Retrospective determination of U and Pu isotopes and atom ratios in lung samples from Vienna, Austria.

Uranium and plutonium isotope concentrations as well as 236U/238U and 240Pu/239Pu atom ratios were measured by AMS in human lung samples from the early 1960s. The 236U concentrations as well as the 236U/238U atom ratios show a maximum in 1964, 239Pu and 240Pu concentrations are increasing continually from 1962 to 1965. 236U/238U atom ratios are lower by two orders of magnitude compared to corresponding aerosol data from Vienna, probably due to older 238U deposited in the lungs, enhanced 238U concentrations in the city air, and activity partition within different particle sizes. The 236U/239Pu atom ratios in lung samples are also lower than expected from the aerosol data, while 240Pu/239Pu atom ratios lie well within the range typical for nuclear bomb fallout.

Germanium nanowire microbolometer.

Near-infrared detection is widely used for nondestructive and non-contact inspections in various areas, including thermography, environmental and chemical analysis as well as food and medical diagnoses. Common room temperature bolometer-type infrared sensors are based on architectures in theµm range, limiting miniaturization for future highly integrated 'More than Moore' concepts. In this work, we present a first principle study on a highly scalable and CMOS compatible bolometer-type detector utilizing Ge nanowires as the thermal sensitive element. For this approach, we implemented the Ge nanowires on top of a low thermal conducting and highly absorptive membrane as a near infrared (IR) sensor element. We adopted a freestanding membrane coated with an impedance matched platinum absorber demonstrating wavelength independent absorptivity of 50% in the near to mid IR regime. The electrical characteristics of the device were measured depending on temperature and biasing conditions. A strong dependence of the resistance on the temperature was shown with a maximum temperature coefficient of resistance of -0.07 K-1atT = 100 K. Heat transport simulations using COMSOL were used to optimize the responsivity and temporal response, which are in good agreement with the experimental results. Further, lock-in measurements were used to benchmark the bolometer device at room temperature with respect to detectivity and noise equivalent power. Finally, we demonstrated that by operating the bolometer with a network of parallel nanowires, both detectivity and noise equivalent power can be effectively improved.

Verifying the band gap narrowing in tensile strained Ge nanowires by electrical means.

Group-IV based light sources are one of the missing links towards fully CMOS compatible photonic circuits. Combining both silicon process compatibility and a pseudo-direct band gap, germanium is one of the most viable candidates. To overcome the limitation of the indirect band gap and turning germanium in an efficient light emitting material, the application of strain has been proven as a promising approach. So far the experimental verification of strain induced bandgap modifications were based on optical measurements and restricted to moderate strain levels. In this work, we demonstrate a methodology enabling to apply tunable tensile strain to intrinsic germanium [Formula: see text] nanowires and simultaneously perform in situ optical as well as electrical characterization. Combining I/V measurements and µ-Raman spectroscopy at various strain levels, we determined a decrease of the resistivity by almost three orders of magnitude for strain levels of âˆ¼5%. Thereof, we calculated the strain induced band gap narrowing in remarkable accordance to recently published simulation results for moderate strain levels up to 3.6%. Deviations for ultrahigh strain values are discussed with respect to surface reconfiguration and reduced charge carrier scattering time.

Electrical characterization and examination of temperature-induced degradation of metastable Ge0.81Sn0.19 nanowires.

Metastable germanium-tin alloys are promising materials for optoelectronics and optics. Here we present the first electrical characterization of highly crystalline Ge0.81Sn0.19 nanowires grown in a solution-based process. The investigated Ge0.81Sn0.19 nanowires reveal ohmic behavior with resistivity of the nanowire material in the range of ∼1 × 10-4Ω m. The temperature-dependent resistivity measurements demonstrate the semiconducting behavior. Moreover, failure of devices upon heating to moderate temperatures initiating material degradation has been investigated to illustrate that characterization and device operation of these highly metastable materials have to be carefully conducted.