Reliable method for testing gross leaks in semiconductor component packages

Simple, reliable, inexpensive method for gross-leak testing has been devised, based upon the conventional fine-leak technique. The sensitivity ranges from the detection of very large leaks down to leaks of 10 to the minus seven cc helium per sec

Orifice gross leak tester Patent

Test chambers with orifice and helium mass spectrometer for detecting leak rate of encapsulated semiconductor device

Entanglement entropy in one-dimensional disordered interacting system: The role of localization

The properties of the entanglement entropy (EE) in one-dimensional disordered interacting systems are studied. Anderson localization leaves a clear signature on the average EE, as it saturates on length scale exceeding the localization length. This is verified by numerically calculating the EE for an ensemble of disordered realizations using density matrix renormalization group (DMRG). A heuristic expression describing the dependence of the EE on the localization length, which takes into account finite size effects, is proposed. This is used to extract the localization length as function of the interaction strength. The localization length dependence on the interaction fits nicely with the expectations.Comment: 5 pages, 4 figures, accepted for publication in Physical Review Letter

Anderson localisation in tight-binding models with flat bands

We consider the effect of weak disorder on eigenstates in a special class of tight-binding models. Models in this class have short-range hopping on periodic lattices; their defining feature is that the clean systems have some energy bands that are dispersionless throughout the Brillouin zone. We show that states derived from these flat bands are generically critical in the presence of weak disorder, being neither Anderson localised nor spatially extended. Further, we establish a mapping between this localisation problem and the one of resonances in random impedance networks, which previous work has suggested are also critical. Our conclusions are illustrated using numerical results for a two-dimensional lattice, known as the square lattice with crossings or the planar pyrochlore lattice.Comment: 5 pages, 3 figures, as published (this version includes minor corrections

The Effects of U.S. Tax Policy on the Income Repatriation Patterns of U.S. Multinational Corporations

U.S. corporations owe taxes to the U.S. Treasury on income earned both inside and outside American borders. This paper examines the incentives created by the U.S. tax system for the legal avoidance of taxes on foreign source income. Using data from 1986 corporate tax returns, we investigate the extent to which U.S. corporations structure and coordinate remittances of income from their foreign subsidiaries to reduce their U.S. and foreign tax liabilities. In contrast to previous work in this area, our estimates of the tax consequences of income remittances from foreign subsidiaries to parent corporations explicitly take into account the ability to use foreign tax credits generated from one source of foreign income to offset the U.S. tax liability generated by other sources of foreign income, withholding tax rates on income remittances, variations in source country corporate income tax systems, and dynamic aspects of the U.S. tax system. Our findings indicate that U.S. multinationals are able to take advantage of the U.S. tax system to avoid paying much U.S. tax on their foreign source income.

Origin of ferromagnetism in (Zn,Co)O from magnetization and spin-dependent magnetoresistance

In order to elucidate the nature of ferromagnetic signatures observed in (Zn,Co)O we have examined experimentally and theoretically magnetic properties and spin-dependent quantum localization effects that control low-temperature magnetoresistance. Our findings, together with a through structural characterization, substantiate the model assigning spontaneous magnetization of (Zn,Co)O to uncompensated spins at the surface of antiferromagnetic nanocrystal of Co-rich wurtzite (Zn,Co)O. The model explains a large anisotropy observed in both magnetization and magnetoresistance in terms of spin hamiltonian of Co ions in the crystal field of the wurtzite lattice.Comment: 6 pages, 6 figure

Critical level statistics and anomalously localized states at the Anderson transition

We study the level-spacing distribution function $P(s)$ at the Anderson transition by paying attention to anomalously localized states (ALS) which contribute to statistical properties at the critical point. It is found that the distribution $P(s)$ for level pairs of ALS coincides with that for pairs of typical multifractal states. This implies that ALS do not affect the shape of the critical level-spacing distribution function. We also show that the insensitivity of $P(s)$ to ALS is a consequence of multifractality in tail structures of ALS.Comment: 8 pages, 5 figure

Chiral single-wall gold nanotubes

Based on first-principles calculations we show that gold atoms can form both free-standing and tip-suspended chiral single-wall nanotubes composed of helical atomic strands. Free-standing, infinite (5,5) tube is found to be energetically the most favorable. While energetically less favorable, the experimentally observed (5,3) tube stretching between two tips corresponds to a local minimum in the string tension. Similarly, the (4,3) tube is predicted as a favorable structure yet to be observed experimentally. Analysis of band structure, charge density, and quantum ballistic conductance suggests that the current on these wires is less chiral than expected, and there is no direct correlation between the numbers of conduction channels and helical strands.Comment: Figures provided in eps forma