4 research outputs found
Morphological Evolution of Nanocluster Aggregates and Single Crystals in Alkaline Zinc Electrodeposition
The
morphology of Zn electrodeposits is studied on carbon-coated
transmission electron microscopy grids. At low overpotentials (η
= −50 mV), the morphology develops by aggregation at two distinct
length scales: ∼5 nm diameter monocrystalline nanoclusters
form ∼50 nm diameter polycrystalline aggregates, and the aggregates
form a branched network. Epitaxial (000Ì…2) growth above an overpotential
of |η<sub>c</sub>| > 125 mV leads to the formation of hexagonal
single crystals up to 2 μm in diameter. Potentiostatic current
transients were used to calculate the nucleation rate from Scharifker
et al.’s model. The expÂ(η) dependence of the nucleation
rates indicates that atomistic nucleation theory explains the nucleation
process better than Volmer–Weber theory. A kinetic model is
provided using the rate equations of vapor solidification to simulate
the evolution of the different morphologies. On solving these equations,
we show that aggregation is attributed to cluster impingement and
cluster diffusion while single-crystal formation is attributed to
direct attachment
Strain-Driven Mound Formation of Substrate under Epitaxial Nanoparticles
We observe
the growth of crystalline SiC nanoparticles on Si(001)
at 900 °C using in situ electron microscopy. Following nucleation
and growth of the SiC, there is a massive migration of Si, forming
a crystalline Si mound underneath each nanoparticle that lifts it
4–5 nm above the initial growth surface. The volume of the
Si mounds is roughly five to seven times the volume of the SiC nanoparticles.
We propose that relaxation of strain drives the mound formation. This
new mechanism for relieving interfacial strain, which involves a dramatic
restructuring of the substrate, is in striking contrast to the familiar
scenario in which only the deposited material restructures to relieve
strain
3D Printed Quantum Dot Light-Emitting Diodes
Developing the ability to 3D print
various classes of materials possessing distinct properties could
enable the freeform generation of active electronics in unique functional,
interwoven architectures. Achieving seamless integration of diverse
materials with 3D printing is a significant challenge that requires
overcoming discrepancies in material properties in addition to ensuring
that all the materials are compatible with the 3D printing process.
To date, 3D printing has been limited to specific plastics, passive
conductors, and a few biological materials. Here, we show that diverse
classes of materials can be 3D printed and fully integrated into device
components with active properties. Specifically, we demonstrate the
seamless interweaving of five different materials, including (1) emissive
semiconducting inorganic nanoparticles, (2) an elastomeric matrix,
(3) organic polymers as charge transport layers, (4) solid and liquid
metal leads, and (5) a UV-adhesive transparent substrate layer. As
a proof of concept for demonstrating the integrated functionality
of these materials, we 3D printed quantum dot-based light-emitting
diodes (QD-LEDs) that exhibit pure and tunable color emission properties.
By further incorporating the 3D scanning of surface topologies, we
demonstrate the ability to conformally print devices onto curvilinear
surfaces, such as contact lenses. Finally, we show that novel architectures
that are not easily accessed using standard microfabrication techniques
can be constructed, by 3D printing a 2 × 2 × 2 cube of encapsulated
LEDs, in which every component of the cube and electronics are 3D
printed. Overall, these results suggest that 3D printing is more versatile
than has been demonstrated to date and is capable of integrating many
distinct classes of materials