Metals by Micro‐Scale Additive Manufacturing: Comparison of Microstructure and Mechanical Properties

Abstract

Many emerging applications in microscale engineering rely on the fabrication of 3D architectures in inorganic materials. Small-scale additive manufacturing (AM) aspires to provide flexible and facile access to these geometries. Yet, the synthesis of device-grade inorganic materials is still a key challenge toward the implementation of AM in microfabrication. Here, a comprehensive overview of the microstructural and mechanical properties of metals fabricated by most state-of-the-art AM methods that offer a spatial resolution ≤10 μm is presented. Standardized sets of samples are studied by cross-sectional electron microscopy, nanoindentation, and microcompression. It is shown that current microscale AM techniques synthesize metals with a wide range of microstructures and elastic and plastic properties, including materials of dense and crystalline microstructure with excellent mechanical properties that compare well to those of thin-film nanocrystalline materials. The large variation in materials' performance can be related to the individual microstructure, which in turn is coupled to the various physico-chemical principles exploited by the different printing methods. The study provides practical guidelines for users of small-scale additive methods and establishes a baseline for the future optimization of the properties of printed metallic objects-a significant step toward the potential establishment of AM techniques in microfabrication.

Mechanical Properties of 3D Nanostructures Obtained by Focused Electron/Ion Beam-Induced Deposition: A Review

“…The authors argued that this is the cause for the relatively large elastic moduli comparable in value to Arnold et al's [47] e-beam curing results. It is of note that for the experiments of Reiser et al [49], homogeneous material can be expected (no core-shell pillar structures), as large area deposits in the micrometer range were measured (which necessitated e-beam scanning), in contrast to the beforehand discussed pillar geometries in this section. Summarizing the FEBID Pt-C results presented above (i), the carbon matrix dominates the elastic modulus, values from 0.06× to 2.7× of the platinum modulus were obtained, and (ii) e-beam curing offers a convenient possibility to tune the properties very precisely from compliant (approximately 10 GPa) to stiff (450 GPa) according to the application needs.…”

“…Only few materials have metal contents above 50 at.%: 86 at.% cobalt FEBID material (this work) and 80 at.% tungsten FIBID material [51] being larger than the percolation threshold together with the 95 at.% SiO 2 FIBID sample. The Au-C and Pt-C [49,90] materials have still metal contents of around 50 at.%. These high metal content materials were grouped in Figure 16b.…”

“…It can be understood in a way that EBC will transform the carbonaceous matrix still rich in hydrogen into material with less volatile elements with curing time and increasing stiffness by the formation of sp 2 and sp 3 carbon bonds; see also the ternary phase diagram in Figure 10. The study of Reiser et al [49] used two methods to determine the elastic modulus independently and revealed 60 to 75 GPa for nanoindentations on about 10 × 10 × 0.5 m 3 pads and 1 × 1 × 2 m 3 -sized pillar compression. The currents used were 3.6 nA and 1 nA, respectively, and they accumulate a relatively large dose in the growing deposit volume, which leads to the simultaneous e-beam curing of the growing structure.…”

“…Pt-Carbon, Fe-Carbon, W-Carbon, and Si-Carbon FIBID Materials Investigations were performed on homogeneous material by Reiser et al [49] for Pt-C containing about 40 at.% Pt and 20 at.% Ga (this composition was taken from Friedli et al's Pt-C FIBID experiments [46]). Thus, the total metal content adds to about 60 at.%, which is around the percolation threshold concentration for both metals; see Figure 15.…”

Additive Manufacturing of Sub-Micron to Sub-mm Metal Structures with Hollow AFM Cantilevers

“…As metal, copper is mainly chosen for ec printing because of its coulombic efficiency (minimum faradaic losses due to side reactions) beside its importance for electronic applications. In a recent comprehensive study, the mechanically properties were compared for two benchmark structures produced with most methods mentioned in this introduction [50].…”