ALBERT

Description: Monitoring of the intrinsic temperature and the thermal management is discussed for the carbon nanotube nano-circuits. The experimental results concerning fabricating and testing of a thermometer able to monitor the intrinsic temperature on nanoscale are reported. We also suggest a model which describes a bi-metal multilayer system able to filter the heat flow, based on separating the electron and phonon components one from another. The bi-metal multilayer structure minimizes the phonon component of the heat flow, while retaining the electronic part. The method allows one to improve the overall performance of the electronic nano-circuits due to minimizing the energy dissipation.

Description: Reactive multilayer foils have the potential to be used as local high intensity heat sources for a variety of applications. Most of the past research effort concerning these materials have focused on understanding the structure-property relationships of the foils that govern the energy released during a reaction. To improve the ability of researchers to more rapidly develop technologies based on reactive multilayer foils, a deeper and more predictive understanding of the relationship between the heat released from the foil and microstructural evolution in the neighboring materials is needed. This work describes the development of a numerical model for the purpose of predicting heat affected zone size in substrate materials. The model is experimentally validated using a commercially available Ni-Al multilayer foils and alloys from the Sn-Bi binary system. To accomplish this, phenomenological models for predicting the variation of physical properties (i.e., thermal conductivity, density, and heat capacity) with temperature and composition in the Sn-Bi system were utilized using literature data.

Description: We have developed a system for tapered fiber measurements of optomechanical resonators inside a dilution refrigerator, which is compatible with both on- and off-chip devices. Our apparatus features full three-dimensional control of the taper-resonator coupling conditions enabling critical coupling, with an overall fiber transmission efficiency of up to 70%. Notably, our design incorporates an optical microscope system consisting of a coherent bundle of 37 000 optical fibers for real-time imaging of the experiment at a resolution of ∼1 μ m. We present cryogenic optical and optomechanical measurements of resonators coupled to tapered fibers at temperatures as low as 9 mK.

Description: Here, we investigate both numerically and experimentally, the polarization conversion capabilities of a rectangular array of holes with two unequal orthogonal periodicities. We show that it is possible to tune the periodicities in such a way that the transmitted light is circularly polarized for a nominated wavelength, λ CPL , when the structure is illuminated with appropriately oriented linearly polarized light at normal incidence. A device was fabricated and experiments confirmed that a degree of circular polarization of 0.89 could be achieved at the resonant wavelength.

Description: A high frequency (88 MHz) traveling strain wave on a piezoelectric substrate is shown to change the magnetization direction in 40  μ m wide Co bars with an aspect ratio of 10 3 . The rapidly alternating strain wave rotates the magnetization away from the long axis into the short axis direction, via magnetoelastic coupling. Strain-induced magnetization changes have previously been demonstrated in ferroelectric/ferromagnetic heterostructures, with excellent fidelity between the ferromagnet and the ferroelectric domains, but these experiments were limited to essentially dc frequencies. Both magneto-optical Kerr effect and polarized neutron reflectivity confirm that the traveling strain wave does rotate the magnetization away from the long axis direction and both yield quantitatively similar values for the rotated magnetization. An investigation of the behavior of short axis magnetization with increasing strain wave amplitude on a series of samples with variable edge roughness suggests that the magnetization reorientation that is seen proceeds solely via coherent rotation. Polarized neutron reflectivity data provide direct experimental evidence for this model. This is consistent with expectations that domain wall motion cannot track the rapidly varying strain.

Description: Irradiation of atomic europium isolated in the solid rare gases, with low intensity laser excitation of the y 8 P← a 8 S resonance transition at ca. 465 nm, is found to produce singly charged europium cations (Eu + ) in large amounts in xenon and in smaller amounts in argon. Confirmation of the formation of matrix-isolated Eu + is obtained from characteristic absorption bands in the UV and in the visible spectral regions. The luminescence produced with excitation of the cation bands is presented in greatest detail for Eu/Xe and assigned. Excitation of the 4f 7 ( 8 S 7/2 )6p 3/2 absorption bands of Eu + between 390 and 410 nm produces emission which is quite distinct from that resulting from excitation of the 4f 7 ( 8 S 7/2 )6p 1/2 absorption (430 to 450 nm) features. The latter consists of narrow, resolved emission bands with Stokes shifts ten times smaller than the former. The observed spectral differences are discussed in relation to the different spatial symmetries of the p 3/2 and p 1/2 orbitals in these j-j coupled (7/2, 3/2) J and the (7/2, 1/2) J levels. Møller-Plesset calculations are conducted to obtain the molecular parameters of the neutral Eu-RG and cationic Eu + -RG diatomics (RG = Ar, Kr, Xe). From the short bond lengths and the strong binding energies obtained for the Eu + -RG species, these values suggest the isolation of the ion in small, possibly interstitial sites especially in xenon. In contrast, but consistent with previous work [O. Byrne and J. G. McCaffrey, J. Chem. Phys. 134 , 124501 (2011)], the interaction potentials calculated herein for the Eu-RG diatomics suggest that the neutral Eu atom occupies tetra-vacancy (tv) and hexa-vacancy (hv) sites in the solid rare gas hosts. Possible reasons for the facile production of Eu + in the solid rare gases are discussed. The mechanism proposed is that atomic europium is also acting as an electron acceptor, providing a temporary trap for the ionised electron in the matrices.

