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Low temperature phase-controlled synthesis of titanium di- and tri-sulfide by atomic layer deposition
摘要： Phase-controlled synthesis of two-dimensional (2D) transition metal chalcogenides (TMCs) at low temperature with a precise thickness control has to date been rarely reported. Here, we report on a process for the phase-controlled synthesis of TiS2 (metallic) and TiS3 (semiconducting) nano-layers by atomic layer deposition (ALD) with precise thickness control. The phase-control has been obtained by carefully tuning the deposition temperature and co-reactant composition during ALD. In all cases, characteristic self-limiting ALD growth behavior with a growth per cycle (GPC) of ~0.16 nm per cycle was observed. TiS2 was prepared at 100 °C using H2S gas as co-reactant, and was also observed using H2S plasma as co-reactant at growth temperatures between 150 and 200 °C. TiS3 was only synthesized at 100 °C using H2S plasma as co-reactant. The S2 species in the H2S plasma, as observed by optical emission spectroscopy, has been speculated to lead to the formation of the TiS3 phase at low temperature. The control between synthesis of TiS2 and TiS3 was elucidated by Raman spectroscopy, X-ray photoelectron spectroscopy, high-resolution electron microscopy, and Rutherford back scattering studies. Electrical transport measurements showed the low resistive nature of ALD grown 2D-TiS2 (1T-phase). Post-deposition annealing of the TiS3 layers at 400 °C in a sulfur-rich atmosphere improved the crystallinity of the film and yielded photoluminescence at ~0.9 eV, indicating the semiconducting (direct bandgap) nature of TiS3. The current study opens up a new ALD-based synthesis route for controlled, scalable growth of transition metal di- and tri-chalcogenides at low temperatures.
关键词： phase-controlled synthesis,low temperature,titanium sulfide,transition metal chalcogenides,atomic layer deposition
更新于2025-09-11 14:15:04
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Atomic-layer deposition of crystalline BeO on SiC
摘要： For the ?rst time, an epitaxial beryllium oxide (BeO) ?lm was grown on 4H silicon carbide (4H-SiC) by atomic layer deposition (ALD) at a low temperature of 250 °C. The BeO ?lm had a large lattice mismatch with the substrate (> 7–8%), but it was successfully grown to a single crystal by domain-matching epitaxy (DME). The bandgap energy, dielectric constant, and thermal conductivity properties of crystalline BeO are suitable for power transistors that require low leakage currents and fast heat dissipation in high electric ?elds. Physical characterization con?rmed the single-crystalline BeO (0 0 2). Raman analysis showed that the E1 and A1 phonon modes of ALD BeO were intermixed with the E2 and A1 phonon modes of SiC, resulting in a signi?cant increase in phonon intensity. After heat treatment at a high temperature, a small amount of SiO2 interfacial oxide was formed but the stoichiometry of BeO was maintained. From the capacitance-voltage (C-V) curves, we obtained a dielectric constant of 6.9 and calculated a low interface trap density of 6 × 1010 cm?2·eV?1 using the Terman method at Ec-Et = 0.6 eV. The high bandgap, thermal conductivity, and excellent crystallinity reduced the dangling bonds at the interface of BeO-on-SiC.
关键词： Interface trap density,Atomic layer deposition,Domain matching epitaxy,Silicon carbide,Beryllium oxide
更新于2025-09-11 14:15:04
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Facile fabrication of ultraviolet-protective silk fabrics via atomic layer deposition of TiO <sub/>2</sub> with subsequent polyvinylsilsesquioxane modification
摘要： To develop ultraviolet (UV) light-protective silk fabrics (SFs), a conformal nanoscale TiO2 coating was deposited using an atomic layer deposition (ALD) method, and polyvinylsilsesquioxanes (PVSs) were further coated onto the SFs to enhance their hydrophobicity and UV light-resistance. Scanning electron microscopy and atomic force microscopy revealed hierarchical microstructures and nanostructures of the TiO2 coatings, which were primarily responsible for the increase of the water contact angle from approximately 0 to 120° after the ALD process. A high mean square surface roughness of 76.325 nm also accounted for this improved water contact angle. Furthermore, TiO2-coated SFs modified with low surface energy PVSs exhibited enhanced hydrophobic properties. More importantly, both the UV-blocking and yellowing-resistance of the SFs were improved without any significant change to the luster of the SFs. The ease and simplicity of this fabrication method makes it applicable to the preparation of multifunctional textiles with both good water repellency and UV-resistance.
关键词： polyvinylsilsesquioxanes,UV-protective,TiO2,silk fabrics,atomic layer deposition
更新于2025-09-11 14:15:04
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Transparent p-Cu0.66Cr1.33O2/n-ZnO heterojunction prepared in a five-step scalable process
摘要： Transparent and electrical conducting p-type off-stoichiometric copper–chromium oxide thin films were used to build p-Cu0.66Cr1.33O2/n-ZnO heterojunctions. The junctions were fabricated in a novel and simple five step process including metal organic chemical vapour deposition, atomic layer deposition, chemical wet etching, and optical lithography. One last step of thermal annealing, with varying temperatures of 650 and 700 °C, is added in order to tune the electrical properties of delafossite and consequently the electrical features of p–n junctions. This work was developed to address the lack of transparent and industrially scalable rectifying p–n junctions that can open multiple application paths in transparent electronics. A competitive ideality factor η of 6.6 and a transmittance in the visible range of 50% were achieved. An understanding of the electronic response of junctions is presented herein as well as a deepening comprehension of the physical properties of materials, with the bands alignment and the Fermi level tuning.
