52 research outputs found
Characterization of surface structure in sputtered Al films: Correlation to microstructure evolution
Quantitative roughness and microstructural analysis of as-deposited Al films, 0.1â1.0 ÎŒm thick, were performed by atomic force microscopy (AFM), one-dimensional power spectral density analysis (1DPSD), transmission electron microscopy, and x-ray pole figure methods. The variation of grain size (d) with thickness (h) in the columnar grained film was dâh0.9.dâh0.9. The initial crystallographic texture was nearly random, with a strong Al (111) fiber texture evolving by â0.2 ÎŒm in deposited thickness. AFM imaging revealed a surface structure with hillocks, grains, and grain boundary grooves, and periodic within-grain ridges extending over entire grains. The root-mean-square surface height variation (RRMS)(RRMS) initially decreased during deposition but increased as RRMSâh0.55RRMSâh0.55 from 0.3 to 1.0 ÎŒm thickness. The 1DPSD analysis revealed three spatially resolved regimes of roughness evolution; a frequency independent regime at low frequency attributed to hillock growth, an intermediate frequency self-similar regime attributed to grains and grain boundary grooves, and a high frequency self-similar regime attributed to within-grain ridges. Two characteristic dimensions (CD) were defined at the inverse frequencies of transition between each 1DPSD roughness regime. CDICDI at high frequency was identified as the peak-to-peak ridge spacing which remained independent of film thickness. The ridge spacing is proposed to represent the upper limit of an effective surface diffusion length (λ0)(λ0) due to the effects of surface diffusion and flux shadowing. The CDIICDII at lower frequency was identified as the grain size which increased with thickness. The evolution and interactions of roughness and microstructural features are discussed in terms of surface diffusion, grain boundary motion, and flux shadowing mechanisms. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70172/2/JAPIAU-85-2-876-1.pd
Superconducting fluctuations and characteristic time scales in amorphous WSi
We study magnitudes and temperature dependences of the electron-electron and
electron-phonon interaction times which play the dominant role in the formation
and relaxation of photon induced hotspot in two dimensional amorphous WSi
films. The time constants are obtained through magnetoconductance measurements
in perpendicular magnetic field in the superconducting fluctuation regime and
through time-resolved photoresponse to optical pulses. The excess
magnetoconductivity is interpreted in terms of the weak-localization effect and
superconducting fluctuations. Aslamazov-Larkin, and Maki-Thompson
superconducting fluctuation alone fail to reproduce the magnetic field
dependence in the relatively high magnetic field range when the temperature is
rather close to Tc because the suppression of the electronic density of states
due to the formation of short lifetime Cooper pairs needs to be considered. The
time scale {\tau}_i of inelastic scattering is ascribed to a combination of
electron-electron ({\tau}_(e-e)) and electron-phonon ({\tau}_(e-ph))
interaction times, and a characteristic electron-fluctuation time
({\tau}_(e-fl)), which makes it possible to extract their magnitudes and
temperature dependences from the measured {\tau}_i. The ratio of
phonon-electron ({\tau}_(ph-e)) and electron-phonon interaction times is
obtained via measurements of the optical photoresponse of WSi microbridges.
Relatively large {\tau}_(e-ph)/{\tau}_(ph-e) and {\tau}_(e-ph)/{\tau}_(e-e)
ratios ensure that in WSi the photon energy is more efficiently confined in the
electron subsystem than in other materials commonly used in the technology of
superconducting nanowire single-photon detectors (SNSPDs). We discuss the
impact of interaction times on the hotspot dynamics and compare relevant
metrics of SNSPDs from different materials
Tomography of photon-number resolving continuous-output detectors
We report a comprehensive approach to analysing continuous-output photon
detectors. We employ principal component analysis to maximise the information
extracted, followed by a novel noise-tolerant parameterised approach to the
tomography of PNRDs. We further propose a measure for rigorously quantifying a
detector's photon-number-resolving capability. Our approach applies to all
detectors with continuous-output signals. We illustrate our methods by applying
them to experimental data obtained from a transition-edge sensor (TES)
detector.Comment: 5 pages, 3 figures, also includes supplementary informatio
Temporal multimode storage of entangled photon pairs
Multiplexed quantum memories capable of storing and processing entangled
photons are essential for the development of quantum networks. In this context,
we demonstrate the simultaneous storage and retrieval of two entangled photons
inside a solid-state quantum memory and measure a temporal multimode capacity
of ten modes. This is achieved by producing two polarization entangled pairs
from parametric down conversion and mapping one photon of each pair onto a
rare-earth-ion doped (REID) crystal using the atomic frequency comb (AFC)
protocol. We develop a concept of indirect entanglement witnesses, which can be
used as Schmidt number witness, and we use it to experimentally certify the
presence of more than one entangled pair retrieved from the quantum memory. Our
work puts forward REID-AFC as a platform compatible with temporal multiplexing
of several entangled photon pairs along with a new entanglement certification
method useful for the characterisation of multiplexed quantum memories
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