Deposition Of Ultrathin Films Research Articles

Ultrathin and Smooth Pheomelanin-like Photoconductive Film.

This study introduces a facile method for the substrate-independent deposition of pheomelanin-like films, revealing unique and promising electrical characteristics. The conventional darkening of a dopamine solution at a basic pH was significantly delayed by the addition of l-cysteine, resulting in a distinctive temporal pattern: an initial quiescent period without apparent color change followed by an abrupt and explosive burst. Surprisingly, within the quiescent period, the deposition of ultrathin and smooth pheomelanin-like films was observed, in addition to rough and thick films formed after the burst. Regardless of thickness or texture, these films exhibited common chemical properties, including moisture-capturing capability and dark- and bright-state conductivities. Particularly noteworthy were consistent photocurrent responses under bias voltage across various pheomelanin-like films, which were not observed in polydopamine films, highlighting the influential role of l-cysteine addition. These findings present a novel avenue for the potential application of pheomelanin-like films in bioelectronics, emphasizing their distinct electrical characteristics and prompting further exploration into their intricate conductive mechanisms. The study contributes to advancing our understanding of melanin-based materials and their potential in diverse scientific and technological domains.

Atomic Layer Deposition of HfAlOx for High-k Gate Dielectrics

Nowadays, the downscaling of CMOS devices requires continued effort to propose high performance components with extremely compact size. Surely, this trend is not achievable without extremely enhanced High-k gate stack materials, inter alia. For years, HfO2-based dielectrics deposited using ALD (Atomic Layer Deposition) technique are perfect dielectrics of choice for various devices and applications (Memristor, resistive random access memory, ferroelectric random access memory, antiferrolectric capacitances, ferroelectric FET...).As such, HfAlOx films present a good compromise between HfO2 and Al2O3 in term of coupling properties and insulating capabilities in comparison with both single HfO2 and Al2O3 films. The purpose of this work is to evaluate binary high-k HfAlOx dielectrics deposited by ALD technique. ALD is well suited for deposition of ultrathin films with exceptional capabilities enabling precise thickness, stoichiometry control and conformal growth at atomic scale. In this work, we focused on Al2O3/HfO2 films fabricated using two approaches: (i) repeatedly alternating the deposition of two different and separate extremely thin oxides (Al2O3 and HfO2; particular focus on HfO2/Al2O3/HfO2/Al2O3/HfO2 multilayer stack with equivalent Al fraction around 30%); (ii) combination of ALD super cycles allowing the formation HfAlOx layers. We analyze the general performance and the behavior of the binary high-k HfAlOx dielectrics (10 nm thin layers deposited at 300°C using TiCl4-TMA-H2O precursors) using physico-chemical (X-ray photoelectron spectroscopy XPS, X-ray reflectometry XRR, wavelength dispersive X-ray fluorescence WDXRF) and electrical measurements (Hg probe measurements, MIM capacitance).The incorporation of Al2O3 in the composition of the HfO2 gate dielectrics allows a perfect monitoring of physico-chemical properties varying from HfO2 layers to Al2O3 layers by controlling the number of Al2O3 and HfO2 ALD cycles. In this respect, we were able to monitor the Al fraction in the range of 5% to ~86% in the mixed binary dielectrics (Figure 1: XRR density of mixed binary layers vs Al/[Al+Hf] ratio, Figure 2: Al and Hf fractions in the mixed layer determined by WDXRF and XPS analysis).The electrical characteristics of the HfAlOx dielectrics confirm the influence of the Al fraction in the HfO2 layer. The leakage currents of the mixed layers decreases with increasing the Al fraction (Figure 3: J/E characteristics of mixed and stacked HfAlOx layers). The breakdown voltages for all mixed HfAlOx layers are greater than that of reference HfO2 layer. On the other hand, the shown multilayer presents an intermediate leakage currents profiles between the two mixed HfAlOx (25%Al and 40%Al). Thus, the incorporation of Al in the construction of HfAlOx system is likely to decrease the number of defects. Furthermore, the fully integrated MIM structures exhibit areal capacitance in the range 10-15 nF/mm2 of ALD-based high-k HfAlOx (10 to 12 nm) depending on the Al fraction. Thus, ALD-HfAlOx with various composition highlight the potential tremendous for high-κ capacitances stack for CMOS semiconductor devices. Figure 1

