研究目的
To compare the content estimation methods such as TEM, Raman, FTIR and H analysis based on nanostructural bonding configurations within a-C:H films and to understand the configurations of curved hexahydric graphite rings embedded in a-C network which had rich olefinic groups and H.
研究成果
In summary, we have discussed the advantage and disadvantage of the TEM, Raman, FTIR and H analysis that had used to measure the content of curved graphite fragments in a-C:H films. Based on the configurations including curved hexahydric graphite rings embedded in a-C network which has rich olefinic groups and H, FTIR method can be considered as an effective method to obtain the content of sp2 carbon forms. We expect that the preceding discussions will enrich the understanding of the detections measuring the content of curved graphite fragments in nanostructural films.
研究不足
1. TEM work has its own shortcomings, owing to the possible structural damage by the electron beam, the near surface regions of 1 nm or so may have already been altered.
2. Raman spectroscopy is a surface detection system with a limit of probing depth of 50-100 nm for visible excitation.
3. The method involving H analysis is limited as follows: it can hardly be taken to be a guarantee that every distributed a-C structures’ sites shall have enough H; the curved graphene structures have been only observed when the hydrogen content does not exceed 30 at.% in a-C:H films.
1：Experimental Design and Method Selection:
The structural films were deposited onto Si (100) and Fe substrates at room temperature using a DC-pulsed plasma chemical-vapor deposition (PECVD) system. The deposition feedstocks were the mixed gas of methane and hydrogen with a partial pressure ratio of 1:2 and 2:1. A dc bias of -1000V was applied to the substrate holder for the films.
2：A dc bias of -1000V was applied to the substrate holder for the films.
Sample Selection and Data Sources:
2. Sample Selection and Data Sources:
The samples were obtained at different deposition times of 2h, 4h and 6h, and called as dc 1:2 (2h, 4h or 6h) and dc 2:1(2h, 4h or 6h).
3：List of Experimental Equipment and Materials:
High resolution transmission electron microscopy (HRTEM, FEI Tecani F30), X-ray photoelectron spectroscopy (XPS, ESCALAB 250Xi), Raman spectra (Jobin-Yvon HR-800) and Fourier transform infrared spectra (FTIR, Nexus 870). The H content was obtained in the elastic recoil detection (ERD) method. The cross-section of the film was measured by field emission scanning electron microscope (FESEM, JEOL JSM-6701F).
4：0). The H content was obtained in the elastic recoil detection (ERD) method. The cross-section of the film was measured by field emission scanning electron microscope (FESEM, JEOL JSM-6701F).
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow:
The plan-view TEM samples for observation were first deposited on the NaCl single crystal substrate and then followed by dissolution of the NaCl substrate with deionized water; the freed fragments of the films were last placed onto Cu grids to conduct observations. The samples were cut to size 10*10mm, and the quantities of hydrogen in the samples could be measured by ERD method using a 2.04 MeV4 He+ beam. The XPS was operating with Al-Ka radiation and detecting chamber pressure of below 10-6 Pa, and the Au thin films about 0.2 nm thick were deposited on the tested carbon film surfaces to minimize the charging effect in the XPS analysis. The samples were detected in Raman spectrometer with a power below 0.5 MWm-2 (can avoid their unintentional damage). The FTIR spectra of the films were obtained using a Harrick Scientific horizontal reflection Ge-attenuated total reflection accessory (GATR, 65° incidence angle).
5：04 MeV4 He+ beam. The XPS was operating with Al-Ka radiation and detecting chamber pressure of below 10-6 Pa, and the Au thin films about 2 nm thick were deposited on the tested carbon film surfaces to minimize the charging effect in the XPS analysis. The samples were detected in Raman spectrometer with a power below 5 MWm-2 (can avoid their unintentional damage). The FTIR spectra of the films were obtained using a Harrick Scientific horizontal reflection Ge-attenuated total reflection accessory (GATR, 65° incidence angle).
Data Analysis Methods:
5. Data Analysis Methods:
The spectra were collected for 64 scans with a resolution of 4 cm-1. The content of curved graphene structures was estimated by the intensity ratio of D peak and G peak obtained by using Raman spectroscopy. The FTIR results were used to measure sp2 carbon content, and considered as an indication of the ratio of curved graphite and a-C structures, which is measured by the intensity ratio of aromatic ring clusters/ olefinic groups.
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