Agilent 5500 afm

CSAFM measurements of passive films before and after hydrogen charging were performed using Agilent 5500 AFM (Agilent Technologies, USA) with the current sensing mode. In addition to the current maps measured by CSAFM, current-voltage curves were acquired by setting the probe tip in contact with the passive films at different locations in ferrite and austenite phases of the current maps, which were done at least 10 times at different locations of the specimen and representative curves were picked out. The equipment was located in a clean room at a constant temperature of 25 °C and relative humidity of about 25%. The probes used in MFM measurements were Bruker magnetic probes (MESP) with force constant of 2.8 N/m, while the probes in CSAFM measurements were AppNano conductive Pt-coated silicon tips with a force constant of 2.8 N/m and a tip radius of 40 nm.
The chemical composition of the passive films formed before and after hydrogen charging was investigated with XPS with a monochromatic Al Ka radiation source and a pass energy of 25 eV. The depth profiling was performed using an Ar⁺ gun with a beam energy of 3 kV and a beam current of 1 μA. The curve fitting was performed using the commercial software XPS Peak, version 4.1, which contains the Shirley background subtraction and Gaussian-Lorentzian tail functions, to achieve better spectra fitting.

Intermittent contact mode images were obtained using an Agilent (5500) AFM with silicon tips (Budget Sensors).

The X-ray diffraction patterns were recorded on a Bruker D8 Advance X-ray diffractometer with Ni filtered Cu Kα radiation at 40 kV and 40 mA. Ultraviolet–visible diffuse reflectance (ultraviolet–visible diffuse reflectance spectrum) spectra were obtained with a self-supporting sample disk on a ultraviolet–visible spectrophotometer (Cary 500), where BaSO₄ was used as a reflectance standard. TEM images were obtained using a JEOL model JEM 2010 EX instrument at an accelerating voltage of 200 kV. AFM images were recorded using Agilent 5,500 AFM (Agilent Technologies, USA). All the images were acquired using tapping mode under ambient conditions (ca. 40−50% relative humidity, 25 °C temperature). The used Si cantilevers/tips (Bruker) have a spring constant of 40 N m⁻¹ and a resonance frequency of 300 kHz. During an AFM experiment, sample was dispersed in ethanol using an ultrasonic bath for 20 min and then the dispersion was diluted in ethanol. A drop of the above diluted dispersion was deposited on a new cleaved mica surface and dried in air. The instrument parameters (set point, amplitude, scan size, scan speed and feedback control) were adjusted for the best resolution of images. Electron spin resonance spectra were obtained over Bruker ESP 300 E electron paramagnetic resonance spectrometer.