C. J. Hirschmugl

Adsorption and reactivity of NO on Cu(111): a synchrotron infrared reflection absorption spectroscopic study

Infrared reflection absorption spectroscopy of NO adsorbed on Cu(111) has been performed in the frequency range 200–2500 cm−1. At low temperatures (T < 120 K), two different states were identified with increasing coverage: adsorption followed by dissociation. At coverages up to one monolayer, NO molecules adsorb on identical sites, which are suggested to be of threefold symmetry, with an upright geometry. Two ordered overlayers are formed in turn: p(3 × 3) and (√7 × √7)R19.1°. The infrared spectra show two absorption bands: the internal stretching mode of NO, which shifts upwards in frequency with increasing coverage, and a low frequency anti-absorption band. The anti-absorption band is assigned, based on its isotopic frequency dependence, to the hindered rotation of the NO molecules. After completion of the monolayer, the NO molecules react and adsorbed N2O molecules are found on the surface bound through the oxygen atom (CuON2 stretching mode at 352 cm−1) with their molecular axis (ONN) parallel to the surface plane. Desorption of the adsorbed N2O occurs at 120 K. No dimers, which are the reaction intermediates in the formation of N2O from NO, have been clearly identified.

Fast bolometric response by high Tc detectors measured with subnanosecond synchrotron radiation

We have measured a fast response by thin‐film YBa2Cu3O7−δ detectors to pulsed, broadband, infrared radiation. Synchrotron light from an electron storage ring was used as the infrared source, providing subnanosecond pulses from far infrared through visible. Pulse responsivities as high as 106 V/J and as fast as 4 ns have been observed. For film thicknesses in the range 400–3200 A, the detector response follows the film absorptivity while the speed varies inversely with thickness, suggesting a bolometric mechanism. Calculations based on such a model are in accord with the data. We find no evidence for any nonbolometric components in the response.

Infrared synchrotron radiation measurements at Brookhaven

We describe the spectrometer and experimental stations on the infrared beamline (IR4) at the National Synchrotron Light Source, Brookhaven. We also report measurements of the source characteristics in the range 30–400 μm (25–350 cm−1), including both flux and brightness and compare them with corresponding measurements from a 1000‐K blackbody source.

Signal to noise improvements with a new Far-IR rapid-scan Michelson Interferometer

In this paper signal‐to‐noise issues in the infrared spectral region are discussed, presenting an update on instrumentation developments that have focused on this topic. Reproducibilities in the 0.01% range for spectra measured in around 1 min on samples with an area of 1 mm2 illuminated with an f/10 beam were achieved. It is shown how this result is consistent with the synchrotron source intensity and detector noise and a comparison with a conventional globar source is also shown. For these new studies, a NicoletTM Impact 400 rapid scan Michelson interferometer was modified by Pike Technologies and installed in vacuum at the U4IR infrared beamline at the NSLS. The instrument is capable of scanning at an optical retardation rate of 3.2 cm/s, and of a data‐collection frequency of 50 kHz triggered by the colinear reference beam of a HeNe laser. A proprietary NicoletTM solid‐state beam splitter was used to cover the range from 10 to 2500 cm−1. Spectra were taken in reflection at grazing incidence off a singl...

A high resolution interferometer for use with synchrotron radiation

Abstract We present the first results from a new instrument which is designed to work at very high resolution in the infrared spectral region but whose principles can be used in the VUV/soft-X-ray region. The instrument is based on an interferometer. For the VUV/soft-X-ray region the beamsplitting is achieved by wavefront division which takes advantage of the spatial coherence of synchrotron radiation. Normally the highest frequency in the spectrum from an interferometer is determined by the sampling frequency, which has to be at least twice that of the highest frequency in the spectrum. We show that this can be avoided if the spectral range is deliberately restricted by a grating or by the use of an undulator. In this case the interferograms contain a known and restricted range of frequencies which lead to an unambiguous assignment during the Fourier processing required to generate the spectrum.

The Application of Infrared Synchrotron Radiation to the Study of Interfacial Vibrational Modes

Synchrotron radiation provides an extremely bright broad-band source in the infrared which is ideally suited to the study of surface and interface vibrational modes in the range 50–3000 cm−1. Thus it covers the important range of molecule-substrate interactions, as well as overlapping with the more easily accessible near-ir region where molecular internal modes are found. Compared to standard broadband infrared sources such as globars, not only is it 1000 times brighter, but its emittance matches the phase-space of the electrochemical cell leading to full utilization of this brightness advantage. In addition, the source is more stable than water-cooled globars in vacuum for both short-term and long-term fluctuations. Thus one can work at high resolution and use isotopic shifts to identify and study very weak modes.

High resolution fourier transform spectroscopy using infrared synchrotron radiation: I. Instrumentation

A compact high resolution (.002 cm−1) vacuum Fourier transform spectrometer for use with far infrared synchrotron radiation was constructed at the National Synchrotron Light Source at Brookhaven National Laboratory. The spectrometer may be operated using a gas cell of path length of 2 m and a He cooled bolometer with NEP of 10−13. The pure rotational spectrum of Ammonia was used to test the spectrometer.

Infrared response of YBa2Cu3O7-delta films to pulsed broadband synchrotron radiation

We report studies of a thin high-Ta film operating as a fast bolometric detector of infrared radiation. The film has a response of several mV when exposed to a 1 W, 1 ns duration broadband infrared pulse. The decay after the pulse was about 4 ns. The temperature dependence of the response accurately tracked dR/dT. A thermal model, in which the films temperature varies relative to the substrate, provides a good description of the response. We find no evidence for other (non-bolometric) response mechanisms for temperatures near or well below T.