关键词： Atomic layer deposition,Optical lithography,Thermal annealing,Delafossite,Metal organic chemical vapour deposition,p-Cu0.66Cr1.33O2/n-ZnO heterojunctions,Transparent electronics,Chemical wet etching,Fermi level tuning
更新于2025-09-10 09:29:36
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Study of the oxidation at the Al <sub/>2</sub> O <sub/>3</sub> /GaSb interface after NH <sub/>4</sub> OH and HCl/(NH <sub/>4</sub> ) <sub/>2</sub> S passivations and O <sub/>2</sub> plasma post atomic layer deposition process
摘要： In this work, the Al2O3/GaSb interface has been studied by x-ray photoelectron spectroscopy in order to improve interfacial and electrical properties of metal–oxide–semiconductor structures based on GaSb. First, different passivations using NH4OH or (NH4)2S were studied with a dilution of 4% and 5%, respectively, in order to reduce native oxides on the GaSb surface. Then, we considered the oxidation of the Al2O3 and GaSb surface after treatments with an oxygen (O2) plasma post atomic layer deposition (ALD) process and with post deposition annealing at different temperatures. We found that (NH4)2S passivation leads to a lower quantity of native oxides on the GaSb surface and that the O2 plasma post ALD process enables the formation of an oxygen-rich layer within the Al2O3 at the interface reducing the GaSb surface oxidation after post deposition annealing of the oxide.
关键词： x-ray photoelectron spectroscopy,(NH4)2S,post deposition annealing,Al2O3/GaSb interface,NH4OH,atomic layer deposition,O2 plasma
更新于2025-09-10 09:29:36
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Enhanced Electrochemical Stability of TiO <sub/>2</sub> -Protected, Al-doped ZnO Transparent Conducting Oxide Synthesized by Atomic Layer Deposition
摘要： Transparent, conductive coatings on porous, three-dimensional materials are often used as the current collector for photoelectrode designs in photoelectrochemical applications. These structures allow for improved light trapping and absorption in chemically-synthesized, photoactive overlayers while minimizing parasitic absorption in the current collecting layer. Atomic layer deposition (ALD) is particularly useful for fabricating transparent conducting oxides (TCOs) like Sn-doped In2O3 (ITO) and Al-doped ZnO (AZO) for structured materials because the deposition is specific to exposed surfaces. Unlike line-of-site deposition methods (evaporation, spray pyrolysis, sputtering), ALD can access the entire complex interface to make a conformal transparent conductive layer. While ITO and AZO can be grown by ALD, they are intrinsically soluble in the acidic and basic environments common for electrochemical applications like water splitting. To take advantage of the unique characteristics of ALD in these applications, is important to develop strategies for fabricating TCO layers with enhanced chemical stability. Ultra-thin coatings of stable materials can be used to protect otherwise unstable electrochemical interfaces while maintaining the desired function. Here, we describe experiments to characterize the chemical and electrochemical stability of ALD-deposited AZO TCO thin films protected by a 10nm TiO2 overlayer. The addition of a TiO2 protection layer is demonstrated to improve the chemical stability of AZO by orders of magnitude compared to unprotected, yet otherwise identically prepared AZO films. The electrochemical stability is enhanced accordingly in both acidic and basic environments. We demonstrate that TiO2-protected AZO can be used as a TCO for both the cathodic hydrogen evolution (HER) and anodic water oxidation (OER) half-reactions of electrochemical water splitting in base and for HER in acid when the appropriate electrocatalysts are added. As a result, we show that ALD can be used to synthesize a chemically stable TCO heterostructure, expanding the range of materials and electrochemical environments available for building complex photoelectrode architectures.
关键词： Water splitting,Transparent conducting oxides,Atomic layer deposition,Electrochemical stability,Al-doped ZnO,TiO2 protection layer
更新于2025-09-10 09:29:36
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Strategies to facilitate the formation of free standing MoS <sub/>2</sub> nanolayers on SiO <sub/>2</sub> surface by atomic layer deposition: A DFT study
摘要： In this study, we employ density functional theory calculations to investigate the very initial formation of a buffer layer during atomic layer deposition of MoS2 at the SiO2 (001) surface. In our previous study, we described that the self-limiting atomic layer deposition (ALD) reactions using Mo(NMe2)2(NtBu)2 as precursor and H2S as co-reagent terminate in the formation of a so-called building block on the SiO2 (001) surface. This building block consists of Mo which shares bonds with the surface O of SiO2 (001) at the bottom and terminal S at the top. Electronic band structure calculations indicate that the subsequently deposited buffer-layer that is composed of these building blocks has (opto)-electrical properties that are far from the ideal situation. Based on our studies, we propose alternative ALD chemistries which lead to the formation of a so-called underpinned building block. In this cluster, the Mo atoms are underpinned by S atoms, suppressing the formation of a buffer layer. This ultimately facilitates the formation of a free standing conformal 2D-MoS2 nanolayer at the interface. Through the proposed chemistries, the opto-electrical properties of the deposited layers will be preserved.
