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Digitale Medien

Electron diffraction studies of metal phthalocyanines, MPc, where M=Sn, Mg, and Zn (reinvestigation) (1999)

Ruan, Chong-yu ; Mastryukov, Vladimir ; Fink, Manfred

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 111 (1999), S. 3035-3041

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The structure of two metal phthalocyanines, MPc where M=Sn and Mg, have been determined by gas-phase electron diffraction for the first time; furthermore, the structure of ZnPc established earlier by the same technique has been reanalyzed. The focus of these studies is the position of the metal ion relative to the 16-membered C8N8 ring. Tin(II)phthalocyanine we find to be nonplanar with the Sn(II) ion 1.0(1) Å above the molecular plane in accordance with its structure in crystal established earlier; the two other molecules were found to be planar. Slight nonplanarity of ZnPc found in the previous study is now removed by a new procedure of structural analysis; this is in accordance with the results of ab initio/DFT calculations for this molecule performed by Pulay. From comparisons presented here we can conclude that there is a close structural similarity of metal phthalocyanines in the gas phase and in crystal. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.479584

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Digitale Medien

Optimization of spherical deflecting analyzer with finite-size effects (1999)

Ruan, Chong-Yu ; Nguyen, Scott ; Fink, Manfred

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 70 (1999), S. 4213-4220

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: Spherical analyzers have been widely used in electron spectroscopy due to their high energy resolution. In this article, we present a way of optimizing the performance of a 90° spherical deflecting analyzer (SDA-90) considering finite-source effects, using an imaging matrix formalism. Results are shown for both symmetrically and asymmetrically charged cases. The asymmetrical case is found to be superior both in transmission and resolution. This unexpected advantage can be explained by the rotation of the image caused by the broken symmetry along the principle trajectory in the analyzer using an asymmetrical potential configuration. The net effect is equivalent to a reduction in the lateral magnification and a gain in energy dispersion. Both factors improve the performance of the analyzer. The fringe fields, carefully controlled by two Herzog lenses, are very important in the optimization. A telefocus electron gun is used to check the numerical result, and to investigate the transverse focusing behavior. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1150054

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Digitale Medien

Emission optics of the Steigerwald-type electron gun (1999)

Ruan, Chong-Yu ; Fink, Manfred

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 70 (1999), S. 4207-4212

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: The emission properties of a Steigerwald-type electron gun are reexamined. Several optical parameters were experimentally determined, and they indicate that the original telefocus mechanism proposed by Steigerwald in 1949 needs to be revised. "Remote focusing" is found to be nonexistent in most of the telefocus electron guns deployed in high-energy electron scattering experiments. Instead, almost parallel beams with variable beam diameters were found. The physical mechanism responsible for producing a very narrow, monochromatic, and highly collimated beam without limiting apertures is explained in this article with supporting evidences from measurements. We think the new emission model proposed here can help new types of electron or ion gun designs and applications using electron gun in electron optical systems. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1150053

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4

Digitale Medien

A specialized torsion balance designed to measure the absolute flux density of hyperthermal molecular beams containing reactive species (1996)

Cook, Steven R. ; Hoffbauer, Mark A. ; Cross, Jon B. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 67 (1996), S. 1781-1789

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: A torsion balance is described that has been used to measure the absolute flux density of seeded hyperthermal molecular beams containing reactive and/or condensable species with uncertainties of approximately ±5%. The balance is ultrahigh-vacuum compatible and can be used in corrosive environments. A specially designed beam stop mounted on the torsion balance lever arm, traps the incoming beam and allows only completely thermalized molecules to exit. The thermalized molecules exit the beam stop in equal numbers per unit time in opposite directions, ensuring that the force exerted on the beam stop by the exiting molecules is zero. The balance was suspended from a 25-μm-diam gold-coated tungsten wire that had a torsion constant of 6.04×10−8 N m/rad and a period of slightly larger than 400 s. Absolute molecular beam flux density measurements were made using both the torsion balance and the effusive method for a variety of pure and seeded molecular beams. The beams were composed of gases that could easily be measured by the effusive method. Measured fluxes ranged from 2.41×1015 mol/s cm2 for a beam of CO seeded in H2 to 1.25×1017 mol/s cm2 for a beam of pure H2. A comparison of the two methods establishes the ability of the torsion balance to accurately measure the flux of molecular beams. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1146974

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5

Digitale Medien

Space-charge controlled fast electron beam pulsing (2001)

Ruan, Chong-Yu ; Fink, Manfred

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 89 (2001), S. 654-661

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The generation of fast electron beam pulses by voltages in the range of 1 V is presented. Two emission mechanisms are described, where the one which utilizes thermal electron confinement in the proximity of a sharp filament proves to be more advantageous. We have observed pulsewidth of 5 ns, limited only by our recording instruments. Due to the superb optical quality and tunability, this electron beam modulation mechanism can find applications in time-resolved diffraction/imaging, microwave system, time-of-flight spectrometer, and electron beam lithography. © 2001 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1286331

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6

Digitale Medien

The vibrationally averaged, temperature-dependent structure of polyatomic molecules. III. N2O (1985)

Miller, Bruce R. ; Fink, Manfred

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 83 (1985), S. 939-944

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: The thermally averaged molecular structure of gas phase N2O has been measured at temperatures between 293 and 932 K. Excellent agreement with the predictions of force field calculations based on the variational wave function method and the moment method is found. The stretch–bend coupling constant in the force field is of particular importance in describing the temperature dependence of the vibrationally averaged structure parameters.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.449420

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7

Digitale Medien

Higher-order caustics and spectra of a Moellenstedt electron energy analyzer (1987)

Tian, Renhe ; Fink, Manfred

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 58 (1987), S. 1450-1455

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: First- and higher-order caustics and spectra of the Moellenstedt analyzer are computed. It is found that the higher-order caustics and spectra are due to multiple deflections of the electrons in the high chromatic aberration region of the Moellenstedt analyzer. These spectra consist of two parts: the caustic spectrum and noncaustic spectra, the so-called "ghost'' spectra. The only reported "ghost'' spectrum is reprodued by the calculation. Finally, the effects of changing the geometrical construction and the importance of determining the optimum operating point are discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1139431

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Digitale Medien

Dispersion and resolution of a Moellenstedt energy analyzer (1987)

Tian, Renhe ; Fink, Manfred

[S.l.] : American Institute of Physics (AIP)

Review of Scientific Instruments 58 (1987), S. 958-967

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ISSN: 1089-7623

Quelle: AIP Digital Archive

Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik

Notizen: The equipotential lines and the trajectories of electrons in a Moellenstedt analyzer are computed. The effects of relativity and the self-magnetic field of the moving electrons are taken into account. The dispersion, resolution, and caustic position are defined and calculated. The sensitivity of the dispersion and resolution to not only the voltage V applied to the electrode rods, the electron energy E, the incident angle φ, or the geometrical construction of the analyzer, but also the distance L between the analyzer and detector has been investigated. The caustic position varies strongly with the incident angle and the geometrical construction of the analyzer. The dependencies of resolution on the incident angle and the geometrical construction are significantly reduced in the vicinity of the caustic with the angular spread of the incident electrons remaining the major contributor to the finite resolution.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1139583

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