22 research outputs found
Breakdown of chiral recognition of amino acids in reduced dimensions
The homochirality of amino acids in living organisms is one of the great mysteries in the phenomena of life. To understand the chiral recognition of amino acids, we have used scanning tunnelling microscopy to investigate the self-assembly of molecules of the amino acid tryptophan (Trp) on Au(111). Earlier experiments showed only homochiral configurations in the self-assembly of amino acids, despite using a mixture of the two opposite enantiomers. In our study, we demonstrate that heterochiral configurations can be favored energetically when l- and d-Trp molecules are mixed to form self-assembly on the Au surface. Using density functional theory calculations, we show that the indole side chain strongly interacts with the Au surface, which reduces the system effectively to two-dimension, with chiral recognition disabled. Our study provides important insight into the recognition of the chirality of amino acid molecules in life. © 2020, The Author(s).1
Surface energy-mediated construction of anisotropic semiconductor wires with selective crystallographic polarity.
ZnO is a wide band-gap semiconductor with piezoelectric properties suitable for opto-electronics, sensors, and as an electrode material. Controlling the shape and crystallography of any semiconducting nanomaterial is a key step towards extending their use in applications. Whilst anisotropic ZnO wires have been routinely fabricated, precise control over the specific surface facets and tailoring of polar and non-polar growth directions still requires significant refinement. Manipulating the surface energy of crystal facets is a generic approach for the rational design and growth of one-dimensional (1D) building blocks. Although the surface energy is one basic factor for governing crystal nucleation and growth of anisotropic 1D structures, structural control based on surface energy minimization has not been yet demonstrated. Here, we report an electronic configuration scheme to rationally modulate surface electrostatic energies for crystallographic-selective growth of ZnO wires. The facets and orientations of ZnO wires are transformed between hexagonal and rectangular/diamond cross-sections with polar and non-polar growth directions, exhibiting different optical and piezoelectrical properties. Our novel synthetic route for ZnO wire fabrication provides new opportunities for future opto-electronics, piezoelectronics, and electronics, with new topological properties
Heterogeneous stacking of nanodot monolayers by dry pick-and-place transfer and its applications in quantum dot light-emitting diodes
Layered assembly structures composed of nanomaterials, such as nanocrystals, have
attracted considerable attention as promising candidates for new functional devices whose
optical, electromagnetic and electronic behaviours are determined by the spatial arrangement
of component elements. However, difficulties in handling each constituent layer in a materialspecific
manner limit the 3D integration of disparate nanomaterials into the appropriate
heterogeneous electronics. Here we report a pick-and-place transfer method that enables the
transfer of large-area nanodot assemblies. This solvent-free transfer utilizes a lifting layer and
allows for the reliable transfer of a quantum dot (QD) monolayer, enabling layer-by-layer
design. With the controlled multistacking of different bandgap QD layers, we are able to
probe the interlayer energy transfer among different QD monolayers. By controlling the
emission spectrum through such designed monolayer stacking, we have achieved white
emission with stable optoelectronic properties, the closest to pure white among the QD lightemitting
diodes reported so far. (c) 2013 Macmillan Publishers Limited. All rights reserved.402
4-O-Carboxymethylascochlorin Inhibits Expression Levels of on Inflammation-Related Cytokines and Matrix Metalloproteinase-9 Through NF–κB/MAPK/TLR4 Signaling Pathway in LPS-Activated RAW264.7 Cells
Toll-like receptor 4 (TLR4) and matrix metalloproteinase-9 (MMP-9) are known to play important roles in inflammatory diseases such as arteriosclerosis and plaque instability. The purpose of this study was to perform the effect of 4-O-carboxymethylascochlorin (AS-6) on MMP-9 expression in lipopolysaccharide (LPS)-induced murine macrophages and signaling pathway involved in its anti-inflammatory effect. Effect of AS-6 on MAPK/NF-κB/TLR4 signaling pathway in LPS-activated murine macrophages was examined using ELISA, Western blotting, reverse transcription polymerase chain reaction (RT-PCR) and fluorescence immunoassay. MMP-9 enzyme activity was examined by gelatin zymography. AS-6 significantly suppressed MMP-9 and MAPK/NF-κB expression levels in LPS-stimulated murine macrophages. Expression levels of inducible nitric oxide synthase (iNOS), COX2, MMP-9, JNK, ERK, p38 phosphorylation, and NF-κB stimulated by LPS were also decreased by AS-6. Moreover, AS-6 suppressed TLR4 expression and dysregulated LPS-induced activators of transcription signaling pathway. The results of this study showed that AS-6 can inhibit LPS-stimulated inflammatory response by suppressing TLR4/MAPK/NF-κB signals, suggesting that AS-6 can be used to induce the stability of atherosclerotic plaque and prevent inflammatory diseases in an in vitro model
Remembering the work of Phillip L. Geissler: A coda to his scientific trajectory
Phillip L. Geissler made important contributions to the statistical mechanics
of biological polymers, heterogeneous materials, and chemical dynamics in
aqueous environments. He devised analytical and computational methods that
revealed the underlying organization of complex systems at the frontiers of
biology, chemistry, and materials science. In this retrospective, we celebrate
his work at these frontiers
A Low-loss Metasurface Antireflection Coating on Dispersive Surface Plasmon Structure
