APS Physics News Ticker: 11/10/13

Wednesday, November 13, 2013

Riding an electron wave into the future of microchip fabrication

Computer simulation explores how intense plasma waves generate suprathermal electrons, which are critical to microchip fabrication



		A plasma wave can give rise to a population of suprathermal electrons.

Advanced plasma-based etching is a key enabler of Moore's Law that observes that the number of transistors on integrated circuits doubles nearly every two years. It is the plasma's ability to reproduce fine patterns on silicon that makes this scaling possible and has made plasma sources ubiquitous in microchip manufacturing.

A groundbreaking fabrication technique, based on what is called a DC-augmented capacitively coupled plasma source, affords chip makers unprecedented control of the plasma. This process enables DC-electrode borne electron beams to reach and harden the surface of the mask that is used for printing the microchip circuits.

More importantly, the presence of the beam creates a population of suprathermal electrons in the plasma, producing the plasma chemistry that is necessary to protect the mask. The energy of these electrons is greater than simple thermal heating could produce—hence the name "suprathermal." But how the beam electrons transform themselves into this suprathermal population has been a puzzle.

Now a computer simulation developed at the U.S. Department of Energy's Princeton

Plasma Physics Laboratory in collaboration with the University of Alberta has shed light on this transformation. The simulation reveals that the initial DC-electrode borne beam generates intense plasma waves that move through the plasma like ripples in water. And it is this beam-plasma instability that leads to the generation of the crucial suprathermal electrons.

Understanding the role these instabilities play provides a first step toward still-greater control of the plasma-surface interactions, and toward further increasing the number of transistors on integrated circuits. Insights from both numerical simulations and experiments related to beam-plasma instabilities thus portend the development of new plasma sources and the increasingly advanced chips that they fabricate.

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Abstracts:
TO6.00005 Collisionless acceleration of plasma electrons by intense electron beam
Session: Low Temperature Plasma Science, Engineering and Technology
9:30 AM–11:06 AM, Thursday, November 14, 2013

Contact:
James Riordon
riordon@aps.org
301-209-3238

Tuesday, November 12, 2013

APS Physics Tip Sheet – Nov 12, 2013

In this issue: Color Darkening in Historical Paintings, Thickening When Stirred, How the Oldest Fossils Were Formed and More

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Color Darkening in Historical Paintings

X-ray studies of medieval murals explain why red pigments in historical paintings have degraded over time.

For over two millennia vermilion (mercury sulfide) has been the painter’s finest red. But in many old paintings the pigment has discolored to a drab brownish black. The reason for the change has been controversial, but a team of researchers from Belgium, Italy and France now claims to have figured out the cause of such degradation. The authors applied X-ray techniques to examine the composition of a discolored vermilion paint layer from a medieval mural in a Catalan monastery. Guided by simulations, they suggest the pigment darkens via a sequence of light-initiated chemical reactions that involve the formation of metallic mercury. The finding clarifies the connection between degradation and environmental conditions and may lead to better ways of protecting paintings through the proper choice of lighting and humidity conditions.

* Fabiana Da Pieve (contact author) et al, “Casting light on the darkening of colors in historical paintings”, Physical Review Letters (expected publication date: Nov 15)

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Thickening When Stirred

Researchers have developed a new model able to predict the behavior of fluids that thicken when stirred.

Certain liquid suspensions like cornstarch in water respond differently than normal liquids to shear: they thicken when they are stirred, becoming solid-like. The phenomenon may be detrimental in industrial applications (e.g. the processing of ink or slurries) but could also be exploited to engineer liquid body armors. Now a research team in New York has developed a numerical model that, for the first time, can accurately describe and predict the shear-thickening transition. The development is based on the recognition of the key role played by friction between particles suspended in the liquid.

* Ryohei Seto (contact author), R Mari, JF Morris, MM Denn, “Discontinuous shear thickening of frictional hard-sphere suspensions”, Physical Review Letters (expected publication date: Nov 18)

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How the Oldest Fossils Were Formed

The analysis of billion-year-old sedimentary rocks provides information on some of the earliest microorganisms on Earth.

Stromatolites are 3.5-billion-year-old sedimentary rocks that are regarded as the fossilized deposits of ancient biological layers. These formations may thus carry information on the oldest life forms on Earth. A team of researchers from MIT and the University of Johannesburg, in South Africa, has developed a model that explains the growth of conical stromatolites, the most simply structured forms of the fossils. They grow as ions of calcium or silica diffuse thorough a biofilm and precipitate as minerals around cells, causing them to fossilize. Over many generations, these structures can grow into meter-sized structures with conical symmetry. The model allowed the authors to estimate some of the properties of the microbial mats that led to the fossils we see today.

* Alexander P Petroff (contact author), NJ Beukes, DH Rothman, T Bosak, “Biofilm growth and fossil form”, Physical Review X (expected publication date: Nov 13)

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Bring a 50,000-degree Plasma into Your Living Room

An online open-user experiment puts users in control of a real physics laboratory.

DENVER, CO— With the rise of online open course platforms such as Khan Academy, MIT
OpenCourseWare and iTunes U, it has never been easier to teach yourself everything
from American history to semiconductor manufacturing. These courses enable students to
advance at their own pace while accessing the limitless resources available on the internet
for supplemental material.

But there’s a glaring exception to this cornucopia of courseware: Online physics classes
that enable students to interact with a real physical experiment. While excellent online
sites like Phet Interactive Simulations have developed virtual labs that simulate
laboratory environments, there is no substitute for actual live experiments.

At the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL), we’ve
developed software for an experiment that can be observed and controlled from anywhere
in the world.

The user can operate the experiment with a set of controls, shown on the left side of the
screen, and watch the effect on the apparatus at PPPL using the web stream video, shown
on the right. This “Remote Glow Discharge Experiment (RGDX)” consists of three main
components:

• A live-streaming video that constantly observes an experimental apparatus housed
at PPPL.
• A set of online controls.
• Information that explains what the user observes and controls, plus more in-depth
resources that explore plasma and its uses.

The RGDX consists of a hollow glass tube with air held under vacuum. Supplying a
voltage of up to 2000V generates a glow discharge within. The user has control of the
pressure inside the tube, the voltage supplied to the plasma and of the strength of an
electromagnet surrounding the tube. Users are guided through steps that gradually
increase their level of engagement and introduce them to new physical concepts and
topics. If the user is interested in the physics behind the voltages, pressures and magnets,
further explanations are given for each topic.

Audiences for the RGDX can range from someone simply interested in controlling a
physical apparatus from afar, to an undergraduate or graduate student who wants to study
phenomena such as instabilities in plasma or the physics behind plasma breakdown
voltages. The RGDX can be used as a novel experimental component of either an online
or in-class physics course, and the software can be adapted to a wide array of experiments
in other fields of physics and, potentially, to experiments in other sciences as well.

Abstracts:
JP8.00006 Remote control of a DC discharge experiment
Session JP8: Poster Session IV: Education and Outreach, MHD, Alpha
Heating & Computational Methods
2:00 PM–5:00 PM, Tuesday, November 12, 2013
Room: Plaza ABC

Contact:
James Riordon
riordon@aps.org
301-209-3238