Fig. 2: Mechanism for fabricating conformal microstructures of nanomembranes on optical microfibers.

a Schematic diagram illustrating the fabrication process using pre-strained nanomembranes (NMs) and surface tension-assisted assembly. b TEM images showing NMs conformally wrapped on optical MF. Scale bar, 250 nm. c Enlarged view of the red-boxed region in (b), showing the tight wrapping of NMs on the microfiber (MF). Left, high-resolution TEM image sequentially displays the Pd NM, Cr NM, and SiO₂ MF. Scale bar: 20 nm. Right, EDX analysis shows the elemental composition of each layer. d Nanoindentation test of Ti NM conformal on MF, arrow points to the critical load when the scratching depth displays a sudden change, indicating delamination of the NM. The inset in (d) shows the optical image after the nanoindentation test, proving the delamination behavior. Scale bar: 20 μm. e, f The systematic analysis for achieving tight wrapping in experiments by tuning structural parameters. For metal NMs (e) and oxide NMs (f), we change diameters of MFs (D) and the thickness of NMs (t), obtaining regions for tight wrapping (blue regions, experimental data are marked as blue squares) and unconformable wrapping (red regions, experimental data are marked as red symbols). g The mechanism for achieving conformal structures. Pre-strain is introduced into the NM layer to induce self-rolling of the NM, and surface forces from the liquid further enhance the conformal wrapping. The theoretical calculation for metal NMs (h) and oxide NMs (i) tightly wrapping on MFs. For NMs conformal on MFs with smaller diameters, the required additional bending energy is increased. When the adhesion energy (dashed line) cannot support such bending energy, NMs are untightly wrapped on MFs. The square symbols in (h, i) are experimental data with tight wrapping, and the “X” symbols are untight wrapping. The insets in (h, i) show the SEM images for tight and untight wrapping structures, respectively. Scale bar: 20 μm.