Synergetic improvements in surface hydrophobicity and wear resistance of TC4 materials via the combination of rapid heating and EtOH quenching methods

Ti-6Al-4V (TC4) materials with high hydrophobicity and wear resistance improve anticorrosion performance when utilized in offshore conditions. In this work, a novel strategy for simultaneously enhancing the surface hydrophobicity and wear resistance of surface textured TC4 (selected laser melting, SLM-TC4) materials was proposed. An in-situ deposition of ultrathin carbon film is realized via rapid induction heating followed by the EtOH quenching (IHQ-TC4) process. After the IHQ process, the surface chemical composition evolves from Ti (SLM-TC4) to the mixture of carbon film and TiO2 nanoparticles (IHQ-TC4), and the corresponding surface roughness decreases, which results in a surface wettability transition from hydrophilicity (SLM-TC4) to hydrophobicity (IHQ-TC4, 125°). Molecular dynamics simulations were utilized to explore the wettability transition mechanism, and found that the surface chemical composition evolution is the dominant factor, and the carbon film is responsible for the hydrophobicity of IHQ-TC4. Moreover, the surface hardness and wear resistance of IHQ-TC4 are greatly enhanced compared to those of SLM-TC4. The collective enhancements to the hydrophobicity and wear resistance of TC4 materials via the IHQ process provide a novel and facile strategy for enhancing the anticorrosion performance of TC4 materials utilized in offshore conditions.

In Pursuit of Next Generation N-Heterocyclic Carbene-Stabilized Copper and Silver Precursors for Metalorganic Chemical Vapor Deposition and Atomic Layer Deposition Processes

Volatile, reactive, and thermally stable organometallic copper and silver complexes are of significant interest as precursors for the metalorganic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD) of ultra-thin metallic films. Well-established CuI and AgI precursors are commonly stabilized by halogens, phosphorous, silicon, and oxygen, potentially leading to the incorporation of these elements as impurities in the thin films. These precursors are typically stabilized by a neutral and anionic ligand. Recent advancements were established by the stabilization of these complexes using N-heterocyclic carbenes (NHCs) as neutral ligands. To further enhance the reactivity, in this study the anionic ligand is sequentially changed from β-diketonates to β-ketoiminates and β-diketiminates, yielding two new CuI and two new AgI NHC-stabilized complexes in the general form of [M(NHC) (R)] (M = Cu, Ag; R = β-ketoiminate, β-diketiminate). The synthesized complexes were comparatively analyzed in solid, dissolved, and gaseous states. Furthermore, the thermal properties were investigated to assess their potential application in MOCVD or ALD. Among the newly synthesized complexes, the β-diketiminate-based [Cu(tBuNHC) (NacNacMe)] was identified to be the most suitable candidate as a precursor for Cu thin film deposition. The resulting halogen-, oxygen-, and silicon-free CuI and AgI precursors for MOCVD and ALD applications are established for the first time and set a new baseline for coinage metal precursors.

Deposition of ultra-thin coatings by a nature-inspired Spray-on-Screen technology

