S. de Cheveigné

Inelastic electron tunneling spectroscopy of carboxylic acids on alumina at low coverage

Abstract The difficulties in assigning certain modes of carboxylic acids adsorbed on alumina are discussed. The study of the spectra of marked acetic acid CH 3 C 18 O 18 OH adsorbed on alumina has allowed us to clarify the assignments of the acetate ion formed. Then an examination of the spectra at very low coverages has enabled us to propose a model for the adsorption, which occurs on (at least) two different sites.

An inelastic electron tunneling spectroscopy study of the adsorption of CO on Rh

Abstract Inelastic Electron Tunneling Spectroscopy of CO adsorbed on alumina supported Rh allows the observation of the low frequency metal-carbon vibrational modes (~1000 cm−1) that cannot be seen by Infrared Spectroscopy. We present a preliminary attempt to assign the modes observed, using istopic shifts C 16 O C 18 O .

Superconductivity in high Debye temperature material

Abstract The theoretical upper limit of the critical temperature of superconducting materials is discussed. It is concluded that a metal that does not have a high Debye temperature (as do metallic H, B, Be or their alloys) cannot become a high Tc superconductor. Various attempts at enhancing the Tc of Be by quench condensing with various elements, by coevaporation with Li and by treatment in an alloyed form : Be 22 Re, are presented. Probably for metallurgical reasons, we were unable to approach the predicted maximum critical temperature but believe we have somewhat clarified the question and the field remains promising.

A study of NO adsorbed on alumina-supported Rh by IETS

Inelastic Electron Tunneling Spectroscopy has been used to study the adsorption of NO on evaporated Rh particles supported on alumina. The molecule adsorbs dissociatively and the nitrogen reacts with hydroxyl groups on the alumina surface to form a RhNHx species, as shown by studies using 15NO and a deuteroxyled alumina surface.

Characterization of a new substrate for tunneling spectroscopy

An insulating layer is produced on aluminum by glow discharge in CF4. This substrate, used as the insulator of metal-insulator-metal diodes is characterized by Inelastic Electron Tunneling Spectroscopy as an aluminum trifluoride AlF3. The adsorption of ammonia, benzylamine. formic and propiolic acid on this substrate is investigated. A comparison between spectra of samples obtained on this insulator and on alumina for the same dopant molecules shows significant differences which are interpreted as revealing an enhanced Lewis acidity of AlF3 relative to Al2O3, determined — at least in part — by an enhanced electronegativity of surface Al+ cations of AlF3.

Morphological instabilities in the solidification front of binary mixtures

To conclude with respect to the present experiments, it is clear that much remains to be done to gain a better understanding of the various phenomena observed. Such studies will certainly provide a wealth of information on the dynamics of morphologic instabilities.

Adsorption of Marked Acetic Acid on Alumina Studied by IETS

The modes of simple carboxylic acids, when adsorbed on alumina are not all undisputably identified. The spectra of marked acetic acid CH3C18O18OH and CD3COOD adsorbed on alumina allow us to clarify the assignments.

Electronic Transitions Studied by Tunneling Spectroscopy

Over the past few years, vibrational tunneling spectroscopy has become an important surface and interface spectroscopy with applications to the study of adsorption phenomena and heterogeneous catalysis. But in these fields, the understanding of the electronic states of molecules is also of fundamental importance. What information can inelastic electron tunneling spectroscopy (IETS) provide?

Cell Shapes and Wavelength Selection in Directional Solidification

In directional solidification the sample, a binary alloy in the present case, initially liquid, is pulled at a given velocity V in a direction parallel to an imposed temperature gradient G set up around its melting temperature so as to solidify it progressively (fig. 1).

Directional Solidification of Transparent Eutectic Alloys

When an alloy at eutectic concentration is solidified, two distinct phases, α and β, of different concentrations separate. In directional solidification, with thin (50 m) samples of the transparent eutectic mixture CBr4-8.4 % C2Cl6, one obtains a periodic structure with lamellae perpendicular to the solidification interface1 (left-hand side of Fig 1). From the point of view of the fundamental physicist, this is an interesting case of pattern formation2. From a more practical point of view, eutectic structures are met during the solidification of a number of metal alloys and it is useful to be able to study their dynamics on a transparent model. The eutectic pattern appears without a threshold, however low the pulling velocity (there is no analogue to the Mullins and Sekerka threshold in cellular growth of dilute alloys). Figure 1 shows one onset mechanism. In this case the sample had been pulled, creating the pattern to the left. Pulling was then stopped and a narrow single phased band developed at the interface, due to the sample being slightly off-eutectic. When pulling was resumed, the other phase nucleated locally, at the tips of previous lamella. One can also observe propagation of the two phase pattern, not yet well organized, along the interface as reported by Seetharaman and Trivedi3.