AVS2013 Session AP-TuP: Atom Probe Tomography Poster Session
Tuesday, October 29, 2013 6:00 PM in Room Hall B
AP-TuP-1 Atom Probe Tomography of Energy and Environmental Materials
Daniel Perea, Arun Devaraj, Robert Colby, Jia Liu, Daniel Schreiber, James Evans, Suntharampillai Thevuthasan (Pacific Northwest National Laboratory)
Buried interfaces and surfaces play an essential role in the function of many materials for energy, environmental, and biological applications. An understanding of the physics and ultimate the ability to engineer materials with specific properties is aided by an atomic level understanding of the composition and morphology of interfaces. Atom probe tomography (APT) is a 3-dimensional compositional mapping technique based on the field evaporation of individual atoms from the tip of a needle-shaped specimen. At the Environmental Molecular Sciences Laboratory (EMSL), we are pushing the limits of APT analysis to study a wide variety of energy and environmental materials. We will present several examples that exemplify the breadth of materials which include semiconductor nanowires for high performance solar cell and transistors, geologic minerals used for atmospheric carbon sequestration, and glass materials for the vitrification of controlled waste.
AP-TuP-2 Advantage of NbTiN over NbN in Superconducting Properties of Ultra-thin Films
Marek Guziewicz, Adam Laszcz, Jaroslaw Domagala, Krystyna Golaszewska, Andrzej Czerwinski, Wojciech Slysz (Institute of Electron Technology, Poland)
Progress in quality of ultra-thin superconducting niobium nitride films for fabrication technology of Superconducting Single Photon Detectors is still observed. Photon detection bases on a recording of current collapse pulse caused by a photon absorbed in the nanostructure film . Materials proved to be effective are Nb-nitride layers and the layers containing Ti . The latter applied in the detector structure have the advantage in the quantum efficiency and reduced noise by one decade compared to the NbN film . So far, there are no known causes of advantages of this material, but can be traced to them in a better quality of structure and uniformity of composition, which reduces the probability of scattering electron pairs on superconductors current defects . The confirmation of these assumptions may be the observation that better parameters are characterized by the detectors made with layers of amorphous than polycrystalline NbN and compete well with epitaxial NbN layers of single crystal characteristics . It can be find some papers where influence of substrate, sputtering deposition parameters and film thickness of NbN or NbTiN on critical temperature were studied. Our niobium nitrides films deposited on (0001)Al2O3 reveal excellent both superconducting and structure properties. Extensive characterization of the films using XRD, high resolution TEM and AFM were performed. High epitaxial quality of NbN and NbTiN films grown on the Al2O3 substrates is proved by HRXRD and HRTEM studies. The results of the studies on both NbN and NbTiN films reveal one cubic phase with NaCl-type structure. The critical temperatures of NbN and NbTiN films with thickness of few nm grown on the Al2O3 substrates are in range 4K ÷ 7K, but post-grown annealing of the films at 1000oC in Ar increases temperature up to 12K or above. Moreover, the 5 nm thick NbTiN film deposited on sapphire at optimized conditions and annealed discloses the best superconducting properties - critical temperature of 14 K as well as extremely high critical current density of 12·MA/cm2, while the critical current density of 3 MA/cm2 was attained for the NbN film. This is the highest value measured on so thin Nb-nitrides films. The improvement in superconductor parameters can be explained due to reduced strain and defects by high temperature annealing of the film. Rocking Curve of the 111 Bragg reflection on the NbTiN is extremely narrow, ≈10 arcsec, characterising the best single crystals. Higher critical current density is almost certainly attained due to lower atomic concentration of oxygen contamination in the NbTiN films than in the NbN films.
AP-TuP-3 He and Au Ion Irradiation Damage Studies on Metallic Nanolaminates
RamaSesha Vemuri, Arun Devaraj, Wahyu Setyawan, Shuttha Shutthanandan, Suntharampillai Thevuthasan, Sandeep Manamdhar, Charles Henager (Pacific Northwest National Laboratory)
There has been growing interest in thin bi-metallic multilayer films for the usage under extreme radiation conditions because of their radiation healing properties. Recent research and discovery indicate that the materials can be hardened against radiation damage by building nanolayered structures with an optimized layer thickness to increase point defect recombination relative to a non-layered structure. In the next generation nuclear reactor materials, transmutation product of helium adds additional complexity to the radiation damage. He precipitates into bubbles inside the grain boundaries of the materials, which leads to drastic embrittlement and degraded mechanical strength of the given material.
In this study, radiation damage effect on metallic multilayers is emulated through He (transmutation) and Au (atomic displacements) ion implantations. He+ ions with an energy of 30 KeV and 4MeV Au ions were implanted into PVD deposited Ti/Al and Ti/Mg multilayers with fluences ranging from 1E15 to 1E17 ions/cm2. Detailed characterization using transmission electron microscopy (TEM), atom probe tomography (APT) and Rutherford backscattering spectrometry (RBS), were carried out in a systematic manner to help develop an in-depth understanding of the interface damage, crystal lattice damage, amorphization and He bubble formations during ion irradiation of nanoscale multilayer thin films and metallic materials. In the case of Ti/Al multilayers, electron microscopy results clearly demonstrate the preferential formation of He bubbles in Ti layers at the interface which agrees with the molecular dynamics (MD) simulations. The MD simulations predict that there was a preferential drift of self-interstitial atoms (SIA) across the interface leaving excess vacancies in the Ti layer near interface. It is speculated that these excess vacancies are responsible for the preferential He bubble nucleation in the Ti layer near interface.