Nanometre-thick, ultrathin coatings applied over a large area are of paramount importance for various application fields such as biomedicine, space and automotive, organic electronics, memory devices, or energy storage devices. So far wet chemical deposition as a cost-effective, scalable, and versatile method can only be used for thicker deposits. Here the formation of uniform ultra-thin coatings with thicknesses below 15 nm using a nature-inspired, roll-to-roll compatible Spray-on-Screen (SoS) technology is reported. For this, the finite micro-droplet generation of Ultrasonic Spray Coating (USSC) is combined with the coating formation from a screen printing mesh. Hydrophobic micro-threads of the mesh, resembling the micro-hair on the legs of water striders, produce millidroplets from micro droplets, and when applying an external pressure to the mesh, dynamic wetting is enforced. The proposed technology is applicable for a wide variety of substrates and applications. It is shown by theory and experiment that ultra-thin coatings below 5 nm homogeneous over a large area can be deposited without the use of extended ink formulation or high substrate temperatures during or after deposition. This simple yet effective technique enables the deposition of ultra-thin films on any substrates, and is very promising to fabricate the organic, inorganic electronics devices and batteries cost effectively.

Direct atomic layer deposition of ultra-thin Al2O3 and HfO2 films on gold-supported monolayer MoS2

In this paper, the atomic layer deposition (ALD) of ultra-thin films (<4 nm) of Al2O3 and HfO2 on gold-supported monolayer (1L) MoS2 is investigated, providing an insight on the mechanisms ruling the nucleation in the early stages of the ALD process. A preliminary multiscale characterization of large area 1L-MoS2 exfoliated on sputter-grown Au/Ni films demonstrated: (i) a tensile strain (from 0.1 to 0.3%) and p-type doping (from 1 × 1012 to 4 × 1012 cm−2) distribution at micro-scale; (ii) an almost conformal MoS2 membrane to the Au grains topography, with some locally detached regions, indicating the occurrence of strain variations at the nanoscale; (iii) atomic scale variability (from ∼ 4.0 to ∼ 4.5 Å) in the Mo-Au atomic distances was detected, depending on the local configuration of Au nanograins. Ab initio DFT calculations of a free-standing MoS2 layer and a simplified MoS2/Au(111) interface model showed a significant influence of the Au substrate on the MoS2 energy band structure, whereas small differences were accounted for the adsorption of H2O, TMA (co-reactant, and Al-precursor, respectively) molecules, and a slight improved adsorption was predicted for TDMAHf (Hf-precursor). This suggests a crucial role of nanoscale morphological effects, such as the experimentally observed local curvature and strain of the MoS2 membrane, in the enhanced physisorption of the precursors. Afterwards the nucleation and growth of Al2O3 an HfO2 films onto 1L-MoS2/Au was investigated in detail, by monitoring the surface coverage as a function of the number (N) of ALD cycles, with N from 10 to 120. At low N values, a slower growth rate of the initially formed nuclei was observed for HfO2, probably due to the bulky nature of the TDMAHf precursor as compared to TMA. On the other hand, the formation of continuous films was obtained in both cases for N > 80 ALD cycles, corresponding to ∼ 3.6 nm Al2O3 and ∼ 3.1 nm HfO2. Current mapping on these ultra-thin films by conductive-AFM showed, for the same applied bias, a uniform insulating behavior of Al2O3 and the occurrence of few localized breakdown spots in the case of HfO2, associated to a less compact films regions. Finally, an increase of the 1L-MoS2 tensile strain was observed by Raman mapping after encapsulation with both high-κ films, accompanied by a reduction in the PL intensity, explained by the effects of strain and the higher effective dielectric constant of the surrounding environment.

Surface Wrinkling with Memory for Programming Adhesion and Wettability

Modulating surface wrinkling is important for a variety of engineering applications. It has been known for more than two decades that the wavelength of surface wrinkles occurring in a metal film–soft polymer system scales linearly with the deposited film thickness. In the current experimental study of ultrathin gold film (0.2–8 nm) deposition on polydimethylsiloxane (PDMS), an unexplored thickness-dependent wrinkling phenomenon is found. By manipulating the deposition sequence as a degree of freedom for tailoring surface topography, we discovered a morphology memory effect where the wrinkle evolution in the subsequent deposition step inherits the surface pattern already formed in the previous step. Moreover, a stepwise deposition targeting 1 nm thick film can lead to 1 order of magnitude higher surface roughness than the one in the continuous deposition. By programming the sequences within 8 nm Au deposition, a surface strain map varying drastically from 0.2% to 27% is realized. Instructed by the strain map, we show the great potentials of tailored wrinkles in alternating surface wettability, enhancing surface Raman scattering, and on-demand tuning of surface adhesion.