Over the years, there has been increasing interest in the integration of metal hole array (MHA) with optoelectronic devices, as a result of enhanced coupling of incident light into the active layer of devices via surface plasmon polariton (SPP) resonances. However, not all incident light contributes to the SPP resonances due to significant reflection loss at the interface between incident medium and MHA. Conventional thin-film antireflection (AR) coating typically does not work well due to non-existing material satisfying the AR condition with strong dispersion of MHA’s effective impedances. We demonstrate a single-layer metasurface AR coating that completely eliminates the refection and significantly increases the transmission at the SPP resonances. Operating at off-resonance wavelengths, the metasurface exhibits extremely low loss and does not show resonant coupling with the MHA layer. The SPP resonance wavelengths of MHA layer are unaffected whereas the surface wave is significantly increased, thereby paving the way for improved performance of optoelectronic devices. With an improved retrieval method, the metasurface is proved to exhibit a high effective permittivity () and extremely low loss (tan δ ~ 0.005). A classical thin-film AR coating mechanism is identified through analytical derivations and numerical simulations
A Low-loss Metasurface Antireflection Coating on Dispersive Surface Plasmon Structure
Over the years, there has been increasing interest in the integration of metal hole array (MHA) with optoelectronic devices, as a result of enhanced coupling of incident light into the active layer of devices via surface plasmon polariton (SPP) resonances. However, not all incident light contributes to the SPP resonances due to significant reflection loss at the interface between incident medium and MHA. Conventional thin-film antireflection (AR) coating typically does not work well due to non-existing material satisfying the AR condition with strong dispersion of MHA’s effective impedances. We demonstrate a single-layer metasurface AR coating that completely eliminates the refection and significantly increases the transmission at the SPP resonances. Operating at off-resonance wavelengths, the metasurface exhibits extremely low loss and does not show resonant coupling with the MHA layer. The SPP resonance wavelengths of MHA layer are unaffected whereas the surface wave is significantly increased, thereby paving the way for improved performance of optoelectronic devices. With an improved retrieval method, the metasurface is proved to exhibit a high effective permittivity () and extremely low loss (tan δ ~ 0.005). A classical thin-film AR coating mechanism is identified through analytical derivations and numerical simulations
Quenching of the Resonant States of Single Carbon Vacancies in Graphene/Pt(111)
For more than a decade, investigations
of single carbon vacancies in graphene have sought to increase the
fundamental understanding of the local electronic, magnetic, and mechanical
properties of such vacancies. The single C vacancy in graphene has
been known to generate a resonant state through the integration of
π orbitals near the missing C atom. Here, we examine single
C vacancies in graphene/Pt(111) to explore the effects of graphene–substrate
interactions on the local electronic properties of imperfect graphene.
Our scanning tunneling microscopy, scanning tunneling spectroscopy,
and related density functional theory calculations show the resulting
modifications, including the complete disappearance of the resonant
state attributable to strong graphene–substrate coupling near
the vacancy. The different relative positions of single C vacancies
corresponding to the Pt atoms lead both to varying C–Pt bonding
structures and strengths and to corresponding changes in the local
density of states
Evolution of Graphene Growth on Pt(111): From Carbon Clusters to Nanoislands
We
study the growth of graphene on a Pt(111) surface in stages
by varying the annealing temperature of the precursor hydrocarbon
decomposition through an atomic-scale analysis using scanning tunneling
microscopy (STM) and studying the geometry-affected electronic properties
of graphene nanoislands (GNs) through scanning tunneling spectroscopy.
STM reveals that graphene grows on a Pt(111) surface from dome-shaped
carbon clusters to flat GNs with the intermediate stages of dome-shaped
and basin-shaped hexagonal GN structures. Density functional theory
calculations confirm the changes in direction of the concavity upon
increase in the size of the GNs. The structural changes are also found
to have a significant effect on the electronic properties. Landau
levels arise from strain-induced pseudomagnetic fields because of
the large curvature, and the nanoscale-size effect promotes electron
confinement
Plasmonic-Layered InAs/InGaAs Quantum-Dots-in-a-Well Pixel Detector for Spectral-Shaping and Photocurrent Enhancement
The algorithmic spectrometry as an alternative to traditional approaches has the potential to become the next generation of infrared (IR) spectral sensing technology, which is free of physical optical filters, and only a very small number of data are required from the IR detector. A key requirement is that the detector spectral responses must be engineered to create an optimal basis that efficiently synthesizes spectral information. Light manipulation through metal perforated with a two-dimensional square array of subwavelength holes provides remarkable opportunities to harness the detector response in a way that is incorporated into the detector. Instead of previous experimental efforts mainly focusing on the change over the resonance wavelength by tuning the geometrical parameters of the plasmonic layer, we experimentally and numerically demonstrate the capability for the control over the shape of bias-tunable response spectra using a fixed plasmonic structure as well as the detector sensitivity improvement, which is enabled by the anisotropic dielectric constants of the quantum dots-in-a-well (DWELL) absorber and the presence of electric field along the growth direction. Our work will pave the way for the development of an intelligent IR detector, which is capable of direct viewing of spectral information without utilizing any intervening the spectral filters