An experimental test of symmetry selection rules in inelastic electron tunneling spectroscopy (IETS)

The inelastic electron tunneling spectrum of a highly symmetric molecule, anthracene, is presented. An analysis of the spectrum shows that the vibrational frequencies as measured by tunneling agree well with optical measurements. The high degree of symmetry of the molecule allows separation of the infrared, Raman, and optically inactive modes. The infrared and Raman active modes have comparable intensities; the optically inactive modes are much weaker. Analysis of these intensities within the framework of existing theories suggests that the coupling of tunneling electrons to the induced dipole moment of molecules is large and cannot be neglected.     

Observation of self-amplified spontaneous emission and exponential growth at 530 nm

Experimental evidence for self-amplified spontaneous emission (SASE) at 530 nm is reported. The measurements were made at the low-energy undulator test line facility at the Advanced Photon Source, Argonne National Laboratory. The experimental setup and details of the experimental results are presented, as well as preliminary analysis. This experiment extends to shorter wavelengths the operational knowledge of a linac-based SASE free-electron laser and explicitly shows the predicted exponential growth in intensity of the optical pulse as a function of length along the undulator.     

Formation and healing of micrometer-sized channel networks on highly mobile Au(111) surfaces

Practical protocols are presented to reproducibly prepare micrometer-sized Au(111) substrates. Au(111) terraces of micrometer dimensions and atomic smoothness were crystallized by flame-annealing vacuum-deposited gold films on glass and on millimetric amorphous gold shots. Gold films and shots that were slowly cooled in a moderately applied stream of nitrogen gas exhibited large and stable crystal surfaces with Au(111) morphologies. Similarly, flame-annealed gold samples cooled with another protocol--in much rougher streams of nitrogen gas--produced morphologically unstable and highly mobile Au(111) layers. Within the first hour after preparation, however, rapid microscale restructuring in the layers produced complex morphologies of hexagonal channel networks and islands that were predominantly triangular. These channeled gold layers fused slowly in the following hours, with velocities of 0.01-0.2 A/s, as quantified by digital image correlation (DIC). Atomically smooth, stable, and predominantly triangular Au(111) terraces on the scale of micrometers were observed approximately 24 h after the sample preparations.     

The kinetic limitation of anti-stokes luminescence of Er3+ and Yb3+ doped infrared upconversion materials

Infrared-to-visible wave-length conversion in the Yb³⁺−Er³⁺ doped phosphors system has been described by a simple three level model based on two ions mechanism. The excitation in the range of 900–1000 nm of an IR-photon is first absorbed by Yb³⁺ ion as a sensitizer attributed to the resonant energy transition in Er³⁺ ion from ⁴ I _3/2 → ⁴ S _15/2 and ¹ F _9/2 → ⁴ I _15/2, respectively for green and red emission. The essential energy transfer processes in this system i.e. upconversion from ⁴ I _11/2 and ¹ I _13/2, cross-relaxation from ⁴ S _3/2 and ¹ F _9/2 are taken into account. The limitations of the rate-equation approach are examined with a focus on the underlying dynamics of this rare-earth system.     

Tunneling spectroscopy as a probe of adsorbate-surface interactions

Tunneling spectroscopy is a sensitive probe of two classes of adsorbate-surface interactions: interactions of the adsorbate with the substrate on which it is adsorbed and adsorbate interactions with the top metal electrode that is evaporated on top of it. The talk by Professor Hipps focuses on the first of these classes. This talk focuses on the second. In general, the interaction of the adsorbed molecules with the top metal electrode produces a down-shift in the vibrational mode position ranging in size from 0.1% to 10% depending on the dipole derivative of the mode and the type of top metal electrode.     

Critical current measurement on Y-Ba-Cu-O

We report critical current measurements on sintered Y_0.35Ba_0.65CuO_y. The sample, in the perovskite phase, shows zero resistance at 87 K. The critical current transition is seen, in zero field and at 77 K, at a current densityJ _c of 50 A/cm².     

Discussion on a possible neutrino detector located in India

We have identified some important and worthwhile physics opportunities with a possible neutrino detector located in India. Particular emphasis is placed on the geographical advantage with a stress on the complimentary aspects with respect to other neutrino detectors already in operation.