Nanometer Space Research Articles

Accounts of the changes in dynamics of hydrogen-bonded materials by pressure, nanoconfinement, and hyperquenching.

A hydrogen-bonding network or hydrogen-bonded cluster is formed in many hydrogen-bonded glass formers. It determines the dynamics of structural α relaxation and the Johari-Goldstein (JG) β relaxation because breaking of hydrogen bonds is the prerequisite. However, the networks and clusters can be substantially reduced or totally removed in the liquid state by high temperature accompanying the applied high pressure in experiments, and in the glassy state by hyperquenching the liquid under pressure. By confining the glass former in nanometer spaces, the extended network cannot form, and in addition the finite size effect limits the growth of the length scale of the α relaxation on lowering temperature. Any of these actions will modify the structure of the original hydrogen-bonded glass former, and also the intermolecular interaction governing the relaxation processes. Consequently the dynamics of the structural α relaxation and the JG β relaxation, as well as the relation between the two processes, are expected to change. An important advance in the study of the dynamics of glass-forming materials is the existence of the strong connection between the α relaxation and the JG β relaxation. In particular, the ratio of their relaxation times, t_{α}(T)/t_{β}(T), is quantitatively determined by the exponent of the Kohlrausch relaxation function of the α relaxation. This property is valid in hydrogen-bonded glass formers as well as in non-hydrogen-bonded glass formers. The interesting question is whether this property continues to hold after the hydrogen-bonded glass former has been modified by high temperature under high pressure, nanoconfinement, and hyperquenching under pressure. Remarkably, the answer is positive as concluded from the analyses of the data in several hydrogen-bonded glass formers reported in this paper. So far the main theoretical explanation of this property has been the coupling model.

Supramolecular Multilayered Templates for Fabricating Nanometer-Precise Spacings: Implications for the Next-Generation of Devices Integrating Nanogap/Nanochannel Components.

Molecular transistors, electromagnetic waveguides, plasmonic devices, and novel generations of nanofluidic channels comprise precisely separated gaps of nanometric and subnanometric spacing. Nonetheless, fabricating a nanogap/nanochannel is a technological challenge, currently tackled by several approaches such as breakdown electromigration and lithography. The aforementioned techniques, though, are limited, respectively, in terms of gap stability and ultimate resolution. Here, nanogaps/nanochannels are templated via the microtomy of metallic thin films embedded in a polymer matrix and precisely separated by a nanometric, sacrificial layer of polyelectrolytes grown via the layer-by-layer (LbL) approach. The versatility of the LbL technique, both in terms of the number of layers and composition of polyelectrolytes, allows to finely tune the spacing across the gap; the LbL template can further be removed by plasma etching. Our findings pave the path toward the realization of molecularly defined functional spacings at the nanometer-scale for the modular implementation of devices integrating nanogap/nanochannel components.

SiC transmission-type polarization rotator using a large magneto-optical effect boosted and stabilized by dressed photons

This paper reports the fabrication and operation of a transmission-type polarization rotator for visible light with a wavelength of 450 nm using indirect-transition-type semiconductor crystalline SiC in which Al atoms were implanted as a p-type dopant. A novel dressed-photon–phonon (DPP)-assisted annealing method was used for fabrication. The fabricated device exhibited a gigantic magneto-optical effect induced by interactions between photons, electrons, phonons, and magnetic fields in a nanometric space, mediated by dressed photons. The optical path length for polarization rotation was as short as the thickness of the p–n junction. It operated with a weak magnetic field on the order of mT, generated by injecting current to a ring-shaped electrode on the device surface. The Verdet constant was as large as 9.51 × 104 rad/T.m at a wavelength of 450 nm. SQUID measurements confirmed that the SiC crystal exhibited conspicuous ferromagnetic characteristics as a result of the DPP-assisted annealing. In this device, the dressed photons boosted the magnitude of the magneto-optical effect and stabilized the device operation of the polarization rotator.