Joint Intercalation of Ultrathin Fe and Co Films under a Graphene Buffer Layer on a SiC(0001) Single Crystal

The joint intercalation of Co and Fe atoms under a graphene buffer layer synthesized on a SiC(0001) single crystal has been studied. Intercalation has been performed by means of the alternating deposition of ultrathin Fe and Co metal films on the substrate heated to 450°C with the subsequent heating to 600°C in 15 min. It has been shown that Co and Fe atoms under these conditions are intercalated under graphene, forming compounds with silicon and with each other. The existence of a magnetic order in the system up to room temperature has been demonstrated using a superconducting quantum interferometer. A possible stoichiometry of the formed alloys has been analyzed using data on the shape and magnitude of hysteresis loops. In addition, it has been found that Fe and Co in the system exposed to the atmosphere are not oxidized. Thus, graphene protects the formed system. This study makes contribution to the investigation of graphene in contact with magnetic metals and promotes its application in spintronic and nanoelectronic devices.

Uniform deposition of ultra-thin TiO2 film on mica substrate by atmospheric pressure chemical vapor deposition: Effect of precursor concentration

The performance of pearlescent pigment significantly affected by the grain size and the roughness of deposited film. The effect of TiCl4 concentration on the initial deposition of TiO2 on mica by atmospheric pressure chemical vapor deposition (APCVD) was investigated. The precursor concentration significantly affected the deposition and morphology of TiO2 grains assembling the film. The deposition time for fully covering the surface of mica decreased from 120 to 10 s as the TiCl4 concentration increased from 0.38% to 2.44%. The grain size increased with the TiCl4 concentration. The AFM and TEM analysis demonstrated that the aggregation of TiO2 clusters at the initial stage finally result to the agglomeration of fine TiO2 grains at high TiCl4 concentrations. Following the results, it was suggested that the nucleation density and size was easy to be adjusted when the TiCl4 concentration is below 0.90%.

Controllable semiconductor flexoelectricity by interface engineering

Flexoelectricity of semiconductors usually exhibits large flexoelectric coefficients due to their significantly enhanced surface piezoelectricity caused by surface symmetry breaking. In this Letter, we reported a general paradigm to tune the semiconductor flexoelectricity through interface engineering. We selected Nb-SrTiO3 (Nb-STO) single crystals as the targets and tuned their surface piezoelectricity through depositing TiO2-terminated and SrO-terminated ultra-thin BaTiO3 (BTO) films. The results suggested that the deposition of TiO2-terminated and SrO-terminated ultra-thin BaTiO3 films to Nb-STO can induce a downward and upward out-of-plane surface polarization, respectively, thereby significantly increasing/decreasing the apparent flexoelectric coefficients of Nb-STO single crystals. Our work proves the feasibility of interface engineering in the application of flexoelectricity and also provides a possible route to achieve the large apparent flexoelectricity of semiconductor materials.

Temperature study of atmospheric-pressure plasma-enhanced spatial ALD of Al2O3 using infrared and optical emission spectroscopy

