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Two-photon stereolithography (TPS) is widely used for the fabrication of various three–dimensional (3D) structures with sub-micron fabrication resolution in a single fabrication process. However, TPS is unsuitable for microstructures with fine-hole patterns. The laser ablation process can be easily drilled, or made holes in various materials. However, in the case of laser ablation, the focal plane of the laser is fixed, which is limited to the processing plane. In this study, a multidirectional ablation process is studied to apply laser ablation to various processing planes of a 3D microstructure fabricated by the TPS process. A 3D hybrid fabrication process with the advantages of both TPS and laser ablation is expected to improve the fabrication efficiency. The 3D hybrid process is proposed based on a single laser source. The microstructure is fabricated using TPS, and the multi-directional ablation process creates a hole in the lateral side of the 3D microstructure. To develop the multidirectional ablation process, the reflecting mirror system should be designed to adaptably rotate the laser focal plane and guide the laser path for the target process plane. Through various examples, we demonstrate the ability of the multi-directional ablation process with various examples. [ABSTRACT FROM AUTHOR]

In this paper, the surface modification of CdSe- and CdZnS-based quantum dots (QDs) with a functional silica shell is reported. Functionalized silica shells are prepared by two routes: either by ligand exchange and a modified Stöber process or by a miniemulsion process with amphiphilic poly(oxyethylene) nonylphenylether also know as Igepal CO-520 (IG) as oligomeric amphiphile and modified silica precursors. The polymerizable groups on the functionalized silica shell allow covalent bonding to a polymer matrix and prevent demixing during polymerization and crosslinking. This allows the homogeneous incorporation of QDs in a crosslinked polymer matrix. This paper furthermore demonstrates that the resulting QDs, which are i) shielded with a proper silica shell and ii) functionalized with crosslinkable groups, can be used in two-photon-initiated polymerization processes in combination with different photoresists to obtain highly luminescent 3D structures. The resulting luminescent structures are attractive candidates for photonics and metamaterials research. [ABSTRACT FROM AUTHOR]

We develop a novel milli-scale mixer (tilted-wings mixing unit, TWM unit) based on the design for additive manufacturing (DfAM). The proposed tilted-wings mixer has basically designed to have three separate wings that split and combine fluids in order to mix together effectively. Its structure is simple for easy fabrication: two major design parameters of angle among three wings and connecting angle between tilted-unit, which are optimized using the computational fluid dynamics (CFD) analysis. From the CFD analysis, we obtain the best-combined mixing module from analyses of various combinations of TWM units for a highly effective mixing ratio. The mixing ratio of three combined units reaches near 100%, which is validated by the experiment and analysis. We believe that the proposed milli-scale mixer can be utilized in diverse chemical continuous mixers and reactors for minimizing of use of chemicals that can pollute the environment. [ABSTRACT FROM AUTHOR]

In additive manufacturing, logical and efficient workflow optimization enables successful production and reduces cost and time. These attempts are essential for preventing fabrication problems from various causes. However, quantitative analysis and integrated management studies of fabrication issues using a digital light processing (DLP) system are insufficient. Therefore, an efficient optimization method is required to apply several materials and extend the application of the DLP system. This study proposes a sequential process optimization (SPO) to manage the initial adhesion, recoating, and exposure energy. The photopolymerization characteristics and viscosity of the photocurable resin were quantitatively analyzed through process conditions such as build plate speed, layer thickness, and exposure time. The ability of the proposed SPO was confirmed by fabricating an evaluation model using a biocompatible resin. Furthermore, the biocompatibility of the developed resin was verified through experiments. The existing DLP process requires several trials and errors in process optimization. Therefore, the fabrication results are different depending on the operator's know-how. The use of the proposed SPO enables a systematic approach for optimizing the process conditions of a DLP system. As a result, the DLP system is expected to be more utilized. [ABSTRACT FROM AUTHOR]

Abstract: Metal nanoparticles exhibit specific electronic, chemical and optical properties due to the thermodynamic size effect, which cannot be observed in bulk materials. Ag NPs show size dependent melting temperature depression phenomena. In this study, the thermal sintering behavior of the self-assembled monolayer protected Ag NPs has been observed using in situ transmission electron microscopy. The thermal characteristics of the Ag NPs have also been examined with a thermogravimetric analysis, a differential scanning calorimetry and a thermal conductivity measurement. These assessments have shown that the melting of the Ag NPs starts at 150°C, which is much lower than the melting temperature of bulk silver (960°C). The measured thermal conductivity of the Ag NPs (0.37W/(mK)) is also lower than that of bulk silver (429W/(mK)). These specific thermal properties of the Ag NPs can be applied to a low-temperature and a high-resolution direct-metal patterning process. [Copyright &y& Elsevier]

