Calculated mechanical properties of structures illustrated in Fig. 2(a) and (b). L is the side length, γ is the atomic fraction of BN, Y is the Young's modulus, σ is the tensile strength, and ε is the ultimate strain.

MD simulations	L (nm)	γ	Armchair	Zigzag	Armchair	Zigzag
			Y (GPa)	Y (GPa)	σ (GPa) [ε]	σ (GPa) [ε]
L 10nm-B376N376	10	0.191	908.31	901.14	96.8 [0.14]	100.1 [0.15]
L 20nm-B1503N1503	20	0.191	907.49	897.72	101.0 [0.14]	100.7 [0.14]
L 30nm-B3383N3383	30	0.194	906.02	896.84	90.9 [0.12]	88.4 [0.12]
L 40nm-B376N376	40	0.012	964.86	956.57	97.2 [0.14]	98.4 [0.14]
L 40nm-B1504N1504	40	0.049	951.71	943.15	96.3 [0.14]	95.5 [0.13]
L 40nm-B3383N3383	40	0.109	932.84	922.16	91.1 [0.12]	88.1 [0.11]
L 40nm-B6013N6013	40	0.194	908.38	897.88	96.4 [0.13]	89.6 [0.12]
L 40nm-B9404N9404	40	0.304	876.81	866.17	88.3 [0.12]	97.6 [0.12]
L 50nm-B9404N9404	50	0.195	904.89	898.38	87.9 [0.11]	92.4 [0.12]
L 100nm-B37588N37588	100	0.195	907.38	897.84	93.4 [0.13]	101.4 [0.15]