Atmospheric-pressure plasma-enhanced spatial atomic layer deposition (PE-s-ALD) is considered a promising technique for high-throughput and low-temperature deposition of ultrathin films for applications where volume and costs are particularly relevant. The number of atmospheric-pressure PE-s-ALD processes developed so far is rather limited, and the fundamental aspects of their growth mechanisms are largely unexplored. This work presents a study of the atmospheric-pressure PE-s-ALD process of Al2O3 using trimethylaluminum [TMA, Al(CH3)3] and Ar–O2 plasma within the temperature range of 80–200 °C. Thin-film analysis revealed low impurity contents and a decreasing growth-per-cycle (GPC) with increasing temperature. The underlying chemistry of the process was studied with a combination of gas-phase infrared spectroscopy on the exhaust plasma gas and optical emission spectroscopy (OES) on the plasma zone. Among the chemical species formed in the plasma half-cycle, CO2, H2O, CH4, and CH2O were identified. The formation of these products confirms that the removal of CH3 ligands during the plasma half-cycle occurs through two reaction pathways that have a different temperature dependences: (i) combustion reactions initiated by O2 plasma species and leading to CO2 and H2O formation and (ii) thermal ALD-like reactions initiated by the H2O molecules formed in pathway (i) and resulting in CH4 production. With increasing temperature, the dehydroxylation of OH groups cause less TMA adsorption which leads to less CO2 and H2O from the combustion reactions in the plasma step. At the same time, the higher reactivity of H2O at higher temperatures initiates more thermal ALD-like reactions, thus producing relatively more CH4. The CH4 can also undergo further gas-phase reactions leading to the formation of CH2O as was theoretically predicted. Another observation is that O3, which is naturally produced in the atmospheric-pressure O2 plasma, decomposes at higher temperatures mainly due to an increase of gas-phase collisions. In addition to the new insights into the growth mechanism of atmospheric-pressure PE-s-ALD of Al2O3, this work presents a method to study both the surface chemistry during spatial ALD to further extend our fundamental understanding of the method.

Dopamine as a bioinspired adhesion promoter for the metallization of multi-responsive phase change microcapsules

This work reports on an environmentally friendly method to produce encapsulated phase change material with a thin nickel coating, applicable for heat conversion, storage and thermal management of heat-sensitive components and suitable for active heating by electromagnetic radiation. A critical issue for the metallization is the adhesion between the polymer capsule shell and the metal layer. Based on previous studies using the bio-molecule dopamine as adhesion promoter in composites and for plastics metallization, commercial paraffin microcapsules were coated with an ultrathin polydopamine film via a simple wet chemical process. Subsequently, a thin, uniform and compact nickel layer was produced by electroless metallization. The successful deposition of both layers was verified with a broad range of imaging and spectroscopic techniques. For the first time, surface-enhanced IR spectroscopy was used to study the deposition of ultrathin PDA films. The combination of SEM and energy-dispersive X-ray spectroscopy allowed resolving the spatial distribution of the elements Ni, N, and O in the MC shell. Electrically conducting paths in the Ni shell were verified by conductive AFM. Thermal analysis revealed that the coated microcapsules show a phase change enthalpy of approx. 170 J/g, suitable for thermal storage and management. Additionally, the nickel layer enhanced the thermal diffusivity of the microcapsule powders and enables a fast heating of the PCM microcapsules by microwave radiation, demonstrating the applicability of the metallized MCs for controlled heating applications.Graphical abstract

Facile deposition of NiFe-LDH ultrathin film on pyrolytic graphite sheet for oxygen evolution reaction in alkaline electrolyte

NiFe-layered doubly hydroxide (LDH) is one of the most active materials for hydroxyl oxidation in an alkaline electrolyte. In this study, we explored a facile method of depositing NiFe-LDH catalyst on pyrolytic graphite sheets (PGSs) to explore the synergistic effects at the substrate–electrocatalyst interface. The catalyst was electrodeposited on PGSs using chronoamperometry. The homogeneous distribution of the catalyst with nanosheet morphology on the PGS's surface produced an ultrathin film. The NiFe25/PGS sample showed a low overpotential (332 mV) and Tafel slope (33 mV dec −1 ). The fitting of the Nyquist plots was performed using an equivalent circuit, and the NiFe25/PGS (1.69 Ω) sample showed the lowest charge transfer resistance among the studied catalysts. In addition, PGS proved a better substrate for the alkaline oxygen evolution reaction compared to glassy carbon and fluorine-doped tin oxide. • Facile deposition of NiFe25 on surface of PGS. • NiFe25/PGS showed a nanosheet morphology. • NiFe25/PGS was effective for oxygen evolution reaction (332 mV at 10 mA cm −2 ). • PGS proved to be a better substrate for the alkaline OER in comparison of GC and FTO.

