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1 Pervasive nanoscale deformation twinning as a catalyst for efficient energy dissipation in a bioceramic armor Ling Li and Christine Ortiz* Department of Materials Science and Engineering, Massachusetts Institute of Technology, MA 02139, USA. * To whom correspondence should be addressed. cortiz@mit.edu Figure S1. Quantification of the mechanical properties of P. placenta in comparison to calcite based on nanoindentation experiments (Berkovich tip). The calculated (a) modulus (E O-P ) and (b) hardness (H O-P ) based on Oliver-Pharr analysis as a function of maximum load (P max ) from 10 µn to 10 mn. Stable E O-P and H O-P are achieved when P max > 2 mn, and the averaged values with P max higher than 2 mn are obtained (E O-P : 71.1 ± 4.2 GPa (P. placenta, n = 241), 73.4 ± 1.7 GPa (calcite, n = 159); H O-P : 3.5 ± 0.3 GPa (P. placenta, n = 241), 2.3 ± 0.1 GPa (calcite, n = 159)). E O-P and H O-P for the two samples are statistically significant through non-parametric Mann-Whitney test (p < 0.05).The increase in E O-P and H O-P with P max below 2 mn might be due to the imperfectness of tip geometry. (c) Averaged indentation curves with maximum loads of 2 and 8 mn (n > 30 for each averaged curves). 1 NATURE MATERIALS 1

2 Figure S2. Quantitative measurement of the fracture patterns for P. placenta and single crystal calcite. The indentation experiments were performed with a conospherical tip (tip radius = ~1 µm; semi-angle = 30 ; maximum load = 10 mn). a, SEM image of a fracture pattern with dimensional parameters labeled: R i, radius of inner indentation crater; R o, radius of entire fracture pattern by fitting it with the smallest-possible circle; C, distance between the centers of inner crater and entire fracture pattern. b, c, Representative SEM images of indentation residues of calcite and P. placenta (Fig. 1d, e). d, e, Quantitative dimensional measurement of the fracture patterns (calcite, n = 24; P. placenta, n = 28). All parameters for the two samples are statistically significant through non-parametric Mann-Whitney test (p < 0.05). Schematic diagrams of the averaged fracture patterns for (f) calcite and (g) P. placenta. The inner and outer circles are based on average values of R i and R o. The square-shaped data points represent the centers of R i for each individual test. L represents the longitudinal direction of the calcitic laths. Figure S3. Quantitative measurement of the permanent deformed depth (h def ) and volume (V def ). The permanently deformed volume is approximated as a cone with the radius of the base R o and the height of h def. The indentation was carried with a conospherical tip (semi-angle = 30 ; tip radius = ~1 µm) with maximum load of 10 mn. 2 2 NATURE MATERIALS

3 SUPPLEMENTARY INFORMATION Figure S4. SEM images showing TEM sample preparation of the indentation residue by FIB. a, An indentation residue before FIB-milling. b, An overall platinum protective layer was deposited first (thickness ~ 0.5 µm); another thick protective platinum layer was then deposited (thickness ~ 1.5 µm). The orientations were chosen either parallel or perpendicular to the longitudinal direction of the laths. c, In-situ pick-up and transfer the slab to a TEM copper grid using the OMNI probe after FIB milling. d, The slab was ion milled step-wisely to final electron transparent. Figure S5. SEM images of indentation residues, demonstrating the excellent capability of damage localization at high loads (conospherical tip; semi-angle = 30 ; tip radius = 2 µm; maximum load = 2.5 N). 3 NATURE MATERIALS 3