关键词： opto-electrical properties,MoS2,SiO2,density functional theory,atomic layer deposition
更新于2025-09-10 09:29:36
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Transparent and Flexible Thin-Film Transistors with High Performance Prepared at Ultralow Temperatures by Atomic Layer Deposition
摘要： High-performance, transparent, and flexible thin-film transistors (TFTs) with polycrystalline channels in a bottom-gate structure are successfully fabricated at extremely low temperatures of 80, 90, and 100 °C by atomic layer deposition (ALD) in which ZnO and Al2O3 are used as channels and dielectric layers, respectively. The transistors are superior to silicon-based TFTs in which high temperatures are necessarily involved in both preparation and postgrowth annealing. Among all devices, TFTs grown at 100 °C exhibit the best performance which can be attributed to the lowest grain boundary trap density. Additionally, the TFTs are successfully transferred to plastic substrates without any performance degradation, which shows a high mobility of 37.1 cm2 V?1 s?1, a high on/off-state current ratio of 107 at VDS = 0.1 V, a small subthreshold swing of 0.38 V dec?1, and a proper threshold voltage of 1.34 V as well as an excellent bias stability.
关键词： bottom gate/top contacts,thin-film transistors,oxide,atomic layer deposition,zinc oxide,aluminum
更新于2025-09-10 09:29:36
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Band alignment of atomic layer deposited SiO <sub/>2</sub> on (010) (Al <sub/>0.14</sub> Ga <sub/>0.86</sub> ) <sub/>2</sub> O <sub/>3</sub>
摘要： The (AlxGa1?x)2O3/Ga2O3 system is attracting attention for heterostructure ?eld effect transistors. An important device design parameter is the choice of gate dielectric on the (AlxGa1?x)2O3 and its band alignment at the heterointerface. The valence band offset at the SiO2/(Al0.14Ga0.86)2O3 heterointerface was measured using x-ray photoelectron spectroscopy. The SiO2 was deposited by atomic layer deposition (ALD) onto single-crystal β-(Al0.14Ga0.86)2O3 grown by molecular beam epitaxy. The bandgap of the SiO2 was determined by re?ection electron energy loss spectroscopy as 8.7 eV, while high resolution XPS data of the O 1s peak and onset of elastic losses were used to establish the (Al0.14Ga0.86)2O3 bandgap as 5.0 eV. The valence band offset was determined to be 1.60 ± 0.40 eV (straddling gap, type I alignment) for ALD SiO2 on β-(Al0.14Ga0.86)2O3. The conduction band offset was 2.1 ± 0.08 eV, providing for a strong electron transport restriction.
关键词： x-ray photoelectron spectroscopy,(Al0.14Ga0.86)2O3,SiO2,atomic layer deposition,conduction band offset,band alignment,valence band offset
更新于2025-09-10 09:29:36
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Enhanced Oxygen Evolution Reaction Activity of Nanoporous SnO <sub/>2</sub> /Fe <sub/>2</sub> O <sub/>3</sub> /IrO <sub/>2</sub> Thin Film Composite Electrodes with Ultralow Noble Metal Loading
摘要： A conductive SnO2 layer and small quantities of IrO2 surface cocatalyst enhance the catalytic efficiency of nanoporous Fe2O3 electrodes in the oxygen evolution reaction at neutral pH. Anodic alumina templates are therefore coated with thin layers of SnO2, Fe2O3, and IrO2 by atomic layer deposition. In the first step, the Fe2O3 electrode is modified with a conductive SnO2 layer and submitted to different postdeposition thermal treatments in order to maximize its catalytic performance. The combination of steady-state electrolysis, electrochemical impedance spectroscopy, X-ray crystallography, and X-ray photoelectron spectroscopy demonstrates that catalytic turnover and e? extraction are most efficient if both layers are amorphous in nature. In the second step, small quantities of IrO2 with extremely low iridium loading of 7.5 μg cm?2 are coated on the electrode surface. These electrodes reveal favorable long-term stability over at least 15 h and achieve maximized steady-state current densities of 0.57 ± 0.05 mA cm?2 at η = 0.38 V and pH 7 (1.36 ± 0.10 mA cm?2 at η = 0.48 V) in dark conditions. This architecture enables charge carrier separation and reduces the photoelectrochemical water oxidation onset by 300 mV with respect to pure Fe2O3 electrodes of identical geometry.
关键词： iridium oxide,water splitting,nanostructures,iron oxide,atomic layer deposition
更新于2025-09-10 09:29:36