Multimaterial Self-Aligned Nanopatterning by Simultaneous Adjacent Thin Film Deposition and Etching.

Printed component sizes in electronic circuits are approaching 10 nm, but inherent variability in feature alignment during photolithography poses a fundamental barrier for continued device scaling. Deposition-based self-aligned patterning is being introduced, but nuclei defects remain an overarching problem. This work introduces low-temperature chemically self-aligned film growth via simultaneous thin film deposition and etching in adjacent regions on a nanopatterned surface. During deposition, nucleation defects are avoided in nongrowth regions because deposition reactants are locally consumed via sacrificial etching. For a range of materials and process conditions, thermodynamic modeling confirms that deposition and etching are both energetically favorable. We demonstrate nanoscale patterning of tungsten at 220 °C with simultaneous etching of TiO2. Area selective deposition (ASD) of the sacrificial TiO2 layer produces an orthogonal sequence for self-aligned patterning of two materials on one starting pattern, i.e., TiO2 ASD on SiO2 followed by W ASD on Si-H. Experiments also show capacity for self-aligned dielectric patterning via favorable deposition of AlF3 on Al2O3 at 240 °C with simultaneous atomic layer etching of sacrificial ZnO. Simultaneous deposition and etching provides opportunities for low-temperature bottom-up self-aligned patterning for electronic and other nanoscale systems.

Toward understanding the phase-selective growth mechanism of films and geometrically-shaped flakes of 2D MoTe2.

Two-dimensional (2D) molybdenum ditelluride (MoTe2) is an interesting material for fundamental study and applications, due to its ability to exist in different polymorphs of 2H, 1T, and 1T', their phase change behavior, and unique electronic properties. Although much progress has been made in the growth of high-quality flakes and films of 2H and 1T'-MoTe2 phases, phase-selective growth of all three phases remains a huge challenge, due to the lack of enough information on their growth mechanism. Herein, we present a novel approach to growing films and geometrical-shaped few-layer flakes of 2D 2H-, 1T-, and 1T'-MoTe2 by atmospheric-pressure chemical vapor deposition (APCVD) and present a thorough understanding of the phase-selective growth mechanism by employing the concept of thermodynamics and chemical kinetics involved in the growth processes. Our approach involves optimization of growth parameters and understanding using thermodynamical software, HSC Chemistry. A lattice strain-mediated mechanism has been proposed to explain the phase selective growth of 2D MoTe2, and different chemical kinetics-guided strategies have been developed to grow MoTe2 flakes and films.

Highly Uniform and Conducting Single-Walled Carbon Nanotube Thin Films via Controlling the Dewetting Phenomenon.

Carbon nanotubes (CNTs) have received substantial attention as alternatives to indium tin oxide for the production of transparent conductors. However, problems associated with the dewetting of liquid thin films have hindered the reliable fabrication of networked conducting CNT films via solution-based processes. In this study, the dewetting of liquid thin films containing single-walled carbon nanotubes (SWCNTs) on substrates is successfully retarded by simply adding ethylene glycol to the SWCNT dispersion, and highly uniform SWCNT thin films are obtained using the meniscus-dragging deposition (MDD) method. The dewetting-free coating conditions for the uniform SWCNT films are determined by calculating the dewetting and drying times of the liquid thin films formed by the MDD method. When the dewetting time was 2.5 times longer than the drying time of the liquid thin layers, uniform SWCNT films are formed over the entire substrates without breakage or rupture of the films. In addition, the transmittance and sheet resistance of the transparent SWCNT films are easily controlled over a wide range by varying the coating parameters.

Highly Transparent and Stretchable Conductors Based on a Directional Arrangement of Silver Nanowires by a Microliter-Scale Solution Process.

We report an effective method for fabricating highly transparent and stretchable large-area conducting films based on a directional arrangement of silver nanowires (AgNWs) driven by a shear force in a microliter-scale solution process. The thin conducting films with parallel AgNWs or cross-junctions of AgNWs are deposited on the coating substrate by dragging a microliter drop of the coating solution trapped between two plates. The optical and electrical properties of the AgNW thin films are finely tuned by varying the simple systematic parameters in the coating process. The transparent thin films with AgNW cross-junctions exhibit the superior electrical conductivity with a sheet resistance of 10 Ω sq(-1) at a transmittance of 85% (λ = 550 nm), which is well described by the high ratio of DC to optical conductivity of 276 and percolation theory in a two-dimensional matrix model. This simple coating method enables the deposition of AgNW thin films with high optical transparency, flexibility, and stretchability directly on plastic substrates.

Novel Synthesis, Coating, and Networking of Curved Copper Nanowires for Flexible Transparent Conductive Electrodes.

In this work, a whole manufacturing process of the curved copper nanowires (CCNs) based flexible transparent conductive electrode (FTCE) is reported with all solution processes, including synthesis, coating, and networking. The CCNs with high purity and good quality are designed and synthesized by a binary polyol coreduction method. In this reaction, volume ratio and reaction time are the significant factors for the successful synthesis. These nanowires have an average 50 nm in width and 25-40 µm range in length with curved structure and high softness. Furthermore, a meniscus-dragging deposition (MDD) method is used to uniformly coat the well-dispersed CCNs on the glass or polyethylene terephthalate substrate with a simple process. The optoelectrical property of the CCNs thin films is precisely controlled by applying the MDD method. The FTCE is fabricated by networking of CCNs using solvent-dipped annealing method with vacuum-free, transfer-free, and low-temperature conditions. To remove the natural oxide layer, the CCNs thin films are reduced by glycerol or NaBH4 solution at low temperature. As a highly robust FTCE, the CCNs thin film exhibits excellent optoelectrical performance (T = 86.62%, R(s) = 99.14 Ω â—»(-1)), flexibility, and durability (R/R(0) < 1.05 at 2000 bending, 5 mm of bending radius).