Tech Briefs Magazine - May 2021 - 43

tional mechanical alloying. The process
has been shown to fabricate components
with 10x improvement in creep rupture
life at 1100 °C and provide a 30% increase
in strength over what is currently possible
with 3D-printed parts.
The ODS-MEA composition may find
applications where ODS alloys are currently used and in areas where such properties are desirable but the resource-

intensive nature and/or inability to produce highly complex geometries via conventional processes ultimately renders
their use uneconomical or infeasible.
Such uses include gas turbine components (for which increasing inlet temperature enables improved efficiency) for
power generation, propulsion (rockets,
jet engines, etc.), industrial processes,
nuclear energy applications, and sample

preparation equipment in the mining
and cement production industries.
NASA is actively seeking licensees to commercialize this technology. Please contact
NASA's Licensing Concierge at AgencyPatent-Licensing@mail.nasa.gov or call us
at 202-358-7432 to initiate licensing discussions. Follow this link for more information:
https://technology.nasa.gov/patent/LEWTOPS-151.

Turning Diamond into Metal
Normally an insulator, diamond becomes a metallic conductor when subjected to large strain.
Massachusetts Institute of Technology, Cambridge

ong known as the hardest of all natural
materials, diamonds are also exceptional thermal conductors and electrical
insulators. Now, researchers have tweaked
tiny needles of diamond in a controlled
way to transform their electronic properties, dialing them from insulating, through
semiconducting, all the way to highly conductive or metallic. This can be induced
dynamically and reversed at will, with no
degradation of the diamond material. The
research may open up a wide array of
potential applications including new kinds
of broadband solar cells, highly efficient
LEDs and power electronics, and new optical devices or quantum sensors.
The team used a combination of quantum mechanical calculations, analyses of
mechanical deformation, and machine

learning to demonstrate that the phenomenon, long theorized as a possibility, really
can occur in nanosized diamond.
The concept of straining a semiconductor material such as silicon to improve its
performance found applications in the
microelectronics industry more than two
decades ago; however, that approach
entailed small strains on the order of about
1%. The new method uses the concept of
elastic strain engineering, which is based
on the ability to cause significant changes
in the electrical, optical, thermal, and
other properties of materials simply by
deforming them - putting them under
moderate to large mechanical strain -
enough to alter the geometric arrangement of atoms in the material's crystal lattice but without disrupting that lattice.

Needle axis
[110]
Bending
direction
-
[110]
[001]

1 μm
9.6%

5.6ev

Indenter tip

Tiny needles of diamond are strained by bending, as seen in electron microscope image (top left).
Computer simulations show the effects, with normal insulating properties in green, and areas
with metallic properties never seen before in diamond, in deep red. (Courtesy of the researchers.
Edited by MIT News)

Tech Briefs, May 2021

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Key to this work is a property known as
bandgap, which essentially determines
how readily electrons can move through
a material. This property is thus key to
the material's electrical conductivity. Diamond normally has a very wide bandgap
of 5.6 electron volts, meaning that it is a
strong electrical insulator that electrons
do not move through readily. In their latest simulations, the researchers show that
diamond's bandgap can be gradually,
continuously, and reversibly changed,
providing a wide range of electrical properties, from insulator, through semiconductor, to metal.
The ability to engineer and design electrical conductivity in diamond without
changing its chemical composition and
stability offers flexibility to custom-design
its functions. For example, a single tiny
piece of diamond, bent so that it has a gradient of strain across it, could become a
solar cell capable of capturing all frequencies of light on a single device - something that currently can only be achieved
through tandem devices that couple different kinds of solar cell materials together
in layers to combine their different absorption bands. These might someday be used
as broad-spectrum photodetectors for
industrial or scientific applications.
The process can also make diamond
into two types of semiconductors, either
" direct " or " indirect " bandgap semiconductors, depending on the intended application. For solar cells, for example, direct
bandgaps provide a much more efficient
collection of energy from light, allowing
them to be much thinner than materials
such as silicon, whose indirect bandgap
requires a much longer pathway to collect
a photon's energy.
For more information, contact Abby
Abazorius at abbya@mit.edu; 617-253-2709.
43

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Tech Briefs Magazine - May 2021

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