Page 56 - Synthesis of Functional Nanoparticles Using an Atmospheric Pressure Microplasma Process - LiangLiang Lin

Chapter 3
TEM grid (Quantifoil Micro Tools, GmbH). A FEI Tecnai 20 (type Sphera) microscope operating with a 200 kV LaB6 filament was employed for TEM analysis. XRD measurements were performed on a Rigaku Geigerflex Bragg-Brentano Powder Diffractometer using Cu- Kα1 radiation with wavelength of 1.54056 Å, at 40kV and 30mA. XPS measurements were carried out with a Thermo Scientific Kα. Spectra were recorded using an aluminium anode (Al Kα=1486.6 eV) operating at 72W and a spot size of 400μm. Survey scans were measured at a constant pass energy of 200 eV and region scans at 50 eV.
3.3 Results and Discussion
First the imaging of microdischarge in argon with and without the precursor admixture is presented to demonstrate the variation in plasma appearance, followed by the discussion of OES analysis to illustrate the influence of precursor flow rate and power on the discharge spectra. Afterwards, the results of morphology and chemical composition analysis of the products using SEM and EDX methods are shown.
Additional complementary information on the products nano-structure is obtained by TEM and HRTEM. Besides, XRD is also applied to investigate the crystallinity. Furthermore, XPS results are shown to give information about elementary composition and characteristic chemical bonds in the obtained products.
3.3.1 Imaging of the Microdischarge in Argon with and without Precursor Admixture
Figure 3.2(a)-(c) represents photographs of plasma operated at fixed power value of 1.05 W. As shown in Figure 3.2(a), for pure Ar, the plasma color is a light blue. When ferrocene is introduced to the plasma at room temperature, no color change is observed. However, the increase of temperature to 323.15 K results in color change from a light blue to cyan-green, which could easily be observed by naked eye. This is because ferrocene vapor pressure changes significantly with temperature. At room temperature the estimated ferrocene concentration in the gas mixture is quite low (2.9 ppm). Increasing the temperature to 323.15 K leads to a drastic raise of ferrocene vapor concentration (29.0 ppm), making ferrocene easily transported to the reactor. Once ferrocene is decomposed in the plasma, the color of emitted light noticeably changes.
Figure 3.2 (a) Discharge of pure Ar, (b) Discharge of Ar containing 2.9 ppm ferrocene vapor. (c) Discharge of Ar containing 29.0 ppm ferrocene vapor. All discharges operated at 1.05 W plasma power
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