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  • 1
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    Enhanced detection sensitivity of higher-order vibrational modes of gold nanodisks on top of a GaN nanorod array through localized surface plasmons (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-11-26
    Description: We report a method that enables the excitation of localized surface plasmons (LSPs) in a gold nanodisk array by placing each nanodisk on top of a GaN nanorod. When the rod length was much longer than the plasmon penetration depth inside the nanorod, the plasmonic field was found to be localized, and coupling between neighboring gold nanodisks was eliminated. The interaction between LSPs and acoustic vibrations in gold nanodisks was then investigated. Owing to the strong localization of the plasmonic field, weak, higher-order vibrational modes of gold nanodisk could be optically observed. Furthermore, such an LSP-based acoustic sensor could be operated at any angle of incident light. Our study not only provides an approach to excite LSPs in high-density metallic arrays, but also opens one of the possible solutions for the development of highly sensitive sub-terahertz hypersonic sensors with high angle tolerance of incident light.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Efficient excitation of guided acoustic waves in semiconductor nanorods through external metallic acoustic transducer (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-12-16
    Description: We demonstrate that guided acoustic waves inside a nanorod can be excited through an external metallic acoustic transducer. By attaching gold nanodisks on top of GaAs nanorods, the femtosecond optical excitation on the external acoustic transducer enables the generation of guided acoustic waves in the rods. The propagation behavior and mode shape of the observed guided acoustic waves are analyzed. These observations would not only lead to the development of superior external transducers for acoustic imaging, but also provide an experimental system for the study of the acoustic phonon transport behavior in nanorods and nanowires.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Frustrated incomplete donor ionization in ultra-low resistivity germanium films (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-12-09
    Description: The relationship between carrier concentration and donor atomic concentration has been determined in n -type Ge films doped with P. The samples were carefully engineered to minimize non-active dopant incorporation by using specially designed P(SiH 3 ) 3 and P(GeH 3 ) 3 hydride precursors. The in situ nature of the doping and the growth at low temperatures, facilitated by the Ge 3 H 8 and Ge 4 H 10 Ge sources, promote the creation of ultra-low resistivity films with flat doping profiles that help reduce the errors in the concentration measurements. The results show that Ge deviates strongly from the incomplete ionization expected when the donor atomic concentration exceeds N d  = 10 17  cm −3 , at which the energy separation between the donor and Fermi levels ceases to be much larger than the thermal energy. Instead, essentially full ionization is seen even at the highest doping levels beyond the solubility limit of P in Ge. The results can be explained using a model developed for silicon by Altermatt and coworkers, provided the relevant model parameter is properly scaled. The findings confirm that donor solubility and/or defect formation, not incomplete ionization, are the major factors limiting the achievement of very high carrier concentrations in n -type Ge. The commercially viable chemistry approach applied here enables fabrication of supersaturated and fully ionized prototypes with potential for broad applications in group-IV semiconductor technologies.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
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    Heat-driven spin transport in a ferromagnetic metal (2014)
    American Institute of Physics (AIP)
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    Publication Date: 2014-12-16
    Description: As a non-magnetic heavy metal is attached to a ferromagnet, a vertically flowing heat-driven spin current is converted to a transverse electric voltage, which is known as the longitudinal spin Seebeck effect (SSE). If the ferromagnet is a metal, this voltage is also accompanied by voltages from two other sources, i.e., the anomalous Nernst effect in both the ferromagnet and the proximity-induced ferromagnetic boundary layer. By properly identifying and carefully separating those different effects, we find that in this pure spin current circuit the additional spin current drawn by the heavy metal generates another significant voltage by the ferromagnetic metal itself which should be present in all relevant experiments.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 5
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    CMOS time-to-digital converter based on a pulse-mixing scheme (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-11-08
    Description: This paper proposes a new pulse-mixing scheme utilizing both pulse-shrinking and pulse-stretching mechanisms to improve the performance of time-to-digital converters (TDCs). The temporal resolution of the conventional pulse-shrinking mechanism is determined by the size ratio between homogeneous and inhomogeneous elements. The proposed scheme which features double-stage operation derives its resolution according to the time difference between pulse-shrinking and pulse-stretching amounts. Thus, it can achieve greater immunity against temperature and ambient variations than that of the single-stage scheme. The circuit area also can be reduced by the proposed pulse-mixing scheme. In addition, this study proposes an improved cyclic delay line to eliminate the undesirable shift in the temporal resolution successfully. Therefore, the effective resolution can be controlled completely by the pulse-mixing unit to improve accuracy. The proposed TDC composed of only one cyclic delay line and one counter is fabricated in a TSMC CMOS 0.35-μm DPQM process. The chip core occupies an extremely small area of 0.02 mm 2 , which is the best among the related works. The experimental result shows that an effective resolution of around 53 ps within ±13% variation over a 0–100 °C temperature range is achieved. The power consumption is 90 μW at a sample rate of 1000 samples/s. In addition to the reduced area, the proposed TDC circuit achieves its resolution with less thermal-sensitivity and better fluctuations caused by process variations.
