10 research outputs found
Design for Approaching Cicada-Wing Reflectance in Low- and High-Index Biomimetic Nanostructures
Natural nanostructures in low refractive index Cicada wings demonstrate ≤1% reflectance over the visible spectrum. We provide design parameters for Cicada-wing-inspired nanotip arrays as efficient light harvesters over a 300–1000 nm spectrum and up to 60° angle of incidence in both low-index, such as silica and indium tin oxide, and high-index, such as silicon and germanium, photovoltaic materials. Biomimicry of the Cicada wing design, demonstrating gradient index, onto these material surfaces, either by real electron cyclotron resonance microwave plasma processing or by modeling, was carried out to achieve a target reflectance of ∼1%. Design parameters of spacing/wavelength and length/spacing fitted into a finite difference time domain model could simulate the experimental reflectance values observed in real silicon and germanium or in model silica and indium tin oxide nanotip arrays. A theoretical mapping of the length/spacing and spacing/wavelength space over varied refractive index materials predicts that lengths of ∼1.5 μm and spacings of ∼200 nm in high-index and lengths of ∼200–600 nm and spacings of ∼100–400 nm in low-index materials would exhibit ≤1% target reflectance and ∼99% optical absorption over the entire UV–vis region and angle of incidence up to 60°
Coherent Brightfield Microscopy Provides the Spatiotemporal Resolution To Study Early Stage Viral Infection in Live Cells
Viral
infection starts with a virus particle landing on a cell
surface followed by penetration of the plasma membrane. Due to the
difficulty of measuring the rapid motion of small-sized virus particles
on the membrane, little is known about how a virus particle reaches
an endocytic site after landing at a random location. Here, we use
coherent brightfield (COBRI) microscopy to investigate early stage
viral infection with ultrahigh spatiotemporal resolution. By detecting
intrinsic scattered light <i>via</i> imaging-based interferometry,
COBRI microscopy allows us to track the motion of a single vaccinia
virus particle with nanometer spatial precision (<3 nm) in 3D and
microsecond temporal resolution (up to 100,000 frames per second).
We explore the possibility of differentiating the virus signal from
cell background based on their distinct spatial and temporal behaviors <i>via</i> digital image processing. Through image postprocessing,
relatively stationary background scattering of cellular structures
is effectively removed, generating a background-free image of the
diffusive virus particle for precise localization. Using our method,
we unveil single virus particles exploring cell plasma membranes after
attachment. We found that immediately after attaching to the membrane
(within a second), the virus particle is locally confined within hundreds
of nanometers where the virus particle diffuses laterally with a very
high diffusion coefficient (∼1 μm<sup>2</sup>/s) at microsecond
time scales. Ultrahigh-speed scattering-based optical imaging may
provide opportunities for resolving rapid virus–receptor interactions
with nanometer clarity
Coherent Brightfield Microscopy Provides the Spatiotemporal Resolution To Study Early Stage Viral Infection in Live Cells
Viral
infection starts with a virus particle landing on a cell
surface followed by penetration of the plasma membrane. Due to the
difficulty of measuring the rapid motion of small-sized virus particles
on the membrane, little is known about how a virus particle reaches
an endocytic site after landing at a random location. Here, we use
coherent brightfield (COBRI) microscopy to investigate early stage
viral infection with ultrahigh spatiotemporal resolution. By detecting
intrinsic scattered light <i>via</i> imaging-based interferometry,
COBRI microscopy allows us to track the motion of a single vaccinia
virus particle with nanometer spatial precision (<3 nm) in 3D and
microsecond temporal resolution (up to 100,000 frames per second).
We explore the possibility of differentiating the virus signal from
cell background based on their distinct spatial and temporal behaviors <i>via</i> digital image processing. Through image postprocessing,
relatively stationary background scattering of cellular structures
is effectively removed, generating a background-free image of the
diffusive virus particle for precise localization. Using our method,
we unveil single virus particles exploring cell plasma membranes after
attachment. We found that immediately after attaching to the membrane
(within a second), the virus particle is locally confined within hundreds
of nanometers where the virus particle diffuses laterally with a very
high diffusion coefficient (∼1 μm<sup>2</sup>/s) at microsecond
time scales. Ultrahigh-speed scattering-based optical imaging may
provide opportunities for resolving rapid virus–receptor interactions
with nanometer clarity
Packing Principles for Donor–Acceptor Oligomers from Analysis of Single Crystals
D–A conjugated
molecules are complicated in both their molecular
and their packing structures. In this perspective, we summarize more
than 40 crystal lattices of conjugated oligomers to identify the morphological
influence of each building block on the D–A molecules. These
lattice structures reveal not only the packing preferences of the
conjugated oligomers but also the conformational disorder in the lattices.
The presence of this disorder in slowly grown crystals implies that
attaining total long-range conformational order is challenging for
D–A oligomers, which are structurally complicated and readily
distorted and which have building blocks of incommensurate packing
dimensions. In optoelectronic applications, a decreased duration of
processing can prevent ordering and trap the thin films of D–A
oligomers from becoming crystalline phases. Although D–A oligomers
conform to packing principles in the formation of a single crystal,
their phase behaviors in the formation of active thin films are much
more difficult to comprehend. Continuous advances in methods of characterization
are still strongly required for the steps of attaining a true structure–property
relation of D–A oligomers in active films for optoelectronic
applications
Theoretical Study of Plasmon-Enhanced Surface Catalytic Coupling Reactions of Aromatic Amines and Nitro Compounds
Taking advantage of the unique capacity
of surface plasmon resonance,
plasmon-enhanced heterogeneous catalysis has recently come into focus
as a promising technique for high performance light-energy conversion.
