Theoretical studies of a hydrogen abstraction tool for nanotechnology

In the design of a nanoscale, site-specific hydrogen abstraction tool, the authors suggest the use of an alkynyl radical tip. Using ab initio quantum-chemistry techniques including electron correlation they model the abstraction of hydrogen from dihydrogen, methane, acetylene, benzene and isobutane by the acetylene radical. By conservative estimates, the abstraction barrier is small (less than 7.7 kcal mol^-1) in all cases except for acetylene and zero in the case of isobutane. Thermal vibrations at room temperature should be sufficient to supply the small activation energy. Several methods of creating the radical in a controlled vacuum setting should be feasible. The authors show how nanofabrication processes can be accurately and inexpensively designed in a computational framework

Rotating solenoidal perfect fluids of Petrov type D

We prove that aligned Petrov type D perfect fluids for which the vorticity vector is not orthogonal to the plane of repeated principal null directions and for which the magnetic part of the Weyl tensor with respect to the fluid velocity has vanishing divergence, are necessarily purely electric or locally rotationally symmetric. The LRS metrics are presented explicitly.Comment: 6 pages, no figure

Evidence for hydrogen two-level systems in atomic layer deposition oxides

Two-level system (TLS) defects in dielectrics are known to limit the performance of electronic devices. We study TLS using millikelvin microwave loss measurements of three atomic layer deposited (ALD) oxide films--crystalline BeO ($\rm{c-BeO}$), amorphous $\rm{Al_2O_3}$ ($\rm{a-Al_2O_3}$), and amorphous $\rm{LaAlO_3}$ ($\rm{a-LaAlO_3}$)--and interpret them with room temperature characterization measurements. We find that the bulk loss tangent in the crystalline film is 6 times higher than in the amorphous films. In addition, its power saturation agrees with an amorphous distribution of TLS. Through a comparison of loss tangent data to secondary ion mass spectrometry (SIMS) impurity analysis we find that the dominant loss in all film types is consistent with hydrogen-based TLS. In the amorphous films excess hydrogen is found at the ambient-exposed surface, and we extract the associated hydrogen-based surface loss tangent. Data from films with a factor of 40 difference in carbon impurities revealed that carbon is currently a negligible contributor to TLS loss.Comment: 11 pages, 4 figures (preprint format

Gravitational Collapse of Dust with a Cosmological Constant

The recent analysis of Markovic and Shapiro on the effect of a cosmological constant on the evolution of a spherically symmetric homogeneous dust ball is extended to include the inhomogeneous and degenerate cases. The histories are shown by way of effective potential and Penrose-Carter diagrams.Comment: 2 pages, 2 figures (png), revtex. To appear in Phys. Rev.

First-principles calculation of intrinsic defect formation volumes in silicon

We present an extensive first-principles study of the pressure dependence of the formation enthalpies of all the know vacancy and self-interstitial configurations in silicon, in each charge state from -2 through +2. The neutral vacancy is found to have a formation volume that varies markedly with pressure, leading to a remarkably large negative value (-0.68 atomic volumes) for the zero-pressure formation volume of a Frenkel pair (V + I). The interaction of volume and charge was examined, leading to pressure--Fermi level stability diagrams of the defects. Finally, we quantify the anisotropic nature of the lattice relaxation around the neutral defects.Comment: 9 pages, 9 figure