Particle beam apparatus

Mass spectrometers Molecular beam apparatus Ion sources Particle accelerators Electron microscopes Electron diffraction apparatus Vacuum spectographs Low-temperature research Production of thin films Surface physics Plasma research Nuclear fusion apparatus Space simulation Material research Preparations for electron microscopy... 

Fig. 10.1 Schematic drawing of a fast beam apparatus. A fast atomic beam enters from the left and is excited sequentially by two different C02 lasers in electric field regions Fj and F3, respectively. F2 avoids a zero field region between them. Ions produced by highly excited atoms being ionized in the biased microwave cavity are energy selected and detected by a Johnston particle multiplier (not shown). The output signal is detected in phase with the mechanically chopped Fj laser beam (from ref. 3).

The skimmed solvent vapour and the helium are mechanically pumped out of the apparatus. This process is repeated in the second pumping stage (about 500 mTorr). Finally, the flow enriched in particles consisting of a narrow particle beam with a diameter smaller than 100 nm is sent into the mass spectrometer source without disturbing the vacuum. In the El or Cl mode, the particles injected into the source are rapidly vaporized before ionization. In the FAB mode, the particle beam is directed onto an FAB nozzle covered by a matrix. Thus the particles collide with the matrix surface and are trapped in it. 

The main components of an LC-MS are the HPLC apparatus, an optional UV or photodiode array detector, the interface, the mass spectrometer and a computer system for data management and evaluation. The interface is the key component of the LC-MS system. All other components must be adapted to the particular interface that is used. Most commercially available systems work with thermospray, electrospray, or particle beam interfaces. Each interface has a distinct mode of action and its own operational parameters. 

The particle beam LC/FT-IR spectrometry interface can also be used for peptide and protein HPLC experiments to provide another degree of structural characterization that is not possible with other detection techniques. Infrared absorption is sensitive to both specific amino acid functionalities and secondary structure. (5, 6) Secondary structure information is contained in the amide I, II, and III absorption bands which arise from delocalized vibrations of the peptide backbone. (7) The amide I band is recognized as the most structurally sensitive of the amide bands. The amide I band in proteins is intrinsically broad as it is composed of multiple underlying absorption bands due to the presence of multiple secondary structure elements. Infrared analysis provides secondary structure details for proteins, while for peptides, residual secondary structure details and amino acid functionalities can be observed. The particle beam (PB) LC/FT-IR spectrometry interface is a low temperature and pressure solvent elimination apparatus which serves to restrict the conformational motions of a protein while in flight. (8,12) The desolvated protein is deposited on an infrared transparent substrate and analyzed with the use of an FT-IR microscope. The PB LC/FT-IR spectrometric technique is an off-line method in that the spectral analysis is conducted after chromatographic analysis. It has been demonstrated that desolvated proteins retain the conformation that they possessed prior to introduction into the PB interface. (8) The ability of the particle beam to determine the conformational state of chromatographically analyzed proteins has recently been demonstrated. (9, 10) As with the ESI interface, the low flow rates required with the use of narrow- or microbore HPLC columns are compatible with the PB interface. 

Figure 4.3 SchemaLic diagnmi of panicle beam apparatus used for studying the bouncing of small particles off surfaces (Dahneke, 1975).

Fig. 2 Portion of the collinear laser-ion beam apparatus. QDl, QD2, electrostatic quadrupole deflectors CEM, channel electron multiplier DP, deflection plates PD, positive ion detector FC, Faraday cup ND, neutral particle detector CG, conducting glass plate AP, aperture MP, metal plate A, any element. The distance between QDl and QD2 is approximately 0.5 m.

The apparatus required for AES studies comprises a radiation or particle beam source and an electron energy analyzer. For X-ray excited Auger spectra the same sources as in XPS may be used, whereas excitation by electrons is performed by means of electron guns designed for kinetic energies typically between 100 eV and 5 keV. Ion excitation is rarely used in surface studies because of the extensive radiation damage caused by heavy particles. 

Figure 7.16 Typicalbeam-gas or crossed molecular beam apparatus, with one or two (pump/probe) tuneable lasers LIF observation of both reagents and products is prepared, at 45° to the particle/laserbeam axes...

Figure 24.1 Top schematic view of the pick-up technique a molecular beam apparatus to investigate the spectroscopy and dynamics of sodium-containing clusters is shown. The metallic cluster is produced by the pick-up technique under crossed-beam conditions. Adapted with permission from Polanyi et al, J. Phys. Chem. 99 13691. Copyright 1995 American Chemical Society. Bottom schematic view of a pick-up technique based on a beam-gas arrangement. After nozzle expansion, a skimmer extracts the beam that subsequently collides with the particles in the gas cell. The cluster beam is ionized by a pulsed laser and mass analysed in a TOE mass spectrometer. Reproduced from Nahler et al, J. Chem. Phys., 2003, 119 224, with permission of the American Institute of Physics...

