K alpha spectrometer

Raman spectroscopy (B&W-Tek) with laser excitation energy of 532 nm (2.33 eV) was used to evaluate the graphene quality and the functionalization results. The spectra were recorded with an acquisition time of 1 s by averaging 10 scans over the range 1200–3000 cm⁻¹. The laser spot size is ~1 μm. The spectral resolution is ~2 cm⁻¹. The functionalized graphene on copper was transferred onto SiO₂ substrate for enhanced Raman signals. Atomic force microscope (NT-MDT) in tapping mode was used for height and phase imaging of graphene pattern and SWNTs. XPS spectra were recorded using a Thermo Scientific K-Alpha spectrometer at pressures lower than 5 × 10⁻⁹ mBar.

X-ray diffraction (XRD) patterns are obtained with DX-2700 X-ray diffractometer (Cu-Ka radiation, λ = 1.54 Å). The morphology of the as-prepared samples was measured using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Raman spectra were recorded on a cryogenic matrix using a 532-nm laser. Fourier transform infrared (FT-IR) spectra were measured with a Thermo Scientific Nicolet iS5 spectrometer, with a resolution of 4.000 cm⁻¹ in the range of 400–4000 cm⁻¹, using the attenuated total reflection mode. The room magnetic temperature hysteresis loops were obtained on a vibrating sample magnetometer (VSM, manufactured by Lakeshore, Inc.). The chemical states and surface components of the samples were measured by X-ray photoelectron spectroscopy (XPS) on an Thermo Scientific K-Alpha spectrometer. Based on coaxial-line theory, the related EMW parameters of samples in the frequency of 2–18 GHz range were measured on a vector network analyzer (VNA, 3672B-S, Ceyear). Samples were wrapped into paraffin at a filling ratio of 15 wt% and then shaped into a toroid with 7 mm outer diameter and 3.04 mm inner diameter. The infrared thermal images (FLIR ONE PRO) were taken to visualize the heat insulation process of the samples on a heating platform. Micromagnetic simulation and cross-section (RCS) simulation were described in detail in the supporting information.

X-ray photoelectron spectroscopy (XPS) was performed on a Thermo Scientific K-alpha+ spectrometer. Samples were analyzed using a monochromatic Al x-ray source operating at 72 W (6 mA × 12 kV), with the signal averaged over an oval-shaped area of approximately 600 × 400 microns. Data was recorded at pass energies of 150 eV for survey scans and 40 eV for a high resolution scan with a 1 eV and 0.1 eV step size, respectively. Charge neutralization of the sample was achieved using a combination of both low energy electrons and argon ions (less than 1 eV), which gave a C(1s) binding energy of 284.8 eV.
All data were analyzed using CasaXPS (Microsoft Corporation, Redmond, WA, USA) (v2.3.17 PR1.1) using Scofield sensitivity factors and an energy exponent of −0.6.
Scanning transmission electron microscopy (STEM) data were collected on the Ru catalysts by using a Hitachi H3300 STEM operated at 200 kV in the Z-contrast mode in which the brightness depended on the thickness and, approximately, the square of the atomic number. Particle sizes were determined by using ImageJ software to process the STEM images.

The epitaxial graphene was synthesized by means of Si sublimation from semi-insulating (SI), Si-face, on-axis, 6H-silicon carbide (SiC) substrates [36 (link)]. The synthesis took place in a commercial chemical vapor deposition reactor at a temperature of 1540 °C and a pressure of 100 mbar under an Ar ambient. The Ar was used to suppress the sublimation of Si in order to control the thickness of the epitaxial graphene layers. Prior to growth, the substrate was in-situ H₂ etched to prepare the SiC surface for epitaxial graphene growth by removing any polishing scratches created during the manufacturing of the SiC substrate and forming bilayer stepped morphology. After growth, the sample was cooled in Ar to 800 °C, at which point the reaction tube was evacuated. The thickness of the epitaxial graphene layers was ≈2 monolayers as determined by X-ray photoelectron spectroscopy (XPS) using a Thermo Scientific K-Alpha spectrometer with a monochromatic Al-Kα source using a 400 µm spot size. Chemical analysis was performed using Avantage.