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2021 Vol. 3, No. 3

Research progress on preparation technology of oxide dispersion strengthened steel for nuclear energy
Jianqiang Wang, Sheng Liu, Bin Xu, Jianyang Zhang, Mingyue Sun, Dianzhong Li
2021, 3(3) doi: 10.1088/2631-7990/abff1a

Nuclear energy is a low-carbon, safe, efficient, and sustainable clean energy. The new generation of nuclear energy systems operate in harsher environments under higher working temperatures and irradiation doses, while traditional nuclear power materials cannot meet the requirements. The development of high-performance nuclear power materials is a key factor for promoting the development of nuclear energy. Oxide dispersion strengthened (ODS) steel contains a high number density of dispersed nano-oxides and defect sinks and exhibits excellent high temperature creep performance and irradiation swelling resistance. Therefore, ODS steel has been considered as one of the most promising candidate materials for fourth-generation nuclear fission reactor cladding tubes and nuclear fusion reactor blankets. The preparation process significantly influences microstructure of ODS steel. This paper reviews the development and perspective of several preparation processes of ODS steel, including the powder metallurgy process, improved powder metallurgy process, liquid metal forming process, hybrid process, and additive forging. This paper also summarizes and analyzes the relationship between microstructures and the preparation process. After comprehensive consideration, the powder metallurgy process is still the best preparation process for ODS steel. Combining the advantages and disadvantages of the above preparation processes, the trend applied additive forging for extreme manufacturing of large ODS steel components is discussed with the goal of providing a reference for the application and development of ODS steel in nuclear energy.

Sub-10 nm fabrication: methods and applications
Yiqin Chen, Zhiwen Shu, Shi Zhang, Pei Zeng, Huikang Liang, Mengjie Zheng, Huigao Duan
2021, 3(3) doi: 10.1088/2631-7990/ac087c

Reliable fabrication of micro/nanostructures with sub-10 nm features is of great significance for advancing nanoscience and nanotechnology. While the capability of current complementary metal-oxide semiconductor (CMOS) chip manufacturing can produce structures on the sub-10 nm scale, many emerging applications, such as nano-optics, biosensing, and quantum devices, also require ultrasmall features down to single digital nanometers. In these emerging applications, CMOS-based manufacturing methods are currently not feasible or appropriate due to the considerations of usage cost, material compatibility, and exotic features. Therefore, several specific methods have been developed in the past decades for different applications. In this review, we attempt to give a systematic summary on sub-10 nm fabrication methods and their related applications. In the first and second parts, we give a brief introduction of the background of this research topic and explain why sub-10 nm fabrication is interesting from both scientific and technological perspectives. In the third part, we comprehensively summarize the fabrication methods and classify them into three main approaches, including lithographic, mechanics-enabled, and post-trimming processes. The fourth part discusses the applications of these processes in quantum devices, nano-optics, and high-performance sensing. Finally, a perspective is given to discuss the challenges and opportunities associated with this research topic.

Investigation of melt-growth alumina/aluminum titanate composite ceramics prepared by directed energy deposition
Yunfei Huang, Dongjiang Wu, Dake Zhao, Fangyong Niu, Guangyi Ma
2021, 3(3) doi: 10.1088/2631-7990/abf71a

Al2O3/Al6Ti2O13 composite ceramics with low thermal expansion properties are promising for the rapid preparation of large-scale and complex components by directed energy deposition-laser based (DED-LB) technology. However, the wider application of DED-LB technology is limited due to the inadequate understanding of process conditions. The shaping quality, microstructure, and mechanical properties of Al2O3/Al6Ti2O13 (6 mol% TiO2) composite ceramics were systematically investigated as a function of energy input in an extensive process window. On this basis, the formation mechanism of solidification defects and the evolution process of microstructure were revealed, and the optimized process parameters were determined. Results show that high energy input improves the fluidity of the molten pool and promotes the uniform distribution and full growth of constituent phases, thus, facilitating the elimination of solidification defects, such as pores and strip gaps. In addition, the microstructure size is strongly dependent on the energy input, increasing when the energy input increases. Moreover, the morphology of the α-Al2O3 phase gradually transforms from cellular into cellular dendrite with increasing energy input due to changing solidification conditions. Under the comprehensive influence of solidification defects and microstructure size, the fracture toughness and flexural strength of Al2O3/Al6Ti2O13 composite ceramics present a parabolic law behavior as the energy input increases. Optimal shaping quality and excellent mechanical properties are achieved at an energy input range of 0.36-0.54 W*min2 g-1 mm-1. Within this process window, the average microhardness, fracture toughness, and flexural strength of Al2O3/Al6Ti2O13 composite ceramics are up to 1640 Hv, 3.87 MPa m1/2, and 227 MPa, respectively. This study provides practical guidance for determining the process parameters of DED-LB of melt growth Al2O3/Al6Ti2O13 composite ceramics.

