Raman spectrometer

SLN-DTX, Blank-SLN, Compritol ATO 888, Span 80 and Pluronic F127 spectroscopic analyses were performed by a confocal Raman spectrometer (Witec GmbH, Germany) with a 532 nm laser at 30 mW. The spectra were recorded at an integration time of 0.15 s per point.

The experimental setup is given in Supplementary Fig. 22. First, h-BN flakes were produced by micromechanical exfoliation of single-crystal h-BN and then deposited on quartz substrates that were previously cleaned with oxygen plasma. The substrates with h-BN flakes were loaded into a furnace equipped with an RF generator (13.56 MHz, MTI Corporation) with a tunable power from 100 to 400 W. The sample temperature in the sample chamber could be controlled from room temperature to 1000 °C. An advanced pump (GX100N Dry Pumping System, Edwards) was connected to the chamber to control the flow rate. After the samples were heated to the preset temperature, hydrogen (oxygen or argon) gas with a flow rate of 3 sccm (~3 Pa) was introduced into the chamber, and then the plasma was formed. The plasma treatment normally took 90, 120 or 150 min. The h-BN flakes were finally removed from the sample chamber for characterization under an optical microscope (Eclipse LV150, Nikon), an atomic force microscope (Dimension Icon, Bruker), and a Raman spectrometer (532 nm, WITec).

Structural characterization was performed through TEM and HR-TEM analysis with a Tecnai G²20 high-resolution TEM operating at a voltage of 200 kV. Samples for TEM/HR-TEM analysis were prepared by casting droplets of an aqueous solution of wsGNS onto a 400 mesh carbon-coated copper grid, followed by drying under 100 W table lamp for 12 h. The UV-Vis absorption analysis were done at room temperature with Perkin Elmer Lambda 35 spectrometer. XPS measurements was recorded in ESCA⁺ omicron nanotechnology oxford instrument. For FT-IR spectra measurements, BRUKER Vector22 IR spectrometer model with pressed KBr pellets was used. Raman spectra were done by WITEC model Raman spectrometer at wavelength 532 nm with an Ar⁺ laser. X-ray diffraction spectra were obtained at 25 °C (Cu Kα1, Kα2, Kβ radiation, with scan rate 2°/min) on a Pananalytical X Pert Pro Powder X-ray diffractometer model. PerkinElmer UV-Vis (NIR) spectrometer was used for carrying out UV-Visible DRS measurements. ¹H NMR measurements were recorded on a JEOL ECS-400 (operating at 400 MHz, in D₂O solvent).

The samples examined are commercially available single crystal substrates of LaAlO₃ and SrTiO₃ (Crystec, GmbH, Germany and MTI Corp. USA), about 5 mm × 5 mm area and 0.5 mm thick with both sides polished. Photoluminescence measurements were done using a JY Horiba LabRAM HR Evolution Raman spectrometer coupled with an air cooled CCD. All the data have been recorded at an excitation wavelength of 514.5 nm from a Lexel SHG 95 Argon Ion Laser. The spectra were collected at periodic temperature intervals from 10 K to 300 K to understand the temperature dependence using an Advanced Research Systems Inc. compressed helium based closed cycle refrigerator coupled with the above spectrometer. Magnetic field-dependent measurements were performed using an attoCube superconducting magnet coupled with a WiTec Raman spectrometer with a 532 nm laser line as the source of excitation. To identify and quantify the contaminants in these single crystal substrates, we have conducted Particle Induced X-ray emission technique (PIXE) by using 2 MeV alphas/protons and detected X-ray’s by using Si (Li) detector.

A field-emission scanning electron microscopy (SEM, FEI Inspect F, Hillsboro, OR, USA) was employed to analyze the morphology of the prepared products. A Raman spectrometer (Witec, Ulm, Germany) equipped with a 488 nm laser was used to analyze the graphene structure. A transmission electron microscope (TEM) was used for microstructural analysis with a Double Cs-corrector FEI Titan Themis G2 60–300 microscope (FEI Inc., Hillsboro, OR, USA). A four-probe meter (Tektronix, Keithley 2400, Cleveland, OH, USA) was used to measure the conductivity by. An electric universal testing machine (Shimadzu, AG-10TA, Kyoto, Japan) was used to analyze the composite’s tensile strength. The S parameters of the PDMS/GN nanocomposites in the X-band frequency range were measured using a vector network analyzer (VNA, Agilent Technologies, E8363B, Santa Clara, CA, USA). A pair of holders 22.9 × 10.2 mm² in size was used to hold the nanocomposite. The holders were connected to two coaxial to waveguide adaptors, which were connected to VNA with two coaxial cables. The incident power was set to be 1 mW.

Raman Spectrometer (WiTec, Ulm, Germany), XRD (Shimadzu, Kyoto, Japan), FTIR spectrometer (Perkin-Elmer 100 series, Waltham, MA, USA), Field emission scanning electron microscope (FESEM) JOEL JSM-6400 (Tokyo, Japan) and inductively coupled plasma-Optical Emission Spectrometer (ICP-OES), Optima 2100 DV Perkin Elmer (Waltham, MA, USA) were used for the characterization of the samples.

Powder X-ray diffraction (XRD) of the crystalline phase identification was carried out using a Shimadzu diffractometer (XRD6000) (Shimadzu, Tokyo, Japan) with Cu Kα (30 kV) radiation. The XRD patterns were recorded in the 2θ range of 10–80° with a scanning speed of 4°/min. Field emission scanning electron microscopy (FESEM) images were recorded with a Nova Nanosem 30 series microscope (FEI Company, Oregon, USA) using 5 kV. Internal morphologies of the samples were obtained via transmission electron microscopy (TEM) using the H-7100 microscope from Hitachi (Tokyo, Japan). Prior to the TEM measurements, the samples were dispersed in ethanol by sonication for 15 min before it was dropped on the copper grid. Textural properties of the samples were determined using nitrogen gas adsorption–desorption techniques with ASAP2000 analyzer, (Micromeritics, Georgia, GA, USA) with degassing was done at 105 °C overnight. The thermal decomposition of the product was investigated using a thermogravimetric analyzer, (TA Instruments, Delaware, DE, USA). The temperature range used for the thermal analysis was from room temperature to 1000 °C with a heating rate of 5 °C/min. Raman spectra of the CQNs were obtained using a Raman spectrometer (WITec, Ulm, Germany) with a 532 nm laser.