In the crossed-beam geometry, the particles encounter each other only once. Alternatively, the decelerated beams can be loaded into a molecular synchrotron, located at the intersection point of the two molecular beams. In a synchrotron containing 20 counterpropagating packets, a packet that completed 100 round trips would have undergone 4000 encounters. We are currently constructing a molecular synchrotron as a collider for neutral polar molecules, which is designed to be combined with the crossed-beam apparatus. 

Even if such high power levels cannot be sustained, it should still be possible to observe two-photon excitation with the help of more sensitive detection methods. Towards this end, U. Boesl and E. Hildum in our laboratory have recently completed construction of a hydrogen atomic beam apparatus, which permits the detection of 2S atoms via photoionization. The resulting charged particles are observed with a time-of flight mass spectrometer. Despite transit time broadening and uncompensated relativistic second order Doppler shifts, we hope to achieve line widths on the order of 1 Mhz in this... 

All the techniques discussed here involve the atomic nucleus. Three use neutrons, generated either in nuclear reactors or very high energy proton ajccelerators (spallation sources), as the probe beam. They are Neutron Diffraction, Neutron Reflectivity, NR, and Neutron Activation Analysis, NAA. The fourth. Nuclear Reaction Analysis, NRA, uses charged particles from an ion accelerator to produce nuclear reactions. The nature and energy of the resulting products identify the atoms present. Since NRA is performed in RBS apparatus, it could have been included in Chapter 9. We include it here instead because nuclear reactions are involved. 

The experiment conducted by Rutherford and his co-workers involved bombarding gold foil with alpha particles, which are doubly charged helium atoms. The apparatus used in their experiment is shown in Figure 14-9. The alpha particles are produced by the radioactive decay of radium, and a narrow beam of these particles emerges from a deep hole in a block of lead. The beam of particles is directed at a thin metal foil, approximately 10,000 atoms thick. The alpha particles are delected by the light they produce when they collide with scintilltaion screens, which are zinc sulfide-covered plates much like the front of the picture tube in a television set. The screen... 

A schematic diagram of the apparatus used in the energy transfer experiments is shown in Figure 8.22. The particles are produced and levitated in an electrodynamic levitator as described previously. Excitation is provided by the filtered output of either a Xe or Hg-Xe high-pressure arc. The intensity produced at the particle was found to be 10-50 mW/cm2. The fluorescence emitted from each of the levitated particles was monitored at 90° to the exciting beam using //3 optics, dispersed with a j-m monochromator, and detected with an optical multichannel analyzer. The levitator could be... 

A force that is as large as the gravitational force can be used to suspend a particle against gravity, provided that it can be controlled and directed upward to balance gravity. One such force is the radiation pressure force or radiometric force. Ashkin and Dziedzic (1977), whose work is discussed in the next section, were the first to use the radiation pressure to levitate a microsphere stably. It was demonstrated by Allen et ai (1991) that the radiometric force can be measured with the electrodynamic balance, and they used the technique to determine the absolute intensity of the laser beam illuminating a suspended particle. This was accomplished in the apparatus displayed in Fig. 13. The laser illuminated the microparticle from below, and... 

Ashkin and Dziedzic (1977) used the radiation pressure force of a laser beam to levitate microdroplets with the apparatus presented in Fig. 15. A polarized and electro-optically modulated laser beam illuminated the particle from below. The vertical position of the particle was detected using the lens and split photodiode system shown. When the particle moved up or down a difference signal was generated then a voltage proportional to the difference and its derivative were added, and the summed signal used to control an electro-optic modulator to alter the laser beam intensity. Derivative control serves to damp particle oscillations, while the proportional control maintains the particle at the null point. 

Cluster ion sources with different production techniques have been devised [10]. The cluster ions are produced, for instance, by vaporizing the materials using a heated oven, a laser ablation apparatus, or sputtering. Essential features of the cluster ion source are increased intensity and stability of the beam, and control of the mass distribution of the particles. Further development of cluster ion sources is in progress at several facilities [7,11]. 

A heavy-ion microbeam provides a unique way to control the number of particles traversing individual cells and localization of dose within the cell. A collimated heavy-ion microbeam apparatus has been installed in a beam line from the AVF cyclotron to develop a novel cell surgery technique [127] (Fig. 34) (Table 5). 

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