Calculation of the electronic structure of carbon films using electron energy loss spectroscopy

被引:9
作者
Alexandrou, I
Papworth, AJ
Rafferty, B
Amaratunga, GAJ
Kiely, CJ
Brown, LM
机构
[1] Univ Cambridge, Dept Engn, Cambridge CB2 1PZ, England
[2] Univ Liverpool, Dept Engn, Liverpool L69 3BX, Merseyside, England
[3] Univ Cambridge, Dept Mat Sci & Met, Cambridge CB2 3QZ, England
[4] Univ Cambridge, Cavendish Lab, Cambridge CB3 0HE, England
关键词
EELS; density of states; carbon; C-60;
D O I
10.1016/S0304-3991(01)00123-1
中图分类号
TH742 [显微镜];
学科分类号
摘要
The detailed understanding of the electronic properties of carbon-based materials requires the determination of their electronic structure and more precisely the calculation of their joint density of states (JDOS) and dielectric constant. Low electron energy loss spectroscopy (EELS) provides a continuous spectrum which represents all the excitations of the electrons within the material with energies ranging between zero and about 100 eV. Therefore, EELS is potentially more powerful than conventional optical spectroscopy which has an intrinsic upper information limit of about 6 eV due to absorption of light from the optical components of the system or the ambient. However, when analysing EELS data, the extraction of the single scattered data needed for Kramers-Kronig calculations is subject to the deconvolution of the zero loss peak from the raw data. This procedure is particularly critical when attempting to study the near-bandgap region of materials with a bandgap below 1.5 eV. In this paper, we have calculated the electronic properties of three widely studied carbon materials; namely amorphous carbon (a-C) tetrahedral amorphous carbon (ta-C) and C-60 fullerite crystal. The JDOS curve starts from zero for energy values below the bandgap and then starts to rise with a rate depending on whether the material has a direct or an indirect bandgap, Extrapolating a fit to the data immediately above the bandgap in the stronger energy loss region was used to get an accurate value for the bandgap energy and to determine whether the bandgap is direct or indirect in character. Particular problems relating to the extraction of the single scattered data for these materials are also addressed. The ta-C and C-60 fullerite materials are found to be direct bandgap-like semiconductors having a bandgaps of 2.63 and 1.59 eV, respectively. On the other hand, the electronic structure of a-C was unobtainable because it had such a small bandgap that most of the information is contained in the first 1.2 eV of the spectrum, which is a region removed during the zero loss deconvolution. (C) 2001 Elsevier Science B.V. All rights reserved.
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页码:39 / 45
页数:7
相关论文
共 19 条
[1]  
[Anonymous], 1975, PHYS TODAY
[2]  
Ashcroft N. W., 1976, SOLID STATE PHYS
[3]   Assessment of electron energy-loss spectroscopy below 5 eV in semiconductor materials in a VG STEM. [J].
Bangert, U ;
Harvey, AJ ;
Keyse, R .
ULTRAMICROSCOPY, 1997, 68 (03) :173-180
[4]   RESOLUTION ENHANCEMENT BY DECONVOLUTION USING A FIELD-EMISSION SOURCE IN ELECTRON-ENERGY LOSS SPECTROSCOPY [J].
BATSON, PE ;
JOHNSON, DW ;
SPENCE, JCH .
ULTRAMICROSCOPY, 1992, 41 (1-3) :137-145
[5]   ELECTRON-ENERGY-LOSS SCATTERING NEAR A SINGLE MISFIT DISLOCATION AT THE GAAS/GAINAS INTERFACE [J].
BATSON, PE ;
KAVANAGH, KL ;
WOODALL, JM ;
MAYER, JW .
PHYSICAL REVIEW LETTERS, 1986, 57 (21) :2729-2732
[6]  
Egerton R. F, 1996, ELECT ENERGY LOSS SP
[7]   INTENSITY OF OPTICAL ABSORPTION BY EXCITONS [J].
ELLIOTT, RJ .
PHYSICAL REVIEW, 1957, 108 (06) :1384-1389
[8]   PROPERTIES OF FILTERED-ION-BEAM-DEPOSITED DIAMOND-LIKE CARBON AS A FUNCTION OF ION ENERGY [J].
FALLON, PJ ;
VEERASAMY, VS ;
DAVIS, CA ;
ROBERTSON, J ;
AMARATUNGA, GAJ ;
MILNE, WI ;
KOSKINEN, J .
PHYSICAL REVIEW B, 1993, 48 (07) :4777-4782
[9]   INVESTIGATION OF HYDROCARBON-PLASMA-GENERATED CARBON-FILMS BY ELECTRON-ENERGY-LOSS SPECTROSCOPY [J].
FINK, J ;
MULLERHEINZERLING, T ;
PFLUGER, J ;
SCHEERER, B ;
DISCHLER, B ;
KOIDL, P ;
BUBENZER, A ;
SAH, RE .
PHYSICAL REVIEW B, 1984, 30 (08) :4713-4718
[10]   Determination of the local microstructure of epitaxial AlN by x-ray absorption [J].
Katsikini, M ;
Paloura, EC ;
Cheng, TS ;
Foxon, CT .
JOURNAL OF APPLIED PHYSICS, 1997, 82 (03) :1166-1171