Structural coloration is closely related to the progress of innovative optoelectronic applications, but the absence of direct, on‐demand, and rewritable coloration schemes has impeded advances in the relevant area, particularly including the development of customized, reprogrammable optoelectronic devices. To overcome these limitations, a digital laser micropainting technique, based on controlled thin‐film interference, is proposed through direct growth of the absorbing metal oxide layer on a metallic reflector in the solution environment via a laser. A continuous‐wave laser simultaneously performs two functions—a photothermal reaction for site‐selective metal oxide layer growth and in situ real‐time monitoring of its thickness—while the reflection spectrum is tuned in a broad visible spectrum according to the laser fluence. The scalability and controllability of the proposed scheme is verified by laser‐printed painting, while altering the thickness via supplementary irradiation of the identical laser in the homogeneous and heterogeneous solutions facilitates the modification of the original coloration. Finally, the proof‐of‐concept bolometer device verifies that specific wavelength‐dependent photoresponsivity can be assigned, erased, and reassigned by the successive application of the proposed digital laser micropainting technique, which substantiates its potential to offer a new route for reprogrammable optoelectronic applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • The double-step laser scanning method allows fabrication of micro 3D structures with exceptional mechanical performance. • The proposed method improves the mechanical properties of the initial interfacial layer between the structure and the substrate. • The induced strong crosslinking in the polymer prevents swelling and delamination, leading to enhanced mechanical properties. • The proposed method is further validated with large-scale microlens arrays, demonstrating improved process yields. Two-photon lithography (TPL) is a representative fabrication process for micro 3D structures with a sub-micron fabrication resolution. As the TPL process is developed and commercialized, the TPL process requires higher process yield to be a considered reliable manufacturing technique for mass production. However, delamination is one of the main factors that reduce the yield of the TPL process. In this study, a double-step laser scanning method is proposed as a reliable high-yield TPS process to reduce the delamination effect. The method entails a simple process that polymerizes the initial interfacial layer between the structures and substrate twice. The additional laser scanning step induces a strong crosslinking in the polymer, and thereby preventing swelling and delamination. Furthermore, the effectiveness of the method is evaluated with large-scale microlens arrays. Although the process time is slightly increased, the process yield is significantly improved through the use of the double-step laser scanning method. Hence, the double-step laser scanning process can be employed as a reliable additive manufacturing process for various 3D microscale devices, and more importantly, it can be used to increase the manufacturing yield through the reduction of defects caused by surface delamination. [ABSTRACT FROM AUTHOR]

[Display omitted] • The ECO mold with a surface-type conformal cooling channel was designed using CFD analysis. • The ECO mold was additively manufactured via LPBF in practice. • The additively manufactured ECO mold was utilized in the casting production line. • The casting time and carbon emission were reduced by 21% and 0.6 kg of CO 2 , respectively. • The microstructural characteristic and mechanical evaluation of the as-cast product were improved. This study proposes an eco-friendly (ECO) mold that is fabricated using the laser powder bed fusion (LPBF) method, which utilizes a three-dimensional (3D) cooling channel. Unlike previous studies, we designed surface-type conformal cooling channels (CCC) based on the design concept for additive manufacturing, at a constant depth corresponding to the casting part. Pin fins were installed inside the surface-type cooling channels and aligned through numerical analysis to induce the turbulence of the coolant uniformly through the cooling channel while generating less thermal stress during solidification of the as-cast Al-Si alloy-based product, which increased the cooling efficiency of the proposed ECO mold. Moreover, the ECO mold was utilized to cast an automobile piston to demonstrate its feasibility at an industrial level. The results showed that, the casting process decreased significantly from 133 to 105 s per piston (21% reduction) compared to the conventional mold with a single columnar cooling channel. Additionally, the average grain size of the ECO mold decreased from 502 to 398 µm. The ultimate tensile strength and Rockwell hardness increased by 12.5% and 5.5%, respectively. [ABSTRACT FROM AUTHOR]

Digital Laser Micropainting: Digital Laser Micropainting for Reprogrammable Optoelectronic Applications (Adv. Funct. Keywords: hydrothermal growth; laser; reprogrammable optoelectronics; structural coloration; thin-film interference EN hydrothermal growth laser reprogrammable optoelectronics structural coloration thin-film interference 1 1 1 01/06/21 20210104 NES 210104 In article number 2006854, Seung Hwan Ko, Sukjoon Hong, and co-workers propose a digital laser micropainting technique, based on controlled thin-film interference, through direct laser growth of the absorbing metal oxide layer on a metallic reflector. Hydrothermal growth, laser, reprogrammable optoelectronics, structural coloration, thin-film interference. [Extracted from the article]

An artificial blood vessel with a tubular structure was additively manufactured via fused deposition modeling (FDM) starting from a single strand of polyvinyl alcohol (PVA) filament coated with a specific thickness of biocompatible polydimethylsiloxane (PDMS), followed by removal of the inner core via hydrogen peroxide leaching under sonication. In particular, we examined the relationship between the extruded deposition diameter and the filament migration speed/nozzle control speed (referred to as the filament/nozzle transition ratio), which is almost independent of the extruded deposition flow rate due to the weak die-swelling and memory effects of the extruded PVA arising from its intrinsically low viscoelasticity. The chemical stability of the PDMS during sonication in the hydrogen peroxide solution was then determined by spectroscopic techniques. The PDMS displayed no mechanical degradation in the hydrogen peroxide solution, resulting in similar fracture elongation and yield strength to those of the pristine specimen without the leaching treatment. As a further advantage, the inside surface of the PDMS was smooth regardless of the hydrogen peroxide leaching under sonication. The potential application of the as-developed scaffold in soft tissue engineering (particularly that involving vascular tissue regeneration) was demonstrated by the successful transplantation of the artificial blood vessel in a right-hand surgical replica used in a clinical simulation. Unlabelled Image • A single strand of PVA was additively manufactured via FDM. • The PVA was dip-coated with a specific thickness of biocompatible PDMS. • PVA was removed from the PVA/PDMS structure with H 2 O 2 leaching under sonication. • The tubular structure of PDMS exhibits chemical stability and mechanical reliability. • The artificial blood vessel was transplanted into a right-hand surgical replica. [ABSTRACT FROM AUTHOR]