Three‐Dimensional Fabrication at Small Size Scales

Despite the fact that we live in a 3D world and macroscale engineering is 3D, conventional submillimeter‐scale engineering is inherently 2D. New fabrication and patterning strategies are needed to enable truly 3D‐engineered structures at small size scales. Here, strategies that have been developed over the past two decades that seek to enable such millimeter to nanoscale 3D fabrication and patterning are reviewed. A focus is the strategy of self‐assembly, specifically in a biologically inspired, more deterministic form, known as self‐folding. Self‐folding methods can leverage the strengths of lithography to enable the construction of precisely patterned 3D structures and “smart” components. This self‐assembly approach is compared with other 3D fabrication paradigms, and its advantages and disadvantages are discussed.

     

Three‐Dimensional Shape Reconstruction System Based on Fiber‐Optic Interference Fringe Imaging

In this article, we describe a three‐dimensional shape reconstruction system based on the Mach–Zehnder interferometer structure and Young's double pinhole interference principle, while utilizing Fresnel reflection on fiber end face and interference at the fourth port of 3‐dB coupler to achieve closed‐loop precise control of fringe phase. A root‐mean‐square phase stability of 4 mrad is measured with the system. The shape of the object is determined by analyzing the fringe pattern. A new algorithm called rotating rectangular window autoselection is used as the band‐pass filter. The measuring time of the whole system is less than 200 ms, and the error of system is 0.27 mm. Meanwhile, the overall complexity of the measuring algorithm is O(n log n).     

A Comparison of Various Patterns of Three‐Dimensional Strain Rosettes

Abstract: The strain tensor, principal strains and precision of the estimates of these values are derived for a range of different layouts of three‐dimensional strain rosettes. These values are based on the Monte Carlo technique applied to experimental work which was carried out on transducers tested in different laboratories. The estimates of precision are determined theoretically and compared with results based on experimental findings. A new design of a miniature tri‐rectangular tetrahedral rosette was manufactured and tested. Results suggest that this transducer does not perform as well as the rectangular patterns.     

Controlled Synthesis of One‐Dimensional Inorganic Nanostructures Using Pre‐Existing One‐Dimensional Nanostructures as Templates

Template‐directed strategy has become one of the most popular methods for the fabrication of one‐dimensional (1D) nanostructures with uniform size and controllable physical dimensions in recent years. This Review article describes the recent progress in the synthesis of 1D inorganic nanostructures by using suitable templates. A brief survey on the templating method based on the organic templates and porous membrane is firstly given. Then, the article is focused on recent emerging synthetic strategies by templating against the pre‐existing 1D nanostructures using different physical and chemical transformation techniques, including epitaxial growth, nonepitaxial growth, direct chemical transformation, solid‐state interfacial diffusion reaction, and so on. The important reactivity role of the 1D nanostructures will be emphasized in such transformation process. Finally, we conclude this paper with some perspectives and outlook on this research topic.     

Band Engineering for Novel Two‐Dimensional Atomic Layers

The discovery of graphene has sparked much interest in science and lead to the development of an ample variety of novel two‐dimensional (2D) materials. With increasing research interest in the field of 2D materials in recent years, the researchers have shifted their focus from the synthesis to the modification of 2D materials, emphasizing their electronic structures. In this review, the possibilities of altering the band structures are discussed via three different approches: (1) alloying 2D materials, so called ternary 2D materials, such as hexagonal carbonized boron nitrides (h‐BCN) and transition metal dichalcogenides (TMDs) ternary materials; (2) stacking 2D materials vertically, which results in 2D heterostructures named van der Waals (vdW) solids (using hexagonal boron nitrides (h‐BN)/graphene and TMDs stacking as examples), and growing lateral TMDs heterostructrues; (3) controlling the thickness of 2D materials, that is, the number of layers. The electronic properties of some 2D materials are very sensitive to the thickness, such as in TMDs and black phosphorus (BP). The variations of band structures and the resulting physical properties are systematically discussed.     

Two‐Dimensional Materials for Halide Perovskite‐Based Optoelectronic Devices

Halide perovskites have high light absorption coefficients, long charge carrier diffusion lengths, intense photoluminescence, and slow rates of non‐radiative charge recombination. Thus, they are attractive photoactive materials for developing high‐performance optoelectronic devices. These devices are also cheap and easy to be fabricated. To realize the optimal performances of halide perovskite‐based optoelectronic devices (HPODs), perovskite photoactive layers should work effectively with other functional materials such as electrodes, interfacial layers and encapsulating films. Conventional two‐dimensional (2D) materials are promising candidates for this purpose because of their unique structures and/or interesting optoelectronic properties. Here, we comprehensively summarize the recent advancements in the applications of conventional 2D materials for halide perovskite‐based photodetectors, solar cells and light‐emitting diodes. The examples of these 2D materials are graphene and its derivatives, mono‐ and few‐layer transition metal dichalcogenides (TMDs), graphdiyne and metal nanosheets, etc. The research related to 2D nanostructured perovskites and 2D Ruddlesden–Popper perovskites as efficient and stable photoactive layers is also outlined. The syntheses, functions and working mechanisms of relevant 2D materials are introduced, and the challenges to achieving practical applications of HPODs using 2D materials are also discussed.     

One‐Dimensional Nano‐Interconnection Formation

Interconnection of one‐dimensional nanomaterials such as nanowires and carbon nanotubes with other parts or components is crucial for nanodevices to realize electrical contacts and mechanical fixings. Interconnection has been being gradually paid great attention since it is as significant as nanomaterials properties, and determines nanodevices performance in some cases. This paper provides an overview of recent progress on techniques that are commonly used for one‐dimensional interconnection formation. In this review, these techniques could be categorized into two different types: two‐step and one‐step methods according to their established process. The two‐step method is constituted by assembly and pinning processes, while the one‐step method is a direct formation process of nano‐interconnections. In both methods, the electrodeposition approach is illustrated in detail, and its potential mechanism is emphasized.