Design and Construction of an ALD Reactor by Growth of Al2O3 Nanostructure Films

Objective: This project focuses on designing, building and commissioning work the atomic layer deposition (ALD) reactor for Al2O3 ultrathin film, which it will be contain specific components and a system's own control unit. Methodology: The ALD reactor was designed under a system to minimize components, flow lines and connections; to reduce manufacturing costs, volume of precursors, among others. Currently, ALD reactors are expensive to sell, maintain and replace parts. The design and manufacture of the ALD reactor manufactured at the University of Sonora (UNISON) is based on the state art with sequential binary reactions of the precursors, for the proposal for the manufacture of solar cells. Contribution: It was possible to build and commission the ALD reactor for the deposition of ultra-thin films, with the characteristics of being reproducible and scalable, which makes it attractive for commercialization. The homemade ALD reactor at UNISON is considered a very interesting equipment for the semiconductor research area, since it is possible to combine different types of materials in the form of films such as oxides and nitrides in the order of Angstroms (Ǻ).

Hyper 100 °C Langmuir-Blodgett (Langmuir-Schaefer) Technique for Organized Ultrathin Film of Polymeric Semiconductors.

In this study, we advanced the conventional Langmuir-Blodgett (LB) method to a high-temperature range (above 100 °C) using a newly manufactured LB machine, which is adaptable to a high-boiling-point subphase, as a universally usable apparatus. A sophisticated trough design, with homogeneous heating capability up to approximately 200 °C, together with automatic film compression and Langmuir-Schaefer type film transfer, enabled the fabrication of highly aligned thin films of polymeric semiconductors with uniaxial alignment of polymer backbones, which is desirable for efficient charge transport. Herein, ultrathin films of semicrystalline thiophene-based semiconductors were prepared on ethylene glycol and heated to 80 °C. The analyses of the transferred films with pressure-area isotherms, atomic force microscopy (AFM), polarized optical microscopy (POM), and grazing-incidence wide-angle X-ray scattering (GIWAXS) indicated that the proposed high-temperature LB method allows ideal deposition of high-quality ultrathin films with molecular layer precision at the selected high-temperature conditions. Furthermore, preparing thin-film donor-acceptor-type copolymers in ionic liquids at high temperatures (up to 140 °C) was a challenging task that was successfully demonstrated in this study. Highly ordered thin films of donor-acceptor polymers with a uniaxial backbone orientation were obtained only at 140 °C. The obtained semicrystalline thin films with uniaxially aligned polymer backbones significantly contribute to the two-dimensional overlap of molecular orbitals, which is likely to promote charge transport. The use of the manufactured automatic LB machines is advantageous for better quality films prepared at higher temperatures (even above 100 °C) from various technical viewpoints, including homogeneous heating, constant compression, and automatic film transfer. The novel methodology proposed herein expands the possibilities of the Hyper 100 °C Langmuir-Blodgett technique, which has not been accessible by the conventional LB method with the aqueous subphase.

Atomic Layer Deposition of Ultrathin ZnO Films for Hybrid Window Layers for Cu(Inx,Ga1-x)Se2 Solar Cells.

The efficiency of thin-film chalcogenide solar cells is dependent on their window layer thickness. However, the application of an ultrathin window layer is difficult because of the limited capability of the deposition process. This paper reports the use of atomic layer deposition (ALD) processes for fabrication of thin window layers for Cu(Inx,Ga1−x)Se2 (CIGS) thin-film solar cells, replacing conventional sputtering techniques. We fabricated a viable ultrathin 12 nm window layer on a CdS buffer layer from the uniform conformal coating provided by ALD. CIGS solar cells with an ALD ZnO window layer exhibited superior photovoltaic performances to those of cells with a sputtered intrinsic ZnO (i-ZnO) window layer. The short-circuit current of the former solar cells improved with the reduction in light loss caused by using a thinner ZnO window layer with a wider band gap. Ultrathin uniform A-ZnO window layers also proved more effective than sputtered i-ZnO layers at improving the open-circuit voltage of the CIGS solar cells, because of the additional buffering effect caused by their semiconducting nature. In addition, because of the precise control of the material structure provided by ALD, CIGS solar cells with A-ZnO window layers exhibited a narrow deviation of photovoltaic properties, advantageous for large-scale mass production purposes.

