Electron beam modulation techniques

A fine - structure technique (see EXAFS). Core holes are excited by monoenergetic electrons. The modulation in the excitation cross section as the beam energy is varied may be monitored through absorption, fluorescence, or Auger emission. 

In 1960 s, CIDEP was less popular than CIDNP because CIDEP did need much faster measuring techniques than CIDNP. This is due to much faster relaxation times (usually less than 1 /r s) of polarised electron spins than those (usually a few second for protons) of nuclear spins. In 1968, Smaller et al. [2] observed a population inversion for the cyclopentyl radical with a 2-MHz ESR apparatus coupled with a 15 MeV electron beam with pulse duration of 0.5 -4.0 /z s. The response time of the system corresponded to a time constant of 1.6/z s. In 1970, Atkins et al. [3] obtained the photo-CIDEP for the ketyl radical from benzophenone in paraffin solvents with a 2-MHz ESR apparatus coupled with a 20-ns laser flash. Under favorable chemical conditions, Wong and Wan [4] demonstrated that the photo-CIDEP for some semiquinone radicals in alcohol solvents could be observed with a commercial ESR spectrometer having a 100-kHz modulation unit and a custom-designed rotating sector giving light pulses. 

Ionization efficiency curves can also be easily obtained in the ion cyclotron resonance spectrometer. As mentioned earlier, the most common modulation techniques now center around some form of electron energy or beam modulation. If the electron beam is amplitude-modulated (switched on and off), it is only necessary to sweep the electron energy to obtain such a curve. With the restriction that the ion residence times are much longer (so that some fragmentation patterns may be different from those obtained in more conventional instruments), the ionization efficiency curves thus obtained should be comparable to those obtained in other mass spectrometers. 

Other modulation techniques are oscillation (tilting) of an interference filter [3] and modulation of the electron beam scan pattern in a vidicon or image-disk-sector photomultiplier spectrophotometer [34]. This was the first nonmechanical wavelength modulation. Wavelength modulation induces a synchronous modulation of the amplitude. If these intensities are expanded, for instance, in the form of a Taylor series in Aq, and the powers of the sine functions are expressed as sine and cosine functions of the corresponding multiple angles, then the derivatives can be obtained from the Fourier coefficients (see Sec. 2.1.3.3) of these series. The second derivative is obtained from the second harmonic of the induced intensity. 

AES measurements were carried out in a differentiated mode with a 2 eV modulation amplitude, at either 3 or 0.5 keV of primary electron energy, and 0.5 pA sample current, using a Perkin Elmer (PHI) 10-155 cylindrical mirror analyzer (CMA). The analysis was conducted at a low beam current to minimize electron beam damage. Spectra were acquired using a digital data acquisition system, and smoothed one time using a 11 point averaging technique.. 

The thermodynamic properties of UC2 have been studied by several scientists. Coninck et al. (1976) conducted experiments on UC2 and provided correlations for the calculation of the thermal diffusivity, thermal conductivity, and emissivity of UC2 as functions of temperature. Coninck et al. (1976) used the modulated electron beam technique in order to determine the thermal diffusivity of UC2 samples. In this technique, an electron gun is used to bombard a material in the form of a thin solid plate from one face. The electron gun is modulated to vary sinusoidally as a function of time. The phase difference between the temperature fluctuations of the two faces of the plate is measured, which is used to determine the thermal diffusivity of the material (Wheeler, 1965). Then, thermal conductivity is calculated as the multiplication of thermal diffusivity, density, and speciflc heat as shown in Eq. [18.3]. 

Wheeler, M.J., 1965. Thermal diffusivity at incandescent temperatures by a modulated electron beam technique. British Journal of Applied Physics 16, 365—376. 

If the analyzer is set to accept electrons of an energy characteristic of a particular element, and if the incident X-ray beam is rastered over the surface to be analyzed, a visual display the intensity of which is modulated by the peak intensity will correspond to the distribution of that element over the surface. The result is also an image and this technique is realized with the Quantum 2000. 

The simulations were carried out on a Silicon Graphics Iris Indigo workstation using the CERIUS molecular modeling and the associated HRTEM module. The multislice simulation technique was applied using the following parameters electron energy 400 kV (lambda = 0.016 A) (aberration coefficient) = 2.7 mm focus value delta/ = 66 nm beam spread = 0.30 mrad. 

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