Off-Shell Quantum Fields to Connect Dressed Photons with Cosmology

The anomalous nanoscale electromagnetic field arising from light–matter interactions in a nanometric space is called a dressed photon. While the generic technology realized by utilizing dressed photons has demolished the conventional wisdom of optics, for example, the unexpectedly high-power light emission from indirect-transition type semiconductors, dressed photons are still considered to be too elusive to justify because conventional optical theory has never explained the mechanism causing them. The situation seems to be quite similar to that of the dark energy/matter issue in cosmology. Regarding these riddles in different disciplines, we find a common important clue for their resolution in the form of the relevance of space-like momentum support, without which quantum fields cannot interact with each other according to a mathematical result of axiomatic quantum field theory. Here, we show that a dressed photon, as well as dark energy, can be explained in terms of newly identified space-like momenta of the electromagnetic field and dark matter can be explained as the off-shell energy of the Weyl tensor field.

Nanolayer-embedded pseudo-photonic crystals

In recent years, novel high-performance nanophotonic devices have been realized by applying ultrathin two-dimensional nanolayer materials to nanophotonics. In this paper, we propose nanolayer-embedded compact pseudo-photonic crystals (PPCs) that enable strong interaction between ultrathin nanolayers and photonic crystal modes. In typical two-dimensional slab photonic crystals, the transverse-magnetic (TM) photonic crystal bandgap is not well formed, making it difficult to operate the TM photonic crystal waveguide modes. However, by utilizing the low-frequency TM PPC bands, a long propagation TM waveguide mode, a slow TM waveguide mode, and a TM photonic bandgap are all readily available. In particular, the insertion of a nanometer-thick low-refractive-index layer in the vertical center of TM PPC waveguide can localize the electric fields tightly in nanometer space, causing strong field interaction with the inserted nanolayer material. Using the TM slow light near PPC band edges, field interaction with the nanolayer is significantly enhanced. We can also realize nanolayer-embedded high-quality-factor (Q-factor > 104) PPC cavities using the TM PPC bandgap. We believe that the proposed TM PPCs will play an important role in the strong interaction of ultrathin nanolayer materials with photonic crystal modes.

Nano-confined crystallization of organic ultrathin nanostructure arrays with programmable geometries

Fabricating ultrathin organic semiconductor nanostructures attracts wide attention towards integrated electronic and optoelectronic applications. However, the fabrication of ultrathin organic nanostructures with precise alignment, tunable morphology and high crystallinity for device integration remains challenging. Herein, an assembly technique for fabricating ultrathin organic single-crystal arrays with different sizes and shapes is achieved by confining the crystallization process in a sub-hundred nanometer space. The confined crystallization is realized by controlling the deformation of the elastic topographical templates with tunable applied pressures, which produces organic nanostructures with ordered crystallographic orientation and controllable thickness from less than 10 nm to ca. 1 μm. The generality is verified for patterning various typical solution-processable materials with long-range order and pure orientation, including organic small molecules, polymers, metal-halide perovskites and nanoparticles. It is anticipated that this technique with controlling the crystallization kinetics by the governable confined space could facilitate the electronic integration of organic semiconductors.

MIR plasmonic liquid sensing in nano-metric space driven by capillary force

Optical spectroscopy in the mid-infrared region (MIR) has been an important tool for non-destructive analysis of molecules through identifying the vibrational modes of chemical bonds. The use of plasmonic antenna array in the MIR region enables high selectivity and sensitivity without the labeling process. In addition, the formation of nanogap between plasmonic nano-antenna and reflective mirror allows for near-field enhancement which can be exploited for sensing applications. However, it is still challenging to realize a sensing platform which effectively delivers biochemical molecules onto the plasmonic nanogap hot-spot. Here, we experimentally demonstrate a capillary driven sensing platform confining chemical samples into a nano-metric space with a plasmonic antenna array. The quadrupole mode resonance of the plasmonic antenna combined with vertical nanogap hot-spot significantly enhanced the confined electrical field. The nano-metric spaces formed by hydrophilic silicon dioxide draw liquids into the sensing chamber by capillary effect, and hence no external liquid driving power source was required. Enhancement of both molecular vibration and plasmonic resonance were observed. Furthermore, label-free quantitative detection was achieved through coupling the plasmonic antenna resonance and the water molecular vibration. The proposed sensing platform has the potential in realizing non-destructive and label-free sensing in the MIR spectral region without an external liquid driving power source, and the enhanced signal paves the way to sense analyte of ultralow concentration.

Surface-Enhanced Infrared Absorption Spectroscopy Using Charge Transfer Plasmons

Plasmonic antennas have been widely used to enhance the infrared absorption of molecular moieties, owing to their ability to localize mid-infrared light into nanometer spaces at desired wavelengths...

