Beam Scanning

10 J/cm. Similar results with CdS have been obtained by Jacobson et al.29 Haas, Adams, Dir, and Mitchelli o obtained a sensitivity of 2.5 X J/cm2 using an unspecified photoconductor and storage- 

The photoconductor-liquid-crystal sandwiches incorporate either a dc driving source or a somewhat complicated multilayer structure. Maydan, Melchior, and Kahn have circumvented both of these aspects by utilizing the thermo-optic properties of nematic-cholesteric mixtures reported by Soref. He showed that nematic-cholesteric 

An improvement of this device has been described in which the nematic-cholesteric mixture is replaced by a smectic material. Thermal writing induces the change of the smectic from the perpendicular to a scattering texture. Unlike the nematic-cholesteric materials, selective erasure is possible with the smectic device. The thermal writing is too slow for television-rate applications because of the thermal inertia of the glass-liquid-crystal system. With a laser-beam power of 20 mW, addressing speed is approximately 10 elements/sec for the smectic device. In the projection mode, the resolution is 50 lines/mm at a contrast ratio of approximately 10 1. 

The different electro-optic phenomena have been classified into those that involve only dielectric forces and those that depend upon the interaction of conduction and dielectric torques. The field-effect phenomena possess several common properties. The resistivity of the materials may be as high as chemically practical, i.e., p 10 ohm-cm. For the induced birefringence, twisted nematic, and guest-host color switching effects, the threshold voltages are less than 3 or 4 

Mailer, K. L. Likins, T. R. Tayloer, and J. L. Fergason, Effect of Ultrasound on a Nematic Liquid Crystal. AppL Phys. Lett., 18, p. 105 (1971). 

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Another basic approach of CL analysis methods is that of the CL spectroscopy system (having no electron-beam scanning capability), which essentially consists of a high-vacuum chamber with optical ports and a port for an electron gun. Such a system is a relatively simple but powerful tool for the analysis of ion implantation-induced damage, depth distribution of defects, and interfaces in semiconductors. ... 

The diffraction pattern obtained in the detector plane when the beam scan in a STEM instrument is stopped at a chosen point of the image comes from the illuminated area of the specimen which may be as small as 3X in diameter. In order to form a probe of this diameter it is necessary to illuminate the specimen with a convergent beam. The pattern obtained is then a convergent beam electron diffraction (CBED) pattern in which the central spot and all diffraction spots from a thin crystal are large discs rather than sharp maxima. Such patterns can normally be interpreted only by comparison with patterns calculated for particular postulated distributions of atoms. This has been attempted, as yet, for only a few cases such as on the diffraction study of the planar, nitrogen-rich defects in diamonds (21). 

Huang, Z., Munro N., Huhmer, A.F.R., and Landers, J.P, Acousto-optical deflection-based laser beam scanning for fluorescence detection on multichannel electrophoretic microchips, Anal. Chem. 71, 5309, 1999. 

The sample environment was filled with He gas to prevent the argon X-ray emission from air. Beam scanning, data acquisition, evaluation and the generation of elemental maps were controlled by a computer. Micro-PIXE measurements were performed with a scanning 2.5MeVH+ microbeam accelerated by the 3 MV single-end accelerator. The beam diameter was 1-2 pm, so that individual particles could be analysed. The beam current was < 100 pA and the irradiation time was about 3(M0 min. 

Figure 4.20. Schematic diagram of the micro-PIXE beam scanning and data acquisition...

Laser Beam Scanning Opto-Mechanical Devices, Systems, and Data Storage Optics, edited by Gerald F. Marshall... 

The field emission display held a particular fascination for this field, because of its potentially large market [36,44-49]. Field emission displays (FEDs) are flat panel displays, which are a flat panel equivalent of the cathode ray tube (CRT), but in which each pixel is addressed by its own electron beam from a field emitter, rather than having a beam scanned across it as in the CRT (Fig. 13.8) [44]. The emitters can be diode or triode type. The triode type is the most elegant, the diode type is lower cost. 

The main differences when compared to conventional fluorescence microscopes are based on several entities. A laser beam - usually an argon-krypton laser-is used for the illumination of the sample. The focused illuminating beam scans across the specimen by means of rotating mirrors, followed by a point-by-point signal collection which results in a raster sweep of the specimen at one particular focal plane. This is indicated by the term laser scanning. ... 

To avoid any flicker in the image, the electron beam is scanned across and down the screen, many times per second, following a predetermined set of parallel lines, the method being known as raster scanning. The phosphor dots are the picture elements or pixels and light up as the beam scans across each one. In colour televisions and monitors additive mixing of the three colours of red, green and blue produces the... 

Laser Beam Scanning Opto-Mechanical Devices, Systems,... 

Europe, the Paul Scherrer Institute (PSI), Villigen, Switzerland has developed (and is planning to further improve) a highly sophisticated beam scanning system in order to exploit all the physical advantages of the proton beams. The scanning beam technique will be dealt with in more detail in the section on heavy ions (Sec. 4.4). 

A 2-D beam scanning system equipped with a set of magnets or electrostatic plates to deflect the beam horizontally and vertically is commonly used for uniform irradiation over a large area, e.g., > 10 x 10 cm. A schematic drawing of the 2-D beam scanning method is shown in Fig. 8. The scanning area may be varied by changing the excitation currents of the... 

Figure 8 Schematic drawing of the two-dimensional beam scanning system using a set of magnets to deflect the beam horizontally and vertically.

Because of the instrumental requirements, these are usually not routine monitoring techniques. However, unlike other methods, they give detailed information on particle shapes. In addition, chemical composition information can be obtained using transmission electron microscopy (TEM) or scanning electron microscopy (SEM) combined with energy-dispersive spectrometry (EDS). The electron beam causes the sample to emit fluorescent X-rays that have energies characteristic of the elements in the sample. Thus a map showing the distribution of elements in the sample can be produced as the electron beam scans the sample. 

Figure 7 shows an aberration-free intensity distribution at the focus of a typical objective lens similar to that used for DLW lithography. Calculations were carried out using a vectorial Debye theory, which accounts for the polarization effects. For the linearly polarized wave it can be seen that the spot is elongated along the polarization vector. To reduce this asymmetry, a X/4-plate can be used to convert the polarization of the incident beam to circular, which can be interpreted as a combination of two mutually perpendicular linearly polarized components. Thus, width of the photomodified line becomes independent of the beam scanning direction in the sample. 

The beam-scan length was continuously variable from 3 to 15 inches, and the beam was about % inch wide. Electron current was adjustable to a maximum of 250 /xa. The material was carried under the beam on a variable-speed, continuous belt, the dry powder being exposed to air at all times. Dosage was controlled by varying scan width, electron beam current, or belt speed. To ensure complete penetration, the polymer bed depth was kept at 0.5 inch or less. 

The components of a single or double beam scanning spectrometer are shown schematically in Fig. 10.9a and b. 

In practice the trace obtained in this way is too faint to be seen when the electron beam scans the screen in a time of 1 ns. An image intensifier camera is needed to make it visible, and in a complete system this would be followed by a CCD camera to store the trace and transmit it to a computer. 

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