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Response to light (from 31)
that the semiconductors changed their
elasticity, a form of mechanical stiff ness,
when exposed to light.
“Think of a bouncy ball”
“Think of a bouncy ball,” says Jaramillo.
“The reason it bounces is because it’s
elastic. When you throw it on the ground,
it deforms but then immediately springs
back (that’s why it bounces).
“What we discovered, which was really
quite surprising, is that the elastic proper-
ties [of semiconductors] can undergo tre-
mendous changes under illumination, and
that these changes are reversible when
the light is switched off .”
In the current work, the team did a variety
of experiments with zinc sulfi de and two
other semiconductors in which they mea-
sured the stiff ness of the materials under
diff erent conditions, such as light intensity,
using a sensitive technique called nanoin-
dentation.
In that technique, a diamond tip moved
across the surface of the material records
how much force it takes to push the pin
into the topmost 100 nanometers, or bil-
lionths of a meter, of the surface.
Computer simulations
They also performed computer simulations
of what could be happening at the atomic
scale, slowly developing a theory for what
was happening.
They discovered that defects, or missing
atoms, in the materials played a signifi cant
role in the materials’ mechanical response
to light.
“These vacancies cause the crystal lattice
of the material to soften because some of
the atoms are farther apart. Think of peo-
ple on a subway car. It’s easier to squeeze
in more people if there are bigger spaces
between them,” Jaramillo says.
“Under illumination, the atoms present are
excited and become more repellent. It’s as
if those people on the subway car sudden-
ly started dancing and throwing their arms
around,” he continued.
Atoms resist
The result: the atoms more strongly resist
being packed more closely together and
the material becomes more mechanically
stiff .
The team quickly discovered that
they could tune that stiff ness by
changing the intensity and color
of the light, and by engineering
R. Jaramillo specifi c defects into the materials.
“It’s nice when you can reduce something
to defect engineering, because then you
can plug into one of materials scientists’
core competencies, which is controlling
the defects,” Jaramillo said. “That’s pretty
much what we do for a living.”
mit.edu
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STAMFORD, Conn. — Marketing bud-
gets have climbed to 9.5% of total
company revenue in 2022, an increase
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ner Inc.
While marketing budgets are increas-
ing this year, they still lag pre-pandemic
spending levels. The annual Gartner 2022
CMO Spend and Strategy Survey was con-
ducted between February and March 2022.
gartner.com