Manipulating of nanometer spacing dual-wavelength by controlling the apodized grating depth in microring resonators

Abstract We propose a passive photonic design for an optically pumped laser system and tunable dual-wavelength generation application by employing optical nonlinear mode coupling of two coupled III–V semiconductor microring resonators, which is connected to a pump and drop waveguide buses. One of the two rings contains a grating, whereas the other has a planar surface. The mechanism underlying the dual-wavelength generation can be explained via the resonance detuning of the spectra that results in nonlinear mode mixing. The tunability of the wavelengths can be achieved by altering the grating depth of the microring resonator and the power coupling coefficients. In the grating design of the microring resonators, we have selected a trapezoidal-profiled apodized grating to obtain low reflectivity at the sidelobes. A time-domain traveling wave (TDTW) analysis yields an InGaAsP core refractive index of 3.3. This core is surrounded by a grating InP cladding with a refractive index of 3.2. We further confirm that the propagation of a Gaussian pulse input with a power of 10 mW and a bandwidth of 0.76 ps is well confined within the system mode propagation. The results show a 2:1 fan-out of two spectrally separate signals, which can be employed for compact and high functional sources on chips.

Electrochemical behavior of a gold nanoring electrode microfabricated on a silicon micropillar

We report on the microfabrication and characterization of a gold nanoring electrode (Au NRE) patterned on top of a silicon (Si) micropillar. An NRE of 165 ± 10 nm in width was micropatterned on 4.6 ± 1 μm diameter × 17.5 ± 2.5 μm long Si micropillar with an intervening 50 nm thick hafnium oxide insulating layer. Scanning electron microscopy and energy dispersive spectroscopy data confirmed excellent cylindricality of the micropillar with vertical sidewalls and a completely intact layer of Au NRE encompassing the entire micropillar perimeter. The electrochemical behavior of the Au NRE was characterized by a steady-state cyclic voltammogram with extremely high signal-to-noise ratios of 2500 and charging currents as small as 1.5 ± 0.3 pA. A “semicircle spectrum” from the Nyquist plot indicates a kinetically-controlled voltammetric current response, which is unique to nanoscale electrodes. The variations in the exchange current values, which are dependent on the NRE area and standard rate constant, place a greater emphasis on the isotropic gold wet etching process that defined the geometry of the Au NRE. Circuit fitting of the electrochemical impedance spectra suggests that the NRE geometry can be varied from inlaid to nanotrench with depths controllable by the etching process. This resulted in differing stead-state voltammetric currents and interfacial properties in terms of charge transfer resistance, constant phase element and trench resistance values. The applicability of Au NREs to electrochemical sensing is demonstrated by detecting lead, a neurotoxin at 100 ppb levels. Also, by surface-modification with multi-walled carbon nanotubes, dopamine, a neurochemical implicated in various brain disorders, is detected at a sensitivity as low as 100 nM with 1000-fold selectivity versus common interferents. The flexibility of the microfabrication approach allows for the creation of multiple NREs of controllable width and nanometer spacing on a single micropillar. This capability and in particular where the NRE is micropatterned on three-dimensional microstructures as will be reported herein, facilitates unique electroanalytical capabilities such as intracellular electrochemistry and highly multiplexed detection for emerging biological applications.

Multi-scale Study of Pollutant Transport and Uptake in Compacted Bentonite

In a previous work, a multiscale model was developed in order to investigate the impact of cation exchange and surface complexation on the hydraulic conductivity of compacted bentonite. Simulation of lead nitrate percolation tests has displayed the strong connection between hydraulic conductivity increase and textural and structural evolutions at different scales. The present developments deal with the modeling of pollutant transport by advection, molecular diffusion within the interlayer and inter-aggregate voids, and pollutant fixation on the smectite layers’ surface. The evolution of the nanometer and micrometer porous spaces is described by relying on a structural investigation of the solid phase conducted at both scales. The multiscale impact of ionic exchange by heavy metal on macroscopic pollutant transport is expressed through upscaling at the different scales of organization within the compacted bentonite. The anisotropy of the mesoscopic diffusion tensor increases with compaction and is well reproduced by using a random distribution of elongated clay platelets in the computations. The macroscopic diffusion tensor computed with elongated and flat ellipsoidal macropores is quasi-isotropic and agrees fairly well with experimental data. Confrontation with experimental breakthrough curves highlights the importance of a realistic description of texture evolution at both the nanometer (progressive interlamellar space reduction) and micrometer (aggregate splitting and inter-aggregate pores development) levels, in order to express the variations of hydraulic conductivity and surface complexation. The computed macroscopic diffusivity is not affected by the microstructure evolution, while pollutant transport appears to take place mainly by advection coupled with pollutant uptake.