Confined Shear Alignment of Ultrathin Films of Cellulose Nanocrystals.

Cellulose nanocrystals (CNCs) are a naturally abundant nanomaterial derived from cellulose which exhibit many exciting mechanical, chemical, and rheological properties, making CNCs attractive for use in coatings. Furthermore, the alignment of CNCs is important to exploit their anisotropic mechanical and piezoelectric properties. Here, we demonstrate and study the fabrication of submonolayer to 25 nm thick films of CNCs via solution-based shear alignment. CNC solution is forced through a sub-millimeter tall channel at high volumetric flow rates generating shear. The half-width at half-maximum of the spread in CNC alignment significantly improves from 78 to 17° by increasing the shear rate from 19 to 19,000 s-1. We demonstrate that the film thickness is increased by increasing the volume of CNC solution flowed over the substrate and/or increasing the CNC solution concentration, with a degradation in film uniformity at higher (≥7 wt %) concentrations, likely due to CNC aggregates in the solution. Deposition of ultrathin aligned CNC films occurs within seconds and the technique is inherently scalable, demonstrating the promise of solution-based shear for the fabrication of ultrathin aligned CNC films, thereby enabling the future study of their inherent material properties or use in high-performance coatings and applications.

Atomic Layer Deposition of Ultrathin Tungsten Oxide Films from WH2(Cp)2 and Ozone

Atomic Layer Deposition of Ultrathin Tungsten Oxide Films from WH₂(Cp)₂ and Ozone

Micro-patterned deposition of MoS2 ultrathin-films by a controlled droplet dragging approach

Micropatterning of transition metal dichalcogenide (TMDC) ultrathin-films and monolayers has been demonstrated by various multi-step approaches. However, directly achieving a patterned growth of TMDC films is still considered to be challenging. Here, we report a solution-based approach for the synthesis of patterned MoS2 layers by dragging a precursor solution droplet with variable velocities across a substrate. Utilizing the pronounced shearing velocity dependence in a Landau-Levich deposition regime, MoS2 films with a spatially modulated thickness with alternating mono/bi- and few-layer regions are obtained after precursor annealing. Generally, the presented facile methodology allows for the direct preparation of micro-structured functional materials, extendable to other TMDC materials and even van der Waals heterostructures.

Multistep atomic layer deposition process for ultrathin superconducting NbN films with high critical current density on amorphous substrate

This study presents a multistep process of plasma-enhanced atomic layer deposition of ultrathin superconductive films of niobium nitride from metal organic precursor tris(diethylamido)(tert-butylimido)niobium(V). While using NH3/Ar and H2/Ar gas mixtures as reactants, a comprehensive analysis was performed pertaining to the influence of operating parameters, such as the duration of plasma exposure to the H2/Ar reactant, gas-flow ratio, plasma exposure duration and power of inductively coupled plasma source for the NH3/Ar reactant, on the obtained films’ parameters, such as resistivity, superconducting transition temperature and critical current density. Amorphous silicon oxide was used as the substrate. It was shown by experiments, that films’ resistivity affects the value of critical current density. As a result, the all-time record resistivity of 147 µΩ·cm was achieved for films with a thickness of 8 nm. When cooling in the Gifford McMahon closed-cycle cryostat, the values of superconducting transition temperature and critical current density were equal to 12.3 К and 9 МА/cm2 at a liquid helium temperature, respectively.