EELS interfaces

EELS interfaced to the TEM column. Elements with an atomic number Z < 4 cannot be detected, and quantification of the signal from elements with Z < 8 is difficult. The accuracy of the quantification procedure in the TEM is about 5%, compared with EPMA (about 1-2%), although the actual mass analysed can be very small ( 10-22g). 

These authors produced TEM samples of Bi-doped, Sb-doped and Ag-doped copper foils, thinned to electron transparency using conventional preparation procedures. In all cases the presence of impurity segregation was confirmed using conventional X-ray energy-dispersive spectrometry. The EELS measurements were carried out with a STEM operating at 100 keV, with a nominal probe size of 1 nm (full width at half maximum) with a current of about 0.5 nA. The conditions required to optimize detection sensitivity for interface analysis require the highest current density and are not consistent with achieving the smallest probes. 

Key words EELS, LELS, Electron-Energy-Loss Spectroscopy, Nanomaterials, interfaces... 

The small size of a nanomaterial implies the existence of interfaces between its components, or between itself and vacuum. These interfaces are often responsible for the special properties observed. That is why the first part of this paper deals with some remarkable and illustrative examples of technologically important interfaces. The second part focuses on nanoobjects, potentially nanomaterials because of their small size but whose application is not yet effective. The third part is dedicated to well-established nanomaterials, the knowledge of which has been vastly improved thanks to EELS in a (S)TEM. Finally, a more prospective part presents the very next challenges to be faced in a near future. In all these parts, both Core Loss and LELS examples are given to demonstrate the complementarity of the two energy domains. 

EELS study of this interface was carried out by Batson [5], It revealed the presence of Si2+ (SiO like layer) and possible defect states at the boundary (Figure 2a). LELS can also give information about the interface. We showed that the use of relativistic formula was essential to explain the shift of the interface plasmon peak (IPP) as the probe was moved away from the interface (Figure 2b). The agreement with the experiment allowed us to conclude that a 1 nm thick SiO layer had to be introduced between Si and Si02 to fit the IPP position precisely [6],... 

Figure 4. Left High resolution TEM image of a SiC-Si02 interface. Right corresponding EELS carhon map. (from Chang K. C., Nuhfer N. T., Porter L. M. and Wahab Q., Appl. Phys. Lett. 77 (2000) 2186 with permission from American Institute of Physics)...

This paper will discuss the use of Near-Edge X-ray Absorption Fine Structure (NEXAFS) Spectroscopy to study the unoccupied n molecular orbital (MO) structures of polymers and polymer-metal interfaces. A collection of systematic NEXAFS and EELS studies of simple organic compounds by J. Stohr and others (1-10) has led to recent advances in the understanding and interpretation of this technique. It s application to complicated polymers and polymer-metal interactions has only begun, but NEXAFS spectroscopy promises to be an important complement to other photoelectron spectroscopies. 

We use an ab-initio local spin density method to investigate the aluminum/polyimide interface at low coverage. We found in agreement with XPS and EELS experiments, that the aluminum atom bonds to the carbonyl group. Our calculations suggest a formation of a linear C-O-AI complex. We calculated core levels chemical shifts and vibrational frequencies in the vicinity of the carbonyl group. 

Figure 4.32 shows an EELS spectrum which provides complementary information about the chemical composition of these particles. The spectrum was recorded in spot mode inside a particle like the one shown in Figure 4.30(a), i.e. imaged in profile. To avoid interference from the support, a region a few times the electron spot size (about 1 nm) far fix>m the particle/support interface was analysed. As deduced from Figure 4.32, the EELS spectrum contains the Rh-M3 and O-K... 

Further detailed TEM/EELS analysis at the center of the gate dielectric was done such that the TEM probe was positioned at the center of the gate dielectric, analyzing the EELS signals from the non-breakdown and then across breakdown location as shown in Fig. 2b. In this case, the TEM probe is always moving parallel to the polysilicion/oxide and oxide/Si substrate interfaces. Any change in... 

Fig. 15 Ge composition line scans determined by high-resolution EELS on (A) a Sio.sGeo.s island grown at 700°C, and (B) a Sio.8Gco.2 island grown at 500° C. The profiles shown below each XTEM image correspond to the line across the substrate/island interface. Scan direction is from the substrate to the vacuum. (From Ref. °l)...

Several distinct energy loss peaks appear within the MgO band gap (between 1 and 5.5eV energy loss [218]) as a function of cluster size. These loss peaks cannot be assigned to low-lying transitions in the atom or in the ion [103,208,219,220]. EEL spectra of vapor deposited Ag, which forms islands and thin films via surface diffusion at sample temperatures between T = 100 and 500 K, have shown losses at 3.8 and 3.2 eV attributed to an Ag surface plasmon and to an Ag-MgO interface plasmon, respectively [218]. In contrast, the EEL spectra shown in Fig. 1.44 and recorded at T = 45K exhibit clearly a size dependence, which reflects the change in the electronic structure of the clusters. A similar behavior has been observed in optical absorption spectra of Ag (n < 21) clusters deposited in rare gas matrices [221], which has been interpreted as a manifestation of collective excitations (Mie plasmons) of the s electrons influenced by the ellipsoidal shape of the clusters. Some similarities but also some differences in the general trend with cluster size have been observed by comparing the optical absorption data shown in [221] with these EELS data [214]. In this context, it is important to note that EELS probes... 

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