First True Atom Images
Since the concept of the atoms as the fundamental unit of matter was introduced by Democritus and Leucippus nearly two and a half millennia ago, scientists have attempted to image individual atoms. The most significant microscopy milestone that was achieved in the last century was the imaging of individual atoms with field-ion microscopy (FIM) by Muller and Bahadur (1956). The FIM is an outgrowth of field emission electron microscope (FEEM) invented in 1936 by Erwin Muller in Gustav Hertz’s laboratory. Today, there are three atomic resolution microscopes – FIM, high resolution electron microscopy and scanning tunneling microscopy. However, images of the single atoms look like relatively wide structureless spots, and hence it is more argued to consider such a situation in recent atomic-resolution microscopy as detecting a single atom rather than obtaining its real image. To date, there have been no reported experimental observations of the spatial form of the atomic orbitals. The experimental evaluation of the electronic orbitals of atoms is one of the most long standing problems in quantum physics, material science, and nanotechnology. The paper presents, for the first time, the direct, sub-angstrom-scale, real-space experimental determination of atomic wavefunction. Here we show that a recently developed high-field technique has made it possible to attain the ultrahigh resolution FEEM, which can be used to direct imaging the electronic orbitals of single atoms, i.e. the internal structure of atom.
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LE12679
ATOMIC CLOCKS SLOW DOWN NEAR WALLS
An Aussie-American team discovered that atomic clocks slow down near walls. For modern clocks the effect is appreciable. The researchers predict that in a very close proximity to surfaces, each second measured by the clock will be off by a 10 billionth fraction of a second. While seemingly small, this slowing down is gigantic in the precision world of modern timekeeping, as the best clocks boast fractional accuracies that are million times better. Slowing of atomic clocks depends on the distance of the clock atoms from the wall. As the separation is increased to about 10 micrometers, the effect becomes negligible. Yet, over this small distance, the feeble force of attraction between the atoms and the wall evolves through three distinct physics laws, spanning nearly 150 years of theoretical developments. Researchers find that atomic clocks may be able to map out these laws in a single experiment, the feat none of the previous attempts has been able to accomplish. Researchers hope that ultimately the clocks may help in discovering new physics laws, such as non-Newtonian gravity, predicted to dwell in close proximity to the walls.
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LE12265
What does a kayak paddle and a bacterium have in common?
A great deal, it turns out. In this paper, we demonstrate that
non-flagellated /E. coli/ strains exhibit closed rotational orbits as
they drift near a surface in the presence of flow, replicating the
periodic motion of a kayak paddle. For the first time in this field, we
precisely characterize these orbital trajectories as a function of
bacterial length and height from the surface. The precision in the data
is made possible by a combination of microfluidics and sophisticated
computer vision algorithms developed in our laboratory, enabling
tracking, automatic analysis and averaging of tens of thousands of
bacterial trajectories. Interactions between the cell bodies and a
surface in the presence of flow is but one component of bacterial
motility, but our data will allow the formulation and calibration of
hydrodynamic models to better understand bacterial migration. For
instance, hydrodynamic surface effects provide a stabilizing influence
on the trajectories of motile bacteria, keeping them near the surface
and leading them to find quiescent routes to swim upstream under a wide
range of flow conditions. Understanding the physics behind these effects
could potentially lead to breakthroughs in the prevention of bacterial
migration and eventual pathogenesis without the need for antibiotics.
The attached picture shows a composite image of E. coli bacteria drifting at slightly different heights (and hence, different speeds) in shear flow near a surface. The periodic, kayak paddle-like motion is clearly visible. The orbital period depends on the length of each bacterium, as well as its height from the surface.
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LD12112AR
Silicon photonic wires are shown to self-align by the forces of light they carry
Laser light may have significant mechanical effects on microscopic objects. In this paper, we theoretically demonstrate that a silicon photonic wire that is broken by a gap and an offset may tend to self-align by the forces generated by the very light it guides. The two parts of the silicon wire, each of cross-section dimensions of a few hundred nanometers, tend to bend to form a continuous wire. Conversely, depending on the geometrical parameters, the light flowing inside the wire may cause the two parts to deflect away from each other. These novel effects we present may be used for nanoscale machines on a silicon chip. The results suggest the guided light may hold a tiny silicon wire cantilever in stable equilibrium or vibrate it, with a promising application in sensing of nanoscale objects.
