5 research outputs found
Terahertz Phase Shift and Its Modulation in NdGaO<sub>3</sub> Single Crystals
Finding
appropriate materials to shape the terahertz (THz) wave
is highly desired due to the increasing development of practical devices
and application systems. In this work, the THz phase shifts of four
typical oxide crystals, i.e., NdGaO3 (NGO), quartz, (LaAlO3)0.3(Sr2AlTaO6)0.35, and sapphire, have been investigated by using THz time-domain spectroscopy.
It is interesting to find that the NGO crystal is the only one that
shows a distinct phase shift. The phase shift (Δφ) of
a ∼500 μm-thick NGO crystal is almost linearly dependent
on the THz frequency and it reaches as large as ∼94° at
1.5 THz with a temperature variation from 100 to 400 K. Moreover,
the THz phase shift of NGO possesses crystal anisotropy and Δφ(100)
> Δφ(001) > Δφ(110). In addition, the
effects
of both electric field and laser illumination on the THz phase shift
in the NGO crystal have also been explored. It is found that the electric
field (∼260 V/cm) has negligible effect, while the laser illumination
can efficiently cause a noticeable THz shift and Δφ ∼
78° with good manipulation stability can be achieved with 20
J/cm2 light fluence. These findings suggest that NGO crystals
are an appropriate candidate for THz phase modulator and their sensitivity
and stability are expected to have a great technological impact and
offer prospects for their applications in THz optics
Detecting Surface Hydration of Poly(2-hydroxyethyl methacrylate) in Solution <i>in situ</i>
Understanding the interfacial molecular
structures of antifouling
polymers in solutions is extremely important in research and applications
related to chemistry, biology, and medicine. However, it is generally
challenging to probe such buried solid/liquid interfaces <i>in
situ</i>. We herein report a molecular-level study on detecting
the interfacial molecular structures of an antifouling hydrogel material,
polyÂ(2-hydroxyethyl methacrylate) (PHEMA), in contact with water and
bovine serum albumin (BSA) solution <i>in situ</i> using
sum frequency generation (SFG) vibrational spectroscopy. To compare
to and validate our <i>in situ</i> experiments, molecular-level
structures of the substrate/PHEMA interface before and after water
exposure were also detected. The detected strong O–H vibrational
signals from water and hydroxyethyl and carbonyl vibrational signals
from PHEMA prove that the PHEMA surface hydration was attributed to
the interaction between water and PHEMA side hydrophilic groups. SFG
experimental results verify that the adsorbed BSA molecules at the
PHEMA/solution interface were disorderly arranged, supported by data
from the laser scanning confocal microscopic (LSCM) experiment. This
indicates the weak interaction between the BSA molecules and PHEMA
surface. This direct detection of the surface hydrated structures
of PHEMA sheds light on understanding the interfacial properties of
antifouling materials in aqueous environments. The capability reported
here to probe the PHEMA/solution interface and the hidden substrate/PHEMA
interface after water exposure can be applied to investigate a broad
range of interfaces of antifouling materials
Sum Frequency Generation of Interfacial Lipid Monolayers Shows Polarization Dependence on Experimental Geometries
Sum frequency generation (SFG) vibrational
spectroscopy has been
widely employed to investigate molecular structures of biological
surfaces and interfaces including model cell membranes. A variety
of lipid monolayers or bilayers serving as model cell membranes and
their interactions with many different molecules have been extensively
studied using SFG. Here, we conducted an in-depth investigation on
polarization-dependent SFG signals collected from interfacial lipid
monolayers using different experimental geometries, i.e., the prism
geometry (total internal reflection) and the window geometry (external
reflection). The different SFG spectral features of interfacial lipid
monolayers detected using different experimental geometries are due
to the interplay between the varied Fresnel coefficients and second-order
nonlinear susceptibility tensor terms of different vibrational modes
(i.e., ss and as modes of methyl groups), which were analyzed in detail
in this study. Therefore, understanding the interplay between the
interfacial Fresnel coefficients and χ<sup>(2)</sup> tensors
is a prerequisite for correctly understanding the SFG spectral features
with respect to different experimental geometries. More importantly,
the derived information in this paper should not be limited to the
methyl groups with a <i>C</i><sub>3<i>v</i></sub> symmetry; valid extension to interfacial functional groups with
different molecular symmetries and even chiral interfaces could be
expected
Green-Solvent-Processable Low-Cost Fluorinated Hole Contacts with Optimized Buried Interface for Highly Efficient Perovskite Solar Cells
Solution-processed hole contact materials, as an indispensable
component in perovskite solar cells (PSCs), have been widely studied
with consistent progress achieved. One bottleneck for the commercialization
of PSCs is the lack of hole contact materials with high performance,
cost-effective preparation, and green-solvent processability. Therefore,
the development of versatile hole contact materials is of great significance.
Herein, we report two novel donor–acceptor (D–A)-type
hole contact molecules (FMPA–BT-CA and 2FMPA–BT-CA)
with low cost and alcohol-based processability by utilizing a fluorination
strategy. We showed that the fluorine atoms lead to the lowered highest
occupied molecular orbital (HOMO) energy levels and larger dipole
moments for FMPA–BT-CA and 2FMPA–BT-CA. Moreover, fluorination
also improves the buried interfacial interaction between hole contacts
and perovskite. As a result, a remarkable power conversion efficiency
(PCE) of 22.37% along with good light stability could be achieved
for green-solvent-processed FMPA–BT-CA-based inverted PSC devices,
demonstrating the great potential of environmentally compatible hole
contacts for highly efficient PSCs