4 May 1998

1- WATCHING SINGLE ATOMS MOVE
Using the scanning tunneling microscope (STM), researchers can
manipulate and image individual atoms on surfaces with a level of
precision that was impossible before the STM's invention. They
can study not only static structures, but also the dynamics of
atoms, triggering motion by changing temperature or depositing
"catalyzers" on the surface, for example. In the 6 April PRL, a
European team demonstrates a new method for studying surface
atom dynamics: removing one atom and watching the vacancy
move as other atoms hop into the newly-created openings. They
also speculate on the method's value for possible atom-scale
devices. (Posted 17 April 1998.)

2- SURPRISING ATOMIC LAYERS
Using evaporation techniques, a layer of metal only a few atoms
thick can be deposited on an ultrasmooth semiconducting surface,
a process which is important for many applications. In the last few
years, researchers have shown that unexpected electronic
properties of the thin metal layer are explained by the confinement
of the electrons to that narrow space, which creates electronic
states akin to those of the quantum mechanical particle-in-a-box
problem. In the 20 April PRL they predict another surprising
phenomenon resulting from electronic confinement: As a film of
antimony (Sb) grows on gallium arsenide (GaAs), the layer should
alternate between metallic and nonmetallic properties as each of
the first several atomic layers is deposited. (Posted 27 April 1998.)

3- SPHERES THAT WON'T MIX
The question is simple to state but difficult to answer: Would a
mixture of basketballs and ping-pong balls filling the Mir space
craft remain mixed or eventually separate? A system of large and
small spheres is a crude model of a colloid, where larger molecules
or particles are suspended in a liquid of smaller molecules, such as
water. Researchers have hotly debated the question, as computer
simulations have given ambiguous results, but in the 27 April issue
of PRL a team in France shows with a new algorithm that the
system clearly separates. (Posted 4 May 1998.)
 
 
 
 
 

11 May 1998
 
 

1- MICROSCOPIC GRAFFITI
Silicon, the raw material of the microchip revolution, can glow at
room temperature. Researchers have extensively studied porous
silicon--the form of silicon that lights up--in the past decade,
because it could lead to electronic circuits seamlessly integrated
with fiberoptic cables, displays, and other "optoelectronic"
applications. Fundamental questions remain about the material,
including the electrochemical process that creates it. In the 4 May
PRL, a team dramatically demonstrates a key element of the
pore-formation process and exploits it for a new method of precisely
"writing" microscopic patterns that can emit light.
devices. (Posted 7 May 1998.)

2- IN SEARCH OF BOILING NUCLEI
A "liquid" of neutrons and protons should boil at sufficiently high
temperature, but observing this proposed phase transition has been
tricky. The biggest problem is finding an accurate thermometer.
Three years ago the international ALADIN collaboration caused a
stir by publishing a "caloric curve" that seemed to show nuclear
matter reaching a constant temperature as more energy was added,
just as a boiling tea kettle remains at a steady 100 degrees Celsius.
In the 4 May PRL, the same group directly compares their previous
thermometer with a more conventional one and finds a
disagreement--but they ascribe the different temperatures to
different parts of the nuclear reaction. (Posted 11 May 1998.)
 
 

19 May 1998
 
 

1- ULTRACOOL ATOMS IN A QUANTUM CAVITY
A small cavity made of near-perfect mirrors can trap a photon
whose frequency is in tune with the cavity. Adding a single atom to
the mix can produce a coherent quantum system in which the
photon strongly couples the atom to the cavity. In the 11 May PRL,
a team from the California Institute of Technology reports on its
studies of single atom-photon interactions inside such a cavity,
including possibly the first evidence of forces that could create a
kind of atom-cavity "molecule." (Phys. Rev. Lett. 80, 4157; posted
14 May 1998.)
 
 

26 May 1998
 
 

1- MOTOR PROTEINS MOVE ON METAL
Proteins are very large molecules that do most of the work in
biology, and in recent years biophysicists have begun to detect the
action of single protein molecules at work, rather than measuring
only ensemble properties. In 1995, a Japanese group observed the
first fluorescence from single working proteins in water, and in the
18 May PRL the team shows that a metal surface can enhance the
fluorescence and allow for a new class of experiments involving
proteins on metal surfaces. (Phys. Rev. Lett. 80, 4606; posted 21
May 1998.)

2- LIQUID CRYSTAL FINGERS
Liquid crystals make the numbers on your digital watch, but they
are also a fascination to physicists who study phase transitions.
This unique class of molecules has several electrical and optical
properties that vary with temperature and make it easy to monitor
the various phases of liquid crystals in the lab. Most phase
transitions, such as salt crystallizing out of solution, propagate with
dendritic, finger-like patterns in two or three dimensions, but
theorists are hard-pressed to completely describe such processes. In
the 18 May PRL, a team describes a liquid crystal phase transition
that propagates in one dimension at uniform temperature--the first
of its kind in any system, and one that may allow deeper
understanding of such growth phenomena in higher dimensions.
(Phys. Rev. Lett. 80, 4478; posted 22 May 1998.)
 
 
 

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