Abstract

The study of the growth, structure and thermal stability of an fcc film likeCu on a bcc substrate like Ta is important for understanding heteroepitaxyand for many technological applications. Such a system is vital to study theeffect of lattice and thermal mistmatch between the film and the substrateon defects and thermal stability of the films. Cu/Ta is one of the materialcombinations employed in the current IC-metallization, where Cu is theinterconnect material and Ta is used as diffusion barrier. Ultrathin Cufilms on bcc substrates have been studied as a model bimetallic catalyst.This talk explains the use of thermal helium desorption spectrometry (THDS)to characterize defects and thermal stability of ultrathin Cu films (5-200Å) deposited on Ta (110) and Ta(100) in ultrahigh vacuum (1×10-10 mbar) byelectron beam evaporation. Helium ion energy used is 1000 or 75 eV in orderstudy induced or native defects in the sample. THDS yields information aboutdefects in the subsurface region of a film, down to 10-100 Å below thesurface, depending on the incident helium energy. After collisional slowdownand thermalization, the implanted helium atoms in the sample diffuseinterstitially until they leave the sample or encounter a defect such asvacancies and vacancy clusters where they are trapped. On heating thesample, the helium is released from these defects at temperatures that arecharacteristic of the helium-defect dissociation energies.Some of the salient results that will be discussed are as follows. Heliumrelease from ultrathin Cu films will be compared to bulk Cu. Cu films onTa(110) and Ta(100) at room temperature are metastable and on heating, thefilms transform into islands. The temperature at which this takes place isstrongly dependent on the Cu film thickness and for a given thickness occursat a lower temperature on Ta(100) than on Ta(110). There is evidence for thestressed states of both the Cu films and the Ta substrates. Helium releasefrom monovacancies and vacancy clusters in Cu films on Ta(110) and Ta(100)was detected at ~750 K and ~800-1000 K respectively. The sublimation of theCu films from the Ta substrates could be observed by the release of retainedhelium at ~1300 K.

Abstract

The quantum physics of identical particles is embodiedin the connection between spin and statistics (the Pauli principle).For many decades it has been thought that this can be understood onlywith ideas from relativity and quantum field theory. But in fact itcan be understood in terms of ordinary few-body nonrelativisticquantum mechanics, if this is reformulated to take proper accountof the geometry of the indistinguishability of particles. This canbe made plausible by conjuring tricks with a belt. The ‘Pauli sign’ (-1)^2Semerges as a geometric phase factor.

Abstract

With coupling unification and neutrino oscillation discovered, one can argue that proton decay remains as The Missing Piece of Grand Unification. The colloquium will explain why this is so and will emphasize the importance of improved searches for proton decay in a large Underground detector, which is yet to be built.

Abstract

nO is of considerable interest for optoelectronic device applications dueto its wide band gap and high exciton binding energy. In spite of decadesof study and recent progress in research on ZnO properties, there remainedunresolved controversies which are mainly related to native defects formedduring crystal growth. Positron annihilation spectroscopy (PAS) is amongthe methods to tackle this structural issue. ZnO nanostructures, like e.g.nanorods and tetrapods, are of special interest for device applications.However, their characterization remains an ongoing challenge. This talkintends to review our recent efforts and latest achievements in thisdirection. Results obtained will comprise PAS in the form of Slow PositronImplantation Spectroscopy (SPIS) and Pulsed Low Energy Positron LifetimeSpectroscopy (PLEPS), Nuclear Reaction Analysis (NRA), Atomic ForceMicroscopy (AFM), conductive AFM (C-AFM), Nuclear Magnetic Resonance(NMR), Electron Spin Resonance (ESR), Photoluminescence (PL) spectroscopy,and latest theoretical investigations of structure-related and positronproperties of selected defects. The fundamental importance of arelationship between fabrication conditions, native defect formation, andresulting optical and electronic properties is demonstrated by gettingeither inferior (nanorods) or significantly improved (tetrapods) opticalproperties compared to single crystal samples, depending on thenanostructure fabrication method.

Abstract

complete description of quantum information theory needs to incorporate simultaneously at least three important concepts or principles, namely: (a) quantum entanglement, (b) quantumcoherence versus decoherence (i.e., in the presence of dissipation),and (c) the quantum- classical limit (or quantum-classical interface). We discuss how the concept of quantum phasespace can be enlarged to provide just such a unified and consistent description. Quantum phase-space methods and, especially, such quantum phase-space distribution functionsas the P-, Q-, Wigner and Weyl functions, have played an important role over many years in quantum mechanics and such allied areas as quantum optics. We introduce here in a very fundamental manner a natural hierarchy of extended quantum phase spaces and associated extended distribution functions with the capacity to describe simultaneously both quantum noise and quantum correlations at increasingly higher-order levels. We show further how the extendedphase-space formalism provides valuable insights into the important issue of quantum versus classical correspondence, and also how it has extremely appealing properties for a consistent description of quantum information theory. At the next-to-lowest (x-p-X-P) level in the extendedhierarchy the description of mixed states becomes unified, and a very convenient means is opened up, for example, to discuss together, and on the same footing, the ordinary Wigner and Weyl functions of a quantal system. The doubling of the number of degrees of freedom, which, rather surprisingly, has its roots in classical mechanics, has strong overlaps with a similar feature of thermo-field dynamics, and hence with the treatment of quantum systems subject to thermal noise.