Reliability of Constant Charge Method for Molecular Dynamics Simulations on EDLCs in Nanometer and Sub‐Nanometer Spaces

AbstractThe front cover artwork is provided by Mr. Jinyuan Yang and Prof. Zheng Bo, Zhejiang University (Zhejiang, China). The image shows the comparison of constant charge and constant potential methods for molecular dynamics simulations on electric double layer capacitance in nano‐confined spaces. Read the full text of the Article at 10.1002/celc.201700447.

Abstract 2310: Molecular dynamics simulation of permeation pathway of cytochrome C through Bax pore

Abstract How cytochrome C is released from the mitochondria to the cytosol via Bax oligomeric pores, a process which is required for apoptosis, is still a mystery. Based on the residue-residue distances detected experimentally for Bax and its homologous protein (Bak), we recently computationally solve the first atomic model for Bax oligomeric pores at the membranes. Next, we investigate the mechanism at the microsecond time- and nanometer space- scale using coarse-grained replica exchange and all-atom MD simulations. Our free energy landscape depicts a low barrier for the permeation of cytochrome C into the Bax C-terminal mouth, with the pathway proceeding to the inner cavity and exiting via the N-terminal mouth. Release is guided by organized charged/hydrophilic surfaces. The hydrophilicity and negative charge of the pore surface gradually increase along the release pathway from the pore entry to the exit opening. Rather than inert passing of cytochrome C through a rigid pore, the flexible pore may selectively aid the cytochrome C passage. The energy barrier is under 4 kcal/mol. Thus, once the Bax pore is formed in the membrane, the release of cytochrome C may be readily achieved through energy fluctuations. Collectively, our work provides mechanistic insight and atomic detail into the release of cytochrome C through Bax oligomeric pores. Citation Format: Mingzhen Zhang, Jie Zheng, Ruth Nussinov, Buyong Ma. Molecular dynamics simulation of permeation pathway of cytochrome C through Bax pore [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2310. doi:10.1158/1538-7445.AM2017-2310

Release of Cytochrome C from Bax Pores at the Mitochondrial Membrane

How cytochrome C is released from the mitochondria to the cytosol via Bax oligomeric pores, a process which is required for apoptosis, is still a mystery. Based on experimentally measured residue-residue distances, we recently solved the first atomic model for Bax oligomeric pores at the membranes using computational approaches. Here, we investigate the mechanism at the microsecond time- and nanometer space- scale using MD simulations. Our free energy landscape depicts a low barrier for the permeation of cytochrome C into the Bax C-terminal mouth, with the pathway proceeding to the inner cavity and exiting via the N-terminal mouth. Release is guided by organized charged/hydrophilic surfaces. The hydrophilicity and negative charge of the pore surface gradually increase along the release pathway from the pore entry to the exit opening. Rather than inert passing of the cytochrome C through a rigid pore, the flexible pore may selectively aid the cytochrome C passage. Once the Bax pore is formed in the membrane, with a low energy barrier, the release of cytochrome C may be readily achieved through energy fluctuations. Collectively, our work provides mechanistic insight in atomic detail into the release of cytochrome C through Bax oligomeric pores.

Fractionated crystallization, polymorphism and crystal transformation of poly(butylene adipate) confined in electrospun immiscible blend fibers with polystyrene

Utilizing electrospun immiscible blend fibers of poly(butylene adipate) (PBA) and polystyrene (PS) and following coating by the high glass transition temperature poly(4-tert-butylstyrene) (P4tBS), confined PBA specimens in nanometer space were effectively prepared.

