Microlattice structures possess properties imparted by the architected microstructure of their constituents (unit cells) and micro/nanofeatures rather than their bulk material properties. Post-processing techniques have revealed intriguing length scale effects, encompassing enhanced behavior or shape morphing of various structures. Although monolithic structures consisting of single unit cells have been successfully fabricated by advanced additive manufacturing techniques, such as multiphoton lithography, innovations towards the tactical architecture of localized failure and design-inherent controllable collapse have been fairly limited. Using as a point of reference the octet truss structure, we designed substitutional unit cells and slip-plane defect-like features inspired by crystalline materials. Through finite element analysis, we investigated how the directional effective stiffness of a material can be augmented and altered in predetermined orientations. Fabricating these structures by multiphoton laser lithography and testing them by in situ scanning electron microscopy-nanoindentation we discovered a remarkable enhancement of the structural integrity, stiffness, and strain energy density, emulating the corollaries of hardening bulk materials. In addition, we observed that these structures demonstrate localized plastic deformation and collapse, distinguishing their mechanical behavior from the conventional layer-by-layer collapse reported in previous studies. The nanofeatures detected in fractographies obtained by helium ion microscopy provided further insight into the collapse mechanisms of the structures. The present design methodology of strategically placed structural features yields architected microstructures with microlattice geometries that can be used to enhance and control the mechanical performance of metamaterial structures.

We demonstrate two patterning techniques based on hydrogen passivation of Ga1-xMnxAs to produce isolated ferromagnetically active regions embedded uniformly in a paramagnetic, insulating host. The first method consists of selective hydrogenation of Ga1-xMnxAs by lithographic masking. Magnetotransport measurements of Hall-bars made in this manner display the characteristic properties of the hole-mediated ferromagnetic phase, which result from good pattern isolation. Arrays of Ga1-xMnxAs dots as small as 250 nm across have been realized by this process. The second process consists of blanket hydrogenation of Ga1-xMnxAs followed by local reactivation using confined low-power pulsed-laser annealing. Conductance imaging reveals local electrical reactivation of micrometer-sized regions that accompanies the restoration of ferromagnetism. The spatial resolution achievable with this method can potentially reach <100 nm by employing near-field laser processing. The high spatial resolution attainable by hydrogenation patterning enables the development of systems with novel functionalities such as lateral spin-injection as well as the exploration of magnetization dynamics in individual and coupled structures made from this novel class of semiconductors. © 2007 Elsevier B.V. All rights reserved.