Fig. 1. Optical and thermal properties of hybrid Sb2Te3 plate–silica microfiber systems. (a) Sketch of a Sb2Te3 plate on top of a suspended microfiber. Zoomed inset: a Sb2Te3 plate is modeled as a dielectric bulk slab sandwiched between two metallic thin layers. (b) Micro-Raman spectrum of a Sb2Te3 plate measured by a 532-nm pumping laser. Inset: confocal laser scanning microscopy image of a mechanical-exfoliated Sb2Te3 plate on a SiO2/Si substrate. (c) Simulated absorption spectrum of a hybrid Sb2Te3 plate–microfiber system under incidence of fundamental HE11⊥ mode of the microfiber. (d) Simulated modal profiles of the HE11⊥ mode without (left panel) and with (right panel) the Sb2Te3 plate. The arrows specify the directions of modal electric fields. (e) Simulated characteristic temperature distributions in the central x−y plane of Sb2Te3 and gold plates at t=10, 100, 1000 ns when heated by pulsed light. In (c)–(e), the microfiber has a radius of 2μm and a refractive index of 1.45. The Sb2Te3 plate has a width of 3μm, a length of 12μm, and a thickness of 300 nm, and its surface and bulk refractive indices are adopted from Ref. 29. The Au plate has the same geometrical parameters as the Sb2Te3 plate. The details of the thermal simulations in (e) are given in Note S1 in the Supplementary Material.

Fig. 2. Experimental observations of a Sb2Te3 plate moving spirally around a microfiber. (a) Sketch of experimental setup implemented in a vacuum chamber. VOA, variable optical attenuator; FC, fiber coupler; MF, microfiber; and PM, power meter. (b) Temporal sequencing SEM images of a Sb2Te3 plate moving around a microfiber. The microfiber has a diameter of 5μm. The supercontinuum laser pulses have 2.6-ns duration, 230-Hz repetition rate, 0.1-mW average power, and wavelength range from 450 to 2400 nm. Scale bar: 5μm (Video 1, MP4, 4.34 MB [URL: https://doi.org/10.1117/1.APN.1.2.026005.s1). (c) Fourier transformation of the detected areas of the Sb2Te3 plate during the motion. The spectral peak specifies the azimuthal rotation frequency of the plate. The Y axis is linear and the shaded region here is to better show its rotation frequency. (d) Translation displacement of the Sb2Te3 plate along the axial direction of the microfiber as a function of time.

Fig. 3. Manipulating motion speed of Sb2Te3 plates by tuning repetition rates of laser pulses. Note that the integrated single-pulse energy remains the same as the repetition rate changes. Scale bars: 30μm (Video 2, MP4, 19.6 MB [URL: https://doi.org/10.1117/1.APN.1.2.026005.s2]).

Fig. 4. Stable motion of a Sb2Te3 plate degenerates into unstable motion by thermal effects. Sequencing SEM images show (a) stable and (b) unstable motions with pulse repetition rates of 2.2 kHz and 4.8 kHz, respectively. Scale bars: 20μm (Video 3, MP4, 9.73 MB [URL: https://doi.org/10.1117/1.APN.1.2.026005.s3]).

Fig. 5. SEM images of a Sb2Te3 plate (a) before and (b) after motion. The red and white dashed circles in (b) mark formed microbumps and a myriad of small spheres, respectively.

Fig. 6. Liquid-like motion of Sb2Te3 plates on microfibers. (a) Time sequencing SEM images of a Sb2Te3 plate showing liquid-like motion. The used supercontinuum laser pulse has 5.4-mW average power and 11.5-kHz repetition rate. A large microbump contacting with the microfiber and a small one is marked with a rectangle and circle, respectively (Video 4, MP4, 895 kB [URL: https://doi.org/10.1117/1.APN.1.2.026005.s4]). (b) Zoomed-in microbump [corresponding to the marked rectangle in (a)] showing asymmetric contact angles. Scale bar: 1μm. (c) Horizontal and (d) vertical displacements of the point A in the Sb2Te3 plate as functions of time. The point A is labeled in (a). (e) Two exemplified samples show that horizontal motion direction of the plates points from a small microbump close to the microfiber (marked with circle) to a large one contacting with the microfiber (marked with rectangle). Scale bars: 1μm (Video 5, MP4, 7.90 MB [URL: https://doi.org/10.1117/1.APN.1.2.026005.s5]).