Nanometric resolution magnetic resonance imaging methods for mapping functional activity in neuronal networks

This contribution highlights and compares some recent achievements in the use of k-space and real space imaging (scanning probe and wide-filed microscope techniques), when applied to a luminescent color center in diamond, known as nitrogen vacancy (NV) center. These techniques combined with the optically detected magnetic resonance of NV, provide a unique platform to achieve nanometric magnetic resonance imaging (MRI) resolution of nearby nuclear spins (known as nanoMRI), and nanometric NV real space localization.•Atomic size optically detectable spin probe.•High magnetic field sensitivity and nanometric resolution.•Non-invasive mapping of functional activity in neuronal networks.

Current-induced giant polarization rotation using a ZnO single crystal doped with nitrogen ions.

Giant polarization rotation in a ZnO single crystal was experimentally demonstrated based on a novel phenomenon occurring at the nanometric scale. The ZnO crystal was doped with N+ and N2+ ions serving as p-type dopants. By applying an in-plane current using a unique arrangement of electrodes on the device, current-induced polarization rotation of the incident light was observed. From the results of experimental demonstrations and discussions, it was verified that this novel behavior originates from a specific distribution of dopants and the corresponding light–matter interactions in a nanometric space, which are allowed by the existence of such a dopant distribution.

Functional assembly of protein fragments induced by spatial confinement.

Natural proteins are often confined within their local microenvironments, such as three-dimensional confinement in organelles or two-dimensional confinement in lipid rafts on cytoplasmic membrane. Spatial confinement restricts proteins' entropic freedom, forces their lateral interaction, and induces new properties that the same proteins lack at the soluble state. So far, the phenomenon of environment-induced protein functional alteration still lacks a full illustration. We demonstrate here that engineered protein fragments, although being non-functional in solution, can be re-assembled within the nanometer space to give the full activity of the whole protein. Specific interaction between hexahistidine-tag (His-tag) and NiO surface immobilizes protein fragments on NiO nanoparticles to form a self-assembled protein "corona" on the particles inside the nanopores of mesoporous silica. Site-specific assembly forces a shoulder-by-shoulder orientation and promotes fragment−fragment interaction; this interaction together with spatial confinement of the mesopores results in functional re-assembly of the protein half fragments. To our surprise, a single half fragment of luciferase (non-catalytic in solution) exhibited luciferase activity when immobilized on NiO in the mesopores, in the absence of the complimentary half. This shows for the first time that spatial confinement can induce the folding of a half fragment, reconstitute the enzyme active site, and re-gain the catalytic capability of the whole protein. Our work thereby highlights the under-documented notion that aside from the chemical composition such as primary sequence, physical environment of a protein also determines its function.

Interface-induced ordering of gas molecules confined in a small space.

The thermodynamic properties of gases have been understood primarily through phase diagrams of bulk gases. However, observations of gases confined in a nanometer space have posed a challenge to the principles of classical thermodynamics. Here, we investigated interfacial structures comprising either O2 or N2 between water and a hydrophobic solid surface by using advanced atomic force microscopy techniques. Ordered epitaxial layers and cap-shaped nanostructures were observed. In addition, pancake-shaped disordered layers that had grown on top of the epitaxial base layers were observed in oxygen-supersaturated water. We propose that hydrophobic solid surfaces provide low-chemical-potential sites at which gas molecules dissolved in water can be adsorbed. The structures are further stabilized by interfacial water. Here we show that gas molecules can agglomerate into a condensed form when confined in a sufficiently small space under ambient conditions. The crystalline solid surface may even induce a solid-gas state when the gas-substrate interaction is significantly stronger than the gas-gas interaction. The ordering and thermodynamic properties of the confined gases are determined primarily according to interfacial interactions.

Molecular dynamics simulation study of glass transition in hydrated Nafion

ABSTRACTThe thermal transition of Nafion is studied using a molecular dynamics simulation through a chemically realistic model. Static and dynamic properties of polymer melts with different water contents are investigated over a wide range of temperatures to obtain viscometric and calorimetric glass transition temperatures. The effect of cooling rate of the simulation on the glass transition of the hydrated polymer is also examined within the well‐known Williams–Landel–Ferry (WLF) equation. Variation of relaxation times versus temperature shows a fragile‐to‐strong transition. The hydration level has a significant impact on the static and dynamic properties of the polymer chains and water molecules confined in nanometric spaces between polymer chains. The results of this study are useful to predict the behavior of Nafion for various applications including fuel cells, sensors, actuators, and shape memory devices at different temperatures. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 907–915