Description: The effect of non-uniformity in bulk particle mass loading on the linear development of a particle-laden shear layer is analyzed by means of a stochastic Eulerian-Eulerian model. From the set of governing equations of the two-fluid model, a modified Rayleigh equation is derived that governs the linear growth of a spatially periodic disturbance. Eigenvalues for this Rayleigh equation are determined numerically using proper conditions at the co-flowing gas and particle interface locations. For the first time, it is shown that non-uniform loading of small-inertia particles (Stokes number (St)

Description: A new two-dimensional Nuclear Magnetic Resonance (NMR) experiment to separate and correlate the first-order quadrupolar and chemical/paramagnetic shift interactions is described. This experiment, which we call the shifting- d echo experiment, allows a more precise determination of tensor principal components values and their relative orientation. It is designed using the recently introduced symmetry pathway concept. A comparison of the shifting- d experiment with earlier proposed methods is presented and experimentally illustrated in the case of 2 H ( I = 1) paramagnetic shift and quadrupolar tensors of CuCl 2 ⋅2D 2 O. The benefits of the shifting- d echo experiment over other methods are a factor of two improvement in sensitivity and the suppression of major artifacts. From the 2D lineshape analysis of the shifting- d spectrum, the 2 H quadrupolar coupling parameters are 〈 C q 〉 = 118.1 kHz and 〈 η q 〉 = 0.88, and the 2 H paramagnetic shift tensor anisotropy parameters are 〈 ζ P 〉 = − 152.5 ppm and 〈 η P 〉 = 0.91. The orientation of the quadrupolar coupling principal axis system (PAS) relative to the paramagnetic shift anisotropy principal axis system is given by ( α , β , γ ) = ( π 2 , π 2 , 0 ) . Using a simple ligand hopping model, the tensor parameters in the absence of exchange are estimated. On the basis of this analysis, the instantaneous principal components and orientation of the quadrupolar coupling are found to be in excellent agreement with previous measurements. A new point dipole model for predicting the paramagnetic shift tensor is proposed yielding significantly better agreement than previously used models. In the new model, the dipoles are displaced from nuclei at positions associated with high electron density in the singly occupied molecular orbital predicted from ligand field theory.

Description: To advance the development of III-V nitride on silicon heterostructure semiconductor devices, we have utilized in-situ x-ray photoelectron spectroscopy (XPS) to investigate the chemistry and valence band offset (VBO) at interfaces formed by gas source molecular beam epitaxy of AlN on Si (001) and (111) substrates. For the range of growth temperatures (600–1050 °C) and Al pre-exposures (1–15 min) explored, XPS showed the formation of Si-N bonding at the AlN/Si interface in all cases. The AlN/Si VBO was determined to be −3.5 ± 0.3 eV and independent of the Si orientation and degree of interfacial Si-N bond formation. The corresponding AlN/Si conduction band offset (CBO) was calculated to be 1.6 ± 0.3 eV based on the measured VBO and band gap for wurtzite AlN. Utilizing these results, prior reports for the GaN/AlN band alignment, and transitive and commutative rules for VBOs, the VBO and CBO at the GaN/Si interface were determined to be −2.7 ± 0.3 and −0.4 ± 0.3 eV, respectively.

Description: We demonstrate aqueous refractive index sensing with 15–30  μ m diameter silicon nitride microdisk resonators to detect small concentrations of Li salt. A dimpled-tapered fiber is used to couple 780 nm visible light to the microdisks, in order to perform spectroscopy on their optical resonances. The dimpled fiber probe allows testing of multiple devices on a chip in a single experiment. This sensing system is versatile and easy to use, while remaining competitive with other refractometric sensors. For example, from a 20  μ m diameter device we measure a sensitivity of 230 ± 20 nm/refractive index units (RIU) with a loaded quality factor of 1.5 × 10 4 , and a limit of detection down to (1.3 ± 0.1) × 10 −6 RIU.