 3 and O 3 pulse lengths, with a growth rate of 0.027 nm/cycle achieved at 200 °C. The In 2 O 3 films grown at temperatures over 175 °C exhibited negligible concentrations of impurities, whereas that grown below 175 °C had concentrations of residual C of 6–8 at.%. Glancing angle X-ray diffraction revealed that the In 2 O 3 films were polycrystalline in nature when the deposition temperature was greater than 200 °C. The In 2 O 3 films grown at 150–200 °C exhibited carrier concentrations of 1.5 × 10 18 –6.6 × 10 19 cm −3 , resistivities of 15.1–2 × 10 −3 Ω cm, and Hall mobilities of 0.8–42 cm 2 /(V s).

Low-temperature growth of In2O3 films was demonstrated at 70–250 °C by plasma-enhanced atomic layer deposition (PEALD) using a newly synthesized liquid indium precursor, dimethyl(N-ethoxy-2,2-dimethylcarboxylicpropanamide)indium (Me2In(EDPA)), and O2 plasma for application to high-mobility thin film transistors. Self-limiting In2O3 PEALD growth was observed with a saturated growth rate of approximately 0.053 nm/cycle in an ALD temperature window of 90–180 °C. As-deposited In2O3 films showed negligible residual impurity, film densities as high as 6.64–7.16 g/cm3, smooth surface morphology with a root-mean-square (RMS) roughness of approximately 0.2 nm, and semiconducting level carrier concentrations of 1017–1018 cm–3. Ultrathin In2O3 channel-based thin film transistors (TFTs) were fabricated in a coplanar bottom gate structure, and their electrical performances were evaluated. Because of the excellent quality of In2O3 films, superior electronic switching performances were achieved with high field effect mo...

New magnesium complexes, [Et2Mg3(dmamp)4] (1) and [(CH2=CH)2Mg3(dmamp)4] (2), were prepared by the reaction of alkylmagnesium bromide with sodium 1-dimethylamino-2-methyl-2-propoxide [Na(dmamp)] in THF. Complexes 1 and 2 were characterized by 1H and 13C NMR spectroscopies, FTIR spectroscopy, elemental analysis, and single-crystal X-ray diffraction (XRD) analysis. The XRD analysis showed that these complexes are trinuclear where the alkoxy O is the μ2-O bridge between the Mg ions. Among the three metal centers, the two terminal Mg ions are five coordinate and have a square–pyramidal geometry, whereas the central Mg is four coordinate with a distorted tetrahedral geometry. The combination of ethyl and vinyl groups with sterically bulky aminoalkoxide ligands plays an important role in stabilizing the molecule.

Novel tin complexes stabilized by alkoxy-functionalized oxime ligands [Sn(L1)2]2 (1) and [Sn(L2)2]2 (2), were prepared and characterized. Single-crystal X-ray diffraction analysis revealed that the complexes were obtained as dimers in which the tin metal centers are bridged by a pair of μ2-oxygen atoms. Due to the ligand steric effects, the metal centers in these complexes adopted an unusual distorted square pyramidal geometry and displayed interesting structural features. The thermo-gravimetric analyses of the complexes showed major mass loss in the 175–380 °C region.

As the device scaling of dynamic random access memory continues, the demand for the development of new dielectric film with high permittivity and low leakage current that may replace the currently used ZrO2/Al2O3-based dielectric film has increased drastically. In this aspect, MgO thin film has been spotlighted due to its high band gap (7-8 eV) and moderate dielectric constant (9-10). In this study, we investigated the growth behavior and film properties of the MgO ALD film using Mg(EtCp)2 precursor and the different reactants of H2O and O2 plasma. MgO thin films were deposited at the temperature range of 200-400°C, and the self-limited surface reaction was observed to secure optimal growth conditions. Glancing angle X-ray diffraction and X-ray photoelectron spectroscopy were used to examine crystalline structure and chemical properties, respectively. To evaluate the electrical characteristics of the MgO films, the Pt/MgO/TiN capacitor was fabricated with different MgO thicknesses at various deposition temperatures. The electrical characteristics such as dielectric constant and leakage current density of the MgO film were examined depending on the reactants, and the leakage current conduction mechanism of the MgO thin films was elucidated. Figure 1

Herein, we report the simultaneous etching of selected metal oxide and sulfide underlayers during the atomic layer deposition (ALD) of Cu2S. The unexpected etch was observed to be prompted by the infiltration of highly mobile Cu+ ions from a top ALD Cu2S layer into underlying films, followed by fragmentation of the underlayers and subsequent outward diffusion of both cations and anions from the underlayers to the Cu2S surface. A strong correlation was observed between the susceptibility to etching, etch rates and the bond dissociation energies of the underlayers. ZnS, ZnO, SnS, and SnO thin films were etched at different rates, while SnO2 exhibited high resistance to etching. Interestingly, the etch process exhibited self-limiting characteristics dependent on the Cu precursor and H2S gas dose times, thus indicating simultaneous Cu2S ALD and controlled sublayer etching reactions. Based on the findings, we proposed a possible mechanism by which the etching proceeds. We further explored, the synthesis of 3-dimensional Cu2S/ZnO and Cu2S nanowires using ALD Cu2S and the observed ZnO etching phenomenon.