Zero-loss filtering

Figure 1.57 Improvement of contrast and resolution of a stained 400 nm thick ABS section produced by zero-loss filtering in an EFTEM (b) compared to global mode imaging (a)...

Omega filter used in the global mode (a) and of the same area by zero-loss filtering (b)[l,2],... 

Zero-loss filtering Both BF TEM images and diffraction patterns contain inelastically scattered electrons. The number of inelastic electrons increases with the increase of specimen thickness and they cause a diffuse background. Using a narrow sUt width (for example, 5 eV) at the ZLP, this filters out the majority of inelastic electrons and thus significantly improves the image contrast. 

Analysis of the energy distribution of electrons that have passed through the specimen (EELS) is used in an energy-filtered transmission electron microscopy (EFTEM). EFTEM offers a powerful tool for the chemical analysis of materials at the nanometer scale. On the other hand, the mode of zero-loss filtering, where only the unscattered and elastically scattered electrons contribute to the image, enhance the conttast and improve the resolution by avoiding... 

Figure 4.8 Zero-loss filtered TEM images of thin MDMO-PPV PCNEPV blend film samples, (a) Sample 1 with low (3500 g mol" ) PCNEPV derivative,...

In an efficient digital simulation, lumped loss factors of the form Gk (0)) are approximated by a rational frequency response Gk(c,mT). In general, the coefficients of the optimal rational loss filter are obtained by minimizing I Ylk (go) - Gk d r ) I with respect to the filter coefficients or the poles and zeros of the filter. To avoid introducing frequency-dependent delay, the loss filter should be a zero-phase, finite-impluse-response (FIR) filter [Rabiner and Gold, 1975], Restriction to zero phase requires the impulse response g.k(n) to be finite in length (i.e., an FIR filter) and it must be symmetric about time zero, i.e., ) k(-n) = gk(n). In most implementations, the zero-phase FIR filter can be converted into a causal, linear phase filter by reducing an adjacent delay line by half of the impulse-response duration. 

Figure 14.6 Zero-loss energy-filtered transmission electron microscopy images of MDMO-PPV PCNEPV blends with low (a), medium (b), and high (c) molecular weights of PCNEPV.(Reprinted with permission from Ref [53]. Copyright 2007, Wiley-VCH VerlagCmbH.)...

The delta-function deconvolution method (FFT) was used to improve the spectral resolution and to remove the plural scattering effect at the core-loss edge in electron energy-loss spectroscopy (EELS). The zero-loss peak (used as an instrumental resolution function) works as a nonattenuation high-pass filter in this technique [17]. Reflectance spectra in the vacuum ultraviolet of microcrystalline 3-BN, prepared by plasma CVD (chemical vapor deposition), and of sintered (3-BN measured with synchrotron radiation in the energy range from 5 to 25 eV, show reflectance peaks near 11.4 and 14 eV and a broad peak near 18 eV. The peaks at 11.4 and 14.0 eV are assigned to the E and E2 peaks of the sphalerite-type semiconductor [18]. 

Zero-loss peak (ZLP) It consists primarily of elastic forward scattered electrons, but also contains electrons that have suffered minor energy losses. The energy spread is mainly from the electron source. The energy spread for a Schottky type field emission gun is about 0.8 eV at 300 keV. Using a Wien-filter type monochromator, this spread can be further lowered to 0.13 eV at 300 keV [18]. 

Figure 3.2. Electron diffraction at 120 kV from a cast micellar film with 3.5-nm spacing at left, unfiltered at right, filtered to include only zero-loss electrons. (From Du Chesne [31], (1999) Wiley-VCH used by permission.)...

An unusual phenomenon was reported in the Arctic in the mid-1980s. Ozone measured at ground level was observed to decrease rapidly to small concentrations, at times near zero (Bottenheim et al., 1986 Oltmans and Komhyr, 1986). As seen in Fig. 6.37, an increase in bromide ion collected on filters (f-Br) was inversely correlated with the 03 decrease (Barrie et al., 1988 Oltmans et al., 1989 Sturges et al., 1993 Lehrer et al., 1997) this could reflect either particle bromide or a sticky gas such as HBr that could be collected on the filter simultaneously. This correlation suggested that the loss of ozone was due to gas-phase chain reactions... 

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