4D Printing Pre-Strained Structures for Fast Thermal Actuation

Four-dimensional (4D) printing is an emerging technology by adding the dimension of time-dependent reconfiguration into 3D printing. It enables the 3D printed structure to change the shape, property, or functionality under external stimuli such as temperature, magnetic field, and light, etc. Among the existing 4D printed structures, thermal responsive structures are widely used for their easy operation. However, the slow actuation of the thermal responsive structures impedes the applications like soft robotics. In the current work, a pre-strained strategy is proposed to accelerate the actuation of thermal responsive structures. A 4D printing platform that can apply strain during the printing process is constructed to fabricate the pre-strained structures under the aid of in-situ tensile of the printing base. A bilayer structure with one pre-strained layer and the other non-pre-strained layer is integrally printed. Through experiments and the finite element analysis, it is demonstrated that the aspect ratio has little effect on the deformation of the bilayer structure, whereas the pre-strain plays a key role in the deformation and also greatly accelerates the actuation of the bilayer structure. Based on the 4D printed pre-strained bilayer structure, an energy-free gripper is fabricated and a fully soft crawler is printed to achieve a high running speed.

InAs/InAsSb Type-II Strained-Layer Superlattice Infrared Photodetectors

The InAs/InAsSb (Gallium-free) type-II strained-layer superlattice (T2SLS) has emerged in the last decade as a viable infrared detector material with a continuously adjustable band gap capable of accommodating detector cutoff wavelengths ranging from 4 to 15 µm and beyond. When coupled with the unipolar barrier infrared detector architecture, the InAs/InAsSb T2SLS mid-wavelength infrared (MWIR) focal plane array (FPA) has demonstrated a significantly higher operating temperature than InSb FPA, a major incumbent technology. In this brief review paper, we describe the emergence of the InAs/InAsSb T2SLS infrared photodetector technology, point out its advantages and disadvantages, and survey its recent development.

Stress and strain effects

This chapter extends this book’s discussion of bandstructure, band discontinuities and transport—much of the text up to this point—to a manipulation of them through stress and strain. Semiconductors can be strained through a variety of techniques, with strained growth leading to a strained layer, and pattern definition leading to local strained region, being the most common. Strain changes bandstructures and interface bandedge energies, distorts and warps bands, removes degeneracies, affects scattering and thus changes a variety of properties. Following a continuum description of stress-strain relationships, effects of stress—biaxial, hydrostatic and uniaxial—are analyzed for bandstructure and transport in electron bands, light-hole bands, heavy-hole bands and split-off bands in group IV and group III-V semiconductors. Transport effects can be particularly strong in quantum-confined conditions, where changes in density of states can be significant, along with other bandstructure and scattering changes.