Dektak 150 surface profiler

By using a D8‐tools Bragg‐Brentano diffractometer with a Cu‐Kα line (λ = 1.54056 Å), X‐ray diffraction (XRD) in the θ–2θ mode was conducted and the structural properties (such as interplanar spacing, crystal orientation, and grain size) of NbB₂ were measured. The microstructure was obtained by HRTEM using a field‐emission JEOL 2010F microscope operated at 200 kV; the sheet specimen for the HRTEM measurement was prepared by mechanically scratching the NbB₂ surface with a clean stainless‐steel blade. Analyses of composition and chemical states were carried out via PerkinElmer PHI‐5702 XPS; before measurement, 15 min Ar⁺ etching (1 keV etching energy) was carried out to remove any surface contaminants. Subsequently, the sectional measurements of NbB₂ were conducted via SU 8010 scanning electron microscope (SEM) to explore the film growth condition. The corresponding surface morphology and root‐mean‐square roughness (R_q) were obtained from using an atomic force microscope (AFM, Dimension Icon, Veeco Instruments, Bruker, Germany). The thickness of film was measured by Veeco Dektak 150 surface profiler. In addition, to determine the hardness and elasticity modulus of NbB₂, nanoindentation measurement was performed with a penetration depth of 500 nm by MTS Nanoindenter XP with a 3‐side pyramidal Berkovich‐type diamond indenter.

Silicon masters were made from 2-inch silicon wafers (Siegert Wafer, Germany) using photo-lithography with an SU8-2025 photoresist (Micro resist Technology) with photomasks (Zitzmann GmbH, 64.000 dpi) designed with AutoCAD. Master wafers were produced in a clean room following manufacturer’s instructions for the desired resist thickness which was measured by a profilometer (Dektak 150 surface profiler, Veeco Instruments). Microfluidic devices were then produced using PDMS soft lithogrpahy. 12 g of PDMS (Sylgard 184, Dow Corning), mixed thoroughly with 1.2 g of its curing agent was poured on a silicon master wrapped in aluminium fold, degassed for 30 min and baked for 1 h at 80°C. Cured PDMS devices were carefully peeled from the master, trimmed with a razor blade and inlet and outlet holes were punched into each device with a biopsy puncher. Glass slides were cleaned thoroughly with 2% Hellmanex III (Hellma) and distilled water then dried for 30 min at 80°C. PDMS devices and glass slides were exposed to O₂ plasma (1 min, 20 sccm, 100 W) bonded together and baked for 1 h at 80°C.

TiO₂ microspheres were prepared using a previously reported solvent extraction/evaporation method [43 (link)]. Firstly, titanium butoxide (1.0 mL, Sigma #244112) was dissolved in ethanol (40 mL), and the resulting solution stirred for 3 min. After this time, the solution was incubated at room temperature for 3 h. The resulting TiO₂ microspheres were then collected by centrifugation at 8000 rpm for 5 min and washed three times with ethanol (Guangzhou Chemical Reagent Co.) and ultrapure water (18.2 MΩ cm), prior to drying in air at room temperature. The TiO₂ microspheres were then annealed at 400 °C for 2 h to obtain anatase TiO₂ microspheres (1.0 μm mean diameter), which were then employed as base particles for the TiO₂–Au light-driven Janus micromotors. After dispersion of the TiO₂ particles (1.0 mg) in ethanol (2.0 mL), the resulting suspension was dropped onto glass slides and dried uniformly at ambient temperature to give particle monolayers. These particles were then partially covered with a thin gold layer by 3 cycles of 60 s ion sputtering (Q150T Turbo-pumped ES sputter coater/carbon coater, Quorum). The resulting metal layer thickness is 40 nm, as measured by a Dektak 150 Surface Profiler (Veeco). Finally, the desired TiO₂–Au Janus micromotors were obtained following sonication of the glass slide in deionized water for 5 s.