Study of machining indentations over the entire surface of a target ball using the force modulation approach
Yuzhang Wang, Yanquan Geng, Guo Li, Jiqiang Wang, Zhuo Fang, Yongda Yan
2021, 3(3) doi: 10.1088/2631-7990/abff19

A modified five-axis cutting system using a force control cutting strategy was to machine indentations in different annuli on the entire surface of a target ball. The relationship between the cutting depths and the applied load as well as the microsphere rotation speed were studied experimentally to reveal the micromachining mechanism. In particular, aligning the rotating center of the high precision spindle with the microsphere center is essential for guaranteeing the machining accuracy of indentations. The distance between adjacent indentations on the same annulus and the vertical distance between adjacent annuli were determined by the rotating speed of the micro-ball and the controllable movement of the high-precision stage, respectively. In order to verify the feasibility and effect of the proposed cutting strategy, indentations with constant and expected depths were conducted on the entire surface of a hollow thin-walled micro-ball with a diameter of 1 mm. The results imply that this machining methodology has the potential to provide the target ball with desired modulated defects for simulating the inertial confinement fusion implosion experiment.

A thermal actuated switchable dry adhesive with high reversibility for transfer printing
Shun Zhang, Hongyu Luo, Suhao Wang, Zhou Chen, Shuang Nie, Changying Liu, Jizhou Song
2021, 3(3) doi: 10.1088/2631-7990/abff69

Transfer printing based on switchable adhesive that heterogeneously integrates materials is essential to develop novel electronic systems, such as flexible electronics and micro LED displays. Here, we report a robust design of a thermal actuated switchable dry adhesive, which features a stiff sphere embedded in a thermally responsive shape memory polymer (SMP) substrate and encapsulated by an elastomeric membrane. This construct bypasses the unfavorable micro- and nano-fabrication processes and yields an adhesion switchability of over 1000 by combining the peel-rate dependent effect of the elastomeric membrane and the thermal actuation of the sub-surface embedded stiff sphere. Experimental and numerical studies reveal the underlying thermal actuated mechanism and provide insights into the design and operation of the switchable adhesive. Demonstrations of this concept in stamps for transfer printing of fragile objects, such as silicon wafers, silicon chips, and inorganic micro-LED chips, onto challenging non-adhesive surfaces illustrate its potential in heterogeneous material integration applications, such as flexible electronics manufacturing and deterministic assembly.

Achieving a sub-10 nm nanopore array in silicon by metal-assisted chemical etching and machine learning
Yun Chen, Yanhui Chen, Junyu Long, Dachuang Shi, Xin Chen, Maoxiang Hou, Jian Gao, Huilong Liu, Yunbo He, Bi Fan, Ching-Ping Wong, Ni Zhao
2021, 3(3) doi: 10.1088/2631-7990/abff6a

Solid-state nanopores with controllable pore size and morphology have huge application potential. However, it has been very challenging to process sub-10 nm silicon nanopore arrays with high efficiency and high quality at low cost. In this study, a method combining metal-assisted chemical etching and machine learning is proposed to fabricate sub-10 nm nanopore arrays on silicon wafers with various dopant types and concentrations. Through a SVM algorithm, the relationship between the nanopore structures and the fabrication conditions, including the etching solution, etching time, dopant type, and concentration, was modeled and experimentally verified. Based on this, a processing parameter window for generating regular nanopore arrays on silicon wafers with variable doping types and concentrations was obtained. The proposed machine-learning-assisted etching method will provide a feasible and economical way to process high-quality silicon nanopores, nanostructures, and devices.

Precision integration of grating-based polarizers onto focal plane arrays of near-infrared photovoltaic detectors for enhanced contrast polarimetric imaging
Bo Feng, Yifang Chen, Duo Sun, Zongyao Yang, Bo Yang, Xue Li, Tao Li
2021, 3(3) doi: 10.1088/2631-7990/abf5c8

Polarimetric imaging enhances the ability to distinguish objects from a bright background by detecting their particular polarization status, which offers another degree of freedom in infrared remote sensing. However, to scale up by monolithically integrating grating-based polarizers onto a focal plane array (FPA) of infrared detectors, fundamental technical obstacles must be overcome, including reductions of the extinction ratio by the misalignment between the polarizer and the detector, grating line width fluctuations, the line edge roughness, etc. This paper reports the authors’ latest achievements in overcoming those problems by solving key technical issues regarding the integration of large-scale polarizers onto the chips of FPAs with individual indium gallium arsenide/indium phosphide (InGaAs/InP) sensors as the basic building blocks. Polarimetric and photovoltaic chips with divisions of the focal plane of 540 × 4 pixels and 320 × 256 superpixels have been successfully manufactured. Polarimetric imaging with enhanced contrast has been demonstrated. The progress made in this work has opened up a broad avenue toward industrialization of high quality polarimetric imaging in infrared wavelengths.

Rapid subsurface damage detection of SiC using inductivity coupled plasma
Yi Zhang, Linfeng Zhang, Keyu Chen, Dianzi Liu, Dong Lu, Hui Deng
2021, 3(3) doi: 10.1088/2631-7990/abff34

This paper proposes a method for the rapid detection of subsurface damage (SSD) of SiC using atmospheric inductivity coupled plasma. As a plasma etching method operated at ambient pressure with no bias voltage, this method does not introduce any new SSD to the substrate. Plasma diagnosis and simulation are used to optimize the detection operation. Assisted by an SiC cover, a taper can be etched on the substrate with a high material removal rate. Confocal laser scanning microscopy and scanning electron microscope are used to analyze the etching results, and scanning transmission electron microscope (STEM) is adopted to confirm the accuracy of this method. The STEM result also indicates that etching does not introduce any SSD, and the thoroughly etched surface is a perfectly single crystal. A rapid SSD screening ability is also demonstrated, showing that this method is a promising approach for the rapid detection of SSD.