    Print ISSN: 0034-6748
    Electronic ISSN: 1089-7623
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Institute of Physics (AIP)
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  • 6
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    Large magneto-electric effects in hexagonal La0.7Ba0.3MnO3-BaTiO3 solid solutions and magneto-electric coupling mechanism discussion (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-10-03
    Description: The solid solutions of La 0.7 Ba 0.3 MnO 3 -BaTiO 3 were first prepared by a solid state method. The XRD showed that the solid solutions formed when the BaTiO 3 transformed from tetragonal to hexagonal phase with sintering temperature increasing. The samples with hexagonal phase exhibited relative large magneto-electric effects. For the sample sintered at 1475 °C, the measured maximum magneto-electric coefficient was 48.6 mV/cmOe, obtained at a frequency of 30 kHz. The first-principles calculations indicated that the magnetic-electric coupling was attributed to the off-centering of Mn ions in coplanar octahedrons in the hexagonal phase. The present results suggest a new candidate for a room temperature multiferroic material with magneto-electric effects.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 7
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    Heat generation by electronic current in a quantum dot spin-valve (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-10-25
    Description: Electric-current-induced heat generation in an interacting single-level quantum dot connected to ferromagnetic leads with noncollinear magnetizations is theoretically investigated. We find that when the two leads' spin polarization rates are identical and much smaller than unit, the magnitude of the heat generation is almost monotonously enhanced as the angle between the leads' magnetic moments is varied from zero to π , while the magnitude of the electric current is continuously suppressed. Moreover, the properties of the heat generation depend on the lead's spin polarization rate in different ways when the angle is varied. If at least one of the leads' spin polarization rate approaches to unit, the spin-valve effect of the heat generation is identical to that of the electric current. Now the previously found negative differential of the heat generation disappears when the angle approaches to π . As compared to the current, the heat generation is more sensitive to the system's asymmetry when one of the electrodes is half-metallic in noncollinear configurations.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 8
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    Fluorescence spectroscopy of UV-MALDI matrices and implications of ionization mechanisms (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-10-25
    Description: Matrix-assisted laser desorption ionization (MALDI) has been widely used in the mass analysis of biomolecules; however, there are a lot of debates about the ionization mechanisms. Previous studies have indicated that S 1 -S 1 annihilation might be a key process in the generation of primary ions. This study investigates S 1 -S 1 annihilation by examining the time-resolved fluorescence spectra of 12 matrices. No S 1 -S 1 annihilation was observed in six of these matrices (3-hydroxy-picolinic acid, 6-aza-2-thiothymine, 2,4-dihydroxy-acetophenone, 2,6-dihydroxy-acetophenone, 2,4,6-trihydroxy-acetophenone, and ferulic acid). We observed two matrix molecules reacting in an electronically excited state (S 1 ) in five of these matrices (2,5-dihydroxybenzoic acid, α-cyano-4-hydroxycinnamic acid, 2,5-dihydroxy-acetophenone, 2,3-dihydroxybenzoic acid, and 2,6-dihydroxybenzoic acid), and S 1 -S 1 annihilation was a possible reaction. Among these five matrices, no S 1 -S 1 annihilation was observed for 2,3-dihydroxybenzoic acid in typical peak power region of nanosecond laser pulses in MALDI, but a very small value of reaction rate constant was observed only in the high peak power region. The excited-state lifetime of sinapinic acid was too short to determine whether the molecules reacted in an electronically excited state. No correlation was observed between the ion generation efficiency of MALDI and S 1 -S 1 annihilation. The results indicate that the proposal of S 1 -S 1 annihilation is unnecessary in MALDI and energy pooling model for MALDI ionization mechanism has to be modified.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 9
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    Enhancement of surface enhanced Raman scattering activity of Au nanoparticles through the mesostructured metallic nanoparticle arrays (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-10-24
    Description: A self-assembly template with a photoreduction agent embedded along mesostructured silicate-surfactant channels is prepared at the air-water interface. The unique template allows uniform and continuous uptake of metallic precursors into the silicate-surfactant channels from the solution subphase. Upon UV irradiation, the metallic precursors result in near-monodisperse nanoparticles homogeneously arrayed in the mesostructured polyoxometalated-silicate-surfactant (PSS) channels until saturation. With three dimensionally densely packed Au NPs of ca. 1.7 nm in the PSS template, hence a very high number density of surface-enhanced Raman scattering (SERS) hot-spots and large absorptive volume, we show that impressive SERS can be measured with 4-nitrothiophenol adsorbed to Au-NPs@PSS.
    Electronic ISSN: 2166-532X
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by American Institute of Physics (AIP)
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  • 10
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    Fluorescence spectroscopy of UV-MALDI matrices and implications of ionization mechanisms (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-10-25
    Description: Matrix-assisted laser desorption ionization (MALDI) has been widely used in the mass analysis of biomolecules; however, there are a lot of debates about the ionization mechanisms. Previous studies have indicated that S 1 -S 1 annihilation might be a key process in the generation of primary ions. This study investigates S 1 -S 1 annihilation by examining the time-resolved fluorescence spectra of 12 matrices. No S 1 -S 1 annihilation was observed in six of these matrices (3-hydroxy-picolinic acid, 6-aza-2-thiothymine, 2,4-dihydroxy-acetophenone, 2,6-dihydroxy-acetophenone, 2,4,6-trihydroxy-acetophenone, and ferulic acid). We observed two matrix molecules reacting in an electronically excited state (S 1 ) in five of these matrices (2,5-dihydroxybenzoic acid, α-cyano-4-hydroxycinnamic acid, 2,5-dihydroxy-acetophenone, 2,3-dihydroxybenzoic acid, and 2,6-dihydroxybenzoic acid), and S 1 -S 1 annihilation was a possible reaction. Among these five matrices, no S 1 -S 1 annihilation was observed for 2,3-dihydroxybenzoic acid in typical peak power region of nanosecond laser pulses in MALDI, but a very small value of reaction rate constant was observed only in the high peak power region. The excited-state lifetime of sinapinic acid was too short to determine whether the molecules reacted in an electronically excited state. No correlation was observed between the ion generation efficiency of MALDI and S 1 -S 1 annihilation. The results indicate that the proposal of S 1 -S 1 annihilation is unnecessary in MALDI and energy pooling model for MALDI ionization mechanism has to be modified.
    Electronic ISSN: 1931-9223
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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