Multimode atomic force microscope

The crystal structure and phase were characterized on an X-ray powder diffractometer (XRD, Shimadzu-6000) and X-ray photoelectron spectrometer (XPS, VG Scientific ESCLAB 220iXL). The size and morphology of the as-synthesized products were determined by a transmission electron microscope (TEM, JEOL-1200) and field emission scanning electron microscope (FESEM, JEOL, JSM-7401F) with an accelerating voltage of 5 kV. Atomic force microscopy (AFM) measurements were collected on a Multimode atomic force microscope (Veeco Instruments, Inc.). Typically, a freshly diluted ethanol solution of the NiFe-LDH samples was ultrasonically treated and then deposited onto a clean mica wafer by drop-casting. The nitrogen adsorption–desorption measurement was conducted on a Micromeritics ASAP 2010 analyzer, and the specific surface areas of samples were determined by Brunauer–Emmett–Teller (BET) analysis. FT-IR spectra were recorded on a PerkinElmer Spectrum 100 Fourier transform infrared spectrometer using KBr pellets.

UV-Vis spectroscopy (Genesys^TM 150; Thermo Fisher Scientific, Waltham, MA, USA) was used to study the effects of incubation time on the green synthesis process. The peak absorbance wavelength was determined using the scanning mode (450–650 nm). Zeta (ζ) potential of the Au NPs (0.4 mM) was measured using a Zetasizer Nano ZS (Malvern, Westborough, PA, USA). Scanning electron microscopy (FE-SEM, Hitachi S-4800 ultra-high resolution cold cathode field emission scanning electron microscope, Kefeld, Germany) was used to image Au NPs (40 mM) that were dried and mounted to aluminum stubs. At the same time, energy dispersive X-ray spectroscopy (EDX, Noran (Si(Li))detector, Thermo Fisher Scientific, Waltham, MA, USA) was used to verify the elemental composition of the Au NPs. Atomic force microscopy (AFM) images, using 1.25 mM Au NP solution, were taken using contact mode on a Bruker MultiMode atomic force microscope (Billerica, MA, USA) with a Veeco Nanoscope IIIa controller (Santa Barbara, CA, USA). Au NPs (oven-dried at 45 °C) were also analyzed using attenuated total reflection Fourier transform infrared (ATR-FTIR; MIRacle 10, IR-Tracer 100; Shimadzu, Kyoto, Japan) spectroscopy. Lastly, powder X-ray diffraction analysis was performed using a Bruker D8 Discover X-ray diffractometer (Billerica, MA, USA) to confirm the crystalline structure of the Au NPs.

The in situ AFM measurements were performed using a fluid cell mounted on a multimode atomic force microscope from Veeco Instruments that was equipped with a liquid-resistant vertical engagement scanner (AS-12V) and operated in tapping mode. The probe consisted of a sharp silicon tip (Arrow-NCR-W; thickness: 4.6 μm, length: 160 μm, width: 45 μm; resonance frequency: 285 kHz, force constant: 42 N m⁻¹) attached to a silicon nitride cantilever. Scan frequencies were between 1 and 8 Hz. A minimum loading force of ∼150 pN or less was applied using the optimized feedback and set-point parameters for good imaging conditions. AFM images were analysed with the software Nanoscope III.
For measurement, a piece of clean Si wafer was fixed on the metal disk by epoxy glue. As a reference, scanning was performed directly on the silicon surface in air (Supplementary Fig. 7a), water (Supplementary Fig. 7b) or supersaturated DL-Glu mother solution (cf. Fig. 1c,d in the main text).
To monitor growth of DL-glutamic acid monohydrate, a single crystal of DL-Glu·H₂O was glued on the Si wafer. Subsequently, ∼0.2 ml of a supersaturated aqueous solution of DL-Glu was pumped into the fluid cell. Both the crystal and the AFM tip were covered by the mother liquor. Scanning was then performed directly on the surface of the crystal.