Effect of Cl2 Radical on Dry Development of Spin-Coated Metal Oxide Resist.

In this study, the effects of Cl2 radicals on dry development of spin-coated metal oxide resist (MOR) and changes in its surface binding states were investigated to verify the mechanism of dry development. Dry development characteristics of tin hydroxide (Tin OH), which is one of the MOR candidates for next generation lithography, were investigated as functions of process time and temperature using a Cl2 radicals source. Non-UV-exposed Tin OH film showed a linear etch rate (1.77 nm/min) from the initial thickness of ∼50 nm, while the UV-exposed film showed slower etch behavior (1.46 nm/min) in addition to the increase of film thickness for up to 3 min during the Cl2 radical dry development. UV-exposed photoresist (PR) contained more oxygen (Sn-O bonding) in the film due to the removal of butyl compounds from the clusters during the UV exposure process. Therefore, due to the lower reaction of chlorine radicals with Sn-O in the UV-exposed Tin OH than the other bindings, the non-UV-exposed PR was preferentially removed compared to the UV-exposed PR. As the temperature decreases, the overall etch rate decreases, but the difference in etch rate between exposed and unexposed Tin OH becomes larger. Finally, at a substrate temperature of -20 °C, the non-UV-exposed Tin OH with a thickness of 50 nm was completely removed, while ∼30 nm thick PR remained for UV-exposed Tin OH. Eventually, a negative tone development was possible with Cl2 radical plasma due to the difference in activation energy between the UV-exposed and non-UV-exposed films. It is believed that dry development using Cl2 radicals will be one of the most important process techniques for next-generation patterning to remove problems such as pattern leaning, line edge roughness, residue, etc., caused by wet development.

Transformation of K2Sb8Q13 and KSb5Q8 Bulk Crystals to Sb2Q3 (Q = S, Se) Nanofibers by Acid-Base Solution Chemistry.

The ability to manipulate crystal structures using kinetic control is of broad interest because it enables the design of materials with structures, compositions, and morphologies that may otherwise be unattainable. Herein, we report the low-temperature structural transformation of bulk inorganic crystals driven by hard-soft acid-base (HSAB) chemistry. We show that the three-dimensional framework K2Sb8Q13 and layered KSb5Q8 (Q = S, Se, and Se/S solid solutions) compounds transform to one-dimensional Sb2Q3 nano/microfibers in N2H4·H2O solution by releasing Q2- and K+ ions. At 100 °C and ambient pressure, a transformation process takes place that leads to significant structural changes in the materials, including the formation and breakage of covalent bonds between Sb and Q. Despite the insolubility of the starting crystals in N2H4·H2O under the given conditions, the mechanism of this transformation can be rationalized by applying the HSAB principle. By adjusting factors such as the reactants' acid/base properties, temperature, and pressure, the process can be controlled, allowing for the achievement of a wide range of optical band gaps (ranging from 1.14 to 1.59 eV) while maintaining the solid solution nature of the anion sublattice in the Sb2Q3 nanofibers.

Multiscale structural control of thiostannate chalcogels with two-dimensional crystalline constituents.

Chalcogenide aerogels (chalcogels) are amorphous structures widely known for their lack of localized structural control. This study, however, demonstrates a precise multiscale structural control through a thiostannate motif ([Sn2S6]4-)-transformation-induced self-assembly, yielding Na-Mn-Sn-S, Na-Mg-Sn-S, and Na-Sn(II)-Sn(IV)-S aerogels. The aerogels exhibited [Sn2S6]4-:Mn2+ stoichiometric-variation-induced-control of average specific surface areas (95-226 m2 g-1), thiostannate coordination networks (octahedral to tetrahedral), phase crystallinity (crystalline to amorphous), and hierarchical porous structures (micropore-intensive to mixed-pore state). In addition, these chalcogels successfully adopted the structural motifs and ion-exchange principles of two-dimensional layered metal sulfides (K2xMnxSn3-xS6, KMS-1), featuring a layer-by-layer stacking structure and effective radionuclide (Cs+, Sr2+)-control functionality. The thiostannate cluster-based gelation principle can be extended to afford Na-Mg-Sn-S and Na-Sn(II)-Sn(IV)-S chalcogels with the same structural features as the Na-Mn-Sn-S chalcogels (NMSCs). The study of NMSCs and their chalcogel family proves that the self-assembly principle of two-dimensional chalcogenide clusters can be used to design unique chalcogels with unprecedented structural hierarchy.