This work performs a theoretical study on the reaction mechanism for
conversions of p-aminothiophenol (PATP) and p-nitrothiophenol (PNTP)
to aromatic azo species, <i>p</i>,<i>p</i>′-dimercaptoazobenzene
(DMAB). In the absence of O<sub>2</sub> or H<sub>2</sub>, the plasmon-driven
photocatalysis mechanism (hot electron–hole reactions) is the
major reaction channel. In the presence of O<sub>2</sub> or H<sub>2</sub>, the plasmon-assisted surface catalysis mechanism (activated
oxygen/hydrogen reactions) is the major reaction channel. The present
results show that the coupling reactions of PATP and PNTP strongly
depend on the solution pH, the irradiation wavelength, the irradiation
power, and the nature of metal substrates as well as the surrounding
atmosphere. The present study has drawn a fundamental physical picture
for understanding plasmon-enhanced heterogeneous catalysis
Stepwise Structural Evolution of a DTS‑F<sub>2</sub>BT Oligomer and Influence of Structural Disorder on Organic Field Effect Transistors and Organic Photovoltaic Performance
An A–D–A oligomer,
DTSÂ(F<sub>2</sub>BT)<sub>2</sub>, was synthesized; its structural
evolution was studied with DSC,
POM, 2D-WAXD, and in-situ GI-XRD. The structural evolution of DTSÂ(F<sub>2</sub>BT)<sub>2</sub> is stepwise and kinetically slow. Both rapid
drying and the presence of PC<sub>71</sub>BM trapped DTSÂ(F<sub>2</sub>BT)<sub>2</sub> in a less ordered nematic (N) phase. PDMS-assisted
crystallization enabled a pristine DTSÂ(F<sub>2</sub>BT)<sub>2</sub> thin film to attain a more ordered equilibrium phase, and enhanced
the OFET mobility of DTSÂ(F<sub>2</sub>BT)<sub>2</sub>. In OPV devices,
DIO additive drove the DTSÂ(F<sub>2</sub>BT)<sub>2</sub> domains in
the DTSÂ(F<sub>2</sub>BT)<sub>2</sub>:PC<sub>71</sub>BM blended film
from the N phase toward the equilibrium phase, and resulted in enhanced
OPV performances. These results reveal the slow ordering process of
the A–D–A oligomer, and the importance of monitoring
the degree of structural evolution of the active thin films in organic
optoelectronics
Influences of Out-Of-Plane Lattice Alignment on the OFET Performance of TIPS-PEN Crystal Arrays
In
organic field-effect transistors (OFETs), the quality of charge-transport
pathway, controlled by crystal structures of organic semiconductors
(OSCs), strongly affects the performance of the device. To achieve
higher charge mobility, solution-processed single-crystal (SPSC) techniques
have been used to decrease crystal defects by aligning the crystals
of OSCs in the in-plane direction. Nonetheless, through SPSC techniques,
whether the crystalline lattices are well-aligned in the out-of-plane
direction and how the out-of-plane lattice misorientaion affects OFET
performances remain unclear. Here, a characterization protocol based
on polarized optical microscope, X-ray diffraction, and electron diffraction
is established to identify the lattice structure, the in-plane and
out-of-plane lattice alignment in the crystal array of 6,13-bisÂ(triisopropylsilylethynyl)Âpentacene
(TIPS-PEN). Regardless of the solvents used in the PDMS-assisted crystallization,
the characterization protocol confirms that all the crystal arrays
share the same lattice structure (form I phase), and have similar
in-plane lattice alignment. However, TIPS-PEN molecules have sufficient
time to unify their out-of-plane orientation and prevent the formation
of low angle grain boundary (LAGB) during crystal growth if high boiling
temperature solvents are used. The improved out-of-plane lattice alignment
increases the hole mobility and decreases the performance fluctuations
of devices. The results confirm that the out-of-plane lattice alignment
significantly impacts the performance of the devices and the reproducibility
of the solution-processed TIPS-PEN OFETs
Understanding the Interplay between Molecule Orientation and Graphene Using Polarized Raman Spectroscopy
We present a systematic
study in investigating the orientation
characteristics of pentacene molecules grown on graphene substrates
using polarized Raman spectroscopy. The substrate-induced orientation
alignment of pentacene can be well distinguished through the polarized
Raman spectra. Interestingly, we found that the nature of polycrystalline
graphene not only provides efficient route to control molecular orientation,
but also acts as an excellent template allowing conjugated molecules
to stack accordingly. The relative orientation of the well-aligned
pentacene molecules and the nearby graphene domains exhibits several
preferred angles due to atomic interactions. This unique feature is
further examined and verified by single domain graphene. Furthermore,
polarized Raman spectroscopy contains abundant information allowing
us to analyze the ordering level of pentacene films with various thicknesses,
which provides insightful perspectives of manipulating molecular orientations
with graphene and spatial organization between conjugated systems,
in a more quantitative manner
High <i>K</i> Nanophase Zinc Oxide on Biomimetic Silicon Nanotip Array as Supercapacitors
A 3D trenched-structure metal–insulator–metal
(MIM)
nanocapacitor array with an ultrahigh equivalent planar capacitance
(EPC) of ∼300 μF cm<sup>–2</sup> is demonstrated.
Zinc oxide (ZnO) and aluminum oxide (Al<sub>2</sub>O<sub>3</sub>)
bilayer dielectric is deposited on 1 μm high biomimetic silicon
nanotip (SiNT) substrate using the atomic layer deposition method.
The large EPC is achieved by utilizing the large surface area of the
densely packed SiNT (∼5 × 10<sup>10</sup> cm<sup>–2</sup>) coated conformally with an ultrahigh dielectric constant of ZnO.
The EPC value is 30 times higher than those previously reported in
metal–insulator–metal or metal–insulator–semiconductor
nanocapacitors using similar porosity dimensions of the support materials