Analysis of rich inelastic electron tunneling spectra: case study of terthiophene on Au(111).

Even moderately small molecules like 2,2':5',2"-terthiophene exhibit quite rich vibrational spectra. Detection and assignment of vibronic transitions of such a single adsorbed molecule in inelastic electron tunneling spectroscopy (IETS) using scanning tunneling microscopy are notoriously hampered by noise and the low efficiency of inelastic channels of typically well below 1%. We demonstrate by a thorough statistical analysis that detection of almost all predicted transitions can be determined experimentally within the energy range 0-120 meV with an estimated detection limit for the efficiency of inelastic channels of ∼0.15%. The maximum accuracy of our transition energies is 2 meV and thus smaller than the thermal broadening at 5 K. On short time scales up to some hours, that accuracy appears to be limited by tunneling current noise. The present analysis confirms earlier results which showed that IETS obeys propensity rules rather than selection rules as observed for optical transitions. Furthermore, the previous indications that anharmonic components in the interaction potentials are important for calculating properties of molecular vibrations were corroborated.

4-Mercaptopyridine on Au(111): a scanning tunneling microscopy and spectroscopy study.

The adsorption of 4-mercaptopyridine (4MPy) molecules on reconstructed Au(111) is investigated by Scanning Tunneling Microscopy (STM) and Spectroscopy (STS) at low temperature and under ultra-high vacuum (UHV) conditions. As made visible by STM, at low coverage (<10%) 4MPy adsorbs preferentially at elbow sites of the Herringbone reconstruction and at step edges of the Au(111). Increasing coverage (but still <30%) results in formation of molecular chains followed, at even higher coverage, by a 3-dimensional growth. Detailed analysis of z-V spectroscopy (ramping the tunneling bias V while keeping the tunneling current constant) provides information on the bias dependent apparent height of a single 4MPy/Au(111) as well as on the local density of states (LDOS) of single and chain 4MPy molecules in comparison to the bare Au(111) surface revealing a significant shift of the lowest unoccupied molecular orbital (LUMO) towards lower energy for molecules within chains. Additionally, the data provide no evidence that for these samples prepared in UHV the adsorption of 4MPy on Au(111) requires mediating Au adatoms. Also, clear indications are given that the adsorption does not induce a strong reduction of the Au DOS close to its Fermi energy. Finally, in context of the apparent STM height of 4MPy molecules, the behavior of the differential barrier height Φ(diff)(V) = (∂(z)∂(V)I/∂(V)I)(2) on bare Au(111) and 4MPy/Au(111) is analyzed and the corresponding experimental values are applied to recover the LDOS of the molecule for unoccupied states according to a previously published numerical recipe [B. Koslowski, H. Pfeifer and P. Ziemann, Phys. Rev. B, 2009, 80, 165419 and M. Ziegler, N. Néel, A. Sperl, J. Kröger, and R. Berndt, Phys. Rev. B, 2009, 80, 125402]. In this way, one obtains a spectrum comprising a constant DOS of the Shockley-like surface state of Au(111) and a Lorentzian line attributed to the LUMO of 4MPy.

Vibrations of a single adsorbed organic molecule: anharmonicity matters!

Vibrational spectroscopy is a powerful tool to identify molecules and to characterise their chemical state. Inelastic electron tunnelling spectroscopy (IETS) combined with scanning tunnelling microscopy (STM) allows the application of vibrational analysis to a single molecule. Up to now, IETS was restricted to small species due to the complexity of vibration spectra for larger molecules. We extend the horizon of IETS for both experiment and theory by measuring the STM-IETS spectra of mercaptopyridine adsorbed on the (111) surface of gold and comparing it to theoretical spectra. Such complex spectra with more than 20 lines can be reliably determined and computed leading to completely new insights. Experimentally, the vibrational spectra exhibit a dependence on the specific adsorption site of the molecules. Theoretically, this dependence is only accessible if anharmonic contributions to the interaction potentials are included. These joint experimental and theoretical advances open new perspectives for structure determination of organic adlayers.

Oxidation-resistant gold-55 clusters.

Gold nanoparticles ranging in diameter from 1 to 8 nanometers were prepared on top of silicon wafers in order to study the size dependence of their oxidation behavior when exposed to atomic oxygen. X-ray photoelectron spectroscopy showed a maximum oxidation resistance for "magic-number" clusters containing 55 gold atoms. This inertness is not related to electron confinement leading to a size-induced metal-to-insulator transition, but rather seems to be linked to the closed-shell structure of such magic clusters. The result additionally suggests that gold-55 clusters may act as especially effective oxidation catalysts, such as for oxidizing carbon monoxide.

Effects of verapamil on anthracycline-induced cardiomyopathy: preliminary results of a prospective multicenter trial.

Previous investigations in animals and one retrospective study in man suggest that verapamil can prevent anthracycline-induced cardiomyopathy. In the following study, patients with acute myeloid leukemia (AML) treated with double induction and consolidation chemotherapy (AML COOP study 1986, [3]) were randomized in a group with and without accompanying low-dose oral verapamil treatment. Since July 1986, 64 patients have been included. Thirty patients have been evaluated for pre- and posttreatment cardiological investigations. So far, no significant difference in cardiotoxicity has been observed either between the verapamil and nonverapamil group or between the two induction chemotherapy regimens (TAD/TAD - TAD/HAM).

Supplement use: vitamin intakes and biochemical indexes in 40- to 108-month-old children.

Intakes and related biochemical indexes of ascorbic acid, thiamin, riboflavin, pyridoxine, vitamin B-12, and folic acid were examined for adequacy in 30 normal children aged 40 to 108 months. Comparisons were made between intake and biochemical index values of children who reported regular use of vitamin supplements and those who reported none. Three-day food records provided nutrient intake data; blood samples, drawn following an overnight fast, were analyzed for biochemical indexes. Student's t-test and the Pearson r were used for comparisons. Mean intakes of most nutrients differed significantly between the supplemented and nonsupplemented groups only when supplements were considered. Mean biochemical indexes differed significantly for riboflavin (p less than .005). Correlations between intakes and respective biochemical indexes were significant for riboflavin (p less than .01) and vitamin B-12 (p less than .01) in the supplemented group and for folate with RBC folate (p less than .005) in the nonsupplemented group. No deficiencies in either group were evident from biochemical indexes; improvement in indexes with supplement use was interpreted as being only relative and not suggestive that such use is beneficial.