Large-Scale Sonochemical Synthesis of Bi-Sn Eutectic Alloy Nanoparticles.

Lead-free Bi-Sn alloy is an alternative solder material with a low eutectic melting temperature and environmental compatibility. Although extensive research has been conducted on this Bi-Sn eutectic alloy, a lack of facile synthetic methods with scalability hinders the implementation of finepatterned interconnectors for emerging electronic applications. In this study, we employed a facile sonochemical synthetic method to synthesize Bi-Sn alloy nanoparticles in large quantities. Highenergy ultrasonication treatment of Bi-Sn bimetallic particles resulted in nanoparticle formation with repeated formation, growth, and collapse of induced gas bubbles. The size of the nanoparticles was controlled from 92 to 506 nm of the mean diameter with variations in ultrasonication power and irradiation time. The nanoparticles exhibited a stable eutectic melting point at 139.8 °C. Interestingly, the sonochemically synthesized nanoparticles exhibited coexistence of metastable Bi2Sn and stable Bi-Sn phases. Finally, we demonstrated that Bi-Sn eutectic nanoparticles could be synthesized at a gram scale of approximately 1.7 g for future mass production.

A skin-like two-dimensionally pixelized full-color quantum dot photodetector.

Direct full-color photodetectors without sophisticated color filters and interferometric optics have attracted considerable attention for widespread applications. However, difficulties of combining various multispectral semiconductors and improving photon transfer efficiency for high-performance optoelectronic devices have impeded the translation of these platforms into practical realization. Here, we report a low-temperature (<150°C) fabricated two-dimensionally pixelized full-color photodetector by using monolithic integration of various-sized colloidal quantum dots (QDs) and amorphous indium-gallium-zinc-oxide semiconductors. By introducing trap-reduced chelating chalcometallate ligands, highly efficient charge carrier transport and photoresistor-free fine-patterning of QD layers were successfully realized, exhibiting extremely high photodetectivity (>4.2 × 1017 Jones) and photoresponsivity (>8.3 × 103 A W-1) in a broad range of wavelengths (365 to 1310 nm). On the basis of these technologies, a wavelength discriminable phototransistor circuit array (>600 phototransistors) was implemented on a skin-like soft platform, which is expected to be a versatile and scalable approach for wide spectral image sensors and human-oriented biological devices.

Facile organic surfactant removal of various dimensionality nanomaterials using low-temperature photochemical treatment.

Deep ultraviolet (DUV)-treatment is an efficient method for the removal of high-energy-barrier polymeric or aliphatic organic ligands from nanomaterials. Regardless of morphology and material, the treatment can be used for nanoparticles, nanowires, and even nanosheets. The high-energy photon irradiation from low-pressure mercury lamps or radio frequency (RF) discharge excimer lamps could enhance the electrical conductivity of various nanomaterial matrixes, such as Ag nanoparticles, Bi2Se3 nanosheets, and Ag nanowires, with the aliphatic alkyl chained ligand (oleylamine; OAm) and polymeric ligand (polyvinyl pyrrolidone; PVP) as surfactants. In particular, Ag nanoparticles (AgNPs) that are DUV-treated with polyvinyl pyrrolidone (PVP) for 90 min (50-60 °C) exhibited a sheet resistance of 0.54 Ω â–¡-1, while thermal-treated AgNP with PVP had a sheet resistance of 7.5 kΩ â–¡-1 at 60 °C. The simple photochemical treatment on various dimensionality nanomaterials will be an efficient sintering method for flexible devices and wearable devices with solution-processed nanomaterials.