4 Figure S6. Light scattering due to the deformation damage. a) Transmission and b) reflection mode optical image of P. placenta after the sample was tested with high load indentation experiment (typical loads >30 N). Notice that in the transmission mode image, the circular dark region surrounding the indentation crater is due to the fact that the original dense micostructure was damaged, most probably due to a large population of interface opening and microcracks. The colored bands at the outer perimeter are due to the light interference of the nanoscopic interface opening (a mineral-airmineral refractive index contrast was generated). Also note their circular feature without any radial cracks. Figure S7. Further evidence of crack deflection within individual building blocks. a, The SEM image of the FIBmilled cross-section of the indentation zone after P. placenta was microindented (conospherical tip; tip radius = 2 µm; semi-angle = 30 ; maximum load = 500 mn). b, High-resolution SEM image of the deformed mineral laths, which shows multiple sites of crack deflection within individual layers (white arrows). 4 4 NATURE MATERIALS

5 SUPPLEMENTARY INFORMATION Figure S8. Formation of large microcracks in single crystal calcite after indentation tests (conospherical tip; tip radius = 1 µm; semi-angle = 30 ; maximum load = 10 mn). a, Bright field TEM image of indentation zone, revealing multiple microcracks and micro-sized fractured pieces (yellow arrows). Inset, top-viewed SEM image of the original indentation residue. The yellow line indicates the location and orientation of the TEM sample prepared through FIB. b, A corresponding dark field TEM image reveals the deformation-induced large-sized misoriented piece which propagates to the bulk surface with a very shallow orientation. Inset, the corresponding SAED pattern with the selected diffraction spot used for the dark field image in b. c, High-magnification bright field TEM image at the tip of the indentation residue. It reveals a vertical crack (yellow arrow) which is brunched with multiple lateral cracks propagating to the bulk surface (white arrows). 5 NATURE MATERIALS 5

6 Figure S9. Deformation twinning in single-crystal calcite observed in the TEM sample prepared parallel to the longitudinal direction (conospherical tip; tip radius = 1 µm; semi-angle = 30 ; maximum load = 10 mn). a, Topviewed SEM image of the original fracture pattern. The yellow line indicates the location and orientation of the TEM sample prepared by FIB. b, Bright field TEM image of the entire cross-section of the deformation residue. The red dotted lines show one-to-one correspondence between the ridges and cracks from the top-viewed SEM image and corresponding twinning boundaries and cracks in the TEM cross-sections. The white arrows indicate the extended dislocation arrays generated from indentation deformation. c, Enlarged TEM image of the deformation twinning as shown in the area in (b). The twinning boundaries are marked by the yellow dashed lines. Matrix and twin regions are labeled by M and T. Note that the matrix was rotated (~ 13 ) from the bulk matrix (Bulk-M) due to fracture (indicated by the white solid lines to the dotted lines). d-f, SAED patterns obtained in regions indicated in (c) (zone axes: [01 0]). Note the mirror symmetry between the twin and matrix region with respect to the twin boundary (TB) of (1 08). Figure S10. Crack deflection by twinning boundaries. a, SEM image of closely-spaced deformation twins in P. placenta. b, Corresponding cross-sectional TEM image of the same region which clearly shows the cracks were deflected multiple times at the twin boundaries. c, Corresponding SAED pattern in (b). d, TEM image showing a crack running across one mineral layer was deflected by the twinning boundaries. 6 6 NATURE MATERIALS

7 SUPPLEMENTARY INFORMATION Figure S11. Deformation confinement by organic interfaces (conospherical tip; tip radius = 1 µm; semi-angle = 30 ; maximum load = 10 mn). (a) Bright-field and (b) corresponding dark-field TEM image of the region close to the tip of the indentation residue. Inset is the SAED pattern with the diffraction spot selected for the dark-field image in (b). Two deformation-induced misoriented blocks of materials underneath the indentation tip (yellow arrows) were stopped by the organic interface. c, High-magnification TEM image showing high density of the dislocation developed in Plate i due to deformation was confined by the organic interface and the mineral layer underneath (Plate ii) was almost free of dislocations. Figure S12. TEM image of P. placenta showing the stretching deformation of organic interfaces where the interface opening are generated due to the deformation twinning in the mineral layers. 7 NATURE MATERIALS 7