The three-dimensional flow structure inside an exhaust hood model of a low-pressure steam turbine was investigated using a particle image velocimetry (PIV) velocity field measurement technique. The PIV measurements were carried out in several selected planes under design operation conditions with simulated total pressure distribution and axial velocity profile. The mean flow fields revealed a complicated vortical flow structure and the major sources of energy loss. Vortices with different scales were observed inside the exhaust hood: a strong separation vortex (SV) behind the tip of the guide vane, a longitudinal vortex (LV) at the exhaust hood top, a large-scale passage vortex (PV) evolving throughout the flow path, and an end-wall vortex (EWV) in the region adjacent to the front end-wall. Both the SV and the large-scale PV seemed to consume large amounts of kinetic energy and reduce the pressure recovery ability. The results indicate that the steam guide vane and the bearing cone should be carefully designed so as to control the vortical flow structure inside the exhaust hood.

Polymer self‐assembly commonly suffers from retarded equilibrium structure formation caused by the large diffusion barrier of long‐chain molecules. In particular, the defect annihilation kinetics of high‐χ block copolymers (BCPs) are generally sluggish because of a slow inter‐block chain diffusion process from strong inter‐block segregation. Therefore, long‐range order of high‐χ BCPs still hard to be obtained by conventional approaches. Here, we introduce near‐infrared laser photothermal treatment to effectively promote high‐χ BCP self‐assembly and demonstrating highly aligned nanoscale patterned structures on silicon substrates. Adequate molecular weight selection of high‐χ PS‐b‐P2VP system enables one‐time laser hot‐zone annealing, resulting in highly ordered nanodomains along laser writing direction. Facile sub‐sequential metal ion loading to P2VP cylinders enables the formation of highly aligned metal nanowires. Moreover, a commonly used silicon substrate without a photoabsorbing layer is employed as a photo‐thermal substrate, demonstrating that the laser writing process is compatible with conventional semiconductor processes.

Although various two-dimensional (2D) materials hold great promise in next generation electronic devices, there are many challenges to overcome to be used in practical applications. One of them is the substrate effect, which directly affects the device performance. The large interfacial area and interaction between 2D materials and substrate significantly deteriorate the device performance. Several top-down approaches have been suggested to solve the problem. Unfortunately, however, they have some drawbacks such as a complicated fabrication process, a high production cost, or a poor mechanical property. Here, we suggest the partially suspended 2D materials-based field-effect transistors (FETs) by introducing block copolymer (BCP) lithography to fabricate the substrate effect-free 2D electronic devices. A wide range of nanometer size holes (diameter = 31~43 nm) is successfully realized with a BCP self-assembly nanopatterning process. With this approach, the interaction mechanism between active 2D materials and substrate is elucidated by precisely measuring the device performance at varied feature size. Our strategy can be widely applied to fabricate 2D materials-based high performance electronic, optoelectronic, and energy devices using a versatile self-assembly nanopatterning process.

Metallic nanoparticle ensemble, with narrow inter-particle distance, is a useful element for diverse optical devices due to highly enhanced electric field intensity at the gap. Self-assembly of block copolymer (BCP) can provide the versatile solution to fabricate precise nanostructures, but this methodology has the intrinsic limitation to realize optically coupled metallic multimer geometry with narrow inter-particle distance. This is because BCP-based nanotemplate possesses a minimum size limit for interparticle distance imposed by its thermodynamic restriction. Herein, we investigate the facile formation of metallic multimer with scalability and area-selectivity through the collapse of self-assembled BCP nanopattern. The capillary-force-induced collapse phenomenon enables a spatial transformation of lateral regular ordering in metallic nanoparticle array and enhances electric field intensity. The fabrication of this metallic nanoparticle ensemble from BCP lithography is successfully utilized for surface enhanced Raman scattering (SERS). The enhancement factor of metal nanoparticle multimer is calculated as ~6.74 × 105 at 1000 cm−1, 2.04 × 106 at 1022 cm−1, and 6.11 × 106 at 1580 cm−1, respectively.

The development of devices that can be mechanically deformed in geometrical layouts, such as flexible/stretchable devices, is important for various applications. Conventional flexible/stretchable devices have been demonstrated using two-dimensional (2D) geometry, resulting in dimensional constraints on device operations and functionality limitations. Accordingly, expanding the dimensions in which such devices can operate and acquiring unique functionality that is difficult to implement in 2D planar structures remain challenging. As a solution, the development of a flexible/stretchable device embedding a three-dimensional (3D) structure fabricated through the precise control of a 2D structure or direct construction has been attracting significant attention. Because of a significant amount of effort, several 3D material systems with distinctive engineering properties, including electrical, optical, thermal, and mechanical properties, which are difficult to occur in nature or to obtain in usual 2D material systems, have been demonstrated. Furthermore, 3D advanced material systems with flexibility and stretchability can provide additional options for developing devices with various form factors. In this review, novel fabrication methods and unprecedented physical properties of flexible/stretchable 3D material systems are reviewed through multiple application cases. In addition, we summarized the latest advances and trends in innovative applications implemented through the introduction of advanced 3D systems in various fields, including microelectromechanical systems, optoelectronics, energy devices, biomedical devices, sensors, actuators, metamaterials, and microfluidic systems.