Vapor-phase synthesis, growth mechanism and thickness-independent elastic modulus of single-crystal tungsten nanobelts

Single-crystal tungsten nanobelts with thicknesses from tens to hundreds of nanometers, widths of several micrometers and lengths of tens of micrometers were synthesized using chemical vapor deposition. Surface energy minimization was believed to have played a crucial role in the growth of the synthesized nanobelts enclosed by the low-energy {110} crystal planes of body-centered-cubic structure. The anisotropic growth of the crystallographically equivalent {110} crystal planes could be attributable to the asymmetric concentration distribution of the tungsten atom vapor around the nanobelts during the growth process. The elastic moduli of the synthesized tungsten nanobelts with thicknesses ranging from 65 to 306 nm were accurately measured using a newly developed thermal vibration method. The measured modulus values of the tungsten nanobelts were thickness-dependent. After eliminating the effect of surface oxidization using a core-shell model, the elastic modulus of tungsten nanobelts became constant, which is close to that of the bulk tungsten value of 410 GPa

Resonance Lifetimes from Complex Densities

The ab-initio calculation of resonance lifetimes of metastable anions challenges modern quantum-chemical methods. The exact lifetime of the lowest-energy resonance is encoded into a complex "density" that can be obtained via complex-coordinate scaling. We illustrate this with one-electron examples and show how the lifetime can be extracted from the complex density in much the same way as the ground-state energy of bound systems is extracted from its ground-state density

Astronomical identification of CN-, the smallest observed molecular anion

We present the first astronomical detection of a diatomic negative ion, the cyanide anion CN-, as well as quantum mechanical calculations of the excitation of this anion through collisions with para-H2. CN- is identified through the observation of the J = 2-1 and J = 3-2 rotational transitions in the C-star envelope IRC +10216 with the IRAM 30-m telescope. The U-shaped line profiles indicate that CN-, like the large anion C6H-, is formed in the outer regions of the envelope. Chemical and excitation model calculations suggest that this species forms from the reaction of large carbon anions with N atoms, rather than from the radiative attachment of an electron to CN, as is the case for large molecular anions. The unexpectedly large abundance derived for CN-, 0.25 % relative to CN, makes likely its detection in other astronomical sources. A parallel search for the small anion C2H- remains so far unconclusive, despite the previous tentative identification of the J = 1-0 rotational transition. The abundance of C2H- in IRC +10216 is found to be vanishingly small, < 0.0014 % relative to C2H.Comment: 5 pages, 4 figures; accepted for publication in A&A Letter

Non-linear dynamics, fluid-structure interactions, and vibrations of microcantilevers in air and liquids

Micro- and nano-scale technologies are enabling scientists to visualize, sense, and measure the world at scales not possible just a few decades ago. In particular, the atomic force microscope (AFM) uses microscale cantilevers for imaging and force sensing down to molecular or even atomic resolution. A distinguishing feature of AFM is its ability to operate in liquid environments. This makes it a key instrument in microbiology and biophysics because of its ability to measure biological samples in their native environment - aqueous solutions. Further, it can be used to study solid-liquid interfaces at nanometer resolution and make electrochemical measurements in situ. Yet, operation of AFM in liquid environments is significantly more complicated than operation in air or vacuum. The dynamics of the microcantilever probe are strongly affected by non-linear surface forces and hydrodynamic loading. Herein, we examine several topics related to fluid-structure interactions and non-linear dynamics of AFM cantilevers in liquids. These results will allow researchers to better interpret experimental data, and design hardware that is suited to exploit the unique dynamics in liquid environments