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Jan 2001

Volume 72, Issue 1, pp. 1-1261

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Effects of temperature and other experimental variables on single molecule vibrational spectroscopy with the scanning tunneling microscope

L. J. Lauhon and W. Ho

Rev. Sci. Instrum. 72, 216 (2001); http://dx.doi.org/10.1063/1.1327311 (8 pages) | Cited 52 times

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Inelastic electron tunneling spectroscopy (IETS) was performed on single molecules with a variable temperature scanning tunneling microscope. The peak intensity, width, position, and line shape of single molecule vibrational spectra were studied as a function of temperature, modulation bias, bias polarity, and tip position for the (C–H,C–D) stretching vibration of acetylene (C2H2,C2D2) on Cu(001). The temperature broadening of vibrational peaks was found to be a consequence of Fermi smearing as in macroscopic IETS. The modulation broadening of vibrational peaks assumed the expected form for IETS. Extrapolation of the peak width to zero temperature and modulation suggested an intrinsic width of ∼ 4 meV due primarily to instrumental broadening. The inelastic tunneling cross section at negative bias was reduced by a factor of 1.7 for the C–H stretch mode. Low energy modes of other molecules did not show such a reduction. There was no evidence of a tip-induced Stark shift in the peak positions. The spatial variation of the inelastic signal was measured to determine the junction stability necessary for the acquisition of single molecule vibrational spectra. © 2001 American Institute of Physics.
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68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.35.Ja Surface and interface dynamics and vibrations
68.08.-p Liquid-solid interfaces
73.20.Hb Impurity and defect levels; energy states of adsorbed species
07.79.Cz Scanning tunneling microscopes

Signals from molecular beams using a surface ionization detector

P. G. Wahlbeck

Rev. Sci. Instrum. 72, 224 (2001); http://dx.doi.org/10.1063/1.1333041 (5 pages)

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The response of a surface ionization detector with a Re-heated filament was examined as a function of arrival rate of CsCl molecules. The source of CsCl was an effusion cell. The surface ionization detector was moved kinematically on a track toward the CsCl source. The intensity was dependent on the vapor pressure of CsCl (dependent on effusion cell temperature), on the inverse square root of absolute temperature of the effusion cell, and on the inverse square of the distance between the source and the detector. For small arrival rates of CsCl with high-Re-filament temperatures (CsCl dissociated on the Re surface), the ion current of Cs+ from the detector was found to be linearly dependent on the arrival rate over a range of magnitude of 160. For larger arrival rates, deviations from linearity were observed which may be explained by desorption of neutral CsCl(ad) molecules [incomplete dissociation of CsCl(ad)] due to the presence of large amounts of Cl(ad). The equilibrium between Cl(ad) and Cl2(ad) also is significant since the formation of Cl2(ad) provides a sink for Cl(ad). In these experiments negative changes in the work function of Re should be insignificant. © 2001 American Institute of Physics.
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37.20.+j Atomic and molecular beam sources and techniques
34.35.+a Interactions of atoms and molecules with surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Integrated optical measurement system for fluorescence spectroscopy in microfluidic channels

Jörg Hübner, Klaus B. Mogensen, Anders M. Jorgensen, Peter Friis, Pieter Telleman, and Jörg P. Kutter

Rev. Sci. Instrum. 72, 229 (2001); http://dx.doi.org/10.1063/1.1326929 (5 pages) | Cited 35 times

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A transportable miniaturized fiber-pigtailed measurement system is presented which allows quantitative fluorescence detection in microliquid handling systems. The microliquid handling chips are made in silica on silicon technology and the optical functionality is monolithically integrated with the microfluidic channel system. This results in inherent stability and photolithographic alignment precision. Permanently attached optical fibers provide a rugged connection to the light source, detection, and data processing unit, which potentially allows field use of such systems. Fluorescence measurements with two dyes, fluorescein, and Bodipy 650/665 X, showed good linear behavior over a wide range of concentrations. Minimally detected concentrations were 250 pM for fluorescein and 100 nM for Bodipy. © 2001 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.Dx Analytical methods involving electronic spectroscopy
42.82.Cr Fabrication techniques; lithography, pattern transfer
07.60.Rd Visible and ultraviolet spectrometers
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