Alpha 300a

The MoS₂ films were wet-transferred onto a quartz substrate by etching away the SiO₂ in a potassium hydroxide solution for subsequent UV-visible spectral measurements on a UV-visible-infrared spectrometer (PerkinElmer, Lambda750). Raman and PL spectra were measured on a micro-Raman system (Horiba Jobin Yvon, LabRAM HR 800) with a 514 nm excitation laser. The Raman and PL images were obtained with a confocal micro-Raman system (WITec, Alpha 300a) with a 532 nm laser. The spatial resolution is approximately 250 nm with a focused laser by a 100× objective lens. The time-resolved PL decay transients were measured with a transient state fluorescence spectrometer (HORIBA Jobin Yvon, FL-TCSPC). Chemical composition analysis was performed using XPS (KRATOS Analytical, AXIS Ultra DLD). The surface morphology of the samples was examined by SEM (FEI, Quanta 200FEG) and AFM (Bruker, Dimension Icon). The microstructures of MoS₂ and GQDs were investigated using HRTEM (FEI, Tecnai G2 F20). For the preparation of the TEM samples, the MoS₂ film was also wet-transferred onto TEM grids.

The topographic and lateral friction signals of the hair surface were measured with an AFM (Witec alpha300A) in contact mode. The hair was placed horizontally, with ratcheted cuticles being perpendicular to the scanning directions. A 25 × 25 µm² measuring area was meshed into 512 scanning lines, for which the cantilever scanned in both forward and backward directions (1 second per line). The topographic profiles were determined by the tip displacements in the vertical direction. The profile images showed consistency between forward and backward scanning directions, indicating the accuracy of topological measurement. During the scanning, any encountered friction would cause a lateral deflection of the tip and torsional deformation of the cantilever, and a feedback voltage was automatically applied to the piezoelectric cantilever to compensate such deformation. Hence, such applied voltage signal was proportional to the friction, serving as a quantitative probe for the lateral friction between the tip and hair surface.

The morphology, crystallinity and composition of three Si-NCs/ZnO-NWs hybrid structures and the pristine ZnO NW sample were characterized using micro-Raman spectroscopy (Alpha300A, Witec, Ulm, Germany), X-ray diffraction (XRD, Bruker-AXS, Billerica, MA, USA), scanning electron microscopy (SEM, Hitachi S-4700II, Tokyo, Japan), energy-dispersive X-ray spectrometer (EDS, JEOL 6610LV, Tokyo, Japan), and transmission electron microscopy (TEM, JEOL 2200FS), and Fourier transform infrared spectroscopy (FTIR, Bruker Alpha, Billerica, MA, USA). The optical response of the as-prepared samples was obtained by photoluminescence (PL) spectroscopy, with the excitation wavelength at 337 nm and the emission filtered by a 345 nm long pass filter. The PL lifetime of the Si NCs was collected using a pulsed nitrogen laser excitation source (λ = 337 nm, pulse duration = 10 ns, and repetition rate = 20 Hz) and a photomultiplier tube for detection. The signal was filtered by a 345 nm long pass filter and a 675 ± 50 nm band pass filter before detection to spectrally isolate the emission from the Si NCs. Diffuse reflectance from the samples was measured with a PerkinElmer LAMBDA 1050 UV/Vis/NIR Spectrophotometer (Waltham, MA, USA) with an integrating sphere attachment.